Michael R. Sandy

Mass Occurrences of the Brachiopod Halorella in Late Triassic Methane-Seep Deposits, Eastern Oregon

The temporally and geographically scattered Phanerozoic record of methane-seep deposits hampers reconstruction of the evolution of life in chemosynthesis-based ecosystems. Unlike modern, Cenozoic, and late Mesozoic seeps, many of the known older seep deposits are typified by assemblages with profuse rhynchonellide brachiopods. Late Triassic (Norian) limestone bodies in eastern Oregon are enclosed in deep-water strata, extend laterally for up to a few hundred meters, and contain the dimerelloid rhynchonellide Halorella in rock-forming quantities. The analysis of two large limestone bodies in the Rail Cabin Member of the Vester Formation exposed near Graylock Butte, Grant County, Oregon, fosters the reconstruction of the paleoenvironmental setting of these unusual Halorella deposits, resulting in the first recognition of Triassic methane-seep deposits. The faunal assemblage includes few fossils other than Halorella. Although occasionally found at seeps, the recognized nuculanids are not seep-endemic bivalves. A Nucinella-like bivalve and a possible permophorid bivalve were likely endemic to this chemosynthesis-based environment; related bivalves lived at Jurassic and Cretaceous seeps. The superabundant, mostly articulated brachiopod shells are enclosed in a variety of micrites, including peloidal to clotted micrite. Early fibrous cement, forming banded and botryoidal crystal aggregates, preferentially occurs at the margin of the large limestone bodies but is scarce overall. Peloidal to clotted micrite and banded and botryoidal cement are common constituents of methane-seep limestones. Their negative δ13C values as low as −36‰ reveal that carbonate formation was induced by the oxidation of methane. The presence of pyrobitumen (i.e., metamorphosed crude oil) in the limestones may indicate that the seepage fluids contained oil in addition to methane. Apart from the diagnostic 13C-depleted carbonate phases, mud injections recognized in one of the two limestone bodies also bear testament to former seepage activity.

IBERGIRHYNCHIA CONTRARIA (F. A. ROEMER, 1850), AN EARLY CARBONIFEROUS SEEP–RELATED RHYNCHONELLIDE BRACHIOPOD FROM THE HARZ MOUNTAINS, GERMANY—A POSSIBLE SUCCESSOR TO DZIEDUSZYCKIA?

Abstract A new genus Ibergirhynchia, a member of the rhynchonellide superfamily Dimerelloidea, is described for the species Terebratula contraria Roemer, 1850, from Early Carboniferous deposits of the Harz Mountains, Germany. Ibergirhynchia contraria is from a monospecific brachiopod limestone that formed on top of the drowned Devonian Iberg Reef which persisted as a seamount during Famennian and Early Carboniferous times. Ibergirhynchia contraria is considered a cold seep-related brachiopod based on this locality. Such seep associations have been observed for Mesozoic representatives of the rhynchonellide superfamily Dimerelloidea. Ibergirhynchia is considered the first Paleozoic representative of the family Rhynchonellinidae. Ibergirhynchia resembles Dzieduszyckia externally and may be derived from this dimerelloid.

Early Mesozoic (Late Triassic-Early Jurassic) Tethyan brachiopod biofacies: possible evolutionary intra-phylum niche replacement within the Brachiopoda

Distributions of brachiopods from low-latitude paleogeographic settings, primarily in the Tethyan Ocean of southern Europe, with additional data from North America allow some observations on the bathymetric distribution of early Mesozoic brachiopod orders. Norian and latest Triassic (Rhaetian) brachiopod biofacies are dominated in shallowest waters by short-looped tere- bratulids (Terebratulidina) while spire-bearing athyrids (Athyrida) are common components of deeper-water environments in the latest Triassic. In the late Early Jurassic (Pliensbachian), shallow- water brachiopod faunas are dominated by rhynchonellids, short-looped terebratulids are commoner in relatively deeper shelf waters, and spiriferids and long-looped terebratulids (Terebratellidina) are abundant in deeper-water shelf environments. Following the end-Triassic extinction event there appears to be niche-replacement in deep-water shelf environments of Late Triassic athyrids by spiriferids and long-looped terebratulids in the Early Jurassic. Rhynchonellids appear to have diversified into shallowest water environments; specialized short-looped terebratulids may have occupied deeper-water niches that resulted ulti- mately in the success of the enigmatic Pygopidae later in the Jurassic and Cretaceous.

