RUI: Paleomagnetism and Tectonic Rotation of the Makah Formation

奥林匹克半岛西北部的Makah组是华盛顿沿岸最厚、最完整的深海始新世-渐新世深海地层之一，由约2,800米的薄层粉砂岩和浊积砂岩组成，位于奥林匹克半岛西北角的西北向线性带上。下半部为回流纪(晚始新世)底栖有孔虫，上半部为泽莫纪(渐新世)有孔虫。根据Pi对华盛顿州林肯克里克组和俄勒冈州Keasey组和AlSea组这些海底有孔虫阶段的磁性地层学校正，他相信Makah组的磁性剖面可以与全球时间尺度相关联。这种对比将有助于我们理解始新世-渐新世过渡期间发生的主要气候变化。此外，Makah组还发现了一些已知的太平洋沿岸最古老的须鲸化石，这些标本的年代测定对于鲸鱼进化的假说很重要。对巴达点Makah组类型剖面的57个古地磁点位进行了分析，获得了稳定的正极性和反极性的原生剩磁，并通过了反转试验。最后，Pi对Makah组的初步采样表明，这些岩石在渐新世后经历了大约30度的逆时针旋转。这与早期的古地磁结果相矛盾，这些结果表明，奥运会中的许多始新世-渐新世沉积单元都有顺时针构造旋转；然而，这些结果与最近在附近进行的逆时针旋转的工作是一致的。对马卡组进行进一步的古地磁分析，将有助于我们对该地区复杂构造的认识。

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.