the relationship of bionts and taphonomic processes in ... · the relationship of bionts and...

Facies (2011) 57:15–37DOI 10.1007/s10347-010-0235-z

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ORIGINAL ARTICLE

The relationship of bionts and taphonomic processes in molluscan taphofacies formation on the continental shelf and slope: eight-year trends: Gulf of Mexico and Bahamas

Eric N. Powell · Carlton E. Brett · Karla M. Parsons-Hubbard · W. Russell Callender · George M. StaV · Sally E. Walker · Anne Raymond · Kathryn A. Ashton-Alcox

Received: 10 March 2009 / Accepted: 2 September 2010 / Published online: 20 October 2010! Springer-Verlag 2010

Abstract The Shelf and Slope Experimental TaphonomyInitiative (SSETI) deployed a suite of molluscan species inenvironments covering a range of depths and sedimenttypes in the Bahamas and on the Gulf of Mexico continen-tal shelf and upper slope for 8 years. Taphonomic staterarely correlated with the distribution of biont guilds amongenvironments. The preservable and nonpreservable biontguilds were also routinely orthogonal. Several coincidences

of taphonomic trait and biont guild occurred, includinggreen discoloration that consistently co-occurred with bor-ing algae and bacterial Wlms associated with the develop-ment of chalkiness and a soft shell surface. Environmentsof preservation (EOPs) of disparate taphonomic signatureand biont guild complement occur in similar sediment typesand environments with similar rates of burial. A paucity ofbiont coverage is no more a reliable indicator of rapidburial than is a limited degree of shell degradation. Thesuggestion that preservable bionts might protect shells fromtaphonomic processes is not well supported. Certain EOPgroups are delineated from others most readily by a combi-nation of biont guild and taphonomic trait. Thus, biontguilds augment taphonomic analysis in diVerentiatingEOPs. Shell preservational state, including taphonomic sig-nature and biont coverage, is inXuenced in a complex wayby environment. The analysis conWrms an expectation thatthe diversity of EOPs should be greater in shallow water.Clustering of EOPs reveals that visually distinctive envi-ronments may be taphonomically and biotically similar.Visually similar environments may be quite disparate intaphonomic state and biont complement. EOPs grouped bysimilarity in taphonomic signature and biont coverage verylikely deWne geographically widespread biological andtaphonomic regimes, which, however, are everywhererestricted locally in areal dimension.

Keywords Taphonomy · Discoloration · Biont guild · Environment of preservation · Dissolution · Burial

Introduction

The central hypothesis of most taphonomic studies is thattaphonomic characteristics co-occur predictably, deWning

E. N. Powell (&) · K. A. Ashton-AlcoxHaskin ShellWsh Research Laboratory, Rutgers University, 6959 Miller Ave, Port Norris, NJ 08349, USAe-mail: [email protected]

C. E. BrettDepartment of Geology, University of Cincinnati, Cincinnati, OH 45221, USA

K. M. Parsons-HubbardDepartment of Geology, Oberlin College, Oberlin, OH 44074, USA

W. R. CallenderNational Oceanic and Atmospheric Administration, National Centers for Coastal Ocean Science (N/SCI), 1305 East–West Highway, Silver Spring, MD 20910, USA

G. M. StaVGeology Department, Austin Community College, NRG Campus, 11928 Stonehollow Drive, Austin, TX 78758, USA

S. E. WalkerDepartment of Geology, University of Georgia, Athens, GA 30602, USA

A. RaymondDepartment of Geology and Geophysics, Texas A&M University, College Station, TX 77843, USA

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“taphofacies”, and that these can be used to characterizemajor environments of preservation (EOPs) (Brett andBaird 1986). Furthermore, the spatial distribution of thesetaphofacies should be associated with environmental gra-dients, such as depth and sediment type, that permitassemblage taphonomic signature to be interpreted withinthe framework of preservation potential and environment(Brett and Baird 1986; Kidwell et al. 1986; Meldahl andFlessa 1990; Callender et al. 1992; Callender and Powell2000). Recognition of taphofacies accordingly can pro-vide insight into the preservational biases that modiWedthe fossil assemblage from the original assemblage oforganisms (e.g., Behrensmeyer 1984; Parsons and Brett1991; Kidwell and Flessa 1995), limited only to thedegree to which the preservational process creating thetaphofacies is understood. Many important taphonomicprocesses aVecting the preservation of the death assem-blage, including decomposition, burial, fragmentation,dissolution, abrasion, precipitation, and infestation byepi- and endobionts (Powell et al. 1989; Smyth 1989;Brett 1990; CanWeld and Raiswell 1991; Parsons and Brett1991; Flessa et al. 1993), can exert a signiWcant inXuencewithin months of death, if not simultaneously with it (e.g.,Simon et al. 1994; Kiene et al. 1995; Christmas et al.1997; Cadée 1999; Walker 2001; Zuschin et al. 2003).The preservational process is modulated by such pro-cesses as burial, exhumation, transportation, and encrusta-tion (Kidwell 1986b; Powell 1992; Zuschin and Pervesler1996; Zuschin et al. 1999; Walker and Goldstein 1999;Walker 2001; Carroll et al. 2003), however, and therebymay be extended signiWcantly in time. Thus, taphofaciesare the product of many processes of considerable tempo-ral extent.

Taphonomic models, both conceptual and numerical,have been developed to describe the process of preservation(Kidwell 1986a; Powell 1992; Shimoyama and Fujisaka1992; Kowalewski and Mimniakiewicz 1993; Olszewski1999; Courville and Collin 2002). Such models suggest thattaphonomic rates are likely themselves to be time-depen-dent, so that knowledge of the preservational state of skele-tal remains at any particular time after death may not bepredictive of a future state. To date, however, only limitedempirical information exists concerning the processesdetermining the fate of skeletal material after the Wrst fewmonths to years of taphonomic time (Callender et al. 1994,2002; Behrensmeyer et al. 2000; Powell et al. 2002, 2008)and, thus, the attainment of the full promise of the taphofa-cies approach is precluded.

Physically destructive processes are not the only altera-tions that begin shortly after death. Occupation of theshell by biont encrusters and borers may occur during life

and proceed rapidly after death (e.g., Black and Peterson1987; Mao Che et al. 1996; Nebelsick et al. 1997; Kaehler1999). Generally, taphofacies analysis has not included anevaluation of biont composition and coverage (e.g., Mel-dahl and Flessa 1990; StaV and Powell 1990; Callenderet al. 1992; Martin et al. 1996; but see Gunter et al. 1957;Aller 1995; Allmon et al. 1995); however, bionts areinXuenced by many of the processes also aVecting shellpreservation, such as burial (Gordillo and Aitken 2000;Parsons-Hubbard 2005), and thus might provide addi-tional information on the process by which preservationbiased the fossil assemblage from the original assemblageof organisms. The degree to which bionts are major tapho-nomic indicators of preservation or provide discrimina-tory information on environment and preservationalprocess is not well understood; nor is the modulatoryinXuence of bionts on the taphonomic process adequatelyfathomed. Certainly bionts are responsible directly orindirectly for a number of destructive processes (Akpanand Farrow 1985; Farrow and Fyfe 1988; Fürsich andPandey 1999) and the protective inXuence of bionts mayalso be consequential (Farrow and Clokie 1979; Kidwell1986a; Zuschin and Pervesler 1996; Zuschin et al. 2003).Accordingly, one expects bionts to inXuence the preserva-tional process signiWcantly in some environments of pres-ervation and thus participate in the creation oftaphofacies. What is limiting further illumination of thispremise is a body of detailed actualistic studies in whichthe act of preservation and biont occupation have beenfollowed and compared to document the role of bionts inthe formation of a fossil assemblage from the originalassemblage of organisms.

In 1993, SSETI (Shelf and Slope Experimental Taphon-omy Initiative) was established with the principal goal ofmeasuring taphonomic rates of skeletal material over anextended period of time (Parsons et al. 1997, Parsons-Hub-bard et al. 1999, 2001). SSETI deployed experiments in theBahamas oV Lee Stocking Island (LSI) (Fig. 1) and in theGulf of Mexico (Fig. 2) in 18 visually distinctive environ-ments. Experiments were retrieved from each of theselocales 8 years later. Powell et al. (2008) discuss the tapho-nomic status of these shells after 8 years on the seaXoor andprovide photographs of a representative suite of theseshells. Dissolution and discoloration were the dominanttaphonomic processes. In this contribution, we comparetaphonomic processes with biont occupation on molluscanshells after 8 years on the seaXoor to determine the relation-ship of biont occupation and shell destruction during thepreservational process and the degree to which the twofacilitate a fuller appreciation of the environment of preser-vation and the preservational process.

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Methods

Site description

Bahamas

Experiments were deployed in 1993 and 1994 by scuba andthe submersible Nekton Gamma along transects AA andBA established by the Caribbean Marine Research Center/National Undersea Research Program (Fig. 1). Transect AAis located directly oV an inlet that separates Lee StockingIsland from Adderly Cay to the NNW. The shallow sites onthe AA transect are subject to fairly high wave and currentenergy and sediment transport due to the close proximity ofthis inlet. Transect BA is southeast of AA about half way

down Lee Stocking Island and, as a consequence, isimpacted by less current energy and sediment transport.Parsons et al. (1997) and Parsons-Hubbard et al. (1999)provide descriptions of these experimental sites.

The experimental sites are located in seven distinctiveEODs along each transect (Fig. 1): in sand channels aboutmidway across the platform top (15 m) and near the plat-form edge (30 m), on ledges (70–88 m) down the wall thatdrops steeply (>60°) into Exuma Sound, on the upper(183 m—transect BA only) and lower (210–226 m) talusslope below the wall characterized by shingled carbonatedebris, large talus blocks and small lithiWed carbonate out-crops, and on the crest (256–264 m) and in the trough (259–267 m) of large sand dunes that roughly parallel the slopeof the reef wall, with each dune crest being deeper than thepreceding one. In addition, a site was established in a shal-low hypersaline coastal lagoon, Norman’s Pond, onAdderly Cay.

Gulf of Mexico

Parsons et al. (1997), Parsons-Hubbard et al. (1999), andPowell et al. (2008) provide descriptions of these sites(Fig. 2). Experiments were deployed in 1993 by the sub-mersible Johnson-Sea-Link at selected sites along the shelfedge and slope to the northeast of Galveston, Texas. Exper-iments were deployed at the East Flower Garden (EFG), adeep reef atop a salt diapir (Bright and Powell 1983; Gard-ner et al. 1998; Lugo-Fernández 1998), on the deep reefalcoralline-algal dominated hardground, in an anoxic brinepool (200‰) (Rezak and Bright 1981; Powell et al. 1986),in a brine-Wlled canyon downslope from the pool (Gittingset al. 1984), at the canyon mouth where dilution returnssalinity to near normal (Powell et al. 1986), on the carbon-ate sand of the canyon fan downslope of the canyon mouth,and in the gravel-to-sandy carbonate sediment downslopeof the hard bank (Powell et al. 1983). Experiments werealso deployed at Parker Bank, another shelf-edge bank situ-ated on top of a salt diapir (Rezak et al. 1990). The centerof this bank has collapsed leaving a central basin Wlled withlarge carbonate blocks and Wne ooze. Experiments weredeployed at two locations 10 m apart in depth on the car-bonate rim that supports a thriving deep-water carbonatehard-bottom community.

Experiments were deployed at two very diVerent petro-leum seeps with lush chemoautotrophic-based communitieson the continental slope. Garden Banks GB425 is a massiveclam (lucinid and thyasirid) community. Green CanyonGC234 is mussel and tubeworm dominated (Callender andPowell 1999, 2000). GC234 and GB425 are in a geologi-cally and bathymetrically complex region characterized byactive salt diapirism, associated faulting (Bouma et al.1980, 1981; Behrens 1988), widespread active seepage of

Fig. 1 Location of SSETI sites oV Lee Stocking Island, Bahamas

Fig. 2 Location of SSETI sites in the Gulf of Mexico. EFG East Flow-er Garden, GC Green Canyon, GB Garden Banks, PB Parker Bank,STX South Texas Shelf

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liquid and gaseous hydrocarbons (Kennicutt et al. 1988a,b), and locally high sedimentation rates (Roberts and Car-ney 1997; MacDonald et al. 2000). More details can befound in Carney (1994), Callender and Powell (1997),MacAvoy et al. (2002), and Bergquist et al. (2003).

In 1995, an additional site was established oV CorpusChristi Bay on the outer Texas shelf. This area is the pur-ported depocenter for suspended sediments originatingfrom the Mississippi River funneled by alongshore Xowdown the Texas coast (Cochrane and Kelly 1986; Siringanand Anderson 1994) and is characterized by a well-devel-oped nepheloid layer (Shideler 1981) and a death assem-blage dominated by burrowing echinoid rather thanmolluscan remains (Hill et al. 1982; our unpubl. data).

Experimental design

The SSETI experimental design is described in detail inParsons et al. (1997). Each experimental array consisted ofa series of 1-cm-mesh bags attached to a 1.5-m PVC pole.To each pole was added a 12-kg weight to counter a 25-cmsquare Xoat made of 6-mm-thick sheet polypropylene. TheXoat rose about 0.5 m above the array and served to markthe location of the experiment even when buried. The PVCpole was unattached to the bottom, anchored only by the12-kg weight, and so was free to move, given suYcient cur-rent and wave action. Two of the mesh bags on each polecontained molluscan shells, typically Wve individuals ofWve diVerent species, each species compartmentalized fromthe others by plastic cable ties. Molluscan species deployedincluded the ocean quahog Arctica islandica, the musselMytilus edulis, the lucinid Codakia orbicularis, the veneridMercenaria mercenaria, the glycymerid Glycymerisundata, the scallop Argopecten irradians, the ceriths Rhi-noclavus vertagus and Telescopium telescopium, the conchStrombus luhuanus, and the turritellid, Turritella terebra.

