Print this pageABSTRACT: Miocene stacking patterns and climatic records: Are the sequences global?
Abreu, Vitor1, George Covington1, Thomas Elliott1,
Andre Droxler2, Andrei V. Belopolsky2, and Anika Mutch2
(1)
Unocal, Sugarland, TX
(2) Rice University, Houston, TX
A reasonable generalization in most basins is that subsidence rates are slower than the rate of glacial eustatic oscillation. Thus, glacial eustasy can predominantly regulate stratigraphic architecture (i.e., creation of accommodation space). This assumption implies that sequences are likely to be global in scale during glacial episodes. In contrast, stratal-stacking patterns in tectonic active areas or during nonglacial intervals may be more regional in scale. Therefore, an improved record of glaciation provides a stronger basis for global sequence stratigraphic interpretations.
Oxygen isotope records from deep-sea sediments represent a proxy for sea level since the Cretaceous. Three low-frequency isotope cycles (~35 Myr.) are recognized, encompassing most of the Late Cretaceous, most of the Paleogene and most of the Neogene period. These isotope cycles are characterized by warming and cooling of the world oceans and growth and decay of high-latitude ice caps. The base of the Neogene cycle is characterized by a cold excursion (dramatic sea-level fall) close to the Rupelian/Chattian boundary (mid-Oligocene), related to major growth of the East Antarctica Ice Sheet. There is a continuous trend to negative values from the Late Oligocene to the Early Miocene (higher sea level), culminating in the Langhian (base of the Middle Miocene). This ~10 Myr. rise in sea level punctuated by higher-frequency fluctuations flooded the continental margins causing mostly backstepping and aggradation during the Early Miocene. The accommodation space created during this transgression was filled on most margins by a Middle Miocene prograding wedge related to a major drop in sea level. Sea level was fairly low also during most of the Late Miocene, high during the Early Pliocene and low in the Late Pliocene and Quaternary. This global climatic record is compared and contrasted with sequence stratigraphic records from basins in Southeast Asia and worldwide, both in tectonic active and passive margins.
AAPG Search and Discovery Article #90913©2000 AAPG International Conference and Exhibition, Bali, Indonesia