Provenance of the Mesozoic Succession of Franz Josef Land (North‐Eastern Barents Sea): Paleogeographic and Tectonic Implications for the High Arctic

Study of the Mesozoic succession of Franz Josef Land (FJL) has shed new insights on the stratigraphy and geological history of the neighboring portion of the Arctic. Based on the composition of pebbles and cobbles from Lower Jurassic conglomerates, we suggest that the pre‐Mesozoic stratigraphy of the NE Barents Sea comprises Cambrian metasandstones intruded by Late Paleozoic granites and overlain by Carboniferous–Permian sedimentary deposits. U‐Pb and ZHe ages of detrital zircons from Uppermost Triassic–Lower Cretaceous strata of FJL reveal Precambrian to Early Mesozoic grains. The most abundant Late Paleozoic detrital zircon population suggests the existence of the same in age magmatic events in the provenance area. ZHe ages show Late Triassic (ca. 225 Ma) exhumation of the provenance area. Moreover, the youngest grains of detrital zircons are Middle‐Late Triassic in age pointing that significant uplift of provenance coincides with magmatic activity. Based on these data, we suggest that the provenance area for Triassic–Lower Cretaceous strata of FJL was characterized by a similar geological composition, as well as magmatic and tectonic history, to the Taimyr fold‐and‐thrust belt and Kara terrane. A comparison of detrital zircon data from coeval strata elsewhere in the Arctic realm suggests that this eastern provenance area was actively sourcing sediments right across the Barents Sea Basin, and possibly as far as the Sverdrup basin, during the Latest Triassic–Jurassic. The period of Late Triassic uplift represented a significant tectonic event across the north‐eastern Barents Sea, and likely initiated an increase in sediment supply and a reorganization of pre‐existing sediment transport pathways.

understanding the provenance for Mesozoic rocks of FJL in order to understand Mesozoic paleogeography of the entire Arctic realm, since FJL was located in close proximity to these other Arctic regions before opening of the North Atlantic and Eurasia Basin during the Cenozoic. Previous provenance studies of the Russian Barents Sea have focused on Middle Triassic-Jurassic rocks of the Severnaya and Heiss Wells (FJL) Soloviev et al., 2015), as well as Triassic-Jurassic rocks collected from wells drilled in the eastern part of the basin . Moreover, there is no published data on the exhumation history of Mesozoic rocks in this region.
Here we present new detrital zircon U-Pb and (U-Th)/He (ZHe) age data from the Triassic-Cretaceous strata of FJL. We also present new data on the age of the pre-Mesozoic succession of FJL and surrounding portion of the Barents Sea, based on detailed petrography, geochemistry and U-Pb dating of pebbles and cobbles collected from the uppermost Triassic-Lower Jurassic conglomerates. The main aims of our study are: (a) Identify the age and composition of the pre-Mesozoic stratigraphy of FJL and surrounding portion of the Barents shelf, as well as coeval tectonic events, (b) Determine the provenance area and tectonic events based on U-Pb and (U-Th)/He dating of detrital zircons from the Triassic-Cretaceous sedimentary succession of FJL, (c) Compare the distribution of detrital zircons in Mesozoic rocks from FJL with coeval rocks from elsewhere in the Arctic, to provide new insights on Mesozoic paleogeography of this complex and poorly studied region.

Tectonic Setting
FJL is located along the north-eastern margin of the Barents Sea basin. The vast Barents and Kara continental shelves supposedly comprise Neoproterozoic and Paleozoic basement domains (Drachev, 2016;Drachev et al., 2010;Henriksen et al., 2011;Pease et al., 2014;Vernikovsky et al., 2013 and references therein) ( Figure 1c). However, a thick overlying sedimentary cover is preserved in a series of large offshore and onshore basins separated by local uplifts (Drachev, 2016;Henriksen et al., 2011). The East Barents Megatrough dominates the Russian Barents Sea, extending over 1,000 km in a north-south direction and 400-450 km in an eastwest direction (Drachev, 2016). The age and continuation of different basement structural domains across the Barents and Kara seas are still debated (e.g., Drachev, 2016;Henriksen et al., 2011 and references therein). The western part of the Barents continental shelf comprises a Caledonian basement (Early Paleozoic) (Drachev, 2016;Gee et al., 2008 and references therein), transitioning to a Timanian basement (latest Precambrian-Early Cambrian) across the eastern Barents shelf. However, there are several differing tectonic models concerning the basement structure of the Barents shelf. Some models suggest that Svalbard represents the eastern limit of the Caledonian deformation front, while other models suggest that Caledonian deformation extended as far east as Novaya Zemlya or even further east to the Kara shelf (see detailed discussion in V. Ershova et al., 2018).
The Kara terrane (also known as North Kara terrane) comprises the northern part of the Kara continental shelf and is believed to comprise a Timanian basement (Drachev, 2016;Drachev et al., 2010;Lorenz et al., 2007;Pease et al., 2014;and references therein). The Kara shelf region was significantly affected by Late Paleozoic tectonic events, resulting in formation of the Taimyr fold-and-thrust belt (Taimyr-Severnaya Zemlya fold belt). The Taimyr fold belt encompasses the entire Taimyr peninsula and extends onto the adjacent Kara shelf and eastern part of the Severnaya Zemlya archipelago (Drachev, 2016;Henriksen et al., 2011;Pease et al., 2014;Vernikovsky et al., 2013). A subsequent Early Mesozoic orogeny formed at a very complex junction between Baltica, Siberia and the northern part of the Late Paleozoic Uralian orogen. It stretches for over 3,000 km across the Yugorsk peninsula, Vaigach island, Novaya Zemlya archipelago, central part of the Kara Sea (North Siberian Arch), and southern Taimyr peninsula (Figure 1c) (e.g., Pease et al., 2014 and references therein). Moreover, significant tectonic uplift and erosion have been suggested from seismic interpretations across the easternmost portion of the Barents Sea and northern portion of the Kara shelf (Kara terrane), coeval with an Early Mesozoic orogeny (Drachev, 2016).

