Detrital K-feldspar Research Articles

Detrital K-feldspar as a novel archive of continental crustal evolution using coupled in situ Rb[sbnd]Sr dating and Pb isotope analysis

Here we present in situ RbSr and Pb isotopic analysis of K-feldspar from the Shap Granite, (Cumbria, UK) and detrital K-feldspar from the associated Shap Wells Conglomerate Formation, to investigate the potential of the detrital K-feldspar record as an archive of crustal composition. We use a unique, collision cell – multi collector inductively coupled plasma tandem mass spectrometer to make the in situ isotope measurements, using ‘chemical resolution’ of 87Rb+ and 204Hg+ isobaric interferences on 87Sr+ and 204Pb+, achieved with SF6 and NH3 reaction gases, respectively. Using this technique, we successfully demonstrate that the majority of detrital K-feldspar RbSr ages, as well as initial Sr and Pb isotope ratios, from the Shap Wells Conglomerate are within uncertainty of those for parental Shap Granite K-feldspar (398 ± 1 Ma, n = 6). Some detrital K-feldspar grains record perturbed RbSr ages, reflecting post depositional alteration events. The majority of samples with disturbed RbSr ages carry distinct petrographic features evident in SEM imaging, prior to in situ dating, which indicates a means to help screen for reliable ages.We further illustrate the potential value of combined RbSr and Pb isotopic information preserved in K-feldspar to estimate the timing and chemical composition of juvenile continental crust formed in the past. Where UPb has been fractionated during juvenile crust formation, the initial Pb isotope ratio provided by the K-feldspar yields model crustal U/Pb (diagnostic of tectonic setting) and extraction age. The contrast in the U/Pb composition of juvenile crust formed in intraplate or subduction settings allows the model U/Pb ratios of the detrital K-feldspars to be used to constrain the style of juvenile crust formation. Additionally, the initial 87Sr/86Sr isotope ratio measured in detrital K-feldspar can be combined with the calculated crustal extraction age and RbSr K-feldspar age to model the Rb/Sr of the juvenile crustal protolith.

Linking Taiwan to the Cathaysia Block during the Cenozoic: Evidence from Pb isotopes in detrital K-feldspar

The Cenozoic sedimentary rocks on the island of Taiwan hold significant implications for understanding tectonic and drainage evolutions in SE China, but the provenance of these rocks remains controversial. Here we derived Pb isotopes in detrital K-feldspars from the drainage systems in western Taiwan to evaluate the provenance of sediments and reveal the evolution of Cenozoic sedimentary. Our findings indicate that the fluvial sediments eroded from the Cenozoic sedimentary rocks were primarily derived from the eastern Cathaysia Block (91%), with minor contributions from the Yangtze River catchment. Spatially, the northern part of Taiwan contains more sediments derived from the Yangtze River catchment than the southern part. The Cathaysia Block has been crucial in supplying detritus to Taiwan since the Eocene, whereas the contribution of the Yangtze Block varies greatly at different sedimentary periods. Two major shifts in provenance occur at the boundaries between Eocene, Oligocene, and Miocene, which may be related to the changes in drainage systems and landscapes in eastern China.

Dynamic collapse and regrowth of the Antarctic Ice Sheet in the Weddell Sea sector during the middle Miocene: A novel multi-proxy sedimentary provenance approach using in-situ87Rb/87Sr dating of detrital K-feldspar

The latest generation of Antarctic paleo-ice sheet models, incorporating bedrock paleo-topography, reconstruct the development of substantial ice-sheet embayments during the Mid-Miocene Climate Optimum, a warm period between ∼17–15 Ma ago. Here, we test these models using ice-rafted debris (IRD) recovered from the central Weddell Sea (Ocean Drilling Program Site 113–694). These IRD are entrained by the ice-sheet expanding into the embayment during the cooling associated with the subsequent Mid-Miocene Climate Transition and ultimately delivered to the deep marine sink by iceberg armadas during higher-frequency instability events. Due to the near-absence of heavy minerals in these volumetrically small samples, we utilise the novel in-situ K-feldspar 87Rb/87Sr provenance technique by laser-ablation inductively coupled mass spectrometer equipped with a mass-filtered reaction cell. We combine these single-grain ages with in-situ Pb-isotope analysis, as well as 40Ar/39Ar dating of a subset of grains. Results identify the Antarctic Peninsula and southern Dronning Maud Land as key sediment sources, including grains sourced from within the Recovery subglacial basin. These findings support ice sheet instability consistent with reconstructions of major ice sheet embayments formed by climatic conditions analogous to those predicted by modern anthropogenic warming trajectories. Additionally, in-situ87Rb/87Sr and Pb-isotope analysis of detrital K-feldspar provide a high-throughput alternative to conventional single grain U-Pb or 40Ar/39Ar analysis, especially in small samples where the heavy mineral fraction is limited or absent.

