Upland Margins Research Articles

Significance Testing of Archeological Site 41SR242, The Cornelio Alvarez Sr. Site, Starr County, Texas

The Texas Department of Transportation (TxDOT), conducted National Register of Historic Places (NRHP) eligibility testing of the Cornelio Alvarez Sr. site (41SR242) as part of the State Loop (SL) 195 project (Project) (CSJ: 3632-01-001) in Starr County, Texas. Subsequent to the field investigations, SWCA Environmental Consultants (SWCA) conducted artifact analysis, reporting, and curation preparation for the multi-component historic and prehistoric site. Investigations were conducted in compliance with Section 106 of the National Historic Preservation Act (54 United State Code 30601) and the Antiquities Code of Texas (9 Natural Resources Code). The investigations assessed the site’s eligibility for listing on the NRHP (36 Code of Federal Regulations 60.4) and for designation as a State Antiquities Landmark (SAL; 13 Texas Administrative Code 26.8, 26.12). Christopher W. Ringstaff served as Principal Investigator under Texas Antiquities Permit Number 7912. TxDOT conducted the field investigations were from February 20–24, 2017, and April 10–14, 2017. Site 41SR242 is primarily a Middle to Late Archaic site with lesser Late Prehistoric and perhaps earlier components. The open occupational site is located on an upland margin landform in a tributary valley a few miles from the Rio Grande. The investigations revealed material assemblages consisting of diffusely scattered burned rock, debitage, and lithic tools, which were predominantly recovered from a 30- to 50-cm-thick stratum of mixed artifacts. However, a few concentrations of artifacts were identified, and each location yielded isolated intact features. Formation and post-depositional processes are generally not conducive to preservation of intact archeological surfaces, patterns, or site structure. Although the overall site lacks integrity and potential data yield, isolated discrete behavioral loci are present. Therefore, site 41SR242 is recommended as eligible for the NRHP and as an SAL. This recommendation pertains to the portions of the site within the APE. The site extends beyond the APE, and the areas outside of the APE have not been evaluated.

Breeding bird assemblages supported by developing upland shrub woodland are influenced by microclimate and habitat structure

ABSTRACTCapsule: Local micro-climate, as well as habitat, influences the abundance of birds within dynamically changing upland habitats.Aims: To identify the relative importance of near-ground temperature (as an index of climate at a scale typical of the territory of breeding passerines) and habitat for some breeding birds in upland Scotland where land uses and habitats are changing.Methods: Timed point counts sampled breeding birds within the marginal uplands of Scotland in habitats at successional stages between pasture and shrubland. Habitat composition and ambient temperatures were recorded at the same sampling points. Generalized linear mixed models were used to assess associations of bird abundance, species richness and species diversity with habitat and ambient near-ground temperature.Results: Species richness increased with mean temperature, was greatest within areas of shrubland and was lowest in open habitats. Different species showed individual associations with temperature and habitat. Species predominantly associated with shrubland tended to have a negative association with temperature.Conclusions: Understanding the habitat and climatic niche requirements of different species will facilitate appropriate land management to be targeted within appropriate climatic patches. For example, open habitats suitable for Whinchats Saxicola rubetra should be within warmer climate patches (typically lower elevation or southern aspects) while shrublands can support Willow Warblers Phylloscopus trochilus at cooler elevations and aspects. Management that delivers a mosaic of habitats, spanning areas of climatic heterogeneity should enhance the diversity of birds supported in the upland margins and potentially their resilience to changing environmental conditions.

Red stamps and green tea: fieldwork negotiations and dilemmas in the Sino‐Vietnamese borderlands

The socialist spaces within the upland Southeast Asian Massif are home to over 70 million people belonging to geographically dispersed and politically fragmented ethnic minority populations. State authorities have long considered these upland margins as frontier regions where ‘inconsequential peoples’ lag behind national standards. Over time, the Chinese and Vietnamese states have worked to enclose these spaces through a range of ‘development’ programmes and politico‐economic strategies. Undertaking qualitative social science research here is underscored by a specific set of challenges (red stamps), dilemmas and negotiations (green tea). In a contemporary context that interweaves economic liberalisation with centralised and authoritarian political structures, I explore how I have negotiated and manoeuvred access to ethnic minority voices. Specifically, I focus on fieldwork endeavours in the Sino‐Vietnamese borderlands to answer two core questions. First, in these socialist arenas, how can researchers negotiate access to still‐marginalised groups misunderstood by the central state? And second, what are the most pressing ethical questions raised by cross‐cultural fieldwork in these spaces and how might these be addressed? While debating these ethical and methodological challenges, I reflect upon the numerous roles of gatekeepers, concerns over the well‐being of interviewees and the importance of self‐censorship.

