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The sedimentological, lithological and textural characteristics of the Brown Tuffs (BT) pyroclastic deposits, combined with their grain-size, componentry and geochemical glass compositions, are here investigated to obtain information on the transport and depositional mechanisms of the corresponding pyroclastic density currents (PDCs). The BT are widespread reddish-brown to grey, ash-rich pyroclastic deposits generated by pulsating hydromagmatic explosive activity from the La Fossa Caldera on Vulcano island during the c. 80–6 ka time-stratigraphic interval, and then distributed on most of the Aeolian Islands and Capo Milazzo peninsula (Sicily) and in the Tyrrhenian and Adriatic Sea regions. Near the source area on Vulcano, the BT are characterised by alternating massive and planar to cross stratified lithofacies that result from the stepwise, repeating aggradation of discrete PDC pulses. This alternance is regulated by either fluid escape or granular flow depositional regimes at high clast concentration or grain by grain traction deposition in the waning diluted stages of the PDCs. Most of the BT on Vulcano show intermittently stratified and massive ash deposits resulting from a pervasive post-depositional disruption of the primary structures. This is induced by upward fluid expulsion associated with dissipation of pore pressure between layers at different grain size (fine to coarse ash) and porosity, as outlined by distinctive upwards bends and pillar-type escape structures through the fluid-filled cracks and rupture points. Massive BT deposits with a faint colour and grain-size banding are widely recognised on Lipari, the nearby island of Vulcano. Based on the presence, at the base of BT depositional units, of cm-thick amalgamation bands containing pumice lapilli, scoria and lithic clasts ripped-up and embedded from the loose underlying pyroclastic units, they are interpreted as deposited by ash-rich PDCs laterally spreading from La Fossa Caldera and moving to Lipari. During their motion to Lipari these currents (likely) crossed a narrow and shallow sea-water inlet which did not stop their advancement but influenced the grain size distribution of those spreading on the Lipari mainland. In this paper, the mechanism of clast erosion and incorporation is outlined across the whole island of Lipari by means of field study, grain-size, and geochemical glass analyses on the different components of the mixed basal bands of the BT. This suggests that the BT PDCs maintained enough flow power as to erode the substratum, hence likely impacting the territory, over a distance up to at least 16–17 km from the volcanic source. Evidence that the BT PDCs exerted a high shear-stress over the loose substratum is also provided by undulated, recumbent flame and rip-up structures at the base of some depositional units in southern and central Lipari. In order to form such bed granular instabilities between the BT and the underlying deposits we calculate that the currents had at least a shear velocity of ca. 2 m s−1 and a shear stress in the range of 1–4.5 kPa. These results add new insights on the large-scale hazard at the Aeolian Islands and shed new lights on the widespread transport and depositional dynamics of ash flows spreading over the sea and reaching nearby islands, and their interactions with the substratum and the pre-depositional topography.

The distribution and morphological characteristics of the shelves around Salina Island have been analyzed and integrated with observations from onshore geological field studies in order to improve knowledge about its evolution, and to demonstrate how shelf width/depth can be used as proxies for reconstructing the development of the volcanic edifice. Insular shelves form essentially through marine erosion of volcanic centres during stages of reduced or inactive volcanism, and are representative of their original extension. Shelves having larger widths (commonly > 1000 m) and deeper edges (over 125 m depth) experienced wave erosion during successive cycles of sea-level fluctuations and subsidence after their formation, thus being indicative of a relatively older age of the eroded volcanic centres. Accordingly, we document offshore Salina the occurrence of presently submerged and largely dismantled volcanic centres (namely Pizzo Capo North and Fossa delle Felci South) predating the oldest subaerial products exposed on the adjacent coastal sectors. These offshore centres have subsided after their erosion and are no more documented on land. Furthermore, the finding of the largest and deepest shelf around the subaerial remnants of Pizzo di Corvo volcanic edifice allows relating it to an earlier stage of evolution of Salina, shedding light on contradictory radiometric ages on land. Narrower shelves (commonly < 1000 m) indicate a lower evolutionary maturity with respect to the larger ones; they are, in fact, formed along the sectors of the island where younger volcanic products are exposed, such as to the north and south of Monte dei Porri. The depths of the shelf edges, mostly at - 110 m (in the areas not affected by later mass-wasting), suggest that these coastal sectors were relatively stable or even slightly uplifted after erosion during Last Glacial Maximum. Moreover, several interacting factors (such as lithology of volcanic products, fetch and exposure to prevailing storms, degree of submarine erosion, relative sea level changes) have been taken into account to explain the morphological setting of the different shelf and coastal sectors of Salina. On the whole, our results show the importance of integrated field and marine studies to unravel the geological evolution of insular volcanoes and to obtain inferences on their vertical mobility.

The concept of turbidite has evolved so much since its original definition by Kuenen and Migliorini in 1950 – i.e. the deposit of turbidity currents exemplified by the sandy flysch successions of the Northern Apennines – that it is now used to define a variety of deposits, some of which have little in common with sandy flysch formations in terms of facies, geometry and geological significance. The extension of the concept to other geodynamic settings and deposits of nonsiliciclastic composition is considered only briefly in the concluding sections. With the diffusion of the concept of turbidity current, in the 1950s and early 1960s, an entirely new branch of sedimentology came into being, concerned with the inventory of sedimentary structures, palaeocurrent measurements and bedding patterns. The most representative expression of this branch came from the ‘Dutch school’ of Philip H. Kuenen and his students. Between the late 1960s and the mid-1970s, there was a new development: facies analysis, in terms of modern environments and depositional systems. This development led to the introduction and discussion of ‘fan models’ that became an increasingly thorny issue with the accumulation of data from modern deepmarine settings. In particular, most researchers emphasized the importance of channel and lobe elements and their mutual relationships in space and time. These models may differ in terms of specific features, e.g. canyon-fed versus delta-fed ramp settings and terminology, but the basic distinction between channels (sediment pathways), lobes and basin plains (sheet-like depositional features) was and still is widely retained – a model that simply refers to a systemwhere a distributary channel passes downstream to a depositional zone, like in most fluvio-deltaic systems. Great caution should, however, be exercised when comparing modern and ancient fans – a problem discussed at length in the Committee on Submarine Fans I convened by A.H. Bouma and held in Pittsburgh in 1982. Different data sets and geological contexts, scaling problems and terminology still cast doubt over how meaningful such a comparison may be. Despite the many problems encountered, the elemental approach provides an easy, essentially descriptive tool to significantly compare recent with ancient, recent with recent, and ancient with ancient systems. Beginning in the 1970s, process-oriented facies analysis led to increasingly complex facies classification schemes, which showed substantial departures from the classic Bouma sequence and introduced many new concepts: proximal versus distal sedimentation, sediment bypass and flow efficiency, in addition to deflection, reflection and ponding of turbidity currents in confined basins. During the last two decades, there has been an increased interest in attempting to interpret the incredibly detailed submarine landscapes obtained through advances in marine geology, technology and high-resolution three-dimensional seismic data provided by the oil industry. Outcrop ‘analogues’ derived from orogenic belts are used commonly to improve the interpretation of seismic-reflection facies, although their actual value may be questioned in many cases. Seismic–stratigraphic concepts are used routinely to describe and interpret turbidite systems of continental margin basins where cyclic sea-level variations are thought to be essentially controlled by eustasy. These concepts are difficult to apply to flysch basins, where the tectonic control on the development of cycles of relative sea-level variations appears to be dominant. In particular, the huge volumes of sediment involved in the infill of flysch basins imply amounts of uplift of the source areas and subsidence of the receiving basins that clearly outstrip those of divergent continental margins controlled by eustasy and thermal subsidence. Cycles of tectonic uplift and denudation (Davisian-type cycles in the sense of Mutti et al., 1996) apparently play a major role here. Most recent attempts to understand turbidite deposition are related to the increased economic importance of turbidite sandbodies as hydrocarbon reservoirs in many offshore basins (e.g. Gulf of Mexico, West Africa, Brazil, the North Sea). The many problems inherent to this situation have been reviewed extensively in a workshop held in Parma in 2002; only some of these problems are reconsidered briefly in this paper. Sandy turbidite systems can be generated by the resedimentation of deltaic deposits through submarine slides or be derived directly from flood-generated hyperpycnal flows; in the latter case, climatic variations must have played a fundamental role in controlling flood frequency and magnitude with time. Recognizing these two different types of system is not always easy and requires a good understanding of the geological context of the basin under consideration and particularly of the role of marginal fluvio-deltaic systems from which turbidites are ultimately derived. Unfortunately, this kind of integrated analysis is still in its infancy. There are other types of turbidite deposits, such as the calcareous flysch of the Western Alps and the Northern Apennines, whose origin still remains a matter of debate in terms of sediment source and triggering mechanisms of large-volume turbidity currents essentially loaded with fine-grained biogenic sediment. Some authors have referred to these sediments either as ‘megaturbidites’ or ‘seismoturbidites’. The importance of tectonic control and geodynamic setting is stressed for turbidite systems of orogenic belt basins, which is justified both by historical reasons (turbidites were from their recognition included in the definition of flysch) and recent studies of thrust belts. The time is now ripe for reconsidering these sediments within a broader framework that takes into account the enormous quantity of data and concepts that have been developed in the last 50 years; this in itself raises a problem, and no small one: the accuracy and quality of data collected in the field and the training of young scientists. How many field geologists are being produced in these times of increasingly computerized geology; and how good are they?

A new genetic facies model for deep-water clastic evaporites is presented, based on work carried out on the Messinian Gessoso-solfifera Formation of the northern Apennines during the last 15 years. This model is derived from the most recent siliciclastic turbidite models and describes the downcurrent transformations of a parent flow mainly composed of gypsum clasts. The model allows clearer comprehension of processes controlling the production and deposition of clastic evaporites, representing the most common evaporite facies of the northern Apennines, and the definition of the genetic and stratigraphic relationship with primary shallow-water evaporites formed and preserved in marginal settings. Due to the severe recrystallization processes usually affecting these deposits, petrographic and geochemical analyses are needed for a more accurate interpretation of the large spectrum of recognized gravity-driven deposits ranging from debrisflow to low-density turbidites. Almost all the laminar ‘balatino’ gypsum, previously considered a deep-water primary deposit, is here reinterpreted as the fine-grained product of high to low-density gravity flows. Facies associations permit the framing of the distribution of clastic evaporites into the complex tectonically controlled depositional settings of the Apennine foredeep basin. The Messinian Salinity Crisis occurred during an intense phase of geodynamic reorganization of the Mediterranean area that also produced the fragmentation of the former Miocene Apennine foredeep basin. In this area, primary shallow-water evaporites equivalent to the Mediterranean Lower Evaporites, apparently only formed in semi-closed thrust-top basins like the Vena del Gesso Basin. The subsequent uplift and subaerial exposure of such basins ended the evaporite precipitation and promoted a widespread phase of collapse leading to the resedimentation of the evaporites into deeper basins. Vertical facies sequences of clastic evaporites can be interpreted in terms of the complex interplay between the Messinian tectonic evolution of the Apennine thrust belt and related exhumation–erosional processes. The facies model here proposed could be helpful also for better comprehension of other different depositional and geodynamic contexts; the importance of clastic evaporites deposits has been overlooked in the study of other Mediterranean areas. Based on the Apennine basins experience, it is suggested here that evaporites diffused into the deeper portions of the Mediterranean basin may consist mainly of deep-water resedimented deposits rather than shallow-water to supratidal primary evaporites indicative of a complete basin desiccation.

The sediments and ostracod assemblages from a small lacustrine basin located in the Montefeltro area (Sapigno Syncline, Romagna-Marche Apennine, Central Italy) have been studied in detail from a section covering a broad interval spanning the Late Messinian post-evaporitic sequence. The latter consists of a non-marine, mainly terrigenous succession with molluscs and brackish-water ostracods; it represents the Lago-Mare phase s.s. and is interpreted as shallow- to relatively deep-water lacustrine deposits characterized by a low salinity with occasional interactions with fluvial and littoral processes. Rich and diverse ostracod assemblages occur throughout the studied succession. Thirty species were recognized, which characterize a Loxocorniculina djafarovi Fossil Assemblage widespread in the western Mediterranean during the latest part of the Messinian. It is a residual assemblage of a non-marine fauna inhabiting hypohaline environments and testifies to the presence of large, interconnected, brackish-water bodies (Lago-Mare) along the margins and in the depths of a Mediterranean basin isolated from the World Ocean. The ostracod faunas have Paratethyan affinities but only a few species are common to both the western Mediterranean and the eastern basins of Paratethys.