Arrays deployed on LSI transect AA were recovered in1999 by scuba and the submersible Delta. Arrays deployedon LSI transect BA were recovered in 2001 by scuba andthe submersible Clelia. Arrays deployed at Gulf of Mexicosites were recovered in 2001 using the submersible John-son-Sea-Link. Due to shell availability for diVerent deploy-ment eVorts, not all species were deployed at each site.Parsons-Hubbard et al. (1999, 2001) analyzed the degree ofburial of these experiments and characterized each arraydeployment as exposed, dusted (by a Wne layer of sedi-ment), or buried at the time of collection 2 years afterdeployment. These observations were updated by Powellet al. (2008). The number of individuals of each speciesrecovered and analyzed from the 6- to 9-year recoveries isprovided in Powell et al. (2008). For simplicity, these willbe combined under the appellation ‘eight-year recoveries’hereafter.

Laboratory analyses

Laboratory analyses of shell specimens were completedwithin 48 h after recovery. During this time, shells weremaintained in chilled seawater, except when under activeanalysis. Each shell was assessed for taphonomic alterationand biont coverage. The types of taphonomic alterationassessed included breakage, edge alteration, periostracumcondition, color alteration, and evidence and severity ofdissolution and abrasion. We recognize that our study doesnot discriminate chemical dissolution from maceration(Poulicek et al. 1981; Glover and Kidwell 1993; Behrens-meyer et al. 2000) and we use the term dissolution to referto both processes. Each of these taphonomic processes wasevaluated using a semiquantitative scale described byDavies et al. (1990) on each of eight standard shell areas forbivalves on the inner and outer surfaces (see Davies et al.1990) and on Wve standard shell areas for gastropods modi-Wed from Davies et al. (1990), namely the spire aperture up,spire aperture down, body whorl aperture up, body whorlaperture down, and the inside aperture/columella complex.Kidwell et al. (2001) provide a critical review of this meth-odology. Bionts were identiWed microscopically to the low-est possible taxon, the genus where possible: coverage wasassigned visually on each of the aforementioned shell areasas a fraction of the total shell surface of that shell area cov-ered. Bionts overgrown by other taxa were allocated theirentire shell coverage fraction, so that total biont coveragecan exceed 100%.

Statistical analyses

Data reduction

To analyze the bionts, biont taxa were Wrst assigned toguilds. Guilds represent a combination of higher taxonomiccategories and modes of life (Root 1967; SimberloV andDayan 1991). Inasmuch as preservability is a critical com-ponent of the study, bionts otherwise in the same guildwere separated into preservable and non-preservable com-ponents. Most preservable taxa had hard-parts attached tothe shell such as carbonate tubes and skeletal elements.However, some preservable taxa were produced by soft-bodied forms or vagrant species that nevertheless left a pre-servable trace such as the grazing marks left by foragingmolluscs (e.g., Farrow and Clokie 1979) and the surfaceimpressions left by some attached organic polychaete tubes(e.g., Fürsich and Pandey 1999).

In the following sections, we will refer to biont guildsand taphonomic traits. The term taphonomic trait refers tothe suite of taphonomic characteristics describing the taph-onomic signature listed in Tables 1 and 2. Some of thesemay be of biotic origin, others abiotic; however, none of

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them can be referred to speciWc biont types. All observablebionts or traces of biont activity that can be referred to spe-ciWc bionts are assigned to biont guilds, not taphonomictraits.

For statistical analysis, biont guilds and taphonomictraits were treated in one of three ways. (1) For dissolutionand for biont guilds, each shell area was assigned a numeri-cal value according to the degree of dissolution or guildcoverage. The average condition for a shell was taken asthe weighted average of the values assigned to each shellarea. Weights assigned were proportional to the fraction oftotal shell surface area contributed by that shell area. Forthis analysis, the weighted average was calculated for theentire shell, both surfaces for bivalves and the entireobservable surface for gastropods. (2) For most taphonomictraits, such as abrasion, discoloration, and edge alteration,and as an alternate way to evaluate dissolution, the mostaltered state observed on any of the discrete shell areas wastaken as the value for that shell. In this case, the analysisfocused on the most extreme condition observed on theshell. This method of evaluation follows the approach usedby StaV and Powell (1990), Callender and Powell (1992)and Callender et al. (1994) and was recommended byKidwell et al. (2001). The simpliWed semiquantitativescales are deWned in Table 1. (3) Some taphonomic traitscannot be apportioned hierarchically by intensity and sowere analyzed as presence/absence attributes. Theseincluded various types of shell discoloration, such as green,orange, gray-to-black, and brown, and various styles of dis-solution, such as pitting and chalkiness (Table 2).

Data analysis

Principal components analysis (PCA) was used to obtainunique descriptors of shell condition from combinations oftaphonomic traits and biont guilds. One PCA was con-ducted for all species using all taphonomic variables and asubset of biont guilds that occurred commonly at multiplesites. The PCA was repeated with the biont guilds restrictedonly to the preservable subgroups. Each variable was stan-dardized to a mean of zero and a standard deviation of 1prior to the PCA. All molluscan species were included inthe PCA. Hierarchical taphonomic traits utilized in thePCA encompass breakage, maximum degree of abrasion,degree of edge alteration, maximum degree of discolor-ation, and maximum and average degrees of dissolution.Presence/absence taphonomic traits utilized in the PCAinclude pitting, the presence of a soft shell surface, the pres-ence of a deeply dissolved surface, the presence of dis-solved perforations in the shell, original coloration, fadedcoloration, gray-to-black discoloration, brown-to-red dis-coloration, orange discoloration, and green discoloration.Biont guilds included green algae, red algae, corallinealgae, brown algae, sponges, tunicates, attached mollusks,non-preservable bryozoans, epibiotic (non-boring) fungi,unidentiWed surface traces, boring fungi, boring algae,agglutinated tubes of polychaetes, carbonate tubes of poly-

Table 1 The simpliWed semiquantitative scale used in statisticalanalysis derived from Davies et al. (1990)

Data were originally recorded using their more complex scales andthen simpliWed in Wnal analysis

Taphonomic trait

Taphonomic state Numerical value

Wholeness Shell whole 1

Shell broken 2

Abrasion Unabraded 0

Small nicks; frosted; sculpture eroded, no holes

1

Highly polished; deeply eroded with holes

2

Edge rounding Edges natural 0

Edges chipped 1

Fragmented; edges sharp 2

Fragmented; edges slightly worn 3

Fragmented; edges smooth 4

Discoloration Original 1

Original, but faded 2

Original color faded to white or discolored (e.g., gray)

3

Dissolution Undissolved 0

Surface chalky; minor pitting 1

Surface pitting moderate to heavy; surface soft; sculpture enhanced

2

Surface sculpture gone; deeply dissolved

3

Table 2 Taphonomic traits treated as present (1) or absent (0) instatistical analysis

Taphonomic trait Taphonomic state

Dissolution style Chalkiness

Pitting

Soft surface

Deeply dissolved, surface gone

Deeply dissolved, surface gone, shell perforated

Discoloration Original color

Original color faded or faded to white

Gray, light to dark; black or black mottled

Brown to red, brown mottled

Orange, orange mottled, orange mottled with black, brown or white

Green, green mottled, green mottled with black, brown or white

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chaetes, preservable bryozoans, non-photosymbioticforaminifera, photosymbiotic foraminifera, skeletonizedcnidaria, bacterial Wlms, non-foraminiferal protists, andmiscellaneous epibionts.

PCA factor scores were tested statistically in two ways.The Wrst used an ANCOVA analysis. Main eVects wereenvironment of preservation (EOP) and molluscan species.SpeciWc deployment locations were assigned to EOPs fol-lowing Powell et al. (2008). Assignment minimized theoccurrence of signiWcant interaction terms in theANCOVA. Depth was included as a covariate becausemany potentially important variables such as light, foodsupply, and benthic secondary production are expected tovary more or less monotonically with depth (e.g., El-Sayed1972; Rowe 1983; Rowe et al. 1990). A second ANCOVAdescribed the dataset in terms of sediment type, degree ofexposure, and water depth. Sediment types included car-bonate sand, terrigenous sand, hardground, veneered hard-ground (hardgrounds covered with a thin veneer of sand),brine, carbonate mud, and terrigenous mud. Degree ofburial was assigned from video documentation to fourexposure categories: exposed, dusted, partly buried, andburied. Allocation to the categories of exposed, dusted, andburied followed the convention of Parsons-Hubbard et al.(1999, 2001). An array with both shell bags completelyburied was assigned to the ‘buried’ category. The category‘dusted’ applied to arrays with shell bags covered by a Wnelayer of sediment through which the bags could still be dis-cerned. In some arrays, bags were partially buried: eitherone bag was buried and the other was not or a portion of abag was buried and the remainder exposed. Arrays of thistype were assigned to the ‘partially buried’ category. Spe-cies was included as a main eVect in all ANCOVAs. In allcases hereafter, the term ‘species main eVect’ will refer tocomparisons among the molluscan species deployed, notfor example to biont taxa that may have subsequently colo-nized these shell substrates. All ANCOVAs also includedall pair-wise interaction terms. A posteriori Tukey’s Stu-dentized Range Tests were used to identify sources of sig-niWcance within the ANCOVA; however we caution thereader that signiWcant interaction terms whenever theyoccur limit the interpretation of the results of Tukey’s Stu-dentized Range Tests.

Preliminary analyses for the primary taphonomic traitsdesigned to detect signiWcant diVerences between bagswhen a species was deployed in both bags on the samearray demonstrated signiWcant diVerences infrequently(9.8%), but signiWcantly more often than expected bychance at ! = 0.05 (binomial test, p = 0.05, q = 0.95,n = 1,476, P < 0.0001), but not at ! = 0.10 (p = 0.10,q = 0.90, P » 0.41). Many species were present only in oneof the two bags on a given array, however, obviating anested analysis of variance that otherwise might be used to

accommodate this variability (Hurlbert 1984). As a conse-quence, when a species was present in both bags on anarray, these data were combined for subsequent analyses.The reader is cautioned that some variability in these casesoriginated from bag placement and this variability has notbeen treated independently in these analyses.

The collected arrays were assigned to 24 EOPs. The tenGulf of Mexico EOPs providing the eight-year recoverydata will be referred to as East Flower Garden (EFG) deep-reef hardground (EFGHD), EFG brine pool (EFGBR), EFGcanyon brine stream (EFGCS), EFG canyon mouth(EFGCM), EFG canyon talus fan (EFGCF), EFG deep car-bonate sand (EFGDS), Garden Banks petroleum seepGB425 (GB425), Green Canyon petroleum seep GC234(GC234), south Texas outer continental shelf (STXS), andParker Bank carbonate rim (PARKR). The petroleum seepat GC234 is characterized by signiWcant taphonomic vari-ability between deployment sites (Cai et al. 2006). Never-theless, this complex taphonomic environment has beenretained as a single EOP. The 14 Bahamian EOPs will bereferred to as Norman’s Pond (NORMP), platform top(AA15M, BA15M), platform edge (AA30M, BA30M),wall (AAWALL, BAWALL), upper talus slope(AA183M), lower talus slope (AATALUS, BATALUS),dune crest (AACREST, BACREST), and dune trough(AATROFF, BATROFF). The AA and BA preWxes dis-criminate the Bahamian EOPs by transect location as wellas depth. Powell et al. (2008) found signiWcantly diVerenttaphonomic signatures in many pairwise comparisonsbetween deployments at the same depth on these two tran-sects. Some EOPs were represented by multiple array col-lections (e.g., GB425), whereas others were represented bya single array collection (e.g., EFGCS) [Powell et al. (2008)provide details], thus obviating a nested analysis of vari-ance that otherwise might be used to accommodate this var-iability. The reader is cautioned that some variability inEOP analyses may have originated from array placementand this variability has not been treated independently inthese analyses.

EOPs were clustered by the PCA factor scores using anunweighted pair-group method with Euclidean distance asthe similarity index (Boesch 1977).

Results

Principal components analysis: all guilds

Fourteen factors described 59% of the variation in tapho-nomic traits and bionts (Table 3). Four of these includedpreservable bionts. The majority of preservable bionts, suchas carbonate polychaete tubes, bryozoans with carbonateskeletons, boring sponges and boring algae, and coralline

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algae, loaded on factor 1. Along with these preservablebionts was a single taphonomic trait, the incidence of greendiscoloration. The attached mollusks and photosymbioticforaminifera, along with brown algae, determined factor 6.The only preservable bionts not loading on factors 1 and 6were skeletal cnidarians that determined factor 14 withminor contributions from a set of nonpreservable bionts andcoralline algae that loaded with green and brown algae onfactor 8. Factors 4 and 13 represented the only uniquely

non-preservable biont groups, the red algae belonged to theformer and the non-preservable bryozoans, sponges, andtunicates to the latter.

