coralline algal assemblages in upper neogene reef and temperate

Coralline algal assemblages in upper Neogene reef andtemperate carbonates in Southern Spain

Juan C. Braga *, Julio AguirreDepartamento de Estratigraf|a y Paleontolog|a, Universidad de Granada, Campus de Fuentenueva s/n, 18002 Granada, Spain

Accepted 31 July 2001

Abstract

Reef and temperate carbonate units alternate in the upper Miocene^Pliocene stratigraphic record of Betic basinspalaeogeographically connected to the Mediterranean. Shallow-water coralline algal assemblages in temperate unitsdiffer in taxonomic composition from those in reef carbonate units. The difference attains the subfamily level since thetemperate lithofacies are characterised by assemblages dominated by lithophylloids (Lithophyllum), whereasmastophoroids (Spongites and Neogoniolithon) predominate in the reef units. The proportion of lithophylloids,however, can be high in samples from shallow-reef palaeoenvironments. The distinction is less marked in deeperplatform deposits since melobesioids (Lithothamnion, Mesophyllum and Phymatolithon) are the major elements in theassemblages from both reef and temperate units. Sporolithon, the only representative of the family Sporolithaceae, isfrequent in reef-slope deposits but very rare in temperate lithofacies. The change in coralline algal assemblages fromtemperate to subtropical/tropical units is probably the result of the palaeophytogeography of the coralline red algaeduring the Late Neogene along climatic belts. Shallow-water floras were dominated by lithophylloids in cooler periods,during which the western Mediterranean was within the temperate belt, as in the present-day situation. In warmerepisodes, subtropical/tropical conditions enveloped the region and the tropical coralline floras, in which mastophoroidspredominate, together with reef corals and green algae inhabited the Betic basins. Similar, less pronounced,phytogeographic patterns can be roughly recognised in modern oceans. Fossil coralline algal assemblages can, thereforehelp to identify the palaeoclimatic context of sedimentation of the rocks in which they are recorded. They constitute apalaeontological tool supplemental to lithofacies and other fossil indicators for characterising such contexts in Cenozoicplatform deposits. ß 2001 Elsevier Science B.V. All rights reserved.

Keywords: Coralline algae; carbonate lithofacies; palaeophytogeography; palaeoclimate; Neogene; southern Spain

1. Introduction

Several intramontane Neogene basins in theBetic Cordillera in southern Spain (Fig. 1) were

connected to the western Mediterranean for mostof their palaeogeographic evolution. The upperMiocene^Pliocene stratigraphic record of theseMediterranean Betic basins comprises alternatingreef and temperate carbonate units. Reef units,dated as lowermost Tortonian, late Tortonian,early Messinian and late Messinian are interca-lated with lower Tortonian, uppermost Torto-nian/lowermost Messinian and Pliocene temperate

0031-0182 / 01 / $ ^ see front matter ß 2001 Elsevier Science B.V. All rights reserved.PII: S 0 0 3 1 - 0 1 8 2 ( 0 1 ) 0 0 3 8 4 - 4

* Corresponding author. Fax: +34-958-248528.E-mail addresses: [email protected] (J.C. Braga),

[email protected] (J. Aguirre).

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Palaeogeography, Palaeoclimatology, Palaeoecology 175 (2001) 27^41

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carbonates. Hermatypic corals and green algaeare the key components in reef carbonates, whilethey are absent or very scarce in temperate ones.Temperate carbonates comprise bryomol (Leesand Buller, 1972) and rhodalgal (Carannante etal., 1988) facies. Bryozoans, molluscs and coral-line red algae are the main components, togetherwith various proportions of barnacles, echinoids,solitary corals and terrigenous particles.

The alternation of reef and temperate carbo-nate units has been interpreted as the result ofclimatic oscillations in the western Mediterraneanthat can also be correlated with sea-level changes(Mart|n and Braga, 1994; Brachert et al., 1996).Reefs grew during warmer periods of high sealevel in which tropical/subtropical conditions pre-vailed in the region, whereas temperate carbo-nates formed in cooler phases with lower sea level.Oxygen isotope values of foraminiferal tests frommarls laterally equivalent to the Messinian carbo-nate deposits con¢rm that sea temperature is amajor factor controlling carbonate types (San-chez-Almazo et al., 2001).

Red algae, like other fossil groups, occur inboth carbonate types, but we demonstrate herethat coralline red algal assemblages are di¡erentin reef and temperate units in the Neogene basinsof southern Spain. We suggest that fossil coralline

algae can be used as an additional tool to de¢nethe palaeoclimatic context in which carbonateunits were deposited.

2. Methods

We have collected samples of coralline red al-gae from selected sections of successive upperMiocene and Pliocene temperate and reef carbo-nate units in the Granada, Sorbas and Almer|a-N|jar basins in southern Spain (Fig. 1). The strati-graphic position and age, as well as the sedimen-tary models of the study units have previouslybeen described in regional and sedimentologicalpapers on the Neogene Betic basins. Where pos-sible, we have sampled coralline algae from deep-er and shallower platform deposits in each unit tocharacterise algal assemblages from di¡erent pa-laeobathymetric settings. Only very shallow-waterupper-Pliocene materials crop out in the regionand thus no deeper-platform coralline algae ofthis age have been sampled.

