RUI: Magnetic Stratigraphy and Miocene Tectonic Rotation of the Calients Range, San Luis Obispo County, California

中新世(5-23 Ma)是地球历史上的一个关键时期，早中新世相对温暖、温和的气候被较凉爽的气候、永久的南极冰川以及温带地区的稀树草原和草原所取代。这些气候和植被的变化显然刺激了许多动物群的变化，包括马、骆驼和其他食草动物的出现，它们有高冠的牙齿来吃砂砾植物。中新世海相动物群也发生了许多重要变化。加州对中新世哺乳动物和海洋生物有着极好的记录，但在过去，这些沉积物及其化石的年代地层学一直非常不准确。加州卡连特山脉的中新世地层是独特的，因为它们包含代表五个叠加的北美陆地哺乳动物“时代”(亚里卡里期到希米利期)的化石，与软体动物、海底有孔虫和钙质纳米化石都能确定年代的海床相互交错，并与古老的火山岩联系在一起。这一地区提供了一个不同寻常的机会来改善这些陆生哺乳动物的年代和相关性。此外，它还包含了长期存在争议的渐新世-中新世瓦克罗斯组中最厚、年代最早的层序之一。利用海底有孔虫和钙质超微化石，应该可以为这个年代较差的单位提供良好的磁性地层对比。因此，对卡连特山脉中新世进行详细的磁性地层学研究，不仅可以提供亚里卡里期到西米利期陆地哺乳动物“时代”的精细年代地层学，还可以提供泽莫尔期到路易斯期的底栖有孔虫阶段，以及瓦奎罗和地震软体动物阶段。随着对这些化石和生物地层单位进行更精确的测年，将有可能比以往任何时候都更详细地研究动物群对这些气候变化的反应。除了这个项目的年代地层方面，卡连特山脉也因构造原因而有趣。自中新世早期以来，西侧横贯山脉的许多地块已经顺时针旋转了90次，但卡连特山脉位于推定的旋转区域的北部，该地块本应沿着圣安德烈亚斯断层向西北滑动，而不是旋转。然而，以前对Cuyama Badland(就在卡连特山脉东南)的客户建造的研究表明，该地块在18-11 Ma之间稳定，然后经历了15 Ma(9-11 Ma之间的顺时针旋转)。在1.7-9 Ma之间，地块再次稳定，自那时以来，它经历了大约24(顺时针)旋转。对卡连特山脉岩石的初步磁学研究也显示了顺时针旋转的证据。对卡连特山脉岩石的详细磁学分析将提供该地块26 Ma至今的连续构造旋转历史，这对该地区的构造争论将是非常重要的。

9805071ProtheroThe Miocene Epoch (from 5 to 23 Ma) was a critical period in earth history, when the relatively warm, mild climates of the early Miocene were replaced by cooler climates, permanent Antarctic glaciers, and savannas and grasslands in temperate latitudes. These climatic and vegetational changes apparently stimulated many faunal changes, including the appearance of horses, camels, and other herbivores with high-crowned teeth for eating gritty vegetation. Many important changes occurred in Miocene marine faunas as well. California has an excellent record of Miocene mammals and marine life, but in the past, the chronostratigraphy of these deposits and their fossils has been very imprecise.The Miocene strata of the Caliente Range in California are unique in that they contain fossils representing five superposed North American land mammal "ages" (Arikareean through Hemphillian) interfingering with marine beds datable by both molluscs, benthic foraminifera, and calcareous nannofossils, and also tied together with dated volcanics. This region provides an unusual opportunity to improve the dating and correlation of these land mammal "ages." In addition, it contains one of the thickest and best dated sequences of the long-controversial Oligocene-Miocene Vaqueros Formation. Using benthic foraminifera and calcareous nannofossils, it should be possible to provide a good magnetostratigraphic correlation of this poorly dated unit. Thus, a detailed magnetostratigraphic study of the Caliente Range Miocene would provide not only fine-scale chronostratigraphy of the Arikareean through Hemphillian land mammal "age," but also the Zemorrian through Luisian benthic foraminiferal stages, and the Vaqueros and Temblor molluscan stages. With more precise dating of these fossils and biostratigraphic units, it will be possible to examine the faunal responses to these climatic changes in much finer detail than ever before.In addition to the chronostratigraphic aspects of this project, the Caliente Range is also interesting for tectonic reasons. Many of the blocks of the western Transverse Ranges have rotated as much as 90( clockwise since the early Miocene, but the Caliente Range is north of the presumed rotated tract, in a block that should have slid northwestward along the San Andreas fault, not rotated. However, previous studies of the Cliente Formation in the Cuyama Badlands (just to the southeast of the Caliente Range) showed that this block was stable between 18 and 11 Ma, then underwent 15( of clockwise rotation between 9-11 Ma. Between 1.7 and 9 Ma, the block was again stable, and since that time, it has undergone about 24( of clockwise rotation. Preliminary magnetic studies of rocks from the Caliente Range also show evidence of clockwise rotation. A detailed magnetic analysis of Caliente Range rocks will provide a continuous history of the tectonic rotation of this block between 26 Ma and present, which would be very important to controversies over the tectonics of this region.