Internal Stratigraphy Research Articles

Multi‐mode gravity tectonics during northern North Sea rifting: the Snorre fault block case

AbstractContinental rifts are characterized by up to 30 km wide rotated fault blocks with stratigraphic dip away from the central rift axis. Although gravity‐induced mass movements are well known features of collapsed fault block crests, I here demonstrate the occurrence of polymodal gravity‐driven mass transport down the back slope of a first‐order rift fault block. I identify (1) early sliding related to syntectonic crestal collapse of second‐order rift faults, (2) large‐scale bed‐parallel sliding of the L‐M Jurassic sedimentary package, and (3) the accumulation of two 7 km long, 1–2 km wide and up to 750 m thick volumes of complexly slumped material in the hanging walls of two ramp‐forming faults. Early sliding is documented by 100 m of repeated Brent Group stratigraphy in a cored well in the study area (well 34/4‐15A). These smaller slides have intact internal stratigraphy but show elevated deformation band densities. The seismic data also show evidence for ca. 2 km of massive translational sliding of the ca. 400 m thick and ca. 300 km2 large Jurassic section above a lowermost Jurassic bedding‐parallel detachment. This translational slide did not deform much internally, except for ductile folding where it slid over underlying active rift faults. Chaotic seismic facies in fault hanging walls are interpreted as contorted Jurassic beds, formed by multiple slumping and sliding events that stacked mobilized sediments into a 750 m thick column. These complex slump volumes occur where fault displacement is highest along two relayed faults. A model is favoured where the large translational slide ruptured with an opening of space against the fault that was progressively filled with slumped material from the footwall. While the large‐scale translational sliding only caused moderate internal subseismic deformation, early sliding and, particularly, the complex slumping caused significant internal deformation. This study shows the importance of carefully searching for and distinguishing between different types of mass movement in rift systems.

Application of handheld/portable spectroscopic tools to the identification, inner stratigraphy and mapping of archaeological metal artefacts

Field handheld/portable instrumentations, such as in-situ geochemical analyzers, have the potential to assist efficiently targeted geochemical archaeometry campaigns in detecting and quantifying specific elements. Non-destructive portable energy dispersive x-ray fluorescence and micro-destructive handheld laser-induced breakdown spectroscopy (LIBS) instrumentation were utilized to investigate the elemental composition, internal stratigraphy by depth profiling and microscale compositional mapping of five copper and two iron alloy artefacts collected from various ancient graves in the Minervino Murge area, Apulia, Italy. The primary elements identified by both techniques included Cu, Sn and Pb in copper alloys, and Fe with minor amounts of Cu and Pb in iron alloys. Furthermore, the elements Al, Ca, Si, Mg, Na and K, mostly originated from soil contamination, and the trace elements Sb, Ni and Zn were detected. The satisfactory performance of both techniques was assessed by their capacity to provide reproducible elemental composition data. Finally, the depth profile and mapping achieved by LIBS contributed to understanding the metal processing and history of the objects studied, so confirming both techniques to be robust analytical tools in outdoor archaeology and archaeometry campaigns.

Paleoproterozoic rift-related volcanism of the Karrat Group, west Greenland: New insights from lithofacies analysis and geochemistry of the Kangilleq Formation

