Silicate and carbonate mixed shelf formation and its controlling factors, a case study from the Cambrian Canglangpu formation in Sichuan basin, China

Abstract

Mixed sedimentation is mainly a phenomenon by which siliciclastic and carbonate are mixed under a similar sedimentary environment. The study of the composition of mixed rock can reflect the sedimentary environment. The mixed sediments of the Canglangpu formation in the eastern Sichuan basin are widely developed and exhibit well exploration prospects. In this study, a classification diagram of mixed sediments suitable for the Canglangpu formation was proposed by combining lithologic characteristics with logging data. Based on the observations of typical outcrop profiles, the identification of thin sections, and drilling and geological logging data, a model was established to identify the electrical responses of the mixed sedimentary rocks in the study area. The results show that (1) the Canglangpu formation can be vertically divided into two complete transgression-regression cycles with the lower part mainly consisting of sedimentary carbonate diamictite and the upper part principally composed of clastic diamictite; (2) mixed sediments in the Canglangpu formation can be divided into six classes, namely carbonate sandstone, argillaceous sandstone, sandy carbonate rock, argillaceous carbonate rock, sandy mudstone, and Carbonate mudstone; (3) the sedimentary environment of the Canglangpu formation be divided into (a) mixed sediments in the shore, which include mixed lagoon and mixed tidal flat, (b) mixed sediments in the shallow marine shelf, which includes mixed beach bar, terrigenous detrital mixed shelf, and carbonate mixed shelf; (4) a mixed shore-mixed shelf sedimentary model has been established; it says that the mixed sediments show obvious characteristics of ring-like development around underwater paleo-heights. The formation mechanism of mixed sedimentation in the eastern Sichuan basin is mainly controlled by the change of sedimentary facies belt, and the development intensity is mainly influenced by early tectonic movement and sea-level change.

Keywords

• eastern sichuan basin
• canglangpu formation
• mixed sedimentation
• distribution law
• controlling factors