Deposition Of Clastic Sediments Research Articles

Petrogenesis of metavolcanics and detrital zircon geochronology of the Mesoarchean western Iron Ore Group supracrustals, Singhbhum Craton (India): Evidence for an intracontinental extension setting

The Singhbhum Craton of eastern India, consisting of well-preserved Paleo- to Mesoarchean granitoids, volcanic and sedimentary rocks, is an excellent archive of early earth processes. In this contribution, we investigated the geological evolution of the Noamundi-Jamda-Koira IOG Basin (WIOG) using detrital zircon U-Pb ages, whole rock geochemical and Nd isotopic data on metavolcanic rocks from this belt including the Jagannathpur volcanics. The metavolcanics of the WIOG and Jagannathpur are compositionally basaltic andesites with enriched LREE and negative anomalies of Nb-Ta and Ti. The ratios of crustal contamination sensitive elements such as La/Sm, Sm/Nd, Nb/La, Th/Yb and Nb/Yb are close to that of bulk continental crust. The Nd isotopic composition of these basaltic andesites are broadly chondritic (εNdt = +0.93 to −1.20). The geochemical and isotopic signatures are consistent with significant assimilation of Paleoarchean granitoids of the Singhbhum Craton. The overlapping geochemical and isotopic compositions support the view that Jagannathpur volcanics is an eastward extension of the ∼3.04 Ga WIOG metavolcanics and shouldn’t be considered as a separate stratigraphic unit. The presence of pillowed structures, vesicularity, absence of volcanic breccia, and their association with clastic sediments clearly indicate a subaqueous and shallow marine eruption for the WIOG basaltic andesites. The deposition of clastic sediments before basaltic magmatism points towards lithospheric thinning and basin opening. The detrital zircon ages from the WIOG ranges from 3.51 to 2.96 Ga and the detritus was mainly sourced from the adjacent Singhbhum granite and Bonai granite. The petrogenesis of the WIOG metavolcanics can be attributed to assimilation-fractional crystallisation of a depleted mantle derived tholeiitic mafic-ultramafic magma in an intracontinental extension setting.

Assembly and Tectonic Evolution of Continental Lower Crust: Monazite Petrochronology of the Ivrea‐Verbano Zone (Val Strona di Omegna)

AbstractMetasediments are common constituents of exhumed lower‐to‐mid‐crustal granulite terranes; understanding their emplacement is significant for the assembly and tectonic evolution of deep continental crust. Here, we report a monazite U‐Th‐Pb petrochronological investigation of the Variscan Ivrea‐Verbano Zone (IVZ) (Val Strona di Omegna section)—an archetypal section of lower crust. Monazite Th‐Pb dates from 11 metapelitic samples decrease with structural depth from 310 to 285 Ma for amphibolite‐facies samples to <290 Ma for granulite‐facies samples. These dates exhibit a time‐resolved variation in monazite trace‐element composition, dominated by the effects of plagioclase and garnet partitioning. Monazite growth under prograde to peak metamorphic conditions began as early as 316 ± 2 Ma. Amphibolite‐facies monazite defines a trend consistent with progressively decreasing garnet modal abundances during decompression and cooling starting at ∼310 Ma; the timing of the onset of exhumation decreases to ∼290 Ma at the base of the amphibolite‐facies portion of the section. Structurally lower, granulite‐facies monazite equilibrated under garnet‐present pressure‐temperature conditions at <290 Ma, with monazite (re)crystallization persisting until at least ∼260 Ma. Combined with existing detrital zircon U‐Pb dates, the monazite data define a <30 Myr duration between deposition of clastic sediments and their burial and heating, potentially to peak amphibolite‐to‐granulite‐facies conditions. Similarly brief timescales for deposition, burial and prograde metamorphism of lower crustal sediments have been reported from continental magmatic arc terranes—supporting the interpretation that the IVZ represents sediments accreted to the base of a Variscan arc magmatic system >5 Myr prior to the onset of regional extension and mafic magmatism.

