We present heavy minerals, detrital zircon data and U-Pb tuff ages from the sedimentary units of the Yukon-Koyukuk Basin (YKB) in Alaska, to investigate and understand its evolution within a tectonic framework. Two basins in Southeast Asia, with similar tectonic settings, serve as modern analogues for comparison. The YKB started to form in middle to late Jurassic after the collision between an intraoceanic volcanic arc and the Arctic Alaska margin, which eventually led to the thrusting of the oceanic basement over the passive continental margin. The basin is flanked by the metamorphic rocks of the Seward Peninsula to the west, the Brooks Range to the north and the Ruby Terrane to the east.Our results are from the whole stratigraphic column of the basin, from the lowermost Kv unit to the uppermost Ks unit:Kv unit: basaltic and andesitic lava flows interbedded with volcanogenic sediments. K-Ar ages vary from 134 Ma and 118 Ma. A single U-Pb zircon age from a tuff is about 138 Ma. Kvg unit: volcaniclastic greywacke with Albian molluscs are interbedded with tuffaceous layers. Two of these are dated at 112 Ma and 110 Ma (Albian). Kmc unit: conglomerate and greywacke with a strong mafic and calcareous imprint. Cretaceous molluscs are widespread. Kqc unit: quartz rich deposits with plant fossils of Cretaceous age. Ks+Kms units: late Cretaceous fluvial to shallow marine and deep marine sandstone and shale layers. We use QEMSCAN® (Quantitative Evaluation of Minerals by Scanning Electron Microscopy) for heavy mineral (HM) analysis, which, along with point counting, petrographic description, paleocurrent data and sedimentary features analysis, helps to constrain sediment provenance. Kv is the only unit reflecting a volcanic source, while the others display the progressive unroofing of the deeper and higher-grade metamorphic rocks surrounding the basin. U-Pb SIMS dating of tuffs and detrital zircons provide, for the first time, an absolute chronology for basin evolution.The combined data indicate the YKB formed in a forearc/backarc setting prior to 138 Ma (deposition of the volcanic-rich Kv unit). With the progressive denudation of the Brooks Range, sedimentation shifted towards greater metamorphic input, leading to the deposition of the Kvg unit at 110 Ma. Ultimately, after the Late Cretaceous uplift of the Ruby Terrane, the main sediment source changed again, and the stratigraphically higher units were deposited from the Cenomanian to at least the Maastrichtian. The Savu Sea and the Taiwan margin in Southeast Asia show similarities in structure, metamorphic grade, sediment composition and tectonic setting, suggesting these are effective modern analogues that can enhance our understanding of both ancient and modern arc-continent collisional systems.

Abstract Despite all the effort made towards an understanding of the sedimentary, tectonic, and diagenetic evolution of the presalt sequence and the Pre-Salt reservoirs of the North Campos Basin (East Brazil), two knowledge gaps have yet to be filled: 1) a detailed study of diagenesis in the crystalline basement and rift phases, and 2) the timing of diagenetic events that affected the presalt succession. In this study, samples from these geologic units were analysed for mineral composition and paragenetic evolution, fluid temperature and salinity, stable isotope compositions, and LA-ICP-MS derived U-Pb ages of carbonate phases. The U-Pb ages of replacive and vein-filling cements reveal three tectono-diagenetic events, named Barremian-Aptian (BADE, 125-117 Ma), Albo-Cenomanian (ACDE, 103-98 Ma), and Campanian-Maastrichtian (CMDE, 83-70 Ma). Each phase is characterised by distinct minerals, precipitation temperatures, and burial conditions. The hydrothermal qualifier, identified by the temperature contrast between fluid and host rock, was initially high during BADE, then diminished over time (through ACDE) until it achieved equilibrium with the host rocks during CMDE. Diagenetic events are not coeval with magmatism but do coincide with known regional tectonic events described in the literature and are interpreted to be the result of increasing intraplate stresses. Multidisciplinary studies that include diagenetic events constrained by geochronological data will certainly lead to more robust conceptual geologic models, and therefore, to a more reliable management of resources and strategies such as Enhance Oil Recovery (EOR), Carbon Capture, Utilisation and Storage (CCUS), and drinking water. Supplementary material at https://doi.org/10.6084/m9.figshare.c.7103900

