Massimiliano Ghinassi

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.

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.

Stratigraphic context and paleoenvironmental significance of minor taxa (Pisces, Reptilia, Aves, Rodentia) from the late Early Pleistocene paleoanthropological site of Buia (Eritrea)

The Buia Homo site, also known as Wadi Aalad, is an East African paleoanthropological site near the village of Buia that, due to its very rich yield from the late Early Pleistocene, has been intensively investigated since 1994. In this paper, which reports on the finds of the 2010-2011 excavations, we include new fossil evidence on previously identified taxa (i.e., reptiles), as well as the very first description of the small mammal, fish and bird remains discovered. In particular, this study documents the discovery of the first African fossil of the genus Burhinus (Aves, Charadriiformes) and of the first rodent from the site. This latter is identified as a thryonomyid rodent (cane rat), a relatively common taxon in African paleoanthropological faunal assemblages. On the whole, the new occurrences documented within the Buia vertebrate assemblage confirm the occurrence of taxa characterized by strong water dependence. The paleoenvironmental characteristics of the fauna are confirmed as fully compatible with the evidence obtained through sedimentology and facies analysis, documenting the sedimentary evolution of fluvio-deltaic and lacustrine systems.

Stratigraphic context and taxonomic assessment of the large cercopithecoid (Primates, Mammalia) from the late Early Pleistocene palaeoanthropological site of Buia (Eritrea)

IntroductionThe Buia-Dandero area (100 km south of Massawa, northernDanakil Depression, Eritrea; Fig. 1A) is well known for the 1-million-year-old Homo cranium from Buia (Abbate et al., 1998;Macchiarelli et al., 2004; Bondioli et al., 2006). The Early-to-Middle Pleistocene stratigraphic series of the Dandero basin,located near the Buia village, presents about 1 km of continentaldeposits. Since its discovery in 1994, this area has been the subjectof research by an international team coordinated by the EarthSciences Department of the University of Florence and the EritreaNational Museum. The investigated area yielded hominin remains(Abbate et al., 1998, 2004a; Rook et al., 2002), abundant fossilvertebrates (Ferretti et al., 2003; Delfino et al., 2004; Martinez-Navarro et al., 2004, 2010), and a rich archaeological record ofMode 1 (Oldowan) and Mode 2 (Acheulean) tool industries in a lateEarly Pleistocene chronological framework (Abbate et al., 2004a).The age of the Homo-bearing sediments (Alat Formation) of theBuia sedimentary succession, established by different investigativeapproaches, falls within the Jaramillo Subchron (C1r.1n), close to1.0Ma(Albianelli and Napoleone, 2004; Bigazzi et al., 2004).In addition to the hominin remains, non-human primates aresolely represented in the Buia faunal assemblage (Alat Formation)by a large cercopithecoid cranial fragment, tentatively listed in theBuia mammal fauna (Martinez-Navarro et al., 2004)asTher-opithecus cf. Theropithecus oswaldi. The genus Theropithecus is verycommon in the Plio-Pleistocene of Africa, occurring at sites inNorth, East and South Africa, within a time span ranging from3.4Mato0.5Ma(Delsonetal.,1993).Weprovidehereadescriptionof the specimen (UA-463), which is housed in the Paleontologicalcollections of the National Museum of Eritrea (Asmara).The mammalian assemblage from BuiaAbbateetal.(1998)publishedapreliminaryvertebratefaunallistfrom Buia. Successive field collections and taxonomic descriptionsallowed updating the Buia vertebrate faunal assemblage, whichrepresentsatypicaleasternAfricanlateEarlyPleistocenefauna.Buiais characterised by the occurrence of evolved last-representativeforms of Elephas recki, Hippopotamus gorgops, Kolpochoerus old-uvaiensis, Kolpochoerus majus, Metridiochoerus aff. M. modestus andBos buiaensis, associated with taxa that persist in the present day,such as Ceratotherium simum, Equus cf. E. grevyi, Tragelaphus cf.Theropithecus spekei, and Kobus cf. K. ellipsiprymnus. The geologicaland sedimentological framework, as well as paleomagnetism andfissiontrackdating(Abbateetal.,2004a;Ghinassietal.,2009)areingood agreement with the mammal biochronology data, attesting toa latest Early Pleistocene age (Martinez-Navarro et al., 2004, 2010).Thisvertebrateassemblageispredominantlycomposedoftaxawithstrong water dependence like hippos, waterbuck, sitatunga, Kolpo-choerus, crocodiles, paleomedusid chelonians and African rock