Trends and Composition—A Sedimentological-Chemical-Mineralogical Approach to Constrain the Origin of Quaternary Deposits and Landforms—From a Review to a Manual

In this study, six basic Quaternary landform series (LFS) and their sedimentary deposits (LFS1 aeolian, LFS 2.1 to 2.2 mass wasting, LFS 3 cryogenic-glacial, LFS 4.1 to 4.6 fluvial, LFS 5.1 to 5.2 coastal-marine, LFS 6.1 to 6.3 lacustrine) are subdivided into subtypes and examined with regard to their sedimentological parameters and their mineralogical and chemical compositions. Emphasis is placed on the textural (related to transport and deposition), compositional (sediment load/weight, Eh and pH) and geodynamic maturity of the sedimentary deposits which are influenced by the parent lithology and bedrock tectonic and by the climate during the last 2 Ma. To constrain the development of the LFS and their sediments, composite trend-line diagrams are designed combining sedimentological (x-axis) and chemical/mineralogical dataset (y-axis): (1) sorting vs. heavy mineral content; (2) sphericity of grains vs. silica/carbonate contents; and (3) median vs. Ti/Fe ratios. In addition, the x-y plots showing the log SiO2/Al2O3 vs. log Na2O/K2O are amended by a dataset of the three most common clay minerals, i.e., kaolinite-, mica-, and smectite-group clay minerals. Such joint sedimentological-chemical-mineralogical investigations focused on the depositional environment of unconsolidated clastic sediments of Quaternary age can be used to describe the economic geology and environmental geology of mineral deposits in the pre-Quaternary sedimentary series according to the phrase: “The Present is the key to the Past”. Both trend diagrams and compositional x-y plots can contribute to constraining the development of the full transect of landform series from the fluvial incision and slope retreat to reef islands fringing the coastal zone towards the open sea as far as they are built up of clastic sedimentary deposits enriched in siliceous and/or carbonate minerals. Climate zonation and crustal maturity are the exogenous and endogenous “drivers”, as can be deduced from the compositional (mineralogy and chemistry) and physical (transport and deposition) variations observed in the Quaternary sediments. The current study bridges the gap between a review only based on literature and a hybrid manual generated by practical field studies devoted to applied geosciences in economic and environmental geology (“E & E issue”).

Grain-size characteristics in lake Fuxian sediments: Implication for dry-humid transformation of Indian summer monsoon over the past 150 years

Polymodal distributions and end-member modeling of grain-size in lacustrine sediments can reveal the changes in sedimentary processes, transportation mechanisms, and climatic changes. The temporal and spatial variation characteristics of grain-size were investigated in six sediment cores of the plateau deep-lake Fuxian, in southwest China, where the climate was driven by Indian Summer Monsoon (ISM). Results indicated that the size of the dominant grain-size exponentially decreased with the declining hydrodynamic condition towards the deep-water zones, with an exception of the maximum grain-size near the outlet of the lake. Measured grain-size distributions were classified into four end-members (EMs) with a basic end-member model algorithm (BasEMMA), of which could be linked to a distinct transport mechanism and source: EM1 (long-term suspended load from atmospheric dust) with the modal size of 0.3–11.2 µm, EM2 (off-shore suspended load from fine riverine input) with 7.9–14.2 µm, EM3 ((near-shore suspended load from coarse riverine input) with 15.9–31.7 µm, and EM4 (near-shore riverbed load from extremely coarse riverine input) with 35.6–70.9 µm, respectively. Temporal variation of EM2 + EM3 components of grain-size in Core F5 are responses to the changes in instrumentally recorded precipitation in Chengjiang (1961–2008) and ISM (1860–2006), which indicates that changes in river flow in response to changes in precipitation is the primary driver of clastic sediment deposition especially in the narrow section of the lake. Our findings indicate grain-size distribution and sediment compositions are significant tools for improving the understanding of the spatiotemporal heterogeneity in dry-humid transformation of ISM over the past 150 years.

Late Quaternary episodes of clastic sediment deposition in the Tarimba Cave, Central Brazil

The study presents three sedimentary profiles from Tarimba cave in central Brazil. The data allow constraining the late Quaternary sedimentary evolution of cave systems in the region. A multi-techniques approach was used to characterize sediment texture (grain size and circularity index), mineralogical composition (X-Ray Diffraction), chemical composition (ICP-OES) and deposition ages (Optically Stimulated Luminescence and radiocarbon). Eight sedimentary facies were identified, including a facies formed by autochthonous sediments (Guano) and seven facies formed by allochthonous siliciclastic sediments. The siliciclastic facies range from clayey to gravelly deposits that correspond to high-density gravity flows (Diamicton) and water laid traction process of varied deposition energy (Channel, Backswamp, and Slackwater). The studied deposits reflect an intense cave filing from the Middle to Late Pleistocene in the last 200 Ka. Subsequent depositional events formed three sedimentation phases: the first before 200 Ka corresponding to a larger granulometric interval, clay to gravel, identified through erosive surfaces; the second, after 197 Ka, is composed of sandy sediments and oscillations in the water flow energy. The third phase between 87 and 52 Ka (which covered the other stages) was responsible for the last fluvial deposition.

Constructing vertical measurement logs using UAV-based photogrammetry: Applications for multiscale high-resolution analysis of coarse-grained volcaniclastic stratigraphy

Volcaniclastic stratigraphy can be difficult to map and describe due to its complex nature. However, such stratigraphy preserves information about fluctuations in volcanic activity and sedimentation and is vital to understanding volcanic systems. Uncrewed aerial vehicle (UAV) based analysis of volcanic stratigraphy can enhance mapping and analysis, especially on vertical surfaces where outcrop exposure is greatest. Here we present a method for using small UAVs to produce vertical grain size and bedding measurement logs, or quantitative stratigraphic columns, of vertical volcaniclastic stratigraphy. We demonstrate the range of high-accuracy measurements and parameters that can be collected for building measurement logs using consumer grade UAVs through a case study in the Marysvale volcanic field where we collected 34,422 grain measurements from 21 individual units. The purpose of producing such measurement logs is to enhance lithofacies analysis through the use of large quantitative datasets and improve the reproducibility of data reporting. Whereas descriptions of volcaniclastic units such as those describing grading are often reported qualitatively, we describe methods for calculating numerical parameters for enhanced lithologic analysis including grain size, grading, clast to matrix ratios, and shape characteristics. The methods described in this paper can enhance field data acquisition, mapping, and quantitative analysis of volcaniclastic deposits and are applicable to a wide range of other geologic settings where coarse-grained clastic sedimentary deposits exist.

Unraveling the timing of the Caviahue depression, Andean Southern Volcanic Zone: insights from the sedimentary infill

The Caviahue–Copahue volcanic complex in the Southern Volcanic Zone of the Andes is composed of the Pliocene–Pleistocene Caviahue depression and the active Copahue volcano. This volcanic complex is located in a zone of profuse volcanic and tectonic activity, and thus, the origin of the depression includes both tectonic and volcanic hypothesis (e.g., formation of a collapse caldera and a pull-apart basin). According to current knowledge, the oldest rocks filling the depression are lavas and ignimbrites of the Pleistocene Las Mellizas Formation. However, clastic sedimentary deposits underlying this unit have been recognized. Here, we document the characteristics of these deposits at the south shore of the Caviahue lake using field data and digital outcrop models (DOM). We have concluded that the deposits are deltaic and alluvial in origin and made up by a prodelta/distal deltaic front, delta front deposits, delta plain sediments and alluvial deposits. An unconformity separates the deltaic deposits from overlying alluvial deposits, indicating the decrease in the stratigraphic base level probably associated with a sudden coarse-grained clastic input and a drop in the lake level. Our study has implications on the timing and evolution of the Caviahue depression and indicates that the depression precedes the Las Mellizas Formation. Thus, Las Mellizas ignimbrite should not be interpreted as the main unit related to the Caviahue caldera as it has been proposed by some authors. If the depression had indeed been formed by a collapse caldera, this event would be previous to the described sediments.

Processes of clastic sedimentation associated with Late Cretaceous ophiolite emplacement in the SW segment of the Antalya Complex (S Turkey)

