Synsedimentary tectonics and sedimentation in the Tertiary Piedmont Basin, northwestern Italy (original) (raw)
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2021
This work focuses on the transition from the Las Leoneras to Lonco Trapial Formations, in the lower part of the Early Jurassic succession of the incipient rift phase of the Cañadon Asfalto Basin (western part of Chubut Province-Patagonia, Argentina). Twenty lithofacies have been identified and grouped into seven facies associations on the basis of field characteristics (sedimentological and lithological) and optical microscope analysis, from two localities representing proximal and distal locations in the basin. The spatial relationship between all the lithofacies provided a four-dimensional reconstruction of the palaeoenvironmental evolution, showing how the original, clastic sedimentation in alluvial/fluvial and lake environments was modified by shortlived volcanic events during three volcanic cycles, and how the environment reacted after the input of huge amounts of volcaniclastics. Progradation of small deltas and subaqueous lobes, retrogradation caused by rising lake levels, and frequent erosion of valleys were typical processes in this environment. When explosive volcanism began, the original tectono-climatic control on sedimentation was replaced by the volcanic control, and the volcanicallyforced sedimentation broke the equilibrium among production, delivery and accumulation of sediments. The nature of the volcanic eruptions and the different propensity of volcanic lithofacies to produce particles of different size and types (lithics, crystals and glass) are also analyzed. The role of volcanism in the production and transport of great volumes of sediments across sedimentary systems needs to be carefully reexamined , and the analysis on the variability in the composition of volcaniclastic deposits must take into account that volcaniclastic particle types may not simply reflect a linear deepening in the dissection of magmatic arcs through time but are often controlled by the style of the eruptions and the lithological variation of the volcanic products.
M. Coltorti et al., The growth of the Chianti Ridge: progressive unconformities and depositional sequences in the S. Barbara Basin (Upper Valdarno, Italy). (IT ISSN 0394-3356, 2007). The Chianti Ridge, elongated in a NW-SE direction, separates the Upper Valdarno from the Siena Basins. It is made of Macigno and Scaglia Toscana Fms. belonging to the Tuscan Nappe that underlies the Ligurian Units. Inside the Upper Valdarno basin three main synthems have been identified, separated by major unconformities; from the bottom: 1. Castelnuovo synthem, subdivided into Spedalino and Meleto subsynthems, 2. Montevarchi synthem and 3. Bucine synthem. The Spedalino subsynthem, that unconformably lies over the pre-Pliocene bedrock, is made up of thin and laterally discontinuous coarse gravels. The Meleto subsynthem, commonly referred to a lacustrine environment, is made of alluvial plain lithofacies, including channel, crevasse splay and swamp depositional systems where a Taxodium forest developed and peat accumulated. Close to the western margin of the basin these subsynthems are tilted up to 60°. The Montevarchi synthem, mainly made of sands and gravels accumulated inside a wide braidplain, and lies unconformably over the previous units. This synthem is tilted eastward up to 20°. Finally, the Bucine synthem lies unconformably over the previuos synthems generating a fluvial terrace of the Arno River. The two lower units date back to the Early Pliocene. In fact the Meleto clays contain mammal remains that can be found in the Triversa Faunal Unit (Early Villafranchian, late Early -Middle Pliocene) as well as in the Ruscinian (Early Pliocene). They are also negatively magnetized and could correspond to the Gilbert Chron. Palaeomagnetic investigations and the presence of aeolian sediments in the Montevarchi synthem and cold pollen flora allowed its attribution to the Middle and Late Pliocene. The relationships between the different synthems and the dominant unconformities coupled with thermochronological data recently obtained in the Apennine ridge to the east allow us to establish that the Chianti Ridge, after a major planation, became the eastern edge of a moderate relief (Spedalino subsynthem) that was later transformed into a wide alluvial plain (Meleto subsynthem). Updoming tilted the previous units before the modelling of a second major unconformity that preceed the deposition of the Montevarchi synthem. It is possible that during this period the Valdarno was still connected to the Siena Basin to the west. A third major unconformity followed finally separating the two basins. These deformations occurred almost at sea level. During the Early and Middle Pliocene, the Apennine Ridge to the east did not exist and the Upper Valdarno represented the western part of the peri-Adriatic Basin. The deepening of the drainage network is due to the generalised uplift that in the nearby areas started during the Early Pleistocene. Finally the creation of the present-day Apennine watershed was not gradual but very rapid in the geological time scale and started mostly during the Early Pleistocene.
New data on the Middle Pliocene sedimentation in the southern Valdelsa basin (Siena, Italy)
Bollettino della Società …, 2005
The Valdelsa basin, one of the widest Neogene-Quaternary extensional basins of central Tuscany, is filled by dominantly clastic deposits of late Miocene and Pliocene age. Within the new regional project of geological cartography, sedimentological, stratigraphic and micropaleontological studies of the Pliocene marine sediments cropping out in the south-western area of the basin have been performed. The most important results are: a) the recovery of Globorotalia crassaformis, which allows to refer these sediments to the Piacenzian G. aemiliana Zone; b) the migration, during the Piacenzian, of the deeper areas of the Valdelsa basin from the central sector towards the eastern one; c) the recognition, during the same period, of a rapid transgression on the eastern margin.
