Clastic Complex Research Articles

Disseminated Gold–Sulfide Mineralization in Metasomatites of the Khangalas Deposit, Yana–Kolyma Metallogenic Belt (Northeast Russia): Analysis of the Texture, Geochemistry, and S Isotopic Composition of Pyrite and Arsenopyrite

At the orogenic gold deposits of the Yana–Kolyma metallogenic belt (northeast Russia) both Au–quartz-sulfide mineralization with native gold and disseminated sulfide mineralization with invisible Au developed. The textural and mineralogical-geochemical features, isotope-geochemical characteristics of gold-bearing sulfides from proximal metasomatites, and possible forms of Au occurrence in pyrite and arsenopyrite have been studied using electron microprobe, atomic absorption, LA-ICP-MS trace element, isotope analysis, and computed microtomography. Four generations of pyrite (Py1, diagenetic; Py2, metamorphic; Py3, metasomatic; Py4, veined) and two generations of arsenopyrite (Apy1, metasomatic; Apy2, veined) have been identified at the Khangalas deposit. In the proximal metasomatites, the most common are Py3 and Apy1. Studying their chemical composition makes it possible to identify the features of the distribution patterns of typochemical trace elements in pyrite and arsenopyrite, and to establish the nature of the relationship between Au and these elements. In Py3 and Apy1, structurally bound (solid solution) Au+ prevails, isomorphically entering the crystal lattice or its defects. Isotope characteristics of hydrothermal sulfides (δ34S = −2.0 to −0.6‰) indicate that mantle/magmatic sulfur was involved in the formation of the deposit, though the participation of sulfur from the host rocks of the Verkhoyansk clastic complex cannot be ruled out. The Khangalas deposit has much in common with other gold deposits of the Yana–Kolyma metallogenic belt, and from this point of view, the results obtained will help to better reveal their gold potential and understand their origin.

Frictional melting and thermal fracturing recorded in pelagic sedimentary rocks of the Jurassic accretionary complex, central Japan

Deep ocean drilling revealed that shallow seismic slip in subduction zones is localized along weak pelagic clay, resulting in devastating tsunamis. However, the actual conditions of earthquake faulting in the deeper portions of subduction zones are largely unknown. The Jurassic chert–clastic complex in central Japan was formed under a cold subduction zone, within which the termination stage of superanoxia in the Middle Triassic was recorded in the pelagic sedimentary rocks. We conducted structural and Raman spectroscopic analyses of the fault rocks distributed along the thrust fault branched from the plate-boundary décollement. The results show that preferential melting of illite, thermal erosion, wall-rock fracturing, and increased carbonization are recorded along a few millimeter-thick pseudotachylyte derived from the black carbonaceous mudstone. A comparison of the clast volume fraction between the pseudotachylyte and black carbonaceous mudstone indicates that half amount of the clasts in the pseudotachylyte originate from the incorporation of fractured wall rocks composed of pelagic chert. Thermal modeling using the thermal diffusivities of wall rocks and the measurement of wall-rock fracture density suggest that fractured wall rocks represent thermal fracturing associated with the alpha–beta transition of quartz in the chert. Our pseudotachylyte study suggests that seismic slip at the deeper portions of the subduction zones is localized along the black carbonaceous mudstone flanked with chert. The intensely fractured wall rocks may be characteristic of pseudotachylyte, which accompanies quartz-rich wall rocks with high thermal diffusivities. The coseismic thermal fracturing of wall rocks potentially affects the dilatancy-induced fluid pressure drop in the slip zone and the reduction of wall-rock stiffness, resulting in the generation of frictional melt and acceleration of seismic slip.

Estimating drawdown magnitudes of the Mediterranean Sea in the Levant basin during the Lago Mare stage of the Messinian Salinity Crisis

The Messinian Salinity Crisis (5.97–5.33 Ma) is one of the most dramatic sea level change events in the global geological record. During this event, marine connection between the Atlantic Ocean and the Mediterranean Sea was restricted, and episodically blocked. While division of the Messinian Salinity Crisis to three major stages is well established and accepted, the scale of sea level change at each stage is still debated. The magnitudes of the Mediterranean fluctuations throughout the Messinian Salinity Crisis have implications for contemporary connectivity between the eastern and western Mediterranean basins.During the third stage of the Messinian Salinity Crisis, commonly known as the Lago Mare, Mediterranean Sea level fluctuated repeatedly. Lago Mare drawdowns in the eastern Mediterranean were estimated earlier to vary between <200 m and all the way down to the abyssal basin. Here we assemble morphological, lithological and stratigraphic evidence for Lago Mare levels across the Israeli margin. We differentiate between low-stands of various scales and durations to constrain the magnitude of discrete Lago Mare drawdowns. Since the rates of syn-Messinian isostatic rebounds in response to water column removal are ambiguous, drawdown magnitudes are estimated here as a range and not as an absolute value.We propose that during the Lago Mare, ravinement along a continuously regressing-transgressing coastline abraded the upper continental margin offshore Israel. The Mediterranean regressed to a depth of 380–550 m below present-day mean sea level, and the eroded strata were evacuated downslope and deposited basinward of this depth as wedge-shape clastic complexes. During relatively short intervals, sea level receded to altitudes ~100 m below the erosional surface. These sea level recessions exposed a pronounced inflection in the slope gradient to sub-aerial processes, generating knickpoints and headward migration of incising gullies. These gullies developed later into channels, conduits for sediment bypass. Fan-deltas were deposited off these channels outlets.A major sea level fall towards the end of the Messinian Salinity Crisis reached 630–900 m below present-day mean sea level. Streams incised into the exposed tops of the clastic wedges and fan-deltas. Additionally, meteoric water dissolved evaporites within the clastic complexes and formed sinkholes and dolines. During this interval the Mediterranean Sea level fell to below the depth of the Sicily Sill, which separated the eastern and western Mediterranean basins. This finding reinforces previously proposed paradigms, which suggested that the Messinian Salinity Crisis was terminated by spillover events from the Atlantic Ocean to the western Mediterranean basin, and consequently from the western to the eastern basin.

The Basal Unit of the Verkhoyansk Sedimentary Complex, Northern Kharaulakh: Lithostratigraphy, Biostratigraphy, and Deposition Environments

Abstract —The origin and biostratigraphic constraints of the Krestyakh conglomerate remain among most controversial issues in the Late Paleozoic history of the Northern Kharaulakh basin. The Krestyakh conglomerate is a sequence of coarse sand to pebble-size sediments at the base of the Late Paleozoic Verkhoyansk clastic complex. According to geological, lithological, and sedimentation data, the Krestyakh conglomerate in the Atyrdakh Formation is composed of debrites i.e., deposits carried by debris flows that fill submarine canyons. The Verkhoyansk clastic deposition began at the middle Visean stage of the Early Carboniferous.

Седиментология и стратиграфическая корреляция вендских отложений на юго-западе Сибирской платформы: выдающийся вклад внешнего источника кластического материала в образование осадочных систем

The study focuses on the sedimentation and stratigraphy of a large Vendian (Ediacaran) sedimentary basin in the southwestern Siberian craton, with implications for the origin of its units and subunits. Sediments are been correlated along the craton edge and inward into the craton interior using stratigraphic sequences, including glacial and post-glacial deposits. Clastic complexes in the Vendian: upper Chapa, Taseeva, Oselok, and Baikal groups composed of fluvial deposits are of special importance for correlations. The structure of the continental Aysa Fm. of the Oselok Group in the Sayany area has been characterized in detail, based on universal classification of lithofacies and their sequences, and correlated with sediments in the craton interior. There are two Ediacaran subunits: a continental-marine complex below and a continental complex above. The continental-marine subunit in the subsided craton margins was deposited mainly upon postglacial plains (sandurs) and marginal sea shelves, with contributions from intracratonic clastic sources. The deposits of the continental subunit belong to centripetal fluvial systems directed from distant craton-margin mountain upland toward the epicontinental sea in the central Siberian craton. The continental subunit is composed of large sections of red and variegated fluvial deposits from a foreland basin which was accumulated mainly in foredeeps in the over-compensation setting and partly reached the slopes of forebulges. Big deep sand rivers with large channel bars were formed at early and late during orogenic activity, while perennial anastomosing and braided mud-sand rivers with levees originate during passive stages of orogeny. The largest progradation of fluvial systems onto the Siberian craton is marked by channel deposits of the lower members from the Nemchanka, Moshakovka, Aysa, Khuzhir and Kachergat fms., as well as by the Bokhan sandstone member of the Chora Fm.