Vanadium mineralization at Los Chihuidos sediment-hosted Cu–V deposit, Neuquén Basin, Argentina: An approach to vanadium ore forming processes

Vanadium mineralization at Los Chihuidos deposit of the Neuquén Basin is linked to the development of a redox front system related to the inflow of hydrocarbons into the red sandstone of the Huincul Formation. Interaction of hydrocarbons with oxidized red beds and connate water generated redox reactions where hematite was dissolved due to iron reduction resulting in the discoloration of the red strata. At the contact between oxidized red sandstone and reduced white sandstone, precipitation of specific mineral phases resulted in the V ore with minor amounts of Cu. With the implementation of the redox interface, abundant V-montmorillonite and V-hematite precipitated at the more oxidizing conditions and Cu-V-corrensite-type at the more reducing conditions of the redox front. As the redox front advanced with fluids constantly migrating into the reservoir, more reducing conditions were stablished, promoting chloritization and minor illitization with V-Cu incorporation and continuous upgrading of the ore. Main ore mineralogy consists of clay minerals including V-bearing montmorillonite, Cu-V-corrensite-type, V-di-trioctahedral chlorite and Cu-tri-trioctahedral chlorite with minor V-illite–smectite mixed-layer minerals and associated secondary V-hematite. Chloritization over illitization was favored due to high amounts of Fe and Mg in detrital clasts and in connate fluids and by low K availability related to low amounts of detrital K-feldspar. The spatial transition of V and /or Cu bearing clay minerals observed through the mineralized redox front at Los Chihuidos deposit (kaolinite → smectite → illite/smectite → corrensite-type → di- trioctahedral -chlorite → tri- trioctahedral -chlorite) and the related variation of V–Cu concentrations in bulk rock are indicative of increasing pH and decreasing Eh of resident solutions from red to white sandstones during the hypogene mineralization process. Late influx of Cu-rich oxidized basinal brines precipitated main copper ore with Cu-sulfides in the white sandstone up to the contact with the redox front in contact with hydrocarbons. During uplift and exhumation, percolation of meteoric water promoted remobilization of V and Cu and the precipitation of oxidized V–Cu ore.

Effect of silica diagenesis on porosity evolution of deep gas shale reservoir of the Lower Paleozoic Wufeng-Longmaxi formations, Sichuan Basin

Silica diagenesis is critical to reservoir properties of shale, including porosity and rock mechanical properties, thus exerting a significant effect on shale gas production, but the role it plays on porosity evolution of deeply-buried shale remains unclear. In order to address this issue, a suite of deep gas shale samples (5910–5965 m depth) recovered from the Lower Paleozoic Wufeng-Longmaxi formations (WF-LMX) of the Sichuan Basin was selected to study silica diagenesis in these deposits and its effect on porosity evolution by the use of optical, SEM and SEM-CL observations, geochemical analysis, and low-pressure gas adsorption experiments. TOC of the WF-LMX shale sample suite that was altered to the thermally overmature stage ranges from 0.63 to 6.70 wt% (average = 3.26 wt%). Quartz hosted by the studied shale samples is present as six forms, including detrital quartz, quartz overgrowth, siliceous skeletal fragments, aggregates of amorphous to euhedral microquartz, silica nanospheres, and matrix-dispersed microquartz. Silica involved in the diagenetic alteration of the WF-LMX samples appears to have been chiefly sourced from the dissolution of siliceous skeletal fragments (mostly radiolarians) and secondarily from the transformation of clay minerals and alteration of detrital K-feldspar. Detrital quartz played a minimal role in porosity preservation, whereas authigenic quartz influenced porosity evolution in two ways. Siliceous skeletal fragments, aggregates of microquartz, silica nanospheres, and early diagenetic matrix-dispersed microquartz formed a rigid framework that shielded organic pores from compaction. However, quartz overgrowth and the precipitation of late stage diagenetic microquartz reduced porosity by filling voids. We estimate that a moderate content of authigenic quartz (Sixs = 10–30%) is optimal for the development and preservation of porosity (especially organic porosity). Organic pores, the dominant and pervasive pore type in the deep shale gas play, appear to have been best preserved in samples containing less than 5.5 wt% TOC. It is noteworthy, however, that some of the larger organic pores in samples containing >5.5 wt% TOC have collapsed in response to compaction. It is apparent, then, that organic porosity of the WF-LMX deep shale has been largely preserved showing great potential for shale gas exploration.

