RUI: Magnetic Stratigraphy and Tectonic Rotation of the Middle Eocene Cowlitz Formation and Equivalents, Oregon and Washington

RUI：俄勒冈州和华盛顿州中始新世考利茨地层及其等效物的磁性地层学和构造旋转

• 批准号: 0001194
• 负责人: Donald Prothero
• 金额: $ 3万
• 依托单位: Occidental College
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2000
• 资助国家: 美国
• 起止时间: 2000-08-01 至 2003-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0001194&HistoricalAwards=false
• 关键词: RUI; Magnetic; Stratigraphy; Tectonic; Rotation

MAGNETIC STRATIGRAPHY AND TECTONIC ROTATION OF THE MIDDLE EOCENE COWLITZ FORMATION AND EQUIVALENTS, OREGON AND WASHINGTONDonald R. ProtheroEAR 0001194 The Eocene-Oligocene transition was a critical point in Earth history, when the tropical "greenhouse" world of the Cretaceous to early Eocene was replaced by essentially modern "icehouse" conditions of the early Oligocene. This project will conduct magnetostratigraphic sampling on key exposures of marine rocks, which record the beginning of the Eocene-Oligocene transition in Washington and Oregon. Some of the most important exposures are of the upper middle Eocene Cowlitz Formation in western Washington. These strata yield the classic "Cowlitz-Coaledo" molluscan faunas, and are also important for their oil and coal deposits. Preliminary results from the type area of the Cowlitz Formation at Olequa Creek show that it yields both normal and reversed polarities. Based on a 40Ar/39Ar date of 38.9 +/- 0.01 Ma, the type section of the Cowlitz Formation probably correlates with magnetic Chron C17n-C17r (36.5-38.5 Ma).PI proposes to sample further sections in the Cowlitz Formation, and its equivalent, the Hamlet Formation of Oregon. The magnetic stratigraphy of these sections offers the potential of much higher-resolution correlation of middle Eocene to Oligocene strata with the global time scale, and with other Eocene-Oligocene strata and faunal sequences. This will allow the underexploited data base of the Pacific Northwest marine molluscs and benthic foraminifera to be compared with the growing body of knowledge about the effects of the Eocene-Oligocene climatic changes on the organisms of the rest of the world. High-precision, high-resolution chronostratigraphy of these strata will also be important to petroleum geologists who study these important reservoir rocks, and to geologists who want to better understand the timing of events in this tectonically active region. In addition, the rocks of the type section at Olequa Creek show a clockwise tectonic rotation of 97 +/- 11 degrees, consistent with other results reported from the region. By sampling a large number of Cowlitz-equivalent outcrops in both Oregon and Washington, PI hopes to improve understanding of the complex tectonic rotations that each structural block has undergone since the Eocene.

俄勒冈州和华盛顿州中始新世柯维利兹组及其对应物的磁性地层学和构造旋转。Protherosteroids 0001194 始新世-渐新世过渡是地球历史上的一个关键点，白垩纪至始新世早期的热带“温室”世界被渐新世早期基本上现代的“冰库”条件所取代。该项目将对记录了华盛顿和俄勒冈州始新世-渐新世过渡开始的海相岩石的关键暴露进行磁性地层取样。一些最重要的暴露是在华盛顿西部的中上始新世考利茨组。这些地层产生了经典的“考利茨-科莱多”软体动物群，也是重要的石油和煤炭矿床。Olequa Creek的考利茨组的模式区的初步结果表明，它产生了正常和反向极性。根据38.9 +/- 0.01 Ma的40 Ar/39 Ar年龄，考利茨组的标准剖面可能与磁性年代C17 n-C17 r（36.5-38.5 Ma）相关。PI建议在考利茨组及其等价物俄勒冈州的哈姆雷特组中进一步取样。这些剖面的磁性地层学提供了中始新世至渐新世地层与全球时间尺度以及与其他始新世-渐新世地层和动物群序列进行更高分辨率对比的可能性。 这将使开发不足的西北太平洋海洋软体动物和底栖有孔虫数据库能够与关于始新世-渐新世气候变化对世界其他地区生物体影响的日益增长的知识进行比较。这些地层的高精度、高分辨率年代地层学对研究这些重要储集岩的石油地质学家以及希望更好地了解这一构造活动区事件发生时间的地质学家也很重要。 此外，Olequa Creek典型剖面的岩石显示出97 +/- 11度的顺时针构造旋转，与该地区报告的其他结果一致。通过对俄勒冈州和华盛顿大量的考利茨等效露头进行采样，PI希望提高对每个构造块体自始新世以来所经历的复杂构造旋转的理解。