Pedogenic carbonates as a proxy for palaeo-CO2 in the Palaeozoic atmosphere

Abstract

According to a model by Cerling (1991Cerling ( , 1999, the carbon isotope composition of calcretes should depend on the soil type and the CO 2 -concentration in the atmosphere. We have tested Cerling's model by investigating 14 Palaeozoic sections with soil profiles. A large number of carbonate types of different genetic origin exist in the localities examined. Comparing the Palaeozoic samples with recent and subrecent calcretes, it can be demonstrated that anhedral, cryptocrystalline (<10 µm) and subhedral microcrystalline (10 -40 µm) carbonates are clearly of pedogenic origin. Crystals of larger size with a poikilotopic texture are of groundwater or burial diagenetic origin. Macro-and micromorphological features, typical of recent calcretes, occur in several soil profiles, but thin section microscopy reveals a strong diagenetic overprint of most pedogenic carbonates. Time equivalent sections with comparable soil types (protosols, calcisols and vertisols) show large variations in carbon isotope composition. On the other hand, different carbonate generations at one site do not differ much. Therefore Palaeozoic calcretes appear to be unsuitable for a deduction of the Palaeozoic CO 2 -concentration.

The origin and significance of pedogenic dolomite from the Upper Permian of the South Urals of Russia

“…5b) surrounded by a coarser microcrystalline matrix (cf. Wright & Tucker, 1991;Quast, Hoefs & Paul, 2006). Occasional (< 1 %) 'floating' grains of very fine quartz (95 μm) are observed that have been replaced by the growth of carbonate (Fig.…”

The terrestrial landscapes of tetrapod evolution in earliest Carboniferous seasonal wetlands of SE Scotland

“…However, it can also be a later diagenetic fabric in which the crystal 458 contacts are characteristically concavo-convex (Fig. 7C), and enclose smaller patches of 459 microcrystalline dolomite (Quast et al, 2006). Most of the carbonate found in the palaeosols 460 in the Ballagan Formation exhibits alpha textures, although the calcified root traces (Fig.…”

Pedogenic carbonates: Forms and formation processes

“…Deviations from these assumptions reveal uncertainties in chronological and reconstructional studies based on PC (Cerling, 1991;Pustovoytov and Leisten, 2002;Quast et al, 2006). Because recrystallization rates depend on various biotic and abiotic factors (Gocke et al, 2011b;Gocke and Kuzyakov, 2011), the resulting errors will differ, especially where recrystallization is relatively fast, e.g.…”

“…Moreover, the difference of δ 13 C values of the remaining GC to that of PC (Fig. 10) leads to a less negative δ 13 C of PC (Pendall et al, 1994;Quast et al, 2006) and consequently to doubtful paleoecological interpretations.…”