1.2.1 Deep Crustal Types

For many years, the form and lithology of the deep structure in the GoM was a matter of conjecture and inferences based upon rare penetrations of basement rock or sometimes-equivocal gravity and magnetic data. Recently, seismic refraction studies have greatly illuminated the form of the mantle and overlying crystalline and sedimentary crust (Van Avendonk et al. Reference Van Avendonk, Eddy and Christeson2013, Reference Van Avendonk, Christeson, Norton and Eddy2015; Christeson et al. Reference Christeson, Van Avendonk, Norton, Snedden and Eddy2014; Eddy et al. Reference Eddy, Van Avendonk and Christeson2014). In addition, new plate tectonic models have altered previous suppositions on timing of basin opening and emplacement of oceanic crust (Norton et al. Reference Norton, Lawver, Snedden, Lowery and Snedden2016). Alternative models, particularly for the pre-spreading rift phase, show convergence toward a consensus solution.

In general, these studies agree that the Gulf basin is largely surrounded by normal continental crust of the North American plate. Most of the structural basin is underlain by transitional crust that consists of continental crust that was stretched and attenuated by Middle to Late Jurassic rifting (Hudec et al. Reference Hudec, Norton, Jackson and Peel2013a). Two types of transitional crust are differentiated (Figure 1.2). The basin margin is underlain by a broad zone of thick transitional crust, which displays modest thinning and typically lies at depths between 2 and 12 km subsea (Sawyer et al. Reference Sawyer, Buffler, Pilger and Salvador1991). The area of thick transitional crust consists of blocks of near-normal thickness continental crust separated by areas of stretched crust that has subsided more deeply. The result is a chain of named arches and intervening embayments and salt basins around the northern periphery of the Gulf basin (Figure 1.3).

Figure 1.2 GoM crustal types.

Modified from Galloway (Reference Galloway and Hsu2008).

Figure 1.3 Key tectonostratigraphic features, northern GoM. Basement depths based on seismic structural mapping. Abbreviations: AB, Alabama basin; AE, Apalachicola Embayment; ANB, Anahuac Block, BB, Burgos basin; AO, Appalachian Orogen (Cretaceous limit); AU, Arbuckle Uplift; BU, Burro Uplift; CCP, Clarke County Platform; CP, Coahuila Platform; DSSB, DeSoto salt basin; EP, Edwards Platform; ETB, East Texas basin; FWB, Fort Worth basin; JD, Jackson Dome; LPB, La Popa basin; LU, Llano Uplift; MA, Muenster Arch; MAU, Marathon Uplift; MB, Mississippi Basin; ME, Mississippi Embayment; MSB, Mississippi salt basin; MU, Monroe Uplift; NLSB, North Louisiana salt basin; OM, Ouachita Mountains; OU, Ocala Uplift; PB, Parras basin; PH, Peyotes High; SAP, Sarasota Platform; SEGE, Southeast Georgia Embayment; SFB, South Florida basin; SP, Southern Platform; SU, Sabine Uplift; TB, Tyler basin; TE, Tampa Embayment; TMM, Tampico–Misantla–Magiscatzin; TP, Tuxpan Platform; TSCA, Tamaulipas/San Carlos Arch; WA, Wiggins Arch; WB, Winnfield basin.

Terminology from various public sources, including Ewing and Lopez (Reference Ewing, Lopez and Salvador1991).

Much of the present inner coastal plain, shelf, and continental slope is underlain by relatively homogeneous thin transitional crust, which is generally less than half of the 35 km thickness typical of continental crust and is buried to depths of 10–16 km below sea level. Reconstructions of deep seismic traverses (Peel et al. Reference Peel, Hossack, Travis, Jackson, Roberts and Snelson1995; Radovich et al. Reference Radovich, Moon, Connors and Bird2007, Reference Radovich, Horn, Nuttall and McGrail2011; Hudec et al. Reference Hudec, Jackson and Peel2013b) indicate that basement may lie below 20 km in the central depocenter beneath the south Louisiana coastal plain and adjacent continental shelf. The deep, central Gulf floor is underlain by an arcuate belt of basaltic oceanic crust that was intruded during Late Jurassic through Early Cretaceous sea floor spreading (Hudec et al. Reference Hudec, Norton, Jackson and Peel2013a; Norton et al. Reference Norton, Lawver, Snedden, Lowery and Snedden2016). Surprisingly, the central Gulf crust generally lacks the magnetic signature typical of oceanic crust (Figure 1.4), which compounds interpretation difficulties, but recent gravity mapping (Sandwell et al. Reference Sandwell, Müller, Smith, Garcia and Francis2014) confirm earlier models of the location of the updip or landward limit of oceanic crust (LOC).

Figure 1.4 Mapped top of seismically defined basement with overlay of EMAG2 magnetic anomaly (Sandwell et al. Reference Sandwell, Müller, Smith, Garcia and Francis2014). Key tectonic features are discussed in the text. The limit of oceanic crust (red dashed line) is based on Hudec et al. (Reference Hudec, Norton, Jackson and Peel2013a, Reference Hudec, Jackson and Peel2013b).

1.2.2 Seismic Refraction Studies of Deep Crust

The majority of data obtained for petroleum exploration is seismic reflection data, which allows both imaging through common depth point solutions and measurement of compressional seismic velocities to depths approaching 40,000 ft (12.2 km), depending on the energy source and cable. Seismic refraction data involves measurement of the compressional seismic velocities at much greater depths, approaching 40 km (25 miles). These velocities are a function of density in the deep earth and allow one to differentiate between mantle, crystalline crust, and sedimentary crust, even where buried below thick intervals of salt and sedimentary rocks (Figure 1.5). In the northern GoM, a series of long (>500 km) seismic refraction lines were collected using bottom sensors (Figure 1.5). A line across the eastern GoM revealed the top of the mantle to shallow from about 34 km (21 miles) below the thick transitional crust below the Florida Platform to depths as shallow as 15 km (9 miles) in the area where oceanic crust is known to be present (Christeson et al. Reference Christeson, Van Avendonk, Norton, Snedden and Eddy2014; Figure 1.5). Above the mantle here lies a crystalline crust interval with unusually low velocities (in comparison to other areas), suggesting moderately attenuated continental crust. The sedimentary interval has compressional velocities in the range of 5.0 km/s (carbonate-dominated platform) to 3.0 km/s, where Miocene and younger strata are known to be present from well penetrations. The seismic refraction data also allow locating the boundaries of the LOC, here at a distance of 350–400 km from the start of the line just offshore of Florida. An intriguing observation is higher-than-expected seismic velocities at the LOC, suggestive of massive basalt emplacement associated with sea floor spreading (Christeson et al. Reference Christeson, Van Avendonk, Norton, Snedden and Eddy2014).

Figure 1.5 Seismic refraction data and interpretation, Gumbo Line 4, eastern GoM.

Modified from Christeson et al. (Reference Christeson, Van Avendonk, Norton, Snedden and Eddy2014).

In the western GoM, seismic refraction data (Gumbo Line 1) revealed an unusual interval between high compressional velocity mantle and penetrated sedimentary crust (Van Avendonk et al. Reference Van Avendonk, Eddy and Christeson2013). Below base of salt lies an unknown interval with considerable lateral crustal heterogeneity, thought to be rifted (attenuated) sedimentary crust with igneous intrusions. This interval ranges from 10–12 km at the top to as deep as 28 km depth above mantle rock. The lateral velocities variations that suggest igneous intrusions are documented in the shallow pre-salt interval of onshore areas, to be discussed in Section 2.2. The LOC is located inboard of the present-day Sigsbee Escarpment, though there is some uncertainty, given the thick salt canopy here (Van Avendonk et al. Reference Van Avendonk, Eddy and Christeson2013). The presence of a pre-salt (Late Triassic[?] to Middle Jurassic[?]) interval in the deep northern GoM is consistent with observations from seismic reflection data in a pre-salt province offshore of Yucatán Province (Williams-Rojas et al. Reference Williams-Rojas, Reyey-Tovar and Miranda Peralta2012; Miranda Peralta et al. Reference Miranda Peralta, Alvarado and Villalón2014; Saunders et al. Reference Saunders, Gieger, Rodriguez and Hargreaves2016).

1.2.3 Seismic Reflection Studies of Deep Crust

Seismic reflection surveys shot for oil and gas exploration provide some corroboration of seismic refraction interpretations, particularly for the eastern GoM where the salt canopy is absent. Here the general position of a Jurassic–Early Cretaceous spreading center in the eastern GoM has been suggested for many years, yet the precise location was not precisely known until Snedden et al. (Reference Snedden, Norton, Christeson and Sanford2014) used several seismic criteria to define its location (Figure 1.6). Lin et al. (Reference Lin, Bird and Mann2019) subsequently refined its structure and evolution using newer vintage seismic reflection and gravity data. The extinct spreading center here displays morphological characteristics associated with slow-spreading mid-ocean ridges (rates of 1–4 cm/year; Perfit and Chadwick Reference Perfit, Chadwick, Buck, Delaney, Karson and Lagabrielle1998): (1) large and wide axial valleys, 5–20 km wide; (2) deep axial valleys, often over 2 km deep; (3) normal faults that dip toward axial valleys; and (4) discontinuous, isolated basement highs, with elevations over 1 km above regional oceanic basement depth. Using seismic refraction data, Christeson et al. (Reference Christeson, Van Avendonk, Norton, Snedden and Eddy2014) calculated a full spreading rate of 2.2 cm/year on a profile (Figure 1.5) in the same area. This estimate falls squarely in the slow spreading rate range globally and specifically for the comparable Mid-Atlantic Ridge system (McDonald Reference McDonald1982). Slow-spreading ridges express wide variety in tectonic and volcanic character, reflecting relatively unfocused magmatism (Sempere et al. Reference Sempere, Lin, Brown, Schouten and Purdy1993).

