Potential Fluid-Migration Pathways Indicated by Multichannel-Seismic Data From the Southeastern Florida Platform

Abstract

2-D and 3-D seismic data and multibeam bathymetry provide new clues to fluid-migration pathways and for the first time evidence for potential long-term seafloor gas expulsion on the SE carbonate Florida Platform. On the Miami Terrace, a seafloor collapse structure is underlain by and in close proximity to paleo-pockmarks, a paleo-collapse structure, and paleo-slumps. The bathymetry of the seafloor collapse structure is funnel-shaped, and about 460-m long and 230-m wide along the top. It truncates mainly late Pliocene to Pleistocene strata and tapers downward to form a bottom slightly within Paleogene carbonate strata delineated at the top by a regional erosional unconformity. Calculated gas-chimney probability meta-attribute analysis suggests the presence of a gas chimney below the seafloor collapse structure. An observational report of the seafloor-depression walls indicates they are stratal outcroppings overlain by a 1-m veneer of soft sub-bottom sediment. In addition, a lower feeder pipe or ‘ring’ faults are suggested by the bathymetry data. These findings may rule out an origin related to a gas blowout and could indicate submarine karstic dissolution linked to fluid expulsion. The paleo-pockmarks occur below and to the east of the sinkhole and above the erosional unconformity, constraining the commencement of seafloor fluid-expulsion activity to probably the late Pliocene. Regional mapping and attribute analyses suggest subsurface migration of gas and fluids upward through a system of faults in Paleogene carbonate rocks and eastward stratiform migration up the western flank of an anticline. Attribute analysis also suggests that gas and fluids vent upward through isolated chimneys possibly focused along fractures on the anticlinal flank. Additionally, numerous buried vertical cone-shaped (apex upward) collapse structures are present beneath southeastern peninsular Florida and adjacent inner continental shelf. One of these structures is about 2.3 km high. The structures may have formed by collapse of paleocave systems and protracted, staged, vertical pathway production and fluid migration along faults, fractures, and karstic breccias. Seismic and multibeam data support a model of stair-stepping fluid migration within the carbonate strata of the Florida Platform, with lateral movement along high-permeablity stratiform pathways punctuated by vertical flow focused along karst-collapse structures, and faults and fractures of tectonic origin.

AAPG Datapages/Search and Discovery Article #90216 ©2015 AAPG Annual Convention and Exhibition, Denver, CO., May 31 - June 3, 2015