66-7 IMPACT OF EARLY APTIAN OCEANIC ANOXIA ON ECOSYSTEMS FROM THE GARGANO PROMONTORY: GEOCHEMICAL AND MICROFACIES EVIDENCE

Session: Environmental Instability During Greenhouse Periods: Impact on Terrestrial and Marine Ecosystems (Posters)

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Abstract:

Carbonate rock series in the Gargano promontory preserve the record of the Apulian Carbona Platform evolution during the Early Cretaceous. Previous works  reported that global oceanic anoxia driven by a warmer climate and marine volcanism is present in these layers, as evidenced by large shifts in isotope geochemical signatures, and the destabilization or local extinction of faunal groups. In particular major and minor changes in carbon isotope composition of carbonates help identify the Oceanic Anoxic Event (OAE)1a within these Aptian sequences.

The goal of this study is to better understand the evolution of carbonate-producing ecosystems during this period of instability within the Gargano Promontory successions.  Two localities at San Giovanni Rotondo and Borgo Cerano are considered to better understand the timing and intensity of the impact of the OAE1a regionally. To identify the OAE1a signal in multiple localities we documented a strong negative shifts in δ¹³C values as well as the changeover in fossil content within the carbonate platform. Moreover X-Ray Fluorescence geochemical data permit to trace periods of paleoenvironmental instability when nutrient and/or detrital input changed.

Our data a sharp decline in local biodiversity associated with a strong negative spike (C3 segment of Menegatti et al., 1998) and a positive pulse (C4 segment) in δ¹³C values, which is paired with an expansion of opportunistic Chondrodonta populations. The appearance and expansion of Chondrodonta and Bacinella-Lithocodium after a dramatic reduction of fauna has taken place suggests a niche vacuum was created during this period. This period is followed by a relatively fast recovery of benthic ecosystems, that was associated with a lower sea level leading to occasional subaerial exposure under a warmer climate interpreted from strata-top dolomitization and sharp increase in magnesium content (San Giovanni Rotondo and Borgo Cerano sections). Elemental geochemical data indicate that no major paleoenvironmental changes occurred during the studied interval: trends in phosphorus and titanium contents are rather flat during the OAE1a with only a minor increase after the δ¹³C negative spike at the base of the event (C3 segment). We conclude that ecosystems now preserved in the carbonate platform deposits of the former Apulian Platform adapted and survived to the OAE1a because paleoenvironmental perturbations were not intense enough to strongly affect their resilience.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-9731

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