Using geochronology of detrital minerals for maximum age of deposition, for paleogeographic reconstruction

Correlating sedimentary rocks and establishing their age is challenging but these aims are essential for establishing regional geological and clastic reservoir prediction models. The difficulty of this task is compounded when relevant sedimentary successions lack diagnostic fossils, or are poorly exposed and reliant on well materials as is often the case for offshore exploration. In such circumstances the relative abundances, and geochronology and geochemistry on certain detrital (especially heavy) minerals, provide an excellent means for well correlation, and for determining the age and sedimentary provenance of clastic units. The interpretation of these data naturally lend themselves to form and test palaeogeographical models and provide an independent test for seismic interpretations.

Many detrital heavy mineral species, such as zircon, rutile, apatite and titanite are sufficiently uranium-rich, or micas and amphibole sufficiently potassium-rich that single grain ages may be determined. In many cases, major and trace element chemical and isotopic data may be collected on the same grain, often concurrently. The information gleaned from these minerals not only uniquely fingerprint sandstones, but also preserve an otherwise lost record of the geological and tectonic events occurring within the sedimentary source region.

The survival of the detrital minerals and information that they record are however, influenced by factors such as climate and burial diagenesis, this can be used to an advantage for palaeo-geographical interpretion but may hinder maximum depositional age investigations. Discussion around the geochronology of detrital minerals will be focussed on the following topics:

1. Uranium-lead geochronology in detrital minerals: how many and what they record.
2. Interpreting young detrital grain ages.
3. Sand to source – climate, storage, fertility and recycling, and why a multi-proxyapproach is essential for palaeogeography.