The Middle Eocene Climatic Optimum (MECO) represents a short-lived interval of global warming that disrupted the long-term cooling episode extending from the middle to late Eocene time. Biostratigraphically the MECO corresponds to the upper interval of planktic foraminiferal zones E11–E12 and the shallow benthic zone 17. Both the planktic and benthic foraminiferal zones are well-documented within the Bartonian mixed siliciclastic‑carbonate sequence of the Kutch Basin in western India. This case study aims to investigate the impact of MECO on the endobenthic community using ichnology as a proxy. The studied sequence comprises the underlying Harudi Formation, consisting of the marine green and grey shale and bioclastic limestone beds, and the overlying Fulra Limestone characterized by benthic foraminifera-rich limestones. The Harudi Formation is bereft of trace fossils except in one bioturbated firmground and two bioeroded hardground horizons. The MECO corresponds to the thin carbonate packstone, the middle green shale, and the rudstone occurring at the middle to upper part of the Harudi succession, established earlier by a concurrent negative δC isotopic excursion. The shelly limestone or bivalve coquina bed deposited immediately prior to the beginning of the MECO consists of a monospecific firmground ichnofabric characterized by . Out of two bioeroded beds, the lower one coincides with the earliest MECO interval and is marked by a brown carbonate hardground colonized with two ichnospecies of . The upper bioeroded horizon corresponding to the end of the MECO is characterized by a series of top- and side-bioeroded (with , , and ) carbonate nodules containing multigenerational septarian cracks. The upper hardground demarcates the top of the coquina bed and the starkest basin-wide sediment starvation, making it a major condensed horizon that developed following a steady glacio-eustatic rise during the warming event. The MECO prompted the subsequent deposition of shallow-marine platform carbonates of the Fulra Limestone by accelerating a sharp rise in the sea-level and proliferation of diverse Larger Benthic Foraminifera in a warm oligotrophic seawater.

中文翻译：

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印度卡奇盆地巴托阶沉积物对中始新世气候最适期 (MECO) 的技术响应

中始新世气候最佳期（MECO）代表了全球变暖的短暂时期，它扰乱了从始新世中期到晚期的长期降温过程。在生物地层学上，MECO 对应于浮游有孔虫区 E11-E12 的上层区间和浅底栖区 17。浮游和底栖有孔虫区在印度西部卡奇盆地的巴顿期混合硅质碎屑-碳酸盐层序中都有详细记录。本案例研究旨在以植物学为代表，调查 MECO 对底栖生物群落的影响。研究的序列包括下面的 Harudi 组，由海洋绿色和灰色页岩和生物碎屑石灰岩层组成，以及上覆的 Fulra 石灰岩，其特征是富含底栖有孔虫的石灰岩。除了一处生物扰动的硬地层和两处生物侵蚀的硬地层外，哈鲁迪地层没有任何痕迹化石。 MECO 对应于 Harudi 序列中上部出现的薄层碳酸盐堆积岩、中部绿色页岩和铁岩，早期由同时发生的负 δ13C 同位素漂移确定。在 MECO 开始之前沉积的贝壳石灰岩或双壳贝壳灰岩床由单一特定的坚固地基织物组成，其特征为 。在两个生物侵蚀床中，较低的一个与最早的 MECO 间隔一致，并以棕色碳酸盐硬地为标志，上面栖息着两种物种。对应于 MECO 末端的上部生物侵蚀层的特征是一系列顶部和侧面生物侵蚀（带有 、 和 ）碳酸盐结核，其中包含多代隔膜裂缝。上部硬地层界定了贝壳灰岩床的顶部和最严重的盆地范围沉积物匮乏，使其成为在变暖事件期间冰川稳定上升后形成的主要凝结层。 MECO加速了海平面的急剧上升和温暖贫营养海水中多种大型底栖有孔虫的增殖，从而促进了富拉石灰岩的浅海平台碳酸盐的随后沉积。