Paleosols as Indicators of Paleoenvironment and Paleoclimate

Abstract

Paleosols are ancient soils that have been incorporated into the geological record. Soils form in response to interactions among the lithosphere, hydrosphere, biosphere, and atmosphere, so paleosols potentially record physical, biological, and chemical information about past conditions near Earth's surface. As a result, paleosols are an important resource for terrestrial environmental and climatic reconstructions. Long-standing paleosol research topics include morphology, classification, and clay mineralogy, all of which provide information about pedogenic processes and local paleoenvironments. Paleosols are also used to infer processes involved in the development of stratigraphic architecture and basin evolution. Recent paleosol research has introduced semiquantitative and quantitative measures for environmental and chronometric reconstructions that provide insight into major regional to global changes in temperature, precipitation, and atmospheric pCO 2 . These new proxies focus on morphological and chemical transfer functions and stable isotope geochemistry to provide estimates of precipitation, temperature, pCO 2 , and productivity, as well as chronometric estimates of mineral crystallization in deep-time pedogenic systems. Looking forward, consensus must be reached on terminology that most effectively communicates paleosol characteristics and implies important processes. Proxy development will continue to improve as data sets become available across greater ranges of environments and timescales. 11.1

Aridification across the Carboniferous–Permian transition in central equatorial Pangea: The Catalan Pyrenean succession (NE Iberian Peninsula)

“…In the same way, the indurated calcic horizons are also commonly cracked (planar septaria of Gascón andGisbert, 1987 andAso et al, 1992). These fractures indicate expansion and retraction of the soil (Mack et al, 1993;Tabor and Myers, 2015). Other common Lower Red Unit pedotypes display no pedogenic features other than carbonate nodules composed of horizons Bk and profiles Bk-Bkk (Stages II and III of Gile et al, 1966 andMachette, 1985) (Fig.…”

“…2; Supplementary Data S2). Carbonate horizons are often linked to arid climates, but they are also developed in regions with high precipitation (AlonsoZarza, 2003;Tabor and Myers, 2015). This is also the case of indurated calcic or platy horizons: in modern soils, they generally form in sub-humid to semi-arid climates where evapotranspiration exceeds precipitation in most months of the year (Alonso-Zarza, 2003).…”

Stratigraphic Unconformities: Review of the Concept and Examples from the Middle-Upper Paleozoic

“…U-Pb dating of soil carbonates, based on U adsorbed in calcite lattice, was demonstrated to provide quantitative estimate of pedogenic processes as old as Carboniferous [49,50]. Also, the production of He isotopes by α-decay of U, Th, and their intermediate decay species was used to develop a (U-Th)/He geochronometer that is able to date materials in the range of a few thousands of years to 4.5 Ga (see review in [51]). …”

“…• Paleosol is an ancient soil or part of it that has been imprinted in the stratigraphic record [47,51]. Soil is defined as (1) the medium rooted and modified by vascular plants (narrow pedologic definition; e.g., [59]) and (2) biologically and chemically active "excited skin" of the subaerial part of the Earth's crust (broad pedologic definition; [60]).…”

Reconstruction of Late Pleistocene Paleoenvironments Using Bulk Geochemistry of Paleosols from the Lake Victoria Region

“…Paleosols provide valuable records of both paleoenvironmental and paleoclimate information (Sheldon and Tabor, 2009;Levin, 2015;Tabor and Myers, 2015), and using paleosols to reconstruct the landscape as a paleo-CZ is particularly useful for understanding hominin evolution because these paleosols represent the past surfaces upon which hominins lived. The earliest fossil remains attributed to Homo sapiens are identified in northwestern Africa at ∼315 ka (Richter et al, 2017) and in East Africa at ∼195 ka (McDougall et al, 2005).…”