Pre-Mesozoic Succession of FJL
The Pre-Mesozoic stratigraphic framework of FJL is based solely on the stratigraphy penetrated by the Nagurskaya well, drilled on Alexandra Land Island in the westernmost part of the archipelago ( Figure 1) (Dibner, 1998;Gramberg et al., 1985;Makariev, 2006). Metamorphic rocks were penetrated between 1,895 and 3,204 m depth. The lower part of the metamorphic succession comprises intensely deformed dark gray or greenish quartz mica schists and phyllites, attaining a total thickness 213 m excluding younger mafic intrusions (Makariev, 2006). The upper part of the metamorphic succession is represented by 231 m of quartzite.
The age of the metamorphic succession is poorly constrained. The depositional age has been assumed as Ediacaran (Vendian) in age based on acritarchs from samples taken at depths of 3,015.3, 3,045.35, 3,094.2, and 3,095.1 m (Dibner, 1998;Makariev, 2006), and whole-rock K-Ar dating of the phyllites yielded a Late Devonian (360 Ma) cooling age (Dibner, 1998). Kaplan et al. (2001) reported 40 Ar-39 Ar cooling ages of 610 Ma for mica from the metamorphic rocks in the Nagurskaya well (in a sample from 2,480.3 m depth), yet a quartz-mica schist sample from the 2,266 to 2,273 m interval yielded a 40 Ar-39 Ar age of 122 Ma, suggestive of secondary heating by Cretaceous mafic intrusions. Pease et al. (2001) reported 40 Ar-39 Ar ages on presumably detrital muscovite from two samples of 665-360 Ma and 750-1,200 Ma, respectively. Knudsen et al. (2019) dated micas from the same samples as analyzed by Pease et al. (2001). This recent study yielded ages of 399.7 ± 3.3 and 404.9 ± 8.3 Ma for the micas. The U-Pd dating of detrital zircons from the same samples showed that youngest grains yielded of ca. 1 Ga age (Knudsen et al., 2019).
Fragments of dolomite and dolomitized limestone containing a Bashkirian fusulinid fauna have been reported along the coast of Victoria Island (westernmost part of FJL: N80°08′46″ E36°43′05″). Moreover, Bashkirian, Moscovian, and Sakmarian foraminifera have also been reported within carbonate pebbles from Quaternary deposits collected on a number of islands across the FJL archipelago (Davydov, 1997).

Mesozoic Stratigraphy of FJL
The Mesozoic succession is comparatively better studied compared to the pre-Mesozoic stratigraphy. However, the correlation of different sedimentary units across FJL is strongly debated due to the remoteness of the region, severe climate and glaciers (Kosteva, 2005;Makariev, 2006Makariev, , 2011Repin et al., 2007). Here, we mainly adopt the stratigraphic scheme of Makariev (2006Makariev ( , 2011 due to its applicability for the whole archipelago and the fact that this is the scheme adopted by published geological maps ( Figure 2).

Triassic
The Belozemel Formation (Induan-Olenekian stages) disconformably overlies Carboniferous limestones in the Nagurskaya well. The formation comprises black argillites with subordinate beds of clayey limestones, attaining a thickness of 657 m.
The Matusevich Formation (Anisian stage) has been described from the Heiss and Severnaya wells, where it mainly consists of silty argillites with the appearance of thin sandstone beds in the upper part of the succession. The lower formation contact has not been penetrated by wells and is not exposed across FJL. A maximum thickness of 784 m has been described from the Heiss well and can be taken as a minimum estimate for the total thickness of the formation.
The Ermakov Formation (Ladinian stage) comprises argillites with subordinate beds of siltstones and sandstones, attaining a thickness ranging from 700 to 1,047 m.
The Graham Bell Formation (Carnian stage) has been described from the central part of the archipelago and has been penetrated by the Severnaya and Heiss wells. The formation conformably overlies argillites of the Matusevich Formation with a gradational contact. Alternating sandstones and siltstones have been reported from the base of the formation, fining upward to intercalating siltstones and argillites, attaining a total thickness of 1,000 m.
The Heiss Formation (Norian stage) is exposed across the central and eastern parts of the archipelago and has been penetrated by several wells. The formation comprises 300-400 m of alternating sandstones, siltstones and argillites in the lower part of the succession, fining upwards to argillites in the upper part.
The Vasiliev Formation (Rhaetian) comprises polymictic sandstones and sands with beds of conglomerates and gritstones, while siltstones and argillites occur rarely. The thickness varies from 100 to 370 m across the archipelago. A significant hiatus has been described between Norian and Rhaetian deposits across FJL (Repin et al., 2007).

Jurassic
The Tegethoff Formation (Hettangian-Lower Toarcian) unconformably overlies various Upper Triassic strata and mainly comprises coarse-to medium-grained polymictic sands and sandstones with gritstone and conglomerate beds. Occasional thin beds of silts and siltstones have been described. Tegethoff Formation is attaining an incomplete thickness ranging from 60 to 350 m (Makariev, 2006(Makariev, , 2011. The Ganza Formation (Toarcian-Volgian) has a patchy distribution across the archipelago due to subsequent Early Cretaceous uplift and erosion. Furthermore, different stratigraphic levels of the Jurassic have been described from different localities, either due to variable erosion or to localized deposition in the Jurassic sedimentary basin. The formation mainly comprises alternating black argillites and siltstones with occasional units of clayey limestones and rare beds of sandstones, attaining an incomplete thickness ranging from 40 to 270 m.

Cretaceous
The Lamon Formation (Oxfordian-Valanginian?) mainly comprises sands and sandstones with units of siltstone and argillite, although limestones have been reported from some areas. The stratigraphic completeness and correlation of different units across the FJL archipelago are debatable due to their localized distribution, with thickness ranging from 25 to 110 m (Kosteva, 2005;Makariev, 2006Makariev, , 2011. The lower formation boundary has been described as both conformable and unconformable across the Archipelago. However, further studies are required to clarify the age and relationship with underlying strata. The Armitidj Formation (Hauterivian (?)-Aptian) unconformably overlies various Triassic-Lower Cretaceous formations, consisting of alternating basalt flows and tuffaceous sandstones with occasional coal beds. Since the formation is unfossiliferous, its age is mainly based on the isotopic dating of mafic rocks. 40 Ar-39 Ar dating of mafic sills and flows has yielded ages ranging from 189 to 125 Ma (Abashev et al., 2020;Grachev, 2001;Karyakin et al., 2021;Koryakin & Shipilov, 2009;Shipilov & Karyakin, 2014). However, the most precise and reliable TIMS U-Pb dating of zircons yielded a crystallization age of 122.7 Ma for a thick sill on Severnaya Well (Graham Bell Island) (Corfu et al., 2013). This younger Aptian age correlates with the age of mafic magmatism on the neighboring Svalbard archipelago, as well as timing of the HALIP event reported across the Arctic (Buchan & Ernst, 2018;Dockman et al., 2018;Polteau et al., 2016;Senger et al., 2014 and references therein). The Armitidj Formation is therefore likely to be Aptian in age.

