Bulletin de la Société belge de Géologie T. 92 fasc. pp. 31 - 53 Bruxelles 1983 Bulletin van de Belgische vereniging voor Geologie v. 92 deel blz. 31 53 Brussel 1983 LATE DEVONIAN AND CARBONIFEROUS OSTRACODE ASSEMBLAGES AND THEIR RELA TIONSHIP TO THE DEPOSITIONAL ENVIRONMENT by M. J. M. BLESS (•) ABSTRACT. - Four main depositional realms have been recognized in late Devonian and Carboniferous sediments. The boundaries between these en­ tities are vague and transitional facies are known. The variations in the sedimentary environment have been clearly expressed in the ostraco­ de faunas. In the late Devonian and Carboniferous strata around the Brabant Massif (Belgium and surrounding areas) the ostracode assembla­ ges indicate the presence of marine near-shore to marine shallow off­ shore environments during late Devonian and Dinantian times, and non­ marine to marine near-shore facies during the Silesian period. INTRODUCTION, The distinction between a wide ran­ sediments, a number of facies-controlled ge of depositional environments, which may ostracode assemblages can be recognized. vary from non-marine to fully marine, is es­ These permit to distinguish between four sential in the reconstruction of the tecto­ broad environmental realms which are ter­ nic evolution of sedimentary basins. Geoche­ med here non-marine, marine near-shore, mistry, sedimentology and paleontology provi­ marine shallow off-shore and marine basin de very valuable tools in a detailed inter­ (figure 1). Within each of these realms, pretation of the conditions of deposition in a number of distinctive ostracode groups the past. Ostracodes form one of the micro­ may be recognized which enable to establish fossil groups which have been applied suc­ an even more detailed environmental zona­ cessfully in the recognition of different tion. A titre d'example, some characteris­ sedimentary facies. Since Paleozoic times, tic late Devonian (late Famennian) and they have adapted themselves to all kind of Carboniferous ostracode assemblages have aquatic environments from the deep-sea been figured here (figures 2-11). to water-filled hollow tree-trumps and flo­ wers, from hotwater springs to arctic seas, The recognition of some of these and from normal fresh-water to sulphuric, ostracode populations in late Famennian and acid, alkaline or hypersaline water. Unfor­ Carboniferous deposits in the area around tunately, too often the papers on fossil os­ the so-called Brabant Massif (Belgium and tracodes are limited to information on their surrounding areas of France, the Netherlands systematics or stratigraphical distribution. and the Federal Republic of Germany) has permitted to confirm the overall pattern of The potential of Paleozoic ostra­ transgressions and regressions during that codes for environmental interpretation has timespan (figures 13-23). These examples been clearly demonstrated in a large number may serve in stimulating further paleoeco­ of papers. An excellent review on the pa­ logical research on Devono-Carboniferous leoecological distribution of Upper Devonian ostracodes. ostracodes has been published recently by LETHIERS (1982). He showed that ostracode NON-MARINE REALM, assemblages can be used in the discrimina­ tion between several marine paleobiotopes, Included are lirnnic and other ranging from lagoonal to bathyal, in the fresh-water facies, as well as oligohaline, Upper Devonian. Also in the Carboniferous brackish-water and estuarine environments. (•)Museum of Natural History Maastricht, Bosquetplein 6-7, 6211 KJ Maastricht, the Netherlands. 31 It should be realized that the latter are pools, lagoons and intertidal to sh~llow transitional to the true marine realm. subtidal facies with sometimes vary1ng sa­ linity, water energy (turbulence) and oxy­ In Carboniferous times, the non­ gen contents, especially if the substratum marine realm was characterized by represen­ consisted of fine-grained carbonates of cal­ tati ves of only a few genera. careous clays and silts. The local occur­ rence of pyrite, pyritized or decalcified Carbonita ( synonyms : Gutschickia, fossils suggests poorly aerated bottom con­ Hi"lbo"ldtina,Pruvostina, WhippfoUa) seems to have ditions with low oxygen values below the been the predominant ostracode genus in ma­ sediment-water interface. Spineless, rela­ ny fresh-water paleobiotopes, but may have tively large (up to several millimeters) shown some tolerance for low salinites. paraparchitaceans have been the most common Carbonita occurs in a variety of non-marine ostracodes in the littoral paleobiotope. (clastic to carbonate) sediments, but seems Also Beyrichiovsis and some hollinellids have to have preferred a clayey-silty substratum bèen recognized frequently in littoral de­ with often abundant organic matter. The