Marine Carbonate Production Research Articles

Carbonate dissolution revealed by silt grain‐size distribution: comparison of Holocene and Last Glacial Maximum sediments from the pelagic South Atlantic

AbstractThe current issue of global warming and the role of the ocean in global exchange of CO2 increases the interest in solid budgets of marine carbonate production and dissolution. The present study utilizes grain‐size composition of pelagic sediments in order to trace spatial and temporal variability of carbonate sedimentation in the South Atlantic for the Holocene and Last Glacial Maximum (LGM, 19–23 cal kyr BP). A decrease in grain size (e.g. sand content, mean grain size of coarse carbonate silt) indicates increased carbonate dissolution as a result of increased fragmentation of calcareous microfossils. The spatial grain‐size pattern suggests a threshold water depth below which a gradual grain‐size decrease becomes increasingly rapid. This water depth is considered as the sedimentary lysocline. For the Holocene time slice, a constant, gradual decrease of foraminifer carbonate of about 5–10% per 1000 m water depth above the lysocline gives evidence for supra‐lysoclinal dissolution. The water depth of the lysocline for the Holocene is tied to the interface of North Atlantic Deep Water and Antarctic Bottom Water (AABW) (ca 4100 m). Submarine ridges which restrict intrusion of AABW into the Angola Basin cause an asymmetry in carbonate preservation across the Mid‐Atlantic Ridge. The lysocline was reconstructed at ca 3100 m for the LGM. These data suggest that the ca 1000 m rise of the lysocline eradicated the Holocene east–west asymmetry.

The stratigraphical relationship between planktonic and larger benthic foraminifera in Middle Miocene to Lower Pliocene carbonate facies of Sulawesi, Indonesia

The Tacipi Formation of Sulawesi was deposited during the late middle Miocene to early Pliocene in a large area of shal- low water, marine carbonate production with deeper water sediments deposited to the north. A detailed biostratigraphical study of 580 samples from 58 measured outcrop sections has led to an understanding of sequence stratigraphic and facies relationships of Cenozoic carbonates in Sulawesi, their importance as the product and record of climatic/oceanic conditions and interchange in tropical/subtropical inner shelf environments, and their role as hydrocarbon reservoirs. Fifteen larger benthic foraminifera species are described and illus- trated with one newly proposed taxon: Lepidocyclina pillaria. Analysis of the larger benthic foraminifera in relationship to the plank- tonic foraminifera allows correlation of the larger foraminiferal assemblage zones (letter stages) of the Far East with the N zones of the Neogene based on planktonic foraminiferal evolution patterns. The co-occurrence and recognition of planktonic foraminifera and larger benthic foraminifera species in the same thin sections is a rare opportunity for correlating the biostratigraphic frameworks based on these two groups and is of regional stratigraphic importance. This has resulted in the refinement of the biostratigraphic ranges of the larger ben- thic foraminifera Katacyclocypeus and Flosculinella, and enlargement of our knowledge about the Tg and Th letter stages.