Pb Detrital Zircon Geochronology Research Articles

Provenance of Upper Paleozoic Sandstones from the Western Carpathians (Slovakia): Petrofacies analysis and U–Pb detrital zircon geochronology

Provenance of Upper Paleozoic Sandstones from the Western Carpathians (Slovakia): Petrofacies analysis and U–Pb detrital zircon geochronology

New paleofloristic and geochronological U–Pb zircon data in late Paleozoic deposits of the Matzitzi formation in southern Mexico

The fossil flora of the Matzitzi Formation, is a fluvial unit of late Paleozoic age exposed in southern Mexico, has been studied since the last century; however, the discovery of new plant elements during the last decade imposes a reevaluation of two aspects that have always been the subject of debate: the depositional age of the unit and the taxonomy of its paleoflora. The objective of the present work is to report new paleofloral records from two areas of the Matzitzi Formation as well as their chronological implications. The study sites are named Carretera and Coatepec. Nineteen genera and 11 species have been identified in beds from the Carretera site, whereas 23 genera and 16 species in beds from the Coatepec site. The analysis of floral assemblages of both sites shows that they share 49% of taxa. Ovopteris, Lesleya, Lobatopteris, and Trigonocarpus are unique to the Carretera site, while Coatepec is characterized by the presence of cf. Bjuvia, Schizoneura, and Velascophyllum. When analyzing the greatest ranges of the paleoflora awareness for the Carretera site indicates that deposition of these beds took place in a time interval that may span between Pennsylvanian and lower Permian. On the other side, the floral assemblage recovered from the Coatepec site indicates that the hosting beds were deposited in upper Permian time. U–Pb detrital zircon geochronology indicates that the maximum depositional age of the fossiliferous beds at the Carretera and Coatepec sites are of 276 ± 15 Ma and 254 ± 11 Ma, respectively. The integration of the paleontological and geochronological data obtained in this work suggests that the analyzed floral assemblage recovered from the Carretera site is of Kungurian age, whereas the one from the Coatepec site is of Lopingian age. Alternatively, we explore the possibility that deposits that are presently grouped within the Matzitzi Formation could be the vestiges of different fluvial cycles associated with different tectonic settings. Finally, the work on this unit has not finished, since there are still localities where its flora and age are still unknown.

Impact of sediment provenance and depositional setting on chlorite content in Cretaceous turbiditic sandstones, Norway

AbstractChlorite minerals, mainly in the form of clay coats, play a critical role in determining the reservoir quality of siliciclastic rocks. They can positively influence reservoir quality by preserving porosity during deep burial, but they can also play a negative role by reducing permeability through pore filling. The main aim of this research is to determine the optimal conditions for chlorite growth in sedimentary basins. This study investigates the Lower Cretaceous turbidite sandstone of the Agat Formation in the North Sea. We used a source‐to‐sink approach to investigate the impact of sediment source composition, chemical weathering and depositional environment on chlorite formation. Understanding the interplay between these processes can help refine exploration and exploitation strategies, optimise hydrocarbon recovery, and reduce exploration risks. Representative samples from two hydrocarbon fields (the Duva and Agat fields) were investigated using petrography, geochemistry, heavy mineral identification and quantification, and U–Pb geochronology of detrital zircons. Our results show a strong heterogeneity in the sediment provenance between the two turbidite systems. In the Duva field, the sandstone is derived from a mixture of mafic and felsic sources, producing Fe‐rich sediments. Intense chemical weathering generates fine fraction materials rich in kaolinite, vermiculite, and hydroxy‐interlayered clays, which are transported into shallow marine settings. Subsequent interaction with seawater results in the formation of glauconitic materials, Fe‐illite, and phosphatic concretions. These Fe‐rich materials are remobilised into deep marine settings, providing precursors for the development of authigenic Fe‐clays such as berthierine and chlorite. Conversely, in the Agat field, the sandstone is predominantly sourced from felsic rocks that underwent low chemical weathering, producing sediment rich in quartz and feldspar with a low amount of clays. With few Fe‐rich materials transported into the basin, the development of chlorite in the Agat field was less pervasive. Basin configuration and depositional environment exerted additional control on chlorite distribution. In the confined turbidite system (e.g. Duva field), chlorite is typically found as coating, whereas in less confined turbidite systems (e.g. Agat field) chlorite shows complex distribution related to depositional environment and dewatering processes. Our findings demonstrate the importance of considering the entire sediment routing system, from source to sink, when predicting chlorite occurrence and its impact on reservoir quality in deep marine settings. This integrated approach can guide exploration and development efforts in deepwater clastic reservoirs.