Clastic sediments provide important clues to the timing and processes of ophiolite emplacement, when integrated into the regional temporal and tectonic framework. Four related settings of Late Cretaceous ophiolite-related clastic sediment deposition are exposed in the SW segment of the Antalya Complex, along the western limb of the Isparta Angle, an orocline in SW Turkey. The restored pre-emplacement paleogeography is indicative of a regional-scale Mesozoic carbonate platform, bordered to the east by a Late Triassic volcanic rift that partially infilled with deep-sea sediments, passing eastwards into several Mesozoic carbonate platforms (floored by pre-rift or syn-rift crust) and finally into the South Neotethys. First, emplacement-related sediments unconformably overlie exhumed ultramafic and gabbroic ophiolitic rocks and comprise locally variable mass-flow deposits (up to several-hundred m thick) that are dominated by subaqueous screes and debris-flow deposits. Fossil evidence (benthic and planktic foraminifera, radiolarians and macrofossils) indicates accumulation during the Campanian-Maastrichtian. Much of the coarse talus was derived from weathering and erosion of intrusive ophiolitic rocks (sheeted dykes, gabbro). Petrographic, XRD and whole-rock geochemical analysis of sandstones and igneous clasts indicate additional derivation from basaltic rocks, interpreted as the eroded extrusive layer of the ophiolite. Additional material was derived from Late Triassic-Cretaceous deep-water volcanics and sediments, and also from Late Cretaceous (and older) platform carbonates. The coarse clastics relate to ophiolite emplacement onto the continental margin, rather than forming in an oceanic setting (e.g., rifted ridge or oceanic fracture zone). The emplacement was associated with crustal extension that exposed ultramafic and gabbroic rocks on the seafloor, where they were covered by clastic debris. Secondly, Late Cretaceous calciturbidites and debris-flow deposits depositionally overlie Late Triassic-Late Cretaceous deep-water passive margin sediments. The clastic debris was derived from the emplacing ophiolite and from an adjacent Mesozoic carbonate platform. Thirdly, calciturbidites and debris-flow deposits also depositionally overlie the same carbonate platform. Fourthly, west of the same carbonate platform, ophiolite-derived mass-flow breccias accumulated locally and were then interleaved with previously emplaced ophiolitic plutonic rocks (mainly serpentinite and gabbro), typically at high angles. The four depositional settings relate to ongoing stages of Late Cretaceous ophiolite emplacement in a setting dominated by regional-scale thrusting and strike-slip (i.e., transpression). The latest Cretaceous deformation and related clastic deposition affected part of the northern, active continental margin of the Southern Neotethys, but without reaching more inboard continental crust (regional Tauride platform), a situation that contrasts with more orthogonally emplaced ophiolites.

Source and deposition age of the Dialé-Daléma metasedimentary series (Kédougou-Kéniéba Inlier, Senegal) constrained by U–Pb geochronology on detrital zircon grains

The Dialé-Daléma metasedimentary series is exposed in the Kédougou-Kéniéba Inlier that corresponds to the northwestern branch of the Eburnean orogenic belt in the southern West African Craton. Here we conducted a U–Pb geochronological study on metapelites, metagraywackes and metavolcanic breccia of the Dialé-Daléma metasedimentary series in order to identify the sedimentary sources and establish the lithostratigraphic sequence of the Kédougou-Kénieba Inlier. This new U–Pb geochronological dataset from five samples representing different stratigraphic levels yields a dominant population of Paleoproterozoic detrital zircon grains with ages ranging from c. 2200 to 2100 Ma. The youngest weighted mean ages at c. 2120 Ma are identical for all five samples within error and provide a maximum deposition age for the sediments of the Dialé-Daléma series. The dominant ages are similar to those obtained on metamorphosed plutonic and volcanic rocks of the Mako belt and thus suggest a dominant proximal source for the clastic sediments of the Dialé-Daléma series and a distal or geographically isolated position relative to the Archean Leo-Man or Réguibat craton nuclei. Deposition ages are only a few Myr older than available ages for metamorphism and intrusion of plutons forming the Saraya batholith. This is consistent with deposition along an active convergence zone marked by the succession, within a few tens of Myr, of (1) magmatic accretion of the Mako plutonic and volcanic rocks in the context of volcanic arc, associated with local uplift, exhumation and erosion at c. 2200-2160 Ma, (2) deposition of clastic sediments forming the Dialé-Daléma series at c. 2120-2110 Ma followed by (3) their burial and exhumation at c. 2090–2060 partially contemporaneous with (4) the intrusion of the Saraya batholith at c. 2080–2070 Ma.

