Poster Number 144
See more from this Division: General Discipline Sessions
See more from this Session: Stratigraphy (Posters)
Abstract:
Cretaceous sequences vary from fluvial to marginal marine to exclusively marine. In marine sequences, the transgressive systems tract (TST) overlies sequence boundaries characterized by: 1) erosional features, 2)weathering profiles, 3) or faunal and floral gaps. In the middle to outer shelf, the TST consists of fine to coarse, retrogradational, fairly well-sorted, thin siliciclastic sand that is commonly glauconitic. TST parasequences are thin (3 m) and each younger parasequence contains finer sand.
The overlying highstand systems tract (HST) represents a series of aggradational and progradational parasequences that first thicken and then thin upward as accommodation moves laterally. Coarser sediments at the top of the HST usually have better porosity and permeability than sediments in the early, more aggradational part of the HST. Gamma-ray log analysis demonstrates that parasequences in the lower HST have greater clay content that gradually diminishes upward in the late HST. Condensed sections usually exhibit the highest gamma ray response within the sequence and are confining units.
Resistivity measurements through a complete marine depositional sequence indicate that suitable aquifer zones are contained within the thinner TST and the upper parts of the thicker HST. In some cases, hydraulic connectivity exists between the HST of an older sequence and the overlying TST of a younger sequence. In sequences where fluvial, fluvial-lacustrine, and deltaic sediments are common, the lower siliciclastic channel sands and distributary mouth bar complexes have the greatest porosity. The gamma-ray log indicates that these sands have little clay and are suitable aquifers.
See more from this Division: General Discipline Sessions
See more from this Session: Stratigraphy (Posters)