Early Ordovician Greenhouse to Late Ordovician Glacial Transition: Effect on the Cyclic Sedimentary Record, Kentucky-Virginia

早奥陶世温室到晚奥陶世冰川过渡：对肯塔基-弗吉尼亚州循环沉积记录的影响

• 批准号: 9316057
• 负责人: James Read
• 金额: $ 18.12万
• 依托单位: Virginia Polytechnic Institute and State University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 1994
• 资助国家: 美国
• 起止时间: 1994-02-01 至 1997-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9316057&HistoricalAwards=false
• 关键词: Early; Ordovician; Greenhouse; Late; Glacial

9316057 Read This proposal request funds to study superb outcrops and the extensive core collections of Middle and Late Ordovician rocks in Kentucky so that we can compare them with the Early Ordovician strata, to search for the stratigraphic evidence of possible change from low amplitude eustasy of Early Ordovician greenhouse times to possible higher amplitude eustasy developed during Late Ordovician Gondwana glaciation. We presently have a very large data base on Early Ordovician and Middle Ordovician rocks characteristic of greenhouse conditions, that will serve as a basis for comparison with the younger units. We propose to log bed-by-bed the later Middle and Late Ordovician carbonates and shales which appear to have developed on storm-dominated ramps, documenting any peritidal and shallow to deeper water subtidal cycles, their degree of lateral continuity, their stacking patterns and relation to depositional sequences, and bounding surfaces. We will also examine the cycles for evidence of: 1. long term climate change and 2. evidence of short term emergence (including paleosols, erosion surfaces, negative departures of stable isotope profiles, and meteoric cementation); all these might become more pronounced if glacially driven sea level amplitudes increased into the Late Ordovician. Using detailed regional cross sections of cyclic lithofacies, we will define depositional sequences, and document the relationships and timing of bounding surfaces to the tectonic history of the foreland basin, including peripheral bulge development and prograding clastic rocks along the tectonically active proximal margin. Finally, we will computer model the cycles and the depositional sequences to better constrain the roles of tectonism, low- and high- frequency eustasy, and sediment supply. Defining the stratigraphic signature of greenhouse to global glacial conditions appears to hold the key for a future more detailed global climate subdivision of the Phanerozoic than h as been attempted.

9316057阅读这份提案申请资金，以研究肯塔基州中、晚奥陶世岩石的卓越露头和广泛的核心收藏，以便我们能够将它们与早奥陶世地层进行比较，以寻找可能从早奥陶世温室时代的低幅度优惠期转变为晚奥陶世冈瓦那冰期可能形成的高幅度优势期的地层学证据。我们目前有一个非常大的早奥陶世和中奥陶世岩石温室条件的数据库，这将作为与更年轻的单位进行比较的基础。我们建议逐层记录中、晚奥陶世晚期的碳酸盐岩和页岩，这些碳酸盐和页岩似乎是在风暴控制的斜坡上发育的，记录了任何潮周和浅水至深水的潮下旋回、它们的横向连续性程度、它们的堆积模式及其与沉积层序和界面的关系。我们还将检查以下周期的证据：1.长期气候变化和2.短期出现的证据(包括古土壤、剥蚀面、稳定同位素剖面的负偏离和陨石胶结作用)；如果冰川驱动的海平面幅度增加到晚奥陶世，所有这些都可能变得更加明显。利用旋回岩相的详细区域剖面，我们将定义沉积序列，并记录边界面与前陆盆地构造历史的关系和时间，包括外围隆起发育和沿构造活动近缘的进积碎屑岩。最后，我们将对旋回和沉积序列进行计算机模拟，以更好地约束构造作用、低频和高频海平面上升以及沉积物供应的作用。定义温室对全球冰川条件的地层学特征似乎是未来对显生界进行更详细的全球气候细分的关键。