Do the Apennines represent a vantage point for studying turbidites? How did research develop in this area? These questions are discussed briefly in the following pages from a historical and autobiographical perspective. Some items are emphasized: the shifting of depocentres, the presence of megabeds (basinwide events), the definition of ‘classical’ turbidites, the facies approach, the recognition and distinction of hyperpycnal flows

The integration of field and subsurface data permits a substantial revision of the sedimentary evolution of the Vena del Gesso basin, a thrust-top basin in the Northern Apennines where shallow-water primary gypsum deposits related to the Messinian salinity crisis were well developed and preserved. As inferred from lateral and vertical facies changes within the underlying deep-marine turbidites of the Marnoso-arenacea Formation, evaporite precipitation occurred in a basin bounded to the north and to the east by a thrust-related anticline actively growing since the late Tortonian. Both gypsum deposition and subsequent deformation were strongly controlled by evolving paleobathymetry driven by tectonics. Primary gypsum precipitated in a shallow, silled basin, while in the adjacent deeper and larger foredeep basin, organic-rich shales were deposited. Gypsum deposits underwent severe postdepositional deformation related to large-scale gravitational collapse, as a result of a regional uplift event, also coincident with the end of the evaporitic phase. Along the inner, shallower-dipping limb of the anticline bounding the basin, large-scale, poorly deformed gypsum slabs moved downslope along a detachment surface developed at the contact with the underlying euxinic shales, forming both extensional and compressional features and showing an overall southwestern vergence. The identification of a south-southwest–dipping paleoslope, here pointed out for the first time, suggests that the deformational features affecting the gypsum unit were probably driven by gravity and not by active thrusting, as thought up to now. The steeper frontal limb of the anticline promoted the transformation of gypsum slides into debris flows and turbidite currents that deposited their load in the adjacent deeper basin. This gravitational deformation was sealed by postevaporitic upper Messinian Lagomare deposits. The sedimentary history of the Vena del Gesso basin suggests that the Messinian salinity crisis in the Apennine foredeep, as well as in the Balearic, Tyrrhenian, Sicily, and Eastern Mediterranean Basins, was tightly linked to tectonic processes. The large-scale, postdepositional collapse of primary evaporitic deposits is a widespread feature in the Mediterranean basins, and it may have altered the original stratigraphic relationships in some places. This finding has potentially important implications for a correct paleoenvironmental reconstruction of the onset of the Messinian salinity crisis.

Combined palaeoecologic and sedimentologic studies reveal remarkable palaeoenvironmental changes in the Pliocene Intra-Apenninic Basin (PIB) of the Bologna Apennines (Northern Italy). At the northern margin of PIB, the stratigraphic succession is approximately 1000 m thick, and displays an overall coarsening-upward trend, including a lower mudstone-dominated succession (Argille Azzurre Formation) of Zanclean age, overlain by a sandstone-rich unit (M. Adone Formation), assigned to the Zanclean-Piacenzian. The vertical succession of biofacies within the Argille Azzurre Fm. indicates an obvious shallowing-upward tendency, from slope/outer-shelf (150–300 m water depths) to inner-shelf (30–50 m) environments. A vertical cyclic pattern of facies, with alternating sandy siltstones and sandstone bodies, characterizes M. Adone Formation. Each elementary cycle, about 30–50 m thick, includes a couple of siltstone-dominated inner-shelf and prodelta deposits, passing upwards into progradational delta front, tabular sand bodies. These high-rank cycles, spanning an interval of time in the order of magnitude of 40 ky, are separated by flooding surfaces, clearly recognizable on the basis of palaeoecologic analysis, and reflect an aggradational stacking pattern of parasequences superposed to the general shallowing-upward trend.

Over 20 occurrences of discontinuous limestone blocks, locally called “calcari aLucina,” were mapped in the Tuscan—Romagna region of the northern Italian Apennines. The limestones, consisting of a variable mixture of authigenic carbonates (calcite, dolomite, and aragonite), sulfides (primarily pyrite), and allogenic silicates, occur in association with turbidite and hemipelagite units that were deposited in foredeep basins during early to late Miocene times. The limestone blocks are interpreted to represent relicts of carbonate buildups formed around methane-rich fluid vents on the basis of their (1) striking petrographic similarities to carbonates from cold vents in the modern oceans; (2) unique chemosynthetic-like fauna, and (3) anomalously negativeδ13C values (δ13C = − 16‰ to − 58‰ PDB). The contemporaneous tectonism of the Apennine orogeny is likely to be the primary cause for the expulsion of the methane-rich fluids to the seabed in a manner analogous to the fluid-flow processes occurring at modern accretionary prisms.

