Mats Olvmo

Palaeosurfaces and associated saprolites in southern Sweden

Abstract Saprolite remnants from different palaeosurfaces in southern Sweden have been analysed by XRD and SEM analyses. They represent two clearly different types. The first is a clay- and silt-rich saprolite with a kaolinite-dominated clay mineral association representative of mature saprolites and with chemically altered quartz grains. This saprolite type is associated with sub-Cambrian, sub-Jurassic and sub-Cretaceous denudation surfaces. The second type is gravelly and in a youthful stage of alteration with mainly vermiculitic clay minerals in the fine fractions. Microtextures developed on quartz grains indicate a mainly mechanical breakdown. Compared to overlying till beds this saprolite is in a more advanced stage of chemical alteration. It is not associated with any specific denudation surface. Its characteristics and thickness indicate a Plio-Pleistocene age. The saprolites represent deep weathering of the bedrock surface at different times. The weathering resulted in thin kaolinitc saprolites during the Late Proterozoic, thick kaolinitic saprolites from the latest Triassic through the Jurassic and Cretaceous, and medium thick immature saprolites from the Pliocene and onwards. The depth of the deep weathering has been decisive for the shape of the present relief and thus etch processes have been of fundamental importance in shaping the relief, even in a formerly glaciated area.

Landscape evolution in Martian mid-latitude regions: insights from analogous periglacial landforms in Svalbard

Abstract Periglacial landforms on Spitsbergen (Svalbard, Norway) are morphologically similar to landforms on Mars that are probably related to the past and/or present existence of ice at or near the surface. Many of these landforms, such as gullies, debris-flow fans, polygonal terrain, fractured mounds and rock-glacier-like features, are observed in close spatial proximity in mid-latitude craters on Mars. On Svalbard, analogous landforms occur in strikingly similar proximity, which makes them useful study cases to infer the spatial and chronological evolution of Martian cold-climate surface processes. The analysis of the morphological inventory of analogous landforms on Svalbard and Mars allows the processes operating on Mars to be constrained. Different qualitative scenarios of landscape evolution on Mars help to better understand the action of periglacial processes on Mars in the recent past.

Inherited landforms and glacial impact of different palaeosurfaces in southwest Sweden

Landforms are used as analytical tools to separate inherited features from the glacial impact on Precambrian basement rocks in southwest Sweden. The study covers three different palaeosurfaces, the sub‐Cambrian peneplain (relative relief (r.r.) 0–20 m) with the character of a pediplain, an uplifted and dissected part of the sub‐Cambrian peneplain (r.r. 5–40 m) and an etch‐surface (r.r. 20–135 m), presumably sub‐Mesozoic. The surfaces were recently re‐exposed, probably due to a Neogene upheaval with some pre‐glacial reshaping. Strong structural control and no alignment with glacial erosional directions other than those coinciding with structures, are arguments for etch processes as a most important agent for relief differentiation. This is strengthened by the occurrence of saprolite residues and etchforms in protected positions. The glacial reshaping of the sub‐Cambrian flat bedrock surfaces is negligible. The glacial impact becomes more evident in the uplifted and dissected parts of the peneplain and within the hilly sub‐Mesozoic surface. The higher the initial relief the more effect of glacial erosion on individual hills, both on the abrading side, with formation of roches moutonnées, and on the plucking side. Detailed etchforms are preserved in protected positions in spite of erosion by a clearly wet‐based ice. The magnitude of the Pleistocene glacial erosion is considerably less than the amplitude of the palaeorelief in the entire area. Landscapes of areal glacial scouring have been described as comprising irregular depressions with intervening bosses scraped by ice and labelled ‘knock and lochan’ topography, but we suggest that an etched bedrock surface is a prerequisite for this type of landscape to develop.

Saprolite Remnants as Indicators of Pre‐Glacial Landform Genesis in Southeast Sweden

Abstract Twenty‐six sites with remnants of gravelly saprolites (grus) have been located in southeast Sweden. Joint block hills (castle kopjes) and steep rock walls with weathered joints as well as rounded boulders are documented to have an origin in deep weathering and subsequent stripping of saprolites. The saprolite remnants and landforms result from the fragmentation of the re‐exposed sub‐Cambrian peneplain along fracture systems. Only shallow saprolites occur on the elevated intact parts of the sub‐Cambrian peneplain, while saprolites up to 20 m thick are encountered in areas where the sub‐Cambrian peneplain is fractured and dissected. Neogene uplift with reactivation of the weathering system is thought to be the main cause of saprolite formation. Deep weathering is thus judged to have been the major agent of landform formation in the study area, while glacial and glaciofluvial erosion has contributed mainly by stripping saprolites, detaching corestones, and plucking joint blocks along weathered joints.

Development of joint-controlled rock basins in Bohus granite, SW Sweden

The granite area of Bohuslan along the Swedish west-coast is characterised by an abundance of rock basins of different sizes. Within a 163 km2 large part of the area over 400 basins occur, ranging ...

