Stratigraphy and sedimentology of eastern equatorial Pacific ODP site 677: Late Miocene through Pleistocene.

摘要

Late Miocene through Pleistocene records of calcium carbonate and biogenic opal rich, pelagic deep sea sediments are described and classified using a three component classification. Seven sedimentary units are identified using this method, which illustrates how the relative amount of each sedimentary component (calcium carbonate, opal, and non-biogenic) changes with time. Smear slide estimates of the opaline component in the sediments of Hole 677A are compared with analytical measurements of % biogenic opal, and are found to overestimate weight percent opal by approximately 10%. The radiolarian event biostratigraphy of 25 indicator species is documented in Holes 503A, 503B, 504, 677A, 677B, and RC12-66 of the eastern equatorial Pacific. Each radiolarian biostratigraphic event is assigned a level of reliability between 1 (highest) and 5 (lowest), based on evidence of species abundance, evolutionary history, bioturbation, and sample size and spacing. The stratigraphic continuity of hydraulic piston cores from DSDP Site 504 and ODP Site 677 is tested using methods of graphic and non-linear correlation. Discontinuities of stratigraphic sections are attributed to technical difficulties of coring, especially ship heave. The biostratigraphy of the sites are also compared using graphic correlation in order to determine whether biostratigraphic events are synchronous between the holes examined. Two radiolarian datum levels, the FAD of Pterocanium prismatium and the FAD of Lamprocyrtis nigriniae are found to be significantly diachronous between the sites. All datum levels are tied to the benthic {dollar}deltasp{lcub}18{rcub}{dollar}O record in Hole 677A. Absolute ages are assigned to 22 radiolarian first and last appearance datum level events by linear interpolation between paleomagnetic ages in dated cores. The dated biostratigraphic events are then used to set up a chronology for ODP Hole 677A. Several age models for Site 677 are generated with this data, and are then compared and tested. The best age model determined for Hole 677A is then used to reduce the uncertainty in the estimated ages of the radiolarian biostratigraphic events, to within 139 kyr. A total of 67 radiolarian species are assessed for stratigraphic significance in the cores and are listed in the appendix.