Palaeoenvironmental assessment of Early Cretaceous limnic ostracods from the Alagamar Formation, Potiguar Basin, NE Brazil

Source rocks from the Alagamar Formation were analysed and fifteen non-marine ostracod species and one foraminifer species were identified. Thecamoebians, gastropods, fish teeth and incertae sedis material also occurred. Among these fossils, an agglutinated foraminifer, Gaudryinella sp. aff. G. sherlocki, and occurrences of foraminiferal organic linings, indicate deposition under transitional marine (paralic) influence. Harbinia crepata is considered holoeuryhaline, Paracypria? elongata brackish stenohaline and the other ostracods are freshwater euryhaline. Limnocytheridae ostracods together with foraminifers occurred in intercalated beds, and this pattern of changes in associations is herein interpreted as a record of temporal changes, characteristic of transitional palaeoenvironments. Previous studies on biomarkers and some articles dealing with palynomorphs also suggest that at least part of this unit was deposited in lagoonal conditions.