Geometry and facies of Tertiary clinothems, Spitsbergen

Sandstone clinothems from the Battfjellet Formation (Palaeogene) on Spitsbergen are locally exceptionally well preserved along depositional dip-parallel mountainsides. The clinothems are more than 1 km wide and more than 100 m thick. Superposition of several sandstone clinothems separated by mudstones reflects repeated shoreline progradation and transgression. Deposition took place partly on‘post-transgressional’ depositional shelves, and partly by contributing seaward-sloping wedges, or clinothems, to a ramp progradation. Shorelines dominated both by mouth bar and shoreface environments have been identified. The clinothems are organized into an overall progradational architecture with a geometry having features in common with progradational seismic facies.     

Dolomitization of the Devonian Swan Hills Formation, Rosevear Field, Alberta, Canada

The Swan Hills Formation (Middle-Upper Devonian) of the Western Canada Basin is host to several NW-SE-trending gas fields developed in massive replacement dolostone. One of these, the Rosevear Field, contains two major dolostone trends along opposing margins of a marine channel that penetrates into a platform-reef complex. Dolostones consist predominantly of branching and bulbous strdmatoporoid floatstones and rudstones with well-developed moldic and vuggy porosity. Replacement dolomite is coarsely crystalline (100-600 μm), inclusion-rich, composed of euhedral through anhedral crystals and has a blotchy to homogeneous red cathodoluminescence. Geochemically, replacement dolomite is characterized by (i) nearly stoichiometric composition (50.1-51.1 mol% CaCO₃), (ii) negative δ¹⁸O values (mean=-7.5‰, PDB) and (iii) variable ⁸⁷Sr/⁸⁶Sr ratios ranging from values similar to Late Devonian-Early Mississippian seawater (～0.7082) to radiogenic compositions comparable to saddle dolomite cements (>0.7100). Dolomitization began after widespread precipitation of early, equant calcite spar and after the onset of pressure solution, implying that replacement dolomite formed in a burial environment. Oxygen isotope data suggest that dolomite formed at 35-75°C, temperatures reached during burial in Late Devonian through Jurassic time, at minimum depths of 450 m. The linear NW-SE orientation of most dolomite fields in the Swan Hills Formation is suggestive of fault control on fluid circulation. Two models are proposed for fault-controlled circulation of dolomitizing fluids at the Rosevear Field. In the first, compaction-driven, updip fluid migration occurred in response to basin tilting commencing in the Late Palaeozoic. Deep basinal fluids migrating updip were focused into channel-margin sediments along fault conduits. The second model calls upon fault-controlled convective circulation of (i) warm Devonian-Mississippian seawater or (ii) Middle Devonian residual evaporitic brines. The overlap in ⁸⁷Sr/⁸⁶Sr and δ¹⁸O compositions, and similar cathodoluminescence properties between replacement and saddle dolomites provide evidence for neomorphism of some replacement dolomite. Quantitative modelling of Sr and O isotopes and Sr abundances suggests partial equilibration of some replacement dolomite with hot radiogenic brines derived during deep burial of the Swan Hills Formation in the Late Cretaceous-Palaeocene. Interaction of replacement dolomite with deep brines led to enrichment in ⁸⁷Sr while leaving δ¹⁸O similar to pre-neomorphism values.     

Postglacial climate and vegetation history, north-central Kola Peninsula, Russia: pollen and diatom records from Lake Yarnyshnoe-3

A sediment core from Lake Yarnyshnoe-3 (69°04'N; 36°04'E), an emerged coastal lake from the tundra of the north-central Kola Peninsula, has been analyzed for fossil pollen and diatoms. The pollen record shows the Younger Dryas event marked by increasing Artemisia coupled with decreases in Poaceae, Cyperaceae and Salix at c. 10 700 to 10 000 BP. This core provides the first well-defined palynological record of the Younger Dryas event on the Kola Peninsula. Stomates from Pinus were recovered from the core interval between 8000 and 6000 BP. The stomates, coupled with elevated values of pine pollen, indicate that Pinus sylvestris grew near the arctic coastline of the central Kola Peninsula in the middle Holocene. However, the small number of stomates suggests that pines were not plentiful. The diatom record from the core reflects basin isolation from the sea and indicates additional limnological changes during the climate transition between c. 5000 and 4000 BP. The broadly similar climate and vegetation history on the north-central Kola Peninsula and in Fennoscandia demonstrates the propagation of late glacial and Holocene climate events from the North Atlantic region into the Eurasian Arctic.     