Habitat suitability modelling of an invasive plant with advanced remote sensing data

AbstractAim Lepidium latifolium (Brassicaceae; perennial pepperweed) is a noxious Eurasian weed invading riparian and wetland areas of the western USA. Understanding which sites are most susceptible to invasion by L. latifolium will allow more efficient management of this weed. We assessed the ability of advanced remote sensing techniques to develop habitat suitability models for L. latifolium.Location San Francisco Bay/Sacramento‐San Joaquin River Delta, California, USA.Methods Lepidium latifolium distribution was mapped with hyperspectral image data of Rush Ranch Open Space Preserve, providing presence/absence data to train and validate habitat models. A high‐resolution light detection and ranging digital elevation model was used to derive predictor environmental variables (distance to channel, distance to upland, elevation, slope, aspect and convexity). Aggregate decision tree models were used to predict the potential distribution of this species.Results Lepidium latifolium infested two zones: near the marshland–upland margin and along channels within the marsh. Topographical data, which are typically strongly correlated with wetland species distributions, were relatively unimportant to L. latifolium occurrence, although relevant microtopography information, particularly relative elevation, was subsumed in the distance to channel variable. The map of potential L. latifolium distribution reveals that Rush Ranch contains considerable habitat that it is susceptible to continued invasion.Main conclusions Lepidium latifolium invades relatively less stressful sites along the inundation and salinity gradients. Advanced remote sensing datasets were shown to be sufficient for species distribution modelling. Remote sensing offers powerful tools that deserve wider use in ecological research and management.

The Effectiveness of Asulam for Bracken (Pteridium aquilinum) Control in the United Kingdom: A Meta-Analysis

Bracken (Pteridium aquilinum) is a major problem for livestock-based extensive agriculture, conservation, recreation, and game management globally. It is an invasive species often achieving dominance to the detriment of other species. Control is essential to maintain plant communities such as grassland and lowland heath or if extensive grazing by domestic stock, particularly sheep, is to be viable on upland margins. Bracken is managed primarily by herbicide application or cutting but other techniques including rolling, burning, and grazing are also utilized. Here we evaluate the evidence regarding the effectiveness of asulam for the control of bracken. Thirteen studies provided data for meta-analyses which demonstrate that application of the herbicide asulam reduces bracken abundance. Subgroup analyses indicate that the number of treatments had an important impact, with multiple follow-up treatments more effective than one or two treatments. Management practices should reflect the requirement for repeated follow-up. There is insufficient available experimental evidence for quantitative analysis of the effectiveness of other management interventions, although this results from lack of reporting in papers where cutting and comparisons of cutting and asulam application are concerned. Systematic searching and meta-analytical synthesis have effectively demonstrated the limits of current knowledge, based on recorded empirical evidence, and increasing the call for more rigorous monitoring of bracken control techniques. Lack of experimental evidence on the effectiveness of management such as rolling or grazing with hardy cattle breeds contrasts with the widespread acceptance of their use through dissemination of experience.

Habitat selection and foraging behaviour of breeding Eurasian Woodcock Scolopax rusticola: a comparison between contrasting landscapes

Diet, feeding behaviour and habitat selection of breeding Eurasian Woodcock Scolopax rusticola were studied by radiotracking birds from March to July in two contrasting situations: a 171‐ha lowland plantation of Sycamore Acer pseudoplatanus, Beech Fagus sylvaticus and pine Pinus sylvestris/P. nigra in Derbyshire, central England, and an area of c. 900 ha of fragmented, naturally regenerating birch Betula pendula/B. pubescens woodland and hill margin in an upland glen in Angus, northeast Scotland. Earthworms were the most important diet component of adults and chicks in terms of biomass at both sites (50–80%), the rest comprising mainly spiders, harvestmen and beetles. In spring both sexes flew c. 1 km after dusk to feed on fields at night, with up to 94% of nocturnal radiolocations on fields in March, dropping to 18% in July. This behaviour probably reflected seasonal changes in the relative availability of earthworms in fields and woodland. Diurnal home range sizes were similar at both sites and the mean size of 30‐day ranges was 62 ± 20 ha (± se), although Woodcock changed locations regularly and areas used for feeding on a daily basis were typically smaller than 1 ha. In the lowland plantation, Sycamore with Dog's Mercury Mercurialis perennis ground cover was highly used relative to availability. In the upland margin study area, the same held for dense sapling‐stage birch. These habitats appear to represent a compromise between food availability and protection from avian predators. Recently documented changes in the structure of British woods during the last 30 years, suggestive of reduced management and increased grazing/browsing, are likely to have been detrimental to breeding Woodcock.

