Two new species ofRetiskenea? (Gastropoda: Neomphalidae) from Lower Cretaceous hydrocarbon-seep carbonates of northern California

Abstract

Two new Mesozoic gastropod species, provisionally attributed to the minute (height < 5 mm) coiled neomphalid genus Retiskenea?, are described from three geographically isolated, Early Cretaceous, hydrocarbon seep-carbonate sites at Wilbur Springs, Rice Valley, and Cold Fork of Cottonwood Creek, northern California (USA). A fourth paleo-seep locality at Paskenta, of probable Upper Jurassic age, also yielded a single specimen of a morphologically similar microgastropod that may be a neomphalid with affinities to the Lower Cretaceous specimens described herein. the limestone lenses are ~2-260 m in length, ~1-5 m in diameter, and surrounded by forearc siliciclastics of bathyal turbidites or sedimentary serpentinites in the Upper Jurassic to Lower Cretaceous (Tithonian-Albian) Great Valley Group and its equivalents. the Lower Cretaceous microgastropods are tentatively placed in Retiskenea? based on similar shell characters: size, globose shape, inflated reticulate protoconch, number and distinct inflation of the body whorls, and fine, prosocline sculpture of the final body whorl. the fossils occur in carbonate microbialites that formed in seafloor sediments during archaeal anaerobic oxidation of methane in the zone of bacterial sulfate reduction, associated with H2S- and CH4-rich fluid seepage. the California Retiskenea? fossils commonly are found in gregarious clusters, or closely affiliated with thin worm tubes or, in one case, a larger gastropod.These Mesozoic records increase the total known species attributable to this cold-seep endemic genus from two to four. Its spatial and temporal distribution thus may have spanned ~9,000 km around the Pacific Rim from at least ~133 m.y. to the present in 10 subduction-related seep sites from California (possibly Upper Jurassic-Lower Cretaceous), Washington (middle Eocene-Upper Oligocene), and modern offshore Oregon, the eastern Aleutians, and the Japan Trench. If the generic placement of these microgastropod fossils is correct, the California records are the oldest-known occurrences of Retiskenea, consistent with an estimated minimum Mesozoic origin for the 'hot vent' Neomphalidae, as inferred from molecular analyses published on other living members of the family.

Mollusks from late Mesozoic seep deposits, chiefly in California

“…The localities (Fig. 1) Campbell et al ( , 2002 and Kiel & Campbell (2005) is at the cliffs of Hamilton Canyon but these were inaccessible during the visit in 2011. However, the original Bear Creek locality does not consist of a single large limestone deposit but of numerous carbonate lumps and blocks scattered throughout the section.…”

“…These 'white limestones' show geochemical signatures that are characteristic for seep deposits (Campbell et al 2002;Birgel et al 2006) and are embedded in turbidities with scattered Buchia and ammonite fragments typical for the late Mesozoic forearc basin along the American West coast (Jones et al 1969;Ingersol 1982). The first fossils from these limestones were described in the late 19 th century Stanton, 1895) but modern taxonomic work on the fauna did not start until recently and has so far focused largely on gastropods (Kiel & Campbell 2005;Campbell et al 2008;Kiel et al 2008bKiel et al , 2010 and the bivalve Caspiconcha (Jenkins et al 2013). Here we report new taxa, new data on known taxa, and a revision of the bivalves from these ancient seep deposits based on newly collected material, museum specimens, and a comparison to Mesozoic seep faunas worldwide.…”

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

“…However, we cannot entirely discard the equally consistent early Aptian Sr-isotope age, but the Hauterivian age is more likely because two of the mollusk species present in the Rice Valley seep carbonate ( Paskentana paskentaensis and Retiskenea ? tuberculata ) are known from other Valanginian-Hauterivian seep deposits, but an Aptian seep deposit from this area (Cold Fork of Cottonwood Creek) contains a different set of taxa [41] , [61] .…”

Mollusks (Gastropoda, Bivalvia) from Miocene cold-seep deposits in northern Italy: revisions and additions

“…The two available specimens are embedded in rock matrix and are rather poorly preserved. They have the size and habitus of specimens belonging to the neomphaline Retiskenea (e.g., Warén & Bouchet 2001;Kiel 2006;Campbell et al 2008;Kaim et al 2014;Kaim 2022), but do not preserve details of the protoconch, which would be needed for a reliable assignment to the neomphalids. The specimens are quite similar to a 'skeneimorph gastropod' reported by us from the Late Miocene Ca' Fornace seep deposit .…”