N o l i n g u i s t i c a l t e r a t i o n s h a v e b e e n m a d e i n t h e a b s t r a c t s .

Program o f the 4 th In te rna t iona l Sympos ium on Foss i l A lgae

Card i f f , Wa les , Un i ted K ingdom (1987)

AWRAMIK, S.M. Archean and Proterozoic stromatolites [1-2]

BARATTOLO, F. Remarks on Neomeris cretacea STEINMANN (Dasycladales) from the Cretaceous of Orizaba (Mexico) [2]

BARATTOLO, F. Fertile and vegetative regions in Triploporella marsicana PRATURLON (Dasycladales) [2]

BASSOULLET, J.-P. Sarfatiella dubari CONRAD & PEYBERNÈS 1973: a junior synonym of Holosporella siamensis PIA 1930 [2-3]

BEADLE, S. Cyclocrinitids [3]

BERTRAND-SARFATI, J. Tussocky microstructure in stromatolites: a biological event recorded in the Upper Proterozoic sediments of the West African craton [4-5]

BOSENCE, D.W.J. Coralline Algae: A review and discussion of recent developments [5-6]

BRAGA, J.C., and MARTIN, J.M. A model for development of rhodoliths on shallow, coastal areas: the Miocene of Bayarque, S.E. Spain [6]

BROOKE, C., and RIDING, R. A new look at the Solenoporaceae [7]

BURNE, R.V. Microbialites: organosedimentary deposits of benthic microbial communities [7-8]

CASANOVA, J. Open Th/U systems in Pleistocene stromatolites from African paleolakes: dating potential [9]

CASANOVA, J. Microbiology and geochemistry of modern lacustrine stromatolites, Lake Annecy, France [9-10]

DALE, B. Recent calcareous dinoflagellate cysts [10-11]

DEY, S., and SMITH, L. Crustose coralline algae forming rhodoliths on the Grenadines Bank, Lesser Antilles [11-12]

DROMART, G., and GAILLARD, C. Late Jurassic deep-marine microbial fabrics across the north-Tethyan margin. Examples from Jura and Ardèche areas, south-eastern France [12-13]

ELLIOTT, G.F. The Dasycladalean algae of the Palaeozoic and Mesozoic [13]

FAIRCHILD, I.J. Stromatolites and associated lagoonal facies from latest Proterozoic of central East Greenland [14]

FEIST, M., and GRAMBAST-FESSARD, N. The genus concept in Charophyta: evidence from Paleozoic to Recent [14-15]

FLÜGEL, E. Triassic and Jurassic marine calcareous algae [15]

GÉNOT, P. Cenozoic and Recent calcified Dasycladales [16]

GOLUBIC, S. Recent stromatolites [16-17]

GOLUBIC, S., KNOLL, A.H, and ZHANG, Y. Phototropic endoliths Hyella-Eohyella: diversity and fossil record [17]

GRANIER, B., and MICHAUD, F. Dasycladales from the Upper Jurassic of south-eastern Mexico [18]

GREY, K., and WILLIAMS, I.R. Possible megascopic algae from the Middle Proterozoic Manganese Group, Bangemall Basin, Western Australia [18-19]

HILLIS-COLINVAUX, L. Recent calcified Halimediaceae [19-20]

KEUPP, H. Fossil calcareous dinoflagellate cysts [20-22]

LEITCH, A. Post-fertilisation development of the calcareous oosporangium in the Characeae [22]

MAMET, B.L. Marine calcareous Carboniferous algae [22-24]

MAURIN, A.F. Microbial Micrites [24-25]

MOHANTI, M., SRIVASTAVA, S.C., and SINGH, A.K. Calcareous algae in the Palaeogene carbonate microfacies of north-western Kutch (Gujarat), India [25-26]

MOORE, L.S. Stromatolites of Lake Clifton formed by the calcification of a benthic microbial community [26]

MU, X.-N. Fossil Udoteaceae and Gymnocodiaceae [27]

NITECKI, M.H. Unsolved problems of receptaculitid affinities [27-28]

PENTECOST, A. Calcification processes in algae and cyanobacteria [28]

POIGNANT, A.-F. Fossil algae: computer aided determination [28-29]

POIGNANT, A.-F. The Solenoporaceae: a general point of view [29-30]

PONCET, J. Revision of the genus Dasyporella STOLLEY [30]

REZAK, R. Meditations on stromatolites [30-31]

ROUX, A. Ordovician algae and global tectonics [31]

SIMMONS, M.D. Calcareous algae from the Thamama Group (Early Cretaceous) and Wasia Group (mid Cretaceous), central Oman Mountains [32]

TSIEN, H.H. Algae and cyanobacteria in the Devonian reef facies of Belgium [32-33]

WINSBOROUGH, B. Fossil and living stromatolites from a desert basin in northeastern Mexico [33]

Abst rac ts o f the 4 th In te rna t iona l Sympos ium on Foss i l A lgae

Card i f f , Wa les , Un i ted K ingdom (1987)

AWRAMIK S.M.

Archean and Proterozoic stromatolites

Stromatolites are among the most ancient fossils known. Their record extends back some 3,500 Ma making the microbial communities that built them the oldest recognized ecosystem. Illuminated, shallow water to periodically wetted environments not subjected to coarse and/or excessive sediment deposition probably harbored stromatolites and stromatolitic microbial mats throughout much of pre-Phanerozoic time.

Archean stromatolites are rare. The tectono-sedimentary attributes of greenstone belts commonly precluded the establishment, development and preservation of stromatolitic microbial mats. However, stable Proterozoic-type conditions did begin on some cratons in the Archean and were accompanied by increased stromatolite development.

By Early Proterozoic time stromatolites became well established in a variety of environments, both marine and non-marine. Although diversity was low, all the major constructional groundplans (bauplans) were present (oncolite, stratiform, domical, columnar, columnar-branching, conical, conical-branching). Enormous variation in size is found among Early Proterozoic columnar and conical stromatolites; diameters for different morphs range from millimeters to meters. Gigantism was not uncommon. The major groups of stromatolite-building cyanobacteria were already established.

The Middle and Late Proterozoic stromatolite record shows increased diversification and abundance, and moderation in size of individuals with most columns less than a meter in diameter. Stromatolites reach their acme of development and certain distinctive morphologies have been found useful for interbasinal correlations even on a global scale. Palaeomicrobiologically, few distinctive stromatolite morphs have been found to contain microfossils. However, numerous stratiform to domical stromatolites contain preserved cyanobacterial microfossils indicating that the microbial communities had already evolved a ‘modern’ appearance.

Latest Proterozoic was a time of crisis for stromatolites. Their diversity during the Vendian drops off sharply presumably due to disruption by animals. In the latest Vendian/earliest Cambrian, a new type of stromatolite, the thrombolite, appears possibly reflecting animal interferences, introduction of coarse bioclastic sediment, inroads by eukaryotic algae, and/or shifts in dominance of cyanobacterial builders.

BARATTOLO F.

Remarks on Neomeris cretacea STEINMANN (Dasycladales) from the Cretaceous of Orizaba (Mexico).

Neomeris cretacea STEINMANN, a Dasycladacean green alga from the Cretaceous (Albian) of Orizaba, Mexico (type-locality) is re-described. Main characters of the thallus, variability and significant biometrical characters and ecology are given.

BARATTOLO F.

Fertile and vegetative regions in Triploporella marsicana PRATURLON (Dasycladales).

Characters of fertile and vegetative regions in Triploporella marsicana PRATURLON (Dasycladales) from the Cretaceous (Aptian) of Matese (South Italy) are illustrated.

The morphology of this species allows us to better define the relationships between the reproductive and vegetative regions of the thallus and the calcification in the genus Triploporella.

BASSOULLET J.-P.

