Effect of the internal plastic deformation of salt structures on the lithologic succession of evaporites: A case study on the Palaeogene Kumugeliemuqun formation, Kelasu Thrust Belt, Kuqa depression, Tarim Basin

Abstract

For a normal saline lake sequence, as long as the depositional setting is the same, the sediments thickness and saline lake sequence are comparable across an area. However, in the Palaeogene Kumugeliemuqun Formation, in wells from similar depositional settings and the same member, the saline lake succession varies greatly. Member 1 of the Kumugeliemuqun Formation, depending on the combination of halite, gypsum, and dolomite (limestone), is divided into four types of saline lake successions: type A, type B, type C, and type D. In the same depositional setting, the saline lake succession and sediment thickness among adjacent areas differ. In member 2 of the Kumugeliemuqun Formation, depending on the association of mudstone and halite, ten different saline lake successions were identified as sequences 1 to 10. Even within the same depositional setting, the saline lake succession and sediment thickness can differ. To explain this phenomenon, we present evidence that includes the sediment thickness, a single cycle of saline lake succession, and an ancient landform, and a salt structure to analyze the role of tectonic deformation in members 1 and 2 of the Kumugeliemuqun Formation. Moreover, waveform indication inversion was used to describe tectonic deformation patterns. The results reveal that saline succession types C and D were the result of tectonic deformation in member 1, while saline lake succession sequence types A and B were not affected by tectonic deformation in member 1. Additionally, the ten diverse saline lake succession sequences in member 2 are all the result of intense tectonic deformation. The inversion results reveal that the inclined thrust, recumbent, and sheath folding are the principal deformation styles in member 2, while flow and hook folds are the main internal deformation styles in member 1. Finally, based on these observations, we conclude that tectonic compression created the plastic flow of rock salt, which induced folding and faulting deformation. The faults produced repetition in the lithologic succession, and the folds resulted in the inversion of the lithologic succession. Therefore, due to the effects of the faults and folds, even within the same depositional setting, the lithologic succession and sediment thicknesses differ from one another. • Features of lithological successions inside salt structures are been studied. • The deformations pattern in members 1 and 2 are been described. • Effect of salt rock deformation on kinds of lithological succession is discussed. • Fold and fault in salt structures produced kinds of lithological succession.