A total of 110 ultrathin sections (4.7U2.5 cm insize and about 10 Wm thick) were cut from sam-ples collected at 89 sampling sites to identify thecoralline algae at the most precise taxonomic levelpossible but many examples cannot be identi¢ed

Fig. 1. Neogene basins in southern Spain. Insets show location of maps in Fig. 2 (1), Fig. 6 (2), and Fig. 11 (3).

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J.C. Braga, J. Aguirre / Palaeogeography, Palaeoclimatology, Palaeoecology 175 (2001) 27^4128

at the species level. We refer to the recognisedgenera and species when describing the algal con-tent in each section. We do not report the namesof a few species to avoid nomenclatorial problemsof introducing new combinations without follow-ing the appropriate procedures. According to themethod proposed by Perrin et al. (1995), propor-tions of the di¡erent taxa have been estimated bypoint-counting the cross-sectional areas that theyoccupy in thin sections. In the diagrams for eachsection we report the relative proportions of theidenti¢ed non-geniculate coralline algae at thefamily and subfamily levels. We also report therelative abundance of geniculate algae as a groupin the section with signi¢cant proportions of thesecorallines.

Family and subfamily circumscriptions followWoelkerling (1988) and Verheij (1993). At the ge-neric level, Neogoniolithon and Mesophyllum areused here in the sense of Braga et al. (1993): Neo-goniolithon and Mesophyllum include mastophor-oids and melobesioids with ventral co-axial core,respectively (see also Aguirre and Braga, 1998 fora discussion on Mesophyllum). Algal growth-formterminology follows Woelkerling et al. (1993).

3. Results

3.1. Lowermost Tortonian reef unit

A lowermost Tortonian unit comprising smallpatch reefs within deltaic deposits is found in scat-tered outcrops in the Granada Basin (Figs. 2 and3) (Braga et al., 1990; Rivas et al., 1999). Theoccurrence of Neogloboquadrina acostaensis Blowpoints to a Tortonian age for this unit (Rivas etal., 1999). Coralline algal remains are scarce andpoorly preserved and have therefore not beenconsidered in detail in this report. The few re-corded assemblages, however, indicate a predom-inance of mastophoroid corallines (Neogoniolithonand Spongites with minor Lithophyllum).

3.2. Lower Tortonian temperate carbonate unit

Bioclastic carbonates with various proportionsof terrigenous components overlie prior Torto-nian and older Miocene units and the Betic pre-Neogene substrate in the Granada Basin (Fig. 3).An early Tortonian age is attributed to this unitsince the ¢rst occurrence of Neogloboquadrina hu-merosa Takayanagi and Saito (indicating the lateTortonian) is recorded in the ¢ne-grained depositsunconformably overlying the carbonates (Mart|n-Perez, 1997). The carbonates are mostly made upof coralline red algae, bryozoans and molluscs,with minor amounts of barnacles and echinoids,which are the characteristic bryomol (Lees and

Fig. 3. Marine Miocene stratigraphy of the Granada Basin(after Braga et al., 1990).

Fig. 2. Simpli¢ed geological map of the Granada Basin andlocation of the study sections.

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J.C. Braga, J. Aguirre / Palaeogeography, Palaeoclimatology, Palaeoecology 175 (2001) 27^41 29

Buller, 1972) and rhodalgal (Carannante et al.,1988) facies components. Two sections from thisunit have been sampled.

3.2.1. Venta del Fraile sectionThis section is located at the southern margin

of the basin overlying the Triassic dolostones ofthe Betic basement (Fig. 2). At the bottom of thesection, a bioclastic breccia up to 1.5 m thick in-cludes oyster, bryozoan, coralline algal fragmentsand angular dolostone clasts, which frequentlyconstitute the nucleus of algal nodules. The restof the section, 33.5 m thick, consists of troughcross-bedded calcirudites and calcarenites(Fig. 4). The wavelength of the troughs changesfrom decimetres to metres to the top. A gradualchange from coastal to deeper shelf deposits isre£ected in the section. Coralline algae occur asfragments of branching and encrusting plantswith larger branch fragments and open-branchingrhodoliths (sensu Bosence, 1976) in the top 4 m.Only lithophylloids and melobesioids have beenrecorded (Fig. 4). Lithophyllum Philippi species(L. incrustans Philippi can be recognised) andMesophyllum Lemoine are the main componentsin the algal assemblages with minor Lithotham-nion Heydrich and other melobesioids unidenti¢-able at the generic level.

