STRATIGRAPHIC ARCHITECTURE AND QUATERNARY EVOLUTION OF THE AGRI INTERMONTANE BASIN (SOUTHERN APENNINES, ITALY)

The Agri Valley is a NW-SE oriented intermontane basin located in the axial zone of the Southern Apennines mountain belt, filled by Quaternary continental deposits. Faults responsible for the basin formation, mainly oriented according to N120\ub0\uf0b110\ub0 and N50\ub0-55\ub0 trends, dissected the Southern Apennines fold and thrust belt and determined the sedimentary evolution of the basin during Pleistocene. The basin consists of three tectonically controlled and diachronous depocenters, bounded by WNW-ESE and NE-SW faults; outcrops occur in the south-eastern one, which was deeply dissected by the drainage network during the Late Pleistocene-Holocene. In this area, four allostratigraphic units represented by lacuo-palustrine and fan-delta, axial braid-plain and alluvial fan deposits accumulated in response to changes in intrabasinal subsidence, catchment relief, regional tectonics and climate. These units form the Agri Valley Allogroup, up to 100 m thick. Their erosional boundaries can be associated with preserved weathering profiles and/or paleosols. The latter developed at the top of alluvial fans (fed from both the northern and southern sides of the basin) and on the NW-SE axial alluvial plain, during geomorphological stability stages. Physical stratigraphy, facies associations, architectural elements and geopedological characterization (mainly micromorphological) are the key to decipher the sedimentary evolution of the basin and the contemporaneous palaeogeographic and climatic changes. This information, in combination with OSL, 14C, AFTA dating methods, provide insights into the tectono-sedimentary evolution of the area during the Pleistocene

STRATIGRAPHIC ARCHITECTURE AND QUATERNARY EVOLUTION OF THE AGRI INTERMONTANE BASIN (SOUTHERN APENNINES, ITALY)

The Agri Valley is a NW-SE oriented intermontane basin located in the axial zone of the Southern Apennines mountain belt, filled by Quaternary continental deposits. Faults responsible for the basin formation, mainly oriented according to N120\ub0\uf0b110\ub0 and N50\ub0-55\ub0 trends, dissected the Southern Apennines fold and thrust belt and determined the sedimentary evolution of the basin during Pleistocene. The basin consists of three tectonically controlled and diachronous depocenters, bounded by WNW-ESE and NE-SW faults; outcrops occur in the south-eastern one, which was deeply dissected by the drainage network during the Late Pleistocene-Holocene. In this area, four allostratigraphic units represented by lacuo-palustrine and fan-delta, axial braid-plain and alluvial fan deposits accumulated in response to changes in intrabasinal subsidence, catchment relief, regional tectonics and climate. These units form the Agri Valley Allogroup, up to 100 m thick. Their erosional boundaries can be associated with preserved weathering profiles and/or paleosols. The latter developed at the top of alluvial fans (fed from both the northern and southern sides of the basin) and on the NW-SE axial alluvial plain, during geomorphological stability stages. Physical stratigraphy, facies associations, architectural elements and geopedological characterization (mainly micromorphological) are the key to decipher the sedimentary evolution of the basin and the contemporaneous palaeogeographic and climatic changes. This information, in combination with OSL, 14C, AFTA dating methods, provide insights into the tectono-sedimentary evolution of the area during the Pleistocene

EVOLUZIONE QUATERNARIA DEL BACINO INTERMONTANO ALTA VAL D\u2019AGRI

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Stratigraphy and sedimentary evolution of the Quaternary Agri Valley Basin (Southern Apennines, Italy)

