Least-Squares Inverse Thermal Modelling and Organic Geochemistry in the Faroe-Shetland Basin

Student thesis: Master's Thesis


Of the many sedimentary basins of the Atlantic Margin, the Faeroe-Shetland Basin (FSB) is located between the Shetland Islands and the Faeroe Islands. It is an 'inboard' basin of the Atlantic Margin region and has an extraordinary long tectonic history probably going back to 350 Ma. The area has been subject to many rifting events, but the most important period is the Cretaceous with at least three stretching episodes responsible for a very high cumulative beta factor.

Continuous thinning of the crust, and the emplacement of the proto-Icelandic plume head at the base of the lithosphere involved severe volcanism in early Tertiary time. This volcanism led to the formation of the north Atlantic basalt province of which the Faeroe Islands is a present-day outstanding feature. Not only copious amounts of extrusive lavas but also voluminous underplating resulted from the magmatic activity. Rapid uplift of rift shoulder areas in conjunction with late Cretaceous early Tertiary rifting caused huge amounts of clastic sediments to be shed into the basin in the Thanetian. These sediments have been an attractive reservoir target and have in places proved to host large amounts of hydrocarbons.

Modelling the temperature history in a sedimentary basin is crucial when estimating hydrocarbon generation. This is far from easy but may be approached using the least squares inverse modelling technique. This technique implies multiple solutions of the forward problem, where introduced parameters and data make up the basis for a priori values. After one run of the forward problem a set of predicted values is obtained, and these values make the basis of a set of a posteriori values. The a posteriori values are compared to the input parameters and data, adjusted according to the least squares method, where after the forward model is solved over again, a posteriori values are adjusted, the forward model run again etc. until a satisfactory model, i.e., with minimal deviations between input parameters and predicted values, is obtained.

The actual inverse modelling program, benefits highly on paleo environmental data. The utility of paleo water depths in the modelling of paleo heat is based on the thought, that heat originating in the asthenosphere causes thermal uplift of the crust that is reflected in measurable changes in water depths.

The inverse thermal reconstruction has been performed using two end-member models: one that accounts for the effects of heat released from magmatic underplating that has been distributed equally in the whole crust. And another model that, like the other, registers the uplift as caused by underplating, but do not account for the thermal effects coming from it. The most reliable model predicting paleo temperatures shall appear to be intermediate between these two end-member models.

As far as thermal maturities are concerned inverse modelled results turn out to fit nicely with those obtained from organic geochemical lab work, reporting maturity data from Rock-Eval pyrolysis, gas chromatography and gas chromatography-mass spectrometry. Several biomarker parameters are interpreted from different chromatograms and listed to compare them with the predicted vitrinite reflectance from the thermal reconstruction.
Date of Award5 Jun 2003
Original languageEnglish
SupervisorSøren Bom Nielsen (Supervisor)

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