Crispin T. S. Little

The early Toarcian (Early Jurassic) and the Cenomanian–Turonian (Late Cretaceous) mass extinctions: similarities and contrasts

Abstract The early Toarcian (eTo) and Cenomanian–Turonian (C–T) mass extinctions are comparable from a wide range of scales and perspectives. From a broad standpoint, their similarities include: virtually identical extinction intensity at the familial and generic levels, widespread basinal facies deposited during sea-level highstands, an overall greenhouse climate, and anoxia as an important causal mechanism. The high-resolution, macroinvertebrate data analyzed here, consisting of stratigraphic ranges, diversity and abundance, point to smaller-scale similarities. The two events resulted in significant ecological disruption and, in both cases, the biotic responses were very similar. Taxa inhabiting the upper water column were unaffected by anoxia and included ammonites and, in the eTo, belemnites. In addition, epifaunal taxa adapted to low-oxygen conditions, such as the buchiids, posidoniids and inoceramids, flourished in the post-extinction environment during the survival interval. As conditions ameliorated, the biota became more diverse and gradually began to resemble pre-extinction biotas. Furthermore, the δ13C curves predict the end of the survival interval and suggest that the period characterized by carbon isotope excursions represent disrupted environmental conditions. This points to the potential application of δ13C as a tool for determining the repopulation modes and timing for other mass extinctions.

Early Jurassic mass extinction: A global long-term event

The end-Pliensbachian extinction event (187 Ma) has been interpreted either as one of 10 global periodically recurring mass extinctions of the past 250 m.y. or as a minor localized European event. Elevated levels of family extinction spanned five ammonite zones during the late Pliensbachian and the early Toarcian, an interval of ∼7.5 m.y., and were distributed unequally in the Boreal, Tethyan, and Austral realms. Detailed sampling of invertebrate macrofaunas through complete expanded sequences in northwest Europe shows that most species extinctions occurred in the early Toarcian, following a regional anoxic event. The Early Jurassic mass-extinction event took place over a long time scale, and it was global in extent.

Cold-Seep Mollusks Are Older Than the General Marine Mollusk Fauna

The origin and possible antiquity of faunas at deep-sea hydrothermal vents and seeps have been debated since their discovery. We used the fossil record of seep mollusks to show that the living seep genera have significantly longer geologic ranges than the marine mollusks in general, but have ranges similar to those of deep-sea taxa, suggesting that seep faunas may be shaped by the factors that drive the evolution of life in the deep sea in general. Our data indicate that deep-sea anoxic/dysoxic events did not affect seep faunas, casting doubt on the suggested anoxic nature and/or global extent of these events.

Evidence for early life in Earth’s oldest hydrothermal vent precipitates

Although it is not known when or where life on Earth began, some of the earliest habitable environments may have been submarine-hydrothermal vents. Here we describe putative fossilized microorganisms that are at least 3,770 million and possibly 4,280 million years old in ferruginous sedimentary rocks, interpreted as seafloor-hydrothermal vent-related precipitates, from the Nuvvuagittuq belt in Quebec, Canada. These structures occur as micrometre-scale haematite tubes and filaments with morphologies and mineral assemblages similar to those of filamentous microorganisms from modern hydrothermal vent precipitates and analogous microfossils in younger rocks. The Nuvvuagittuq rocks contain isotopically light carbon in carbonate and carbonaceous material, which occurs as graphitic inclusions in diagenetic carbonate rosettes, apatite blades intergrown among carbonate rosettes and magnetite–haematite granules, and is associated with carbonate in direct contact with the putative microfossils. Collectively, these observations are consistent with an oxidized biomass and provide evidence for biological activity in submarine-hydrothermal environments more than 3,770 million years ago.

