|
publications > paper > application of carbonate cyclostratigraphy and borehole geophysics to delineate porosity and preferential flow in the karst limestone of the Biscayne aquifer, SE Florida
Application of carbonate cyclostratigraphy and borehole geophysics to delineate porosity and preferential flow in the karst limestone of the Biscayne aquifer, SE Florida
Kevin J. Cunningham
Robert A. Renken
Michael A. Wacker
Michael R. Zygnerski
U.S. Geological Survey, Fort Lauderdale, Florida 33315, USA
Edward Robinson
University of West Indies, Kingston, Jamaica
Allen M. Shapiro
G. Lynn Wingard
U.S. Geological Survey, Reston, Virginia 20192, USA
| Cunningham, K.J., Renken, R.A., Wacker, M.A., Zygnerski, M.R., Robinson, E., Shapiro, A.M., and Wingard, G.L., 2006, Application of carbonate cyclostratigraphy and borehole geophysics to delineate porosity and preferential flow in the karst limestone of the Biscayne aquifer, SE Florida, in Harmon, R.S., and Wicks, C., eds., Perspectives on karst geomorphology, hydrology, and geochemistry-A tribute volume to Derek C. Ford and William B. White: Geological Society of America Special Paper 404, p. 191-208, doi: 10.1130/2006.2404(16). Posted with permission from GSA. |
ABSTRACT
Combined analyses of cores, borehole geophysical logs, and cyclostratigraphy
produced a new conceptual hydrogeologic framework for the triple-porosity (matrix,
touching-vug, and conduit porosity) karst limestone of the Biscayne aquifer in a
0.65 km2 study area, SE Florida. Vertical lithofacies successions, which have recurrent stacking patterns, fit within high-frequency cycles. We define three ideal high-frequency cycles as: (1) upward-shallowing subtidal cycles, (2) upward-shallowing
paralic cycles, and (3) aggradational subtidal cycles. Digital optical borehole images,
tracers, and flow meters indicate that there is a predictable vertical pattern of porosity
and permeability within the three ideal cycles, because the distribution of porosity and
permeability is related to lithofacies. Stratiform zones of high permeability commonly
occur just above flooding surfaces in the lower part of upward-shallowing subtidal
and paralic cycles, forming preferential groundwater flow zones. Aggradational subtidal
cycles are either mostly high-permeability zones or leaky, low-permeability
units. In the study area, groundwater flow within stratiform high-permeability zones
is through a secondary pore system of touching-vug porosity principally related to
molds of burrows and pelecypods and to interburrow vugs. Movement of a dye-tracer
pulse observed using a borehole fluid-temperature tool during a conservative tracer
test indicates heterogeneous permeability. Advective movement of the tracer appears
to be most concentrated within a thin stratiform flow zone contained within the lower
part of a high-frequency cycle, indicating a distinctly high relative permeability for
this zone. Borehole flow-meter measurements corroborate the relatively high permeability
of the flow zone. Identification and mapping of such high-permeability flow zones is crucial to conceptualization of karst groundwater flow within a cyclostratigraphic
framework. Many karst aquifers are included in cyclic platform carbonates.
Clearly, a cyclostratigraphic approach that translates carbonate aquifer heterogeneity
into a consistent framework of correlative units will improve simulation of karst
groundwater flow.
Keywords: carbonate cyclostratigraphy, borehole geophysics, karst, hydrogeology, Florida.
Introduction >
MANUSCRIPT ACCEPTED BY THE SOCIETY 22 SEPTEMBER 2005
|