posi ts. A ra ther peculiar form is Copefon­ presence of other ostracode genera - e.g. d,eUa novascotica from the Dinantian of Darwinuia - has sometimes been reported. Re­ southeastern Canada. The overall shape of markable is the (rare) occurrence of the cy­ this beyrichiacean ostracode strongly re­ pridinacean Eocypridina (synonym : Radiicypri­ sembles that of the hollinellids. CopefondeUa dina) in non-marine Upper Carboniferous stra­ may have occupied the same ecological niche ta of North America and Northwestern Europe. as the latter ones, since it occurs in asso­ ciation with paraparchitaceans and the non­ Sorne species of Geisina (formerly of­ marine genus Carbonita (BLE SS & JORDAN, 19 71) . ten assigned to Jonesina) and SansabeUa have been observed frequently in strata which A characteristic inhabitant of the have been interpreted as brackish-water de­ marine near-shore environment in late Devo­ posi ts. These ostracodes may occur also in nian and Dinantian times was CryptophyUus. true fresh-water sediments (together with This eridostracan genus disappeared at the Carbonita) or in possibly marine, littoral de­ beginning of the Dinantian in Canada, posits (with lingulid brachiopods, aggluti­ Northern Europe and the U.S.S.R. But in a nating foraminifers with arenaceous test more southern belt (Australia - JONES, 1974; and/or paraparchitacean or hollinellid os­ Iran and Libya - BLESS & MASSA, 1982), tracodes). CryptophyUus has been found also in Lower and Upper Dinantian strata. CryptophyUus Non-marine ostracode assemblages ha­ and related genera have been reported also ve been described from both the Dinantian from much younger deposi ts ( CryptophyUus and Upper Carboniferous throughout the from Upper Jurassic of North America - world. Identification of species or even SWAIN & PETERSON, 1951; Ankumia from late genera is often difficult because of the Cretaceous of the Netherlands - VAN VEEN, poor preservation of non-marine ostracodes. 1932). Lateral outline, hingement, muscle scars and surface ornamentation may have been ob­ Apart from the paraparchitaceans, scured ·~n steinkerns or external molds of hollinellids (or Cope"land,eUa in the Dinan­ the frequently crushed, wrinkled, decalci­ tian of southeastern Canada) and Cryptophyl,­ fied or recrystallized valves. This makes ius, most of the Carboniferous ostracodes in the discrimination between several genera the marine near.,.·shore realm have been rela­ and families of practically smooth-shelled, ti vely small (rarely over 1 mm). Many of more or less bean-shaped ostracodes of these are smooth-shelled or possess a Carbonita type by means of practically never slightly ornamented carapace (punctate, gra­ observed details such as muscle attachment nulose, striate). Spines are practically scars (as advocated by SOHN, 1977) to a me­ absent or very small (healdiids, Rhadamese?,- rely academic problem,especially as long as 7,a). Kloedenellaceans, cavellinids and no systematic review of muscle scars in all healdiids are relatively frequent. Quasil­ Late Paleozoic non-marine ostracode species litaceans (a.o. GraphiadactyUis, RhadameseUa) has been carried out. However, one should occur in some Dinantian near-shore assem­ be aware of the fact that possibly all the blages. These groups may be common also in above genera are "sack-genera". This means the marine shallow off-shore realm. that SOHN's (1977) criteria for splitting up Carbonita are valid, and may be applied Low numbers of more ornamented ostra­ also to Geisina and Eocypridina. code genera are present in many near-shore deposits. The most frequent group is that of the kirkbyaceans. However, these may MARINE NEAR-SHORE REALM, occur as well in the shallow off-shore and basin facies. Sometimes, small spinose, Included are several environments, lobate or nodose forms occur. In the exam­ which have been termed a.o. (eu-)littoral, ples shown here, one should notice the pre­ supratidal to shallow subtidal, shallow ne­ sence of such ostracodes in the latest ritic or epicontinental, inner shelf or Devonian and Dinantian of Lybia ( Mammoides, platform, restricted marine, and lagoonal by Aec'hrnineUa) and Northwestern Europe different authors. Transitional facies to (KeUettina acuUfobata), and in the Silesian the non-marine and shallow marine off-shore of Northwestern Europe ( CornigeUa). Presu­ realms are knm-m. mably, these occupied a special niche with­ in the nearshore realm. The Carboniferous littoral paleobio­ topes have been characterized by relatively Bairdiacean ostracodes are practical­ monotonous, epi- or endobenthonic faubas, ly absent in typical near-shore environments. which flourished on a substratum of predo­ minantly fine-grained clastic sediments. More diverse assemblages occurred in tide 32 MARINE