(Table 2) Sub-bottom depths, biostratigraphic zones, and ages for major reflectors at DSDP Site 85-574

• Main Authors: Mayer, Larry A, Shipley, Thomas H, Theyer, Fritz, Wilkens, Roy H, Winterer, Edward L
• Format: Dataset
• Language: English
• Published: PANGAEA 1985
• Subjects: 85-574_Site; AGE; maximum/old; minimum/young; Color description; COMPCORE; Composite Core; Deep Sea Drilling Project; Depth; bottom/max; sediment/rock; top/min; Diatom zone; DSDP; Glomar Challenger; Leg85; Nannofossil zone; North Pacific/TROUGH; Planktic foraminifera zone; Radiolarian zone; Antarctic; Drake Passage; Pacific; Antarc*
• Online Access: https://doi.pangaea.de/10.1594/PANGAEA.803640; https://doi.org/10.1594/PANGAEA.803640

The analysis of high-resolution watergun seismic profiles collected in support of DSDP Leg 85 drilling reveals several major, regionally traceable reflectors that can be correlated over more than 360,000 km**2 in the central equatorial Pacific. Synthetic seismograms generated from shipboard physical property measurements (carefully corrected to in situ values) for DSDP Site 574 show excellent agreement with the field records; the agreement suggests that the traveltimeto- depth conversion is accurate and permits the precise (± 5 m) location of reflectors in the cored section. The reflectors can be dated (±0.5 Ma) as follows: Orange, 21.5 to 22.5 Ma; Yellow, 20.5 to 21.5 Ma; Lavender, 16 to 17 Ma; Red, 13.5 to 14.5 Ma; Purple, 11 to 12 Ma; Brown, 7 to 8 Ma; and Green, 3 to 4 Ma. Similar analyses at the other Leg 85 sites result in identical ages. The reflectors are thus time surfaces; this chapter relates them to major paleoceanographic events and changes in the relative sea-level curve. The Orange and Yellow reflectors are associated with a marked increase in d13C, a major change in planktonic foraminiferal assemblages, the development of the deep Circum-Antarctic Current, and the establishment of steep thermal gradients between tropical and polar regions. This reorganization of the oceanic circulation system was probably a response to the opening of the Drake Passage, and it resulted in changes in the chemistry of tropical Pacific waters that caused the induration (and thus impedance contrasts) associated with these reflectors. The Lavender reflector is associated with a large carbonate minimum, the "Chron 16 carbon shift," a widespread hiatus (NH2), major eustatic sea-level fluctuations, and a significant increase in silica deposition in the Pacific. It is not associated with 18O enrichment or climatic cooling. We conclude that this event represents an intensification in Antarctic Bottom Water (AABW) circulation and the partitioning of silica between the Atlantic and the Pacific, caused by the introduction of ...