Turbiditic sediments are associated with all stages of development of the Apennines orogen: not only the classical “flysch” of Oligo-Miocene age (Macigno, Cervarola, Marnoso-arenacea) but also the coeval, smaller bodies based on thrust sheets (“Loiano” of “Ranzano” Sequence) and the younger “molasse” of the Plio-Pleistocene Foredeep. Except for more recent ones (Quaternary), turbidite units are affected to some degree by thrusting and later block-faulting The equivalent marginal deposits were also deformed, uplifted and eroded to a great extent. However, identification and correlation of sequences and paleoenvironments across the orogenic belt can be helped by (a) deposits with rather strong eustatic imprint (high stands), and (b) preservation of marginal sediments by early remobilization (cannibalism) into deeper depocentres. The following categories of basins can be recognized: • — main foreland basin, or foredeep, in front of thrust sheets; based on undeformed or previously rifted continental crust; • — thrust-top basins (meso-autochthonous auct.) in absence of a well-defined, major foredeep; • — satellite basins: thrust-based but inwardly associated with a foredeep, and of much smaller size (linear dimensions in the order of kilometers and ten of kilometers, volume of fill in the order of tens to hundreds cubic kilometers). The foredeep persisted for the whole orogenic cycle but changed its character and was more or less segmented; two main stages can be recognized, conventionally labelled as the flysch stage (up to the late Miocene, Appenines mostly submerged) and the molasse stage (late Miocene to Recent, present relief already in existence). Satellite basins “floating” on the Ligurian Sheet (Epi-Ligurian) persisted up to the mid-Pliocene but received turbidites only in the Oligocene and Miocene. Others were created later on thrusts of different style involving the foreland sedimentary cover (piggyback basins of Ori and Friend, 1984). Turbidite lithosomes of the flysch group are the largest ones (volumes up to 30,000 km 3 ), with maximum size and lateral continuity of individual beds (megaturbidites). They are not seen as overlapping units filling coexisting and adjacent basins but as distinct, superposed isochronous units, within which only, time-transgressive sedimentation could occur. Macigno thus stands for all Oligocene turbidites of the northern Apennines foredeep, Cervarola for early Miocene ones, and Marnoso-arenacea for mid-late Miocene ones. It is assumed that these units reflect sedimentary cycles of some order, correlatable with “global” charts and splittable into depositional sequences sensu Vail and collaborators.

The post-evaporitic Messinian in the northern sector of the Adriatic foredeep is characterized by the occurrence of abundant terrigenous deposits which have been subdivided into two allostratigraphic units (p-ev1, p-ev2) separated by an erosional unconformity of regional importance. The p-ev1 consists of basal complex of resedimented evaporites overlain by monotonous succession of mudstone/siltstone alternations (thin bedded turbidites) with an overall coarsening and shallowing upwards trend. It is possibly related to the rapid basin infill after the end of the salinity crisis. The upper unit (p-ev2) shows, in the most marginal areas, a clear cyclical stacking pattern made up of three fining-up sequences with fan-delta conglomerates at the base of each cycle. Here, a peculiar feature of the p-ev2 deposits is the occurrence of three distinct laminated limestone horizons (termed colombacci) interbedded with fine grained, varved mudstones. These limestones are abiotic, despite the occurrence of abundant Ostracod assemblages (Lago–Mare fauna) in the interbedding pelites, and are interpreted as inorganically precipitated, deposited in a relatively deep-water environment, possibly anoxic and related to permanent stratification of water mass events during periods of lake level maxima. The combination of petrographical and geochemical observations on carbonate layers reveals that they correspond to events characterized by significant variations of environmental conditions. However, δ18O (−5.30/+0.2) and δ13C (−9.28/+1.68) signatures suggest that the precipitation of low-Mg calcite often occurred in a non-marine environment and that meteoric water input had a considerable influence on late Messinian sedimentation. Moreover, the limestones have a uniform 87Sr/86Sr composition (0.70864–0.70875) in the range of other Lago–Mare sediments from elsewhere in the Mediterranean, suggesting that some of the major Mediterranean basins were likely interconnected during the Lago–Mare phase. A strongly reduced rate of hydrological exchange with the ocean is also possible, but the possibility of marine influence during this stage is not completely excluded.

