Provenance Interpretation Research Articles

Garnet trace element geochemistry as a sediment provenance indicator: An example from the Qaidam basin, northern Tibet

Abstract Major element geochemistry of detrital garnet is a widely-used approach for sedimentary provenance analysis, in particular for unravelling parent-rock lithology of siliciclastic sediments. However, garnets from felsic crystalline rocks (e.g., intermediate–acidic igneous rocks and metapelites) often have similar major element composition. This results in ambiguity of provenance interpretation in most cases. Here, we collect trace element data of garnets from different rock types to explore the feasibility of detrital garnet trace element geochemistry in sediment provenance analysis. The Qaidam basin in northern Tibet is taken as an example and provenance of Cenozoic sedimentary rocks therein is interpreted based on detrital garnet trace element composition. We find that garnets in intermediate–acidic igneous rocks have much higher heavy rare earth element (ΣHREE > 600 ppm) and yttrium (Y > 800 ppm) abundances than garnets in metapelites (ΣHREE 4 ppm) and zinc (Zn > 150 ppm) abundances than garnets in low-, medium-grade metapelites (up to amphibolite facies). Based on these findings, we suggest that Fe- and Mn-rich detrital garnets in the Cenozoic sedimentary rocks from the northern Qaidam basin were probably derived from low-, medium-grade metapelites and Mg-rich, Ca-poor detrital garnets therein were most likely derived from granulite-facies metapelites. This provenance interpretation supports that the Qilian Mountains to the north was the major source for the northern Qaidam basin and major deformation style along the Altyn Tagh Fault to west have been dominated by large-amplitude lateral offset and extrusion, rather than crustal thickening and uplift during the early Cenozoic. This study emphasizes high potential of detrital garnet trace element geochemistry in provenance analysis and reconstruction of tectono-sedimentary evolution of clastic sedimentary basins.

Multi-stage arc magma evolution recorded by apatite in volcanic rocks

AbstractProtracted magma storage in the deep crust is a key stage in the formation of evolved, hydrous arc magmas that can result in explosive volcanism and the formation of economically valuable magmatic-hydrothermal ore deposits. High magmatic water content in the deep crust results in extensive amphibole ± garnet fractionation and the suppression of plagioclase crystallization as recorded by elevated Sr/Y ratios and high Eu (high Eu/Eu*) in the melt. Here, we use a novel approach to track the petrogenesis of arc magmas using apatite trace element chemistry in volcanic formations from the Cenozoic arc of central Chile. These rocks formed in a magmatic cycle that culminated in high-Sr/Y magmatism and porphyry ore deposit formation in the Miocene. We use Sr/Y, Eu/Eu*, and Mg in apatite to track discrete stages of arc magma evolution. We apply fractional crystallization modeling to show that early-crystallizing apatite can inherit a high-Sr/Y and high-Eu/Eu* melt chemistry signature that is predetermined by amphibole-dominated fractional crystallization in the lower crust. Our modeling shows that crystallization of the in situ host-rock mineral assemblage in the shallow crust causes competition for trace elements in the melt that leads to apatite compositions diverging from bulk-magma chemistry. Understanding this decoupling behavior is important for the use of apatite as an indicator of metallogenic fertility in arcs and for interpretation of provenance in detrital studies.

POLITICAL CRIME IN POLISH SYSTEMIC CONDITIONS IN THE 20TH CENTURY

Political offences are a specific ‘set’ of prohibited acts listed by the legislator, undertaken by the perpetrator in specific political and normative conditions, and determined by the shape of the state’s political system. The legislator in the Penal Code of 1932, 1969 and 1997, as well as numerous non-code criminal law acts (e.g. in 1928, 1934, in the years 1944–1946), distinguished acts directed against a state that have features of criminal acts of a political nature. In the period of the Second Polish Republic, despite changes to systemic conditions in 1926, the state's attitude towards these prohibited acts have yet to be uniformly assessed. The first normative act defining the perpetrator's action against the state was the Regulation of the President of the Republic of Poland against espionage of 1928. After 1944/1945, the term ‘counter-revolutionary crime’ emerged in the doctrine of communist criminal law. Counter- revolutionary action was explicitly treated as a political crime. Systemic changes in 1956 significantly modified the interpretation of this act prohibited by law enforcement and judicial authorities, but until 1989, the legal status set out in the Criminal Code of 1969 remained. After 1956, the interpretation of political provenance changed, however the code solutions introduced in the system remained in force. Yet, after the turn of 1989, in the new normative and political reality it was necessary to refer the legislator to acts (political) committed under the previous system, consistent with the legal norms of that time but classified in new legal and political circumstances as crimes committed on behalf of state organs or as state crimes. Similarly, it turned out that the legislator had to respond to acts committed in the previous system and considered illegal; however, after the system was changed in 1989, they were already treated as acts directed towards the Polish state. In the Penal Code of 1997, the catalog of acts directed against the state, which are described as political crimes, was stipulated inarticles 127–137.