Latest evidence of Palaeoamasia (Mammalia, Embrithopoda) in Turkish Anatolia

ABSTRACT Geological investigation of the Boyabat Basin in north-central Anatolia, Turkey, yielded palaeoamasid (Embrithopoda, Mammalia) gnathodental fossil specimens from two localities dated to the Eocene—Oligocene transition. These specimens include an upper incisor (BOY-1) and maxillary fragment preserving M2–M3 (BOY-2), and are geologically the youngest embrithopods known from Eurasia. The maxillary specimen is taxonomically more useful and, among embrithopods preserving the same molars, is most similar to the late Paleocene—middle Eocene Turkish palaeoamasid Palaeoamasia kansui. However, the new specimens are cautiously classified as Palaeoamasia. sp. nov., based on distinctions between BOY-2 and P. kansui in M3 morphology. Features distinguishing the M3 in BOY-2 are intermediate between those of P. kansui and the more derived Afro-Arabian arsinoitheriid embrithopods Arsinoitherium spp. and Namatherium blackerowense, although the new Turkish specimens are stratigraphically too young to be ancestral to these middle Eocene—late Oligocene arsinoitheriids. Salient differences in dental and gnathic morphology between contemporaneous Eurasian and Afro-Arabian embrithopods indicate long, separate phylogenetic trajectories for these taxa, supporting the view that they are divisible at the family level into Palaeoamasidae and Arsinoitheriidae, respectively. Improved documentation of the lengthy paleogeographic separation of palaeoamasids and arsinoitheriids confirms that Afro-Arabia was sufficiently isolated from Eurasia during the Paleogene to limit embrithopods to rare sweepstakes dispersal between these landmasses.

Facies associations of the northern Dandiero Basin (Danakil depression, Eritrea, including the Pleistocene Buya homo site)

The Dandiero Basin is located on the northern part of the 300 km-long Danakil depression. The geologic succession filling the Dandiero Basin is up to 1000 m thick and consists of three synthems, inascending order: the Early-to-Middle Pleistocene Maebele Synthem of fluvio-lacustrine origin; the Late Pleistocene Curbelu Synthem of alluvial deposits and the Late Pleistocene to Holocene Samoti Synthem alluvio-eolian sand. This study and map (1:5000 scale) focuses on the Maebele Synthem exposed in a 3.8 km2 area near Mt. Alat. Regionally, the Maebele Synthem consists of six lithostratigraphic units, in ascending order: (1) the Bukra Sand and Gravel, (2) the Alat Formation, (3) the Wara Sand and Gravel, (4) the Goreya Formation, and (5) Aro Sand, (6) Addai Fanglomerate. The Bukra Sand and Gravel is about 150–200 m thick and made up mainly of fluvial sand. The Alat Formation is 70–100 m thick and consists of alternating fluvial, lacustrine and deltaic deposits. Fluvial deposits consist of sand-filled channels that occur as amalgamated or isolated bodies within floodplain mud. Lacustrine sediments consist of mud, whereas deltaic deposits are represented by sandy shallow-water and Gilbert-type deltas. The Wara Sand and Gravel (250 m thick) is made up of fluvial sand. The Goreya Formation (50 m thick) consists of lacustrine, deltaic and fluvial deposits. The fluvial deposits consist of sand-filled channels the lacustrine sediments consist of mud with subordinate limestone, and the deltaic deposits are represented by sandy shallow-water deltas. The Aro Sand consists of fluvial sand up to 120 m thick. The Addai Fanglomerate (250–300 m thick) consists of coarse-grained alluvial fan.

Geological map of Pliocene-Pleistocene deposits of the Ambra and Ombrone valleys (Northern Siena Basin, Tuscany, Italy)

The study area is located across the Chianti Ridge (Tuscany, Italy), between the Upper Valdarno Basin and the Siena Basin. This area covers about 25 km2, forming a narrow belt oriented N–S and drained by the Ambra and Ombrone creeks, which flow northward and southward, respectively. Field mapping was carried out at 1:10,000 scale through an allostratigraphic-sedimentological approach. The study area deposits represent the infill of a SW-draining paleovalley, cut both in pre-Neogene bedrock and marine Pliocene deposits of the Siena Basin. The valley-fill succession consists of two main allounits (V1 and V2), which are conformably stacked in the northern sector of the study area, and unconformably offset in the southern sector. V1 comprises gravelly to sandy fluvial deposits, whereas V2 deposits show noticeable downvalley variability. V2 consists of poorly drained floodplain deposits in the northern sector of the paleovalley, whereas gravel and sand-bed river deposits fill its southern part. Alluvial-fan and palustrine deposits are also associated with V2 fluvial facies. A normal fault trending NW–SE is the main structural feature of the area. This fault cuts the V2 unit lowering the upstream reach and is thought to have promoted the marked facies changes observed in the fluvial deposits of unit V2.

