Stratigrafia fisica ed analisi di facies della formazione marnoso-arenacea, affiorante fra la valle Santerno e la valle Savio (Langhiano-Serravalliano, Appennino settentrionale, Italia)

Questo lavoro ha avuto come oggetto la stratigrafia e l’analisi di facies di un intervallo di circa 2.500 m di spessore nei depositi torbiditici della successione stratigrafica langhiana e serravalliana della Formazione Marnoso-arenancea (FMA). Seguendo le orme del lavoro di Ricci Lucchi & Valmori (1980), la correlazione stratigrafica ad alta risoluzione è stata realizzata attraverso la misura di sette sezioni stratigrafiche fra le valli del Santerno e del Savio per un totale di 6.715 m. I risultati di questo lavoro mostrano chiaramente come la stratigrafia e l’ambiente deposizionale della Fm. Marnoso-arenacea siano molto più complessi di quelli proposti nei lavori precedenti. Questa complessità è dovuta, principalmente, all’influenza che la tettonica, legata l’evoluzione del bacino, ha avuto sulla distribuzione delle facies. La storia evolutiva della successione sedimentaria della Formazione Marnoso-arenacea, infatti, è strettamente legata alla propagazione dei fronti compressionali verso NE che portano alla progressiva chiusura del bacino di avanfossa. Nella FMA, perciò, si registra una forte interazione tra strutture a vergenza appenninica e apporti sedimentari diretti verso sud-est. Le analisi stratigrafico-sedimentologiche all’interno dell’intervallo studiato hanno permesso di individuare cinque (5) unità stratigrafiche informali (Unità I, II, III, IV e V). Queste unità sono state differenziate principalmente in funzione del controllo strutturale messo in evidenza dalla presenza di alti strutturali e depocentri e dalla progressiva comparsa e scomparsa di determinati tipi di strati che registrano un’intergioco tra efficienza del flusso e fisiografia del bacino. Più precisamente, l’Unità I è stata misurata soltanto nella porzione più distale (sezioni D, E ed F) e ha uno spessore di circa 240m. Il passaggio all’unità soprastante è marcata da un controllo tettonico che cambia drasticamente la sedimentazione. L’unità II, infatti, presenta una grande variazione di spessore che va da circa 50 m, nella sezione più prossimale B al di sopra del Caotico di Acquadalto, a circa 230 m nella sezione D. L’unità III, invece, è deposta durante la massima espansione del bacino dove la grande maggioranza degli strati possono essere correlati regionalmente per circa 30x120 Km (Ricci Lucchi & Valmori, 1980 e Amy & Talling, 2006). L’Unita IV, a sua volta, è caratterizzata da un più evidente ritorno dell’attività tettonica, rappresentata principalmente dall’innalzamento dalla porzione più distale (vedasi sezione F nella zona di Verghereto). Il registro più significativo relativo alla chiusura del bacino avviene proprio al passaggio di questa unità all’Unità V con la deposizione dei caotici di Casaglia e Nasseto, considerati qui tempo equivalente come già suggerito da Ricci Lucchi (1981 e 1986) e Lucente & Pini (2002). In questo periodo l’alto a sud, ubicato nella zona di Verghereto, diventa sempre più accentuato e i sedimenti torbiditici del sistema Firuenzola (nel senso di Mutti et al., 2002), depositati più a nord, passano sottocorrente alle Marne di Verghereto. Queste marne che vengono deposte al di sopra di questo alto strutturale a partire del caotico di Nasseto, cioè nel Serravalliano superiore (Amorosi, 1987), sono oggi preservate a causa di un’importante faglia diretta caratterizzata da un rigetto di circa 600 m. Questa faglia e il relativo rigetto sono stati individuati in questo lavoro grazie soprattutto allo studio stratigrafico effettuato. In questo periodo, inoltre, a causa di questo alto, il depocentro viene forzato a spostarsi verso nordest, cioè nella zona più esterna dove è ubicata la sezione G. Queste cinque unità stratigrafiche, come detto prima, registrano la progressiva chiusura del bacino e sono influenzate dall’alto di Verghereto, soprattutto durante la deposizione delle unità stratigrafiche più sommitali IV e V. Quest’ultima unità nella sezione B nella Valle del Senio, che è spessa quasi 2.000 metri, raggiunge il sistema di Firenzuola che insieme al sistema del Paretaio, nella Valle del Santerno, preannunciano il passaggio ai sistemi misti di