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. 2. Macroscopic and microscopic features of samples and testing points. (a) Powder crystal dolomites with anhydrite concretions, gypsum mold pores are products of corrosion of anhydrite concretion and fully filled with dolomitic silts and calcites, Ma51, Well Yu113, 2674.98 m, cast thin section, plain-polarized light; (b) Powder crystal dolomites with anhydrite concretions, gypsum mold pores filled with dolomitic silts with dark red light and calcites with red light, Ma51, Well Yu113, 2674.98 m, cathodoluminescence image; (c) Powder crystal dolomites with anhydrite concretions, gypsum mold pores partially filled with dolomitic silts and fine-medium crystalline dolomites, geopetal structure, Ma52, Well Tong67, 3802.70 m, cast thin section; plain-polarized light; (d) Powder crystal dolomites with anhydrite concretions, wall rock (powder crystal dolomite) with dark light; interstitial dolomites with red light, fine-medium crystalline dolomites without light, Ma52, Well Tong67, 3802.70 m, cathodoluminescence image; (e) Thrombolite dolomites, pores fully filled with white calcites, Ma56, Well Jin4, 3688.27 m, U-Pb dating target sample photo; (f) Thrombolite dolomites, pores fully filled with white calcites, Ma56, Well Jin4, 3688.27 m, cast thin section, plain-polarized light; (g) Thrombolite dolomites, pores filled with 2-phase dolomites, Ma58, Well Tao112, 3449.19 m, U-Pb dating target sample photo; (h) Thrombolite dolomites, pores filled with Phase 1 blade-shaped dolomites and Phase 2 crystalline dolomites, Ma58, Well Tao112, 3449.19 m, cast thin section, plain-polarized light; (i) Dolarenite/dolorudite, pores fully filled with white calcites, Ma56, Well Tao112, 3321.29 m, photo of target sample for U-Pb dating; (j) Dolarenite with some bioclasts, dissolved pores fully filled with calcites, Ma56, Well Tao112, 3392.11 m, target sample photo for U-Pb dating; (k) Oolitic dolomites, dissolved pores fully filled with calcites and dolomites, Ma56, Well Tao86, 3679.73 m, thin section, plain-polarized light; (l) Oolitic dolomites, oolites with dark red light, calcites with red light, medium crystalline dolomites without light, Ma56, Well Tao86, 3679.73 m, cathodoluminescence image; (m) Powder crystal dolomites with cracks filled with calcites, Ma56, Well Tao112, 3316.77 m, photo of target sample for U-Pb dating.