The Rio Sassito sedimentary succession (Ordovician): a pinpoint in the geodynamic evolution of the Argentine Precordillera
The Rio Sassito sedimentary succession (Ordovician): a pinpoint in the geodynamic evolution of the Argentine Precordillera
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Rio Sassito 沉积层序（奥陶纪）：阿根廷 Precordillera 地球动力学演化的精确点
DOI：
10.1007/s005310050213
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发表时间：
1998
期刊：
影响因子：
--
通讯作者：
O. Lehnert
中科院分区：
文献类型：
--
作者：
M. Keller;O. Lehnert
在阿根廷西部的Precordillera， llanddelian的硅质塑料和Caradocian的灰岩（里约热内卢Sassito演替）的孤立露头揭示了中晚奥陶世Precordillera的构造和沉积历史之间复杂的相互作用。该序列由下硅质碎屑层段和上碳酸盐层段组成，上下由侵蚀不整合面划分。这些不整合面在许多地方合并形成一个单一的表面，对它们的年代测定表明，最重要的侵蚀事件发生在里约热内卢- Sassito演替沉积之前。这一侵蚀事件与大陆分裂和前科迪勒拉与劳伦西亚分离的伸展构造有关。在卡拉多克期，地块断裂与地堑和地垒构造的形成为海相碳酸盐岩台地的形成提供了地形条件。在我们看来，没有迹象表明这些现象与前科迪勒拉向冈瓦纳的增生或奥陶系超大陆的形成有关。碳酸盐沉积物是典型的温水环境，其特征是缺乏类、类和藻类，而存在大量的磨损生物碎屑、内碎屑和似球粒。对温带水环境的推断，并不像先前假定的那样，表明了前科迪勒拉向冈瓦纳的增生，而更有可能与阿什吉利冰期之前的全球降温有关。
In the Precordillera of western Argentina, an isolated outcrop of Llandeilian siliciclastics and Caradocian limestones (Rio Sassito succession) reveals a complex interplay between the tectonic and the sedimentary history of the Precordillera during Middle and Late Ordovician times. The succession is composed of a lower siliciclastic interval and an upper carbonate interval and is bounded below and above by erosional unconformities. Dating of these unconformities, which in many places merged to form one single surface, demonstrates that the most important erosional event took place prior to the deposition of the Rio Sassito succession. This erosional event is correlated to extensional tectonics during continental breakup and the separation of the Precordillera from Laurentia. Block faulting with the formation of horst and graben structures provided the topography for the establishment of a pelagic carbonate platform during the Caradoc. In our view, there are no indications that these phenomena are related to the accretion of the Precordillera to Gondwana or to the formation of an Ordovician supercontinent. The carbonate sediments are typical of temperate-water settings, characterized by the absence of ooids, oncoids, and algae, and by the presence of abundant abraded bioclasts, intraclasts, and peloids. The inference of a temperate-water environment does not, as previously supposed, indicate the accretion of the Precordillera to Gondwana, but is more likely related to global cooling prior to the Ashgillian glaciation.