Mario Sagri

A one-million-year-old Homo cranium from the Danakil (Afar) Depression of Eritrea

One of the most contentious topics in the study of human evolution is that of the time, place and mode of origin of Homo sapiens. The discovery in the Northern Danakil (Afar) Depression, Eritrea, of a well-preserved Homo cranium with a mixture of characters typical of H. erectus and H. sapiens contributes significantly to this debate. The cranium was found in a succession of fluvio-deltaic and lacustrine deposits and is associated with a rich mammalian fauna of early to early-middle Pleistocene age. A magnetostratigraphic survey indicates two reversed and two normal magnetozones. The layer in which the cranium was found is near the top of the lower normal magnetozone, which is identified as the Jaramillo subchron. Consequently, the human remains can be dated at ∼1 million years before present.

The eugeosynclinal sequences

The eugeosynclinal sequences of the Northern Apennines are characterized by the presence of ophiolites both as a primary stratigraphic substratum and as olistostromes and olistoliths interbedded in the sedimentary succession. A further characteristic is extensive turbidite sedimentation of Late Cretaceous-Eocene age, which preceded similar terrigenous deposition in the miogeosyncline. The eugeosynclinal sequences underwent intense horizontal displacements from a Tyrrhenian area, overriding the miogeosynclinal rocks. In spite of tectonic dismembering, several of the original stratigraphic successions have been reconstructed. The eugeosynclinal sequences have been grouped into: (1) Helminthoid Flysch sequences (Upper Triassic-Eocene); (2) Vara Supergroup (Jurassic?-Paleocene); (3) Calvana Supergroup (Upper Cretaceous-Eocene) and (4) Canetolo Complex (Paleocene-Miocene?). The Helminthoid Flysch sequences include most of the eugeosynclinal deposits, generally with remarkable thickness of calcareous and, subordinately, arenaceous turbidites of Late Cretaceous age. In this paper stratigraphic units of the Helminthoid Flysch and of the other major sequences are described, as well as their mutual tectonic relations. Schematically, the following upward geometric succession has been assumed, starting from the top of the miogeosynclinal rocks of the Tuscan and Umbrian sequences: the Canetolo Complex, the Calvana Supergroup, the Helminthoid Flysch sequences and the Vara Supergroup. Locally, this succession is present only in part, due to tectonic reductions. According to the structural positions and on the basis of various stratigraphic and sedimentological considerations, we have attempted to sketch the paleogeography of the eugeosyncline. The reconstruction is largely incomplete up to the Lower Cretaceous, whereas numerous paleogeographic data are available for the Upper Cretaceous and the Eocene. The areas of deposition of the Vara Supergroup and of those parts of the Helminthoid Flysch sequences with abundant Upper Cretaceous and Paleocene arenaceous turbidites, are believed to have been located along the internal (western) margin of the eugeosyncline. To the east of it, it is supposed, was located the basin of the Helminthoid Flysch sequences with calcareous turbidites. The external (eastern) margin of the eugeosyncline was occupied by the Calvana Supergroup and by the Canetolo Complex. The relations between the Alpine realms and the Apennines geosyncline are briefly discussed, especially in respect to the provenance of the clastics of the Apennines turbidites. The Corsica-Sardinia Massif is supposed to have been the main source area during the Cretaceous and Paleocene for the arenaceous clastics, whereas the coeval calcareous turbidites mainly derived from the South-Alpine zone and from the internal margin of the Brianconnais facies belt. A critical review of alternative paleogeographic reconstructions proposed by various authors, has also been attempted.

The miogeosynclinal sequences

Abstract The Tuscan and Umbrian sequences represent miogeosynclinal deposition in the Northern Apennines. They are composed of five major rock groups, which are here described in detail and interpreted. The sequences start with a terrigenous basal section, Upper Carboniferous to Carnian, composed of clastic rocks with shallow-marine, lagoonal and continental facies, and of acid volcanics. This group probably represents the Hercynian postgeosynclinal stage. A carbonate-evaporitic section follows, Noric to Rhaetic, overlain by Hettangian neritic limestones. These facies are of wide extent; a geosynclinal basin in the Northern Apennines had probably not yet differentiated. A progressive deepening of the sea began in the Sinemurian; the carbonate-siliceous section (Lower Jurassic-Lower Cretaceous) is made of frequently siliceous micritic limestones and marlstones, and contains bedded cherts, but locally there are biostromal and oolitic limestones. In parts of the geosyncline, submarine dissolution on top of tectonic rises caused the development of paraconformities. The pre-flysch section includes pelitic and marly formations, with some bedded chert, and graded limestones (prototurbidites) in the Tuscan sequence (Lower Cretaceous to Lower Oligocene); limestones and marlstones in the Umbrian sequence (Upper Cretaceous to Middle Miocene). The pre-flysch stage indicates a further deepening of the sea and a considerable slowing of the rate of deposition, but the bottom physiography was in parts irregular and paraconformities were formed. The topmost flysch section consists of thick turbidite formations, migrating in age from west to east, Early-Middle Oligocene to Early Miocene in the Tuscan sequence, Early to Late Miocene in the Umbrian sequence. Each flysch unit starts abruptly and is typically arenaceous in the lower part (ortotubidites), but it becomes progressively marly-argillaceous in the upper part (kataturbidites).