Development of a protocol to obtain the composition of terrigenous detritus in marine sediments -a pilot study from International Ocean Discovery Program Expedition 361

The geochemical and isotopic composition of terrigenous clays from marine sediments can provide important information on the sources and pathways of sediments. International Ocean Discovery Program Expedition 361 drilled sites along the eastern margin of southern Africa that potentially provide archives of rainfall on the continent as well as dispersal in the Agulhas Current. We used standard methods to remove carbonate and ferromanganese oxides and Stokes settling to isolate the clay fractions. In comparison to most previous studies that aimed to extract the detrital signal from marine sediments, we additionally applied a cation exchange wash using CsCl as a final step in the sample preparation. The motivation behind the extra step, not frequently applied, is to remove ions that are gained on the clay surface due to adsorption of authigenic trace metals in the ocean or during the leaching procedure. Either would alter the composition of the detrital fraction if no cation exchange was applied. Moreover, using CsCl will provide an additional measure of the cation exchange capacity (CEC) of the samples.However, no study so far has evaluated the potential and the limitations of such a targeted protocol for marine sediments. Here, we explore the effects of removing and replacing adsorbed cations on the clay surfaces with Cs+, conducting measurements of the chemical compositions, and radiogenic isotopes on a set of eight clay sample pairs. Both sets of samples underwent the same full leaching procedure except that one batch was treated with a final CsCl wash step. In this study, organic matter was not leached because sediments at IODP Site U1478 have relatively low organic content. However, in general, we recommend including that step in the leaching procedure.As expected, significant portions of elements with high concentrations in seawater were replaced by Cs+ (2SD 2.8%.) from the wash, including 75% of the sodium and approximately 25% of the calcium, 10% of the magnesium, and 8% of the potassium. Trace metals such as Sr and Nd, whose isotopes are used for provenance studies, are also found to be in lower concentrations in the samples after the exchange wash.The exchange wash affected the radiogenic isotope compositions of the samples. Neodymium isotope ratios are slightly less radiogenic in all the washed samples. Strontium and Pb isotopes showed significant deviations to either more or less radiogenic values in different samples. The radiogenic isotopes from the CsCl-treated fractions gave more consistent correlations with each other, and we suggest this treatment offers a superior measure of provenance. Although we observed changes in the isotope ratios, the general trend in the data and hence the overall provenance interpretations remained the same. However, the chemical compositions are significantly different. We conclude that a leaching protocol including a cation exchange wash (e.g. CsCl) is useful for revealing the terrestrial fingerprint. CEC could, with further calibration efforts, be useful as a terrestrial chemical weathering proxy.

Enhanced deposition of coal fragments at the Chukchi margin, western Arctic Ocean: Implications for deglacial drainage history from the Laurentide Ice Sheet

Distribution and composition of coarse particles (>250 μm) were investigated in 13 sediment cores from the Chukchi margin, western Arctic Ocean. Petrographic clast identification is supplemented by XRF core scanning, EDS analysis of coal fragments, and AMS 14C dating of planktic foraminifera for age control. Coal debris distribution is also investigated in surface sediments of the study region for provenance interpretation. The sediment-core study focuses on the interval between the Last Glacial Maximum and the Holocene for constraining provenance and timing of the deglacial discharge. We find that this interval is characterized by a distinct enrichment in sedimentary rock fragments, including coal. Comparison with longer stratigraphic records indicates that this composition is unique for the time interval since at least Maine Isotope Stage 5. Based on the timing, interpreted provenance, and geographic distribution of the coal enrichment, we conclude that the most likely primary source was the deglacial discharge from the Mackenzie drainage basin of the Laurentide Ice Sheet (LIS). The identified coal-bearing layer, also expressed in the XRF sulfur record, can be thus used as a stratigraphic marker for the LIS discharge to the Arctic Ocean during the last deglaciation.