The Yukon-Koyukuk Basin is a wide, triangular depression in northern Alaska that initiated as the consequence of the collision between an intraoceanic arc and the Arctic Alaska margin. It is bordered by the metamorphic terranes of the Seaward Peninsula, the Brooks Range and the Ruby Terrane. The Yukon-Koyukuk Basin is divided into two sub-basins separated by remnants of the volcanic arc. Two different models have been suggested for its formation. One model interprets the Yukon-Koyukuk Basin to have formed during collision in a forearc-backarc setting, while the other favours an extensional regime that was active after the cessation of collision. To test the two models, ten sedimentary samples from the two stratigraphically lowest units cropping out along the middle reaches of the Koyukuk River were analysed. Point counting and Quantitative Evaluation of Minerals by Scanning Electron Microscopy (QEMSCAN (R)) are used to evaluate sedimentary provenance. This study also presents zircon U-Pb ages from three interbedded tuffaceous layers to better constrain the age of the units. The base of the succession indicates a volcanic source (enriched in clinopyroxene) deposited at ca 138.3 +/- 0.8 Ma (2 sigma), while younger overlying strata are dominated by metamorphic input (enriched in garnet and epidote) reflecting the erosion of the surrounding metamorphic terranes at ca 112.6 +/- 1.1 Ma (2 sigma). The application of a multi-method provenance approach has been essential in constraining the formation and evolution of the northern Yukon-Koyukuk Basin. This is of significant importance for advancing the understanding of Alaskan geology and for providing insights into modern basins within analogous tectonic settings, such as the Banda Arc in Southeast Asia.

The importance of topography generated by Eocene Eurekan deformation as a sediment source for sandstones deposited on the western Barents Shelf margin is evaluated through a sediment provenance study conducted on wellbore materials retrieved from Spitsbergen and from the Vestbakken Volcanic Province and the Sørvestsnaget Basin in the southwest Barents Sea. A variety of complementary techniques record a provenance change across the Paleocene-Eocene boundary in wellbore BH 10-2008, which samples Paleogene strata of the Central Tertiary Basin in Spitsbergen. Sandstones containing K-feldspar with radiogenic Pb isotopic compositions, chrome spinel in the heavy mineral assemblage, and detrital zircons and rutiles with prominent Palaeoproterozoic and Late Palaeozoic—Early Mesozoic U-Pb age populations are up-section replaced by sandstone containing albitic plagioclase feldspar, metasedimentary schist rock fragments, a heavy mineral assemblage with abundant chloritoid, metamorphic apatite with low REE contents, metapelitic rutile with Silurian U-Pb ages and zircons with predominantly Archaean and Palaeoproterozoic U-Pb age populations. Our results clearly demonstrate the well-known regional change in source area from an exposed Barents Shelf terrain east of the Central Tertiary Basin during the Paleocene to the emerging Eurekan mountains west and north of the Central Tertiary Basin during the Eocene. Eocene sandstones deposited in the marginal basins of the southwestern Barents Shelf, which were sampled in wellbores 7316/5-1 and 7216/11-1S, contain elements of both the Eurekan and the eastern Barents Shelf provenance signatures. The mixing of the two sand types and delivery to the southwest margin of the Barents Shelf is consistent with a fill and spill model for the Central Teritary Basin, with transport of Eurekan-derived sediment east then south hundreds of kilometres across the Shelf.

A multi-proxy provenance study of Late Carboniferous to Middle Jurassic sandstones from the eastern Sverdrup Basin was undertaken employing optical petrography and heavy mineral analysis, chemical analysis of apatite, garnet and rutile grains, as well as detrital zircon U–Pb geochronology and Hf isotope analysis. Late Carboniferous to Middle Jurassic strata on the southern basin margin are inferred as being predominantly reworked from Silurian to Devonian strata within the adjacent Franklinian Basin succession. Higher-grade metamorphic detritus appeared during Middle to Late Triassic times and indicates exhumation and erosion of lower (Neoproterozoic to Cambrian) levels within the Franklinian Basin succession and/or a direct detrital input from the Canadian-Greenland Shield. The provenance of northern-derived sediments is more enigmatic owing to the subsequent opening of the Arctic Ocean. Northern-derived Middle Permian to Early Triassic sediments were likely derived from proximal areas of the Chukotkan part of the Arctic Alaska-Chukotka microplate. Late Triassic northern-derived sediments have different detrital zircon U–Pb age spectra from Middle Permian to Early Triassic ones and were likely derived from the Uralian orogenic belt and/or the Arctic Uralides. The loss of this sand input during latest Triassic times is interpreted to reflect drainage reorganisation farther upstream on the Barents Shelf. Middle Jurassic sands in the northern and axial parts of the basin were largely reworked from local northern-derived Late Triassic strata. This may have been facilitated by rift flank uplift of the northern basin margin in response to rifting in the adjacent proto-Amerasia Basin.

