Early Eocene to early Miocene magnetostratigraphic framework for IODP Expedition 371 (Tasman Frontier Subduction Initiation and Paleogene Climate)

摘要

abstract_textpInternational Ocean Discovery Program (IODP) Expedition 371 (Tasman Frontier subduction initiation and Paleogene climate) was designed (1) to investigate the timing and dynamic of the Tonga-Kermadec subduction initiation and (2) to understand regional oceanography and climate in the southwest Pacific during the Cenozoic, in particular the Eocene. A total of 2506 m of sediments and volcanic rocks were recovered at six sites, drilled on the continental crust of northern Zealandia (Sites U1506-U1510) and on the eastern Tasman abyssal plain (Site U1511). Sediments from Sites U1506 to U1510 consist of late Cretaceous to Pleistocene nannofossil and foraminiferal ooze or chalk that contain volcanic or volcaniclastic intervals with variable clay content. Site U1511 recovered a series of Paleocene to Pleistocene abyssal clay and diatomite, with only minor amounts of carbonate. Shipboard magnetic polarity age-control of the carbonate-rich sediment is limited to the uppermost Eocene-Oligocene, while for the abyssal clay and diatomite, to the early-middle Eocene. To extend and refine the magnetostratigraphy of Expedition 371, we collected a total of 273 discrete paleomagnetic orientated samples from Holes U1507B, U1508C, and U1511B after the cruise. Reliable paleomagnetic directions were obtained in all sites. The correlation of carbonate-dominated sediments of Sites U1507 and U1508 with the geomagnetic polarity time scale indicates that the sedimentary succession extends from C21r to C5E (48-18 Ma), thus spanning a 30 Myr-long interval from the early Eocene to the early Miocene. The abyssal clay and diatomite at Site U1511 range from Chron C24n in the early Eocene to Chron C17n in the late Eocene, with unresolved magnetostratigraphy correlation across Chron C23n (52-51 Ma) due to coring disturbance. The improved age-model provides a robust chronological framework for understanding the evolution of Tonga-Kermadec subduction zone and paleoceanographic variations in the Tasman region during the Cenozoic./p/abstract_text