Aspects of Middle-Late Jurassic-Cretaceous Tethyan brachiopod biogeography in relation to tectonic and paleoceanographic developments

Abstract Important tectonic and paleoceanographic events during the Middle to Late Jurassic and Cretaceous resulted in modifications to the biogeographic distributions of Tethyan brachiopod genera from Europe. The development of the Central Atlantic Ocean during the Jurassic-Early Cretaceous led to an increase in the number of brachiopod genera common to both the Mexico/Eastern Pacific and Northwestern Europe/Tethyan regions. Brachiopod genera recorded from Tethys in Europe show evidence of migration via at least four major routes as a consequence of tectonic developments (dates in parentheses indicate stages where evidence exists for generic links): (1) Northwestern Europe via Mexico/Caribbean region (Oxfordian) to South America (Valanginian, Hauterivian, Cenomanian); (2) Eastern Tethys via Eastern Africa (East African Seaway) to the South Atlantic Ocean (Late Turonian-Early Coniacian, Santonian-Campanian); (3) Northwestern Europe via the Central Atlantic to the opening South Atlantic, reaching the Antarctic Peninsula region (late Albian, Santonian, Campanian); (4) Europe northward to higher latitudes (Russian Platform to Barents Sea, Berriasian-Valanginian; Europe to East Greenland, Valanginian; Europe-Canadian Arctic Islands, Albian and also earlier during the Jurassic). For routes (1)–(3) direction of dispersal may prove to have been in either direction, at times it appears to have been in a southerly direction for route (3). Stratigraphic age relationships suggest a south to north dispersal for routes considered under (4) (except for the link to the Canadian Arctic Islands, which is inconclusive). By the Late Cretaceous the low-latitude faunas of Europe and America had become isolated by the increasing width of the Central Atlantic Ocean although some genera appear to be cosmopolitan.

The Paleoecology, Habitats, and Stratigraphic Range of the Enigmatic Cretaceous Brachiopod Peregrinella

Modern and Cenozoic deep-sea hydrothermal-vent and methane-seep communities are dominated by large tubeworms, bivalves and gastropods. In contrast, many Early Cretaceous seep communities were dominated by the largest Mesozoic rhynchonellid brachiopod, the dimerelloid Peregrinella, the paleoecologic and evolutionary traits of which are still poorly understood. We investigated the nature of Peregrinella based on 11 occurrences world wide and a literature survey. All in situ occurrences of Peregrinella were confirmed as methane-seep deposits, supporting the view that Peregrinella lived exclusively at methane seeps. Strontium isotope stratigraphy indicates that Peregrinella originated in the late Berriasian and disappeared after the early Hauterivian, giving it a geologic range of ca. 9.0 (+1.45/–0.85) million years. This range is similar to that of rhynchonellid brachiopod genera in general, and in this respect Peregrinella differs from seep-inhabiting mollusks, which have, on average, longer geologic ranges than marine mollusks in general. Furthermore, we found that (1) Peregrinella grew to larger sizes at passive continental margins than at active margins; (2) it grew to larger sizes at sites with diffusive seepage than at sites with advective fluid flow; (3) despite its commonly huge numerical abundance, its presence had no discernible impact on the diversity of other taxa at seep sites, including infaunal chemosymbiotic bivalves; and (4) neither its appearance nor its extinction coincides with those of other seep-restricted taxa or with global extinction events during the late Mesozoic. A preference of Peregrinella for diffusive seepage is inferred from the larger average sizes of Peregrinella at sites with more microcrystalline carbonate (micrite) and less seep cements. Because other seep-inhabiting brachiopods occur at sites where such cements are very abundant, we speculate that the various vent- and seep-inhabiting dimerelloid brachiopods since Devonian time may have adapted to these environments in more than one way.

OLDEST RECORD OF PEDUNCULAR ATTACHMENT OF BRACHIOPODS TO CRINOID STEMS, UPPER ORDOVICIAN, OHIO, U.S.A. (BRACHIOPODA; ATRYPIDA: ECHINODERMATA; CRINOIDEA)

A hand-specimen, bedding-plane sample of limestone (wackestone) from the Upper Ordovician Waynesville Formation has numerous brachiopod specimens (at least 60) exposed on its surface (Figure 1). The brachiopods have been identified as members of the atrypid species Zygospira modesta (Say in Hall) 1847 (the type species of the genus Zygospira Hall, 1862) and are concentrated in an area measuring approximately 9 cm x 2 cm. A wide range of specimen sizes from juvenile to adult are present and are believed to represent a brachiopod life-assemblage (Figure 2).

Color banding in the Triassic terebratulid brachiopod Coenothyris from the Muschelkalk of Central Europe

The Triassic terebratulid brachiopod Coenothyris frequently displays preserved color patterns; such patterns have commonly been recorded from Paleozoic terebratulid brachiopods. Despite the frequency with which color patterns are preserved in Coenothyris, there has been no recent investigation of the cause and significance of this phenomenon. Shell material is well-preserved; energy-dispersive spectroscopy and microprobe analysis has been unable to detect compositional differences between colored and noncolored shell. This supports the organic origin of the color patterns as suggested for Devonian terebratulids by Richter (1919); color patterns originate from organic pigment in the primary shell layer. Three subtypes of radial color banding are identified: subtype A with a relatively large number (up to 80) of delicate color bands on each valve; subtype B with fewer and generally wider color bands (less than 20) on each valve of adult specimens; subtype C with faint to fairly wide but very short color bands along the anterior margin (ranging from a few to more than 50 in number). Serial sections prepared from subtypes A and B confirm their congeneric status. As shell form (length/width/thickness ratio) and maximum size varies, color pattern types differ in various stratigraphic horizons and also in isochronous populations from different geographic localities, indicating different facies. However, the variation in color patterns is not due to systematic differences at the species or subspecies level but rather reflects a tendency among Coenothyris vulgaris to respond to different environmental parameters. This variation in color patterns is ecophenotypic.