Figure 1.6 Seismic line interpretation in eastern GoM, extending from the Florida Platform across the inferred axial graben of the extinct spreading center showing lapout of HVB, CVB, and CVK supersequences onto oceanic crust. Other correlated horizons are SH, NT, and Paleogene (Wilcox) supersequences.

Modified from Snedden et al. (Reference Snedden, Norton, Christeson and Sanford2014). Seismic line courtesy of Spectrum. Abbreviations HVB, Haynesville–Buckner; CVB, Cotton Valley–Bossier; CVK, Cotton Valley–Knowles; SH, Sligo–Hosston; NT, Navarro–Taylor; BMT, basement.

Structural-balanced restorations of the eastern Gulf further confirm the LOC location and timing of sea floor spreading (Curry et al. Reference Curry, Peel, Hudec and Norton2018). Upper Jurassic (Smackover and Norphlet) strata downlap onto oceanic crust, suggesting oceanic crust formation contemporaneous with deposition (Figure 1.6; see also Section 3.3.4). Latest Upper Jurassic (Haynesville-equivalent) and Cotton Valley intervals extend across all oceanic crust, constraining the end of sea floor spreading at about 155 Ma. These units are also contemporaneous with post-Smackover rafting in the eastern Gulf, suggesting a genetic relationship, as will be explored in Section 3.3.4.

1.2.4 Magnetic Data

Early attempts at mapping the extinct spreading center and LOC (Figure 1.4) were challenged by the generally indistinct character on magnetic data collected from the northern Gulf (e.g., Imbert and Phillippe Reference Imbert and Phillippe2005). This can be partly attributed to the low paleolatitude of the Gulf during the Jurassic, resulting in shallow magnetization vectors that subdued magnetic intensity at the surface but also the poor resolution of older surveys. Newer aeromagnetic data acquired for hydrocarbon exploration in Mexico have better constrained the location of oceanic crust, particularly when integrated with comparable vintage northern Gulf data (Pindell et al. Reference Pindell, Miranda, Ceron, Hernandez, Lowry and Snedden2016). One prominent magnetic anomaly located in the central GoM has a distinctive pattern of orthogonally cross-cutting linear features superimposed upon an elongate margin parallel magnetic anomaly, thought to indicate the location of the youngest oceanic crust and thus the position of the extinct spreading center (Pindell et al. Reference Pindell, Miranda, Ceron, Hernandez, Lowry and Snedden2016). The calculated full spreading rates of 1–3.6 cm/year for the entire GoM are comparable to the slow spreading rates (2.2 cm/year) estimated for the eastern GoM (Christeson et al. Reference Christeson, Van Avendonk, Norton, Snedden and Eddy2014). Another trend, called the Campeche magnetic anomaly, is located downslope of the Yucatán Platform margin and constrains the Yucatán (Mayan) block position at the start of pre-salt deposition here, as discussed in Chapter 3.

1.2.5 Gravity Data

Sandwell gravity maps (Sandwell et al. Reference Sandwell, Müller, Smith, Garcia and Francis2014) also provide further documentation of the present-day crustal types and their position. Continental crust is generally indicated by gravity highs (e.g., Yucatán block) and oceanic crust by gravity lows, but local variations can occur as a function of igneous intrusions, salt, and depth variations along prominent escarpments.

1.3.1 Growth Fault Families and Related Structures

Growth faults tend to nucleate and grow during active deposition at the continental margin (Winker Reference Winker1982; Watkins et al. Reference Watkins, Bryant and Buffler1996b; Jackson and Hudec Reference Jackson and Hudec2017). Here, extension results from basinward gravitational gliding or translation of the sediment wedge along a detachment zone, typically found within salt or overpressured deep marine mud (Rowan et al. Reference Rowan, Peel, Venderville and McClay2004). Extension creates a family of features, including primary synthetic growth faults, splay faults, antithetic faults, and rollover anticlines (Figure 1.7A). In many parts of the GoM, updip extension is more or less balanced by a similar degree of contraction in downdip areas, as discussed in the following sections.

(A) Linked extension and compression.

(B) Roho salt detachment.

(C) Salt withdrawal minibasin.

From Galloway (Reference Galloway and Hsu2008).

Figure 1.7 GoM gravity tectonics.

1.3.2 Basin-Floor Contractional Fold Belts

Basinward gravity spreading or gliding along a detachment zone, and resultant updip extension, requires compensatory compression at the toe of the displaced sediment body (Weimer and Buffler Reference Weimer and Buffler1992; Hall et al. Reference Hall, Bowen, Rosen, Wu and Bally1993; Fiduk et al. Reference Fiduk, Weimer and Trudgill1999; Trudgill et al. Reference Trudgill, Rowan and Fiduk1999). Contractional features include anticlinal toe folds and reverse faults (Figure 1.7A). They commonly form at the base of the slope, but can also extend onto the basin plain where a stepped discontinuity or termination of the decollement layer occurs. The deepwater fold belts (Atwater, Mississippi, etc.) are thought to represent adjustments to significant updip extension (Radovich et al. Reference Radovich, Moon, Connors and Bird2007). In other areas, extension may be balanced by squeezing salt bodies or salt weld development (Jackson and Hudec Reference Jackson and Hudec2017; see Section 1.3.6).

1.3.3 Allochthonous Salt Bodies, Including Salt Canopies and Salt Sheets

Loading of the Louann Salt has resulted in regional extrusion of salt basinward and upward (Diegel et al. Reference Diegel, Karlo, Schuster, Shoup, Tauvers, Jackson, Roberts and Snelson1995; Fletcher et al. Reference Fletcher, Hudec, Watson, Jackson, Roberts and Snelson1995; Peel et al. Reference Peel, Hossack, Travis, Jackson, Roberts and Snelson1995). Allochthonous salt canopies typically develop beneath the continental slope, where salt rises as a series of coalescing diapirs or as injected tongues. Salt may also be extruded to the surface, forming salt sheets, or nappes, which move basinward, much like salt glaciers (Jackson and Hudec Reference Jackson and Hudec2017).

1.3.4 Roho Fault Families

Lateral salt extension by gravity spreading creates a linked assemblage of extensional faults and compensating, downslope compressional toe faults, anticlines, and salt injections in the overlying sedimentary cover (Rowan Reference Rowan, Jackson, Roberts and Snelson1995; Schuster Reference Schuster, Jackson, Roberts and Snelson1995). In some cases, the top of allochthonous salt can acts as a decollement surface for faults (Figure 1.7B), as does autochthonous salt previously described. These are called roho systems and often occur in stratigraphically distinct fault groups or fault families.

1.3.5 Salt Diapirs and Their Related Withdrawal Synclines and Minibasins

In the Gulf margin basins and embayments, salt diapirs rise directly from the autochthonous Louann ‘‘mother’’ salt (Seni and Jackson Reference Seni and Jackson1983; Fletcher et al. Reference Fletcher, Hudec, Watson, Jackson, Roberts and Snelson1995; Rowan Reference Rowan, Jackson, Roberts and Snelson1995; Rowan and Weimer Reference Rowan and Weimer1998). Basinward, depositional loading of salt canopies and sheets beneath shelf and slope areas also causes renewed salt stock evacuation, creating high-relief salt diapirs and intervening depressions (Figure 1.7C). Progressive salt evacuation creates shifting, localized sites of extreme subsidence and sediment accumulation. Resulting features include withdrawal synclines created by local evacuation of salt from diapir flanks, bathymetric depressions, called minibasins, that form local depocenters, turtle structures, and local fault families, including down-to-basin ramp faults, counter-regional flap faults, and crestal faults above salt bodies.

1.3.6 Salt Welds

Salt welds are surfaces or zones that join strata originally separated by either autochthonous or allochthonous salt (Hudec and Jackson Reference Hudec and Jackson2011). These are present where nearly complete expulsion of salt from stock feeders, dikes, salt tongues, or salt canopies has occurred (Jackson and Cramez Reference Jackson and Cramez1989; Jackson et al. Reference Jackson, Vendeville and Schultz-Ela1994; Figure 1.7B,C). Because the welds form some time after the deposition of adjacent strata, these juxtapose discordant stratigraphic intervals, sometimes with significant angularity of converging reflections (Hudec and Jackson Reference Hudec and Jackson2011). Primary, secondary, and tertiary welds can be identified on the basis of the type of salt body that was welded (Jackson and Hudec Reference Jackson and Hudec2017). Welds can also serve as detachment surfaces for younger listric faults.

Younger (secondary) sedimentary minibasins may be welded against older (primary) minibasins, resulting in drastically different ages, lithologies, and subsurface pressures (Pilcher et al. Reference Pilcher, Kilsdonk and Trude2011; Figure 1.8). These are particularly prominent in a portion of the central GoM, the so-called “bucket weld” province. These bucket welds can act as lateral boundaries to hydrocarbon traps.

(A) Schematic salt geometries based on seismic interpretation.

(B) Primary top basin interpretation.

(C) Primary basin trap style. Letters indicate different trap styles in subsalt domain.

Modified from Pilcher et al. (Reference Pilcher, Murphy and Ciosek2014).

Figure 1.8 Schematic cross-sections of the bucket weld province.

Salt welds can also act as regional decollement surfaces even when obvious linkage to downdip contraction is lacking. Regional decollements at welds are also known to be significant horizontal pressure barriers, with a significant increase in pressure in sub-weld intervals and attendant increase in risk, uncertainty, and well costs (see Section 9.20.1 on the Wilcox deep shelf play). Reverse faults can occur along welds (thrust welds), as observed in Campeche.

1.3.7 Rollovers and Expulsion Rollovers

Thickening and bending of strata toward a listric normal fault is commonly observed in the GoM Cenozoic and Mesozoic intervals. If expulsion of salt occurs to cause stratal thickening and rotation, with or without a fault, this structure is referred to as an expulsion rollover (Ge et al. Reference Ge, Jackson and Vendeville1997; Jackson and Hudec Reference Jackson and Hudec2017). Large expulsion rollover structures have been identified in the Mississippi Canyon protraction block and represent some of the largest undrilled prospects in the basin (Harding et al. Reference Harding, Walker, Ehlinger, Chapman, Lowery and Snedden2016). The orientation of these expulsion rollovers may indicate the general direction of sediment transport and loading (McDonnell et al. Reference McDonnell, Loucks and Galloway2008), though these features are several orders of magnitude larger than depositional clinoforms and should not be used to indicate the location of paleo-shelf margins.

1.3.8 Carapaces and Rafts

When moving salt carries roof material that is not firmly attached to surrounding strata, stratigraphic discontinuities can occur. Transported roof material can be tens of kilometers in lateral extent and sometimes as thick as the salt body (Jackson and Hudec Reference Jackson and Hudec2017). The term carapace is used here in a restrictive sense to describe detached blocks above salt that have moved vertically relative to the surrounding strata, either actively by diapir rise or passively as younger sediments are deposited around the salt-supported blocks (Figure 1.9). Early drilling at or around the allochthonous salt canopy encountered blocks which tended to be older, thinner, and/or more stratigraphically condensed than the adjacent non-carapace interval (Hart et al. Reference Hart, Jacek, Martin, Post, Olson and Lyons2004). Carapaces are often structurally much higher than the regional level of coeval strata. For example, the Norton well (GB 754 #1) penetrated a carapace block where Top Cretaceous was encountered at 7180 ft (2189 m), much shallower than the regional depths of Cretaceous, closer to 30,000 ft (9.1 km; Cunningham et al. Reference Cunningham, Snedden and Norton2016). Initially, stratigraphic discontinuities within carapaces caused considerable confusion, including the misinterpreted Middle Cretaceous unconformity (MCU), which later analyses proved was actually the Cretaceous–Paleogene boundary (K–Pg; Dohmen Reference Dohmen2002).

Figure 1.9 Development of a salt-related carapace structure.

Modified from M. Rowan (pers. comm.).

Carapaces do accumulate sediment above a diapir documenting that diapir’s history, but also record information on older strata that is relevant to regional or basin reconstructions. Carapaces containing organically enriched intervals within both the Tithonian and Ceno-Turonian intervals provide critical evidence in characterization of these source rocks (Cunningham et al. Reference Cunningham, Snedden and Norton2016).

Rafts are more complicated salt tectonic features that are defined in two different ways. First, we recognize rafts as stratigraphic blocks formed as part of raft tectonic processes. Raft tectonics is a form of thin-skinned extension, with unusually large degrees of extension such that the footwall and hanging wall are often not in contact, unlike growth faults (Jackson and Hudec Reference Jackson and Hudec2017). Raft gaps are filled in by synkinematic (syn-extensional) strata. Raft tectonics is well-documented in the Albian interval of Angola and the Oxfordian interval of the DeSoto Canyon protraction block (Pilcher et al. Reference Pilcher, Murphy and Ciosek2014).

A second use of the term raft applies to stratigraphic blocks that have been moved considerable distances downslope by allochthonous salt. For example, it is established from 3D seismic analysis that the salt canopy in the deepwater northern GoM has transported over 20 raft blocks across the Alaminos Canyon, Keathley Canyon, Walker Ridge, and Green Canyon protraction blocks, with distances ranging from less than 3 km to more than 80 km from their original positions (Fiduk et al. Reference Fiduk, Clippard and Power2014). Over 3100 km² of rafted strata was identified, largely accumulating near the terminus of the salt canopy.

Primary or secondary minibasins (terminology of Pilcher et al. Reference Pilcher, Kilsdonk and Trude2011) can become encased in salt as allochthonous salt flows over the minibasin subsiding onto a deeper salt level (Hudec and Jackson Reference Hudec and Jackson2011). In some cases, salt evacuation continues, and the minibasin is instead surrounded by welds (Rowan and Inman Reference Rowan and Inman2011).

Thus, it is very important to consider the tectonic history of vertical and lateral salt transport when analyzing stratigraphic information from carapaces, rafts, and encased minibasins. Stratigraphic discontinuities are common, and in areas of poor seismic imaging are only revealed by drilling and biostratigraphic analysis. Some wells have penetrated salt-overturned intervals, where biostratigraphic datums are encountered in reverse order, resulting in major drilling “surprises” (Box 1.1).

Box 1.1 Stratigraphic Surprises Caused by Salt Tectonics

Seismic correlations in the deepwater GoM are often challenging due to the complexity of salt tectonics, limits on illumination below the thick and continuous allochthonous salt canopy, and imaging constraints around parautochthonous salt. In some areas, seismic imaging has failed to reveal the true stratal geometries, resulting in unanticipated structural interpretation problems encountered while drilling (Olson et al. Reference Olson, Snedden and Cunningham2015).

A prime example is a well drilled in the Green Canyon protraction block 639 (GC 639 #1), drilled in 2009 (Figure 1.10). After drilling through a normal Pleistocene to Pliocene stratal interval, and then a thick allochthonous salt body, the well began to encounter Cretaceous strata in reverse stratigraphic order. The quality of biostratigraphic tops was reasonably good, with most referred to as “definite” (DEF). Plotting the absolute ages of the various biohorizons indicates some variation but an overall downward younging of the interval (Figure 1.10A). This must have caused some concern, particularly if the trend was unanticipated. The well reached total depth (TD) near the top of the overturned Cretaceous. It is likely that the Mesozoic interval penetrated by GC 639 #001 was overturned by salt (Figure 1.10B).

Figure 1.10

(A) Age–depth comparison of three deepwater GoM wells with depths (in feet) normalized to shallowest Mesozoic horizon penetrated in each well. Diversity of Mesozoic well penetrations in the deep GoM basin are illustrated by (B).

(B) Well GC 639 #1 shown on a schematic structural configuration drawn from the original 2D seismic line.

(C) Well GB 754 #1 (modified from Hart et al.Reference Hart, Jacek, Martin, Post, Olson and Lyons2004) is shown with stratigraphic horizons used in this book shown to the left of the well bore.

(D) Well LL 399 #1 on a schematic structural configuration drawn from the original 2D seismic line. Sediment accumulation rates and structural geology related to the wells are discussed in the text.

The GC 639 #1 well contrasts with the normal stratigraphic order encountered by two other wells penetrating the same stratigraphic interval elsewhere in the basin (Figure 1.10). GB 754 #1 (Norton Prospect) drilled through a stratigraphically condensed interval above a shallow salt structure or carapace feature (Figure 1.10C). LL 399 #1 (Cheyenne Prospect) tested a deep (parautochthonous) salt structure (Figure 1.10D).

GB 754 #1 has a relatively continuous, but low-sloping trend in comparison with most of the LL 399 #1 interval penetrated (the exception being the bottom 30.48 m [100 ft] just above the salt). The estimated sediment accumulation rates (<16 ft/my [4.8 m/my]) of GB 754 #1 are far lower than those of LL 399 #1 (>55 ft/my [16.7 m/my]), consistent with the former well having penetrated a condensed interval on a salt–carapace structure (Figure 1.10C). LL 399 #1 well penetrated a lower relief salt structure, with high sediment accumulation rates above the salt-influenced zone and lower rates just above the salt (Figure 1.10D). Seismic data confirm these structural differences. Taking overturning of the Mesozoic interval by salt into account, calculated sediment accumulation rates of >47 ft/my (14.3 m/my) for GC 639 #1 is more comparable with that of LL 399 #1 than with GB 754 #1, consistent with the idea that the interval penetrated in GC 639 #1 was originally within a subsiding, deepwater, primary basin until salt emplacement overturned the Mesozoic interval, rather than a modified carapace structure or other structural oddity.

Numerous other wells have encountered either reverse stratigraphic intervals, thin and condensed intervals on carapaces, or intervals that are spatially out of place due to salt rafting (Hart et al. Reference Hart, Jacek, Martin, Post, Olson and Lyons2004; Fiduk et al. Reference Fiduk, Clippard and Power2014). Biostratigraphic analyses are a key tool for understanding such stratigraphic surprises, particularly where imaging and illumination are hampered by salt thickness and complexity.

1.4.1 Basement Structural Province

The periphery of the greater GoM basin, underpinned by thick transitions to the continental crust, is segmented by a series of prominent basement structures (Figure 1.3; Ewing and Lopez Reference Ewing, Lopez and Salvador1991). Their influence on overlying stratigraphy has long been known as early exploration efforts targeted these, based on gravity, magnetics, or early single- or multi-fold seismic reflection. Established structures include a halo of embayments (epicratonic basins that open to the central Gulf) and closed basins and intervening arches and uplifts (Figure 1.3; Ewing Reference Ewing and Salvador1991). The basins and embayments typically contain a significant thickness of Louann Salt and thicker sequences of Jurassic and Lower Cretaceous strata relative to the adjacent arches and uplifts. Salt-floored basins, including the East Texas basin, North Louisiana salt basin, Mississippi salt basin, and Apalachicola Embayment (also known as the DeSoto Canyon salt basin) contain well-described families of salt domes and related structures (e.g., Seni and Jackson Reference Seni and Jackson1983).

