Drought and institutional adaptation in the Great Plains of Alberta and Saskatchewan, 1914–1939

Agriculture in the southern Great Plains of Canada has been particularly vulnerable to prolonged episodes of drought. Using climate data and a precipitation minus potential evapotranspiration index, the extent of the region’s exposure to drought is examined. Between 1914 and 1917, the Dry Belt was particularly vulnerable to drought, whereas after 1928, a much larger region known as the Palliser Triangle covering most of southern Alberta and Saskatchewan was much more exposed to drought. These droughts provoked major institutional adaptation, in particular the establishment of the Special Areas Board by the Government of Alberta, and the creation of the Prairie Farm Rehabilitation Administration by the Government of Canada. Both organizations have proved to be relatively permanent public adaptations to the natural hazard of drought in the region. Moreover, these earlier experiences with prolonged drought as well as institution-building may be of value in helping the residents of the Palliser Triangle adapt to predicted climate changes in the future as well as anticipate some of the barriers to effective institutional adaptation.     

AGRICULTURAL EXPANSION IN NORTHERN ALBERTA

ABSTRACT. Since the early 1980s some 40,000 acres of forested land have been cleared and placed under cultivation by Mennonite farmers near the small town of La Crete in northern Alberta's Peace River district. This incipient agriculture has been accompanied by dramatic increases in road building and home construction and by the establishment of churches and schools. The principal force behind the acquisition of land has been a desire of families to have homes in rural areas where they can enjoy lifestyles based on traditional Mennonite values. Because most new farmers cannot earn a living in the district from agriculture alone, they must rely on the wood industries to supplement their incomes. Demand is building for the province to open still more land, but disagreements between the government and the Mennonite community about the most appropriate location for developing new farms has put further expansion on hold until the conflict can be resolved.     

The June 2013 Alberta catastrophic flooding event – part 2: fine‐scale precipitation and associated features

Data obtained from a variety of sources including the Canadian Lightning Detection Network, weather radars, weather stations and operational numerical weather model analyses were used to address the evolution of precipitation during the June 2013 southern Alberta flood. The event was linked to a mid‐level closed low pressure system to the west of the region and a surface low pressure region initially to its south. This configuration brought warm, moist unstable air into the region that led to dramatic, organized convection with an abundance of lightning and some hail. Such conditions occurred in the southern parts of the region whereas the northern parts were devoid of lightning. Initially, precipitation rates were high (extreme 15‐min rainfall rates up to 102 mm h^?1 were measured) but decreased to lower values as the precipitation shifted to long‐lived stratiform conditions. Both the convective and stratiform precipitation components were affected by the topography. Similar flooding events, such as June 2002, have occurred over this region although the 2002 event was colder and precipitation was not associated with substantial convection over southwest Alberta. Copyright © 2016 Her Majesty the Queen in Right of Canada. Hydrological Processes. © John Wiley & Sons, Ltd.     

Fault-controlled dolomitization at Swan Hills Simonette oil field (Devonian), deep basin west-central Alberta, Canada

The partly dolomitized Swan Hills Formation (Middle‐Upper Devonian) in the Simonette oil field of west‐central Alberta underwent a complex diagenetic history, which occurred in environments ranging from near surface to deep (>2500 m) burial. Five petrographically and geochemically distinct dolomites that include both cementing and replacive varieties post‐date stylolites in limestones (depths >500 m). These include early planar varieties and later saddle dolomites. Fluid inclusion data from saddle dolomite cements (T_h=137–190 °C) suggest that some precipitated at burial temperatures higher than the temperatures indicated by reflectance data (T_peak=160 °C). Thus, at least some dolomitizing fluids were ‘hydrothermal’. Fluorescence microscopy identified three populations of primary hydrocarbon‐bearing fluid inclusions and confirms that saddle dolomitization overlapped with Upper Cretaceous oil migration. The source of early dolomitizing fluids probably was Devonian or Mississippian seawater that was mixed with a more ⁸⁷Sr‐rich fluid. Fabric‐destructive and fabric‐preserving dolostones are over 35 m thick in the Swan Hills buildup and basal platform adjacent to faults, thinning to less than 10 cm thick in the buildup between 5 and 8 km away from the faults. This ‘plume‐like’ geometry suggests that early and late dolomitization events were fault controlled. Late diagenetic fluids were, in part, derived from the crystalline basement or Palaeozoic siliciclastic aquifers, based on ⁸⁷Sr/⁸⁶Sr values up to 0·7370 from saddle dolomite, calcite and sphalerite cements, and ²⁰⁶Pb/²⁰⁴Pb of 22·86 from galena samples. Flow of dolomitizing and mineralizing fluids occurred during burial greater than 500 m, both vertically along reactivated faults and laterally in the buildup along units that retained primary and/or secondary porosity.     

Late-glacial vegetation and environment on the eastern slope foothills of the Rocky Mountains, Alberta, Canada

Stratigraphic pollen analysis done on sediment cores from two sites in the upper North Saskatchewan drainage basin of the eastern slopes foothills of the Rocky Mountains in west central Alberta, Canada combined with sedimentological data provide a local vegetational and environmental history. Radiocarbon AMS dates provide a chronology back to 17960 BP. Reconstruction and interpretation of the local pollen zones includes reevaluation of steppe and grassland as analogs for full- and late-glacial vegetation. Regional vegetation from c. 17960 to 16 100 BP is interpreted as an extremely cold semi-arid Artemisia steppe, the vegetation c. 16 100 to 11 900 BP as an Artemisia-Betula shrubland, and the vegetation c. 11 900–10 200 BP as a Picea woodland, in an environment characterized by consistently arid and windy conditions. This reconstruction emphasizes the significance of aridity, as opposed to simply low temperatures, as the critical factor in determining the late Quaternary vegetation of Alberta.This is the 18th in a series of papers published in this special AMQUA issue. These papers were presented at the 1994 meeting of the American Quaternary Association held 19–22 June, 1994, at the University of Minnesota, Minneapolis, Minnesota, USA. Dr Linda C. K. Shane served as guest editor for these papers.     

Mud dispersal across a Cretaceous prodelta: Storm‐generated,wave‐enhanced sediment gravity flows inferred from mudstone microtexture and microfacies

Determining sediment transport direction in ancient mudrocks is difficult. In order to determine both process and direction of mud transport, a portion of a well‐mapped Cretaceous delta system was studied. Oriented samples from outcrop represent prodelta environments from ca 10 to 120 km offshore. Oriented thin sections of mudstone, cut in three planes, allowed bed microstructure and palaeoflow directions to be determined. Clay mineral platelets are packaged in equant, face‐face aggregates 2 to 5 μm in diameter that have a random orientation; these aggregates may have formed through flocculation in fluid mud. Cohesive mud was eroded by storms to make intraclastic aggregates 5 to 20 μm in diameter. Mudstone beds are millimetre‐scale, and four microfacies are recognized: Well‐sorted siltstone forms millimetre‐scale combined‐flow ripples overlying scoured surfaces; deposition was from turbulent combined flow. Silt‐streaked claystone comprises parallel, sub‐millimetre laminae of siliceous silt and clay aggregates sorted by shear in the boundary layer beneath a wave‐supported gravity flow of fluid mud. Silty claystone comprises fine siliceous silt grains floating in a matrix of clay and was deposited by vertical settling as fluid mud gelled under minimal current shear. Homogeneous clay‐rich mudstone has little silt and may represent late‐stage settling of fluid mud, or settling from wave‐dissipated fluid mud. It is difficult or impossible to correlate millimetre‐scale beds between thin sections from the same sample, spaced only ca 20 mm apart, due to lateral facies change and localized scour and fill. Combined‐flow ripples in siltstone show strong preferred migration directly down the regional prodelta slope, estimated at ca 1 : 1000. Ripple migration was effected by drag exerted by an overlying layer of downslope‐flowing, wave‐supported fluid mud. In the upper part of the studied section, centimetre‐scale interbeds of very fine to fine‐grained sandstone show wave ripple crests trending shore normal, whereas combined‐flow ripples migrated obliquely alongshore and offshore. Storm winds blowing from the north‐east drove shore‐oblique geostrophic sand transport whereas simultaneously, wave‐supported flows of fluid mud travelled downslope under the influence of gravity. Effective wave base for sand, estimated at ca 40 m, intersected the prodelta surface ca 80 km offshore whereas wave base for mud was at ca 70 m and lay ca 120 km offshore. Small‐scale bioturbation of mud beds co‐occurs with interbedded sandstone but stratigraphically lower, sand‐free mudstone has few or no signs of benthic fauna. It is likely that a combination of soupground substrate, frequent storm emplacement of fluid mud, low nutrient availability and possibly reduced bottom‐water oxygen content collectively inhibited benthic fauna in the distal prodelta.     

Verification of the Weather Research and Forecasting Model when Forecasting Daily Surface Conditions in Southern Alberta

The Weather Research and Forecasting (WRF) model was compared with daily surface observations to verify the accuracy of the WRF model in forecasting surface temperature, pressure, precipitation, wind speed, and direction. Daily forecasts for the following two days were produced at nine locations across southern Alberta, Canada. Model output was verified using station observations to determine the differences in forecast accuracy for each season.

Although there were seasonal differences in the WRF model, the summer season forecasts generally had the greatest accuracy, determined by the lowest root mean square errors, whereas the winter season forecasts were the least accurate. The WRF model generally produced skillful forecasts throughout the year although with a smaller diurnal temperature range than observed. The WRF model forecast the prevailing wind direction more accurately than other directions, but it tended to slightly overestimate precipitation amounts. A sensitivity analysis consisting of three microphysics schemes showed relatively minor differences between simulated precipitation as well as 2?m surface temperatures.     

Tectonic and eustatic control on deposition and preservation of Upper Cretaceous ooidal ironstone and associated facies: Peace River Arch area, NW Alberta, Canada

The Late Coniacian, shallow-marine Bad Heart Formation of the Western Canada foreland basin is very unusual in that it contains economically significant ooidal ironstone. Deposition of shallow-water and iron-rich facies appears to have been localized over the crest and flanks of a subtle intrabasinal arch, in part interpreted as a forebulge and partly attributed to reactivation of the long-lived Peace River Arch. The formation comprises two upward-shoaling allomembers, typically 5–10 m thick, that are bounded by regionally mappable ravinement surfaces. The lower unit, allomember 1, grades up from laminated mudstone to bioturbated silty sandstone, which is abruptly overlain by bioturbated ooidal silty sandstone grading into an almost clastic-free ooidal ironstone up to 7 m thick. Ooidal ironstone was concentrated into NW- to SE-trending ridges, kilometres wide and tens of kilometres long. Ironstone formation appears to have been promoted by: (a) drowning of the arch, which progressively curtailed sediment supply; and (b) enhanced reworking over the shallowly submerged arch and over a fault-bounded block that underwent episodic vertical movement of 10–20 m during Bad Heart deposition. Allomember 2 also shoals upwards from mudstone to bioturbated and laminated silty sandstone but lacks ooids, apparently reflecting a rejuvenated supply of detrital sediment from the arch. The marine ravinement surface above allomember 2 is a Skolithos firmground, above which is developed a regional blanket of ooidal sediment. In the east, ooids are dispersed in a bioturbated silty sandstone with abundant evidence of repeated reworking and early siderite and phosphate cements. Westwards, this facies grades, over about 40 km, into almost clastic-free ooidal ironstone about 5 m thick; the lateral facies change may reflect progressive clastic starvation distal to a low-relief source area. The two allomembers are interpreted to reflect eustatic oscillations of about 10 m, superimposed on episodic tectonic warping and block-faulting events. The development of ooidal ironstone immediately above initial marine flooding surfaces indicates a close relationship to marine transgression, reflecting sediment-starved conditions. Ironstone does not appear to be related to either sequence boundaries or maximum flooding surfaces. The Bad Heart Formation is blanketed by marine mudstone deposited in response to major flexural subsidence and rejuvenation of clastic sources in the Cordillera to the SW.