Temperature and basinal fluid controls on feldspar diagenesis, Lower Cretaceous sandstones, Scotian Basin, Canada

The passive-margin Scotian Basin accumulated thick Upper Jurassic–Lower Cretaceous deltaic sandstones and shales, which were influenced by high heat flow in the mid-Cretaceous and deformed by salt tectonics. This study takes advantage of the complex thermal history and record of saline fluid flow in the basin to determine the relative importance of burial depth, temperature, salinity of basinal brines, overpressure, and sandstone permeability in controlling the dissolution of detrital feldspar and growth of authigenic K-feldspar and albite. Feldspar grains and volcanic lithic clasts from two transects, with differing thermal and salt tectonic histories, were studied by scanning electron microscope (SEM) backscattered electron images, energy-dispersive spectroscopy, SEM cathodoluminescence (CL) imaging, and hot-cathode CL microscopy. Published fluid inclusion measurements are integrated with burial history curves and timing of deformation on salt detachment surfaces to provides a new synthesis of the post-Jurassic thermal and saline fluid flow history of the basin. Surface-controlled dissolution of K-feldspar and growth of authigenic K-feldspar rims occur from 1.5 to 3.1 km. More destructive transport-controlled dissolution, down to 3.9 km, is more effective in thick-bedded permeable sandstones that acted as fluid pathways. Albitization of detrital K-feldspar and sodic plagioclase, and of feldspars in volcanic lithic clasts was facilitated by high Na+ content of formation waters migrating preferentially through such pathways at the time of silica and carbonate cementation, with strong albitization coinciding with transport-controlled dissolution of K-feldspar. Authigenic albite partially fills pores created by K-feldspar dissolution. Overpressured conditions enhance albite authigenesis, as a result of slower fluid advection. Episodic release of hot, saline, overpressured fluids in the zone of surface-controlled dissolution of K-feldspar favoured albitization but had no detectable effect on K-feldspar dissolution. Basin hydrology plays a definitive role in feldspar diagenesis, producing patterns that cannot be interpreted as a simple consequence of temperature and activity of Na+.

Cenozoic reorganization of fluvial systems in eastern China: Sedimentary provenance of detrital K-feldspar in Taiwan

Cenozoic passive margin sediments in Taiwan provide an important natural archive to reconstruct drainage reorganization in eastern China. In this study, we used Pb isotope compositions of detrital K-feldspar to investigate the sedimentary provenance of Cenozoic strata in Taiwan and to constrain fluvial system evolution in eastern China. Eocene to lower Oligocene sandstones in Taiwan are characterized by radiogenic K-feldspar grains (206Pb/204Pb>18.4), indicating that the eastern Cathaysia Block served as the dominant sediment contributor. In contrast, a late Oligocene sample has a Pb isotopic character indistinguishable from that of the Gan River, a major tributary of the Yangtze River. This provenance change is interpreted as the result of headward (westward) migration of the paleo-Min River to the Wuyishan (Wuyi Mountains) during the late Oligocene. Miocene deposits are enriched in relatively unradiogenic K-feldspar (206Pb/204Pb<17.0) which can be reliably traced back to the Dabie and Sulu orogenic belts. Since the early Miocene, the paleo-Yangtze River, mainly draining the Yangtze Craton and the Dabie orogenic belt, delivered a large volume of detritus to the East China Sea Shelf Basin and also to the proto-Taiwan region.

Critical evaluation of geochemical indices of palaeosalinity involving boron

Despite years of research, palaeosalinity remains one of the most difficult palaeoenvironmental proxies to reconstruct. Numerous approaches have been proposed. Those utilising boron, gallium, strontium, barium, and potassium are among the most commonly used in palaeoenvironmental reconstructions. The comparison of chemical and mineralogical data obtained for hundreds of samples from various sedimentary basins of different ages and burial histories indicated that those proxies are highly sensitive to detrital and authigenic mineralogy changes. It has been shown that boron is preferentially accumulated in the 2:1 clays (illite 1Md and 2M1, illite–smectite), 1:1 clays (kaolinite), and hematite, which all are of non-synsedimentary origin. An increase in the weathering products input, high flux of the detrital mica, and/or enhanced burial diagenesis may increase B/K and B/Ga ratios, suggesting the marine environment of deposition. On the other hand, an increased input of the detrital K-feldspars or plagioclases may decrease those ratios implying freshwater sedimentation. Mineralogy is also responsible for the Sr/Ba ratio variability, resulting in spurious palaeoenvironmental interpretations. Isotope techniques may be more appropriate, especially if the finest clay fractions are used and the diagenetic fluid flow is confined to the analysed basin.