Basement highs, arches, and anticlines like the Wiggins Arch, Sabine Uplift, Llano Uplift, Middle Ground Arch, etc., are known to have been reactivated multiple times during multiple Mesozoic and Cenozoic tectonic events (Ewing Reference Ewing and Salvador1991). Several of these marginal highs, including the San Marcos Arch, Sabine Arch, and Monroe Uplift display short pulses of uplift of as much as a few hundred meters, creating angular unconformities in Middle Cretaceous and Lower Eocene strata (Laubach and Jackson Reference Laubach and Jackson1990). These pulses generally correlate to stages of Laramide thrusting, in turn related to changing rates of Pacific margin plate convergence and changing intracratonic compressional stress. Extensive crustal heating across northern Mexico and the southwestern USA (Gray et al. Reference Gray, Pottorf, Yurewicz, Bartolini, Buffler and Cantú-Chapa2001) uplifted and tilted Mesozoic and Early Cenozoic strata of the western Gulf. The boundary between thick and thin transitional crust is reflected by a subsidence hinge that became the focus for development and stabilization of the Cretaceous continental shelf margin, most clearly marked by an extensive reef system.

Most of these structures formed in the Mesozoic, but their influence on depositional trends persisted into the Cenozoic. The basement highs sometimes acted as drainage divides between major paleo-river systems. For example, mapping of the Tuscaloosa paleo-river system indicated that fluvial channels avoided the structural highs of the Wiggins Arch and surrounding positive features, terminating at the coeval lowstand shelf margin where the Ceno-Turonian interval is greatly expanded (Woolf Reference Woolf2012; Snedden et al. Reference Snedden, Virdell, Whiteaker and Ganey-Curry2016b).

The Middle Ground Arch (Southern Platform), which is entirely offshore, is thought to have influenced radial rafting of the Smackover–Norphlet interval (Pilcher et al. Reference Pilcher, Murphy and Ciosek2014), as will be discussed in Section 3.3.4.

1.4.2 Gravity Tectonic Domains

Downdip of the basement structures is a mosaic of genetically related gravity tectonic features that can be grouped into two distinct structural domains, above and below the allochthonous salt canopy (Peel et al. Reference Peel, Hossack, Travis, Jackson, Roberts and Snelson1995; Hudec et al. Reference Hudec, Jackson and Peel2013b; Figures 1.11 and 1.12). The configuration of basement rock below the canopy controlled the original Louann Salt distribution and its immediate post-depositional downdip migration onto contemporaneous or newly formed oceanic crust. The near-end of Cretaceous canopy architecture in turn influenced Cenozoic depositional patterns and faulting, detachment, and further basinward translation of salt and sediments.

Figure 1.11 Tectonostratigraphic provinces with cross-section locations (blue lines) for Figures 1.13–1.22.

Figure 1.12 Subcanopy structural domain with cross-section locations (Figures 1.13–1.22).

Modified from Hudec et al. (Reference Hudec, Jackson and Peel2013b)

1.5.1 Cross-Section 1: Sigsbee Abyssal Plain to Peninsular Arch

Cross-section 1 is a transect from the northeastern Gulf, passing from the abyssal plain at the USA–Mexico international border to onshore northern Florida (Figure 1.13). Continental crust rises to depths as shallow as <1500 m (4920 ft) on the Peninsular Arch, as crystalline basement has been drilled in a number of onshore wells (Jordan et al. Reference Jordan, Applin and Caldwell1949). Penetrations include granites dated at 159 ± 3 Ma and basalts and diabases as young as 183 ± 5 Ma in the exotic Suwannee terrane of south Florida (Heatherington and Mueller Reference Heatherington and Mueller2003). While the Cenozoic interval is relatively thin in comparison to the central Gulf (reflecting limited fluvial input), the Mesozoic interval thickens substantially to the southwest, into the area of the Florida Middle Ground Arch and Tampa Embayment. The physicographic slope marks an abrupt termination of many Mesozoic units at the Florida Escarpment. Cretaceous strata have actually been dredged from the sea floor, suggesting that the escarpment is an erosional remnant inherited from the K–Pg impact event and subsequent slope failures and adjustments (Freeman-Lynde Reference Freeman-Lynde1983).

The shelf portion of the cross-section includes an interpreted pre-salt interval, sedimentary rocks likely of Triassic–Middle Jurassic age, known in onshore areas as the Eagle Mills. The interpreted seismic structure is that of a horst/graben, possibly a continuation of the east coast rift system documented in the coastal plain of South Carolina, Georgia, and other states (Heffner Reference Heffner2013; Goggin and Rine Reference Goggin and Rine2014; Rine et al. Reference Rine, Hollon, Fu, Houghton and Waddell2014). The nearby well GV-707 penetrated a poorly dated siliciclastic interval between the Cretaceous (Aptian–Valanginian) Sligo–Hosston and Paleozoic carbonates.

Further seaward is the basinal portion of the Tampa Embayment where Louann Salt diapirs and Mesozoic rafts of Smackover and Norphlet are thought to be present, as observed in the DeSoto Canyon area (see discussion of cross-section 2, Figure 1.14). No salt canopy formed here, reflecting the general thinning of original salt toward the southeast.

A pronounced step up in basement, a change in elevation of several kilometers, is coincident with the termination of Louann Salt. This marks the seaward limit of transitional continental crust. A short segment of uncertain crust gives way seaward to oceanic crust, documented by magnetic and gravity data, as discussed in Section 1.2.4).

The downlap of Mesozoic stratigraphic units onto transitional and oceanic crust provides some indication of timing of oceanic crust emplacement (Snedden et al. Reference Snedden, Eddy and Christeson2013). Oxfordian Norphlet and Smackover rafts appear to have glided onto the oceanic or uncertain crust, suggesting that salt was present during the initial stages of sea floor spreading in order to provide a decollement. In other areas, locally thick minibasins (primary basins) are thought to contain Norphlet- or Smackover-equivalent strata (M. Hudec, pers. comm.).

The Haynesville (Kimmeridgian) and basal Cotton Valley–Bossier (Tithonian) strata continue across the oceanic crust before lapping out onto the oceanic crust near the extinct spreading center. Subsequent depositional units continue across the section, though distal thinning is observed on the seismic sections.

A pronounced structural feature, located at the basement step, fits the established characteristics of a seamount, a basement feature with an elevation greater than 1 km (3280 ft) above the regional basement level (Snedden et al. Reference Snedden, Norton, Christeson and Sanford2014). Such seamounts are relatively common across this area of oceanic crust (Stephens Reference Stephens2009, Reference Stephens2010). As mentioned in Section 1.2.4, the slow spreading rates associated with the GoM opening are thought to be associated with unfocused magmatism and in turn the poorly organized distribution of seamounts like this. Cenozoic strata from Cretaceous upward to Middle Wilcox drape the seamount, and compactional related features extend upward to the Oligocene. A number of these structural features have been leased in recent years, yet no drilling plans have yet been filed with the = Bureau of Ocean Energy Management (BOEM) or Bureau of Safety and Environmental Enforcement (BSEE).

As mentioned, Cenozoic deposition on the Middle Ground Arch and adjacent onshore Florida is thin, with limited accommodation on the Mesozoic platform here. By contrast, Neogene strata, particularly the Pleistocene interval of 5000 ft (1524 m), thicken substantially over the abyssal plain. This marks the Pleistocene Mississippi River input, but also the Miocene contributions by the paleo-Tennessee system. Paleogene deposition thins toward the platform margin, reflecting general western (Laramide) sources and linked drainage networks.

1.5.2 Cross-Section 2: Florida Shoreline to USA–Mexico International Border

Cross-section 2 is located further to the west, extending from the USA international border to just seaward of the Florida shoreline (Figure 1.14). Mesozoic strata, particularly Jurassic and Early Cretaceous intervals, thicken dramatically into the DeSoto salt basin, also known as the Appalachicola Embayment. The Florida Middle Arch is prominent and its extension into the deepwater is the site of significant industry exploration efforts and nearby Norphlet reservoir discoveries such as the Appomattox Prospect (see Section 9.6).

The Norphlet raft province is well illustrated here (Figure 1.14). As described in Section 3.3.4, raft tectonics is a form of thin-skinned extension, with unusually large degrees of extension such that the footwall and hanging wall are often not in contact (Jackson and Hudec Reference Jackson and Hudec2017). The dismembering of stratigraphic units occurs as blocks glide downslope on a detachment surface, in this case the top of the Louann Salt. Intervening troughs between raft blocks are filled with younger units, providing age control on the timing of rafting. Rafting apart of the Norphlet–Smackover interval must have been contemporaneous with deposition of the Haynesville–Buckner and Cotton Valley–Bossier as these fill in the gaps between rafts. In some areas Cotton Valley–Knowles and even basal Sligo–Hosston also fill raft gaps. The timing of sea floor spreading and rafting is similar enough to consider the possibility that there is a genetic linkage. Rafting is largely toward the oceanic crust, though radial rafting reflecting the Middle Arch structure has been suggested (Pilcher et al. Reference Pilcher, Murphy and Ciosek2014). The Smackover–Norphlet Rafts can be separated by diapirs or depositional troughs, making paleogeographic reconstructions very difficult, but essential to exploration well locations, as will be discussed in Section 3.3.4.