Of the remaining eight factors, Wve were dominantlytaphonomic in character. One, factor 7, described abrasion,shell breakage and edge rounding. Dissolution wasdescribed by factor 2, including the average and maximumvalue for the shell and two speciWc dissolution types, pittingand deep dissolution. Three described various states of

Table 3 Biont guilds and taphonomic traits loading on the Wrst 14 factors from a principal components analysis using all deployed bivalve andgastropod species and both preservable and non-preservable biont guilds

Listed variables have loading scores ¸0.25 or ·¡0.25

Biont/taphonomic variable Factor load Biont/taphonomic variable Factor load

Factor 1 Preservable bryozoans 0.69 Carbonate polychaete tubes 0.63

Boring sponges 0.60 Boring algae 0.60

Green discoloration 0.59 Non-photosymbiotic foraminifera 0.51

Coralline algae 0.41 Surface traces 0.28

Incidence of chalkiness ¡0.25

Factor 2 Maximum degree of dissolution 0.88 Incidence of deeply dissolved surface 0.84

Average degree of dissolution 0.67 Incidence of pitting 0.55

Factor 3 Maximum degree of discoloration 0.82 Incidence of brown discoloration 0.82

Maximum degree of abrasion 0.26 Incidence of original color ¡0.63

Factor 4 Miscellaneous epibionts 0.91 Red algae 0.91

Factor 5 Bacterial Wlms 0.80 Incidence of a soft shell surface 0.78

Incidence of a dissolved surface with holes 0.45 Average degree of dissolution 0.35

Incidence of chalkiness 0.26

Factor 6 Attached molluscs 0.69 Photosymbiotic foraminifera 0.58

Brown algae 0.51 Boring algae 0.37

Carbonate polychaete tubes 0.34

Factor 7 Degree of breakage 0.71 Degree of edge rounding 0.67

Surface traces 0.31 Agglutinated polychaete tubes 0.25

Maximum degree of abrasion 0.26

Factor 8 Green algae 0.76 Coralline algae 0.66

Brown algae 0.37

Factor 9 Incidence of orange discoloration 0.68 Maximum degree of abrasion 0.45

Incidence of gray-to-black discoloration 0.40 Agglutinated polychaete tubes 0.35

Maximum degree of discoloration 0.26 Incidence of original color ¡0.25

Factor 10 Incidence of faded color 0.82 Agglutinated polychaete tubes ¡0.26

Incidence of brown discoloration ¡0.30 Incidence of original color ¡0.44

Factor 11 Boring fungi 0.70 Incidence of gray-to-black discoloration 0.64

Epibiotic fungi 0.35

Factor 12 Non-foraminiferal protists 0.66 Incidence of chalkiness 0.47

Epibiotic fungi 0.43 Incidence of pitting 0.29

Average degree of dissolution 0.29

Factor 13 Non-preservable bryozoans 0.80 Sponges 0.54

Tunicates 0.27

Factor 14 Skeletal cnidarians 0.65 Tunicates 0.43

Sponges 0.32 Agglutinated polychaete tubes 0.32

Incidence of dissolved surface with holes ¡0.28 Surface traces ¡0.37

22 Facies (2011) 57:15–37

123

discoloration; brown discoloration on factor 3, orange discol-oration on factor 9, and fading of original color on factor 10.

A unique set of three factors combined a taphonomictrait with a microbial biont group. Factor 11 combinedgray-to-black discoloration with the incidence of boringfungi. Factor 12 combined the incidence of chalkiness withnon-foraminiferal protists and, to a lesser extent, epibioticfungi. Factor 5 combined bacterial Wlms with the develop-ment of a soft shell surface.

The 14 factors document a substantial dichotomybetween bionts and taphonomic traits. Two examples onlyresolve relationships between biont guild and taphonomictrait. The Wrst is three cases in which one or more microbialbionts occur with one or more taphonomic traits, one formof discoloration in one case and two degrees of chalkiness,simple chalkiness and the development of a soft shell sur-face, in the other two. The second example is the relation-ship between green discoloration and a suite of preservablebionts including boring green algae. Zoobionts relate littleto taphonomic traits beyond those correlated with boringgreen algae and consequently adventitiously associatedwith green discoloration.

Principal components analysis: preservable guilds

Restricting the analysis to just the preservable biont guilds,and the suite of taphonomic traits, produced nine factors

garnering 58% of the variation in the data (Table 4). Thebiont guilds contributed in similar measure to their contri-bution in the former analyses. Factor 1 contained the major-ity of preservable bionts, including the preservablebryozoans, coralline algae, boring sponges, boring algae,carbonate polychaete tubes, and non-photosymbioticforaminifera. Of lesser (but still of substantial importance)in factor 1 is green discoloration. With a single exception,the remaining preservable bionts fell on factor 4, thesebeing principally the attached molluscs and photosymbioticforaminifera.

The remaining factors segregated into three primarygroups. In the Wrst were two factors describing various aspectsof taphonomic degradation by means of dissolution. One, fac-tor 2, combined pitting with a deeply dissolved surface. Theother, factor 5, combined chalkiness with a soft shell surfaceand a dissolved perforated surface. The second group, a sin-glet of factor 6, described breakage and edge rounding. Thethird comprised three factors describing various types of dis-coloration: Factor 3 was determined by the incidence ofbrown discoloration; factor 7, by the incidence of a faded shellsurface; and factor 8, by orange discoloration.

One factor, factor 9, combined gray-to-black discolor-ation with surface traces. Allowing surface traces the statusof a biont guild conjoins factor 9 with factor 1 as the onlyfactors encompassing at least one taphonomic trait and onebiont guild.

Table 4 Biont guilds and taphonomic traits loading on the Wrst nine factors from a principal components analysis using all deployed bivalve andgastropod species, but only the preservable biont guilds

Listed variables have loading scores ¸0.25 or ·¡0.25

Biont/taphonic variable Factor load Biont/taphonomic variable Factor load

Factor 1 Preservable bryozoans 0.74 Coralline algae 0.63

Boring algae 0.62 Carbonate polychaete tubes 0.61

Boring sponges 0.58 Non-photosymbiotic foraminifera 0.55

Incidence of green discoloration 0.47

Factor 2 Maximum degree of dissolution 0.89 Incidence of dissolved surface 0.86

Average degree of dissolution 0.61 Incidence of pitting 0.56

Factor 3 Maximum degree of discoloration 0.85 Incidence of brown discoloration 0.75

Maximum degree of abrasion 0.30 Incidence of original color ¡0.71

Factor 4 Attached mollusks 0.70 Photosymbiotic foraminifera 0.68

Carbonate polychaete tubes 0.38 Boring algae 0.38

Incidence of deeply dissolved surface 0.26

Factor 5 Incidence of soft shell surface 0.65 Incidence of deeply dissolved surface with holes 0.63

Average degree of dissolution 0.53 Incidence of chalkiness 0.49

Factor 6 Degree of breakage 0.75 Degree of edge rounding 0.71

Incidence of gray-to-black discoloration ¡0.29

Factor 7 Incidence of fading 0.86 Incidence of brown discoloration ¡0.42

Incidence of original color ¡0.45

Factor 8 Incidence of orange discoloration 0.86 Maximum degree of abrasion 0.41

Factor 9 Surface traces 0.69 Incidence of gray-to-black discoloration 0.62

Facies (2011) 57:15–37 23

123

InXuence of depth and EOP

We examined the inXuence of depth and EOP on the distri-bution of biont guilds and taphonomic traits using the PCAfactor scores for all species, all taphonomic traits, and allbiont guilds. The covariate depth was signiWcant in onlyone of 14 cases (Table 5), an outcome likely to occur bychance (binomial test, P > 0.05). In contrast, EOP was sig-niWcant in seven of 14 cases, an occurrence rate far exceed-ing chance (binomial test, P < 0.0001) (Table 5). ThesigniWcant factors encompassed a range of taphonomictraits and biont guilds, including brown discoloration (fac-tor 3), edge rounding and breakage (factor 7), gray-to-blackdiscoloration (factor 11), red algae (factor 4), green andcoralline algae (factor 8), and non-preservable bionts (fac-tors 13 and 14). Notably absent was factor 1 that encom-passed most preservable biont guilds and the factorsdescribing various states of dissolution.

The signiWcance for factor 3 originated from a series ofdeepwater carbonate EOPs where brown discoloration wasparticularly common, in the Bahamas and at the EastFlower Garden, and a few stations where brown discolor-ation was particularly uncommon, the brine-aVected sites atthe East Flower Garden and the 30-m sites in the Bahamas(Table 6). The signiWcance of factor 4 originated from aseries of carbonate sand and hardground sites in the Baha-mas, at Parker Bank, and at the East Flower Garden inwhich red algae were unusually common (Table 7). Edgerounding occurred most often at the 15-m sites in the Baha-mas and the deeper carbonate sites at the East Flower Gar-den (Table 7) and this contributed to the signiWcance offactor 7. Factor 8 scores were unusually high for shellsdeployed on the hardground of the East Flower Gardenwhere coralline algae were unusually frequent (Table 8).The signiWcance of factor 11 originated from a series oflocations on Bahamian transect BA where shells hadunusually high incidences of gray-to-black discolorationand boring fungi (Table 8). These EOPs encompassed thedepth range of the transect (Table 8). Gray-to-black discol-oration was also relatively common on shells from thedeeper sites of Bahamian transect AA. Factor 13 was deW-ned by a series of non-preservable bionts. These were mostcommon at Parker Bank (Table 9). Factor 14 encompasseda series of non-preservable bionts plus the skeletal cnidari-ans and achieved highest factor scores for shells deployedat the wall EOPs in the Bahamas, on the Parker Bankveneered hardground, at carbonate sites at the East FlowerGarden, and at Norman’s Pond (Table 9). Consequently,the cases for which EOP was signiWcant distinguished aseries of carbonate sites from the Bahamas, the East FlowerGarden, and Parker Bank from the remaining EOPs.

Molluscan species generated a signiWcant main eVectonly twice, for factors 11 and 13 (Table 5). Rhinoclavusvertagus and Telescopium telescopium tended to have ahigh incidence of gray-to-black discoloration and boringfungi, but much of this was due to the coincidentalrestricted deployment of these species at a preponderanceof sites where shells were so characterized. A suite of non-preservable bionts described by factor 13 were more com-mon on Mytilus edulis. As mussels were deployed at mostsites, the tendency for non-preservable biont guilds to aVectM. edulis is likely a shell structural or periostracal facilita-tion. SigniWcant interaction terms occurred in 13 of 56cases (Table 5), more frequently than expected by chance(binomial test, P < 0.0001). Most involved the species maineVect and likely originated predominately from the deploy-ment of selected species at only a subset of sites (Powellet al. 2008, list location of deployment by species). SigniW-cant interaction terms, however, also were frequently asso-ciated with factors characterized by signiWcant EOP maineVects, indicating that the inXuence of EOP was modulated

Table 5 ANCOVA using, as dependent variables, the 14 factorsobtained from the PCA using all biont guilds, preservable and nonpre-servable, and all taphonomic traits

NS not signiWcant at ! = 0.10, EOP environment of preservation

* An interaction term

Factor 1 Factor 2 Factor 3 Factor 4 Factor 5

EOP NS NS 0.0001 0.0001 NS

Species NS NS NS NS NS

EOP*species 0.0006 NS NS NS NS

Depth NS NS NS NS NS

Depth*EOP NS NS 0.012 0.0003 NS

Depth*species NS NS NS NS NS

Depth*EOP*species 0.0025 NS NS NS NS


EOP NS 0.034 0.025 NS NS

Species NS NS 0.051 NS NS

EOP*species NS NS 0.0004 NS NS


Depth*EOP NS NS NS NS NS

Depth*species NS NS 0.011 NS NS

Depth*EOP*species NS NS 0.0019 NS NS

Factor 11 Factor 12 Factor 13 Factor 14

EOP 0.0001 NS 0.0001 0.026

Species 0.0001 NS 0.0001 NS

EOP*species 0.021 NS 0.0001 NS

Depth NS 0.031 NS NS

Depth*EOP NS NS 0.0001 NS

Depth*species NS NS 0.0001 NS

Depth*EOP*species NS NS 0.0001 NS

24 Facies (2011) 57:15–37

123

by the composition of the deployed species and also by thedepth of the deployment sites.

Restricting the biont guilds to the preservable subsetyielded nine PCA factors (Table 4). These much less fre-quently were characterized by signiWcant main eVects(Table 10). For EOP, only factor 3 achieved signiWcance.Factor 3 was a general discoloration index, also character-ized by brown discoloration. Some East Flower Garden andBahamian AA transect sites ranked highest for this factor,whereas the brine sites at the East Flower Garden and the30-m Bahamian sites ranked lowest (Table 11). Factor 1,though not signiWcant at ! = 0.05, was nearly so (Table 11).This factor encompassed the majority of the preservablebiont guilds. Depth was in no case signiWcant and a signiW-cant species main eVect occurred only once, for factor 1that encompassed most preservable biont guilds (Table 10).