Implications for Provenance since the Last Glaciations in Southeastern Andaman Sea Sediments by Clay Mineralogy

This study presents high-resolution clay mineralogy of Core MASS-III-10, located in the southeastern Andaman Sea. The study aimed to investigate terrigenous sedimentary input from various potential provenances throughout different periods of geological time. The clay mineral assemblages of MASS-III-10 reveal a high amount of smectite at 73% (65-79%), a moderate kaolinite at 12% (10-17%), and a low illite and chlorite content(<15%) over the last 45 ka. Provenance analysis suggests the most fine-grained terrigenous sediments originated from the Irrawaddy Delta Shelf (IDS), with minor sediments deriving from the Andaman Islands, the East Continental Shelf (ECS), and Sumatra provenance. The results show that IDS were predominantly smectite (~44%) while the ECS largely produced kaolinite (47%). The provenance interpretation based on the smectite content revealed that over time there has been no change in the main source of sediment in the Andaman Sea, despite changes in the volume of sedimentary input. Since the last glaciation, the Myanmar provenance (including IDS) has always contributed clay minerals, while other sources made up only minor contributions to the Andaman Sea. The clay minerals from the Myanmar provenance increased when the sea level was at a low stand (MIS 2), potentially due to shoreline retreat which enabled easier transportation of sediment from other sources. During the interglacial period (MIS 1 and 3), the study found a decrease in Myanmar-sourced clay minerals, which may be because the higher sea level made clay mineral deposition more difficult.

Provenance of the Neogene sediments from the Solimões Formation (Solimões and Acre Basins), Brazil

This study investigates the provenance of middle-late Miocene to Pliocene sediments of the Solimões Formation, in western Brazilian Amazonia, to complement the geological history and fill the gap left by similar studies on other foreland basin deposits and in the Amazonian fan. The major and trace element concentrations and Sr–Nd isotopic compositions of sixteen samples from the 1AS 33AM borehole and fifteen samples from two sections outcropping in the Acre and Yaco rivers were measured for determining their provenance. Additionally, the heavy mineral assemblages of the sixteen borehole samples were determined to complement the geochemical provenance interpretation of the borehole sediments. The Nd isotopic compositions of the Solimões Formation indicate that the Andes was the principal source of these Neogene sediments. While the middle-late Miocene borehole sediments are dominated by stable assemblage (zircon, tourmaline, and rutile) and less radiogenic Nd isotopic values, the Pliocene borehole sediments have a larger amount of more unstable mineral assemblages (epidote, pyroxene, and amphibole) and more radiogenic Nd isotopic values. These mineral and isotopic differences between the middle-late Miocene and Pliocene sediments are interpreted to reflect a change in provenance with increasing contribution of metamorphic and young Nd radiogenic source in the Pliocene most probably related to the late Miocene uplift of the Peruvian Eastern Cordillera. These changes that precede the paleoenvironmental changes highlighted by the palynological study of Leite et al. (2017) suggest that the Andean tectonics drove the middle to late Miocene paleoenvironmental changes of the Amazon basin from the Pebas mega-wetland to the more fluvial Acre phase.

Application of X‐ray fluorescence spectroscopy to provenance studies of Algerian archaeological pottery

The North African regions boast a multimillenary tradition of pottery production that represents a decisive progress in all societies. In this paper, we present the analysis of several fragments of pottery dating from the Middle Ages and collected in the archaeological site of Gouraya in Béjaïa (Algeria). Energy‐dispersive X‐ray fluorescence measurements were performed to obtain the elemental composition of the clays and to attempt a classification of the samples through multivariate analysis methods, connecting them to the archaeological information about the sites. Hierarchical clusters analysis (HCA) identified two possible different groups, related to different production sites, even if only one source of clay seem to be used, consistently with the geological contest. Based on the results, a tentative provenance interpretation could be proposed on historical bases. We put in place a strategy that made it possible to perform provenance studies respecting sample integrity as we aim to extend our research also to integer and well‐preserved object from museum, to create a database for Algerian production of in the Middle Ages.