Four-Hundred-and-Ninety-Million-Year Record of Bacteriogenic Iron Oxide Precipitation at Sea-Floor Hydrothermal Vents

Fe oxide deposits are commonly found at hydrothermal vent sites at mid-ocean ridge and back-arc sea floor spreading centers, seamounts associated with these spreading centers, and intra-plate seamounts, and can cover extensive areas of the seafloor. These deposits can be attributed to several abiogenic processes and commonly contain micron-scale filamentous textures. Some filaments are cylindrical casts of Fe oxyhydroxides formed around bacterial cells and are thus unquestionably biogenic. The filaments have distinctive morphologies very like structures formed by neutrophilic Fe oxidizing bacteria. It is becoming increasingly apparent that Fe oxidizing bacteria have a significant role in the formation of Fe oxide deposits at marine hydrothermal vents. The presence of Fe oxide filaments in Fe oxides is thus of great potential as a biomarker for Fe oxidizing bacteria in modern and ancient marine hydrothermal vent deposits. The ancient analogues of modern deep-sea hydrothermal Fe oxide deposits are jaspers. A number of jaspers, ranging in age from the early Ordovician to late Eocene, contain abundant Fe oxide filamentous textures with a wide variety of morphologies. Some of these filaments are like structures formed by modern Fe oxidizing bacteria. Together with new data from the modern TAG site, we show that there is direct evidence for bacteriogenic Fe oxide precipitation at marine hydrothermal vent sites for at least the last 490 Ma of the Phanerozoic.

New perspectives on the ecology and evolution of siboglinid tubeworms

Siboglinids are tube-dweling annelids that are important members of deep-sea chemosynthetic communities, which include hydrothermal vents, cold seeps, whale falls and reduced sediments. As adults, they lack a functional digestive system and rely on microbial endosymbionts for their energetic needs. Recent years have seen a revolution in our understanding of these fascinating worms. Molecular systematic methods now place these animals, formerly known as the phyla Pogonophora and Vestimentifera, within the polychaete clade Siboglinidae. Furthermore, an entirely new radiation of siboglinids, Osedax, has just recently been discovered living on whale bones. The unique and intricate evolutionary association of siboglinids with both geology, in the formation of spreading centres and seeps, and biology with the evolution of large whales, offers opportunities for studies of vicariant evolution and the calibration of molecular clocks. Moreover, new advances in our knowledge of siboglinid anatomy coupled with molecular characterization of microbial symbiont communities are revolutionizing our knowledge of host-symbiont relationships in the Metazoa. Despite these advances, considerable debate persists concerning the evolutionary history of siboglinids. Here we review the morphological, molecular, ecological and fossil data in order to address when and how siboglinids evolved. We discuss the role of ecological conditions in the evolution of siboglinids and present possible scenarios of the evolutionary origin of the symbiotic relationships between siboglinids and their endosymbiotic bacteria.

Early Jurassic hydrothermal vent community from the Franciscan Complex, San Rafael Mountains, California

The Figueroa massive sulfide deposit, located in Franciscan Complex rocks in the San Rafael Mountains of California, preserves the only known Jurassic hydrothermal vent fossils. The Figueroa fossil assemblage is specimen rich but of low diversity and comprises, in order of decreasing abundance, vestimentiferan worm tubes, the rhynchonellid brachiopod Anarhynchia cf. gabbi and a species of ?nododelphinulid gastropod. The Figueroa fossil organisms lived at a deep-water, high-temperature vent site located on a mid-ocean ridge or seamount at an equatorial latitude. The fossil vent site was then translated northwestward by the motion of the Farallon plate and was subsequently accreted to its present location. An iron-silica exhalite bed, the probable lateral equivalent of the Figueroa deposit, contains abundant filamentous microfossils with two distinct morphologies and probably represents a lower-temperature, diffuse-flow environment. The Figueroa fossil community was subject to the same environmental conditions as modern vent communities, but it is unique among modern and other fossil vent communities in having rhynchonellid brachiopods.

