Virtual Field Trip of Selected Exposures of the Miami Limestone In Miami-Dade & Broward counties, Florida

Introduction

The Miami Limestone, formerly known as the Miami Oolite (Sanford 1909), is one of three distinct Pleistocene rock formations in southeastern Florida. The formation was deposited during the Sangamon interglacial and Wisconsin glacial stages as a narrow band of oolitic carbonate in a north-south trending barrier bar system along the eastern portion of present day Miami-Dade and Broward counties. Osmond, Carpenter, and Windom (1965) and Broecker and Thurber (1965) through uranium-series dating concluded that the Miami Limestone is about 130,000 years old. Sub-aerial exposure of the deposits occurred during the lowering of sea level during the Wisconsian. Rain water at this time flowed through the pore spaces allowing calcite to precipitate around the grains and formed the indurated rock (Halley and Evans).

Lithology

The formation has two distinct facies -- an eastern oolitic facies that forms the Atlantic Coastal Ridge, and the bryozoan facies to the west, in the Everglades. The bryozoan facies is comprised entirely of one species, Schizoporella floridana (Osburn 1914).

The oolitic facies can be further divided into a cross-bedded and a bioturbated facies. The stratigraphic sequence throughout the formation is alternating sections of the two facies. At the southernmost locale, Ingraham Park, the bioturbated facies is on the bottom, then a section of cross-bedding, with a final bioturbated section at the top of the formation.

The cross-bedding throughout the formation is differentially weathered. Differential weathering, or selective cementation, is visible in 2 cm couplets, with the well cemented layers being more resistant.

The limestone is composed mainly of ooids with some quartz sand and small mollusk fossils (Figure 1) . The Miami Limestone ooids are small coated carbonate grains, which contain a nucleus of either a shell fragment, or a quartz grain (Figure 2) . These small round spheres were formed by the deposition of one to five concentric layers of aragonite. Most of the aragonite has now been converted into calcite (Halley and Evans, 1983). The Miami Limestone can be classified as oosparitic, or oolitic grainstone, since it is grain supported, and lacks lime mud.

The stops for this field trip ranged from south Miami-Dade county, to the most northerly exposure in central Broward county. Several locations such as Alice Wainwright Park, Coral Way, and numerous outcrops along Bayshore Drive are low-lying bluffs, with Silver Bluff being a wave cut cliff, or bench.

The Miami Limestone is one of three contemporaneous deposits in South Florida; with the Anastasia Formation to the north, and the Key Largo Limestone to the south.

A similar active ooid shoal environment now exists in the Bahamas (Hoffmeister, Stockman, and Multer, 1967).

Localities

References

Cooke, C.W. 1945, Geology of Florida; Florida Geological Survey Bulletin No. 29, p. 249-262

Halley, Robert B. and Charles C. Evans, 1983, The Miami Limestone, A Guide to Selected Outcrops and Their Interpretation, Miami Geological Society,

Hoffmeister, J.E., 1974, Land From the Sea, University of Miami Press, Coral Gables, Florida

Hoffmeister, J.E., K.W. Stockman, and H.G. Multer, 1967, Miami Limestone of Florida, and it's recent Bahamian Counterpart: Geological Society of America, v. 78, p. 175-190.

Osmond, J.K., J.R. Carpenter, and H.L. Windom, 1965, 230Th/234U age of the Pleistocene corals and oolites of Florida: Journal Geophys. Res., v. 70.

Puri, H. S. and R.O. Vernon, 1964, Summery of the geology of Florida and a guidebook to the classic exposures: Florida Geological Survey Special Bulletin No. 5.

Puri, Harbans S. and George O. Winston, 1974, Geologic Framework of the High Transmissivity Zones in South Florida: Florida Geological Survey Special Bulletin No. 20.

Randazzo, Anthony F. and Douglas S. Jones, 1997, The Geology of Florida, University of Florida Press, Gainesville, Florida

Shinn, E.A., 1968, Burrowing in recent lime sediments of Florida and the Bahamas; Journal Paleontology, v. 42, p. 879-894.

Acknowledgements

This website was created under the tutelage of Dr. Anton Oleinik.
All microscope photos: Anton Oleinik.
Questions? E-mail: geologist@bellsouth.net.