section_path: Geology
section_name: Geology
paragraph_text: Geology
  
  The consensus among geologists is that before the late Triassic, the Gulf of Mexico did not exist. Before the late Triassic, the area consisted of dry land, which included continental crust that now underlies Yucatán, within the middle of the supercontinent Pangaea. This land lay south of a continuous mountain range that extended from north-central Mexico, through the Marathon Uplift in west Texas and the Ouachita Mountains of Oklahoma, and to Alabama where it linked directly to the Appalachian Mountains. It was created by the collision of continental plates that formed Pangaea. As interpreted by Roy Van Arsdale and Randel T. Cox, this mountain range was breached in the late Cretaceous by the formation of the Mississippi Embayment.
  
  The rifting that created the basin was associated with zones of weakness within Pangaea, including sutures where the Laurentia, South American, and African plates collided to create it. First, there was a late Triassic–early Jurassic phase of rifting during which rift valleys formed and filled with continental red beds. Second, the continental crust was stretched and thinned as rifting progressed through early and middle Jurassic times. This thinning created a broad zone of transitional crust, which displays modest and uneven thinning with block faulting and a broad zone of uniformly thinned transitional crust, which is half the typical 40 km (25- mile) thickness of continental crust. At this time, rifting first created a connection to the Pacific Ocean across central Mexico and later eastwards to the Atlantic Ocean. This flooded the opening basin to create an enclosed marginal sea. The subsiding transitional crust was blanketed by the widespread deposition of Louann Salt and associated anhydrite evaporites. During the late Jurassic, continued rifting widened the basin and progressed to the point that seafloor spreading and formation of oceanic crust occurred. At this point, sufficient circulation with the Atlantic Ocean was established that the deposition of Louann Salt ceased. Seafloor spreading stopped at the end of the Jurassic, about 145–150 mya.
  
  During the late Jurassic through early Cretaceous, the basin experienced a period of cooling and subsidence of the crust underlying it. The subsidence resulted from crustal stretching, cooling, and loading. Initially, the crustal stretching and cooling combination caused about 5–7 km (3.1–4.3 miles) of tectonic subsidence of the central thin transitional and oceanic crust. The basin expanded and deepened because subsidence occurred faster than sediment could fill it. Later, loading of the crust within the basin and adjacent coastal plain by the accumulation of kilometers of sediments during the rest of the Mesozoic and all of the Cenozoic further depressed the underlying crust to its current position about 10–20 km (6.2–12.4 miles) below sea level. Particularly during the Cenozoic, a time of relative stability for the coastal zones, thick clastic wedges built out the continental shelf along the northwestern and northern margins of the basin.
  
  To the east, the stable Florida Platform was not covered by the sea until the latest Jurassic or the beginning of Cretaceous time. The Yucatán Platform was emergent until the mid-Cretaceous. After both platforms were submerged, the formation of carbonates and evaporites has delineated the geologic history of these two stable areas. Most of the basin was rimmed during the early Cretaceous by carbonate platforms, and its western flank was involved during the latest Cretaceous and early Paleogene periods in a compressive deformation episode, the Laramide Orogeny, which created the Sierra Madre Oriental of eastern Mexico.
  
  The Gulf of Mexico is 41% continental slope, 32% continental shelf, and 24% abyssal plain with the greatest depth of 12,467 feet in the Sigsbee Deep. Seven main areas are given as:
  
  The consensus among geologists is that before the late Triassic, the Gulf of Mexico did not exist. Before the late Triassic, the area consisted of dry land, which included continental crust that now underlies Yucatán, within the middle of the supercontinent Pangaea. This land lay south of a continuous mountain range that extended from north-central Mexico, through the Marathon Uplift in west Texas and the Ouachita Mountains of Oklahoma, and to Alabama where it linked directly to the Appalachian Mountains. It was created by the collision of continental plates that formed Pangaea. As interpreted by Roy Van Arsdale and Randel T. Cox, this mountain range was breached in the late Cretaceous by the formation of the Mississippi Embayment.
  
  The rifting that created the basin was associated with zones of weakness within Pangaea, including sutures where the Laurentia, South American, and African plates collided to create it. First, there was a late Triassic–early Jurassic phase of rifting during which rift valleys formed and filled with continental red beds. Second, the continental crust was stretched and thinned as rifting progressed through early and middle Jurassic times. This thinning created a broad zone of transitional crust, which displays modest and uneven thinning with block faulting and a broad zone of uniformly thinned transitional crust, which is half the typical 40 km (25- mile) thickness of continental crust. At this time, rifting first created a connection to the Pacific Ocean across central Mexico and later eastwards to the Atlantic Ocean. This flooded the opening basin to create an enclosed marginal sea. The subsiding transitional crust was blanketed by the widespread deposition of Louann Salt and associated anhydrite evaporites. During the late Jurassic, continued rifting widened the basin and progressed to the point that seafloor spreading and formation of oceanic crust occurred. At this point, sufficient circulation with the Atlantic Ocean was established that the deposition of Louann Salt ceased. Seafloor spreading stopped at the end of the Jurassic, about 145–150 mya.
  
  During the late Jurassic through early Cretaceous, the basin experienced a period of cooling and subsidence of the crust underlying it. The subsidence resulted from crustal stretching, cooling, and loading. Initially, the crustal stretching and cooling combination caused about 5–7 km (3.1–4.3 miles) of tectonic subsidence of the central thin transitional and oceanic crust. The basin expanded and deepened because subsidence occurred faster than sediment could fill it. Later, loading of the crust within the basin and adjacent coastal plain by the accumulation of kilometers of sediments during the rest of the Mesozoic and all of the Cenozoic further depressed the underlying crust to its current position about 10–20 km (6.2–12.4 miles) below sea level. Particularly during the Cenozoic, a time of relative stability for the coastal zones, thick clastic wedges built out the continental shelf along the northwestern and northern margins of the basin.
  
  To the east, the stable Florida Platform was not covered by the sea until the latest Jurassic or the beginning of Cretaceous time. The Yucatán Platform was emergent until the mid-Cretaceous. After both platforms were submerged, the formation of carbonates and evaporites has delineated the geologic history of these two stable areas. Most of the basin was rimmed during the early Cretaceous by carbonate platforms, and its western flank was involved during the latest Cretaceous and early Paleogene periods in a compressive deformation episode, the Laramide Orogeny, which created the Sierra Madre Oriental of eastern Mexico.
  
  The Gulf of Mexico is 41% continental slope, 32% continental shelf, and 24% abyssal plain with the greatest depth of 12,467 feet in the Sigsbee Deep. Seven main areas are given as: