CaCO3, organic carbon and mass accumulation rates at DSDP Site 75-532

• Main Authors: Gardner, James V, Dean, Walter E, Wilson, Christine R
• Format: Dataset
• Language: English
• Published: PANGAEA 1984
• Subjects: 75-532; 75-532A; 75-532B; Deep Sea Drilling Project; DRILL; Drilling/drill rig; DSDP; Glomar Challenger; Leg75; South Atlantic; Pacific; Northeast Atlantic
• Online Access: https://doi.pangaea.de/10.1594/PANGAEA.810144; https://doi.org/10.1594/PANGAEA.810144

Detailed carbonate and organic-carbon stratigraphies were constructed from samples collected every 20 cm in a 250-m hydraulic piston core recovered at DSDP Site 532 on Walvis Ridge. This sampling interval represents about one sample every 5000 yr., based on sediment accumulation rates calculated from nannofossil biostratigraphic zones. All samples were analyzed for percent CaCO3, resulting in a detailed carbonate stratigraphy for the past 5.0 m.y. The samples for the top 110 m of section were also analyzed for organic carbon in order to construct a detailed organiccarbon stratigraphy for the last 2.5 m.y. The recovered section has distinct dark-light color cycles with average periodicities of 55, 58, and 30 k.y. for the Quaternary, upper Pliocene, and lower Pliocene, respectively. Periodicities of carbonate cycles are similar to the color cycles; most carbonate minima correspond to the dark parts of color cycles. The average periodicity for carbonate cycles is about 36 k.y. Darker parts of color cycles usually contain higher concentrations of organic carbon, but the organic- carbon record does not follow the cyclicity of the color cycles in detail, at least for the last 2.5 m.y. Organic-carbon cycles have an average periodicity of about 34 k.y. for the Quaternary and upper Pliocene. The cycles of CaCO3 and color have periodicities similar to those reported from carbonate stratigraphies from the northeast Atlantic, Caribbean, and eastern equatorial Pacific. The carbonate cycles at Site 532 are the result of external forcing, probably related to global climate, that affected fluctuations in both sediment supply from the African continental margin and productivity of siliceous organisms. The organic-carbon cycles have similar periodicities and similar changes in periodicities to those of the CaCO3 cycles. Semiquantitative estimates of diatom abundance from smear slides and concentrations of biogenic SiO2 calculated from chemical analyses suggest that upwelling at Site 532 was minor until about 3 m.y. ago. The ...