Mafic volcanic rocks of the Paleoproterozoic Kangilleq Formation of the Karrat Group of West Greenland represent a submarine mafic volcanic sequence, erupted and deposited on the Rae craton of Greenland. The formation ranges from <100 m-thick to ∼500 m-thick, and consists of mafic volcaniclastic rocks, pillow lavas and massive basalt lavas that have undergone greenschist facies metamorphism, yet preserve primary volcanic textures such as pillows, drainage cavities, lobes, flow banding, autoclastic breccias, hyaloclastite, scoria and layering.Rocks of the Kangilleq Formation overlie the Archean Qeqertarssuaq Complex and are interleaved with and overlain by the ca. 1950 Ma Nûkavsak Formation. Based on detailed (1:200) mapping and high-precision geochemistry, rocks of the Kangilleq Formation are subdivided into the Kangiusiap and Umiammakku members. The Kangiusiap member is dominated by mafic, scoria-rich breccias, has sulfide mineralization, and is bound at the bottom and top by the Nûkavsak Formation. This member has subalkaline, transitional to tholeiitic, mid-ocean ridge basalt (MORB) to back arc basin basalt (BABB) signatures with a Nd-isotope value similar to the depleted mantle at 1.88 Ga. The Umiammakku member is dominated by pillow lavas, with subordinate amounts of massive lavas and volcaniclastic rocks, overlies the Qeqertarssuaq Complex and is overlain by, and interleaved with, the Nûkavsak Formation. It is alkaline with characteristics similar to modern ocean island basalts and Nd-isotopic values slightly lower than the depleted mantle at 1.88 Ga.The rocks of the Kangilleq Formation represent non-arc suites or suites that have only minor subduction zone or crustal input, and display geochemical signatures similar to basalts found in modern intracontinental back arc settings. Lithofacies, bedforms, internal stratigraphy, and the identification of synvolcanic faults, suggest it is the product of volcanic eruptions during incipient rifting within a back arc setting, and seafloor mass wasting events at fault scarps related to rifting. Based on the geological characteristics and its petrogenetic and tectonic history, the Kangilleq Formation is interpreted to be correlative with the Bravo Lake Formation of the Piling Group of northeastern Canada and records incipient rifting of the southern margin of the Rae craton in the Paleoproterozoic.

Picture Gorge Basalt: Internal stratigraphy, eruptive patterns, and its importance for understanding Columbia River Basalt Group magmatism

AbstractThe Picture Gorge Basalt (PGB) of the Columbia River Basalt Group (CRBG) has been previously thought to be limited in its eruptive volume (&amp;lt;3000 km3) and thought to not extend far from its type locality. At present, PGB represents only 1.1 vol% of the CRBG with a relatively limited spatial distribution of ~10,000 km2. New age data illustrate that the PGB is the earliest and longest eruptive unit compared to other main-phase CRBG formations and that some dated basaltic flows reach far (~100 km) beyond the previously mapped extent. This study focuses on extensive outcrops of basaltic lavas and dikes south of the type locality at Picture Gorge, in order to reassess the spatial distribution and eruptive volume of the PGB. Field observations coupled with geochemical data indicate that PGB lava flows and mafic dikes covered a significantly greater area than shown on the published geologic maps. We find that additional mafic dikes located farther south of the original mapped distribution have geochemical compositions and northwest-trending orientations comparable to the dikes of the Monument dike swarm. We also identify new lava flows that can be correlated where stratigraphic control is well defined toward the original mapped PGB distribution. Our analyses and correlations are facilitated by comparison of 20 major- and trace-element abundances via a principal component analysis. This statistical comparison provides a new detailed distribution of PGB with stratigraphic significance that more than doubles the total distribution of PGB lavas and dikes and brings the eruptive volume to a new minimum of at least ~4200 km3. Geochemically correlated basaltic lavas and dikes in the extended distribution of PGB represent the earlier and later sections of the internal PGB stratigraphy. This is an intriguing observation as new geochronological data suggest an eruptive hiatus of ~400 k.y. during PGB volcanic activity, which occurred from 17.23 Ma to 15.76 Ma.The geochemical identifiers used to differentiate PGB from other main-phase CRBG formations include lower TiO2 (&amp;lt;2 wt%) concentrations, lower incompatible trace-element (i.e., La, Th, and Y) abundances, and a more pronounced enrichment in large- ion- lithophile elements (LILEs) on a primitive mantle–normalized trace-element diagram (Sun and McDonough, 1989). Geochemical characteristics of PGB are interpreted to represent a magmatic source component distinct from the other main-phase CRBG units, possibly a localized backarc-sourced mantle melt. However, this source cannot be spatially restricted as there are observed PGB lava flows and dikes extending as far east as Lake Owyhee and as far south as Hart Mountain, covering at least 15,000 km2. In context with the existing stratigraphy and the new extent of PGB lavas and dikes, these ages and coupled geochemical signatures demonstrate this mantle component was not spatially localized but rather tapped across a wide region.

