The Late Oxfordian to Kimmeridgian history of the Rob Roy and Ivanhoe Fields, Outer Moray Firth

• Main Author: Brealey, Simon
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: UCL (University College London) 1991
• Subjects: Earth sciences; Biostratigraphic anomaly; Greenland; Hess; Cromarty; East Greenland
• Online Access: https://discovery.ucl.ac.uk/id/eprint/10124167/1/The_Late_Oxfordian_to_Kimmerid.pdf; https://discovery.ucl.ac.uk/id/eprint/10124167/

A biostratigraphic anomaly posed by the co-existence of characteristic Late Oxfordian dinoflagellate cyst floras and Kimmeridgian ammonites in the Humber Group of the Outer Moray Firth is thoroughly investigated. Fossils from ten sequences in U.K. Blocks 15/2la and 15/22 cored by Amerada Hess Ltd. are compared with those from onshore Late Oxfordian to Kimmeridgian sequences at South Ferriby (South Humberside), Eathie (Cromarty), and between Brora and Helmsdale in the Moray Firth. The results indicate that the key dinoflagellate cyst marker species Scriniodinium crystallinum (Deflandre) and Endoscrinium galeritum (Deflandre) have ranges extending into younger sediments than previously supposed; both are recorded in the Mutabilis Zone of the Northern North Sea. Ammonite faunas collected from both the North Sea wells and onshore provide support for an informal subzonation of the Cymodoce and Mutabilis Zones of the Sub-Boreal Kimmeridgian. This detailed biostratigraphic control is applied to give precise definition of the timing of transgressive and tectonic events and their relationship to resultant sedimentary responses. The "I Shale" Transgression is demonstrated to be basal Kimmeridgian in age, and the Kimmeridge Clay transgression is dated as early Eudoxus Zone. It is considered likely that the Kimmeridge Clay transgression accompanied the onset of Late Cimmerian tectonism within the Witch Ground Graben, and a Eudoxus Zone age is suggested for this event. By comparison with East Greenland sections an assessment is made of the degree of overprinting of regional sea-level events by local tectonic events. The conclusions are important in the construction of a depositional model for the reservoir sands of the area.