Geochemistry and paleogeography of the Rajang Group, Northwest Borneo, Malaysia

Abstract

The Late Cretaceous to Late Eocene Rajang Group in Borneo is one of the world's largest deep-sea sedimentary fans. The volume of the Rajang Group cannot be explained by erosion of the Schwaner Mountains in SW Borneo and the Malay Peninsula. To identify other contributing sources, this study examined the provenance history of the Rajang Group and the overlying Tatau Formation. A combination of bulk rock geochemistry, zircon morphological analysis and U–Pb geochronology is used to better constrain the provenance of the Rajang Group. Bulk rock Nd data, supported by detrital zircon data indicates that a late Mesozoic magmatic belt include the Schwaner Mountains was an important source before the Paleocene, after which sediment supply was dominated by older crustal sources, consistent with the Malay Peninsula. The increased contribution from older crustal material is considered to be the consequence of collapse of the magmatic arc and collision between Australian microcontinental fragment(s) and the southern margin of Sundaland. Paleocene river systems that flowed through the Malay Peninsula, transported large amounts of sediments to the marine basins including the deep-sea Rajang Group. A strong signal of sediment recycling for the Tatau Formation indicates uplift and denudation of lower Rajang Group in Late Eocene.