The role of the Computerized Tomography versus laboratory micro-excavation in the study of ancient cineraria. Ancillary or complementary?

Cremation is one of the most common treatments of a dead body in the prehistoric and ancient historic societies and it represents a challenge for physical anthropologists. The cinerary urn is a complex artifact that is the result of a series of funerary rites that includes the cremation ceremony, the selection of cremated remains, their position in the urn and the presence of funerary goods. Currently micro-excavation is considered a very precise method in the study of ancient cineraria. However, the Multi-Detector Computerized Tomography (MDCT) analysis allows a non-destructive archaeological and anthropological assessment of the urn. This technique appears to be, in a certain way, very similar to the traditional laboratory procedures of micro-excavation. This procedure allows for the possibility of a morphological study of the urn and of the funerary goods. The internal stratigraphy, the consistency of the ossilegium, the spatial arrangement of the cremated bone fragments, the metric and the morphological study of the bone fragments, and the paleopathological aspects can also be analyzed. Hereby we present our methodological experience with MDCT on several urns of different age, culture and geographical origin, comparing the MDCT data with the micro-excavation results.

Holocene ice-stream shutdown and drainage basin reconfiguration in northeast Greenland

Reliable knowledge of ice discharge dynamics for the Greenland ice sheet via its ice streams is essential if we are to understand its stability under future climate scenarios. Currently active ice streams in Greenland have been well mapped using remote-sensing data while past ice-stream paths in what are now deglaciated regions can be reconstructed from the landforms they left behind. However, little is known about possible former and now defunct ice streams in areas still covered by ice. Here we use radio-echo sounding data to decipher the regional ice-flow history of the northeastern Greenland ice sheet on the basis of its internal stratigraphy. By creating a three-dimensional reconstruction of time-equivalent horizons, we map folds deep below the surface that we then attribute to the deformation caused by now-extinct ice streams. We propose that locally this ancient ice-flow regime was much more focused and reached much farther inland than today’s and was deactivated when the main drainage system was reconfigured and relocated southwards. The insight that major ice streams in Greenland might start, shift or abruptly disappear will affect future approaches to understanding and modelling the response of Earth’s ice sheets to global warming.

Integrated geophysical and geomatic studies at Ghar Dalam Cave, Malta’s oldest prehistoric site

Abstract The Ghar Dalam cave, southern Malta, hosts the oldest human evidence in the Maltese archipelago. Although the internal stratigraphy of the cave and its biotic record is well studied, the possibility of archaeological / paleontological prospects in the surrounding areas requires additional studies. In this work we use aerial and ground-based photogrammetry to reconstruct the interior and the surface of the cave, and various geophysical techniques (GPR, passive seismic and ERT) to study the subsurface of the cave and its surroundings. The results have clarified the geometry of the soil-rock contact above and at the entrance of the cave and possible karstic structures have been identified. The authors conclude that this multidisciplinary methodology allows more reliable results to be achieved and is essential for studies where direct observation is not possible.

A Fully Automatic Algorithm for Reflector Detection in Radargrams Based on Continuous Wavelet Transform and Minimum Spanning Tree