Breeding bird communities in the upland margins (ffridd) of Wales in the mid-1980s

Capsule The bird communities in the Welsh marginal uplands were frequently distinct from those of adjacent habitats and consisted of heterogeneous mixtures of species strongly influenced by vegetation composition and land-use. Aims To provide a unique description of the influence of vegetation, altitude and regional position on the bird communities of upland margins and to create a baseline against which future changes in these communities may be assessed. Methods Survey data collected at 120 sites in 1985–87 were used to identify broad relationships between habitat and bird communities. This was complemented by habitat descriptions made at exact locations occupied by individual birds. Results Bird communities in Bracken-dominated sites, especially those with relatively high numbers of scattered trees and bushes, held more species than sites dominated by grassland and other moorland vegetation. Relationships between species and habitat were broadly consistent at both the scale of whole sites and the scale of patches occupied by individual birds. Abundance of scattered trees and bushes was important for a diverse range of passerines; extent of Gorse Ulex spp. scrub was important for several species. Geographical location and topography appeared to have secondary effects on bird communities relative to those of vegetation composition. Conclusions The Welsh marginal uplands hold diverse bird communities, strongly affected by local vegetation composition and usually different from those of adjacent moorland, woodland and farmland. Tree Pipit Anthus trivialis, Whinchat Saxicola rubetra, Linnet Carduelis cannabina and Yellowhammer Emberiza citrinella were among the species likely to be more abundant in the upland margins than in adjacent habitats. There is a need to assess whether these communities have changed since the mid-1980s, especially in relation to high sheep grazing pressure. However, agricultural abandonment of marginal areas may occur in the future which could eventually reduce habitat availability for several bird species and reduce avian diversity in the Welsh uplands.

GIS and the application of a model of pollen deposition and dispersal: a new approach to testing landscape hypotheses using the POLLANDCAL models

The recent advances in computer-based modelling of pollen dispersal and deposition through the POLLANDCAL (POLlen-LANDscape CALibration) network have enabled landscape simulations to be constructed and tested, both to validate the theoretical models, and to validate modelled landscapes using empirical data. This paper presents the first attempt to develop simulations based on real landscapes, by placing distinct vegetation communities using reclassified digital elevation models (combined slope and altitude data). The approach is tested by modelling a palynological signature for the expansion of mixed agriculture into an upland margin, and the results for 49 simulated pollen deposition sites, across an altitudinal range for a series of landscape scenarios, is compared with existing empirical data. The broad trends within the two data sets are in general accordance, and variation between them is attributed to local variation in vegetation heterogeneity. The results show that the POLLANDCAL models offer a new and exciting method by which sub-fossil pollen assemblages can be examined, theoretical models of landscape use tested, and will offer a significant tool in the interpretation of environmental data in archaeology, in particular when combined with GIS-based models of the physical environment.

Geoarchaeology of the Brook Run site (44CU122): an Early Archaic jasper quarry in Virginia, USA

Abstract The Brook Run site (44CU122) is an Early Archaic jasper quarry situated near the eastern margin of the Triassic-age Culpeper Basin in Virginia, USA. It occupies the upland margin of a relatively broad and shallow, first-order tributary valley of the Rapidan River. Archaeological and geological investigations focused on site stratigraphy, chronology, and formation processes as well as attributes of the quarried jasper. The Brook Run jasper occurs as large blocks of red-to-yellow brecciated masses of microcrystalline quartz that are cemented together by minor amounts of black chert. These jasper blocks, which were the targets for prehistoric quarrying, occur only within a ca. 1-m-wide Triassic-age fault zone and appear to “float” in a matrix of very weathered, fine-grained fault gouge. 14C age estimates indicate that aboriginal quarrying began by 10 kyBP and proceeded by excavating a ca. 4 m deep pit to remove jasper blocks from the fault. Quarrying ceased by 9.4 kyBP, and the site was abandoned soon after. Petrological and geochemical analyses show that the jasper and black chert formed in stages from hydrothermal fluids injected into the fault zone during Triassic–Jurassic volcanic activity. Unique characteristics of the jasper were also identified that may aid in sourcing artifacts derived from the quarry.

