Földtani Közlöny 125/3-4, 241-258 (1995) Budapest
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Földtani Közlöny 125/3-4, 241-258 (1995) Budapest A review of some Palaeozoic and Mesozoic brachiopods as members of cold seep chemosynthetic communities: "unusual" palaeoecology and anomalous palaeobiogeographic patterns explained Paleozóos és mezozóos brachiopodák, mint a tengeralatti forrásokhoz kapcsolódó, kemoszintézisen alapuló életközösségek tagjai: a különleges paleoökológiai vonások és az anomális paleobiogeográfiai elterjedés magyarázata Michael R. SANDY 1 (1 table, 1 plate) Key words: Palaeozoic, Mesozoic, Brachiopoda, palaeoecology, palaeobiogeography Abstract The apparently anomalous palaeoecology and palaeobiogeography of a number of Palaeozoic and Mesozoic brachiopod genera known from only a few geographically dispersed localities (or even only one), can be understood by interpreting their occurrences as members of, or associates of chemosynthetic communities (cold seeps, or low-temperature hydrothermal vents). This is based on an assessment of aspects of their geological setting-stratigraphy, sedimentology and palaeontology. A cold seep interpretation is significant in explaining disjunct problematic palaeobiogeographic patterns and palaeoecological models with no modern analogues that have previously been proposed to explain their occurrence. Összefoglalás Számos paleozoós és mezozoós brachiopoda nemzetség képviselői csupán néhány, földrajzilag egymástól távol eső lelőhelyről (vagy éppen csak egy lelőhelyről) ismertek. E nemzetségek látszólag anomális paleoökológiai és paleobiogeográfiai eloszlása érthetővé válik, ha képviselőiket (tenge ralatti, hidegvízű forrásokhoz kapcsolódó) kemoszintézisen alapuló életközösségek tagjaiként értelmezzük. Ez az értelmezés a lelőhelyek földtani (rétegtani, szedimentológiai és paleontológiái) kiértékelésén alapul. A "hideg forrás" ("cold seep") értelmezés fontos lehet a problematikus, széttagolt paleobiogeográfiai eloszlások, valamint az olyan paleoökológiai modellek esetében, melyeknek magyarázatára eddig nem sikerült recens analógiát találni. 'Department of Geology, University of Dayton, Dayton, Ohio 45469-2364, U.S.A. 242 Földtani Közlöny 125/3-4 Introduction In view of recent advances in identifying chemosynthetic communities in the fossil record, it seems opportune to review and discuss a number of Palaeozoic and Mesozoic brachiopod genera with apparently anomalous palaeoecological and palaeobiogeographical distributions. Considering them as members of, or associates of chemosynthetic communities (cold seeps, or low-temperature hydrothermal vents) appears to present a credible model for the palaeoecological and palaeobiogeographical patterns observed. Clearly there are other alternative interpretations for each of the occurrences discussed herein, such as stressed environments, hypersalinity, opportunistic colonization, or taphonomic shell-lag concentrations (e.g., FÜRSICH and HURST 1980). Therefore it is necessary for detailed investigations of these occurrences to determine whether they are associates of chemosynthetic environments. Most of the discussion herein focuses on cold seep (i.e., methane) chemosynthetic communities because records of brachiopods in such settings appear to be the most numerous in the fossil record, to date. Chemosynthetic communities Modern cold seep chemosynthetic communities (i.e., non-hydrothermal vent) have been identified in a range of marine environments and tectonic settings (e.g., subduction zones in active continental margins, brine seeps in passive margins, petroleum seeps in active and passive margins and submarine fans, see references in CALLENDER et al. 1992) from depths between 75 to 3,850 m in several oceans (see references in BEAUCHAMP et al. 1989; and VON BITTER et al. 1992). High-temperature hydrothermal vents occur on oceanic rises. Subtidal and freshwater chemosynthetic communities have also recently been identified (references in VON BITTER et al. 1992). It appears to be the availability of CH4 and/or H2S as a nutrient source that determines the development of the chemosynthetic community rather than whether they are "cold", "hot", "deep" or "shallow" (VON BITTER et al. 1992, p. 474 and references therein). Ancient hydrothermal vent and cold seep communities can be regarded as forming something of a continuum in terms of geologic setting, fauna and associated deposits (e.g., GAILLARD et al. 1992, fig. 10). Hydrothermal vent and cold seep communities may resemble each other but their geological products can be very distinct. High-temperature vents are associated with massive sulfide deposits, with tube-worms as an important faunal element. Low-temperature hydrothermal vents and cold seeps typically have isotopically light methane-derived authigenic carbonate