3.2.2. Los Cahices sectionThis is the section farthest from the basin mar-

gins, in which the distalmost deposits in the unitcrop out (Fig. 2). It consists of decimetric-to-met-ric beds of calcirudites and calcarenites, locallyexhibiting metric-scale trough cross-bedding(Fig. 4). Coralline algae, bryozoans, pectinidsand oysters are the main carbonate components,together with serpulid-worm tubes, barnacles andechinoids. Coralline algae occur as loose, open-branching rhodoliths, small rhodoliths made upof branching, protuberant and encrusting plants,and fragments of all these growth types. Thesedeposits probably formed in an o¡shore shelf en-vironment (Rodr|guez-Fernandez, 1982). Algal as-semblages comprise melobesioids and lithophyl-loids in variable proportions (Fig. 4).Lithothamnion and Mesophyllum are the maincomponents, with minor Lithophyllum in mostsamples, including L. incrustans and L. agaricifor-mis (Pallas) Lamarck (probably equal to L. den-tatum (Ku«tzing) Foslie according to Woelkerling,1998, and referred to L. dentatum in Braga andAguirre, 1995). Lithophyllum can be locally dom-inant. No other coralline genera have been recog-nised, although some thin encrusting plants prob-ably belong to Phymatolithon Foslie and a smallproportion of melobesioid thalli have not beenidenti¢ed at the generic level.

3.3. Upper Tortonian reef unit

Upper Tortonian coral reefs in the GranadaBasin grew as small patch-reefs on delta depositsand on the substrate formed by previous Neogenerocks (Fig. 3). Fine-grained distal delta sedimentsand laterally equivalent marls contain upper Tor-tonian foraminifers (Braga et al., 1990). We havesampled the reefs and related carbonates in theMonachil section, the best exposed of the unit.

3.3.1. Monachil sectionThis section is located at the southeastern mar-

gin of the Granada basin (Fig. 2) and consists ofthree major subunits of prograding fan delta de-posits. Reef carbonates occur in the last subunit,showing a complex architecture resulting from theinteraction between terrigenous sedimentation

Fig. 4. Lithological columns and relative proportions of cor-alline algal subfamilies in selected sections of the lower Tor-tonian temperate carbonates in the Granada Basin.

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and several episodes of reef growth (Braga et al.,1990). In each reef episode, the coral framework isup to 40 m across and up to 3 m thick. Frame-work facies pass successively downwards into cor-al breccias, calcirudites and calcarenites formed ofbioclasts derived from the reef and organisms thatlived on the delta slope (Fig. 5).

The reef framework was built on terrigenousclasts by Porites Link and Tarbellastraea Alloi-teau, with minor Platygyra Ehrenberg, Sideras-trea de Blainville and Palaeoplesiastraea Milne-Edwards and Haime (Braga et al., 1990). Coral-line algae occur as thin coatings of encrusting towarty plants on the coral colonies and as frag-ments and small rhodoliths in the internal sedi-ment ¢lling the spaces between the coral skele-tons. Mastophoroids (Neogoniolithon Setchelland Mason and Spongites Ku«tzing) are the maincomponents in the framework assemblages, withminor contributions of lithophylloids (Lithophyl-lum species, such as L. incrustans, L. pustulatum(Lamouroux) Na«geli, and L. agariciformis), melo-besioids (Lithothamnion), and geniculate corallines(Corallina Linnaeus, Amphiroa Lamouroux andJania Lamouroux) (Fig. 5).

Reef-slope deposits extend downwards for sev-eral tens of metres. Coralline remains comprisescarce rhodoliths made up of encrusting andwarty thalli and abundant fragments of geniculateand non-geniculate plants. Melobesioids (Litho-thamnion and Mesophyllum) are the main compo-nents in the rhodoliths. Lithophylloids (Lithophyl-lum), mastophoroids and the above-mentioned

geniculate genera can be recognised in the frag-ments dispersed throughout the matrix (Fig. 5).

3.4. Uppermost Tortonian^lowermost Messiniantemperate unit

This unit crops out extensively in the Neogenebasins overlying the upper Tortonian reef unitand older rocks and is known in the area as theAzagador Member (Ruegg, 1964) (Fig. 6). It con-sists of mixed bioclastic carbonates and siliciclas-tics. Bryozoans, molluscs and red algae are themain carbonate components, exhibiting the litho-facies characteristic of temperate carbonates. Wehave selected two well-exposed sections in theSorbas Basin (Fig. 7) that represent proximaland distal platform facies of the unit.

3.4.1. Alfaix sectionThis section is located at the northern margin

of the Sorbas Basin in its transition to the VeraBasin, in the valley £oor of the R|o Jauto river,below the bridge at Alfaix village (Fig. 7). TheAzagador Member onlaps the Betic substrateand an older Neogene continental unit. At thislocality calcarenites/calcirudites with mixed silici-clastics exhibit low-angle, parallel lamination

Fig. 5. Lithofacies scheme (modi¢ed after Braga et al., 1990),sample location and relative proportions of coralline algalgroups in the Monachil-Reef section (late Tortonian). Insetshows details of coral framework.

