Identification and Evolution of Different Genetic Types of Deep Karst Caves Controlled by Faults—A Case Study in Huanjiang Sag, Guangxi Province, South China

Abstract

In recent years, it has become more and more common to drill deep karst caves as a part of deep shale gas resource exploration and engineering construction in South China. However, the amount of research on the genesis and development mechanism of deep karst caves is relatively low. Based on drilling core karst morphology analysis and two-dimensional (2D) seismic and wide-field geophysical exploration methods, it is revealed that the deep karst in the Huanjiang area is mainly composed of net cracks, holes expanding along cracks and dolomite honeycomb pores, and that large karst caves are also developed, which are related to NW-trending faults. The deep karst is developed in the hanging wall of the fault, with a width of 500 m and a height of 1500 m, and a linear distribution along NW faults in the region. Based on Th-U dating, inclusion testing and rare earth elements from cave fillings, it is revealed that the development of deep karst space is related to two deep karst genetic types: The first is the hypogene hydrothermal karst, which developed in the Yanshanian period and is related to regional magmatism. The second is the groundwater deep circulation karst, mainly developed after the Himalayan period, which is related to the deep circulation of meteoric water. The genesis of deep karst space is the result of multi-stage karst superposition and is mainly controlled by faults. It is difficult to determine the specific time points of these two types of deep karst transformation, but according to regional tectonic evolution, we speculate that the Yunnan-Guizhou Plateau has been uplifted since the Himalayan period (>3.54 Ma), and the Carboniferous carbonate rocks and early faults in the Huanjiang area have been exposed, leading to the change and evolution of deep karst. Through comprehensive analysis, a fault-controlled hypogene hydrothermal karst pattern and a meteoric water deep karst pattern are established. The genetic pattern of deep karst provides theoretical support for predicting this kind of karst in southern China and for avoiding drilling deep karst caves as a part of resource exploitation.

Comparative Study of Soil Microbial Diversity on Different Slope Orientations in Karst Rocky Mountains of Guangxi, China

“…China has the largest distribution of karst landscapes in the world, primarily found in the south-western subtropical mountains (Wang et al, 2004;Chen et al, 2021). Karst landscapes are characterized by unique carbonate rock formations (Sweeting, 1995), elevated organic matter content (Ahmed et al, 2012), a doublelayered structure (Dan et al, 2022) and limited soil-forming capacity (Liao et al, 2018). These landscapes are susceptible to disturbance, degradation, erosion, slow community succession, and pose challenges for ecosystem restoration (Zhang et al, 2021(Zhang et al, , 2022.…”