Neogene Stratigraphy and Sedimentology of the Gargano Promontory (Southern Italy
Eclogae geol. Helv. , 2000
The Gargano Promontory has revealed a succession of Neogene shallow-water rocks, unconformably covering the Mesozoic substratum. of an Early Miocene Lo Late Pliocene age. Thc lowermost unit consists of a tidal platform of poorly constrained age (Torre Mileto Fm .. Chathian-Aquitanian?). topped by contincntal deposits. and covered by a lower Burdigalian to lower Langhian shallow-water complex (Torre Rossa Fm.). A drowning sequence separates the Torre Rossa Fm. from the overlying Langhian to Tortonian plankton-rich chalks and calcarenites. the Lauro Formation. Th, e subsequent diatomites and tidal carbonates should be referred to lower Mcssinian Tripoli and Calcare di base [ormations. An ero sional unconformity separates the latter from the Rignano Formation (Late Messinian?). mainly a conglomeratic unit of deltaic origin. Post-Miocene ma rine deposits consist of shallow-water calcarcnit.cs of Middle to Late Pliocene age and referred 10 as. Gravina Cakaren_ ite. The sequence-stratigraphic evolution has becn rcconstructed. Thc main cbanges in the sedimcntation are related to second and third order climato-eu static cycles. whereas ongoing tectonics produced only locai unconformities (up to 50° of tilting) with negligible effects on the sediment composition. Pre-Mioccne distribution of emerged land coupled with Miocene contrac tional tectonics controlled the geometry and width of the Neogene basins. which wcre mainly narrow and elongated. and separated by emerging ridges.
Marconi et al.: Provenance of the Cotignola quarry sands (Northern Apennines) as a tool for palaeogeographical studies on the action of Senio and Santerno rivers in the Romagna floodplain. (IT ISSN 0394-3356, 2008). Palaeogeographic studies on western Romagna plain focus on the location of the ancient pattern of Santerno river, that nowadays joins Reno river before reaching the Adriatic sea near Ravenna. Several authors agree on locating this river in an eastern position during Roman Age and suggest an overlap of Santerno and Senio rivers in the Cotignola floodplain (Fig. 2). Outcrops of recent fluvial sediments are exposed at Cotignola quarry, near Faenza (Northern Apennines, Italy). According to the the present hydrography, the top sediments (age: ca 1.000 yrs) were deposited only by the action Senio river. On the contrary, the most ancient alluvial deposits of Cotignola quarry display different geological features suggesting a combination of Santerno and Senio contributions. In the sediment source areas of both rivers there are extensive sandstones and marls outcrops belonging to the " Marnoso-Arenacea " formation. Though, the Santerno source area stands out because it also contains basic volcanic and metamorphic rocks, coarse-grai-ned carbonates and cherts (deep oceanic and ophiolithic lithotypes belonging to the " Ligurian Units "). These rocks can be considered as petrographic tracers of Santerno drainage basin provenance. Sand samples were collected at Cotignola quarry and compared by means of petrographical analysis to the present day fluvial sands of Santerno deposits, which are to be considered as compositional standard for sediments resulting from the contribution of this river. At Cotignola quarry basic volcanic and metamorphic, coarse-grained carbonate and chert rock fragments occur in the most ancient sediments, whereas they decrease or disappear upward in the more recent sediments. These results prove that the upper sand top of Cotignola quarry is due only to sedimentation by Senio river, while the lower layers can be considered as the result of contributions from both rivers. Furthermore, a sand sample was collected near Maiano Monti (age: ca 2.200 yrs BP, radiometric dating), which is located in the flood-plain included between Senio and Santerno close to the northern part Senio river (Fig. 4). The petrographic analyses detect the presence of the ophiolithic tracers in the composition of sands collected at Maiano-Monti. The sediments provenance implement the hypothesis of an eastern location of Roman Santerno river in the Cotignola floodplain and suggest an overlap of its ancient pattern with that of Senio river, according to the archeologic and stratigraphic evidences (Fig. 2 and 3). Riassunto: Marconi et al.: Provenienza delle sabbie alluvionali recenti della cava di Cotignola e implicazioni sullo studio della paleo-geografia dei fiumi Senio e Santerno nella pianura romagnola (IT ISSN 0394-3356, 2008). Gli studi di paleoidrografia storica della porzione occidentale della pianura romagnola sono imperniati, soprattutto, sulla ricerca del tracciato antico del fiume Santerno, il quale proviene dall'Imolese e attualmente confluisce nel fiume Reno poco prima della foce di questo nell'Adriatico, a