Location 1. Wilczek Land, Ganza Cape Area
Samples 7-v15-9 and 15AP25 were collected from outcrops located 3 km to the northwest of Ganza Cape, where planar and cross-bedded medium-to fine-grained sandstones with rare layers of siltstones (Vasiliev Formation) crop out. The samples were collected from the middle part of this succession (Figures 1 and 2, Figure S1).
Sample 11-v15-1 was collected from outcrops located 1 km to the north of Ganza Cape, where the Ganza Formation crops out (Figures 1 and 2, Figure S1). This formation mainly comprises black argillites with subordinate thin layers of siltstone. In the upper part of the succession, several beds of limestone and an approximately 2-m-thick sandstone bed (sample 11-v15-1) occur. The sample has been dated as latest Kimmeridgian based on ammonite findings from this locality (Hoplcardioceras elegans (Spath) identified by Dr. M. Rogov).

Location 2. Hall Island, Tegethoff Cape
Samples 15-v15-25, 15-v15-28, 15AP27, and 15AP30 were collected from the Mesozoic succession of Hall Island on Tegethoff Cape (Figures 1 and 2, Figure S1). The lower part of the succession (Unit 1) comprises a 60 m-thick unit of matrix-supported conglomerates, with pebbles and cobbles of a variety of different compositions and ranging in size from 2 to 10 cm in diameter and 15AP27).
Unit 2 comprises 236 m of sandstone with rare lenses of gritstone and conglomerate. The sandstones are mediumto coarse-grained, planar and cross-bedded, with occasional thin (2-10 cm) layers of siltstone and argillite occurring throughout the unit.
Unit 5 consists of dark gray argillites with layers of siltstone (34 m thick). Basalts and tuffaceous sandstones of the Armitidj Formation (Aptian?) overlain Unit 5 and attain a thickness of more than 20 m.

Location 3. Berghaus Island
Sample 13-v-15 1 was collected from the upper part of the outcropping Mesozoic succession (Figures 1 and 2, Figure S2). The lower part of this succession comprises Upper Jurassic (Volgian) argillites with rare siltstone layers (Ganza Formation). The Ganza Formation is unconformably overlain by 60 m of medium-to fine-grained sandstones, comprising the Lamon Formation. The dated sample was collected from 30 m above the base of the Lamon Formation. This formation is overlain by basalt flows of the Armitidj Formation.

Location 4. Graham Bell Island
Samples and 15AP39 were collected from the Mesozoic succession of Graham Bell Island on Cape Kohlsaat (Figures 1 and 2, Figure S2). The lower part of the succession is represented by 2 units. The first unit comprises 2 m of silts and clays and 12 m of medium-grained sandstones, overlain by the second unit comprising a 57-m-thick coarse-grained sandstone package and 15AP39). A 30-m-thick bed of matrix-supported conglomerates occurs at the base of this coarse-grained second unit, containing pebbles and cobbles of a variety of compositions and ranging in size from 2 to 10 cm. Units 1 and 2 (Tegethoff Formation) have been dated as Lower Jurassic based on rare palynological data (Kosteva, 2005).

Petrography and Geochemistry
Petrographic analyses were performed using Olympus BX51 and Leica DM4000 P LED optical microscopes. The analytical results are provided in Figure S3.
The whole-rock geochemical analyses were carried out at the Central Laboratory of VSEGEI, St. Petersburg. All samples underwent conventional crushing and grinding. The major oxide concentrations were determined on an ARL 9800 XRF spectrometer, while concentrations of minor elements (including REE) were determined on an OPTIMA 4300DV emission spectrometer and an ELAN 6100 DRC mass spectrometer. Geochemical data are provided in Data Set S1.

LA-ICP-MS Zircon U-Pb Analysis and (U-Th)/He Dating of Zircons, UTChron Geochronology Facility
Mesozoic clastics from FJL were analyzed for detrital zircon U-Pb ages at the UTChron geochronology facility in the Department of Geological Sciences at the University of Texas, Austin. Samples underwent conventional heavy mineral separation and were grain mounted (no polishing) on one-inch round epoxy pucks with double-sided tape. All grains were depth-profiled using a Photon Machines Analyte G2 ATLex 300si ArF 193 nm Excimer Laser, equipped with a Helix two-volume ablation cell. The ablated aerosols were transported using He gas to, and analyzed with, a Thermo Fisher Element2 single collector, magnetic sector-ICP-MS. 206 Pb/ 238 U ages are reported for grains which are younger than 1,000 Ma. Zircons Plesovice (Sláma et al., 2008) and GJ1 (Jackson et al., 2004) were used as U-Pb standards. Histograms were constructed using the detzrcr software (University of Oslo, Oslo, Norway) (Andersen et al., 2018). U-Pb analytical results are provided in the in Data Set S2.
Detrital zircon (U-Th)/He (ZHe) were performed to provide additional geochronologic constraints. Specific grains that were at least 70 μm in diameter were chosen, and they appeared to have few, if any, visible inclusions. Due to the detrital nature of the samples and potential dispersion of (U-Th)/He cooling ages, up to 13 single grains per sample were analyzed for some samples, resulting. Analyses were conducted following analytical procedures described in Wolfe and Stockli (2010). All ages were corrected for the effects of α-ejection (Farley, 2002) and are reported with a ∼8% (2σ) analytical uncertainty. Analytical results are provided in the in Data Set S3.

LA-ICP-MS Zircon U-Pb Analysis, Russian Geological Research Institute (VSEGEI), St. Petersburg
Metasandstones from pebbles of Lower Jurassic conglomerates were analyzed for U-Pb ages at the at the Center of Isotopic Research, Russian Geological Research Institute (VSEGEI). All grains were analyzed with ArF laser COMPex-102, with ablation system DUV-193 (Lambda Physik Complex 102. The ablated aerosols were analyzed with, a Neptune (Thermo-Quest Finnigann MAT) collector ICP-MS. Zircons 91500 (Wiedenbeck et al., 1995) and Temora (Black et al., 2003) were used as U-Pb standards. 206 Pb/ 238 U ages are reported for grains which are younger than 1,000 Ma. Histograms were constructed using the detzrcr software (University of Oslo, Oslo, Norway) (Andersen et al., 2018). U-Pb analytical results are provided in the in Data Set S4.

