Paul M. Harris

Endolith microborings and their preservation in Holocene-Pleistocene (Bahama-Florida) ooids

Holocene ooids from Joulters Ooid Shoal (Bahamas) are bored in various ways by blue-green algae that groove along the grain surface, reside just beneath the grain surface, and tunnel extensively a few tens of microns within the grain. The microborings, morphologically distinctive, are documented with scanning electron micrographs of open borings and resin casts. Gentle dissolution of ooid aragonite permits identification of several algal genera by light microscopy and enables comparison with the microboring casts. Pleistocene ooids from the Miami Limestone (Florida) contain natural casts of microborings, some of which are similar in form to Holocene examples. Significantly, these aragonite casts are more resistant to solution than surrounding ooid aragonite. They remain after most of the ooid is leached away and survive replacement of the ooid by low-Mg calcite. Dissolution or precipitation may occur along the walls of microborings, causing morphological alteration during their preservation. This points out a difficulty in the specific identification of endoliths on the basis of fossilized microborings in ancient rocks composed of original aragonite grains.

The Growth Potential of a Bypass Margin, Great Bahama Bank

ABSTRACT Observations and sampling to 350 m from a two-person submersible off Chub Cay, Berry Islands, Bahamas, suggest that accretion is occurring to varying degrees in all subdivisions of the platform margin profile. At the Chub Cay dive site, a nearly vertical wall extends to 140 m subsea; below, and extending to the limit of the dives, is a low-relief, fore-reef slope, ca. 50°, of limestone veneered with sediment. This study supports the idea that the upper portion of the wall from 30 to 85 m, the brow or deep-reef, is a principal source of talus, now cemented, that foots the windward margins of Great Bahama Bank. We infer that the brow grows outward so rapidly that it calves periodically. The resulting debris largely bypasses the deeper wall, but some is perched on the steep fore-reef slope below, where it is soon incorporated into the slope by submarine cementation. This model further explains the observation that carbonate platform margins tend to steepen through time and shows how those steepened slopes can be maintained during their continued growth.

Satellite Imagery, Visualization and Geological Interpretation of the Exumas, Great Bahama Bank: An Analog for Carbonate Sand Reservoirs

The Exumas Islands and surrounding carbonate sand bodies of Great Bahama Bank are an important training venue, an area of interest to researchers of modern carbonates, and a valuable modern analog for understanding carbonate sand bodies in the subsurface. This DVD makes readily available a set of processed satellite images, offshore/onshore digital elevation model (DEM), and interpretation maps organized into a GIS, along with several examples of how this data can be visualized and used for geological interpretation.

Guadalupe Mountains, West Texas and New Mexico: Key excursions

The carbonate and siliciclastic outcrops of the Guadalupe Mountains in the Permian Basin of West Texas and New Mexico have provided a rich set of basic and advanced conceptual models for geologists across the entire spectrum of experience for carbonate-ramp and steep-rimmed–platform settings as well as the adjacent deep-water siliciclastics not dealt with here. Fundamental questions regarding the scale and continuity of reservoir pay facies, the depositional patterns and profiles of shelf-to-slope clinoforms, the width of facies tracts on ramps and rimmed platforms, the distribution and internal composition of reef complexes, the link between reef development and slope depositional patterns, styles of early and late diagenesis including dolomitization and karstification, and structural patterns can all be addressed in the Guadalupe Mountains exposures.

Satellite Imagery, Visualization and Geological Interpretation of the Exumas, Great Bahama Bank

The Exumas Islands and surrounding carbonate sand bodies of Great Bahama Bank are an important training venue, an area of interest to researchers of modern carbonates, and a valuable modern analog for understanding carbonate sand bodies in the subsurface. This DVD makes readily available a set of processed satellite images, offshore/onshore digital elevation model (DEM), and interpretation maps organized into a GIS, along with several examples of how this data can be visualized and used for geological interpretation.