Spaceborne radar sounding is a powerful technique in planetary subsurface exploration due to its large penetration ability into loose desiccated materials. Three radar sounders, Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS), shallow radar (SHARAD), and Mars Orbiter Subsurface Investigation Radar (MOSIR), are orbiting Mars and have obtained a large quantity of radargrams. These direct observations provide valuable information for deciphering subsurface structure and composition of Mars, which are critical for understanding internal stratigraphy, climate change, and orbital variation in the planet. For this reason, automatic, effective, and precise extraction of subsurface reflectors in radargrams is a prerequisite and remains as a challenge though recent studies have made great progresses. In this study, we propose a fully automatic method for reflector detection in radargrams using transform domain techniques and graph theory. In the preprocessing step, the spatial spectrum information is used to automatically extract region with reflectors in a radargram, which can significantly reduce the computational cost. Then, continuous wavelet transform (CWT) with double threshold is used to detect peaks in each frame, and minimum spanning tree (MST) is further used to connect the peaks based on global information. Our proposed method can quickly reconstruct the reflectors in radargrams with a relatively low tracking error rate, which is better than previous methods based on local information. To testify the effectiveness of the algorithm, we applied our algorithm to SHARAD radargrams in the two polar regions. The results show that more than 90% (80%) of the reflectors can be well-detected in the strong (weak) echo regions, and their subsurface information can be extracted efficiently. Compared with previous methods, our method has a higher degree of automation and a wider applicability. The proposed algorithm can be applied to analyze radargrams over large regions of Mars and other bodies.

Revealing Underdrawings in Wall Paintings of Complex Stratigraphy with a Novel Reflectance Photoacoustic Imaging Prototype.

Revealing precious hidden features by a completely non-invasive approach is one of the crucial issues in the Heritage Science field. In this regard, concealed fresco paintings still represent an analytical challenge. This paper addresses the specific issue in wall painting diagnostics by the photoacoustic (PA) imaging technique, already proven to be efficient in revealing underdrawings and internal stratigraphy in movable paintings on paper and canvas. A newly set-up reflection PA prototype was applied here for the first time to probe the charcoal, graphite and sinopia hidden sketch drawings in concealed (gypsum, limewash, overpainted) wall paintings. The results presented here push forward the frontiers of the PA imaging technique and point to its potential effectiveness of revealing hidden underdrawings in historical wall paintings with complex stratigraphy.

Subsistence shift and socio-economic response to cultural and climate changes among north-central Iberian megalithic groups

The insufficient attention traditionally paid to the complex mortuary biographies of megalithic graves has long obscured a significant amount of synchronic and diachronic information. The Rioja Alavesa region of north-central Iberia holds a number of megalithic graves with large skeletal assemblages that can generally be ordered by internal stratigraphy and/or relatively fine-grained radiocarbon chronologies, providing a rare opportunity to assess the potential of such information. Here, we undertake stable carbon and nitrogen isotope analyses of 125 human and seven animal bone collagen samples from six late prehistoric megalithic graves (La Cascaja, El Sotillo, San Martín, Alto de la Huesera, Chabola de la Hechicera and Longar) which, together with 107 previously published Late Neolithic/Early Chalcolithic (ca. 3600-2900 BC) bone collagen samples (100 humans and six animals) from the same tombs, are used to explore subsistence trends over time. This approach provides a means to address the socio-economic response of northern Iberian megalithic communities to the cultural and climatic changes occurring in late prehistory. Isotopic data are contextualized using palaeoenvironmental and osteoarchaeological information. The results show a significant shift in diet between the late Middle Neolithic and the Late Neolithic/Early Chalcolithic that coincides with marked changes in burial practices that are likely related to the transition from mainly pastoral to mixed farming economies. There may also be a change in subsistence between the Late Neolithic/Early Chalcolithic and the following periods, suggested by differences in δ15N values between the layers of the Alto de la Huesera megalithic grave, as well as in population and funerary dynamics. By contrast, an apparent continuity in subsistence is seen, at least isotopically, from the Middle Chalcolithic to the Bronze Age, despite clear changes in beliefs and socio-economic practices. These findings support the existence of substantial asynchronous changes in lifeways and ideology among Iberian megalithic groups and challenge the traditional idea of a long and uniform stability in late prehistoric northern Iberia.