Assessing mineral fertility and bias in sedimentary provenance studies: examples from the Barents Shelf

Abstract The development of laser ablation techniques using inductively coupled plasma mass spectrometry has enabled the routine and fast acquisition of in situ U–Pb and Pb–Pb isotope ratio data from single detrital grains or parts of grains. Detrital zircon dating is a technique that is increasingly applied to sedimentary provenance studies. However, sand routing information using zircon analysis alone may be obscured by repeated sedimentary reworking cycles and mineral fertility variations. These biases are illustrated by two clear case studies from the Triassic–Jurassic of the Barents Shelf where the use of U–Pb geochronology on apatite and rutile and Pb–Pb isotopic data from K-feldspar is highly beneficial for provenance interpretations. In the first case study, U–Pb apatite ages from the (Induan – Norian) Havert, Kobbe and Snadd formations indicate an evolving provenance and identify possible episodes of storage within foreland basins prior to delivery onto the Barents Shelf. In the second case study, U–Pb rutile and Pb isotopic analyses of K-feldspar from the Norian–Pliensbachian Realgrunnen Subgroup provide a clear distinction between north Norwegian Caledonides and Fennoscandian Shield sources and suggest that a similar approach may be used to test competing models for sand dispersal for this Subgroup in regions farther north than this study.

Is Cr-Spinel Geochemistry Enough for Solving the Provenance Dilemma? Case Study from the Palaeogene Sandstones of the Western Carpathians (Eastern Slovakia)

The provenance of the Proč and Strihovce sandstones is crucial for understanding the relationship between the Pieniny Klippen (PKB) and Flysch (FB) belts in the easternmost part of the Western Carpathian realm. Detrital Cr-spinels in these tectonic units were assertively interpreted as sourced from the southern sources representing the Meliata mélange. In this study, we use the geochemistry of detrital chromian spinels to identify the mafic and ultramafic source of the sediments and to compare them each other. Simultaneously, we compare their chemical compositions with those from the different Western Carpathian geological units, which could feed the Proč and Krynica basins during the Paleogene, where the Proč and Strihovce formations (fms), respectively, were deposited. Chromian spinels from the Proč and Strihovce fms exhibit similar geochemical characteristics (Cr# = 0.44–0.88 and 0.29–0.89, Mg# = 0.17–0.68 and 0.2–0.72, TiO2 = 0.0–3.67 and 0.01–2.08 wt.%, respectively). The spinels show both supra-subduction zone (SSZ) peridotite signatures and volcanic origin. Whereas volcanic spinels from the Proč Formation (Fm.) were formed under an ocean island basalt (OIB) and back-arc basin basalt (BABB) geodynamic setting, those from the Strihovce Fm. suggest a predominantly mid-ocean ridge basalt (MORB) origin. To avoid mistakes in the provenance interpretations, the data from garnet geochemistry of both formations is supplied. The analysed Cr-spinels do not absolutely overlap with spinels reported from the Meliata Unit, and their composition indicates at least two independent sources.

Erratum for ‘The provenance of the Devonian Old Red Sandstone of the Dingle Peninsula, SW Ireland; the earliest record of Laurentian and peri-Gondwanan sediment mixing in Ireland,’ Journal of the Geological Society, London, 175, 411–424

Samples in this paper have been assigned formations based on the Geological Survey of Ireland shapefile released prior to the commencement of the study. However, the authors were not aware that, since obtaining the samples, an updated shapefile had been released. This update affects three of the four apatite samples assigned to the Lower Devonian Ballymore Formation. The location of samples Mb-1, Mb-4 and Mb-5 now places them well within the undifferentiated, Upper Devonian Slieve Mish Group. As outlined in our paper, the apatite ages were originally produced concurrently with apatite fission track analysis and were later used in our study to provide additional provenance information in support of the detrital zircon geochronological data. In the second paragraph of the discussion section we say the following: et al. (1999) obtained an age of 411 Ma for the Cooscrawn Tuff Bed in the Ballymore Formation, which is older than 22 of the 70 detrital apatites analysed in this formation. The reassignment of the three samples to the Upper Devonian Slieve Mish Group nullifies the above statement. However, our interpretation that the depositional age of the Ballymore Formation is younger than the 411 Ma age given by Williams et al. (1999) is predominantly based upon the evidence given by the six youngest detrital zircons from the formation which underlies the Ballymore Formation (i.e. the Slea Head Formation). These zircons give a concordia age of 405 ± 4 Ma. This suggests that the Ballymore Formation was more than likely deposited after 409 Ma. We do not believe that the reassignment of the three samples has any major impact on our provenance interpretations. The ∼420 Ma age of the majority of the apatites in samples Mb-1, Mb-4 and Mb-5 actually fits with the range of Palaeozoic detrital zircons in sample AK-17 which was taken from the Slieve Mish Group, thereby supporting minor input of rocks affected by end-Scandian metamorphism.

