Kilometre‐scale sand injectites in the intracratonic Murzuq Basin (South‐west Libya): an igneous trigger?

Mount Telout, situated at the edge of the Murzuq Basin, is a 325 m high conical hill within a circular collapse structure that records 0·5 km³ of sand intrusion into Silurian shales. Based on a comparison with other similar circular collapse structures around the Murzuq Basin, it is argued that sand injection in the form of pipes occurred during the Devonian. The overpressures triggering the process are inferred to result from a combination of: (i) tectonic uplift at a basin scale that initially focused regional ground water flows; and (ii) igneous intrusion within the sand‐rich Cambrian–Ordovician strata. The palaeorelief buried under the regionally extensive Silurian shales may have locally focused overpressures and localized sand injection at the 1 to 10 km scale. The Mount Telout injected sandbody and related features offer exceptional, seismic‐scale outcrop analogues for sand injections that are often identified in seismic reflection data. Large‐scale sand injections might be essential in petroleum exploration of the North African Lower Palaeozoic basins as they form seal‐bypass systems.     

Controls on large‐scale patterns of fluvial sandbody distribution in alluvial to coastal plain strata: Upper Cretaceous Blackhawk Formation,Wasatch Plateau,Central Utah,USA

Current models of alluvial to coastal plain stratigraphy are concept‐driven and focus on relative sea‐level as an allogenic control. These models are tested herein using data from a large (ca 100 km long and 300 m thick), continuous outcrop belt (Upper Cretaceous Blackhawk Formation, central Utah, USA). Many channelized fluvial sandbodies in the Blackhawk Formation have a multilateral and multistorey internal character, and they generally increase in size and abundance (from ca 10% to ca 30% of the strata) from base to top of the formation. These regional, low‐resolution trends exhibit much local variation, but are interpreted to reflect progressively decreasing tectonic subsidence in the upper Blackhawk Formation and overlying Castlegate Sandstone. The trend may also incorporate progressively more frequent channel avulsion during deposition of the lower Blackhawk Formation. Laterally extensive coal zones formed on the coastal plain during shallow‐marine transgressions, and define the high‐resolution stratigraphic framework of the lower Blackhawk Formation. Large (up to 25 m thick and 1 to 6 km wide), multistorey, multilateral, fluvial channel‐complex sandbodies that overlie composite erosion surfaces occur at distinct stratigraphic levels, and are interpreted as fluvial incised valley fills. Low amplitude (<30 m) relative sea‐level variations are interpreted as the dominant control on stratigraphic architecture in the lower Blackhawk Formation, which was deposited up to 50 km inland from the coeval shoreline. In contrast, the high‐resolution stratigraphy of the upper Blackhawk Formation is poorly defined, and channelized fluvial sandbodies are poorly organized. Vertical and laterally offset stacking of a small proportion (<10%) of sandbodies produced ‘clusters’ that are not confined by ‘master’ erosion surfaces. Avulsion is interpreted to dominate the stratigraphic architecture of the upper Blackhawk Formation. This data‐driven analysis indicates that alluvial to coastal plain stratigraphic architecture reflects a combination of various allogenic controls and autogenic behaviours. The relative sea‐level control emphasized in sequence stratigraphic models is only rarely dominant.     

The coal geology of China

Known coal reserves in China are about 1031 billion tonnes, while the predicted resources are 3800 billion tonnes. China is currently the world's largest coal producer, with over 1 billion tonnes'production in 1990. It is not surprising to discover, therefore, that coal is not only geographically widespread in the country but also occurs in every stratigraphic interval upwards from the Devonian (and even earlier) and is found in almost every conceivable depositional setting. With seams over 200 m thick in some basins, Chinese coals offer many geological as well as mining challenges .     

