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AAPG/PESGB Basin Mastery follow on course

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January 17

This was the first follow on course to the series of one-day workshops focused on “Basin Mastery”, hosted by AAPG Europe and PESGB. The subject of this workshop was Mexico and the Caribbean, held at the PESGB training facility in Croydon, less than twenty minutes by train from Central London.

This event is now over.

Tuesday 17th January 2017

PESGB Training Facility, 7th Floor, No. 1 Croydon, 12-16 Addiscombe Road, CR0 0XT

Geology, tectonic evolution, and hydrocarbon systems of the greater Gulf of Mexico, Caribbean and northern South American Region - Dr. James Pindell (Adjunct Professor, Rice University/Research Fellow, Cardiff University/Director, Tectonic Analysis, Ltd.)

Review by Jonathan Brown (JB Geosciences), peer reviewed by Henry Dodwell

Regarding tectonic evolution and plate movement reconstructions, Jim Pindell is one of the world’s leading experts, and this one day workshop was an opportunity to see the master in action. The lecture room on the 7th floor of the curious ‘No. 1 Croydon’ building was full of a wide demographic of wise geos. The workshop atmosphere enabled us to freely comment at any time, and Jim admirably fielded comments and questions with aplomb, patience, and excellent humour. 

The region reviewed here is immensely complex, and as the title of the workshop suggests, the agenda was formidable but Jim somehow managed to take us through it piece by piece, and things started, literally, to slide into place. This was achieved using a wealth of presentation material mostly taken from Jim’s ‘Tectonic Analysis’ group’s work, with significant contributions from Pemex and ION Geophysical, and by running through some simple and robust methodology.

Context was set by reviewing the opening history of the Atlantic and three important constraints emerged: Africa stayed more or less fixed above its ‘mantle reference frame’; the Americas whizzed off roughly northwest at 20 to 55 mm per year; the Caribbean microplate was also fixed on its own local ‘mantle reference frame’ and the Americas drifted around it. Oh, and Cuba moved relative to North America about 1,300 km northeast from the Pacific and the Chortis block (that’s the Honduras/Nicaragua triangular chunk southeast of Belize and Guatemala) travelled relatively about the same distance eastwards along the Pacific plate margin.

We were all given an A3 sheet from Getech displaying offshore free-air gravity and onshore topography, as appeared on the cover of GSL SP 328 (a better version from Getech’s global gravity dataset 2017 is seen above), which served as a useful reference, and subtle detail therein on the western margin of the Mexican part of the Gulf of Mexico (GoM) confirmed hints of the youngest (Tithonian-Berriasian) of three defunct spreading ridge systems. Jim used his animation of plate movements from -195 (Sinemurian) to -125 MY (early Cretaceous) to show how these spreading ridges can be zipped back in sequence to close the gulf, almost joining up the Houston and Campeche igneous anomalies – probably a ‘Tex-Mex’ igneous rift that was split into two. Carefully selected pauses in the animation also showed how source rock distribution relevant to Mexican GoM exploration could be constrained by these reconstructions, and the paleo-geography onto which both the Louann salt (famously responsible for providing much of the USA’s GoM regional seals) and Campeche (now Mexican) evaporites were deposited during the Callovian-Early Oxfordian. It was striking how the three spreading ridge systems were shown to be distinct  through time, with three different poles of rotation, clearly demonstrating that plate production movement had to jump to accommodate the rotation of the Yucatan and the asymmetric opening of the GoM.

Displays of vertical slices were represented by stunning seismic profiles up to 35km deep showing interpreted oceanic and continental crust, thinned in some areas, and the Moho. Tomographic sections showed the distribution of subducted slabs graphically portraying how the Pacific Cocos and the Atlantic subduction zones developed either side of the buoyant Caribbean plate as the Americas wrapped around it.

The Caribbean plate was stretched as North and South America shunted around it, and Cuba motored relatively to the northeast past the eastern Yucatan margin through a tectonic window between two strike slip zones until it locked up in its obducted present location at -46 MY (Lutetian). A wonderful geo-seismic cross section showed this – something of a tectonic car crash. Further strike slip movement along the Caribbean-North American plate boundary facilitated the SW-NE sinistral Cayman Trough (a linear pull apart basin 1,100 km in length extending from the Belize margin to north of Jamaica) as the Chortis block docked into its present position. Evidence of these restless micro plates includes exquisite polymict conglomerates with clasts derived from hinterland which is no longer juxtaposed.

The buoyancy of the Caribbean plate is bad news for hydrocarbon prospectivity in the Caribbean, where there is only rarely enough sedimentary column to enable maturation of potential source rocks. In Colombia, the Caribbean plate’s buoyancy means that subduction there is more like a mega thrust that helps to hold the Andes up. Subduction here could be called ‘continental obduction’, and there is a series of eastwards younging foredeep sedimentary wedges – important for kitchen timing. In Venezuela and Colombia, one of the reasons for the Maracaibo and Bolivar areas to be so productive is that movement past the Caribbean plate provoked maturation of two major source rock regions one at a time, with a see-saw tilt between, causing a double hydrocarbon charge.

As a seismic interpreter, I was enjoying the seismic displays with (mostly) convincing interpretations, but I was also delighted to hear about Jim’s work on type 2 sequence boundaries in Colombia and western and eastern Venezuela. Jim and his team identified just seven eustatic type 2 boundaries compared to Haq’s 31! I especially enjoyed the comment, ‘These guys went to see all the nice sections in a variety of basins of different ages, and picked boundaries. Well, all the best basins have tectonics affecting them!’ Quite. 

Regarding exploration in the Mexican GoM, Jim said that there may be ‘Brazil type’ pre-salt environments and units, and the seismic images certainly had rift, sag and salt geometries. For the southern Gulf of Mexico where the Campeche and Cantarell giant fields are, Jim gave a brief review of the north verging salt enabled contraction. Gorgeous marine seismic lines running S-N showed updip extension and rollover and downdip toe thrusting rather like the eastern proximal part of Santos basin, Brazil. The Pemex staff apparently delight in calling these sections ‘train crashes’. Related onshore tectonics in the Chiapas foldbelt south of Yucatan features salt cored box folds.

I could go on but I will stop here by saying that one of the overwhelming conclusions is that there remains significant exploration potential in this region, especially in Mexican waters. A truly spectacularly informative day.

 

Previously covered in this series - 

An Overview of the Petroleum Geology of Myanmar (Onshore and Offshore Basins)
An Overview of the Petroleum Geology of Eastern Canada
An Overview of the Atlantic Equatorial Margins 
 


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