Age and tectonic setting of the Quinebaug-Marlboro belt and implications for the history of Ganderian crustal fragments in southeastern New England, USA

Abstract Crustal fragments underlain by high-grade rocks represent a challenge to plate reconstructions, and integrated mapping, geochronology, and geochemistry enable the unravelling of the temporal and spatial history of exotic crustal blocks. The Quinebaug-Marlboro belt (QMB) is an enigmatic fragment on the trailing edge of the peri-Gondwanan Ganderian margin of southeastern New England. SHRIMP U-Pb geochronology and geochemistry indicate the presence of Ediacaran to Cambrian metamorphosed volcanic and intrusive rocks dated for the first time between ca. 540–500 Ma. The entire belt may preserve a cryptic, internal stratigraphy that is truncated by subsequent faulting. Detrital zircons from metapelite in the overlying Nashoba and Tatnic Hill Formations indicate deposition between ca. 485–435 Ma, with provenance from the underlying QMB or Ganderian crust. The Preston Gabbro (418 ± 3 Ma) provides a minimum age for the QMB. Mafic rocks are tholeiitic with trace elements that resemble arc and E-MORB sources, and samples with negative Nb-Ta anomalies are similar to arc-like rocks, but others show no negative Nb-Ta anomaly and are similar to rocks from E-MORB to OIB or backarc settings. Geochemistry points to a mixture of sources that include both mantle and continental crust. Metamorphic zircon, monazite, and titanite ages range from 400 to 305 Ma and intrusion of granitoids and migmatization occurred between 410 and 325 Ma. Age and chemistry support correlations with the Ellsworth terrane in Maine and the Penobscot arc and backarc system in Maritime Canada. The arc-rifting zone where the Mariana arc and the Mariana backarc basin converge is a possible modern analog.

Joint Inversion for Surface Accumulation Rate and Geothermal Heat Flow From Ice‐Penetrating Radar Observations at Dome A, East Antarctica. Part I: Model Description, Data Constraints, and Inversion Results

AbstractIce‐penetrating radar data contain a wealth of information about the bed and internal structure of the ice sheet. While these data have long been used to diagnose the presence of basal water, infer attenuation rates, or explore the internal stratigraphy of the ice sheet, they have rarely been used jointly in a formal inverse model for the ice sheet temperature structure. Here, we invert a coupled thermomechanical ice sheet and basal hydrology model to infer both geothermal heat flow (GHF) and accumulation rate from multiple classes of radar observations in the area around Dome A, East Antarctica. Our forward model solves for a coupled steady state between the ice sheet flow field, temperature, and basal hydrology, including melt, water transport, and freeze‐on. We fit radar observations of basal water, freeze‐on, and internal layers, along with a GHF prior based on aeromagnetic observations. We minimize the combined misfit function by first using an evolutionary algorithm followed by localized perturbation tests. In addition to inferring the spatial distribution of GHF and accumulation rate, we are also able to estimate the uncertainty about our best‐fit answer, as well as quantify how our result depends on each individual data constraint. Our results demonstrate a new method for combining multiple glaciological constraints into a single inverse model of the ice sheet, and give us a more rigorous picture of the information content provided by each data set. In a companion paper we analyze and interpret the best‐fit model.

New constraints on the chemical composition and outgassing of 67P/Churyumov-Gerasimenko

