J. Harold Hudson

Sclerochronology: A tool for interpreting past environments

X-radiographs of stony coral slabs reveal two types of annual density bands. Detailed studies of these bands in relation to known variations in air temperatures indicate that sclerochronology is a valid tool for documenting time sequences and changing environmental conditions on a coral reef.

Limestone compaction: An enigma

Compression of an undisturbed carbonate sediment core under a pressure of 556 kg/cm2 produced a “rock” with sedimentary structures similar to typical ancient fine-grained limestones. Surprisingly, shells, foraminifera, and other fossils were not noticeably crushed, which indicates that absence of crushed fossils in ancient limestones can no longer be considered evidence that limestones do not compact.

Last interglacial reef growth beneath Belize barrier and isolated platform reefs

We report the first radiometric dates (thermal-ionization mass spectrometry) from late Pleistocene reef deposits from offshore Belize, the location of the largest modern reef complex in the Atlantic Ocean. The results presented here can be used to explain significant differences in bathymetry, sedimentary facies, and reef development of this major reef area, and the results are significant because they contribute to the knowledge of the regional geology of the eastern Yucatan. The previously held concept of a neotectonically stable eastern Yucatan is challenged. The dates indicate that Pleistocene reefs and shallow-water limestones, which form the basement of modern reefs in the area, accumulated ca. 125–130 ka. Significant differences in elevation of the samples relative to present sea level (>10 m) have several possible causes. Differential subsidence along a series of continental margin fault blocks in combination with variation in karstification are probably the prime causes. Differential subsidence is presumably related to initial extension and later left-lateral movements along the adjacent active boundary between the North American and Caribbean plates. Increasing dissolution toward the south during Pleistocene sea-level lowstands is probably a consequence of higher precipitation rates in mountainous southern Belize.

Growth Rate and Carbonate Production in Halimeda opuntia: Marquesas Keys, Florida

The importance of the calcareous green alga Halimeda as a major sediment producer was first cited by Finckh (1904) and his colleagues, who reported on the core and dredged material recovered during the historic deep borings at Funafuti Atoll. Although these remarkable plants have been recognized for over three quarters of a century as significant contributors to the geologic record, their growth rate has, until very recently, remained virtually unknown. Ironically, Finckh (1904) was also the first to attempt field observations on growth in this species. His singular and entirely accidental success was an unknown species of Halimeda that in 6 weeks grew up through a hole in a submerged board to form a hemispherical clump 3 inches (7.6 cm) in diameter. Dry weight of the calcareous matter thus produced was 14.38 g. No detailed studies on growth in this species were attempted until Colinvaux et al. (1965) maintained numerous green algae, including six species of Caribbean Halimeda, in laboratory aquaria for 19 months. This work was followed by that of Merton (1971), who conducted a 10-month ecological study of H. macroloba on Guam. A similar investigation was carried out by Bach (1979), who estimated standing crop, growth, and production of calcareous algae (which included three species of Halimeda) over a period of 12 months in a south Florida lagoon. A third, and to the author’s knowledge, most recent study is that of Wefer (1980), who used the Alizarin Red-S staining technique to calculate growth of H. incrassata and two other calcareous algal species at various intervals over a period of 27 days in Harrington Sound, Bermuda. In addition to the above publications, the treatise on Halimeda by Hillis-Colinvaux (1980) includes growth and environmental data on this species previously unpublished.

Pleistocene Barrier Bar Seaward of Ooid Shoal Complex Near Miami, Florida

An ooid sand barrier bar of Pleistocene age was deposited along the seaward side of an ooid shoal complex southwest of Miami, Florida. The bar is 35 km long, about 0.8 km wide, elongate parallel with the trend of the ooid shoal complex and perpendicular to channels between individual shoals. A depression 1.6 km wide, interpreted as a back-barrier channel, isolates the bar from the ooid shoals. During sea-level fall and subaerial exposure of the bar, the ooid sand was cemented in place, preventing migration of the barrier. No Holocene analogue of this sand body is recognized, perhaps because of the relative youthfulness of Holocene ooid shoals. This Pleistocene ooid shoal complex, with its reservoir-size barrier bar, may serve as a refined model for exploration in ancient oid sand belts.

Chapter 17 Effects of Drilling Mud on the Growth Rate of the Reef-Building Coral, Montastrea Annularis

Publisher Summary This chapter determines the possible long-terms effects of drilling mud on the growth rate of Montustreu annuluris. A major function of barium-base drilling mud is to flush out material excavated by the drill mud. This is recirculated and most of the mud-coated cuttings are discarded into the water. Periodic cleanout of sand and silt traps also contribute additional mud to the water column. Experimentally treated Montustreu unnularis are highly concentrated doses of unused drilling mud reduced growth rate of M. annularis . Barium higher than normal background levels is incorporated into three of eight treated coral skeletons of M .annularis. The barium is thought to have been trapped in voids caused by boring organisms.

