Microforaminiferal linings as proxies for paleosalinity and pollution: Danube Delta example

Acid-resistant, chitin-like organic linings of foraminiferal tests in palynological assemblages are commonly considered reliable indicators of marine transgressions despite sparse information on the relationship between the organic and inorganic skeletal components. This knowledge gap constrains reliable application in paleoecological studies. Foraminiferal lining recovery in palynological samples also varieswith the chemicals and temperature used for extraction of organic residues, and care is needed to avoid damage by hydrolysis or over-oxidation. Using samples treated onlywith cold acid, we describe the test-lining relationship for five common benthic foraminiferal species from order Rotaliida in the polluted, eutrophic, microtidal environment of the Black Sea. Papillate and granulate ornament on lining surfaces reflect the morphology of benthic foraminiferal living in the low oxygen environments of the Black Sea where pore size and frequency may be related to survival. Data from 23 surface samples from the Danube delta plain and offshore in the northwest (NW)Black Sea demonstrate the relationship between benthic foraminifera and their linings in a qualitative model characterising environments from delta plain (-1.8 m water depth) to outer shelf and continental slope (>90 m), along a surface salinity gradient from about 5 to 17 psu. Compared with microforaminiferal assemblages in high salinity deltaic and coastal environments of Atlantic and Pacific Oceans, the lining abundances of the semi-marine Danube- region sediments are relatively low but they often exceed the foraminiferal abundances at the same site.A Dissolution Index based on log (organic lining: test ratio) shows that calcite preservation is low in most of the Danube Delta sub-environments. Test and lining deformity, large pore-size, and pyritization of tests and linings appear to reflect hypoxia and eutrophication. The new data provide a baseline for paleocological studies of coastline changes in the Danube Delta region, and for better understanding of marine transgressions in Paratethyan basins.