Indicators of former sea-levels are recognised on the emergent portion of Lipari, Aeolian Islands. They correlate with three raised shorelines, located at elevations of 43–45 m above present sea-level (I), 23–27 m (II) and about 12 m (III). According to stratigraphical constraints, these shorelines correlate with the sea-level highstands corresponding to marine oxygen isotope substages 5e (124 ka), 5c (100 ka) and 5a (81 ka), respectively. The correlation of the shoreline I with substage 5e is supported by a U/Th age (119 ± 6 ka) obtained from corals. Chronological and height data relevant to the fossil shorelines indicate that Lipari was affected by uplift with an average rate of 0.34 mm yr−1 during the past 125 ka. This uplift rate accords with the average uplift rates obtained, during the same time period, from the nearby islands of Filicudi (0.31 mm yr−1) and Salina (0.36 mm yr−1). Combined, these data suggest a similar uplift trend related to regional tectonic processes. In contrast to the long-term uplift, a localised submergence trend, documented especially for the last century, affects the eastern coast of Lipari. This subsidence is related to neo- and/or volcano-tectonic processes. Copyright © 2002 John Wiley & Sons, Ltd.

The turbidite beds of the Northern Apennines offer some of the most spectacular exposures of deep water synorogenic sediments in the world and have been often taken as representative of the typical foredeep basin fill. For the Miocene Marnoso-arenacea (MA) Formation in particular, the presence of several marker beds and of a well assessed biostratigraphy, coupled with an excellent stratal continuity, has allowed geologists to work out the shape of the basin through time, despite the tectonic slicing following the accretion of the sediments into the Apennine fold-and-thrust belt. The MA turbidites, however, represent just a time interval of a much longer story of foredeep sedimentation and migration that started in the late Oligocene and that continues at present (Ricci Lucchi, 1986b). For several reasons, the stratigraphy and geometry of the sedimentary beds of the Northern Apennine foredeep units have not always been documented in the same accurate way as the MA and the overall stratigraphie scheme is still to be refined. Within these limitations, this contribution aims at presenting a review of the stratigraphy, basin geometry and tectonic signature of the Tertiary foredeep deposits outcropping in the Northern Apennines. The Recent foredeep basin, which is located in the Po Plain and in the Adriatic Sea, is used as a modern analogue.

On-thrust sedimentation is not so common in mobile belts outside the Apennines. One of the relevant contributions to Apenninic geology by the florentine Giovanni Merla in the 1950's is the recognition of these traveller or “floating” sequences. This concept of semi-allochthon (as Merla called it) is reviewed here and discussed in the light of recent advances in stratigraphy and basin analysis. Several unconformities are detected in the sequence, which make it possible to split it into cycles or depositional sequences at variance with classical formations. Correlations have been attempted with sediments deposited behind and in front of the thrust belt; in comparison with foredeep flysch sequences, semi-allochthonous ones show better preserved stratigraphical relations (vertical stacking) and less deformation, which emphasizes their possible role as reference sections for syn-orogenic sedimentation in the Apennines.

Submarine fans of different sizes, geometry, and petrology were built in the Marnoso-arenacea Basin, a migrating foredeep within an active continental margin. In an initial depositional stage, a well-developed basin plain received sediment from flows that by-passed restricted fan systems, now buried, located near the north end of an elongated basin. Minor fans grew near the steeper, tectonically deformed side of the basin. In the later stage, turbidite deposition was stopped in the former basin plain. Sediment sources and feeder channels shifted and fed fan lobes that prograded in a narrower trough and were distored (choked). The tectonic control on development of megasequence and sand bodies is stressed here in contrast with previous emphasis on “inner” or “autocyclic” mechanisms.