Microbial Mats and Microbialites in the Freshwater Laguna Bacalar, Yucatan Peninsula, Mexico

Laguna Bacalar, a karstic freshwater lake in the state of Quintana Roo, Yucatan Peninsula, Mexico (Fig. 1) features in its southern part possibly the largest freshwater microbialite structures known. These structures extend continuously for over 10 km (Gischler et al. 2008). The laguna is a narrow, elongated body of freshwater, about 40 km long and 1–2 km wide, extending NE to SW with an adjacent strip of periodically flooded lowland. The lagoon is tectonically rooted on the Bacalar fault, which is the northern continuation of the Rio Hondo fault zone (Kenkmann and Schonian 2006, their fig. 6). Laguna Bacalar gets as deep as 20 m with the deepest areas located between Bacalar and Zipline Point. The lake is located in the low Neogene karstic landscape and fed by a series of karstic springs originating from deep circular sinkholes locally called cenotes. Based on hydrogeochemical analyses of groundwater on the Yucatan peninsula, Perry et al. (2009) concluded that the cavern system that includes the Bacalar cenotes probably predates the Tertiary; strontium isotopes suggest that waters derive their ion load from late Cretaceous and/or Paleogene carbonates and evaporites. As in other karstic systems, the emerging groundwater is supersaturated with respect to carbonate and this condition and strong currents along the narrow passages of the lagoon are closely associated with carbonate precipitation and microbialite accretion.

Controls on Late Quaternary Coral Reefs of the Florida Keys

The Florida Keys is an arcuate, densely populated, westward-trending island chain at the south end of a karstic peninsular Florida Platform (Enos and Perkins 1977; Shinn et al. 1996; Kindinger et al. 1999, 2000). The “keys” mark the southernmost segment of the Atlantic continental margin of the United States. The islands are bordered by Florida Bay to the north and west, the Atlantic Ocean to the east and southeast, Gulf of Mexico to the west, and Straits of Florida to the south. Prevailing southeasterly trade winds impinge on the keys, creating a windward margin . The largest coral reef ecosystem in the continental United States rims this margin at a distance of ~5–7 km seaward of the keys and occupies a shallow (generally <12 m), uneven, westward-sloping shelf (Parker and Cooke 1944; Parker et al. 1955; Enos and Perkins 1977). The platform is tectonically stable at present (Davis et al. 1992; Ludwig et al. 1996; Toscano and Lundberg 1999). The reefs and 240-km-long island chain parallel the submerged shelf margin, corresponding roughly to the 30-m depth contour that marks the base of a fossil shelf-edge reef (studies cited use the same criterion). The modern reef tract extends west-southwest from Soldier Key southeast of Miami (25°60′ N, 80°20′ W) to the Dry Tortugas in the Gulf of Mexico (24°40′ N, 83°10′ W). Reef-tract habitats lie within the protective domain of the Florida Keys National Marine Sanctuary (Fig. 2.1a–c; Multer 1996). Prehistoric Paleoindians inhabited the Floridan Peninsula around 12 ka (Zeiller 2005). The Archaic Period of human progress followed (from ~7 to 2 ka) as aboriginal tool making became more sophisticated. The Formative or Ceramic Period (from ~2 ka to ad 1513) was next as the creation of pottery for transportation and storage of food and water became important. The Historic Period began in 1513. By the mid-1500s, Florida had become part of a Spanish monopoly in the Americas. Conquistadors first settled in La Florida in St. Augustine on the East Coast in 1567. In 1763, England took Canada from France, and Spain ceded all of La Florida to England. Spain again took possession of La Florida in the 1783 Treaty of Paris (Zeiller 2005). The United States acquired Florida from Spain by treaty in 1821 largely for the potential military advantage that the Florida Keys offered (see articles in Gallagher et al. 1997, and selected humaninterest notes in Appendix 2.A). The government recognized a need to protect shipping between the Atlantic and Gulf Coasts, and the keys were natural sites for military bases for this purpose. The US Army and US Navy established bases on several islands, and upon admission to the Union as the 27th State in 1845, forts were built at Key West (Fort Zachary Taylor) and the Dry Tortugas (Fort Jefferson). The Florida Keys played major roles in the Second Seminole War (1835–1842), the SpanishAmerican War (April–August 1898), World War I (1916–1918, when Key West first became a major naval training base), World War II (1941–1945), the Cuban Missile Crisis (1962), the war on drugs 2 Controls on Late Quaternary Coral Reefs of the Florida Keys

Non-Oolitic, High-Energy Carbonate Sand Accumulation: the Quicksands, Southwest Florida Keys: ABSTRACT

Approximately 162 km of high-resolution subbottom seismic reflection profiles, collected in the Quicksands area west of the Marquesas Keys off south Florida, indicate extensive westward transport of Halimeda sand. The east-west-oriented, carbonate-sand accumulation is up to 12 m thick and encompasses an area 13 by 29 km. The Quicksands area is ornamented by east-west-trending submarine sand dunes 2 to 3 m high, which are shaped by strong, reversing north-south tidal currents. Many dunes break the surface at low tide. Submarine dunes lie directly on Pleistocene bedrock at the eastern end of the study area, but at the western end, dunes lie on 7 to 10 m of Holocene carbonate sand. Near the western terminus, the sands have accreted over carbonate muds. Westward drift, probably caused by prevailing east and southeast winds superimposed on the tidal currents, is indicated by (1) thickening of the Holocene accumulation to the west and (2) large-scale, westward-dipping, accretionary bedding. Seismic reflection profiles show spitlike accretionary bedding in a package up to 1 km long at the western end, where carbonate sands spill onto deeper water muddy carbonates. The submarine sand body is surrounded on the south, west, and north by equivalent-age, topographically lower lime muds End_Page 629------------------------------ and silts up to 7 m thick. The configuration and pattern of deposition suggest that this area could be used as a petroleum exploration model. The model consists basically of a reservoir-size porous carbonate-sand ridge surrounded downdip by organic-rich carbonate muds, which could serve as source beds. Reversing tidal currents and bed forms are identical to those of oolitic areas in the Bahamas, however, the Quicksands area does not contain ooids. End_of_Article - Last_Page 630------------