New evidence and interpretation of facies, provenance and geochemistry of late Triassic-early Cretaceous Tethyan deep-water passive margin-related sedimentary rocks (Ayios Photios Group), SW Cyprus in the context of eastern Mediterranean geodynamics

The late Triassic-early Cretaceous deep-sea sedimentary succession exposed in western Cyprus is used here to help understand the wider context of continental break-up and seafloor spreading in the easternmost Mediterranean region. The restored sequence begins with late Triassic, base-of-slope sandstone turbidites and mudrocks, and fines upwards into mudrocks, distal calciturbidites and metalliferous sediments. After a hiatus, late Jurassic-early Cretaceous non-calcareous mudstones and radiolarites accumulated beneath the carbonate compensation depth, together with redeposited shallow-water-derived carbonates, including calcirudites. The succession culminates in late Jurassic-early Cretaceous very thickly bedded and highly mature quartzarenites that accumulated by mass-flow processes. The fine-grained siliciclastic sediments are terrigenous in origin, as indicated by whole-rock, trace element and REE analysis. Fe, Mn and trace metal enrichment in the late Triassic represents hydrothermal input related to submarine volcanism that was probably triggered by the nearby onset of seafloor spreading. The late Triassic sandstones were derived from a low to intermediate-grade metamorphic source terrane. The late Jurassic-early Cretaceous sandstones reflect extreme physical and chemical maturity in the source area, followed by transport and mass flow to a deep-water base-of-slope setting. Regional facies variation and locally available palaeocurrent data suggest sediment supply, originally from a continental block, no more than tens of km to the west or north. Similar successions are exposed in W Turkey, represented by the Antalya Complex. In the light of alternatives, the sedimentary succession is restored as the base-of-slope apron of a rifted microcontinental block, adjacent to the northern margin of the S Neotethys. The overall succession indicates (unstable) passive margin development after regional latest Triassic-early Jurassic continental break-up, with implications for plate reconstructions and hydrocarbon exploration.

Compositional variations in deep-sea gravity-flow deposits. A case study from the Voirons Flysch (Voirons-Wägital complex, Chablais Prealps, France)

Grain-size control is frequently invoked to explain the compositional variation of detrital sediments in fluvial sediments. A similar possibility is here investigated in the fossil deep-sea gravity-flow deposits from the Voirons Flysch (Voirons-Wägital complex, Chablais Prealps). About 270 samples of diverse depositional settings were analysed using the framework composition, including cement and porosity, Mutti facies and grain-size measurements. Six lithofacies have been identified from cluster analysis. They correspond to channel (L1 to L3) and lobe (L4 and L5) depositional settings and to reworked turbidites (L6). Our results emphasize the close relationship between petrography and grain-size which alters the detrital signal from extrabasinal sources. The abundant polycrystalline component of proximal deposits is progressively removed while skeletal grains and additional intrabasinal grains become more abundant in distal deposits. Alongside, porosity is reduced by the simultaneous increase of cement which constrains subsequent diagenetic modifications. Hence, proximal depositional settings keep most of the inherited signal from extrabasinal sources whereas distal deposits will be homogenised. When plotted in provenance-analysis diagrams, the successive depositional settings show distinct fields possibly corresponding to different tectonic settings of the Dickinson model. This compositional variation thus creates a bias in provenance interpretation resulting from both grain-size control and flow mechanisms. Finally, our results emphasize that petrographic data must be handled with care in provenance analyses, especially when comparing various deep-sea gravity flow systems with different grain-size ranges.

