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听Anastasia Formation

General Information

The Anastasia Formation was given its name by Sellards (1912). He used it to describe 鈥渢he extensive deposit of coquina rock found along the east coast.鈥� The type locality is Anastasia Island in St. John鈥檚 County. The Anastasia extends for at least 150 miles (320 km) south of the island, where it grades into Miami Limestone. It makes up the Atlantic Ridge north of Boca Raton. The formation rarely extends more than three miles inland from the Intracoastal Waterway (Cooke, 1945). Various authors disagree on exactly how far inland the Anastasia Formation goes (Scott, 1992). According to Puri (1964), the Anastasia merges into the Ft. Thompson Formation at the Lake Okeechobee-Everglades depression. A small section is also exposed on the west coast near Sarasota. The seaward extent of the formation is not known (Randazzo and Jones, 1997).
The bottom of the Anastasia has not been exposed; it is assumed to rest unconformably on Caloosahatchee marl. In most places, the overlying formation is Pamlico Sand (Cooke, 1945).

The Anastasia has been estimated at several ages, all of which place the formation in the Pleistocene. McNeill (1985) estimates the age to be 130,000 to 100,000 years old. Randazzo and Jones (1997) call it a 鈥渕ulticyclic deposit鈥� which formed during several transgressions of the sea. Perkins (1977) recognized at least two disconformities in the formation. He also states that the Anastasia is the youngest lithified marine deposit that can be found in Florida鈥檚 coastal areas. Fossil mollusk assemblages found in coquina deposits well inland from today鈥檚 coast were deposited in the early Pleistocene (Petuch, 1992). The Anastasia grades in the Miami Limestone, dated as 130,000 years old (Halley and Evans, 1983).

The Anastasia in Palm Beach and Martin Counties is a sandy coquinoid limestone. The ratio of quartz sand to shell fragments varies by outcrop (Randazzo and Jones, 1997). The size of the grains varies from a coarse-grained shell fragment limestone to a sandstone of composed of quartz sand and very small shell fragments or 鈥渃oral sand鈥� (Cooke, 1945). These fragments are held together by a calcareous matrix (Scott, 1992). The rock is white to tan in color on a fresh surface; it turns gray and brown when weathered. The rock is fairly soft but hardens on the surface when exposed to the atmosphere. Planar bedding can be observed in the formation. Several outcrops contain herringbone cross-bedding, avalanche cross-bedding, or both (Lovejoy, 1998).

Fragments of molluscan shells are present in all of the Anastasia outcrops. However, some of the fragments are no larger than sand size. Intact shells become more common northward from Palm Beach. The shell fragments are well worn, indicating a high-energy environment, such as the crest of an offshore bar. These conditions can also occur in the breaker zone of a beach. The best locality for finding intact fossils is Blowing Rocks Preserve, in Martin County. Some of the fossils found in the Anastasia include Anadara 听蝉辫., Busycon contranum, Chione cancellata, Crassostrea virginica, Crepidula fornicata, Dinocardium robustum, Donax variabilis, Glycymeris americanus, Mercenaria mercenaria, Noetia ponderosa, Oliva 听蝉辫., Pecten ziczac, and Monastrea annularis , as well as a scutellid sand dollar and remains of a turtle shell. The mollusks of the Anastasia still inhabit the sandy bottom just offshore (Lovejoy, 1998). Microfossils are present offshore, however, the only species identified in coquina outcrops were in Nassau County by Cole (1931).

Bioturbation is highly prevalent in the Anastasia of Palm Beach and Martin Counties. Tubular structures are inferred to represent fossilized burrow (Lovejoy, 1987). The burrows are extremely well developed at Ocean Reef Park, Blowing Rocks Preserve, and the House of Refuge. These structures fall into two categories; small and large burrows. Small burrows are closely spaced and can be found on the upper surface of the outcrop. They can extend downward more than 2 meters. The roughly circular cross sections range from 1 鈥� 2.5 cm in diameter. The paths of the burrows can be straight, irregular, or curved. The burrows are mud-lined and smooth inside. The interiors are hollow or filled in with coquinoid limestone. The burrows often stand out from the upper surface of the outcrop because the mud linings are harder than the surrounding limestone. From the side, the burrows resemble 鈥渋nterwoven rods鈥� (Lovejoy, 1998).

Large burrows range from 2.5 鈥� 5 cm. Some cross sections are circular, while others are more oval in shape. These burrows can also be filled in and stand out from the outcrop. The identity of the organisms that caused these burrows is not certain since the organisms have not been fossilized. Since two different sizes and styles of burrows have been found, it is assumed that more than one organism was involved in their creation. Callianassa , a species of shrimp, is considered to have formed small burrows in the Miami Limestone that are similar to those in the Anastasia (Halley and Evans, 1983). The burrow left behind is referred to as the trace fossil Ophiomorpha (Lovejoy, 1998).

