Geochemistry of Middle Oligocene-Pliocene sandstones from the Nanpu Sag, Bohai Bay Basin (Eastern China): Implications for provenance, weathering, and tectonic setting

Abstract

Petrographic and geochemical compositions of thirty-seven Middle Oligocene-Pliocene sandstone samples from the Nanpu Sag in Bohai Bay Basin were analyzed to evaluate their provenance, weathering, and tectonic setting. These sandstones comprise mainly arkoses and lithic arenites and a few graywackes, characterized by low to moderate quartz/ total feldspar ratios (1.31-6.11, average 2.72 ± 0.98) and CIA values (45.87-70.13, 57.49 ± 5.93). The Middle-Upper Oligocene sandstones have average lower SiO 2 (71.72 ± 5.16%), and higher Fe 2 O 3 (3.06 ± 1.26%) and MgO (1.65 ± 0.39%), in contrast with the Miocene samples that generally have high SiO 2 (76.46 ± 4.26%) and low Fe 2 O 3 (3.04 ± 1.51%) and MgO (0.69 ± 0.32%) contents. Following the deposition, Fe 2 O 3 (3.17 ± 1.00%) and MgO (1.07 ± 0.38%) contents increased again in the Pliocene samples. Such a compositional variation trend is interpreted as a change of tectonic activity in the sag from Middle Oligocene to Pliocene, i.e., stronger in the Middle Oligocene, weaker in the Miocene and to stronger again in the Pliocene. Qt-F-L plot, trace element provenance discrimination diagrams (e.g., Eu/ Eu*, Co/Th, and La/Sc), and REE characteristics suggest that the source rocks were mainly derived from felsic igneous rocks, possibly from Mesozoic granitoids and felsic volcanic lavas in the Yanshan Fold Belt. Tectonic discrimination diagrams (e.g., SiO 2 -K 2 O/Na 2 O, Fe 2 O 3 * + MgO-TiO 2 , and Th-Sc-Zr/10) show that these sandstones were mainly deposited in an active continental margin setting, implying a remobilized intra-continental environment.

The Paleogene multi-phase tectono-sedimentary evolution of the syn-rift stage in the Nanpu Sag, Bohai Bay Basin, East China

“…The Cenozoic succession includes the Eocene Shahejie (Es), Oligocene Dongying (Ed) Formations, and the Miocene Guantao (Ng) and Minghuazheng (Nm) Formations (Chen et al., 2016; Jiang et al., 2009; Liu and Zhang, 2011). The Paleocene Kongdian Formation (Ek) and the Eocene Member 4 of the Shahejie Formation are absent within the Nanpu Sag (Figure 3).…”

Determination of Paleocurrent Directions Based on Well Logging Technology Aiming at the Lower Third Member of the Shahejie Formation in the Chezhen Depression and Its Implications

“…In previously published papers, many studies have focused on the stratigraphy, sedimentology, microtectonics, oil-gas exploration, and thermal evolution history of the eastern Bohai Bay basin [4][5][6][7][8][9]. However, due to limited seismic and well logging data, studies focused on the macroscopic direction of paleocurrents are scarce, and the coupling relationship between paleocurrents and the tectonic background has not received enough attention [10,11].…”

Provenance and tectonic setting of the Early and Middle Devonian Xueshan Formation, the North Qilian Belt, China

“…Generally, the chemical composition of sediments can be used to draw a clear picture indicating the characteristics of the sediment source (Roser & Korsch, ). For example, the chemical composition of sedimentary rocks has been used to infer the potential provenance, constrain the tectonic settings of sedimentary basins, and reveal possible paleosedimentary conditions (Armstrong‐Altrin et al, ; Cullers, ; Liu et al, ; Ramadan & Zaid, ; Young, Pitawala, & Ishiga, ; Zhang, Wang, Yan, & Wan, ). Recently, sedimentary geochemistry has been used to study orogenic belts (Kasanzu, Maboko, & Manya, ; Lambeck, Huston, & Maidment, ; Long, Sun, & Yuan, ).…”