Mechanism and mode of albitization of detrital feldspar in the Devonian Padeha Formation, Eastern Alborz, Iran

The Early to Middle Devonian Padeha Formation in the eastern Alborz, is a thick terrestrial syn-rift succession of Early to Middle Devonian age. Sandstones in the basal 115 m, mainly of submature, mature and supermature in terms of their grain angularity, sorting, and matrix content. Most of the studied sandstones are characterized by their quartzofeldspathic nature, and are classified as quartzarenite, subarkosic and arkosic composition. Also, based on petrographic results, a paragenetic sequence is proposed for the sandstones, including three general stages. The sandstones have been examined using scanning electron and hot-cathodoluminescence microscopy to study the albitized detrital feldspars. Detrital K-feldspar is the major feldspar type that has been partly to albitized throughout the study sandstone. The textural variation is considerable, with vein-like, blocky, and patchy forms. Probable sodium sources for albitization include smectite to illite or chlorite transition, diabase sills, detrital albite dissolution, and replacement of detrital sodium plagioclases by authigenic minerals. From comparison with other basins worldwide, a temperature estimate of 75–130°C for the mesodiagenetic albitization is inferred, suggesting a burial depth of 2000-5500 m based on thermal burial model for the basin. The model suggests that the temperature at the base of the Padeha Formation did not exceed 150°C, constraining conditions for albitization.

No connection between the Yangtze and Red rivers since the late Eocene

The unusual drainage pattern in the southeastern Tibetan Plateau has been proposed to result from the breakup of a single paleo-Red River system. However, whether there or not was a major early Cenozoic “paleo-Red River” flowing from southeastern Tibet to the South China Sea is still highly debated. In this study, we have used Pb isotopic analyses of detrital K-feldspar to constrain the sedimentary provenance of the Cenozoic deposits from the onshore Jianchuan Basin and offshore Yinggehai and Qiongdongnan basins, and further to decipher the drainage evolution of the upper-middle Yangtze and Red Rivers. Detrital K-feldspar from the Baoxiangsi Formation in the Jianchuan Basin shows an apparent mixture of sand delivery from both the upper Yangtze and Yalong rivers, indicating that there was a river draining the Qiangtang Block and Songpan-Ganzi that used to flow through the Jianchuan Basin during the Eocene. In contrast, K-feldspar Pb isotopes from the Eocene to Pliocene deposits of the Yinggehai and Qiongdongnan basins are different from those of the Jianchun Basin and Yangtze, Salween, and Mekong rivers, but similar to that of the modern Red River. These lines of evidence suggest that major rivers draining southeastern Tibet have not been tributaries of the paleo-Red River and hence, there has been no fluvial connection between southeastern Tibet and the South China Sea since at least the late Eocene.

First-cycle sand supply and the evolution of the eastern Canadian continental margin: Insights from Pb isotopes in the Mesozoic Scotian Basin

Abstract Provenance analysis provides a powerful means to understand, connect, and reconstruct source-to-sink systems and Earth surface processes, if reliable toolkits can be developed, refined, and applied. Deciphering sediment routing to the Scotian Basin, offshore eastern Canada, is marred by sedimentary recycling but is critical to understanding the evolution of the Canadian margin in response to the evolving Labrador rift. In this study, Pb isotopes in detrital K-feldspars were fingerprinted in 13 wells across the Scotian Basin to track first-cycle sand supply. Unlike previous approaches, which utilized less labile proxies such as zircon, detrital K-feldspars are unlikely to survive multiple sedimentary cycles. The Pb-isotopic data reveal a dynamic seesaw effect between hinterland sources across the Jurassic-Cretaceous boundary, reflecting the complex interplay between the northward propagation of uplift along the rising Labrador rift flank and the reactivation of fault systems in the lower drainage basin. Pb isotopes in K-feldspar record progressively increasing long-distance supply from eastern Labrador, as early as the Callovian in the central basin, alongside diminishing but persistent local sourcing from adjacent Appalachian terranes. Comparison with more resilient mineral proxies, notably zircon, appears to confirm recycling in the lower drainage basin and highlights the limitations of using a single mineral proxy in isolation. This case study serves as an example of the growing potential of multiproxy provenance toolkits not only to decipher sediment-routing corridors in paleodrainage systems, but to better define and connect the drivers, mechanisms, and spatial and temporal ranges of Earth surface processes and tectonic events.