Early development of the Patagonian fold and thrust belt and the onset of foreland sedimentation in the Austral-Magallanes basin

Retroarc basins register the onset of compressional exhumation during the Cretaceous in the Andes, evidenced by sequences showing sedimentary provenance from the orogen. We present U–Pb detrital zircon geochronology from the Austral-Magallanes basin in the Southern Patagonian Andes (∼47–48°SL), where the foreland stage began in the Early Cretaceous. The littoral sandstones from basal foreland sequences of the Río Belgrano Formation yield ∼123 Ma maximum depositional ages, confirming previous studies that the basin infill is early Aptian. The detrital zircon ages showed two main clusters of 129-115 Ma and 151 -140 Ma, that are derived from the coetaneously exhumed Andean arc and earlier Jurassic magmatic sources. The zircons which overlap with ages of Upper Jurassic Andean synrift volcanics, confirms orogenic exhumation coeval with sedimentation. A sequence of retroarc volcanism dated between 119 and 97 Ma overlies the basal foreland littoral-continental deposits, and it is followed by a Late Cretaceous-Paleocene hiatus. Further analysis of detrital zircons ages distribution and geological considerations, indicates that the studied northern depocenter was a source region of sedimentary supply after its Cenomanian exhumation.

A revised Proterozoic tectono-stratigraphy of the South Nicholson region, Northern Territory, Australia—insights from SHRIMP U–Pb detrital zircon geochronology

New SHRIMP U–Pb detrital zircon geochronology on Mesoproterozoic and Paleoproterozoic siliciclastic rocks from the South Nicholson region, in concert with recently acquired complementary regional geophysical datasets, have enabled comprehensive revision of the regional Proterozoic tectono-stratigraphy. The identification of analogous detrital zircon spectra of units deposited in half-graben hanging walls of major east-northeast-trending extensional faults, offers compelling evidence for regional tectono-stratigraphic correlation. This study sampled units from the hanging walls of the Benmara, Bauhinia, and Maloney-Mitchiebo (east-northeast-trending) faults, which identified immature proximal lithofacies hosting a small yet persistent population of ca 1660–1640 Ma aged zircon and lack Mesoproterozoic detritus. The timing of this event is consistent with deposition coincident with crustal extension during the extensional River Event at ca 1640 Ma, an event previously identified from the Lawn Hill Platform in western Queensland. This finding suggests the hanging wall sequences are chrono-stratigraphically equivalent to the highly prospective sedimentary rocks of the Isa Superbasin, host to world-class sediment-hosted base metals deposits across western Queensland and northeastern Northern Territory. Subsequent inversion of the extensional faults resulted in development of south-verging thrusts, and exhumation of late Paleoproterozoic hanging wall siliciclastic rocks through overlying Mesoproterozoic South Nicholson Group rocks as fault propagated roll-over anticlines. These geochronology data and interpretations necessitate revision of the existing stratigraphy and the renaming of a number of stratigraphic units in the South Nicholson region. Accordingly, the distribution of the highly prospective late Paleoproterozoic units of the McArthur Basin, Lawn Hill Platform and Mount Isa Province is greatly expanded across the South Nicholson region. These findings imply that the underexplored South Nicholson region is a highly prospective greenfield area for energy and mineral resources. KEY POINTS SHRIMP U–Pb detrital zircon geochronology provides a basis for revision of the Proterozoic stratigraphy in the South Nicholson region. Correlation of sedimentary units across the region is based on closely matching zircon age spectra, lithofacies and tectono-sedimentary setting. Revision of the Proterozoic stratigraphy increases the prospectivity for sediment-hosted base metal resources across the South Nicholson region.

Origin, timing and paleogeographic implications of Paleogene karst bauxites in the northern Transdanubian range, Hungary

Paleogene karst bauxites in the northeastern Transdanubian Range and their cover sequences provide valuable sedimentary archives, despite their weathered nature and vague paleontological records. U–Pb detrital zircon geochronology combined with heavy mineral analysis indicates ‘local’ Alpine aeolian and fluvial sources and ‘distant’ aeolian sources connected to the Bohemian Massif. Records of episodic Paleogene volcanic eruptions related to igneous complexes of the Adamello and probably also the Bergell, Recsk and Balkan Peninsula, are reflected by euhedral zircon crystals. Their U–Pb geochronology supplies age constraints for the phases of subaerial exposure of the karstic surface and the accumulation of bauxitic protoliths and helps to improve the existing stratigraphic records and to define stages of denudation in the northeastern Transdanubian Range. Distinct phases of subaerial exposure and accumulation of the bauxite's protoliths are identified as ca. 42, 35 and 31 Ma; alternating with episodes of subsidence, represented by siliciclastic and carbonatic sequences at ca. 38, 32 and 31 Ma. Besides Paleogene volcanism, zircon dating also revealed contributions from the Middle Triassic tuffs of the Transdanubian Range. Garnet, epidote, kyanite, staurolite, and xenotime/monazite crystals suggest fluvial drainage of diverse metamorphic units of the Austroalpine basement from the Eastern- and Southern Alps, which also supplied most of the pre-Mesozoic zircons. However, the unexpectedly high proportion of Variscan ages in the bauxites most likely relate to igneous rocks of the Bohemian Massif, thus suggesting additional long-distance aeolian sources. The new data allow for detailed reconstructions of the Paleogene evolution and palaeogeography of the northeastern Transdanubian range.