Mesozoic tectonostratigraphic evolution of the North Carnarvon Basin unlocked using regional 3D seismic

Interpretation of regional scale merged 3D seismic data sets covering the North Carnarvon Basin has for the first time enabled a detailed description of Mesozoic stratigraphic and structural features on a basin scale. Isoproportional slicing of the data enables direct interpretation of Triassic depositional environments, including contrasting low-stand and high-stand fluvial channel complexes, marginal marine clastic systems and reef complexes. Channels vary dramatically between sinuous-straight single channels within low net:gross floodplain successions, to broad channel belts within relatively high net:gross fluvial successions. The latter can be traced from the inboard part of the basin to the outer areas of the Exmouth Plateau. 3D visualisation and interpretation has demonstrated the huge variety of structural styles that are present, including basement-involved extensional faults, detached listric fault complexes, polygonal faults, and regional scale vertical strike-slip faults with flower structures. Fault trends include north–south, north–northeast to south–southwest, and northeast–southwest, with deformation events occurring mainly between the Rhaetian and Valanginian. Extensional and compressional deformation has created multiple horsts, three-way fault closures, fold belts and associated four-way anticlinal traps. Wrench tectonics may also explain pock-mark trains with the interpreted transfer of over-pressure from Triassic to Early Cretaceous levels. The use of regional scale merged 3D seismic data sets is now shedding light on tectonostratigraphic features on a basin scale that were previously unrecognised or enigmatic on 2D seismic or local 3D seismic data sets.

The origin and composition of flysch deposits as an attribute to the excessive erosion of the Slani Potok valley („Salty Creek“), Croatia

Flysch deposits that crop out in the elongated coastal area of the Vinodol Valley (External Dinarides), and particularly in the Slani Potok (‘Salty Creek’) catchment, are characterized by excessive erosion. Formation of badlands, creeping and sliding processes have been related to crystallization of thenardite. Unusually intense erosion is caused by the dispersive effect of sodium on clay particles (derived from pelitic flysch intervals) in solution, as well as by expansion of thenardite during transformation into a deckahydrate (with a four fold increase in volume). The search for a sodium source required for thenardite crystallization has focused on a particular composition of Slani Potok Eocene fl ysch rock types. Slani Potok flysch is predominantly composed of pelitic intervals, with subordinate sandstones and biocalcirudites. Sandstones and biocalcirudites contain appreciable amounts of siliciclastic detritus. Lithic fragments are represented by volcanic rocks revealing porphyry structures - possibly andesite or altered volcanic glass fragments, quartzite, schists, shales, and carbonate grains. High amounts of sodium and barium (0.93–1.09 % and 267–276 mg/kg respectively), in marls and sandstones, is essentially ascribed to a particular composition of flysch, refl ecting its area of provenance. A Palaeozoic clastic complex with barite mineralization, (black shales, sandstones and conglomerates), as well as a Mesozoic hornblende andesite located near Fužinski Benkovac in the Gorski Kotar region, are interpreted as flysch source rocks. Sodium at least could be partly leached from the lithic and feldspar grains in clastic rocks, due to circulation of pore fluids. An increased amount of sulphur, barium and strontium in flysch can be related to that of a barite ore complex in the source area of the Gorski Kotar region. Transportation and deposition of material eroded from the hinterland (North of Slani Potok), suggests turbidity current flow was transverse to the main axis of the Eocene foreland basin striking NW-SE.

Trace elements and characteristics of the sources of clastic material in the Devonian and Carboniferous sedimentary formations of the eastern zones of the Southern Urals

This paper focuses on the characteristics of possible provenances for the Devonian and Carboniferous clastic complexes of the eastern zones of the Southern and, in part, Central Urals on the basis of the investigation of trace- and rare-earth element geochemistry, accounting for petrographic evidence. It was found that the material of basic and silicic volcanics, ultrabasic rocks, and metamorphic complexes influenced the geochemical characteristics of the clastic rocks. It was shown that the main sources of the Devonian clastic material were probably subalkaline volcanic rocks from an ensialic oceanic island arc similar to the Silurian arc of the Central Urals, including displaced ones, and the main sources of the Carboniferous sediments were Devonian island-arc complexes and, in part, continental margin volcanics. An eastern source of material existed probably in the Carboniferous in the southern part of the Eastern Ural megazone. The geochemical features of the sedimentary rocks of the Irendyk Formation (upper Emsian-Eifelian) indicate a differentiated source of clastic material.

