Christine Iannello1, Steve Dorobek1
(1) Texas A&M University, College Station, TX
ABSTRACT: Regional Characteristics, Timing, and Significance of Dissolution-Collapse Features in Lower Cretaceous Carbonate Platform Strata, DeSoto Canyon Area, Offshore Alabama-Florida
Lower Cretaceous carbonate strata from the central DeSoto Canyon area, offshore Alabama and Florida, were studied to determine the extent, intensity, and controlling factors on dissolution-collapse features within these strata. Using a tight 2-D seismic grid, the collapsed zones across the study area were mapped, both horizontally and vertically. The zones of dissolution collapse are anastomosing in plan view with the average direction of elongation of the dissolution features subparallel to regional dip (northeast-southwest) on the Lower Cretaceous platform. More intense collapse features developed near the modern erosional margin that defines the seaward limit of the Lower Cretaceous platform in the study area. Middle Cretaceous to lower Oligocene strata have numerous compaction-related faults above the apparent dissolution-collapse features in Lower Cretaceous strata; vertical offset on these faults is the same throughout the Middle Cretaceous to lower Oligocene interval. Seismic stratigraphic relationships show no evidence of bidirectional onlap of Middle Cretaceous strata into the apparent collapse features. In contrast, bidirectional onlap can be found in collapse features along the middle Oligocene unconformity because the collapse zones in the Lower Cretaceous platform propagated upward and created seafloor topography during middle Oligocene time. These relationships suggest that a regional confined freshwater aquifer system developed within the Lower Cretaceous interval during middle Oligocene time. Groundwater flowed from eastern recharge areas in onshore Florida and discharged along the western erosional escarpment of the Lower Cretaceous platform. Development of an extensive mixing zone near the erosional escarpment may explain the more intense dissolution there.
AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado