The genetic sequence stratigraphy of the Hettangian to Oxfordian succession, Inner Moray Firth

Abstract

Application of sequence stratigraphic principles to the Hettangian–Oxfordian succession of the Inner Moray Firth basin has led to a new understanding of its sedimentary fill history at a greater resolution than has been previously possible. This interval was deposited in a variety of shallow marine to terrestrial environments, punctuated by a number of regionally correlatable transgressive events, during a phase of gentle thermal subsidence, prior to the renewal of major extensional rifting in Kimmeridgian times.Recognition of a significant regional stratigraphic break, the ‘Mid-Cimmerian Event’, allows this succession to be divided into two component depositional packages (Jla: Hettangian–Toarcian; J1b: Bathonian–Late Oxfordian). Identification of seven maximum flooding surfaces permits further subdivision into eight genetic stratigraphic sequences and enables the construction of a new basin-wide stratigraphic template. Erection of such a framework has important implications for our understanding of the basin’s sedimentary and tectonic evolution, and thus enables the Inner Moray Firth to be placed within its regional North Sea setting.Construction of palaeogeographic maps for a number of J1b genetic stratigraphic sequences allows accurate facies and, hence, reservoir prediction. Furthermore, stratigraphic data give important insights into the nature of the ‘Mid-Cimmerian Event’. The observed progressive increase in amount of truncation below this unconformity, together with the successive migration in the locus of sedimentary onlap above this unconformity, maximizes the stratigraphic separation towards the east. Similar temporal stratigraphic relations elsewhere in the North Sea suggest that this unconformity is related to the initiation and early subsidence of a regional ‘dome’ prior to its more significant collapse between Kimmeridgian and Early Cretaceous times.