473 resultados para Depth Keying
Resumo:
Five sections drilled in multiple holes over a depth transect of more than 2200 m at the Walvis Ridge (SE Atlantic) during Ocean Drilling Program (ODP) Leg 208 resulted in the first complete early Paleogene deep-sea record. Here we present high-resolution stratigraphic records spanning a ~4.3 million yearlong interval of the late Paleocene to early Eocene. This interval includes the Paleocene-Eocene thermal maximum (PETM) as well as the Eocene thermal maximum (ETM) 2 event. A detailed chronology was developed with nondestructive X-ray fluorescence (XRF) core scanning records and shipboard color data. These records were used to refine the shipboard-derived spliced composite depth for each site and with a record from ODP Site 1051 were then used to establish a continuous time series over this interval. Extensive spectral analysis reveals that the early Paleogene sedimentary cyclicity is dominated by precession modulated by the short (100 kyr) and long (405 kyr) eccentricity cycles. Counting of precession-related cycles at multiple sites results in revised estimates for the duration of magnetochrons C24r and C25n. Direct comparison between the amplitude modulation of the precession component derived from XRF data and recent models of Earth's orbital eccentricity suggests that the onset of the PETM and ETM2 are related to a 100-kyr eccentricity maximum. Both events are approximately a quarter of a period offset from a maximum in the 405-kyr eccentricity cycle, with the major difference that the PETM is lagging and ETM2 is leading a 405-kyr eccentricity maximum. Absolute age estimates for the PETM, ETM2, and the magnetochron boundaries that are consistent with recalibrated radiometric ages and recent models of Earth's orbital eccentricity cannot be precisely determined at present because of too large uncertainties in these methods. Nevertheless, we provide two possible tuning options, which demonstrate the potential for the development of a cyclostratigraphic framework based on the stable 405-kyr eccentricity cycle for the entire Paleogene.