New Paleocene Rhynchonellide brachiopods from the Potrerillos Formation, northeast Mexico

Abstract Two new species of the rhynchonellid brachiopod Probolarina are described, Probolarina neoleonensis new species and Probolarina papalotensis new species. They were collected from a Paleocene limestone lens associated with a diapir in the La Popa basin, northeastern Mexico. Thousands of these brachiopods occur in this lens and constitute the first report of brachiopods for the Difunta Group, from which a diverse paleobiota has been previously reported. This occurrence represents the oldest record for the genus in the Western Hemisphere, as the only other Paleocene occurence of this genus was reported from New Zealand. Recent studies suggest that the carbonate lentil from which the brachiopods were collected were deposited in the shadow-effect area adjacent to the diapir, which affected the sediment influx into the basin.

Early jurassic spiriferid brachiopodsfrom Alaska and their paleogeographic significance

Spiriferid brachiopods are described in detail for the first time from the Jurassic of North America. The specimens are referred to the genera Liospiriferina and Callospiriferina, both originally described from the Early Jurassic of Morocco and Spain by Rousselle (1977). The species identified herein, Liospiriferina rostrata and Callospiriferina tumida, are known from Europe, South America, and northern Africa, with L. rostrata also recorded from Indonesia. The new occurrences in Alaska indicate a lower-latitude placement during the Early Jurassic, at least temperate latitudes, for the Farewell (probably during the Sinemurian) and Peninsular (Sinemurian-basal Toarcian) terranes. Liospiriferina and Callospiriferina range through much of the Early Jurassic. These new occurrences are significant because they indicate further parallels between the composition of Mesozoic brachiopod faunas of Europe, where faunas were initially monographed in the nineteenth century, and those of North America and South America. The spiriferids therefore show evidence of survival in North America beyond end-Triassic extinctions, underscoring the global nature of the continuity of the Spiriferida into the Jurassic before their demise by the end of the Early Jurassic. In terms of the composition of Mesozoic brachiopod faunas spiriferids have been identified as preferring deeper-water shelf environments. It has not been determined if this was the case for these Jurassic spiriferids: the collections studied herein show Liospiriferina to be associated with sandy lithologies while Callospiriferina was collected from a black shale. Based on external morphology Liospiriferina is closely homeomorphic with the cosmopolitan Triassic athyrid brachiopod Oxycolpella. However, on closer examination and preparation of serial sections of internal structures the Alaskan specimens showed the presence of dental lamellae, a large, persistent median septum, a spiralium (spiral brachidium), and punctate shell, indicating affinities to the Spiriferida. The material had originally been tentatively identified as terebratulids.

Brachiopods from Late Jurassic—Early Cretaceous hydrocarbon seep deposits, central Spitsbergen, Svalbard

Late Jurassic-Early Cretaceous (Late Volgian-latest Ryazanian) rhynchonellate brachiopods are described from eight out of 15 hydrocarbon seep deposits in the Slottsmøya Member of the Agardhfjellet Formation in the Janusfjellet to Knorringfjellet area, central Spitsbergen, Svalbard. The fauna comprises rhynchonellides, terebratulides (terebratuloids and loboidothyridoids) and a terebratellidine. The rhynchonellides include: Pseudomonticlarella varia Smirnova; Ptilorhynchia mclachlani sp. nov.; and Ptilorhynchia obscuricostata Dagys. The terebratulides belong to the terebratuloids: Cyrtothyris? sp.; Cyrtothyris aff. cyrta (Walker); Praelongithyris? aff. borealis Owen; and the loboidothyridoids: Rouillieria cf. michalkowii (Fahrenkohl); Rouillieria aff. ovoides (Sowerby); Rouillieria aff. rasile Smirnova; Uralella? cf. janimaniensis Makridin; Uralella? sp.; Pinaxiothyris campestris? Dagys; Placothyris kegeli? Harper et al.; and Seductorithyris septemtrionalis gen. et sp. nov. The terebratellidine Zittelina? sp. is also present. Age determinations for all but one of the brachiopod-bearing seeps are based on associated ammonites. Five of the seep carbonates have yielded Lingularia similis?, and it is the only brachiopod species recorded from two of the seeps. Other benthic invertebrate taxa occurring in the seeps include bivalves, gastropods, echinoderms, sponges, and serpulid and non-serpulid worm tubes. The brachiopod fauna has a strong Boreal palaeobiogeographic signature. Collectively, the Spitsbergen seep rhynchonellate brachiopods exhibit high species richness and low abundance (<100 specimens from 8 seeps). This contrasts markedly with other Palaeozoic---Mesozoic brachiopod-dominated seep limestones where brachiopods are of low diversity (typically monospecific) with a super-abundance of individuals. The shallow water environmental setting for the Spitsbergen seeps supported a diverse shelf fauna, compared to enigmatic Palaeozoic-Mesozoic brachiopod-dominated seeps.