Hybrid event beds (HEBs) are tiered deep-water deposits that can include significant intervals of organic-rich muddy sandstone and sandy mudstone. They are emplaced by decelerating sediment gravity flows in which turbulence becomes extinguished due to increasing cohesion. Whilst several studies have addressed the distribution of organic matter (OM) in turbidites, the extent to which OM is segregated between the component HEB divisions has yet to be quantitatively addressed for clastic systems. Here we document bed scale fractionation of terrestrial OM in HEBs drawn from a range of deep-water sub-environments (basin floor sheets, outer fan fringes and mid-fan lobes) preserved in the Ross Sandstone Formation, western Ireland, a tropical Pennsylvanian deepwater fan complex. A suite of bulk geochemical techniques (TOC, Rock-Eval pyrolysis, delta 13C isotopes, and XRF scanning) and petrographic analyses were applied to HEB-dominated core intervals retrieved from four behindoutcrop boreholes. Results shows that muddy sandstones (H3 divisions) of the HEBs have significantly higher OM (average TOC = 1.2 wt% and up to 2.7 wt%) and mud contents than co-genetic cleaner sandstones (H1 divisions; average TOC = 0.2 wt% and up to 0.7 wt%). Muddy caps (H5 divisions) to the event beds have higher mud but relatively low OM contents (average TOC = 0.7 wt% and up to 1 wt%) compared to H3 divisions, implying textural fractionation of OM components, greater burn-down linked to slower suspension settling and/or downward propagation of oxidation fronts. HEBs can dominate distal lobe stratigraphy and are thus an important but under-represented sink for terrestrial carbon with enhanced preservation of OM in H3 divisions on account of rapid en-masse deposition, high mud abundances offering enhanced protection, and where thick, emplacement beyond the reach of oxidation fronts descending from the sea floor. The present study has important implications for understanding how carbon is buried and distributed in deep-water successions.

ABSTRACT This study documented the stratigraphy and provenance of the El Salto Formation in southern Baja California, Mexico, which represents an early Oligocene–early Miocene forearc basin developed during the subduction of the Farallon plate, in the immediate vicinity of La Reforma caldera, central part of Baja California Sur, Mexico. In the study area, El Salto Formation consists of three stratigraphic members. The lower member is characterized by intercalations of sandstones and conglomeratic sandstones that exhibit eolian large-scale cross-stratification. U-Pb detrital zircon geochronology implies maximum depositional ages of ca. 33–31 Ma. The middle member is characterized by successions of conglomeratic sandstones and sandstones with eolian and tidal large-scale cross-stratification. The member also contains ignimbrites, tuff, and andesite deposits, and its maximum deposition age is ca. 30–28 Ma. The ignimbrite collected at the top of this member has a crystallization age of ca. 28 Ma. The upper member is characterized by conglomerates, sandstones, and shales, with maximum depositional ages ranging from 28 to 23 Ma. Petrographically, sandstones of the El Salto Formation are composed of three petrofacies. Petrofacies A is rich in quartz with a greater contribution of felsitic volcanic lithic grains (Q55F21L24; recycled orogenic provenance). Petrofacies B is rich in lathwork and microlitic volcanic lithic fragments with minor contributions of quartz and feldspar (Q39F12L42; recycled orogenic and dissected arc), while petrofacies C is rich in microlitic volcanic fragments and lathwork with subordinate quartz and feldspar (Q21F25L54; transitional arc setting). U-Pb ages of >600 zircon grains from nine samples contained three populations: (1) 35–23 Ma (early and late Oligocene; 22% of all grains), (2) 120–60 Ma (Cretaceous; 32%), and (3) 170–140 Ma (Middle Jurassic–Early Cretaceous; 46%). Detrital zircon grains with ages of ca. 40–20 Ma showed rare earth element patterns and trace-element ratios similar to those formed in a continental arc. Volcanic rocks sampled in this work contained chemical signatures, including Nb, Pb, and Rb anomalies, that indicate their magmas were created in a subduction zone. In addition, high concentrations of heavy rare earth elements (La/Yb = 14–19) suggest that the magmas contain a component of partial melting of the mantle wedge and crust, probably as a result of asthenospheric upwelling. These features support a model in which the El Salto Formation was developed due to the rollback of the Farallon plate in the period 50–25 Ma.

