By JAMES PINDELL, LORCAN KENNAN, and STEPHEN BARRETT
Editor's note: Pindell, Kennan and Barrett are with Tectonic Analysis Ltd. in Sussex, England (email@example.com), and Houston. Pindell also is adjunct associate professor at Rice University, Houston.
The Geophysical Corner is a regular column in the EXPLORER, produced cooperatively by the AAPG Geophysical Integration and SEG Interpretation committees, and edited by M. Ray Thomasson and R. Randy Ray. This column is the last in a four-part series titled "Regional Plate Kinematics: Arm Waving, or Underutilized Exploration Tool?"
Putting It All Together Again
Click on the figure below to view greater detail.
In the second and third parts of this four-article Geophysical Corner series we defined a kinematic framework for the evolution of the Gulf of Mexico region by restoring Andean deformations and progressively closing the Atlantic Ocean.
This month, we further evolve this framework to build a palinspastically quantitative reassembly of continents and continental blocks that were separated during the Mesozoic rifting and subsequent drift in the Gulf of Mexico region -- key features of which are shown in figure 1.
Figures 2-4 show primary developmental stages in the Gulf's evolution:
The kinematic elements applicable to the reconstructions are as follows.
First, our Oligocene reconstruction of northern South America (article two) is further modified for Late Jurassic and Cretaceous time by removing island arc and other terranes that were accreted to in the Late Cretaceous and Early Tertiary (shape portrayed in figures 2 and 3).
We can then estimate and restore Jurassic extension in the rift basins of the Andes (using principles outlined in the August EXPLORER, which gives us an Early Jurassic shape for the northern Andes that can be closed against North America (figure 4).
Second, figures 2-4 show that the entire region of Florida, the Blake Plateau and the Bahamas (and the "Cuban autochthon" beneath the Cuban arc) were strongly controlled by fracture zone trends of the early Atlantic.
In this region, plate separation was achieved by NW-SE stretching of crustal elements separated by transcurrent faults. Middle Jurassic basalt extrusion was commonplace in zones of high stretching.
Each crustal "corridor" between transcurrent faults underwent different amounts of stretching and displacements relative to the others. The conjugate margin to the Southern Bahamas flank is the transcurrent margin of Guyana.
Third, unlike the Florida region, the Yucatan Block moved independently -- in two distinct stages -- of the larger continents as the Gulf opened.
At the time of figure 4, there is only a small range of paleo-positions in which Yucatan could have fit geometrically without overlap of palinspastically restored (i.e., rift-related stretching removed) areas of continental crusts. This position can be achieved by rotating present-day Yucatan clockwise about "pole A" (figure 4), which closes most of the Gulf by placing Yucatan snugly against the northeast Mexico-Texas-northwest Florida paleo-margin.
It definitely does not, however, close the southeastern Gulf. There, the crust of South Florida -- including that of the "Tampa Arch" -- must be retracted northwestward against Yucatan and out of an overlap position with Demerara Rise, off the Guyana margin.
Fourth, the geology of the eastern Mexican margin and the occurrence of Louann and Campeche salt suggest that the Gulf opened in two stages.
The first, or syn-rift, stage -- between the times of figures 3 and 4 -- involved intra-continental stretching between Yucatan and North America about "pole B1," and between Yucatan and South America about "pole B2," in figure 4.
This migration defined an arcuate transcurrent trend defined by basement contours along the northern Tamaulipas Arch in south Texas. It also created a sinistral shear couple in the Louisiana-Mississippi area, which allowed for minor counterclockwise rotation of the Wiggins and Middle Grounds arches (figures 1 and 4) and the associated formation of the wedge shaped East Mississippi and Apalachicola salt basins to the north of each, respectively.
This syn-rift stage about "pole B1" can be modeled satisfactorily to Early Oxfordian time to achieve a good reconstruction of the Louann and Campeche salt provinces flanking the central Gulf (figures 1 and 3).
In our modeling, we see no need to invoke significant salt deposition on oceanic crust in the Gulf. Also, during this stage, the southern Bahamas crustal corridor migrated southeast in addition to undergoing internal stretching -- hence, the Everglades fracture zone and the Guyana marginal fault zone were both active at this time.
The migration of Yucatan from its pre-rift to its present position requires that eastern Mexico was a transform rather than a rifted margin. We consider that Yucatan did not have the Chiapas Massif attached to it during the syn-rift phase.
The second stage of Yucatan motion began about "pole C" of figure 3, in the Early Oxfordian, at the end of salt deposition.
This second stage of motion and its pole of rotation are constrained by:
We believe that the Chiapas Massif was picked up by Yucatan in this stage as a consequence of the onset of seafloor spreading in the Central Gulf -- and because the pole of rotation changed in Stage 2, the orientation and position of transforms also must have changed. This new phase of motion had a more southerly direction than the previous one.
