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，当时中新世早期相对温暖、温和的气候被较冷的气候、永久的南极冰川以及温带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，这些食草动物具有高冠的牙齿，可以吃沙砾状的植被。 中新世海洋动物群也发生了许多重要变化。 加州有着极好的中新世哺乳动物和海洋生物的记录，但在过去，这些沉积物及其化石的年代地层学非常不精确。加州的卡连特山脉的中新世地层是独一无二的，因为它们含有代表五个叠加的北美陆地哺乳动物"时代"的化石。（Arikareean通过Hemphillian）与可由软体动物、底栖有孔虫和钙质超微化石确定年代的海相地层交指，并与过时的火山岩联系在一起。 这个地区提供了一个不寻常的机会，以改善这些陆地哺乳动物的年龄和相关性。"此外，它还包含了长期有争议的渐新世-中新世Vaqueros地层中最厚和最好的年代序列之一。 利用底栖有孔虫和钙质超微化石，应该可以提供一个很好的磁性地层对比，这个可怜的过时的单位。 因此，对Caliente山脉中新世进行详细的磁性地层学研究，不仅可以提供Arikareean到Hemphillian陆地哺乳动物"年龄"的精细年代地层学，还可以提供Zemorrian到Luisian底栖有孔虫阶段以及Vaqueros和Temblor软体动物阶段的年代地层学。 随着对这些化石和生物地层单位的更精确测年，将有可能比以往更详细地研究动物群对这些气候变化的反应。除了该项目的年代地层学方面，卡连特山脉也因构造原因而有趣。 自中新世早期以来，横贯山脉西部的许多地块已经旋转了90度（顺时针方向），但卡连特山脉位于假定的旋转地带以北，该地块应该沿着圣安德烈亚斯断层向西北沿着，而不是旋转。 然而，先前对Cuyama荒地（就在Caliente山脉东南部）的Cliente组的研究表明，该地块在18至11 Ma之间是稳定的，然后在9 - 11 Ma之间经历了15次顺时针旋转。 在1.7~9 Ma之间，该地块再次稳定，从那时起，它经历了大约24 °的顺时针旋转。 对卡连特山脉岩石的初步磁性研究也显示了顺时针旋转的证据。 对Caliente山脉岩石的详细磁性分析将提供该地块26 Ma至今的构造旋转的连续历史，这对该地区构造的争议非常重要。

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.