Late Triassic to Early Jurassic carbon isotope stratigraphy and organo-facies evolution in a basin-margin transect of the North German Basin

Profound climatic and environmental changes at variable timescales are documented throughout the Late Triassic to Early Jurassic (c. 210-170 Ma) and were linked to the emplacement of large igneous provinces, tectonic processes, as well as transient climate fluctuations. Climate and environmental change triggered bio- and geosphere evolution, and impacted on sedimentary archives of marine and terrestrial basins. Most severe environmental change events, involving global carbon cycle and ecosystem perturbations, occurred at Triassic-Jurassic boundary (TJB; c. 201 Ma) and during the early Toarcian Oceanic Anoxic Event (T-OAE, c. 182 Ma).

We here discuss the differential response of depositional settings and organo-facies towards secular and transient environmental change along a basin-margin transect of the NW European Epicontinental Seaway (North German Basin), an expanded and intensively structured shallow shelf sea.

Stable carbon isotope values (d¹³C_org) revealed diagnostic trends that allow the precise intercorrelation along the transect, as well as correlation with far-apart sites. The TJB and the T-OAE are indicated by prominent negative carbon isotope excursions.

Programmed pyrolysis data indicate spatio-temporal organo-facies trends that on a temporal scale occurred in response to changes in deposition, such as climate and sea level evolution, while spatial pattern reflect basin morphology and paleobathymetry. Marine organic matter is best preserved at anoxic basinal sites, while marginal settings received increased land plant contributions and/or experienced more intense oxic degradation of marine organic matter. Substantial TOC accumulations occurred only in association with the T-OAE during high sea level and were most continuous at basinal sites.