Formation and Evolution of a Paleosol across the Lower Silurian‐Lower Permian Boundary in Zunyi District, Northern Guizhou, China and Its Paleoenvironment and Paleoclimate Implications

Abstract

This paper presents a set of bulk geochemical and mineralogical data from a paleoweathering profile located in Zunyi District, Northern Guizhou, China. It was formed at the top of the Hanjiadian Formation of the Lower Silurian. A truncated, argillic, gleyed, kryptic paleospodosol is recognized in the paleoweathering profile. Ratios of immobile elements (Ti/Zr, Ti/Al) and their binary (e.g., Nb vs. Zr/TiO2 and Th/Sc vs. Zr/Sc), triangular diagrams (La‐Th‐Sc, Th‐Sc‐Zr/10, Zr‐Cr‐Ga) reflect that the Gaojiayan paleosol is the product of in‐situ weathering of gray‐green silty mudstone of the underlying Hanjiadian Formation. Mass balance calculations indicate K enrichment and Na enrichment in the upper and lower portions of paleosol, respectively. These findings both are the results of transgression, which brings substantial concentrations of such elements as K, Na, and Sr. In particular, K enrichment is achieved by the illitization of kaolinite. The biological processes of terrestrial vascular plants also enhance K concentration, especially at the top of the paleosol. Na enrichment is a consequence of albitization and/or adsorption by clay minerals through cation exchange. The mass distributions and relative mass changes of rare earth elements (REEs) in the studied profile display characteristics of vertical zonation. Three peaks in total REEs content are observed, indicating two paleoclimatic or paleoenvironmental changes. Mineralogical characteristics indicate that the paleoclimate changed first from warm and humid to cold and dry and later, to dry and lightly warmer. The corresponding soil environment varies from weakly acidic to strongly alkaline and later, to weakly acidic. Mass translocation characteristics of REEs and several transition metals suggest that the Gaojiayan paleosol may have undergone top erosion.

Multiproxy Paleosol Evidence for Jurassic Paleoclimate Fluctuations in the Sichuan Basin, SW China

“…Soils, which are developed at the Earth's surface, are considered a comprehensive product of organisms, climate, time, parent material, and topography (Retallack, 2001;Tabor et al, 2017). Paleosols, known as fossil soils, can potentially provide an archive of stratigraphic, ecological, hydrologic, geographic, environmental and climatic conditions that are preserved in continental settings during their formation (e.g., Retallack, 2001;Sheldon and Tabor, 2009;Tabor and Myers, 2015;Tabor et al, 2017;Guo et al, 2019;Lü et al, 2022), especially with respect to paleoclimatic and paleoatmospheric CO 2 conditions (e.g., Huang et al, 2012;Breecker and Retallack, 2014;Xiong et al, 2015;Li et al, 2016;Gao et al, 2021). Additionally, paleosols have served as potential indicators for environmental change in response to critical geological events throughout geological history (e.g., Huang et al, 2013;Zhang L et al, 2018;Li J et al, 2020a;Retallack, 2021).…”