Mauro Coltorti

Geomorphic and tectonic evolution of the Ecuadorian Andes

Abstract In Early Miocene times the Cordillera did not exist and the Pacific Ocean reached the Oriente. In the Middle Miocene, the uplift of an elongated swell, consisting of Palaeozoic and older rocks, created the Eastern Cordillera. Decollements were activated diverging away from the Eastern Cordillera. In the eastern trench, located approximately in correspondence with the present day Interandean Depression, many thousands of meters of sediments were deposited. A planation surface was created at the end of Lower Pliocene from the Costa to the Oriente graded to sea level. Later, ignimbric flows covered much of the planation surface. Uplift brought the planation surface to 3500–4000 m. The Interandean Depression, bounded by normal faults, was created during the Upper Pliocene, and large strato-volcanoes erupted at this time. The volcanic activity contributed to the filling of an accumulation plateau preserved today in many parts of the Interandean Depression. The creation of the Interandean Depression is the result of lateral spreading activated as a consequence of uplift of the Cordillera. In the Middle and Late Pleistocene the Cordillera and the Accumulation plateau were mostly affected by downcutting with minor episodes of accumulation during the cold phases.

Quaternary faults and seismicity in the Umbro-Marchean Apennines (Central Italy): evidence from the 1997 Colfiorito earthquake

Abstract Analyses of structural and geomorphological data combined with remote sensing interpretation confirm previous knowledge on the existence of an extensional Quaternary tectonic regime in the Colfiorito area (Umbro-Marchean Central Apennines). This is characterized by a maximum principal axis of finite strain oriented approx. NE–SW, which is the result of a progressive deformation process due to pure and radial extension. Surface geological data, the crustal tectonic setting (reconstructed using a CROP 03 seismic reflection profile), and seismological data relative to the autumn 1997 Colfiorito earthquake sequence constrain the following seismotectonic model. We interpret the seismogenic SW-dipping low-angle normal fault pictured by seismic data as an inverted thrust ramp located in the basement at depth between 5 and 10 km. The surface projection of this seismogenic structure defines a crustal box within which high-angle normal faults are responsible for the deformation of the uppermost crust. The regional patterns of pre-existing basement thrusts therefore control the seismotectonic zoning of the area that cannot be directly related to the high-angle normal fault systems which cut through different crustal boxes; the latter system records, in fact, re-shear along pre-existing normal faults. Moreover, Quaternary slip-rates relative to high-angle normal faults in the Central Apennines are closely related to seismic hazard within each crustal box.

A late Lower Pliocene planation surface across the Italian Peninsula: a key tool in neotectonic studies

Abstract An integrated geological–geomorphological approach is proposed in order to provide more information for the assessment of neotectonic deformation in the Apennines. On this basis, it can be stated that: (1) a major flat planation surface is recognisable across the whole Italian Peninsula; (2) it is better preserved on harder rocks and in the higher parts of the local relief; (3) it cuts strata ranging in age from Palaeozoic to early Lower Pliocene; (4) it smoothed tectonic structures older than early Lower Pliocene; (5) it is buried below continental and marine deposits younger than late Lower Pliocene; (6) it is displaced and deformed by local thrust re-activation and, since the Lower Pleistocene, by high angle normal faults. Displacement analysis of this morphological feature at local scale allowed us to discriminate between pre- and post-planation tectonic deformations, hence providing useful information about the rates of uplift and faulting in the Apennines.

Last Glacial mammals in South America: a new scenario from the Tarija Basin (Bolivia)

The chronology, sedimentary history, and paleoecology of the Tarija Basin (Bolivia), one of the richest Pleistocene mammalian sites in South America, are revised here based on a multidisciplinary study, including stratigraphy, sedimentology, geomorphology, paleontology, isotope geochemistry, and 14C geochronology. Previous studies have indicated a Middle Pleistocene age for this classic locality. We have been able to obtain a series of 14C dates encompassing all the fossil-bearing sequences previously studied in the Tarija Basin. The dated layers range in age from about 44,000 to 21,000 radiocarbon years before present (BP), indicating that the Tarija fauna is much younger than previously thought. Glacial advances correlated to marine isotopic stages (MIS) 4 and 2 (ca. 62 and 20 ka BP, respectively) are also documented at the base and at the very top of the Tarija–Padcaya succession, respectively, indicating that the Bolivian Altiplano was not dry but sustained an ice cap during the Last Glacial Maximum. The results of this multidisciplinary study enable us to redefine the chronological limits of the Tarija sequence and of its faunal assemblage and to shift this paleontological, paleoclimatological, and paleoecological framework to the time interval from MIS 4 to MIS 2.