Late Devensian and Holocene depositional environments associated with the coversand around Caistor, north Lincolnshire, UK

Sand deposits described at three sites near Caistor, north Lincolnshire (UK), provide a record of Late Devensian (Late Weichselian) to Holocene palaeoenvironments at the western margin of the European sand belt. Thermoluminescence (TL) and radiocarbon analyses provide for the first time a chronological framework for the demise of proglacial Lake Humber and the onset of coversand deposition. The reconstructed palaeoenvironmental history suggests that proglacial Lake Humber had receded from its initial high-level stand before c. 18 ka, exposing the lake floor to periglacial conditions marked by the development of thermal contraction cracks. In the period between c. 18 and 14 ka, sand-depositional processes changed from dominantly fluvial to aeolian. The fluvial activity was possibly a consequence of ameliorating winter climates between c. 17 and 16 ka. The aeolian coversand deposition in this period has not been previously recognized in Britain and correlates with the Older Coversand II and Younger Coversand I deposits elsewhere in the European sand belt. Peat accumulation followed during the Windermere (Bølling/Allerød) Interstadial and early part of the Loch Lomond Stadial (Younger Dryas) before regionally extensive coversand deposition took place in the later part of the Loch Lomond Stadial. This coversand correlates with the widespread Younger Coversand II deposits found both within the UK and across the European sand belt. The Holocene has been characterized by widespread stability with the development of soils on the coversand punctuated with periods of localized reworking through to the present day.     

Sedimentary facies and geomorphic evolution of a blocked‐valley lake: Lake Futululu,northern Kwazulu‐Natal,South Africa

Blocked‐valley lakes are formed when tributaries are impounded by the relatively rapid aggradation of a large river and its floodplain. These features are common in the landscape, and have been identified in the floodplains of the Solimões‐Amazon (Brazil) and Fly‐Strickland Rivers (Papua New Guinea), for example, but their inaccessibility has resulted in studies being limited to remotely sensed image analysis. This paper documents the sedimentology and geomorphic evolution of a blocked‐valley lake, Lake Futululu on the Mfolozi River floodplain margin, in South Africa, while also offering a context for the formation of lakes and wetlands at tributary junctions. The study combines aerial photography, elevation data from orthophotographs and field survey, and longitudinal sedimentology determined from a series of cores, which were sub‐sampled for organic content and particle size analysis. Radiocarbon dating was used to gauge the rate and timing of peat accumulation. Results indicate that following the last glacial maximum, rising sea‐levels caused aggradation of the Mfolozi River floodplain. By 3980 years bp , aggradation on the floodplain had impounded the Futululu drainage line, creating conditions suitable for peat formation, which has since occurred at a constant average rate of 0·13 cm year^?1. Continued aggradation on the Mfolozi River floodplain has raised the base level of the Futululu drainage line, resulting in a series of back‐stepping sedimentary facies with fluvially derived sand and silt episodically prograding over lacustrine peat deposits. Blocked‐valley lakes form where the trunk river has a much larger sediment load and catchment than the tributary stream. Similarly, when the relative difference in sediment loads is less, palustrine wetlands, rather than lakes, may be the result. In contrast, where tributaries drain a steep, well‐connected catchment, they may impound much larger trunk rivers, creating lakes or wetlands upstream.     

THE UTILITY OF CARBORNE RADIOMETRIC SURVEYS IN PETROLEUM EXPLORATION OF GLACIATED REGIONS*

Carborne gamma radiation surveys over petroleum reservoirs and faults in the glaciated Michigan Basin suggest that this mobile technique may be useful in reconnaissance subsurface exploration, especially in fault detection. This conclusion assumes favorable surface conditions, as well as proper instrumentation, field procedures, and interpretive techniques. Glaciated regions are relatively undesirable terrains for gamma radiation surveys. Thick deposits of glacial drift appear to repress the detection of subsurface features. Furthermore, extremely heterogeneous soil conditions, which are characteristic of many glaciated regions, result in excessive radiation interference. The operational conditions which produced optimum results consisted of continuous profiling on unconsolidated roads, employing two simultaneously operated scintillation counters. Optimum detection was obtained during relatively cool nighttime traverses.     

Seismic modeling of Tertiary sandstone clinothems, Spitsbergen

Two-dimensional seismic modelling has been undertaken on an overall progradational succession of sloping mudstone and sandstone units from the Palaeogene of Spitsbergen. The modelling shows that the main geometric features of the section would be resolved at 1500 m depth (with frequencies below 60 Hz, which is common in seismic data at these depths). However, interference between the base and top of lithological units gives lateral amplitude variations and discrepancies between the seismic image and the geometrical model. This is particularly prominent in low-frequency models. Terminations of reflectors, resembling toplap and onlap, may be interpreted, but are artefacts of the general convergence of lithological units present in the geometrical model. The geological section causes a seismic pattern resembling sigmoid progradational seismic facies. Two-dimensional seismic modelling is an efficient tool in bridging the gap between outcrop observations and subsurface data. Hence, modelled outcrop sections are important as reference points' for improved seismic stratigraphic interpretation.     

The Australian Wool Crisis: Farm Adjustment Pressures and Strategies

Farm adjustment has resulted from the present crisis of production within the Australian agricultural sector. Farm adjustment pressures of the wool growers of the Southern Tablelands of New South Wales are outlined. The primary management strategies adopted by the wool producers are identified. Three farm adjustment strategies were noted; extensification, diversification and expansion. Choice of farm strategy was dependent on the characteristics of both the individual farm and farmer.