How To Discriminate Athalassic and Marginal Marine Microfaunas: Foraminifera and Other Fossils from an Early Holocene Continental Lake in Northern Saudi Arabia

The occurrence of athalassic foraminiferal species, along with the brackish-water ostracod Cyprideis torosa, the barnacle Amphibalanus amphitrite, and brackish-water gastropods, prove the existence of a saline lake at Tayma, northern Saudi Arabia, during the early to mid-Holocene. Outcrops at the former shoreline, as well as a single sediment core, allow a reconstruction of the history of the main lake phase. Whereas these outcrops contain masses of calcareous micro- and macrofossils, the core from the modern sabkha does not.Four foraminiferal species were identified: Ammonia tepida is dominant, Quinqueloculina seminula is common, Flintinoides labiosa and Discorinopsis aguayoi are rare. Sieve-pore analysis and shell chemistry of C. torosa, as well as varying but generally high proportions of test anomalies (up to 50%) in foraminifers, indicate fluctuating, mostly hypersaline lacustrine conditions. We suggest, based on these results and on a literature overview on the worldwide distribution of Quaternary athalassic foraminifer taxa, that a combination of low diversity, exclusively marginal marine taxa, combined with occurrences of test anomalies >10% can be used to recognize athalassic saline waters in the fossil record.