Provenance of the Late Cretaceous Pab Formation, Sulaiman fold‐thrust belt, Pakistan: Insight from the detrital zircon U–Pb geochronology and sandstone petrography

This study provides an insight to the provenance of the Late Cretaceous Pab Formation exposed in the Sulaiman fold‐thrust belt, Pakistan. The methodology adopted consisted of sandstone petrography and U–Pb detrital zircon geochronology. The sandstone petrography indicates craton interior and recycled orogenic provenances that points to an Indian provenance. The observed basaltic lithics were possibly derived from Rajmahal traps instead of Deccan traps, supported by younger detrital age. The detrital zircon ages exhibit a resemblance to the central and southern Indian provenances, while some detritus also matches the age spectrum of Tethyan Himalayas (~400–800 Ma). Combining sandstone petrography and U–Pb geochronology results, it is suggested that in the Late Cretaceous time, the sediments were mainly fed by the southern and central sources of the Indian Craton. This provenace is possible, as during the Cretaceous time, thermal doming of Indian Plate in the southern part occurred when it was passing over a mantle hotspot. This movement over the hotspot uplifted the southeastern region and increased sediment supply from southern and central Indian provenances and deposited along the western margin as the Pab Formation.

U–Pb detrital zircon geochronology and source provenance in the Moroccan Meseta (Variscan belt): A perspective from the Rehamna massif

Metasandstones from early Cambrian to early Carboniferous stratigraphic successions were sampled in the Rehamna massif of the Western Meseta in Morocco. The early Cambrian sample shows a single Paleoproterozoic population at ca. 2 Ga suggesting a local basement source. The Ordovician sample is largely dominated by a Cryogenian-Ediacaran population and minor Paleoproterozoic peaks. The Devonian sample reveals age populations similar to North-West African Cambrian to Devonian age spectra indicating that the southern-derived West Gondwana source essentially pertained up to the Devonian. The two early Carboniferous samples show more heterogeneous zircon age spectra with a marked Ediacaran peak accompanied by Paleoproterozoic and Mesoproterozoic sub-peaks indicating important re-organization of the drainage systems. One sample also shows presence of Upper Devonian to early Carboniferous zircon grains, which suggests local magmatic sources associated to the formation of intracontinental extensional basins. The comparison of detrital zircon spectra with paleogeographic reconstructions indicate that the early Carboniferous change in detrital zircon sources can be interpreted in the framework of the opening of the Paleotethys ocean with coeval erosion of orogenic topographies linked to the emplacement of a Mid-Variscan Allochthon, and/or collision of an Avalonian indenter to the north.

Provenance and Palaeogeomorphology study of the southwestern North China Craton during Middle-Late Triassic and its geological implication

ABSTRACT The study of tectonic, provenance, and paleogeomorphologic systems is important for defining the basin evolution and it is also the basis for the accurate evaluation of oil and gas potential of a basin. The provenance and paleogeomorphology of the western Ordos Basin and the Hexi Corridor in the southwestern North China Craton(sw-NCC) have long been debated. In this study, detrital zircon geochronology, petrography and geochemistry methods are used to analyse the evolution of provenance and paleogeomorphology in the sw-NCC during the Middle–Late Triassic, and the provenance and paleogeomorphic relationships with tectonic events are discussed. The U–Pb detrital zircon geochronology of the Yaoshan samples in the western Ordos Basin are clear and consistent, and shows that there are three major age populations, 2700–2200 Ma, 2150–1650 Ma and 450–220 Ma. While the age spectrums of the samples from different formations in the Hexi Corridor are complex, showing significant differences. The whole results imply that the Hexi Corridor and the west margin of the Ordos Basin had a unified source during the Middle Triassic, which is the western NCC. However, in the Late Triassic, the sediment of the Hexi Corridor was mainly from the Qilian–Qaidam Terrane while the source of the western Ordos Basin remained unchanged. Besides the provenance analysis, the stratigraphic correlation, petrology and geochemistry analyses also support that the Hexi Corridor was temporarily connected with the Ordos Basin during the Middle Triassic but was separated from the Ordos Basin by a small-scale, underwater paleo-uplift during the Late Triassic. The evolution of the provenance and paleogeomorphology in the southwestern Ordos Basin was related to the closure of the shallow shelf of the Paleo-Tethys Ocean.

