RUI: Paleomagnetism and Tectonic Rotation of the Makah Formation

PROtheroRUI-0309538：Makah组的古地磁和构造旋转西方学院摘要奥林匹克半岛西北部的Makah组是华盛顿沿海最厚、最完整的深海始新世-渐新世层序之一，由约2800米的薄层粉砂岩和浊积砂岩组成，位于西北-沿着奥林匹克半岛西北角的线性地带。下半部分为Refugian（始新世晚期）底栖有孔虫，上半部分为Zemorrian（渐新世）有孔虫。根据PI对华盛顿的林肯溪组和俄勒冈州的Keasey组和Alsea组中这些底栖有孔虫阶段的磁性地层学校准，他相信马卡组中的磁性部分可以与全球时间尺度相关联。这种相关性将有助于我们理解始新世-渐新世过渡期发生的主要气候变化。此外，马卡组产生了一些最古老的化石须鲸已知的太平洋沿岸，这些标本的年代是重要的假设鲸鱼进化。对巴达点Makah组典型剖面的57个古地磁测点进行了分析，得到了一个稳定的正极性和反极性的原始剩磁，并通过了反转测试。最后，PI对Makah组的初步取样表明，岩石经历了大约30度的后渐新世逆时针旋转。这与早期的古地磁结果相冲突，古地磁结果表明，奥林匹克运动会中的许多始新世-渐新世沉积单元具有顺时针构造旋转;然而，这些结果与最近的研究结果一致，显示逆时针旋转。对马卡组的进一步古地磁分析将提高我们对该地区复杂构造的理解。

EAR-0309538ProtheroRUI: Paleomagnetism and Tectonic Rotation of the Makah FormationDonald Prothero (EAR-0309538)Occidental CollegeABSTRACTThe Makah Formation in the northwest Olympic Peninsula is one of the thickest and most complete deep-marine Eocene-Oligocene sequences in coastal Washington, consisting of about 2800 meters of thin-bedded siltstones and turbidite sandstones that lie in a northwest-trending linear belt along the northwestern corner of the Olympic Peninsula. It yields Refugian (late Eocene) benthic foraminifera in the lower half, and Zemorrian (Oligocene) foraminifera in the upper half. Based on PI's magnetostratigraphic calibration of these benthic foraminiferal stages in the Lincoln Creek Formation of Washington and the Keasey and Alsea Formations of Oregon, he is confident that magnetic sections in the Makah Formation can be confidently correlated to the global time scale. Such correlations will aid in our understanding of the major climatic changes occurring during the Eocene-Oligocene transition. In addition, the Makah Formation yields some of the oldest fossil baleen whales known from the Pacific Rim, and dating of these specimens is important to hypotheses about whale evolution. Over 57 paleomagnetic sites from the type section of the Makah Formation at Baada Point were analyzed and yield a stable primary remanence with both normal and reversed polarities, which passed a reversal test. Finally, PI's preliminary sampling of the Makah Formation shows that the rocks have undergone about 30 degrees of post-Oligocene counterclockwise rotation. This conflict with earlier paleomagnetic results showing that many of the Eocene-Oligocene sedimentary units in the Olympics have clockwise tectonic rotations; however, these results are consistent with recent work nearby showing counterclockwise rotations. Further paleomagnetic analyses of the Makah Formation would improve our understanding of the complex tectonics of this region.