Rapid evolution of the Eocene accretionary complex (Hyuga Group) of the Shimanto terrane in southeastern Kyushu, southwestern Japan

Abstract Detailed geologic examination of the Eocene accretionary complex (Hyuga Group) of the Shimanto terrane in southeastern Kyushu revealed that the oceanic plate was composed of Paleocene to Lower Eocene mudstone and siliceous mudstone, lower Middle Eocene red mudstone, and mid‐Middle Eocene trench‐fill turbidite with siltstone breccia, successively overlying the pre‐Eocene oceanic plate. This oceanic plate sequence was overlain by Upper Eocene siltstone. Deposition of the lower Middle Eocene red mudstone was accompanied by basalt flows and it is interbedded with continental felsic tuff, which indicates that the basalt and red mudstone were deposited near the trench just before accretion. The Hyuga Group has very similar geological structure to that of the chert–clastic complexes found in the Jurassic accretionary complexes in Japan: that is, a decollement fault formed in the middle of an oceanic plate sequence, and an imbricate structure formed only in the upper part of the sequence. Thus, it appears that the Hyuga Group was formed by the same accretionary process as the Jurassic accretionary complexes. No accretion occurred before the Middle Eocene, and the rapid accretion of the Hyuga Group was commenced by the supply of coarse terrigenous sediments in the mid‐Middle Eocene, when the direction of movement of the Pacific Plate changed. The pre‐Eocene oceanic basement and lower Middle Eocene volcanic activity suggest that the oceanic plate partly preserved in the Hyuga Group was very similar to the northern part of the present West Philippine Sea Plate.

Trace elements and REE in the Cevonian clastic complexes of the Magnitogorsk Megazone, Southern Urals

The first data on trace-element geochemistry, REEs included, of the Devonian clastic and volcanosedimentary complexes in the Magnitogorsk Megazone have been obtained with ICP-MS. The correlation links and the character of distribution indicate that many elements, including those readily passing into solutions during weathering, were transferred as mechanical suspensions. Therefore, minerals concentrating these elements were largely preserved, as also were the distribution and concentrations of elements inherent to the source rocks. Both accessory minerals (apatite, zircon, Ti-minerals, and magnetite) and rock-forming minerals (pyroxene, amphibole, biotite, serpentine, chlorite, and plagioclase) were found among mineral concentrators. Clay minerals also seem to have participated in the processes. The typical elements of various complexes were identified. The distribution of trace elements is correlated with the stratigraphic position of rocks and depends on the character of the petrographic provinces.

Cretaceous-Paleogene boundary deposits at Loma Capiro, central Cuba: Evidence for the Chicxulub impact