Apart from Bouma sequences, recurrent patterns of sedimentation can be recognized at two hierarchic levels in turbidite formations of the northern Apennines. First order cycles (turbidite suites) encompass most of the basin fill, second order cycles (megasequences) occur as organized groups of beds 2-70 m thick within the suites. The Marnoso-arenacea (Lower-Upper Miocene) is an example of a progradational or offlapping suite with thickening and coarsening upward trend. The Laga Formation (Upper Miocene-Lower Pliocene) is characterized by a "transgressive" (retrogradational) or onlapping trend. Vertical facies changes go either way through the following steps: basin plain outer fan midfan inner fan slope deposits ( = prograding, = receding). Both suites are enclosed by hemipelagic pelites and chaotic deposits, the start of turbidite sedimentation being gradual in the progradational case, and abrupt (large scale erosion) in the reverse one. Second order cycles follow each other or are separated by monotonous (uniform or irregularly bedded) sequences of extremely variable thickness (2 to more than 1,000 m) composed either of fan (overbank, fringe) or basin plain deposits (with key beds laterally continuous up to 175 km). The trend of cycles may be asymmetric (termed positive when beds thin upward, negative when they thicken upward), symmetric, composite or not definable. Thick to massive beds with sand/shale ratio >> 1 or > 1 and well developed coarse divisions (products of high density turbidity currents, grain flows, debris flows, fluidized flows) form the thicker bedded portion of cycles and sometimes the whole cycle. One hundred and thirty-two cycles were analyzed and subdivided into simple and complex (= multiple or composite). By splitting multiple cycles into simple components, a total of 170 cycles was reached. Thirty-nine of them were measured in channelized deposits, 131 in non-channelized turbidites, laterally continuous exposures enabling the distinction to be made. Results of sequence analysis are illustrated by columnar profiles and bed thickness diagrams, i.e. CD (coarse division) and L (layer) diagrams. Eighty percent of channelized cycles show a positive trend, whereas a negative trend characterizes 60% of non channelized cycles. This strengthens the assumption that most positive cycles reflect filling of fan channels, while negative cycles are the expression of prograding depositional lobes, i.e. localized areas of preferred sand accumulation in front of distributary channels. Among progradational cycles, a distinction was made between "fast" and "slow" accretion types by means of relative number of beds (L/T ratio), relative number of coarse divisions (L/CD ratio), and frequence of interbedded hemipelagites. The possible non-prograd tional nature of some "slower" cycles is discussed; they could alternatively reflect sporadic phases of sand accumulation in the basin plain environment due to huge flows triggered by tectonic events and bypassing the fan system (or independent from a fan system). Attempts of correlation of negative cycles both downcurrent and across current are shown.

The Messinian Vena del Gesso Basin in the Northern Apennines is filled by very thick (up to 35 m) beds of coarse crystalline gypsum (selenite) associated with thinner carbonate and shaly (euxinic) intercalations. The conventional Usiglio model of salt fractionation does not apply to this evaporitic sequence for the following reasons: carbonate which underlies gypsum is not evaporitic but algal in origin; most gypsum did not precipitate from surface brines but at and below a sediment-water interface occupied by algal mats; a significant portion (10–80%) of gypsum beds is composed of redeposited selenite which was removed from the margins and transported toward the centre of the basin by slope-controlled currents and gravity flows (debris flows). We call this process cannibalistic because of its intraformational character (connected with evaporative fall of water level) and volumetric importance. A recurrent vertical pattern of six main facies (euxinic to gypsum fanglo-merates) is interpreted as a bathymetric, regressive cycle controlled by both sedi-mentological and tectonic-eustatic factors. The inferred environmental setting is a residual turbidite trough (Marnoso-arenacea) evolving abruptly toward lagoonal conditions and filled up to sea level by evaporitic and mechanical (mostly fluvial) processes. Repeated inundations of restricted-marine water started the depositional cycle thirteen or fourteen times.

Eighteen stratigraphic sections, 200 m thick on average, were logged in basin plain deposits of the Marnoso-arenacea Formation (Miocene, northern Apennines) over an area of 123 × 27 km. Turbidites form 80–90% of the facies association, hemipelagites the remainder. Thin and thick-bedded turbidites are separated by an approximate statistical boundary at 40 cm; most prominent beds (> 1 m thick) are qualified as megaturbidites. With reference to the main supply-dispersal system (NW to SE), the basin plain can be axially subdivided into proximal, intermediate and distal segments by means of the following parameters: bulk sand content, sand/shale ratio in turbidites, mean thickness of individual layers and component beds, and frequency of thick layers. Almost 40% of thick-bedded turbidites can be traced over the whole study area. These basin-wide deposits form the bulk of the basin fill. Geometrical reconstruction shows that some sandstone beds taper downcurrent from the proximal plain or the adjacent fan area while others thin upcurrent suggesting sand by pass of the fan. Mudstone beds in general thicken towards the end and the margins of the plain indicating that turbidite mud, besides bypassing the fan as a rule, was affected by ponding in the plain. Thin-bedded turbidites have a low sand/shale ratio or are completely muddy representing either tails of sandier turbidites of the outer fan (lobe and fringe deposits) or sheets extending to a great part of or to the whole plain. Sandstone lobes advanced from fans into the plain for 40–50 km gradually thinning and shaling out over a transitional zone of 10–20 km. Their internal geometry shows simple and complex growth patterns: end members are defined as progradational and aggradational. Estimates of original length, width and volume of individual turbidites strongly suggest that flows were usually confined and deflected by basin slopes regardless of source location. Basinal deposits are thus characterized by great thickness and volume, abundance of mud and fine sand, extremely low lateral gradients of thickness and grain size (but rapid wedging near the sides). The basin plain developed as a part of an elongated, oversupplied basin with a ‘highly efficient’, probably delta-fed, dispersal system.