Characteristics and distribution of clay minerals and their effects on reservoir quality: Huagang Formation in the Xihu Sag, East China Sea Basin

The characteristics and distribution of clay minerals and their effects on reservoir quality in the Huagang sandstones in the Xihu Sag, East China Sea Basin were studied by using X-ray diffraction, casting thin-sections, scanning electron microscopy, electron microprobe analysis, fluid inclusion analysis, constant-rate mercury injection and nuclear magnetic resonance. Clay minerals consist of kaolinite, chlorite, illite and illite–smectite mixed layer (I/S); kaolinite forms from dissolved feldspars, chlorite occurs as clay coatings that are transformed from clay precursors owing to the flocculation of suspended detrital clays or the crystallisation of pore fluids, and illite forms from the illitisation of detrital smectite, authigenic kaolinite and K-feldspars. Clay distribution is controlled by sedimentary environments, burial history and lithologies. Typical reservoirs in the western sub-sag are thin and developed in braided river facies at relatively shallow burial depths with clays dominated by kaolinite. However, typical reservoirs in the central inversion tectonic zone are thicker and developed in a braided delta front facies at deeper burial depths with clays mainly consisting of chlorite, illite and I/S. High-quality reservoirs are characterised by coarse granularity, high quartz content and low clay content with widespread development of chlorite coatings that inhibit quartz cements at low temperatures. At higher temperatures, the high-quality reservoirs develop more pores providing growth space for quartz cements and result in the coexistence of chlorite coatings and quartz cements. The high-quality reservoirs are controlled by their lithological characteristics rather than chlorite coatings. Illite and I/S clays create severe damage to reservoirs by reducing the size and connectivity of pore-throats.

Relationship between diagenesis and the emplacement of bitumen in the Lower Triassic Piramboia Formation sandstones, Paraná Basin, SW Brazil

Outcrops of eolian sandstones of the Lower Triassic Piramboia Formation in the eastern margin of the intracratonic Paraná Basin are known as the main occurrence of tar sandstones in Brazil because contain heavy oil (“tar”). In order to investigate the migration of oil into the sandstones petrographic analyses of dune facies were performed. Optical (transmitted, reflected and epifluorescence lights) and Field Emission Scanning Electron (FE-SEM) microscope studies together with X-Ray Diffraction (XRD) analyses showed that the Piramboia Formation sandstones have not been affected by intense diagenesis. Eogenetic features includes mainly thin, continuous inherited ferruginous clay coatings and minor mechanically infiltrated clay coatings around detrital mineral grains. The authigenesis of smectite and K-feldspar overgrowths precipitation begin to develop and during shallow mesodiagenesis, authigenic smectite was gradually transformed into mixed-layer illite-smectite; K-feldspar overgrowths, quartz overgrowths continuous to develop, and pore-filling calcite cement were formed locally. In the late mesodiagenesis the emplacement of oil occurred, filling pores and covering grains, clay coatings and calcite. During later surface exposure, water washing by meteoric fluids and biodegradation transformed the oil into a heavy oil rich in asphaltenes. The influx of acid meteoric waters caused dissolution of detrital K-feldspars as well as meteoric waters generate organic acids which also caused the dissolution of K-feldspars and the consequent generation of secondary porosity with the precipitation of inter- and intragranular vermicular kaolinite. However, kaolinite can be also a product of eodiagenetic process similar to the occur in the telodiagenesis. To evaluate the porosity of the sandstones microtomography analysis were preformed revealing high porosity volume (ca. 26%) and high volume of porous with connectivity (ca. 26%). Although not currently commercially exploited nowadays the knowledge of the Piramboia tar sandstones diagenetic evolution contributes for a better understanding of the Paraná Basin sedimentary fill during the Lower Triassic.

All mixed up: Pb isotopic constraints on the transit of sands through the Mississippi-Missouri River drainage basin, North America

AbstractPb isotope data from over 2400 detrital K-feldspars in &gt;50 modern sands sampled across the Mississippi-Missouri River drainage basin of North America have been collected in order to construct the first basin-wide provenance model using geochemical signals in a framework, rather than an accessory, mineral. This study represents a critical initial step in understanding the long-term routing of framework sand grains through the Mississippi-Missouri River drainage basin.Four unique Pb isotopic groups, otherwise petrographically and geochemically indistinguishable, are identifiable. Source comparisons reveal two groups corresponding to the Archean Superior and Wyoming terranes to the north of the catchment. The remaining two Pb groups represent a mixture of Appalachian, Grenville and older Granite-Rhyolite, and Yavapai-Mazatzal sourced-grains in the east of the catchment, with noteworthy input from Cenozoic volcanic rocks along the western fringe of the catchment to tributaries west of the Mississippi River, confirming prior assertions of zircon recycling in the lower drainage basin.Tracing suites of Pb isotopic groups provide a detailed map of previously undocumented tributary mixing and reveals the importance of long-lived, naturally formed impoundments in the Upper Mississippi River, which locally sequester and release sand. Tentative proportioning of sediment contributions to the terminus of the Mississippi River from individual tributaries produces similar results to recent U-Pb zircon models, boding well for the use of framework grain based modeling of sediment fluxes.The study is the largest application of Pb-in-K-feldspar fingerprinting to date and advocates its potential as a new and necessary tool for constraining relative source contributions to sinks—which will have wide applicability—especially if combined with provenance information from detrital grains of varying resilience, within large drainage systems.