Sarfatiella dubari CONRAD & PEYBERNES 1973: a junior synonym of Holosporella siamensis PIA 1930

Holosporella siamensis, dasyclad alga described by J. Pia in 1930 from the Burmo-Siamese frontier, was found in the Kamawkala Limestone considered to be of Upper Triassic age. Since then it has not been found at the same stratigraphic level or elsewhere. Later a similar, but apparently different, form was described by M.A. Conrad and B. Peybernès from the Dogger of France (1973): Sarfatiella dubari.

Type sections of J. Pia’s species were lost, but the sample studied by that author was found again in the J.W. Gregory’s collection at Glasgow University. Revision shows identity of the two species.

Holosporella was recently discovered in many places in Thailand and at the Burmo-Thai Border in lower Dogger levels. The widespread peritethysian distribution: SE Asia, Himalaya, North Africa, Western Europe is emphasized and the stratigraphical range, Dogger with rare citations from Malm, discussed.

BEADLE S.

Cyclocrinitids

The cyclocrinitids are a small group of Middle Ordovician to Early Silurian macrofossils. They are usually regarded as an extinct tribe of dasycladacean algae, since they were morphologically very similar to the Recent dasyclad Bornetella. Their main axes bore whorls of lateral branches; these expanded at their tips to form thick lateral heads, which were hexagonal or subhexagonal in outline and usually 1-3mm wide. The lateral heads were tightly packed together to form a faceted outer cortex, which was spherical to claviform in shape and typically 1-4cm in size. The thallus was encrusted by calcium carbonate, particularly around the lateral heads. Cyclocrinitids are often abundant locally and may be significant rock-builders; several rock units have been informally named after them. Cyclocrinitids were restricted to shallow, quiet waters at low latitudes; they were important associates of many benthic invertebrate communities. Ecophenotypic thallus-size variation between different populations has been used locally to indicate relative depths. Cyclocrinitid preservation is highly variable, which has led to a profusion of species names. A thorough revision of European forms is badly needed. Cyclocrinitids have considerable potential value as Ordovician palaeoecological indicators; they may also prove useful in interregional correlation.

BERTRAND-SARFATI J.

Tussocky microstructure in stromatolites: a biological event recorded in the Upper Proterozoic sediments of the West African craton.

Stromatolites are widespread in the Upper Proterozoic cover of the West African craton, cropping out over thousands of kilometers (Atar, El Hank, Ahnet). The stromatolite succession, together with the microstructure succession, displays a very constant pattern. One of the microstructures is worthy of note for its biological implications: the tussocky microstructure.

Stromatolites are entirely built by superimposed tussocks forming uneven laminae. The tussocks are hemispherical or bean shaped elements, sparitic, clear or dark, displaying a radiating pattern of rods. The size of the tussocks if very variable, from 0.9 to 1.15mm and sometimes to 2mm. Despite the size variations they have a very constant shape. Differences are found in the arrangements of tussocks forming the laminae. They can be fortuitously aligned and even anastomosed over short distances, but generally they are superimposed in disorder, climbing over the biggest, overgrowing each other. The nature of the overgrowth is also variable, generally a dark film outlines the upper part of the tussocks, or appears in concentric line within some big ones, in other stromatolites they are surrounded by clear sparite in which radiating rods are still visible coming out of the tussocks.

These variations correspond to variations in the column shape and also to diverse gross morphologies, the latter being related to differences in the environment. In Atar, the columns form patch reefs and higher (60m) up juxtaposed clusters. The two are separated by siltstones, sandstones and carbonates indicating for shallow water, moderately agitated conditions. The stromatolite environments are very distinct: high energy for the patch reef, less energy for the clusters, but the tussocks are almost the same and both are trapping silt size quartz in the spaces between tussocks. In El Hank, 500km away, the columns form a single biostrome of ramified columns. The tussocks are more often aligned and they are separated by sparite. In the Ahnet, included in the pan-African orogenic belt, they form two biostromes of juxtaposed clusters, columns and tussocks similar to those of the Hank.

This example of a widespread extension of a specific microbial community almost exclusive of any others is unique, being only reported from the West African craton. It is clear that the extension is related to the stability of the cratonic sedimentary area, but the biological evolutionary trend which produced the “tussock” builder radiation, is unique in Proterozoic times.

BOSENCE D.W.J.

Coralline Algae: A review and discussion of recent developments

This critical review focuses on three areas of current research on the coralline algae:

Calcification and microstructure. Recent work has clarified calcification in corallines as being a two-stage process; firstly tangential and secondly radial calcite is deposited within the matrix of the cell walls. This internal calcification of cell walls is unique to the coralline algae and should be used to interpret early calcareous algae in which other structures are not present. The recent descriptions of subcrustal aragonite from corallines shows that this form of mineralisation is not restricted to the squamariaceans as has been recently proposed.

Taxonomic revisions of genera. New investigations on Recent coralline algae by workers in Australia and Britain is leading to important revisions of well-known Recent and fossil genera. The time is appropriate to assess the implications of this

work for paleontology. Important questions are the preservation of taxonomic characters and the relationships between fossil taxa and groups of Recent taxa. Specific determination of many fossil corallines suffers from excessive splitting, on the basis of too few characters, by previous workers. The importance of detailed measurements and statistics is emphasized.

Ecology and palaeoecology of coralline algae. The longevity of coralline genera, together with their ecological restrictions and plasticity of growth forms in relation to environmental parameters, makes the corallines a good group for palaeoecological investigation. Recent work has shown the strong relationships between growth form and hydraulic energy and the generic composition of floras and water depths. The latter has the exciting potential for erecting quantitative palaeobathymetric zones for the Cenozoic.

BRAGA J.C. and MARTIN J.M.

A model for development of rhodoliths on shallow, coastal areas: the Miocene of Bayarque, S.E. Spain

On the southern margin of the Almanzora corridor (a Neogene basin in southern Spain), at Bayarque, during the Upper Tortonian, rhodoliths developed on a coastal system comprising a coastal platform (originally at a depth of 1-2m) and a coastal talus slope (at up to 35-40m depth).

On the coastal platform the rhodoliths are mainly made up of a detrital nucleus covered with massive crusts and columns of Lithophyllum viennoti. In the deeper talus slopes this first stage of algal growth is followed by branching growths of Lithothamnium floreabrassica covered, in turn, predominantly by thin, leafy crusts of Mesophyllum koritzae.

The greater the depth the greater the diversity of species; the relationship between the nucleus and the algal covering diminishes and the rhodolith shape relies less on that of the nucleus.

Hydraulic energy seems to control the morphology and distribution of species within the rhodoliths. The massive crusts are capable of withstanding the high-energy levels of the coastal platform which cause frequent overturning and severe abrasion. In the deeper talus-slope zone this frequency of overturning diminishes as the rhodolith increases in size and the massive crusts give way quickly to the more-delicate, laminar and/or branching growths.

This work forms part of project 79/84 C4-03 (CAICYT - CSIC).

BROOKE C. and RIDING R.

A new look at the Solenoporaceae

The genus Solenopora was created by Dybowski in 1877 for a problematical. organism described from the Ordovician of Estonia, which has been referred to the stromatoporoids, chaetetids, tabulates and, most recently, to the red algae.

Solenopora gives its name to the Solenoporaceae, an important family of calcareous algae which have been major reef builders and rhodolith formers through much of the Palaeozoic and Mesozoic; these ecological rôles providing a direct comparison with the Corallinaceae. However, the ancestry of the Corallinaceae has been more often placed with certain Upper Palaeozoic genera collectively known as the “Ancestral Corallines” (Wray 1977). This is because members of the Solenoporaceae

lack features of the corallines such as tissue differentiation and preserved reproductive organs. They have therefore been regarded as an important, but separate, lineage of the red algae.

