Thomas E. Pyle

Light transmissivity, suspended sediments and the legal definition of turbidity

Abstract Evaluation of current methods of measuring turbidity in estuaries indicates a need to calibrate rapid, in situ optical measurements of beam transmittance with the units specified in water quality standards and with quantitative and qualitative data on the composition of suspended matter. Our results include curves relating per cent light transmission to Formazin Turbidity Units and the concentrations of monotnineralic suspensions of Ca-montmorillonite and kaolinite. Beam attenuation coefficients calculated from transmissivity measurements vary linearly with concentrations (mg/l) of suspended clay particles measured in the laboratory. Field measurements of total suspended load ( C in mg/l) and attenuation coefficients (α) in a west Florida estuary plot between the extremes defined by these laboratory data on two clay minerals. The relationship C ∼- 3·3 α determined for the Anclote estuary in August 1971, is compared with the results of previous studies. Such comparisons may be appropriate in restricted geographic areas or during certain seasons but the multitude of factors influencing natural turbidity measurements indicates the futility of searching for a universal equation applicable outside the laboratory. Instead of trying to apply instruments developed for optical oceanographers and geologists to the basically biological problems of estuarine turbidity variations, we recommend a long-term effort to determine the light and siltation tolerances of the organisms we are trying to protect. Field and laboratory measurements of light received or silt deposited, rather than tenuously related parameters, should determine the appropriateness of existing arbitrary water quality standards.

Metamorphic rocks from northwestern Caribbean sea

During 1971, several dredge hauls were collected in the area between the Yucatan Peninsula-British Honduras, on the south and west, and Cuba on the northeast. One of the dredge hauls recovered metasediments which petrographically are very similar to the Early-Middle Jurassic San Cayetano Group of Pinar del Rio Province, westernmost Cuba. Interpretation of K-Ar dates of these rocks suggests that they are approximately 65 million years old. Therefore, the latest thermal event to affect them occurred during the “Laramide” orogeny. The presence of these rocks southwest of Cuba, close to the Yucatan Peninsula and British Honduras, indicates that the Greater Antilles orthogeosyncline extends to the Central America mainland.

Morphology and sedimentary processes in and around Tortugas and Agassiz Sea Valleys, southern Straits of Florida

Abstract Continuous seismic reflection profiling and new bathymetry data in the southern Straits of Florida over an area dominated by the Tortugas and Agassiz Valley systems have allowed a more detailed analysis of the morphology and sedimentary processes active in this region. Four dives in the submersible DSV “Alvin” supplement the seismic and bathymetric data. The continental slope in the study area can be divided into two physiographic provinces: (I) an irregular topography controlled by the Florida Escarpment west of Tortugas Valley; and (II) the remainder of the continental slope which contains the majority of features under investigation. Seismic data indicate that the valleys are being filled shoreward of 290 fathoms (530 m) by a wedge of prograding sediments derived from the Florida shelf. The morphology of the two valley systems reflects probable differences of origin. Tortugas Valley appears to have originated coincident with the eastern terminus of the Florida Escarpment and province-I-type topography. The Agassiz valleys may have an origin associated with jointing patterns observed by divers aboard DSV “Alvin”. Current meter readings and bottom photographs from “Alvin” indicate that currents are relatively sluggish and not very effective in the transport of sediment within the valleys. An area of undulations west of Pourtales Terrace was investigated and concluded to be erosional in origin. Slumping appears to have played a large part in shaping many features in the study area. The bottom morphology and sediment distribution on the continental slope and in the axis of the Straits of Florida suggest that bottom currents are active in shaping the entire area.

