The Middle Mesozoic Drift and Cooling Phase begins with the main phase of sea floor spreading, slowly but steadily opening the Gulf of Mexico basin. Initially hypersaline conditions resulted in basin-wide deposition of an original thickness of 4 km of evaporites (halite and updip anhydrite), called the Louann Salt, which likely formed with episodic seawater influx from the Atlantic Ocean. Strontium seawater analysis suggests 170 Ma as a proxy age for the Louann Salt. The arid eolian Norphlet Formation is subsequently deposited, followed by marine carbonates, evolving from ramp microbalites (Smackover) to platform margin reef systems of the Haynesville and Cotton Valley. Rafting apart of the Smackover and Norphlet in the northeast Gulf of Mexico began in this phase, possibly associated with oceanic crustal cooling which created a dip slope to the south and west. This set up a major new petroleum province which is host to several new giant oil discoveries. Periods of reduced bottom circulation resulted in at least two phases of source rock development, in the Oxfordian and Tithonian stages, that are linked to petroleum generation for both conventional and unconventional plays.

The Middle Miocene marked the emergence of the Appalachian uplands as a significant sediment source to the Gulf of Mexico. As a result, the Tennessee River joined the Mississippi in creating the dominant fluvial/deltaic depocenter. At the same time, supply from western interior uplands decreased. Two Miocene deposodes and multiple eustatically modulated high-frequency Pliocene—Pleistocene deposodes are recorded in northern Gulf stratigraphy. The continental slope wedge prograded onto the shallow Sigsbee salt, initiating canopy deformation and rapid basinward canopy advance. Salt-encased minibasins created rugose slope topography with multiple, efficient sediment traps. Nonetheless, large volumes of sediment bypassed the continental slope and constructed a series of large, long-lived abyssal plain fans. A narrow coastal plain and shelf prograded along the western Gulf margin. Extensional growth faulting was compensated basinward by compressional faulting and folding above Paleogene detachments. In the Sureste, the river-fed, prograding continental margin and ongoing basement deformation mobilized salt of the Campeche Salt Basin.

The Gulf of Mexico Mesozoic depositional history can be subdivided into a series of tectonostratigraphic phases, with the first phase covering sedimentation associated with post-Quachita–Marathon orogenic successor basin-fill and rifting. In this early Mesozoic timeframe, the basin precursor units called Eagle Mills (USA) and equivalents in Mexico were deposited, draining diverse Appalachian, pan-African, and other source terranes. The new tectonostratigraphic model is based upon updated plate tectonic reconstructions, detrital zircon geochronology from deep wells, and analysis of new seismic reflection data in Mexico and the USA. Newly developed concepts depart from conventional GoM thinking both in terms of timing and kinematics. Evidence suggests the South Georgia–Newark rift system does not extend into Texas–Louisiana and much of the Triassic Eagle Mills deposition here occurred in a successor basin overlying the deformed Quachita–Marathon system. Pre-salt deposition in northern Yucatan forms a seaward dipping wedge of younger (likely Early Jurassic) continental deposition derived from erosion of exposed Yucatán basement.

The Middle Miocene marked the emergence of the Appalachian uplands as a significant sediment source to the Gulf of Mexico. As a result, the Tennessee River joined the Mississippi in creating the dominant fluvial–deltaic depocenter. At the same time, supply from Western Interior uplands decreased. Two Miocene deposodes and multiple eustatically modulated high-frequency Pliocene–Pleistocene deposodes are recorded in northern Gulf stratigraphy. The continental slope wedge prograded onto the shallow Sigsbee salt, initiating canopy deformation and rapid basinward canopy advance. Salt-encased minibasins created rugose slope topography with multiple, efficient sediment traps. Nonetheless, large volumes of sediment bypassed the continental slope and constructed a series of large, long-lived abyssal plain fans. A narrow coastal plain and shelf prograded along the western Gulf margin. Extensional growth faulting was compensated basinward by compressional faulting and folding above Paleogene detachments. In the Sureste, the river-fed, prograding continental margin and ongoing basement deformation mobilized salt of the Campeche salt basin.

