From cylindrical to non‐cylindrical foreland basin: Pliocene–Pleistocene evolution of the Po Plain–Northern Adriatic basin (Italy)

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SHORT NOTES ON THE SHIMSHAL VALLEY GEOLOGY (WESTERN KARAKORUM-PAKISTAN)

A geological reconnaissance carried out during Summer 1982 along the lower and middle Shimshal Valley allows to identify some lithostratigraphic units madc up of slates (shaly and sandy deep— sea turbidites), shelf limestones and dolomites. The Upper Paleozoic age of some fossiliferous limestones is well documented. Ultrabasic dykes discordant to both bedding and cleavage intruded slates and dolomites

LIVELLI CALCAREI CLASTICI DEL MIOCENE SUPERIORE E PLIOCENE NEL SOTTOSUOLO MOLISANO-PUGLIESE

The Molise and Apulia subsurface exploration has found clastic calcareous layers at the top of the Mesozoic—Miocene carbonate sequence and within the Middle Pliocene turbidites. The first are the result of Karst—fissures and crushing on the structural highs and mass flows at the base of fault slopes. Within the turbidites a biocalcarenitic horizon IS an electric good marker which proves an event of a shelf build up. It corresponds to the Middle Pliocene gap widely developed in the Apennines

Sustained quasi-steady turbidity current : outcrop evidence from the Pliocene peri-Adriatic foredeep (Cellino Fm., Central Italy)

The aim of this work is to investigate the nature of the numerous, very thick deep-water sheet-sandstones that dominate the lower portion of the Cellino Formation (Central Italy). The studied turbidite system (about 2,500 m thick) represents the Lower Pliocene turbiditic filling of the outer Abruzzo sector of the Periadriatic foredeep. The foredeep was affected by compressional deformation linked to the overall migration of the chain-foredeep system toward the east. Tectonic activity was mostly coeval with the sedimentation and propagated towards the foreland; thrusting became progressively younger from W to E. The Cellino Basin has been intensely explored, being the site of hydrocarbon-bearing sands. The turbidite beds can be distinctively resolved in the well logs and correlated to the measured sedimentary sections on outcrop. Based on well log correlation, tens of individual beds up to 23 m thick have been traced along the axis of the basin over distance in excess of 100 km and, perpendicularly to the basin, over distance of 30-40 km (Carruba et al. in press), with sand volumes on the order of a few 10’s Km3 (10 – 80 Km3). Palaeocurrent data taken from basal flute structures indicates southerly-directed flows, parallel to the depocentral axis of the basin. The thickest beds show a basin-wide extension, onlapping the basin margins without significant thickness variation. The internal organization of the studied megabeds provides evidence for occurrence of long-lived flows and suggests deposition by gradual aggradation from sustained currents (sustained turbidity current; Kneller and Branney, 1995). The following features have been argued to be characteristic for sustained currents: (i) turbidite beds of extraordinary volume and thickness, (ii) very thick massive basal division (0.5 – 6 m thick), (iii) very frequent alternation of structureless and laminated intervals associated to internal scour surfaces, (iv) thick massive mudstone cap (1-10 m) that terminates the vertical organization of the sedimentary structures, (v) crudely developed grain-size profile that is overall upward fining (normally graded), (vi) abundant organic matter, (vii) extensive water-escape features. The very thick massive basal division observed in the studied megabeds can be explained with progressive aggradation and absence of traction at the depositional flow boundary. The very frequent alternation of structureless and laminated intervals observed within the studied deposits, and their internal scour surfaces reflect temporal variation in flow velocity and sediment flux within the same current, as indicated by the discontinuity of the scour surface and the constant grain size above and below the surfaces. The graded upper part of the studied megabeds (a thick massive mud cap terminates the vertical organization of the sedimentary structures) represents the deposits of the waning stage of the current. Assuming a quasi-steady flow scenario we can explain the nature of the numerous very thick megabeds within the Cellino Fm considering that the determining factors of the thickness of the studied deposits are the confinement of the basin and the rate and the duration of deposition, which may proceed as long as the current maintains a flux of grains towards the site of deposition. The origin of these large-volume turbidity currents and their high rate of occurrence can be related to an interaction of many factors and external controls, which are typical of the ancient foredeep basins (Mutti et al., 2003). Our data suggest that the studied megabeds could be originated from catastrophic floods and sediment failures during relative falling- and low-stand stage of sealevel forced by dramatic tectonic uplift of basin margins. Where the mountains fronts are close to shoreline, floods would be able to carry the majority of sediment load directly to the sea; the final depositional area of the ancient fluvial system that probably fed the Cellino basin lies in the deep water, far away from river mouths, and it is recorded by basinal turbidite sandstones and megabeds. Although an understanding of climatic controls is extremely difficult on the basis of available data, high-frequency climatic pulses (that provided the water through which sediments were periodically flushed to the Periadriatic foredeep by flood-related process) could explain the amount of stacked megabeds. In this model, lower-frequency tectonically-forced cycles of uplift/denudation account for sediment availability through time. Consequently, the lower portion of the Cellino Formation could correspond to a stage of a single uplift/denudation cycle. In this stage, the tectonically active Cellino basin reaches its highest instability because the elevation of drainage basins is maximum and its proximity to the shoreline minimum