Most outcrops in the Anastasia Formation contain laminated calcium carbonate crusts. These crusts are, on average, 2.5 cm thick. The crusts undulate, following the surface of the rock. The upper surface is usually reddish-brown and smooth. Individual laminae are alternating white and red-brown layers approximately 1 mm thick. At Blowing Rocks Preserve, botryoidal growths and root impressions can be found on the surface of the crusts. Radiating calcium carbonate crystals that grew in supersaturated waters probably formed the botryoidal growths. The crusts themselves were probably formed in a subaerial environment by leaching and reprecipitation of calcium carbonate (Lovejoy, 1998).

Two types of solution features have been found in the Anastasia Formation. Surface pits are shallow depressions on the surface of the outcrop. Holes deeper than 1 meter have been called 鈥渟olution pipes鈥� by Perkins (1977). The pits were probably formed by acidic standing water. Downward drainage of that water is likely to have helped in the formation of pipes. Pipes with an open bottom can act as 鈥渂low holes鈥� during high tide. Blowing Rocks Preserve is named for this feature. Pipes with a closed bottom can be either partially or completely filled by calcium carbonate lithified infillings. The lithology of the infillings is different than that of the surrounding rock, which makes them easily identifiable (Lovejoy, 1998).

The Anastasia Formation displays many characteristics of a wave-erosion coast. Notches form at the bottom of sea cliffs. Small sea caves will occasionally form. Most cliffs have a wave abrasion platform at the base, which is often covered with sand. Small sea arches will form at the base of promontories that jut into the ocean.
Large masses of bedrock break off the cliffs and fall into the surf zone (Lovejoy, 1998)

There are several points of evidence for a high-energy depositional environment in the Anastasia Formation. The size of the shell fragments, as well as the amount of abrasion to the fragments, suggests high energy. Intact foraminifera and micromollusks indicate the same thing. The known habitat of most of the fauna of the Anastasia is also a high-energy environment. This evidence could either indicate an offshore bar origin or a beach origin. Some outcrops have strata that are oppositely inclined on both sides, which would favor the bar origin (McNeill, 1985; Lovejoy, 1987), while the size distribution of grains favors the beach origin (McNeill, 1985).

There are two major ideas on how the Anastasia Formation was lithified. One states that the Anastasia represents ancient beach rock and that the cementation occurred in the tidal zone as seawater evaporated at low tide. The second idea states that Anastasia was cemented above sea level by the dissolution and reprecipitation of calcium carbonate caused by the circulation of meteoric waters. The second method seems more likely since beach rock only forms on tropical coasts (Ginsburg, 1953). The first idea only holds if the tropical waters had extended all the way to St. Augustine during interglacial periods (Lovejoy, 1998).

Commercially, the Anastasia Formation is one of the three main stones of interest along the east coast of Florida. The formation contains quartz sand deposits, and crushed stone is used in road base and concrete aggregates, as well as chemical, agricultural, and metallurgical applications. The Anastasia is also a locally productive water resource. It forms a portion of the Biscayne aquifer system in the south and makes up smaller surficial aquifers to the north (Randazzo and Jones, 1997).

Historically, the Anastasia Formation was used by early settlers in construction. The Spaniards used the coquina to build their fortifications. Buildings are still present today in St. Augustine (Cooke, 1945).

Virtual Field Trip of Selected Exposures of the Miami Limestone

Miami-Dade & Broward counties, Florida

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. Rainwater at this time flowed through the pore spaces allowing calcite to precipitate around the grains and formed the indurated rock (Halley and Evans).

The formation has two distinct facies -- an eastern oolitic facies that form 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 faces. 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

Ingraham Park

Alice Wainwright Park

Coral Way & 1st Avenue

Greynolds Park

Victoria Park

Anemone Garden

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, Summary 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

Acknowledgments

This website was created under the tutelage of Dr. Anton Oleinik.

All microscope photos: Anton Oleinik.

Questions or comments? E-mail: geologist@bellsouth.net

Jap Rock

Jap Rock is located at the south end of Highland Beach, north of Spanish River Park. The outcrop extends discontinuously in the surf zone for 1.7 miles (2.7 km) to the north. Solution pits, lithified infillings, and laminated calcium carbonate crusts cover the surface, along with large and small burrows. Herringbone cross-bedding are present, as well as planar bedding. The cliffs are low and contain many notches.

Solution pitting

Planar bedding