Preliminary laboratory investigations of ejecta emplacement dynamics and morphology with planetary applications

The preponderance of impact craters and the associated crater ejecta facies are leading agents of geomorphic change across the Solar System. Interpretation of planetary landscape evolution, sample provenance, and regolith gardening all benefit from a thorough understanding of ejecta emplacement dynamics. Constraining the type and range of these dynamics has eluded experimentation even as the effects of primary impacts have become well-constrained from experiments and numerical simulations and have been shown to follow power law scaling relationships. To address the knowledge gap surrounding granular ejecta emplacement, we built and characterized a novel ejecta emplacement catapult and showed it to accurately reproduce the ejecta mass and velocity profiles predicted for in-flight natural ejecta curtains. Based on this dynamic similarity to larger, natural systems, we proceeded with a preliminary exploratory suite of experiments to constrain runout and erosion efficiencies of flowing ejecta. Our quantitative results at low speeds may suggest a new set of scaling relationships for erosion via ballistic ejecta versus crater formation and erosion from hypervelocity clustered projectiles. Our results also show significant ejecta runout efficiencies of ∼1–2 (only slightly below the efficiencies of terrestrial debris flows 12 decades more voluminous) with important erosive efficiencies of ∼2–4%. Our qualitative results reveal a stochastic and heterogeneous system: ejecta “saltation” and implantation, and regolith exhumation, erosion, and shearing. Together with the initial results showing ejecta emplacement to be violently dynamic, the development of this new laboratory technique will enable more detailed studies to better inform interpretations of sample provenance, ejecta stratigraphy, and geochemical boundaries.

Trace and rare earth element (REE) characteristics of mudstones from Eocene Pinghu Formation and Oligocene Huagang Formation in Xihu Sag, East China Sea Basin: Implications for provenance, depositional conditions and paleoclimate

Abstract The interpretation of depositional conditions, provenance and paleoclimate provide important information to understand hydrocarbon source rock formation and distribution. The concentrations of trace elements and rare earth elements (REEs) of fifty mudstone samples from Eocene Pinghu Formation and Oligocene Huagang Formation in Xihu Sag, East China Sea Basin were determined by inductively coupled plasma-mass spectrometry (ICP-MS) to test the depositional conditions, provenance and paleoclimate. Evidences from the visual comparisons of the simple bivariate plots diagrams and statistical comparisons of the Mann-Whitney Rank Sum Test suggest that there may be a common source for the Pinghu Formation and Huagang Formation mudstones. Sedimentary provenance from bivariate plots diagrams of Hf versus La/Th and La/Sc versus Co/Th shows that Pinghu Formation mudstones are mainly composed of mixed felsic/basic source and acidic source whereas Huagang Formation is mainly acidic source. Additionally, the ∑REE vs La/Yb discrimination diagram shows that the property of the provenance for the Pinghu Formation mudstones consists sedimentary rock, alkaline basalt and a small amount of continent tholeiitic basalts whereas that of the Huagang Formation is mainly alkaline basalt and sedimentary rock. Discriminant diagrams, consisting of La-Th-Sc and Th-Co-Zr/10, suggest that the mudstones of two formations were deposited in continental island arc and active continental margin tectonic setting. Redox proxies (V/Ni, V/(V + Ni) and δCe) indicate that most of the mudstones of two formations were deposited in a relatively dysoxic/anoxic condition. The cool and humid climate (represented by Sr/Cu and Rb/Sr ratios) were prevailing in Xihu Sag during the Eocene and Oligocene period, and the Oligocene was cooler than Eocene. Moreover, five long term base level cycles (SIII1∼SIII5) and four sequence boundaries (Sb2∼Sb5) were recognized in the Pinghu Formation and Huagang Formation based on the previous research. We find that the abnormal surfaces of geochemical parameters, such as V/Ni, Sr/Ba, U/Ti, V/Ti, Ti and ΣREE, to some extent, agree with sequence boundaries (Sb2, Sb3, Sb4 and Sb5) in mudstones. Additionally, the increment of Ti and ΣREE concentrations and the decrease of Sr/Ba, V/Ni, U/Ti and V/Ti ratios above the Sb4 indicates that terrigenous clast grew significantly and the sea level dropped after late Eocene, which is related with the late Eocene tectonic movement.