Evoluzione del Bacino del Cellino : geometria ed analisi di facies dei pricipali corpi sabbiosi (avanfossa Periadriatica pliocenica, Italia centrale)

Lo studio dell\u2019evoluzione del Bacino del Cellino durante il Pliocene inferiore permette di interpretare, sulla base di nuove osservazioni sedimentologiche, il riempimento torbiditico dell\u2019avanfossa Periadriatica nel settore Abruzzese. In una prima fase (Pliocene basale) il bacino si apre verso sud permettendo la sedimentazione di spessi strati di conglomerato (conglomerati di Pietranico) con provenienza meridionale dal vicino Massiccio della Maiella. La presenza di indicatori di corrente alla base degli strati, la natura dei clasti e il loro sviluppo dimostrano la loro origine meridionale. Nello stesso tempo, un\u2019estensione flessurale si verifica nella zona di cerniera della placca Adriatica in sottoscorrimento (downbending), originando faglie longitudinali dirette N-S, parallele alla direzione delle strutture appenniniche. Il depocentro, suddiviso in graben paralleli, raggiunge la sua massima profondit\ue0 e diventa l\u2019area di accumulo di torbiditi questa volta con provenienza settentrionale, cos\uec come avviene di norma nell\u2019avanfossa Periadriatica. All\u2019inizio le correnti torbiditiche hanno volumi limitati e composizione molto argillosa (fase di starvazione), ma rapidamente il tasso di sedimentazione cresce con uno sviluppo di una sequenza di tipo \u201ccoarsening and thickening upward\u201d. In questo momento iniziano ad accumularsi spessi strati sabbiosi intercalati a torbiditi sottilmente stratificate. Il bacino assume una nuova forma, con la chiusura a sud dovuta al sollevamento di una struttura trasversale al bacino stesso (Alto del Cigno). La dimensione del bacino pu\uf2 essere stimata in almeno 150 km nella direzione parallela all\u2019asse del bacino e 30 \u2013 40 km nella direzione perpendicolare (Carruba et al., 2006). Il grande volume delle correnti di torbida permette la sedimentazione di strati che si depositano nell\u2019intero bacino: le correlazioni strato a strato, effettuate grazie all\u2019utilizzo di dati di pozzo (log elettrici) mostrano un ottimo grado di correlazione senza apprezzabili variazioni di natura e di spessore degli strati (Fig.1). I flussi torbiditici sono probabilmente molto diluiti e quindi in grado di muoversi per lunghe distanze e quindi estendersi per l\u2019intera area del bacino; nel Bacino del Cellino questa caratteristica (e cio\ue8 la presenza di strati con estensione bacinale) \ue8 peculiare della porzione inferiore della successione stratigrafica (membri E \u2013 D \u2013 C della Formazione di Cellino). Contrariamente a quanto avviene per i suddetti membri, i megastrati del soprastante membro B mostrano (come si pu\uf2 dedurre dalle correlazioni di sottosuolo) una estensione laterale limitata ad alcune aree del bacino e sensibili variazioni di spessore. Il membro A, che chiude la Formazione di Cellino, \ue8 costituito principalmente da torbiditi sottilmente stratificate con rari megastrati di estensione areale limitata e di difficile correlazione. Mentre in passato si \ue8 studiata attentamente la geometria di questi megastrati a scala bacinale sulla base di dati di sottosuolo, nel presente studio ci siamo focalizzati su un\u2019accurata analisi di facies partendo da dati raccolti in affioramento. Ci\uf2 ha permesso di effettuare nuove considerazioni sui meccanismi di trasporto e deposizione. In particolare \ue8 stato osservato quanto segue: 1) membri E - D - C La porzione inferiore della Formazione di Cellino (Fig.2) \ue8 costituita da megastrati tabulari con alla base arenarie molto spesse e massicce. La loro organizzazione interna indica la presenza correnti \u201csostenute\u201d che durano a lungo nel tempo (sustained turbidity current; Kneller and Branney, 1995) e depositano importanti spessori di sedimento in aggradazione. Le