A quantitative approach to soil occurrence in alluvial deposits and its application to the Old Red Sandstone of Britain

Abstract

Palaeosols (fossil soils) are a major component of alluvial deposits in the geological record. Not only do these typically show considerable variations in their degrees of development within single formations, but they also exhibit highly complex stratigraphic relationships with one another. A simple quantitative approach to these variations is presented which provides a graphical means of assessing differences in soil (palaeosol) development within a sequence with calcic or petrocalcic horizons. To illustrate the approach, a range of palaeosols from the Siluro-Devonian (Old Red Sandstone) of Britain are characterized in terms of the likely frequency and magnitude of depositional events which occurred during their formation. In particular, two alluvial suites from the Manorbier area of South Wales are analysed using this approach. The technique should be widely applicable to other alluvial successions and provides a means of graphicallv presenting relationships between multiple palaeosols, although the wide range of rates of formation of calcic and petrocalcic horizons precludes their use to provide narrow estimates of deposition rates.

Taphonomical and palaeoecological investigation of the Late Cretaceous (Maastrichtian) Tuştea vertebrate assemblage (Romania; Haţeg Basin) - insights into a unique dinosaur nesting locality

“…The presence of calcic horizons (stage 3 type according to Tucker, 1991 andMarriott, 1996; Fig. 2A) inside the well-developed paleosol section (Unit 1+…”

“…However, the thickness of sediment increments deposited during high flood events was larger than that of an individual paleosol horizon, which led to the stacking of successive paleosol profiles in the Tuştea succession (Wright and Marriott, 1996;Kraus, 1999;Therrien, 2005). Moreover, the paleosol horizons at Tuştea show incomplete profiles where the "A horizon" is not represented, most probably because this soil horizon was overprinted by the pedogenic features of a second paleosol that developed on top of it (see also Therrien, 2005).…”

“…Moreover, the paleosol horizons at Tuştea show incomplete profiles where the "A horizon" is not represented, most probably because this soil horizon was overprinted by the pedogenic features of a second paleosol that developed on top of it (see also Therrien, 2005). The composite paleosol profile with calcrete horizons (at a Stage 3 of development) indicates a depositional environment where sedimentation rates were usually low, but significant amounts of fresh sediment were deposited periodically during peak flood events (e.g., Wright and Marriott, 1996).…”

“…(3) Evapotranspiration exceeded precipitation during the drier periods of the subhumid climate that characterized the Tuștea locality sedimentation (Therrien, 2005: Bojar et al, 2005, 2010b and thus the meteoric water evaporated before reaching the watertable, which resulted in the precipitation of dissolved carbonates forming the calcic (B k ) horizons at the Tuştea site (e.g., Wright and Tucker, 1991;Wright and Marriott, 1996;Khadkikar et al, 2000). (4) These circumstances created a thick pedogenically-modified red mudstone with secondary carbonate precipitation that formed calcic horizons situated around the average depth of rainfall or soil water percolation (Wright and Marriott, 1996;Therrien, 2005;Retallack, 2008), depth which, in the case of the Tuştea site, was up to 40 cm deep according to Bojar et al (2010b). The welldeveloped geochemical trends (reported by Therrien, 2005) and the presence of well-defined calcrete horizons in the section suggest that pedogenesis was uninterrupted by the addition of new material to the paleosol profile, thus indicating a prolonged period of pedogenesis between two higher-magnitude aggradation events.…”

Palaeoenvironmental significance of palustrine carbonates and calcretes in the geological record

“…If sedimentation is steady, thick cumulative soils can form (Kraus, 1999); thick laminar caleretes are a good example of this situation (Alonso-Zarza et aI., 1998a) . Wright and Marriott (1996) have ellabo rated a quantitative and more sophisticated model to estimate the rates of fl oodplain aggradation using ca1cretes. These authors consider that the residence time of the sediments in the zone of active pedo genesis is controlled by the frequency of the deposi tional events and by the thickness of sediment deposited in each event.…”