Strong heterogeneities in the composition of the volatile species have been detected in the coma of comet 67P/Churyumov-Gerasimenko (67P/C-G) by the ROSINA instrument onboard the ESA’s Rosetta spacecraft. However, it is not clear if these heterogeneities are indicative of heterogeneities in the near-surface nucleus composition or if the coma composition is mainly insolation-driven. In order to clarify the link between the composition of the nucleus and the composition of the coma we have performed numerical simulations and compare our results with measurements acquired by ROSINA/DFMS for three major volatile species namely, H2O, CO2, and CO. We use a previously published thermo-physical numerical model designed to study cometary nucleus evolution, including volatile outgassing and internal stratigraphy, as the comet orbits the Sun. The model follows schemes used for much of the past three decades to model cometary outgassing. Our results match well the experimental volatiles density measurements of ROSINA/DFMS for most of the Rosetta mission. They suggest that the outgassing pattern is mainly insolation-driven and the variations are caused by the tilt of rotation axis and eccentricity of the nucleus. The nucleus shows to 1st order a homogeneous composition and therefore we can provide constraints on the bulk volatiles composition of 67P/C-G nucleus which is dominated by H2O (91.4% ​± ​4.5%), then CO2 (6.7% ​± ​3.5%) and CO in small amount (1.9% ​± ​1.2%). However, in details, a dichotomy in composition between the northern and southern hemispheres of the comet is revealed. A CO/CO2 bulk composition ratio of about 0.6 ​± ​0.1 is required to reproduce the measurements from the northern hemisphere and about 0.2 ​± ​0.1 for the southern hemisphere. To match the data, the thermal properties of the nucleus surface must be modified by adding a thin desiccated dust mantle (~5 ​mm) for northern latitudes while this appears not to be necessary for southern latitudes. This may be related to the observed dichotomy in putative airfall deposits. We suspect that, because of thermal inertia, seasonally non-illuminated areas continue to outgas and influence the ROSINA measurements. This effect cannot be reproduced with the model. Therefore during some periods of the mission, the fits are not ideal. Finally, the outgassing of the different ices leads to a layered internal structure defined by the sublimation front of each ice and formation of harder layers close to the surface due to sublimation/condensation processes. However, the thermo-physical model overestimates the absolute volatiles production (mainly in the southern hemisphere) leading to an overestimation of the erosion rates. Further investigations will be performed to improve the thermo-physical model and the sensitivity analysis.

High-resolution portable-OSL analysis of Vegetated Linear Dune construction in the margins of the northwestern Negev dunefield (Israel) during the late Quaternary

Abstract Vegetated Linear Dunes (VLDs) are elongated dunes whose construction is controlled by vegetation and wind. Common in southern hemisphere drylands, they were mainly active in the late Pleistocene. VLDs vertically accumulate sand during elongation episodes and their internal stratigraphy thus serves as a proxy for major periods of strong winds. However, the framework of VLD buildup and elongation is constrained by low-resolution luminescence chronology. To overcome this gap this study applies high-resolution Portable Optically Stimulated Luminescence (POSL) profiling coupled with OSL dating and sedimentology of an exposed VLD section, combined with successive sections along a fluvially truncated downwind elongation trace of the dune at the margin of the stabilized northwestern Negev dunefield, Israel. POSL profiling of the VLD section revealed three statistically distinct stratigraphic units. Winnowing of very fine sand and silt grains can explain a higher ratio between quartz and heavy minerals in the upper VLD unit. This winnowing decreased dose rates and, consequently, reduced bulk POSL luminescence signals and De values in the upper unit. The two upper units of the VLD section date to the Younger Dryas while the basal unit dates to the Heinrich-1 event. OSL ages at the lower unit and at the section bases along the downwind elongation trace of the dune indicate initial elongation during the Heinrich-1 event, and even prior. The study demonstrates that beyond delineating accumulation stages and assigning stratigraphic units, POSL is a sensitive sensor of sedimentological and mineralogical differences within a dune profile, enabling correlation with OSL measurements.

Internal Stratigraphy of the Mesoarchean Keonjhar Siliciclastics, Singhbhum Craton, Eastern India: Paleogeographic Implications.

Abstract In comparison to the greenstone belt volcano-sedimentary successions, mature arenite dominated sedimentary deposits are very rarely preserved in Paleo-Mesoarchean rock record. Such arenitic deposits may be important for the recognition of extensive development of continental freeboard and onset of Phanerozoic style plate tectonics. The Keonjhar siliciclastics are ~715-m thick mature arenite-dominated Mesoarchean succession that unconformably overlies Paleo-Mesoarchean granite-greenstone core of the Singhbhum craton. The succession is mapped on 1:50,000 scale, and is designated as the Keonjhar Quartzite. It is subdivided into conglomerate dominated lower unit as the Asurkhol Member and mature arenite dominated upper unit as the Kamalpur Member. A lensoid body of iron ore clast bearing conglomerate unconformably overlies the Keonjhar Quartzite, and is designated here as the Chamakpur Conglomerate. The succession is repeated by three westerly dipping reverse faults that have upthrown the deeper parts of the basinal transects against shallower parts. The Asurkhol Member represents subaerial part of a coastal alluvial fan. The Kamalpur Member represents shallow-shelf depositional setting. Detailed mapping and recognition of the fault slices led to the reconstruction of the paleogeographic setting. The present study also highlights the importance for the stratigraphic correlation of the Keonjhar Quartzite with underlying metabasics of Malangtaoli- Jagannathpur lava and the overlying western IOG succession. The internal stratigraphic classification proposed here is also significant from economic point of view with regard to the occurrences of uraniferous QPCs in the Asurkhol Member and detrital iron ore deposits in the Chamakpur Conglomerate.

The Hell Creek Formation, Montana: A Stratigraphic Review and Revision Based on a Sequence Stratigraphic Approach

The Upper Maastrichtian fluvial Hell Creek Formation of the Fort Peck Lake area, Montana (and regional equivalents) is notable for its vertebrate fossils and for the K-Pg mass extinction at or near its upper contact. Despite intense study, internal stratigraphy of the Hell Creek Formation is still poorly constrained, hindering study. This work reviews the stratigraphy of the Hell Creek Formation, as currently understood, and proposes important revisions to the recently proposed type section, particularly concerning complexity of the Hell Creek Formation basal contact. This work also subdivides the Montanan Hell Creek Formation into four 4th order depositional sequences, superimposed over a 3rd order marine transgression. Sequence boundaries are defined by four, laterally continuous disconformities formed by pauses in the creation of accommodation space, marked by overlying amalgamated channel complexes, or less commonly, correlative interfluve paleosols. Cyclicity in Montana may be correlative with similar 4th order cyclicity and marine influence documented in North and South Dakota, Alberta, and Saskatchewan. Magnetostratigraphy and new biostratigraphic data support correlation of the upper Montanan sequence with the North Dakotan Cantapeta tongue (and overlying fines) and Canadian Scollard and Frenchman Formations.

Glaciological and Meteorological Conditions at the Chinese Taishan Station, East Antarctica

The glacio-meteorological characteristics of Princess Elizabeth Land in East Antarctica are poorly known due to a lack of measurement. This is problematic given the importance of this area for understanding ice sheet dynamics and climate change. We present a comprehensive approach (including field surveys, reanalysis data, remote sensing, and ice flow models) to investigate the glaciological and meteorological conditions in the vicinity of the new Chinese Taishan Station (73.864°S, 76.974°E) in Princess Elizabeth Land. We collected the datasets of satellite-derived ice surface velocities, surface mass balance, and wind field; mapped the ice thickness and internal layers around the Taishan Station site; and constructed profiles of the surface snow temperature and snow density. Also, we used transient thermodynamical 1-D vertical models to simulate the age of ice and the basal temperature with surface meteorological data and subglacial topography as boundary conditions. These investigations showed that Taishan Station is subject to a relatively high wind velocity, low temperatures (about -36 °C), and simple ice flow. The well-behaved internal layer stratigraphy implies that the ice flow of Taishan Station has been relatively stable, possibly for a long time. The fact that the internal layers are conformal with bed topography, there is a relatively higher basal ice age from ice modelling, and that the site lies over a bed depression filled with ice 1900 m thick, suggests that Taishan Station may be a good location for obtaining undisturbed old ice at depth. The combination of glacio-meteorological parameters suggests that Taishan Station is a potential drill site for the Chinese Antarctic Research Expedition (CHINARE) and an ideal logistical support location for proposed scientific field activities in the East Antarctic ice sheet (e.g. Dome A, Grove Mountains, and Princess Elizabeth Land).

