**4. Paleopedology and paleoaquifer studies**

Soils blanket most of the terrestrial landscape [47]. As approximated by Landsat-based NARWidth model of North American river surface, only about 0.55% of the continent is covered with rivers [52]. This model includes measurements of rivers that are ≥30 m wide and extrapolated estimate of streams that are 1.6–30 m wide. Natural lakes and reservoirs excluding human-made impoundments cover about 3% of the World's land surface [53]. Therefore, at this momentary snap of the geologic time, it appears that no less than 96% of the land terrain is exposed above permanent water level if timed back to pre-industrial landscape. This emphasizes the high probability that a geologist will encounter in particular section a subaerial unconformity with a paleosol or what is left after its transgressive erosion, rather than non-pedogenized fluvial or lake sediments (**Figure 3**). This considers paramount importance to recognition of paleosols, regoliths, and former meteoric aquifers, although these are usually subtle features masked by diagenetic alteration and not readily picked with geophysical surveys.

Recognition of fossil soils in pre-Quaternary strata commenced early in nineteenth century with description of "dirt beds" with fossil wood stumps in the Upper Jurassic of the Dorset Coast Stratigraphic Unconformities: Review of the Concept and Examples from the Middle-Upper Paleozoic http://dx.doi.org/10.5772/intechopen.70373 107

to the *asymmetrica* zone [41]. Other workers argued that the Canol base is a conformity [42, 43] and indicated Ramparts-Canol interfingering in allochthonous debris units [41]. Nevertheless, this hiatus survived in the territorial table of formations until recently [44]. Decisive in retiring this hiatus are (1) updates in conodont data showing Canol base time gliding from the Frasnian *transitans-punctata* on top of Kee Scarp carbonate banks to the upper Givetian *norrisi* in offbank depressions [44]; (2) carbonate-bank slope depositional setting of allochthonous bioclastic debris interfingering with laminated black shales; and (3) absence of any evidence of subaerial exposure or vadose processes, like oxidation of pyrites and organic matter and characteristic

An absolute majority of disconformities are subzonal or do not bear index fossils immediately below or above. Relative proxy for the duration of a hiatus is the maturity of a paleosol profile, e.g., progression from entisols to any of mature soil profiles defined by soil taxonomy [47], or stages of calcrete development [48], but the ability to deconvolute time is quite limited: paleosol appearance is a multivariate product of exposure duration, precipitation regime, temperature, relief, availability and type of vascular vegetation (and other soil biota), and transgressive truncation, with variable masking of paleonvironmental signals by burial diagenetic overprints. Most tools of radiogenic dating used to reveal soil age are not applicable to deep-time examples because of short isotope decay lifetime. 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

Soils blanket most of the terrestrial landscape [47]. As approximated by Landsat-based NARWidth model of North American river surface, only about 0.55% of the continent is covered with rivers [52]. This model includes measurements of rivers that are ≥30 m wide and extrapolated estimate of streams that are 1.6–30 m wide. Natural lakes and reservoirs excluding human-made impoundments cover about 3% of the World's land surface [53]. Therefore, at this momentary snap of the geologic time, it appears that no less than 96% of the land terrain is exposed above permanent water level if timed back to pre-industrial landscape. This emphasizes the high probability that a geologist will encounter in particular section a subaerial unconformity with a paleosol or what is left after its transgressive erosion, rather than non-pedogenized fluvial or lake sediments (**Figure 3**). This considers paramount importance to recognition of paleosols, regoliths, and former meteoric aquifers, although these are usually subtle features masked by diagenetic alteration and not readily picked with

Recognition of fossil soils in pre-Quaternary strata commenced early in nineteenth century with description of "dirt beds" with fossil wood stumps in the Upper Jurassic of the Dorset Coast

redistribution of Fe and Mn, prior to the onset of Canol deposition [45].

106 Seismic and Sequence Stratigraphy and Integrated Stratigraphy - New Insights and Contributions

(see review in [51]).

geophysical surveys.

**4. Paleopedology and paleoaquifer studies**

**Figure 3.** Conceptual expression of disconformities: (A) in floodplain succession, formally modified from Kraus [54]; (B and C) in shallow-marine carbonate succession; (B) deposited under wet climate with precipitation sufficient for open stream drainage; (C) deposited in drier climate with underground karst drainage. Paleo-vadose zones associated with "intraformational" unconformities (not shown here for simplicity) extend to various depth beneath paleosols, depending on base level fall, and frequently overprint; lower major unconformity (LMU) and upper major unconformity (UMU); incised fluvial channels (ic); a deep incised valley (iv) developed from UMU; and overbank (ob) floodplain deposits. Units in (B) and (C) bounded by disconformity surfaces are numbered; note that depending on researcher's knowledge, they may be described as sequences if subaerial unconformities are adequately characterized, as parasequences if surfaces known but their genesis is uncertain, or merged in one sequence bounded by LMU and UMU if surfaces remain below resolution with available tools.

[55–57]. Paleopedology (study of fossil soils) is a discipline nursed on soil science, specifically Quaternary soil chronosequences [58] and later expanded back in the geologic time, even to other planets, with adsorption of geologic and biotic evolutionary concepts [47, 57]. A short glossary of basic concepts is given below.


Under different climate and hydrologic regimes, soil-forming processes create diverse soil profiles described by national and international soil classifications. The North American soil taxonomy [66] is the one that has earned greatest recognition in paleopedologic studies [47, 51]. Diagnostic criteria for pre-Quaternary paleosols and instrumental proxies for landscape and climate reconstructions are reviewed in [47, 51, 54, 67, 68].

Diagnostics of subaerial exposure profiles and paleokarst systems in carbonate rocks (**Figure 3B**, **C**) were developed by sedimentary geologists as a parallel story to paleopedology, which was driven by economic importance of karst as (1) hydrocarbon reservoir-making factor and (2) a host for bauxite [34] and rare metal accumulation [69]. This move has generated very practical terminology focused on horizons of high preservation potential, first of all caliches (calcretes) and paleokarsts, with various degree of reconciliation with the soil science lexicon [48, 69-71].