Crustal stabilization: Evidence from the geochemistry and U–Pb detrital zircon geochronology of quartzites from Simlipal Complex, Singhbhum Craton, India

Cratonic stabilization was a critical crustal process during the Hadean to Archean for the formation of cratons. The understanding of how and where this process took place is significant to evaluate the architecture of continents. The Singhbhum Craton of eastern India has well preserved Precambrian volcano-sedimentary sequences. The Simlipal volcano-sedimentary complex of Singhbhum Craton consists of circular bands of mafic volcanic rocks interlayered with quartzites/ shales/phyllites. In the present study, we report petrographic and geochemical characteristics of quartzites from Simlipal Complex coupled with U–Pb ages of detrital zircons and zircon geochemistry to understand the provenance and depositional conditions and its connection with the crustal stabilization in the Singhbhum Craton. The quartzites are texturally mature with sub-angular to sub-rounded quartz grains followed by feldspars embedded in a silty matrix. Based on modal compositions and major element ratios, these quartzites are categorized as quartz arenite and sub-lithic arenites. Trace element abundances normalized to Archean Upper Continental Crust (AUCC) display positive anomalies at U, Zr, Hf and negative anomalies at Nb. REE patterns are characterized by negative Eu anomalies (Eu/Eu* = 0.47–0.97) and flat HREE suggesting felsic provenance. These quartzites show depletion of LILE, enrichment of HFSE and transition metals relative to AUCC. High weathering indices such as CIA, PIA, and ICV are suggestive of moderate to intense chemical weathering. Low trace element ratios such as Th/Cr, Th/Sc, La/Sc, La/Co and Th/Co indicate a predominantly felsic source for these rocks. The overall geochemical signatures indicate passive margin deposition for these quartzites. Detrital zircons from the Simlipal quartzites yield U–Pb ages 3156 ± 31 Ma suggesting Mesoarchean crustal heritage. The trace element geochemistry of detrital zircons suggests that the zircons are magmatic in origin and possibly derived from the 3.1 Ga anorogenic granite/granitoid provenance of Singhbhum Craton. These observations collectively indicate the Mayurbhanj Granite and Singhbhum Granite (SBG-III) provenance for these quartzites, thereby tracking the stabilization of the eastern Indian Shield/Singhbhum Craton back to Mesoarchean.

Was there an exchange of detritus between the northern and southern Black Sea terranes in the Mesozoic-early Cenozoic?

Resolving the time of rifting of the Black Sea basin is critical to reconstructing the tectonic evolution of the Pontides arc in northern Turkey. U–Pb geochronology of detrital zircons from Middle Jurassic, Upper Cretaceous, and lower Eocene formations in the Eastern Pontides (NE Turkey), as well as published data from circum-Black Sea terranes, reveals that sediments preserved along with the northern (East European Craton-Scythian Platform) and southern (Eastern and Central Pontides-southern flank of the Greater Caucasus-Transcaucasus) margins of the Eastern Black Sea basin display distinct detrital provenances. The U–Pb detrital zircon ages of the sedimentary samples from the Eastern Pontides have distinct populations with ages of ~650–540, ~200, ~170, ~80, and ~50 Ma. In contrast, the ages of the sedimentary samples from the northern Black Sea terranes are characterized by age peaks of ~1400 and ~1100 Ma compared to those of the Eastern Pontides. Only a few detrital zircons in the range of ~650–540 Ma and <200 Ma are identified in the sedimentary samples from the northern Black Sea terranes. This contrast in detrital zircon ages, together with modal analysis of the samples and published paleocurrent data, suggests that Middle Jurassic–lower Eocene sedimentary samples in the Eastern Pontides were locally sourced from Gondwana affinity crustal basement rocks and associated Mesozoic–Cenozoic igneous rocks. Furthermore, there was no exchange of detritus across the Eastern Black Sea basin during the Middle Jurassic–early Eocene. These inferences require the Eastern Black Sea basin to have rifted in a back-arc setting behind the Eastern Pontides arc by the Middle Jurassic or survived as a relict basin of the Paleotethys.

