Genetic mechanism of the dolostones from the upper part of the fourth member of the Leikoupo Formation in the Pengzhou region, western Sichuan depression

The types and genetic mechanism are examined in details for the dolostones from the upper part of the fourth member of the Leikoupo Formation in the Pengzhou region, western Sichuan depression on the basis of core observation, thin section examination, cathodoluminescence images, scanning electronic microscope, carbon, oxygen and strontium isotopic measurement, whole-rock analysis, trace element analysis and X-ray diffraction analysis. The deeply buried dolostones in the study area mainly consist of micritic and silty dolostones with fine grains, and euhedral and subhedral crystals. The finely crystalline dolostones are rarely observed. The δ¹³C values range between -4.8‰ and 3‰, with an average of 1.92‰, indicating low positive values. The δ¹³O values vary between -8.1‰ and 0.6‰, with an average of -5.04‰, indicating moderately negative values. The ⁸⁷Sr/⁸⁶Sr ratios vary from 0.7077 to 0.7087. The dolostones in the study area are characterized by higher Fe²⁺ contents, lower Mn²⁺ contents, lower ordering and Mg/Ca ratios. They have firstly a sedimentary origin and secondly a burial origin, representing the intertidal-supertidal syngenetic and parasyngenetic dolostones.