Restoration of formation processes of dolomite reservoirs based on laser U-Pb dating: A case study of Ordovician Majiagou Formation, Ordos Basin, NW China

ZHOU Jingao,YU Zhou,WU Dongxu,REN Junfeng,ZHANG Daofeng,WANG Shaoyi,YIN Chen,LIU Yuxin

Table 2. U-Pb isotopic ages and carbon and oxygen isotopic composition in Majiagou Formation

Well name Well depth/m Sample Isotopic age/Ma δ13C/‰ δ18O/‰ Yu113 2674.98 Fine powder crystal dolomite wall rock 492.0 -0.94 -8.25 Tong67 3802.70 Fine powder crystal dolomite wall rock 453.0 0.69 -6.12 Jin4 3688.27 Coarse powder crystal dolomite wall rock 444.0 0.46 -5.81 Tao112 3392.11 Dolomite psammitic wall rocks 476.0 -1.51 -6.34 Tao112 3449.19 Thrombolite wall rock 493.0 1.21 -7.73 Tao86 3679.73 Dolomitic oolitic wall rock 494.0 Tao86 3679.73 Dogtooth-shaped dolomites 467.0 (Phase 1) 0.78 -6.68 Tao112 3449.19 Blade-shaped interstitial dolomite 440.0 (Phase 1) 1.35 -6.95 Tong67 3802.70 Interstitial dolomitic silts 381.0 (Phase 2) -1.26 -8.51 Yu113 2674.98 Interstitial dolomitic silts 316.5 (Phase 2) Tao 112 3449.19 Interstitial crystalline dolomites 354.0 (Phase 3) 1.38 -7.48 Yu113 2674.98 Gypsum mold pores filled with calcites 303.0 (Phase 4) -4.53 -11.43 Tao 112 3321.29 Dissolved pores filled with calcites 292.7 (Phase 4) -5.09 -9.08 Tao 112 3316.77 Cracks filled with calcites 319.0 (Phase 4)