Seismostratigraphic and sedimentological characterization of deepwater channel systems on the NW Borneo margin: Sediment sources and structurally-controlled routing system

Abstract

• Late Miocene folding in deepwater NW Borneo influenced submarine channel development. • The Champion sediment-supply system comprised in its onshore part multiple rivers. • The paleo-Padas River was one of the primary rivers supplying lithic-rich sediment. • Variation in catchment-area geology influenced deepwater sediment composition. The northwest (NW) Borneo margin is one of the geologically most complex regions of Southeast Asia characterized by a steep slope gradient and an extensive deepwater fold and thrust belt. This area is economically important because of large-volume hydrocarbon accumulations in the deep-marine sandstones in fold and thrust anticlines. Although much attention has been paid to the distribution of deepwater reservoir rocks, the provenance of these rocks and compositional variations are yet not fully understood. In this study we present geomorphological and petrological analyses of Late Miocene deepwater channel deposits that form important reservoirs in the region. Our results reveal the presence of a northwest-trending deepwater channel system displaying morphological variations induced by syn -sedimentary structural development. Petrological analyses of core samples show a predominant lithic-rich rock composition in the reservoir sandstones, suggesting sediment supply from a lithic-rich Crocker Formation hinterland, probably through a paleo-Padas River. This rock composition differs from the quartz-rich rock composition of an adjacent contemporaneous deepwater reservoir mainly comprising reworked quartz-rich Meligan sandstones. The observed petrological differences are interpreted to reflect a Late Miocene multi-source sediment supply system that drained offshore different NW Borneo hinterland areas. Offshore, sediment transport to and across the slope was dominantly margin-perpendicular, linear or of low sinuosity, in the deepwater locally affected by faulting and folding. This study provides new insights into the complexity of sediment routing systems along continental margins, highlighting the influences of the configuration of the sediment supply system and tectonics on deepwater sedimentation.