Climate change and 'anomalous' glacier fluctuations: the southwest outlets of Mrdalsjökull, Iceland

Evidence of past glacier fluctuations is valuable palaeoenvironmental data, but determining their relationship to climatic change is sometimes complex because of differing glacier sensitivities and patterns of response. In Iceland, a diverse range of glaciation creates changing geographical patterns of response to climatic changes. The outlet glaciers of the Márdalsjökull ice cap in southern Iceland have produced detailed, but differing, records of change. For a key southwestern sector of the ice cap, we specifically searched for evidence equivalent to the c . 4500 BP, c . 3100 BP and c . 1200 BP advances of Sólheimajökull reported earlier. A combination of geomorphological mapping and dating by tephrochronology and lichenometry was used to constrain the glacier advances and determine the relative magnitude of Neoglacial glacier episodes. This is a key step towards creating a record of the changes for the entire ice cap. Major glacier advances c . 4500–1000 BP previously identified on the southern margin of Márdalsjökull are shown not to have occurred in this sector, where Neoglacial maxima occur post-1755 AD.     

Sedimentary facies of a glacially influenced continental succession in the Pennsylvanian Jericho Formation, Galilee Basin, Australia

Recent work on the Late Palaeozoic Ice Age in eastern Australia has shown the Joe Joe Group in the eastern Galilee Basin, Queensland, to be of critical importance as it is one of few records of Pennsylvanian glacial activity outside South America. This paper presents detailed sedimentological data, from which the Late Palaeozoic environment of the region is reconstructed and which, consequently, allows for robust comment on the broader Gondwanan glaciation. The Jericho Formation, in the lower Joe Joe Group, was deposited in an active extensional basin in lacustrine to fluvial environments, during the mid‐Namurian to early Stephanian. The region experienced a cool climate during this time, and polythermal mountain or valley‐type glaciers periodically advanced into the area from highlands to the north‐east. The Jericho Formation preserves a suite of proglacial to terminal glacial facies that is characterized by massive and stratified diamictites deposited from debris flows, massive and horizontally laminated conglomerates and sandstones deposited from hyperconcentrated density flows, laminated siltstones with outsized clasts and interlaminated siltstone/conglomerate deposited through ice‐rafting into lakes, and sedimentary dykes and breccias deposited through overpressurization of groundwater beneath permafrost. Non‐glacial facies are dominated by fluvial sandstones and lacustrine/overbank siltstones. The glacigenic rocks of the Jericho Formation are confined to discrete packages, recording three separate glacial advances during the latest Namurian to late Westphalian. This arrangement is consistent with the temporal distribution of glacigenic rocks from around the remainder of Australia and Gondwana, which supports the theory that glacial deposits occurred in discrete intervals. The Joe Joe Group is a key succession in the world in this context as, at this time, eastern Australia provides the only unequivocal evidence of a Namurian/Westphalian glaciation outside South America. The continuous record of sedimentation through the Pennsylvanian and Early Permian is indicative of significant warming between glacial intervals, which is difficult to reconcile with the development of long‐lived, cold‐based ice sheets across the supercontinent.     

QUANTIFYING UNCERTAINTY IN USING MULTIPLE DATASETS TO DETERMINE SPATIOTEMPORAL ICE MASS LOSS OVER 101 YEARS AT KÅRSAGLACIÄREN,SUB‐ARCTIC SWEDEN

Glacier mass balance and mass balance gradient are fundamentally affected by changes in glacier 3D geometry. Few studies have quantified changing mountain glacier 3D geometry, not least because of a dearth of suitable spatiotemporally distributed topographical information. Additionally, there can be significant uncertainty in georeferencing of historical data and subsequent calculations of the difference between successive surveys. This study presents multiple 3D glacier reconstructions and the associated mass balance response of Kårsaglaciären, which is a 0.89 ± 0.01 km² mountain glacier in sub‐arctic Sweden. Reconstructions spanning 101 years were enabled by historical map digitisation and contemporary elevation and thickness surveys. By considering displacements between digitised maps via the identification of common tie‐points, uncertainty in both vertical and horizontal planes were estimated. Results demonstrate a long‐term trend of negative mass balance with an increase in mean elevation, total glacier retreat (1909–2008) of 1311 ± 12 m, and for the period 1926–2010 a volume decrease of 1.0 ± 0.3 × 10^–3 km³ yr^–1. Synthesising measurements of the glaciers’ past 3D geometry and ice thickness with theoretically calculated basal stress profiles explains the present thermal regime. The glacier is identified as being disproportionately fast in its rate of mass loss and relative to area, is the fastest retreating glacier in Sweden. Our long‐term dataset of glacier 3D geometry changes will be useful for testing models of the evolution of glacier characteristics and behaviour, and ultimately for improving predictions of meltwater production with climate change.     