Flow of partially molten crust controlling construction, growth and collapse of the Variscan orogenic belt: the geologic record of the French Massif Central

We present here a tectonic-geodynamic model for the generation and flow of partially molten rocks and for magmatism during the Variscan orogenic evolution from the Silurian to the late Carboniferous based on a synthesis of geological data from the French Massif Central. Eclogite facies metamorphism of mafic and ultramafic rocks records the subduction of the Gondwana hyperextended margin. Part of these eclogites are forming boudins-enclaves in felsic HP granulite facies migmatites partly retrogressed into amphibolite facies attesting for continental subduction followed by thermal relaxation and decompression. We propose that HP partial melting has triggered mechanical decoupling of the partially molten continental rocks from the subducting slab. This would have allowed buoyancy-driven exhumation and entrainment of pieces of oceanic lithosphere and subcontinental mantle. Geochronological data of the eclogite-bearing HP migmatites points to diachronous emplacement of distinct nappes from middle to late Devonian. These nappes were thrusted onto metapelites and orthogneisses affected by MP/MT greenschist to amphibolite facies metamorphism reaching partial melting attributed to the late Devonian to early Carboniferous thickening of the crust. The emplacement of laccoliths rooted into strike-slip transcurrent shear zones capped by low-angle detachments from c. 345 to c. 310 Ma is concomitant with the southward propagation of the Variscan deformation front marked by deposition of clastic sediments in foreland basins. We attribute these features to horizontal growth of the Variscan belt and formation of an orogenic plateau by gravity-driven lateral flow of the partially molten orogenic root. The diversity of the magmatic rocks points to various crustal sources with modest, but systematic mantle-derived input. In the eastern French Massif Central, the southward decrease in age of the mantle- and crustal-derived plutonic rocks from c. 345 Ma to c. 310 Ma suggests southward retreat of a northward subducting slab toward the Paleotethys free boundary. Late Carboniferous destruction of the Variscan belt is dominantly achieved by gravitational collapse accommodated by the activation of low-angle detachments and the exhumation-crystallization of the partially molten orogenic root forming crustal-scale LP migmatite domes from c. 305 Ma to c. 295 Ma, coeval with orogen-parallel flow in the external zone. Laccoliths emplaced along low-angle detachments and intrusive dykes with sharp contacts correspond to the segregation of the last melt fraction leaving behind a thick accumulation of refractory LP felsic and mafic granulites in the lower crust. This model points to the primordial role of partial melting and magmatism in the tectonic-geodynamic evolution of the Variscan orogenic belt. In particular, partial melting and magma transfer (i) triggers mechanical decoupling of subducted units from the downgoing slab and their syn-orogenic exhumation; (ii) the development of an orogenic plateau by lateral flow of the low-viscosity partially molten crust; and, (iii) the formation of metamorphic core complexes and domes that accommodate post-orogenic exhumation during gravitational collapse. All these processes contribute to differentiation and stabilisation of the orogenic crust.

Rifting in SW China: structural and sedimentary investigation of the initial crustal response to emplacement of the Permian Emeishan LIP

AbstractDetailed structural, volcanic, and sedimentary investigations of the crustal response to the emplacement of the Middle–Late Permian Emeishan large igneous province show that a rifting system developed prior to the main stage of flood basalt eruptions, in the form of sedimentary breccias, clastic sedimentary deposits and mafic hydromagmatic units. Detrital zircon grains from sandstones yield ~750–800 Ma LA-ICP-MS 206Pb/238U age clusters, showing that material was sourced from the Yangtze crystalline basement. Gabbros and pegmatites intruded along the normal faults of the rift system yield zircon ages of 264–260 Ma, and thus constrain the timing of rifting. N–S-trending rift zones developed along the western flank of the Pan-Xi palaeo-uplift, with NE–SW- and NNE–SSW-trending rifts on the eastern side and along the western and eastern margins of the Yangtze Block. The rifting progressed in pulses, with an initial phase of normal faulting followed by rapid deposition of breccias. Later there was lower-energy deposition of sandstone, with accompanying rhyolitic eruptions. This was followed by low-energy sedimentation of mudstones and dolomites, with accompanying hydromagmatic deposits. Rift system formation was constrained by a combination of far- and near-field tectonic stresses due to plate motions and lithospheric interaction with initial Emeishan volcanism.

