Salvatore Critelli

Paleogeographic and paleotectonic evolution of the Himalayan Range as reflected by detrital modes of Tertiary sandstones and modern sands (Indus transect, India and Pakistan)

Detrital modes of sandstones derived from the Himalayan suture belt record the history of the mountain range since initial collision between India and Asia, which began in latest Paleocene time. Tertiary clastic wedges deposited in fore-arc, foreland, and remnant-ocean basins, and exposed along the Indus transect from northernmost India to the Arabian Sea, represent the best opportunity to study sedimentary responses to successive tectonic events during continental collision. Quartzose “continental-block” and feldspatholithic “magmatic-arc” sandstones were deposited, respectively, on the passive Indian (Tethys Himalayan succession) and active Asian (Indus Group) continental margins during Late Cretaceous–Paleocene time. Closure of the Neotethys was marked by sudden arrival of volcanic and ophiolitic detritus on the passive continental margin of the Indian plate during deposition of sediments dated at foraminiferal zones P6 (Pakistan) to P8 (India). Starting in early Eocene time (deposition of Chulung La Formation and Murree Supergroup), volcanic and ophiolitic to metasedimentary detritus was accumulated in rapidly subsiding “piggy-back” and foreland basins. Homogeneous petrographic composition within the Eocene–lower Miocene Murree Supergroup, with only slight progressive increase of detrital feldspars, suggests erosion of largely supracrustal rocks involved in thrusting in the north. In middle Miocene time, marked enrichment in medium- to high-grade metamorphic detritus in foreland sandstones (Siwalik Group) reflects rapid uplift of a warm wedge of Indian crust, which was carried southward along the Main Central thrust. This major paleogeographic change was recorded also by quartzolithic remnant-ocean turbidites, which were fed great distances along transverse fracture zones and later accreted in the coastal Makran subduction complex (Panjgur association and Makran Group). Recycled-orogen detritus derived from the elevated Himalayan chain is still accumulating today in the Indus fan. Enrichment in feldspars with respect to ancient sandstones reflects deep erosion levels into mid-crustal rocks along the core of the growing orogen.

Detrital modes and provenance of Miocene sandstones and modern sands to the Southern Apennines thrust-top basins (Italy)

ABSTRACT The Cilento Group (Lower-Middle Miocene), the Monte Sacro Conglomerate (Upper Miocene), the Gorgoglione Formation (Upper Miocene), and the Crati submarine fan (Holocene) are four turbidite sequences deposited in northwest-southeast-trending thrust-top basins of the southern Apennines (Italy) foreland region. The Corigliano basin is a part of the modern Taranto Gulf foredeep basin that developed since the late Pleistocene. Sandstone detrital modes of the Miocene turbidite units are quartzofeldspathic (Petrofacies 1, 2a, 4, 5, 8; Q62F25L13), quartzolithic (Petrofacies 2b; Q60F16L24), and arkosic (Petrofacies 7; Q50F45L5, reflecting a collisional orogenic provenance. Volcanolithic sandstones (Petrofacies 3, Q23F11L66) suggest an important contribution also from a volcanic source area related to the convergent-continental-margin volcanism connected with the collisional tectonic regime that affected the western Mediterranean (e.g., Sardinia volcanic arc). Individual carbonatoclastic beds (hybrid arenite, biocalcarenite, and mudstone) are interbedded with sandstone units of the ilento Group. They have siliciclastic content of about 35% and are quartzofeldspathic (Petrofacies 6; Q53F23L24). These beds (0.10-65 m thick) record impulsive gravitational collapses of the carbonate-platform passive margin to the east and southeast. The petrologic parameters show a temporal evolution from metasedimentary to granitic-gneissic provenance ascribed to different tectonostratigraphic units of the Calabrian arc. Nine Miocene petrofacies suggest dynamic evolution of the source terranes from Laughian to Tortonian time. Facies, dispersal patterns, and petrologic parameters of the Miocene sandstones suggest a provenance from the northern and western margins of the basins. Comparison between the Holocene Crati Fan (Petrofacies 9; Q54F24L22) and Miocene detrital modes suggests that the sandstones of the Cilento Group, the Monte Sacro Conglomerate, and the Gorgoglione Formation were derived from unroofing of the thrusted basement block, transported by torrential-type, fluvio-deltaic systems and then funneled into a major turbidite dispersal system, analogous to the modern Crati submarine fan of the Corigliano thrust-top basin.

