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Open AccessArticle

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

1
State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation, Chengdu University of Technology, Chengdu 610059, China
2
College of Energy Resources, Chengdu University of Technology, Chengdu 610059, China
3
School of Geoscience and Technology, Southwest Petroleum University, Chengdu 610500, China
4
Shale Gas Evaluation and Exploitation Key Laboratory of Sichuan Province, Chengdu 610091, China
5
Sichuan Keyuan Testing Centre of Engineering Technology, Chengdu 610091, China
6
PetroChina Dagang Oilfield Company, Tianjin 300280, China
*
Authors to whom correspondence should be addressed.
Minerals 2019, 9(10), 620; https://doi.org/10.3390/min9100620
Received: 23 September 2019 / Accepted: 3 October 2019 / Published: 8 October 2019
(This article belongs to the Special Issue Mineralogy of Shale Gas and Other Low Permeability Reservoirs)
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. View Full-Text
Keywords: albitization of K-feldspar; diagenesis; fine-grained rocks; Qiongzhusi formation albitization of K-feldspar; diagenesis; fine-grained rocks; Qiongzhusi formation
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Min, H.; Zhang, T.; Li, Y.; Zhao, S.; Li, J.; Lin, D.; Wang, J. 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. Minerals 2019, 9, 620.

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