Detrital K-feldspar Pb isotopic evaluation of extraregional sediment transported through an Eocene tectonic breach of southern California's Cretaceous batholith

Sedimentary provenance studies have come to be overwhelmingly based upon U–Pb geochronologic measurements performed with detrital zircon while alternative and potentially complementary approaches such as conglomerate clast studies and heavy mineral analysis have faded in importance. Measurement of Pb isotopic compositions in detrital K-feldspar is among the under-utilized approaches available to ascertain sedimentary source regions. While it has been long recognized that common Pb isotope compositions recorded by K-feldspar vary widely and reflect the crustal provinces from which the host basement rocks crystallized, use of the approach has suffered due to a lack of appropriate statistical models and ground truth compositional data from source regions. In this paper, we: (1) present high-throughput LA-ICPMS analysis protocols needed to generate statistically meaningful detrital K-feldspar Pb isotope data sets; (2) develop an interpretative approach based upon 208Pb/206Pb vs. 207Pb/206Pb that incorporate information from the U- and Th-decay systems into one two-dimensional plot that is amenable to analysis using two-dimensional Kolmogorov–Smirnoff statistical tests; (3) generate new Pb isotopic data from basement rocks from southwestern North America to improve knowledge of the Pb isotopic properties of potential source regions; and (4) generate new Pb isotopic data from Lower Eocene to Lower Miocene sedimentary rocks to evaluate changes in drainage patterns that occurred in response to deformation that affected the southern California margin. Through this case study, we demonstrate how our new analytical and interpretative methods could be profitably applied to future geochemical and provenance studies and tectonically driven re-organization of drainage patterns.

Clay Cutans and the Origin of Illite Rim Cement: An Example from the Siliciclastic Rotliegend Sandstone in the Dutch Southern Permian Basin

Abstract In Permian Rotliegend sandstones in the Dutch part of the Southern Permian Basin illite can be a practical annoyance because it strongly influences reservoir properties. Despite its practical importance, the origin and in particular the prediction of the distribution of authigenic illite in siliciclastic sandstone is still under discussion. Three main types of authigenic illite exist, each of which result from different diagenetic processes at different stages during burial. The earliest illite is tangential illite, parallel to the grain surfaces. It has formed by infiltration of suspended clay-size particles into loose surficial sands and can be interpreted as cutanic clay. The clay cutans were occasionally formed in situ but are mostly inherited with grains having been reworked from interdune and sabkha areas by fluvial and aeolian action. The second illite type is authigenic and occurs on top of the clay cutans. Commonly two or three illite generations with different crystal habit are present, ranging from platy to hairy. Clay cutans were nucleation sites and generated the mass for the illite rim cement. Different amounts and habits of illite rim cement are linked to differences in the thickness and completeness of the clay cutans. The more iron oxide in the cutans, the less authigenic illite formed. The illite rim cement precipitated after mechanical compaction, and is probably related to illitization of smectitic clay in the cutans. Illite rim cement is thus related to the local paleogeography of the basin, including aridisol development and erosion of such soils. The third type of authigenic illite occurs in secondary pores after dissolution of detrital K-feldspar or rock fragments containing K-feldspar. The latter illite is not the product of kaolinite illitization but it precipitated as a primary mineral without a kaolinite precursor. The illite in secondary pores after feldspar dissolution thus depends on the detrital composition. Only the illite rim cement reduces intergranular porosity to microporosity, thereby increasing the specific surface area. This results in a high irreducible water content. In consequence the permeability for a given porosity can be reduced by up to two orders of magnitude. The other two types of illite have no significant influence on reservoir properties.

The complexity of sediment recycling as revealed by common Pb isotopes in K-feldspar

Detrital zircon U–Pb geochronology has become the gold standard in evaluating source to sink relationships in sedimentary basins. However, the physical and chemical robustness of zircon, which make it such a useful mineral for provenance studies, is also a hindrance as zircon can be recycled through numerous sedimentary basins, thus obscuring the first cycle source to sink relationship. An elegant approach to addressing this potential issue is to compare the Pb isotope composition of detrital K-feldspar, a mineral which is unlikely to survive more than one erosion-transport-deposition cycle, with that of magmatic K-feldspar from potential basement source terranes. Here we present new in situ Pb isotope data on detrital K-feldspar from two Proterozoic arkosic sandstones from Western Australia, and magmatic K-feldspar grains from potential igneous source rocks, as inferred by the age and Hf isotope composition of detrital zircon grains. The data indicate that the detrital zircon and K-feldspar grains could not have been liberated from the same source rocks, and that the zircon has most likely been recycled through older sedimentary basins. These results provide a more complete understanding of apparently simple source to sink relationships in this part of Proterozoic Western Australia.

