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The AAPG/Datapages Combined Publications Database

AAPG Bulletin

Abstract


Volume: 68 (1984)

Issue: 3. (March)

First Page: 333

Last Page: 362

Title: Graben Hydrocarbon Occurrences and Structural Style

Author(s): T. P. Harding (2)

Article Type: Meeting abstract

Abstract:

Major hydrocarbon occurrences, types of traps, and structural styles have been synthesized from the Sirte basin, the Suez and Viking grabens, and from other normal faulted regions. Hydrocarbons occur in a stacked succession of one or more basins: pregraben, graben fill, and interior sag. Preservation of pregraben accumulations depends on late initiation of crustal arching and limitation of uplift to the graben shoulders. Furthermore, a stable pregraben tectonic environment is required to ensure internal continuity of subsequent fault-block closures.

Hydrocarbon traps in the pregraben and graben-fill sediments are primarily dependent on the multidirectional orientation of normal faults, tilting of fault blocks, and, in many cases, flexing or erosion parallel with block edges. The fault pattern is dominated by longitudinal faults subparallel with the graben axis and, secondarily, by oblique faults. The direction and degree of block rotation are influenced by fault profile (planar or listric), degree of extension, fault pattern (doglegs, junctions, terminations), downwarping of the subsequent sag basin, and isostatic adjustments between large blocks. Fold closures result from the upward termination of faults into forced folds, which may be accentuated by drag during renewed faulting. Passive drape and differential compaction extend he folds to shallower depths. Because they form along block edges, the flexures have trends that mimic the multidirectional fault patterns. Truncation traps are usually developed from the erosional retreat of fault scarps and they can also mimic the fault patterns.

Where the sedimentary succession is complete, an interior sag basin is superimposed across the graben. Its lower part is structured mostly by drape and differential compaction across the underlying graben fault blocks and fault-block topography. The upper part is usually an unsegmented syncline, and hydrocarbon traps at this level include depositional buildups (reefs, turbidite mounds), and salt diapirs or other structures caused by superimposed deformation unrelated to graben tectonics.

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