From studying genera and species included within the Solenoporaceae it can be seen that previous classifications are over-simplistic and give rise to a heterogeneous grouping of unrelated organisms which probably includes cyanobacteria and metazoans as well as red algae. This study also has implications for the ancestry of the Corallinaceae, since one group of Silurian solenoporaceans shows such strong similarities to extinct red algae that it is reasonable to suggest that they could be the earliest representatives of this line of evolution.

BURNE R.V.

Microbialites: organosedimentary deposits of benthic microbial communities

Microbialites are organosedimentary deposits formed from interaction between benthic microbial communities and detrital or chemical sediments. Processes involved in the formation of calcareous microbialites can include: trapping and binding of detrital sediment (forming microbial boundstones), inorganic calcification (forming microbial tufa), and biologically influenced calcification (forming microbial framestones). The latter process is probably the result either of chemical changes associated with photosynthesis, or the nucleation of crystals on the polysaccharide bearing sheaths of the microorganisms. Elevated äl3C values in these cements may reflect isotopic fractionation associated with the biological setting of the mineralisation. Microbialites contrast with other biological sediments in that they are generally not composed of skeletal remains. Once formed, the primary framework of the microbialite becomes the locus of secondary cementation. To distinguish them from the bioherms and biostromes of skeletal origin, microbialite build-ups are termed “microbial lithoherms or “microbial lithostromes”. The morphogenesis of these structures is a function of environmental influence, biological and ecological controls, and processes and rates of lithification. The internal structures of microbialites are best identified by descriptive terms that do not imply a particular origin. Consideration of the term “stromatolite” shows that it is currently used in at least three distinct ways: to refer to products of microbial sedimentation in general, to describe laminated structures of probable microbial origin, or to describe discrete laminated lithified bodies. I recommend that the term be restricted to refer to microbialites with an internal structure of fine, more or less planar laminations. Published distinctions between thrombolites (microbialites characterized by a clotted internal structure) and stromatolites have been assessed in the light of some present-day Australian occurrences. These show that thrombolites are mot always constructed by coccus-dominated BMC’s, nor are stromatolites always constructed from filament-dominated BMC’s. Although there are examples of modern thrombolitic structures forming where biogenically influenced calcification dominates, and stromatolitic structures forming where trapping and binding of either detrital sediment or seasonally precipitated carbonate dominates, both structures could be produced by other processes. Other terms used to describe internal structures of microbialites include oncolitic (concentrically laminated), spherulitic, and cryptic. It is hoped that the ability to differentiate between the processes involved in the genesis of microbialites will lead to a better understanding of factors such as the morphogenesis of microbialites, their evolution through geological time, and their potential as tools for biostratigraphical correlation.

CASANOVA J.

Open Th/U systems in Pleistocene stromatolites from African paleolakes: dating potential

Algal stromatolites built at the margins of ancient lakes in intertropical Africa are an example of open Th/U radioactive systems in relation to post-depositional U-leaching. Because they incorporated, during their growth, detrital particles previously depleted in uranium by similar leaching processes in soil profiles, they had et their origin a strong 230Th-excess over 234U (with ratios as high as 7) which can give access to a time-control. In the East-African Rift, several phases of stromatolite construction are recorded in the lakes of the Natron-Magadi basin (Tanzania/Kenya) and also around Lake Manyara (Tanzania). The youngest phase was radiocarbon dated at ca. 10,000/12,000 BP, in the former case, and at 23,000/25,000 BP, in the second one. This independent time-control permitted separate calculation of the initial 230Th/232Th ratios of the detrital component which came out to be ca. 0.87 and 0.65 respectively. Isotopic measurements on clay particles deposited nowadays yielded identical results. Assuming similar ratios during the earlier phases of stromatolite building, 230Th-excess ages could be evaluated with the help of iterative calculations, which also yield an estimation of the residence time for U in the stromatolites. The ages of the corresponding lacustrine episodes came out to be clustered around 130,000 and 240,000 yrs, i.e. around each Glacial/Interglacial transition.

CASANOVA J.

Microbiology and geochemistry of modern lacustrine stromatolites, Lake Annecy, France.

The algal reef in the littoral to sublittoral environments of Lake Annecy provides a present-day model for describing carbonate sedimentation in lakes. Discontinuous series of bioherms may extend over distances of several kilometers, from the present lake level to as much as 20m depth. Seasonal analysis of microbial mats from a bathymetric profile reveals that Schizothrix lateritia and S. pulvinata are the dominant species respectively of: (1) the warmer and shallower zones; (2) the cooler and deeper zones. The diverse and seasonally variable microbial community also includes Chrococcus, Rivularia biassolettiana, Phormidium usterii, P. tenue, Calothrix and Dichothrix. Oxygen isotopic measurements on biogenic calcite make it possible to calculate an average temperature of c. 14°C during precipitation. Given the temperature of the lake, this indicates that stromatolites grow throughout the year, with a small increase during summer. In winter the microbial precipitation is active to a depth of 12m, while in the summer it ceases at l0m. This limit corresponds to the chimiocline, which is mainly marked by a high concentration of orthophosphates (0.35mg/l). Likewise, the potential bathymetry of the stromatolite growth seems to be related to the trophic level of the surrounding waters.

DALE B.

Recent calcareous dinoflagellate cysts

Very little work has been done on recent calcareous dinoflagellates and they have generally been overlooked. Biologists interested in dinoflagellate cysts have been mainly concerned with toxic species (none of which is calcareous), while paleontologists have been mostly interested in the acid resistant cysts (i.e. non-mineralized) recovered by standard palynological methods (including HCl and HF) that destroy calcareous cysts. The cysts, in the size range 25-60µm, are generally too large to be routinely included in coccolith analysis, and too small for foraminiferal analysis.

About twenty different morphotypes are known so far, though there are probably many more not yet discovered. Only two types have been correlated with their

motile stages, but these together with cyst morphologies suggest that calcareous cysts are produced by a small monophyletic group of dinoflagellates including species of the genera Scrippsiella and Ensiculifera.

Most known calcareous cysts are from tropical to subtropical regions, where they may outnumber non-calcareous cysts, but at least one type is found in cold temperate to arctic regions (e.g. N. Norway and Alaska). Oceanic cyst assemblages are overwhelmingly dominated by a few calcareous cyst types.

These seem to be characteristic oceanic types that are found in pelagic regions of both the Pacific end Atlantic oceans, but are not reported so far from coastal waters.

A distinction is made between calcareous meeting cysts (presumed to be hypnozygotes in a sexual cycle) and thoracosphaerids (a very distinctive group of dinoflagellates with non-motile vegetative cells housed in a characteristic calcareous shell), though the latter have been suggested to be cysts by other workers. Deep sea sediment traps have now made it possible to investigate production of pelagic cysts sedimenting out in the open ocean. The first results show that calcareous cysts are routinely produced by several pelagic dinoflagellates (fluxes of up to 14,500 m2/day were recorded from the Demerara abyssal plain, tropical N. Atlantic). Thoracosphaerids were about ten times more abundant than calcareous cysts in deep sea sediment traps, supporting the suggestion that thoracosphaerids are vegetative cells produced more often than resting cysts.

It is suggested that calcareous cysts and thoracosphaerids are mineralized non-motile stages offering the possibility for incorporating a sinking strategy (e.g. analogous to that of diatoms) to the otherwise basically swimming strategy of dinoflagellates.

DEY S. and SMITH L.

Crustose coralline algae forming rhodoliths on the Grenadines Bank, Lesser Antilles.