SHRIMP-II Ion Microscope U-Pb Analysis, Russian Geological Research Institute (VSEGEI), St. Petersburg
U-Pb dating of zircons was carried out with a SHRIMP-II ion microscope at the Center of Isotopic Research, Russian Geological Research Institute (VSEGEI), St. Petersburg. U-Pb ratios were measured on the SHRIMP-II following the technique described by (Williams, 1998), and data were processed in the SQUID program (Ludwig, 2000). U-Pb ratios were normalized to 0.0668, that is, to the value assigned to the standard TEMORA zircon, corresponding to an age of 416.75 Ma (Black et al., 2003). Uncertainties in single analyses (ratios and ages) were brought to conformity at a level of ±1σ, and uncertainties in calculated concordant ages at a level of ±2σ. The ISOPLOT program was used to construct graphs with concordia (Ludwig, 2003). U-Pb dating results are provided in Data Set S5.

Pebbles From Matrix-Supported Jurassic Conglomerates of the Tegethoff Formation
In total, 284 pebbles were studied in 4 samples collected from two sections exposed on Graham Bell and Hall islands. Most of the pebbles and cobbles (excluding the quartz pebbles) were cut for thin section analysis ( Figure S3). The studied pebbles and cobbles range in size from 2 to 15 cm, with most between 5 and 10 cm. They can be divided into four major groups based on their composition: magmatic, metamorphic, sedimentary, and veined quartz. The proportion of different pebble types varies between samples, with pebbles composed of clastic rocks constituting 0%-26%, carbonates 10%-22%, cherts 10%-44%, intrusive rocks (mainly granites) 0%-20%, effusive rocks (mainly rhyolites) 7%-12%, metamorphic rocks 17%-25%, and veined quartz 6%-16% ( Figure 3).
Pebbles of sedimentary rocks comprise three main groups, including clastic rocks, carbonates, and chert. The carbonate pebbles range from partly to fully recrystallized and have often been affected by secondary silicification. Thin veins of recrystallized calcite occur in places, as well as networks of opaque veins. Several types of carbonate have been recognized. The first type comprises poorly sorted foraminiferal packstone, dominated by foraminifera bioclasts with rare fragments of bryozoans, algae, brachiopods, and indeterminable bioclasts, surrounded by a micrite matrix which is often either partly dissolved or recrystallized to sparite. The second type comprises recrystallized wackestones with bryozoans, algae, brachiopod needles, and small foraminifera shells. Most bioclasts have been replaced by sparry calcite, although some retain a foliated microstructure. The matrix is dominated by micrite, although significant sparry calcite also occurs ( Figure S3).
The third and most numerous type comprises highly silicified limestones of initial mudstone to wackestone composition, but due to secondary alternation, bioclasts could not be identified.
The foraminifera identified from these carbonate pebbles suggest a Serpukhovian-Late Carboniferous age for the primary carbonates from which the conglomerate clasts were derived (V. . Chert pebbles are mainly composed of amorphous to cryptocrystalline silica, whilst microcrystalline quartz forms smaller domains and veinlets ( Figure S3). Poorly preserved radiolaria could be recognized by their round shape. Some samples contain very poorly preserved initially carbonate bioclasts, which have been fully replaced by chalcedony. Therefore, the studied cherts constitute both primary sedimentary cherts and fully silicified carbonates. Due to the poor preservation of primary fabrics, it was not possible to fully distinguish between these two types. However, we classified cherts containing relatively well-preserved initially carbonate bioclasts (brachiopods, bryozoans, foraminifers etc.) as silicified carbonates rather than primary sedimentary cherts. The cherts are often cross-cut by quartz veins.
Clastic rock pebbles are represented by two major groups, including argillites and sandstones. Argillites are black to dark gray in color, composed of clay minerals with rare quartz grains of fine silt size, often silicified and crosscut by quartz veins.
Sandstone pebbles form two groups, including quartz arenites and arkosic arenites. Quartz arenites are moderately to well-sorted with medium-to well-rounded grains. The clasts mainly comprise mono-mineralic quartz with rare fragments of fine-grained quartzites, cemented by a siliceous or occasionally carbonate cement. Arkosic arenites are poorly to moderately sorted and composed of quartz, feldspar, and siliceous lithic fragments. The grains are angular to sub-rounded and cemented by a clay, silica or carbonate cement ( Figure S3).
Metamorphic pebbles mainly comprise quartzites with a few clasts of crystalline schist. The crystalline schists pebbles are composed of quartz, muscovite, biotite, and feldspar. They exhibit a foliation and/or penetrative schistosity, determined by the preferential alignment of platy mica flakes. The quartzites pebbles are medium-to fine-grained, composed predominantly of quartz with trace amounts of sericite and chlorite, and grains range from sub-rounded to well-rounded. The three pebbles composed of quartzite from both studied sections (samples 15-V15-25-1, 15-V15-28-3, and 18-v15-35-1) are characterized by comparable detrital zircon U-Pb age distributions. About 15%-20% of the dated grains are Archean and Paleoproterozoic in age and do not group in prominent peaks. Mesoproterozoic zircons comprise up to 22% of the total population, with the majority of grains ranging in age between 1,600 and 1,200 Ma ( Figure 4). Most of the dated zircons are of Late Neoproterozoic-Early Cambrian age, with most ages concentrated between 650 and 530 Ma. The youngest cluster forms peaks around 540-550 Ma. The Maximum depositional age (MDA) based on the YC2σ(3+grains) approach (Dickinson & Gehrels, 2009) ranges from 525.2 ± 15 (sample 15-V15-25-1) to 506 ± 11 Ma (sample 15-V15-28-3), suggesting a Cambrian or younger age for the quartzites.
Furthermore, (U-Th)/He dating of detrital zircons from the same quartzite pebbles has been carried out. In total, 11 grains were dated and range in age from 178.4 ± 14.3 to 277.7 ± 22.2 Ma, with a weighted average value of 222 ± 19 Ma suggesting exhumation during the Triassic in the provenance area ( Figure 5).
Magmatic pebbles were collected from both sections of studied conglomerates and can be categorized into two main types, including effusive and intrusive rocks. All studied pebbles composed of intrusive igneous rocks are granitic in composition.
Granitic pebble from Graham Bell Island (sample 18-v15-34) is composed of medium-grained biotite-amphibole granites with an equigranular texture. Plagioclase grains (40%) are euhedral and sharply twinned, while orthoclase grains (30%) are tabular, quartz grains (20%) are euhedral, amphibole grains (7%) are prismatic, and biotite grains (3%) occur as laths. Accessory apatite and zircon are also present. The rock contains 73.8 wt.% SiO 2 , 4.91 wt.% Na 2 O, 4.77 wt.% K 2 O, and are classified as granites (Figure 6a) on a TAS classification diagram (Middlemost, 1994). It is ferroan and metaluminous according to the classification of Frost et al. (2001), and alkalic as defined by the modified alkali-lime index (Figures 6b-6d). On a chondrite-normalized diagram, this rock characterized by an enrichment in LREE, depletion in HREE (La N /Yb N = 3.51), and a negative Eu anomaly (Eu/Eu* = 0.46) (Figure 6e). On a primitive mantel-normalized multielement diagram, the granite is enriched in Ba, Th, U, but depleted in Sr and Ta (Figure 6f). On the discrimination diagrams of Pearce et al. (1984) (Figures 6g and 6h), the composition point of the rock fall in the field of within-plate granitoids.
Zircons were separated from the granitic pebbles and dated by SHRIMP (U-Pb). The zircons from sample 18-V15-34/8 (medium-grained biotite-amphibole granite, Graham Bell Island) are heterogeneous, with elongation ratios ranging from 1 to 4 and a few grains containing inclusions. The U content in the analyzed grains ranges from 215 to 1,045 ppm. Eight out of 10 analyzed grains define a concordia age of 520.2 ± 1.3 Ma (Early Cambrian) (Figure 7). Thus, the granitic pebble from Graham Bell Island differs from the Hall Island's granitic pebbles not only by the geochemistry data but also by age.
Felsic volcanic clasts are abundant within both sections (Hall and Graham Bell Islands). However, the ages of these felsic volcanic rocks are poorly constrained as zircons have not been successfully extracted from them. The effusive rocks are classified as rhyolites with a porphyritic texture. Crystal content ranges from 20% to 40%, with phenocrysts represented by quartz and plagioclase in a spherulitic groundmass. The rocks contain 68.1-84.1 wt.% SiO 2 , 1.86-5.56 wt.%, Na 2 O, 0.24-11.39 wt.% K 2 O, and are classified predominantly as rhyolites ( Figure 8a) on a TAS classification diagram (Middlemost, 1994). They are ferroan to slightly magnesian and peraluminous according to the classification of Frost et al. (2001), and are calc-alkalic or calcic as defined by the modified alkali-lime index (Figures 8b-8d). On a chondrite-normalized diagram, they are characterized by a negative Eu anomaly (Eu/Eu* = 0.14-0.86) (Figure 8e). On a primitive mantel-normalized multielement diagram, the granites are enriched in Th, U, La, and Zr, but depleted in Sr, Ba, Nb, and Eu (Figure 8f). On the discrimination diagrams of Pearce et al. (1984) (Figures 6g and 6h), the composition point of the rock fall in the fields of volcanic arc, syncollisional and within-plate granitoids.