Morphometric convergence between Proterozoic and post-vegetation rivers

Proterozoic rivers flowed through barren landscapes, and lacked interactions with macroscopic organisms. It is widely held that, in the absence of vegetation, fluvial systems featured barely entrenched channels that promptly widened over floodplains during floods. This hypothesis has never been tested because of an enduring lack of Precambrian fluvial-channel morphometric data. Here we show, through remote sensing and outcrop sedimentology, that deep rivers were developed in the Proterozoic, and that morphometric parameters for large fluvial channels might have remained within a narrow range over almost 2 billion years. Our data set comprises fluvial-channel forms deposited a few tens to thousands of kilometres from their headwaters, likely the record of basin- to craton-scale systems. Large Proterozoic channel forms present width:thickness ranges matching those of Phanerozoic counterparts, suggesting closer parallels between their fluvial dynamics. This outcome may better inform analyses of extraterrestrial planetary surfaces and related comparisons with pre-vegetation Earth landscapes.

Morphodynamics and facies architecture of streamflow-dominated, sand-rich alluvial fans, Pleistocene Upper Valdarno Basin, Italy

Abstract The overwhelming documentation of coarse-grained alluvial fans dominated by mass flow contrasts with the scarce accounts of finer grained, traction-dominated alluvial fans. To fill this gap, we present sedimentological and architectural data from a set of sand-rich, streamflow-dominated Pleistocene fans flanking the eastern Upper Valdarno Basin, Italy. The routing of sand-rich sediment resulted from the fast, intense weathering of the feldspar-rich, carbonate-deprived sandstone bedrock underlying the fan catchments. Although capable of entraining large boulders, high water discharge sustained tractional reworking along the proximal facies belts, hindering mass flow. The medial facies belts have a channelized, braided planform and are dominated by processes hardly distinguishable from those characterizing fluvial environments. Along the distal facies belts, extensive overbank tracts are composed of terminal splays and crevasse lobes, the spatial arrangement of which controlled the evolution of through-going tributary channels connected to the axial basin drainage. This study focused on the sedimentary processes, stratal architecture and morphodynamics of the alluvial fans and considered the effect of bedrock inheritance on their development. The results underline how granulometry and mass flow dominance are not distinctive of alluvial fan sedimentation per se and indicate how the critical detection of piedmont, radial palaeomorphology is crucial in the identification of ancient alluvial fans.

Field migration rates of tidal meanders recapitulate fluvial morphodynamics

Significance Meandering tidal channel networks play a central role in the ecomorphodynamic evolution of the landscapes they cut through. Despite their ubiquitous presence and relevance to sedimentary and landscape features, few observations of tidal-meander evolution exist, and we lack a full understanding of the governing processes. Field analyses show that tidal meanders, traditionally viewed as stable landscape features, display modes of migration and migration rates per unit width quite similar to those characterizing their fluvial counterparts, with important implications for the characterization of the related sedimentary products. The results presented here contribute to our understanding of the morphological evolution of tidal landscapes. The majority of tidal channels display marked meandering features. Despite their importance in oil-reservoir formation and tidal landscape morphology, questions remain on whether tidal-meander dynamics could be understood in terms of fluvial processes and theory. Key differences suggest otherwise, like the periodic reversal of landscape-forming tidal flows and the widely accepted empirical notion that tidal meanders are stable landscape features, in stark contrast with their migrating fluvial counterparts. On the contrary, here we show that, once properly normalized, observed migration rates of tidal and fluvial meanders are remarkably similar. Key to normalization is the role of tidal channel width that responds to the strong spatial gradients of landscape-forming flow rates and tidal prisms. We find that migration dynamics of tidal meanders agree with nonlinear theories for river meander evolution. Our results challenge the conventional view of tidal channels as stable landscape features and suggest that meandering tidal channels recapitulate many fluvial counterparts owing to large gradients of tidal prisms across meander wavelengths.