The Ziway–Shala lake basin (main Ethiopian rift, Ethiopia): a revision of basin evolution with special reference to the Late Quaternary

Abstract The Ziway–Shala basin, in the Main Ethiopian Rift (MER), is a reference site for regional to global paleoclimatic reconstructions. We undertook and interpreted a stratigraphical, pedological and geomorphological study, including a new geological map scale 1:250,000, to provide a Late Quaternary-centred revised geological history of the basin. 1 We mapped several Late Quaternary sedimentary units and arranged them in four major unconformity-bounded stratigraphic units (synthems), recording equivalent phases of geomorphic change. A new, extensive, soil survey allowed us to establish a pedostratigraphic unit, the T’ora geosol, as a distinctive marker of landscape stability and instability in the area during the Holocene. Climate change was a major control on geo-morphologic evolution of this area during the intense climate fluctuations of the last 100,000 years. Extensive lake systems developed during relatively humid Last Glacial interstadials and in the early-mid Holocene; this last was characterized by short, but high-amplitude, regressions during arid pulses. Major lakes’ lowering occurred in the terminal Pleistocene and in the last 5000 years. Evidences for high or very high terminal Pleistocene lake levels suggest possible non-climatic controls on changes in lakes’ extension and volumes between Late Pleistocene and Holocene. We suggest that modifications of hydrological thresholds, due to activity of structures parallel and transversal to the MER, established new lakes’ boundaries between terminal Pleistocene and early Holocene, setting the maximum level of Holocene lake systems at about 1670 m a.s.l. The integrated analysis of lacustrine, fluvial, slope and soil systems provided a basis for a general interpretation of relations between climatic changes and geomorphic processes at a basin scale.

Introduction to the geology of the Northern Apennines

According to Aubouin (1965) the sedimentary evolution of the Northern Apennines geosyncline is divided into a geosynclinal stage proper, represented by eu- and miogeosynclinal sequences, a late geosynclinal and a postgeosynclinal stage. In the Apennines the eugeosynclinal rocks are almost entirely allochthonous. Their interpretation as autochthonous is held to be unrealistic on structural and paleogeographic grounds. The late geosynclinal stage is defined here mainly on the base of tectonic criteria: sediments deposited over folded eugeosynclinal rocks, later subjected to lateral tectonic transport in the same manner as their allochthonous substratum. Owing to the eastward progression of tectonic movements in the Northern Apennines, the tecto-sedimentary stages tend to overlap and coexist (e.g., Oligocene-Miocene miogeosynclinal flysch and late geosynclinal sediments). The eugeosynclinal stage is characterized by the presence of ophiolites and the early development of flysch. Four main groups of sequences are distinguished: (1) Upper Cretaceous to Eocene Helmynthoid Flysch sequences; (2) Jurassic to Eocene Vara Supergroup; (3) Upper Cretaceous to Middle Eocene Calvana Supergroup; and (4) Paleogene Canetolo Complex. The largely autochthonous miogeosynclinal rocks are represented by the Tuscan (Lower Triassic to Lower Miocene) and Umbrian (Carnian to Upper Miocene) sequences. The late geosynclinal sequences are Middle Eocene to Messinian in the Emilian Apennines, Lower and Middle Miocene in Tuscany and Romagna. The postgeosynclinal sediments are Upper Miocene to Pleistocene in the southwest (Tuscany-Latium), Pliocene and Pleistocene in the northeast and east (Emilia and Marche). Four major structural areas are distinguished: 1. (1) The Tyrrhenian area, a zone of intense crustal shortening, containing the axis of symmetry between the structure of the Apennines and that of the Western Alps and “Alpine Corsica”. 2. (2) Southwestern Tuscany, characterized by a fault block structure and an incomplete Tuscan sequence. 3. (3) The main fold range, with reverse faults, overturned folds and overthrusts, all directed eastward and northeastward. There are two major northwest-southeast lines of thrusting and overturned folding, and two major tectonic windows (Alpi Apuane and Monte Pisano), in which the Tuscan sequence is doubled. 4. (4) The outer foothills and Po Valley, where the asymmetric folding and reverse faulting become gradually attenuated. Metamorphism is generally of low grade (greenschist facies), and affects the lower part of the Tuscan sequence in small areas of western Tuscany (Alpi apuane, Monte Pisano, Montagnola Senese, Elba Island). Metamorphism tends to be associated with the tectonic doubling of the sequence. Theories on the tectonic interpretation of the Northern Apennines are summarized. The authors are inclined to accept features of both the “decollement” nappe model of Trevisan et al. (1965) and the orogenetic landslide model of Migliorini (1948) and Merla (1951). The emplacement of the allochthon was essentially through gravitational gliding; detachment and gliding affected also, in parts, rocks of the Tuscan sequence (Tuscan nappe of the Alpi Apuane). Uplift and differential movements (block faulting?) in the miogeosyncline from the Triassic to the Cretaceous are indicated by slumping and unconformities. Much slumping occurred during the Cretaceous in the eugeosyncline. The first recorded eastward gliding movements of nappes are Upper Cretaceous to Paleocene in the southern part of the eugeosyncline, Eocene in the northern part of it. Parts of the eugeosynclinal sequences were folded in the Lower-Middle Eocene and at the Eocene-Oligocene transition. The advancement of nappes onto the miogeosynclinal rocks, accompanied by folding, began at the Oligocene-Miocene transition. It continued, gradually moving eastward, until the Lower Pliocene. The detachment of rocks of the Tuscan sequence in the Alpi Apuane and southern Tuscany (Tuscan nappe) seemingly occurred in the Lower and Middle Miocene.