Cenozoic history of the Gulf of Mexico basin was dominated by changing rate and geography of sediment supply. Most sediment entered through eight fluvial–deltaic axes along the northern basin margin, and one axis in Campeche. Deltaic depositional systems constructed the continental platform along these axes. Strike-reworking in coastal and shelf systems infilled the bights between deltaic depocenters. Depositional offlap of delta- and shelf-fed slope aprons prograded the shelf edge about 200 km (125 miles) from its Cretaceous precursor. Abyssal plain submarine fan systems were deposited during the Paleocene and Middle Miocene–Pleistocene. Sediment bypass from basin-margin uplands directly to the deep basin dominated the western GoM until the Neogene; tectonic margin aprons and submarine channel systems dominated. Pervasive gravity and salt tectonics produced a diverse array of extensional and compressional structures. These, in turn, create a great variety of trap configurations that help make the Gulf a global petroleum giant.

The Gulf of Mexico petroleum habitat is broad and diverse, with virtually every depositional unit or supersequence producing hydrocarbons onshore or offshore in the USA, Mexico, or Cuba. Oil and gas fields and undiscovered resources follow a concentric trend, with Mesozoic hydrocarbons resources surrounding the prolific Cenozoic basin center. The most recent and expected future discoveries are in the deepwater subsalt domain of the USA and Mexico, though a potential pre-salt frontier remains to be tested. Characterization of emerging (deepwater Tuscaloosa and Norphlet), existing (deepwater Wilcox), and mature (Plio-Pleistocene minibasin) conventional exploration plays yields new insights but also important exploration lessons, such as the Perdido fold belt BAHA wells, which ultimately set-up deepwater Wilcox exploration in the Gulf of Mexico, with large discoveries as recently as 2017. Unconventional onshore plays are well-established (Eagle Ford), emerging (Agua Nueva), or technically challenged (Tuscaloosa Marine Shale). The seismic technology evolution that underpins current success in the subsalt of the US sector will undoubtedly impact new exploration in the Campeche salt province of Mexico.

The Laramide orogeny, which extended along the length of North America, had both direct and indirect impacts on the Gulf of Mexico basin. Along the western Gulf margin, compressional deformation created a series of uplands and foreland troughs. Gravity transport systems constructed sandy slope/basin aprons in the troughs. To the north, tectonic uplands of the Western Interior supplied sediment to several evolving continental river systems that flowed southeastward into the northern Gulf. There, large delta systems prograded the coastal plain, shore zone, shelf, and continental slope tens of kilometers beyond the inherited Cretaceous shelf margin. Four principal depositional episodes are recorded in the stratigraphy of the northern margin: the Paleocene Lower Wilcox and Middle Wilcox, the early Eocene Upper Wilcox, and the Middle Eocene Queen City and Sparta. Sediment supply and construction of basinal submarine fan systems peaked in the Paleocene, and then decreased as supply waned in the Early Eocene.

Defined by the updip limit of the first basin-wide depositional unit, the Louann Salt, the Gulf of Mexico sedimentary basin extends from the southern US coastal plain to southern Mexico, Chiapas and Tabasco regions, and east across Yucatán to Cuba, the Florida Straits, and onshore Florida. The unique structural setting of salt and extensional tectonics (and Neogene Mexico compressional events) controls how the Mesozoic and Cenozoic depositional history evolves. This is illustrated by basin-scale cross-sections across the USA, Mexico, and Cuba, onshore to offshore. The 200-million-year depositional history is viewed through a six-stage tectonostratigraphic framework reflecting hinterland source terrane uplift, sediment routing, basin accommodation, and sea-level change. Stratigraphic terminology for Mesozoic and Cenozoic strata and depositional systems classifications for ancient carbonates and siliciclastics are explained, facilitating detailed unit descriptions. The database of seismic reflection interpretations, biostratigraphy, well logs, provenance analysis, carbonate reef, and siliciclastic shelf margin and deepwater system mapping that underpins the paleogeographic maps is detailed.