Foraminifera of the Early Miocene upper part of the Anahuac Formation from a well in Vermilion Parish, Louisiana, USA

The Anahuac Formation in the United States Gulf of Mexico coastal plain has been previously placed in the middle to late Oligocene based on larger benthic foraminifera. In the subsurface of Vermilion Parish, Louisiana, the upper part of the Anahuac Formation of the #1 J.W. Steen well is assigned an early Miocene age based on planktic foraminifera. More precisely, both the Globigerinoides primordius Interval Subzone (M1a) and Globorotalia kugleri/Globoquadrina dehiscens Concurrent Range Subzone (M1b) of the Globorotalia kugleri Total Range Zone (M1) and the Catapsydrax dissimilis Partial Range Zone (M2) are represented. The benthic foraminiferal Heterostegina and Discorbis zones are present and the Oligocene-Miocene boundary probably occurs within the Heterostegina Zone but beneath the studied interval, Paleoenvironmental reconstructions based on benthic and planktic foraminifera indicate that the Anahuac Formation in the #1 J.W, Steen well was deposited at outer neritic depths (100-250 m) during the earliest Miocene. Deposition shallowed to middle neritic depths (50-150 m) within Zone Mlb, The uppermost studied section within the Catapsydrax dissimilis Zone (M2) was deposited in slightly shallower (20-100 m), but still middle neritic conditions. Three candidate maximum flooding surfaces are identified. Seventy three planktic and benthic taxa are illustrated via scanning electron micrographs.