The fore-reef slope on the eastern portion of the southern Grenadines Bank shows rhodolith development at depths between 12 and 100m. The leafy crusts of Neogoniolithon, Porolithon, Lithophyllum, Lithoporella, Hydrolithon, and Lithothamnium are the dominant nodule builders. A complex set of physical, chemical and biotic factors control the distribution of coralline algae forming the rhodoliths. Upper slope nodules show dense, tight, concentric algal laminae. Deeper-water varieties exhibit irregular crusts and large constructional voids. This, together with variation in nodule size, shape, texture and mineralogy, reflects the shift in the ecology of the coralline taxa.

Some nodules show isolated megacrusts of articulate red algae with micrite and other bioclasts between. The non-laminated and homogeneous nature of these materials (comparable to thrombolites?) are attributed to both organic and inorganic processes.

The algal encrustations of the coated grains alternate with internal sediments, acicular aragonite and Mg-calcite cement. The micritized areas indicate periods of destruction and non-development during nodule formation. Initial, algal, cellular porosity is filled with blocky and acicular cement. Neomorphic spar can totally obscure the original algal fabric.

Structure, composition, growth form and cementation of the nodules are indicative of the ecologic regime and diagenetic environments that formed them.

DROMART G. and GAILLARD C.

Late Jurassic deep-marine microbial fabrics across the north-Tethyan margin. Examples from Jura and Ardèche areas, south-eastern France.

A number of Late Jurassic deep-water carbonates enclosing stromatolites- thrombolites have recently been documented on the margins of both the Central Atlantic and Tethys oceans. Microbial fabrics of Middle Oxfordian age have been identified at the base of Upper Jurassic sequence, south-eastern France at the north-Tethyan margin. They occur in zones that bordered the Subalpine Basin in which shales accumulated. Depositional environments for these microbial developments have been determined from thorough sedimentological and palaeoecological investigations. An ideal profile, from the outer shelf down to the basin, is reconstructed by juxtaposing the Jura and Ardèche domains.

Stromatolites are planar, columnar and reticulate in shape, with generally well-developed internal dome-shaped lamination. Occasional oncolites are present. Clotted, peloidal microfabric has rarely been recognized. Stromatolitic crusts rest on diverse but always hard substrates (siliceous sponge skeletons, ammonite molds, clasts, hard-grounds, etc.). Some of them also floor cavities (endostromatolites). Absence of burrows into stromatolites, presence of encrusting foraminifers and production of firm tuberolitic debris suggest that stromatolites were calcified early.

Characters of microbial fabrics change across the paleoprofile. At the paleoshelf edge, intensive and various stromatolitic developments built bioherms replete with sponges. In the upper slope zone, the presence of separate, low and planar forms indicates that microbioaccretion slowed down. In the Lower-slope zone, columnar forms dominated and were accompanied by small carbonate mud-mounds.

Reconstructions disclose that microbiotic communities thrived in environmental niches at depths from around 100 to several hundred meters, on marine floors not or a little lighted. The intensity and form of microbial developments are believed to have been controlled by rate of sediment accumulation and morphology-size-mobility of substrates.

The study reveals that deep-water bacteria or cyanobacteria characterize the slope depositional zone, the result of combined drowning of the Tethyan margin and original paucity of sediments.

ELLIOTT G.F.

The Dasycladalean algae of the Palaeozoic and Mesozoic

A very general review of the evolution of the Dasycladales of the Palaeozoic and Mesozoic, and of the history of their classification, leads to consideration of their survival between Permian and Triassic times. Old-world areas where evidence of this may possibly be preserved are suggested, and the importance of such evidence is stressed.

FAIRCHILD I.J.

Stromatolites and associated lagoonal facies from latest Proterozoic of central East Greenland

A distinctive 50m shallowing-upwards sequence exists at the top of the 300m Canyon Formation, passing from offshore dolomitic mudrocks, through hummocky-cross bedded sands and debris flows to lagoonal facies dolomitic mudrocks,

stromatolites and sandstones with increasing evidence of emergence upwards. The lagoonal facies are identical with those of member 3 of the Dalradian Bonahaven Formation, Islay, Scotland (Fairchild 1980, Journal of Sedimentary Petrology), but the bathymetric relationships are better determined in East Greenland, where there is also an absence of metamorphism.

The flat-laminated to broad-domical, sometimes biohermal nature of the stromatolites is distinctive in this environmental setting. Growth was initiated on variably-mobile substrates in a few metres water depth. Conditions were moderately hypersaline at times. Laboratory work will be directed towards characterizing the microstructures, which even in the metamorphosed Dalradian examples are occasionally well-preserved, and to make a geochemical comparison of the stromatolitic dolomite and the apparently non-stromatolitic dolomite of adjacent beds. Some lines of evidence from the Scottish examples suggest there is nothing geochemically distinctive about the stromatolitic carbonate, but this will be more thoroughly tested in the East Greenland material.

FEIST M. and GRAMBAST-FESSARD N.

The genus concept in Charophyta: evidence from Paleozoic to Recent

In fossil Charophyta, the generic criteria are based on characters of the calcified fructifications (gyrogonite or utricle). However, the classification of living forms is based mainly on vegetative parts. An alternative system employing gyrogonite characters might permit the classification of both living and fossil members of the Characeae. Thus the systematics of fossil Charophyta may be considered as founded on natural taxa and not on organ-genera. Examples of Paleozoic to Recent representatives demonstrates the various criteria used to distinguish genera in the different families. Phylogenetic lineages of species illustrate the notion of a phyletic genus, especially in the Clavatoraceae. Relationships between genera outline the main phylogenetical trends in Charophyta.

FLÜGEL E.

Triassic and Jurassic marine calcareous algae

The information on Triassic and Jurassic calcareous algae is scattered in about 1,600 papers, published between 1820 and 1987. 60% of the papers dealing with Triassic algae and about 80% of the papers on Jurassic algae have been published since 1950. This reflects the increasing interest in the biostratigraphical and palaeoecological importance of these algae. Very useful bibliographies exist for Triassic algae (Emberger, 1979), for Jurassic and Cretaceous dasycladaceans (Bassoullet et alii, 1978) as well as for the udoteacean algae (Bassoullet et alii, 1983).

This review deals with porostromate ‘algae’, green algae (dasycladaceans, udoteaceans) and red algae (solenoporeceans, corallinaceans, gymnocodiaceans).

Four major topics will be emphasized: (1) Data base: number of genera and species, distribution in time, taxonomic problems. (2) Diversity, extinction and organization: relationship between Upper Permian and Triassic algae; diversity patterns of Triassic and Jurassic dasycladacean algae; extinction and origination rates of dasycladaceans, udoteaceans and porostromate ‘algae’; Tethyan dispersal patterns. (3) Biostratigraphical value of Triassic and Jurassic algae. (4) Sedimentological implications: accumulation of carbonate sediment (halimediform algae; formation of

oncoids), algal mats and microbial crusts (Triassic and Upper Jurassic examples); reef environments (algal/cement reefs; Carnian/Norian turnover of reef biota).

Future research should be focused on: taxonomic revisions considering environmentally controlled variations of calcification patterns and of quantitative data used for species differentiation; study of calcareous algae from non-Tethyan regions; study of Lower and Middle Jurassic algal floras, search for Scythian algae; synecological studies of paleocommunities including the investigation of distributional patterns; bio- and geochemical investigation of ancient microbial crusts.

GÉNOT P.

Cenozoic and Recent calcified Dasycladales

Cenozoic Dasycladales are represented by 43 genera and more then 200 species. The number of Recent genera is reduced to 8, with about 40 species. Three of the living genera are also known as fossils: Neomeris, Cymopolia and Halicoryne.

Preservation of sterile and fertile organs is very variable according to genera and species, even sometimes between individuals of the same species. It mainly depends on the extent of the initial calcification during the life of the alga and of the conditions of fossilization: in numerous Cenozoic species, such as those of Acicularia and Terquemella, reproductive ampulla are the only organs which have been calcified, whereas other species have a heavy calcification which covers the whole organs, as in Cymopolia species.