The spreading ridge almost reached the Mexican coast and, hence, the new transform along eastern Mexico would have picked up an additional wedge of crust, which we believe is Chiapas Massif and which had been emplaced there during the syn-rift phase by sinistral transcurrent motions within greater Mexico.
As with the Gulf of Mexico, the synchronous creation of the "Proto-Caribbean Basin" also must have involved a rotational opening between Yucatan and Venezuela-Trinidad.
In figures 2-4, we show the approximate flowlines along which this basin opened, as well as a hypothetical geometry of its Jurassic rifted margins -- now wholly overthrust by allochthonous Caribbean terranes.
Many elements of northern South America's and possibly eastern Yucatan's hydrocarbon potential pertain directly to the geometries of these rifted margins, such as the positions of marginal re-entrants that define differing stratigraphic sequences due to differing subsidence histories.
Our working Gulf kinematic model has some interesting implications for exploration.
First, the Eastern Mexican margin (unlike that of Texas) was a Jurassic fracture zone in the north (Burgos-Tampico basins) and a transform -- with active structuring until its Early Cretaceous death -- in the south (Veracruz Basin).
Heat flow, subsidence history, occurrence of salt, distribution/thickness of Late Jurassic source rocks and basement controls on future structural development will all vary along strike along this margin due to differing crustal properties and histories.
In the U.S. Gulf margins, early syn-rift stretching was NNW-SSE until Early Oxfordian times, but most of the stretching toward the end of this phase occurred well offshore.
Second, although salt deposition is generally assumed to be of Callovian age, there is little evidence of open marine conditions in the Gulf margins until upper Oxfordian (Norphlet-Smackover transition), and thus salt deposition may have continued until Early Oxfordian.
Our Early Oxfordian reconstruction accommodates known salt occurrence in the Gulf ("salt fit"); hence, we consider that onset of seafloor spreading, the change in the Yucatan-North America pole position, separation of Louann and Campeche salt provinces, and initiation of open marine conditions were nearly coeval and possibly causally related.
Third, although the syn-rift stretching of the Florida Shelf region was NW-SE, the extension direction in the deep eastern Gulf during stage 2 (seafloor spreading) was NE-SW about a nearby pole, such that small circles (transform traces) should be arcuate and convex to the northwest.
In Cuba, a significant area of Bahamian crust was overthrust by Cuban arc assemblages in the Paleogene. In the Jurassic, the southern Bahamian margin (beneath Cuba) experienced sinistral strike-slip tectonics along the Guyana margin of South America, followed by the eastward migration of a Late Jurassic seafloor spreading ridge (Yucatan/South America boundary) along the western half of the overthrust zone.
The transform nature of this Jurassic margin should be considered in interpretations of the Paleogene development of the Cuban thrust belt, Mesozoic source rock paleogeography and oil migration pathways during Eocene maturation.
In the Proto-Caribbean, the kinematics require westward-propagating Early and Middle Jurassic rifting, followed by Late Jurassic seafloor spreading. The trends of marginal re-entrants such as that defined by the Urica basement transfer zone are defined by the first stage of Yucatan's motion.
Further, Venezuela-Trinidad's passive margin section is predicted to have existed from the end of Middle Jurassic, not Cretaceous as is commonly thought. A several kilometer-thick, probable Late Jurassic shelf section in Eastern Venezuela has not received much attention from exploration, and the "Berriasian or older" salt in Gulf of Paria could be Middle Jurassic (as is the salt in the Bahamas, Guinea Plateau and Demerara Rise and Tacatú Basin).
Note the proximity of these areas on figure 4.
In Sierra Guaniguanico of western Cuba, the conjugate margin of Eastern Venezuela, the lower Middle Jurassic San Cayetano strata indicate the existence of a juvenile passive margin of that age, becoming fully marine for Late Jurassic, as predicted here for Venezuela and Trinidad.
In summary, regional plate kinematic analysis is extremely cost-effective and deserves an important role in the exploration of complex areas, both early on and long-term.
The kinds of implications we have drawn here also can be made from kinematic analysis in other parts of the world. When applied properly to appropriate areas, it is not arm waving.
Much can be gleaned about:
And all that is gleaned can lead to the creation or dismissal of numerous play concepts.
In addition, an explorationist with a comprehensive kinematic framework available to him or her will work more confidently -- and therefore, more efficiently -- on nearly all other aspects of the exploration process.
Finally, in frontier evaluation programs, regional kinematic analysis may not tell you exactly where to drill, but it can often help to tell you where not to drill.