A revised Permian–Triassic stratigraphic framework for the northeastern Galilee Basin, Queensland, Australia, and definition of a new Middle–Upper Triassic sedimentary unit

The upper Paleozoic–lower Mesozoic strata in the northeastern Galilee Basin are important for their hydrocarbon and groundwater potential; however, despite numerous previous investigations, the nature of this stratigraphic interval remains enigmatic. This study integrates lithostratigraphy, palynology and U–Pb zircon geochronology of well-exposed Permian and Triassic sedimentary rocks and nearby stratigraphic cores from the Hughenden district to determine their maximum depositional ages and then revises the stratigraphy where necessary. The newly defined Galah Tuff Bed was discovered at the top of the Betts Creek beds in Porcupine Gorge and was dated at 251.9 ± 3 Ma. This provides an important age constraint for the Betts Creek beds and is a tie-point for correlations with coeval units in the adjacent Bowen Basin and the Sydney and Gunnedah basins to the southeast. The Galah Tuff Bed is interpreted to correlate with the Yarrabee Tuff in the Bowen Basin. Unconformably overlying the Betts Creek beds is a newly recognised stratigraphic unit, defined herein as the Porcupine Gorge Formation. Detrital zircon maximum depositional ages and palynology indicate a significant depositional hiatus of up to 20 million years between the Betts Creek beds and Porcupine Gorge Formation. The hiatus indicates that the lower part of the Porcupine Gorge Formation is at least upper Middle Triassic, whereas the upper part of the unit extends into the Late Triassic. This age also constrains the overlying Warang Sandstone, which is considerably younger locally than previously reported and is likely diachronous across the northeastern Galilee Basin. KEY POINTS An integrated lithostratigraphy, palynology and U–Pb detrital zircon geochronology methodology is applied to the Permian–Triassic succession the northeastern Galilee Basin. Two new stratigraphic units were recognised: the upper Permian Galah Tuff Bed (251.9 ± 3 Ma) and the late Middle–Late Triassic Porcupine Gorge Formation (238.7 ± 3 Ma). The Galah Tuff Bed, correlative of the Yarrabee Tuff in the Bowen Basin, is evidence for widespread volcanism in the late Permian. The age of the Porcupine Gorge Formation indicates diachroneity of the Triassic succession in the Galilee Basin, warranting further examination.

Tectono-sedimentary evolution of the Paleoproterozoic succession of the Carajás Basin, southeastern Amazonian Craton, Brazil: Insights from sedimentology, stratigraphy, and U–Pb detrital zircon geochronology

The Carajás Basin, situated in the southeastern Amazonian Craton in northern Brazil, hosts a > 6 km thick pile of volcano-sedimentary rocks deposited from the Neoarchean to the early Paleoproterozoic eras (ca. 2.75–2.06 Ga). It is claimed that this basin started as a rift configuration in which volcanic and banded iron formation strata were deposited during the Neoarchean Era. However, the tectono-sedimentary evolution of this basin through the Paleoproterozoic Era remains unexplored. Based on a sedimentological, stratigraphic, and U–Pb detrital zircon geochronological investigation of a marine to a fluvial succession of this basin, this study suggests that the Carajás Basin evolved in a foreland setting during the early Paleoproterozoic Era. Probably, the Carajás Foreland Basin was sedimented in the underfilled stage (ca. 2.5–2.3 Ga) by deep-marine strata (i.e., glaciogenic submarine fan deposits), likely from the Siderian–Rhyacian Serra Sul Formation. Subsequently, shallow-marine deposits of the Azul Formation were deposited in the filled stage (ca. 2.3–2.1 Ga), followed by deposition of the fluvial to alluvial deposits of the Águas Claras and Gorotire formations during the overfilled stage (ca. 2.1–1.9 Ga). The Azul and Águas Claras formations were supplied mainly by Meso- to Neoarchean source rocks, whereas Paleoproterozoic and Paleoarchean rocks played the role of a subordinate source of sediments. The youngest U–Pb age cluster, at ca. 2.27 Ga, is interpreted as its maximum depositional age. In terms of paleogeography, the occurrence of Rhyacian zircon grains in the Azul Formation deposits suggests, at least partially, a connection between the Carajás Protocontinent with the Bacajá Domain during that period. The integrated data corroborate the hypothesis that the foreland basin was formed in a scenario of collision between the Bacajá Domain and the Carajás Protocontinent during the Transamazonian Cycle. These dramatic upheavals are directly related to the configuration of the Columbia Supercontinent, which initially led to the emergence of the Carajás Foreland Basin, and soon after, the cratonization of proto-Amazonia