Definition of Cenozoic and Recent Dasycladales is based on the following main features: position of reproductive organs on branches, type of reproductive organs, division of branches, shape and type (segmented or not) of the thallus.

The richest assemblages of Dasycladales species have been found in the Paleocene of Belgium (Mons Basin), France (Aquitaine-Pyrénées area and Paris Basin), Italy (Sardinia), Yugoslavia (Slovenia), Czechoslovakia (Carpathian Mountains), Middle East (Iraq, Iran) and China (Tibet); in the Eocene of France (Paris Basin, Brittany), southern England (Sussex), Hungary and China (Xizang); and in the Miocene of Romania and Poland.

Living species are known in the Indo-Pacific area, the Atlantic area (mainly tropical America and the West Indies) and the Mediterranean area. They are confined to shallow water marine or brackish waters.

GOLUBIC S.

Recent stromatolites

Interpretation of ancient stromatolites, particularly those dominating pre- Phanerozoic strata, has been the main driving force in the study of their modern counterparts. Discovery of Precambrian microbial fossils and their associated with stromatolitic structures further stimulated the studies of modern stromatolitic microbiota. Over the past two decades, Recent stromatolites and microbial mats attracted the attention of researchers from different disciplines, such as sedimentology, geochemistry, limnology and microbial ecology, and became the focal point of interdisciplinary research. As a result of these studies, some early overgeneralizations could be corrected, definitions refined, and the scope of stromatolite-related phenomena, and environments within which they occur, significantly widened. The insight into structural, and particularly functional

complexity of modern stromatolites highlighted the importance of the microbial role in promotion and regulation of biogeochemical cycling of elements in modern as well as ancient ecosystems. Although the studies of modern stromatolites sought the key for the past, the results often revealed the limitations of such extrapolations. The values and constraints of modern hypersaline, marine, brackish and freshwater stromatolitic environments as interpretational models for ancient stromatolitic settings are discussed.

GOLUBIC S., KNOLL A.H. and ZHANG Y.

Phototropic endoliths Hyella-Eohyella: diversity and fossil record

Hyella is probably the most morphologically complex genus of coccoid cyanobacteria. It bores intricate, ramifying tunnels in carbonate substrates. Two species from marine habitats, B. caespitosa Bonnet et Flahault 1889 (type) and H. balani Lehmann 1903, as well as two from freshwater habitats, B. fontana Huber & Jadin 1892 and H. jurana Chodat 1898, were described in Europe at the turn of the century. Most later reports have used these names. However, recent revision of the original descriptions, as well as new endolith studies, show that this genus is more diversified then previously thought. A fossil, possibly ancestral, endolithic cyanobacterium Eohyella, was discovered in the 1.7 Ga Dahong Yu formation of northern Chine, which also marks the earliest occurrence of any endolith in the fossil record. Another entire endolith fossil assemblage was found in silicified ooids in the late Precambrian strata of Greenland and Spitzbergen (0.8-0.7 Ga). This assemblage contains several species of the same generic morphotype as modern Hyella, and is comparable with modern endolith assemblages in ooids of the Bahamas and Arabian Gulf.

GRANIER B. and MICHAUD F.

Dasycladales from the Upper Jurassic of south-eastern Mexico.

Upper Jurassic strata from Chiapas (south-eastern Mexico) yield a large number of algae. More than ten species of Dasycladales have been identified:

- Salpingoporella annulata (CARROZI) (Kimmeridgian & Portlandian), - Heteroporella lusitanica (RAMALHO) (Callovian ? - Oxfordian), - Heteroporella lemmensis (BERNIER) (Kimmeridgian), - Macroporella espichelensis (DELOFFRE & RAMALHO) (Portlandian), - Linoporella capriotica (OPPENHEIM) (Kimmeridgian or Portlandian), - Radoiciciella n.sp. (Kimmeridgian & Portlandian), - Clypeina n.sp (Kimmeridgian & Portlandian), - Apinella jaffrezoi (GRANIER, MICHAUD & FOURCADE) (Kimmeridgian), - Deloffrella quercifoliipora (GRANIER & MICHAUD) (Kimmeridgian & Portlandian), - Draconisella bernieri n.gen. n.sp. (Portlandian).

The diagnosis of this new genus is: “Pearl necklace” thallus consisting of several large ring-shaped segments bearing at least three whorls of branches each. Primary branches thickening toward the outer ends; open pore (no secondary branches) and proximal narrowing. Cysts unknown. Calcification more or less important.

From the palaeobiogeographic point of view it can be pointed out that: some species, such as Clypeina jurassica or Actinoporella podolica, never have been recorded in Central America and that some new species are cosmopolitan (Deloffrella quercifoliipora, Apinella jaffrezoi), while others could be (?) endemic (Draconisella bernieri, etc.). More data are needed to some to a conclusion about it.

GREY K. and WILLIAMS I.R.

Possible megascopic algae from the Middle Proterozoic Manganese Group, Bangemall Basin, Western Australia

Enigmatic bedding-plane markings forming isolated strings of beads were previously reported from the middle Proterozoic Belt Supergroup of Canada. Similar structures occur in sandy and argillaceous strata of the middle Proterozoic Manganese Group of the Bangemall Basin, east of Newman, Western Australia, in rocks about 1.1 Ga. Markings are abundant at two localities and traces are found in a third. The sediments contain numerous current-generated structures, but the chains are randomly orientated.

The chains of beads are similar in both morphology and dimension to Belt Supergroup structures, and like them show a uniformity of size and spacing within each string. They occur as concave depressions on both upper and lower bedding-plane surfaces, and must have been formed by serially-arranged subspheroidal structures 1-3mm in diameter. some beads are linked by a fine thread.

Comparisons have been made with a variety of biogenic and nonbiogenic structures. The mode of formation still cannot be determined with certainty, but the evidence favours a biogenic origin. Affinities with the green or brown algae are suggested, an origin consistent with records of megascopic algae from rocks of similar age.

HILLIS-COLINVAUX L.

Recent calcified Halimediaceae

Five Recent genera of Halimediaceae calcify: Halimeda, Penicillus, Rhipocephalus, Tydemania and Udotea. All are essentially tropical. Only the two pantropical genera Halimeda and Udotea contain more than 10 species. Penicillus and Tydemania produce extensive populations in some regions of the western Atlantic and Indo-Pacific respectively, but only Halimeda exists in large enough populations worldwide to be globally significant. Habitats within reefs are much broader than usually portrayed. They include both sand and rock substrata, and cover a bathymetric range extending from the intertidal to at least -140m. Plant density can be high; Halimeda achieves close to 100% net only in lagoons but in the extreme shallows of the back-reef where there are moderately strong currents, and on the fore-reef wall.

All five genera contribute to present day reef systems by providing (1) habitats for a variety of organisms, (2) organic carbon through photosynthesis and (3) carbonate sand and rock by the loss of modules during growth (Halimeda and possibly other genera), by burial, and most dramatically by death following sexual reproduction.

Halimeda is superbly adapted to and successful in the modern reef. Different methods of dispersal and growth probably contribute significantly to its present day predominance over the other four genera.

KEUPP H.

Fossil calcareous dinoflagellate cysts

Two groups of marine dinoflagellates are able to construct calcareous walls (low Mg-calcite): the vegetative coccoid stages of the Thoracosphaerales, (Tangen 1981), (known from the Paleocene to the Recent) and the cyst-family Calciodinellaceae

(Deflandre 1947 of the order Peridiniales (Haeckel 1894), known in the fossil record since the late Triassic. During the Mesozoic, calcareous dinoflagellate cysts have been a very common, partly rock-forming, microfossil group (diameter between 10 and about 100ìm) found in open shelf environments. Previously, members of this group were generally placed in the incertae sedis family “Calcisphaerulidae (Bonet 1956)”. Their principal morphology has been described by Keupp 1981.

