COLLABORATIVE RESEARCH: Neogene Sediments of the San Timoteo Badlands, Southern California: Tectonic Implications Along the San Andreas and San Jacinto Faults

本研究拟研究圣铁莫特奥荒地的地层学、生物地层学和地质年代学。它包含约12,000英尺厚的非海相沉积物序列，年龄从5到0.7 Ma不等，整个序列中都有哺乳动物化石的遗骸，并且包含适合磁地层学和同位素年龄分析的岩性。伊甸山（Mt. Eden）和圣提莫特奥（San Timoteo）地层的矿床位于一个背斜的露头，该背斜向西北倾斜，在西南边缘被目前活跃的圣哈辛托断层截断。圣哈辛托是南加州圣安德烈亚斯断层系统中最活跃的一条，在过去的200万年里，它经历了大约24公里的右滑动。古海流资料表明，沉积物从北部和东北部被输送到San Timoteo盆地。岩石中独特的碎屑岩套与现在位于荒地东北方向的物源衍生相一致；位于现在的圣安德烈亚斯断层（s.s）以东。因此，圣蒂莫特奥地层在空间和时间上都处于理想的位置，可以促进对过去500万年圣安德烈亚斯断层系统各元素滑动历史的研究。这些层是南加州这一地区在这段时间内相对连续积累的唯一层序。对这些床的年龄的详细分析从未尝试过。年龄分析项目将包括脊椎动物古生物学和生物地层学、磁地层学和同位素年代学。如果成功的话，研究结果将极大地提高我们重建圣蒂莫特奥地层沉积历史的能力，以及重建包含它们的构造块体相对于该地区相邻的地体的能力。这些数据对于解决从圣安德烈亚斯断层链到圣哈辛托断层的区域滑动转移的时间也很有价值，将提高我们评估整个圣安德烈亚斯系统何时以及如何被有效“锁定”在该地区的能力；将加强对圣安德烈亚斯断层滑动率的当地调查，以及太平洋和美洲板块之间的区域剪切是如何通过横向山脉传播的。

This proposal is to study the stratigraphy, biostratigraphy, and geochronology of the San Timoteo Badlands. It contains a sequence of nonmarine deposits about 12,000 feet thick that ranges in age from about 5 to 0.7 Ma, yields remains of fossil mammals throughout the sequence, and contains lithologies amenable to magnetostratigraphic and isotopic age analysis. The deposits, the Mt. Eden and San Timoteo formations, occur in well exposed outcrops of an anticline that plunges gently northwestward and is truncated on its southwestern edge by the currently active San Jacinto fault. The San Jacinto, the most active strand of the San Andreas fault system in southern California, underwent about 24 km of right slip during the past two million years. Paleocurrent data indicate that the sediments were transported to the San Timoteo basin from the north and northeast. Distinctive clast suites in the rocks are consistent with derivation from sources in those directions now northeast of the Badlands; some east of the present San Andreas fault (s.s). The San Timoteo beds thus are ideally situated in space and time to promote investigations of the slip history of elements of the San Andreas fault system during the past 5 million years. These beds are the only sequence that accumulated relatively continuously during this span of time in this part of southern California. A detailed analysis of age of these beds has never been attempted. The program of age analysis will include vertebrate paleontology and biostratigraphy, magnetostratigraphy and isotope chronology. If successful, the results will dramatically improve our ability to attempt a reconstruction of the sedimentary history of the San Timoteo beds, and palinspastic reconstructions of the tectonic block that contains them relative to the then adjacent terranes in this region. The data also will be valuable in addressing the timing of transfer of regional slip from the San Andreas fault strands (s.s) to the San Jacinto fault, will improve our ability to evaluate when and how the entire San Andreas system became effectively "locked" in this region; will sharpen the focus of local investigations of slip rates on the San Andreas, and on how regional shear between the Pacific and American plates is propagated through the Transverse Ranges province.