四川盆地晚中生代古淋溶土发生学特征与形成因素研究

目的]理解和揭示深时古土壤的形成与演化有助于了解地球宜居性的形成与演化、促进土壤发生学理论的发展.方法]以四川盆地晚中生代侏罗系和白垩系地层发育的古土壤为研究对象,通过对典型剖面的形态与微形态、矿物组成、颗粒组成以及地球化学等发生学特征的观察与分析,开展深时古土壤发生学特征与分类研究,并基于母质、气候、生物、地形和...

Pedogenesis of Argosol-like Paleosol Formation in the Late Mesozoic Sichuan Basin

  Objective  Understanding and revealing the details of genesis and evolution of soils in deep time can help us know the formation and evolution of the habitable Earth and advance the development of theory in soil genesis.  Method  In this paper, a total of 30 paleosol profiles, developed on the Jurassic and Cretaceous strata of the Mesozoic Era in the Sichuan Basin, Southwest China, were identified and characterized macro- and micromorphologically and assessed for mineral, particle size distribution, and geochemical compositions to summarize their pedogenic characteristics, to perform their classification and reference, and to further discuss the deep-time paleosol-forming processes based on the soil-forming factors (i.e., paleoclimate, topographic setting, organisms, parent material, and time).  Result  The investigated paleosols of the late Mesozoic Sichuan Basin comprise distinctive pedogenic characteristics that include the evidence of root traces, presence of color variations, and development of soil structures and argillic horizons. All the paleosol horizons were predominantly made up of quartz, feldspar and calcite in mineralogy with minor proportions of smectite, chlorite, goethite, illite and muscovite. From top of the paleosol profile to bottom, as the CIA-K value increased, it was accompanied by an increase in clayeyness (Al₂O₃/SiO₂) and leaching (Ba/Sr) and consequently lessens in base loss (ΣBases/Al) values.  Conclusion  Formation factors of paleosols showed that paleosols formed in well-drained environments of the abundant vegetation ranging from woodland to open forest. Moreover, these paleosols are weathering products of sedimentary and residual deposits which developed under climates of MATs ranging from 10 ± 4.4 ℃ to 13 ± 4.4 ℃ and MAPs ranging between 515 ± 182 mm year?1 and 1 140 ± 182 mm year?1. The time factor lasted for over 10 ka, allowing paleosols to develop with Bt-horizons and block structures.