Research Article| September 01, 2005 Cretaceous-Paleogene boundary deposits at Loma Capiro, central Cuba: Evidence for the Chicxulub impact Laia Alegret; Laia Alegret 1Department of Earth Sciences, University College London, WC1E 6BT London, UK, and Departamento de Ciencias de la Tierra, Universidad de Zaragoza, 50009 Zaragoza, Spain Search for other works by this author on: GSW Google Scholar Ignacio Arenillas; Ignacio Arenillas 2Departamento de Ciencias de la Tierra, Universidad de Zaragoza, 50009 Zaragoza, Spain Search for other works by this author on: GSW Google Scholar José A. Arz; José A. Arz 2Departamento de Ciencias de la Tierra, Universidad de Zaragoza, 50009 Zaragoza, Spain Search for other works by this author on: GSW Google Scholar Consuelo Díaz; Consuelo Díaz 3Instituto de Geología y Paleontología, La Habana, Cuba Search for other works by this author on: GSW Google Scholar José M. Grajales-Nishimura; José M. Grajales-Nishimura 4Instituto Mexicano del Petróleo, 07730 Mexico D.F., Mexico Search for other works by this author on: GSW Google Scholar Alfonso Meléndez; Alfonso Meléndez 5Departamento de Ciencias de la Tierra, Universidad de Zaragoza, 50009 Zaragoza, Spain Search for other works by this author on: GSW Google Scholar Eustoquio Molina; Eustoquio Molina 5Departamento de Ciencias de la Tierra, Universidad de Zaragoza, 50009 Zaragoza, Spain Search for other works by this author on: GSW Google Scholar Reinaldo Rojas; Reinaldo Rojas 6Museo Nacional de Historia Natural, 10100 La Habana, Cuba Search for other works by this author on: GSW Google Scholar Ana R. Soria Ana R. Soria 7Departamento de Ciencias de la Tierra, Universidad de Zaragoza, 50009 Zaragoza, Spain Search for other works by this author on: GSW Google Scholar Author and Article Information Laia Alegret 1Department of Earth Sciences, University College London, WC1E 6BT London, UK, and Departamento de Ciencias de la Tierra, Universidad de Zaragoza, 50009 Zaragoza, Spain Ignacio Arenillas 2Departamento de Ciencias de la Tierra, Universidad de Zaragoza, 50009 Zaragoza, Spain José A. Arz 2Departamento de Ciencias de la Tierra, Universidad de Zaragoza, 50009 Zaragoza, Spain Consuelo Díaz 3Instituto de Geología y Paleontología, La Habana, Cuba José M. Grajales-Nishimura 4Instituto Mexicano del Petróleo, 07730 Mexico D.F., Mexico Alfonso Meléndez 5Departamento de Ciencias de la Tierra, Universidad de Zaragoza, 50009 Zaragoza, Spain Eustoquio Molina 5Departamento de Ciencias de la Tierra, Universidad de Zaragoza, 50009 Zaragoza, Spain Reinaldo Rojas 6Museo Nacional de Historia Natural, 10100 La Habana, Cuba Ana R. Soria 7Departamento de Ciencias de la Tierra, Universidad de Zaragoza, 50009 Zaragoza, Spain Publisher: Geological Society of America Received: 01 Feb 2005 Revision Received: 13 May 2005 Accepted: 16 May 2005 First Online: 02 Mar 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 Geological Society of America Geology (2005) 33 (9): 721–724. https://doi.org/10.1130/G21573.1 Article history Received: 01 Feb 2005 Revision Received: 13 May 2005 Accepted: 16 May 2005 First Online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Laia Alegret, Ignacio Arenillas, José A. Arz, Consuelo Díaz, José M. Grajales-Nishimura, Alfonso Meléndez, Eustoquio Molina, Reinaldo Rojas, Ana R. Soria; Cretaceous-Paleogene boundary deposits at Loma Capiro, central Cuba: Evidence for the Chicxulub impact. Geology 2005;; 33 (9): 721–724. doi: https://doi.org/10.1130/G21573.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract A newly discovered Upper Cretaceous to lower Paleogene section at Loma Capiro (central Cuba) has provided new evidence for a Cretaceous-Paleogene boundary age for the Chicxulub impact. The studied sediments at Loma Capiro consist of a foraminifera-rich marl and sandstone hemipelagic sequence, and a 9.6-m-thick intercalated clastic complex. Planktic foraminifera indicate an upper Maastrichtian age for the sediments below the clastic complex and a lowermost Danian age for those just above this complex. Small benthic foraminifera from below and above the clastic complex indicate deposition at middle to lower bathyal depths. The fining-upward clastic complex consists of a basal breccia that is overlain by microconglomerates and coarse- to fine-grained sandstones. The clastic complex contains reworked foraminifera from different ages and different paleoenvironments and, toward the top, impact material such as altered microtektites, shocked quartz, terrestrial chondrules, and accretionary lapilli. These microfacies suggest deposition from gravity flows that eroded sediments from upper-slope and shelf settings and redeposited them in deeper bathyal environments. We suggest that the origin of the clastic complex may be linked to the collapse of the Cuban platform, triggered by the Cretaceous-Paleogene impact at Chicxulub. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Vertical and lateral organization of a carbonate deep-water slope marginal to a submarine fan system, Miocene, southern Turkey

Organization is recognized in the forereef–deep water slope–submarine fan system of the Burdigalian-Langhian Kaplankaya Formation. A basinwards transition from a prograding shelfal reef complex, through forereef talus, deep-water slope and laterally encroaching bypass deep-water clastic system is described, although the deep-water slope makes up the bulk of the succession. Considerable thickness variations occur between the reef and deep-water clastic complexes; these are controlled by sea-floor topography, carbonate foreslope gradient and degree of mass wasting off the platform and foreslope. The vertical and lateral heterogeneity of the Kaplankaya deep-water slope system is described from a number of localities along a 40-km-long and up to 3-km-wide exposed section of the northern margin of the Miocene Adana Basin, a foreland basin setting resulting from thrust sheet loading from the north during the Tauride Orogeny. Detailed field mapping is supplemented with vertical sedimentary logs, photomosaics, palaeontological and petrological data to investigate stratal variation, diagnostic architectural elements, controls on slope progradation, differential timing of basinward encroachment of the reefal complex and lateral onlap of the deep-water clastic system onto the slope. Three-dimensional models are presented showing the vertical and lateral facies associations in different parts of the deep-water slope system, and provide a basis for architectural prediction of geometry and relative position in such environments.