Some of the calcareous cysts reflect a more or less complete orthohexa-tabulation. Only the mode of the paratabulations, not the principal type, show wide variety: holotabulate crests or sutures on the outer and inner calcareous wall-layers respectively, intratabular tubercles, gonal cyst shape (hercotabulate), often cingotabulate or sometimes cryptotabulate (polygonale archaepyle). Occasionally, the organic acid-insoluble phragms situated on the base of each wall-layer show a paratabulation (Keupp 1980, Hultberg 1985). Due to the uniform type of ancestral paratabulation and the early appearance of calcareous cysts, the Calciodinellaceae are a monophyletic group, possible the phylogenetic ancestors of the Peridiniales (compare Davies and Bujak 1983).

On the basis of the single to triple layered calcareous wall structure, three subfamilies can be distinguished (Keupp 1987): (1) Orthopithonelloideae: the crystals of the (outer) calcareous wall are orientated perpendicularly; (2) Obliquipithonelloideae: the orientation of the (outer wall) crystals is irregularly oblique or tangential; (3) Pithonelloideae: the orientation of the (outer wall) crystals is uniformly oblique.

Due to the extracellular mineralization, the phenotypes (especially of the Obliquipithonelloideae and the Orthopithonelloideae) seem to be controlled by the physical conditions of the biotope (temperature, salinity) rather than by genetic impulse (Keupp 1982, Keupp and Mutterlose 1984, Bandel and Keupp 1985). Therefore, the taxonomic problems of this group continue to be important.

In addition, fossil assemblages can be interpreted for palaeoecological, palaeoceanographical and biostratigraphical purposes using the reaction of the cyst morphology to changing environments. For example, during the early and middle Cretaceous of the moderate Boreal region, a stratigraphically usable succession of floral assemblages can be recognized, due to Tethyan or arctic influence in connection with transgressions and regressions respectively (Keupp 1981, 1987).

Despite the findings concerning calcareous dinoflagellate cysts made by some scientists during the last twenty years, our knowledge of this important fossil and Recent group remains poor.

References

Bandel, K. & Keupp, H. 1985. Analoge Mineralisation bei Mollusken und kalkigen Dinoflagsellaten-Zysten. N. Jb. Geol. Paläont. Mh., 1985, 2, 65-86. Bujak, J. P. & Davies, E. H. 1983. Modern and fossil Peridiniineae. AASP Contr. Ser., 13, 1-203. Hultberg, S. U. 1985. Pithonella organica - a new calcareous dinoflagellate with an inner organic wall. Grana, 24, 115-120. Keupp, H. 1980. Pithonella patriciagreeleyae (Bolli 1974), eine kalkige Dinoflagellaten-Zyste mit interner Paratabulation. N. Jb. Geol. Paläont. Mh., 1980, 9, 513-524. Keupp, H. 1981. Die kalkigen Dinoflagelleten-Zysten des borealen Unter-Kreide (Unter-Hauterivian bis Unter-Albium). Facies, 5, 1-190. Keupp, H. 1982. Die kalkigen Dinoflagelleten-Zysten der späten Apt und frühen Alb in Nordwestdeutschland. Geol. Jb., A 65, 307-363. Keupp, H. 1987. Die kalkigen Dinoflagelletenzysten des Mittelalb bis Untercenoman von Escalles/Boulonnais (N-Frankreich). Facies, 16, 37-88. Keupp, H. & Mutterlose, J. 1984. Organismenverteilung in den D-Beds von

Speeton (Unterkreide, England) unter besonderer Berücksichtigung der kalkigen Dinoflagelleten-Zysten. Facies, 10, 153-178.

LEITCH A.

Post-fertilisation development of the calcareous oosporangium in the Characeae.

The oosporangium is a unique and complex structure consisting of a central reproductive cell (the oospore) surrounded by vegetative cells. In the subfamily Chareae, six vegetative unsheathing cells (i.e. five spiral cells and one basal cell), completely surround the oospore end are in intimate contact with it. After fertilisation, a thick multiplayer wall, the compound oosporangial wall (C.0.W.) forms around the oospore. This wall is derived by the simultaneous deposition of four layers by the ensheathing cells and four layers by the oospore. A calcified layer in deposited onto the C.0.W. by the ensheathing cells. Calcification occurs outside the plasmalemma of each ensheathing cell but within the confines of the cell wall; this is extracellular calcification. The ensheathing cells secret an organic matrix towards the C.0.W. that nucleates calcite development, ramifies throughout the calcified layer and is presumably involved in crystal shaping. The calcite crystals of Chara are tabular, arranged in stacks, forming columns (like gastropod shell). The differences seen in the calcified layer of Chara and Lemprothamnium are largely a matter of emphasis; which is being seen, the columns of calcite or the organic matrix?

MAMET B.L.

Marine calcareous Carboniferous algae

While the Carboniferous microflora contains a few long-ranging non-diagnostic Palaeozoic algae (Girvanella, Ortonella, Solenopora) and a few Devonian taxa (Palaeoberesella, Issinella), it is characterised by numerous first occurrences. The majority of this new flora is restricted to the system although some are the roots of the highly diversified Permian assemblages.

As a rule, the flora is highly diverse and abundant in the Tethyan Realm, moderately diverse in North America and quite poor in the Taimyr-Alaska Realm.

Spongiostromids, Girvanella and Rectangulina are common in lagoonal environments (with the notable exception of North America). Nodular codiaceans (Bevocastria, Ortonella, Garwoodia, Pseudohedstroemia, Mitcheldeania) form complex oncolites in the Lower Carboniferous. Halimedoides, Nansenella and Ellesmerella play the same role in the Upper Carboniferous. The udoteaceans (Orthriosiphon and Orthriosiphonoides) have a characteristic renewal in the Late Tournaisian - Early Viséan. Phylloid algae (Eugonophyllum, Neoanchicodium, Ivanovia) are notable reef-builders from the Middle Carboniferous to the Early Permian. Cosmopolitan palaeoberesellids (Palaeoberesella, Pseudokamaena, Kamaena, Exvotarisella) are prolific in Lower Carboniferous platforms and are overlain by the Middle Carboniferous Anthracoporellopsis flora, and Donezella flora and finally the Beresella-Dvinella-Uraloporella flora.

Dasycladaceans have a rapid phylogenic outburst. Simple vermiporellids, dasyporellids, issinellids and koninckoporids are observed at the base of the Carboniferous. They are rapidly associated with much more advanced forms, such as Columbiapora, Pekiskopora and Windsoporella in America or with Eovelebitella and Cabrieropora in the Tethys. The Middle and Upper Carboniferous are characterized by the proliferation of advanced Macroporella, Diplopora, Gyroporella, Epimastopora and Clavaporella.

By comparison, rhodophytes are much less diversified, but they start to be quite prolific. In addition to the solenoporids, ungdarellids (Ungdarella-Komia) form boundstones in the Middle Carboniferous. Stacheeids are very common in the Viséan-Namurian. They are succeeded by Archaeolithophyllum-Masloviporidium-Cuneiphycus-Foliophycus in the Bashkirian-Moscovian.

Among the incertae sedis, Renalcis dies out in the Lower Carboniferous. Prininella, Wetheredella, Palaeomicrocodium, Asphaltinella, Richella and Nostocites play various roles in sedimentation. Tubiphytes becomes an important builder from the Moscovian upwards.

Among charophytes and related groups, Devonian umbellinids and sycidiales disappear in the Tournaisian. Palaeocharaceae and Procharaceae first occur in the Middle Carboniferous.

MAURIN A.F.

