ABSTRACT: Sequence Stratigraphy of the Rhaetian-Oxfordian Succession, Inner Moray Firth: Implications for the Origin of the "Mid-Cimmerian" Unconformity

UNDERHILL, J. R., University of Edinburgh, Edinburgh, Scotland, M. PARTINGTON, BP Exploration, Glasgow, Scotland, R. HEDLEY, Ultramar Exploration, London, England, and KEVIN JOHN STEPHEN,* Univerity of Edinburgh, Edinburgh, Scotland

Application of sequence stratigraphic methodology to the Rhaetian-Oxfordian succession of the Inner Moray Firth (IMF) basin has led to a new understanding of its sedimentary fill history at a greater resolution than has been previously possible. This succession was deposited in a variety of shallow marine to terrestrial environments, punctuated by a number of marine flooding events, during a phase of gentle (thermal) subsidence, prior to the (Kimmeridgian) renewal of major extensional rifting.

Recognition of a significant regional stratigraphic break (the "Mid-Cimmerian Event") allows this succession to be divided into two component parts (J1a: Rhaetian-Toarcian; J1b: Bathonian-Late Oxfordian). Identification of eight maximum flooding surfaces enables further subdivision into nine subsequences and allows for the construction of a new basinwide stratigraphic template.

Erection of such a scheme has important implications for our understanding of the basin's sedimentary and tectonic evolution. First, construction of paleogeographic maps for a number of J1b subsequences allows for accurate facies prediction, and second, stratigraphic data highlight the true nature of the "Mid-Cimmerian Event." The observed progressive increase in amount of truncation, together with the successive migration in the locus of sedimentary onlap, maximizes the stratigraphic separation toward the east. Similar temporal stratigraphic relations elsewhere (e.g., Viking Graben) suggest a casual link with the development of the North Sea triple junction. As such, it is likely that this sequence boundary is related to the initiation and early subsidence of a regional "dome" prior o its more significant collapse between the Kimmeridgian and Early Cretaceous.

AAPG Search and Discovery Article #91012©1992 AAPG Annual Meeting, Calgary, Alberta, Canada, June 22-25, 1992 (2009)