Abstract
Abstract The black rock series in the Qiongzhusi Formation contains important geochemical information about the early Cambrian tectonic and ecological environment of the southwestern Yangtze Block. In this paper, major, trace, and rare earth element data are presented in an attempt to reveal the sediment source during the deposition of the early Cambrian Qiongzhusi Formation and to reconstruct the sedimentary tectonic environment and weathering intensity during that time. The basin primarily received continental clastic material with neutral-acidic igneous rocks from a stable source and with a moderate level of maturity during the depositional period of the Qiongzhusi Formation. Furthermore, the strata were weakly influenced by submarine hydrothermal fluids during diagenesis. The reconstruction of the sedimentary environment and weathering intensity shows that P2O5 enrichment and water body stratification occurred due to the effects of upwelling ocean currents during the depositional period of the Qiongzhusi Formation. The combination of upwelling and bottom-water hydrothermal fluids led to environmental changes in the study area, from dry and hot to moist and warm. Last, the reconstruction of the tectonic environment of the Qiongzhusi Formation indicates that deposition occurred in continental slope and marginal marine environments associated with a continental arc tectonic system. These findings provide an essential basis for the comprehensive reconstruction of the early Cambrian sedimentary environment of the Yangtze Block.
Highlights
The early Cambrian was a very important period of geological history [1,2,3,4] because Ediacaran fauna disappeared at the end of the Neoproterozoic and an important biological diversification event called the Cambrian explosion occurred during this epoch, during which skeletal animals emerged [4,5,6,7]
1) The early Cambrian Qiongzhusi Formation was primarily deposited during a transgressive period; the lithofacies transitioned from tidal facies to shallowsea shelf facies, and the types of sediment deposited gradually changed from fine clastics to muddy sediments according to field observations and laboratory analysis
2) The sediment source region was thoroughly reconstructed, and the results indicated that the Qiongzhusi Formation received continental clastic material with neutral-acidic igneous rocks from a stable source and moderate maturity based on the analysis of major elements, trace elements, and rare earth element (REE)
Summary
The early Cambrian was a very important period of geological history [1,2,3,4] because Ediacaran fauna disappeared at the end of the Neoproterozoic and an important biological diversification event called the Cambrian explosion occurred during this epoch, during which skeletal animals emerged [4,5,6,7] This diversification event produced considerable organic matter, leading to the formation of high-quality oil and gas deposits, and this organic matter was preserved in various sedimentary environments and paleoclimates at that time [7,8,9,10]. Our studies provide basic data for understanding the sedimentary and tectonic evolution along the southwestern margin of the Yangtze Block during the early Cambrian, and they provide an essential basis for the comprehensive reconstruction of the early Cambrian sedimentary and tectonic environment of the Yangtze Block
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