Anomalous Crust Beneath West Florida Shelf

A new Bouguer gravity anomaly map of the west Florida continental margin reveals a landward salient of high positive values in the vicinity of St. Petersburg. A 20,000 sq km area of the shelf characterized by anomalies greater than +30 mgal is thought to be underlain by a crust having a thickness intermediate between that of continents and that of oceans. A transition from oceanic toward continental crust in this area may have been accomplished by reef progradation across an ancient oceanic embayment. Alternatively, a transition from continental toward oceanic crust may have been produced by rotation of Florida and consequent rifting. The reef-progradation hypothesis is most consistent with what is known of the deep structure and tectonic setting of the Florida platform.

Magnetic Anomalies in Straits of Florida

Seismic-reflection and magnetic profiles across three topographic highs in the western end of the Straits of Florida and southeastern Gulf of Mexico reveal the presence of diapiric structures which have magnetic anomalies greater than 100 ^ggr. These deep-water knolls may be related to the volcanic-anomaly belt of the Florida platform, the ultramafic rock outcrops of northwestern Cuba, or Cretaceous andesitic intrusive rocks of Yucatan and Florida.

Sands and Sand Transport on Palimpsest Carbonate Shelf: ABSTRACT

The West Florida Shelf east of Cape San Blas, an End_Page 700------------------------------ area of about 250,000 sq km, is the only major shelf of the continental United States which is presently dominated by carbonate sedimentation. The veneer of sediments which comprises the present surface of the shelf is called the West Florida Sand Sheet. It is composed of greater than 75% carbonate and is the latest expression of a 5 km thick accumulation of carbonate rocks and evaporites of Mesozoic and Tertiary ages which has been cut off from major clastic provenance since Jurassic time. The West Florida Sand Sheet differs from many great carbonate banks such as those of the Bahamas, the Persian Gulf, and the Great Barrier reef in that it extends as far north as 29°30^prime and is composed mostly of residual carbonate, specifically of patches of molluscan shell hash, foraminiferal, algal, and even oolitic sands. Only a few patch reefs and one relatively large deep-water (>20 m) tropical reef, called the Florida Middle Ground, are present. Sediments resemble more closely those of the shelf of the southeastern Atlantic United States, with the clastic components removed, than those in other carbonate banks. Inshore of the carbonate sands and separated from them by a transition zone of mixed composition lies a mature fine quartz sand, which also comprises the beaches of southwest Florida. The quartz sand appears to have been deposited at lower sea-level stands and then to have been moved up and down the peninsula in a seasonally changing longshore current system. Side-scan and seismic surveys of the West Florida shelf show that far from being a featureless plain beneath the relatively low-energy gulf, the sand sheet has a full suite of bed forms from giant sand waves to small-scale ripples. These suggest that the seafloor is undergoing major redistribution and reworking of sediments, probably primarily as the result of passage of major storms. End_of_Article - Last_Page 701------------

Geophysical Studies of South Florida Continental Margin and Western Straits of Florida: ABSTRACT

Seismic-reflection profiles off the western coast of Florida south of 27° N lat. have been recorded during two cruises of Texas A&M Universitys R/V Alaminos in May 1967 and June 1968. They show that the anticlinal ridge present near the top of the West Florida escarpment, which has been proposed to be an extension of the Washita-Fredericksburg reef trend, may possibly be traced southward to the latitude of the Florida Keys. Several crossings have been made of a large knoll in the western end of the Straits of Florida. Preliminary analysis of the real-time records, without benefit of playback, indicates the presence of a terrace at a water depth of 840 fm, and the possibility that an anticlinal feature, remarkably similar to that seen on the Florida escarpment toward the north, is present. Reexamination of earlier data from the Campeche Bank and comparison with those presented here reveal several similarities and provide evidence that the Campeche Bank and the Florida escarpment once might have been connected. However, the presence of deep-water Lower Cretaceous in northern Pinar del Rio Province, western Cuba, may indicate that no connection ever existed. If the two escarpments ever were connected, it is not known whether grabenlike faulting, erosion, or both caused the separation of these two features. More information is being sought in geomagnetic and sedimentological studies now in progress. End_of_Article - Last_Page 1830------------