941 resultados para 73-523
Resumo:
Fil: Chazarreta, Daniela Evangelina. Universidad Nacional de La Plata. Facultad de Humanidades y Ciencias de la Educación; Argentina.
Resumo:
Fil: Dip, Nicolás. Universidad Nacional de La Plata. Facultad de Humanidades y Ciencias de la Educación; Argentina.
Resumo:
Fil: Chazarreta, Daniela Evangelina. Universidad Nacional de La Plata. Facultad de Humanidades y Ciencias de la Educación; Argentina.
Resumo:
We present a revised calibration of Sr isotopes to the geomagnetic polarity timescale (GPTS) using closely spaced (~0.15 m.y. resolution) samples from the classic uppermost Eocene through lowermost Miocene section at Site 522, eastern South Atlantic. The Sr isotopic data are fit with two linear segments with a sharp change in slope at circa 27.5 Ma from 0.000038/m.y. (27.5 to 34.4 Ma) to 0.000051/m.y. (23.8 to 27.5 Ma). Regression analysis indicates that stratigraphic resolution ranges from ±1 m.y. (for one analysis) to ±0.6 m.y. (for three analyses) for the younger interval and ±1.2 m.y. (for one analysis) to ±0.7 m.y. (for three analyses) for the older interval, representing an increase in resolution from previous studies of ±1-2 m.y. The paleoceanographic significance of this change in slope is unclear. It occurs during an interval of intermittent Antarctic glaciation, between the Oi2a and Oi2b glaciations. The subsequent interval from circa 27 to 24 Ma appears to be an interval of minimal glaciation. Thus this observation does not support previous suggestions that increases in rates of Sr isotopic change are directly associated with the frequency of Antarctic glaciations. Rather, the increase in slope may be related to increased weathering associated with the "mid-Oligocene" glaciation.