Provenance of the Lower Tertiary Murree redbeds (Hazara-Kashmir Syntaxis, Pakistan) and initial rising of the Himalayas

Abstract The Murree Supergroup of northern Pakistan is represented by an over 6 km thick succession of deltaic redbeds and intercalated impure foraminiferal limestones of latest Palcocene to Middle Eocene (Ilerdian to Lutetian) age, cropping out in the northern part of the Hazara Syntaxis, and by redbeds of younger age (early Middle Eocene to Early Miocene) cropping out in the southern part of the Syntaxis (Rawalpindi area). The quartzolithic composition of the Murree redbeds testifies to a “collision orogen” provenance. Detritus was derived from a suture belt including thrust sheets of metasedimentary and subordinately sedimentary rocks, volcanic or volcaniclastic rocks, and ophiolites. Phyllite rock fragments are most common in the Ilerdian sandstones, whereas volcanic and carbonate rock fragments are more abundant in the Lutetian sandstones. Minor quantities of chert and serpentineschist, indicating contribution from uplifted subduction complex sources, as well as siltstone, shale and limestone grains, are invariably present. Detrital modes of sandstones and southwestward progradation of Tertiary clastic wedges both testify to provenance from the proto-Himalayan chain located to the north, and uplifted since the very first stages of the India/Asia continental collision at the end of the Paleocene. The coeval Chulung La redbeds of the Tethys Himalaya instead, consisting of volcanic and subordinate ophiolitic detritus, testify to exclusive provenance from the obducting Trans-Himalayan are—trench system. This major petrographic difference may be accounted for by the different structural setting of the Chulung La “piggy-back” and Murree foreland basins. These two distinct collisional basins have been separated probably since the onset of collision by a fold-thrust belt, beginning to rise in the position occupied today by the High and Lesser Himalayan structural domains. Throughout the Murree Supergroup, main petrographic parameters do not vary greatly, and volcanic, sedimentary, low-grade metasedimentary and ophiolitic detritus persisted until the Early Miocene, indicating slow progressive growth of the chain. Only during the Middle Miocene, when the highly metamorphosed rocks of the High Himalaya were carried southward along the Main Central Thrust (MCT), the mountain range began to rise to dramatic heights, and huge amounts of detritus started to feed the Siwalik foreland basin sandstones and the remnant ocean turbidites of the Indus and Bengal Fans.

Compositional and Geochemical Signatures for the Sedimentary Evolution of the Middle Triassic-Lower Jurassic Continental Redbeds from Western-Central Mediterranean Alpine Chains

Compositional and chemical analyses suggest that Middle Triassic–Lower Liassic continental redbeds (in the internal domains of the Betic, Maghrebian, and Apenninic chains) can be considered a regional lithosome marking the Triassic-Jurassic rift-valley stage of Tethyan rifting, which led to the Pangaea breakup and subsequent development of a mosaic of plates and microplates. Sandstones are quartzose to quartzolithic and represent a provenance of continental block and recycled orogen, made up mainly of Paleozoic metasedimentary rocks similar to those underlying the redbeds. Mudrocks display K enrichments; intense paleoweathering under a hot, episodically humid climate with a prolonged dry season; and sediment recycling. Redbeds experienced temperatures in the range of 100°–160°C and lithostatic/tectonic loading of more than 4 km. These redbeds represent an important stratigraphic signature to reconstruct a continental block (Mesomediterranean Microplate) that separated different realms of the western Tethys from Middle-Late Jurassic to Miocene, when it was completely involved in Alpine orogenesis.

Sourceland controls on the composition of beach and fluvial sand of the northern Tyrrhenian coast of Calabria, Italy: implications for actualistic petrofacies

Abstract The northern Tyrrhenian margin of Calabria in southern Italy provides a natural laboratory for sampling sand at different scales: small drainages (first order), rivers draining mountain ranges (second order), and marine environments (beach to deep-marine; third order). Calabrian mountain ranges represent an uplifted and variable dissected thrust belt constituted by Palaeozoic through Pleistocene plutonic, metamorphic, ophiolitic, carbonate and siliciclastic rocks. The modern setting includes a mountainous coast, having high rates of fluvial discharge, and the deep-marine Paola Basin. The composition of modern fluvial and beach sands is useful for the interpretation of sediment transported into deeper-water environments. Modern beach and fluvial sands of the northern Tyrrhenian margin of Calabria define three distinct petrologic provinces, from north to the south: (1) the Lao Littoral Province has calclithite sand derived from erosion of dominantly carbonates of the southern Apennines; (2) the Coastal Range Littoral Province has quartzolithic sand derived from dominantly metamorphic (schist and phyllite) Coastal Range; and (3) the Santa Eufemia Littoral Province has quarzofeldspathic sand derived from dominantly metamorphic Coastal Range and Sila Massif and plutono-metamorphic Mount Poro provenances. Deep-marine turbidites of the Paola Basin have basinwide quartzolithic turbidite sands having close compositional relations with Coastal Range littoral petrofacies. Only at the northern boundary of the Paola Basin, calclithite turbidite sand record deep-water dispersal of the Lao littoral sands. Comparison of detrital modes from mainland to deep-marine environments contribute to the models of dispersal pathways and geographical extension of actualistic sand petrofacies.