Further seaward, the uncertain zone between oceanic and continental crust is also accompanied by a basement step, though with less relief than observed on cross-section 1 (Figure 1.13). Salt appears to have crept onto unequivocal oceanic crust. Though the Louann Salt is now relatively close to its original position, the basinward translation necessitates modification of the term “autochthonous” salt to “parautochthonous” salt, following the nomenclature of Hudec et al. (Reference Hudec, Norton, Jackson and Peel2013a). This is also the area where a small segment of the Mississippi Fan–Atwater fold belt is present, with local thrust faults indicating some early crustal shortening.

The extinct spreading center is nicely developed toward the seaward end of the cross-section (Figure 1.14). Here is a large axial valley, about 20 km (12 miles) wide, with bounding basement structures (possible seamounts) and a dim to opaque infill interval below the Haynesville–Buckner seismic horizon. Normal faults dip toward the axial valley, similar to what has been previously described in the area (Snedden et al. Reference Snedden, Norton, Christeson and Sanford2014; Lin et al. Reference Lin, Bird and Mann2019).

The total basin-fill is relatively thin, depressing the crust only to depths between 26,000 and 36,000 ft (8–11 km). The sedimentary interval is a bit deeper in the DeSoto salt basin at nearly 38,000 ft (12 km). Louann Salt is particularly thick here, exceeding 8000 ft (2.4 km) in the DeSoto salt basin, though this clearly reflects salt inflation.

Mesozoic platforms are well developed, particularly for the Jurassic Haynesville–Buckner (HVB), Cotton Valley–Bossier (CVB), and Cotton Valley–Knowles (CVK) at a position about 30 km (19 miles) seaward of the modern shelf edge. The Cretaceous Sligo–Hosston seems to be located in a similar position, indicating that the crustal boundary between thick and thin transitional crust has pinned the shelf margins due to changes in subsidence rates. Cenozoic shelf margins are all inboard of the Cretaceous and Jurassic platform margins. The Florida Escarpment is less pronounced here, instead a steep margin at Top Cretaceous (Top Navarro–Taylor) is observed, perhaps a byproduct of the Chicxulub impact event.

Growth faults are few in the Cenozoic interval and only Mesozoic growth along salt-detached faults is locally developed. Rafting is the dominant structural style, as discussed earlier.

Cenozoic deepwater reservoirs have been penetrated in portions of the area, but results to date have been disappointing in comparison to the Mississippi Canyon area, where giant discoveries (e.g., Thunderhorse Field) have been made. The lack of Cenozoic traps is one cause, though stratigraphic traps such as termination against the Cretaceous shelf margin have been considered, as will be discussed in Chapter 2.

1.5.3 Cross-Section 3: Onshore Texas to Onshore Florida

Cross-section 3 (Figure 1.15) is a transect from the onshore south Texas to the eastern basin margin and Florida onshore as described in cross-sections 1 and 2. The section in its central portion is located seaward of the Sigsbee Escarpment, where the salt canopy affects the sea floor. The abyssal plain section here illustrates trends in both Neogene and Paleogene strata, and thus is a veritable natural archive of the attendant sedimentary processes.

The variations between the western and eastern margins are notable. The sedimentary load on the west has depressed the crust to over 50,000 ft (15 km) near the present-day shelf margin offshore Texas (Figure 1.15). Gravity tectonics dominates the western margin, with numerous growth faults and multiple levels of fault detachment. The upper decollement is at a salt weld where Oligocene and Miocene age faults detach. The lower detachment surface for older Paleogene strata is founded upon the parautochthonous salt. The updip extension associated with this multi-level extension appears to be balanced, to some degree, by contraction within the Oligo-Miocene and Perdido fold belts, though local squeezing of salt can also occur (Radovich et al. Reference Radovich, Moon, Connors and Bird2007). Some faults nucleated at or near the Mesozoic platform margin or at the top of the Cretaceous. Faults also detach on the salt canopy.

The section crosses the Vicksburg Detachment, a well-known listric fault that nearly becomes horizontal as it slips along the Jackson Group Shales (Combes Reference Combes1993; Feragen et al. Reference Feragen, Millman, Feldman, Bierley and Perkins2007). The eastern portion of the cross-section shows limited salt stocks, which rise from the largely evacuated autochthonous Louann below, defining the eastern margin of the slope minibasins domain. Again, the Norphlet raft province is located just seaward of the Middle Ground Arch.

The Cenozoic sedimentary architecture is intimately convolved with the structural domains on the western margin. Shelf margins for each of the major Neogene and Paleogene units appear to be located at or just landward of the major growth and expansion of the various intervals. For some units like the Oligocene, much of the expanded interval represents slope deposition. Well penetrations indicate that much of the Oligocene interval is dominated by muddy lithologies and drilling in the Oligocene–Miocene interval has been challenging due to abnormal fluid pressures (P. Flemings, pers. comm.).

The Perdido fold belt is known to be linked to updip Oligo-Miocene extension (Trudgill et al. Reference Trudgill, Rowan and Fiduk1999; Gradmann et al. Reference Gradmann, Beaumont and Albertz2009; Radovich et al. Reference Radovich, Horn, Nuttall and McGrail2011). These contractional folds have high relief and thickness due to the high sedimentation rates in the Cretaceous to Miocene interval that was shortened in the Neogene.

In the central portion of the cross-section (Figure 1.15), the abyssal plain, regional thickness trends provide a window on the source-to-sink processes of the Cenozoic basin-fill. Paleogene units (Middle and Upper Wilcox, Oligocene Frio–Vicksburg, and more condensed Upper Eocene Jackson Yegua Sparta) show clear eastward thinning, suggesting the Laramide source terranes were most important (Galloway Reference Galloway and Hsu2008). The Lower Miocene shows a transition to eastward thickening in the Neogene stratigraphic interval, reflecting the rejuvenation of the Appalachians and rise of the Tennessee River as a major contributor to sand-prone fans in the Mississippi Canyon area (Galloway et al. Reference Galloway, Whiteaker and Ganey-Curry2011). The Pleistocene Mississippi Fan, the largest of the submarine fans to be formed, is apparent in the kilometer-scale interval above the Pleistocene Trim A (PTA, see Section 7.2) horizon that is banked against the Florida Escarpment. As will be discussed in Chapter 7, large Plio-Pleistocene channel–levee, mass transport, and lobate fans can be identified on high-resolution seismic data (Weimer Reference Weimer1990).

1.5.4 Cross-Section 4: Black Warrior Basin to Yucatán Channel

Cross-section 4 (Figure 1.16) is a transect from the onshore Black Warrior basin to the USA–Mexico abyssal plain to the Cuban Platform, finally extending to the Yucatán Straits gateway to the Caribbean basin. The margin of the GoM basin can be defined at the hinge line between the Black Warrior basin, where Paleozoic sedimentary and basement rock are present near the surface, and the Mississippi salt basin to the south. The substantial thickening of the Jurassic strata in the Mississippi salt basin is clear evidence supporting placement of the GoM basin boundary here. Louann Salt also terminates near this margin and the Louann lapout and associated fault breakway zone are often used to demarcate the salt basin boundary (Ewing and Lopez Reference Ewing, Lopez and Salvador1991).

The Wiggins Arch basement structure borders the Mississippi salt basin to the south in Louisiana (Figure 1.16). Besides hosting a number of onshore discoveries, the Wiggins Arch acts as initiation point for successive downdip detachment zones starting with the Middle Cretaceous detachment zone. The crust is loaded to 50,000 ft (15.2 km), but as much as 40,000 ft (12.2 km) of that sedimentary interval is Cenozoic in age, a sign of the long-lived transport through the Mississippi River and its ancestors.

Isolated salt bodies and thick primary basins filled with Miocene to Cretaceous sediments give way to first extensive salt canopy just seaward of the modern shelf slope break. The Terrebone trough roho system, where extensional faults detach on one of the allochthonous salt bodies and/or welds, is denoted as the Oligo-Miocene salt weld (Hudec and Jackson Reference Hudec and Jackson2011). Reconstructions of the Terrebone trough roho system show Early to Middle Miocene progradation expelled allochthonous salt seaward, toward the toe of the canopy, accompanied by considerable extension. By the Late Miocene, salt was largely expelled along the strike or dissolved, leaving the roho detachment, isolated salt rollers, and an extensive weld (McBride et al. Reference McBride, Rowan and Weimer1998). Seaward rollover into an expulsion rollover near the Bay Marchand salt diapir (Schuster Reference Schuster, Jackson, Roberts and Snelson1995) is not shown on this cross-section.

Further seaward are numerous supracanopy structures, including young secondary minibasins in Green Canyon and Atwater Canyon protraction blocks, where the section turns east–west (Figure 1.16). Below and at the seaward end of the salt canopy lies the Plio-Miocene Atwater fold belt, where deep salt diapirs (parautochthonous salt) occur along anticlinal axes. At this point, the cross-section turns to become more northwest–southeast trending across the abyssal plain and onward to Cuba.

Below the salt canopy on the modern slope of the USA sector is a relatively thick succession of Louann Salt that is conservatively estimated to be more than 5000 ft (1524 m) thick and to cover 220 km (136 miles) of lateral extent (Hudec et al. Reference Hudec, Norton, Jackson and Peel2013a). The inner basin is the deepest portion of the Louann salt basin, where the greatest accumulation of evaporite-bearing interval is thought to have been deposited. Like elsewhere, there is substantial step up in acoustic basement, the inner ramp of Hudec et al. (Reference Hudec, Norton, Jackson and Peel2013a). Note that some portion of the relief is generated by the turn in the section at the Atwater fold belt.

