Sea-level Eustatic Cycles and Potash Formation Event: A Case Study of Triassic Sichuan Basin

Abstract

Identification of the favorable salt-and potash-forming layer, we still mainly rely on logging interpretation and coring verification. However, we both know that the continuously carbonate platform is cyclical growing. It has recorded valuable information about the phase transition of carbonate rocks, which were synchronized with the relative sea-level cycles. This paper presents a fast and efficient way to preliminary judge favorable potassium-rich intervals: utilizing the natural gamma ray logging data, using numerical simulation, highfrequency sedimentary cycles could be identified effectively from the sedimentary record, then we can inverse the distribution model and stacking patterns of these cycles, restore the ancient relative sea-level trends，and finally deduce the favorable salt-and potashforming phases from the low-stand depositional system. On the basis of these principles, in this paper, a case study has been taken in Triassic of Guang'an area, in the central of Sichuan Basin. We deem that the interval form the Fifth Member of the Jialingjiang Formation to the First Member of the Leikoupo Formation is the most potential salt-and potash-forming layer (Fig. 1). The favorable potassium interval that we identified is consistent with the potassiumrich layer which is realized by other academics according to the drill core. It shows that this ZHOU Jiayun, GONG Daxing, CHEN Kegui, LI Chunmei and LI Meng, 2014. Sea-level Eustatic Cycles and Potash Formation Event: A Case Study of Triassic Sichuan Basin. Acta Geologica Sinica (English Edition), 88(supp. 1): 285-286. Fig. 1. Integrated column of sea-level change in the early and middle Triassic, in Guang'an area, Sichuan, China.

Implications of the application of δ 37 Cl analysis to a new type of polyhalite potassium deposit identified in northeast Sichuan, China

“…In addition, the characteristics of the strata above and beneath the evaporites are obviously different due to detachment (Fig. 1D) [33][34][35] .…”

“…In the early 1980s, the advent of high-precision measurements of δ 37 Cl allowed meaningful chlorine isotope measurements of evaporites to be obtained 9,[11][12] ; thus, the chlorine isotope geochemistry of evaporite deposits has been studied extensively [9][10][13][14] . Compared with 35 Cl, 37 Cl preferentially enters salt sediments in the brine evaporation process due to its greater bonding energy 15,16 ; that is, the heavier chlorine isotope is removed preferentially from the brine as the brine becomes lighter. Therefore, the halite that precipitates later has a lighter isotopic composition 17 .…”

Seawater composition variation in the eastern Sichuan evaporite formation basin

“…The continuous uplift of the Luzhou-Kaijiang palaeouplift may be one of the main reasons for the westwards migration of the basin. From the late Permian to Middle Triassic, the Luzhou-Kaijiang palaeo-uplift mainly existed in the form of underwater uplift, and secondary uplift depressions developed on the palaeo-uplift [24][25] .…”