Formation mechanisms of calcite cements in tight sandstones of the Jurassic Lianggaoshan Formation, northeastern Central Sichuan Basin. Issue 5 (4th July 2019)

• Record Type: Journal Article
• Authors: Qing, Y. H.; Lü, Z. X.; Wu, J. Y.; Yang, J. J.; Zhang, S. L.; Xiong, C. H.; Liu, J. F.
• Is Part Of: Australian journal of earth sciences. Volume 66:Issue 5(2019)
• Page Start: 723
• Page End: 740
• Publication Date: 2019-07-04
• Subjects: Central Sichuan Basin -- Lianggaoshan Formation -- sandstone -- calcite -- carbon and oxygen isotopes -- formation mechanism -- diagenesis; Earth sciences -- Australia -- Periodicals; Earth sciences -- Periodicals; Geology -- Australia -- Periodicals; Geology -- Periodicals; 559.405
• DOI: 10.1080/08120099.2018.1564935
• Languages: English
• ISSNs: 0812-0099

Abstract

Abstract: The characteristics and formation mechanism of calcite cements in the tight sandstone of the Jurassic Lianggaoshan Formation in the northeastern Central Sichuan Basin were analysed using petrographic and isotopic techniques. In the tight sandstone of the Lianggaoshan Formation, cements are mostly calcite and occur as poikilitic, pore-filling, fracture-filling and replacement of clastic particles. Contents of Al, Si, Fe and Mn in the poikilitic calcites are significantly less than that in the dissolution pore-filling and metasomatic calcites. Three stages (early, middle and late) of authigenic calcites correspond to temperature ranges of <60, 60–100 and ≥100 °C, respectively, with most calcite cements formed under lower temperature (<100 °C) conditions. The δ 18 O values of the early–middle authigenic calcites are in equilibrium with connate water, and the δ 18 O values of late calcites are depleted in 18 O indicating equilibrium at higher temperatures. The early authigenic calcites precipitated in a relatively open system associated with CO2 from bacterial fermentation at an immature to low-mature stage, and a Ca 2+ - and alkaline-rich environment owing to hydration–hydrolysis and dissolution of silicate minerals during phase A of eodiagenesis. The middle–late authigenic calcites precipitated in a relatively closed system with CO2 from decarboxylation of organic acids and Ca 2+ from dissolution of silicate minerals and transformation of clay minerals during phase B of eodiagenesis to mesodiagenesis. Calcite cements mainly occur in the medium and fine sandstones of sand flats and beach bars. Authigenic calcite dissolution is extremely weak, and calcite cementation is pore-space destructive.