Sedimentology Stratigraphy and Microfossils of Mid – Late Tertiary Clastic, Sandakan Formation in NE Borneo

Sandakan Formation of Segama Group is exposed across Sandakan Peninsula. The Upper Miocene Formation, part of the Segama Group, unconformably overlies the Garinono Formation and is conformably overlain by Bongaya Formation in the study area in East Sabah. This formation was investigated with a detailed logging and microfossils analysis in order to clarify the depositional facies and sedimentary environment.

This study reveals three lithofacies 1) thick brackish mudstone, 2) shallow water sandstone and mudstone interbedded facies, and 3) thick cross-bedded sandstone with internal erosional basal surface. Based on the presence of Rhizophora, Brownlowia, Florchuetia sp., Polypodium, Stenochleana Palustris, Ascidian Spicule, low angle cross bedding, pinch and balls, very fine grained sandstone, thin alternations of very fine sandstone, silt and clay layers showing cyclicity (muddy rhythemites), it is interpret as estuarine facies.