Astronomical Pacing of Middle Eocene Sea‐Level Fluctuations: Inferences From Shallow‐Water Carbonate Ramp Deposits

IF 3.2 2区地球科学 Q2 GEOSCIENCES, MULTIDISCIPLINARY

Paleoceanography and Paleoclimatology Pub Date : 2023-11-01 DOI:10.1029/2023pa004633

T. C. Brachert, C. Agnini, C. Gagnaison, J.‐P. Gély, M. J. Henehan, T. Westerhold

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Abstract

Abstract Astrochronologically calibrated deep‐sea records document the Cenozoic (66–0 Ma) global climatic cooling in great detail, but the magnitude of sea‐level fluctuations of the middle Eocene Warmhouse state (47.8–37.7 Ma) and the ∼40.3 Ma warming event of the Middle Eocene Climatic Optimum (MECO) is not well constrained. Here, we present a sequence stratigraphic classification of a shallow marine mixed carbonate—clastic ramp system for this time interval in Paris basin, France. Based on sedimentologic, paleogeographic and biostratigraphic data, we hypothesize that the 22 elementary sequences recognized each correspond to the long cycle of orbital eccentricity (0.405 Myr). With the exception of the MECO, the shoreline trajectory of superimposed, third‐order depositional sequences evolved in phase with the very long cycles of orbital eccentricity (2.4 Myr), suggesting significant polar ice build‐up leading to sea level lowstands during nodes of the very long eccentricity cycle. Inferred from Fischer Plot methodology, Lutetian third‐order eustasy was in the order of 5–10 m and during the MECO 30 m or more. Furthermore, the shallow‐water record implies that third order sea‐level changes were astronomically paced in the middle Eocene Warmhouse climate state, but a decoupling occurred during the transient MECO warming.

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中始新世海平面波动的天文步调:来自浅水碳酸盐斜坡沉积的推论

天文年代学校准的深海记录非常详细地记录了新生代(66-0 Ma)全球气候变冷，但中始新世暖室状态(47.8-37.7 Ma)和中始新世气候优化(MECO)的~ 40.3 Ma变暖事件的海平面波动幅度没有得到很好的约束。本文对法国巴黎盆地这一时期的浅海混合碳酸盐-碎屑斜坡体系进行了层序地层分类。根据沉积学、古地理和生物地层学资料，我们假设22个已识别的基本层序对应于轨道偏心长旋回(0.405 Myr)。除MECO外，叠加的海岸线轨迹，三级沉积序列与轨道偏心旋回(2.4 Myr)相演化，表明在极长偏心旋回的节点期间，显著的极地冰积聚导致海平面低水位。根据Fischer样地方法推断，Lutetian三阶海平面上升幅度为5-10 m, MECO期间为30 m或更大。此外，浅水记录表明，在始新世中期的暖化气候状态中，三级海平面的变化是以天文速度进行的，但在短暂的MECO变暖期间发生了解耦。

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来源期刊

Paleoceanography and Paleoclimatology Earth and Planetary Sciences-Atmospheric Science

CiteScore

6.20

自引率

11.40%

发文量

107

期刊介绍： Paleoceanography and Paleoclimatology (PALO) publishes papers dealing with records of past environments, biota and climate. Understanding of the Earth system as it was in the past requires the employment of a wide range of approaches including marine and lacustrine sedimentology and speleothems; ice sheet formation and flow; stable isotope, trace element, and organic geochemistry; paleontology and molecular paleontology; evolutionary processes; mineralization in organisms; understanding tree-ring formation; seismic stratigraphy; physical, chemical, and biological oceanography; geochemical, climate and earth system modeling, and many others. The scope of this journal is regional to global, rather than local, and includes studies of any geologic age (Precambrian to Quaternary, including modern analogs). Within this framework, papers on the following topics are to be included: chronology, stratigraphy (where relevant to correlation of paleoceanographic events), paleoreconstructions, paleoceanographic modeling, paleocirculation (deep, intermediate, and shallow), paleoclimatology (e.g., paleowinds and cryosphere history), global sediment and geochemical cycles, anoxia, sea level changes and effects, relations between biotic evolution and paleoceanography, biotic crises, paleobiology (e.g., ecology of “microfossils” used in paleoceanography), techniques and approaches in paleoceanographic inferences, and modern paleoceanographic analogs, and quantitative and integrative analysis of coupled ocean-atmosphere-biosphere processes. Paleoceanographic and Paleoclimate studies enable us to use the past in order to gain information on possible future climatic and biotic developments: the past is the key to the future, just as much and maybe more than the present is the key to the past.