Rock magnetic and paleomagnetic applications to Paleogene climate change and tectonics: Studies from eastern North America and Central Tibet

This dissertation is composed of three individual studies that utilize rock and paleomagnetism to investigate environmental change and regional tectonics during two major events that characterize the Paleogene period (∼65--24 Ma): the Paleocene-Eocene Thermal Maximum (PETM) and the continental collision between India and Asia.;In Chapter 2, I use magnetic hysteresis measurements, low-temperature demagnetization techniques, and transmission electron microscopy to show that the sudden appearance of single-domain magnetite at the Paleocene-Eocene boundary (∼55.5 Ma) on the eastern North American continental shelf is due to the enhanced production and preservation of biogenic magnetite at the onset of the PETM. The discovery of biogenic magnetite indicates that significant changes in the ecological communities, productivity, and redox conditions of the water and sediment column on the eastern North American continental shelves accompanied the sudden global warming and carbon cycle perturbation that characterize the PETM. I conclude that seasonally enhanced runoff and increased stratification and nutrient loading of the coastal oceans in eastern North American led to hypoxic conditions that fostered the production, diversification, and preservation of magnetite-producing microorganisms.;Chapters 3 and 4 focus on the paleomagnetism of Paleogene and Neogene volcanic and sedimentary rocks from Central Tibet. The goals of these studies are manifold, but remain focused on the central problem of calculating a reliable paleolatitude estimate for Central Tibet for the late Paleogene. In Chapter 3, I describe the paleomagnetic results from 40--30 Ma volcanic rocks from Central Tibet. These lavas record an unbiased maximum likelihood paleolatitude of 25.9+/-5.6°N Importantly, these results are the first Cenozoic volcanic data from the Tibetan Plateau with enough units to average secular variation well enough to yield a reliable paleolatitude estimate. This paleolatitude estimate is significantly lower than the ∼36+/-3°N predicted for Central Tibet by late Paleogene Eurasian reference poles, consistent with the so-called Central Asian inclination/paleolatitude anomaly, but is indistinguishable from values predicted from late Paleogene reference poles for Mongolia. The mean inclination of coeval sedimentary rocks from Central Tibet is 7.5+/-6.5° shallower than our volcanic results, but not significantly different when flattening of the remanent magnetization by sedimentary processes is corrected by Elongation/Inclination methods. Therefore, I conclude that most of the inclination/paleolatitude anomaly that remains after removal of sedimentary flattening probably is due to the combined effect of reference poles that are not representative of stable Asia and by Cenozoic intracontinental shortening within Central Asia. My results from these volcanic rocks and compilation of other paleomagnetic data from Qiangtang further suggest that the southern margin of pre-India Asia was located at least as far south as 21°N in Early Eocene time (∼50 Ma).;In Chapter 4, I present new paleomagnetic data from Cretaceous and upper Oligocene to lower Miocene lavas and sediments as well as a review of published paleomagnetic data from rocks of these ages. The goal is to evaluate the post-middle Cretaceous latitudinal displacement of Central Tibet and the distribution of vertical axis rotations in space and time throughout this region. My results suggest that Central Tibet maintained a relatively stable latitude of ∼20°N from the middle Cretaceous to the late Paleogene. Furthermore, I document large pre-Miocene counterclockwise rotations in Central Tibet that are consistent with localized block rotation by basin bounding sinistral strike-slip faults and suggest that strike-slip faulting may have been active in the plateau interior prior to the Miocene.;Chapter 4 concludes with a review of the latitudinal displacements of terranes surrounding Central Tibet beginning in the middle Cretaceous and the distribution of post-middle Cretaceous crustal deformation throughout the Himalayan-Tibetan orogen. Distinct changes in the distribution of crustal deformation within the orogen occurred ∼30--25 Ma and again ∼20--15 Ma. These events correlate well with significant changes in the boundary forces surrounding the Tibetan plateau and the spatial extent of the high elevation plateau as inferred from crustal thickness estimates and paleoaltimetry studies. I suggest that changes in the boundary conditions, internal strength, and gravitational potential energy of the proto-plateau drove strain partitioning throughout the orogen. (Abstract shortened by UMI.)...