Florida Geological Survey


cates that such stratigraphic relationships are not apparent between boreholes in Brevard County and a karst collapse origin for the shortened sections in the D. B. Lee and West Melbourne wells is unlikely.

 Core from each of the four wells for which core was available exhibited some degree of fracturing. In general, fractures appear to be restricted to well-indurated or highly cemented carbonates of the Floridan aquifer system in Brevard County. Consequently, fractures are more prevalent in dolostones due to their consistently highly indurated nature than in limestones. Moderately- to poorly-indurated mudstones, wackestones, packstones and grainstones may act as mechanical boundary layers preventing the vertical propagation of fractures from dolostone beds. However, several core samples of poorly to moderately-indurated carbonates did have slickensided surfaces but lacked well defined fracture planes. The slickensides may be the unique expression of fracture-related strain consistent with the mechanical properties of the less indurated carbonate rocks.

 The majority of observed fractures are high angle, approaching vertical and are probably tensional in origin. What appear to be shear fractures were observed in core recovered in the Harris #2 within the interval from 1,903 to 1,912 feet BLS. These fractures occur in a moderately-indurated mudstone sequence and have dip angles of approximately 50 degrees. The fractures have well developed, polished slickensided surfaces and could be related to faulting. Other data, such as anomalous differences in marker bed structural elevations between the Harris #2 and the Port Malabar well and shortened stratigraphic sections in the Harris #2 (between 2,000 and 2,130 feet BLS) and the Merritt Island (between 510 and 900 feet BLS) are also suggestive of possible small displacement faulting (<50 feet of throw). A second possible fault, downthrown to the west with northsouth strike, is suggested by the apparent dip


reversal occurring between the Harris #2 and Port Malabar wells (Figure 7 and Plate 2).

 Tensional fractures in Brevard County could be related to several different processes in terms of their origin. These processes may include release fracturing as a result of sea level changes, fracturing associated with possible uplift of the Brevard Platform, and tension gash fracturing in proximity to fault planes.

 The origin of faulting here is less clear given the apparent passive nature of the North American Atlantic coastal margin and the absence of salt-related tectonics that is typical of Gulf Coastal Plain regions. The most recent major tectonic event involving the FloridaBahama Platform region was the Late Cretaceous through Eocene convergence of the Caribbean plate with the North American plate in the northern Cuba and southern Bahama platform region (Sheridan et al., 1981). Sheridan et al. (1988) explained the present configuration of deep channels and shallow platforms of the Bahamas and Eocene faulting along the Abaco Canyon as the result of north-south compression associated with Caribbean-North American plate convergence. Convergence-related stresses reactivated old (Jurassic) planes of crustal weakness (Sheridan et al., 1988) such as the Abaco and Bahama Fracture Zones of Klitgord, et al. (1984) with possible left lateral shear displacement (Sheridan et al., 1981, 1988). The effect of these stresses along the projected trend of the Bahama Fracture Zone across the Florida peninsula (Figure 9) (and the Florida Atlantic Coastal Margin) has not been addressed, and the possibility of deformation similar to that proposed in the Bahamas cannot be ruled out.