Table 6 Results of an a posteriori Tukey’s Studentized Range Testfor factor 3 obtained from the PCA using all biont guilds and tapho-nomic traits

Variables loading on factor 3 include the maximum degree of discolor-ation and the incidence of brown discoloration (Table 3). DiVerent let-ters indicate a signiWcant diVerence between EOPs at P < 0.05. Thus,for example, AA30M identiWed by the letter K is signiWcantly diVerentfrom EFGCS, but not from EFGBR. EFGBR identiWed by the letters Jand K is not signiWcantly diVerent from AA30M, BA30M, or EFGCS,but is signiWcantly diVerent from all EOPs listed above BA30M

A EFGCM

A B EFGCF

A B C AACREST

A B C EFGDS

A B C D AATROFF

B C D E GC234

B C D E F EFGHD

B C D E F G AATALUS

B C D E F G BA183M

B C D E F G PARKR

B C D E F G BATALUS

B C D E F G GB425

B C D E F G BAWALL

C D E F G AA15M

D E F G H BA15M

E F G H I BACREST

F G H I AAWALL

G H I NORMP

G H I BATROFF

G H I STXS

H I J BA30M

I J EFGCS

J K EFGBR

K AA30M

EOP AbbreviationsGulf of Mexico

East Flower Garden deep-reef hardground EFGHD

East Flower Garden brine pool EFGBR

East Flower Garden brine canyon EFGCS

East Flower Garden canyon mouth EFGCM

East Flower Garden canyon talus slope EFGCF

East Flower Garden deep carbonate sand EFGDS

Petroleum seep GB425 GB425

Petroleum seep GC234 GC234

South Texas outer continental shelf STXS

Parker Bank carbonate rim PARKR

Caribbean

Norman’s Pond NORMP

Platform top, Transect AA AA15M

Platform top, Transect BA BA15M

Platform edge, Transect AA AA30M

Platform edge, Transect BA BA30M

Wall, Transect AA AAWALL

Wall, Transect BA BAWALL

Upper talus slope, Transect BA BA183M

Lower talus slope, Transect AA AATALUS

Lower talus slope, Transect BA BATALUS

Dune crest, Transect AA AACREST

Dune crest, Transect BA BACREST

Dune trough, Transect AA AATROFF

Dune trough, Transect BA BATROFF

Table 7 Results of an a posteriori Tukey’s Studentized Range Testfor factors 4 and 7 obtained from the PCA using all biont guilds andtaphonomic traits

Variables loading on factor 4 include miscellaneous non-preservableepifauna and red algae. Variables loading on factor 7 include breakageand edge rounding (Table 3). DiVerent letters indicate a signiWcantdiVerence between EOPs at P < 0.05. See Table 6 for further explana-tion of letter designations. EOP abbreviations deWned in Table 6

____________Factor 4___________ ________Factor 7________

A AA15M A BA15M

A B PARKR A B EFGCF

A B C EFGHD A B AA15M

A B C EFGDS A B C STXS

A B C EFGCF A B C D EFGDS

A B C BAWALL B C D E AA30M

B C EFGCS B C D E F GC234

B C BATALUS B C D E F GB425

B C BACREST B C D E F G BA30M

B C BA183M B C D E F G EFGCM

B C GC234 C D E F G H BAWALL

B C AA30M C D E F G H BA183M

B C BATROFF C D E F G H EFGBR

B C EFGBR C D E F G H EFGCS

B C BA30M D E F G H AATROFF

B C AACREST D E F G H BATALUS

B C EFGCM D E F G H PARKR

B C NORMP D E F G H AACREST

B C AAWALL E F G H EFGHD

B C GB425 E F G H BATROFF

B C AATROFF F G H AATALUS

B C STXS F G H BACREST

C BA15M G H NORMP

C AATALUS H AAWALL

Facies (2011) 57:15–37 25

123

Once again, this result accrued from the limited range ofdeployment of some species; Telescopium telescopiumbeing deployed predominately at the Bahamian sites is anexample (Powell et al. 2008). SigniWcant interaction termsoccurred in four of 36 cases, more frequently than expectedby chance. These were exclusively explained either by thevariation in deployment sites among species or a diVeren-tial inXuence of depth on EOP.

InXuence of sediment type and degree of exposure

An ANCOVA using sediment type, degree of exposure,and water depth as unique EOP descriptors produced sig-niWcant main eVects for nearly all nine factors determinedby preservable biont guilds and taphonomic traits. Interac-tion terms were routinely signiWcant (Table 12). The analy-sis discloses that, whereas EOPs frequently have a uniquecombination of depth, degree of exposure, and sediment

type, these three characteristics are insuYciently determi-native of the distribution of biont guilds and taphonomicprocesses to adduce from them a unique EOP description.Powell et al. (2008) point out the frequency at which visu-ally comparable environments produced distinctive diVer-ences in taphonomic signature.

Distribution of EOPs among factors

The biont guilds and taphonomic traits that form the PCAfactors are diVerentially distributed among EOPs. Factorscores, which vary substantially among EOPs, may pro-vide disproportionate information in the discrimination ofEOPs. We evaluated the distribution of factor scoresamong EOPs by calculating the variance-to-mean ratio foreach of the 14 factors obtained from the PCA using allbiont guilds and taphonomic traits. These variance-to-mean


Variables loading on factor 8 include green algae and coralline algae.Variables loading on factor 11 include boring fungi and incidence ofgray-to-black discoloration (Table 3). DiVerent letters indicate a sig-niWcant diVerence between EOPs at P < 0.05. See Table 6 for furtherexplanation of letter designations. EOP abbreviations deWned inTable 6

__________Factor 8__________ __________Factor 11__________

A EFGHD A BA183M

B AA15M A B BACREST

B C BA15M B C BA15M

B C EFGDS C AATALUS

B C D AATALUS C BATALUS

B C D BAWALL C D AACREST

B C D BA183M C D E AATROFF

B C D BATALUS C D E F NORMP

B C D GB425 C D E F G BATROFF

B C D EFGCF D E F G H AA15M

B C D EFGCM D E F G H BAWALL

B C D AATROFF E F G H I BA30M

B C D AACREST F G H I EFGCS

B C D BACREST F G H I PARKR

B C D EFGBR G H I AA30M

B C D GC234 G H I STXS

B C D BATROFF H I GC234

B C D EFGCS H I EFGDS

B C D STXS H I EFGCF

B C D AA30M H I GB425

B C D NORMP H I EFGHD

C D BA30M I EFGBR

C D PARKR I EFGCM

D AAWALL I AAWALL


Variables loading on factor 13 include non-preservable bryozoans,sponges, and tunicates. Variables loading on factor 14 include skeletalcnidarians (Table 3). DiVerent letters indicate a signiWcant diVerencebetween EOPs at P < 0.05. See Table 6 for further explanation of letterdesignations. EOP abbreviations deWned in Table 6

__________Factor 13__________ __________Factor 14__________

A PARKR A BAWALL

B AATROFF A B PARKR

B C EFGHD A B C AAWALL

B C D ATTALUS A B C D NORMP

B C D BA15M A B C D E EFGHD

B C D STXS A B C D E EFGCS

B C D AACREST B C D E BA183M

C D NORMP B C D E AATALUS

C D BA30M B C D E BACREST

C D BAWALL C D E AACREST

C D BATALUS C D E EFGCF

C D AAWALL C D E GC234

C D EFGCS C D E EFGCM

C D BATROFF C D E GB425

C D BACREST C D E STXS

C D EFGDS C D E BATALUS

C D GB425 D E EFGDS

C D AA30M D E BATROFF

C D BA183M D E AA30M

D GC234 D E EFGBR

D AA15M D E BA30M

D EFGCM D E F AATROFF

D EFGCF E F AA15M

D EFGBR F BA15M

26 Facies (2011) 57:15–37

123

ratios reveal that some factors were relatively distributedamong EOPs, whereas others were not (Table 13). Great-est variability occurred for factors 1, 5, 7, 8, 12, and 14.This group included three of the four factors subsumingthe preservable biont guilds: Factors 1, 8, and 14. Two oth-ers included the two dissolution factors that diVerentiatedchalkiness and the formation of a soft shell surface fromother dissolution styles. The Wnal one, factor 7, describedbreakage and edge rounding. Not among this group werefactors deWned by nonpreservable biont guilds, nor werefactors describing discoloration represented; thus preserv-able biont guilds and dissolution styles were most discrim-inative of EOPs.

Exclusion of the nonpreservable biont guilds from thePCAs only varied this picture to a small degree (Table 13,Figs. 3, 4). The primary factor deWned by preservable biontguilds, factor 1, and the primary factor deWned by chalki-ness and the incidence of a soft shell surface, factor 5, wereamong the three factors showing greatest variability amongEOPs. The third, factor 7, diVerentiated fading of the origi-nal shell color from other forms of discoloration. This fac-tor did not demonstrate this degree of variability with thePCA that included the nonpreservable biont guilds. Vari-ability was increased in each case by the presence of a fewEOPs in which these factor scores were unusually high(Figs. 3, 4). For factor 1, these EOPs were 15-m EOPs onBahamian transects BA and AA, the East Flower Gardenhardground, and the wall on Bahamian transect AA

(Fig. 3). The other wall EOP (BA) and the Parker Bankveneered hardground also had moderately high factor 1scores (Fig. 3). Extreme values of factor 5 (soft shell sur-face) were found for shells deployed in the East FlowerGarden brine canyon (Fig. 4). The petroleum seep atGC234 and a number of the deeper locations on Bahamiantransect AA also had shells with moderately high factor 5scores (Fig. 4). Factor 7 achieved extreme scores on shellsdeployed at the two shallower EOPs on Bahamian transectBA, at 15 m and at 30 m, on shells deployed at the EFGbrine canyon and in Norman’s Pond (Fig. 4). Most EOPson Bahamian transect AA had unusually low values for fac-tor 2 indicating limited pitting and deep dissolution(Fig. 3). Orange discoloration (factor 8) occurred unusuallyoften at some of the deeper sites on Bahamian transect AAand on shells deployed in Norman’s Pond (Fig. 4).

Table 10 ANCOVA using, as dependent variables, the nine factorsobtained from the PCA using the preservable biont guilds only and alltaphonomic traits

NS not signiWcant at ! = 0.10, EOP environment of preservation



EOP 0.067 NS 0.0001 NS NS

Species 0.0027 NS NS NS NS

EOP*species 0.0001 NS NS NS NS


Depth*EOP NS NS 0.029 NS NS

Depth*species 0.0009 NS NS NS NS

Depth*EOP*species 0.0001 NS NS NS NS


EOP NS NS NS NS

Species NS NS NS NS

EOP*species NS NS NS NS

Depth NS NS NS NS

Depth*EOP NS NS NS NS

Depth*species NS NS NS NS

Depth*EOP*species NS NS NS NS

Table 11 Results of an a posteriori Tukey’s Studentized Range Testfor factor 1 and factor 3 obtained from the PCA using preservable biontguilds only and all taphonomic traits

Variables loading on factor 1 include preservable bryozoans, corallinealgae, boring algae, carbonate polychaete tubes, boring sponges, non-photosymbiotic foraminifera and incidence of green discoloration.Variables loading on factor 3 include maximum degree of discolor-ation and incidence of brown discoloration (Table 11). DiVerent lettersindicate a signiWcant diVerence between EOPs at P < 0.05. See Table 6for further explanation of letter designations. EOP abbreviations deW-ned in Table 6

___________Factor 1___________ __________Factor 3___________

A EFGHD A EFGCM

A BA15M A B AACREST

B AA15M A B EFGCF

B AAWALL A B C AATROFF

C BAWALL A B C D EFGDS

C PARKR A B C D BA15M

D BA30M A B C D PARKR

D E AA30M A B C D GC234

D E F EFGCM A B C D E BA183M

D E F G NORMP A B C D E F AATALUS

D E F G H EFGDS B C D E F EFGHD

E F G H AATALUS B C D E F BATALUS

E F G H STXS B C D E F BAWALL

E F G H EFGCF B C D E F G NORMP

E F G H AATROFF B C D E F G AA15M

E F G H EFGCS B C D E F G GB425

E F G H GB425 C D E F G BACREST

E F G H BATROFF D E F G H BATROFF

F G H EFGBR E F G H AAWALL

G H GC234 F G H STXS

G H BATALUS G H BA30M

H BACREST H I EFGCS

H BA183M I J EFGBR

H AACREST J AA30M

Facies (2011) 57:15–37 27

123

Distribution of factors among EOPs

The EOPs were clustered based on their factor scores.EOPs clustered using the PCA that included all biont guildsresembled the clustering obtained using the PCA limited topreservable biont guilds (Figs. 5, 6) and, consequently, thislatter PCA is focused upon here. The deepwater EOPs onBahamian transect BA, along with the 30-m EOP on tran-sect BA, clustered together (Fig. 6). These EOPs were sim-ilarly characterized by relatively even factor scores with theexception of lower factor 1 scores, indicating a paucity ofthe majority of preservable bionts (Fig. 7). Dissolution waspredominately described by pitting rather than chalkiness(factor 2 > factor 5). Little edge rounding occurred (factor6). The 30-m site diverged from the remainder by having ahigher factor 7 score (Fig. 7), indicating somewhat morefading (factor 7). Gray-to-black discoloration was alsocommon at some of these sites.

The East Flower Garden brine seep (EFGBR) and thesouth Texas shelf site (STXS) clustered together (Fig. 6).

The similarity accrued from the tendency for most factorsto have moderately low to low factor scores (Figs. 8, 9).Shells from these EOPs were characterized by little discol-oration or chalkiness, and a limited coverage of preservablebionts. The EFG brine seep was distinguished by the verylimited degree of discoloration.

Three East Flower Garden EOPs, namely the three EOPsdownslope of the brine canyon (EFGCM, EFGCF,EFGDS), and the two petroleum seep EOPs (GC234,GB425) clustered together (Fig. 6). These EOPs had rela-tively high factor scores for factors 3 and 6, more so for theEast Flower Garden EOPs, indicating discoloration, domi-nated by brown discoloration, and a relatively high degreeof edge rounding (Figs. 8, 9). All Wve EOPs had low factors1 and 9 scores indicating little biont coverage and littlegrey-to-black discoloration. The two petroleum seep siteswere distinguished by the relatively higher degree of disso-lution (factor 2), distinguished by the development ofchalkiness and a soft shell surface, than the East FlowerGarden EOPs (Figs. 8, 9).