Microbial Micrites

Since Monty’s (1982) “Microbial Spars”, studies of microbial micrites have been split into five different complementary trends:

1. The close association between micrites and spars, and their interconnection within so-called “cements”, requires a uniformitarian approach to the biological origin of calcium carbonate.

2. Dolomites were under similar investigation for more than a decade, but the first publication on the microbial origin (for some of them) is again by Monty (1986). The close chemical links between Ca and Mg justify such ”biorelationships”, as has been demonstrated earlier for Fe and Mn, and for other metals.

3. Chafetz and Folk (1984) did initiate the study of fossil carbonates linked to bacteria clumps or colonies but discarded the individual formation, around isolated bacteria, or coccoons transforming into rhombohedrons or scalenohedral prisms (Maurin-Noel 1977). Numerous papers followed such pioneer action. Descriptions of fossil microbial micrites range from SEM imagery to thin section analysis. Today, careful descriptions in micrites of “broad (mm to cm) biological structures appear scientifically fashionable.

4. Early work in the seventies by Krumbein (and team) on Recent marine data (aragonite), then by Monty (and team) both on marine and continental Recent material (calcite) help in the understanding of the formation of crystalline embryos. Such early crystals vary and evolve depending on the species and social habits of bacteria, isolated or in colonies. This fact represents an answer to Chafetz and Folk’s doubts.

5. After Drew (1911) microbiology enters the geological picture, bacteriological experiments and observations on different metabolisms (Castanier et alii 1986) are going to provide geology with a major jump into biotechnologies.

MOHANTI M., SRIVASTAVA S.C. and SINGH A.K.

Calcareous algae in the Palaeogene carbonate microfacies of north-western Kutch (Gujarat), India.

Coralline algae occur in the upper part of the Fulra Limestone Formation and the Maniyara Fort Formation of Middle Eocene and Oligocene age respectively. Some

muddy carbonates of the Oligocene contain dasycladacean segments. The carbonate microfacies are principally foraminiferal rudstones and floatstones associated with mudstones and dolomites.

The calcareous algae are mostly associated with larger foraminifers like Discocyclina, Nummulites, Alveolina, Lepidocyclina and Spiroclypeus. Coralline algae encrust some larger foraminifers. They are also found associated with corals in the Oligocene in muddy environments. Amongst other forms, discrete forms of spheroidal to ovoid rhodoliths occur in the Middle Eocene and the Oligocene. Archaeolithothamnium and Lithophyllum are among the coralline algae present.

Voids in the algae framework have been filled with sparite and muddy internal sediments. Some skeletal algae have been fractured, probably during late diagenesis.

The calcareous algae thrived in Foraminifera-rich banks and lagoons and also in mudmound-like build-ups in sheltered environmental settings in shallow marine waters. High influx of siliciclastics and ”glauconites” probably have not been conducive to good algal growth. Algal distribution in parts of the stratigraphic sequence probably indicates a shoaling regressive” tendency.

MOORE L.S.

Stromatolites of Lake Clifton formed by the calcification of a benthic microbial community

Lake Clifton is located on the south-western coast of Western Australia. Living, lithified stromatolites form a major ecological component of the shallow water margins of this lake. They occur as a marginal reef 10km long and 30m wide and isolated columnar forms have recently been discovered in a deep water channel. The stromatolites are actively calcifying - a process which involve the intimate association between cyanobacterial filaments (Scytonema sp.) and the properties of the aqueous microenvironment. The lake is hyposaline (15-30 gl-1), fed by fresh, highly alkaline ground water. The distribution of the stromatolites correlates with regions of groundwater discharge.

The internal structure of the stromatolites consists of a calcified framework. This framework is composed of mineralized aggregates of the Scytonema filaments. It is an irregular framework with interstices in which unconsolidated sediments, including ostracode and gastropod shells, accumulate. The internal structure is not laminated and is, therefore, more correctly termed thrombolitic.

Although gross morphology varies between localities, the dominant microbial components and the internal framework remain consistent. It appears that the major process involved in the formation of the Lake Clifton stromatolites is the precipitation of a mineral phase in a manner and environment determined by the character of the benthic microbial community, i.e. biologically influenced, non-skeletal calcification.

The Lake Clifton stromatolites provide an analogue for several Phanerozoic microbial carbonates including Cambrian thrombolites.

MU X.-N.

Fossil Udoteaceae and Gymnocodiaceae

The Gymnocodiaceae and fossil Udoteaceae (erect) are similar to each other both in growth form and in vegetative structure. They differ in that the former contains

internal reproductive organs which are usually absent in the latter. It is generally accepted that the former belongs to the red algae and the latter to the green algae. Well-preserved silicified Gymnocodiaceae can reveal some detail of cell filaments, reproductive organs and parasitism. However, its precise systematic position still remains to be resolved. The fossil record of the Udoteaceae is better, but its biological characters are less well known and much discrepancy exists in its nomenclature, definition and content. No information is available at present about pigments, storage products, and chemical characters of cell wall, as well as reproductive process. In view of the fact that fossil material can only provide limited data on the anatomy of the algae and that parallelism is frequently found in different groups of living algae, the Gymnocodiaceae and fossil Udoteaceae are considered heterogeneous and in practice it is often difficult to distinguish between them. In order to resolve these problems, search for better preserved, permineralized, fossil material and close cooperation between students of fossil and living algae are badly needed.

NITECKI M.H.

Unsolved problems of receptaculitid affinities

Receptaculitids do not fit a bauplan of any living organism, and are therefore strange, problematic and in need of explanation. The history of their study is essentially a search for their systematic placement through the attempts to explain (1) their relationship to other forms, (2) their mineralogy, and, particularly, (3) the functional morphology of their central axis and meroms. Receptaculitids will become interesting when, and only when, we can assign them unequivocally to a kingdom. Without such assignment it is unclear what to look for and how to interpret their morphology, and it is impossible to decide which organs are most important to solve the problem of receptaculitids.

A number of models have been proposed and choices among them made. However, acceptance of a model has unfortunately always been accompanied by the total rejection of other models. It is possible that some anatomical entities as yet undiscovered may clarify their affinities. However, receptaculitids have been known for over 180 years, and little new knowledge has been added since the work of Rauff (1892). We must rephrase old questions and re-examine and re-analyze past presuppositions. It is necessary to determine which characters are plant-like, which are of animal-like, which, if day, are half-plant or half-animal, each which are one kingdom and at the same time specifically forbidden by other kingdoms. We must at least demonstrate which group they could not have belonged to.

PENTECOST A.

Calcification processes in algae and cyanobacteria

The current concepts of calcification processes are reviewed and some recently proposed classification schemes discussed. In algae end cyanobacteria calcification is always associated with organic matter. Where analyses have been made, the material has been found to consist predominantly of polysaccharide but no specific polysaccharide appears to be associated with calcification.

Two aspects of the mineralization merit special consideration: photosynthesis has long been considered the major driving force causing a depletion in aqueous CO2 and increase in CO3

2-. Thus photosynthesis will always favour calcification and the magnitude of the effect will depend upon rates and diffusion paths. Second, at the ocean surface, the precipitation of calcium carbonate is thermodynamically favored

even in the absence of photosynthesis, which suggests a widespread evolution of calcification inhibitors. Today, the majority of aquatic plants are uncalcified. some of the known inhibitors of calcification are described.

POIGNANT A.-F.

Fossil algae: computer aided determination

The use of a clear and simple dialogue (questions with one or more possible answers) allows the specification of genus and species.

The criteria retained are those which the geologist has at his disposal:

- qualitative criteria: external morphology, internal morphology and structure, reproductive organs, etc.

- quantitative criteria: size of the cells, walls and reproductive organs, etc.

A data bank completes the descriptions. The user is then offered two possibilities:

- determination: it is enough to answer the questions asked, not all the answers are compulsory;

- data bank: the computer can be consulted to find out about the characteristics of a genus, a species or a group of taxa with the some characteristics.