seguenti caratteristiche interne posso indicare flussi \u201csostenuti\u201d: (i) strati torbiditici con spessori e volume enormi, (ii) presenza di una porzione massiva basale molto spessa (0.5 \u2013 6 m), (iii) frequenti ripetizioni verticali di intervalli deposizionali massivi e a laminazione parallela e incrociata, associate a sottili superfici di erosione, (iv) porzione sommitale pelitica molto spessa (1 \u2013 10 m) oppure rappresentata da torbiditi sottili, (v) profilo granulometrico dello strato non ben sviluppato ma che in generale indica una diminuzione della granulometria verso l\u2019alto, (vi) abbondante materia organica, (vii) importanti strutture dovute a fuga d\u2019acqua. La presenza dello spesso intervallo massivo alla base pu\uf2 essere spiegata come il risultato di una progressiva aggradazione e assenza di trazione. La frequente ripetizione verticale di strutture sedimentarie (intervalli massivi e intervalli laminati) e la presenza di superfici erosive all\u2019interno dei megastrati riflettono le variazioni nel tempo della velocit\ue0 del flusso all\u2019interno della stessa corrente (flussi quasi-stazionari). La porzione superiore gradata (da sabbie fini a silt) dei megastrati rappresenta la fase finale della corrente, quando si assiste ad una sua progressiva diminuzione della velocit\ue0 nel tempo. Assumendo uno scenario caratterizzato dalla presenza di flussi torbiditici quasi-stazionari (e cio\ue8 che durano a lungo nel tempo), risulta pi\uf9 semplice spiegare la presenza dei numerosi megastrati che caratterizzano la porzione inferiore della Formazione di Cellino. In quest\u2019ottica, i fattori che determinano lo spessore degli strati sarebbero il confinamento del bacino, il tasso e la durata dell\u2019evento deposizionale che, come spiegato precedentemente, pu\uf2 perdurare fino a quando la corrente \ue8 in grado di mantenere (sostenere) un flusso di sedimento verso le aree deposizionali del bacino. 2) membro B Una riattivazione dell\u2019attivit\ue0 tettonica da origine a una nuova morfologia del bacino che si caratterizza per un generale sollevamento dell\u2019area settentrionale e conseguente approfondimento delle regioni meridionali del bacino, dovuto ad una migrazione verso sud del depocentro dell\u2019avanfossa. Nella porzione inferiore di questo membro i megastrati diventano meno frequenti e tendono ad assottigliarsi verso sud (flussi depletivi sensu Kneller and Branney, 1995), mentre nella porzione superiore del membro B I flussi tendono ad oltrepassare le aree sopracorrente e a depositarsi nelle porzioni pi\uf9 meridionali del bacino (flussi accumulativi sensu Kneller and Branney, 1995). L\u2019efficienza di trasporto \ue8 ancora molto alta: i megastrati si caratterizzano per la presenza di sequenze di Bouma troncate alla base ma con un intervallo pelitico a tetto molto sviluppato. 3) membro A Durante la deposizione del membro A il sollevamento delle aree settentrionali aumenta: come ben documentato dai dati di pozzo (es. le superfici erosionali e i depositi di riempimento di canale nei pozzi Bellante) si sviluppano superfici erosionali associate alla presenza di canali profondamente incisi che progradano verso i quadranti meridionali del bacino. Questa progradazione verso sud, associata ad un generale assottigliamento degli strati, \ue8 ben osservabile sul terreno lungo il torrente Fino e i suoi affluenti. I nostri dati suggeriscono che l\u2019evoluzione sedimentaria del bacino del Cellino \ue8 da ricollegarsi all\u2019interazione di diversi fattori di controllo, interni ed esterni al bacino, che sono caratteristici di molti bacini di avanfossa. In particolare, i megastrati del membro E potrebbero essere dovuti a flussi catastrofici e/o franamenti di sedimento da una scarpata durante un abbassamento relativo del livello marino indotte da un\u2019intensa fase di sollevamento tettonico delle aree marginali del bacino stesso