U–Pb geochronology of detrital zircons from San Carlos Basin, Costa Rica: Evidence of Miocene volcanism and implications for the Precambrian and Paleozoic history of the Central American isthmus

U–Pb geochronology on detrital zircons from the Neogene sediments of San Carlos Basin in Costa Rica, yielded a wide range of ages, from Paleoproterozoic to Cenozoic. The most representative is the Miocene population, constrained to a maximum depositional age of 6.9 ± 0.2 Ma. It reflects the local volcanic activity of the evolving island arc and late Miocene to Pliocene basin sedimentation. Cenozoic ages vary from ca. 5.8–56.1 Ma and Mesozoic ages from ca. 68.9–243 Ma. Other zircon grains yielded a variety of older ages: Paleozoic (ca. 264.9–536.5 Ma) and Proterozoic (ca. 552–1910 Ma). Such ages previously undiscovered in Costa Rica bring new insights on provenance and indicate multistage zircon recycling from a variety of sources. The presence of pre-Mesozoic detrital zircons indicates the influx of recycled sediments from older units (continental and sedimentary rocks), possibly from exhumed Precambrian and Paleozoic continental terranes or blocks from the north of Central America (Chortís and Patuca) in Guatemala, Honduras, north of Nicaragua, and probably from southern México.

On the timing and metallogenic implications of the sediment-hosted stratiform copper–silver mineralization in the Creston Formation (Belt-Purcell Supergroup), British Columbia, Canada

Sediment-hosted stratiform copper–silver mineralization is common in Middle Creston strata of southeastern British Columbia, a correlative lithostratigraphic unit of the Ravalli Group of western Montana. The Ravalli Group hosts the largest sediment-hosted stratiform copper–silver deposits of the Belt-Purcell Supergroup. Strata of the Belt-Purcell Supergroup accumulated between ~1540 and 1300 Ma in a pericratonic rift basin (Belt-Purcell basin) constructed over Archean and Paleoproterozoic blocks of Laurentia. The basin underwent several events of deformation and metamorphism at ~1380–1325 Ma (East Kootenay orogeny), ~1200–1000 Ma (Grenvillian), and 900–800 Ma (Goat River orogeny) prior to Meso-Cenozoic Cordilleran tectonism. U–Pb geochronology of detrital zircons from Middle Creston rocks define a maximum age of deposition of ~1470 Ma, in agreement with the established age range for the Belt-Purcell Supergroup in southeastern British Columbia. Molybdenite is locally part of the sediment-hosted stratiform copper–silver mineralization in the region, either as isolated grains within mineralized strata or in paragenetic sequence with the cupriferous sulfides. Re–Os geochronology on molybdenite reveals repetitive episodes of fluid flow through Middle Creston strata in the study area, with principal events at 1170–1140 and 1043–990 Ma. Paragenetically constrained molybdenite, in growth sequence with bornite and chalcocite, yields an age of 1043 ± 6 Ma. Hence, the fluid responsible for the sediment-hosted stratiform copper–silver mineralization in southeastern British Columbia permeated the host sequence ~440 m.yr. after its deposition, coincident with the Grenville-age metamorphic event at ~1200–1000 Ma. Such tectono-thermal activity extended along the western margin of Laurentia beyond the limits of the Belt-Purcell basin, and was a far-field response to orogen-scale collisions taking place off Laurentia during Rodinia assembly.

Sedimentology and provenance of the Lower Old Red Sandstone Grampian outliers: implications for Caledonian orogenic basin development and the northward extension of the Midland Valley Basin

Reconstructing regional geological histories is challenging where basins have limited and/or fragmentary preservation. Several isolated outlier basins of Lower Old Red Sandstone (LORS) occur on the Scottish Grampian terrane; however, their sedimentology and relationship to other similar-aged LORS deposits has been poorly constrained, as has their significance in the wider Caledonian orogenic framework. Here we present a combination of new sedimentological and multidisciplinary provenance analyses for the LORS outliers at Aberdeen, Cabrach, New Aberdour, Rhynie and Tomintoul. Three facies associations are identified, the deposits of locally derived conglomeratic alluvial fans, which pass upward into fluvial channel and floodplain facies associations. Provenance data from conglomerate clast populations, sandstone petrography, heavy mineral assemblages, and U–Pb detrital zircon geochronology indicate derivation from the surrounding Dalradian Supergroup, with local influence from contemporaneous volcanic or plutonic lithologies. These data suggest a similar provenance to that of the northern Midland Valley Basin LORS, and a direct relationship between the LORS north and south of the Highland Boundary Fault. This indicates that the preserved outliers represent fragments of wider, unpreserved LORS cover that accumulated between the late phases of the Caledonian Orogeny and onset of post-orogenic collapse in the Mid-Devonian.