The Cenozoic interval thins substantially toward Cuba and the Yucatán Straits to the south. Miocene strata alone thin from 8000 ft (2.4 km) to a few hundreds of feet (>30 m) as the interval lapouts onto the Cuba Platform margin. Mesozoic intervals are also thinner than known in the adjacent South Florida basin. The crystalline basement is as shallow as 12,000–16,000 ft (3.7–4.9 km) in the Yucatán Straits. These trends point to: (1) a distal position relative to major siliciclastic sources and linked river systems; and (2) the relatively recent joining of western and eastern Cuba microplates during the Eocene.

1.5.5 Cross-Section 5: Sabine Uplift to Sigsbee Escarpment

Cross-section 5 (Figure 1.17) extends from onshore Texas to deepwater GoM near the USA–Mexico international boundary. The Mexia–Talco fault zone is an extensional breakaway where salt thins to a zero edge (Hudec and Jackson Reference Hudec and Jackson2011). The East Texas salt basin contains a series of generally north–south oriented diapirs and salt pillows toward the center of the basin where the original salt was thicker. Turtle structures formed by salt withdrawal into the adjacent diapirs is seen on nearby seismic lines (Jackson and Seni Reference Jackson and Seni1984). Note the over-thickened Albian and Aptian interval (Paluxy–Washita to Sligo–Hosston supersequences) located on the flanks of several salt domes. The intervening saddle is a remnant high that in some cases promoted reef development (Seni and Jackson Reference Seni and Jackson1983; Pashin et al. Reference Pashin, Guohai and Hills2016).

Further seaward is a prominent basement structure called the Toledo Bend Flexure. It is notable as it marks the separation of the updip interior salt basins (East Texas, North Louisiana) and the central Louann basin proper (Hudec et al. Reference Hudec, Norton, Jackson and Peel2013a). It is also thought to localize Mesozoic platform margins (Anderson Reference Anderson1979).

Strata south of the Toledo Bend Flexure dip rather steeply into the basin to the south, where Mesozoic horizons become difficult to trace basinward under a thick Cenozoic interval and allochthonous salt canopy (Figure 1.17). The Tiber well (KC 102 #1) penetrated the Top Cretaceous at 32,250 ft TVD-ss (true vertical depth subsea) (9830 m), which seismic mapping indicates is the regional level in the Keathley Canyon (KC) protraction block. In other wells, the Top Cretaceous may appear from first glance to be much shallower, but these are usually penetrations of salt-rafted carapace blocks, carried upward by differential salt movement, as described in Section 3.3.4.

Important transitions shown on the section include the rimmed platform margins, built up from the Jurassic to the end of the Albian, which give way seaward to several Cenozoic structural belts, including the Paleogene–Eocene expansion zone, the Oligocene–Miocene detachment zone, and the Pliocene–Pleistocene roho system on the present-day shelf (Peel et al. Reference Peel, Hossack, Travis, Jackson, Roberts and Snelson1995). The present-day slope encompasses numerous Neogene canopies and secondary minibasins. These salt structures terminate at the Sigsbee Escarpment, where the salt canopy clearly impacts the sea floor morphology.

The section nicely illustrates the structure of the northern GoM basin depocenter located beneath the present continental shelf and slope. The Top Cretaceous is as deep as 40,000 ft (12.2 km) in places, loaded by Cenozoic siliciclastic deposition. The Cenozoic prism extends beneath the coastal plain and shelf, reaching its thickest point near the present continental margin. In many areas, the continental slope extends basinward to about the position of the transitional/oceanic crust boundary. Beneath this sediment prism, a large portion of the autochthonous Louann Salt has been expelled, forming a primary salt weld on the basal Jurassic unconformity that is a decollement zone for growth faults. Other detachments occur at salt welds, allochthonous salt canopies, or are rooted in decollements located within deep basinal mudstones of indeterminate age.

As with several previous sections, sedimentary architectures are influenced greatly by accommodation created by gravity tectonics. Shelf margins prograde progressively into the basin from Cretaceous to Neogene, reflecting the robust depositional systems extending from source terrane to basinal sink in this central GoM transect.

1.5.6 Cross-Section 6: San Marcos Arch to Sigsbee Escarpment

Cross-section 6 (Figure 1.18) starts at the San Marcos Arch, where Miocene uplift set up a steeply dipping basement surface, to the Perdido fold belt on the abyssal plain on the international border. Several levels of fault detachment are observed: (1) Paleo-Eocene detachment at or seaward of the Cretaceous margin; (2) Oligo-Miocene canopy detachment; and (3) the Corsair–Wanda fault zone.

In contrast to the central and northeastern GoM, this transect across the northwestern Gulf displays broad, complex Middle Cenozoic compressional domains, including the Perdido and Port Isabel (Oligo-Miocene canopy) fold belts. The Port Isabel fold belt is linked by a decollement to the Miocene Clemente-Thomas, Corsair, and Wanda fault zones of the Oligocene–Miocene canopy detachment province (Hall et al. Reference Hall, Bowen, Rosen, Wu and Bally1993).

The Corsair–Wanda fault zone is particularly prominent on this section (Figure 1.18). Over 30,000 ft (9.1 km) of growth along the bounding fault is apparent on seismic sections, with much of it being Miocene in age. The fault detaches on the deep salt allochthon.

Like the Mississippi Fan fold belt, the Perdido fold belt is located near the original depositional limit of the basal (parautochthonous) Louann Salt (Fiduk et al. Reference Fiduk, Weimer and Trudgill1999). The isopachous Cretaceous to Early Cenozoic interval is considered pre-kinematic (deposited before deformation), while the synkinematic (during deformation) phase in the Miocene and younger interval shows lateral variations in thickness (Jackson and Hudec Reference Jackson and Hudec2017). Additional contraction was accommodated by the compound salt canopy that has been injected up into the Oligocene and Miocene interval.

Interpretation of the remnant thickness of the autochthonous salt is challenging at the depths where it is present. Portions of the salt are deflated and welds likely remain in many unpenetrated structures. Amplitudes of folds in the Perdido trend suggest considerable salt thickness, but few wells penetrate deeply enough to verify this view.

1.5.7 Cross-Section 7: Quetzalcoatl Extensional Detachment, Northern Mexican Ridges to Chicxulub Crater

Cross-section 7 (Figure 1.19) is a west-to-east transect from the slope of eastern Mexico to the Yucatán Platform, the site of the Chicxulub impact event that ended the Mesozoic. The present-day physiography of a narrow shelf and steep slope reflects relatively recent Neogene tectonic activity associated with Pacific plate subduction (Padilla y Sánchez Reference Padilla y Sánchez2007; Witt et al. Reference Witt, Brichau and Carter2012). Associated loading and subsequent gravitational sliding in the Quetzalcoatl extension is linked with compression in the Mexican Ridges fold belt. Uplift in eastern Mexico associated with the Middle Miocene Chiapanecan orogeny resulted in deep incision and canyon formation along a narrow shelf and slope leading to delivery of large volumes of coarse-grained sediments to the basin floor (Ambrose et al. Reference Ambrose, Wawrzyniec and Fouad2005).

While the fold and thrust belt shown on the middle of this section is commonly grouped with the Mexican Ridges to the south, newer seismic data suggests that this contractional belt may have also experienced the additional effects of salt being pushed from west to east (M. Hudec, pers. comm.). Though published evidence is currently lacking, there is a notable change in orientation of folds and faults south of this section (Figure 1.19) and a gap in the structure, implying some change in the tectonic forcing mechanism. Another observation is that the southern portion of the Mexican Ridges tends to show more expansion along the Quetzalcoatl faults versus the northern areas. This leads one to suspect pure gravity tectonics in the southern Mexican Ridges versus salt-involved compression in the north. Another difference in between this section and cross-section 8 to the south is the existence of a roho system detached at the Top Upper Miocene level, documented on better seismic data by CNH (2015b). Salt or a weld may be present at the Top Upper Miocene level, but is not shown in the CNH (2015b) compilation. The proximity to salt would be required in any case.

Cross-section 7 (Figure 1.19) continues across the relatively undeformed abyssal plain region of the south-central Gulf before passing across the Yucatán salt subprovince or subbasin (terminology of Hudec and Norton Reference Hudec and Norton2018). Two tectonic styles are recognized: (1) a salt diapir complex with high-amplitude salt structures; and (2) lower-amplitude salt rollers. The former occurs near or at the transition from continental crust, thus uncertain crust. There is an interpreted basement step just seaward, where parautochthonous salt is observed to terminate.

The Yucatán salt roller domain has a remarkable similarity to the salt raft structures of the deepwater Norphlet salt raft exploration area of the northeastern GoM (Saunders et al. Reference Saunders, Gieger, Rodriguez and Hargreaves2016; Hudec and Norton Reference Hudec and Norton2018). It has been suggested that this area is a conjugate to that Norphlet exploration arena, separated by sea floor spreading (Miranda Peralta et al. Reference Miranda Peralta, Alvarado and Villalón2014; Steier and Mann Reference Steier and Mann2019). However, there are no well penetrations in this area other than the shallow DSDP core sites (see Buffler et al. Reference Buffler, Schlager and Pisciotto1984).

The Yucatán salt roller domain also overlies a new, distinctly different structural province with possible pre-salt sedimentary fill. First noted by Williams-Rojas et al. (Reference Williams-Rojas, Reyey-Tovar and Miranda Peralta2012), this interval shows a wedge-shaped or rift-graben form, onlapping the Yucatán Platform margin (Hudec and Norton Reference Hudec and Norton2018; Rowan Reference Rowan, McClay and Hammerstein2018). This interval may be analogous to the pre-salt Eagle Mills (Triassic to Middle Jurassic) of the eastern USA (Heffner Reference Heffner2013). High-amplitude, seaward dipping reflections (SDRs) appear at the base of the probable sedimentary interval, evoking global analogs of SDRs associated with initial stages of continental rifting (Norton et al. Reference Norton, Carruthers and Hudec2015). Alternatively, these may simply be layered volcanics (Hudec and Norton Reference Hudec and Norton2018), as commonly observed in the eastern USA pre-salt section (Heffner Reference Heffner2013). We informally refer to this area as the Ria Celestun pre-salt province, named after a local geographic feature. A similar pre-salt interval is noted on seismic sections in the Campeche subbasin to the southwest (Hudec and Norton Reference Hudec and Norton2018).

