For the explorationist to fully understand the petroleum systems of any basin, an appreciation of the tectonic evolution in determining present-day characteristics is imperative. Palaeogeographic reconstructions, enhanced with reservoir and source rock data, provide the necessary medium by which new play concepts can be identified and the hydrocarbon potential of different areas of the basin predicted. Such maps also highlight how the distribution and quality of source rocks determine where future areas of exploration should be targeted. This approach can then be used to understand the distribution and quality of reservoirs and seals, which together with source rocks provide the essential elements of the petroleum system.
We have applied these techniques to the Gulf of Mexico Basin and surrounding area. This article is intended to highlight some of the key issues in the tectonic development of the Gulf of Mexico and the influence of tectonics and climate change on the supply of sediment into the basin.
Tectonic framework
In global terms, the tectonic framework of the Gulf of Mexico is relatively simple. However, the timing of oceanic crust development and the very presence of oceanic crust in the central Gulf of Mexico has been a source of discussion and debate for the past 2 decades and remains a perplexing enigma to this day.
One of the most controversial issues with respect to understanding the opening history of the Gulf of Mexico Basin is the distribution of oceanic crust. Quantifying the amount of "growth" of the continental crust by stretching and the addition of basic igneous material in the Gulf of Mexico creates its own problems, as significant differences in the amount of crustal attenuation across the basin prevent a simple two-fold division of the basement into continental or oceanic crust.
In common with many authors who have worked in this area over the past 25 years, we suggest that the Yucatan peninsula and surrounding area was initially located in the northern part of the Gulf and the southward movement of the block was accomplished by a combination of translation and rotation and by the development of oceanic crust in the center of the basin. This movement occurred as a response to major crustal instability associated with the break-up of Pangaea. The identification of first-order structural elements that can be directly related to the opening phase of the Gulf of Mexico and the rotation of the Yucatan block remains enigmatic. Several different trends, at relatively high angles to each other, have been identified (Figure 1).
In an attempt to provide a solution to this problem, an unbiased approach has been developed regarding each set of basement features as an integral part of the basin's fabric and, therefore, part of the structural development and opening history. The principal aim for each set was to identify the possible mechanisms responsible for their creation (i.e. extension directions and poles of rotation) and whether, based on the distribution of crustal types, the basement fault sets could be classified as either continental (transfer fault) or oceanic (transform fault) systems in order to elucidate their history of development and their function during the opening of the basin. With this basic framework in place, it has been possible to create a model that satisfies some of the problems outlined above and identifies the main phases of structural development in the history of the basin. Furthermore, by testing these observations against potential fields data it has been possible to create a dynamic plate model that honors the existing data and identifies the main phases of basin development.
Our model suggests two important phases: first, a sudden increase in attenuation of continental crust at the end of a dominantly translational phase during the Middle Jurassic and subsequent onset of oceanic crust development and rotation of Yucatan from the Late Jurassic into the earliest Cretaceous (165 million years ago to 143 million years ago). Second, we suggest that oceanic crust development was not an instantaneous process and resulted from ridge propagation from west to east and the establishment of slow (west) to ultra-slow (east) spreading centers.
Drainage development
The newly developed tectonic model forms a framework for mapping reservoir and source facies on restored bases. To aid with understanding reservoir development at the regional scale, an attempt has been made to consider the entire "source to sink" depositional system. This modeling has included applications in drainage network analysis of the entire hinterland to the Gulf of Mexico using both mapped networks and processing of digital elevation models (Figure 2) and satellite data. A fundamental concept for this analysis is that modern landscapes, including to varying degrees drainage patterns, preserve information about their evolutionary history over geological timescales. Although potentially controversial, there is increasing evidence for the persistence of geomorphic elements in the landscape, and an ability to read this information might, therefore, increase our understanding of drainage development. The technique provides a potentially powerful predictive tool with direct application to hydrocarbon exploration by increasing our understanding of sediment supply evolution.
For the Gulf of Mexico, the present-day hinterland area encompasses the greater part of the North American continent, an enormous and geologically complex area. After deconvoluting the glacial modifications of northern parts of the continent, our analysis demonstrates the fundamental impact of tectonic evolution of the whole North American craton on sediment supply to the Gulf of Mexico. Importantly, the flux in sediment supply does not have a simple causal link with episodes of tectonic uplift, and the role of climate evolution is shown to be important. Our models highlight a probable Rocky Mountain source for Palaeogene sandstones in the northeastern Gulf and suggest a significantly larger hinterland for pre-Miocene drainage systems into the eastern Gulf coast, in Mexican waters.
Conclusion
Our Gulf of Mexico work was an iterative process of adjusting our tectonic model to fit the hard data we had access to and which we used in our project. Our new ideas about the tectonic evolution of the Gulf of Mexico combined with our thorough evaluation of all elements of the petroleum systems should prove useful in future exploration efforts in the prolific Gulf of Mexico.

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