Insights into drumlin development from ground-penetrating radar at Múlajökull, Iceland, a surge-type glacier

AbstractDrumlins form at the ice/bed interface through subglacial processes that are not directly observable. The internal stratigraphy of drumlins provides insight into how they developed and associated subglacial processes, but traditional stratigraphic logging techniques are limited to natural exposures and excavations. Using ground-penetrating radar, we imaged the internal stratigraphy of seven drumlins from a recently exposed drumlin field in the forefield of Múlajökull, Iceland. Data were collected with 100 and 200 MHz antennas with maximum resolvable depths of 8 and 4 m, respectively. Longitudinal echograms contained coherent down-ice dipping reflectors over the lengths of the drumlins. Near the drumlin heads (i.e., stoss sides), down-glacier dipping beds lie at high angles to the surface, whereas on the lee sides, the down-glacier dipping beds lie at low angles, or conform, to drumlin surfaces. Transverse echograms exhibited unconformities along the flanks of drumlin heads and conformable bedding across the lee side widths of the drumlins. These observations were ground-truthed with stratigraphic logs from a subset of drumlins and good agreement was found. The stratigraphic patterns support previous conclusions that drumlins at Múlajökull formed on a deformable bed through both depositional and erosional processes which may alternate between its surge and quiescent phases.

Neoproterozoic sedimentation and tectonics of the Laurentian midcontinent: Detrital zircon provenance of the Jacobsville Sandstone, Lake Superior Basin, USA and Canada

AbstractThe Neoproterozoic Jacobsville Sandstone outcrops along the south and east shores of Lake Superior, USA. It records intraplate deformation, some during its deposition and some afterwards, after the c. 1,100 Ma Midcontinent Rift (MCR) failed. Here we analyse 549 new detrital zircon ages from five sites, combined with prior data. Initially, local palaeo‐topography controlled the source material, including the MCR‐adjacent Penokean and Archaean rocks. With time the percentage of distal sources increased, including the c. 1,300–980 Ma Grenville orogeny and 1,480–1,360 Ma Granite‐Rhyolite Province. Sites near the Keweenaw fault contain a significant number of MCR‐age zircons, presumably uplifted to the surface, indicating fault motion during deposition. Only a relatively small percentage of 1,090–980 Ma Grenville‐age zircons from collisions to the east are present, suggesting that they were not efficiently transported to the Lake Superior area. This work is innovative in that it is the first to use detrital zircon geochronology to understand the internal stratigraphy of the Jacobsville Sandstone, whose provenance provides new information about the Neoproterozoic tectonic and sedimentary history of Laurentia.

Surface accumulation in Northern Central Greenland during the last 300 years

AbstractThe internal stratigraphy of snow and ice as imaged by ground-penetrating radar may serve as a source of information on past accumulation. This study presents results from two ground-based radar surveys conducted in Greenland in 2007 and 2015, respectively. The first survey was conducted during the traverse from the ice-core station NGRIP (North Greenland Ice Core Project) to the ice-core station NEEM (North Greenland Eemian Ice Drilling). The second survey was carried out during the traverse from NEEM to the ice-core station EGRIP (East Greenland Ice Core Project) and then onwards to Summit Station. The total length of the radar profiles is 1427 km. From the radar data, we retrieve the large-scale spatial variation of the accumulation rates in the interior of the ice sheet. The accumulation rates range from 0.11 to 0.26 m a−1ice equivalent with the lowest values found in the northeastern sector towards EGRIP. We find no evidence of temporal or spatial changes in accumulation rates when comparing the 150-year average accumulation rates with the 321-year average accumulation rates. Comparisons with regional climate models reveal that the models underestimate accumulation rates by up to 35% in northeastern Greenland. Our results serve as a robust baseline to detect present changes in either surface accumulation rates or patterns.