Cenozoic and Mesozoic stratigraphic units all taper and largely lapout against the steep Yucatán Platform margin. Continental crust basement rises from depths greater than 36,000 ft (11 km) to less than 10,000 ft (3048 m) over a short distance. Further inboard on the platform, basement abruptly drops and then rises to depths of less than 6000 ft (1829 m). This unusual basement architecture is a result of the Chicxulub impact, as documented by numerous studies (Denne et al. Reference Denne, Scott and Eickhoff2013; Sanford et al. Reference Sanford, Snedden and Gulick2016) and recent IODP coring at site M0077A (Morgan et al. Reference Morgan, Gulick and Bralower2016). Basement upwarp indicates the location of the peak ring, the deep crustal response to the bolide impact that ended the Cretaceous. Seaward of the peak ring, the Top Cretaceous reflection is relatively flat in the area of the exterior ring but drops 3–4 km on the platform margin. Clinoforming successions representing the post-impact crater fill are evident in this area.

As mentioned, few exploration wells are present in the eastern portion of the area, in spite of prominent salt-cored structural closures and prospective traps. Several factors may preclude any near-term drilling: (1) water depths greater than 12,000 ft (3.7 km); (2) distal thinning of Paleogene reservoirs like the Wilcox and parallel decreases in sand content away from siliciclastic source terranes. Neogene sandy intervals are present in DSDP core sites 87 and 91, but these are likely derived from southern Mexico rather than any local sources. The progressive sorting associated with the distal turbidity flows likely means a reduced grain size of any potential reservoirs.

1.5.8 Cross-Section 8: Mexican Ridges to US Abyssal Plain

Cross-section 8 (Figure 1.20) extends from the Quetzalcoatl extensional detachment to the southern end of the Mexican Ridges, across the Yucatán salt subbasin and continuing northward to the abyssal plain at the USA–Mexico border. As with cross-section 7 (Figure 1.19), both extensional faults and, further seaward, folds and low-angle thrusts of the Mexican Ridges are observed on this transect. However, the expansion along the Quetzalcoatl detachment faults is much greater, for reasons discussed earlier. Drilling of the Pemex Puskon #1 well documented the substantial growth along listric faults of the Quetzalcoatl extensional detachment zone (Alcocer Reference Alcocer2012; Porres Luna Reference Porres Luna2018). The linked extensional–contractional system is thought to detach on overpressured Upper Eocene Shales, with a possible additional detachment surface in the Oligo-Miocene interval, similar to major multi-level detachments documented in the northern GoM (e.g., Radovich et al. Reference Radovich, Moon, Connors and Bird2007, Reference Radovich, Horn, Nuttall and McGrail2011). The Upper Miocene interval in the extensional zone is generally thinner here than on cross-section 7, similar to observations made by CNH (2015b).

Large folds of the Mexican Ridges have wavelengths of 10–12 km (6–7 miles) and amplitudes of 300 m to 1 km (984–3280 ft) (Padilla y Sánchez Reference Padilla y Sánchez2007). The Mexican Ridges developed as a consequence of gravitational spreading processes, synchronous with growth faulting of the western onshore and continental shelf areas. Deformation occurred in several stages from Middle Miocene to the present day (Salomon-Mora et al. Reference Salomon-Mora, Aranda-Garcia, Roman Ramos, Bartolini and Roman Ramos2009). This deformation correlates with highly active petroleum systems, including migration and trapping of hydrocarbons, in turn forming direct hydrocarbon indicators, overpressured traps, gas chimneys, gas hydrates, and sea floor hydrocarbon seeps that are being investigated as part of new regional exploration efforts. Drilling has concentrated largely on the folds of the Mexican Ridges, with a few wells like Puskon #1 testing the updip extensional systems.

The Yucatán salt subbasin (high-amplitude salt diapir domain) in the middle of the section is entirely developed over uncertain or possible oceanic crust. Hudec and Norton (Reference Hudec and Norton2018) hypothesized significant seaward translation after salt deposition due to the lack of a confining structural boundary, in contrast to the perched Campeche salt subbasin where the BAHA high is present. Shortening is evident in the shallow Cenozoic interval of the Yucatán salt subbasin, with the timing of deformation likely as Miocene or younger.

One interesting observation is the differential thickening and thinning trends of the Mesozoic and Cenozoic. Mesozoic strata thicken toward the salt diapir domain, while Cenozoic strata generally thin toward that area, trends noted both north and south of the subbasin. Local thickening into zones of salt evacuation is noted but does not change the inferred pattern. The Mesozoic thickening may signal development of an inner basin in Mexico, a conjugate to that in the northern GoM, where salt and overlying Mesozoic strata were deposited in greater magnitudes than elsewhere.

1.5.9 Cross-Section 9: Catemaco Fold Belt to Bahamas Platform

Cross-section 9 (Figure 1.21) is a basin-spanning strike transect from the Catemaco fold belt to the Bahamas Platform. The section includes a small segment of the Catemaco fold belt, unfortunately crossing oblique to the westerly verging folds. The Catemaco fold belt has been previously described as a linked extensional–contractional gravity-driven system with tectonic transport to the northwest (Mandujano-Velaquez and Keppie Reference Mandujano-Velazquez, Keppie, Murphy, Keppie and Hynes2009). Northward salt evacuation in the Campeche salt subbasin (terminology of Hudec and Norton Reference Hudec and Norton2018) is thought to have occurred during the Middle Miocene Chiapanecan orogeny (Gutiérrez Paredes et al. Reference Gutiérrez Paredes, Cantuneanu and Hernandez Romano2017). However, new WAZ seismic data acquired in the Campeche salt basin suggests a longer duration of shortening, initiated in the late Paleogene and continuing today (Snyder and Ysaccis Reference Snyder and Ysaccis2018). The nearby Veracruz basin was likely deformed during the Chiapanecan uplift, closely followed by uplift of the Anegada High and Los Tuxtlas volcanic massif (Jacobo Albarabn et al. Reference Jacobo Albarabn, Garduño, Innocenti, Pasquare and Tonarini1992).

The section continues across the fringe of the Campeche salt subbasin, crossing into the Yucatán salt subbasin which is also observed on cross-sections 7 and 8 (Figures 1.19 and 1.20). Not obvious at this scale are the counter-regional fault systems that accommodated a thick Neogene interval, partly aided by salt expulsion rollovers (Gomez-Cabrera and Jackson Reference Gomez-Cabrera, Jackson, Bartolini and Roman Ramos2009a, Reference Gomez-Cabrera, Jackson, Bartolini and Roman Ramos2009b). CNH (2015a) notes in regional structural intervals that there is a major expansion of the Upper Miocene and Lower Pliocene in the adjacent Comalcalco basin, of up to 200–300 percent.

Like cross-section 7, cross-section 9 (Figure 1.21) carries onward across the Yucatán salt roller domain and underlying Ria Celestun pre-salt province, over the Yucatán Platform and Chicxulub exterior ring. Notable is the elevation of basement near the Chicxulub impact exterior ring <12,000 ft (<3.7 km), dropping several kilometers (to 20,000 ft; 6.1 km) on the rest of the platform. Basement appears to be quite shallow in the Florida Straits, less than 15,000 ft (<4.6 km) regionally and locally near the seabed, such as at Catoche Knoll, where DSDP cores 538 and adjacent cores 536 and 537 were retrieved (Buffler et al. Reference Buffler, Schlager and Pisciotto1984).

The cross-section continues to the Bahamas Banks or Platform where basement deepens, depressed under the thick Mesozoic succession (>11,000 ft; 3.4 km) largely Aptian to Albian carbonates (Ladd and Sheridan Reference Ladd and Sheridan1987; Epstein and Clark Reference Epstein and Clark2009). Evaporites are interpreted on the far eastern end of the line, making an appearance in the hypothesized seawater entry point for the GoM basin, as will be discussed in Section 4.4.

Exploration has primarily been concentrated in the Catemaco fold belt and adjacent areas (including key discoveries at Kunah #1 and other undeveloped resources), the Mexican Ridges, and adjacent Campeche salt subbasin. Limited drilling has been attempted elsewhere along the cross-section. The eastern end of the cross-section skirts the Cuban fold and thrust belt, where a handful of international companies have drilled wells without success in deepwater and older shallow-water wells near the Bahamas Banks (Epstein and Clark Reference Epstein and Clark2009; Melbana Energy 2017).