The two wall EOPs at the Bahamas (AAWALL,BAWALL), the deep reef at Parker Bank (PARKR), andthe East Flower Garden hardground (EFGHD) clusteredtogether (Fig. 6). Each of these was characterized by rela-tively high coverage of preservable bionts as indicated byhigh factor 1 scores (Figs. 7, 8, 9, 10). The four EOPs wererelatively dissimilar from each other in comparison to theprevious clusters, however. Dissimilarity originated in anumber of ways. The Parker Bank deep reef was character-ized by shells with relatively limited chalkiness in compari-son to pitting and a higher degree of brown discoloration(factors 2 vs. 5, 3) (Fig. 9). Shells from the EFG hard-ground (EFGHD), in contrast, had few photosymbioticforaminifera (factor 4), more fading, and many more of theskeletal bionts typical of factor 1 (Fig. 8). The wall EOP onBahamian transect BA was very similar to the Parker Bankdeep reef (Fig. 7), whereas the wall EOP on Bahamian tran-sect AA had an unusually low degree of dissolution in com-parison to the other EOPs in the group (factor 2) and muchless fading (factor 7) (Fig. 10).

The deepwater EOPs on Bahamian transect AA alsoformed a cluster, as had the deepwater EOPs on the BAtransect, but these two groups were dissimilar (Fig. 6).Shells from the EOPs of transect AA were characterized byfewer preservable bionts (factor 1), a high degree of browndiscoloration (factor 3), increased chalkiness as opposed topitting (factors 2 vs. 5), and the presence of unusually highlevels of orange discoloration (factor 8).

Five sites were particularly unusual. These separatedfrom all others and each from the other four. The Norman’sPond site was characterized by orange discoloration, gray-to-black discoloration, and fading (factors 7–9, Fig. 9). Thiscombination of discoloring processes was unusual among

Table 12 ANCOVA using, as dependent variables, the nine factorsobtained from the PCA using the preservable biont guilds only and alltaphonomic traits

NS not signiWcant at ! = 0.10



Sediment type 0.0001 NS 0.0001 0.0001 0.0001

Species 0.0001 0.0001 0.0001 0.0001 0.0004

Degree of exposure 0.0001 0.0001 0.0001 0.0001 0.0001

Depth 0.0001 NS NS 0.018 NS

Sediment type*species

0.0001 0.0002 0.0001 0.04 0.0001

Sediment type*exposure

0.0001 0.0014 0.01 0.0079 0.0001

Sediment type*depth 0.0001 NS 0.0001 0.0001 0.0001

Exposure*species 0.0001 0.0001 0.0053 0.0001 NS

Depth*species 0.0001 NS 0.0001 0.012 0.0001

Exposure*depth 0.0001 0.0001 0.0001 0.0001 0.0001


Sediment type 0.017 0.018 0.0041 NS

Species 0.0001 0.001 0.0004 0.0001

Degree of exposure 0.0001 0.0014 0.0024 NS

Depth NS NS NS NS

Sediment type*species 0.0001 0.0001 0.0001 0.0001

Sediment type*exposure 0.0001 0.0004 0.05 NS

Sediment type*depth NS NS NS NS

Exposure*species 0.0044 0.019 0.0001 0.02

Depth*species 0.0001 0.0049 NS 0.0001

Exposure*depth 0.0005 0.0001 0.0001 0.0001

28 Facies (2011) 57:15–37

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all EOPs. The EFG brine canyon EOP (EFGCS) was char-acterized by an unusually high degrees of dissolution lead-ing to a soft shell surface (factor 5) and a high degree offading (factor 7) (Fig. 8). Shells from the 15-m EOP on theBA transect were characterized by more preservable biontsthan most (factor 1), grey-to-black discoloration (factor 9),faded shells (factor 7), and little dissolution (Fig. 7). Arraysat the 15-m location of Bahamian transect BA were movedtens of meters downcoast between 1996 and 2001, probablyas a result of hurricanes. Shells from the equivalent depthon the AA transect were characterized by a much highercoverage of photosymbiotic foraminifera (factor 4), a simi-lar frequency of other preservable bionts (factor 1), but lessfading and a lower frequency of grey-to-black discoloration(Fig. 10). Shells from the 30-m EOP on the AA transectwere unique in the limited degree of pitting and deep disso-lution (factor 2) and the near absence of discoloration (fac-

tor 3), including fading (Fig. 10). The arrays at 30 m wereburied within the Wrst year after deployment on both tran-sects and not subsequently re-exposed (as far as observa-tions permit).

Discussion

The relationship of taphonomic traits and biont guilds

The relationship of the various biont guilds and tapho-nomic traits was relatively consistent, regardless of theinclusion or exclusion of the nonpreservable biont guilds.Taphonomic traits and biont guilds were consistentlyorthogonal, in the main. Thus, the distribution of tapho-nomic traits among EOPs rarely correlated with the distri-bution of biont guilds. These two primary descriptors of

Table 13 Variance-to-mean ratio for each of the factors identiWed in the PCA using all biont guilds and in the PCA restricted to the preservablebiont guilds

The ratio is constructed using the absolute value of the mean of each of the EOP mean scores; that is, the mean of the means. The variance similarlyis the variance of the EOP mean scores. A higher value indicates a greater dispersion of mean scores among EOPs

All Biont PCA

Factor 1 19.56 Preservable bryozoans, carbonate polychaete tubes, boring sponges, boring algae, green discoloration, non-photosymbiotic foraminifera

Factor 2 2.42 Maximum degree of dissolution, incidence of dissolved surface, average degree of dissolution, incidence of pitting

Factor 3 4.99 Maximum degree of discoloration, incidence of brown discoloration

Factor 4 1.52 Miscellaneous epibionts, red algae

Factor 5 16.40 Bacterial Wlms, incidence of soft shell surface

Factor 6 3.73 Attached molluscs, photosymbiotic foraminifera, brown algae

Factor 7 11.57 Degree of breakage, degree of edge rounding

Factor 8 10.77 Green algae, coralline algae

Factor 9 3.93 Incidence of orange discoloration

Factor 10 3.56 Incidence of faded color

Factor 11 3.64 Boring fungi, incidence of gray-to-black discoloration

Factor 12 15.38 Non-foraminiferal protists, incidence of chalkiness

Factor 13 7.65 Non-preservable bryozoans, sponges

Factor 14 30.99 Skeletal cnidarians

Preservable Biont PCA

Factor 1 14.99 Preservable bryozoans, coralline algae, boring algae, carbonate polychaete tubes, boring sponges, non-photosymbiotic foraminifera, incidence of green discoloration

Factor 2 2.67 Maximum degree of dissolution, incidence of dissolved surface, average degree of dissolution, incidence of pitting

Factor 3 3.92 Maximum degree of discoloration, incidence of brown discoloration

Factor 4 4.94 Attached mollusks, photosymbiotic foraminifera

Factor 5 48.21 Incidence of soft shell surface, incidence of dissolved surface with holes, average degree of dissolution, incidence of chalkiness

Factor 6 7.28 Degree of breakage, degree of edge rounding

Factor 7 11.64 Incidence of fading

Factor 8 2.59 Incidence of orange discoloration

Factor 9 3.91 Surface traces, incidence of gray-to-black discoloration

Facies (2011) 57:15–37 29

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Fig. 3 DiVerential representation of taphonomic trait and biont guild forfactors 1–4 (Table 4) among EOPs. Factor scores were obtained from thePCA using all taphonomic traits and the preservable biont guilds by aver-aging individual scores from all shells across all species. Bubble diame-ter indicates mean factor score. Solid bubbles, positive mean factorscores. Shaded bubbles, negative mean factor scores. Factor 1: preserv-able bryozoans, coralline algae, boring algae, carbonate polychaetetubes, boring sponges, non-photosymbiotic foraminifera, incidence ofgreen discoloration. Factor 2: maximum degree of dissolution, incidenceof deeply dissolved surface, average degree of dissolution, incidence ofpitting. Factor 3: maximum degree of discoloration, incidence of browndiscoloration. Factor 4: attached mollusks, photosymbiotic foraminifera

1 2 3 4

Mean Factor Score for Factors 1-4

-2

0

2

AA15M

AA30M

AAWALL

AATALUS

AACREST

AATROFF

BA15M

BA30M

BAWALL

BA183M

BATALUS

BACREST

BATROFF

EFGHD

EFGBR

EFGCS

EFGCM

EFGCS

EFGDS

NORMP

STXS

PARKR

GB425

GC234

Fig. 4 DiVerential representation of taphonomic trait and biont guildfor factors 5–9 among EOPs (Table 4). Factor scores were obtainedfrom the PCA using all taphonomic traits and the preservable biontguilds. Bubble diameter indicates mean factor score. Solid bubbles,positive mean factor scores. Shaded bubbles, negative mean factorscores. Factor 5: incidence of soft shell surface, incidence of dissolvedsurface with holes, average degree of dissolution, incidence of chalki-ness. Factor 6: degree of breakage, degree of edge rounding. Factor 7:incidence of fading. Factor 8: incidence of orange discoloration. Factor9: surface traces, incidence of gray-to-black discoloration

AA15M

AA30M

AAWALL

AATALUS

AACREST

AATROFF

BA15M

BA30M

BAWALL

BA183M

BATALUS

BACREST

BATROFF

EFGHD

EFGBR

EFGCS

EFGCM

EFGCS

EFGDS

NORMP

STXS

PARKR

GB425

GC234

5 6 7 8 9


-2

0

2

30 Facies (2011) 57:15–37

123

shell condition provided distinctly diVerent informationon the EOP.

The preservable and nonpreservable biont guilds werealso routinely orthogonal. Only the co-occurrence of greenalgae and coralline algae (Table 3) represented a substan-tive exception. Thus, the failure of the nonpreservable biontguilds to be preserved removed information about the envi-ronment generating the assemblage that was not indepen-dently recorded by preservable biont guild or taphonomictrait.

After removal of the nonpreservable biont guilds, theEOPs could be distinguished by nine PCA factors (Table 4).Two factors apportioned the preservable bionts into twogroups. One, factor 1 (Table 4) amalgamated the borers, thecarbonate forming polychaetes, and a number of skeleton-forming guilds such as the bryozoans. This factor encom-passed the vast majority of preservable biont guilds. Theother, factor 4 (Table 4) encompassed the attached molluscsand photosymbiotic foraminifera. These two guilds wereuniquely abundant in the two 15-m sites in the Bahamas

(Fig. 3). Of the remaining factors, two described a dichot-omy of dissolution trajectories leading to pitting and deepdissolution on the one hand and chalkiness and the forma-tion of a soft shell surface on the other. Breakage and edgerounding fell on a single factor. Discoloration encompassedthe Wnal four factors that diVerentiated brown, orange, andgray-to-black discoloration from fading of the original color

Fig. 5 EOPs clustered by the average scores of the 14 factorsobtained from the PCA using all biont guilds and all taphonomic traits

AA

15M

BA

15M

AA

30M

AA

CR

ES

TA

AT

RO

FF

AA

TA

LUS

BA

183M

BA

TA

LUS

BA

CR

ES

TB

AT

RO

FF

ST

XS

GB

425

GC

234

EF

GC

FE

FG

CM

EF

GD

SB

A30

ME

FG

BR

AA

WA

LLB

AW

ALL

PA

RK

RN

OR

MP

EF

GH

DE

FG

CS

0

2

4

6

8

10

12

Rel

ativ

e S

imila

rity

Fig. 6 EOPs clustered by the average scores of the nine factorsobtained from the PCA using the preservable biont guilds only and alltaphonomic traits

AA

15M

BA

15M

AA

30M

AA

CR

ES

TA

ATR

OF

FA

ATA

LUS

BA

183M

BA

CR

ES

TB

ATA

LUS

BAT

RO

FF

BA

30M

EF

GB

RS

TX

SE

FG

CF

GB

425

BC

234

EF

GC

ME

FG

DS

NO

RM

P AA

WA

LLB

AW

ALL

PAR

KR

EF

GH

DE

FG

CS

0

2

4

6

8

10

12

Rel

ativ

e S

imila

rity

Fig. 7 The relative importance of the nine PCA factors obtained usingonly the preservable biont guilds and all the taphonomic traits for theEOPs on Bahamian transect BA. Bubble diameter indicates mean fac-tor score. Solid bubbles, positive mean factor scores. Shaded bubbles,negative mean factor scores. See Table 4 for factor descriptions

1 2 3 4 5 6 7 8 9Mean Factor Score for Factors 1-9

-2 0 2

BA15M

BA30M

BAWALL

BA183M

BATALUS

BACREST

BATROFF

Fig. 8 The relative importance of the nine PCA factors obtained us-ing only the preservable biont guilds and all the taphonomic traits forthe EOPs on the East Flower Garden transect. Bubble diameter indi-cates mean factor score. Solid bubbles, positive mean factor scores.Shaded bubbles, negative mean factor scores. See Table 4 for factordescriptions

1 2 3 4 5 6 7 8 9


-2 0 2

EFGHD

EFGBR

EFGCS

EFGCM

EFGCF

EFGDS

Facies (2011) 57:15–37 31

123

and established these four outcomes as the likely result offour independent processes (Fig. 3, Table 3). The richness ofinformation in shell discoloration has rarely been as advan-tageously used as its value herein indicates [see Wehmilleret al. (1995) and Powell et al. (2008) for example].