Evaluating the impact of Pb volatilization during 40Ar/39Ar CO2 laser fusion upon LA-ICP-MS measurement of Pb isotopic composition of detrital K-feldspar

Abstract The information provided by detrital studies can be greatly enhanced by coupling geochronology and isotopic measurements from the same grains. While accessory minerals like zircon and apatite have been widely exploited in this regard, modal phases have been under-utilized. The benefits of using K-feldspar in detrital studies are twofold: K-feldspar 40Ar/39Ar has shown promise as a detrital thermochronometer and incorporation of common Pb into K-feldspar allows its Pb isotope composition to be used as a provenance tool. In this paper, we quantitatively investigate the effects of laser fusion during 40Ar/39Ar analyses of K-feldspar upon subsequent LA-ICP-MS measurement of Pb isotopic ratios. The results reveal that significant Pb volatilization occurs during laser fusion of K-feldspar. While Pb isotopes do not appear to be significantly fractionated, counting statistics suffer as Pb concentrations are lowered. Conversely, neutron irradiation appears to have a small though inconsequential impact upon Pb isotopic measurement of K-feldspar. Consequently, K-feldspar can be analyzed for Pb isotopes prior to total fusion 40Ar/39Ar analysis. Despite this artifact, coupled 40Ar/39Ar and Pb isotopic measurements constitute a promising approach for provenance studies that seek to constrain the geochemical nature and thermal evolution of basement source regions.

Potassium Distribution and Metasomatism In Pelites and Schists: How and When, Relation To Postdepositional Events

A large global database for over 9000 Archean to Holocene pelites in numerous basins has been developed to evaluate diagenetically unaltered and altered compositions. The mineralogy and geochemistry of Quaternary muds and ancient mudstones provide first-order controls on diagenetic potassium metasomatism in pelites. Clay mineralogy of Quaternary muds is dominated by smectite and kaolinite with minor detrital mica and illite. Thus, K2O is < 4%, K/Al is < 0.25, and K/Rb is < 220 in most Quaternary muds. With diagenetic alteration of clays to illite–smectite and illite, K2O content increases to 4–8% and K/Al rises to 0.2–0.5 or more. In extreme potassium metasomatism, authigenic K-feldspar develops. Sources of potassium are internal to shale–sandstone units wherein detrital K-feldspar is dissolved during diagenesis, providing K for clay illitization in closed-system (isochemical) alteration as in some Gulf Coast and North Sea Basin cases. Potassium in amounts greater than that available from closed-system alteration is provided from extraformational circulating brines in open-system diagenesis. K/Rb, with diagenesis, varies according to whether the metasomatizing fluid was relatively poor in Rb (seawater derived brines) or richer in Rb as in many hydrothermal waters. Diagenetic fluids may originate from seawater, or meteoric water enriched in cations by water–rock interactions along their subsurface migration paths and/or by dissolution of evaporites. Potassium metasomatizing fluids penetrate low-permeability pelites through faults, fractures, and microfractures and by diffusion in the mineral matrix. Typically, K-metasomatism, possibly with Pb, Zn, Cu, Ba, and F mineralization, occurs long after sediment deposition and burial at temperatures of 50° to 150°C+, related to tectonic activity and fluid movement. Different modes of metasomatism are recognized and correlated with geological setting. In the passive-margin Gulf Coast Tertiary basin, open-system K-metasomatism, where present, is limited to areas adjacent to steeply dipping growth faults which act as conduits for episodic pulses of altering fluids migrated upward from deeper basin sources. In contrast, widespread pervasive open-system K-metasomatism produced by continuous long-term gravity, advective, and diffusive flow of brine from the late Paleozoic Appalachian–Ouachita–Wichita Mountains highland to altered earlier Paleozoic shales plus sandstones, bentonites, and carbonates in the Illinois and Anadarko–Ardmore foreland basins. This mode of K-alteration following major mountain-building events is characteristic of many Precambrian and Paleozoic collision orogens and associated foreland basins. Another mode is in rift basins with no external drainage in which indigenous waters are evaporated to brines. These brines cause albitization of K-feldspar to yield potassium for illitization of detrital clays.

