Conglomerate Units Research Articles

First Report of Tuff in Neoproterozoic Bhima Basin: Field Evidence, Petrography and Geochemical Studies

Abstract We report here the presence of tuffs from the Neoproterozoic Bhima basin unreported hitherto. These are exposed near Hotpet, Hulkal, Kanchankavi, and Ukinal area along two different stratigraphic horizons (1) within carbonates of Shahabad Formation and (2) above shale of Hulkal Formation. Tuffs are of two types: 1. Ash fall tuff and 2. Lapilli tuff, occurring as beds, matrix of a conglomeratic unit and patchy discontinuous layers. Physically ash fall tuff is thinly bedded (2-6 cm) and light-weight, lapilli tuff is hard, compact and individual beds are not discernible in the field. Presence of petrological features like bipyramidal quartz, fiamme structures, embayed quartz grains, blue CL colours of quartz grains, volcanic layering and banding, altered glass, and stretched and elongated volcanic glasses, are clear indications of its volcanic affinity. The tuff is anomalously high in silica content ranging from 71.4-91.2wt% and have low alumina value ranging from 0.75-4.11 wt % compared with that of the normal felsic tuffs, rhyolites and high silica rhyolites. REE in the tuffs can be grouped into two types, 1. Ash fall tuff with enriched LREE and fractionated HREE, 2. Lapilli tuff with flat LREE and HREE pattern. Tuff shows high Hf, overall enrichment of large ion lithophile elements (LILE Rb, Th, K and Pb) and depletion in HFSEs (Nb, Ta, Ti, P). The tuff is probably generated from continental crust source and the depositions are episodic and have more than one eruptive pulses of volcanic activity.

Muddy and sandy conglomerates: Mixing between gravelly slurry flow and substrates in a fan-delta system, Junggar Basin, Northwest China

Mixing of a gravity flow with substrate over which it travels can control flow transformations with implications for the structure of the deposit that is left; however, the effects of mixing in conglomerate-dominated gravelly underflow in lacustrine environments remain poorly understood. This study documents two types of interactions between gravelly underflow and substrate and the resulting conglomerate deposits across a lacustrine fan-delta system in the Junggar Basin, northwest China. The resulting conglomerates are typically massive, poorly sorted, clast-supported without reserve grading; rich in mudstone clasts; and having been emplaced by river-derived hyperpycnal flow. Based on the character of the matrices between the clasts, conglomerates are divided into three sub-categories: (i) muddy (mud-rich) conglomerates with a mainly fine-grained muddy matrix, (ii) sandy (mud-poor) conglomerates with a mainly sandy matrix, and (iii) mud-bearing sandy conglomerates with a coexisting mud-sand matrix. Furthermore, two distinct lithological associations were identified: (i) a regularly recurring tripartite conglomerate unit interlayered with mudstone (S I) and (ii) a regularly recurring tripartite conglomerate unit interlayered with sandstone (S II). Both lithological associations contained a recurring tripartite conglomerate unit with a basic tripartite structure consisting of muddy conglomerates in the lower division, mud-bearing sandy conglomerates in the middle division, and sandy conglomerates in the upper division. There was more sand in the upper layers of the tripartite conglomerate unit matrix. Muddy conglomerates with large amount of mudstone clasts are thought to form through extensive erosion and mixing between the lower part of the flow with mud-substrate on the lake bottom, whereas central mud-bearing conglomerates and upper sandy conglomerates are considered to be generated by successively weaker mixing in the upper part of the flow. The consequent sandy trailing flow resting upon the previously-emplaced tripartite conglomerate unit forms a thinner sandstone bed that acts as a “sand mat” for the next incoming gravelly flow. A single sandy conglomerate bed subsequently forms above when gravel mixes with the sand substrate, as opposed to forming muddy conglomerates that were generated by mud from eroded substrate. Our results show that the erosion and mixing of sediment flow with substrate are important factors in flow transformation and deposition and that the substrate type (muddy or sandy) along the flow path plays a crucial role in controlling flow behavior and reservoir characteristics.