nord di Ravenna. La maggioranza degli autori recenti concorda sull'ipotesi che durante l'epoca romana il Santerno avesse in pianura un tracciato più orientale di oltre una decina di kilometri rispetto all'attuale, attraversando la zona di Cotignola, a nord di Faenza, oggi solcata dal solo torrente Senio (Fig. 2). Nella porzione sommitale della cava per laterizi di Cotignola affiorano sabbie alluvionali (deposte circa 1.000 anni fa secondo la profon-dità del piano di calpestio medievale nell'area) geomorfologicamente correlabili con il vicino dosso fluviale del Senio. A profondità di oltre 5-6 m affiorano argille e sabbie in facies di piana esondabile sottostanti i piani di calpestio di età romana. Allo scopo di verificare la provenienza delle alluvioni di età romana e pre-romana della cava di Cotignola, sono stati raccolti dei cam-pioni di sabbie per l'analisi petrografica lungo l'intera sezione stratigrafica e confrontati con un campione di sabbie prelevate nell'alveo attuale del Santerno, circa 10 km a valle di Imola. Infatti, in entrambi i bacini appenninici fonte di sedimento per il Senio e il Santerno affiorano estesamente le arenarie arcosiche e le marne della formazione " Marnoso-Arenacea " , ma solamente in quello del Santerno affiorano anche rocce basiche vulcaniche e meta-morfiche, selci e carbonati a grana grossa, cioè litotipi oceanici profondi e ofiolitici delle " Unità Liguridi ". Questi ultimi (ed in particolare le ofioliti) hanno quindi assunto, ai fini di questo lavoro, il significato di traccianti per discernere la provenienza dei granuli dall'area fonte del Santerno. Le sabbie basali della cava Cotignola risultano ricche in carbonati a grana grossa e selci e contengono frammenti di rocce basiche vul-caniche e metamorfiche, mentre quelle sommitali sono relativamente povere in queste componenti. In sostanza, i risultati dell'analisi modale confermano la deposizione da parte del solo Senio per gli strati sommitali della cava, mentre indicano, ragionevolmente, un contributo anche da parte del Santerno per la deposizione dei sedimenti profondi e più antichi. Un ulteriore confronto è stato eseguito con un campione di sabbie medio-grossolane, per cui la datazione radiometrica (14 C) ha indica-to un'età compresa tra 2.300-2.110 e 2.200-2.090 anni, prelevato in carotaggio a profondità di circa 11 metri presso Maiano Monti, località prossima al corso del Senio ubicata circa 12 km a nord di Cotignola (Fig.4). Anche la composizione di questo campione di sabbie depostesi in età immediatamente pre-romana mostra un probabile contributo di granuli provenienti dal bacino di drenaggio del Santerno, inclusa la presenza dei traccianti ofiolitici, analogamente ai sedimenti basali della cava di Cotignola Dallo studio sulla provenienza delle sabbie della piana di Cotignola si conferma più compiutamente l'ipotesi, in accordo con le ricostru-zioni paleoidrografiche su base archeologica descritte in Figura 2, della presenza di un tracciato in questa zona del Santerno in età romana e pre-romana, al quale, dopo il suo spostamento verso ovest in epoca medievale, si è poi sovrapposto l'attuale dosso fluviale del Senio.
Italian Journal of Geosciences, 2016
The Burdigalian-Tortonian Epiligurian succession in the Val Marecchia area comprehends different lithostratigraphic units deposited in a wedge-top basin during the northeastern migration of the thrust belt. The succession includes shallow-water carbonates passing to mixed carbonate-siliciclastic and to fine-grained pelitic sediments, capped by fluvio-deltaic coarse-grained deposits. Detailed field work and stratigraphy has allowed to characterize depositional units and unconformities and to delineate the sedimentary and tectonic evolution of the basin. Tectonics exerted a primary control at different stages. During the Burdigalian, a general uplift of the area allowed the onset of shelfal carbonate sedimentation on underlying Ligurian and Epiligurian deep-water sediments. At the Serravallian the sedimentation was influenced by the thrust reactivations which caused a marked asymmetry in the basin geometry and fill. The subsidence increase in the rear part of the basin determined the deposition of a thick succession of relatively deep fine-grained sediments (up to 800 m water-depth) (Serravallian, MNN6a through MNN6b subzones based on nannofossil biostratigraphy) and fossiliferous clays (lower Tortonian, biozones MNN8b-MNN9). Conversely, uplift is activated in the frontal part of the basin, causing the partial erosion of the Burdigalian-Langhian shallow-water carbonates. A relevant amount of this carbonate detritus is delivered to the foredeep, supplying the Marnoso-arenacea Fm. A general uplift of the area in the late Tortonian leads to the deposition of fluvio-deltaic conglomerates supplied by emerged rear sectors of the basin.