RUI: Magnetic Stratigraphy of the Marine Eocene-Oligocene Transition in the Santa Cruz Mountains California

小行星9706046 始新世-渐新世过渡是地球历史上的关键时期，始新世早期的“温室”条件被渐新世的“冰库”条件所取代。 这种气候变化引起的生物大规模灭绝和其他生物反应已在许多地方进行了研究，但在加州海相地层中发现的软体动物和有孔虫化石记录却相对较少，因为年代地层学的分辨率和校准都很差。 圣克鲁斯山脉的中始新世至渐新世海相地层提供了加州纳里济阶、雷富阶和泽莫尔阶底栖有孔虫阶段的最佳叠加记录，这些阶段也是由南极微体化石标定的。 对圣洛伦索河晚Narizian-Refugian-早Zemorrian段的初步磁性分析结果表明，晚Narizian-Refugian段与Cron C13 r-C13 n（34.5-33.0 Ma）对应，早Zemorrian段与Cron C12 r（31.5- 31.0 Ma）对应。 将在该地区的另外三个部分进行采样：一个跨越早期和晚期Narizian，第二个跨越早期和晚期Zemorrian，第三个是圣洛伦索组的Twobar页岩和Rices泥岩成员的典型部分。 在圣克鲁斯山脉的整个Narizian到Zemorrian间隔的磁性地层学将大大有助于这些长期有争议的底栖有孔虫阶段的对比和校准。 这种高分辨率的年代地层学，反过来，将使我们能够将太平洋海岸始新世-渐新世过渡期间的事件与墨西哥湾和大西洋海岸的良好记录，与陆地部分记录的动物群和植物群变化以及全球记录相关联。

9706046 Prothero The Eocene-Oligocene transition was critical period in Earth history, when the "greenhouse" conditions of the early Eocene were replaced by the "icehouse" conditions of the Oligocene. The mass extinctions and other biotic responses caused by this climatic change have been studied in many places, but the excellent fossil record of molluscs and foraminifera found in California marine strata has been relatively little studied because the chronostratigraphy has been so poorly resolved and calibrated. The middle Eocene to Oligocene marine strata of the Santa Cruz Mountains provide the best superposed record in California of the Narizian, Refugian, and Zemorrian benthic foraminiferal stages that are also calibrated by planktonic microfossils. Preliminary magnetic analysis of the late Narizian-Refugian-early Zemorrian interval in San Lorenzo River yielded results which pass both a fold test and reversal test, and show that the latest Narizian-Refugian correlate with Chrons C13r-C13n (34.5-33.0 Ma), and the early Zemorrian with late Cron C12r (31.5-31.0Ma). Three additional sections in the area will be sampled: one spans the early and late Narizian, the second the early and late Zemorrian, and the third is the type section of the Twobar Shale and Rices Mudstone members of the San Lorenzo Formation. Magnetostratigraphy of the entire Narizian through Zemorrian interval in the Santa Cruz Mountains will greatly help in the correlation and calibration of these long-controversial benthic foraminiferal stages. Such high-resolution chronostratigraphy, in turn, will allow us to correlate events during the Eocene-Oligocene transition in the Pacific Coast with the excellent records in the Gulf and Atlantic Coasts, with faunal and floral changes recorded in terrestrial sections, and with the global record/