The Late‐glacial reoccupation of the British Isles and the Creswellian

AbstractThis paper presents a review of AMS radiocarbon dating evidence for human occupation of Britain during the Late‐glacial Interstadial. The dates are all on humanly modified materials, including artefacts, and on human bone. The CalPal program is used to test whether the earliest evidence of human presence shows any correlation with more widespread climatic events, and if the British chronology differs significantly from that of neighbouring regions of northwest Europe. In the second part of the paper a number of well‐dated sites with British Late Upper Palaeolithic ‘Creswellian’ technology are examined and compared with lithic assemblages from The Netherlands and Belgium. The main conclusions of this work are that expansion of human populations into the northern edge of the upland zone just before or at the beginning of GI‐1 was followed by repopulation of the British Isles possibly with very little time‐lag. The British Creswellian sites offer evidence of this earliest resettlement, which is mainly focused on the upland margins of western and central Britain. Copyright © 2003 John Wiley & Sons, Ltd.

Briza media L.

A loosely tufted perennial with short rhizomes from which arise vegetative shoots. Culms 15-60 (-100) cm high, slender, erect, 2-3-noded, solitary, smooth. Leaves with dull glaucous to mid-green adaxial and abaxial surfaces, hairless; blades usually 4-20 (-28) cm long, 2-4 (-7) mm wide, with minute acroscopic teeth on the margins, with a slender boat-shaped tip; ribs numerous, closely packed, less obvious on the abaxial surface; sheaths smooth, entire, soon splitting, dark reddish-brown at base; ligules up to 1.5 mm long, membranous, blunt with irregular margins. Culm leaves 3 or 4, uppermost with long sheaths. Panicles 410 (-18) cm long, lax, roughly pyramidal, with up to 20 branches, and up to 60 spikelets, sparsely divided, spreading, with scabrous hair-like pedicels 5-20 (-50) mm long and slightly thickened below the spikelets. Spikelets 4-7 mm long and wide, loosely scattered and drooping, broadly elliptic to broadly ovate, laterally compressed, generally purplish-brown, usually breaking up at maturity beneath the lemmas but many spikelets remaining undispersed on the branches and shed from the panicle intact, 4-9 (-12)-flowered. Glumes slightly unequal, deeply concave, hooded at the apex, boat-shaped, 2.5-3.5 mm long, with 3-5 veins, firmly membranous, dull-purple with white and shiny margins. Lemmas 3.7-4.1 mm, strongly cordate at the base, bluntly keeled in the lower half, closely overlapping, rounded on the back, with 7-9 veins, variegated purple and green, with hyaline margin. Paleas flat, thin, almost as long as the lemma, with two keels, narrowly winged. Lodicules 2, linear-lanceolate, acute. Grain enclosed within the papery lemma and palea, c. 2 mm long, rounded on the back, flattened on the front; mean oven-dry weight 0.53 mg. The root system is a dense mat of whitish fibrous roots. The primary roots are up to 1 mm in diameter and are largely unbranched, but there is a dense network of branching secondary roots. The root mass is fairly vertical with an average root length of c. 40 cm. The species produces pale brown rhizomes up to 13 cm long and 1.5 mm in diameter. Native. Subspecies media occurs throughout the range; subspecies elatior (Sibth. & Sm.) Rohlena occurs in south-east Europe.

