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

Fig. 3. Results of in-situ laser U-Pb isotopic dating for carboante minerals. (a) Fine powder crystal dolomite wall rock with U-Pb isotopic age of (492.0±36) Ma, Well Yu113, 2674.98 m, Ma5 1; (b) Fine powder crystal dolomite wall rock with U-Pb isotopic age of (453.0±32) Ma, Well Tong 67, 3802.70 m, Ma52; (c) Coarse powder crystal dolomite wall rock with U-Pb isotopic age of (444.0±31) Ma, Well Jin4, 3866.27 m, Ma56; (d) Thrombolite dolomite wall rock with U-Pb isotopic age of (493.0±42) Ma, Well Tao112, 3449.19 m, Ma58; (e) Dolomitic oolitic wall rock with U-Pb isotopic age of (494.0±26) Ma, Well Tao86, 3679.63 m, Ma56; (f) Dolomite psammitic wall rock with U-Pb isotopic age of (476.0±36) Ma; Well Tao112; 3392.11 m; Ma56; (g) Dogtooth-shaped dolomitic cements with U-Pb isotopic age of (467.0±16) Ma, Well Tao86, 3679.73 m, Ma56; (h) Blade-shaped dolomitic cements with U-Pb isotopic age of (440.0±47) Ma, Well Tao112, 3449.19 m, Ma58; (i) Interstitial fine powder crystal dolomitic silts with U-Pb isotopic age of (381.0±27) Ma, Well Tong67, 3802.70 m, Ma52; (j) Interstitial fine powder crystal dolomitic silts with U-Pb isotopic age of (316.5±6) Ma, Well Yu113, 2674.98 m, Ma51; (k) Crystalline dolomites with U-Pb isotopic age of (354.0±46) Ma, Well Tao112, 3449.19 m, Ma58; (l) Interstitial black calcites with U-Pb isotopic age of (303.0±23) Ma, Well Yu113, 2674.98 m, Ma51; (m) White calcites filled in cracks with U-Pb isotopic age of (319.0±18) Ma, Well Tao112, 3316.77 m, Ma56; (n) White calcites filled in dissolved pores with U-Pb isotopic age of (292.7±3) Ma, Well Tao112, 3321.29 m, Ma56.