Abstract Introduction Material & Methods Lithostratigraphy Petrography, Biostratigraphy & Sr-isotope Analysis Conclusions References Figures Tables Appendix 1 Appendix 2 PDF version

Lithostratigraphy

Figure 2. Generalized stratigraphic column for southern Florida. Of the late Pleistocene interfingering units, only the Miami Limestone might be expected in the study area. The lithostratigraphic classification for the section from the Tamiami Formation to the Hawthorn Group is currently being revised by the Florida Geological Survey (figure is modified after Allmon, 1992 and Scott, 1992b). [larger image]

Unnamed formation

In the studied cores, the sediments from the bottoms of the cores to the base of the Tamiami Formation are dominantly siliciclastics with subordinate carbonates. Regionally, these sediments have variously been placed in the Miocene Coarse Clastics, Hawthorn Group and lower Tamiami Formation (Knapp and others, 1986; Smith and Adams, 1988), within the Tamiami Formation (Peck and others, 1979), or entirely within the Hawthorn Group (Peacock, 1983; Campbell, 1988; Missimer, 1997). Green and others (1990) referred to these sediments as “undifferentiated coarse siliciclastics” and suggested that the sediments were, at least in part, Pliocene. For this investigation, the sub-Tamiami sediments are placed in an unnamed formation until more data are obtained to facilitate regional correlations.

The unnamed formation consists of variably phosphatic and fossiliferous combinations of quartz gravel, sand, silt, clay, and carbonate rock and sediments. Fossils occur as whole entities, fragments, molds, and casts. The fossils recognized in this unit include mollusks, foraminifers, ostracodes, echinoids, bryozoans, corals, dinocysts, and red algae.

Clay generally occurs as matrix within the siliciclastic and carbonate sediments, although scattered, variably silty, sandy clay beds are recognized within the section. Mica, phosphate, feldspar, and heavy mineral grains are widespread, but generally minor, components of the sediment. These sediments range from unconsolidated to well indurated. The top of this unit ranges from 106 feet below sea level to 31 feet below sea level (figs. 3-9). The unit is as much as 187 ft thick in the studied cores, and its base was not encountered.

Limestone and dolostone are present and generally subordinate within the unnamed formation. The carbonates contain varying proportions of quartz gravel, sand, silt, clay, and phosphate, and vary from poorly indurated to well indurated.

Discoid quartzite pebbles and well-rounded pea-gravel are scattered within the unnamed formation in many of the cores. Pebbles range up to nearly 2 cm (longest dimension) within an apparent beach deposit at 171 feet below land surface in the Collier-Seminole core. Discoid quartzite pebbles similar to those observed in these cores have been noted in the Pliocene Cypresshead Formation, Hawthorn Group and associated sediments in central and northern Florida (Scott, 1988b). In southern Florida, the pebbles have been recognized both in sediments assigned to the Hawthorn Group and in the unnamed formation. Concentrations of large pebbles have been noted in cores to the north and west of the present study area (T. Scott, unpublished data, 1997).

The unnamed formation appears to be laterally equivalent to and interfingering with at least part of the Peace River Formation, Hawthorn Group; few beds within this section consist of lithologies characteristic of the Peace River Formation. The carbonate beds at the base of the Picayune Strand core are lithologically similar to carbonates in the upper Arcadia Formation, Hawthorn Group in southern Florida. However, the top of the Arcadia Formation is projected to be nearly 400 feet below sea level in this area, well below the base of the core (Scott, 1988a). Also, discoid quartzite pebbles, such as those in the carbonate sediments at Picayune Strand (at 187 ft), have not been recognized from the Arcadia Formation.

The upper portion of the unnamed formation may grade laterally into the basal Tamiami Formation. The upper contact between the unnamed formation and the Tamiami Formation appears to vary from sharp to rapidly gradational across the study area. The determination of the nature of the contact is hampered in some cores by poor recovery.

The siliciclastic sediments forming the foundation of the Florida Keys and underlying southernmost peninsular Florida have been named the Long Key Formation (Cunningham and others, 1998). The unnamed formation could possibly be the updip extension of the Long Key Formation; however, its inclusion in the Long Key Formation cannot be verified at this time.

