Daniel M. Robbin

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.

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

A New Holocene Sea Level Curve for Upper Florida Keys and Florida Reef Tract: ABSTRACT

A new Holocene sea level curve for the upper Florida Keys and Florida reef tract has been constructed by integrating existing and new data from 14C age analyses. New data are derived from 21 mangrove peat samples from 5 locations and 3 laminated CaCO3 soilstone crust (caliche) samples from 3 locations. The new sea level curve is based on 14C ages ranging from 360 ± 60 y.B.P. to 14,000 ± 160 y.B.P., and indicates a fluctuating sea level rise of approximately 0.3 mm/yr (from 14,000 to 7,000 y.B.P., sea level rose from 9.2 to 7.0 m, 30.2 to 23 ft, below MSL), approximately 1.2 mm/yr (from 7,000 to 2,000 y.B.P., sea level rose from 7.0 to 0.75 m, 23 to 2.5 ft, below MSL), and approximately 0.3 mm/yr (from 2,000 y.B.P. to present, sea level rose from 0.75 m, 2.5 ft, below MSL to present MSL). No evidence was found in this area that, during the last 14,000 yr, any highstand was greater than the present sea level. The rate of rising sea level, however, has varied. Sea level stand in this area at 14,000 y.B.P. is much shallower than indicated on other published curves for the east coast of the United States. End_of_Article - Last_Page 522------------

Fire and Limestone: Origin of Black Pebbles: ABSTRACT

The origin and meaning of blackened limestone grains and lithoclasts that occur throughout the geologic record have long been a mystery. The Pleistocene-Holocene unconformity and those within the Pleistocene throughout the Caribbean are often characterized by the presence of blackened limestone lithoclasts. Thoroughly blackened fragments may consist of laminated soilstone crusts (i.e., caliche or calcrete), coral, or oolitic, pelletal and skeletal grainstone derived from the underlying limestone. Blackened fragments occur sporadically or in pockets comingled with nonblackened but otherwise identical fragments. Simple cooking experiments with typical Pleistocene and Holocene limestone fragments showed that only laminated soilstone crusts, poorly cemented pelletal and oolit c grainstone, and aragonitic coral fragments are selectively blackened, whereas well-cemented, nonaragonitic fragments retained their light color. Blackening is caused by charring of organic matter within the rock. Heat from forest fires and smoldering humus accumulations is interpreted to cause the naturally occurring blackened lithoclasts. Fire-blackened limestone lithoclasts differ from the more well-known salt-and-pepper sands, which typically result from selective blackening of individual Foraminifera, mollusk fragments and other fossils under subtidal conditions. Subtidal blackened grains are associated usually with unconformities and tidal channel deposits where they become mixed with unstained grains. Correct identification of the 2 differing types, when detected in ancient limestone, offers important environmental information, not only to distinguish marine and subaerial unconformities, but for clues to paleoclimate, vegetation, and soil development. End_of_Article - Last_Page 527------------

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------------

Experimental Compaction of Lime Sediment: ABSTRACT

More than 30 in-situ cores of modern lime sediments, including environments from tidal flat to shallow marine, have been compressed under loads simulating depths ranging from 280 to 14,000 m of burial. Cores 10 cm in diameter and 30 to 40 cm in length were reduced to between one-quarter to one-third of their original length, resulting in porosity reduction from an initial 70 to 80% to 30 to 45%. Experimental compaction produced sedimentary structures common to many ancient limestones, including (1) wavy organic seams similar to horsetail or microstylolite swarms; (2) reorientation of randomly oriented fossils toward a more horizontal posture; (3) flattening of filled burrows; (4) complete obliteration of birdseye voids; and (5) color mottling in tidal flat sediments produced by collapse and flowage of oxidized sediment surrounding burrows. These studies have shown that, during geologically instantaneous periods of compaction (up to 30 days), the bulk of porosity reduction occurred under conditions simulating less than 300 m of overburden. Although fossils generally are not crushed during compaction, the obliteration of birdseye voids indicates that early cementation or infill by evaporitic minerals was necessary for preservation of ancient birdseye or fenestral structures. Pellets in soft lime mud were obliterated, but slightly hardened pellets in Bahamian muds were preserved during experimental compaction. This observation suggests that well-preserved pellets in ancient limestone indicate predepositional hardening or synsedimentary cementation. Heating of cores to 100°C during compaction has produced hydrocarbon effluents, suggesting that some ancient limestones may have been source rocks. End_of_Article - Last_Page 783------------