Sandstone-hosted uranium deposits of the Colorado Plateau, USA

More than 4,000 sandstone-hosted uranium occurrences host over 1.2 billion pounds of mined and in situ U3O8 throughout the Colorado Plateau. Most of the resources are in two distinct mineral systems with deposits hosted in the Triassic Chinle and Jurassic Morrison Formations. In the Chinle mineral system, base metal sulfides typically accompany mineralization. The Morrison mineral system is characterized by V/U ratios up to 20. The uranium source was likely volcanic ash preserved as bentonitic mudstones in the Brushy Basin Member of the Morrison Formation, and lithic volcanic clasts, ash shards, and bentonitic clay in the lower part of the Chinle Formation. Vanadium originated from two possible sources: iron–titanium oxides that are extensively altered in bleached rock near deposits or from similar minerals in variably bleached red beds interbedded with and beneath the Morrison. In Chinle-hosted deposits, in addition to volcanic ash, a contributing source of both vanadium and uranium is proposed here for the first time to be underlying red beds in the Moenkopi and Cutler Formations that have undergone a cycle of reddening-bleaching-reoxidation. Transport in both systems was likely in groundwater through the more permeable sandstones and conglomerate units. The association of uranium minerals with carbonate and more rarely apatite, suggests that transport of uranium was as a carbonate or phosphate complex. The first comprehensive examination of paleoclimate, paleotopography, and subsurface structure of aquifers coupled with analysis of the geochronology of deposits suggests that that there were distinct pulses of uranium mineralization/redistribution during the period from about 259 Ma to 12 Ma when oxidized mineralizing fluids were intermittently rejuvenated in the Plateau in response to changes in tectonic regime and climate. Multiple lines of evidence indicate that deposits formed at ambient temperatures of about 25 °C to no greater than about 140 °C. In both systems, deposits formed where groundwater flow slowed and was subject to evaporative concentration. Stagnant conditions allowed for prolonged interaction of U- and V-enriched groundwater with ferrous iron-bearing reductants, such as illite and iron–titanium oxides, and more rarely organic material such as plant debris. Paragenetically late in the sequence, reducing fluids introduced additional organic matter to some deposits. Reducing fluids and introduced organic matter (now amorphous and altered by radiolysis) may originate from regional petroleum systems where peak oil and gas generation was from ∼ 82 to ∼ 5 Ma. Our novel analysis indicates that these reducing fluids bleached rock and protected affected deposits from remobilization during exposure and weathering that followed uplift of the Plateau (∼80 to 40 Ma).

Lateral and temporal variations of a multi-phase coarse-grained submarine slope channel system, Upper Cretaceous Cerro Toro Formation, southern Chile

ABSTRACTUnderstanding variations in the sedimentary processes and resulting stratigraphic architecture in submarine channel systems is essential for characterizing sediment bypass and sedimentary facies distribution on submarine slopes. In the Santonian to Campanian Cerro Toro Formation, southern Chile, a coarse-grained slope system, informally known as the Lago Sofia Member, developed in a structurally controlled environment, with complex and poorly established relationships with the surrounding mud-rich heterolithic deposits.A detailed architectural analysis of the most continuous and best-exposed channel system in the Lago Sofia Member, the Paine C channel system, provides insights on lateral facies transitions from channel axis to margin, stacked in a multi-phase sequence of events marked by abrupt changes in facies, facies associations, and architecture.The Paine C channel system is incised into siltstones and claystones interbedded with thin-bedded very fine sandstones, interpreted to be either channel-related overbank or unrelated background deposits. The coarse-grained deposits are divided into a lower conglomeratic unit and an upper sand-rich unit. The lower conglomeratic unit can be further subdivided into three phases: 1) highly depositional and/or aggradational, dominated by thick and laterally continuous beds of clast- to matrix-supported conglomerate, herein named transitional event deposits; 2) an intermediate phase, including deposits similar to those dominant in phase 1 but also containing abundant clast-supported conglomerates and lenticular sandstones; and 3) a bypass-dominated phase, which records an architectural change into a highly amalgamated ca. 45-m-thick package composed purely of lenticular clast-supported conglomerates with local lenticular sandstones. Between the conglomeratic phases, a meter-scale package composed of interbedded thin- to medium-bedded sandstone and mudstone deposits is interpreted to drape the entire channel, indicating periods of weaker gravity flows running down the channel, with no evidence of bedload transport.The upper sand-rich unit is divided into lower amalgamated and upper non-amalgamated phases, and represents a rapid architectural change interpreted to record an overall waning of the system. The sandstone unit laps out onto a mass-transport complex which is interpreted to have been triggered initially at the same time as major architectural change from conglomerates to sandstones.While mindful of the fact that each system is a complete analogue only for itself, we propose a new depositional model for coarse-grained submarine channel systems, in which particular characteristics can provide significant insights into architectural heterogeneity and facies transitions in channelized systems, allowing substantial improvement in subsurface facies prediction for fluid reservoirs.