10.1029/2022TC007348
14 of 27 and group in a prominent peak at ca. 1,800-1,850 Ma. The few grains of Archean age do not form any significant peaks.

The Combined U-Pb and (U-Th)/He (ZHe) Dating of Zircons From the Triassic-Cretaceous Succession of FJL
Six samples ranging from Triassic to Cretaceous in age were analyzed for detrital zircon (U-Th)/He (ZHe) geochronology. ZHe ages are older than the depositional ages of the sedimentary succession, suggesting that these rocks were not buried deeper than 6-7 km since deposition (assuming a typical continental crust geothermal gradient of 30°C/km) and were not significantly heated during the HALIP event. Therefore, the ZHe ages can be interpreted to reflect the timing of exhumation and cooling in the provenance area.

Pre-Mesozoic Succession of FJL and Surrounding Areas
Our detailed study of the polymictic conglomerates sheds new light on the composition and age of the buried pre-Mesozoic succession of FJL and surrounding areas of the Barents shelf. The sizes of the cobbles and pebbles, along with their immature composition, are suggestive of a proximal provenance area.
Early Cambrian quartzites are the oldest rocks and were found at both studied localities. Most of the detrital zircons range in age between 650 and 520 Ma and correlate with the age of the Timanian orogeny (Gee & Pease, 2004;Kuznetsov et al., 2007Kuznetsov et al., , 2010 and refences therein), which represented a clastic sediment source for much of the Arctic and the interior of Baltica during the late Ediacaran-earliest Cambrian (V. B. Ershova, Ivleva, et al., 2019;Kuznetsov et al., 2010;Lorenz et al., 2008Lorenz et al., , 2013. In addition, the crystallization age (520.2 ± 1.3 Ma) of granitic pebbles from the easternmost part of FJL (Graham Bell Island) is similar to the MDA calculated for the quartzite pebbles. The proximal provenance for these pebbles raises the possibility that Timanian (Ediacaran(?)-Early Cambrian) magmatism extended northward from the Timan Ridge to the north-eastern Barents shelf (modern coordinates). However, further studies, including the drilling of offshore uplifts, are required to confirm this suggestion. The next major geological event is a latest Devonian-Early Carboniferous magmatic event, evidenced by granitic pebbles collected from Hall Island (363-322 Ma) (V. B. Ershova, Prokopiev, Sobolev, et al., 2017). This magmatic event has not been widely reported across the study region. Angular clasts of granitoids from basal sediments on Victoria Island (westernmost part of FJL) yielded 40 Ar-39 Ar ages of ca 363, 369, and 344 Ma (Makariev, 2006). These ages were obtained from granitoid clasts lacking any indications of metamorphic overprinting. Moreover, plagioclase and pyroxene were used for the 40 Ar-39 Ar dating. Makariev (2006) interpreted these ages as granitoid crystallization ages and assumed that clasts were sourced from a neighboring offshore uplift, providing evidence for Late Paleozoic magmatism offshore to the west of FJL. These 40 Ar-39 Ar ages are similar to those obtained during our study, providing further evidence that Late Paleozoic magmatism occurred more widely across the study region than previously supposed. However, further studies are needed to give greater confidence to this suggestion.
The closest Carboniferous-Permian granitoids have been reported from the Taimyr and Severnaya Zemlya Lorenz et al., 2007;Vernikovsky et al., 2020). Beside the different proposed models of Late Paleozoic magmatism of Taimyr (for review see Vernikovsky et al., 2020) their geochemical features are similar to those of studied pebbles ( Figure 6) pointing to their possible similarity. Based on geochemistry, the studied granitic pebbles are similar to Devonian-Carboniferous suprasubduction granites of Alaska (Ruks et al., 2006) and Carboniferous suprasubduction granites of Urals (Bea et al., 2002) (Figure 6). The studied effusive pebbles do not have a reliable age constraints. Thus, we can hypothesize that they likely connected to the Late Paleozoic felsic magmatism revealed by numerous intrusive pebbles. However further studies including new sampling of effusive pebbles are necessary to clarify this assumption.
Moving upwards, the next part of the pre-Mesozoic succession within the study area is the Serpukhovian-Late Carboniferous carbonate succession. Carboniferous carbonates have been previously described from the Nagurskaya well (Gramberg et al., 1985;Makariev, 2006) in the westernmost part of the FJL. Based on our data, the FJL and adjacent north-eastern part of the Barents shelf were occupied by a shallow marine carbonate platform from at least the end of the Early Carboniferous to the beginning of the Permian. Basal Carboniferous strata in the Nagurskaya well comprise poorly sorted continental sandstones, which could be tentatively inferred as the source of poorly sorted arkosic arenite pebbles comprising a similar composition in the Mesozoic succession of FJL. Furthermore, Early Permian foraminifera have been reported from limestone fragments within Quaternary sediments across a number of the islands of FJL (Davydov, 1997), suggesting that carbonate platform environments may have persisted until the Early Permian. This proposition is supported by a comparable Carboniferous-Lower Permian lithological succession on Svalbard in the north-western Barents Sea (Ahlborn & Stemmerik, 2015;Larssen et al., 2002;Stemmerik & Worsley, 2000 and references therein). We therefore propose that a shallow marine carbonate platform extended across the entire Barents shelf during the Carboniferous-Early Permian. The abundant black cherts and dark gray to black silicified argillite pebbles do not have any reliable time constraints. However, we can infer a Permian age based on the lithological succession described from Svalbard, where the Kapp Starostin Formation comprises shales with dark to light-colored chert horizons and strongly silicified fossiliferous carbonates (Blomeier et al., 2011Bond et al., 2018;Dustira et al., 2013;Ehrenberg et al., 2001;Hüneke et al., 2001). We suggest that a comparable Permian succession was also deposited across FJL and the adjacent part of the Barents shelf. Our proposed model for the pre-Mesozoic stratigraphy, tectonic and magmatic events of the north-eastern Barents shelf is shown on Figure 11. Based on our (U-Th)/He data, the pre-Mesozoic stratigraphy was exhumed during the Late Triassic, signifying the next major tectonic event in the north-eastern Barents shelf region.