Folded Basinal Compartments of the Southern Mongolian Borderland: A Structural Archive of the Final Consolidation of the Central Asian Orogenic Belt

The Central Asian Orogenic Belt (CAOB) records multiple Phanerozoic tectonic events involving consolidation of disparate terranes and cratonic blocks and subsequent reactivation of Eurasia’s continental interior. The final amalgamation of the CAOB terrane collage involved diachronous closure of the Permian-Triassic Solonker suture in northernmost China and the Jurassic Mongol-Okhotsk suture in northeast Mongolia and eastern Siberia. The distribution, style, and kinematics of deformation associated with these two terminal collision events is poorly documented in southern Mongolia and northernmost China because these regions were later tectonically overprinted by widespread Cretaceous basin and range-style crustal extension and Miocene-recent sinistral transpressional mountain building. These younger events structurally compartmentalized the crust into uplifted crystalline basement blocks and intermontane basins. Consequently, widespread Cretaceous and Late Cenozoic clastic sedimentary deposits overlie older Permian-Jurassic sedimentary rocks in most basinal areas and obscure the deformation record associated with Permian-Triassic Solonker and Jurassic Mongol-Okhotsk collisional suturing. In this report, satellite image mapping of basinal compartments that expose folded Permian-Jurassic sedimentary successions that are unconformably overlapped by Cretaceous-Quaternary clastic sediments is presented for remote and poorly studied regions of southern Mongolia and two areas of the Beishan. The largest folds are tens of kilometers in strike length, east-west trending, and reveal north-south Late Jurassic shortening (present coordinates). Late Jurassic fold vergence is dominantly northerly in the southern Gobi Altai within a regional-scale fold-and-thrust belt. Local refolding of older Permian north-south trending folds is also evident in some areas. The folds identified and mapped in this study provide new evidence for the regional distribution and kinematics of Jurassic and Permian-Triassic contractional tectonism in the southern Mongolia-northern China borderland region. The newly mapped folds are also important potential targets for hydrocarbon exploration and vertebrate paleontological discoveries.

English

A structural evaluation of a post stack time migrated (PSTM) 3D seismic data over an X–Field in the eastern Niger Delta has been attempted. The objective of the study is to structurally evaluate the field with a view to identifying structural features such as faults, map geologic horizons and analyze reflection characteristics that might be a good lead to probable hydrocarbon accumulations. Results revealed that six growth faults (F1, F2, F3, F4, F5, and F6) and three seismic horizons (HI, H2 and H3) were delineated on the seismic section.  F1, F2, F4, F5 and F6   are synthetic, while F3 is antithetic growth faults. The synthetic faults trend northeast-southwest and dips southwestward, while the antithetic fault trend northwest-southeast and dips southeastward. The seismic horizons are fault truncated with hanging wall/footwall fault assisted closures characterized by distinctive high amplitude reflection events. The horizons have good reflection continuity, moderate to strong reflection strength and medium to high amplitudes. These suggests wide spread and uniform deposition of clastic sediments with thick sand facies and inter-bedding shales, which is the characteristic of a hydrocarbon reservoir in the Niger Delta basin. The potential for hydrocarbons is high in this prospect field based on our preliminary study, which could be explored.   Key words: Growth faults, seismic horizons, fault closures, post stack time migrated (PSTM) 3D seismic data.

New isotopic data on karst development in the northern Kraków-Wieluń Upland (southern Poland)

The Krakow-Wielun Upland is one of the major palaeokarst regions in Poland. However, the stages of karst development in this area are neither well documented nor reconstructed. A series of samples from a new location in the vicinity of Raciszyn was analysed. On the basis of the results of U-series dating, four phases of speleothem deposition were distinguished: (1) older than 600 ka, (2) from more than 600 ka to 290 ka, (3) around 150 ka, and the youngest (4), younger than 3 ka. On the basis of all geochronological data from the region, eight stages of karst development were described. The structure of the oldest speleothems indicates even more stages of deposition and erosion that cannot be recognized using the 230 Th/ 234 U dating method. These results indicate that the initial creation of empty spaces in the limestone took place in pre-Pleistocene time. After 600 ka ago, climatic conditions were stable for more than 300 ka, allowing the continuous deposition of speleothems. Several episodes of erosion, deposition of clastic sediments and speleothem growth during the Middle and Early Pleistocene were described. This variability of the sedimentation regime clearly reflects climate changes during that period.