The high Agri River valley is a WNW-ESE oriented intermontane basin located in the axial part of the Southern Apennines. The basin developed after strike-slip and extensional deformation which affected the pre-existing fold-and-thrust belt since the lower Pleistocene. In the south-eastern portion of the Agri Valley Basin, the Pertusillo depocenter exposes the Quaternary succession, more than 100 thick. The palaeogeography and the basin evolution were reconstructed by a new field survey of the intermontane basin fill, closely integrating physical stratigraphy, facies analysis, geopedology methods with different dating techniques (14C, OSL and AFTA). We present a new stratigraphic framework for the outcropping part of the Agri Valley Basin fill, which has been subdivided into four allostratigraphic units, following the recognition and correlation of the major basin-wide unconformities. The lowermost Lago di Pietra del Pertusillo Alloformation (I, Middle Pleistocene) is composed of lacuo-palustrine silty-clay and silt with interbedded fan-delta lens-shaped gravel bodies, prograding into the lacustrine area. Sources were from both the western and the southern slopes of the basin. Upward-coarsening sequences are common in the fan fringe lacustrine deposits where carbonate layers, root traces and vertebrate remains occur locally. The erosional surface between Alloformations I and II delineates the change from lacustrine to alluvial environment (Valle del Nasillo Alloformation; II, Middle-Late Pleistocene). The latter includes coarse-grained conglomerates and gravels with subordinate silts and fine sands deposited in coalescent alluvial fans. The fans prograded north-northeastwards, forming wedge-shaped bodies that filled the lacustrine area. In the upper part of Valle del Nasillo Alloformation, a laterally continuous, truncated fersiallitic palaeosol indicates decreasing aggradation rate during a fan-surface stability stage. This palaeosol suggests a rather humid climate with hot and dry seasons, alternating with semiarid ones, and provides a key-surface for correlation at the basin-scale. Subsequently the fans retreated and were overlain by the deposits of an axial braided alluvial system (Vallone dell\u2019Aspro Alloformation; III, Late Pleistocene) that drained towards the SE. This unit is made up of multistory gravel/sand bodies (channel fills and gravel-sand bars). The poorly drained environment of the alluvial plain is documented by hydromorphic palaeosols. Transverse alluvial fan bodies interfinger with the axial unit from the southern and northern basin margins. A centimetre thick ash-fall deposit is locally preserved in the intermediate portion of this unit. Chemical composition and OSL chronology, suggest to correlate this layer with the Tufo Verde Epomeo of Ischia and the pyroclastic fall deposit Y-7 recognised in the central Mediterranean cores, dated as 56 ka. The proposed correlation suggests an Upper Pleistocene age for the upper part of Alloformation III. As a consequence, the Middle-Late Pleistocene age of Alloformation II at present can be only inferred. The boundary between Alloformations III and IV (Torrente Casale Alloformation, Late Pleistocene-Holocene?) is an erosional surface, locally underlined by the remains of a reddish brown palaeosol. Alloformation IV is represented by prograding-aggrading coarse alluvial fan deposits developing from both the northern and the southern borders of the basin. Asymmetric subsidence in the Middle(?)\u2013Late Pleistocene Agri Valley Basin is indicated by the accumulation of a very thick pile of aggrading deposits, restricted to the north-eastern faulted margin of the basin (alloformations I and III; unpublished subsurface data). The alluvial depocenter gradually moved towards the south-western border of the Agri basin during the latest Pleistocene, testifying to the shift of maximum subsidence towards the opposite (southern) basin margin

Soil evolution and origin of landscape in a late Quaternary tectonically mobile setting : the Po Plain-Northern Apennines border in Lombardy (Italy)