Two Palaeozoic Hydrothermal Vent Communities from the Southern Ural Mountains, Russia

The Sibay and Yaman Kasy massive sulphide deposits contain macrofossil assemblages that represent some of the oldest known hydrothermal vent communities. The deposits are hosted respectively by Middle Devonian and Silurian arc-related volcanic rocks in the Ural Mountains of Russia, and formed under the same environmental constraints as modern vent sulphides. The Sibay palaeocommunity comprises, in order of decreasing abundance, tubes of an indeterminate ?annelid and the vestimentiferan Tevidestus serrriformis Shpanskaya, Maslennikov and Little and articulated specimens of the modiomorphid bivalve Sibaya ivanovi gen. et sp. nov. The Yaman Kasy palaeocommunity comprises, in order of decreasing abundance, tubes of the ?polychaete Eoalvinellodes annulatus gen. et sp. nov. and the vestimentiferan Yamankasia rifeia Shpanskaya, Maslennikov and Little, and specimens of the ?kirengellid tergomyan Themoconus shadlunae gen. et sp. nov., the lingulate brachiopod Pyrodiscus lorrainae gen. et sp. nov., an indeterminate vetigastropod, and the ambonychiid bivalve Mytilarca sp. Some of these taxa have affinities to endemic taxa at modern hydrothermal vent sites and some belong to taxa that are typical of Palaeozoic non-vent marine palaeocommunities. Therefore, there has been movement of taxonomic groups in and out of the vent ecosystem through the Phanerozoic.

Late Cretaceous hydrothermal vent communities from the Troodos ophiolite, Cyprus

The Kinousa, Memi, Kambia, Kapedhes, and Sha massive sulfide deposits located in the Troodos ophiolite, Cyprus, contain fossils from Late Cretaceous hydrothermal vent communities that lived on a spreading ridge above a subduction zone in the Neotethys ocean. The Troodos vent fossils provide unequivocal evidence for the exhalative origin of the host massive sulfide deposits, including those that are now located deep within the lava pile. The fossil vent assemblages are of low diversity; they contain numerous vestimentiferan worm tubes, uncommon cerithioid and epitoniid gastropods, and rare (?)serpulid worm tubes. Among the reported modern and ancient vent communities the presence of epitoniid gastropods is unique to Cyprus. At least three of the Troodos vent communities were living on the sea floor around the same time and were as closely spaced as vent communities on modern fast-spreading ridges. Together with slightly older vent worm tubes from the Semail ophiolite of Oman, currently 2500 km from Cyprus, the Troodos fossils show that hydrothermal vent communities were present in the Neotethys ocean from the Cenomanian to the Turonian, a time span of ∼5 m.y.

EARLY JURASSIC HYDROTHERMAL VENT COMMUNITY FROM THE FRANCISCAN COMPLEX, CALIFORNIA

Abstract The Figueroa sulfide deposit located in Franciscan Complex rocks in the San Rafael Mountains, California, contains the only known Jurassic hydrothermal vent community. Based on radiolarian biostratigraphy it is Pliensbachian (early Jurassic) in age. The Figueroa fossil organisms lived at a deepwater, high temperature vent site located on a mid-ocean ridge or seamount at an equatorial latitude. The vent site was then translated northeastward by the motion of the Farallon Plate and was subsequently accreted to its present location. The vent fossils are preserved as molds of pyrite and there is no remaining shell or tube material. The fossil assemblage is specimen rich, but of low diversity, and comprises, in order of decreasing abundance, vestimentiferan worm tubes, rhynchonellide brachiopods (Anarhynchia cf. gabbi), and trochoidean gastropods (Francisciconcha maslennikovi new genus and species). These fossils represent only primary consuming organisms, some of which may have had chemosynthetic microbial endosymbionts, like many modern dominant vent animals. The Figueroa vent assemblage shares vestimentiferan tube worms and gastropods with other fossil and modern vent communities, but is unique in having rhynchonellide brachiopods. It shares this feature with contemporary Mesozoic cold seep communities. Many other taxonomic groups found at modern vent sites are missing from the Figueroa assemblage. The presence of vestimentiferan tube worm fossils in the Figueroa deposit is at odds with the supposed time of origin of the modern vestimentiferans (∼100 Ma), based on molecular data.