Fontanelice e Sarsina (nel senso di Mutti et al., 2002 e Roveri et al., 2002). Questa tettonica compressiva, perciò, ha avuto un ruolo importante nel controllare il tipo di facies e facies tract della FMA attraverso la formazione di depositi relativamente più complessi rispetto a quelli dei modelli classici presenti in letteratura. Fra i circa 8.000 strati descritti e misurati, i cinque tipi di strati e relativi facies tract (nel senso di Mutti, 1992) considerati particolarmente rappresentativi di questa interazione sono: 1) Strati tripartiti da spessi a molto spessi caratterizzati da unità intermedie a slurry, che passano sottocorrenti in modo brusco a strati sottili d’arenaria molto fine laminata. 2) Strati tripartiti molto spessi caratterizzati da un’unità caotica intermedia tipo slump. Questi strati, come quelli tipo 1, passano sottocorrente in modo brusco a strati sottili d’arenaria molto fine laminata. 3) Strati gradati da spessi a molto spessi d’arenaria media e fine con una spessa unità pelitica sommitale, generalmente caratterizzati da un’aumento di spessore sottocorrente e da evidenti cambi di paleocorrenti rispetto a quelle basali indicate dalle strutture di fondo. 4) Strati gradati da spessi a medi caratterizzati soprattutto da arenaria medie e fini che diventano progressivamente più fini e sottili sottocorrente. 5) Strati sottili di arenaria molto fine. Essi sono presenti specialmente nelle zone più distali o nei pressi di alti topografici. In particolare, gli strati tripartiti del tipo 1 sono interpretati essere legati ad intensi fenomeni di erosione seguiti da decelerazioni relativamente brusche, gli strati di tipo 2, invece, sono visti legati più direttamente ad un controllo tettonico mentre gli strati tipo 3 e 5 vengono interpretati come il prodotto di processi di rebound e ponding. Il controllo strutturale nella formazione di tutti questi tipi di strati, a parte gli strati tipo 4 che sono deposti da flussi che decelerano nel tempo e nello spazio in modo più uniforme, è qui considerato di fondamentale importanza.This work presents the stratigraphy and facies analysis of an interval of about 2,500 metres in the Langhian and Serravallian stratigraphic succession of the foredeep turbidites of Marnoso-arenacea Formation. High-resolution stratigraphic analysis was made by measuring seven stratigraphic logs between the Sillaro and Marecchia lines for a total thickness of about 6,700 metres. The results of this work show that the stratigraphy and depositional setting of the Marnoso-arenacea Fm. was deeply influenced by syn-depositional structural deformation. As a result, the vertical stacking pattern of the Marnoso-arenacea actually records a close interaction between thrust propagation towards the NE and deposition from turbidity currents flowing towards the SE, i.e. parallel to the thrust front. In fact, the stratigraphic succession under study was subdivided into five informal stratigraphic units (I, II, III, IV, V) particularly on the basis of the formation of structurally controlled topographic high and depocentres. The Unit I has only been identified in the southern part of the studied area (logs D, E and F) and has a thickness of about 240 metres. The Unit II has a basal boundary marked by an important surface related to a tectonic control that drastically changes the sedimentation conditions. This unit in the northern zone is relatively thin, with a total thickness of around 60 m in the Senio Valley (log B ). In the more southern zone (Bidente Valley, log D), on the contrary, the thickness is about 230 m, thus highlighting the formation of an important depocentre. This basin physiography is associated to the north (logs A, B and C) with a tectonic uplift able to generate the Acquadato chaotic unit (mass transport complex) whose origin depends more probably on the propagation of the Monte Castellaccio thrust (see also Lucente, 2004). The Unit III shows a relatively scarce tectonic activity. At this time due to this relatively quiescent tectonic activity, the foredeep basin reached its maximum extension. The bed at the base of this unit (bed 138) corresponds to the A1 bed of Ricci Lucchi and Valmori (1980), and marks the first deposit that can be regionally correlated above the Acquadalto Chaotic unit. The basin’s relative