A-Tents in the Central Sierra Nevada, California: A Geomorphological Indicator of Tectonic Stress

A-tents and blisters are minor landforms associated with the release of compressive stress in combination with erosional off-loading in hard crystalline bedrock. The uplifted and westward tilted granitic batholith of the Sierra Nevada, California, comprises hundreds of Cretaceous intrusions, where sheeted bornhardts stand juxtaposed, and have been exposed to compressional stress during several time periods. Field mapping north of Yosemite Valley identified 79 A-tents with a preferred orientation ENE-WSW suggesting the application of directionally applied stress. A-tent, joint, and bornhardt orientation imply NE-SW tension and NW-SE compression. The stress has probably been released after the rapid Tertiary uplift and erosional unloading in the late Quaternary. We suggest that the A-tents in this part of the Sierra Nevada are related to intrinsic compressional stress imposed on the bedrock during emplacement but before mid-Cretaceous transpression.

The South Swedish Dome : a key structure for identification of peneplains and conclusions on Phanerozoic tectonics of an ancient shield

Abstract The relationships between different denudation surfaces/peneplains formed across crystalline basement rocks give valuable information to the tectonic development of ancient shields. The denudation surfaces can be identified by the aid of their landforms, tilt and remnant weathering mantles in relation to cover rocks. Three types of denudation surfaces are identified across south Sweden (1) a tilted flat plain, (2) a tilted hilly surface with relative relief below 150 m and (3) stepped horizontal plains with residual hills. All three types of denudation surfaces are peneplains, denudation surfaces graded to specific base levels. The re-exposed parts of the inclined flat sub-Cambrian peneplain (SCP) extend as a landscape feature from below cover rocks in the north and east and reaches up on the highest summits of the South Swedish Uplands. The SCP (the exact unconformity) is encountered again below Cambrian covers outside the west coast. Thus south Sweden is a geological dome, the South Swedish Dome (SSD), in relation to the Cambrian cover. The southern and western low flanks of the exposed part of the dome are instead characterized by a hilly peneplain, the inclined sub-Cretaceous denudation surface, with remnants of thick, kaolinitic, clayey saprolites. This sub-Cretaceous peneplain is cut off at a distinct level in the south and west by the almost horizontal South Småland Peneplain, a never covered, epigene, peneplain. The uplift history of the SSD aids to the understanding on the development of late Tertiary drainage systems of the Baltic Basin by the Eridano River.

An Analysis of Soil Productivity Parameters and Livelihoods in West Shewa and South Wollo, Ethiopia

Abstract A vast majority of the Ethiopian population lives in rural areas and agricultural activities are the main income for them. The aim of this study is to analyse soil productivity parameters and problems with food production in regional and local contexts. At local level two villages in Wenchi district in West Shewa are compared while a comparison with Tehuledere district in South Wollo is done at the regional level. Soil samples from 70 fields were analysed at the Soil Laboratory in Addis Ababa with respect to pH, organic matter, cation exchange capacity, macronutrients, and soil texture among others. Physical observations and semi-structured interviews with farmers were also conducted to obtain the goals. When comparing the two districts, results indicate minor differences in terms of soil fertility. The very low amount of organic content (1%) in Tehuledere must be mentioned though. Low values of organic content have a negative impact on soil productivity. In conclusion, we emphasize the importance to study several parameters, such as farm area, livelihood assets and rainfall pattern to understand the problems the rural population has to face to secure food production.

Cultivated land – a scarce commodity in a densely populated rural area in South Wollo, Ethiopia

ABSTRACT Cultivated and settlement areas were studied in a small area (14 km2) in South Wollo, Ethiopia, by aerial photos, satellite images, field observations and interviews. Areas for cultivation/rural settlement decreased a few per cent between 1958 and 2013. Cultivated land per household slowly decreased in 1958–2003 but in 2003–2013 the annual decrease was 3–4 times higher. New farm buildings are often built on cultivated land, and abandoned buildings areas return to cultivation. Rainwater harvesting ponds have increased the areas with perennial crops that are important as a source of income. Tin roofed buildings are signs of improved livelihood. Very small farm size and rain-dependent agriculture combined with climate variability make food security vulnerable. Land-use inventories including remote sensing and local knowledge would be a valuable approach to assess livelihood needs. Further, it should involve decision makers at different levels, but local agricultural extension officers may play a central role.

A weathered diamicton beneath Upper Weichselian sediments at Silvereke, southeastern Sweden

Abstract An at least 2 m thick, weathered, non‐glacial diamicton, buried beneath a 6 m thick Upper Weichselian glaciogenic sequence at Silvereke in SE Sweden, is composed of variously coloured angular/rhombohedral to rounded clasts set in a red or reddish‐brown matrix of clayey silty sand. The clasts (mainly local metavolcanic rock and Cambrian sandstone) are generally thoroughly weathered and would hardly survive transport, suggesting weathering after deposition. XRD‐analysis of the clay fraction of individual argillized clasts reveals an assemblage dominated by kaolin minerals, probably including halloysite. The matrix has a more complex clay mineralogy, including vermiculite. The petrography and mineralogy as well as the extensive argillization of the diamicton contrast to the composition and texture of the overlying Upper Weichselian till. Apart from small amounts of pollen, mainly Pinus, Betula and NAP, the unit is almost devoid of organic matter. Since most pollen are well‐preserved, they were proba...