Material and Methods

Corehole sites

Continuous cores were recovered from seven sites in western Collier County listed in table 1. Descriptions of the cores are given in Weedman and others (1997).

X-ray diffraction

Semi-quantitative analysis of X-ray diffraction of samples from the Collier-Seminole State Park, Old Pump Road, Fakahatchee Strand-Ranger Station (lower part of the core only), Fakahatchee Strand-Gate 12, Fakahatchee Strand-Jones Grade, and Picayune Strand State Forest cores was done on a Diano X-ray diffraction spectrometer. Digitized X-ray data were collected every 0.02 degrees 2-theta, for 0.95 seconds per step. Data were collected from 5.00 to 60.00 degrees 2-theta. Copper K-alpha radiation was generated at 45 KV and 25 MA. A 1-degree sollor slit, a 0.1-degree detector slit, a graphite monochromator, and a 6-degree take-off angle were used. Each sample were was split or quartered, and ground in a mortar until all of the material passed through a 75-µm or smaller sieve. The samples were prepared as smear mounts. The program used to evaluate each run was designed by Hosterman and Dulong (1989). This program uses a library file of the peaks of selected minerals, in this case calcite, dolomite, aragonite, and quartz, against which it compares the peaks of the sample unknowns. The library file contains reference intensity ratios, which are weighting factors used to put the pattern of each of the minerals into proportion with the others. Before analysis, the reference intensity ratios of calcite, aragonite, and dolomite were set by running a series of known mixtures. These mixtures were:

25 percent quartz, 75 percent calcite
50 percent quartz, 50 percent calcite
50 percent quartz, 50 percent dolomite
50 percent quartz, 50 percent aragonite
95 percent quartz, 5 percent calcite
95 percent quartz, 5 percent dolomite
95 percent quartz, 5 percent aragonite

The resulting ratios were compared to the known ratios, and the reference intensity ratios were then set to achieve the best fit.

Two slides were made for each known mixture to check the quality of the mixture. Based on the results of these known mixtures, the overall reliability of the results reported is within ± 5 percent. The detection limit is estimated to be around 1 percent. Pure samples of each of the four minerals also were run to check the peak intensity values in the library file. For all runs, the d-spacings were computer-adjusted to the quartz 3.343 Å peak. All results were rounded to the nearest 5 percent. Minerals that were identified, but present in concentrations of less than 5 percent of the sample, were reported as “trace.” Potassium feldspar and plagioclase were identified in many samples. Together with various unidentified minor peaks, these minerals generally comprise less than 5 percent of the total sample composition and were not included in the percent calculations.

Petrography

Seventy-six samples were selected for petrographic analysis from all cores except for Southern States Utilities. Samples were impregnated with blue-stained epoxy and made into standard thin sections. These were examined petrographically to identify grains and pore types, determine cement compositions, describe textures, and assess the degree of diagenetic alteration. Skeletal-grain molds are pores; however, they are included in descriptions as grains to document their occurrences as original grains. Samples were examined from the unnamed formation and the Ochopee Limestone Member of the Tamiami Formation. Unconsolidated sediments were not prepared as thin sections.

Paleontological material

Core material was examined for dinocysts, pollen, mollusks, and foraminifers. Dinocyst and pollen samples were treated with hydrochloric and hydrofluoric acids, oxidized with nitric acid, and stained with Bismark brown. All samples were observed with a light microscope under differential interference contrast. A total of 61 samples were examined; over half (38) yielded dinocysts. Due to the relative rarity of dinocysts in the material, up to 1.2 ft of material was processed. Sample depth is given to the nearest foot in table 3 and the text. Appendix 2 lists the full depth interval sampled. For sections with abundant molluscan material, representative samples were taken where an apparent change in faunal or lithologic content occurred, and at least one sample was taken every 10 ft. For sections with sparse molluscan material, samples were taken wherever calcareous material was observed. Unconsolidated sediments were washed through an 850-µm and a 63-µm sieve; samples greater than 850 µm were picked for molluscan material. Latex molds and casts or clay impressions were prepared to aid in the identification of the mollusks preserved as molds and casts in the limestones. Readily identifiable mollusks are included; additional species present that would require further investigation are not included. Foraminiferal samples from the Collier Seminole and Fakahatchee Strand-Ranger Station cores consisted of well to poorly lithified limestone, calcareous sandstone, and dolostone. Due to the lithified nature of the samples, a freeze-thaw processing procedure was used to liberate the microfaunal components (ostracodes and foraminifers) from the samples. The sample residues were sieved at greater than 63 µm, which was then analyzed for planktonic foraminifers only. Studies on ostracodes are ongoing. Pollen samples were sparse and not age-diagnostic (Debra Willard, personal communication, 1997).

Strontium-isotope stratigraphy

Individual shells or shell fragments of calcitic mollusks were collected for strontium-isotope analysis. Samples were dissolved in 5M acetic acid and the soluble fraction was centrifuged and separated by standard ion-exchange techniques. Strontium was loaded on a single Ta oxidized filament. Isotope ratios were measured on a VG54 Sector thermal ionization mass spectrometer in dynamic mode. Each data value is the average of two or more individual runs of 180 ratios each, measured on a 5x10^-10 amp beam. Ratios were averaged using Isoplot (Ludwig, 1990). All ⁸⁷Sr/⁸⁶Sr data have been normalized to a value of 0.1194 for ⁸⁶Sr/⁸⁸Sr. The data were collected between November 1996 and March 1997, during two different periods of analysis. Measured values for the USGS modern-carbonate standard EN-1, a large Tridacna shell collected live from Enewetak lagoon were 0.709198 ± 0.000017 (2 standard deviations, n=36) and 0.709213 ± 0.000015 (2 standard deviations, n=23). Ages in millions of years ago (Ma) are assigned using the data table of Howarth and McArthur (1997).