Effects of diabase intrusions on surrounding clastic rock reservoir in early diagenetic stages: A case study of the Early Permian Fengcheng Formation in the Dabasong uplift, Junggar Basin

Abstract

A stage of mafic magmatic activity occurred in Early Permian in the Dabasong Uplift of Junggar Basin, part of the magma intruded into the normal sedimentary and shallow buried fine sandstone to form diabase, and part of the magma erupted to form basalt. The surrounding fine sandstone just entered in the early diagenetic stage A when the magma intruded. The compaction of the surrounding clastic rock and rupture of a small number of clastic grains were caused by the extrusion of the magma intrusion. The presence of chemically deposited alkaline minerals such as calcite, dolomite, shortite, natural alkali, and northupite indicates an alkali lake sedimentary environment for the Fengcheng Formation. Primary alkaline minerals dissolved from the surrounding rocks were subsequently transported and precipitated to form cements. The formation of the calcite cements and calcite metasomatism resulted in considerable densification of the surrounding rock during early diagenesis and destruction of the reservoir quality. The mafic magma had abundant Fe2+ and Mg2+ ions and was deficient in K+ ions, resulting in large amounts of chlorite and iron precipitation in the surrounding rock mainly composed of clay. We have analyzed the influence of an ultrashallow intrusion on the surrounding clastic rock during the early diagenetic period, which provided a typical reference for establishing a systematic mechanistic model of how magmatic intrusions affect the surrounding rock.

Impact of magmatic intrusion on diagenesis of shallow marine sandstones: An example from Qasim Formation, Northwest Saudi Arabia

“…The injection of magmatic fluids into cooler sandstone reservoirs can have significant impacts on porosity (Einsele et al, 1980;Senger et al, 2014;Sydnes et al, 2019b;Haile et al, 2019). The extent of magmatic sill-induced diagenetic alterations in sandstones largely depends on their proximity to the sill, the thickness of the sill, the depth at which the sill intrusions occur, and the clusters of the sill (Aarnes et al, 2011;Sydnes et al, 2019b;2019a;Chen et al, 2021). Previous studies on the role of magmatic intrusions on sandstones porosity evolution and diagenesis have come to contrasting conclusions of both positive and negative impacts on porosity (Feng and Tang, 1997;Mckinley et al, 2001;Grove et al, 2017;Chen et al, 2021).…”

“…The extent of magmatic sill-induced diagenetic alterations in sandstones largely depends on their proximity to the sill, the thickness of the sill, the depth at which the sill intrusions occur, and the clusters of the sill (Aarnes et al, 2011;Sydnes et al, 2019b;2019a;Chen et al, 2021). Previous studies on the role of magmatic intrusions on sandstones porosity evolution and diagenesis have come to contrasting conclusions of both positive and negative impacts on porosity (Feng and Tang, 1997;Mckinley et al, 2001;Grove et al, 2017;Chen et al, 2021). In the present study, intergranular porosity Frontiers in Earth Science frontiersin.org decreases away from the magmatic sill contact (Figure 18A).…”