Statistical analysis of gravel deposits: a powerfull tool for reconstructing changes in landscape evolution

rnformat1on about the geomorph1c-sedimentary landscape evolution in response to tecton1cs an d/or relat1ve sea-level changes. The Lower Pleistocene deposits croppmg aut 1n the Lower Cec1na Valley are a useful means far reconstructing past changes m the supply area because they represent an ancient coastal zone. When marine sediments are reworked and conglomeratic layers are d1scont1nuous the clast litholog1cal analys1s becomes an invaluable tool to determine stratigraphic correlations between outcrops. Grave l deposits are part1cular powerfully far th1s arm because they reflect the lithologies cropping out m the anc1ent dramage area s. Three gravel layers have bee n recognized in the study area, belong1ng to three d1fferent Allostratigraphic Units (AUs) and clearly d1splaced by tectonics. Two statistica l analyses of gravel clasts, mtegrated by facres and paleontolagical data, from the Lower Pleistocene deposits in the Lower Cecina Valley {Tuscany, Italy) have been combined to unravel changes in the palaeo-drainage system. Data from sixteen outcrops were collected and 6400 clasts described. Although facies analysis, mrcrofmacro-palaeontology and petrographic characteristics of the gravel depos1ts have h1ghllghted the presence of three Aus, clast lithology difference has resulted to be the mai n discriminator in their identificati an. Cluster and principal component analyses of the 6400 clasts have permitted to i m prove the stratrgraphy of the Lower Plerstocene depos1ts and to constrain the re-routing ofthe_lower palaeo-Cecina River from a supposedly SE-NW to the present E-W drrect1on. The dramage systems in zone characterized by the presence of half-grabens with intrabasin transfer zones tends to intersect the main tectonic lineaments in arder to cut the footwall and pass to the hanging-wall basins. By contrast,_ when transfer zones are not present the drainage system tends to arrange 1tself parai lei to the depression of the half-graben and remains in the hanging-wall, like the major river of the Tuscany. The absence of deltaic depos1ts related to the dra1nage system of the paleo-Cecina River in the outsk1rt of the study area confrrm that during the beginning of the Early Pleistocene the river flowed northward. The diversion of the paleo-Cecina River took piace dunng the Early Pleistocene when a strike-slip fault started to create the Lower Cecina Valley

I depositi Del Pleistocene inferiore della Bassa val Di Cecina (Toscana, Italia): ricostruzione stratigrafico-deposizionale e proposta di suddivisione in unità allostratigrafiche

In the area comprised between the villages of Riparbella and Casale Marittimo (lower Cecina Valley, Tuscany, Italy) a large amount of Pleistocene deposits outcrops. Through a detailed geological survey integrated with facies analysis five litostratigraphic units, grouped in three Allostratigraphic Units (UA), have been detected. The oldest (UA7), lower pleistocenic in age, is formed by two litostratigraphic units (“Conglomerati delle Ginepraie” and “Sabbie ed argille ad Arctica islandica”) showing latero-vertical relationships and are organized in a transgressive-regressive cycle. The “Conglomerati delle Ginepraie” are arranged in a fining upwards trend and were deposited in small coalescent deltaic environments. Three depositional facies are recognized within the “Sabbie ed argille ad Arctica islandica” recording a fining-coarsening and deepening shallowing upward trend. The UA7 lies in unconformity above pre-quaternary deposits. The second (UA6), lower pleistocenic in age, is also constituted by two heteropic and transgressive litostratigraphic units (“Conglomerati delle Lame” and “Arenarie e Sabbie di Montescudaio”) lying in angular unconformity on the UA7. The “Conglomerati delle Lame”, showing a well developed imbrication, were deposited in a foreshore to upper shoreface depositional environment. The “Arenarie e Sabbie di Montescudaio” are characterized by a high to low planar-cross stratification and sometimes by overturned stratification and were deposited in a shallow marine environment. The regressive phase of this UA is not preserved due to erosive processes. The youngest unit (UA4, “Conglomerati di Serra all’Olio”), was instead deposited in fluvial-braided environment and lies in angular unconformity on the others UA. The middle pleistocenic age of this unit has been inferred on the basis of its stratigraphic position. This stratigraphic reconstruction strongly conflict from previous interpretations. Important climatic and geological remarks derive from the finding of two taxa (Arctica islandica and the coral Cladocora caespitosa) at different stratigraphic positions within the oldest unit (“Sabbie ed argille ad Arctica islandica”). The Arctica islandica testifying cold temperatures (4°C to 13°C) characterizes the first 5 meters of the unit, while beds of Cladocora caespitosa (15°C to 22°C the temperature range of this coral) only occur upwards. We retain that the deposition of the “Sabbie ed argille ad Arctica islandica” takes place during a warming phase and that the development of Cladocora caespitosa beds could be related to the maximum flooding conditions at the end of the transgressive phase. This interpretation leads to some notable chronostratigraphic implications

Paleogeographic reconstruction in extensional basins using statistical analysis of gravels deposits

The analysis of the basin-fill architectural stratigraphy provides quantitative constraints on the sediment supply to the basins which is in turn is controlled by the interaction of climate and tectonics. When marine sediments are reworked and conglomeratic layers are discontinuous the clast lithological analysis becomes an invaluable tool to deterrnine stratigraphic correlations between outcrops. The clast count in conglomerates deposits, often combined with other types of analysis (e.g. facies analysis, paleocurrent analysis), is a very powerful tool for correlating the conglomeratic layers. Two statistica! analyses of grave] clasts from the Lower Pleistocene deposits in the Lower Cecina Valley (Tuscany, ltaly) have been combined to unravel changes in the palaeo-drainage system. Data from sixteen outcrops were collected and 6400 clasts described. Facies analysis, micro and macro-palaeontology and petrographic characteristics of the grave! deposits have highlighted the presence of three allostratigraphic units. Clast lithology has resulted to be the main discriminator among the different units. Cluster and principal component analyses of the 6400 clasts h ave permitted to improve the stratigraphy of the Lower Pleistocene deposits and to constrain the re-routing of the lower palaeo-Cecina River from a supposedly SE-NW to the presentE-W direction. Short rivers feeding small fan deltas represented by the oldest allostratigraphic unit were abandoned in the Lower Pleistocene, when the re-routing of the Cecina River caused the captures of these streams. This evolution suggests a change in the tectonic regime of the area. The fan deltas developed on the hanging wall of norma! faults sub-parallel to the coast; a change to a transtensile tectonic regime caused the deviation of the main river channel toward the present coast and the formation of a pull-apart basin, which is now exploited by the Cecina River. This case study illustrates the usefulness of statistica! analyses on grave! deposits to infer the tectonic evolution of an area

L'edificio strutturale della media Val Nure (Appennino settentrionale): nuovi dati strutturali e biostratigrafici

In: Atti ticinesi di scienze della terra, serie speciale, v. 1, p. 105-116Consiglio Nazionale delle Ricerche - Biblioteca Centrale - P.le Aldo Moro, 7, Rome / CNR - Consiglio Nazionale delle RichercheSIGLEITItal

Elementi di correlazione stratigrafica tra il membro di Bersatico (Formazione delle Marne rosate di Tizzano ed il Membro di Poviago (Formazione di Val= Luretta) nell'Appennino settentrionale

In: Atti ticinesi di scienze della terra, serie speciale, v. 1, p. 117-122Consiglio Nazionale delle Ricerche - Biblioteca Centrale - P.le Aldo Moro, 7, Rome / CNR - Consiglio Nazionale delle RichercheSIGLEITItal