Four exhumed hydrocarbon traps
crop out in the Traill Ø region of East Greenland, each at the footwall
crest of a fault-block formed during Early Cretaceous rifting. Former oil
accumulations are indicated by a pore fill or pore lining of solid bitumen
within the Jurassic sandstone-dominated Vardekløft and Olympen formations.
The Vardekløft Formation is divided into an undated
fluvial-dominated lower unit (0-520 m) and
a Bajocian-Callovian upper unit (65-1020 m) deposited in a shallow-marine
environment. The Oxfordian Olympen Formation (0-250 m) contains shallow-marine
and fluviodeltaic deposits. The sandstones are dominantly quartzarenites,
and petrographic fabrics, such as dissolved feldspar, late quartz cement,
and stylolites, are consistent with burial depths in excess of 2.5 km.
Porosities ranged from 7 to 27% (generally about 20%, about one-half of
which was primary), and permeabilities ranged from 1 to 622 md, prior to
the formation of solid bitumen. The distribution of solid bitumen in each
trap can be mapped out, allowing sealing elements and original oil-water
contacts to be defined. Three of the four exhumed traps (Mols Bjerge, Laplace
Bjerg, and Bjørnedal) were simple one-seal structural traps. Conformable
Upper Jurassic mudstone, unconformable Albian-Cenomanian mudstone, and
normal faults are the three top-sealing elements.
1997. The American Association of Petroleum Geologists. All rights reserved.
received October 4, 1995; revised manuscript received March 1, 1996; final
acceptance September 17, 1996.
Arctic Shelf Programme, Department of Earth Sciences, University of Cambridge,
Downing Street, Cambridge CB2 3EQ, United Kingdom.
work forms part of a field-based project in East Greenland for which we
gratefully acknowledge past and present funding from Amoco, BP, Conoco,
Enterprise Oil, Esso, JNOC, Mobil, Shell, and Texaco. In addition to numerous
geologists from these companies, we would like to thank James Brodie, Flemming
G. Christiansen, Andrew King, Dave Latin, David Macdonald, John Marshall,
Lars Stemmerik, Simon Tull, and Nicky White for helpful discussions, and
Crispin Day and Kenn Nielsen for logistical support. We are grateful to
John Callomon and Simon Kelly for undertaking the ammonite identifications
used in this article. Comments from Tony Spencer greatly improved an earlier
version of the manuscript. In addition we would like to thank AAPG Elected
Editor Kevin Biddle and Finn Surlyk, G. Bertram, and Dietmar Schumacher
for judicious reviews, which further improved this article. Department
of Earth Sciences Contribution No. 4582.