Sequence analysis of Western Venezuelan cretaceous to Eocene sediments using Palynology: Chronopaleoenvironmental and paleovegetational approaches
1997
Rull, Valentí
Palynological evidence currently used to determine the global eustatic cycles of Haq et al. (1987) requires the existence of sediments from both continental and marine environments. The present work is a contribution to sequence analysis using sediments of continental nature. The boundaries of palynological zones help to locate and date sequence boundaries (SB) and maximum flooding surfaces (MFS); the SB is characterized by hiatuses and/or sudden floral changes (type 1 SB) and barren intervals with oxidized kerogen (type 2 SB), while the MFS may have a few brackish or marine water representatives. When marine fossils are absent, only paleovegetational criteria can be used. In this case, multivariate methods are used to find the most reliable pollen associations. Among them, the coastal and the more inshore associations are selected to compute an index that estimates the position of the tidal limit (TLI). The lateral movements of this tidal limit are recorded and correlated with corresponding sea level fluctuations, thus inferring the SB and MFS from paleovegetational data. The application of these methodologies to two wells from the Maracaibo Basin (western Venezuela) allowed determination of Maastrichtian to Eocene 3rd order cycles from the supercycle sets Upper Zuni A and Tejas A, as well as reconstruction of the local paleogeography of the coastal area.
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