High-Resolution Biostratigraphy in Miocene–Pleistocene Sediments from Two Wells in the Western Gulf of Mexico

Abstract

An integrated high-resolution biostratigraphic study was conducted using calcareous nannofossils, planktonic and benthic foraminifers, and palynomorphs from two wells in the western Gulf of Mexico. Sediments range in age from early Pleistocene to middle Miocene. The early Pleistocene is represented by nannoflora of biozone NN19 and microfauna from the Globorotalia truncatulinoides truncatulinoides biozones and by the dinocyst species Spiniferites delicatus, Spiniferites membranaceous, Multispinula quanta, and Hystrichokolpoma rigaudiae. These sediments were deposited under inner to middle neritic bathymetric conditions. The Pliocene was characterized by nannofossil biozones NN18, NN17, NN16, and NN15, and the NN14–NN12 interval; foraminifera biozones of Globorotalia miocenica, Globorotalia tosaensis tosaensis, Globorotalia margaritae, and the dinoflagellate cyst species; and Polysphaeridium zoharyi, Lingulodinium machaerophorum, Melitasphaeridium choanophorum, and Operculodinium crassum. Paleobathymetry was inner neritic-upper bathyal. Late Miocene sediments produced microfossils indicating nannofossil biozones NN11, NN10, NN9, and the Globorotalia humerosa and Globorotalia acostaensis planktonic foraminiferal biozones. Dinoflagellate cysts found in these sediments were Spiniferites mirabilis, Dapsilidinium pastielsii, Sumatradinium hispidum, and Achomosphaera andalusiensis. These sediments were deposited under outer neritic-upper bathyal conditions. Middle Miocene strata are represented by calcareous nannofossil biozones NN9, NN8, NN6, and NN5, and by the planktonic foraminiferal biozones Globorotalia mayeri, Globigerinoides rubber, Globorotalia fohsi lobata-Globorotalia fohsi robusta, Globorotalia fohsi fohsi, and probably by the upper part of the Globorotalia fohsiperipheroronda biozone. These strata were deposited mainly in outer neritic-upper bathyal environments. Nannofossil diversity and abundance show notable variations throughout the two wells. A strong predominance of calcareous nannofossils and marine palynomorphs is present in outer neritic settings, and a planktonic foraminifer increase is observed mainly in the upper bathyal of well A. Continental palynomorphs are abundant in inner neritic-middle neritic settings, and a reduction is observed in the outer neritic-upper bathyal in well B.