Regional characteristics, timing, and significance of dissolution and collapse features in Lower Cretaceous carbonate platform strata, Desoto Canyon area, offshore Alabama-Florida

Abstract

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. The collapsed zones across the study area were mapped using a tight 2-D seismic grid. The zones of dissolution-collapse form a crude rectilinear pattern in plan view with the average trend of more elongated sections of the dissolution features being subparallel to regional southwestward dip on the Lower Cretaceous platform. Larger collapse features developed near the modern erosional margin that defines the seaward limit of the Lower Cretaceous platform in the study area. Middle Cretaceous strata up to approximately the Coniacian-Santonian unconformity (middle Late Cretaceous age) have numerous compaction-related faults around sagged areas above apparent dissolution-collapse zones within Lower Cretaceous strata. Bi-directional stratal onlap into the collapsed and sagged zones is only found above the Coniacian-Santonian unconformity. These relationships suggest a regional confined freshwater aquifer system developed within the Lower Cretaceous interval at about Coniacian-Santonian time when meteoric groundwater likely flowed from recharge areas to the north in central Alabama and discharged along the western erosional escarpment of the Lower Cretaceous platform. This meteoric groundwater may have mixed either with seawater that infiltrated the platform from the escarpment edge or with hydrogen-sulfide-rich basinal fluids that migrated to structurally high areas (where the dissolution-collapse zones are found). Alternatively, some combination of these mixing processes may have been responsible for the intense and likely still ongoing dissolution in this area of the Lower Cretaceous carbonate platform.