tectonic stability allows the formation of beds characterized by such great tabularity and lateral extension that the single beds can be traced for an area of about 120x30 Km (Ricci Lucchi and Valmori, 1980; Amy and Talling; 2006). The Unit IV marks an increase of tectonic activity with the formation of an unmistakable depocentre in the northern zones, mainly in the Lamone (log C) and Senio (log B) valleys. More precisely, the thickness of this stratigraphic unit in log B is about 800 m while in log F it is about 550 m with, therefore, a thinning gradient of 5.5m/km, which is about nine times greater than Unit III, showing the progressive uplifting of the basin’s southern portion that led also to the formation of the Susinello chaotic unit. The basal boundary of the Unit IV is marked by the presence of the Casaglia and Nasseto chaotic units, that are considered here as time-equivalent, as already suggested by Ricci Lucchi (1981 and 1986). This tectonic control of the sedimentation is clearly observed where the thick beds in the more westerly proximal zone (Fiorenzuola System di Mutti et al, 2002) pass downcurrent into very thin beds associated with the Verghereto Marl. This Marl is deposited above a structural high beginning from the Nasseto chaotic unit, i.e. upper Serravallian (Amorosi, 1987) and today is preserved by erosion thanks to an important normal fault with NW-SE direction and a dip slip of about 600 m. In that time, related of that high, the depocentre is forced to shift toward northeaster external zones (log G). These five stratigraphic units, therefore, record the progressive closure of the foredeep, due to the northeastward propagation of the various thrust sheets and are strongly influenced by the Verghereto high, particularly during the deposition of the upper units IV and V. Each unit, moreover, was singled out thanks also to the progressive appearance and disappearance of five types of bed and thus as particularly significative facies tracts, since they are believed to be strongly related to an interaction between flow efficiency and basin physiography. The five types of bed and thus the facies tract distinguished are: Type 1 bed: Thick [30 cm 100 cm) tripartite beds characterized by internal slurry unit that pass downcurrent into thin and fine-grained beds relatively suddenly. These beds are interpreted as related to relatively sudden decelerations of mud-rich turbidity currents. Type 2 bed: Very thick (H >> 100 cm) tripartite beds characterized by an internal slump-type chaotic unit. These beds pass downcurrent into thin and fine-grained beds in a sudden way. These beds are found at the base of structural controlled stratigraphic units and are here interpreted as elements indicating tectonic uplift. Type 3 bed: Thick (30 cm > 100 cm) fine-grained beds capped by a thick mudstone unit generally characterized by an increase in thickness downcurrent. These beds are interpreted as associated with rebound and ponding processes. Type 4 bed: Medium (10 cm < H < 30 cm) to thick (30 cm < H < 100 cm) fine-grained beds that become progressively finer and thinner downcurrent due to deposition from depletive waning turbidity currents. Type 5 bed: Thin to very thin (H < 10 cm) fine-grained beds characterized by combined flow structures associated with reflection and ponding processes. These are present especially in distal zones or near topographic highs. The lateral geometries of these types of bed are quite different. Type 1 and 2 beds pass downcurrent into thin and fine-grained beds in a relatively abrupt way (see also Amy and Talling, 2006), while type 3 beds tend either to thicken or to maintain more or less the same thickness downcurrent. Type 4 beds on the other hand tend to become progressively thinner and finer downcurrent whereas type 5 beds tend to be present only in more distal zones and above or in proximity of topographic highs. In conclusion, type 1 and 2 tripartite beds characterized by intermediate slurry and chaotic unit respectively, thick type 3 beds, related to rebound and ponding processes, and type 5 beds are here considered particularly diagnostic in identifying the structurally-controlled depocentres and consequently the five informal stratigraphic units singled out in the stratigraphic succession studied

Rhizobium strains competitiveness on bean nodulation in Cerrado soils

The objective of this work was to identify the most competitive and effective Rhizobium strains in order to increase common bean yield by nitrogen fixation as alternative or complementation to the nitrogen fertilization. Competitiveness tests were lead in axenic conditions, in Cerrado soil pots and in three field experiments, with native Rhizobium strains that were previously identified, according to their effectiveness and genetic variability. The identification of strains in nodules was performed using serological tests (axenic conditions) - agglutination and enzyme linked immunosorbent (Elisa) assays - and random amplified polymorfic DNA (RAPD) (Cerrado soil). Plant yield was determined using the dry weight (greenhouse conditions), total N and grain yield (field experiments). Among the analyzed Rhizobium strains, native strain SLA 2.2 and commercial strain CIAT 899 were the dominant nodules in plants of the most productive plots, presenting yield productivity similar or higher to those obtained in treatments where 20 kg ha-1 of N were applied.O objetivo deste trabalho foi identificar as estirpes de Rhizobium mais efetivas e competitivas, a fim de maximizar a produtividade do feijoeiro por meio da fixação de nitrogênio, como alternativa à adubação nitrogenada. Foram conduzidos testes de competitividade em condições axênicas, em vasos com solo do Cerrado e em três experimentos de campo, com estirpes de Rhizobium nativas, previamente selecionadas quanto à efetividade e à variabilidade genética. A identificação das estirpes nos nódulos foi efetuada por meio das técnicas de aglutinação e ensaio imunoabsorvente de ligação de enzimas (Elisa), em condições de casa de vegetação, e pela técnica de DNA polimórfico amplificado ao acaso (RAPD), em solo de Cerrado. A produtividade das plantas foi determinada pela produção de matéria seca, teor de N e produção de grãos (condições de campo). A estirpe nativa SLA 2.2 e a estirpe comercial CIAT 899 foram dominantes nos nódulos das plantas das parcelas mais produtivas, com índices de produtividade iguais ou superiores aos obtidos nos tratamentos em que foram aplicados 20 kg ha-1 de N

Influence of flow containment and substrate entrainment upon sandy hybrid event beds containing a co-genetic mud-clast-rich division

Individual sandstone beds containing a co-genetic mud-clast-rich (MCR) division are being increasingly described from the distal reaches of many deep-water fan systems. These deposits, termed hybrid event beds, are considered to record a flow whose composition and rheology changed significantly to become increasingly more argillaceous (clay-rich), MCR and turbulence-suppressed during the deposition of a single event bed. Studies of confined systems, in which gravity flows were affected by confining sea-floor topography, have documented similar deposits recording turbulence suppression in proximity to confining sea-floor topography (e.g., basin margins). In new research from a confined, contained system from the Castagnola Basin of NW Italy, lateral transects of individual sandstone beds 5 km in extent show that individual sandstone beds contain a co-genetic MCR division which is often; 1) extensive across the basin rather than localised adjacent to confining topography; 2) exhibits rapid, significant and repeated variation in depositional character over short length scales (tens to hundreds of metres), specifically in terms of the thickness of co-genetic MCR divisions and the size and abundance of clasts contained within them; and 3) exhibits variation in depositional character over larger length scales (> 1 km) which is non-systematic in relation to palaeoflow direction or increasing proximity towards the counter slope of the downstream confining northern basin margin. A suite of factors within the Castagnola Basin is thought to have resulted in the deposition of these co-genetic MCR divisions whose thickness and distribution are less predictable in relation to confining sea-floor topography than those described from other confined uncontained settings. Specific factors include; 1) recent and voluminous entrainment of muddy substrate at seemingly random locations across the basin floor and their support and transport within a high sediment concentration gravity flow; and 2) containment (ponding) of gravity flows within a confined basin, which is thought to have established extensive and complex three dimensional flow dynamics across the basin following flow interaction with multiple basin margins. This research highlights the role of entrainment of muddy substrate and subsequent transport processes of muddy substrate for developing co-genetic MCR divisions, as well as the importance of understanding the degree of containment depositional systems experienced when considering the spatial distribution of depositional facies, and thus reservoir quality, in topographically complex settings

Hybrid event bed character and processes linked to turbidite system sub-environments: the North Apennine Gottero Sandstone (north-west Italy)

This study documents the character and occurrence of hybrid event beds (HEBs) deposited across a range of deep-water sub-environments in the Cretaceous–Palaeocene Gottero system, north-west Italy. Detailed fieldwork (>5200 m of sedimentary logs) has shown that hybrid event beds are most abundant in the distal confined basin-plain domain (>31% of total thickness). In more proximal sectors, hybrid event beds occur within outer-fan and mid-fan lobes (up to 15% of total thickness), whereas they are not observed in the inner-fan channelized area. Six hybrid event bed types (HEB-1 to HEB-6) were differentiated mainly on basis of the texture of their muddier and chaotic central division (H3). The confined basin-plain sector is dominated by thick (maximum 9·57 m; average 2·15 m) and tabular hybrid event beds (HEB-1 to HEB-4). Their H3 division can include very large substrate slabs, evidence of extensive auto-injection and clast break-up, and abundant mudstone clasts set in a sandy matrix (dispersed clay ca 20%). These beds are thought to have been generated by highly energetic flows capable of delaminating the sea floor locally, and carrying large rip-up clasts for relatively short distances before arresting. The unconfined lobes of the mid-fan sector are dominated by thinner (average 0·38 m) hybrid event beds (HEB-5 and HEB-6). Their H3 divisions are characterized by floating mudstone clasts and clay-enriched matrices (dispersed clay >25%) with hydraulically fractionated components (mica, organic matter and clay flocs). These hybrid event beds are thought to have been deposited by less energetic flows that underwent early turbulence damping following incorporation of mud at proximal locations and by segregation during transport. Although there is a tendency to look to external factors to account for hybrid event bed development, systems like the Gottero imply that intrabasinal factors can also be important; specifically, the type of substrate available (muddy or sandy) and where and how erosion is achieved across the system producing specific hybrid event bed expressions and facies tracts

Stratigraphy and Depositional Setting of Slurry and Contained (Reflected) Beds in the Marnoso-arenacea Formation (Langhian-Serravallian) Northern Apennines, Italy

This work presents the stratigraphy and facies analysis of an interval of about 2500 m in the Langhian and Serravallian stratigraphic succession of the foredeep turbidites of the Marnoso-arenacea Formation. A high-resolution stratigraphic analysis was performed by measuring seven stratigraphic logs between the Sillaro and Marecchia lines (60 km apart) for a total thickness of about 6700 m. The data suggest that the stratigraphy and depositional setting of the studied interval was influenced by syndepositional structural deformations. The studied stratigraphic succession has been subdivided into five informal stratigraphic units on the basis of how structurally controlled topographic highs and depocentres, a consequence of thrust propagation, change over time. These physiographic changes of the foredeep basin have also been reconstructed through the progressive appearance and disappearance of thrust-related mass-transport complexes and of five bed types interpreted as being related to structurally controlled basin morphology. Apart from Boumalike Type-4 beds, Type-1 tripartite beds, characterized by an internal slurry unit, tend to increase especially in structurally controlled stratigraphic units where intrabasinal topographic highs and depocentres with slope changes favour both mud erosion and decelerations. Type-2 beds, with an internal slump-type chaotic unit, characterize the basal boundary of structurally controlled stratigraphic units and are interpreted as indicating tectonic uplift. Type-3 beds are contained-reflected beds that indicate different degrees ofbasin confinement, while Type-5 are thin and fine-grained beds deposited by dilute reflected turbulent flows able to rise up the topographic highs. The vertical and lateral distribution of these beds has been used to understand the synsedimentary structural control of the studied stratigraphic succession, represented in the Marnoso-arenacea Formation by subtle topographic highs and depocentres created by thrust-propagation folds and emplacements of large mass-transport complexes

The Miocene turbidite deposits of the Marnoso-arenacea Formation (northern Apennines, Italy)

