Palynological evidence for sustained deep-marine conditions during the Eocene–Miocene in the southern Gulf of Mexico distal continental margin

Abstract

The present study represents the first attempt to provide palynological data about the southern Gulf of Mexico distal continental margin during the Eocene−Miocene time interval. In addition to documenting the types of fossil palynomorphs preserved in these economically critical rock sequences, this study also provides important information about the accumulation and preservation of total sedimentary particulate organic matter along with their paleoenvironmental and paleoceanographic implications. This was accomplished through the analysis of cored sediments from the Deep Sea Drilling Project Site 94 north of the Yucatan Peninsula and Site 540 south of the Western Florida Escarpment. The present findings from the deep waters of southern Gulf of Mexico are expected to greatly assist hydrocarbon geoscientists in their exploration and development efforts, reducing investment risk and drilling uncertainty. Two palynofacies assemblages were recognized based on particulate organic matter analysis: marine-dominated palynofacies A and terrestrially influenced palynofacies B. The organic compositions of these two palynofacies along with the recovered dinoflagellate cyst community suggest that while sustained oceanic depositional conditions were prevalent, occasional influxes of terrestrial organic material of variable magnitudes occurred. These short-term influxes were especially pronounced during the late Eocene and earliest Oligocene and appear to have happened in response to the cooling and slight global sea-level drop that occurred at ca. 38−33.5 Ma. The preserved terrestrial palynomorphs in the samples indicate coastal plain and estuarine vegetation sources in general, except during the Eocene-Oligocene transition, when anemophilous pollen specimens mostly derived from farther inland and montane sources were recovered.