Fig. 6. Messinian to lower Pliocene stratigraphy of the Sor-bas Basin (after Mart|n and Braga, 1994).

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(Fig. 8). They change laterally into similar sedi-ments with conspicuous, decimetre- to metre-scaletrough cross-bedding. They have been interpretedas beach deposits deepening seawards (to thesouth) into a shoal area (Braga et al., 1999). Bryo-zoan, mollusc, and coralline algal particles are themain carbonate components. Coralline algae oc-cur as sand- to gravel-sized fragments of plants.Lithophylloids (L. incrustans can be locally recog-nised) are the most common components at thelower half, whereas particles of melobesioids(Mesophyllum and Lithothamnion, unidenti¢ableat the species level), predominate in the upperpart of the section (Fig. 8).

3.4.2. Cerro La Molata sectionThis section is located in the centralmost out-

crop of the Azagador Member in the Sorbas Ba-sin (Fig. 7), i.e. where the distalmost platformdeposits of the unit can be expected. The lime-stones overlie upper Tortonian pelagic marlswith an angular unconformity. The basal 10 mconsist of massive, locally crudely laminated, cal-cirudites and calcarenites rich in coralline algae,bryozoans and pectinid and oyster shells (Fig. 8).Serpulid-worm tubes, barnacles, brachiopods andechinoid fragments can also be found (Wood,1996). The degree of breakdown of the bioclasticmaterial is low and the fossil assemblage can be

considered para-autochthonous in a shelf environ-ment (Wood, 1996). Coralline algae occur asopen-branching plants and rhodoliths made upof superimposed encrusting and warty thalli, to-gether with fragments of both types. Melobesioidsare dominant in the coralline assemblages (Fig. 8),in which Lithothamnion is the most frequent ge-nus. Mesophyllum is also common and can locallypredominate, while Lithophyllum species (L. agari-ciformis and L. incrustans) are always present andconstitute up to 40% in a few samples.

A 30-cm-thick shell bed with an erosional baseoverlies the bioclastic calcirudites (Fig. 8). Rho-doliths of encrusting and warty corallines are dis-persed in the densely packed shells of pectinids(Chlamys seniensis Lamarck) and terebratulids.Coralline assemblages are similar to those re-corded in the underlying calcirudites. This shellconcentration has been interpreted as a storm de-posit (Wood, 1996). At the top of the shell bed,the lithology changes to ¢ne-grained sandy calcar-enites (Fig. 8), rich in red algal fragments andforaminiferal tests that represent o¡shore shelfsediments transitional to the overlying basinalmarls (Wood, 1996). Globorotalia mediterraneaCatalano and Sprovieri, indicating a Messinianage, is ¢rst recorded in the silty marls on top ofthe calcarenites (Sierro et al., 1993). In this centralsection, the Azagador Member therefore formedduring the late Tortonian, but the Azagador lime-stones that are the lateral equivalents of the pe-

Fig. 7. Geological map of the Sorbas Basin and section sites(modi¢ed from Montenat, 1990).

Fig. 8. Lithological columns and percentages of coralline al-gal subfamilies in the selected sections of uppermost Torto-nian/lowermost Messinian temperate carbonates in the Sor-bas Basin.

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lagic marls at the basin margins are early Messi-nian in age (Braga et al., 1999).

3.5. Lower-Messinian reef units

Messinian reef units overlie the Azagador lime-stone and older rocks (Fig. 6). They crop out ex-tensively in the Sorbas and Almer|a-N|jar basins(Fig. 1) but can also be traced into several adja-cent basins in southeast Spain. Two successivelower Messinian reef units have been distinguised:a lower Bioherm Unit, comprising coral patch-reefs and Halimeda bioherms, and an upperFringing Reef Unit consisting of progradingfringing Porites reefs (Fig. 6) (Riding et al.,1991; Mart|n and Braga, 1994; Braga et al.,1996). Palaeobathymetric gradients can be bestdelimited in the Fringing Reef Unit outcropsand we have selected one section in this unit tostudy coralline algal assemblages from both deep-er- and shallow-water palaeoenvironments.

3.5.1. Cariatiz sectionThis locality lies at the northern margin of the

Sorbas Basin (Fig. 7). Facies of the Fringing Reefat Cariatiz were described in detail by Riding etal. (1991) and the geometries of reef progradationin relation to relative sea-level changes were re-ported by Braga and Mart|n (1996). In a singleepisode of reef development, horizontal lagoonbeds change southwards to subvertical frameworkfacies that grade downwards to steeply dippingtalus-slope breccias and then to more gently dip-

ping slope sediments (Fig. 9). Slope sedimentsthin basinwards before merging into the basinalmarls. The samples were collected in a single epi-sode of reef development from the deepest basinalfacies to the reef framework. The following faciescan be distinguished from bottom to top (Fig. 9):(a) silty marls intercalated with ¢ne-grained cal-carenite beds and Neopycnodonte shell concentra-tions. These deposits formed at the transitionfrom the reef slope to the basin. No red algalremains have been recorded. (b) Calcarenitesand calcirudites with fragments of corals, mol-luscs, serpulid-worm tubes, Halimeda and coral-line algae. They were deposited in the fore-reefslope. Most coralline remains are unidenti¢ablesand-grade fragments, but some algal nodules oc-cur at the transition to the overlying facies. Theycomprise melobesioids (Phymatolithon and otherunidenti¢able plants), together with mastophoroidcorallines (Spongites and Neogoniolithon) in thecore of some nodules. (c) Framework blocksand coral breccias derived from the frameworkupslope. Coralline algae occur as rhodolithsmade up of encrusting and warty thalli, crustson coral clasts, fragments dispersed in the brecciamatrix, and rhodoliths and crusts inside frame-work blocks. Except for the latter, it is quite dif-¢cult to ascertain whether the coralline algae grewon the slope or fell downslope from higher set-tings prior to or after their death. The nodulesand coralline fragments in the matrix are mainlymade up of the mastophoroid Spongites. The me-lobesioid Phymatolithon constitutes the outer por-tion of some rhodoliths and locally abundant lith-ophylloids, such as Lithophyllum pustulatum andL. byssoides (Lamarck) Foslie ( = L. lichenoidesPhilippi), also occur (Fig. 9). (d) The reef frame-work comprises : (1) basal pinnacles made up ofstick-like Porites colonies connected by laminarPorites bridges. The coral skeletons are encrustedby red algae, foraminifers and thick microbial mi-crite crusts. The remaining voids are ¢lled with amicritic matrix. In addition to the thalli encrust-ing the coral colonies there are fragments of coral-line algae and small rhodoliths dispersed in thematrix. (2) A thicket zone of more continuouscoral colonies and similar framework compositionand coralline occurrence. (3) A reef crest-zone

Fig. 9. Lithofacies scheme (modi¢ed from Riding et al.,1991) and relative proportions of coralline algal groups inthe Cariatiz-Reef section (late Messinian). Letters in bracketsrefer to the sections in the text.

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made up of laminar contorted and locally smallstick Porites colonies, overgrown by red algae,foraminifers and thick microbial micritic crusts.Pockets of coarse-grained matrix include rhodo-liths, branching coralline fragments, echinoidsand molluscs. The mastophoroid Spongites is themost common coralline alga in the reef frame-work. Neogoniolithon and Lithoporella that alsobelong to the subfamily Mastophoroideae are mi-nor components in the framework assemblage.Lithophylloids (L. byssoides and L. pustulatum)occur in most samples and are dominant in a

few samples from the matrix in the pinnacles,where thin Sporolithon Heydrich plants can alsobe found (Fig. 9).

Lagoon deposits do not occur at the Cariatizsection but they have been sampled in the nearbyBarranco de la Mora section (Braga and Mart|n,1996). They contain coralline algal nodules anddebris with Spongites as the main component aswell as Lithophyllum, Neogoniolithon and Litho-thamnion.

3.6. Lower Pliocene temperate unit

Lower Pliocene marine deposits (Unit I sensuAguirre, 1998a) are restricted to the Neogene ba-sins closest to the present-day Mediterranean.They generally consist of terrigenous sedimentsincluding diverse proportions of carbonates(Fig. 10), which unconformably overlie olderNeogene rocks and the Betic basement. Carbo-nate components are temperate in character asthey mainly comprise bryozoans, molluscs andred algae. The occurrence of Globorotalia marga-ritae Bolli and Bermudez together with G. puncti-culata Deshayes and G. crassaformis Gallowayand Wissler indicates a Lower Pliocene age forthis unit (Aguirre, 1998a). We have selected twosections in the Carboneras sub-basin (Fig. 11),which after a Miocene evolution as a part of theAlmer|a-N|jar Basin, was a small embaymentopen to the east during the Pliocene (Aguirre,1998a).

Fig. 10. Messinian to Pliocene stratigraphy of the northeast-ern sector of the Almer|a-N|jar Basin. Pliocene units I and IIaccording to Aguirre (1998a).

Fig. 11. Simpli¢ed geological map of the Almer|a-N|jar Basin and location of the sampled sections (modi¢ed from Montenat,1990). The enlarged area corresponds to the Carboneras sub-basin.

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3.6.1. El Cigarron sectionThis section is located at the westernmost mar-

gin of the Pliocene outcrops in the Carbonerassub-basin, close to the crossroad to El Llano deDon Antonio (Fig. 11). The lower Pliocene depos-its here overlie upper Messinian carbonates andvolcanic Miocene rocks. The section consists ofup to 1.5 m of well-cemented bioclastic carbo-nates mixed with terrigenous sands and pebbles(Fig. 12). The main carbonate components arecoralline algae, barnacles, bivalves (mostly oys-ters), Strombus Linnaeus and other gastropods.Low-angle lamination dipping to the east andchanging in the same direction to small troughcross-bedding is characteristic of beach deposits.Red algae occur as small rhodoliths and sand-to-granule-sized particles. Fragments of unidenti¢-able species of melobesioids are the most commonalgal remains (Fig. 12). They mainly include Lith-othamnion but Phymatolithon (P. calcareum (Pal-las) Adey and McKibbin) and Mesophyllum canalso be recognised. Lithophylloids (Lithophyllum)together with very few Sporolithon fragments anda mastophoroid alga account for the rest of the

coralline assemblages. Most coralline grains, how-ever, cannot be identi¢ed.