The evolution of Montebestia landslide (Umbria, Central Italy). Site investigations, in-situ tests and GPS monitoring

The study of the Montebestia landslide (Umbria, Central Italy) is related to the general analysis of the types and causes of landslides which frequently involve the continental plio-pleistocenic sediments (gravels, sands, silts and clay) of the fluvial-lacustrine facies of the “Ancient Tiberian Lake Basin” (“Villafranchiano” Auctorum).The geological structure of the area is characterised by the presence of apenninic master faults and by antiapenninic joints and faults influencing the evolution of the landscape and the hydrographic network.The landslide is located in the Upper Tiberian Valley, next to Montone (in the province of Perugia).The stratigraphic sequence involved by the movement comprehends: silts (from clayey silts to sandy silts) with thin layers of gravels and sands; upper gravels and sands, bringing up the series. The dip of the clastic complex is towards SW, with an angle of inclination near to the slope inclination.The morphological evolution of the area was reconstructed by ancient cartographic documents and by aerial photos related to several flies (from 1954 to 1991). It shows that the lithological, structural and stratigraphic features were able to guide type, location, geometry and evolution of the mass movement.The results of the monitoring carried out by an inclinometer (to measure deep displacements), a GPS network (to measure surface movements) and piezometers (to control the relationships with groundwater) show a differentiated evolution, according to the type of mass movements recognisable in this area: multiple surface movements situated at a shallow depth and very slow movements (which are nonetheless constant over time) located at a major depth along a slide surface, which guided the various evolutive states.So this landslide, that can be classified as “complex landslide”, according to UNESCO (WP/WLI, 1993a; 1993b) owing to the described features, represents a significant example of the gravitational phenomena occurring in the clastic plio - pleistocenic sediments of the tuscan-umbrian “Villafranchiano” Auctorum, in Central Italy.

Mass transfer from the Alps to the Apennines: volumetric constraints in the provenance study of the Macigno–Modino source–basin system, Chattian–Aquitanian, northwestern Italy

A quantitative provenance approach is applied to the Late Oligocene–Early Miocene Macigno–Modino turbidite complex which accumulated in the foreland basin developed in front of the growing Northern Apennines, but was supplied from the rapidly rising Western Alps, at the northwestern end of the basin. As well as the traditional recognition of source rock lithologies and their gross paleogeographic location, the provenance approach adopted here evaluates the relative contributions to the clastic complex from different types of source rock, and estimates the volume of material transferred from the Alps to the Apennines within the Macigno–Modino source–basin system, and the overall volume of rock assumed to have undergone erosion in order to supply it. These elements are used to constrain the possible source of the clastics and to infer the main paleogeological features of the source area. It is concluded that an estimated volume of ca. 17–20×10 3 km 3 of basement (mainly metamorphic) rocks, together with ca. 10 3 km 3 of intermediate composition volcanic rocks was transferred as detritus from the Western Alps area to the Northern Apennines foreland basin, creating the 250–300 km long, 50 km wide and up to 2.7 km thick Macigno–Modino clastic complex. Lithology and paleogeography, combined with volume estimates and current knowledge of the regional geology of the Western Alps, consistently suggest that the bulk of the sediments funnelled into the Macigno–Modino complex were derived from the uplifted Ivrea crustal block, which formed a crystalline massif some 5000 km 2 in extent, that rose ca. 3 km during the Oligocene, forming one of the main elements of Western Alpine geology during that time.

