Molecular records of the Triassic-Jurassic and the early Toarcian climate events at the land-sea interface

The Triassic-Jurassic boundary (TJB) and the early Toarcian are characterized by greenhouse warming, caused by the emplacement of large volcanic provinces. Despite similar trigger mechanisms, the two events differ in their character. Most significantly, the early Toarcian records the genesis of an Oceanic Anoxic Event (T-OAE), while the TJB event lacks robust evidence for widespread marine anoxia and organic matter (OM) accumulation.

Here, we present bulk, isotope, and molecular geochemical data from a continuous drill core, taken in the northeastern part of the North-German Basin that spans upmost Triassic and Lower Jurassic strata (Rhaetian-Toarcian). The sediment archive represents a near-shore environment, proximal to an estuary. This setting at the land-sea-interface was particularly susceptible to sealevel, climate, and environmental change and records the response of a shallow marine environment to major Late Triassic-Early Jurassic climate events.

In contrast to the predominantly OM-lean Triassic-Jurassic strata, the TJB interval and the T-OAE are characterized by increased OM contents, but their compositions differ significantly. At the TJB, increased abundances of soil and land plant OM accumulated under semi-arid conditions in mesosaline and well-oxygenated shallow marine setting. By contrast, during the T-OAE, OM-rich sediments accumulated under short-lived anoxic-euxinic conditions. Development of oxygen-deficient conditions was favored by a high sea level and persistent freshwater stratification caused by enhanced riverine discharge under humid climate conditions. Land plant wax lipid, algal molecular fossils, and wildfire combustion residues further revealed that the TJB and the T-OAE were accompanied by substantial changes in both the continental and marine ecosystems.