Weathering of gneiss in Calabria, Southern Italy

Abstract The effects of weathering in a Mediterranean climate on the mineralogy and microfabric of Paleozoic gneiss of the Sila Massif, Calabria, southern Italy, have been studied. Field observations show highly weathered rock forms a residual soil. Micromorphological and mineralogical properties of bedrock and saprolite show that the weathering process is characterized by at least two major stages, having two distinct rock microfabrics. In the first stage, the morphological features of the original rock are preserved and weathering is manifested mainly by microfracturing, and large portions of the rock remain unaltered. The second stage of weathering involves further development of microcracks and progressive chemical attack on the minerals. This latter stage occurs along both compositional and microstructural discontinuities, with etch pitting of feldspar, and neoformation of clay minerals and ferruginous products replacing feldspar, biotite, and iron-bearing garnet. The determination of quantitative petrographic indices provides a measure of the various stages of weathering.

Link between thrust tectonics and sedimentation processes of stratigraphic sequences from the southern Apennines foreland basin system, Italy

We discuss here tectonics and sedimentation processes occurring during continent-continent collision and relationships between accretionary processes on overplate, flexural lithosphere on underplate and related controls on clastic sedimentation in developing foreland basin systems. This paper focuses on and clastic sedimentation developed during the sequential history of the southern Italy orogenic system. These clastic trends, covering a large time span from pre-collisional Early Mesozoic to the present, may contribute: (1) to the paleogeographic and paleotectonic reconstructions of the southern Italy portions of the western Mediterranean orogen, and (2) to the general models of complex relationships between clastic sedimentation and paleotectonic history of other major orogens. The evolutionary record of Earth’s processes preserved in the form of sedimentary rocks has been pivotal in paleogeographical and paleotectonic reconstructions of source/basin systems. Compositional trends of clastic strata through space and time are used to infer the structural history of adjacent mountain belts and to monitor the key geodynamic changes during orogenic processes (e.g. Dickinson, 1985, 1988; Critelli & Ingersoll, 1994; Critelli, 1999). The controls on the composition and dispersal pathways of clastic strata along the convergent plate margins have long been debated (e.g. Dickinson, 1988; Ingersoll et alii, 1995). Clastic infilling of sedimentary basins in orogenic systems have been used as important indicators of tectonic activity and climatic changes. In the orogenic systems, clastic sedimentation may record the accretionary processes, the accomodation of the thrust units, and the flexural features of the foreland plate. The development of an orogenic wedge during continental collision results in thickening of the crust. The excess mass of this thickened crust acts as a load on the underthrust plate, causing it to be flexed downwards close to the load, so developing a foreland basin (e.g. Beaumont, 1981; Sinclair and Allen, 1992). During plate convergence, the vertically acting load of the mountain belt migrates over the foreland plate, thus resulting in the migration of the associated foreland basin. The foreland is the region between the front of a thrust belt and the adjacent craton (e.g. Dickinson, 1974; Bally and Snelson, 1980; Allen et alii, 1986; Miall, 1995). Large volumes of clastic sediment are derived from erosion of the thrust belt and deposited in the foreland basin. The foreland basin generally is defined as an elongate trough that forms between a linear contractional orogenic belt and the stable craton, mainly in response to flexural subsidence caused by thrust-sheet loading in the orogen.Foreland basin stratigraphy records tectonic, eustatic, and climatic changes at convergent plate margins (e.g. Miall, 1995). The formation of unconformities is the results of the interplay of temporal variations in the erosion and lateral progradation rates of the orogenic wedge, as well as tectonic and eustatic sea-level changes (e.g. Beaumont, 1981; Jordan, 1981; Schedl & Wiltsc hko, 1984; Peper et alii, 1995).