Carbonate rocks undergo low-temperature, post-depositional changes, including mineral precipitation, dissolution, or recrystallisation (diagenesis). Unravelling the sequence of these events is time-consuming, expensive, and relies on destructive analytical techniques, yet such characterization is essential to understand their post-depositional history for mineral and energy exploitation and carbon storage. Conversely, hyperspectral imaging offers a rapid, non-destructive method to determine mineralogy, while also providing compositional and textural information. It is commonly employed to differentiate lithology, but it has never been used to discern complex diagenetic phases in a largely monomineralic succession. Using spatial-spectral endmember extraction, we explore the efficacy and limitations of hyperspectral imaging to elucidate multi-phase dolomitization and cementation in the Cathedral Formation (Western Canadian Sedimentary Basin). Spectral endmembers include limestone, two replacement dolomite phases, and three saddle dolomite phases. Endmember distributions were mapped using Spectral Angle Mapper, then sampled and analyzed to investigate the controls on their spectral signatures. The absorption-band position of each phase reveals changes in %Ca (molar Ca/(Ca + Mg)) and trace element substitution, whereas the spectral contrast correlates with texture. The ensuing mineral distribution maps provide meter-scale spatial information on the diagenetic history of the succession that can be used independently and to design a rigorous sampling protocol.

The geometry, distribution, and rock properties (i.e. porosity and permeability) of turbidite reservoirs, and the processes associated with turbidity current deposition, are relatively well known. However, less attention has been given to the equivalent properties resulting from laminar sediment gravity-flow deposition, with most research limited to cogenetic turbidite-debrites (i.e. transitional flow deposits) or subsurface studies that focus predominantly on seismic-scale mass-transport deposits (MTDs). Thus, we have a limited understanding of sub-seismic MTDs ability to act as hydraulic seals and their effect on hydrocarbon production, and/or carbon storage and sequestration. We investigate the gap between seismically resolvable and sub-seismic MTDs and transitional flow deposits on long-term reservoir performance in this analysis of a small (<10 km radius submarine fan system), Late Jurassic, sandstone-rich stacked turbidite reservoir (Magnus Field, northern North Sea), which is supported by a relatively long (c. 37 years) and well-documented production history. We use core, petrophysical logs, pore fluid pressure, quantitative evaluation of minerals by scanning electron microscopy (QEMSCAN), and 3D seismic-reflection datasets to quantify the type and distribution of sedimentary facies and rock properties. A range of sediment gravity deposits are recognised: (i) thick-/thin- bedded, structureless and structured turbidite sandstone, constituting the primary productive reservoir facies (c. porosity = 22%, permeability = 500 mD), (ii) a range of transitional flow deposits, and (iii) heterogeneous mud-rich sandstone interpreted as debrites (c. porosity = <10%, volume of clay = 35%, up to 18 m thick). Results from this study show that over the production timescale of the Magnus Field, debrites act as barriers, compartmentalising the reservoir into two parts (upper and lower reservoir), and transitional flow deposits act as baffles, impacting sweep efficiency during production. Prediction of the rock properties of laminar and transitional flow deposits, and their effect on reservoir distribution, has important implications for: (i) exploration play concepts, particularly in predicting the seal potential of MTDs, (ii) pore pressure prediction within turbidite reservoirs, and (iii) the impact of transitional flow deposits on reservoir quality and sweep efficiency.