A human deciduous tooth and new 40Ar/39Ar dating results from the Middle Pleistocene archaeological site of Isernia La pineta, southern Italy

Isernia La Pineta (south-central Italy, Molise) is one of the most important archaeological localities of the Middle Pleistocene in Western Europe. It is an extensive open-air site with abundant lithic industry and faunal remains distributed across four stratified archaeosurfaces that have been found in two sectors of the excavation (3c, 3a, 3s10 in sect. I; 3a in sect. II). The prehistoric attendance was close to a wet environment, with a series of small waterfalls and lakes associated to calcareous tufa deposits. An isolated human deciduous incisor (labelled IS42) was discovered in 2014 within the archaeological level 3 coll (overlying layer 3a) that, according to new 40Ar/39Ar measurements, is dated to about 583–561 ka, i.e. to the end of marine isotope stage (MIS) 15. Thus, the tooth is currently the oldest human fossil specimen in Italy; it is an important addition to the scanty European fossil record of the Middle Pleistocene, being associated with a lithic assemblage of local raw materials (flint and limestone) characterized by the absence of handaxes and reduction strategies primarily aimed at the production of small/medium-sized flakes. The faunal assemblage is dominated by ungulates often bearing cut marks. Combining chronology with the archaeological evidence, Isernia La Pineta exhibits a delay in the appearance of handaxes with respect to other European Palaeolithic sites of the Middle Pleistocene. Interestingly, this observation matches the persistence of archaic morphological features shown by the human calvarium from the Middle Pleistocene site of Ceprano, not far from Isernia (south-central Italy, Latium). In this perspective, our analysis is aimed to evaluate morphological features occurring in IS42.

Hypothesis on the cause of extinction of the South American mastodonts

Abstract Paleontological, geomorphological and sedimentological investigations on the Cangahua Formation in the Interandean depression of Northern and Central Ecuador have provided information on the evolution of the Andean paleoenvironment during the Late Pleistocene. Pyroclastic and windblown sediments were deposited during cold and dry phases of the last glaciation, interrupted many times by the development of forest-steppe and steppe paleosoils during interstadials. An erosional phase which closed the Cangahua sedimentation was followed by the deposition of colluvial sediments, characterized by a high number of minor pedogenetic episodes. The colluviums are confidently referable to the Holocene. The upper part of the Cangahua Formation is rich in mammal fossils and is probably referable to the Last Glacial Maximum. The fossiliferous sequences suggest that mastodonts disappeared before mylodonts and equids. We hypothesize that the increased cold and aridity of the Last Glacial Maximum, which deeply affected the Cordillera, caused the extinction of most of the megafauna and the mastodonts seem to have been the most sensitive to the environmental degradation. The final history of South American mastodonts, represented by Haplomastodon and Stegomastodon, spans the latest Pleistocene and probably the earliest Holocene. Haplomastodon was dispersed in the highlands within the tropical belt and Stegomastodon in plains of the southernmost part of Brazil, in Paraguay, Uraguay, Argentine, central and northern Chile. Both Haplomastodon and Stegomastodon suffered the same negative effects of the Last Glacial Maximum when their habitats underwent intense desertifications under dry and cold conditions. They disappeared in a mosaic way in the course of the latest Pleistocene, the last representatives probably surviving in favorable restricted areas where however the considerably increased selective pressure was in the long run devastating. In our opinion the human impact was not a determinant in causing mastodont extinction.

