Abstract Introduction Background >Methods Seismic Sequences Discussion Conclusions & Acknowledgments References Tables PDF Version

About 290 km of digital, single-channel, high-resolution seismic-reflection data were acquired using the R/V Price in 1999 over the length of the Caloosahatchee River from Lake Okeechobee extending into San Carlos Bay (Fig. 1). The seismic-reflection survey was performed using an Elics Delph2 digital acquisition and processing system, a Huntec electrodynamic "boomer" source, and an Applied Acoustics CSP-100 power supply with power settings of 700 or 1,000 J. The speed of the R/V Price was typically 6-8 km/hr. Shot rate was one second with a sampling rate of 8 kHz and shot spacing about 2-2.5 m. An Innovative Transducer ST-5 ten-channel hydrophone array was used to detect the return pulse, and the range of the recording window was from 0 to 300 ms. Real-time navigational positions were obtained using a differential global positioning system (GPS), and seismic shot-point positions were corrected for the offset between antenna and boomer. Post-cruise data processing included bandpass filtering with a 480-2100 Hz window; gain using a fixed baseline, plus automatic gain control with a 3 ms window; and trace summing by means of a three-shot moving average.

Approximate depth scales for seismic profiles were calculated from twoway traveltimes using velocities of 1,620 m/s for relatively shallow Late Miocene to Pliocene siliciclastic sediment, and 2,500 m/s for underlying Late Oligocene to Late Miocene carbonate-dominated rocks. These velocities are based on correlation of core data (see below) to seismic profiles and indicate that with typical penetration of 250 ms, we were imaging about 245 m of section. Description and interpretation of seismic-reflection configuration patterns are based on comparison to examples in Mitchum et al. (1977).

Ground-penetrating radar (GPR) was used to obtain continuous images of shallow geologic units at the Indian Mound archaeological site, approximately 3 km north of the Caloosahatchee River, as shown in Figure 1B. All GPR data were collected using a SIR System-10A1 with a dual 100-Mz antenna array towed 17 m behind a truck with a connecting rope and cable at a rate of about 0.8 km/hr. The transmitter rate was 1024 samples/scan and digital sampling rate was 20 scans/m. Processing included horizontal filtering of the continuous survey data using RADAN for WinNT software. Approximate depth scales for radar profiles were calculated from two-way traveltimes employing velocities of 0.15 m/ns for unsaturated sand and 0.06 m/ns for saturated sand (Davis and Annan 1989).

Six 5-cm-diameter cores (533 m in cumulative length) were drilled continuously by the Florida Geological Survey (FGS) during 1999 to 2001 using a Failing 1500 wireline coring drill rig to constrain seismic-reflection interpretations, develop a seismic-sequence stratigraphy, and provide samples for developing a chronostratigraphy (Fig. 1). Recovery averaged approximately 75% for the six cores. Corehole sites are located no more than 100 m from the seismic-profiles tracks, and corehole locations were sited on seismic profiles using geographic positions acquired at the wells with a twelve-channel GPS receiver. The cores are archived in the FGS wellcutting and core repository in Tallahassee, Florida. All wells are identified by FGS ascension numbers, which have "W-" as a prefix. Detailed lithologic descriptions of the cores can be found in Cunningham et al. (2001b).

Coccoliths and diatoms were prepared and identified using standard methods (Barron et al. 1984) at the U.S.G.S. Micropaleontology Laboratory in Menlo Park, California. Coccolith floras were assigned to the bioistratigraphic zones of Okada and Bukry (1980) with normalized additions of Subzones CN12aA, aB, and aC from Bukry (1991). Diatom floras were dated using the zonations of Barron (1992). There was no evidence for reworking of nannofossils based on the occurrence of asynchronous species mixed together into unnatural associations, or mixing of fossils with varying degrees of preservation.

Information contained in Bock et al. (1971), Poag (1981), and Jones (1994) was used to help identify benthic foraminifera at the genus level. Paleoenvironmental interpretations are based on Murray's (1991) grouping of individual benthic foraminiferal associations and species into broad depth categories of inner and outer shelf, which are defined as mean sea level to approximate water depths of 100 m and 100 to 200 m, respectively.