Devonian contourites in oceanic passageways between Gondwana and Laurussia

尽管海底洋流在大陆边缘形成过程中的基本作用现在已经有了充分的文献记载，但无论是在经济上还是在科学界，对深水环流的过程和产物仍然知之甚少。沉积或受到这些海底洋流显著影响的沉积物被称为等高沉积岩。该项目将重点研究泥盆纪中晚期形成的钙质等高线岩化石，这些钙质等高线岩形成于靠近的冈瓦纳大陆和劳鲁西亚大陆之间狭窄的海洋通道中，以及各种夹在一起的微大陆之间。泥盆纪的例子是古代记录中为数不多的被认可的底流沉积的例子之一。在国际地球科学计划“等高线”的框架内：“过程与产物”（IGCP 619），我们的目标是(1)建立更好的识别化石轮廓岩的诊断标准，完善轮廓岩沉积体系的现有相模式；(2)绘制泥盆系轮廓岩的产状和分布图，为更详细的古海洋和古地理重建提供线索；(3)评价泥盆系轮廓岩漂移作为储层研究的露头类似物。在所有海洋环境中对等高线岩的观察越来越多，需要更明确的诊断标准，以更好地整合小尺度特征（沉积相、序列）、中尺度特征（漂移几何、内部建筑、相分布和趋势、侵蚀不整合）和大尺度特征（古海洋环境）为基础。这可以通过参考陆地上的位置，牢固地建立基于露头的古等高线识别来实现。由于海洋深水和浅水环流是由板块构造控制的，所以厚质沉积物是过去地球动力学变化的有用记录者，因此将有助于更好地重建大陆和海洋板块。海洋通道在一系列古海洋学过程中起着重要作用；它们的打开和关闭在地质历史上对海洋的物理环流和全球气候都发挥了重要作用。在这种背景下，泥盆纪等长岩的出现是一个非常重要的事实。这些轮廓岩保存了一个独特的记录，为深海钙质软泥的底流改造提供了强有力的证据。在沉积学和地层学研究的基础上，研究了与冈瓦纳和劳鲁西亚之间的海洋门户及其逐步关闭有关的泥盆纪轮廓岩沉积体系的具体古海洋记录。在确定由特别强烈的底流引起的相关侵蚀不连续面和磷酸盐沉积的年龄和范围时，我们的目标是建立轮廓岩古海洋特征的全球对比。

Although the fundamental role of bottom currents in the construction of continental margins has by now been well documented, the processes and products of deep-water circulation remain poorly understood, both economically and in the scientific community. The sediments deposited or significantly affected by these bottom currents are known as contourites. The project will focus on fossil calcareous contourites formed during the Middle-Late Devonian in the narrowing oceanic passageways between the approaching continents Gondwana and Laurussia, as well as between the various sandwiched micro-continents. The Devonian case represents one of the few previously recognized examples of bottom-current deposits from the ancient record. Within the framework of the International Geoscience Programme "Contourites: Processes and Products" (IGCP 619), we aim to (1) establish better diagnostic criteria for the identification of fossil contourites and refine the existing facies models for contourite depositional systems, (2) chart the occurrence and distribution of Devonian contourites, to provide clues for more detailed palaeoceanographic and palaeogeographic reconstructions, and (3) evaluate the Devonian contourite drifts as outcrop analogues for reservoir studies. The increasing observation of contourites in all marine environments calls for more unambiguous diagnostic criteria, based upon a better integration of small-scale characteristics (sediment facies, sequences), medium-scale (drift geometry, internal architecture, facies distribution and trends, erosional disconformities), and large-scale (palaeoceanographic setting). This can be achieved by firmly establishing the outcrop-based recognition of ancient contourites with reference to localities on land. Since oceanic deep- and shallow-water circulation is controlled by plate tectonics, the contouritic deposits are useful recorders of past geodynamic changes and will therefore assist in a better reconstruction of the continental and oceanic plates. Ocean passageways are prominently involved in a range of palaeoceanographic processes; their opening and closing played an important role in the geological past in the ocean s physical circulation and the global climate at large. In the light of this context, the occurrence of Devonian contourites is a hugely important fact. These contourites preserve a unique record giving strong evidence for bottom-current reworking of calcareous deep-sea oozes. Based on sedimentologic and stratigraphic investigations, we aim to decode the specific palaeoceanographic record of Devonian contourite depositional systems associated with the oceanic gateways between Gondwana and Laurussia and their stepwise closing. In determining the age and extent of the associated erosional discontinuities and phosphatic deposits, which are caused by particularly strong bottom currents, we aim to establish a global correlation of the contourite palaeoceanographic signatures.