Sustained turbidity currents : evidence from the Pliocene Periadriatic foredeep (Cellino Basin, Central Italy)

The aim of this work is to investigate the nature of the numerous, very thick deep-water sheet-sandstones that dominate the lower portion of the Cellino Formation (Central Italy). The studied turbidite system (about 2,500 m thick) represents the Lower Pliocene turbiditic filling of the outer Abruzzo sector of the Periadriatic foredeep. The foredeep was affected by compressional deformation linked to the overall migration of the chain-foredeep system toward the east. Tectonic activity was mostly coeval with the sedimentation and propagated towards the foreland; thrusting became progressively younger from W to E. The Cellino Basin has been intensely explored, being the site of hydrocarbon-bearing sands. Very thick beds can be distinctively resolved in the well logs and correlated to the measured sedimentary sections on outcrop. Based on well log correlation, tens of individual beds up to 23 m thick have been traced along the axis of the basin over distance of at least 150 km and, perpendicularly to the basin, over distance of 30-40 km (Carruba et al., 2006). Palaeocurrent data taken from basal flute structures indicates southerly-directed flows, parallel to the depocentral axis of the basin. The thickest beds show a basin-wide extension, onlapping the basin margins without significant thickness variation. The Cellino Formation is mostly buried and crops out in a narrow belt a few kilometers west of the Cellino gas field. The internal organization of the studied megabeds provides evidence for occurrence of long-lived flows and suggests deposition by gradual aggradation from sustained currents (sustained turbidity current, Kneller & Branney, 1995). Assuming a quasi-steady flow scenario we can explain the nature of the numerous very thick megabeds within the Cellino Fm considering that the determining factors of the thickness of the studied deposits are the confinement of the basin and the rate and the duration of deposition, which may proceed as long as the current maintains a flux of grains towards the site of deposition. The origin of these large-volume turbidity currents and their high rate of occurrence can be related to an interaction of many factors and external controls, which are typical of the ancient foredeep basins (Mutti et al., 2003). The depocenter migration of the Periadratic Foredeep caused the accumulation of thick sedimentary bodies, which developed progressively within the depositional axes. Since the collisional margins were convergent, there was longitudinal migration of depocenters. Our data suggest that the studied megabeds could be originated from catastrophic floods and sediment failures during relative falling- and low-stand stage of sea-level forced by dramatic tectonic uplift of basin margins and turbidity systems already deposited in the northern areas

From seismic to bed : surface\u2013subsurface correlations within the turbiditic Cellino Formation (central Italy)

The area east of the Gran Sasso Chain in Central Italy has been explored in detail because it holds a hydrocarbon field (Cellino Field), located in the Lower Pliocene foredeep turbidites of the Cellino Formation. Correlation has been made between the hydrocarbon-bearing sedimentary bodies and the same stratigraphic intervals cropping out only few kilometers to the west. The area thus offers a rare example where lithofacies, observed in the field, electrofacies displayed by the electric logs of the wells and seismofacies revealed by seismic survey can be compared. This surface-subsurface integrated study of the Cellino Formation has revealed the presence of different turbiditic facies associations, their related electrical expressions and the possibility of a seismostratigraphic subdivision of the unit. These correlations exemplify the different resolution of these three complementary methods of investigation

Nuovi dati sull'assetto geologico e sull'evoluzione paleogeografica giurassica del M. Coro (Val Sabbia, Brescia). New data n the geologic setting and on the Jurassic paleogeographic evolution of the M. Coro (Sabbia Valley, Brescia, Southern Alps).

