Journal of Petroleum Geology, Vol.5,
No.3, pp.245-260, 1983
©Copyright 2000 Scientific Press,
Ltd.
THE PETROLOGY OF THE
MIDDLE JURASSIC SANDSTONES FROM THE MURCHISON FIELD, NORTH SEA
A. C. Morton* and B. Humphreys*
* Petrology Unit, Institute of
Geological Sciences, Ring Road Halton, Leeds LS15 8TQ, UK.
Abstract
A petrographical investigation of the
sandstones of the Brent Group (Middle Jurassic) from the
Murchison field has produced evidence for the existence of two
transgressive events within the sequence, one occurring
immediately above the Etive Fm., the other within the upper part
of the Ness Fm. These transgressions have not been previously
recorded in Murchison and their discovery demands that some
modification be made to the existing depositional model for the
Brent Group of this area. A volcanic ash horizon has been found
in a similar stratigraphic position to that recorded from
Statfjord, and if this, and the two transgressive horizons noted
above, are of more than local extent they could prove to be
useful stratigraphic markers. Although the diagenesis of the
Brent Group sandstones in Murchison differs little from that
recorded elsewhere in the Brent province, the interpretation of
the timing of the development of certain phases differs somewhat
from those of other authors. In particular, kaolinite development
appears to have taken place soon after burial in response to
periods of emergence and weathering during Brent Group
deposition, rather than through groundwater circulation during
the Kimmerian tectonic phase.