Architecture Elements of the Lemat Formation of the Lubuk Bernai Region, Batang Asam District, Tanjung Jabung Barat Regency, Jambi Province

The study of facies analysis and interpretation of the depositional environment of the Lemat Formation located at Bukit Tiga Puluh aims to clarify the problems found in Paleogene sediments in the South Sumatra Basin. A detailed analysis of the fluvial facies has been carried out in the Lubuk Bernai track. A number of observations, profiling, and measured stratigraphic section have been carried out. The stratigraphy of the study area can be divided into 5 units from old to young, namely the Mentulu-metamorphic sandstone unit, Lemat conglomerate unit, Lemat gravel-sandstone unit, Benakat volcanic-siltstone unit, and the alluvial deposit unit. The stratigraphic relationship between Mentulu metamorphic-sandstone unit and Lthe emat conglomerate unit is nonconformity. The relationship between Lthe emat conglomerate unit and Lemat gravel-sandstone unit and Benakat volcanic-siltstone unit is interfingering. The relationship between alluvial deposit units with Lemat conglomerate units and Lemat gravel-sandstone units is aan ngular unconformity. Analysis of lithofacies and architectural elements of the study area showed a fluvial depositional environment. The resulting architectural elements are 8 associations: SG (sedimentary gravity flow), GB (gravel bedform), SB (sandy bedform), CH (channel), DA (downstream accretion), HO (scour-hollow fill), AC (abandoned channel) and FF (overbank fine). The depositional environment of the Lemat Formation; Lemat conglomerate unit in alluvial fans environment, Lemat gravel sandstone unit in the shallow environment, gravel-bed braided river. In the Benakat tuffaceous-siltstone unit, it was deposited in a flashy, ephermal, sheet flood, sand-bed river environment.

GEOLOGY OF PONELO REGION AND SURROUNDINGS, NORTH GORONTALO REGENCY

The research area is one of the islands in the District of Ponelo Islands, North Gorontalo Regency, Gorontalo Province. This study aims to determine the geological conditions of the area using the geological mapping method. The results showed that the geomorphology of the study area was divided into 3 units, namely Lava Flow Hills, Denudasional Hills, and Marin Plains. The stratigraphy of the research area is divided into 5 unofficial units sorted from oldest to youngest, namely Sandstone Unit, Conglomerate Unit, Porphyry Andesite Unit, Basalt Lava Flow Unit (Late Pliocene-Early Pleistocene), and Coastal Sediment Unit (Recent age). The geological structures observed were Shear Fracture, Tension, Sheeting Joint, and Columnar Joint. The geological history of the research area starts from the Late Pliocene to Early Pleistocene where the Lokodidi Formation and Pinogu Volcano Formation were formed, resulting in sandstone and conglomerate units (Lokodidi Formation), porphyry andesite units and basalt lava flow units (Pinogu Volcano Formation). Then the alluvial deposition process which is still ongoing today is the result of weathering of rocks in the research area.

3D Phase tensor inversion and Joint inversion using impedance and phase tensor components aiming better subsurface mapping and interpretation in Dhanjori basin, Singhbhum craton, eastern India

Dhanjori formation, a significant member of Singhbhum Craton, Eastern India, is well-known for its complex mineralogical character and huge content of Au-mineralization. This 2.1 Ga old Paleoproterozoic formation is composed of siliciclastic metasedimentary rocks interlayered with mafic/ultramafic volcanic rocks. Traces of gold has been spotted by many researchers in the sulfide-hosted mafic-ultramafic volcanic rocks and quartz pebble conglomerate units by different studies. Regional Audio Magnetotelluric (AMT) survey was conducted in 10 kHz–10 Hz frequency range over various lithological units of Dhanjori and adjacent Iron Ore Group. The key challenge faced during the analysis of magnetotelluric (MT) data is due to the presence of near-surface heterogeneities. The amplitude of the MT response gets distorted by galvanic effects which further create difficulties in modelling and inversion. If the effect is not removed in advance, it might lead to erroneous subsurface modelling and interpretations. On the contrary, the phase tensor data does not show any change in values even in the presence of galvanic distortion. Though phase tensors are the computed values from impedance tensor, still the response is free from any shallow level ambiguities unlike impedance data. We have performed 3-D inversion of phase tensor data to generate a conductivity model of Dhanjori basin. The objective was to verify whether the inclusion of phase tensor components in the inversion routine was able to provide some extra information that might add value to the analysis. Model from phase tensor inversion indicates only relative variation in the subsurface conductivity structure due to lack of amplitude information in the data. Hence, we also performed 3D joint inversion including both impedance and phase tensor components for obtaining the final conductivity model of Dhanjori to recover the absolute subsurface conductivity structure unaffected by galvanic distortion. Correlation of the conductivity model with available geoscientific information in Dhanjori and adjacent geological units helped us to relate the conductors to the sulfide mineralization prospect.

