Franco Ricci Lucchi

Seismoturbidites: a new group of resedimented deposits

Abstract 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.

Sedimentary and tectonic evolution of the Vena del Gesso basin (Northern Apennines, Italy): Implications for the onset of the Messinian salinity crisis

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.

Petrography and stable isotope aspects of cold-vent activity imprinted on Miocene-age “calcari aLucina” from Tuscan and Romagna Apennines, Italy

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.

Ostracod faunas and brackish-water environments of the late Messinian Sapigno section (northern Apennines, Italy)

Abstract 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.

Turbidites in foreland and on-thrust basins of the northern Apennines

Abstract 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.

Semi-allochthonous sedimentation in the apenninic thrust belt☆

Abstract 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 1950s 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.

Influence of Transport Processes and Basin Geometry on Sand Composition

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.

Crati Fan, Mediterranean

The Crati Fan is located in the tectonically active submerged extension of the Apennines chain and foretrough. The small fan system is growing in a relatively shallow (200 to 450 m), elongate nearshore basin receiving abundant input from the Crati River. The fan is characterized by a short, steep, channelized section (inner or upper fan) and a smooth, slightly bulging distal section (outer or lower fan). The numerous subparallel channels head in the shelf or littoral zone and do not form branching distributary patterns. Sand and mud depositional lobes of the outer fan stretch over more than 60% of fan length.

The Crati Submarine Fan, Ionian Sea

The Crati Fan is located in the tectonically active submerged extension of the Apennines chain and foretrough. The small fan system is growing in a relatively shallow (200 to 450 m), elongate nearshore basin receiving abundant input from the Crati River. The fan is characterized by a short, steep, channelized section (inner or upper fan) and a smooth, slightly bulging distal section (outer or lower fan). The numerous subparallel channels head in the shelf or littoral zone and do not form branching distributary patterns. Sand and mud depositional lobes of the outer fan stretch over more than 60% of fan length.

The stratigraphic role of marine deposits in the geological evolution of the Panarea volcano (Aeolian Islands, Italy)

Using reconstructed unconformity-bounded stratigraphy, the geological evolution of Panarea and surrounding islets can be described in terms of the interaction between the growing volcano and sea-level fluctuations. From the recognition of marine deposits corresponding to marine oxygen isotope stage (MIS) 5 and of widespread Brown Tuff-type pyroclastic deposits on Panarea, two first-order unconformities (UI and UII) of regional stratigraphic significance can be correlated with the island of Lipari and adopted as a means of correlation on an inter-island scale in the Aeolian Volcanic District. Then, two second-order and three third-order unconfomities, consisting of erosional surfaces related to minor sea-level fluctuations or to subaerial reworking operating during the phases of volcanic inactivity, are introduced. The construction of the volcanic edifice occurred during seven successive eruptive epochs of local volcanic activity, between 150 and 10 ka, with intervening dormant periods characterized by the activation of reworking processes in subaerial and marine environments, and by the emplacement of widespread pyroclastic deposits of external provenance.