The end-Triassic Mass Extinction (ETME) was one of the "Big 5" mass extinctions of the Phanerozoic and is thought to have been caused by a series of environmental changes triggered by the emplacement of the Central Atlantic Magmatic Province (CAMP). While the overall driver of the ETME is well-accepted, the specific roles of subsequent environmental changes in driving the extinction remain unresolved due to both spatial and temporal biases within existing geochemical records. Additionally, recent studies suggest that environmental deterioration may have preceded the emplacement of both CAMP and the ETME. Here, we present nitrogen isotope (δ15N) and iron speciation data from a sedimentary succession located in Grotto Creek, Alaska in order track changes in the marine nitrogen cycle and redox across the upper Norian Stage of the Triassic through lower Hettangain Stage of the Jurassic (~215 to 198 million years ago). The geologic succession at Grotto Creek represents deeper water marine deposition in eastern equatorial Panthalassa, likely capturing regional oceanic redox trends. δ15N records from Grotto Creek show a pronounced positive excursion of +3‰ that initiates in the upper Norian, peaks near the Norian-Rhaetian boundary (NRB; ~208.5), and declines through the ETME and into the Hettangian. Throughout this interval, iron speciation data show persistent anoxic conditions and occasional euxinia occurred in the local bottom waters. We propose that the positive δ15N and iron speciation data from Grotto Creek reflect a progressive deoxygenation of the upper water column with the expansion of the equatorial oxygen minimum zone (OMZ). Specifically, the δ15N excursion reflects a shift in the dominant processing of bioavailable nitrogen from uptake and nitrification under oxic conditions to incomplete denitrification followed by complete denitrification as deoxygenation progressed. Records from existing study sites in other regions of the Panthalassa reflect similar redox fluctuations and support that this deoxygenation was a regional phenomenon. Other recent studies of the Late Norian and Rhaetian also document declines in biodiversity that predate the ETME, as well as, carbon isotope excursions, likely reflecting perturbations to the carbon cycle. Together, this evidence suggests that increasingly low-oxygen conditions initiated at least ~8 Ma before the emplacement of CAMP and likely paved the way for the ETME. / Master of Science / The end-Triassic mass extinction (ETME) occurred ~ 201 million years ago and was associated with a large drop in global diversity. The extinction is thought to be due to a warming climate resulting from greenhouse gasses released during the eruption of the Central Atlantic Magmatic Province (CAMP). Although the ETME is one of the largest extinction events of the last ~500 million years, the environmental changes leading to the extinction, and before the CAMP eruption, are not well understood. We studied the Grotto Creek section in Alaska which is a sequence of sedimentary rocks that record the deep ocean environment from the ancient Panthalassa or Paleo-Pacific Ocean. This section also provides a relatively complete record of the time before, during, and after the ETME. Here, we present the stable isotopes of nitrogen (δ15N) from these rocks that show disturbances to the nitrogen cycling that occurred in the ocean more than ~ 8 million years before the ETME. We show that δ15N and iron data from Grotto Creek document falling ocean oxygen levels before the ETME. We also find that our δ15N agrees with other environmental proxies that also reflect declining oxygen levels in the oceans along with decreases in marine animal diversity well before the ETME. These geochemical records help to show a more complete picture of how environments changed in the Panthalassa before the ETME

The end–Triassic mass extinction event (ca. 201 Myr ago) has received particular attention over recent decades since Sepkoski (1981) classified it as one of the ‘‘big five’’ biotic crises in Earth's history. In the geological record of Greenland and Sweden, 80% of the species of terrestrial plants disappeared at this boundary. In the last two centuries, Triassic–Jurassic plant remains from Skåne, southern Sweden, have been collected, curated, and studied. However, the paleoflora from the lowermost part of the Helsingborg Member (Lower Jurassic: Hettangian) is poorly understood. Here, a taxonomic study is presented of two novel plant assemblages collected from the Boserup beds (basal Hettangian) in NorraAlbert Quarry, Skåne. The exposures in Skåne are among the few localities in the world that record the terrestrial ecosystem aftermath of the end–Triassic extinction event. Plant macrofossils were studied using macrophotography and fluorescence microscopy. The flora is composed of sphenophytes(Neocalamites), ferns (Cladophlebis, Eboracia), ginkgophytes (Czekanowskia, Pseudotorellia,Ginkgoites), and conifers (Pityophyllum, Brachyphyllum). These earliest Jurassic assemblages were deposited in floodplain environments and revealed a relatively low diversity of flora in the aftermath of the end-Triassic extinction but a fast recovery later. Additionally, the flora was compared with the relative lowermost Jurassic beds in East Greenland, Poland, and Germany, disclosing that ginkgophytes were widely distributed across the northern region of Pangea.

The End-Triassic Extinction (ETE) has long remained one of the lesser known among the so-called “Big Five”. There exist several hypotheses regarding the probable cause of this extinction, which can mainly be divided into  events of  a decline in the rate of diversification  in the late Triassic contra a sudden and significant extinction event. Primary amongst the sudden events is the one of outgassing and climate/environmental change induced by Central Atlantic Magmatic Province (CAMP) volcanism. This  study  aims to  describe  the ETE using  fluvial, lacustrine, deltaic  and  marginal-marine  microbial sedimentary  structures (MS), carbonatized microbial mats (CMM) as well as  wrinkle structures, microbially  induced  sedimentary  structures (MISS) from the latest  Triassic-  earliest  Jurassic  (TJB: Triassic-Jurassic boundary interval, Rhaetian to Hettangian) of Skåne, Southern Sweden. The MISS in these sites show a high diversity of structures, indicating microbial communities with high diversity in an environment usually dominated by bioturbating invertebrates. We observed structures that include top-surface (“Elephant skin”) and subsurface (“Kinneyia”) structures, carbon-rich fossilized microbial mats, microbial sideritic concretions, sideritized microbial mats, stromatolite-like layers and oncoids. Scanning Electron Microscopy (SEM) sampling also revealed structures related to the presence of both coccoidal and filamentous cyanobacteria.  Overall,  the diversity in observed structures indicate a thriving microbial community, with diversified and abundant ichnofossils or body fossils of possible bioturbators only observed in the early Rhaetian and younger Mid-Late Hettangian samples of deltaic or marginal-marine affinities. The lack of metazoan communities to such an extent indicates that the local environment could have reversed to a pre-Substrate Revolution state. The occurrence of abundant and  diversified  microbial structures in the studied  TJB  section,  representing  a relatively  short time interval, reflects anachronistic facies and development of abnormal biota. This supports the occurrence of several environmental distresses (abnormal hydrochemical and physical conditions) on the Triassic-Jurassic boundary interval, in turn lending credence to the hypothesis of an abrupt climactic event such as possibly that of CAMP volcanism. / <p>Presentation was carried out online over zoom due to the at the time ongoing COVID-19 pandemic.</p> / Resurrecting a lost world in Skåne: new light on the end-Triassic mass extinction and the origin of the dinosaur dominated ecosystem / Dinosaur grave from Skåne: microbiology, taphonomy and paleomolecules of exceptionally preserved theropod remains