Abstract Introduction Material & Methods Lithostratigraphy Petrography, Biostratigraphy & Sr-isotope Analysis Collier-Seminole >Old Pump Road F.S.-Ranger Station F.S.-Gate 12 F.S.-Jones Grade Picayune Strand Southern States Conclusions References Figures Tables Appendix 1 Appendix 2 PDF version

Old Pump Road core

The Old Pump Road corehole site (fig. 1, table 1) is near the intersection of Union Road with Old Pump Road, on the South Florida Water Management District easement on the east side of the Faka Union Canal, about 1/4 mile behind the Port of the Islands Resort, north of U.S. Route 41. Drilling was completed in March 1996 to a depth of 196 ft. The core (fig. 4) was sampled for thin sections, X-ray diffraction, strontium analysis of shells, and for its foraminifer, mollusk, ostracode, pollen, and dinocyst content.

Core recovery was very poor in this corehole, and depths, therefore, are uncertain. From 196 to 111 ft is the unnamed formation. The unit is moderately well-lithified dolostone and limestone from 196 to 171 ft and is overlain by unconsolidated calcareous quartz sand. Well-lithified limestone of the Ochopee Limestone Member of the Tamiami Formation occurs from about 101 to 17 ft (moderate induration from 111-101 ft). Sediments from about 29 to 17 ft include limestone rubble, sand, and more limestone. The sand may be a channel-fill into the Ochopee. From about 17 to 3 ft is an unconsolidated sand. The upper 3 feet of sediment in this core appears to be manmade fill.

Semi-quantitative, X-ray diffraction results for this core are shown in table 7. Quartz sand is common in most samples analyzed from the unnamed formation, including the limestones and dolostones from the lower part of the formation. Calcite is the dominant mineral in samples near the base of the core from 190.4 to 188.9 ft and a minor component in most of the samples from the formation. Dolomite is rare in most of the core except in samples from 183.1 to 175.8 ft. It occurs in trace amounts in higher samples. Aragonite is rare in most of the core, but well represented from 190.4 to 175.8 ft, and in trace amounts in the depth range of 169.8 to 110.5 ft. Within the Ochopee Limestone Member of the Tamiami, calcite is a subordinate mineral that forms cement for the quartz sandstone at 110.0 ft. In samples from 96.2 to 29.8 ft, calcite is the primary mineral. Aragonite constitutes 25 percent of the sample at 81.8 ft.

Petrography. Eleven thin sections were made from samples of the unnamed formation in the Old Pump Road core. This unit is highly variable in composition and texture, from a molluscan wackestone-packstone to sandy dolostone to unconsolidated quartz sand and silt.

Samples from 195.2 to 186.1 ft are similar in composition and texture, typically a pisolitic molluscan wackestone with 5 to 20 percent medium quartz sand. The sample at 189.1 ft is anomalous in that the micrite does not form a matrix but coats grains, and this sample may be called a grainstone. Skeletal grains in this depth range include mollusks with some original aragonite still present (table 7), benthic foraminifers, ostracodes, echinoid and coral fragments, and barnacles. Mollusks, coral, and foraminifers show some leaching. Porosity is typically moldic and in vugs and channels, and there is minor precipitation of a sparry calcite cement on void surfaces in most samples. Pisolites are common to all but the deepest sample. The core at 186 ft is pale orange and distinctly different in texture and color from the overlying limestone and dolostone.

The sample at 184.0 ft is a molluscan wackestone with about 20 percent medium quartz and 40 percent micrite matrix. It differs in several ways from the underlying rock in the absence of pisolites, a greater amount of micrite matrix, a greater amount of blocky void-filling cement, and a yellowish-gray color instead of pale orange. The skeletal grains are similar with molluscan molds and fragments, benthic foraminifers, ostracodes, and echinoid fragments.

Overlying the molluscan wackestone, in a gradational contact, is a dolostone that extends from 186 to 171 ft (table 7). The samples at 176.6, 176.8, and 180.9 ft contain small amounts of biogenic calcite (mollusks, ostracodes, bryozoans, red algae) and peloidal mud clasts in a dolomicrite matrix and dolospar on void surfaces. Quartz-sand content of the dolostone decreases from the base to the top of this interval from 30 to 10 percent; sand ranges from fine to medium. Skeletal grain concentration decreases upward; grains include mollusks, ostracodes, bryozoans, and red algae at 180.9 to 176.6 ft, and sparse foraminifer and molluscan molds at 174.8 ft.

There is unconsolidated quartz sand from 171 to 111 ft that is part of the unnamed formation. No thin sections were made of this sand, which was described by Weedman and others (1997).

Thirteen thin sections were made of samples from the Ochopee Limestone Member from the Old Pump Road core. The member ranges from 111 to 17 ft and is primarily a molluscan wackestone to packstone, with abundant quartz sand from 111 to 75 ft. The lower four samples from 95.5 to 74.7 ft are recrystallized; skeletal grains are difficult to identify, the matrix is a microspar to blocky calcite (neomorphosed micrite), and voids are lined with dogtooth spar. Aragonite shells are preserved in samples from 95.5 to 74.7 ft and from 56.4 to 39.2 ft. Planktonic foraminifers occur in samples from 86 to 64.6 ft.

