Facies pattern and sea-level dynamics of the early Late Cretaceous transgression: a case study from the lower Danubian Cretaceous Group (Bavaria, southern Germany)
Facies pattern and sea-level dynamics of the early Late Cretaceous transgression: a case study from the lower Danubian Cretaceous Group (Bavaria, southern Germany)
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晚白垩世早期海侵的相貌和海平面动态：以多瑙河下游白垩系群（德国南部巴伐利亚）为例
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发表时间：
2010
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通讯作者：
M. Kling
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作者：
M. Wilmsen;B. Niebuhr;Patrick Chellouche;Thomas Pürner;M. Kling
利用综合地层学方法，在详细测井、细分和对比的基础上，结合岩相、生物相和微相分析，评价了德国南部巴伐利亚州多瑙河组下白垩统的相发育和超覆模式。与文献中的说法相反，雷根斯堡组的海侵上覆是在雷根斯堡-凯尔海姆地区开始的，该地区早在Cenomania早期的Mantellicera Mantellicera菊石带中，而不是在Cenomian晚期。晚更新世早期，近岸海绿石-生物碎屑砂岩占优势(Saal段)，其次为中、下部早更新世中陆架硅质碳酸盐岩夹层细砂至粉砂质泥灰岩(Bad Abbach段)。始于中、晚更新世(Metoicocera geslinianum菊石带)，更新世-吐鲁尼亚界线事件(CTBE)期间的一次相当大的加深脉冲启动了艾布伦组更深的陆架粉质泥灰岩的沉积，范围一直延伸到吐鲁世早期。在CTBE海侵期间，近端的Bodenwöhrer Senke(雷根斯堡东北约40公里处)也被淹没，这表明雷根斯堡组与波西米亚地块的瓦里斯坎花岗岩重叠，被最下面的都罗尼亚Eibrunn组的薄舌覆盖。从这一浅水环境中恢复了全球海洋缺氧事件2的正δ13C漂移的详细记录。应用生物、事件、碳稳定同位素和层序地层学相结合的方法对剖面进行对比，并对整个海侵沉积体系的动力学进行了破译。塞诺马期层序显示了五个明显的不整合，这些不整合与欧洲和其他地方盆地中已知的不整合相关，表明它们来自海平面。CTBE期间海平面上升的速度表明，冰川作用是晚更新世海平面变化的驱动机制。多瑙河组下白垩统的雷根斯堡组和艾布伦组是高度历时的岩石地层单位。它们的区域分布和在波西米亚地块西南缘的东北向超覆格局，可以很容易地用大致与海岸平行(即NW/SE向)的陆架体系的横向运动解释，该陆架体系是在向东北上升的基底上侵位的。塞诺马尼亚海岸线从雷根斯堡西南部侵入罗丁东南的地势较高的花岗岩悬崖花了大约600万马赫(=60亿公里)。
The facies development and onlap pattern of the lower Danubian Cretaceous Group (Bavaria, southern Germany) have been evaluated based on detailed logging, subdivision, and correlation of four key sections using an integrated stratigraphic approach as well as litho-, bio-, and microfacies analyses. Contrary to statements in the literature, the transgressive onlap of the Regensburg Formation started in the Regensburg–Kelheim area already in the early Early Cenomanian Mantelliceras mantelli ammonite Zone and not in the Late Cenomanian. In the Early Cenomanian, nearshore glauconitic-bioclastic sandstones prevailed (Saal Member), followed by Middle to lower Upper Cenomanian mid-shelf siliceous carbonates intercalated with fine-sandy to silty marls (Bad Abbach Member). Starting in the mid-Late Cenomanian (Metoicoceras geslinianum ammonite Zone), a considerable deepening pulse during the Cenomanian–Turonian Boundary Event (CTBE) initiated the deposition of the deeper shelf silty marls of the Eibrunn Formation, which range into the early Early Turonian. During the CTBE transgression, also the proximal Bodenwöhrer Senke (ca. 40 km NE of Regensburg) was flooded, indicated by the onlap of the Regensburg Formation onto Variscan granites of the Bohemian Massif, overlain by a thin tongue of lowermost Turonian Eibrunn Formation. A detailed record of the positive δ13C excursion of the global Oceanic Anoxic Event (OAE) 2 has been retrieved from this shallow-water setting. An integrated approach of bio-, event-, carbon stable isotope and sequence stratigraphy was applied to correlate the sections and to decipher the dynamics of this overall transgressive depositional system. The Cenomanian successions show five prominent unconformities, which correlate with those being known from basins in Europe and elsewhere, indicating their eustatic origin. The rate of sea-level rise during the CTBE suggests glacio-eustasy as a driving mechanism for Late Cenomanian sea-level changes. The Regensburg and Eibrunn formations of the lower Danubian Cretaceous Group are highly diachronous lithostratigraphic units. Their regional distribution and northeast-directed onlap pattern onto the southwestern margin of the Bohemian Massif can readily be explained by the lateral movements of roughly coast-parallel (i.e., NW/SE-trending) facies belts of a graded shelf system transgressing on a northeastward-rising substrate. It took the Cenomanian coastline ca. 6 Ma to transgress from southwest of Regensburg to the topographically elevated granite cliffs southeast of Roding in the Bodenwöhrer Senke (=60 km distance).