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Carlson, Janine L.; Wingard, G. Lynn; Robinson, Edward; Wacker, Michael A.
About 60 mi of GPR profiles were acquired and used to calculate the depth to shallow geologic contacts and hydrogeologic units, image karst features, and produce a qualitative perspective of the porosity distribution within the upper part of the karstic Biscayne aquifer in the Lake Belt area of north-central Miami-Dade County. Descriptions of lithology, rock fabric, cyclostratigraphy, and depositional environments of 50 test coreholes were linked to geophysical data to provide a more refined hydrogeologic framework for the upper part of the Biscayne aquifer. Interpretation of depositional environments was constrained by analysis of depositional textures and molluscan and benthic foraminiferal paleontology. Digital borehole images were used to help quantify large-scale vuggy porosity. Preliminary heat-pulse flowmeter data were coupled with the digital borehole image data to identify potential ground-water flow zones.
In 1998, the U.S. Geological Survey (USGS), in cooperation with the South Florida Water Management District (SFWMD), initiated a study to provide a regional-scale hydrogeologic framework of a shallow semiconfining unit within the Biscayne aquifer of southeastern Florida. Initially, the primary objective was to characterize and delineate a low-permeability zone in the upper part of the Biscayne aquifer that spans the base of the Miami Limestone and uppermost part of the Fort Thompson Formation. Delineation of this zone was to aid development of a conceptual hydrogeologic model to be used as input into the SFWMD Lake Belt ground-water model. The approximate area encompassed by the conceptual hydrogeologic model is shown as the study area at <https://sofia.usgs.gov/exchange/cunningham/bbwelllocation.html>. Subsequent analysis of the preliminary data suggested hydraulic compartmentalization occurred within the Biscayne aquifer, and that there was a need to characterize and delineate ground-water flow zones and relatively low-permeability zones within the upper part of the Biscayne aquifer. Consequently, preliminary results suggested that the historical understanding of the porosity and preferential pathways for Biscayne aquifer ground-water flow required considerable revision.
Quinn, J. F., Jr.; Bogan, A. E.; Coan, E. V.; Hochberg, F. G.; Lyons, W. G.; Mikkelsen, P. M.; Neves, R. J.; Roper, C. F. E.; Rosenberg, G.; Roth, B.; Scheltema, A.; Thompson, F. G.; Vecchione, M.; Williams, J. D.
Carlson, Janine L.; Wingard, G. Lynn; Robinson, Edward; Wacker, Michael A.
Wacker, Michael A.; Robinson, Edward; Gefvert, Cynthia J.; Krupa, Steven L.
Davis, J. L.
Annan, A. P.
Vail, P. R.; Sangree, J. B.
Payton, C. E., ed.
Ham, W. E., ed.
Klovan, J. E.
See WRI 03-4208 for a more complete description of the data.
Nearly all of the 50 test coreholes were drilled following GPR data acquisition. Test coreholes were located along the GPR profile tracts where they would be most useful for verification of GPR attributes. Collection of continuous 3.4- or 4-in. diameter cores was preferred to the normal rotary method, which produces small cutting samples collected over relatively wide depth intervals. The test coreholes were drilled by either Amdrill Inc., employing a wireline coring method, or by U.S. Drilling Inc., using a conventional coring method. Borehole geophysical logs were collected by the USGS in 45 of the 50 test coreholes drilled during this study and included induction resistivity, natural gamma ray, spontaneous potential, single-point resistivity, caliper, and digital borehole image logs. Borehole geophysical logs were not collected at the G-3694 and G-3697 test coreholes due to problems with locating the well or destruction of the well after drilling. The borehole geophysical-logging tools were run in boreholes filled with clear freshwater. Each borehole was cased with 3.5- or 5-in. solid polyvinyl chlorinated (PVC) surface casing set to a depth between 4 and 19 ft below land surface. Data were acquired in digital format and archived in the USGS National Water Information System (NWIS) database. The digital borehole image logs were acquired using an RaaX BIPS digital optical logging tool. A Mount Sopris Model HFP-2293 heat-pulse flowmeter was used to assess borehole fluid movement in the G-3710 test corehole. A technique described by Paillet (2000) to estimate vertical groundwater borehole flow was utilized with the flowmeter measurements collected in the G-3710 test corehole.
Core samples were described using a 10-power hand lens and binocular microscope to determine vertical patterns of microfacies, sedimentary structures, and lithostratigraphic boundaries, to characterize porosity, and to estimate "relative" permeability. Limestones were classified by combining the schemes of Dunham (1962), Embry and Klovan (1971), and Lucia (1995). The rock color of dry core samples was recorded by comparison to a Munsell rock-color chart (Geological Society of America, 1991). Core-sample descriptions were classified as rock-fabric facies.
Horizontal and vertical permeability of 71 whole-core samples, horizontal permeability of 36 core-plug samples, and porosity and grain density of all 107 samples were measured at Core Laboratories, Inc. Numerous (318) core-sample thin sections were examined using standard transmitted-light petrography to characterize and interpret rock properties and small-scale porosity.
Borehole images are digital photographs of the borehole wall recorded by a sonic-velocity or electrical-resistivity probe, or optical device. A BIPS borehole imaging tool was used to log continuous digital photographic images in 45 test coreholes. These images provide 100-percent circumferential coverage of the borehole wall and can yield critical information regarding the presence or absence of vuggy porosity, its spatial distribution, and vuggy pore shape and size.
Mollusks from 46 samples collected from 12 test coreholes were prepared and identified at the USGS Paleontology Laboratory in Reston, Va. Most of the mollusks present in the strata were preserved as molds and casts. Core samples were initially examined under a binocular microscope to observe diagnostic characteristics of the molluscan remains and to make identifications based on their comparison with published species. Clay squeezes or latex casts were made of the molluscan molds where appropriate to aid in identification. After initial identifications were made, samples were split open to expose fresh surfaces and the process repeated. Identification of benthic foraminifera was made at the genus level, where possible, for 67 thin sections selected by lithology from five test coreholes. Six biofacies were recognized.
Paleoenvironments and stratigraphic age of the Fort Thompson Formation were evaluated in the 46 core samples collected for molluscan paleontology from 12 test coreholes. Molluscan species diversity in the samples was low, and most of the species identified have a broad tolerance to change in salinity and water depth, so the samples have been classified within only three paleoenvironments based on the mollusks: shallow shelf to outer estuarine, inner estuarine, and freshwater.
Geophysical logging used Mount Sopris portable logging equipment and was completed by USGS Miami, Florida Integrated Science Center for Water and Restoration Studies personnel. Processing and display of results used WellCAD software from Advanced Logic Technology (ALT). WellCAD log display was then exported in PDF format and when possible individual log data sets were exported for archiving in LAS format.
See Water-Resources Investigations Report 03-4208 for more complete information on the data processing.
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