Il giacimento fossilifero pleistocenico superiore di Moncucco Torinese

The Moncucco Torinese upper Pleistocene fossil deposits

Abstract

An account is given of the various features of fossil deposits rich in flora (pollens, a fungus, woods, spores) and fauna (molluscan fauna, Vertebrates, and micromammals) discovered a few years ago in continental deposits on the southern slope of the Collina di Torino Monferrato hills. The deposits are formed of grey silts, with sub horizontally layered peaty intercalations. The silts form an up to 5 m thick lenticular body that filled a depression and appears to be covered with an approximately 3 metres thick bed composed of brown-yellowish silts. Their geometry, lithofacies, and paleontological contents indicate that the fossil-bearing sediments represent the filling up of an oxbow swamp: the overlying silts are the result of river overflow and underlie a paleosol with an alteration thickness of 3 meters, marked by weak oxidization of iron compounds (color 10 YR 5/4) and slight clay formation with very discontinuous patinas. The geological data showed that the fluvial deposits are linked to a drainage pattern that is completely different to the present one. The differences lie not only in the catchment basin, which was much more extensive, since it included the entire S Piedmontese basin as opposed to just the hilly area, but also the size, organization, and arrangement of the stream net. The previous pattern includes a few main branches draining from W to E, whereas today several equally important watercourses flow to both the E and the W, and the affluent system runs almost at right angles. Its high flow rates and very gentle slopes of the previous network point to a virtual absence of distinct reliefs. The deposits are linked to a left-hand affluent from the S slope of the Rilievo del Monferrato. This formed part of the older pattern, whose main collector flowed further to the S in the Altopiano di Poirino – Rilievi dell’Astigiano sector. They form a terraced strip preserved within a broad valley (average width: 600 m) running N-S. This has since been reshaped to a considerable extent. The fossil flora includes: a fungus (Ganoderma applanatum), conifer strobilus (Pinus diploxylon «grande»), woods (Abies nordmanniana and Pinus diploxylon «grande»), pollens and spores (the arboreal species being mostly Pinus diploxylon « grande », P. silvestris, Alnus sp.; the non-arboreal Myryophyllum, Graminaceae, and Cyperaceae). The molluscan fauna includes typical species, such as Vallonia costata (MULLER), Discus (D.) rotundatus (MULLER) and Cochlodina (C.) laminata (MONTAGU). Vertebrates are represented by the teeth of Bos sp. and fragments of Cervus elaphus antlers. The micromammals include Talpa, Sorex, Apodemus, Clethrionomys, Pitymys savii, Microtus arvalis and Microtus agrestis. The several specialists engaged on the study independently came to the same conclusion concerning the age and paleoambient features of the bed, namely upper Pleistocene and a damp, temperate climate. Carbon-14 dating of two wood fragments indicated an age of over 40000 and 45000 yr respectively. Evaluation by means of the amino-acid racemisation method on four Bos sp. teeth gave a spread of value around 40000 and 20000 years respectively. Only the older value refers to the deposits, since the more recent value is probably attributable to filling of a posterior karstic cavity. These findings are of general importance insofar as they offer a fully calibrated element for appraisal of the pedostratigraphy of N-Italy. They are also of local interest for their presentation of a chronological benchmark for reconstruction of the recent development of the Piedmontese hills. This led to the almost total establishment of the present relief, and diversion of the S-Piedmont basin collectors to form the present Po and Tanaro rivers.