Several coincidences of taphonomic trait and biont guildmerit note as exceptions to the overwhelming orthogonalityof these two divergent descriptors of shell condition. Suchco-occurrences augur causal connections between biontguild and taphonomic process. Green discoloration consis-tently co-occurred with boring algae and a number of otherpreservable biont guilds that correlated in their distribution(factor 1, Tables 3, 4). Very likely, the boring algae impartthe green discoloration to the shells (Wilkinson and Burrows

1972; Kiene et al. 1995; Parsons-Hubbard 2005). Threemicrobial guilds correlated with selected taphonomic traits,a fact intrinsically of some note. No other group of biontguilds was so consistently associated with taphonomictraits. The Wrst, bacterial Wlms, was associated with thedevelopment of chalkiness and a soft shell surface (factor 5,Table 3). The origin of this dissolution style is likely theattack on the shell by acid produced via sulWde oxidation(Reaves 1986; McNichol et al. 1988; Tribble 1993). Suchattack may be mediated in its extreme form by bacterialWlms that create strong chemical micro-gradients (Jørgen-sen et al. 1979; Jørgensen and Revsbech 1985; Levin2002), though the simple co-occurrence of the two wouldalso be expected. The second, boring fungi, is most oftenassociated with black-to-gray discoloration (factor 11,Table 3). We cannot distinguish causation from environ-mental correlation in this case. Also likely is the possibilitythat the borings of fungi, always diYcult to observe (e.g.,Curry 1983), are simply more easily observed when shellsare thusly discolored. The coincidence of chalkiness withthe non-foraminiferal protists in the third case (factor 12,Table 3) is almost certainly an environmental correlate asboth attributes were most common on shells deployed inthe deeper EOPs. Surface traces were associated with gray-to-black discoloration (factor 9, Table 4). These traces werelikely produced by limpets (Farrow and Clokie 1979) orchitons (Farrow et al. 1984). Once again, the coincidence ofenvironment or the ease of observation is a more likelyexplanation than causality.

Thus, we can with conWdence identify only one casualrelationship between biont guild and taphonomic trait. Bor-ing green algae produced green discoloration. With morehesitance, the data suggest that bacterial Wlms are instru-mental in creating a soft shell surface in a number of EOPs.The suggestion that some preservable bionts might protectshells from taphonomic processes is not well supported byour set of EOPs, but we note that surface traces and carbon-ate polychaete tubes were orthogonal attributes in keepingwith the suggestion by Farrow and Clokie (1979) that tubesimpede gastropod grazing.

Reaching these conclusions does not necessarily obviatethe importance of biotic processes in taphonomic degradation.We have distinguished biont guilds from taphonomic traitsduring analysis. The term ‘taphonomic trait’ refers to thesuite of taphonomic characteristics describing the tapho-nomic signature listed in Tables 1 and 2. Some of thesemay be of biotic origin, others abiotic; however, none ofthem can be referred to speciWc biont types that might oth-erwise have been observed. Thus, we note an associationbetween bacterial Wlms and the development of chalkinessand a soft shell surface that we suspect is, at least in part, aproduct of microbial activity, but we do not have incontro-vertible evidence of cause and eVect, as we might between

Fig. 9 The relative importance of the nine PCA factors obtained us-ing only the preservable biont guilds and all the taphonomic traits formiscellaneous EOPs in the Gulf of Mexico and Bahamas. Bubblediameter indicates mean factor score. Solid bubbles, positive meanfactor scores. Shaded bubbles, negative mean factor scores. SeeTable 4 for factor descriptions

1 2 3 4 5 6 7 8 9


-2 0 2

NORMP

STXS

PARKR

GB425

GC234

Fig. 10 The relative importance of the nine PCA factors obtained us-ing only the preservable biont guilds and all the taphonomic traits forthe EOPs on Bahamian transect AA. Bubble diameter indicates meanfactor score. Solid bubbles, positive mean factor scores. Shaded bub-bles, negative mean factor scores. See Table 4 for factor descriptions

1 2 3 4 5 6 7 8 9


-2 0 2

AA15M

AA30M

AAWALL

AATALUS

AACREST

AATROFF

32 Facies (2011) 57:15–37

123

a grazing trace and the grazing mollusc producing it. Thus,the assignment of an observed shell feature to a taphonomictrait does not necessarily imply an abiotic origin; some-times, in fact, our data implicate a biotic mechanism. Howcommonplace biotic intermediation is remains unknown.

Relationship of taphonomic trait and biont guild to EOP

EOP was a signiWcant main eVect in ANCOVA analysis insome cases. Depth rarely achieved signiWcance and signiW-cant interaction terms were uncommon. The failure ofdepth to exert a signiWcant eVect on PCA factors describingbiont guilds and taphonomic traits is well supported bycluster analysis that identiWes many cases where EOPs ofdisparate depths are characterized by shells with similartaphonomic traits and biont guild compositions (Figs. 6, 7,8, 9, 10). Although biont composition is known to be depthdependent (Kiene et al. 1995; Golubic et al. 1984), theinXuences of diVerential burial and variability in geochemi-cal environment limit the range of inXuence of water depthat SSETI EOPs.

A more detailed ANCOVA in which EOP was replacedby sediment type and degree of exposure yielded morecomplex results. The taphonomic process is thought to berelated in some way to the degree of exposure of shells onthe bottom, as expressed by the concept of the TAZ [tapho-nomically active zone, Davies et al. (1989)] (Walker andGoldstein 1999; Walker 2001; Barbieri 2001), and the sedi-mentary environment should inXuence sediment chemistry(Goldhaber et al. 1977; Lin and Morse 1991; Green et al.1992). Accordingly, taphonomic signature should be sig-niWcantly inXuenced by sediment type and degree of expo-sure. Bionts likewise should be inXuenced by the rate ofburial and likely by sediment type (Conover 1975; May andPerkins 1979; Voight and Walker 1995).

The main eVects of sediment type and degree of expo-sure were routinely highly signiWcant in this analysis aswere most interaction terms between them. However, thecomplexity of these ANCOVA results contrasts starklywith the simplicity of most ANCOVA results in whichlocation (EOP) was used as a main eVect and generates sus-picion that the main eVects of sediment type and degree ofexposure, as compartmentalized here, are poor descriptorsof the taphonomic and biotic environment. That is, EOPs ofdisparate taphonomic signature and biont guild comple-ment have similar sediment type and degree of exposure.The obverse also occurs. Examination of cluster analyses(Figs. 5, 6) reveals a number of examples. The deepwaterEOPs from the East Flower Garden clustered with thepetroleum seep EOPs for example, despite having radicallydisparate sediment types. The EOPs on the BA and AAtransects rarely clustered together despite having very simi-lar sediment types and degrees of exposure. Thus, for nei-

ther biont guild nor taphonomic trait is sediment type anddegree of exposure an adequate descriptor of EOP. Theexpectation that degree of burial (e.g., Davies et al. 1989;Powell 1992; Walker 2001) or the titration of acid by abun-dant carbonate in surrounding sediments minimizes disso-lution (e.g., Powell et al. 1989; Rogers and Kidwell 2000)is not corroborated by the taphonomic state of shellsdeployed for 8 years at SSETI EOPs. As well, althoughburial certainly inhibits biont colonization as suggested byGordillo and Aitken (2000) and Parsons-Hubbard (2005), apaucity of biont coverage is not a reliable indicator of rapidburial because biont colonization proceeds slowly in deeperwater so that biont coverage can be low even on shellsexposed for a prolonged period.

The simpler ANCOVA with EOP as a main eVect identi-Wes the consistent diVerence between deepwater carbonateEOPs and most others. This diVerential is recapitulated bycluster analysis that discriminates three groups of carbonateEOPs, the deepwater carbonate sands on transect BA, thedeepwater carbonate sands on transect AA, and the deepreef and hardground sites in the Bahamas and Gulf of Mex-ico. The similarity of the sites falling into the latter group isnoteworthy in comparison to the distinctiveness of neigh-boring EOPs such as the sites from the deepwater sands ofthe two Bahamian transects.

The simpler ANCOVA with EOP as a main eVect, on theother hand, also elucidates a surprising incongruity. SigniW-cant factor scores normally do not include the principal dis-solution factors and the preservable biont factors, factors 1and 2 in the preservable biont-all taphonomic trait PCAsbeing good examples. Nevertheless these factors are impor-tant discriminators of EOP. A simple comparison of thevariance and mean of mean factor scores identiWes thesefactors as among the most diverse among EOPs. That is,among the EOPs are cases of extremes in these factors thatsupersede the variation for most factors among EOPs.These extremes are also identiWed by cluster analysis(Fig. 6). Five EOPs are uniquely dissimilar from each otherand from the remaining EOPs and their uniqueness isstrongly inXuenced by biont coverage and dissolution state.Interaction terms with species normally are important inthese ANCOVAs, which suggests that the incongruity maybe resolved by increased between-species within-site vari-ance for these factor scores which limits resolution of EOPmain eVects in the ANCOVA.

The clustering of visually distinctive EOPs

ANCOVA comparisons suggest that the expectation thatEOP diVerentiation can be based on simple edaphic andenvironmental variables is inadequate. Powell et al. (2008)argued that geochemical conditions might be of greaterimportance and these tend to be EOP speciWc to some

Facies (2011) 57:15–37 33

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degree. The ANCOVA also indicates that visual distinc-tiveness is not a good predictor of preservational state.Visually distinctive environments may be taphonomicallyand biotically similar. Visually similar ones may be quitedisparate in taphonomic state and biont complement. Clus-tering of factor scores by EOP reveals a number of subsetsof similar EOPs and their conjoining is dependent uponsimultaneous input of information on biont guild and tapho-nomic trait. These sometimes encompass a visually diverseset of environments. That is, the discrimination of EOPsand assignment to higher-order EOP groups encompassingsimilar preservational states would be less complete wereanalysis limited to comparisons of one or the other datasource.

The EOPs segregate into a number of categories. Firstare Wve unique EOPs that do not cluster with any others.These Wve, the 15-m sites on Bahamian transects AA andBA (AA15M, BA15M), the 30-m EOP on transect AA(AA30M), the brine canyon at the East Flower Garden(EFGCS), and to a lesser extent the saline lagoon of Nor-man’s Pond (NORMP), diVer substantively from each otherand all other EOPs. These include dominantly the shallow-est sites and one of the most unique of the deeper sites. Theanalysis conWrms an expectation from community ecologyand zoogeography (e.g., Zezina 1997; Grill and Zuschin2001) that the diversity of EOPs should be greater in shal-low water.

Once these Wve are removed, the analysis identiWes threediVerent carbonate sites and two mixed carbonate-clasticgroups. No unique terrigenous cluster is revealed. This dis-parity may issue from some bias in the selection of SSETIEOPs (e.g., Powell et al. 2008) or perhaps unique propertiesof some carbonate regimes do not have counterparts in theterrigenous realm. The more limited selection of terrige-nous EOPs limits further investigation of this alternative.

The allocation of carbonate EOPs to three groups oVers asurprise. Two of the three separate the deepwater sites ontransect AA from those on BA, while amalgamating thevisually distinctive EOPs within each transect. Interest-ingly, the talus slope (AATALUS, BATALUS), dune crest(AACREST, BACREST) and dune trough (AATROFF,BATROFF) EOP pairs are remarkably dissimilar tapho-nomically between transects. The respective representativesfrom each pair are similar taphonomically within transect,however. By contrast, all six sites retain a very similar com-plement of bionts based on guild coverage. This provides agood example of EOP groups that can be diVerentiated onlythrough a taphonomic analysis. Why these two transectsdiverge so is a mystery; but their divergence emphasizesthe danger of assuming that similar habitats judged visuallyor by crude criteria such as water depth and sediment typeare adequate descriptors of the preservational milieu [seealso Callender et al. (2002), Powell et al. (2008)].

Interestingly, in comparison to the diVerences in shellcondition on the local geographic scale in the Bahamas, thedeep reef sites are relatively similar regardless of location.SSETI sampled four deep reef and hardground locations,the wall EOPs on the two Bahamian transects (AAWALL,BAWALL), the veneered hardground of Parker Bank(PARKR), and the East Flower Garden hardground(EFGHD). Some distinctions between these four locationscan be identiWed and these distinctions are both biotic andtaphonomic, but the similarities far outweigh the diVer-ences. All four locations are characterized by high coverageof most preservable biont guilds that composed factor 1(Tables 3, 4). The degree to which the photosymbioticforaminifera and attached molluscs are present was dis-criminative to a certain degree, as were the degree of dis-coloration and fading and the degree of dissolution.Nevertheless, it is interesting that this geographically wide-spread group of EOPs comprise EOPs about as similar asthe deepwater EOPs on Bahamian transect AA or BA andthe diVerential between this EOP cluster and others wasabout as great as the diVerential between the deepwater BAand AA transect clusters whose sites were very muchnearer geographically. Thus, these EOPs when grouped bysimilarity in taphonomic signature and biont coverage verylikely correspond to geographically widespread biologicaland taphonomic regimes, which, however, are everywhererestricted locally in areal dimension.

The composite carbonate-terrigenous EOP groups arealso geographically dispersed as well as dispersed in depth.Their relative similarity in taphonomic trait and biont guildstructure suggests that a range of distinctive habitat typescan produce grossly similar outcomes. Of course, we havenot attempted to delve into the biont complement at the spe-cies level where diVerences certainly must exist nor havewe evaluated alternative guild groupings that might proWt-ably reveal diVerent trends (e.g., Kaiho 1994).

The Wrst of these two groups includes the deepwatercarbonate EOPs at the East Flower Garden and the petro-leum seeps. Shells from these sites are characterized byincreased dissolution, mostly chalkiness and the moreextreme soft shell surface, and brown discoloration. Thelatter is most likely of microbial origin (Powell et al.2008). These sites are biont poor. The second group is acurious combination of the south Texas shelf terrigenoussite and the brine pool at the East Flower Garden. Shellsfrom these two sites are uniquely characterized by limitedtaphonomic degradation and limited biont coverage. Theirapparent similarity is primarily a result of the absence ofshell-altering agents and biont colonization rather than theequivalency of biological and physico-chemical pro-cesses. The results impose a constraint on the taphofaciesconcept, as not all taphonomic signatures imply a uniqueset of originating processes.

34 Facies (2011) 57:15–37

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Why include bionts?

