Diagenetic Heterogeneity of Deep Sandstones and Its Relationship to Oil Emplacement: A Case Study from the Middle Jurassic Toutunhe Formation in the Fukang Sag, Central Junggar Basin (NW China)

Figure 7

Thin section images of sandstones (pore space is highlighted in blue). ((a) and (b)) Sample 4133.6 m, well D-7, PPL, and CL, respectively: calcite displaying a rather patchy and local cementation and having yellow to orange luminescence. (c) Sample 4429.45 m, well D-2, and PPL: quartz overgrowth precipitated on a detrital quartz grain where there is a break in the continuity of the chlorite coat. ((d) and (e)) Sample 4514.65 m, well D-7, PPL, and XPL: partially dissolved analcime postdating chlorite coats and replaced by calcite. ((f) and (g)) Sample 4258.85 m, well D-6, PPL, and XPL: partially dissolved analcime replaced by calcite. (h) Sample 4837.5 m, well D-1, and XPL: anhydrite cements filling pores in patches and locally replacing detrital grains. (i) Sample 5506.5 m, well D-3, and XPL: quartz overgrowths engulfed by anhydrite. (j) Sample 4837.5 m, well D-1, and XPL: feldspar overgrowths overlain by anhydrite. (k) Sample 5506.5 m, well D-3, and XPL: anhydrite cements commonly juxtaposed with some of calcite cements. (l) Sample 4133.6 m, well D-7, and PPL: hematite occurring as very thin rims around detrital grains. Framework grains: quartz (Qtz), feldspar (Fs), volcanic rock fragment (VRF); cement: calcite (Cal), chlorite coat (Chl-c), analcime (Anl), anhydrite (Adr), quartz overgrowth (Qtz-o), feldspar overgrowth (Fs-o), and hematite (Hem); primary porosity (PP) and secondary porosity (SP).

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