Micromorphology and formation of pedogenic ooids in calcic soils and petrocalcic horizons

Paleoenvironmental Analysis of (Petro)calcic Soil Horizons in the Mojave Desert

“…Field work measuring section, describing soil profiles, and sampling was conducted in June, 2018. Three sites were chosen for detailed analysis: (1) the previously studied Mormon Mesa Riverside site (e.g., Brock and Buck, 2009;Brock-Hon et al, 2012;Robins et al, 2012;Robins et al, 2014;Robins et al, 2015), and two previously undescribed profiles in exposures at (2) Flat Top Mesa East, and (3) Flat Top Mesa West (Figure 2). Additionally, surface samples (top 10 cm) were collected for geochemical analysis from two Mormon Mesa transects, one Flat Top Mesa transect, and from representative geomorphic features on both mesas.…”

“…The Mormon Mesa soil profile ( Figure 3) has been previously described and variably interpreted (Gardner, 1972;Bachman and Machette, 1977;Brock and Buck, 2009;Soil Survey Staff, 2019). Its currently accepted geomorphic history was interpreted by Brock and Buck (2009), and models for its mineral evolution (Robins et al, 2012) and the genesis of its pedogenic ooids (Robins et al, 2015) have been recently published also. The uppermost MCF strata exhibit carbonate nodules (a stage II paleosol), and are capped by a popcorn-textured, stage III "transitional" horizon forming the base of the Mormon Mesa profile (Brock and Buck, 2009).…”

“…Locally, fluvial incision and backfilling has produced younger, nested profiles with petrocalcic horizons that cross-cut the older soil (Conley et al, 2018). Further, pedogenic laminae, pisoliths (e.g., irregular, > 2mm concretions indicative of rotation), dissolution voids and other features reflect complex episodes of calcite precipitation, horizon brecciation, and re-cementation (Brock and Buck, 2009;Robins et al, 2015).…”

“…For instance, the model inadequately illustrates the mineralogical evolution of (petro)calcic horizons (e.g., Robins et al, 2012), each of which can include unique assemblages including palygorskite, sepiolite, and even barite (Brock-Hon et al, 2012) or fluorite (Bouza et al, 2007). Nor does the model address the timing and evolution of all micromorphological features found in calcic horizons, for instance excluding pedogenic ooids (Robins et al, 2015). Finally, the model is horizon-centric, meaning that individually tailored profile-scale models (e.g., Alonzo-Zarza et al, 1998;Brock and Buck, 2009;Alonzo-Zarza and Silva, 2002) must be developed on a site-by-site basis for polygenetic profiles, and for any soil with more than one calcic or petrocalcic horizon.…”

Sea-level fluctuations in the late Middle Permian estimated from palaeosols of the Sichuan Basin, SW China

“…These are distinct from pedogenic carbonates, which commonly show a mixture of calcite with phyllosilicates, quartz and other minerals, and have various sizes and forms, e.g. fracture fillings or brecciated fragments (Khormali et al 2006;Wanas & Abu El-Hassan, 2006;Cleveland et al 2008;Robins et al 2015).…”