--> --> Abstract: Eocene-to-Miocene Karst Seismic-Sag Structural Systems, Southeastern Florida Platform, by Kevin J. Cunningham, Cameron Walker, and Jeffrey N. King; #90124 (2011)

Datapages, Inc.Print this page

Making the Next Giant Leap in Geosciences
April 10-13, 2011, Houston, Texas, USA

Eocene-to-Miocene Karst Seismic-Sag Structural Systems, Southeastern Florida Platform

Kevin J. Cunningham1; Cameron Walker2; Jeffrey N. King1

(1) U.S. Geological Survey, Fort Lauderdale, FL.

(2) Walker Marine Geophysical Company, Boca Raton, FL.

High-resolution, multichannel, seismic-reflection profiles recently acquired in and east of Biscayne Bay, and in canals of southeastern peninsular Florida, exhibit numerous vertically arranged sags and disruptions in reflections. In the study area, a southeastern part of the Florida Platform, the vertical features occur within mostly Eocene-to-middle Miocene karsted carbonates and uncommonly in upper Miocene siliciclastics. The sags are buried by upper Miocene-to-Holocene sedimentary rocks and sediments; however, they likely manifest as well-documented sinkholes along the submarine surface of the Pourtales and Miami Terraces. The vertical sags and disruptions in reflections are interpreted to be suprastratal deformation above collapsed paleocaves or collapsed paleocave systems, and represent (1) fractures; (2) faults; (3) narrow (hundreds-of-m-scale wide) seismic-sag structural systems; and (4) broad (km-scale wide) seismic-sag structural systems. Maximum height of the karst structures has been measured up to about 500 m; however, some may extend deeper, but no reliably interpretable stratal patterns exist within chaotic reflection-seismic configurations that prevail within the lower part of the seismic profiles. At most, the vertical relief on the sags is about 50 m. Commonly the seismic-sag structural systems are multistoried, exhibited as a vertical arrangement of cyclic zones of sagging reflections that suggest a progressive evolution from (1) cave formation; (2) cave collapse; (3) suprastratal sag; and (4) in some cases, final infill of the upward termination of sag zones. The seismic imaging provides clues as to the sealing capacity of confining units within the carbonate Floridan aquifer system. Faults or fractures or both associated with the large-scale, seismic-sag structures may promote the vertical flow of groundwater across relatively low-permeability carbonate strata that separates aquifers or subaquifers. Seismic-sag structures, and associated faults and fractures could act as regional “confinement” bypass systems. Preliminary numerical modeling in southeastern Florida corroborates the suggestion that “confinement” bypass systems act as potential pathways for the vertical migration of groundwater across relatively low-permeability carbonate strata within the Floridan aquifer system. The Florida seismic-sag structures provide an excellent analog for karst-related migration of hydrocarbons across seals in platform carbonate reservoir systems.