Figure 3. Lithology, lithostratigraphy, and age information for the Collier-Seminole State Park core. [larger image]

Figure 4. Lithology, lithostratigraphy, and age information for the Old Pump Road core. [larger image]

Figure 5. Lithology, lithstratigraphy, and age information for the Fakahatchee Strand-Ranger Station core. [larger image]

Figure 6. Lithology, lithostratigraphy, and age information for the Fakahatchee Strand-Gate 12 core. [larger image]

Figure 7. Lithology, lithostratigraphy, and age information for the Fakahatchee Strand-Jones Grade core. [larger image]

Figure 8. Lithology, lithostratigraphy, and age information for the Picayune Strand State Forest core. [larger image]

Figure 9. Lithology, lithostratigraphy, and age information for the Southern States Utilities core. [larger image]

Figure 10. West to east transect along and near Interstate 75, in the northern part of the study area. Dashed lines indicate lithic changes within formations. (See fig. 1 for location, line A-B.) [larger image]

Figure 11. West to east transect along and near U.S. Route 41, in the southern part of the study area. Dashed lines indicate lithic changes within formations. (See fig. 1 for location, line A-C.) [larger image]

Figure 12. North to south transect along and near State Route 29, in the eastern part of the study area. Dashed lines indicate lithic changes within formations. (See fig. 1 for location, line B-C.) [larger image]

Tamiami Formation

The Tamiami Formation overlies the unnamed formation throughout the study area. The complexity of the facies relations within the Tamiami Formation and the predominantly subsurface nature of the formation have rendered correlations difficult (see Missimer, 1992). The concepts of Missimer (1992) were utilized in recognizing the subdivisions of the Tamiami Formation in the study area. The Ochopee Limestone Member of the Tamiami is widespread in southern Florida and was recognized in all the cores (figs. 3-12). Further coring and analyses of the sediment will aid in better understanding of the Tamiami.

The Ochopee Limestone Member, as described by Hunter (1968), is “a light gray to white, sandy calcarenite, containing abundant, identifiable molds of aragonite fossils together with specimens of calcite fossils. . .” The quartz sand content can range from five percent to eighty percent, from a slightly sandy limestone to a calcareous sand to sandstone (Missimer, 1992). The Ochopee Limestone Member recognized in the study cores is a white to light gray, variably sandy, unconsolidated to well-indurated, variably moldic, fossiliferous limestone (packstone to wackestone) to a light gray, variably calcareous, unconsolidated to moderately indurated, variably moldic, fossiliferous sand to sandstone. Phosphate grains occur scattered throughout these sediments. Fossils include mollusks, foraminifers, echinoids, corals, bryozoans, ostracodes, and dinocysts. The sand is generally very fine to medium. Sand content of the Ochopee Limestone Member decreases with decreasing depth. In the studied cores, the Ochopee grades from a sand into a sandstone into a limestone.

The Ochopee Limestone Member is unconformably overlain by undifferentiated sand in the Collier-Seminole State Park and Old Pump Road cores (figs. 3, 4), by artificial fill in the Fakahatchee Strand-Ranger Station, Fakahatchee Strand-Gate 12, Fakahatchee Strand-Jones Grade, and Picayune Strand State Forest cores (figs. 5-8), and by natural soil in the Southern States core (fig. 9). The top of the unit ranges from 24 feet below sea level to 10 feet above sea level. The greatest thickness of the Ochopee Limestone Member is 101 feet in the Picayune Strand State Forest core; the thinnest section encountered is 34 feet in the Fakahatchee Strand Gate 12 core.

Undifferentiated sand and artificial fill

Unnamed quartz sands overlie the limestones in the Collier-Seminole State Park core and the Old Pump Road core (figs. 3, 4). These unconsolidated, very fine to medium sands may have been deposited in erosional lows on the top of the Tamiami Formation. Artificial fill occurs at the top of all cores except the Southern States Utilities core, where a sandy soil lies on top of the limestone.