GEOLOGY OF TEMBUNI AREA AND SURROUNDINGS IN BINTUNI REGENCY, WEST PAPUA PROVINCE

Administratively, the study area is located in Tembuni and surrounding area District of Bintuni Papua Barat Province. Geographically located at coordinates 01 ° 47 '00 "latitude - 01 ° 50' 00" latitude (south latitude) and 133 ° 54 '00 "E - 119 ° 57' 00" (East Longitude). The method used for the study is the collection of field data and geological mapping of the surface by recording at each station, taking rock samples for petrographic analysis is then performed based on the data processing is done. The purpose of this study was to obtain geological information in the form aspect of geomorphology, stratigraphy, structural geology, historical geology and extractive potential in the area of further research conducted geological map-making research areas based on four aspects. The research area is divided into three geomorphological units, namely the denudational geomorphological unit with weak-strong waves (D1), the denudational geomorphological unit with strong waves-hills (D2), and the denudational plains unit (D5). The stratigraphy of the study area is divided into two (2) rock units and one (1) sediment, based on lithostratigraphy in order from oldest to youngest, namely: Mudstone Unit, conglomerate unit, and Alluvium and littoral deposits unit. The structure of the research area only found geological structures that developed in the form of a joint secondary structure. The excavated materials found in the research area are excavated materials in the form of rocks originating from alluvial deposits found along the Mogoi Baru village, which are then used as building materials.

Lithological Signatures of Early Carboniferous Events in the Northeastern Siberian Craton (Western Verkhoyansk Region)

Abstract The paper focuses on presumable sources of coarse carbonate material transported into the Visean Northern Kharaulakh basin. The sand to pebble components of the Krestyakh conglomerate unit originated by medium and distant transport by debris flows (turbidity currents) along submarine canyons from the place of their initial littoral deposition to relatively deep accommodation basins. The carbonate material was most likely derived from Ordovician, Silurian, and Devonian sediments, which are currently represented by their analogs in Kotelny Island. The sediments of the Northern Kharaulakh basin store a record of two geological events: (1) middle Visean collision of Siberia with the Laurussian supercontinent and rifting of some terranes off the Siberian сraton, and (2) late Visean collision of the Kara terrane with the northern margin of Siberia.

U-Pb zircon-titanite-apatite age constraints on basin development and basin inversion in the Kiruna mining district, Sweden

To constrain the tectonothermal evolution of the type locality for iron oxide-apatite deposits, we have obtained U-Pb zircon, titanite, and apatite age data for the Kiruna mining district in northernmost Sweden. The results indicate that the host basin initiated in an overall extensional regime as indicated by the deposition of alluvial conglomerates and greywackes. A volcanic intercalation in a conglomerate unit approximately 1 km northwest of the Luossavaara iron oxide-apatite deposit yields a U-Pb zircon concordia age of 1887 ± 3 Ma representing the timing of the earliest Orosirian volcanism in the central Kiruna mining district coinciding with the onset of basin development. In-situ analysis of titanite sitting on hydrothermally altered fracture planes within a cataclastic fault damage zone (c. 270 m from the fault core system associated with the Luossavaara iron oxide-apatite deposit) yields complex U-Pb data. Applying a strict discordance filter yields seven analyses (<1.5 % relative discordance which included six common Pb-corrected analyses and one analysis where no significant common Pb was detected) that yield a 207Pb/206Pb weighted average age of 1889 ± 26 Ma that we interpret as the most probable minimum age of fault initiation. The overlap in age of the host volcanic rock and the fault implies that during basin development, contemporaneous volcanism and syn-volcanic faults may have played an important role during iron ore emplacement. A U-Pb lower intercept age of apatite from the Nukutus iron oxide-apatite deposit provides a first indication that the area was subsequently buried and metamorphosed under upper greenschist-facies conditions and later tectonically exhumed and cooled below the apatite closure temperature at 1805 ± 26 Ma. Further temporal constraints on exhumation and basin inversion is given by syn-tectonic titanite along a brittle-ductile reverse shear zone to the east of the study area that shows limited presence of significant common Pb and is part of a sodic-calcic + Fe + Cl hydrothermal alteration assemblage. Titanite grains that show a well-developed zonation yield a U-Pb concordia age of 1812 ± 3 Ma, which we interpret as the onset of basin inversion. Titanite grains from the same sample that show less pronounced zonation yield a U-Pb concordia age of 1802 ± 8 Ma, tentatively indicating that the tectonothermal activity lasted up to c. 20 m.y.