Heavy minerals are typically rare but important components of siliciclastic sediments and rocks. Their abundance, proportions, and variability carry valuable information on source rocks, climatic, environmental and transport conditions between source to sink, and diagenetic processes. They are important for practical purposes such as prospecting for mineral resources or the correlation and interpretation of geologic reservoirs. Despite the extensive use of heavy mineral analysis in sedimentary petrography and quite diverse methods for quantifying heavy mineral assemblages, there has never been a systematic comparison of results obtained by different methods and/or operators. This study provides the first interlaboratory test of heavy mineral analysis. Two synthetic heavy mineral samples were prepared with considerably contrasting compositions intended to resemble natural samples. The contributors were requested to provide (i) metadata describing methods, measurement conditions and experience of the operators and (ii) results tables with mineral species and grain counts. One hundred thirty analyses of the two samples were performed by 67 contributors, encompassing both classical microscopic analyses and data obtained by emerging automated techniques based on electron-beam chemical analysis or Raman spectroscopy. Because relatively low numbers of mineral counts (N) are typical for optical analyses while automated techniques allow for high N, the results vary considerably with respect to the Poisson uncertainty of the counting statistics. Therefore, standard methods used in evaluation of round robin tests are not feasible. In our case the 'true' compositions of the test samples are not known. Three methods have been applied to determine possible reference values: (i) the initially measured weight percentages, (ii) calculation of grain percentages using estimates of grain volumes and densities, and (iii) the best-match average calculated from the most reliable analyses following multiple, pragmatic and robust criteria. The range of these three values is taken as best approximation of the 'true' composition. The reported grain percentages were evaluated according to (i) their overall scatter relative to the most likely composition, (ii) the number of identified components that were part of the test samples, (iii) the total amount of mistakenly identified mineral grains that were actually not added to the samples, and (iv) the number of major components, which match the reference values with 95% confidence. Results indicate that the overall comparability of the analyses is reasonable. However, there are several issues with respect to methods and/or operators. Optical methods yield the poorest results with respect to the scatter of the data. This, however, is not considered inherent to the method as demonstrated by a significant number of optical analyses fulfilling the criteria for the best-match average. Training of the operators is thus considered paramount for optical analyses. Electron-beam methods yield satisfactory results, but problems in the identification of polymorphs and the discrimination of chain silicates are evident. Labs refining their electron-beam results by optical analysis practically tackle this issue. Raman methods yield the best results as indicated by the highest number of major components correctly quantified with 95% confidence and the fact that all laboratories and operators fulfil the criteria for the best-match average. However, a number of problems must be solved before the full potential of the automated high-throughput techniques in heavy mineral analysis can be achieved.

The first step in most geochronological studies is to extract dateable minerals from the host rock, which is time consuming, removes textural context, and increases the chance for sample cross contamination. We here present a new method to rapidly perform in situ analyses by coupling a fast scanning electron microscope (SEM) with Energy Dispersive X-ray Spectrometer (EDS) to a Laser Ablation Inductively Coupled Plasma Mass Spectrometer (LAICPMS) instrument. Given a polished hand specimen, a petrographic thin section, or a grain mount, Automated Phase Mapping (APM) by SEM/EDS produces chemical and mineralogical maps from which the X-Y coordinates of the datable minerals are extracted. These coordinates are subsequently passed on to the laser ablation system for isotopic analysis. We apply the APM+LAICPMS method to three igneous, metamorphic, and sedimentary case studies. In the first case study, a polished slab of granite from Guernsey was scanned for zircon, producing a 6098 Ma weighted mean age. The second case study investigates a paragneiss from an ultra high pressure terrane in the north Qaidam terrane (Qinghai, China). One hundred seven small (25 mu m) metamorphic zircons were analyzed by LAICPMS to confirm a 4194 Ma age of peak metamorphism. The third and final case study uses APM+LAICPMS to generate a large provenance data set and trace the provenance of 25 modern sediments from Angola, documenting longshore drift of Orange River sediments over a distance of 1,500 km. These examples demonstrate that APM+LAICPMS is an efficient and cost effective way to improve the quantity and quality of geochronological data. Plain Language Summary Much progress has been made in improving the accuracy and precision of geochronological data. However, many Earth Science applications do not so much require better, but simply more data. We have developed a new analytical workflow that is more than twice as efficient than the current state of the art. This new workflow combines a fast scanning electron microscope with a mass spectrometer to simultaneously characterise the chemical, mineralogical and isotopic composition of rocks and minerals. We have applied the new instrument suite to three distinct geological settings to generate high quality data in a fraction of the time that it would have taken conventional studies of the same size and scope.

Thick Triassic siliciclastic units form major reservoir targets for hydrocarbon exploration on the Barents Shelf; however, poor reservoir quality, possibly associated with variation in provenance, remains a key risk factor in the area. In this study, sandstone dispersal patterns on the southwest Barents Shelf are investigated through petrographic and heavy mineral analysis, garnet and rutile geochemistry and zircon U-Pb geochronology. The results show that until the Early Norian Maximum Flooding Surface, two contrasting sand types were present: (i) a Caledonian Sand Type, characterised by a high compositional maturity, a heavy mineral assemblage dominated by garnet and low chrome-spinel:zircon (CZi) values, predominantly metapelitic rutiles and mostly Proterozoic and Archaean detrital zircon ages, interpreted to be sourced from the Caledonides, and (ii) a Uralian Sand Type, characterised by a low compositional maturity, high CZi values, predominantly metamafic rutiles and Carboniferous zircon ages, sourced from the Uralian Orogeny. In addition, disparity in detrital zircon ages of the Uralian Sand Type with contiguous strata on the northern Barents Shelf reveals the presence of a Northern Uraloid Sand Type, interpreted to have been sourced from Taimyr and Severnaya Zemlya. As such, a coincidental system is inferred which delivered sand to the Northern Barents Shelf in the late Carnian/early Norian. Following the Early Norian Maximum Flooding Surface, a significant provenance change occurs. In response to Late Triassic/Early Jurassic hinterland rejuvenation, supply from the Uralian Orogen ceased and the northern Scandinavian (Caledonian) source became dominant, extending northwards out on to the southwest Barents Shelf. The data reveal a link between reservoir quality and sand type and illustrate how provenance played an important role in the development of clastic reservoirs within the Triassic of the Barents Shelf.

