Discussion Of The Relationship Between Tectonic Activity Of The Ordovician Central Paleouplift And The Palaeokarst

Ordos Basin, the Chinese second largest petroleum basin, is located in the central China. The central paleo-uplift in the Ordos Basin is an important hydrocarbon accumulation zone. So the research on the central paleo-uplift is now a hot topic and attracting lots of attentions.In this dissertation, we begin with the research of the development of the Ordovician Palaeokarst in the Ordos Basin, trying to establish a semi-quantitative method to identify Palaeokarst. Then through the relationship between the Palaeokarst and the Palaeotectonic activity, we find the internal relations between the Palaeokarst and the tectonic evolution of the paleo-uplift in the Ordovician Ordos Basin and propose an evolutional model. It is a new idea and method for the paleo-uplift study.Several techniques have been evoked to indentify the palaeokarst including observation, description, slice identification and apparent porosity analyse of core samples. With these identification methods, we can determine the features and scale of the Ordovician Palaeokarst in the Ordos Basin and establish the single well karst histograms. Then using these histograms, we establish six connecting-well sections and determine three stages of palaeokarst zones which relate to paleo-structure.Integrating the six sections, we find that the high point of the palaeokarst migrated from east to west. And in the plane distribution maps of the palaeokarst stages, we also find that the region with the maximum thickness of the palaeokarst migrated from east to west. Meanwhile, the sedimentary depocenter and the region with maximum palaeokarst thickness show corresponding relationship in the eastern part of the paleo-uplift. Therefore, we suggest a model to interpret the relationship between the paleo-uplift and the karstification, in which the paleo-uplift occurred during Ordovician and migrated from east to west.