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1561095 ADELAIDE GEOSYNCLINE -- GEOLOGY
NEARSHORE ENVIRONMENTS BEFORE THE EVOLUTION OF LAND PLANTS;
B.O’Connell, M.W.Wallace, A.S.Hood, M.A.Lechte and E.M.Mahon (Melbourne Univ; McGill Univ)..
PRECAMBRIAN RESEARCH v.382, Nov. 2022. (ISSN 0301-9268; Article no.106883)
The long-term evolution of the biosphere has caused fundamental shifts in environmental conditions and sedimentation at Earth’s surface. While effects of the evolution of terrestrial vegetation on river systems have been explored in detail, facies models and possible shifts in sedimentation in pre-vegetation nearshore marine settings have not been sufficiently explored. The circa 800-million-year-old Burra Group, exposed in the Adelaide Fold Belt of South Australia, is a terrestrial to nearshore transgressive sedimentary succession associated with rifting. The Burra Group provides a record of marginal and shallow marine environments before the evolution of land plants. Environments are interpreted to record deposition in low energy fine-grained tidal flat, lagoon, tidal inlet, and beach-barrier environments (a beach-barrier system). The thick mudflats (up to 30 m) of the studied units indicate that vegetation is not essential for mudflat accumulation, contrary to some models. The fluvial-marine transition and the back-barrier-tidal inlet-beach-barrier transition is highly regular and there is little interbedding of units. The Tonian beach-barriers of the Burra Group do not backstep into the back-barrier region and aggrade much like stable modern systems backed by peat. These observations are suggestive of a stable barrier system in the absence of land plants. The high mud percentage and/or early carbonate cementation (including microbialite and stromatolite deposition during transgression) may have contributed to the stability of this beach-barrier system. (c2022 Elsevier B.V.)
1561096 ADRIATIC PLATFORM -- GEOLOGY
NEW CONSTRAINTS ON THE PETM RECORD IN SHALLOW-MARINE CARBONATES FROM THE ADRIATIC CARBONATE PLATFORM, NE ITALY;
M.Sabbatino, M.Franceschi, J.Dell'Anno, G.Frijia, L.Consorti, E.Petranich, N.Barago, A.Corradetti, S.Covelli et al. (Trieste Univ)..
21ST INTERNATIONAL SEDIMENTOLOGICAL CONGRESS [ISC] (Beijing, China, 8/22-26/2022) ABSTRACT BOOK pp.184-185, 2022. (Available at http://www.isc2022.org.cn as of 9/22/2022; Abstract only)
The Paleocene-Eocene Thermal Maximum (PETM; ca 56 Ma) was an interval of extreme transient climate change, associated with global warming and a massive perturbation of the global carbon cycle (e.g., Zachos et al., 2003). This latter is testified by a sharp Negative Carbon Isotope Excursion (N-CIE) in the global marine and terrestrial d13C records, linked to the injection of large volumes of isotopically light carbon into the ocean-atmosphere system. The source of such 13C-depleted carbon is still a matter of debate. The emplacement of the North Atlantic Igneous Province (NAIP) with the release of huge amounts of CO2 is suspected to be one of the factors that may have caused such a relevant change in the composition of the atmosphere/ocean carbon reservoirs and the associated abrupt climate perturbation. Research is increasingly exploring mercury (Hg) anomalies as tracers of volcanism during the Paleocene-Eocene interval mostly in deep-water and subordinately in shallow-water settings (e.g., Tremblin et al., 2022 and references therein), arguing about their possible relationship to the NAIP emplacement and its impact on the PETM onset and duration. The aim of this contribution is to present an integrated study of sedimentology, stratigraphy (bio and chemo), and geochemistry of the deposits belonging to the Adriatic Carbonate Platform cropping out in the Classical Karst area of Friuli Region (NE Italy), encompassing the PETM event. In particular, here we show paired new carbon- and oxygen-isotope data combined with Hg concentrations and TOC analyses from two shallow-water marine carbonate sections across the Paleocene-Eocene boundary. The two investigated sections were deposited during the migration of the foreland basin related to the Dinaric orogeny and are today exposed in the Classical Karst area near Trieste (Italy) for about 50 and 300 meters, respectively, of Paleocene-Eocene platform carbonates evolving upward to hemipelagic marls and then to siliciclastic deposits. Vertical facies evolution of the carbonate platform indicates that an initial inner- to mid-ramp setting underwent a relative deepening and then was followed by multiple emersion episodes intercalated by proximal marine deposition (i.e., innermost to inner ramp environments). This latter was followed by a return to open marine facies which then persisted until the final drowning of the Adriatic platform that in our study area occurred in the late early Eocene. Our results show in both sections a negative excursion in the carbon-isotope record that, associated with biostratigraphic data, can be correlated with the PETM N-CIE and is comparable to other coeval d13C records, both in shape and amplitude.