In the cases of the Mesozoic and Cenozoic Floridae, 37 genera have been identified; we have also identified 25 Cretaceous species of Archaeolithothamnium. The same principle allows 54 genera of Mesozoic Dasycladales to be obtained.

POIGNANT A.-F.

The Solenoporaceae: a general point of view

There is a great deal of confusion surrounding the generic and specific allocations and classification system. Even today, it is still possible to hesitate between green algae and red algae.

There are but few generic or specific determination tests, and even then they seem far from convincing. The outer structure seems to alter very slightly in relation to time, the inner structure is more complex: hypothallus (?), perithallus, partitions, walls, pores, reproductive organs (?) are examined.

The classification of the Solenoporaceae is very difficult to establish as the criteria which may be used are scarce and not very reliable. For fifty years, numerous phylogenic theories from Solenoporaceae to Corallinaceae have been suggested but, of course, all these phylogenic ideas must be restudied if Mamet and Roux’s new classification is to be accepted.

As long as a certain order is not established, the stratigraphical distribution is meaningless. It is now the moment to reestablish those shapes which make up one distinct family.

PONCET J.

Revision of the genus Dasyporella STOLLEY

The genus Dasyporella was created by Stolley in 1893. Later, two species were assigned to this genus under the specific name Dasyporella norvegica. One of them was misinterpreted by Johnson & Konishi which introduced a confusion in the genus definition. Revision of the genus Dasyporella was therefore necessary. Studies of new specimens belonging to the ill-identified species have led to the creation of a new genus: Californiella. The creation of Californiella clarifies the concept of Dasyporella with the reinstatement of its original definition.

REZAK R.

Meditations on stromatolites

Knowledge concerning stromatolites has grown to tremendous proportions in the last two decades. The simplistic concepts of the 195O’s, such as the intertidal models and Pia’s classification of Schizophyta, have evolved into the current multiplicity of environmental models and a broadening of the definition of the term stromatolite to include non-laminated structures such as thrombolites and dendritic or digitate microfabrics. The microbiology of three structures continues to be intensively studied. With the great increase in our knowledge of stromatolites, why is it that there are still serious problems in utilizing stromatolites for environmental interpretation and stratigraphic zonation? The stromatolite taxonomist is interested in categorizing an almost infinite variety of growth forms that may or may not be controlled by environment or biotic assemblage. The microbiologist is interested mainly in components of the biota and how they relate to each other and the substrate. Petrographic descriptions of fossil microfabrics frequently fail to recognize secondary alteration affects in fossils. We have each done our own “thing” with only a token amount of communication between specialities. It is time that we begin to work together to recognize the complex relationships between microbiota, modern microfabrics, and diagenetic alteration during and after burial.

ROUX A.

Ordovician algae and global tectonics

In order to prove that fossil algae may be a useful tool for paleogeographic reconstruction, I have studied the worldwide stratigraphic and geographic distribution of significant rhodophytes and chlorophyte genera.

The simultaneous occurrence of many taxa in such regions as north-eastern and eastern North America, southern Scotland, Scandinavia, Estonia and Kazakhstan suggests possible communications between the Ordovician carbonate platforms.

However, although some udoteacean genera (Dimorphosiphonoides, Lowvillia) are exclusively American and unknown in the Prototethys during the Middle Ordovician, other genera (Dimorphosiphon, Paleaoperella), which are Tethyan during the Middle and Upper Ordovician, also become American only during the Silurian.

Some dasyclads (Rhabdoporella, Vermiporella) become American or cosmopolitan during the Upper Ordovician or the Silurian. This was due to migrations from Prototethys to North America or vice versa during the Upper Ordovician, in relation to the progressive closing of the Protoatlantic, which should have taken place as early as the Upper Ordovician.

Recent paleogeographic reconstructions (Scotese et alii 1979) are not in accordance with distribution of these microfloras; it is therefore necessary to modify the

proposed positions of the land masses; in particular, the Baltic shield must be moved northward at least by 30-40°.

SIMMONS M.D.

Calcareous algae from the Thamama Group (Early Cretaceous) and Wasia Group (mid Cretaceous), central Oman Mountains.

Diverse and sometimes abundant algal assemblages occur within the Early-mid Cretaceous platform carbonates of the Oman Mountains. Together with benthic foraminifera they provide an excellent means of subdividing the succession biostratigraphically and provide useful age information. They allow for the refinement of palaeoenvironmental models, by providing information on water depth, current energy, etc.

The Dasycladaceae are the most prominent and stratigraphically useful group of calcareous algae in these sediments, with several species of the genus Salpingoporella being present, together with species of Cylindroporella, Clypeina, Acroporella and several other genera. Gymnocodiaceae are also common, particularly the genus Permocalculus (including one new species). Several incertae sedis forms such as Bacinella - Lithocodium and Thaumatoporella occur. Corallinaceae occur only rarely.

Some taxa are recorded for the first time from the Middle East, although in general the assemblages from Oman are similar to those described from elsewhere in the Middle East by G.F. Elliott and other workers.

TSIEN H.H.

Algae and cyanobacteria in the Devonian reef facies of Belgium

Six different types of reefs are to be found in the Devonian of Belgium. Most of them (fringing reef, biostrome, barrier reef, patch reef and bioherm complex) have developed during relatively stable phases (tectonically calm periods, clear water, free from clastic sediment contaminations). During transgressive phases, as long as subsidence was not too rapid, micrite mounds tended to develop. Algae and cyanobacteria are abundant in micrite mounds and bioherm complexes. They are common in patch reefs, barrier reef and fringing reefs, but rare in biostromes. Algae and cyanobacteria are the principal reef or mound builders in micrite mounds. In bioherm complexes they are abundant, but are nevertheless subordinate to stromatoporoids and corals and developed mostly among stromatoporoid and coral colonies. Cavities and fissures are numerous and occur in many different shapes and sizes in reefs. Renalcis, Epiphyton and Frutexites are to be found in some of these cavities and fissures. Epiphyton and Frutexites are generally characterized by important iron-oxide deposits suggesting that they could accumulate iron from sea water through some particular metabolic pathway. The fact that they lived in the dark suggests that they were probably algal-microbial colonies. Renalcis, Epiphyton and Frutexites flourished also in lime mud rich in organic substances and in decaying organisms. In the central lagoons of bioherm complexes, much of the debris is encrusted with algae (Rothpletzella and Girvanella) or bryozoans. Successive encrustations of thin laminar stromatoporoids by Rothpletzella straelenii, stromatolites and/or bryozoans are frequent. Debris of Rothpletzella, Girvanella, dasycladaceans and other algae are common in the reef facies. All these facts suggest that most algae in reef facies developed in calm or protected areas

WINSBOROUGH B.

Fossil and living stromatolites from a desert basin in northeastern Mexico.

Stromatolites and algal mats grow under a variety of different chemical and physical conditions in spring-fed streams, ponds, and evaporitic lakes of the Cuatro Ciénegas Basin, northeastern Mexico. There are at least five different stromatolite morphologies which are not only structurally different from each other, but support their own distinct biological community. Adjacent to the modern springs, at a slightly higher elevation, are fossilized stromatolites associated with a former higher water level. About a hundred meters from one of the flowing springs is a much older (Plio-Pleistocene?) spring-lake deposit with over 40m thick by 400m horizontal of laminated stromatolite and algal mat deposits rising above the present valley floor. At least three separate and repeating facies are readily distinguishable in this biogenic deposit. The modern stromatolitic structures are contrasted with the various facies represented in the fossil deposits. This study is part of a comprehensive effort to interpret the ecology and paleoecology of the stromatolitic habitats of the Cuatro Ciénegas Basin.

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