Fluid Inclusion, Isotopic, and Elemental Geochemistry Studies of Cave-Filling Calcite in the Lower–Middle Ordovician Yingshan Formation of Tahe Oilfield, NW China: Implication for Karstification in Non-exposed Limestone

Improving the recognition of paleo-fluid circulation history is great significance to reconstruct pore evolution during carbonate diagenesis. Integrated petrography, fluid inclusion, isotopic and elemental geochemistry (laser ablation inductively coupled plasma mass spectrometry) studies, calcites generated in paleocaves, fractures were investigated. This study aims reveal origin karstification event within nonexposed limestone Lower–Middle Ordovician Yingshan Formation Tarim Basin. The only generation blocky calcite growing along karst paleocave fracture walls [cave-filling (CFC)] crosscuts burial stylolites. secondary inclusions obtained from CFC are characterized by coexistence liquid-only liquid-dominated aqueous with low salinities values (0–2.4 wt%), suggesting that has experienced a low-temperature environment (<50°C). depleted δ 18 O (−15.32‰ 12.45‰), seawater-like yttrium rare earth element patterns, ΣREE (<0.65 ppm) have recorded major episode meteoric water leaching limestone. view was further confirmed calculated parent fluids (−14.3‰ 2.2‰). relatively higher 87 Sr/ 86 Sr ratios (0.70942–0.70994) interpreted as result interacting overlying Silurian detrital rock when percolated downward. geochemical evidence indicates for possibly took place Early Hercynian period late Devonian. Therefore, percolating downward penetrating insoluble strata and/or migrating laterally permeable deemed responsible event, although thick coverage area.