Erosional unroofing of Himalaya in far western Nepal: a detrital zircon U-Pb geochronology and petrography study

Since the collision between the Indian and Asian plates, several peripheral foreland basin were formed, and started to accumulate the sediments from the hinterland Himalayan orogeny. The sediments deposited at the northern tip of the Greater India have been uplifted, exhumed after the activation of several south propagating thrusts and finally transported to the foreland basin by southward flowing fluvial system. We present petrography and detrital zircon dating for the interpretation of possible provenance of the Neogene Siwalik foreland basin sediments in far western Nepal. The QFL ternary plot for provenance analysis show a 'recycled orogeny' field for the studied sandstone samples, indicating Tethys Himalaya, Higher Himalaya and Lesser Himalaya as the source of the foreland basin sediments. The detrital zircon U-Pb ages of the studied samples have shown that during the time of deposition there was dominant numbers of detritus supplied from the Tethys and upper Lesser Himalaya. Subsequently the amount of the Higher and Lower Lesser Himalaya increased during the time of deposition of the Middle Siwalik.

Zircon size-age sorting and source-area effect: The German Triassic Buntsandstein Group

This study stresses how zircon-grain length versus age correlation significantly can improve provenance interpretations. Hence, taking sedimentary sorting effects into account, we present a detrital-zircon provenance study for continental deposits of the Central European, Lower Triassic Buntsandstein Group in Germany. The Buntsandstein Group was deposited in an extended intracontinental sag basin of Pangea under arid climate conditions. It included several intrabasinal tectonic swells, some of which have been assumed topographic highs acting as detrital source areas. This study of the Lower and Middle Buntsandstein subgroups in Central Germany indicates that particularly the Massif Central and the Bohemian Massif contributed to the basin fill of the central part of the Central European Basin. The Rhenish Massif, an assumed highland, was submerged. This interpretation is based on >1000 zircon grains from 12 sandstone beds. The unbroken grains in seven of the zircon separates have mean lengths of 190–220μm and five are composed 100–140μm long grains in average. All have a main population of 340–320Ma Carboniferous ages, representative of granitic, probably zircon-rich, rocks from the Variscan Orogen of the Massif Central and the Bohemian Massif. This first-cycle detritus was mixed with recycled, abraded zircon grains from Ediacaran to Palaeozoic metasedimentary units feeding the basin with 610–460Ma (Ediacaran to Ordovician) and 2Ga age grains, as is typical for Gondwana-derived material. The Ediacaran to Ordovician age population is common only in five samples with mean grain lengths of 100–140μm. Grains of such ages mainly are <130μm in the east, but equally common in all grain sizes in western sandstone beds. A western group was fed from the Massif Central and an eastern group derived from the Bohemian Massif. However, abrasion, age-population variations for pre-Variscan grains, and dominating wind directions indicate that two different fluvial systems delivered the Bohemian material and that this was combined with aeolian and alongshore lacustrine transport from the south and west. We conclude that interpretation of detrital zircon ages preferably are separately for different size classes, because zircon studies performed on broad grain-size intervals without considering possible size-age correlations may disguise sorting effects that potentially can lead to a misleading source-area interpretation.

A multivariate discrimination scheme of detrital garnet chemistry for use in sedimentary provenance analysis

Garnet chemistry provides a well-established tool in the discrimination and interpretation of sediment provenance. Current discrimination approaches, however, (i) suffer from using less variables than available, (ii) subjective determination of discrimination fields with strict boundaries suggesting clear separations where in fact probabilities are converging, and (iii) significant overlap of compositional fields of garnet from different host-rock groups. The new multivariate discrimination scheme is based on a large database, a hierarchical discrimination approach involving three steps, linear discriminant analysis at each step, and the five major host-rock groups to be discriminated: eclogite- (A), amphibolite- (B) and granulite- (C) facies metamorphic rocks as well as ultramafic (D) and igneous rocks (E). The successful application of statistical discrimination approaches requires consideration of the a priori knowledge of the respective geologic setting. This is accounted for by the use of prior probabilities. Three sets of prior probabilities (priors) are introduced and their advantages and disadvantages are discussed. The user is free to choose among these priors, which can be further modified according to the specific geologic problem and the level of a priori knowledge. The discrimination results are provided as integrated probabilities of belonging to the five major host-rock groups. For performing calculations and results a supplementary Excel® spreadsheet is provided.The discrimination scheme has been tested for a large variety of examples of crystalline rocks covering all of the five major groups and several subgroups from various geologic settings. In most cases, garnets are assigned correctly to the respective group. Exceptions typically reflect the peculiarities of the regional geologic situation. Evaluation of detrital garnets from modern and ancient sedimentary settings of the Western Gneiss Region (Norway), Eastern Alps (Austria) and Albertine Rift (Uganda) demonstrates the power to reflect the respective geologic situations and corroborates previous results. As most garnet is derived from metamorphic rocks and many provenance studies aim at reconstructing the tectonic and geodynamic evolution in the source area, the approach and the examples emphasize discrimination of metamorphic facies (i.e., temperature-pressure conditions) rather than protolith composition.