and low diversity, bivalve-dominated communities (see references in BEAUCHAMP et al. 1989). CALLENDER and POWELL (1992) have recently commented on the similarity between autochthonous petroleum-seep assemblages (cold seep) of the Upper Continental slope off Louisiana, U.S.A. and a number of ancient occurrences of autochthonous shell M. SANDYIA review of some Palaeozoic and Mesozoic brachiopods 243 beds, but pointed out that there was little difference in the taphonomic signatures of non-seep and some seep assemblages (CALLENDER et al. 1992). Brachiopods in association with fossil cold seeps and hydrothermal vents Ancient cold seep and hydrothermal vent communities have now been identified as far back as the middle to late Palaeozoic (references in VON BITTER et al. 1990; TUNNICLIFFE 1992; CAMPBELL et al. 1993, CAMPBELL and BOTTJER 1995a). Records of brachiopods from fossil cold seep or hydrothermal vents settings are not numerous. The occurrences of cold seep-associated brachiopods have been described in some detail from the Cretaceous of the Canadian Arctic (BEAUCHAMP et al. 1989; BEAUCHAMP and SAVARD 1992) and the Jurassic-Cretaceous of California, U.S.A. (CAMPBELL et al. 1993, CAMPBELL and BOTTJER 1995b). Therefore a total of three brachiopod taxa have been identified from cold seep communities; Modestella jeletzkyi SANDY, Cooperrhynchia schucherti (STANTON), and Peregrinella whitneyi (GABB). Brachiopods are now being identified associated with modern cold seeps (e.g., BARRY et al. 1993), although none of these present-day brachiopod occurrences have been described in detail. A brachiopod was recorded from Early Carboniferous low-temperature hydrothermal vent communities by VON BITTER et al. (1990, 1992) but these deposits currently lack substantiating stable isotope evidence. A Devonian bedded barite deposit in "oceanic" strata of Nevada, U.S.A. and Mexico contains the rhynchonellid Dzieduszyckia. These brachiopods and associated tubes have been interpreted as members of vent communities (POOLE 1988). TUNNICLIFFE (1992, p. 348) suggested that the hydrothermal origin for this deposit could be re-evaluated in the light of information about modern seeps. Also relevant is the geological setting of Dzieduszyckia (Plate J) from the Devonian of Morocco (ACER et al. 1976), discussed herein. Additionally, brachiopods are common constituents of a number of in situ (autochthonous) fossil assemblages identified by CALLENDER and POWELL (1992, table 16) in a comparison with modern petroleum-seep assemblages. More recently CAMPBELL and BOTTJER (1995a) have published a compendium of fossil brachiopod and bivalve occurrences interpreted to be associated with chemosynthetic communities, based on field evidence and literature review. A number of the brachiopod taxa they considered are discussed herein although most of my comments refer to Mesozoic genera with which I am acquainted. The first published record of a brachiopod as part of a cold seep community appears to be that of a terebratulid from the Lower Cretaceous of Prince Patrick Island, Canadian Arctic Islands (BEAUCHAMP et al. 1989). This brachiopod was referred to Taimyrothyris by JELETZKY (BEAUCHAMP et al. 1989) but was subsequently named Modestella jeletzkyi (Plate D by SANDY (1990) although the seep-related aspect of the taxon was overlooked by me. As is often the case with studies of fossilised long-looped terebratellids, an ontogenetic study of 244 Földtani Közlöny 125/3-í the brachidium of this species was not possible (owing to lack of juveniles and also only a few specimens being deposited in the collections of the Geological Survey of Canada, Ottawa). If the identification is correct, it represents the first record of Modestella from the Western Hemisphere. This genus was previously recorded in England, northern Germany, northern France and Poland although none of these records are presently suspected to be in seep communities. A short-looped terebratulid Beecheria was considered a member of low-temperature hydrothermal vent communities in Lower Carboniferous rocks of Newfoundland (VON BITTER et al. 1990, 1992). The spiriferid Martinia is interpreted to have been an opportunistic settler prior to the build-up of carbonate mounds in these vent settings; it has an anomalous occurrence in that it appears here stratigraphically earlier than other known occurrences of the genus (VON BITTER et al. 1992). The work of CAMPBELL and BOTTJER (1991, 1993), and CAMPBELL et al. (1993) has identified a number of cold seep-related carbonates in the Great Valley Group of California. At least three of these lens-shaped carbonates contain rhynchonellid brachiopods (CAMPBELL et al. 1993). Cooperrhynchia schucherti STANTON (Plate T) in the Tithonian is known from one locality and Peregrinella whitneyi GABB is known from at least