The examination of a shell for taphonomic state invariablyexposes the researcher to biont coverage, the evaluation ofwhich, at guild level, increases analytical time only moder-ately. Of course, many of the bionts oVer taxonomic imped-iments that increase analysis time dramatically withincreased taxonomic precision (e.g., White 2002). Guilds,however, have proven useful in a number of applications(e.g., Scott 1978; Walker 1995; Radenbaugh and McKin-ney 1998). And, taphonomic traits are analogous to guildsin some properties. Discoloration, for example, encom-passes a number of disparate processes (Powell et al. 2008),as does what is simplistically termed dissolution (e.g., Pou-licek et al. 1981; Glover and Kidwell 1993; Behrensmeyeret al. 2000; Arvidson et al. 2003). Thus, in a sense, biontguilds are on par with taphonomic traits in being readilyassessed functional groups, the more detailed evaluation ofwhich would prohibitively increase analytical time. SSETIdeployments reveal opportunities in a joint analysis, whilealso identifying inherent limitations.

The limitations are twofold. First, biont guilds used foranalysis must be restricted to the preservable species inapplication to the study of the fossil record. Much of themultifariousness of biont guilds is lost in preservation,unfortunately. The same, of course, could be said for tapho-nomic traits some types of which, such as some types ofdiscoloration, may no longer be distinguished as the preser-vational process proceeds. Second, although a variety ofguilds remain, such as the preservable bryozoans, theforaminifera, and the carbonate tubes of polychaetes, not tomention the borings left by algae, fungi, and sponges, mostof the preservable guilds coalesce into two PCA axes. Theevidence is that most biont guilds are inXuenced similarlyby environmental regulatory processes and thus develop atequivalent tempos across habitat types.

Despite these perhaps disappointing limitations on thevalue of biont guild converge in demarcating EOPs, certainEOP groups are delineated from others most readily by acombination of biont guild and taphonomic trait. And,lesser though important diVerences delineate EOPs withinEOP groups. The utility of the combination stems from thenearly complete orthogonality of the two data sources.Taphonomic traits and biont guilds rarely correlate. Amongthose that do, nearly all are represented by nonpreservablebiont guilds. Of the PCA factors describing the preservablebiont guilds, only green discoloration as it correlates withalgal borings and the coincidence of surface traces withgray-to-black discoloration exist as exceptions to the inde-pendence of these two descriptors of shell condition. Thus,this analysis supports the inclusion of biont guilds to aug-ment taphonomic analysis in diVerentiating EOPs.

The caveat of time

Powell et al. (2008) emphasized the danger of assumingthat 8 years on the seaXoor is adequate to diVerentiate taph-onomic processes at the EOP level. A comparison of tapho-nomic status of shells deployed for 2 and 8 years wasunsettling in that many conclusions after 8 years were notpresaged after two. The inXuence of exposure period onbiont complement (e.g., Goren 1979; Zuschin and Pervesler1996) would sustain the same caveat. Thus, we should notblithely accept the conclusions identiWed herein as they rep-resent inferences from an as yet intermediate state of along-term process that might, in the end, diVerentiallyemphasize the biotic and taphonomic descriptors as evidenttoday. Despite this uncertainty, the SSETI experience sug-gests that EOPs are not simply manifestations of sedimen-tary regime, water depth, or macro-community ecology.These coarse descriptors are inadequate to the task. Acloser examination of the biotic, geochemical, and physicaldetails of preservation would appear to be required.

Acknowledgments The submersible work required for the deploy-ment and recovery of experiments was made possible through a seriesof grants from NOAA’s National Undersea Research Programs at theUniversity of North Carolina at Wilmington and the Caribbean MarineResearch Center, and the National Science Foundation-Geology andPaleontology Program. We would like to thank the NSF and these twoNURP programs for the consistent funding of the nine major WeldeVorts that permitted deployment and recovery over such a large re-gional area. We would like to thank the support crews of the Clelia,Johnson-Sea-Link, and Nekton Gamma submersibles and support ves-sels. We appreciate the eVorts of the CMRC staV on Lee Stocking Is-land and the NURP personnel from UNCW and CMRC that took partin these Weld programs.

References

Akpan EB, Farrow GE (1985) Shell bioerosion in high-latitude low-energy environments: Firths of Clyde and Lorne, Scotland. MarGeol 67:139–150

Aller JY (1995) Molluscan death assemblages on the Amazon shelf:implication for physical and biological controls on benthic popu-lations. Palaeogeogr Palaeoclimatol Palaeoecol 118:181–212

Allmon WD, Spizuco MP, Jones DS (1995) Taphonomy and paleoen-vironment of two turritellid-gastropod-rich beds, Pliocene ofFlorida. Lethaia 28:75–83

Arvidson RS, Ertan IE, Amonette JE, Lutige A (2003) Variation in cal-cite dissolution rates: a fundamental problem? Geochim Cosmo-chim Acta 67:1623–1634

Barbieri R (2001) Taphonomic implications of foraminiferal composi-tion and abundance in intertidal mud Xat, Colorado River delta(Mexico). Micropaleontology 47:73–86

Behrens EW (1988) Geology of a continental slope oil seep, northernGulf of Mexico. AAPG Bull 72:105–114

Behrensmeyer AK (1984) Taphonomy and the fossil record. Am Sci72:558–566

Behrensmeyer AK, Kidwell SM, Gastaldo RA (2000) Taphonomy andpaleobiology. Paleobiology 26(suppl):103–147

Facies (2011) 57:15–37 35

123

Bergquist DC, Ward T, Cordes EE, McNelis T, Howlett S, KosoV R,Hourdez S, Carney R, Fisher CR (2003) Community structure ofvestimentiferan-generated habitat islands from Gulf of Mexicocold seeps. J Exp Mar Biol Ecol 289:197–222

Black R, Peterson CH (1987) Biological vs physical explanations forthe non-random pattern of host occupation by a macroalga attach-ing to infaunal bivalve molluscs. Oecologia (Berl) 73:213–221

Boesch DF (1977) Application of numerical classiWcation in ecologi-cal investigations of water pollution. U.S. Department of Com-merce NTIS PB-269-604, EPA-60013-77-033

Bouma AH, Martin RG, Bryant WR (1980) Shallow structure of uppercontinental slope, central Gulf of Mexico. OVshore Technol ConfPap OTC 3913:583–592

Bouma AH, Feeley MH, Kindinger JL, Stelting CE, Hilde TWC(1981) Seismic stratigraphic characteristics of upper Louisianacontinental slope: an area east of Green Canyon. OVshore Tech-nol Conf Pap OTC 4098:283–291

Brett CE (1990) Obrution deposits. In: Briggs DEG, Crowther PR(eds) Palaeobiology: a synthesis. Blackwell ScientiWc Publishers,Oxford, pp 239–243

Brett CE, Baird GC (1986) Comparative taphonomy: a key to paleoen-vironmental interpretation based on fossil preservation. Palaios1:207–227

Bright TJ, Powell EN (1983) The East Flower Garden brine seep, aunique ecosystem. In: Reefs and banks of the northwestern Gulf ofMexico: their geological, biological, and physical dynamics. North-ern Gulf of Mexico Topographic Features Synthesis, Final Report,Contract No. AA851-CT1-55, U.S. Dept. Interior, Minerals Man-agement Service, Outer Continental Shelf OYce, pp 277–310

Cadée GC (1999) Shell damage and shell repair in the Antarctic limpetNucella concinna from King George Island. J Sea Res 41:149–161

Cai W-J, Chen F, Powell EN, Walker SE, Parsons-Hubbard KM, StaVGM, Wang Y, Ashton-Alcox KA, Callender WR, Brett CE (2006)Preferential dissolution of carbonate shells driven by petroleumseep activity in the Gulf of Mexico. Earth Planet Sci Lett248:227–243

Callender WR, Powell EN (1992) Taphonomic signature of petroleumseep assemblages on the Louisiana upper continental slope: rec-ognition of autochthonous shell beds in the fossil record. Palaios7:388–408

Callender WR, Powell EN (1997) Autochthonous death assemblagesfrom chemoautotrophic communities at petroleum seeps: paleo-production, energy Xow, and implications for the fossil record.Hist Biol 12:165–198

Callender WR, Powell EN (1999) Why did ancient chemosyntheticseep and vent assemblages occur in shallower water than they dotoday? Int J Earth Sci 88:377–391

Callender WR, Powell EN (2000) Long-term history of chemoautotro-phic clam-dominated faunas of petroleum seeps in the northwest-ern Gulf of Mexico. Facies 43:177–204

Callender WR, Powell EN, StaV GM, Davies DJ (1992) Distinguishingautochthony, parautochthony and allochthony using taphofaciesanalysis: can cold seep assemblages be discriminated from assem-blages of the nearshore and continental shelf? Palaios 7:409–421

Callender WR, Powell EN, StaV GM (1994) Taphonomic rates of mol-luscan shells placed in autochthonous assemblages on the Louisi-ana continental slope. Palaios 9:60–73

Callender WR, StaV GM, Parsons-Hubbard KM, Powell EN, RoweGT, Walker SE, Brett CE, Raymond A, Carlson DD, White S,Heise EA (2002) Taphonomic trends along a forereef slope: LeeStocking Island, Bahamas. I. Location and water depth. Palaios17:50–65

CanWeld DE, Raiswell R (1991) Carbonate precipitation and dissolu-tion: its relevance to fossil preservation. In: Allison PA, BriggsDEG (eds) Taphonomy: releasing the data locked in the fossilrecord. Plenum, New York, pp 412–453

Carney RS (1994) Consideration of the oasis analogy for chemosyn-thetic communities at Gulf of Mexico hydrocarbon vents. Geo-Marine Lett 14:149–159

Carroll M, Kowalewski M, Simões MG, Goodfriend GA (2003) Quan-titative estimates of time-averaging in terebratulid brachiopodshell accumulations from a modern tropical shelf. Paleobiology29:381–402

Christmas JF, McGinty MR, Randle DA, Smith GF, Jordan SJ (1997)Oyster shell disarticulation in three Chesapeake Bay tributaries.J ShellWsh Res 16:115–123

Cochrane JD, Kelly FJ (1986) Low-frequency circulation on theTexas-Louisiana continental shelf. J Geophys Res C OceansAtmosph 91:10645–10659

Conover MR (1975) Prevention of shell burial as a beneWt hermit crabsprovide to their symbionts (Decapoda, Paguridea). Crustaceana29:311–313

Courville P, Collin PY (2002) Taphonomic sequences—a new tool forsequence stratigraphy. Geology 30:511–514

Curry GB (1983) Microborings in Recent brachiopods and the func-tions of caeca. Lethaia 16:119–127

Davies DJ, Powell EN, Stanton RJ Jr (1989) Relative rates of shell dis-solution and net sediment accumulation—a commentary: canshell beds form by the gradual accumulation of biogenic debris onthe sea Xoor? Lethaia 22:207–212

Davies DJ, StaV GM, Callender WR, Powell EN (1990) Description ofa quantitative approach to taphonomy and taphofacies analysis:all dead things are not created equal. In: Miller III W (ed) Paleo-community temporal dynamics: the long-term development ofmultispecies assemblages. Spec Publ Paleontol Soc 5:328–350

El-Sayed SZ (1972) Primary productivity and standing crop of produc-tion. In: Bushnell VC (ed) Chemistry, primary productivity, andbenthic algae of the Gulf of Mexico. American Geographic Soci-ety, New York, pp 8–13

Farrow GE, Clokie J (1979) Molluscan grazing of sublittoral algal-bored shells and the production of carbonate mud in the Firth ofClyde, Scotland. Trans R Soc Edinburgh 70:139–148

Farrow GE, Fyfe JA (1988) Bioerosion and carbonate mud productionon high-latitude shelves. Sediment Geol 6:281–297

Farrow GE, Allen NH, Akpan EB (1984) Bioclastic carbonate sedi-mentation on a high-latitude, tide-dominated shelf: NortheastOrkney Islands, Scotland. J Sediment Petrol 54:373–393

Flessa KW, Cutler AH, Meldahl KH (1993) Time and taphonomy:quantitative estimates of time-averaging and stratigraphic disor-der in a shallow marine habitat. Paleobiology 19:266–286

Fürsich FT, Pandey DK (1999) Genesis and environmental signiW-cance of Upper Cretaceous shell concentrations from the CauveryBasin, southern India. Palaeogeogr Palaeoclimatol Palaeoecol145:119–139

Gardner JV, Mayer LA, Clarke JEH, Kleiner A (1998) High-resolutionmultibeam bathymetry of East and West Flower Gardens andStetson Banks, Gulf of Mexico. Gulf Mexico Sci 16:131–143

Gittings SR, Bright TJ, Powell EN (1984) Hard-bottom macrofauna ofthe East Flower Garden brine seep: impact of a long-term, sulfu-rous brine discharge. Contrib Mar Sci 27:105–125

Glover CP, Kidwell SM (1993) InXuence of organic matrix on thepost-mortem destruction of molluscan shells. J Geol 101:729–747

Goldhaber M, Aller R, Cochran J, RosenWeld J, Martens C, Berner R(1977) Sulfate reduction diVusion and bioturbation in Long IslandSound sediments: report of the Foam Group. Am J Sci 277:193–237

Golubic S, Campbell SE, Drobne K, Cameron B, Balsam WL, Ciner-man F, DuBois L (1984) Microbial endoliths: a benthic overprintin the sedimentary record, and a paleobathymetric cross-referencewith foraminifera. J Paleontol 58:351–361

Gordillo S, Aitken AE (2000) Palaeoenvironmental interpretation ofLate Quaternary marine molluscan assemblages, Canadian ArcticArchipelago. Géogr Phys Quatern 54:301–315