Cretaceous biostratigraphy and lithostratigraphy of the Glinzendorf Syncline based on well Gänserndorf UeT3 (Vienna Basin, Austria)

Abstract The 2200 m thick Cretaceous units of well Gänserndorf UeT3 have been biostratigraphically analyzed based on cuttings from 3210 m to 5140 m. The deposits from the Tirolic Glinzendorf Syncline (a part of the buried Northern Calcareous Alps) can be largely correlated with the Lower Gosau Subgroup of the Grünbach Syncline. An exception is the basal unit, which has no equivalent in the Grünbach Syncline. This lower unit is subdivided into a non-marine lower and a largely marine upper part. No age constraints are available for the lower part, whereas the upper part has a possible age range from middle Turonian to Coniacian. For this unit, which is documented for the first time from the Glinzendorf Syncline, we propose Glinzendorf Formation as new lithostratigraphic term. The Glinzendorf Fm. is overlain by the Grünbach Fm., which is intercalated by a thick unit of conglomerates. These are interpreted as equivalents of the Dreistetten Conglomerate Mb. The calcareous nannofossils of these units suggest a latest Santonian to early Campanian age. Non-marine conditions prevailed during deposition of the Grünbach Fm., but marine incursions are indicated for parts of the Dreistetten Conglomerate Mb. The top of the Grünbach Fm. is formed by an about 50-m-thick unit of coal, rich in Characeae oogonia, which, together with the Dreistetten conglomerates serve as marker layer for correlation with the outcrops in the Grünbach Syncline. The Grünbach Fm. is overlain by marls and silty shales of the Piesting Fm. for which a late Campanian and Maastrichtian age is documented. Marine conditions predominated during this interval. The topmost unit in well Gänserndorf UeT3 is overthrusted on the Maastrichtian Piesting Fm. and represents Campanian sandstones and conglomerates of the Grünbach Fm. This Gänserndorf Thrust is detected and biostratigraphically constrained for the first time.

Geological and Petrographic Factors Affecting Formation of Active Landslides in the North of Biga Peninsula, NW Turkey

The study includes landslide movements that take place on Eocene and Middle-Upper Miocene aged the terrestrial and marine sedimentary rock units on the Canakkale basin in the Biga Peninsula. In this study, the active Ambaroba Landslide, Şevketiye and Adatepe Landslides located on the northern coasts of Biga Peninsula were investigated.The geological studies in the Ambaroba landslide have shown the integrity of the Bayramiç formation and the Şapcı volcanics in this area have shown their influence in the Miocene period.The sandstones in the Bayramiç formation are not very well paste and are yellow, dirty yellow and gray in color.The sliding surface units in the moving masses consist of non-hardening, very large blocky, pebbly and loose cement-bonded pebbles. In the Şevketiye and Adatepe Landslides, a sliding movement has occurred on the sandstone and conglomerate units with yellowish brown colors in the Fıçıtepe formation. The sandstones in these landslide areas are massive and well cemented. Conglomerates are weaker than sandstones and are fond of a gray-beige color that does not harden. Precipitation data and GPS measurements of the landslide areas were evaluated together with the lithological properties of the rocks.Loose sandstones and pebbles in the entire landslide areas studied can easily move due to seasonal precipitation.This movement was mostly seen in the Şevketiye landslide area and then in the Adatepe and Ambaroba areas, respectively. Although their effectiveness has decreased, the movements will continue, as the lithological features will not change in these areas. As a result, the measures specified in this study should be taken into account in order to eliminate the destructive effects of landslides.

Magnetostratigraphy and AMS study of a late Cretaceous-Paleogene succession in the eastern Xining basin: constraint on K-Pg boundary tectonic event in NE Tibet Plateau

Cretaceous-Cenozoic basins developed in the NE Tibetan Plateau contain key archives to unravel the growth history of the plateau in response to the India-Eurasia collision. Here we present magnetostratigraphic results of a Late Cretaceous to Paleogene succession of the Zhongba section outcropping at the southern margin of the eastern Xining basin. This succession consists of three lithological units punctuated by two stratigraphic unconformities, which best recorded the deformation history of this foreland basin. Detailed magnetostratigraphic investigation show that the lower terrestrial sedimentary rock unit, the Minhe Group, was deposited in latest Cretaceous in the time span of ~74.5-69.2Ma; the middle unit was deposited in Paleogene in the time span of ~49.3-22Ma; and the upper conglomeratic unit, not dated, possibly was deposited in early Miocene. Accordingly, the K-Pg unconformity, widely observed in the foreland basins of NE Tibet, represents a sedimentary hiatus of ~19.9Ma duration from ~69.2 Ma to ~49.3 Ma, which possibly recorded the far-field response to the tectonic transition from Neo-Tethys oceanic plate subduction to the India-Eurasia collision in southern Tibet. AMS results show a clockwise rotation of the shortening direction from NEN-SWS in Latest-Cretaceous to NE-SW in Paleogene, which support the view that the compressional environment may dominate the NE Tibet in Early-Cenozoic period.