Provenance of detrital K-feldspar in Jianghan Basin sheds new light on the Pliocene–Pleistocene evolution of the Yangtze River

Research Article| September 01, 2016 Provenance of detrital K-feldspar in Jianghan Basin sheds new light on the Pliocene–Pleistocene evolution of the Yangtze River Zengjie Zhang; Zengjie Zhang 1School of Earth Sciences, China University of Geosciences, Wuhan 430074, China2UCD School of Earth Sciences and UCD Earth Institute, University College Dublin, Belfield, Dublin 4, Ireland Search for other works by this author on: GSW Google Scholar Shane Tyrrell; Shane Tyrrell 3Earth and Ocean Sciences, School of Natural Sciences, National University of Ireland, Galway, Ireland Search for other works by this author on: GSW Google Scholar Chang’an Li; Chang’an Li † 1School of Earth Sciences, China University of Geosciences, Wuhan 430074, China †chanli_cug@sohu.com Search for other works by this author on: GSW Google Scholar J. Stephen Daly; J. Stephen Daly 2UCD School of Earth Sciences and UCD Earth Institute, University College Dublin, Belfield, Dublin 4, Ireland Search for other works by this author on: GSW Google Scholar Xilin Sun; Xilin Sun 1School of Earth Sciences, China University of Geosciences, Wuhan 430074, China4Faculty of Earth and Life Sciences, Vrije Universiteit Amsterdam, De Boelelaan 1085, Amsterdam, Netherlands Search for other works by this author on: GSW Google Scholar Aoife Blowick; Aoife Blowick 2UCD School of Earth Sciences and UCD Earth Institute, University College Dublin, Belfield, Dublin 4, Ireland Search for other works by this author on: GSW Google Scholar Xu Lin Xu Lin 5Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China Search for other works by this author on: GSW Google Scholar Author and Article Information Zengjie Zhang 1School of Earth Sciences, China University of Geosciences, Wuhan 430074, China2UCD School of Earth Sciences and UCD Earth Institute, University College Dublin, Belfield, Dublin 4, Ireland Shane Tyrrell 3Earth and Ocean Sciences, School of Natural Sciences, National University of Ireland, Galway, Ireland Chang’an Li † 1School of Earth Sciences, China University of Geosciences, Wuhan 430074, China J. Stephen Daly 2UCD School of Earth Sciences and UCD Earth Institute, University College Dublin, Belfield, Dublin 4, Ireland Xilin Sun 1School of Earth Sciences, China University of Geosciences, Wuhan 430074, China4Faculty of Earth and Life Sciences, Vrije Universiteit Amsterdam, De Boelelaan 1085, Amsterdam, Netherlands Aoife Blowick 2UCD School of Earth Sciences and UCD Earth Institute, University College Dublin, Belfield, Dublin 4, Ireland Xu Lin 5Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China †chanli_cug@sohu.com Publisher: Geological Society of America Received: 23 Oct 2015 Revision Received: 10 Feb 2016 Accepted: 31 Mar 2016 First Online: 02 Jun 2017 Online Issn: 1943-2674 Print Issn: 0016-7606 © 2016 Geological Society of America GSA Bulletin (2016) 128 (9-10): 1339–1351. https://doi.org/10.1130/B31445.1 Article history Received: 23 Oct 2015 Revision Received: 10 Feb 2016 Accepted: 31 Mar 2016 First Online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Zengjie Zhang, Shane Tyrrell, Chang’an Li, J. Stephen Daly, Xilin Sun, Aoife Blowick, Xu Lin; Provenance of detrital K-feldspar in Jianghan Basin sheds new light on the Pliocene–Pleistocene evolution of the Yangtze River. GSA Bulletin 2016;; 128 (9-10): 1339–1351. doi: https://doi.org/10.1130/B31445.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract The Yangtze River is the largest fluvial system draining the Tibetan Plateau, yet its time of formation—pre-Miocene versus Pleistocene—has been debated for more than a century, with a particular focus on the incision of the Three Gorges. In this study, we used laser-ablation–multiple collector–inductively coupled plasma–mass spectrometry (LA-MC-ICP-MS) to measure Pb isotope compositions of detrital K-feldspars from Pliocene–Pleistocene sediments in the Jianghan Basin, located just downstream of the Three Gorges. Our new Pb results indicate that feldspars from the Songpan-Ganzi terrane were already being delivered to the Jianghan Basin by ca. 3.4 Ma. Therefore, we suggest that the Three Gorges was incised prior to the late Pliocene. Moreover, the Pb isotopic data also record the first delivery of detritus from the Hanjiang River, one of the Yangtze’s largest tributaries in the middle reaches, into the Jianghan Basin at ca. 1.8 Ma. Most K-feldspar grains from the mid-late Pleistocene samples have similar Pb isotopic compositions to those from the major tributaries in the upper reaches, i.e., Minjiang and Jialingjiang Rivers, indicating that the eastern Tibetan Plateau, as the major sediment supplier to the Jianghan Basin and mid-lower Yangtze River, has played a key role in the sediment source-to-sink transport of this river. This study sheds light on the factors that control the supply of detrital K-feldspar in large-scale drainage systems. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.