FACIES AND SANDSTONE CHARACTERISTICS OF THE KUDAT FORMATION, SABAH, MALAYSIA
The Kudat Formation, formed the major rock unit of Kudat Peninsula in the northern tip of Borneo Island, is made up of interbedded sandstone and mudstone with fossiliferous limestone lenses. Lithostratigraphically, it is divided into Tajau Member and Sikuati Member. The Tajau Member differs from t...
| Main Authors: | , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Zibeline International
2017-01-01
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| Series: | Geological Behavior |
| Subjects: | |
| Online Access: | https://geologicalbehavior.com/archives/2gbr2017/2gbr2017-20-25.pdf |
| Summary: | The Kudat Formation, formed the major rock unit of Kudat Peninsula in the northern tip of Borneo Island, is
made up of interbedded sandstone and mudstone with fossiliferous limestone lenses. Lithostratigraphically, it is
divided into Tajau Member and Sikuati Member. The Tajau Member differs from the Sikuati Member by the
thicker coarsening upward sequence and the presence of limestone lenses. Field mapping and petrographic
analysis were utilized to study the facies and sandstone characteristics. The formation as a potential reservoir is
largely dependent on the original sandstone composition, which was influenced by deposition in a shallow
marine setting and local sourcing activity. The succession of the sequence is composed of a major shoreface
deposits during the late Early Miocene. The measured sections are predominantly composed of interbedded
sandstone and mudstone usually show sedimentary structures which are indicative of wave and tidal processes,
such as swaley, hummocky, trough and planar cross stratifications. The sequence grades up-section into facies
packages of increasing tidal energy and terminate with the deposition within the upper regime shoreline
settings. The selected Tajau sandstones in this study are texturally and mineralogically mature quartz arenites
with good sorting. However, the presence of unstable lithic grains and feldspars during diagenetic processes
contributed to the reduction of porosity, giving irregular porosity, due to deformation by compaction, and
susceptibility to chemical alteration of labile minerals. Reservoir quality was also influenced by the subsequent
diagenesis of the sandstones, which was driven by increase overburden pressure and could be culminated by
increase temperature during the proceeding depth. Lithic fragments, feldspars and authigenic cements were
altered to form diagenetic mineral suites, which tend to occlude porosity; however, dissolution and chemical
reactions of some of these grains also enhanced secondary porosity development. Most observed porosity in the
sandstone sequence is secondary, developed from dissolution of both carbonate cement and unstable
framework grains. Mean porosity suggested a weak decreasing trend with depth of burial. However, detailed
examination of several localities revealed that porosity development was strongly influenced by local factors.
Thus, sandstones of the Kudat Formation are generally fair reservoir characteristics, due to the presence of
unstable framework grains, early carbonate cementation and authigenic/diagenetic mineral suites. |
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| ISSN: | 2521-0890 2521-0491 |