Facies distribution and dissolution depths of surface sediment components from the Vema channel and the Rio Grande rise (southwest Atlantic Ocean)

Facies Evolution, Carbonate Dissolution Cycles in Sediments from the Eastern South Atlantic (DSDP Leg 40) Since the Early Cretaceous

“…The degree of fragmentation of planktonic foraminifers observed in the coarse fraction is considered to reflect the degree of carbonate dissolution. In general, the dissolution of calcareous nannofossils increases with increasing water depth (Berger, 1973;Melguen and Thiede, 1974). With increasing carbonate dissolution the abundance of planktonic foraminifers decreases while the abundance of benthic calcareous foraminifers, which on the whole are more resistant to dissolution, increases.…”

“…With increasing carbonate dissolution the abundance of planktonic foraminifers decreases while the abundance of benthic calcareous foraminifers, which on the whole are more resistant to dissolution, increases. Therefore deep-sea sediments show an increasing benthic-to planktonic-foraminiferal ratio with progressive dissolution, and calcareous benthic foraminifers persist at oceanic depths greater than the depth at which all planktonic foraminifers have been destroyed (Melguen and Thiede, 1974;Adelseck, 1977). Dissolution of calcareous fossils leads to a relative enrichment of fish debris in the sediments.…”

“…The boundary in fact is a zone, or range of depths, but is narrow enough to be considered effectively as a specific depth. This level is considered equivalent to the "foraminiferal-lysocline:" In the Rio Grande Rise area it is 500 meters higher than the CCD (Melguen and Thiede, 1974). Elsewhere this depth difference can vary by several hundred meters (Berger et al, 1976;Biscaye et al, 1976;Venkatarathnam et al, 1976).…”

Carbonate Spikes and Displaced Components at Deep Sea Drilling Project Site 515: Pliocene/Pleistocene Depositional Processes in the Southern Brazil Basin

“…First, the present-day lysocline and CCD in the Rio Grande Rise region are about 4050 m and 4200 m, respectively (Melguen and Thiede, 1974). If these levels had fluctuated by only 100 to 200 m, alternate preservation and nonpreservation of CaCO 3 should result, and could possibly explain the record we see in Hole 515A.…”

“…Hole 515A was cored at a water depth of 4252 m. Previous studies of core top samples from this region have shown the carbonate lysocline to be at about 4050 m, and the carbonate content of sediments from depths in excess of 4200 m to be negligible as a result of the increase in CaCO 3 dissolution with depth (Melguen and Thiede, 1974;Johnson et al, 1977;Broecker and Takahashi, 1978). However, during routine analyses on Barker,P.…”