Miocene Drowning of Temperate (Foramol) Carbonate Platform: Upper Miami Terrace

Gabrielle Carannante, Lucia Simone, Conrad Neumann

Oligocene neritic rocks dredged from 350 m on the upper Miami Terrace exhibit repeated phosphatization as well as a filled void system containing post-Burdigalian foraminifera. During drowning, a neritic hardground was subjected to both pelagic deposition (infills) and repeated marine exposure (borings, P-coatings, etc). The neritic grainstone-packstone contains large benthic foraminifera, red algae, bryozoans, pelecypods, ahermatypic corals, echinoids, and some planktonic foraminifera. This compositional association is the Foramol type characteristic of temperate to subtropical neritic environments such as the present Mediterranean, Brazilian, and New Zealand shelves. These temperate sediments derive from the local biocoenose, and accumulate slowly in deep sheets of loos skeletal debris. They become relict seaward where they are often bored, corroded, stained, glauconitized, and cemented into hardgrounds. Locally, hemipelagic cover might produce a palimpsest sequence. Recent Foramol-type platforms are undergoing drowning. The Miami Terrace is compared to very similar Miocene Foramol-type platforms now exposed in the southern Apennines. Both are characterized by neritic sequences passing upward into hemipelagics, via a palimpsest interval marked by glauconitic, phosphatic, iron-stained grains often mineralized into hardgrounds. The drowning of the Miami Terrace hence coincided with and, we suppose, was a result of the shift from a rapid, oligotrophic, tropical accumulation to a slow, temperate, eutrophic carbonate accumulation caused in turn by a tempora y paleo-oceanographic shift to cooler, richer, neritic conditions within the history of this now subtropical setting.

AAPG Search and Discovery Article #91043©1986 AAPG Annual Convention, Atlanta, Georgia, June 15-18, 1986.