Provenance of metasedimentary rocks of the western Dom Feliciano Belt in Uruguay: Insights from U–Pb detrital zircon geochronology, Hf and Nd model ages, and geochemical data

New isotopic and geochemical data for the Paleo- Meso- and Neoproterozoic metasedimentary cover of the southern Dom Feliciano Belt (Brasiliano/Pan-African) are presented and evaluated combined with published information. Whole-rock major and trace element geochemistry indicates that the dominant source for all the units had a composition similar to average upper continental crust. The geochemistry is similar even for late Ediacaran successions with a source component from slightly older Ediacaran granites, due to the crustal origin of these granites. Age constraints based on detrital zircon, fossil content, interbedded volcanic rocks and isotope geochemistry confirm Paleo-, Meso-, and Neoproterozoic successions, despite uncertainties remain in some cases. Detrital zircon data show the dominance of Archean (3.3–2.8 Ga) to Paleoproterozoic (2.2–1.9 Ga), and subordinated Mesoproterozoic (1.5–1.3 and 1.1 Ga) and Neoproterozoic (0.5–0.6 Ga) ages. Lu–Hf zircon and Sm–Nd whole-rock model ages confirm that the Archean and the Paleoproterozoic were the major crustal growth periods for the source areas. U–Pb detrital zircon age distributions and model ages demonstrate that the Nico Pérez Terrane and not the Río de la Plata Craton was the source for most metasedimentary rocks of the western Dom Feliciano Belt. Likewise, comparison of Archean, Paleo-, Meso- and Neoproterozoic events supports that the Nico Pérez Terrane could represent a fragment of the Congo Craton.

Elemental and isotopic compositions of trench-slope black shales, Bohemian Massif, with implications for oceanic and atmospheric oxygenation in early Cambrian

This study examines a lower Cambrian pyrite-bearing black shale–graywacke succession in the Czech Republic interpreted as infill of a deep-marine, extensional trench-slope basin on top of an accretionary wedge that developed during subduction of an oceanic plate beneath the northern margin of Gondwana. The new U–Pb detrital zircon geochronology of the graywacke constrains the maximum age of deposition to 533 +5/−6 Ma, whereas the Re–Os dating of pyrite yielded a younger age of 507 ± 16 Ma. Distribution of major and trace elements and calculated enrichment factors (EF) indicate that this succession was deposited under changing redox conditions over a short time span and that the basin was presumably controlled by tectonic subsidence and varying supply of terrigenous arc-derived material. This depositional setting is reflected by largely variable EFs and δ98Mo and δ53Cr values. Euxinic conditions detected at the base of the sampled black shale interval are documented by the highest values of EFs of redox-sensitive metals (e.g., Mo, U, V, Ni, Co, As) and also the Corg/P (>1000) and DOPT (>0.7) values. Black shales show lower δ56Fe values due to the excess of authigenic pyrite-Fe with a mean δ56Fe value of −0.02‰ over detrital Fe in graywacke with a mean δ56Fe value of +0.25‰. However, the Fe isotopic signatures of the black shales are not consistent with iron shuttling, mixing of authigenic and detrital sources, or hydrothermal metal enrichment. Instead, they most likely resulted from partial oxidation of pyrite through the syndepositional oxidizing hydrothermal fluids (Si–Ba enrichment), which resulted in precipitation of isotopically heavy Fe-oxyhydroxides. We propose that our maximal recorded δ98Mo value (+ 0.98‰) might represent the best estimate for the ancient local seawater Mo composition at around 533 Ma and argues against deep-ocean oxygenation in the early Cambrian. On the other hand, the Se/Co ratios of synsedimentary pyrite indicate a mean atmosphere O2 value of ~27%.

Stratigraphy and U–Pb detrital zircon provenance, Crixás Greenstone Belt, Goiás-Brasil: Gold-bearing vs barren siliciclastic rocks