The Liassic carbonate sequence outcropping on the M. Coro area was affected by extensional events causing its break-up and the sinking of blocks of marginal platform. The irregular relief was the site of gravitational slides along new formed fault-slopes. The movement took place along sub-parallel sets of planes during the Early Jurassic. Fragments of platform (Corna limestone) were therefore resedimented at the footwall of faults (megabreccias) or interbedded as olistoliths into the pelagic sequence (Medolo Formation) at different levels. The geological researches, extended outside the M. Coro area, give moreover evidence of the paleorelief: highs are located west- and north-wards (Teglie), lows along the well-exposed section of the Chiese River (South of Vobarno)

Sedimentary evolution in a migrating foredeep basin : geometry and facies analysis of the massive sandy bodies of the Cellino Formation (Lower Pliocene Periadriatic foredeep, Central Italy)

The sedimentary evolution of the Lower Pliocene Periadriatic Foredeep in Central Italy is described on the basis of integrated facies analysis of the numerous turbidite massive sandy bodies (megabeds) and correlations of well log-field data, which give new perspectives on the effects of the basin migration. The basin evolution shows four major morphological changes during the Lower Pliocene. In a first phase, the basin was fed From the south, as testified by coarse clastic, turbiditic sediments coming from the Maiella Massif. Subsequently (second stage) its Southern feeding system was switched off by the uplift of a structural high (Cigno structural high) and the basin received turbidite fill from northern source areas. Basin-wide, very thick (2 to 22 m) megabeds are the result of aggradation of high efficiency, large-volume turbidites that can be interpreted as deposited from sustained (long-lived) currents flowing in a confined basin. The foredeep migration towards the south-east, common in the entire Periadriatic foredeep, caused, in the third phase, a reactivation of the sedimentation with megabeds thinning southward in the northern uplifting area, followed by megabeds prograding and aggrading into a new depocenter located to the south. In the final stage, the increasing uplift of the northern part of the basin, due to thrusts active in the north-western area, gave rise to its deep erosion, above a relevant unconformity, development of channels filled by sands in the inner fan and progradation of the outer fan southward. It is hoped that this study can be applied to other migrating basins of the Periadriatic Foredeep

Sedimentary evolution in a migrating foredeep basin: Geometry and facies analysis of the massive sandy bodies of the Cellino Formation, Lower Pliocene Periadriatic Foredeep (Central Apennines, Italy)

The sedimentary evolution of the Lower Pliocene Periadriatic Foredeep in Central Italy is described on the basis of integrated facies analysis of the numerous turbidite massive sandy bodies (megabeds) and correlations of well log-field data, which give new perspectives on the effects of the basin migration. The basin evolution shows four major morphological changes during the Lower Pliocene. In a first phase, the basin was fed from the south, as testified by coarse clastic, turbiditic sediments coming from the Maiella Massif. Subsequently (second stage) its southern feeding system was switched off by the uplift of a structural high (Cigno structural high) and the basin received turbidite fill from northern source areas. Basin-wide, very thick (2 to 22 m) megabeds are the result of aggradation of high efficiency, large-volume turbidites that can be interpreted as deposited from sustained (long-lived) currents flowing in a confined basin. The foredeep migration towards the south-east, common in the entire Periadriatic foredeep, caused, in the third phase, a reactivation of the sedimentation with megabeds thinning southward in the northern uplifting area, followed by megabeds prograding and aggrading into a new depocenter located to the south. In the final stage, the increasing uplift of the northern part of the basin, due to thrusts active in the north-western area, gave rise to its deep erosion, above a relevant unconformity, development of channels filled by sands in the inner fan and progradation of the outer fan southward. It is hoped that this study can be applied to other migrating basins of the Periadriatic Foredeep