Geomorphological evidence for anti-Apennine faults in the Umbro-Marchean Apennines and in the peri-Adriatic basin, Italy

Abstract The Apennines are a relatively recent mountain chain which has been affected by uplift movements since the Upper Pliocene. In fact the remnants of an “erosional surface”, reduced close to base level, is preserved at the top of the relief. There is no general agreement on the geodynamic stress field and mechanisms which are creating the chain. However, it is largely accepted that uplift occurred together with the activation, on the western side of the chain, of extensive faults, oriented in the Apennine direction (NW-SE), which have been linked to the opening of the Tyrrhenian sea. A great debate is going on about the presence and significance of anti-Apennine faults (NE-SW) which have been observed by some authors but completely denied by others. The main evidence is represented by[ (1) block faulting of the remnants of the “erosional surface”. Along the Marchean Ridge, more elevated relief, delimiting relatively depressed areas, was created in correspondence with the Sibillini Mts. and Mt. S. Vicino. Similar evidence has been found in the Umbro-Marchean Ridge. Locally more than 1500 metres of displacement have been observed between more and less uplifted remnants. (2) Block faulting of fan deltas and related beaches, of Sicilian to Crotonian age, with more elevated sediments preserved between the Tronto and Tenna rivers and between the Musone and Esino rivers. Maximum displacement along a transect parallel to the coast is 200 metres. (3) fault-scarps affecting the Middle Pleistocene river terraces, as observed along the Esino, the Tronto, the Chienti and the Tenna river valleys. Maximum displacements are in the order of 50 metres. (4) Faulting of horizontal karst galleries and reorientation of the cave network, as in the Frasassi Gorge. Maximum displacements are about 100 metres. (5) Captures and alignments in the drainage network of the main river courses. (6) Large-scale gravitational movements, as in the Ancona landslide, and along the Chienti and Esino rivers. Their activation occurred in most cases after the Lower Pleistocene and although their displacements may be of relatively limited extent, dispite their recent activity, they played a major role in the modelling of the landscape. These faults display transtensive, extensional and trascurrent movements. Apart from the controversial geodynamic significance of these faults, from a geomorphological point of view they must be considered transverse elements of the stress field from blocks more or less uplifted along the Apennine chain. The importance and timing of activity of these faults in the Quaternary geomorphological evolution of the Umbria-Marchean Apennines is demonstrated using evidence usually underestimated by structural geologists, which can contribute to a debate based on a multidisciplinary approach.

The Wonji fault belt (Main Ethiopian Rift): structural and geomorphological constraints and GPS monitoring

Abstract The Wonji Fault Belt (WFB), Main Ethiopian Rift, forms a network of faults oriented NNE-SSW with a Quaternary direction of extension oriented c. N95° E. Faults are spaced between 0.5 and 2 km, show a fresh steep scarp, recent activity and slip rates of up to 2.0 mm a−1. This high value of deformation along the rift floor with respect to the plate separation rates suggests that most of the active strain could be accommodated by magma-induced faulting within the rift. However, the mountain front morphology associated with a displacement of 300–400 m since the Middle Pleistocene, tilted-blocks, brittle-seismic fault rock fabric and historical earthquakes with M>6 support a tectonic origin of the Asela boundary fault. Therefore, we propose a model that considers the possible coexistence of both magmatic deformation at the rift floor and brittle faulting at the rift margin. We also report the data relative to a GPS network installed in December 2004, along two transects across the WFB, between Asela and the Ziway Lake.

The Geomorphological Map of Mt. Amba Aradam Southern Slope (Tigray, Ethiopia)

Abstract Please click here to download the map associated with this article. The geomorphological map described below covers an area of about 100 km, located on the southeastern slope of Mt. Amba Aradam (northern Ethiopia). It has been produced within the Ethio-Italian Cooperation Programme, in order to understand the recent evolution and present-day trends of the area as a basic tool for land reclamation/rehabilitation projects. The survey was carried out in three successive work campaigns (February 1995, February-March 1996 and December 2002) following the Italian Environmental Agency guidelines. The main geomorphological processes responsible for present-day landscape modelling in the investigation area, are gravity-driven mass movements and slope erosion due to running water. They strongly affect human activities, especially in terms of agriculture and infrastructure management. This map may therefore represent a useful document for land management as well as the initial step for the assessment of geomorphological hazard and risk.

A new vertebrate fossiliferous site from the Late Quaternary at San José on the north coast of Ecuador: preliminary note

A new fossiliferous site is described south of Manta on the north coast of Ecuador. Estuarine sediments overlying Quaternary terraced deposits contain abundant vertebrate remains belonging to the following taxa: Eremotherium cf. laurillardi or E. rusconii, Haplomastodon chimborazi, and Geochelone s.l. On the basis of geological context and the fossil assemblage, a probable Early Holocene age is suggested, although a latest Pleistocene age cannot be ruled out. This discovery will provide crucial new information to enhance knowledge of the geologic and faunistic evolution of the area.