Comparison of nitrogen cycling in salt marsh zones related to sea-level rise

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 221:1-16 (2001) - doi:10.3354/meps221001 Comparison of nitrogen cycling in salt marsh zones related to sea-level rise Cassondra R. Thomas1,*, Robert R. Christian2 1University of Virginia, Department of Environmental Science, Charlottesville, Virginia 22903, USA 2East Carolina University, Department of Biology, Greensville, North Carolina 27858, USA *E-mail: crt6b@virginia.edu ABSTRACT: Zones in salt marshes can be distinguished by different community and ecosystem properties. As marshes respond to changes in sea level, one might expect alterations in the relative proportions of these zones and, hence, alterations in overall functioning. We used ecological network analysis to assess potential changes in 1 ecosystem function, nitrogen cycling. We constructed nitrogen cycle networks of zones (creekbank, low marsh, and high marsh) for 3 salt marshes on the East Coast of the USA; Great Sippewissett in Massachusetts, Upper Phillips Creek in Virginia, and Sapelo Island in Georgia. The same network structure was applied to all zones, largely using data derived from the literature on the 3 marshes. The factors used to analyze how nitrogen flowed through each zone included how nitrogen imported into the marsh was exported, how imports were related to primary productivity, and how much nitrogen was cycled within the system. Emphasis was placed on identifying patterns across zones that were consistent for all 3 marshes. When precipitation and tidal particulate nitrogen (PN) were the imports, export from active cycling via burial and denitrification significantly increased in importance moving across the marsh from the creekbank to the high marsh. Relative nitrogen cycling also significantly increased from creekbank to high marsh. As the area of the marsh zones decrease or increase in response to sea-level rise, nitrogen dynamics will change as a consequence. If the landscape slope is low allowing the marsh to migrate overland, the high marsh zone will increase in area. Nitrogen cycling as a percentage of total system throughput will increase per unit area averaged over the total marsh. If, however, the marsh stalls because of a steep slope at the upland margin, cycling will decrease on a per unit area basis. If the supply of sediment is great and the marsh progrades toward the sea, nitrogen cycling within the marsh may decrease. Therefore, as relative sea-level rises, the response of a salt marsh¹s nitrogen cycle will depend on the slope and sediment supply available to the marsh. KEY WORDS: Salt marsh · Nitrogen cycle · Network analysis · Sea-level rise Full text in pdf format NextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 221. Online publication date: October 18, 2001 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2001 Inter-Research.

Holocene Climatic and Environmental Change in the Texas Coastal Zone: Some Geoarchaeological and Ecofactual Indicators

Three kinds of evidence potentially useful for inferring broad Holocene paleoclimatic trends on the Texas coast are discussed. Stratigraphic evidence from the central and lower Texas coastal plain indicates widespread erosion of upland margins prior to ca. 5000 BP, suggesting sparse vegetation cover and possibly patterns of relatively low precipitation. Examination of archaeological molluskan remains permits inferences concerning long-term trends in estuarine water salinities and temperatures, both of which have possible correlates in paleoclimatic trends recently posited for inland Texas.

Matrimonial politics and core-periphery interactions in twelfth- and early thirteenth-century Scotland

The medieval kingdom of Scotland was an amalgam of diverse ethnic elements which included Gaels, Britons, Anglo-Saxons, Scandinavians and Normans. This paper explores one mechanism which is generally considered to have been of tremendous importance in fostering accommodation and understanding between cultures in medieval society: matrimony. An examination of the marriage alliances of prominent members of the native nobility of eastern Scotland demonstrates that matrimony played a crucial role in binding Scottish families to Anglo-Norman newcomers, to the Normanophile Scottish monarchs, and to one another. However, the marriage alliances of the powerful west-coast princes contrast sharply to those of the eastern nobility and demonstrate how matrimonial alliances also served another purpose: namely, building up and maintaining an alliance of princes in the upland margins of the kingdom who opposed Anglo-Norman ways and the extension of feudalism into these regions. This in turn suggests that there existed a fundamental dichotomy in Scottish society between the feudal kingdom of Scotland and those regions ringing the Irish Sea. Close examination of the matrimonial patterns of the twelfth-century Scottish nobility therefore reinforces some long-held convictions about the fabric of Scottish society, while calling others into question

Groundwater-Discharge Fens in the Tanana Lowlands, Interior Alaska, U.S.A.