3.6.2. Torre Vieja sectionThis is the distalmost section in the lower Plio-

cene unit in the Carboneras sub-basin (Fig. 11). Adistinctive conglomeratic bed, up to 1 m thick,overlies Messinian reef deposits. This bed is com-posed of andesite boulders and cobbles from thevolcanic basement and of Messinian coral blocks(Aguirre, 1998a). It changes upwards into 35-m-thick bioclastic calcarenites and calcirudites fromwhich only the bottom 20 m have been sampled(Fig. 13). Coralline algae, pectinids, bryozoansand echinoids are the main carbonate compo-nents, with minor brachiopods. The algae occuras rhodoliths comprising encrusting, warty andfruticose thalli as well as fragments of rhodolithsand individual plants. Melobesioids predominatein the algal assemblages (Fig. 13). Mesophyllumis the most common component, followed byLithothamnion. Lithophylloid species, including

Fig. 13. Lithological column and relative proportions of thecoralline algal subfamilies in the Torre Vieja section in theCarboneras sub-basin.

Fig. 12. Lithological column and relative proportions of thecoralline algal subfamilies in the selected lower Pliocene ElCigarron section in the Carboneras sub-basin.

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L. pustulatum, account for less than 3% of thealgal volume (Fig. 13). These materials havebeen interpreted as nearshore shelf deposits(Aguirre, 1998a). At the top of the sequence,beach deposits prograde on the underlying sedi-ments.

3.7. Upper Pliocene temperate unit

The emerged upper Pliocene marine deposits(Unit II sensu Aguirre, 1998a) in southeasternSpain are restricted to small areas close to thepresent-day Mediterranean coast (Aguirre,1998a). This unit comprises terrigenous littoralsediments with small proportions of carbonateproduced by bivalve shell concentrations, bar-nacles, coralline algae and Cladocora corals(Aguirre and Jimenez, 1997, 1998). Cladocora Eh-renberg is an ahermatypic coral (Schuhmacherand Zibrowius, 1985) and thus the carbonatecomponents can be considered of the temperatetype. We have sampled the best-exposed sectionin the Almer|a-N|jar Basin, located east-northeastof El Alquian (Fig. 11).

3.7.1. Rambla Quebrada sectionThe upper Pliocene unit consists of alternating

debris-£ow conglomerates and sands, changingupwards into silts including coral banks of Clado-cora caespitosa (Linnaeus) Milne Edwards andHaime (Fig. 14), which in turn are overlain byprograding conglomerates and sands. These de-posits formed in a fan-delta prograding into asheltered shallow bay. The conglomerates repre-sent the littoral facies while the Cladocora banksdeveloped in sheltered shoreface settings (Aguirreand Jimenez, 1997, 1998).

Coralline algae occur as attached crusts on topof the boulders of the debris-£ow conglomerates.Lithophylloids (L. incrustans, L. agariciformis andL. pustulatum) are the only representatives of thealgal assemblages (Fig. 14). The corallines in thecoral banks appear as thin crusts on epizoans,such as vermetid gastropods and worm-tube ser-pulids, that grew on the coral skeletons and asrhodoliths dispersed between the colonies. Themastophoroid Spongites fruticulosus Ku«tzing isthe most common alga, followed by the above-

mentioned species of lithophylloids (Fig. 14).Mesophyllum and geniculate coralline plants areminor components.

4. Discussion

4.1. Neogene coralline algal assemblages

The algal assemblages recorded di¡er in taxo-nomic composition according to the carbonatelithofacies in the successive units of the Neogenebasins in southern Spain (Fig. 15). They alsoshow di¡erences in relation to proximal/distal gra-dients within each unit.

Coralline algae from the subfamily Lithophyl-loideae Setchell predominate in shallow-water car-

Fig. 14. Lithological column (after Aguirre and Jimenez,1998) and relative proportions of coralline algal subfamiliesin the upper Pliocene Rambla Quebrada section.

