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From Khersonian drying to Pontian “flooding”: Late Miocene stratigraphy and palaeoenvironmental evolution of the Dacian Basin (Eastern Paratethys)
Global and Planetary Change ( IF 3.9 ) Pub Date : 2020-09-01 , DOI: 10.1016/j.gloplacha.2020.103224
S. Lazarev , A. de Leeuw , M. Stoica , O. Mandic , C.G.C. van Baak , I. Vasiliev , W. Krijgsman

Abstract In the late Miocene, a large inland sea known as the Eastern Paratethys stretched out across the present-day Black Sea – Caspian Sea region. The basin was mostly endorheic and its water budget thus strongly dependent on regional climate. The basin was therefore prone to high-amplitude water-level fluctuations and associated turnovers in water chemistry and fauna. Profound palaeoenvironmental changes happened in the Eastern Paratethys during this time period. This article documents the evolution of the Dacian Basin of Romania, the westernmost branch of the Eastern Paratethys, during the time interval between 7.7 and 6.0 Ma. Our integrated study of sedimentary facies, micro- and macro fauna along the Slănicul de Buzău Section was constrained with a timeframe based on magnetostratigraphy. The remarkable 1.3 km-thick sedimentary record, high depositional rate (0.65–1.26 m/kyr) and abundance of fossils along this section provide a unique opportunity to study sedimentary and biotic turnovers in high detail. Our analyses reveal several marked water-level and salinity changes: A predominance of freshwater coastal plain environments, only occasionally flooded, indicates a low water-level in the Khersonian (~7.7–7.63 Ma). The coastal plain deposits are overlain by offshore muds revealing a low mesohaline early Maeotian transgression, which was followed by the installation of littoral/nearshore environments with freshwater molluscs in shallow settings and oligohaline ostracods in slightly deeper settings. Subsequent delta progradation and a prevalence of freshwater fauna in both marginal and more distal environments characterize the late Maeotian. This was followed by a remarkable freshwater transgression that started at 6.3 Ma and led to predominantly offshore deposition. The late Maeotian fossil record suggests brackish water pulses from Lake Pannon (Central Paratethys), followed by mass occurrences of Coelogonia novorossica. At 6.1 Ma, a short influx of meso- to polyhaline microfauna including benthic and planktonic foraminifera defines the “Pontian Salinity Incursion”. Molluscs, including Eupatorina littoralis, that biostratigraphically mark the onset of the Pontian arrived with a negligible delay of ~5 kyr after the microfauna influx. The onset of the Pontian at Slănicul de Buzau at 6.1 Ma (± 5 kyr), is thus synchronous with the onset in other Paratethys basins. Our integrated approach, placing the preserved fossil fauna in its respective sedimentary environment, allows for a detailed insight into the salinity of coeval marginal as well as basinal environments and could be more widely applied in the Paratethys realm and other semi-isolated basins with a deviant salinity.

中文翻译:

从 Khersonian 干燥到 Pontian“洪水”:晚中新世地层学和达契亚盆地 (Eastern Paratethys) 的古环境演化

摘要 中新世晚期,一个被称为东帕拉提提斯的大型内海横跨现今的黑海-里海地区。该盆地主要是内陆流域,因此其水资源收支强烈依赖于区域气候。因此,该盆地容易出现高幅度的水位波动以及水化学和动物群的相关变化。这一时期东帕特提斯发生了深刻的古环境变化。本文记录了东帕拉提提斯最西支罗马尼亚达契亚盆地在 7.7 至 6.0 Ma 的时间间隔内的演化。我们对 Slănicul de Buzău 剖面沿线沉积相、微观和宏观动物群的综合研究受到基于磁地层学的时间框架的限制。非凡的 1.3 公里厚的沉积记录,高沉积率 (0.65–1.26 m/kyr) 和沿此部分的丰富化石为详细研究沉积和生物周转提供了独特的机会。我们的分析揭示了几个显着的水位和盐度变化:淡水沿海平原环境占主导地位,只是偶尔被洪水淹没,表明赫尔松阶的水位较低(~7.7-7.63 Ma)。沿海平原沉积物覆盖着近海泥浆,揭示了早期 Maeotian 海侵的低中盐度,随后在浅层环境中安装了淡水软体动物的沿海/近岸环境,在稍深的环境中安装了寡盐类介形动物。随后的三角洲进积和边缘环境和更远端环境中淡水动物群的盛行是晚期 Maeotian 的特征。随后发生了显着的淡水海侵,从 6.3 Ma 开始并导致主要的近海沉积。晚期 Maeotian 化石记录表明来自 Pannon 湖(Central Paratethys)的微咸水脉动,随后是 Coelogonia novorossica 的大量出现。在 6.1 Ma 时,包括底栖和浮游有孔虫在内的中到多卤化微动物群的短暂流入定义了“笨珍盐度入侵”。软体动物,包括 Eupatorina littoralis,在生物地层学上标志着 Pontian 的开始,在微型动物群涌入后延迟了约 5 kyr,可以忽略不计。Slănicul de Buzau 的 Pontian 发生在 6.1 Ma(± 5 kyr),因此与其他 Paratethys 盆地的发生同步。我们的综合方法,将保存完好的化石动物群置于其各自的沉积环境中,
更新日期:2020-09-01
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