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

始新世中期Cowlitz组的磁性地层学和构造旋转，俄勒冈州和WashingtonDonald R.ProtheroEar 0001194始新世-渐新世的转变是地球历史上的一个临界点，白垩纪到早始新世的热带“温室”世界被渐新世早期的基本上现代的“冰库”条件所取代。该项目将对海相岩石的关键暴露进行磁性地层学采样，记录了华盛顿州和俄勒冈州始新世-渐新世过渡的开始。一些最重要的曝光是华盛顿州西部始新世中上段的考利茨组。这些地层产生了经典的“考利茨-科莱多”软体动物动物群，对它们的石油和煤炭矿藏也很重要。Olequa Creek考利茨组类型区的初步结果表明，它既有正极性，也有反极性。根据38.9 Ma+-0.01 Ma的40Ar/39Ar年龄，考利茨组的类型剖面可能与C17n-C17r(36.5-38.5 Ma)的磁时相对应。PI建议对考利茨组及其对应的俄勒冈州哈姆雷特组进一步取样。这些剖面的磁性地层学提供了更高分辨率的中始新世与渐新世地层与全球时间尺度的对比，以及与其他始新世-渐新世地层和动物群序列的对比。这将使开发不足的太平洋西北海洋软体动物和底栖有孔虫数据库与有关始新世-渐新世气候变化对世界其他地区生物影响的不断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于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时间的地质学家也将非常重要。此外，Olequa Creek类型剖面的岩石显示出97+/-11度的顺时针构造旋转，这与该地区报道的其他结果一致。Pi希望通过在俄勒冈州和华盛顿州采集大量与考利茨相当的露头样本，提高对每个构造块自始新世以来经历的复杂构造旋转的理解。

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.