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Abstract

The continental margin of the northern Gulf of Mexico extends from DeSoto Canyonto northern Mexico and from more than 300km in land in the central Gulf Coast to the deepgulf floor.It is composed of abroadwedge of Mesozoic and Cenozoic strata that accumulated almost continuously from Jurassic time to the present. Mesozoic and Cenozoic deposits are more than 15km thick beneath the lower coastal plain and adjacent continental shelf. Forthe mostpart,the margin is a Cenozoic clastic embankment built by the inpouring of sediments from the continental interior after the Late Cretaceous-Paleocene Laramide orogeny.Sediment supplies generally exceeded the subsidence rate,prograding the seaward face of the margin more than 400 km from the edge of Cretaceous carbonate platform deposits under the coastalplain,to the present position of the continental slope.Along the inner regions of the coastal plain from Alabama to southwestern Texas,updip members of Mesozoic and Cenozoic units rest unconformably on complexly folded and faulted Paleozoic rocks of the Ouachita and Appalachian tectonicbelts.

Major structural anomalies affecting the Mesozoic-Cenozoic sequence of the coastalplain,shelf,and slope are salt diapirs,growth faults,and shale uplifts.Salt structures are concentrated in interior basins in the inner coastal plain,along the lower coast from central Texas to DeSoto Canyon,and across the continental shelf to the foot of the slope.Regional systems of growth faults slice through Cenozoic units beneath coastal Texas and Louisiana and in the adjacent shelf.Many of these faults formed as a response to sediment overloads along Tertiary and Quaternary shelf edges,to differential compaction associated with abrupt changes insediment thickness and gross lithology,and(locally)to the withdrawal of large volumes of salt from depth during diapiric growth.

The continental margin of the eastern Gulf of Mexico is dominated by the Florida platform,compose do fathick accumulation of bathyal to neritic carbonate rocks and evaporite deposits of Mesozoic and Cenozoicage.The platform is fronted by aprominent escarpment built by shelf-edge reef complexes during the Early Cretaceous.The northern half of the platform was built on a continental foundation composed of upper Precambrian and lower Paleozoic igneous and meta mor-phic rocks and capped by undeformed clastic sediments of Ordovician, Silurian, and Devonian age.Triassic red beds and associated diabase are common in the extensive graben systems that underlie northwestern Florida.Southern peninsular Florida is underlain by basement composed of volcanic and hypabyssal rocks of Triassic and Early Jurassic age. Geophysical data suggest similar basement complexes beneath the West Florida Shelf and Slope.

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