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bonate deposits with bryomol or rhodalgal facies,i.e. lithophylloids are the most common algalcomponents in lithofacies characteristic of shallowtemperate carbonates (Fig. 15). Lithophyllum (in-cluding Titanoderma Na«geli as a younger syno-nym, Campbell and Woelkerling, 1990; Woelker-ling and Campbell, 1992) is in fact the onlylithophylloid genus recorded, comprising severalspecies. Members of the subfamily Melobesioi-deae Bizzozero occur together with Lithophyllumin proximal temperate carbonate settings and canbe the most common components locally but gen-erally their abundance increases towards deeperpalaeoenvironments. The melobesioids Litho-thamnion, Mesophyllum and Phymatolithon arethe main elements in the algal assemblages in dis-tal sections of the studied temperate carbonateplatforms, where Lithophyllum is subordinate. Ex-cept for the upper Pliocene unit, discussed below,algae from the Mastophoroideae Setchell subfam-ily are completely absent or very scarce in theassemblages from temperate units. Geniculatecorallines are very rarely recorded, always repre-senting less than 1% of the algal content.

In contrast, mastophoroids are the main com-ponents in the shallow-water algal assemblagesfrom reef units (Fig. 15). The genera Spongitesand Neogoniolithon predominate in the crusts onthe coral skeletons and in the algal nodules thatgrew when the westernmost Mediterranean was

under tropical/subtropical climatic conditions.Lithoporella occurs as a secondary componentand other, very thin laminar thalli may corre-spond to other subfamily representatives, but thepoor preservation of plants with very small cellsprevents any certain identi¢cation. Lithophyllumspecies are subordinate but always present inreef algal assemblages. Melobesioids occur inlow proportions in shallow-water reef palaeoen-vironments, whereas they tend to predominate inthe deeper reef slopes. Lithothamnion, Mesophyl-lum and Phymatolithon are the recorded membersof this subfamily. Sporolithon, of the family Sporo-lithaceae Verheij, appears as a minor componentin the reef frameworks and is more common inthe slope deposits. Geniculate corallines are usu-ally rare but can be very abundant locally, such asin the slope deposits of the upper Tortonian reefsin the Granada Basin (Fig. 5).

In summary, there is a clear-cut contrast in thetaxonomic composition of shallow-water corallinealgal assemblages from temperate and reef carbo-nate units (Fig. 15). This di¡erence attains thesubfamily level since the temperate-carbonate lith-ofacies are characterised by algal assemblagesdominated by lithophylloids, whereas mastophor-oids predominate in the reef units. Mastophoroidsare scarce or totally absent in the temperate lith-ofacies, while the proportion of lithophylloids canbe high in samples from shallow-reef palaeoenvi-ronments. The distinction becomes less noteworthyin distal/deeper deposits since melobesiod plantspredominate in the assemblages from reef andtemperate units. Nevertheless, the accompanyingplants belong to the Lithophylloideae in the tem-perate carbonates and mostly to the Mastopho-roideae in the reefs. In addition, the sporolithaceanSporolithon is common in reef units but veryrarely recorded in temperate carbonates.

The algal assemblages from the upper Plioceneunit represent a certain exception to this well-de-¢ned pattern. The lithofacies in the unit can beconsidered temperate in character since the re-corded corals are not hermatypic and no greenalgae are found. Lithophylloids are the majorcomponents in the bulk composition of the algalassemblages in the unit but in the Cladocorabanks Mastophoroideae are very abundant and

Fig. 15. Successive upper-Miocene/Pliocene carbonate unitsin the Mediterranean Neogene basins in southern Spain andtheir characteristic coralline algal components at generic andsubfamily levels in shallow-water fossil assemblages.

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Spongites is the most common alga in many sam-ples. This intermediate character of the algal as-semblages may re£ect a transitional nature in thepalaeoclimatic context of the unit. Although Cla-docora banks grow in the present-day Mediterra-nean, certain features of the unit suggest forma-tion in temperatures closer to those typical forsubtropical areas. In particular, the occurrenceof Saccostrea cuccullata Born in this unit, re-stricted to tropical and subtropical areas in mod-ern oceans, points to warmer water temperaturesduring the Late Pliocene than in the modern west-ern Mediterranean (Aguirre, 1998b,c). Alterna-tively, the abundance of Spongites in the Clado-cora banks can be a local feature similar tomodern examples of Mediterranean localitieswith high proportions of mastophoroids (see be-low).

This change in coralline algal assemblages fromtemperate to subtropical/tropical units may be theconsequence of the palaeobiogeographic distribu-tion of the coralline red algae during the LateNeogene along climatic belts. The palaeoclimaticoscillations in southern Spain during the LateNeogene have been interpreted as the result ofsouthward and northward displacements of theclimatic belts, following climatic changes and re-lated glacio-eustatism (Mart|n and Braga, 1994;Brachert et al., 1996; Mart|n et al., 1999). In cool-er periods, the region was inside the temperateclimatic belt, as in the present-day situation, andshallow-water £oras were dominated by lithophyl-loids. In warmer episodes, subtropical/tropicalconditions reached the western Mediterranean lat-itudes and the tropical coralline £oras (in whichmastophoroids predominate), together with reefcorals and green algae, spread over the region.

