Abstract Volcanic particles have particular geodynamic significance. Despite abundant datasets on volcanic-derived sand(stone), the distinction between spatial and temporal distribution of volcanic particles within the sedimentary record is poorly documented. One of the most intricate tasks in optical analysis of volcaniclastic sand(stone) is the distinction of grains eroded from ancient volcanic rocks (palaeovolcanic, noncoeval grains) from grains generated by active volcanism during sedimentation (neovolcanic coeval grains). Petrologic methods are useful for deciphering temporal significance of volcanic particles in detail between palaeovolcanic and neovolcanic, and for active volcanism to decipher syneruptive v. posteruptive processes during deposition in sedimentary basins close to volcanoes. Sedimentary processes during syneruptive, intereruptive and posteruptive phases are well described in continental environments in terms of changing sedimentary facies, for example, the architecture (from body scale to stratigraphic scale), width/depth ratios of palaeochannels, palaeosols and composition of fluvial-channel deposits, whereas they are less documented in deep-marine environments. Examples of volcaniclastic sedimentation derived from both palaeovolcanic and neovolcanic sources are found in diverse geotectonic settings.

ABSTRACT Middle Triassic to Lower Jurassic continental conglomerate, sandstone, and mudrock are widely exposed in the highest tectonostratigraphic terranes (internal domains) of western and central circum-Mediterranean orogenic belts. These red beds are a key tectonic facies assemblage representing onset of the Tethyan rift-valley stage in the western Mediterranean, during which plate and microplate boundaries were localized during breakup of Pangea. These red beds likely define the boundary of the Mesomediterranean microplate, which played a key role in the Cenozoic evolution of the western Mediterranean. Red beds unconformably overlie Paleozoic metasedimentary and locally plutonic rocks, and they are covered by Early Jurassic and younger sedimentary strata; they are generally mildly deformed and only locally metamorphosed. Sandstone detrital modes vary from quartzarenite to quartzolithic, reflecting a provenance from Cambrian–Carboniferous metasedimentary rocks similar to those underlying the red beds. Reevaluation of previously published petrographic databases and detailed hot-cathodoluminescence (H-CL) analysis of quartz grains indicate that most quartz grains were derived from heterogeneous metamorphic, plutonic, and volcanic rocks. Evaluation of the diagenetic evolution of red beds using chemical-mineralogical analyses and H-CL analyses indicates that compaction and cementation played key roles. Compaction consists of brittle deformation, with breakage of quartz grains and production of early quartz cement, which closed the fractures, followed by a second stage of quartz cementation. Carbonate cements consist of dolomite, ankerite, and calcite. This last cement, related to dedolomitization/calcitization processes, produced carbonate crystals with iron oxides. The sandstone experienced intense reduction of intergranular volume during early stages of burial, as indicated by contrasting compactional porosity loss (COPL; mean of 31.1%) versus cementational porosity loss (CEPL; mean of 8.5%). These data demonstrate the minor role of cementation in reducing porosity and the prevalence of compaction as the main process destroying primary pores. The diagenesis of the analyzed red beds is variable within several internal domains of the orogenic belts, suggesting local influences related to the provenance and geotectonic evolution of each basin.

The Paleogene turbiditic sedimentation in the eastern Southern Alps represents the sedimentary response to tectonic activity related to the Mesoalpine phase, which involved the surrounding chains from Paleocene time onward. Field and petrographic analyses have allowed us to classify these turbiditic successions as multisource deposits, as demonstrated by the common presence of allochemical, mainly bioclastic detritus, associated with different types of terrigenous arenites. For all units, field data suggest more proximal sources for allochemical supply and distal sources for terrigenous material, characterized by the presence of chert, carbonate rocks, and metamorphic rock fragments. All the investigated successions display transparent heavy mineral associations, marked by the common presence of chrome spinel, alkaline amphibole, staurolite, epidote, and zoisite, which point to similar metamorphic sources. The location of the source of metamorphic rock fragments is uncertain, but inputs from the internal Dinaric belt are possible. The source of the allochemical detritus was located in the nearby reactivated Friuli Platform.