Post-Oligocene Sediment-Dispersal Systems and Unroofing History of the Calabrian Microplate, Italy

The composition as well as stratigraphic and structural relations of sandstone and sand derived from erosion of the Calabrian Arc provide constraints for paleogeographic and tectonic models of southern Italy. Clastic detritus in the following sedimentary assemblages was derived mainly from provenance terranes within the strongly deformed Calabrian Arc allochthon: (1) the Paleogene Liguride Complex accretionary wedge, deposited in a remnant ocean basin that lay east of the Calabrian Arc and west of the Adria margin; (2) Burdigalian to lower Messinian foreland basin successions, widely developed in the southern Apennines, representing progressively shifted foredeep basins and related wedgetop basins; (3) upper Tortonian to Messinian, mainly nonmarine to shallow-marine successions, cropping out in the western Calabrian Arc, representing synrift clastic wedges related to backarc rifting in the Tyrrhenian area; and (4) the Quaternary of the northern Calabrian Arc, represented by foredeep and related wedgetop b...

Clay Mineral Assemblages and Sandstone Compositions of the Mesozoic Longobucco Group, Northeastern Calabria: Implications for Burial History and Diagenetic Evolution

Mesozoic mudrocks and sandstones from the Longobucco Group (Sila Unit, North Calabria) were mineralogically, chemically, and petrographically analyzed for their burial, diagenesis, and sourcearea weathering histories. These sediments mark an important phase of the regional geological evolution along internal domains of the circum-Mediterranean chains from the Gibraltar Arc (Spain and Morocco) to the Calabria-Peloritani orogen (Italy). The effects of diagenesis on quartzose sandstone-mudstone lithotypes in the Mesozoic Longobucco Group succession are quantified. The basal Longobucco Group consists of continental clastic redbeds deposited in a rapidly subsiding rift-valley basin, overlain by shallow-marine to deep-marine carbonate and clastic strata. These sediments were analyzed using thin-section petrography, SEM/EDS, X-ray diffraction (XRD), and fluorescence. Quartzarenites display heterogeneous distributions of authigenic quartz, kaolin, illite, feldspar, and minor carbonate cementation. Authigenic zoned syntaxial overgrowths on detrital quartz represent the principal cement, and interstitial clay is an important component of these lithotypes. The mineralogical assemblage of mudrocks is dominated by illite and illite/smectite mixed layers. This observation, coupled with the CIA index and the A-CN-K plot, suggests post-depositional K-enrichment. Paleoweathering indices (CIW and PIA ratios) suggest that the source experienced intense weathering and that mudrocks likely record recycling from metasedimentary basement rocks. Clay-mineral distributions of sandstone/mudstone lithotypes indicate that mixed-layer illite/smectite with ordered interstratification (from R = 1 to R = 3) dominates mudstone mineralogy. Authigenic clays in sandstone are kaolinite, illite, chlorite, and kaolinite illitization as pore filling and lining. These authigenic clays show a distinct distribution, reflecting differences in burial/temperature history. The illite crystallinity index, the illitization of kaolinite, and the occurrence of high-illite I/S mixed-layer clay minerals suggest burial depths of at least 4-6 km and a temperature typical of the boundary between late diagenesis to low anchizone.

Sandstone detrital modes in the Makran accretionary wedge, southwest Pakistan: implications for tectonic setting and long-distance turbidite transportation

Detrital modes of Early Miocene to Early Pliocene sandstones from the Makran accretionary wedge in southwest Pakistan show a mainly quartzolithic composition with an evolution from the transitional recycled to quartzose recycled. The lithic types, however, indicate two distinct petrofacies. Accreted abyssal plain turbidites have Qp11Lvm27Lsm62 and Lm39Lv27Ls34, showing a predominant supply from sedimentary and metasedimentary source terranes whereas slope and shelf facies sediments deposited on the accretionary wedge have Qp7Lvm47Lsm47 and Lm22Lv48Ls30 due to an increase of volcanic detritus. The detrital modes of the abyssal plain sediments suggest a recycled orogenic source, probably the Himalayan collision zone. The facies and longitudinal dispersal pattern suggest deposition in an Oligo-Miocene analogue of the present Indus fan. The sediment must have been transported across strike, parallel to the transform structure linking the Makran wedge to the Himalayas (Chaman-Ornach Nal fault system), and fed into the fan at the western end of the subduction zone. The detrital modes also show an increase in volcanic detritus with time (Lv/L = 0.27 for the Early Miocene abyssal plain sediments to 0.47 for the slope sequences). This may have been derived from Late Mesozoic volcanic terrains in northern Baluchistan or the Ladakh Himalayas, or more probably from the Early to middle Miocene andesitic volcanic centre in the northern Makran.