The taphonomy of deep-sea benthic foraminifera: comparisons of living and dead assemblages from ☐ and gravity cores taken in the Sulu Sea

Abstract

Comparisons between Soutar ☐ core faunal data and gravity core-top data from about 500 m to 4000 m in the Sulu Sea show that living (stained) benthic foraminiferal assemblages have similar faunal patterns to those observed in living + dead assemblages. For both assemblages, faunal abundances and diversities decrease with increasing water depth to 4000 m, and ☐ core samples and gravity core-top sediments taken from the same water depth yield similar dominant taxa. The similarity of living and living + dead assemblage data indicates that at least most of these faunal patterns are independent of seasonal variations, and that neither seasonality nor post-depositional effects can account for the absence of significant numbers of Bolivina, Bulimina, Globobulimina, Chilostomella, and Uvigerina below about 1500 m in the Sulu Sea. The distribution of these taxa are similar in both ☐ cores and gravity core-top sediments, reconfirming the conclusion that the distributions of living representatives of these taxa are not due to bottom-water oxygen concentrations. Differences which exist between living assemblages and combined living and dead assemblages of deep-sea benthic foraminifera from about 500 m to 4000 m in the Sulu Sea result primarily from surficial material loss in gravity core samples, mixing of older material from subsurface sediments, and postdepositional destruction of some taxa. Based on the additional examination of the living + dead assemblages found in 0.5 and 1 cm intervals of the top 10 cm in two ☐ cores (1980 m and 3000 m), differences in abundance and percentage patterns for fauna found at 2000 and 3000 m in the Sulu Sea are not correlated with sedimentation rate, but appear to be more strongly influenced by mixing from older material and postdepositional processes in the sediments. Increasing the interval of sediments examined does not necessarily improve the similarity between living assemblage faunal patterns and those of the dead or combined living and dead assemblage.