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A major sea-level drop briefly precedes the Toarcian oceanic anoxic event: implication for Early Jurassic climate and carbon cycle.

ABSTRACT: Sea-level change is an important parameter controlling the expansion of oxygen-depleted conditions in neritic settings during oceanic anoxic events (OAEs). Despite this fundamental role, it remains on a short timescale (<1?Myr) one of the least constrained parameters for numerous OAEs. Here we present sedimentological and geochemical evidence from Morocco and East Greenland showing that a forced regression shortly precedes (ca.10² kyr) the major transgression associated with the Toarcian OAE. The forced regression can be correlated over distances greater than 3000?km in numerous Tethyan and Boreal basins, indicating that the relative sea-level change was driven by eustastic fluctuations. The major amplitude (>50?m) and short duration of the forced regression suggests that it was most likely related to the transient waxing and waning of polar ice sheet. We suggest that this short-lived glaciation might have a genetic link with the inception of the Toarcian OAE. Indeed, during the deglaciation and the accompanying sea-level rise, the thawing permafrost may have released important quantities of methane into the atmosphere that would have contributed to the Toarcian OAE rapid warming and its characteristic negative carbon isotope excursion. This study offers a hypothesis on how some hyperthermal events might be rooted in short-lived "cold-snap" episodes.

SUBMITTER: Krencker FN

PROVIDER: S-EPMC6715628 | biostudies-literature | 2019 Aug

REPOSITORIES: biostudies-literature

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A major sea-level drop briefly precedes the Toarcian oceanic anoxic event: implication for Early Jurassic climate and carbon cycle.

Krencker François-Nicolas FN Lindström Sofie S Bodin Stéphane S

Scientific reports 20190829 1

Sea-level change is an important parameter controlling the expansion of oxygen-depleted conditions in neritic settings during oceanic anoxic events (OAEs). Despite this fundamental role, it remains on a short timescale (<1 Myr) one of the least constrained parameters for numerous OAEs. Here we present sedimentological and geochemical evidence from Morocco and East Greenland showing that a forced regression shortly precedes (ca.10<sup>2</sup> kyr) the major transgression associated with the Toarc ...[more]

PMID: 31467345

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Project description:The Toarcian Oceanic Anoxic Event (TOAE; Early Jurassic, ca. 182 Ma ago) represents one of the major environmental disturbances of the Mesozoic and is associated with global warming, widespread anoxia, and a severe perturbation of the global carbon cycle. Warming-related dysoxia-anoxia has long been considered the main cause of elevated marine extinction rates, although extinctions have been recorded also in environments without evidence for deoxygenation. We addressed the role of warming and disturbance of the carbon cycle in an oxygenated habitat in the Iberian Basin, Spain, by correlating high resolution quantitative faunal occurrences of early Toarcian benthic marine invertebrates with geochemical proxy data (δ18O and δ13C). We find that temperature, as derived from the δ18O record of shells, is significantly correlated with taxonomic and functional diversity and ecological composition, whereas we find no evidence to link carbon cycle variations to the faunal patterns. The local faunal assemblages before and after the TOAE are taxonomically and ecologically distinct. Most ecological change occurred at the onset of the TOAE, synchronous with an increase in water temperatures, and involved declines in multiple diversity metrics, abundance, and biomass. The TOAE interval experienced a complete turnover of brachiopods and a predominance of opportunistic species, which underscores the generality of this pattern recorded elsewhere in the western Tethys Ocean. Ecological instability during the TOAE is indicated by distinct fluctuations in diversity and in the relative abundance of individual modes of life. Local recovery to ecologically stable and diverse post-TOAE faunal assemblages occurred rapidly at the end of the TOAE, synchronous with decreasing water temperatures. Because oxygen-depleted conditions prevailed in many other regions during the TOAE, this study demonstrates that multiple mechanisms can be operating simultaneously with different relative contributions in different parts of the ocean.

Dataset Information

A major sea-level drop briefly precedes the Toarcian oceanic anoxic event: implication for Early Jurassic climate and carbon cycle.

Publications

A major sea-level drop briefly precedes the Toarcian oceanic anoxic event: implication for Early Jurassic climate and carbon cycle.

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