DIVERSE EXHUMATION IN THE CRETACEOUS BORNU BASIN DETERMINED BY APATITE FISSION TRACK THERMOCHRONOLOGY

Abstract

This research work is designed to investigate the magnitude and the temporal, as well as spatial extent of exhumation events in the Bornu basin. This is to be able to identify major periods of heating and cooling, so as to quantify how the temperature has varied through time and; as pointer to how they affect the generation of liquid Hydrocarbon in the basin as a guide to further exploration. The Apatite Fission Track Analysis data were obtained from the ditch cutting samples of Six carefully selected wells in the Three major depressions identified in the Bornu basin : Kutchali – 1, Mbeji – 1 and Kasade-1 in the Chadian section (Depression A); Gaibu-1 and Kinasar-1 in the Maiduguri SE (Depression C) and Ngor-1 in the Maiduguri SW (Depression D). The data collection procedure began with mineral separation, mounting and etching using FrantzTM isomagnetic separator, Epoxy-ResinTM (epo-thin) and 5.5M Nitric acid (HNO3) at exactly 200C, respectively. Temperature-time histories are calculated by inverse modelling approach using the version 1.67 of HeFTy with a multi-compositional annealing model and the Dpar values as kinetic parameters. The Apatite Fission Track ages of data point of each well was plotted against both their Mean Track Length and their stratigraphic ages to produce the thermal history and consequently exhumation events in each well. Inferences and observations from the results show that it can be strongly argued that the paleotemperatures observed in the area of study are due primarily to greater depth of burial, with contribution from increased paleogeothermal gradient and other factors such as intrusions caused by magmatism. Hence, it is clear that two significant paleothermal events are captured by the AFTA data obtained from the Bornu basin i.e the Upper Cretaceous (89 – 67 Ma) cooling episode, which is widespread and; the Paleocene (62.5 – 62 Ma) episode which may be much restricted. The Temperature-time plots also shows that cooling from paleothermal maximum did not begin at the same period