GEOLOGICAL SOCIETY OF THE PHILIPPINES
| NEW INSIGHTS INTO THE NW PALAWAN BASIN FROM RECENTLY ACQUIRED 2 & 3D SEISMIC TECHNIQUES TO ACHIEVE INTEGRATED HIGH RESOLUTION STRATIGRAPHY IN BRUNEI DARUSSALAM’S DEEP WATER AREA |
Shirley E. van Heck1
The sediments of the Baram Delta and adjacent areas consist of Neogene clastics. Sedimentation rates are very high, resulting in a demand for high resolution stratigraphy. This poses a challenge to get more out of biostratigraphy and fully integrate all available data into a sequence stratigraphical framework.
As a result of often unfavourable environments and poor preservation, age diagnostic planktonic foraminifera and calcareous nannofossils are rare or absent in many BSP wells and palynostratigraphy is therefore an important tool. Although the deep water wells are relatively rich in planktonics, compared to other areas the yield and preservation are poor. In the search for a higher resolution for the deep water wells in Brunei, routine microscope scanning of foraminiferal slides for QC purposes revealed that the original species determinations of planktonics could be improved upon. Morphological changes were observed in several groups of planktonics which might be used for further subdivision. Stricter species concepts and recording of coiling directions gave a considerable improvement in zonation and well correlation. Other morphological changes, several of which appear to be ecophenotypic, may offer scope for further subdivision and improved correlation. This highlights that stratigraphers cannot afford to turn away from microscope work if any improvement on previous work is to be expected. The Shell palynological zonation, as developed by Müller in the sixties, is augmented by further subdivision based on quantitative assemblage changes that are interpreted as climatically induced.
Well sequence stratigraphic interpretations are based on an integration of log stacking patterns, sedimentological data, palynostratigraphical and climatical signals, foraminiferal and nannoplankton ages and frequency data and palaeobathymetrical/ palaeoenvironmental data as derived from foraminifera. After all data have been plotted on stratigraphical summary sheets, well sequence stratigraphical interpretations are integrated with seismic data in interaction with the interpreter, to arrive at a mutually agreed upon sequence stratigraphic interpretation.
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