The Modena alluvial plain is located on the northern side of the northern Apennines fold-and-thrust belt, where streams draining the chain flow toward the northeast into the Po River. The alluvial plain is characterized by a spectacular abundance of archaeological sites of various ages and can be considered a natural laboratory for the reconstruction of the recent sedimentary evolution of the Po Plain. Detailed modal analyses of modern sands of the Modena Plain streams indicate that the provenance signal can be distinguished on the basis of key components, such as quartz, feldspar, carbonate, and lithic fragments. The compositional fields of the streams depend on the extent of the watershed, the recycling of older fluvial sediments, and the sediment input from tributary streams. The modal analyses demonstrate that sand composition of the major rivers (Panaro and Secchia) has not changed during the Holocene, when sediment production, storage, and dispersal were probably dominated by colluvial aggradation in an environment characterized by dense vegetation cover. In the late Pleistocene, fluvial sands were characterized by higher feldspar contents compared with modern and Holocene sands. This feldspar abundance could reflect a high-frequency signal in sediment supply rates linked to secular variations of weathering processes, and it reveals the strong denudation and sediment removal conditions of the last glacial stage (15–18 ka). The implication of this study is that provenance of Holocene sediments now buried in the floodplain can be determined by a simple comparison with modern sand composition. Sand composition studies may represent a useful tool to reconstruct the Pleistocene-Holocene fluvial sediment supply and the evolution of human settlements as function of climate and drainage system changes.

Provenance studies most commonly apply the classical approach based on petrographic modal analysis of arenites. In this paper, a modal analysis of arenites is combined with both a petrographic study on conglomerate clasts and a geochemical investigation of major and trace elements of pelites. The Ligure-Piemontese oceanic basin, a branch of Western Tethys, and its continental margins were consumed during the Eocene collisional events that led to the formation of the Alpine-Apennine belt. Remnants of Cretaceous sedimentary successions supplied by the continental margins are today preserved as tectonic units in the Alpine-Apennine belt: Balagne Nappe in Alpine Corsica and Internal and External Ligurian units in the Northern Apennines. The petrography of pebbles from rudites and lithic fragments from are-nites shows that Corsica and Internal Ligurian units contain debris from granitoids, low-grade metamorphic rocks, and carbonate platform rocks, while the External Ligurian units contain debris from low- to high-grade metamorphic rocks, a mantle-rock source, carbonate platform, and pelagic siliceous and carbonate rock sources. Geochemical data on pelites indicate a more mafic-ultramafic character for External Ligurian units (enrichment in Cr, Co, Ni, and Th/Sc/Cr/V/Ni relationships that show a systematic shift toward an ultramafic contribution). Petrographic and chemical data indicate that the source for sediments of Corsica and Internal Ligurian units was made up of the upper part of a continental basement and its carbonate sedimentary cover (the Corsica-Europe continental margin). On the other hand, the External Ligurian units were supplied by a source area where a complete lithospheric section was exposed, from the upper mantle up to the deep-sea sedimentary cover (the Adria continental margin). These findings are useful in order to unravel the processes related to the opening mechanisms of the Ligure-Piemontese oceanic basin: among the different rifting models in existence, our data support an asymmetric mechanism dominated by a west-dipping detachment fault, with the Adria margin acting as the lower plate.

In the central Apennines, interacting siliciclastic and carbonate marine clastic wedges filled the foreland basin system during the late Miocene. Conjunction of collisional thrust tectonics and prethrusting normal faults generated a complex foredeep with intrabasinal structural highs that represented additional source areas to the basin. Detrital modes of the late Miocene central Apennines orogenic system range in composition from intrabasinal carbonate to quartzofeldspatholithic and calclithite arenites. The external zone of the foredeep is characterized by hemipelagic deposits, called the Orbulina Marl. Their arenite beds are composed by intrabasinal carbonate, with dominant bioclasts and minor intraclasts, and glauconite derived from an active shallow-marine carbonate source. These hemipelagic deposits are partly coeval with and partly overlain by siliciclastic turbidites of the Frosinone and the Argilloso-Arenacea Formations, and they represent deposition within local foredeep depocenters. Siliciclastic turbidite sandstones are quartzofeldspatholithic, which documents provenances from metamorphic, plutonic, ophiolitic, and sedimentary rocks. Carbonate intrabasinal structural highs were the main source for carbonate breccias, intrabasinal arenites, and calclithites of the Brecce della Renga Formation, the deposits of which are locally interbedded with the coeval siliciclastic turbidite sandstones. Evolution of late Miocene sandstone detrital modes reflected the changing nature of the central Apennines thrust belt through time and the complex architecture of the foreland basin system; it records the history of accretion, deformation of the foredeep, and progressive areal reduction of carbonate-producing areas along with the sedimentary and structural evolution of local intrabasinal highs.