Seasonal changes in basal conditions at Briksdalsbreen, Norway: the winter–spring transition

The winter–spring transition is a dynamic time within the glacier system, because it marks a period of instability as the glacier undergoes a change in state from winter to summer. This period is normally associated with sudden pressure fluctuations resulting in hydrological instabilities within the subglacial drainage system. New data are presented from wireless multi-sensor subglacial probes incorporated within the till at Briksdalsbreen, Norway. Water pressure readings recorded a two-phase winter–spring transition. Event 1 occurred early in the year (December–January) and marked the start of activity within the subglacial environment following the winter. However, this did not result in any permanent changes in subglacial activity and was followed by a period of quiescence. Event 2 occurred later in the year in accordance with changing external weather conditions and the retreat of the snow pack. It was characterized by high-magnitude pressure peaks and diurnal oscillations in connected regions. The variations in sensor trends that followed this event suggested that a transition in the morphology of the subglacial drainage system had occurred in response to these pressure fluctuations. Event 2 also showed some similarities with spring events recorded at valley glaciers in the Alps. A conceptual model is presented associating the form of the winter–spring transition with respect to the location of the probes within connected and unconnected regions of the subglacial drainage system. These data provide further evidence for temporal and spatial heterogeneous subglacial drainage systems and processes. The identification and analysis of subglacial activity during the winter–spring transition can contribute to the interpretation of hydro-mechanical processes occurring within the subglacial environment and their effect on glacier dynamics.     

Thermochemical sulphate reduction in the Upper Devonian Cairn Formation of the Fairholme carbonate complex (South-West Alberta, Canadian Rockies): evidence from fluid inclusions and isotopic data

The Fairholme carbonate complex is part of the extensively dolomitized Upper Devonian carbonate reefs in west-central Alberta. The studied formations contain moulds (up to 10 cm in diameter), which are filled partially with (saddle) dolomite, quartz and calcite cements. These cements precipitated from a mixture of brines that acquired high salinity by dissolution of halite and brines derived from evaporated sea water. The fluids were warm (homogenization temperature of primary fluid inclusions of 76 to 200 °C) and saline (20 to 25 wt% NaCl equivalent) and testify to thermochemical sulphate reduction processes. The latter is deduced from S in solid inclusions, CO₂ and H₂S in volatile-rich aqueous inclusions and depleted δ¹³C values down to −26‰ Vienna Pee Dee Belemnite. High ⁸⁷Sr/⁸⁶Sr values (0·7094 to 0·7110) of the cements also indicate interaction of the fluids with siliciclastic sequences. The thermochemical sulphate reduction-related cements probably formed during early Laramide burial. Another (younger) calcite phase, characterized by depleted δ¹⁸O values (−23·9‰ to −13·9‰ Vienna Pee Dee Belemnite), low Na (27 to 37 p.p.m.) and Sr (39 to 150 p.p.m.) concentrations and non-saline (∼0 wt% NaCl equivalent) fluid inclusions, is attributed to post-Laramide meteoric water.     

Geomorphology of the eastern Badia basalt plateau, Jordan

The eastern Badia of the Hashemite Kingdom of Jordan is a landscape developed predominantly on late Tertiary and Quaternary basalt lava flows, which vary in age between 8.9 million and 0.1 million years. Pyroclastic deposits are associated with remnant volcanic cones. There is limited, seasonal rainfall. Natural vegetation regenerates during cool, damp months. Slopes, which range from concave to convex forms and have varying relief, can be related to different basalts and the time since emplacement. Much of the ground surface is mantled with boulders. In many places the continuity of boulder cover produces a desert pavement. Clasts show differing degrees of burial or exhumation, depending on the surrounding topography. Water and sediment movement are important to landscape development. Much sediment is deposited in pans, which evolve at topographic lows. The pans, known locally as Qa, vary in form depending on drainage network development. Transitional forms, known as Marab, develop where wadis widen out and sediments are deposited along ephemeral channels. Groundwater is significant, with three aquifers beneath much of the eastern Badia. Recharge of the upper aquifer is predominantly on the footslopes of the Druze Mountains, with north to south flow. Groundwater extraction has resulted in the expansion of agriculture, with consequent changes in soil and water quality.     

Bar development in a fluvial sandstone (Westphalian 'A'), Scotland

The fluvial sandstone beneath the Mill Coal in the Westphalian ‘A’ of Scotland erosively overlies a lake mudstone. Slightly erosive surfaces within the sandstone, traceable for over 200 m, are used to divide it into two types of major sedimentary units termed type A and type B. Type A sand units are approximately 200 m wide, up to 7 m thick, convex upward, and lenticular in all directions. The constituent cosets overlap to the ENE and dip mainly at 1–2° downcurrent (NNW), but locally at 10–15°. Where thickest, type A sand units display a vertical facies sequence commencing with trough cross-bedded and massive sandstone, overlain by a thick zone of ripple cross-lamination, a thin zone of trough cross-beds, and a variably eroded silt drape up to 0.4 m thick. Attenuated lateral margins are dominated by flat bedded sandstone with primary current lineation. Type A sand units are interpreted as deposits which were accreted on to a large fluvial bar during successive flood events. The bar is thought to have had a similar topographic significance to sand waves described from the Brahmaputra and slip face bounded bars observed in the South Saskatchewan river. Palaeocurrents measured from trough cross-bed sets 0.3–1.0 m thick within type B sand units indicate flow to the WSW, perpendicular to the palaeoflow direction measured from type A units. In sections perpendicular to the WSW flow direction type B units are lenticular, and in ENE-WSW trending sections they can be traced for over 80 m at a constant thickness. Type B sand units are interpreted as the product of low stage channels which flowed across bar fronts and tops. The sandstone described herein is interpreted as a braided-type river deposit but is atypical, because it is fine grained and has an internal structure dominated by ripple cross-lamination and upper phase plane beds. The palaeoriver is thought to have been of low sinuosity, 7–10 m deep, with a high suspended load and large rapidly fluctuating discharge. At low stage a braided-type flow pattern developed around submerged bars. The regime of the palaeoriver was probably controlled by the fine sediment grain size and humid tropical climate.