The interactions among Quaternary (paleo-) soil-forming, erosion, re-deposition and geomorphic processes at the origin of the present-day landscape are discussed at three isolated tectonic reliefs of the Southern Po Foredeep Basin of Lombardy (San Colombano, Casalpusterlengo and Zorlesco reliefs, Italy). These sites offer the possibility to combine different scales of geopedological, geomorphological, stratigraphic and structural ob- servations, to unravel the contribution of climate and tectonics to the Quaternary geological evolution and to the origin of the landscape. Field surveys, laboratory analyses and soil micromorphology were used to characterize the Late Quaternary pedogenic processes acting on different (paleo)-surfaces, in combination with the detailed study of seven se- lected soil profiles. Pedo-stratigraphic correlations revealed that two alluvial/loess-paleosol sequences, which originated from the Late Pleistocene to Holocene glacial/interglacial fluctuations, are differently preserved throughout the present-day hill landscape. In situ paleosols allowed to localize the paleo-topographic surfaces of geomorphic, tectonic and sedimentary stabilization; redeposited paleosols, occurring systematically close to the main faults and/or at the erosional bottom of paleo-valleys, allowed to mark the stages of tectonic instability. The integrated approach contributed to unravel the composite nature and rank of the stratigraphic boundaries. Polycyclic loess-soil aggradation characterized the stable paleo-highs, uplifted during different phases of active thrusting of the northernmost Emilian arcs of the Apennine, while valley incision, fluvial terracing, soil truncation and redeposition occurred in the intervening structural lows. In the San Colombano hill area, Late Pleistocene transtensional faulting induced changes of the drainage network and enhanced redeposition of pa- leosols in colluvial wedges on the hangingwalls, along the fault scarps. LGM loess was preserved above different dissected remnants of the paleo-topography composing the hilltops. These new constraints permit to refine the Late Quaternary tectono-depositional history and landscape evolution at the southern margin of the Po Basin

Paleoclimatic significance of the last interglacial paleosols of the Baratti Gulf cliff section (southern Tuscany, Italy)

Paleopedological studies of littoral deposits provide potentially useful tools for understanding the response of the sedimentary systems to tectonics (i.e. uplift and subsidence) versus climate and sea- level changes occurred along the Mediterranean coasts, during the late Quaternary. An example is reported from the Baratti Gulf cliff section formed during the last interglacial cycle. The upper Pleistocene-Holocene succession of the Baratti Gulf exhibits significant vertical changes from marine to continental deposits, marked by several erosional discontinuities. Four stacked transgressive units capped by buried weathering profiles have been recognized (Cortemiglia et a!., 1983). These transgressions, recorded by foreshore to upper shoreface deposits (Sarti eta!., 2005), should correspond to four sea-level high-stands correlated with MIS 5c, MIS Sa, MIS 3 and the transition of MIS 2-1, respectively (Mauz, 1999). A continental deposit of aeolian origin with an oligotypical mollusc assemblage separates the younger two transgressive units from the older two. Tentatively this layer has been correlated with MIS 4 (Sarti et a!., 2005). A detailed geopedological survey (mainly micromorphological) was conducted on selected vertical profiles, in order to improve the stratigraphic and depositional history of the Baratti Gulf deposits. Fieldbased profile descriptions of paleosols evidenced that they are incomplete (absence of topsoil horizons), and deeply truncated by erosion. Moreover, the paleosols show a different degree of pedogenic expression, progressively more intense from younger to older paleosols. Their major pedogenic features and formative processes occurred polycyclically, attesting distinct and relict pedogenetic phases not in equilibrium with the present- day environmental condition. Each paleosols developed in a moist, warm and forest environment, and at the end of each pedogenetic cycle a decline of the vegetation cover associated to a climatic deterioration caused a general retrogradation of the soil properties (polygenetic soil evolution). The effect of "glacial phases" is mostly reflected in erosion and soil truncation processes recorded by the bounding surfaces at the top of the transgressive cycles. Following the previous considerations, the transgressive events probably took place at the onset of the warm-humid interglacial periods while the subsequent subaerial exposure and pedogenesis of the marine-coastal deposits represent the closing events of the interglacial cycles. The paleosols of the Baratti Gulf cliff section record regional and global climatic events providing information into the tectono-sedimentary and climate evolution of the area during the late Pleistocene. This study may support the knowledge of the variability of the most important climatic events during last interglacial soil evolution on the Mediterranean area