Terrestrial records of the early Albian Ocean Anoxic Event: Evidence from the Fuxin lacustrine basin, NE China

Abstract

The early Albian Oceanic Anoxic Event 1b (OAE 1b) is well documented in the Tethys, Pacific and North Atlantic, but few studies have evaluated whether or not terrestrial records of OAE 1b exist. In order to identify terrestrial records of the early Albian OAE 1b and to infer possible driving mechanisms, an integrated multi-proxy study from the late Aptian to Albian in the Fuxin lacustrine basin was conducted, including thick, organic-rich black mudstones, total organic carbon (TOC), organic carbon isotopes (δ13Corg), mercury concentration (Hg) and results from pyrolysis analyses (S2, Tmax and HI). Results show three distinct short-term negative δ13Corg excursions corresponding with relatively high TOC values, which could be counterparts of the Kilian, Paquier and Leenhardt sub-events of the early Albian OAE 1b. Atmospheric CO2 concentration (pCO2) recovered from C3 plant δ13Corg compositions indicates an increasing trend in Unit C during the early Albian, and there are three short-term increases of pCO2 corresponding to the three sub-events of OAE 1b at this time interval. We infer that a trend of increasing pCO2 during the Kilian sub-event in the study area is closely related to volcanism. Continental weathering calculated using chemical weathering indices (CIA, WIP and MIA(O)) show an increasing trend during the OAE 1b interval, likely resulting from warmer and more humid conditions. Mixed sources of terrestrial plants and lacustrine plankton demonstrated by pyrolysis analyses (HI vs. Tmax and S2 vs. TOC), indicate a terrestrial contribution to the organic-rich sediments of the Kilian, Paquier and Leenhardt sub-events of OAE 1b. We suggest that a CO2-forced greenhouse effect during the early Albian might have triggered the relatively warm and humid palaeoclimatic conditions, and intensified chemical weathering that combined to create high nutrient and organic matter levels that were flushed into lakes contributing to eutrophication and anoxia in lacustrine and in contemporaneous oceanic systems.