Neogene—Quaternary basins of the inner Apennines and Calabrian arc

The objective of this chapter is to review key evidence and genetic hypotheses pertaining to the Neogene—Quaternary basins of the internal (western) side of the Apennines and Calabrian arc (Fig. 22.1). The basins of the Northern Apennines will be treated first and they will be compared and contrasted with those of the Southern Apennines and Calabrian arc. Sediment terms such as clay, sand and gravel are generally used rather then rock terms, because most materials are uncemented or only slightly cemented.

Late-Holocene catastrophic floods in the terminal Arno River (Pisa, Central Italy) from the story of a Roman riverine harbour

The results of the stratigraphic and sedimentological analysis carried out at an exceptional archaeological site situated in the coastal plain of the Arno and Serchio Rivers (western Tuscany, Italy) are reported. The site, discovered near central Pisa, records a 1000-yr history of a riverine harbour built by the Etruscans and used by the Romans. This harbour was adjacent to the Arno River, located within an abandoned channel then still connected to the sea, thus allowing efficient stock transfer to and from Roman Pisa. The archaeological importance of this site is primarily due to the discovery of at least 16 well-preserved Roman ships and many other remains mostly deriving from their cargoes. The sedimentological relevance of this record is related to the recurrent, catastrophic, destruction of the harbour documented by the features of the sediment encasing the ships and by the ships’ distribution and age. Such repeated destruction was related to catastrophic flood flows generated by levee crevassing of the Arno River during high-magnitude floods that occurred between the second century BC and the fifth century AD. The Pisa harbour tells a story of river channel instability. The repeated flooding of the harbour indicates that the Roman Arno River attempted to abruptly change its course, exploiting a pre-existing river channel. The concomitance of climatic and eustatic causes is expounded upon to explain the sedimentary dynamic of a coastal floodplain during historical times.

The Plio-Pleistocene fluvio-lacustrine Upper Valdarno Basin (central Italy): Stratigraphy and basin fill evolution

The Upper Valdarno Basin stands out from the Neogene-Quaternary basins of the Northern Apennines given its outstanding fossil mammal record, good quality of natural and artificial outcrops and remarkable chronological control on the basin-fill succession. The present paper aims to summarize the stratigraphic and sedimentological studies focused on the Upper Valdarno Basin during the past decades, and integrate them with recent investigations. The Upper Valdarno Basin is located about 35 km SE of Florence between the Chianti Mountains and the Pratomagno Ridge. It consists of a main asymmetric tectonic depression filled with 550 m of Plio-Pleistocene fluvio-lacustrine deposits (Upper Valdarno Basin s.s.) and a minor basin known as the Palazzolo sub-basin. The Upper Valdarno Basinfill is made of three unconformity-bounded units, named Castelnuovo dei Sabbioni (CSB), Montevarchi (VRC), Torrente Ciuffenna (UFF) synthems, whereas the Palazzolo sub-basin fill consists of the Fosso Salceto (OLC) and Torrente Ciuffenna (UFF) synthems. The Upper Valdarno Basin formed during Late Pliocene because of the tectonic damming of a northeastward flowing drainage. The early phase of basin development is recorded by the accumulation of fluvial gravels in vallive settings, whereas the definitive of these streams damming caused the development of lacustrine conditions at about 3.1 Ma. The accumulation of deltaic sand fed from the SW margin caused the lake filling and stopped the deposition of the CSB Synthem.Before 2.58 Ma, a tectonic phase caused uplift of the basin and partial erosion of the CSB deposits. Deposition of the lower part of the VRC Synthem occurred during a marked basin broadening and accumulation of alluvial fan successions, which were capped by aeolian-reworked alluvial sand deposited at about 2.5 Ma. At about 2.3 Ma, a new deformative phase caused further basin widening, erosion along the SW margin and development of a small lake inthe central areas. Deposition of the upper part of the Montevarchi Synthem started just after this tectonic phase and was characterized by development of axial fluvial drainage and marginal alluvial fans.During the Early Pleistocene (Olduvai Subchron, 1.95-1.78 Ma) a subsidence pulse promoted development of floodplain lakes and swamps in the axial part of the basin, where thick organic-rich mud were accumulated. During late Early Pleistocene the capture of the paleo-Arno River, which started to flow into the basin, caused the development of a marked unconformity. This unconformity was covered by fluvial and alluvial fan deposit in the axial part and along the margin respectively.

