Contrasting environmental memories by ancient soils on different parent rocks in the South-western Italian Alps
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Data di Pubblicazione:
2014
Citazione:
Contrasting environmental memories by ancient soils on different parent rocks in the South-western Italian Alps / M.E. D'Amico, M. Catoni, E. Bonifacio, E. Zanini. ((Intervento presentato al convegno EGU General Assembly tenutosi a Vienna nel 2014.
Abstract:
Ancient soils (pre-Holocenic paleosols and vetusols) are uncommon on the Alps, because of the extensive
Pleistocenic glaciations which erased most of the previously existing soils, the slope steepness and climatic
conditions favoring soil erosion. However, in few sites, particularly in the outermost sections of the Alpine range,
Pleistocene glaciers covered only small and scattered surfaces because of the low altitude reached in the basins,
and ancient soils could be preserved for long periods of time on particularly stable surfaces.
We described and sampled soils on 11 stable surfaces in the Upper Tanaro valley, Ligurian Alps (Southwestern
Piemonte, Italy). The sampling sites were characterized by low steepness and elevation between 600 to 1600
m, under present day lower montane Castanea sativa/Ostrya carpinifolia forests, montane Fagus sylvatica and
Pinus uncinata forests or montane heath/grazed grassland, on different substrata. In particular, we sampled soils
developed on dolomite, limestone, quartzite, gneiss and shales.
The soils were always well representative of the pedogenic trends active on the respective parent materials, i.e.
the skeletal fraction in each soil was always composed of just one rock type, despite the proximity of lithological
boundaries and the small dimensions of the different outcrops, often coexisting on the same stable surface.
All the considered profiles showed signs of extremely long pedogenesis and/or different phases of intense
pedogenesis interrupted by the deposition of periglacial cover beds in the steepest sites. Up to four phases of
intense pedogenesis were recognized where cover beds were developed, presumably during cold Pleistocene
phases, as present-day climate is not cold enough to create such periglacial morphologies. In such cases, each
cover bed underwent similar pedogenesis, strongly dependent on the parent material: on quartzite, podzols with
thick E horizons and well developed placic ones were formed in all phases except the most superficial one (i.e.
Holocene phase), where non cemented spodic horizons or weakly cemented ortstein were formed; placic horizons
were never found in Holocene soils. On limestone, each cover bed separated soils with extremely hard petrocalcic
horizons overlaid by argillic ones.
Where no cover beds were observed, podzols with extremely thick E horizons (up to more than 2 m thick) and a
very hard, very thick ortstein were formed on quartzite. Red Nitisols-like or reddish brown Luvisols were formed
on limestone and dolomite, while red, extremely acidic Alisols, with or without fragipan horizons were formed on
shales. Very large stone circles and other large patterned ground features, which can be interpreted as evidence of
past permafrost conditions, were preserved on coarse quartzitic conglomerate.
These soils represent excellent pedo-signatures of different specific past climatic or environmental conditions,
as a response of different lithologies to specific soil-forming environments, which range from warm and humid
climates typical of red Luvisols and Nitisols, to cool and wet climates leading to the formation of Podzols with
placic or ortstein horizons, to extremely cold and dry ones characterizing permafrost sites and often associated
with fragipan formation, to warm and dry leading to the cementation of petrocalcic horizons. The precise dating
and interpretation of these soils are intriguing.
Tipologia IRIS:
14 - Intervento a convegno non pubblicato
Keywords:
paleosuolo; alpi lguri
Elenco autori:
M.E. D'Amico, M. Catoni, E. Bonifacio, E. Zanini
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