STONE‐BANKED LOBES AS A PRODUCT OF MILD FREEZE–THAW ACTION: AN EXAMPLE FROM WESTERN TASMANIA,AUSTRALIA

This paper interprets a stone‐banked lobe on the upper western face of Mt Rufus, at an altitude of 1380 m in western Tasmania, Australia. The morphology of the deposit resembles that of a solifluction lobe. Field observations show vertical and downslope movement of pebbles, cobbles and small boulders over a single winter season. The movement is largely related to frost pull (10–15 cm) and shallow freeze–thaw processes promoting the downslope (up to 50 cm yr^–1) creep of material and the accumulation of coarse clasts at the lobe riser. The climate of Mt Rufus is strongly maritime and this is reflected in the limited duration and depth of penetration of frozen ground at this site during the 2013 winter. Despite the relatively mild climatic conditions, freeze–thaw processes are clearly the dominant geomorphic force operating at the site. These findings support observations of active stone‐banked lobes on sub‐Antarctic islands where intense freezing is absent. Both there and at Mt Rufus, movement is dominated by freeze–thaw processes operating in the upper c. 20 cm of the regolith. These are typical landforms of marginal freeze–thaw settings.     

Simulating forest and habitat change in south-east Alaska with the landscape model PAYSAGE

We used the landscape model PAYSAGE to demonstrate the use of GIS and simulation models for ecosystem management over a portion of Mitkof Island in the Tongass National Forest. The objectives of the study were to: 1) depict the natural heterogeneity in environment and resource distributions across the study area; 2) quantify changes in vegetation and vertebrate habitats (brown creeper, orange-crowned warbler, marten) during the period of commercial timber harvest (1954 to the present); and 3) simulate likely long-term changes in vegetation and vertebrate habitat under three management scenarios – the Tongass Forest Plan, the wildlife habitat conservation strategy, and the Pacific Fisheries Task Force strategy. The results indicated that productive forest lands and vertebrate habitats are naturally patchy in the study area due to topography and climate. This natural fragmentation was exacerbated by past logging, which targeted high-productivity old growth stands. This stand type was reduced in area by 76 per cent from 1954 to 1994. Patch density and mean patch size decreased during this time while mean nearest neighbour distance increased. Simulations of the three management scenarios for a 200-year period projected relatively minor differences in landscape patterns among the scenarios. This is because the forest plan scenario is relatively restrictive in timber harvest and because most of the area protected in the other two scenarios does nor currently support old growth. We discuss the role of decision-support tools such as PAYSAGE in adaptive ecosystem management and evaluate limitations of the model.     

Toward a model for airflow on the lee side of aeolian dunes

The interaction between dunes and the primary wind results in a complex pattern of secondary airflow on the lee side of dunes. From 15 dunes studied during transverse flow conditions at Padre Island in Texas, White Sands in New Mexico, and the Algodones in California, distinct flow regions can generally be recognized, with the overall flow structure comparing favourably to that proposed for subaqueous bedforms. Downwind of dunes with flow separation is a back-flow eddy that extends about four dune-brink heights downwind from the brink of the dune. Beyond the separation cell, the velocity profiles can be divided into regions based upon segments separated by ‘kinks’ in the velocity profiles. The interior is an area above the dunes of relative high wind speed but low velocity gradient. Beneath the interior is the wake, which consists of two layers. The upper wake exhibits an uppermost portion where the flow decelerates while the remainder exhibits accelerating flow, so that the overall velocity gradient decreases downwind. The lower wake exhibits low velocity gradients and wind speeds that accelerate downwind at all heights, but primarily near the top of the layer, thereby causing the velocity gradient to increase downwind. At about eight dune heights downwind, the upper and lower wakes equilibrate to a single profile with the kink between them no longer apparent. The lowest recognizable region is the internal boundary layer. It is recognized by a relatively steep velocity gradient below the wake, and never exceeds a few tens of centimetres in height for our data set. Because of acceleration and increasing shear stress within this layer, interdune flats are at least potentially erosional. Overall, the wake and internal boundary layer show a downward transfer of momentum from upper regions so that the flow recovers. Where flow separation does not occur, simple flow expansion down the lee-face causes flow deceleration.