147-3 Investigating the impacts of global vs regional vs local processes on the geological record and sulfur cycling: A case study of the OAE-2 Bonarelli Level, Central Italy

Session:

Poster Booth No.: 170

Presenting Author:

Liam Olden

Authors:

Olden, Liam Jon¹, Karagiannis, Mariana², Zhai, Ruixiang³, Lee, Yun Suk⁴, Lau, Kimberly⁵, Fendley, Isabel M.⁶, Kelley, Brian M.⁷, Freeman, Katherine H.⁸, Macalady, Jennifer L.⁹, Dawson, Kat¹⁰, Meyer, Frances M.¹¹, Webb, Sam¹², International Geobiology Course, 2025¹³, International Geobiology Course, 2024¹⁴, International Geobiology Course, 2023¹⁵

(1) Earth and Planetary Sciences, Johns Hopkins University, BALTIMORE, MD, USA, (2) Marine Science, UC Santa Barbara, Santa Barbara, CA, USA, (3) Earth and Environmental Science, Boston College, Boston, MA, USA, (4) Earth and Environmental Sciences, Seoul National University, Seoul, Korea (The Republic of), (5) Geosciences, Penn State University, State College, PA, USA, (6) Geosciences, Penn State University, University Park, PA, USA, (7) Geosciences, Penn State University, University Park, PA, USA, (8) Geosciences, Penn State Geosciences, University Park, PA, USA, (9) Geosciences, Pennsylvania State University, University Park, PA, USA, (10) Environmental Sciences, Rutgers University, New Brunswick, NJ, USA, (11) Geosciences, Pennsylvania State University, University Park, PA, USA, (12) Stanford Synchrotron Radiation Laboratory, Stanford University, Stanford, CA, USA, (13) International Geobiology Course 2025, State College, PA, USA, (14) International Geobiology Course 2024, State College, PA, USA, (15) International Geobiology Course 2023, State College, PA, USA,

Abstract:

Earth’s climate has fluctuated throughout geological history, with the mid-Cretaceous standing out as an extreme hothouse climate. During this interval, the emplacement of Large Igneous Provinces and their associated release of CO2, and the enhanced supply of weathering-derived nutrients, results in a period of enhanced marine anoxia. The Cretaceous Oceanic Anoxic Event 2 (OAE2), which occurred at the Cenomanian–Turonian boundary (~94 Ma), stands out as a period of intensified marine anoxia. Notably, marine deoxygenation during OAE2 was heterogeneous on a global scale. The proto-North Atlantic region experienced marine anoxia prior to OAE2, whereas other regions, represented by the Tethys Sea, never reached anoxia until the onset of OAE2. The spatial redox heterogeneity is mirrored by a global inconsistency of sulfur isotopic composition of carbonate-associated sulfate (δ³⁴S_CAS): proto-North Atlantic δ³⁴S_CAS values of 10‰ and Tethys Sea δ³⁴S_CAS values range around 18-25‰. This indicates a unique global disequilibrium in the marine sulfate reservoir, highlighting a rare geochemical anomaly in Earth's history.

These raise two key scientific questions: (1) What mechanisms drove the regional differences in ocean redox and sulfur isotopic signature observed during OAE2? (2) Do finer-scale, site-specific variations exist that reveal more localized redox processes or oceanographic constraints?

To address these questions, we combined new petrographic, geochemical and isotopic analyses from two OAE2 sections in central Italy (Visipi Quarry and Furlo) with published data, and developed a new two-box model for the OAE2 sulfur cycle. Through this interdisciplinary approach, we show that these two sections experienced fluctuation between oxic and suboxic-anoxic conditions, and produced smaller Δ³⁴S (pyrite vs CAS) values compared to other sites, implying a lower sulfate concentration. The results of our box model suggest that differences in regional sulfur-bearing species and burial fluxes, lower sulfate concentrations (around 0.5 to 1 mM), and extremely limited mixing between ocean basins collectively contributed to the observed δ³⁴S_CAS disparities and decoupled biogeochemical cycles across ocean basins. This study highlights that even during periods of rapid global climatic changes, local environmental conditions can vary significantly across regions and sites, controlling the development of marine anoxia. Thus, understanding such site-specific responses in the deep past is critical for accurately reconstructing Earth’s climate system and anticipating the heterogeneous impacts of ongoing climate change.

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

doi: 10.1130/abs/2025AM-11067

© Copyright 2025 The Geological Society of America (GSA), all rights reserved.