The Albitization of K-Feldspar in Organic- and Silt-Rich Fine-Grained Rocks of the Lower Cambrian Qiongzhusi Formation in the Southwestern Upper Yangtze Region, China

Abstract

The albitization of K-feldspar is a common diagenetic process that has thus far received little attention and is not fully understood in fine-grained sedimentary rocks. To better understand the albitization of K-feldspar, studies in organic- and silt-rich fine-grained rocks of the lower Cambrian Qiongzhusi Formation in the southwestern Upper Yangtze region, China, were carried out via X-ray diffractometry (XRD) and field emission scanning electron microscopy (FE-SEM). The results show that five types of albitized K-feldspar textures have developed: microcrystal albite replacement, irregular blocky replacement along margins, cleavage planes or microcracks of K-feldspars, complete pseudomorphic replacement, albite overgrowth, and albite pore filling. Organic- and silt-rich fine-grained rocks differ from sandstones and mudstones in terms of the rock structure and mineral assemblage, which results in differences in the textures and degree of albitization of K-feldspar. Illitization of clay has an impact on the albitization of K-feldspar. In provenance analyses using feldspar, fine-grained rocks, especially those that underwent mesogenesis, should be treated with caution because detrital feldspars have been destroyed. Theoretically, the albitization of K-feldspar could increase the porosity of reservoirs, although, from our observations, most of the related secondary pores are cancelled out or became isolated pores due to other diagenetic processes (compaction, cementation, etc.) in organic- and silt-rich fine-grained rocks.

Diverse Behaviors of Feldspar Grains during Sandstone Diagenesis: Example from the Xujiahe Formation in the Western Sichuan Basin, China

“…One assumption that could explain the diagenetic destruction of K-feldspar but retention of plagioclase is albitization. In some sedimentary sequences from other basins, the albitization process has been shown to be important for the largescale destruction of detrital K-feldspars [79][80][81]. If this is the case for our Xu-2 samples, the previously existing detrital K-feldspars in the uppermost samples must have been overall albitized.…”

Impact of Minerals and Sealing Systems on the Pore Characteristics of the Qiongzhusi Formation Shale in the Southern Sichuan Basin

“… 23 Additionally, the pores in some feldspars may be related to the albitization of K-feldspar. Min et al 44 observed the albitization of K-feldspar in the Qiongzhusi Formation shale and suggested that feldspar shrank in bulk and formed new pores, which were often filled with OM, clay, and pyrite during the diagenetic process. Compared to OM, siliceous minerals often cannot adsorb methane, 11 but IntraP pores modified by OM in feldspar might provide adequate adsorption space for shale gas.…”

The effect of composition and holding time on glaze production using basalt rock as a base

“…In speciments A, B, and C, by extending the holding time for making the glaze, several SiO2 compounds read from quartz and coesite tended to associate to form feldspar plagioclase bonds. This phenomenon is influenced by the reduced feldspar composition triggering SiO2 to associate more to form aluminosilicate(Min et al, 2019).The phases formed in the characterization of B8 and C1 glaze have similarities with the phases formed in the study(Andrić et al, 2012) including olivine, anorthite, and pyroxene phases. In another study, it was also stated that the phases formed were magnetite, anorthite and quartz (Gultekin E. E, 2018).…”

“…In speciments A, B, and C, by extending the holding time for making the glaze, several SiO2 compounds read from quartz and coesite tended to associate to form feldspar plagioclase bonds. This phenomenon is influenced by the reduced feldspar composition triggering SiO2 to associate more to form aluminosilicate (Min et al, 2019).…”