Facies Architecture and Sedimentary Structures in the drill cores of Uranium Bearing Sediments of Banganapalle Formation of Palnad Sub-basin, Guntur District, Andhra Pradesh

The Banganapalle Formation, the lowest member of the Neoproterozoic Kurnool Group of rocks, resting over the basement granites, has been identified as the host rock for uranium in Koppunuru area in the western part of Palnad sub-basin. The uppermost arenite facies of the Banganapalle Formation is exposed on surface and shows only few bedform indicators like ripple marks, planer laminations etc. Down-hole lithological examinations on course of core drilling in Koppunuru and adjoining areas identified five recognizable lithofacies of Banganapalle Formation, viz. basal conglomerate unit, quartzite-shale intercalated facies, and two quartz arenite facies separated by a grey shale dominated argillaceous facies.&#x0D; The polymictic conglomerate, with unsorted grit to pebble size clasts of granite, shale, quartzite, vein quartz and dolerite indicate short distance transportation and derivation from nearby granitoids traversed by quartz reef/dolerite dykes. Cyclic repetitions of arenaceous and argillaceous sediments in Banganapalle lithocolumn above the basal conglomerates point to alternate rhythmic marine transgression and regression regimes. These units can also be discriminated based on their sedimentary texture, bedforms and several soft-sedimentary penecontemporaneous deformational structures (PCD) like load structure, convolute bedding/laminations, and slump structures such as micro-slips, gravity faults and folds. These syn-sedimentary structures clearly indicate perturbation and submergence of the basin contemporaneous to deposition. Cross-beds suggests change in current direction/intensity while bi-directional symmetrical ripples in outcrops of upper arenite facies suggests that the Banganapalle sediments are derived from the basement granitoids exposed to the north as well as upper Cuddapah sediments to its west. Overall, the sedimentary structures, textural and composition variation of the lithounits suggest deposition of these sediments in marginal marine, inter- to supra-tidal flat environment. The porous and permeable nature of the quartz arenite and the basal conglomerates and the presence of available reductants in the form of sulphides and carbonaceous matter make them the best suited loci for fluid movement and precipitation of uranium.

Magnetostratigraphic study of a Late Cretaceous–Paleogene succession in the eastern Xining basin, NE Tibet: Constraint on the timing of major tectonic events in response to the India-Eurasia collision

Abstract Cretaceous-Cenozoic basins developed in the NE Tibetan Plateau contain key archives to unravel the growth history of the plateau in response to the India-Eurasia collision. Here we present magnetostratigraphic results of a Late Cretaceous to Paleogene succession of the Zhongba section outcropping at the southern margin of the eastern Xining basin. This succession consists of three lithological units punctuated by two stratigraphic unconformities, which best recorded the deformation history of this foreland basin. Detailed magnetostratigraphic investigation show that the lower terrestrial sedimentary rock unit, the Minhe Group, was deposited in latest Cretaceous in the time span of ca. 74.5–69.2 Ma; the middle unit was deposited in Paleogene in the time span of ca. 49.3–22 Ma; and the upper conglomeratic unit, not dated, possibly was deposited in early Miocene. Accordingly, the Cretaceous–Paleogene unconformity, widely observed in the foreland basins of NE Tibet, represents a sedimentary hiatus duration of ∼19.9 m.y., from ca. 69.2 Ma to ca. 49.3 Ma, which possibly recorded the far-field response to the tectonic transition from Neo-Tethys oceanic plate subduction to the India-Eurasia collision in southern Tibet. Changes in provenance, sedimentary accumulation rate, and mean susceptibility value at ca. 33–30 Ma, and the total prolate anisotropy of magnetic susceptibility (AMS) ellipsoids and provenance shifting since ca. 23–19 Ma, point to the pulsed growth of West Qinling, and rapid uplift of Laji Shan, respectively, indicating an enhanced effect of the India-Eurasia collision in Oligocene and early Miocene. AMS results show a clockwise rotation of the shortening direction from NEN-SWS in latest Cretaceous to NE-SW in Paleogene.

