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<p>The study systematically investigates sedimentary environment and spheroidal weathering of sandstones from the Taiyuan Formation in Shimenzhai area. Regarding the sedimentary environment, grain-size cumulative curve analysis reveals a wide grain-size distribution range (0.5 mm to 5.5 mm), with a gentle, nearly straight cumulative curve and poor sorting, indicative of a high-energy gravel marine beach sedimentary environment. Regarding spheroidal weathering, based on the geometric morphology of the spheroids and their relationship with rock fabric, five morphotypes are identified: “equant spheroids”, “ellipsoids”, “oblate spheroids”, “irregular spheroids”, and “composite spheroids”. Equant spheroids exhibit uniform development and a nearly spherical shape, representing homogeneous sandstone under structural control during chemical weathering. Ellipsoids, the most common type, have long axes parallel to bedding, reflecting the control of bedding on weathering anisotropy. Oblate spheroids have a thickness significantly less than their diameter, display a lenticular shape, and are strictly distributed along bedding planes, representing extreme bedding-controlled weathering. Irregular spheroids lack symmetrical morphology, have uneven surfaces, and are closely associated with calcareous concretions, siliceous masses, and bioturbation structures. Composite spheroids include coalesced, nested, and multinucleate subtypes, recording the superposition and interaction of multiphase weathering events. The development of different spheroidal weathering morphotypes is jointly controlled by rock fabric, cement type, tectonic fractures, and weathering fluid pathways, exhibiting distinct geochemical zonation. The reverse S-shaped P-wave curve clearly indicates that the degree of spherical weathering in sandstone is negatively and physically correlated with the P-wave velocity. The study concludes that the genesis of spheroidal weathering is complex and cannot be explained by a single model. Future research should emphasize systematic investigation of pre-weathering internal rock changes.</p>

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Sandstone alternation as revealed by spheroidal weathering in the Carboniferous Taiyuan Formation of Shimenzhai Area, Liujiang Basin

  • 期刊论文

  • 发表日期：

    2026年7月27日

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  • Shiqiang Xia,
  • Hongwen Deng,
  • Zhen Liu,
  • Nadeem Ahmad,
  • Taotao Yan,
  • Wei Wu,
  • Quan Li,
  • Guiyu Dong,
  • Haigang Lao,
  • Xiaoying Han,
  • Bin Gao

摘要

The study systematically investigates sedimentary environment and spheroidal weathering of sandstones from the Taiyuan Formation in Shimenzhai area. Regarding the sedimentary environment, grain-size cumulative curve analysis reveals a wide grain-size distribution range (0.5 mm to 5.5 mm), with a gentle, nearly straight cumulative curve and poor sorting, indicative of a high-energy gravel marine beach sedimentary environment. Regarding spheroidal weathering, based on the geometric morphology of the spheroids and their relationship with rock fabric, five morphotypes are identified: “equant spheroids”, “ellipsoids”, “oblate spheroids”, “irregular spheroids”, and “composite spheroids”. Equant spheroids exhibit uniform development and a nearly spherical shape, representing homogeneous sandstone under structural control during chemical weathering. Ellipsoids, the most common type, have long axes parallel to bedding, reflecting the control of bedding on weathering anisotropy. Oblate spheroids have a thickness significantly less than their diameter, display a lenticular shape, and are strictly distributed along bedding planes, representing extreme bedding-controlled weathering. Irregular spheroids lack symmetrical morphology, have uneven surfaces, and are closely associated with calcareous concretions, siliceous masses, and bioturbation structures. Composite spheroids include coalesced, nested, and multinucleate subtypes, recording the superposition and interaction of multiphase weathering events. The development of different spheroidal weathering morphotypes is jointly controlled by rock fabric, cement type, tectonic fractures, and weathering fluid pathways, exhibiting distinct geochemical zonation. The reverse S-shaped P-wave curve clearly indicates that the degree of spherical weathering in sandstone is negatively and physically correlated with the P-wave velocity. The study concludes that the genesis of spheroidal weathering is complex and cannot be explained by a single model. Future research should emphasize systematic investigation of pre-weathering internal rock changes.