Late Jurassic seismic sequences, Inner Moray Firth, U. K. North Sea: Do local influences invalidate a key segment of Exxon's sea-level chart

Conference · Fri Mar 01 00:00:00 EST 1991 · AAPG Bulletin (American Association of Petroleum Geologists); (United States)

OSTI ID:7012871

Underhill, J R ^[1]

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1. Univ. of Edinburgh (United Kingdom)

Exxon workers used seismic reflector terminations in the Late Jurassic of the Inner Moray Firth (IMF) to define seven sequence boundaries within the late Oxfordian-Berriasian marine interval. The seven are incorporated in their global chart showing relative changes of coastal onlap and eustatic sea level because it was considered that data from the IMF showed no evidence that tectonics caused the unconformities. However, the new interpretation casts doubt on Exxon's conclusions. Interpretation of a comprehensive seismic and well data base has only led to the recognition of five sequences within a late Oxfordian-Berriasian (J2) megasequence. Geometric, thickness, and sedimentary facies variations in this megasequence demonstrate the likelihood that synsedimentary tectonism created them in a fully marine domain, rather than coastal onlap in a basin that was tectonically quiescent. Additional evaluation of the onlap-defined sequence boundaries suggests that they were largely the result of extensional activity caused by fault-block rotations in association with half-graben development. Furthermore, the work shows that onlaps within a fully marine sequence should not be used to define coastal onlap because they may represent purely sedimentary processes, such as submarine fan avulsion untied to any rise in sea level. Indeed, independent work generally shows that such sedimentary responses are more likely to be associated with sea-level lowstands when sediment supply rates are much greater. The reappraisal of an integrated data base from the IMF type area casts doubt on the local controls on and global applicability of the Late Jurassic section of Exxon's sea-level chart.

• OSTI ID: 7012871
• Report Number(s): CONF-910403-; CODEN: AABUD
• Journal Information: AAPG Bulletin (American Association of Petroleum Geologists); (United States), Vol. 75:3; Conference: Annual meeting of the American Association of Petroleum Geologists (AAPG), Dallas, TX (United States), 7-10 Apr 1991; ISSN 0149-1423
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
02 PETROLEUM
SEDIMENTARY BASINS
SEISMIC SURVEYS
STRATIGRAPHY
DATA ANALYSIS
UNITED KINGDOM
EXPLORATION
GEOLOGIC MODELS
JURASSIC PERIOD
NORTH SEA
PETROLEUM DEPOSITS
SEA LEVEL
ATLANTIC OCEAN
DEVELOPED COUNTRIES
EUROPE
GEOLOGIC AGES
GEOLOGIC DEPOSITS
GEOLOGIC STRUCTURES
GEOLOGY
GEOPHYSICAL SURVEYS
LEVELS
MESOZOIC ERA
MINERAL RESOURCES
RESOURCES
SEAS
SURFACE WATERS
SURVEYS
580000* - Geosciences
020200 - Petroleum- Reserves
Geology
& Exploration