The Watershed Tungsten Deposit, Northeast Queensland, Australia: Permian Metamorphic Tungsten Mineralization Overprinting Carboniferous Magmatic Tungsten

Abstract The Watershed tungsten deposit (49.2 Mt avg 0.14% WO3) lies within the Mossman orogen, which comprises deformed Silurian-Ordovician metasedimentary rocks of the Hodgkinson Formation intruded by Carboniferous-Permian granites of the Kennedy Igneous Association. The Hodgkinson Formation in the Watershed area comprises skarn-altered conglomerate, psammite, and slate units that record four deformation events evolving from ductile, isoclinal, colinear folding with transposition (D1–D3) to brittle ductile shear zones (D4). Multiple felsic to intermediate dikes cut across the metasedimentary rocks at Watershed including the following: (1) Carboniferous, monzonite dikes (zircon U/Pb age of 350 ± 7 Ma) emplaced during D1–2; and (2) Permian granite plutons and dikes (zircon U/Pb ages of 291 ± 6, 277 ± 6, and 274 ± 6 Ma) and diorite (zircon U/Pb age of 281 ± 5 Ma) emplaced during D4. Tungsten mineralization is largely restricted to skarn-altered conglomerate, which preserves a peak metamorphic mineralogy formed during ductile deformation and comprises garnet (Grt40–87 Alm0–35Sps1–25Adr0–16), actinolite, quartz, clinopyroxene (Di36–59Hd39–61Jhn1–5), and titanite. A first mineralization event corresponds to the crystallization of disseminated scheelite in monzonite dikes (pre-D3) and adjacent units, with scheelite grains aligned in the S1–2 fabric and affected by D3 folding. This event enriched the Hodgkinson Formation in tungsten. The bulk of the scheelite mineralization formed during a second event and is concentrated in multistaged, shear-related, quartz-oligoclase-bearing veins and vein halos (muscovite 40Ar-39Ar weighted average age of 276 ± 6 Ma), which were emplaced during D4. The multistage veins developed preferentially in competent, skarn-altered conglomerate units and formed synchronous with four retrograde alteration stages. The retrograde skarn minerals include clinozoisite after garnet, quartz, plagioclase, scheelite, and phlogopite with minor sodium-rich amphibole, which formed during retrograde stages 1 and 2, accompanied by later muscovite, calcite, and chlorite formed during retrograde stage 3. Retrograde stage 4 was a late-tectonic, noneconomic sulfide stage. The principal controls on scheelite mineralization at Watershed were the following: (1) early monzonite dikes enriched in scheelite; (2) D4 shear zones that acted as fluid conduits transporting tungsten from source areas to traps; (3) skarn-altered conglomerate lenses that provide a competent host to facilitate vein formation and a source for calcium to form scheelite; and (4) an extensional depositional environment characterized by vein formation and normal faulting, which provide trapping structures for tungsten-bearing fluids, with decompression being a likely control on scheelite deposition. The coexistence of scheelite with oligoclase in monzonite dikes and veins suggests that tungsten was transported as NaHWO40. Exploration in the area should target Carboniferous monzonite, associated with later syn-D4 shear zones cutting skarn-altered conglomerate.

Algorithmic Optimization of an Underground Witwatersrand-Type Gold Mine Plan

In the mining environment, mine planning is complicated by the presence of unfavorable environmental conditions, limited knowledge of the shape and size of the deposit, ore body characteristics, and volatile market conditions. In this paper, we propose a top-down algorithmic approach to strategically optimize the cutoff grade and net present value (NPV), and implement its solutions at the operation level, while simultaneously mitigating operation risks, to maximize the life of an ultra-deep gold mine from the Witwatersrand Basin, South Africa. To date, the Witwatersrand Basin has contributed about 28% of the world’s total gold supply from a series of Mesoarchaean quartz pebble conglomerate units (referred to as reefs). Through a quantitative analysis using algebraic and stochastic methods, we ranked mining variables in terms of their margin sensitivity and impact/adjustability efficacy. The results of this study showed the following. By using our proposed approach, an underground mine plan can be optimized by focusing on few key variables. Strategic mining of combinations of high-grade panels with low-grade panels and counter-balancing their risk profiles can yield optimal executable mine plan results (i.e., higher NPV, ideal profit margin, and lower risk) without sterilizing a given mineral resource for underground mining operations.

Clasts in Archean conglomerates and implications for uplift: Evidence from the 2.7 Ga Agnew Greenstone Belt (Western Australia)