4.2. Modern coralline algal phytogeography

Climatic^biogeographic di¡erentiations in cor-alline algal £oras can be recognised in modernoceans. Mastophoroid algae predominate in thealgal assemblages from shallow-water settings intropical areas (Adey, 1979, 1986; Adey et al.,1982; Bosence, 1985; Borowitzka and Larkum,1986). Hydrolithon Foslie (including PorolithonFoslie as a younger heterotypic synonym, Penrose

and Woelkerling, 1992) and Neogoniolithon arethe most abundant genera in coral reefs andhigh-energy algal ridges, but Lithophyllum can lo-cally be the major builder in moderate-energyridges in the Caribbean (Bosence, 1984; Adey,1986). The melobesioids, together with Sporoli-thon, increase in abundance with depth (Adey,1979; Adey et al., 1982; Lund et al., 2000). It isremarkable that thick plants of Hydrolithon, char-acteristic of coralline crusts and rhodoliths inmodern reefs, have not been recorded in the Neo-gene reefs from southern Spain, where Spongitesand Neogoniolithon predominate. Hydrolithon oc-curs in Neogene deposits from the Paci¢c (Mart|net al., 1993) and the Caribbean (Beckmann andBeckmann, 1966), but never reached the high-lat-itude reef areas of the western Mediterranean.

In the subtropical Canary Islands mastophor-oids, in particular Neogoniolithon and Hydrolithon(as Porolithon), characterise the coralline £oras inthe meso-littoral and shallow infra-littoral zones,although lithophylloid species are signi¢cant com-ponents in those zones as well (Afonso-Carrillo etal., 1984).

In shallow-water environments in temperateseas, Lithophyllum is the most common genus(Adey, 1986). Lithophylloids are the most fre-quent coralline algae in the infralittoral-zone as-semblages in the Mediterranean (i.e. Cormaci etal., 1985; Giaccone et al., 1985). Lithophyllum isalso the major builder of trottoirs at sea level inthe northern and western Mediterranean (Adey,1986; Di Geronimo et al., 1993; Giaccone et al.,1993). Neogoniolithon notarisii (Dufour) Setchelland Mason, however, can be the main trottoirelement locally, especially in the warmer southernand eastern regions of that sea (Adey, 1986), thusconstituting a certain exception to the generaldominance of Lithophyllum. It is worth notingthat no Hydrolithon species with thick thallihave been found in the Mediterranean. The re-ported species of this genus correspond to thosewith very thin thalli (formerly included in FosliellaHowe), which probably have a very low preserva-tion potential as fossils, since they have beenrarely found even in Pleistocene deposists (DiGeronimo, 1998). A few records of the multistra-tose species H. samoe«nse (Foslie) Keats and

PALAEO 175 27-12-01


Chamberlain, however, have been reported fromhigher latitudes (Chamberlain, 1994). In deeperplatform settings, melobesioids are common, butLithophyllum and mastophoroids are also fre-quent in rhodoliths and pebble coatings (Bosence,1983; Basso, 1998). Lithophyllum is the dominantgenus in the widespread rhodoliths in the temper-ate Gulf of California as well (Riosmena-Rodri-guez et al., 1999). Lithophyllum species occurthroughout southern Australia, a typical regionof temperate carbonate deposition (James et al.,1992; Boreen and James, 1993) and can dominatein some shallow-water collections (Woelkerlingand Campbell, 1992). Nevertheless, detailed £oris-tic accounts on boulder substrates from shallowhabitats indicate that species of Hydrolithon, Phy-matolithon and Mesophyllum were dominant inthree analysed sites from southern Australia inwhich Lithophyllum species were minor compo-nents (Daume et al., 1999).

Melobesioids seem to be the dominant elementsin coralline assemblages from both shallow anddeep environments in cool temperate and coldwaters (Adey, 1986), but Lithophyllum can be lo-cally common in meso- and infra-littoral zones(Irvine and Chamberlain, 1994).

5. Concluding remarks

In summary, the change in coralline algal £orasfrom reef to temperate carbonate lithofacies isprobably the regional expression in fossil assem-blages in the western Mediterranean of the cli-matic/biogeographic distribution of coralline al-gae during the Late Neogene. This £oristicdi¡erentiation is best marked in shallow-water en-vironments, where it can be recognised at the sub-family level. Such phytogeographic patterns areless pronounced, but can be recognised in modernoceans as well, since di¡erent coralline £oras aretypical of di¡erent climatic belts. Present-day cor-alline algal phytogeographic areas, however, arebest characterised at the generic and speci¢c lev-els. Therefore, it seems that fossil coralline algalassemblages may help to identify the climatic con-text of deposition of the rocks in which they arerecorded. Local exceptions to the general pattern,

however, are likely to occur and, therefore, anumber of samples from several localities of thegeological unit under study must be analysed toassess the palaeoclimatic character of its coralline£ora.

Acknowledgements

This work was supported by `Fundacion RamonAreces' Project: `Cambios climaticos en el sur deEspan¬a durante el Neogeno' and by DGICYT(Spain) Project PB97/0808. We thank ChristineLaurin for correcting the English text. We areindebted to Davide Bassi and Werner Piller fortheir constructive reviews.

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