Basin Modelling: Past progress and future directions

Speaker - Tony Watts, University of Oxford

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The meeting format for each lecture will be as follows:

17.30 Lecture begins
18.30 Short reception
19.30 Depart

Abstract

Sedimentary basins are important because they are the “tape recorder” of the Earth’s past environmental changes and the world’s main source of hydrocarbons. The deepest basins are associated with the main plate boundaries and are of three main types: rift, foreland and strike-slip. Backstripping studies of data from stratigraphic test wells in rift-type basins suggest that the main cause of their subsidence is sediment loading and thermal contraction following heating and thinning of the lithosphere at the time of rifting. Other processes contribute (e.g. sediment compaction, salt collapse, and sea-level change) but their contribution to the subsidence is small compared to that of the two main factors. In the early 80s, stratigraphic models of basins were constructed that were based on simple geometrical schemes for the sediment infill. The most notable were the “clinoform break” progradation and the “steer’s head” aggradation models. These models showed that sediment loading - in combination with thermal contraction - could account for the large-scale “architecture” of many rift-type basins and, in some cases, details of their internal onlap and offlap patterns. They also demonstrated that while it is difficult to infer sea-level change directly from stratal geometries, it is possible to use them to calculate the thermal and maturation history of a basin. In the early 90s, D. T. Lawrence and colleagues at Shell pioneered the development of forward stratigraphic models that took into account clastic input, carbonate growth potential, slope instabilities, and laterally varying facies belts. This work led to the development of the STRATAFORM program, the main goal of which is to incorporate the dynamics of sediment transport processes directly into basin models. The models are impressive, but they have the disadvantage that they do not honour the data very well. During the past few years, therefore, there has been a renewed interest in the use of inverse methods that determine information on the basin forming mechanisms directly from observations. The most notable are strain rate inversion, which uses backstrip curves, and Process-Oriented Gravity Modelling (POGM) that is based on sediment thickness data. These approaches have revealed new information on the long-term thermal and mechanical properties of extended continental lithosphere, both during and following rifting. Despite this, a number of outstanding questions remain in basin modelling. These include the dynamics of initial rifting, the time-scales of isostatic adjustment, and the rate of sea-level change. The acquisition of new scientific deep drill (e.g. by IODP) and seismic refraction data, together with improved 3D forward and inverse modelling, offers the most promise of addressing these questions in the future.

Speaker Biography

Tony Watts is Professor of Marine Geology and Geophysics in the Department of Earth Sciences at the University of Oxford. He received his BSc. in Geology and Physics from University College, London and his Ph.D in Marine Geophysics from the University of Durham. After graduating, he joined the Bedford Institute of Oceanography, Dartmouth, Canada and then the Lamont-Doherty Geological Observatory of Columbia University, New York, USA. He has participated in some 18 cruises of scientific research ships to each of the world’s ocean basins and their margins and has been involved in all aspects of the acquisition, reduction, and interpretation of marine geological and geophysical data. His current research is focussed on the structure and evolution of the Amazon rifted margin, the Canary and Cape Verde islands, and the United Arab Emirates foreland basin.