Fossils of a 'Lost City' Hydrothermal Ecology From Cretaceous Spain

Fluid mixing and the deep biosphere of a fossil Lost City-type hydrothermal system at the Iberia Margin

Authors:

Klein et al

Abstract:

Subseafloor mixing of reduced hydrothermal fluids with seawater is believed to provide the energy and substrates needed to support deep chemolithoautotrophic life in the hydrated oceanic mantle (i.e., serpentinite). However, geosphere-biosphere interactions in serpentinite-hosted subseafloor mixing zones remain poorly constrained. Here we examine fossil microbial communities and fluid mixing processes in the subseafloor of a Cretaceous Lost City-type hydrothermal system at the magma-poor passive Iberia Margin (Ocean Drilling Program Leg 149, Hole 897D). Brucite−calcite mineral assemblages precipitated from mixed fluids ca. 65 m below the Cretaceous paleo-seafloor at temperatures of 31.7 ± 4.3 °C within steep chemical gradients between weathered, carbonate-rich serpentinite breccia and serpentinite. Mixing of oxidized seawater and strongly reducing hydrothermal fluid at moderate temperatures created conditions capable of supporting microbial activity. Dense microbial colonies are fossilized in brucite−calcite veins that are strongly enriched in organic carbon (up to 0.5 wt.% of the total carbon) but depleted in 13C (δ13CTOC = −19.4‰). We detected a combination of bacterial diether lipid biomarkers, archaeol, and archaeal tetraethers analogous to those found in carbonate chimneys at the active Lost City hydrothermal field. The exposure of mantle rocks to seawater during the breakup of Pangaea fueled chemolithoautotrophic microbial communities at the Iberia Margin, possibly before the onset of seafloor spreading. Lost City-type serpentinization systems have been discovered at midocean ridges, in forearc settings of subduction zones, and at continental margins. It appears that, wherever they occur, they can support microbial life, even in deep subseafloor environments.

Wrangellian Volcanism in the Late Ladinian Caused the Biotic Crisis in the Carnian Triassic?

Cause of Upper Triassic climate crisis revealed by Re-Os geochemistry of Boreal black shales

Authors:

Xu et al

Abstract:

The Triassic Period is bracketed by two of the ‘big five’ Phanerozoic mass extinctions. Though long viewed as a period of climatic stability, emerging data suggest multiple climatic swings and at least one severe ecological crisis. Linking these climatic instabilities with probable causes is hampered by poor age control within the Triassic time scale. Here we present new Re-Os ages for shale sections straddling Middle-Upper Triassic stage boundaries. Nominal Re-Os isochron ages of 236.6 and 239.3 Ma for the top and base of the Ladinian (upper Middle Triassic) bring absolute time into the contentious Triassic time scale, and place the beginning of the Late Triassic about 12 m.y. earlier than previously assigned. A marked decrease in initial 187Os/188Os in Upper Ladinian shale records input from Wrangellian flood basalts – an instigator in the Carnian (Late Triassic) Pluvial Event and accompanying radiation of key fossil groups (e.g., dinosaurs and calcareous nanoplankton). An absolute time scale is proposed for the Anisian – Ladinian – Carnian boundaries based on Re-Os geochronology.

Bay of Biscay Drilling Project in 1981 Yields Interesting Early Cretaceous Paleobotanical Insights

Plant remains from Early Cretaceous deposits on the Goban Spur, Bay of Biscay, North Atlantic Ocean, and their palaeoenvironmental significance

Authors:

Batten et al

Abstract:

Site 549 of the Deep Sea Drilling Project was drilled on the Goban Spur in the Bay of Biscay in 1981. The core recovered from this North Atlantic location included 290 m of Barremian and possibly partly Hauterivian “syn-rift” deposits overlain unconformably by rocks of early Albian age. The number and variety of spores and pollen grains in the palynomorph assemblages and associated palynofacies through these units together with the presence of some pieces of wood, fragments of foliage, and a few megaspores in the lowest part of the Cretaceous succession suggest that the source area vegetation was, at least initially, relatively close to the site of deposition. Ginkgoalean, bennettitalean, and other gymnosperm groups are represented in the plant mesofossil assemblage but most of the fragments of foliage show cheirolepidiaceous characteristics. Five species belonging to this family have been identified and described. Two of these, Frenelopsis atlantica Zhou and Batten and Frenelopsis? alvinii Zhou and Batten, are new and one is unnamed. The composition of the three informally identified suites of spore and pollen assemblages recovered from 49 samples through the Early Cretaceous succession is consistent with age determinations of parts of it determined previously on the basis of dinoflagellate cysts, foraminifera, nannoplankton, and other fossils.