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papers > sequence stratigraphy... > carbonate ramp and bounding siliciclastics > unnamed sand > lithostratigraphy
SEQUENCE STRATIGRAPHY OF A SOUTH FLORIDA CARBONATE RAMP AND BOUNDING SILICICLASTICS (LATE MIOCENE-PLIOCENE)
CARBONATE RAMP AND BOUNDING SILICICLASTICS TEMPORAL AND SPATIAL BOUNDARIES
Unnamed Sand
Lithostratigraphy
An unnamed sand that overlies the Ochopee Limestone has been mapped in the study area (Fig. 9). The stratigraphic relation to existing Pliocene-Pleistocene units, such as the Pinecrest Member of the Tamiami Formation, has not been resolved. Future analysis of mollusks could help to clarify relations, but Scott and Wingard (1995) have discussed the problems associated with biostratigraphy and lithostratigraphy of the Plio-Pleistocene in southern Florida.
Three lithofacies have been identified within the unnamed sand for an area shown in Figure 1: (1) a quartz sand facies, (2) a pelecypod lime rudstone and floatstone facies, and (3) a terrigenous mudstone facies (Table 7). The quartz sand facies is characteristic of most of the unnamed sand.
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| Figure 9. Structure contour map of an unnamed sand that overlies the Ochopee Limestone Member of the Tamiami Formation. Structure contours show altitude in feet below sea level of base of the Pinecrest Sand. [larger image] |
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| Table 7. Lithofacies characteristics of the unnamed sand for the area outlined in Figure 1
[Visual estimation was made for porosity. Hydraulic conductivity was estimated by comparison of corehole from Fish and Stewart (1991, table 6)]
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| Characteristic |
Lithologic description |
| Quartz Sand Facies |
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Depositional textures
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Quartz sand with locally abundant fossils
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Color
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Mainly yellowish-gray 5Y 8/1 and yellowish-gray 5Y 7/2; locally medium-gray N5 to very light gray N8, very pale orange 10yR 8/2, light-olive-gray 5Y 6/1, light-olive-gray 5Y 5/2, grayish-yellow 5Y 8/4, grayish-orange 10YR 7/4, and dark-yellowish-orange 10 YR 6/6
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Grain size
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Mainly very fine to fine quartz sand; ranges from silt to very coarse quartz sand; carbonate grains range from silt to pebble size
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Carbonate grains
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Pelecypods (local oysters), undifferentiated skeletal fragments, echinoids, serpulids, bryozoans, and benthic and planktic foraminifers
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Accessory grains
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Trace to 3 percent phosphate and heavy mineral grains; local trace mica; local minor terrigenous clay
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Porosity
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Mainly intergrain and local intragrain, ranges from 5 to 25 percent
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Hydraulic conductivity
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Mainly low (0.1 to 10 feet per day); ranges from very low (less than 0.1 foot per day) to moderate (10 to 100 feet per day)
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| Pelecypod Lime Rudstone and Floatstone Facies |
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Depositional textures
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Pelecypod lime rudstone or floatstone with quartz sand-rich lime packstone and grainstone matrix
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Color
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Yellowish-gray 5Y 8/1, medium-gray N5 to light-gray N7, very pale orange10yR 8/2, pale-yellowish-brown 10yR 6/2
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Grain size
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Carbonate grains up to pebble size; quartz sand mainly very fine to fine and ranges from silt to coarse size
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Carbonate grains
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Pelecypods, undifferentiated skeletal fragments, gastropods, oysters, serpulids, bryozoans, cerithiids, and echinoids
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Accessory grains
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Trace to 3 percent phosphate and heavy mineral grains
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Porosity
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Mainly intergrain and moldic; local intragrain and shelter; ranges from 5 to 15 percent
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Hydraulic conductivity
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Mainly low (0.1 to 10 feet per day); ranges from very low (less than 0.1 foot per day) to moderate (10 to 100 feet per day)
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| Terrigenous Mudstone Facies |
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Depositional textures
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Silty terrigenous mudstone to quartz sand-rich terrigenous mudstone; locally grades into terrigenous clay-rich lime mudstone
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Color
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Light-olive-gray 5Y 5/2, light-olive-gray 5Y 6/1 and yellowish-gray 5Y 8/1 ; locally pale-olive 10y 6/2, light-olive-gray 5Y 6/1, dusky-yellow-green 5GY 5/2, and yellowish-gray 5Y 7/2
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Grain size
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Mainly terrigenous clay; quartz grains range from silt to fine sand size; local medium to coarse quartz sand
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Carbonate grains
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Pelecypods (local oysters), benthic and planktic foraminifers, undifferentiated skeletal fragments, and fish scales
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Accessory grains
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Locally common quartz grains; trace to 1 percent phosphate grains; trace to 3 percent heavy mineral grains; local trace mica; trace plagioclase and microcline
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Porosity
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Intergrain; less than or equal to 5 percent
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Hydraulic conductivity
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Very low (less than 0.1 foot per day)
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The terrigenous mudstone facies occurs mainly in the north-central part of the study area outlined in Figure 1 where the facies typically occurs as one or two units within the lower part of the unnamed sand. The pelecypod lime rudstone is found only locally as discrete beds within or near the top of the unnamed sand. Figure 6 shows that the unnamed sand is probably equivalent to much of Interval II and all of Interval III defined by Guertin et al. (1999) within the Long Key Formation.
The unnamed sand ranges from 20 to 60 feet in thickness in most of the study area. The unnamed sand is thickest (about 120 feet) in central and south-central Miami-Dade County. A structure contour map of the base of the unnamed sand (Fig. 9) shows that the unit pinches out in the western portion of the Florida peninsula. In southern Miami-Dade County, the unnamed sand merges with siliciclastics of the Long Key Formation as defined by Cunningham et al. (1998) in the Florida Keys. The structure contour map at the base of the unnamed sand and the cross sections shown in Figures 5 and 6 indicate that quartz sands of the unnamed sand were transported southward mostly along the southeastern coast of Florida to the Long Key Formation in the Florida Keys.
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