QUARTZ-ALBITE CORRELATION AS A SHALE PROVENANCE INDICATOR, UPPER TRIASSIC ZHANGJIATAN SHALE, ORDOS BASIN, CHINA

The sediment source of shales is complex. This study examines the grain compositions of Upper Triassic Zhangjiatan (ZJT) Shale determined by XRD analysis to identify its provenance. Results show multiple provenances and reveal that the correlation of quartz-albite is a useful provenance indicator. A test using mineral standards in 20 experiments indicates that XRD analysis can produce accurate relative abundance data. The depocenter of ZJT Shale coincides with the E-W oriented foreland trough. Two major mineral trends are observed. First, quartz-albite is positively correlated on the northern slope of the trough, but negatively correlated on the southern slope. 167 samples from three outcrop sections in the north show positive correlation, whereas 75 samples from two outcrop sections in the south show negative correlation. Second, the lower and upper parts of the ZJT Shale deposited in the lake center have different trends. 13 samples from the lower part show no quartz-albite correlation, whereas 46 samples in the upper part show positive correlation. It has been speculated that sediments on the southern slope were derived from the Qinling suture zone ~300 km to the south, whereas those on the northern slope from the Yinshan suture zone ~700 km to the north. Thickness patterns on the isopach map of the lower shale part from 52 wells suggest three possible source directions from the NE, SE and SW. The patterns for the upper part from 31 wells suggest only one possible source direction from the north; and the shale coarsens to the north. Overall, the positive correlation of quartz-albite in the northern part and the upper part indicates a Yinshan provenance, whereas the negative correlation in the southern part indicates a Qinling provenance, and non-correlation in the lower part suggests multiple sources. The underlying causes of the variable quartz-albite correlation are still being investigated, although a previous study has shown that both the quartz and albite are detrital, suggesting an extrabasinal origin. The preliminary results suggest that the persistent correlation of mineral components can be used to differentiate shales of variable provenances.