Turbidite beds of exceptionally large volume and areal extent occur in both modern and ancient deep-water basins. These beds, which may reach individual volumes in excess of 100 km3, are apparently the product of catastrophic gravity flows triggered by earthquakes along the margins of highly mobile basins, most commonly elongate “flysch” troughs. Turbidite beds produced by these catastrophic events are generally characterized by very distinctive geometry, internal structures, and composition, and are termed herein seismoturbidites. Characteristically, these sediments lack time-persistent features of deep-sea fans such as channels and lobes. Seismoturbidites may occur as scattered intercalations diluted within otherwise “normal” turbidite sequences, thus forming generally excellent markers for basin-wide correlations, or as closely spaced, repetitive units comprising the bulk of the sedimentary fill of certain flysch basins. In both cases, they may offer a tremendously useful tool for a better understanding of the distribution of paleoseismic zones in time and space.

This contribution is an attempt to bridge some gaps between source= minded and emplacement-minded students of clastic sediments. The first part outlines a simple conceptual frame of basin topography, hydrodynamic base levels, transport-deposition processes and the resulting modification of sand before and after final deposition (pre-emplacement vs pre-burial). The second part emphasizes geome= try, fill and dispersal pattern of elongated basins in orogenic foreland settings. Factual information from the mediterranean area (particularly the Apennines and Po Plain subsurface) is summarized.

Submarine fans of different sizes, geometry, and petrology were built in the Marnoso-arenacea Basin, a migrating foredeep within an active continental margin. In an initial depositional stage, a well-developed basin plain received sediment from flows that by-passed restricted fan systems, now buried, located near the north end of an elongated basin. Minor fans grew near the steeper, tectonically deformed side of the basin. In the later stage, turbidite deposition was stopped in the former basin plain. Sediment sources and feeder channels shifted and fed fan lobes that prograded in a narrower trough and were distorted (choked). The tectonic control on development of megasequence and sand bodies is stressed here in contrast with previous emphasis on “inner” or “autocyclic” mechanisms.

The Miocene Marnoso-arenacei and Laga Formations form two of the largest outcropping turbidite units of the north-central Apennines,where extensive exposures make facies analysis feasible. Following a more general model proposed by Mutti and Ricci Lucchi (which utilizes bed geometry), sedimentary structures and texture, facies association (slope, submarine fan, basin plain) and sedimentary facies (conglomeratic sandstones, sandstones, sandstones with shale interbeds, shales with sandstone interbeds, chaotic deposits, hemipelagic pelites) were recognized. The value of sequential analysis for comparing stratigraphic subunits within a submarine fan system, and particularly for differentiating between inner fan, mid-fan, outer fan, and basin-plain environments, is emphasized. Recurrent patterns of sedimentation (megasequences or megarhythms, 10-100 m thick) are composed of sets of thick, mostly arenaceous, massive, graded, or crudely laminated layers, with alternate finer grained beds, which are thinly laminated in the lower part. Two main types of "ordered" megasequences are recognized: (A) positive, or thinning upward, interpreted as filling of fan valleys or channels; and (B) negative, or thickening upward, considered to be prograding outer fans along nonchanneled distributaries. Three monotonous, or random, sequences composed of finer grained sediments are also present: (C) slope deposits (thin layers, with a sandstone/shale ratio less than 1); (D) interdistributary fan deposits (thin to medium layers, sand/shale ratio less than 1; and (E) basin-plain dep sits (medium to thin layers, with sporadic isolated thick turbidite units, sandstone/shale ratio greater than 1). The vertical association of these subunits, and especially those of the A and B megasequences, show both similarities and differences in the sedimentary history and tectonic control of the Miocene basins. Further application of these criteria to other turbidite basins probably will aid in predicting the location and geometry of sandstone bodies. End_of_Article - Last_Page 801