Provenance of the Uppermost Triassic-Cretaceous Clastic Succession
The distribution of detrital zircon ages within the dated samples is very similar, strongly suggesting a common provenance area for the entire Mesozoic succession of FJL.
The next prominent zircon population lies between 470 and 420 Ma in age, with coeval magmatic events only reported from the Severnaya Zemlya archipelago (Kurapov et al., 2020;Lorenz et al., 2007;Prokopiev et al., 2019). Moreover, zircons of a similar age distribution are abundant within Ordovician-Carboniferous clastic rocks from the Severnaya Zemlya archipelago (V. Ershova et al., 2018;V. B. Ershova, Prokopiev, Nikishin, et al., 2015;Lorenz et al., 2008), but rare within Ordovician-Devonian sandstones of the Novaya Zemlya archipelago (Lorenz et al., 2013). Furthermore, several ZHe ages suggest an exhumation event occurred around 420 Ma across the provenance area (Figure 10b). Thus, erosion of Devonian and older clastic strata can provide all the Devonian and older detrital zircon grains. Even more the Ordovician-Devonian exhumation ages have been revealed from the coeval strata of Severnaya Zemlya archipelago (V. Ershova et al., 2018), as well as Devonian metamorphism have been proposed for basement rocks of Nagurskaya well (Knudsen et al., 2019), those ages a in a good agreement with subordinate populations of exhumation ages reveled from the dated samples.
Late Paleozoic zircons represent the most abundant detrital zircon population within the dated samples. The detrital zircon populations clearly indicate major magmatic events within the provenance area between ca. 345-290 Ma and again between ca. 255-220 Ma. Thus, two main magmatic events occurred within the provenance area during the Carboniferous-Early Permian and the Latest Permian-Triassic. The Late Paleozoic magmatic and tectonic events within the Arctic realm can be attributed to the Uralian orogeny, which resulted from continental collision between Kazakhstan, Siberia, and Laurussia (Biske, 2004;Brown et al., 2006;Puchkov, 2009;Zonenshain et al., 1990). The suture of the Uralian orogeny can be traced over 2,000 km from the Aral Sea to the Polar Urals, although its northern continuation toward the Arctic region is debated (Pease et al., 2014;Puchkov, 2009;Scott et al., 2010;Şengör et al., 1993;Vernikovsky et al., 2013). However, most researchers support its continuation as far as the Taimyr peninsula (e.g., Pease et al., 2014 and references therein). Furthermore, Vernikovsky et al. (2020 and references therein) and  provide evidence for voluminous magmatism across the southern part of the Kara terrane (northern Taimyr and Severnaya Zemlya archipelago) from the Bashkirian (ca.315 Ma) to the Artinskian (ca. 282 Ma) and from the Visean (ca. 344 Ma) until the Artinskian (ca. 288 Ma), respectively. The ages of multiple episodes of Carboniferous-Permian magmatic activity across the Kara terrane correlate strongly with the prominent Late Paleozoic detrital zircon age peaks within the Mesozoic strata of FJL. Furthermore, a subordinate population of ZHe ages support an exhumation event across the provenance area during the Carboniferous. In addition, the only viable source of Latest Permian-Triassic zircons is from the Taimyr region, where coeval in age (ca 255-225 Ma) voluminous magmatism have been reported (Kurapov, Ershova, Khudoley, Luchitskaya, Stockli, et al., 2021;Vernikovsky et al., 2003). The youngest detrital zircon age population in the Mesozoic clastics of FJL displays similar ages to those of sedimentation, especially for Upper Triassic-Lower Jurassic sandstones, suggesting the existence of coeval magmatic activity. Moreover, the dated samples plot in the convergent to collisional field on a CA-DA diagram (Cawood et al., 2012) (Figure 12), supporting the existence of an orogenic belt across the provenance area.
Furthermore, ZHe ages support Late Triassic (ca. 225 Ma) exhumation of the provenance area. Moreover, the youngest grains of detrital zircons are Middle-Late Triassic in age pointing that significant uplift of provenance coincides with magmatic activity. Late Triassic-earliest Jurassic uplift across Taimyr and the Novaya Zemlya archipelago is supported by Apatite Fission Track data Zhang, Pease, Carter, Kostuychenko, et al., 2018;, while Late Paleozoic magmatism, metamorphism and significant uplift of the Taimyr-fold-thrust belt are supported by 40 Ar-39 Ar data . Therefore, the provenance area for the Upper Triassic-Lower Cretaceous strata of FJL was characterized by a very similar geological history to the Taimyr region and Kara terrane, including major magmatic and uplift events during the Late Paleozoic and Triassic. Moreover, the distribution of Precambrian and Early Paleozoic detrital zircon age populations in the Mesozoic clastic rocks of FJL is comparable to the Early-Middle Paleozoic clastic rocks deposited across the Kara terrane, Novaya Zemlya and Taimyr, suggesting reworking of these older clastic strata in the provenance area (V. B. V. B. Ershova, Prokopiev, Nikishin, et al., 2015;Lorenz et al., 2008Lorenz et al., , 2013. A long-distance sediment transport pathway from distal Taimyr to FJL would seem unlikely, especially for the coarse-grained Upper Triassic-Lower Jurassic clastics, since the presence of pebbles and cobbles suggests a proximal source region. However, the Taimyr-Severnaya Zemlya fold-and-thrust belt and northern part of the Novaya Zemlya archipelago are connected by the submarine North Siberian Arch  (Cawood et al., 2012) showing the cumulative curve for each dated sample (data are obtained by subtracting the sedimentation age of the sample from the crystallization age of each zircon).