New isotopic data on karst development in the northern Kraków-Wieluń Upland (southern Poland)

The Kraków-Wieluń Upland is one of the major palaeokarst regions in Poland. However, the stages of karst development in this area are neither well documented nor reconstructed. A series of samples from a new location in the vicinity of Raciszyn was analysed. On the basis of the results of U-series dating, four phases of speleothem deposition were distinguished: (1) older than 600 ka, (2) from more than 600 ka to 290 ka, (3) around 150 ka, and the youngest (4), younger than 3 ka. On the basis of all geochronological data from the region, eight stages of karst development were described. The structure of the oldest speleothems indicates even more stages of deposition and erosion that cannot be recognized using the 230 Th/ 234 U dating method. These results indicate that the initial creation of empty spaces in the limestone took place in pre-Pleistocene time. After 600 ka ago, climatic conditions were stable for more than 300 ka, allowing the continuous deposition of speleothems. Several episodes of erosion, deposition of clastic sediments and speleothem growth during the Middle and Early Pleistocene were described. This variability of the sedimentation regime clearly reflects climate changes during that period.

Late Holocene fluctuations of Quelccaya Ice Cap, Peru, registered by nearby lake sediments

ABSTRACTRecords of clastic sediment from lakes that receive glacial meltwater provide a means for inferring past glacial fluctuations. However, increased clastic sedimentation has been interpreted to indicate both glacial advance and recession. Here we examine the timing of clastic sediment deposition in Challpacocha, a glacially fed lake located downvalley from Quelccaya Ice Cap (QIC), Peru, in comparison with known ice cap margin fluctuations. Using a comparison with a nearby non‐glacial lake, Yanacocha, we document that a record of clastic sediment flux from Challpacocha reflects meltwater‐derived sediment. We then compare the clastic sediment record from Challpacocha with the Qori Kalis glacier moraine record. We find that organic‐rich sediment was deposited primarily during the late Holocene advance of QIC (before ∼CE 1490). In contrast, clastic sediment was deposited during QIC recession (∼CE 1490–1970). Peaks in clastic sediment flux are associated with the onset of ice retreat. We suggest that this pattern of clastic sediment deposition reflects changing meltwater production and/or glacial erosion during ice advance and retreat and supports models of increased clastic sedimentation during ice retreat.

Dating the initiation of Piemonte-Liguria Ocean subduction: Lu–Hf garnet chronometry of eclogites from the Theodul Glacier Unit (Zermatt-Saas zone, Switzerland)

The Penninic nappe stack in the Central and Western Alps was formed in a collision zone environment after the closure of the Penninic oceans in the Paleogene. This study reports Lu–Hf garnet-whole rock ages of 56.5 ± 2.7 and 58.2 ± 1.4 Ma for two eclogite samples from the Theodul Glacier Unit, which is inserted within the structurally uppermost parts of the ophiolitic Zermatt-Saas Zone. The distribution of major elements, Mn, Y, and Lu in garnet, and specifically an enrichment of Lu in the cores, indicate that the ages record prograde growth of garnet during pressure increase. They provide direct evidence for the continuation of subduction during the “Paleocene restoration phase”, often regarded as a tectonically quiescent period due to a reduction in clastic sediment deposition, lack of folds and thrusts of this age, and a cessation of Africa–Europe convergence as derived from the magnetic anomaly pattern in the Atlantic Ocean. The evidence for ongoing subduction in the absence of Africa–Europe convergence suggests that the subduction system was driven by gravity acting on the downgoing slab in a rollback setting, and that subduction was balanced by extension of the upper plate. The overlap of the Lu–Hf ages of both samples from the Theodul Glacier Unit show that this tectonic element represents a coherent body. The difference with respect to the 48 Ma Lu–Hf age of the Lago di Cignana Unit, another element of the Zermatt-Saas Zone, shows that the Zermatt-Saas Zone consists of tectonic subunits, which reached their respective pressure peaks over a prolonged period of approximately 10 Ma.