36 Facies (2011) 57:15–37

123

Goren M (1979) Succession of benthic community on artiWcial substra-tum at Elat (Red Sea). J Exp Mar Biol Ecol 38:19–40

Green MA, Aller RC, Aller JY (1992) Experimental evaluation of theinXuences of biogenic reworking on carbonate preservation innearshore sediments. Mar Geol 107:175–181

Grill B, Zuschin M (2001) Modern shallow- to deep-water bivalvedeath assemblages in the Red Sea—ecology and biogeography.Palaeogeogr Palaeoclimatol Palaeoecol 168:75–96

Gunter G, Dawson CE, Demoran WJ (1957) Determination of howlong oysters have been dead by studies of their shells. Proc NatlShellWsh Assoc 47:31–33

Hill GW, Roberts KA, Kindinger JL, Wiley GD (1982) Geobiologicstudy of the south Texas outer continental shelf. US Geol SurvProf Pap 1238:1–36

Hurlbert SH (1984) Pseudoreplication and the design of ecologicalWeld experiments. Ecol Monogr 54:187–211

Jørgensen BB, Revsbech NP (1985) DiVusive boundary layers and theoxygen uptake of sediments and detritus. Limnol Oceanogr30:111–122

Jørgensen B, Revsbech N, Blackburn T, Cohen Y (1979) Diurnal cycleof oxygen and sulWde microgradients and microbial photosynthe-sis in a cyanobacterial mat sediment. Appl Environ Microbiol38:46–58

Kaehler S (1999) Incidence and distribution of phototrophic shell-degrading endoliths of the brown mussel Perna perna. Mar Biol(Berl) 135:505–514

Kaiho K (1994) Benthic foraminiferal dissolved-oxygen indexand dissolved-oxygen levels in the modern ocean. Geology22:719–722

Kennicutt MC II, Brooks JM, Bidigare RR, Denoux GJ (1988a) Gulfof Mexico hydrocarbon seep communities—I. Regional distribu-tion of hydrocarbon seepage and associated fauna. Deep-Sea Res35:1639–1651

Kennicutt MC II, Brooks JM, Denoux GJ (1988b) Leakage of deep,reservoired petroleum to the nearsurface on the Gulf of Mexicocontinental slope. Mar Chem 24:39–59

Kidwell SM (1986a) Models for fossil concentrations: paleobiologicimplications. Paleobiology 12:6–24

Kidwell SM (1986b) Taphonomic feedback in Miocene assemblages:testing the role of dead hardparts in benthic communities. Palaios1:239–255

Kidwell SM, Flessa KW (1995) The quality of the fossil record: popu-lations, species and communities. Annu Rev Ecol Syst 26:269–299

Kidwell SM, Fürsich FT, Aigner T (1986) Conceptual framework forthe analysis and classiWcation of fossil concentrations. Palaios1:228–238

Kidwell SM, Rothfus TA, Best MMR (2001) Sensitivity of tapho-nomic signatures to sample size, sieve size, damage scoring sys-tem, and target taxa. Palaios 16:26–52

Kiene W, Radtke G, Gertidis M, Golubic S, Vogel K (1995) Factorscontrolling the distribution of microborers in Bahamian reef envi-ronments. Facies 32:176–188

Kowalewski M, Mimniakiewicz W (1993) Reliability of quantitativedata on fossil assemblages: a model, a simulation, and an exam-ple. Neues Jahrb Geol Palaontol Abh 187:243–260

Levin LA (2002) Deep-ocean life where oxygen is scarce. Am Sci90:436–444

Lin S, Morse JW (1991) Sulfate reduction and iron sulWde mineral for-mation in Gulf of Mexico anoxic sediments. Am J Sci 291:55–81

Lugo-Fernández A (1998) Ecological implications of hydrography andcirculation to the Flower Garden Banks, northwest Gulf of Mex-ico. Gulf Mexico Sci 16:144–160

MacAvoy SE, Carney RS, Fisher CR, Macko SA (2002) Use of che-mosynthetic biomass by large, mobile, benthic predators in theGulf of Mexico. Mar Ecol Prog Ser 225:65–78

MacDonald IR, Buthman DB, Sager WW, Peccini MB, Guinasso NLJr (2000) Pulsed oil discharge from a mud volcano. Geology28:907–910

Mao Che L, Campion-Alsumard T le, Boury-Esnault N, Payri C, Golu-bic S, Bézac C (1996) Biodegradation of shells of the black pearloyster, Pinctada margaritifera var. cumingii, by microborers andsponges of French Polynesia. Mar Biol (Berl) 126:509–519

Martin RE, Wehmiller JF, Harris MS, Liddell WD (1996) Comparativetaphonomy of bivalves and foraminifera from Holocene tidal Xatsediments, Bahia la Choya, Sonora, Mexico (Northern Gulf ofCalifornia): taphonomic grades and temporal resolution. Paleobi-ology 22:80–90

May JA, Perkins RD (1979) Endolithic infestation of carbonate sub-strates below the sediment-water interface. J Sediment Petrol49:357–378

McNichol AP, Lee C, DruVel ERM (1988) Carbon cycling in coastalsediments: 1. A quantitative estimate of the remineralization oforganic carbon in the sediments of Buzzards Bay, MA. GeochimCosmochim Acta 52:1531–1543

Meldahl KH, Flessa KW (1990) Taphonomic pathways and compara-tive biofacies and taphofacies in a recent intertidal shallow shelfenvironment. Lethaia 23:43–60

Nebelsick JH, Schmid B, Stachowitsch M (1997) The encrustation offossil and recent sea urchin tests: ecological and taphonomic sig-niWcance. Lethaia 30:271–284

Olszewski T (1999) Taking advantage of time-averaging. Paleobiol-ogy 25:226–238

Parsons KM, Brett CE (1991) Taphonomic process and biases in mod-ern marine environments: an actualistic perspective on fossilassemblage preservation. In: Donovan SK (ed) The processes offossilization. Belhaven Press, London, pp 22–65

Parsons KM, Powell EN, Brett CE, Walker SE, Callender WR (1997)Shelf and Slope Experimental Taphonomy Initiative (SSETI):Bahamas and Gulf of Mexico. In: Proceedings of 8th InternationalCoral Reef Symposium, vol 2, pp 1807–1812

Parsons-Hubbard K (2005) Molluscan taphofacies in recent carbonatereef/lagoon systems and their application to sub-fossil samplesfrom reef cores. Palaios 20:175–191

Parsons-Hubbard KM, Callender WR, Powell EN, Brett CE, WalkerSE, Raymond AL, StaV GM (1999) Rates of burial and distur-bance of experimentally deployed molluscs: implications forpreservation potential. Palaios 14:337–351

Parsons-Hubbard KM, Powell EN, StaV GM, Callender WR, Brett CE,Walker SE (2001) The eVect of burial on shell preservation andepibiont cover in Gulf of Mexico and Bahamas shelf and slopeenvironments after two years: an experimental approach. In: AllerJY, Woodin SA, Aller RC (eds) Organism-sediment interactions.Belle W. Baruch Library in Marine Science #21, University ofSouth Carolina Press, pp 297–314

Poulicek M, Jaspar-Versali MF, GoYnet G (1981) Étude expérimen-tale de la dégradation des coquilles de mollusques au niveau dessédiments marins. Bull Soc R Sci Liège 50:513–518

Powell EN (1992) A model for death assemblage formation. Can sed-iment shelliness be explained? J Mar Res 50:229–265

Powell EN, Bright TJ, Woods A, Gittings S (1983) Meiofauna and thethiobios in the East Flower Garden brine seep. Mar Biol (Berl)73:269–283

Powell EN, Bright TJ, Brooks JM (1986) The eVect of sulWde and anincreased food supply on the meiofauna and macrofauna at theEast Flower Garden brine seep. Helgol Meeresunters 40:57–82

Powell EN, StaV GM, Davies DJ, Callender WR (1989) Macrobenthicdeath assemblages in modern marine environments: formation,interpretation and application. Crit Rev Aquat Sci 1:555–589

Powell EN, Parsons-Hubbard KM, Callender WR, StaV GM, RoweGT, Brett CE, Walker SE, Raymond A, Carlson DD, White S, He-ise EA (2002) Taphonomy on the continental shelf and slope:

Facies (2011) 57:15–37 37

123

two-year trends—Gulf of Mexico and Bahamas. Palaeogeogr Pal-aeoclimatol Palaeoecol 184:1–35

Powell EN, Callender WR, StaV GM, Parsons-Hubbard KM, Brett CE,Walker SE, Raymond A, Ashton-Alcox KA (2008) Molluscanshell condition after eight years on the sea Xoor—taphonomy inthe Gulf of Mexico and Bahamas. J ShellWsh Res 27:191–225

Radenbaugh TA, McKinney FK (1998) Comparison of the structure ofa Mississippi and a Holocene pen shell assemblage. Palaios13:52–69

Reaves CM (1986) Organic matter metabolizability and calcium car-bonate dissolution in nearshore marine muds. J Sediment Petrol56:486–494

Rezak R, Bright TJ (1981) SeaXoor instability at East Flower GardenBank, northwest Gulf of Mexico. Geo-Marine Let 1:97–103

Rezak R, Gittings SR, Bright TJ (1990) Biotic assemblages and eco-logical controls on reefs and banks of the northwest Gulf of Mex-ico. Am Zool 30:23–35

Roberts HH, Carney RS (1997) Evidence of episodic Xuid, gas, andsediment venting on the northern Gulf of Mexico continentalslope. Econ Geol 92:863–879

Rogers RR, Kidwell SM (2000) Associations of vertebrate skeletalconcentrations and discontinuity surfaces in terrestrial and shal-low marine records: a test in the Cretaceous of Montana. J Geol108:131–154

Root RB (1967) The niche exploitation pattern of the blue-gray gnat-catcher. Ecol Monogr 37:317–350

Rowe GT (1983) Biomass and production of the deep-sea macroben-thos. In: Rowe GT (ed) Deep sea biology. The sea, vol 8. Wiley-Interscience, New York, pp 97–121

Rowe GT, Sibuet M, Deming J, Tietjen J, KhripounoV A (1990)Organic carbon turnover time in deepsea benthos. Prog Oceanogr24:141–160

Scott R (1978) Approaches to trophic analysis of paleocommunities.Lethaia 11:1–14

Shideler GL (1981) Development of the benthic nepheloid layer on thesouth Texas continental shelf, western Gulf of Mexico. Mar Geol41:37–61

Shimoyama S, Fujisaka H (1992) A new interpretation of the left-rightphenomenon during spatial diVusion and transport of bivalveshells. J Geol 100:291–304

SimberloV D, Dayan T (1991) The guild concept and the structure ofecological communities. Annu Rev Ecol Syst 22:115–143

Simon A, Poulicek M, Velimirov B, MacKenzie FT (1994) Comparisonof anaerobic and aerobic biodegradation of mineralized skeletalstructures in marine and estuarine conditions. Biogeochemistry5:167–195

Siringan FP, Anderson JB (1994) Modern shoreface and inner-shelfstorm deposits oV the east Texas coast, Gulf of Mexico.J Sediment Res B Strat Global Stud 64:99–110

Smyth MJ (1989) Bioerosion of gastropod shells: with emphasis oneVects of coralline algal cover and shell microstructure. CoralReefs 8:119–125

StaV GM, Powell EN (1990) Taphonomic signature and the imprintof taphonomic history: discriminating between taphofacies ofthe inner continental shelf and a microtidal inlet. In: Miller IIIW (ed) Paleocommunity temporal dynamics: the long-termdevelopment of multispecies assemblages. Spec Publ PaleontolSoc 5:370–390

Tribble GW (1993) Organic matter oxidation and aragonite diagenesisin a coral reef. J Sediment Petrol 63:523–527

Voight JR, Walker SE (1995) Geographic variation of the shell biontsin the deep-sea snail Gaza. Deep-Sea Res 42:1261–1271

Walker SE (1995) Taphonomy of modern and fossil intertidal gastro-pod associations from Isla Santa Cruz and Isla Santa Fe, Galapá-gos Islands. Lethaia 28:371–382

Walker SE (2001) Below the sediment-water interface: a new frontierin taphonomic research. Palaios 16:113–114

Walker SE, Goldstein ST (1999) Taphonomic tiering: experimentalWeld taphonomy of molluscs and foraminifera above and belowthe sediment-water interface. Palaeogeogr Palaeoclimatol Palae-oecol 149:227–244

Wehmiller JF, York LL, Bart ML (1995) Amino acid racemizationgeochronology of reworked Quaternary mollusks on U.S. Atlan-tic coast beaches: implications for chronostratigraphy, taphon-omy, and coastal sediment transport. Mar Geol 124:303–337

White S (2002) Encrusting foraminifera from Lee Stocking Island,Bahamas: taphonomy, shelf-to-slope distribution, and behavior.M.S. Thesis, University of Georgia, Athens, Georgia, 150 pp

Wilkinson M, Burrows EM (1972) The distribution of marine shell-boring green algae. J Mar Biol Assoc UK 52:59–65

Zezina ON (1997) Biogeography of the bathyal zone. Adv Mar Biol32:389–426

Zuschin M, Pervesler P (1996) Secondary hardground-communitiesin the northern Gulf of Trieste, Adriatic Sea. Senckenb Marit28:53–63

Zuschin M, Stachowitsch M, Pervesler P, Kollman H (1999) Struc-tural features and taphonomic pathways of a high-biomass epi-fauna in the northern Gulf of Trieste, Adriatic Sea. Lethaia32:299–317

Zuschin M, Stachowitsch M, Stanton RJ Jr (2003) Patterns and pro-cesses of shell fragmentation in modern and ancient marine envi-ronments. Earth-Sci Rev 63:33–82

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