beneath the Kara Sea, which is believed to represent the offshore continuation of the Taimyr-Severnaya Zemlya fold-and-thrust belt and represents the Early Mesozoic orogen (Drachev, 2016;Pease et al., 2014 and references therein). Therefore, we can speculate that the North Siberian Arch is characterized by a comparable geological history, structure and stratigraphy including multiple episodes of magmatic and tectonic activity as reported from the Taimyr region and Kara terrane. It is possible that this structure also extends further to the north-west across the Barents shelf than previously assumed, forming the basement to the east and north of FJL and representing the main proximal provenance for Mesozoic clastics deposited across FJL.
There are no significant differences between detrital zircon populations of different formations within the Upper Triassic-Lower Cretaceous succession of FJL, suggesting that the provenance area remained the same throughout this time. However, we cannot rule out the possible reworking of proximal Triassic and Lower Jurassic strata during the Middle Jurassic-Cretaceous. The predominantly continental Upper Triassic-Lower Jurassic sediments are very coarse-grained, with pebbles and cobbles probably derived from a proximal mountainous provenance area. Meanwhile, Middle-Upper Jurassic sediments comprise marine black argillites with subordinate thin beds of fine-grained sandstones and siltstones, indicating peneplanation of provenance area. Further detailed studies of the stratigraphy and depositional environments in this region will help to further refine paleogeographic reconstructions of this remote and poorly studied region.

Implications for Barents Sea Sediment Pathways and Arctic Paleogeography
Our new data provide new constraints for reconstructing Mesozoic sediment pathways in the Arctic region, with a focus on the sedimentary history of the Barents shelf. These data can also be used to validate pre-existing models for the provenance area of Mesozoic clastics in the Sverdrup Basin, for which two contrasting models currently exist. The first model (Anfinson et al., 2016;Omma et al., 2011) proposes a provenance within the Uralian/ Barents region for Triassic-Jurassic sediments, while the second model proposes a proximal provenance located within a magmatic arc along the northern margin of Laurentia Hadlari et al., 2018;Midwinter et al., 2016).
The distribution of detrital zircon ages in Lower Triassic strata of FJL containing abundant Late Paleozoic ages spanning 270-350 Ma, which correlate with magmatism of the Uralian orogeny Puchkov, 2009 and references therein) ( Figure 13). Controversially, Lower-Middle Triassic deposits of Svalbard are dominated by Proterozoic to Neoarchean zircons, which are believed to have been sourced from northern Greenland and potentially Canada to the west (Pózer Bue & Andresen, 2014). Lower Triassic deposits of Sverdrup basin are characterized by wide range of Proterozoic zircons, the Early Paleozoic population and Middle to Late Paleozoic population Anfinson et al., 2016;Hadlari et al., 2018;Midwinter et al., 2016;Omma et al., 2011). However, the Lower Triassic samples from the Sverdrup Basin have a detrital zircon age gap between 340 and 300 Ma , which are numerous within Lower Triassic strata of studied region. Therefore, we propose that Lower-Middle Triassic clastic wedge sourced from the east (in modern coordinates), extended across the eastern Barents shelf, but did not reach the westernmost portion of the Barents shelf and Sverdrup basin.
A significant change occurred during the Late Triassic, with clastic sediments of this age throughout the Barents shelf region and Sverdrup Basin characterized by a comparable detrital zircon age distribution containing abundant Late Paleozoic and Triassic zircons. Therefore, sediments deposited across this large geographic area were sourced from a common provenance which was magmatically active while, or shortly before, these sediments were being deposited. Moreover, our detrital ZHe ages suggest a significant episode of uplift in the provenance area of Upper Triassic strata deposited across FJL (Figures 5 and 10). We propose that a major tectonic event occurred in the provenance area and, based on the coarse-grained composition of Upper Triassic-Lower Jurassic clastics, it must have been located proximally to FJL, either to the east or north. Furthermore, a Norian unconformity can be traced across much of the Barents shelf, including Svalbard and possibly FJL, and has also been reported from the Sverdrup Basin (Embry & Beauchamp, 2019). Therefore, we propose that a significant amount of sediment was deposited across the Barents shelf region and Sverdrup Basin during the Late Triassic, sourced from a newly formed orogenic belt. An eastern sediment source for the Barents shelf region has been determined from seismic studies (Gilmullina et al., 2021), although there is evidence for both local and distal sediment sources across the south-western Barents Sea, suggesting that this region formed the western depositional limit for the eastern-sourced clastic wedge (Fleming et al., 2016).  Anfinson et al., 2016;Fleming et al., 2016;Hadlari et al., 2018;Khudoley et al., 2019;Klausen et al., 2017;Midwinter et al., 2016;Omma et al., 2011;Pózer Bue & Andresen, 2014;Soloviev et al., 2015).
Middle Jurassic sediments across the Barents shelf region are characterized by a comparable distribution of detrital zircons to Upper Triassic rocks, suggesting a common provenance and sediment transport pathway or the significant reworking of zircons from Upper Triassic-Lower Jurassic strata. A major shift in sediment transport pathways occurred in the latest Jurassic-Early Cretaceous (Figure 14), with Tithonian sediments of the Sverdrup basin derived from the Canada-Greenland shield (Omma et al., 2011;Røhr et al., 2010) and Cretaceous sandstones of Svalbard sourced from local uplifts or western provenance areas (Røhr & Andersen, 2009). By this time, there is no evidence for any clastics sourced from the eastern provenance, or for reworking of Upper Triassic-Middle Jurassic deposits across Svalbard and the Sverdrup Basin. However, distributions of detrital zircons from Tithonian and lowermost Cretaceous strata on FJL are comparable to Upper Triassic-Middle Jurassic strata, suggesting local reworking of these older deposits.

