See more from this Division: Gulf Coast Association of Geological Societies
See more from this Session: Applied Micropaleontology: Tools and Techniques for the 21st Century
Tuesday, 7 October 2008: 8:20 AM
George R. Brown Convention Center, 310CF
Richard A. Denne, Applied Biostratigraphix, The Woodlands, TX
Abstract:
Due to their comparatively low resolution and the paucity of species restricted to open-ocean or nearshore environments, the standard calcareous nannofossil zonation schemes generally do not adequately subdivide expanded continental margin deposits. As attention has focused on the reservoir-prone Middle to Lower Miocene transition in the deep-water Gulf of Mexico, several new or often overlooked calcareous nannofossil taxa have proved useful in subdividing Martini (1971) zones NN6 NN3. These taxa include two forms of
Cyclicargolithus labeled
C. floridanus neogammation and
C. minutus, a variety of
Discoaster sanmiguelensis labeled
Catinaster sp. A, two forms of
Reticulofenestra (
R. aff.
R. daviesii and
R. gartneri), and a form of
Umbilicosphaera labeled
Umbilicosphaera sp. A. Although these forms are often lumped with other species, they are relatively common when care is taken to differentiate them. Utilizing last occurrences and downhole abundance increases (bioevents) of these forms as well as of those more typically identified, 42 bioevents of 19 different taxa were identified in the study interval. These bioevents were used to differentiate four horizons in the lower portion of zone NN6, seven horizons within zone NN5, seven horizons in zone NN4, and three horizons in zone NN3. These horizons are tied to abundance increases correlated to high order Maximum Flooding Surfaces.
Although rare forms are generally not reliable biostratigraphic markers, their highest occurrences can be used to indicate the presence of specific zones. These flags include both well-known and new forms. The most useful forms in the study interval include a large variety of Discoaster musicus near the NN6 / NN5 boundary, Helicosphaera obliqua and Triquetrorhabdulus milowii in zone NN5, Helicosphaera euphratis in zone NN4, Reticulofenestra lockeri in the lower portion of zone NN4, and Sphenolithus tintinnabulum and a form of Helicosphaera labeled H. neorecta in zone NN3.
See more from this Division: Gulf Coast Association of Geological Societies
See more from this Session: Applied Micropaleontology: Tools and Techniques for the 21st Century