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

[805071 . prothero]中新世（5 ~ 23 Ma）是地球历史上的一个关键时期，中新世早期相对温暖、温和的气候被较冷的气候、南极永久冰川和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的变化，包括马、骆驼和其他食草动物的出现，这些食草动物有高冠牙齿，可以吃沙质植物。中新世海洋动物群也发生了许多重要的变化。加利福尼亚有很好的中新世哺乳动物和海洋生物的记录，但在过去，这些沉积物和化石的年代地层一直很不精确。加利福尼亚Caliente山脉中新世地层的独特之处在于，它们包含了代表五个重叠的北美陆地哺乳动物“时代”（Arikareean到Hemphillian）的化石，这些化石与软体动物、底栖有孔虫和钙质纳米化石的海洋地层相交织，并且还与年代久远的火山活动联系在一起。这个地区提供了一个不同寻常的机会来改进这些陆地哺乳动物“年龄”的年代测定和相关性。此外，它还包含了长期争议的渐新世-中新世Vaqueros组最厚和最准确的年代序列之一。利用底栖有孔虫和钙质纳米化石，应该有可能为这个年代不确定的单元提供一个良好的磁地层对比。因此，对Caliente山脉中新世进行详细的磁地层学研究，不仅可以提供Arikareean到Hemphillian陆生哺乳动物“时代”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。有了这些化石和生物地层单位更精确的年代测定，就有可能比以往更详细地研究动物对这些气候变化的反应。除了这个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，横断山脉西部的许多地块已经顺时针旋转了90度，但卡连特山脉位于假定的旋转区域的北部，在一个应该沿着圣安德烈亚斯断层向西北滑动的地块上，而不是旋转。然而，以往对Cuyama Badlands（位于Caliente山脉东南部）的客户组的研究表明，该地块在18 -11 Ma之间是稳定的，然后在9-11 Ma之间经历了15（顺时针旋转）。在1.7到9毫安之间，该块再次稳定下来，从那时起，它经历了大约24英里的顺时针旋转。对卡连特山脉岩石的初步磁性研究也显示出顺时针旋转的证据。对Caliente Range岩石的详细磁分析将提供该地块自26 Ma至今的连续构造旋转历史，这将对该地区的构造争议非常重要。

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.