Mahlon M. Ball

Early Cretaceous shelf-edge deltas of the Baltimore Canyon Trough: principal sources for sediment gravity deposits of the northern Hatteras Basin

We present evidence that the principal sources for Early Cretaceous (Berriasian-Valanginian) gravity-flow deposits of the northern Hatteras Basin were three large shelf-edge deltas located along the outer margin of the Baltimore Canyon Trough, ∼ 100 km southeast of Cape Charles, Virginia, Ocean City, Maryland, and Long Branch, New Jersey. Sedimentary detritus from the central Appalachian highlands and the Maryland-Virginia coastal plain was transported across the Early Cretaceous continental shelf to form the Cape Charles and Ocean City deltas, whereas deposits of the Long Branch delta came chiefly from the Adirondack and New England highlands. Each delta supplied sediment gravity flows to large slope aprons and submarine-fan complexes on the Early Cretaceous continental slope and rise. The most conspicuous distributary of sediment on the Early Cretaceous continental rise extends 500 km basinward from the Ocean City delta, where its distal deposits were cored at Deep Sea Drilling Project Site 603.

Seismic Expression of Carbonate to Terrigenous Clastic Sediment Facies Transitions of Western Florida Shelf: ABSTRACT

Transitions from carbonate to terrigenous clastic sedimentary deposits are commonplace in the Mesozoic-Cenozoic section of the northwestern Florida shelf. On a regional scale, these transitions are responsible for a large seismic velocity variation between the areas of the Destin dome and the Middle Ground arch. In the Destin region, clayey shales and sands are more prevalent, interspersed with carbonates and evaporites, with the result that seismic transmission velocities are relatively low. Toward the south on the Middle Ground arch, the increased carbonate-evaporite content of the section results in much higher velocities. An example of this variation is that a reflection two-way travel time of 2 sec corresponds to a depth from 2.5 to 2.8 km (1.5 to 1.7 mi) in the Dest n area while this same reflection time corresponds to a depth of 4 km (2.5 mi) in the vicinity of the Texaco 2516 well on the Middle Ground arch. Analyses of stacking velocities indicate that the transition is a gradual one to the north and west of Middle Ground arch. On a local scale, transitions or terminations related to facies changes, erosion, or sediment body geometries are a potentially important factor in prediction of reservoir rock on the as yet uncondemned, 12 km (7.4 mi) broad, deep structural culmination west of the Destin tests and on the untested, 9 km (5.5 mi) broad, deep structure 20 km (12.4 mi) south of the Destin dome. The deep Exxon test on the Destin dome encountered 20 m (66 ft) of Norphlet quartz sand with porosity ranging from 20 to 30% and permeability of 1 darcy. This potentially excellent reservoir bed at a depth of 5,224 m (17,138 ft) is more than 150 m (492 ft) below the deep structural crest on the Destin dome. The Sun test, 25 km (15.5 mi) east of the Exxon well, penetrated 6 m (19.6 ft) of Smackover oomoldic dolomit with porosities of 13 to 15% and failed to find any Norphlet sand as it bottomed in Louann salt immediately below the Smackover. A study of a combination of velocity analyses, density and velocity logs, and synthetic seismograms allows speculations that the deep Destin dome and the structure on its south flank are still viable exploration prospects. End_of_Article - Last_Page 417------------

Destin Dome and Western Florida Shelf: ABSTRACT

The U.S.G.S. has acquired a network of 1,280 km (800 mi) of common-depth-point seismic data connecting eight wildcat wells north of the latitude of Tampa and tied to the Destin dome area in the northeastern Gulf of Mexico. Line layout facilitates ties to onshore and offshore wells and to the regional multichannel net of the University of Texas. These lines reveal the structural growth of the salt-related Destin dome and a salt pillow with Jurassic and Early Cretaceous growth 30 km (20 mi) south of the Destin structure. Elsewhere in the West Florida Shelf, numerous low relief anticlines are present above basement highs. Destin dome is a large, west-northwest trending anticlinal structure off northwest Florida. The dome is more than 80 km (50 mi) long and 30 km (20 mi) wide and has relief of a kilometer (3,000 ft) on Lower Cretaceous rocks. The dome appears to be the result of a salt swell that was uplifted during the Late Cretaceous and early Cenozoic. In 1973, 32 tracts (184,320 acres) constituting the eastern half of this structure were leased for

