TY - JOUR

T1 - A comparative study of total organic carbon-δ13C signatures in the Triassic–Jurassic transitional beds of the Central European Basin and western Tethys shelf seas

AU - Schobben, Martin

AU - Gravendyck, Julia

AU - Mangels, Franziska

AU - Struck, Ulrich

AU - Bussert, Robert

AU - Kürschner, Wolfram M.

AU - Korn, Dieter

AU - Sander, P. Martin

AU - Aberhan, Martin

N1 - Funding information: We acknowledge Joachim Thater of Lucking Ziegelwerke for permission to sample the Bonenburg section. We thank Martin Profft for assistance in faunal sampling and identifications, Michael Mertens for assistance in the field, and Manja Hethke for identification of conchostracans. We are indebted to Ralf Thomas Schmitt and Kathrin Krahn (Museum fur Naturkunde Berlin) for performing the XRF element analysis on the samples. Marianne Falk (MfN, Berlin) is thanked for assistance with the carbon isotope analysis and Mufak S. Naoroz (University of Oslo) for assistance with palynological sample preparation. We are, furthermore, indebted to Thomas Borsch (Botanical Garden and Botanical Museum Berlin) for providing the microscope for palynofloral analysis and Julien Bachelier (Freie Universitât Berlin) for proofreading as well as Martin Blumenberg (Bundesanstalt fur Geowissenschaften und Rohstoffe) and an anonymous reviewer for constructive comments that significantly improved the manuscript. Funding was provided by the LWL-Museum fur Naturkunde, Munster, Germany and by the MfN Innovationsfond (institute internal grant). This project is associated with the DFG Research Unit TERSANE (FOR 2332: Temperaturerelated stressors as a unifying principle in ancient extinctions).

PY - 2019/9/12

Y1 - 2019/9/12

N2 - Stratigraphic studies are an integral component in understanding the chronology of events that led to the end-Triassic mass extinction, by resolving causal relationships between environmental upheavals and biotic response. Successful correlation of Triassic-Jurassic (Tr-J) successions is complicated by the disappearance of macro-fossils that are otherwise central components in stratigraphic studies. This problem is exacerbated in multiple Tr-J sections situated in Europe, where the so-called “Event Beds”-assumed to demarcate the extinction interval are virtually devoid of fossils. An alternative stratigraphic approach entails the reconstruction of carbon isotope records, where stratigraphic fluctuations in carbon isotope composition are considered to track changes in the global biogeochemical carbon cycle. The predominance of carbonatelean sections has prompted the reconstruction of total organic carbon (TOC)-based carbon isotope records. However, bulk rock derived TOC is the diagenetically stabilized remnant of organic components that accumulated on the sea floor, and which can originate from multiple sources. In this study, we assess long-term TOC-based carbon isotope trends at two sites: Bonenburg (Central European Basin) and Kuhjoch (the Tr-J Global Stratotype Section and Point; western Tethys shelf seas). We focus on the TOC 13C-enrichment of the Event Beds with the aim of deciphering stratigraphic fluctuations in relation to their main driver (the exogenic carbon pool versus organic matter source changes). By studying the systematic co-variance of several sedimentary parameters (TOC, total nitrogen [TN], and the palynomorph composition), we infer that the TOC composition is possibly characterized by insignificant organic matter source changes in terms of the marine and terrestrial organic carbon contributions. By contrast, a clay mineralogical shift to more K-depleted minerals as well as the elevated occurrence of wood fragments in the Event Beds suggest a terrestrial organic matter source shift from immature substrates to substrates predominated by “pre-aged” or “fossil organic matter” under a changing continental weathering regime. This outcome urges for reservations when interpreting TOC-based carbon isotope records in terms of global C-cycle perturbations, especially when coinciding with lithological and mineralogical changes. On a more positive note, the shift towards positive carbon isotope values appears to be a recurring feature, possibly testifying to a globally significant climatecontrolled weathering regime shift.

AB - Stratigraphic studies are an integral component in understanding the chronology of events that led to the end-Triassic mass extinction, by resolving causal relationships between environmental upheavals and biotic response. Successful correlation of Triassic-Jurassic (Tr-J) successions is complicated by the disappearance of macro-fossils that are otherwise central components in stratigraphic studies. This problem is exacerbated in multiple Tr-J sections situated in Europe, where the so-called “Event Beds”-assumed to demarcate the extinction interval are virtually devoid of fossils. An alternative stratigraphic approach entails the reconstruction of carbon isotope records, where stratigraphic fluctuations in carbon isotope composition are considered to track changes in the global biogeochemical carbon cycle. The predominance of carbonatelean sections has prompted the reconstruction of total organic carbon (TOC)-based carbon isotope records. However, bulk rock derived TOC is the diagenetically stabilized remnant of organic components that accumulated on the sea floor, and which can originate from multiple sources. In this study, we assess long-term TOC-based carbon isotope trends at two sites: Bonenburg (Central European Basin) and Kuhjoch (the Tr-J Global Stratotype Section and Point; western Tethys shelf seas). We focus on the TOC 13C-enrichment of the Event Beds with the aim of deciphering stratigraphic fluctuations in relation to their main driver (the exogenic carbon pool versus organic matter source changes). By studying the systematic co-variance of several sedimentary parameters (TOC, total nitrogen [TN], and the palynomorph composition), we infer that the TOC composition is possibly characterized by insignificant organic matter source changes in terms of the marine and terrestrial organic carbon contributions. By contrast, a clay mineralogical shift to more K-depleted minerals as well as the elevated occurrence of wood fragments in the Event Beds suggest a terrestrial organic matter source shift from immature substrates to substrates predominated by “pre-aged” or “fossil organic matter” under a changing continental weathering regime. This outcome urges for reservations when interpreting TOC-based carbon isotope records in terms of global C-cycle perturbations, especially when coinciding with lithological and mineralogical changes. On a more positive note, the shift towards positive carbon isotope values appears to be a recurring feature, possibly testifying to a globally significant climatecontrolled weathering regime shift.

KW - Carbon cycle

KW - Chemostratigraphy

KW - Mass extinction

KW - Palynostratigraphy

KW - Weathering

UR - http://www.scopus.com/inward/record.url?scp=85071385375&partnerID=8YFLogxK

U2 - 10.1127/nos/2019/0499

DO - 10.1127/nos/2019/0499

M3 - Article

VL - 52

SP - 461

EP - 486

JO - Newsletters on stratigraphy

JF - Newsletters on stratigraphy

SN - 0078-0421

IS - 4

ER -