Geochemistry of Eocene Bawang Member turbidites of the Belaga Formation, Borneo: Implications for provenance, palaeoweathering, and tectonic setting

Abstract

The Belaga Formation of the Rajang Group or Rajang Fold and Thrust Belt (Late Cretaceous to Late Eocene) is mostly exposed in Sibu Zone along with some exposures in the Miri Zone of Central Sarawak. This entire turbiditic sequence was believed to have been deposited in a deep marine environment in a basin having an overall passive margin setting, that is, the Rajang Sea. However, the Eocene age‐related stratigraphic record of this group (including Bawang Member) is much more complex, due to the complicated geological and tectonic settings which prevailed during their deposition. Here, we present field observations along with the application of various geochemical proxies and their constraints for the understanding of provenance, palaeo‐weathering, and tectonic evolution of the area during the deposition of Bawang turbidites. Based on field observation, it has been found that this member consists of four main lithofacies, including massive sandstone facies (MSF), thick‐bedded facies (TBF), heterolithic facies (HF), and mud facies (MF). Using geochemical data, chemical weathering indices (CIA and CIW) values and A‐CN‐K plot show that the source area for Bawang turbidites has undergone a moderate to an intense degree of chemical weathering and was influenced by the recycling effect. The slight depletion in sandstones and shales for Cr, Ni, and V values is consistent with the felsic dominated source region; however, La/Sc versus Co/Th and La/Th versus Hf plots show a mixed source (felsic and intermediate volcanic source) with some input of recycled sediments from the older sedimentary to metasedimentary rocks. Various geochemical ratios and discriminant diagrams verify that the Schwaner Mountains and its metamorphic group of rocks were the principal provenances for these sediments, along with some input from West Borneo. The results of the geochemical analysis also show that Bawang turbidite sediments were deposited in a basin associated with an initial active continental margin setting and the basin was shifting towards a passive setting (Late Eocene–Oligocene). The volcanic input in Bawang Member during the Late Eocene also suggests the involvement of some subsequent possible arc setting around the “Bawang subbasin”.

Facies analysis and distribution of Late Palaeogene deep‐water massive sandstones in submarine‐fan lobes, NW Borneo

“…The geology of South‐East Asia is considered a vital avenue for hydrocarbon generation and petroleum production in the Tertiary sedimentary successions (Al‐Masgari et al, 2021; Imran et al, 2020, 2021; Usman, Siddiqui, Zhang, et al, 2020). The generation of large amounts of sediments from various local sources and their deposition in the deep‐marine environments is believed to be associated with the complex geology of Borneo in the Tertiary period (Ahmed, Siddiqui, Rahman, et al, 2021; Ahmed, Siddiqui, Ramasamy, et al, 2021; Hall et al, 2008; Ogawa & Back, 2022; Siddiqui et al, 2017; Usman, Zhang, Siddiqui, & Jamaluddin., 2020). Borneo is associated with tectonic subduction coupled with obduction of ophiolites and closure of palaeo‐basins (Hall, 2013; Mathew et al, 2014; Ramkumar et al, 2021; Siddiqui et al, 2019; Usman et al, 2021; Usman, Siddiqui, Mathew, et al, 2020).…”

Subduction history of the Proto-South China Sea: Evidence from the Cretaceous - Miocene strata records of Borneo

“…Late Cretaceous -Late Eocene mudstones of the Rajang Group, Kuching Supergroup and the Lubok Antu mélange are characterized by Chondrite-normalized LREE-enriched REE patterns and negative Eu anomalies, and the UCC-normalized trace element patterns show a Sr negative (Fig. 6a, 6b; Ferdous & Farazi, 2016;Ramasamy et al, 2021;Ahmed et al, 2021;Baioumy et al, 2021;Zhao et al, 2021;Zhu et al, 2021). In the Zr-TiO 2 provenance discrimination diagram, samples from the Kayan and Ketungau Groups of the Kuching Supergroup plot in the felsic region, and Lubok Antu Mélange samples and the Lower Rajang Group (Lupar Formation, Layar Member and Lower Kapit Member) are closer to the intermediate region, while samples from the Upper part of the Rajang Group mostly fall into the felsic region (Fig.…”

Facies Analysis and Sedimentary Architecture of Hybrid Event Beds in Submarine Lobes: Insights from the Crocker Fan, NW Borneo, Malaysia

“…Borneo exhibits complex geological history, particularly during the Tertiary Period when thousands of meters-thick deep-marine sedimentary successions were deposited in an active tectonic regime [51][52][53][54][55][56]. Active tectonic subduction in Borneo resulted in the closure of paleo-basins and development of ophiolite rocks [57,58].…”