Sedimentology
and Significance of Linked Turbidite-Debris Flows in the West Crocker Fm
(Oligocene-Miocene), NW Borneo,
Zakaria, Abdullah Adli1,
Howard D. Johnson2, Christopher A.L. Jackson3, Felix
Tongkul4, Paul D. Crevello5 (1) Imperial College London,
London, United Kingdom (2) Imperial College, University of London (3) Imperial
College, (4) Universiti Malaysia Sabah, Kota Kinabalu, Malaysia (5) Petrex Asia
Reservoir & Stratigraphy Group, Kuala Lumpur, Malaysia
Exposures of the West Crocker Fm in NW
Borneo, Malaysia indicate a common upward transition from well-sorted
sandstones interpreted as turbidite deposits to either (1) mud-rich sandstones
or (2) clast-rich mudstones interpreted as the products of debris flows. The
sandstones are fine to coarse-grained, have sharp, erosive bases and are up to
5 m thick. Internally the sandstones are massive or weakly-graded, and may
contain convolute or sub-horizontal stratification and water-escape pipes. The
contacts between the turbidites and overlying debris flow units are sharp but
may be undulose due to the development of clastic injections sourced from the
turbidite sandstones. The overlying debris flow units consist of either
mud-rich sandstones or clast-rich mudstones which are up to 0.44 m thick, are
rich in shale, sandstone and/or coal fragments and may be capped by
current-rippled fine sandstones. Based on the depositional facies, their
vertical relationships and the nature of the unit contacts, the deposits are
interpreted as being sourced from the same flow event with the debris flows
transported and emplaced on the just deposited, still liquefied sandstones.
Palaeogeographic considerations suggest that debris flows units within such
flows may have been transported >100 km down the slope and across the
basinfloor. Quantitative analysis of the thickness of the turbidite and debris
flow components of the gravity-flows indicates that no significant relationship
exists between the thicknesses of the units, suggesting fluctuations in the
type of sediment incorporated in the parent flow or the manner in which
material was segregated during transport.
AAPG Search and Discover Article #90063©2007 AAPG Annual Convention, Long Beach, California