The sandstone-hosted Pb occurrence of Rio Pischinappiu (Sardinia, Italy): a Pb-carbonate end-member

The discovery of a new type of Pb–Ba deposit in a clastic complex near Monti Ferru, Sardinia, Italy is discussed with respect to source of metals and conditions of deposition, in a near-shore oxidizing and high-pH environment, as well as conditions of diagenesis and metal concentration. Unlike most red-bed-type Pb deposits, this occurrence is characterized by oxidized minerals, without sulphides, with both clastic material and metals coming from a Tertiary volcanic edifice. The main anions, comprising carbonate, sulphate and chloride species, are of both continental and marine origin. The reconstruction of the mineralizing phenomena in this coastal environment is based on evidence of: transport of metals, composition of the pore waters, pH–Eh conditions, and differences in solubility of the possible species accounting for the predominance of barite and cerussite. The main mineralized stratum was originally an ash tuff bed transformed into an aggregate of authigenic K-feldspar and cerussite during diagenesis. In this less-permeable `trap-level', intercalated in the normal sedimentary series, the mobility of Pb was restricted, resulting in deposition of ore-grade quantities of cerussite.

Les complexes détritiques de marge glaciaire active du Bas Chablais oriental : implications hydrogéologiques .

The presence of a wurmian glacier in the Geneva lake basin has blocked the alluvial lateral deposits of the Chablaisian torrents. So, two thick clastic complexes deposited, the first during the englaciation (Evian), the second during the déglaciation (Thonon). The build up of the glacial margin accumulation is detailed for a better understanding of the glacial paleodynamics. Groundwaters in the permeable media show hydrogeochemical and bacteriological characteristics specific to each geological complex , to its origin and therefore, to its hydrodynamic. The Evian complex is particularly identified by the very performing filtration of its sandy-gravelly sedimentologic composition and by a natural protection provided by the upper wurmian morainic cover.

Stratigraphic evidence for a deep Eocene Lake Uinta, Piceance Creek Basin, Colorado

Relief on a prograding clastic complex is used to estimate the water depth of Eocene Lake Uinta in the Piceance Creek Basin of western Colorado. Relief of as much as 412 in is present today on the complex. Postdepositional compaction can account for only about 100 m of this relief; therefore, the remaining 312 m appear to represent paleorelief on the floor of Lake Uinta—the lake was apparently more than 300 m deep. Authigenic saline minerals were precipitated in the unlithified sediments of the deeper areas of the lake, suggesting that at least the lower part of the water column was highly saline. The evidence presented here indicates that the deep stratified lake model is more appropriate than the more generally accepted shallow or playa-lake model for Lake Uinta.

Bryozoan Ecology and Sedimentary Environments in Central Appalachian Upper Ordovician: ABSTRACT

Trepostomatous bryozoans are abundant in the upper Reedsville Formation (Ordovician) in the central Appalachians from Pennsylvania to Tennessee. A study of their faunal associations and zoogeographic distribution has emphasized the close relation between sedimentary environments and bryozoan morphology, abundance, and diversity. Reconstruction of the Late Ordovician environmental setting outlines a broad, gently sloping shelf with a prominent clastic wedge or deltaic complex in south-central Pennsylvania. Coarse sand and silt were common on the shelf in the north, and graded southward into silty mud and mud. The external morphology of the central Appalachian trepostomes shows little change along the north-south shoreline. The zoarial types usually are branching, either subcylindrical or flattened plates; such forms are most common today in quiet sublittoral waters. The Ordovician trepostomes are abundant only north and south of the clastic wedge. Recent bryozoans usually are found in nonturbid environments on a slightly mobile surface of attachment; therefore, they are abundant only away from delta fronts and sediment-laden currents. Similarly, there is no reason to expect that the Upper Ordovician bryozoans reflect any lesser sensitivity to substratum mobility or to have been more tolerant of turbidity. Where taxonomic diversity is mapped in Recent environments, those bryozoan assemblages with the highest diversity are found only where the rates of deposition are moderate to low. Generic diversity along the central Appalachian Upper Ordovician shoreline shows a sharp gradient from low diversity in the north to high diversity in the south. Two genera are common in the north, each isolated from the other but both equally abundant on the flanks of the clastic wedge. In southwestern Virginia and northern Tennessee, well off the apron of the clastic wedge, as many as 5 to 7 genera may be abundant at any one locality. The distributional pattern of the Upper Ordovician trepostomes in the central Appalachians, especially the pronounced diversity gradient, appears to be directly related to areas of sediment influx and to rates of sedimentation. End_of_Article - Last_Page 521------------