Exploration History, North U.S. Atlantic Margin: ABSTRACT

728,000,000. The highest bid lease (near the crest of the anticline) was purchased for

Petroleum Potential of Continental Margin off Southeastern United States: ABSTRACT

211,997,600 (

Geology and geophysics of the Bahamas

36,805/acre). Leases were not offered on the western half of the dome as it lies within a bombing range administered by the U.S. Department of Defense. Structural crests of Lower End_Page 544------------------------------ Cretaceous and Jurassic strata within the bombing range are more than 150 m higher than in the leased area to the east. Nine dry holes have been drilled in the vicinity, seven of them concentrated on a structural high in Upper Cretaceous strata on the eastern flank of the dome. End_of_Article - Last_Page 545------------

Comment and Reply on Scalloped bank margins: Beginning of the end for carbonate platforms?

The Baltimore Canyon Trough is the site of 26 exploration wells and two stratigraphic tests. As of November 1981, six dry holes had been drilled on the Great Stone Dome. This structure appeared to be the largest and most promising in the basin. Seventeen wells have been drilled along the edge of the continental shelf with significant hydrocarbon shows reported from five wells. Combined daily flow rate is 90 mmcf. This flow is approximately one-half the amount required to warrant construction of a production platform and pipeline. Georges Bank basin is characterized by an older thick carbonate and evaporite sequence (0 to 8 km) of Late Triassic-Early Jurassic age; a middle sequence of interbedded limestone, sandstone, mudstone, and red shale of Middle Jurassic to Early Cretaceous age (0 to 2.5 km); and a thin sequence (middle Cretaceous and younger) of transgressive shelf limestone and regressive claystone and siltstone (0.5 to 2 km). Elevated patch reefs beneath the shelf and a massive reeflike carbonate buildup under the slope form potential hydrocarbon traps. The patch reefs, which are elongate to circular and as much as several kilometers across, have caused a broad arching of younger strata. They may be built on salt swells or elevated basement blocks. A two-dimensional, finite-difference simulation of the main basins thermal history of crustal stretching and subsidence suggests that some of the oldest sedimentary sections over the seaward part of rift-stage crust and extending out to oceanic crust are thermally mature for oil generation. End_of_Article - Last_Page 545------------

Comment and Reply on “Segmentation and coalescence of Cenozoic carbonate platforms, northwestern Great Bahama Bank”COMMENT

The continental margin off the southeastern United States is underlain by two major basins, the Carolina trough off North Carolina and South Carolina and the Blake Plateau Basin off Florida and Georgia, with the latter basins landward extension, the Southeast Georgia embayment. The embayment, beneath the continental shelf is the only area in which drilling has taken place. Strata of the landward part of the Blake Plateau Basin including the embayment form a wedge of onlapping marine End_Page 563------------------------------ deposits that might provide stratigraphic traps, such as pinch-outs, barrier islands, and channels. Drapes over basement highs might trap petroleum. The seaward part of the Blake Plateau Basin contains a thick (14 km), landward-dipping section, probably composed mainly of carbonate platform deposits. Carbonate banks and an Albian-Aptian rudist reef might provide traps, although the seaward part of the platform has been breached by erosion. In the Carolina trough, flow of Jurassic(?) salt has formed diapirs, and withdrawal of salt has caused a large growth fault complex to form along the landward side of the trough. Because the block of sedimentary rock (12 km thick) above the salt is subsiding almost vertically, structures at the fault may include compressional features. The diapirs and faults may provide traps. A large shelf-edge anticline exists more than 150 km long and with a closure of as much as 500 m. Other possible traps might result from stratigraphic features of the onlapping sedimentary wedge landward of the Carolina trough and the eroded and buried paleoslope on the seaward side of the trough. End_of_Article - Last_Page 564------------