There is a reduction in quartz-sand content at about 75 ft depth, and the overlying limestone has less than 5 percent quartz silt and sand in the matrix. Skeletal grains include benthic and planktonic foraminifers (to 64.6 ft; only benthics occur in higher samples), molluscan molds and fragments, echinoid fragments, ostracodes, bryozoans, and barnacles. Nearly all skeletal grains are bored in the sample from 39.2 ft; leaching typically occurs in the mollusks and some foraminifers.

Evidence for an early, leached fibrous cement is seen in samples from 56.4 to 47.6 ft as fibrous-shaped space between echinoid fragments and in the syntaxial overgrowths, and as a similar jagged void around mollusk grains. Fragments of aragonitic mollusks are preserved in this depth interval as well. Several of the samples higher in the core have traces of quartz silt.

Lithologic and petrographic summary. At least two carbonate and one siliciclastic depositional units occur within the unnamed formation. The lower one, a sandy limestone, occurs from the bottom of the core, and probably deeper, to about 186 ft. The top of this unit is identified by the pale orange color, typically associated with subaerial exposure, and the occurrence of pisoids, commonly associated with vadose and pedogenic processes.

The second carbonate unit is predominantly a dolostone and ranges from 186 to 171 ft; it exhibits an upward decrease in quartz sand from 180.9 to 171 ft. An oyster bed occurs between this dolomite and the overlying unconsolidated quartz sand at 171 ft.

The Ochopee Limestone Member of the Tamiami Formation in this core is similar to that in the core at Collier-Seminole State Park, in that it appears to be one depositional unit of a sandy wackestone at the base and a nearly sand-free wackestone-packstone in the upper part. There is a zone of planktonic foraminifers from 86 to 64.6 ft and evidence for a now-leached fibrous (perhaps aragonite) cement in the upper part of the formation (56.4 to 47.6 ft). The uppermost samples do not show an early cement; however, in those samples the grains are surrounded with micrite and do not provide a nucleation surface for cements to precipitate.

Biostratigraphy. Although nine samples were examined for dinocysts, only two contain them (appendix 2, table 3). The sample at 146 ft is middle or late Miocene based on the overlapping ranges of Habibacysta tectata Head et al. and Selenopemphix brevispinosa Head et al. subsp. brevispinosa. The sample at 120 ft could be middle Miocene, late Miocene, or Pliocene, based on the dinocysts present. The assemblage is similar to the samples from 101 and 88 ft in the Collier-Seminole core; however, the absence of typical late Miocene forms is less compelling in the Old Pump Road core because so many lower samples were unproductive.

Twelve samples were examined for molluscan faunal content. Nine samples from 196 to 27 ft contained mollusks identified for this report (table 4). Two samples from 195.9 and 188.1 ft contain late early to early middle and late Miocene mollusks. Turritella subvariabilis, present at 195.9 ft, has been reported from the lower upper Miocene, molluscan zone M9 (Ward, 1992b). Carditimera apotegea (questionably identified at 195.9 and 188.1 ft) was reported from the Chipola Formation and ?Oak Grove Sand (upper lower and (or) lower middle Miocene). Identifiable mollusks are sparse in the samples from 107 to 26.5 ft. The sample at 86 ft contains Turritella perattenuata and the sample at 50.3 ft contains Carditimera arata. According to published range data for T. perattenuata, samples containing this species should be restricted to the late Pliocene or early Pleistocene. Data gathered in this study, however, indicate T. perattenuata may have a much longer range than previously discovered. Carditimera arata has been reported from the Pinecrest Beds of the Tamiami Formation and the Caloosahatchee faunal unit in Florida, and from the Yorktown (upper portion), Raysor, Chowan River, and James City Formations in the mid-Atlantic region (Ward, 1992a). These units are late Pliocene (or possibly late early Pliocene) to Pleistocene in age.

Strontium-isotope stratigraphy. Samples in the lower part of the core (195 to 188 ft) produce calculated ages of 9.5 to 9.0 Ma ± 0.5 m.y. (late Miocene). Samples somewhat higher (170.8, 141 ft) yield younger calculated ages around 5.8 Ma ± 0.5 m.y. (very late Miocene). Two higher samples (67, 27 ft) yield calculated ages around 4 Ma ± 1.5 m.y. (early Pliocene, but with a margin of error that includes both latest late Miocene and late Pliocene) (table 6).

Age summary. The unnamed formation (196 to 101 ft) in the Old Pump Road core is late Miocene from the base up to about 140 ft. Strontium-isotope stratigraphy indicates that the lithologic break at 171 ft is an unconformity that represents a hiatus of approximately 2 m.y. Dinocysts and mollusks corroborate the strontium-derived Miocene age up to 146 ft. Material above this could be either late Miocene or Pliocene, on the basis of the dinocysts present.

The Ochopee Limestone Member of the Tamiami Formation (111 to 17 ft) is Pliocene. Mollusks suggest a Pliocene and (or) Pleistocene age, which is consistent with strontium-isotopes analysis (early Pliocene age with a margin of error that includes the latest Miocene and the late Pliocene).

The unnamed, undifferentiated quartz sand (17 to 3 ft) is undated. It overlies material containing late Pliocene and (or) early Pleistocene mollusks.