Miocene Isotope Chronostratigraphy: North-central Gulf of Mexico

Abstract

Isotope chronostratigraphy has proven extremely useful in providing high resolution stratigraphic correlations and detailed information relating to the complex nature of sediment accumulation rates in Plio-Pleistocene exploration wells of the north-central Gulf of Mexico (GOM). Current research on the isotopic composition of foraminifera recovered from Miocene age sediments in the north-central GOM indicate that the glacio-eustatic cycles documented in the Plio-Pleistocene are found to continue into the late Miocene. During the middle Miocene ample isotopic signals (3 per mil) exist to provide a high resolution stratigraphy. {delta}{sup 18}O data from the planktonic foraminifera Orbulina universa from Eureka core 66-73 in the Desoto Canyon form a relatively complete record from approximately 8.5-16 Ma. The record displays a greater than 3 per mil range in {delta}{sup 18}O values through the middle Miocene. This Miocene {delta}{sup 18}O record from E66-73 is compared to exploration wells from the following areas: Mississippi Canyon, central GOM, East Breaks, South Galveston, and the Green Canyon. In the downdip, deeper water sections, the primary water column signal appears to be well preserved through the middle Miocene. When working updip in shallower water depths, there appears to be some diagenetic zones displaying extremely negative {delta}{sup 18}O values ({gt}-6 permore » mil) that could be related to fluid migration events or possibly related to sand occurrence. Also found in these updip wells is a zone of consistent diagenetic overprint in the lower section of the well. In this interval, the base line for the {delta}{sup 18}O values is shifted by as much as 3-4 per mil in the negative direction.« less