Evaluation and formation model of Cambrian high-quality source rocks in the southeast margin of North China Plate

Abstract

In response to the question of whether effective Cambrian source rocks are developed in the North China Plate, field investigations on the southern margin of North China have been carried out. High-quality marine argillaceous source rocks of continuous thickness of 35 m in the Lower Cambrian were discovered in the south-eastern margin of North China Plate. Phosphorus nodules are common in the source rocks. The TOC is 1.19%∼29.70%, with the average of 7.31%. The organic matter comes from low-level biological algae. Because the carbon isotope of kerogen is relatively more negative, it is judged to be mainly benthic algae. The converted vitrinite reflectance (Ro) from measured bitumen reflectance is 2.24%∼3.45%, which is an over-mature source rock. The Lower Cambrian source rocks in the southern margin of North China occurred under the background of rising sea levels. After the glaciers on the southern margin of the North China Plate melted, the Qinling rift trough developed and the stratum subsidence caused rapid transgression of seawater from southeast to northwest. At this time, algae multiply in large numbers, and after death they accumulate with phosphorus-containing materials to form phosphorus-containing organic matter. Benthic algae mainly live in deep-water shelf not affected by waves and tides. Therefore, the development of source rocks is mainly in the deep water shelf.