In the northern Apennines, thick and laterally extensive terrigenous turbidite successions were deposited during the late Oligocene and Miocene, as the fill of elongated, NW-stretched foredeeps formed in front of the growing Apennine orogenic wedge. These turbidites, which are the classic sandy flysch formations (Macigno, Cervarola,Marnoso-arenacea) upon which Migliorini (1943) elaborated his fundamental concept of resedimentation, were progressively incorporated into the frontal part of the orogen during its propagation towards the NE (see also Kuenen & Migliorini, 1950). Among these turbidite units, the Marnoso-arenacea Formation (Langhian to Tortonian in age) is the best exposed and less structurally deformed due to its relatively external position within the Apennine orogen. Thanks to the early works by Ricci Lucchi (1969, 1975, 1978, 1981, 1986),Mutti & Ricci Lucchi (1972), Ricci Lucchi & Pignone (1979) and Ricci Lucchi & Valmori (1980), the Langhian to Tortonian Marnoso-arenacea Formation (MAF) is probably the most famous among the clastic units, which record the structural evolution of the Apennine thrust belt. However, recent studies have shown that the MAF’s stratigraphy and depositional settings are more complex than previously thought, due to the accompanying structural deformation that exerted a control over basin geometry, facies distribution patterns and emplacement of mass-transport complexes (de Jager, 1979; Ricci Lucchi, 1986; Argnani & Ricci Lucchi, 2001; Mutti et al., 2002a, 2003; Roveri et al., 2002; Lucente & Pini, 2002, 2003; Lucente, 2004; Bonini, 2006).As a result, the vertical stacking pattern of the Marnoso-arenacea records a close interaction between thrust propagation towards the NE and deposition from turbidity currents flowing towards the SE, i.e. parallel to the thrust fronts. This view has prompted a re-examination of the MAF’s stratigraphy and facies starting with the Turbidite Workshop held in Parma in 2002 (Mutti et al., 2002a). The main intent of this field trip is to present the preliminary results of the continuation of this study, illustrating the sedimentary characteristics of the stratigraphic succession of MAF (about 4000m thick) that records the progressive closure of the foredeep due to the NE propagation of thrust fronts. In particular, this guide will present a detailed stratigraphic cross-section (with bed-by-bed correlations) of the upper Langhian to Serravallian stratigraphic succession of MAF outcropping in Romagna Apennines (Muzzi Magalhaes, 2009; see also Muzzi Magalhaes and Tinterri, 2009). This interval covers a thickness of about 2,500m and a distance of about 60km in a SE direction, i.e. parallel to the paleocurrents. It has well-exposed outcrops with good lateral continuity and numerous key beds - many of which are mapped on the geological maps of the Emilia-Romagna region (Cerrina Feroni et al., 2002; Martelli et al., 1994).These characteristics have proved fundamental for many MAF field studies attempting high-resolution stratal correlations over significant distances.The pioneering work in this sense was Ricci Lucchi & Valmori (1980), which took into account a stratigraphic interval of 200m around the Contessa key bed, for a horizontal distance of 120km. More recently, Amy et al. (2005), Amy and Talling (2006) presented correlations of a high number of stratigraphic logs covering an interval of about 25m comprised between the Contessa and Colombina 1 key beds

Synsedimentary-structural control on foredeep turbidites: an example from Miocene Marnoso-arenacea Formation, northern Apennines, Italy

This work discusses the synsedimentary structural control affecting the turbidites of the Marnosoarenacea Formation (MAF) deposited in an elongate, NW-stretched foredeep basin formed in front of the growing Northern Apennines orogenic wedge. The stratigraphic succession of the MAF (about 4000 m thick) records the progressive closure of the Apennine foredeep basin due to the NE propagation of thrust fronts. In this setting, Langhian to Serravallian turbidites are overlain by Tortonian mixed turbidite deposits, i.e. sandstone-rich low-efficiency turbidites. The high-resolution stratigraphic framework of basin-plain turbidites has made it possible to identify five informal stratigraphic units (I, II, III, IV, V) mainly on the basis of the structural control highlighted by: 1) the presence of topographic highs and relative depocentres detected through a progressive flattening approach, and 2) the presence of thrustrelated mass-transport complexes and the progressive appearance and disappearance of five bed types (Types 1, 2, 3, 4, 5) considered important to understand the interaction between flow efficiency and basin morphology. By contrast, the upper part of the MAF succession (Tortonian in age) is formed by more sandstone-rich systems characterized by beds whose origin is likely to depend, at least in part, upon flow decelerations related to topographic confinement due to the progressive closure of the foredeep. The vertical and lateral distribution of these types of beds is, therefore, useful for the reconstruction of the morphological evolution of structurally controlled basins; in the MAF example, this is mainly due to the progressive narrowing of the foredeep caused by the propagation of the main thrust fronts toward the foreland