Downhole High-Resolution Palynozonation of the Al Khlata Formation in the Mukhaizna Field, Oman, Based Mainly on Cuttings Samples

Michael H. Stephenson¹*, Asya Al Rawahi², and Brian Casey^2
1British Geological Survey, UK
²Occidental, Oman
*[email protected]

Palynology is the main method of correlating the subsurface glacigene Al Khlata Formation of Oman, due to lateral variability of facies, and poor seismic resolution. Up to now, however, it has been difficult to apply a palynozonation using mainly cuttings samples because published in-house schemes use mainly quantitative variations in palynomorph groups, which tend to render the use of cuttings samples difficult, due to downhole caving. Studies in the Mukhaizna field in Oman have revealed a small number of palynomorph types, which combined with quantitative assemblage character, distinguish five biozones working downhole with cuttings samples. The highest, Biozone A, is consistently associated with the Rahab Shale, which was deposited in a large deglacial lake covering much of southcentral Oman. Biozone B is associated with shaley diamictites and sands with considerable lateral variability. Biozone C is associated with thick sequences of shaley diamictites that occur throughout the field with relatively little lateral variability, suggesting very long-lived, large, proglacial or subglacial lakes. The lowest of the biozones, Biozone D, is associated with mainly thick, stacked sandstone sequences and sandy diamictites with extremely high lateral variability. The thickness of the upper biozones, A to C, is relatively constant, and log character is fairly consistent. However, Biozone D varies greatly in thickness. Biozone D may be considerably older than Biozone C, and may represent the first Gondwana glacial activity in the Namurian-Westphalian, while the biozones above represent the later, more intense, glaciation of latest Pennsylvanian and earliest Permian.

AAPG Search and Discovery Article #90077©2008 GEO 2008 Middle East Conference and Exhibition, Manama, Bahrain