1.5.10 Cross-Section 10: US Abyssal Plain to South Florida Basin

Cross-section 10 (Figure 1.22) completes the circum-GoM tour, running from the international border to onshore Florida. The Florida Escarpment is particularly steep, coinciding with the interpreted continental to oceanic crustal boundary. The Mesozoic succession is relatively thin on oceanic crust (<7000 ft, 2134 m) compared to the South Florida basin, where it exceeds 12,000 ft (3.7 km) on the continental crust. Over the Sarasota Arch, a major basement-cored structure, the Mesozoic is as thin as 5000 ft (1524 m), documented by the nearby Charlotte Harbor-672 #1 and 622 #1 wells. Unlike cross-section 2, the Jurassic and Early Cretaceous platform margins are not observed, leading to alternative hypotheses of non-reefal development, or more likely K–Pg-related margin collapse (Denne and Blanchard Reference Denne and Blanchard2013) and continued retrogradational failures of the margin well past the original platform margin position. Inboard well penetrations (e.g., Vernon Basin 654 #1) document only carbonate shelf and platform interior facies. Repeated margin failures and adjustments (Mullins et al. Reference Mullins, Gardulski and Hine1986) also reflect ocean current bottom erosion during a period of accelerated current flow in the Miocene and Pliocene, linked to progressive closure of the equatorial seaway and development of the Isthmus of Panama (Snedden et al. Reference Snedden, Galloway, Whiteaker and Ganey-Curry2012).

As will be discussed in Section 4.5, the Glen Rose supersequence is particularly well developed in the South Florida basin, including extensive evaporites, mainly anhydrite of the Ferry Lake Sequence and stratigraphic equivalents (Punta Gorda Formation of Florida). The center of the basin is known to contain halite as well as anhydrite, indicating restricted conditions and hypersalinity during the Albian. The presence of evaporites in the Albian interval east of the Sarasota Arch is indicated by distinctive high-amplitude continuous seismic reflections.

The Cenozoic interval shows an opposite trend in thickness. On oceanic crust, 14,000 ft (4.3 km) of Cenozoic is present, much of it Neogene siliciclastic sedimentation (9000 ft; 2744 m) linked to the Mississippi Fan and older systems like the paleo-Mississippi and paleo-Tennessee Rivers, which were sourced by the rejuvenated Appalachians. However, Cenozoic deposition on the platform is much less at 5000 ft (1524 m) and is dominated by carbonate sediments.

Due to the long-standing US drilling moratorium on the Florida shelf, no deepwater wells have been permitted; few wells have been drilled since 1985, all of these dry holes. Sizable onshore discoveries were made as recently as 1964 in the Sunniland trend (e.g., Felda Field) where carbonate reservoirs (grainstone banks and tidal shoals) are well documented (Mitchell-Tapping Reference Mitchell-Tapping1986, Reference Mitchell-Tapping2002). These small fields are largely sealed by extensive evaporites of the coeval Glen Rose interval. However, few wells have been drilled other than field infill wells, related to environmental concerns and other non-geologic factors.

1.5.11 Other Areas: Bravo Trough of Mexico

Between cross-sections 3 and 7 is a zone of major salt evacuation, only recently identified on new WAZ 3D seismic surveys (CNH 2015b; Hudec et al., Reference Hudec, Dooley, Peel and Sotoaccepted). Depth to basement is in the range 45,000–52,000 ft (13–16 km), shallowing to 40,000 ft (12.2 km) on the adjacent BAHA high (Figure 1.4). Salt evacuation-related over-thickening of Oligocene sediments into this structural trough in the offshore portion of the Burgos basin is called the Bravo Trough (M. Hudec, pers. comm.). Some thickening of the Oligocene in this extensional zone was shown by Davison et al. (Reference Davison, O’Bierne, Faull and Steel2015), but not to the scale of 8000 m (5 km) of expanded Upper Oligocene interval observed on new WAZ data in Mexico. A well drilled by Hess (Port Isabel 526 #1) in Bravo Trough penetrated nearly 17,000 ft (5.2 km) of sandstone-poor Oligocene interval before terminating. The thick Oligocene interval overlies a thin or absent Paleogene and Mesozoic interval, suggesting that a large salt body or diapir was present prior to Latest Eocene/Early Oligocene salt evacuation (Hudec, pers. comm.).

The lack of seismic reflectivity in the trough fill implies a shale-dominated interval. The US GoM interval with a similar seismic character is the basinal Oligocene (Frio–Vicksburg) interval of the Oligo-Miocene canopy detachment and contractional zones including the Port Isabel fold belt, as will be discussed in Section 6.5. Contributing rivers were likely mud-dominated, including volcanics altered to clays.

1.14.1 Cuban Mesozoic Stratigraphic Framework

The Mesozoic stratigraphic framework of Cuba largely reflects the evolution of the GoM basin, as major differentiation of the GoM and Caribbean basins did not occur until the Late Cretaceous to Paleogene (Escalona and Yang Reference Escalona and Yang2013). While the proto Caribbean plate did form during the Late Triassic to Early Jurassic separation of North and South America, the stratigraphic intervals are remarkably similar (Figure 1.32). Initially, interpreted continental to shallow marine siliciclastics filled half-grabens (Escalona and Yang Reference Escalona and Yang2013), a pattern also observed in the northern and south GoM at this time. It is important to note that Sequence 1 of Escalona and Yang (Reference Escalona and Yang2013) has not been penetrated in the offshore area to date, but its seismic character and geometry are suggestive of a syn-rift interval analogous to the Eagle Mills drilled in the northeastern GoM (Marton and Buffler Reference Marton, Buffler and Mann1999).

Figure 1.32 Mesozoic and Paleogene stratigraphy of Cuba.

Compiled from Escalona and Yang (Reference Escalona and Yang2013), Gordon et al. (Reference Gordon, Mann, Caceres and Flores1997), and Melbana Energy (2017)

Late Jurassic rotation of the Mayan (Yucatán) block during GoM sea floor spreading also generated important tectonic elements in Cuba (Escalona and Yang Reference Escalona and Yang2013). Jurassic platform carbonates (Remedios district; Figure 1.32) and coeval distal slope or scarp facies of Oxfordian to Tithonian age show similarities in lithology with the limestones and carbonate mudrocks of the areas to the north (e.g., Smackover, Haynesville, Cotton Valley Formations).

This was followed by a period of relative tectonic quiescence in the Early Cretaceous, with progressive drowning of the proto Caribbean plate and deposition of deep marine carbonates (Sequence 2 of Escalona and Yang Reference Escalona and Yang2013). Shallow marine carbonates were restricted to the highest structural features (e.g., Upper Perros Formation of the Remedios district; Morena and Margarita Formations of the Placetas and Camajuani districts, respectively). Palenque Formation carbonates of the Remedios district are correlative to the Aptian to Albian interval of the GoM basin (e.g., Sligo–Hosston, Glen Rose, Paluxy–Washita supersequences; Figure 1.32). Ceno-Turonian equivalents of the Eagle Ford–Tuscaloosa and Austin Chalk supersequences (e.g., Purio Formation of the Remedios district) were deposited just prior to major plate collision in the Late Cretaceous, as described in Section 2.2 on plate tectonic reconstructions. DSDP core site 537, drilled to the north of Cuba, penetrated deep marine to shallow marine carbonates of Early Cretaceous age (Schlager et al. Reference Schlager, Buffler, Angstadt, Phair, Buffler and Schlager1984).

DSDP cores to the north of Cuba also penetrated limestone breccia units with strong similarity to onshore Cuba deposits related to the Chicxulub impact event on nearby Yucatán. Sanford et al. (Reference Sanford, Snedden and Gulick2016) described over 130 ft (40 m) of carbonate breccia in DSDP Leg 77 Sites 540 and 536 cores, linked to mass transport processes generated by the seismic wave that moved across the entire basin within minutes of the impact. The corresponding Cuba outcrops of the Penalver Formation and Cacarajícara Formations, also related to the impact event, are well documented (Tada et al. Reference Tada, Iturralde-Vinent, Matsui, Bartolini, Buffler and Blickwede2003; Cobiella-Reguera et al. Reference Cobiella-Reguera, Cruz-Gámez and Blanco-Bustamante2015).

1.14.2 Cuban Cenozoic Stratigraphic Framework

The Late Cretaceous to Eocene strata collision between the greater Arc of the Caribbean and North American plates set up significant differences in stratigraphy between the two basins. The original Jurassic strata that were laterally continuous to the GoM basin were now subducted beneath the upper Caribbean plate in several stages, forming the Cuban fold and thrust system. Distal shales of Mesozoic age were thrust into the upper plate while more proximal carbonate facies are present in the lower plate, separated by a major mid-level detachment at the Eocene level. Escalona and Yang (Reference Escalona and Yang2013) confine this collision phase to their Paleocene–Eocene age Sequence 3 and the Oligocene portion of their Sequence 4 (Figure 1.32).

Paleocene to Eocene foredeep sedimentation took place north of the thrust belt, as documented by deposition of the Vega Alta and Vega-Rosas Formations (Gordon et al. Reference Gordon, Mann, Caceres and Flores1997; Melbana Energy 2017). Later back-thrusting within the upper plate further complicated the present-day structural architecture and has made unraveling the Cenozoic stratigraphy much more difficult (Escalona and Yang Reference Escalona and Yang2013). It is also important to note that the western half of Cuba merged with the eastern half during the west-to-east tectonic transport, so the pre-collision strata in western Cuba are linked more closely with the Yucatán (Mexico) stratigraphy (e.g., San Cayetano Formation; Haczewski Reference Haczewski1976).

Post-collision Cenozoic strata are influenced by development of the Cayman trough and the Loop Current Gulf stream flowing through the Florida Straits. Large, deep sea erosional features (channels) and constructional sediment drifts of Miocene to Holocene age are present between Cuba and the Florida Escarpment, documenting vigorous bottom currents flowing from the northern Caribbean into the Straits of Florida and to the North Atlantic (Gordon et al. Reference Gordon, Mann, Caceres and Flores1997). Post-collision strata constitute the Miocene portion of Sequence 4 and the entirety of Sequence 5 (Pliocene to end Pleistocene; Escalona and Yang Reference Escalona and Yang2013).