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

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“冰窖”条件所取代。气候变化引起的大灭绝和其他生物反应已经在许多地方进行了研究，但是在加利福尼亚海洋地层中发现的软体动物和有孔虫的优秀化石记录却很少得到研究，因为年代地层学的解析和校准都很差。圣克鲁斯山脉中始新世至渐新世海相地层提供了加利福尼亚Narizian， Refugian和Zemorrian底栖有孔虫阶段的最佳叠加记录，这些记录也由浮游微化石校准。对圣洛伦佐河地区晚纳里兹—雷弗吉安—早泽莫里安地层的初步磁分析结果表明，纳里兹—雷弗吉安地层与c13r—c13n期（34.5 ~ 33.0 Ma）相关，早泽莫里安地层与C12r期（31.5 ~ 31.0Ma）相关。该地区将对另外三个剖面进行采样：一个剖面跨越早期和晚期Narizian，第二个剖面跨越早期和晚期zemorian，第三个剖面是圣洛伦佐组的Twobar页岩和rice泥岩。圣克鲁斯山脉整个Narizian至Zemorrian段的磁地层学将极大地有助于这些长期存在争议的底生物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沿岸始新世-渐新世过渡时期的事件与墨西哥湾和大西洋沿岸的优秀记录，陆地部分记录的动物和植物变化以及全球记录联系起来

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/