Seminar

In this talk, the speaker will present two examples of paleomagnetic studies to show how fossil magnetic records can contribute to better understanding of tectonics and environmental changes by providing a refined chronology. The first example concerns the subduction of Cocos Ridge (CR), which plays a critical role in governing the tectonic evolution of the Central American margin, a typical erosive convergent margin. One outstanding question in understanding the tectonic evolution of this region is the timing of the initial CR subduction. Estimates from the upper plate vary widely from late Miocene to Pleistocene. Paleomagnetic data from IODP Site U1381, which was drilled directly on the CR, and analyses of sedimentary records from other ODP/IODP sites on Cocos Plate provide a minimum age estimate of 1.52 Ma for the onset of the CR subduction. The refined chronology contributes to better understanding of material flux at the erosive convergent margin. The second example is focused on the late Paleogene terrestrial record from Maoming Basin in Southern China. Although drastic changes in lithology are commonly recognized should indicate major environmental changes, the available fossil-based chronology does not offer adequate temporal resolution to decipher environmental changes.  Detailed magnetostratigraphic data, together with litho-, bio-stratigraphy of the Upper Paleogene strata in Maoming Basin, are used to establish an integrated stratigraphy that constrains a major environmental transition from lacustrine environment to a deltaic environment at ~33.88 Ma. This age coincides with the Eocene-Oligocene climate transition (EOT) at ~33.7 to ~33.9 Ma. Therefore, the ~33.88 Ma environmental change in Maoming Basin represents terrestrial responses to the global cooling at EOT.