Print this pageThe Syn-Tectonic Stratigraphy of the Late Miocene-Pliocene Deltaic Shelf Margin of Brunei, Northwest Borneo
CREVELLO, PAUL, and CHRIS MORLEY
The late Miocene-Pliocene stratigraphy of offshore and onshore NW Borneo (induding Brunei and Sabah) comprises a very thick section (up to 15 km) of alternating sandstone and shale. In general the depocenters young seaward. The gravitational instability of the thick pile of sediments triggered widespread growth faulting and shale diapirism. In addition, movements of basement blocks has episodically triggered localized inversion tectonics. The result is the creation of a number of sub-basins both onshore and offshore within the regional depocenter which may be partially controlled by growth faulting, shale diapirism, and or inversion.
Growth faults and inversion structures impose distinctive signatures on the stratigraphy and facies of syn-tectonic sediments. Examples are examined and the syntectonic versus eustatic controls are discussed. Syn-tectonic stratigraphic records include angular unconformities, inverted structures (anticiines and shale diapirs), shelfal and turbidite growth fault sub-basins, incised shelf margins, exotic structural blocks and coarse conglomeratic beds. Growth fault sub-basins record dramatic vertical aggradational and accommodation of deltaic shelf margins. Stratigraphic modeling of the deltaic shelf margin illustrates a 5 to 6-fold increase in accommodation during aggradation of the vertically growth fault sub-basins versus the progradational margins. Outcrop and subsurface facies pattens and unconformities illustrate growing structural highs that serve as local sources for sediment, but equally importantly act as barriers to sediment dispersal, confining facies to juxtaposed synformal sub-basins. Evaluation of the outcrop and subsurface data provide robust models for interpretation of stratigraphic relationships and facies pattems viewed in younger, less well constrained strata from offshore subsurface data sets.