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The AAPG/Datapages Combined Publications Database

AAPG Bulletin


Volume: 67 (1983)

Issue: 3. (March)

First Page: 555

Last Page: 556

Title: Modeling Basin Subsidence and Stratigraphy: Blake Plateau Basin: ABSTRACT

Author(s): B. A. Swift, W. P. Dillon, D. S. Sawyer, K. M. Kent

Article Type: Meeting abstract


Blake Plateau basin on the continental margin off Georgia and Florida contains 12 to 13 km (39,000 to 43,00 ft) of Jurassic and younger sedimentary rock. Although such thicknesses of strata are common to sedimentary basins off the eastern United States, the Blake Plateau basin is underlain by unusually thick basement rocks (20 to 24 km; 66,000 to 79,000 ft) and is much wider (350 km; 220 mi) in comparison with other basins. Simple extensional models for the basin's origin would suggest thinner basement to correspond with the observed sedimentary thicknesses, i.e., basement 4 to 16 km (13,000 to 52,000 ft) thick. In contrast, a two-dimensional gravity model across the continental margin details the anomalous crustal structure. The basement is about 30 km (98,000 ft) thick nder the shelf; 18 km (59,000 ft) under the basin, thickening seaward to 24 km (79,000 ft) under the basin's eastern edge; and 6 km (20,000 ft) thick seaward of the Blake Escarpment.

The basin's subsidence history places limits on possible models of the crustal development of this part of the margin. Because of the paucity of well data, a detailed "backstripping" analysis of the stretched continental-crust area is not possible, but an estimation

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can be made of the post rift, thermal-subsidence history using multichannel seismic data. Stratigraphic control for Cretaceous and younger reflectors observed in these seismic profiles is available from the Continental Offshore Stratigraphic Test GE-1 well on the landwardside and from an eroded exposed escarpment on the seaward edge of the basin. The Jurassic age assignments were based on correlations with Jurassic sea level history.

When a different and simplified technique is used, the subsidence due to stretching and cooling, but not to sedimentation, during the pre-, syn-, and post-rift periods combined, can be obtained by calculating the depth of basement that would exist without a sedimentary load. Unlike the other east coast basins, in the Blake Plateau basin this unloaded basement depth indicates local maximum values in both the subsidence due to stretching and cooling and in sedimentary thickness. These maxima occur where the gravity model shows a transition to increasing crustal thickness seaward and near the southwest continuation of the trend of the East Coast Magnetic Anomaly, which marks where, on the rest of the margin, the stretched continental crust finally separated and new oceanic crust began to form. Rifted crust of the Blake Plateau basin never failed, and generation of new oceanic crust seems finally to have begun far to the east, east of the present Blake Plateau and almost against the West African craton.

The presence of rift-stage crust on either side of this aborted break, and lack of an extensional basin on the opposing African margin south of Senegal basin, and the paleoreconstruction of the area imply that the Blake Plateau basin continued to be rifted after the rift-to-drift transition had taken place in the basins to the north. This extended period of rifting may be responsible for the anomalous width of the Blake Plateau basin and for continued volcanism (dike injection?) which produced the unusual thickness of its rift stage crust.

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