Two Dimensional Restoration of Seismic Reflection Profiles from Mozambique: Technique for Assessing Rift Extension Histories

J. E. Iliffe, M. Debuyl, C. G. St. C. Kendall, I. Lerche

Seismic reflection data from offshore Mozambique between longitudes 25° and 26° and latitudes 34° and 35° reveals a V-shaped rift, the apex of which points northward, toward the coast.

Within the rift, fault blocks are generally tilted eastward and delineated by normal faults with a strong north-south orientation and transfer faults of a more north-northeast to south-southwest trend.

Brittle faulting may have developed as early as the Jurassic and continued through the Early Cretaceous; later growth faulting occurred in Upper Cretaceous to lower Tertiary sediments.

This study retraces the rift's extensional history by geometric reconstruction of seismic profiles, selected perpendicular to tectonic strike. Depth conversions are performed, followed by bed length and volume balancing to test the interpretations and calculate a total extension value for the extension factor. The sediments are then backstripped in sedimentary sequences, restoring the increments of throw on faults accordingly. After each sequence is removed, the sediments are decompacted in an attempt to recover the original volume prior to the sequence deposition.

The extension factor is again calculated. This process is repeated down the sequences until the result is the pre-rift state of the basin.

This analysis results in an extension estimate for each sequence-time increment, as a percentage of the total extension.

From this method, a detailed crustal extension history is deduced, which, when coupled to the thermal history from subsidence backstripping and paleoheatflow studies, could be used in the basin analysis assessment of the oil potential of this and other rifts.

AAPG Search and Discovery Article #91043©1986 AAPG Annual Convention, Atlanta, Georgia, June 15-18, 1986.