Enhanced provenance interpretation using combined U–Pb and (U–Th)/He double dating of detrital zircon grains from lower Miocene strata, proximal Gulf of Mexico Basin, North America

Detrital zircon U–Pb analysis is an effective approach for investigating sediment provenance by relating crystallization age to potential crystalline source terranes. Studies of large passive margin basins, such as the Gulf of Mexico Basin, that have received sediment from multiple terranes with non-unique crystallization ages or sedimentary strata, benefit from additional constraints to better elucidate provenance interpretation. In this study, U–Pb and (U–Th)/He double dating analyses on single zircons from the lower Miocene sandstones in the northern Gulf of Mexico Basin reveal a detailed history of sediment source evolution. U–Pb age data indicate that most zircon originated from five major crystalline provinces, including the Western Cordillera Arc (<250 Ma), the Appalachian–Ouachita orogen (500–260 Ma), the Grenville (1300–950 Ma) orogen, the Mid-Continent Granite–Rhyolite (1500–1300 Ma), and the Yavapai–Mazatzal (1800–1600 Ma) terranes as well as sparse Pan-African (700–500 Ma) and Canadian Shield (>1800 Ma) terranes. Zircon (U–Th)/He ages record tectonic cooling and exhumation in the U.S. since the Mesoproterozoic related to the Grenville to Laramide Orogenies. The combined crystallization and cooling information from single zircon double dating can differentiate volcanic and plutonic zircons. Importantly, the U–Pb–He double dating approach allows for the differentiation between multiple possible crystallization-age sources on the basis of their subsequent tectonic evolution. In particular, for Grenville zircons that are present in all of lower Miocene samples, four distinct zircon U–Pb–He age combinations are recognizable that can be traced back to four different possible sources. The integrated U–Pb and (U–Th)/He data eliminate some ambiguities and improves the provenance interpretation for the lower Miocene strata in the northern Gulf of Mexico Basin and illustrate the applicability of this approach for other large-scale basins to reconstruct sediment provenance and dispersal patterns.

Unmixing detrital geochronology age distributions

AbstractDespite recent advances in quantitative methods of detrital provenance analysis, there is currently no widely accepted method of unmixing detrital geochronology age distributions. We developed a model that determines mixing proportions for source samples through inverse Monte Carlo modeling, wherein mixed samples are compared to randomly generated combinations of source distributions, and a range of best mixing proportions are retained. Results may then be used to constrain a forward optimization routine to find a single best‐fit mixture. Quantitative comparison is based on the Kolmogorov‐Smirnov (KS) testDstatistic and Kuiper testVstatistic for cumulative distribution functions, and the Cross‐correlation coefficient for finite mixture distributions (probability density plots or kernel density estimates). We demonstrate the capacity of this model through a series of tests on synthetic data, and published empirical data from North America mixed in known proportions; this proof‐of‐concept testing shows the model is capable of accurately unmixing highly complex distributions. We apply the model to two published empirical data sets mixed in unknown proportions from Colombia and central China. Neither example yields perfect model fits, which provides a cautionary note of potentially inadequate characterization of source and/or mixed samples, and highlights the importance of such characterization for accurate interpretation of sediment provenance. Sample size appears to be a major control on mixture model results; small (n &lt; 100) samples may lead to misinterpretation. The model is available as a MATLAB‐based stand‐alone executable (.exe file) graphical user interface.