GEOLOGY OF THE HOMO -BEARING PLEISTOCENE DANDIERO BASIN (BUIA REGION, ERITREAN DANAKIL DEPRESSION)

This paper deals with the geological context of the northernmost site in the East Africa Rift system which has yielded Homo erectus -like remains. They are dated ca. 1 Ma and have been found in the deltaic deposits of the Alat Formation belonging to the Dandiero group. This newly defined group crops out extensively in an elongated belt from the Gulf of Zula to the North to the Garsat area to the south. In the Buia-Dandiero area it ranges in age from the Early to the Middle Pleistocene, and incorporates six formations, from bottom up: the fluvial Bukra Sand and Gravel, the deltaic and lacustrine Alat Formation, fluvial Wara Sand and Gravel, the lacustrine Goreya Formation, the fluvio-deltaic Aro Sand and alluvial Addai Fanglomerate. This succession is bounded by two major unconformities, which separate it from the Neoproterozoic basement and from the overlaying Boulder Beds fanglomerate, and has been designated the Maebele Synthem. The latter is the result of two lacustrine transgression and regressions evidenced by two depositional sequences. The unconformities bounding the Maebele Synthem are related to the tectonic history of the basin fill and its substrate. The development of the two sequences was, instead, mainly controlled by lake level fluctuations and, hence, by climatic variations connected with the weakening and strengthening of the monsoons in the northwestern Indian ocean. The environment where the Buia Homo lived was a savannah with some scattered water pools. This environment probably extended farther north along the western coastal plain of the Red Sea, and was a preferential pathway for the dispersal of the hominids from East Africa toward Eurasia.

Depositional environments of the Plio-Pleistocene Upper Valdarno Basin (Tuscany, Italy)

The Upper Valdarno Basin is located about 35 km SE of Florence between the Chianti Mountains and the Pratomagno Ridge. The basin fill is made of four synthems named as Castelnuovo dei Sabbioni, Montevarchi, Fosso Salceto and Torrente Ciuffenna synthems. The Castelnuovo dei Sabbioni Synthem (Late Pliocene) consists of coarse-grained, stream gravels grading upwards into sheet-like, alluvial sand. These sands are overlain by a muddy lacustrine unit bearing, at its base, two well-developed lignitiferous seams accumulated in a coastal marsh setting. The lacustrine mud grades upwards into deltaic sand accumulated in a shallow-water delta under repeated lake-level oscillations. The Montevarchi Synthem (Late Pliocene to Early Pleistocene) consists of two portions separated by an unconformity surface passing basinward into a correlative conformity. The lower portion of the Montevarchi Synthem is made of alluvial fan gravel and sand passing upwards into fluvio-aeolian sandsheet deposits, consisting of aeolian-reworked, alluvial sand bearing isolated channels. Fluvio-aeolian sandsheet deposits are covered by mollusc-rich, alluvial sand which makes lateral transition into lacustrine muddy deposits. The upper portion of the Montevarchi Synthem consists of fluvial and alluvial fan deposits. Fluvial deposits occupy the axial part of the basin and are referred to sandy channels wandering through a muddy floodplain hosting shallow lakes and swamps. Alluvial fan deposits occur along the basin margins and consist of proximal gravels grading downfan into gravelly sand and a variety of sandy facies. Floodplain lakes deposits are well-developed in the middle part of the upper Montevarchi Synthem and in the Palazzolo sub-basin (Fosso Salceto Synthem), where they are overlain by alluvial-fan gravels. The Torrente Ciuffenna Synthem (Early to Middle Pleistocene) consists of fluvial sediments in axial part of the basin and alluvial fans deposits along the basin margins. The axial fluvial deposits were accumulated by the paleoArno River and consist of gravel and overlying sand. The basal gravels were deposited by low-sinuosity channels, whereas sandy deposits were formed by moderate to high-sinuous channels. The alluvial fan deposits consist of proximal gravels passing downfan into gravelly sand and sandy facies.