Macroecological patterns of the terrestrial vegetation history during the end-Triassic biotic crisis in the central European Basin: A palynological study of the Bonenburg section (NW-Germany) and its supra-regional implications

The end-Triassic mass extinction is often linked to environmental and climate change triggered by the activity of the Central Atlantic Magmatic Province ca. 201 Mya. In the German Triassic Basin, the transition from pre-extinction to the so-called extinction interval is documented from the fossil-rich Contorta Beds to the mostly barren Triletes Beds. However, despite the lack of macrofossils, plant microfossils are present and studying palynomorph diversity and assemblages still give us a detailed insight into the impact of environmental changes on the flora. Here, we present data from 64 samples taken from the new Triassic-Jurassic section ‘Bonenburgʼ, which originates from a brick quarry in North Rhine-Westphalia (Germany), and encompasses the Triassic–Jurassic transition in the Germanic Basin. Using palynofacies analysis, we document changes in the depositional environment. Based on terrestrial and marine palynological analysis, we also document quantitative changes in four assemblage zones for correlation with other European sections. Further, we discuss the vegetation history with special focus on the transition from the pre-extinction to extinction interval (Contorta to Triletes Beds). Additionally, we investigate palynofloral diversity patterns especially prior to the Triassic-Jurassic transition, to evaluate the ecological impact of environmental upheaval on the flora. Furthermore, we document intraspecific palynomorph variability, indicating a variety of aberrant spore, pollen, and tetrad formation, in the middle Rhaetian, the lowermost upper Rhaetian, and the lowest Hettangian. Our study supports existing paleogeographical reconstructions for the region and reveals, that vegetation underwent gradual changes with intermediate successional stages rather than dramatic extinction or drastic turnover as documented for animals. Diversity patterns coinciding with aberrant palynomorph occurrences, potentially associated with episodes of increased environmental stress, suggest three disturbances pulses of probably increasing severity. Although environmental stress in the context of diversity patterns seems a likely explanation for the occurrence of aberrant palynomorphs, further investigations are needed to better understand the underlying mechanisms and their evolutionary significance and temporal connection with biotic crises

Macroecological patterns of the terrestrial vegetation history during the end-Triassic biotic crisis in the central European Basin: A palynological study of the Bonenburg section (NW-Germany) and its supra-regional implications

The end-Triassic mass extinction is often linked to environmental and climate change triggered by the activity of the Central Atlantic Magmatic Province ca. 201 Mya. In the German Triassic Basin, the transition from pre-extinction to the so-called extinction interval is documented from the fossil-rich Contorta Beds to the mostly barren Triletes Beds. However, despite the lack of macrofossils, plant microfossils are present and studying palynomorph diversity and assemblages still give us a detailed insight into the impact of environmental changes on the flora. Here, we present data from 64 samples taken from the new Triassic-Jurassic section ‘Bonenburgʼ, which originates from a brick quarry in North Rhine-Westphalia (Germany), and encompasses the Triassic–Jurassic transition in the Germanic Basin. Using palynofacies analysis, we document changes in the depositional environment. Based on terrestrial and marine palynological analysis, we also document quantitative changes in four assemblage zones for correlation with other European sections. Further, we discuss the vegetation history with special focus on the transition from the pre-extinction to extinction interval (Contorta to Triletes Beds). Additionally, we investigate palynofloral diversity patterns especially prior to the Triassic-Jurassic transition, to evaluate the ecological impact of environmental upheaval on the flora. Furthermore, we document intraspecific palynomorph variability, indicating a variety of aberrant spore, pollen, and tetrad formation, in the middle Rhaetian, the lowermost upper Rhaetian, and the lowest Hettangian. Our study supports existing paleogeographical reconstructions for the region and reveals, that vegetation underwent gradual changes with intermediate successional stages rather than dramatic extinction or drastic turnover as documented for animals. Diversity patterns coinciding with aberrant palynomorph occurrences, potentially associated with episodes of increased environmental stress, suggest three disturbances pulses of probably increasing severity. Although environmental stress in the context of diversity patterns seems a likely explanation for the occurrence of aberrant palynomorphs, further investigations are needed to better understand the underlying mechanisms and their evolutionary significance and temporal connection with biotic crises

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

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 carbonate-lean 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 climate-controlled weathering regime shift

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

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 carbonate-lean 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 climate-controlled weathering regime shift