Nanoplankton wapienny i okrzemki środkowego miocenu w rejonie Buska i Kazimierzy Wielkiej (północna część zapadliska przedkarpackiego)

MIDDLE MIOCENE CALCAREOUS NANNOFOSSILS AND DIATOMS FROM THE BUSKO AND KAZIMIERZA WIELKA AREA (NORTHERN PART OF THE CARPATHIAN FOREDEEP) Abstract. The results of detailed analysis of calcareous nannoplankton in Miocene deposits from the northern part of the Carpathian Foredeep enabled stratigraphic conclusions. Marly clays of the uppermost part of the Skawina Formation in the Busko (Mlyny) PIG-1 borehole section are correlated with the NN5 Sphenolithus heteromorphus Zone that corresponds with the Middle Badenian in the Paratethys and the upper Langhian/ Lower Serravalian in the Mediterranean region. The Krzyzanowice Formation, which includes evaporites (gypsum and clay intercalations), and the Machow Formation represent the NN6 Discoaster exilis Zone. By a comparison with other Paratethyan basins, the Badenian/ Sarmatian boundary is proposed just below a 20-metres thick set of diatomaceous siltstone layers. Among the calcareous nannofossil species, the appearance of Rhabdosphaera poculi Bona et Kernerne and Rhabdosphaera procera Martini may point to the Lower Sarmatian transgression. Clayey sequences of the Machow Formation in the Kazimierza Wielka (Donosy) PIG-1 borehole correspond with the NN6 Discoaster exilis Zone. Abundance of diatom floras observed in the Busko (Mlyny) PIG-1 borehole suggests a proximity of a river mouth that supplied water with nitrates, phosphates and silica. Preservation of delicate siliceous diatom frustules was possible due to rapid deposition of clastic sediments above diatomaceous siltstone.

Myodocope ostracods from the Silurian of Australia

The Silurian of Australia contains at least three genera (one new, Canalarta gen. nov.) and three species (two new, Canalarta papata sp. nov. and Bolbozoe beccata sp. nov.) of myodocope ostracods. These fossils were recovered from clastic sedimentary deposits in the lower Silurian (probably Homerian) Walker Volcanics unit of New South Wales that may represent mudflow deposits. In having the youngest occurrence of Entomozoe aff. tuberosa and the oldest known Bolbozoe species, the Australian myodocopes represent a chronologically intermediate assemblage between previously known early and late Silurian myodocope faunas. Several fossil groups from the Silurian of Australia, such as ostracods, trilobites, brachiopods and corals, apparently have a cosmopolitan distribution at generic level. The presence of many continental and micro-continental landmasses that existed along and within the tropical pan-Tethyan seaway, together with the prevailing ocean circulation, could explain this distributional pattern. The depositional setting, sedimentary deposits and faunal associates do not provide conclusive evidence concerning the lifestyle of the Australian myodocopes. They could represent nektobenthic species, as has been suggested for other early to mid Silurian myodocopes, or hyperbenthic/pelagic species, as was proposed for known late Silurian forms.http://zoobank.org/urn:lsid:zoobank.org:pub:D49A6C9C-13A8-443A-8BD4-73C34C1D0630

Geochemical Correlation In An Exhumed Submarine Channel Complex (Tabernas Basin, Se Spain): Comparison To Sedimentological Correlation At Various Length Scales

Abstract Whole-rock, inorganic, geochemical data have previously been used to aid characterization and stratigraphic correlation of fossil-poor clastic sedimentary deposits, although this approach has not yet been calibrated by testing chemostratigraphic correlations against physical stratigraphic correlations from outcrop. Chemical data from a well-exposed siliciclastic succession in a Tortonian (late Miocene) submarine slope channel system in the Tabernas Basin of southern Spain were generated using X-ray fluorescence supplemented by X-ray diffraction, SEM analysis, and light microscopy. Amongst the > 60 elements measured, nearly a quarter of them have proved to be useful or reliable for geochemically based correlation at the tested scales (∼ 10 m, ∼ 50 m, ∼ 100 m). These elements are SiO2, K2O, Al2O3, CaO, and TiO2, as well as Zr, Nb, Th, Rb, Cs, As, and the rare earth elements, La, Nd, and Ce. High-resolution, bed-to-bed geochemical correlation is feasible over short distances (∼ 10 m). Geochemical data from sections in beds that are traceable suggest that a given stratigraphic level seems to be geochemically homogeneous with respect to some key elements. Geochemical data also provide a useful aid for high-resolution sedimentary correlation, at distances of several tens of meters up to at least 100 m. Since each individual bed seems to be broadly homogeneous in composition, at a larger scale it is possible to discern a provenance signal in geochemical data. Chemical stratigraphy thus seems to work even in stratigraphically complicated submarine channel complexes.