Sandstone framework-grain petrography, optical and QEMSCAN (Quantitative Evaluation of Minerals by Scanning Electron Microscopy) heavy mineral analysis carried out on 40 samples collected from east and west southern Taimyr are used to constrain the provenance and tectonic history of Late Carboniferous to Late Jurassic siliciclastic sequences. The tectonic settings of provenance evolved gradually from a mix of volcanic arc and recycled orogen to craton interior. Much of the detritus in the Late Paleozoic to Mesozoic siliciclastic succession came from proximal sources with contributions from multi-type source rocks including acid igneous rocks, basalts, sedimentary rocks and low to medium-grade metamorphic rocks. Carboniferous to Permian sandstones contain low-diversity suites of heavy minerals, including apatite, tourmaline, zircon, rutile, Cr-spinel, monazite and titanite. Cr-spinel indicates probable influx from exposed ophiolitic basement. Abundant euhedral zircon and apatite suggest a volcanic arc source related with Uralian collision. The appearance of garnet in the early Triassic signals the unroofing of a metamorphic source. The abrupt increase of clinopyroxene in Middle to Late Triassic sandstones indicates the influx of detritus from basic rocks related with Siberian Trap magmatism. The decrease of Cr-spinel and an abundance of staurolite in Jurassic samples indicate that unroofing of an ophiolitic source ceased and that stripping of a different thrust sheet containing plenty of staurolite-bearing metamorphic rocks commenced.

The sedimentary and provenance characteristics of seven Permo-Carboniferous and two early Cretaceous samples from the Taimyr Peninsula provide information about the latest evolution of Uralian orogeny and the opening of the Amerasian Basin. The Permo-Carboniferous samples have a mixed provenance of recycled and first cycle sediment, sourced from metamorphic and igneous terranes. U-Pb detrital zircon ages represent a mixture of Precambrian-Paleozoic grains with euhedral, penecontemporaneous late Carboniferous and Permian grains consistent with derivation from the Uralian Orogen, plus additional Timanian and Caledonian material presumably derived from Baltica. Differences between the late Permian sample and the other Carboniferous and early Permian samples are interpreted to reflect the final collisional stage of Uralian orogeny. Early Cretaceous sediments deposited at the time of the Amerasian Basin opening preserve a mixed provenance of mainly first cycle metamorphic and igneous source material, as well as an unstable heavy mineral assemblage dominated by staurolite, suggesting local derivation. Detrital zircon ages fall almost exclusively into one late Permian-early Triassic cluster, indicating a Siberia Trap-related magmatic source. The detrital zircon age spectra support a passive margin setting for Taimyr during the opening of the Amerasian Basin in the early Cretaceous.

The Arctic region is dominated by the Arctic Ocean, which contains two deep oceanic basins and is surrounded by the shallow shelves of Alaska, the Canadian Arctic Islands, Greenland, Scandinavia and the Russian Arctic. The Arctic Ocean basins, the Amerasia and Eurasia basins, formed by rifting and spreading during Cretaceous and Tertiary time. Whilst the tectonic history of the Eurasia Basin is fairly well understood, there is great uncertainty surrounding the opening history of the Amerasia Basin. It is unclear how various Arctic plates were juxtaposed prior to Amerasia Basin formation and when and how they separated.

Summary The Late Paleozoic-Mesozoic strata of the Sverdrup Basin and the overlying Cenozoic deposits have been examined during three field seasons on Ellesmere and Axel Heiberg islands, Canadian Arctic. These field studies are supported by an ongoing analytical programme involving integrated biostratigraphic analysis and a variety of sediment provenance analyses. The results from this integrated study will help to constrain not only the tectonic evolution of the Sverdrup Basin and its Cenozoic exhumation, but will also define the character of the sediment sources which were eroded to generate its fill. Here, we present some preliminary data and