Conclusions
1. Polymictic Upper Triassic-Lower Jurassic conglomerates shed new light on the composition and age of the pre-Mesozoic stratigraphy of FJL and surrounding offshore areas of the Barents Sea. The sizes of the cobbles and pebbles, along with their immature composition, suggest a proximal provenance area. Therefore, we propose that the metamorphic basement of this region comprises Early Cambrian quartzite intruded by Late Paleozoic granitoids. After a period of significant erosion and non-deposition, Carboniferous clastic sediments were deposited unconformably on the metamorphic basement. These clastics are overlain by a Serpukhovian-Late Carboniferous carbonate succession. The youngest pre-Mesozoic strata are cherts of an inferred Permian age. Based on the ZHe ages, the pre-Mesozoic succession experienced significant uplift during the Late Triassic, signifying the next major tectonic event within the study region. 2. The distribution of detrital zircon ages is very similar, suggesting a common provenance area for Upper Triassic-Lower Cretaceous clastic sediments of FJL. The distributions of Archean to Early Neoproterozoic zircons correlate with known ages of the basement of Baltica, while Ediacaran-Early Cambrian zircons correlate strongly with the Timanian orogeny and Early-Middle Paleozoic zircons correlate with a Caledonian event. The most abundant Late Paleozoic detrital zircon population suggests the existence of the same in age magmatic events in the provenance area, displaying a close similarity to the ages of Late Paleozoic intrusions across the Kara terrane. Granitic pebbles collected from Lower Jurassic conglomerates of FJL provide evidence for the existence of Late Paleozoic magmatism in a proximal source area. The youngest Middle-Late Triassic detrital zircon population provides evidence for magmatic activity of this age within the provenance area, while our detrital ZHe ages denote an episode of major uplift (up to 6 km) at ca. 225 Ma. Both Triassic magmatism and uplift have been reported from the Taimyr fold-thrust belt. While a direct long-distance sediment transport pathway from Taimyr is unlikely due to numerous coarse-grained clastic units within studied succession. We propose that the North Siberian Arch (probably representing a continuation of the Taimyr-Severnaya Zemlya fold-and-thrust belt) is characterized by a similar geological history and stratigraphy. We suggest that this geological structure possibly extends further to the north-west across the north-eastern Barents shelf than previously assumed, forming the main proximal provenance for Mesozoic clastic sediments of FJL. The shift from carse-grained clastics in the Late Triassic-Early Jurassic to fine-grained clastics in the Middle Jurassic likely signifies a cessation of tectonic activity and peneplanation of the provenance area. 3. A comparison of detrital zircon age distributions between coeval rocks from the Barents shelf region and the Sverdrup Basin can provide new constraints for the Mesozoic paleogeography of the Arctic realm.
During the Early and Middle Triassic, the eastern North Siberian Arch provenance area possibly sourced clastic sediment deposited across the eastern Barents shelf region and FJL, while a local or western provenance sourced clastics across the western Barents shelf including Svalbard. A major change occurred during the Late Triassic, when the clastic wedge from the eastern source area reached the westernmost part of the Barents shelf and Sverdrup Basin. This change corresponds to a significant episode of uplift in the eastern provenance area as determined by ZHe ages, a major episode of Triassic magmatic activity within the Taimyr fold-thrust belt as evidenced by abundant zircon ages close to the depositional age of the sediments, and a widespread Norian unconformity across the Barents shelf region. The next prominent shift in provenance area occurred in the Late Jurassic-Early Cretaceous, when local or western provenance areas became the main sources of clastics across the western Barents shelf and Sverdrup Basin.  Fleming et al., 2016;Hadlari et al., 2018;Khudoley et al., 2019;Klausen et al., 2017;Midwinter et al., 2016;Omma et al., 2011;Pózer Bue & Andresen, 2014;Røhr & Andersen, 2009;Røhr et al., 2010). The color bars legend is shown on Figure 13.

Data Availability Statement
Data files are available in https://zenodo.org/record/7322759#.Y3X3aXZBzb0. This work was supported by project "Changes at the Top of the World through Volcanism and Plate Tectonics: A Norwegian-Russian-North American collaboration in Arctic research and education" (NOR-R-AM2) 309477. Mesozoic Stratigraphic and paleogeographic study were supported by RSF Grant 21-17-00245. Interpretation of isotopic study and correlation with Taimyr-Severnaya Zemlya were supported by RSF Grant 20-17-00169. Basic funding of AP through a subsidy of DPMGI SB RAS.