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GEOCHEMICAL VARIATIONS ACROSS THE JURASSIC/CRETACEOUS BOUNDARY IN CENTRAL MEXICO. INSIGHTS FOR CORRELATION WITH TETHYAN AREAS.
Journal of South American Earth Sciences ( IF 1.7 ) Pub Date : 2020-04-01 , DOI: 10.1016/j.jsames.2020.102521
Ricardo Barragán , Rafael López-Martínez , Bruno Chávez-Vergara , Fernando Núñez-Useche , Hugo Salgado-Garrido , Agustín Merino

Abstract A multiproxy study of a 29 m-thick carbonate succession in the Apulco area, Puebla State in central Mexico including pyrite framboids, δ13Ccarb, δ18Ocarb, Total Inorganic Carbon (TIC), Total Organic Carbon (TOC) and Organic Matter (OM), reveals minor geochemical changes across the Jurassic/Cretaceous boundary. Anoxic bottom conditions during the Tithonian were registered by high values of TOC and OM, and low values of δ13Ccarb and TIC. Near the Jurassic/Cretaceous boundary, signatures of all measured proxies changed drastically due to processes related with the organic matter preservation in the basin. These changes can be associated with the late Tithonian sea level drop and paleoclimatic variations passing from dry to semi-arid conditions. Otherwise, on late early to late Berriasian facies, values of all proxies tend to the stabilization indicating more oxygenated bottom conditions. The δ13Ccarb goes to positive values while δ18Ocarb and TIC remain constant, the organic matter and total organic carbon decrease to the lowest values. The geochemical behavior of the Apulco section is similar to those reported from other Tethyan sections as Brodno and DSDP 534A and can be preliminary correlated by its chemostratigraphic signal. Additionally, a central age of 141.65 Ma (87Sr/86Sr) in the very base of the calpionellid Elliptica Subzone strengthens the calpionellid biostratigraphic framework for Mexican sections.

中文翻译:

墨西哥中部侏罗纪/白垩纪边界的地球化学变化。与特提斯地区相关性的见解。

摘要 对墨西哥中部普埃布拉州 Apulco 地区 29 m 厚碳酸盐岩层序的多重代理研究,包括黄铁矿小枝状体、δ13Ccarb、δ18Ocarb、总无机碳 (TIC)、总有机碳 (TOC) 和有机质 (OM),揭示了侏罗纪/白垩纪边界的微小地球化学变化。Tithonian 期间的缺氧底部条件由 TOC 和 OM 的高值以及δ13Ccarb 和 TIC 的低值记录。在侏罗纪/白垩纪边界附近,由于与盆地有机质保存相关的过程,所有测量代理的特征都发生了巨大变化。这些变化可能与提通阶晚期的海平面下降和从干燥到半干旱条件的古气候变化有关。否则,在晚早到晚贝里亚斯相,所有代理的值都趋于稳定,表明底部氧化程度更高。δ13​​Ccarb 为正值,而 δ18Ocarb 和 TIC 保持不变,有机质和总有机碳降至最低值。Apulco 剖面的地球化学行为类似于其他特提斯剖面(如 Brodno 和 DSDP 534A)的地球化学行为,可以通过其化学地层学信号初步关联。此外,位于 calpionellid Elliptica Subzone 底部的 141.65 Ma (87Sr/86Sr) 的中心年龄加强了墨西哥剖面的 calpionellid 生物地层框架。Apulco 剖面的地球化学行为类似于其他特提斯剖面(如 Brodno 和 DSDP 534A)的地球化学行为,可以通过其化学地层学信号初步关联。此外,位于 calpionellid Elliptica Subzone 底部的 141.65 Ma (87Sr/86Sr) 的中心年龄加强了墨西哥剖面的 calpionellid 生物地层框架。Apulco 剖面的地球化学行为类似于其他特提斯剖面(如 Brodno 和 DSDP 534A)的地球化学行为,可以通过其化学地层学信号初步关联。此外,位于 calpionellid Elliptica Subzone 底部的 141.65 Ma (87Sr/86Sr) 的中心年龄加强了墨西哥剖面的 calpionellid 生物地层框架。
更新日期:2020-04-01
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