The Crixás Greenstone Belt, located in an Archean-Paleoproterozoic terrane within the Neoproterozoic Tocantins Province, hosts an important gold deposit in Brazil with an endowment of 7 Moz currently operated by AngloGold Ashanti. Its stratigraphy is composed of an Archean komatiite and basalt basal sequence followed by a Paleoproterozoic sedimentary sequence composed of carbonaceous phyllites, dolomite-rich marbles with minor siliciclastic lenses (Ribeirão das Antas Formation) followed by a uniform siliciclastic sequence (Córrego Geral Formation). At the mining area, the entire sequence is stratigraphically overturned and metamorphosed under greenschist to lower amphibolite facies conditions. The orebodies are structurally controlled by thin-skinned low-angle thrust faults, and are mainly hosted by the sedimentary sequence in dilation zones named locally, from the shallowest to the deepest, as Structure Palmeiras, Structure IV and Structure III. The gold mineralization occurs in association with disseminated sulfides, massive sulfide lenses or quartz veins. Structure III is the deepest mineralized structure with gold mostly occurring in quartz veins cutting carbonaceous phyllites. Siliciclastic lenses occurring within the Structure III interval show variable gold grades, while siliciclastic rocks from the uniform deeper sequence just below Structure III are barren. The chronology of the sedimentary deposition, metamorphism and mineralization is still poorly understood. Detailed drill core logging, petrography and U–Pb geochronology of detrital zircons from siliciclastic rocks were carried out in order to better understand the relationship between the two metasedimentary packages and gold distribution. Petrographically there are no relevant differences between Au-bearing siliciclastic rocks (Ribeirão das Antas Formation) and barren siliciclastic rocks (Córrego Geral Formation), except for the presence of sulfides in the former. The new dataset of detrital zircon U–Pb ages revealed a ubiquitous Paleoproterozoic peak in all samples, with nearly no Archean contribution. K-feldspar and lithic angular fragments, zircons with low to medium roundness, and the U–Pb results indicate a Rhyacian provenance from a proximal source. Neoproterozoic overgrowths are found on detrital zircons from the barren siliciclastic interval of the Córrego Geral Formation, providing unequivocal evidence of a Neoproterozoic event around 600 Ma that affected the rocks. The Neoproterozoic partial reset, possibly related to the overriding of the Mara Rosa Magmatic Arc onto the Crixás Greenstone Belt, is unlikely to be linked to the mineralization considering that zircons from the barren rocks are the most thermally affected by this event. The Au mineralization is more likely related to Paleoproterozoic events, a time period known as a major global episode of orogenic gold deposit formation.

Provenance of late Paleozoic glacial/post-glacial deposits in the eastern Chaco-Paraná Basin, Uruguay and southernmost Paraná Basin, Brazil

The Paraná Basin, Brazil and the Chaco-Paraná Basin, Uruguay both contain sedimentary records that are critical to reconstructing late Paleozoic ice centers in central Gondwana. The orientations of subglacial landforms and glaciotectonic structures suggest that late Paleozoic glacial deposits in the eastern Chaco-Paraná Basin and the southernmost Paraná Basin are genetically related, as they were likely glaciated by the same ice center. However, the location and extent of the ice center responsible for depositing these sediments are unclear. Furthermore, changes in sediment dispersal patterns between glacial, inter-glacial, and post-glacial intervals are not understood for this region of Gondwana. Therefore, this study utilized U–Pb detrital zircon geochronology to assess the provenance of glacial and post-glacial sediments from the eastern Chaco-Paraná Basin (San Gregorio, Cerro Pelado, Tres Islas Formations) and the southernmost Paraná Basin (Itararé Group). Results show dominant age peaks at ~520–555 Ma, ~625 Ma, 750–780 Ma, and 900–1000 Ma in all samples from the eastern Chaco-Paraná Basin. These zircons are interpreted to have been derived from sources in the Cuchilla Dionisio Terrane and Punta del Este Terrane in southeastern Uruguay, and possibly the Namaqua Belt in southern Namibia. Another important source was likely Devonian sedimentary rocks of the Durazno Group in central/eastern Uruguay. Meanwhile, a sample of the glaciogenic Itararé Group from the southernmost Paraná Basin contains a different detrital zircon signature with peaks at ~580 Ma, ~780 Ma, ~2110 Ma, and ~2500 Ma that closely resembles underlying sedimentary and meta-sedimentary rocks of the Precambrian/Cambrian Camaquã Basin. Detrital zircon ages in the glacial and post-glacial sediments indicate that local sources were dominant. In contrast, zircon ages from relatively ice-distal glaciomarine intervals in the Chaco-Paraná Basin reflect more distal sources to the east and southeast, which indicates a larger drainage catchment opened when glaciers retreated and/or the zone of maximum subglacial erosion shifted. Although most zircon ages in the Chaco-Paraná Basin can be attributed to Uruguayan sources, results support the hypothesis that glaciers emanated from southern Namibia and southeast Uruguay into the Chaco-Paraná Basin. From there, ice flowed northwest into the Paraná Basin and then receded back towards Africa as the paleoclimate warmed. The detrital zircon inventory in our study region is distinct from the eastern Paraná Basin, suggesting at least two unique African source regions for glaciers that deposited sediments in the Paraná and Chaco-Paraná Basins.