Archean greenstone belts commonly consist of a stratigraphy that records subaqueous deposition capped by subaerial sedimentation, yet it remains unclear if the controls on this change were driven by horizontal or vertical processes. Clasts in conglomerates can provide important constraints on this question because they inform on the changing nature of sources. The 2.7 Ga Agnew Greenstone Belt, Yilgarn Craton, Australia, provides the ideal opportunity for such a study because it contains abundant and diverse conglomerate facies and its basal stratigraphy is well understood. This study focusses on the texture and composition of lithic clasts derived from three stratigraphic conglomerate units and their host successions. The lowermost conglomerate-bearing unit, hosted in the Vivien Formation, unconformably overlies the mafic-ultramafic lavas and intrusions of the Kalgoorlie Group (ca. 2720–2690 Ma) and is dominated by aphyric to porphyritic mafic and felsic volcanic clasts. The conformably overlying Maria Mine Formation conglomerates contain a higher proportion of felsic clasts with medium- and plutonic groundmass textures. The Vivien and Maria Mine Formations (ca. 2690–2670 Ma) are dominated by cherts, turbidites and conglomerates, and represent subaqueous sediments formed in the ring-plain surrounding an emergent volcanic island. The unconformably overlying Scotty Creek Formation (ca. 2665–2655 Ma) contains conglomerates with many plutonic felsic clasts, and is dominated by bedded and cross-bedded sandstones formed in a subaerial environment. Whole-rock geochemistry of mafic and ultramafic clasts matches the local Kalgoorlie Group rocks and indicates progressive erosion of the underlying supracrustal sequence. Undeformed conglomerates lack clasts with metamorphic foliations, indicating uplift by horizontal compression could not have been significant before ca. 2655 Ma, which is considered as the time of the first major compressional event in many published structural frameworks for the region. The systematic erosion of a felsic stratovolcano, its associated plumbing system, and any resultant upwarping of underlying sequences through vertically-driven diapirism, better explains the progressive changes observed in clast texture and composition, as opposed to horizontally-driven uplift, such as compression associated with subduction.

The stratigraphic significance of early Cambrian (Series 2, Stage 4) trilobites from the Smith Bay Shale near Freestone Creek, Kangaroo Island

The fossiliferous lower Cambrian (Series 2) successions along the north coast of Kangaroo Island, South Australia—known collectively as the Kangaroo Island Group—can be divided into two main areas: a western succession located between Snelling Beach and Smith Bay, which comprises the Mt McDonnell Formation (base), Stokes Bay Sandstone and Smith Bay Shale; and an eastern succession that extends from Emu Bay to Point Marsden, represented by exposures of the White Point Conglomerate (base), Marsden Sandstone, Emu Bay Shale and Boxing Bay Formation (top), with an overlap in the Cape d’Estaing/Emu Bay area. Some previous interpretations of the Kangaroo Island Group stratigraphy suggest that the western succession stratigraphically underlies the eastern succession. Most of the previously reported and described Cambrian fossils come from the eastern succession, especially the internationally significant Emu Bay Shale Konservat-Lagerstätte. Here we report the trilobites Redlichia takooensis and Balcoracania dailyi from the Smith Bay Shale near Freestone Creek, indicating that the eastern and western successions are at least partly contemporaneous. The present investigation indicates that the Smith Bay Shale of the western succession can be correlated with the stratigraphic interval represented by the Marsden Sandstone and the overlying Emu Bay Shale of the eastern succession. The Kangaroo Island Group was deposited as part of a fan delta system with the eastern succession representing the proximal part, and the western succession representing the distal part of the fan delta. The lack of substantial conglomerate units within the Kangaroo Island Group to the west of Cape d’Estaing suggests that the tectonic uplift that led to the deposition of the White Point Conglomerate was concentrated in the area immediately to the north of Emu Bay.

DEPOSITI DELTIZI PLIOCENICI ALLO SBOCCO DELLA VAL BREMBANA (PREALPI BERGAMASCHE)

At the outlet of the Brembo valley into the upper Lombardy Plain a conglomerate unit is present, about 30 m thick and outcropping over an area of about 1.5 km 2 . This conglomerate was in the past attributed to the Villafranchian and considered as the lowermost part of the "Ceppo", a thick and widespread formation composed of well cemented coarse fluvial deposits.&#x0D; The conglomerate unit here described, called Madonna del Castello Conglomerate, is interpreted as a Late Pliocene deltaic deposit. It shows a large scale cross—stratification affecting the whole thickness of the unit; single beds show decreasing gradient from the top to the base, with a concave up profile. Beds are prevailingly composed of matrix supported conglomerate, with elongated clasts parallel to the dip of bedding. Both geometry and structures are indicative of foreset beds.&#x0D; The petrographic composition of the Madonna del Castello Conglomerate is characterized by prevailing clasts of Mesozoic limestones of local provenance, while subordinate and often absent are metamorphic, volcanic and arenaceous rocks deriving from the Sudalpine crystalline basement and from its Paleozoic cover, which outcrop at the head of the Brembo valley.&#x0D; The Madonna del Castello Conglomerate overlies Early to Middle Pliocene fossiliferous mudstones (Tornago Formation) and represents a terminal regressive phase of the marine Pliocene sedimentation at the foot of the Lombardy Prealps.