Large expanses of herbaceous floating mat wetlands (FMW) bordered by slightly higher uplands with forest or scrub occur in the northwest corner of the Tanana Flats between the Alaska Range and the Tanana River. Five major FMW systems, together with other outliers and extensions, are linear in shape and cover over 20 km2. Nutrient-rich and circumneutral water flows slowly through these areas toward the northwest and through outlets to the Tanana River. The floating mat vegetation consists of tall emergent macrophytes; mosses, in particular Sphagnum spp., are conspicuously absent and shrubs are infrequent. Although species dominance shifts over short distances on the mat, four community types can be recognized: (1) Menyanthes trifoliata, (2) Carex aquatilis, (3) Typha latifolia, and (4) Calla palustris. Below the water surface, the mat extends to a depth of 0.5 to 1.0 m and consists of rhizomes and roots in a matrix of well-decomposed peat and water. The mat then either directly overlies unfrozen gray silts at a depth of 1 m, or more commonly, floats on a clear-water or loose peat zone above more consolidated peat lying on unfrozen silt at a depth of 1.5 to 2.5 m. No permafrost or frozen ground was detected in late August or late winter below these floating mats but it is ubiquitous on the bordering uplands, 0.5 to 2 m above the FMW. The topographic location, apparent absence of permafrost, water chemistry, and vegetation composition suggest that these areas are fens fed by groundwater sources flowing out of the Alaska Range. Permafrost degradation and lateral expansion of these FMW is indicated by slumped blocks of forest peat, dead trees, and open water moats along the upland margin. Although floating mats are frequently described in the literature as occupying the edge of northern ponds and lakes, the FMW described here do not and they appear to be unique because of their large extent, absence of mosses, physiographic position, and presumed origin.

Hydrology and chemistry of groundwater and seasonal ponds in the Atlantic Coastal Plain in Delaware, USA

The hydrochemistry of small seasonal ponds was investigated by studying relations between ground-water and surface water in a forested Coastal Plain drainage basin. Observation of changes in the water table in a series of wells equipped with automatic water-level recorders showed that the relation between water-table configuration and basin topography changes seasonally, and particularly in response to spring recharge. Furthermore, in this study area the water table is not a subdued expression of the land surface topography, as is commonly assumed. During the summer and fall months, a water-table trough underlies sandy ridges separating the seasonal ponds, and maximum water-table altitudes prevail in the sediments beneath the dry pond bottoms. As the ponds fill with water during the winter, maximum water-table altitudes shift to the upland-margin zone adjacent to the seasonal ponds. Increases in pond stage are associated with the development of transient water-table mounds at the upland-margin wells during the spring. The importance of small local-flow systems adjacent to the seasonal ponds also is shown by the similarities in the chemistry of the shallow groundwater in the upland margin and water in the seasonal ponds. The upland margin and surface water samples have low pH (generally less than 5.0), and contain large concentrations of dissolved aluminum (generally more than 100 μg 1 −1), and low bicarbonate concentrations (2 mg l 4 or less). In contrast, the parts of the surficial aquifer that do not experience transient mounding have higher pH and larger concentrations of bicarbonate. These results suggest that an understanding of the hydrochemistry of seasonally ponded wetlands requires intensive study of the adjacent shallow groundwater-flow system.

Transitional morphology in West Deuteronilus Mensae, Mars: Implications for modification of the lowland/upland boundary

West Deuteronilus Mensae, which lies along the lowland/upland boundary of Mars at 45° latitude, 345° longitude, exhibits both gradational ( L. A. Rossbacher, 1985,in Models in Geomorphology (Woldenberg, Ed), pp. 343–372, Allen & Unwin, Boston) and fretted terrain ( R.P. Sharp, 1973, J. Geophys. Res. 78, 4073–4083) boundary types. To the west, the boundary is gradational and to the east it is defined by fretted terrain. The two types of boundaries do not merge with one another within the west Deuteronilus Mensae region, however. The gradational boundary materials appear to overlap the fretted terrain by about 500 km. Contacts between units associated with the gradational boundary and the fretted terrain boundary can both be recognized in the region of overlap. The fretted terrain can be identified as much as 300 km north of the gradational boundary in this region. Lowland units associated with the gradational boundary embay canyons of the fretted terrain in a topographically conformal fashion. Changes in the fretted terrain across the gradational boundary (from uplands to lowlands) include a reduction of canyon wall slopes and depths, such that the fretted terrain north of the gradational boundary appears mantled but not obscured. There are at least two major classes of processes which might explain the lateral overlap: (1) erosion of stratified upland terrain and (2) deposition of plains materials onto the sloping upland margin and fretted terrain. Erosion of stratified upland terrain does not adequately explain the plainward decrease in crater densities across the gradational boundary nor is it consistent with evidence that lowland plains material appears to onlap the sloping upland margin in several places. Of the possible plains emplacement mechanisms, eolian deposition would not produce the sharp, apparently topographically conformal gradational unit contacts. Volcanics plains emplacement would not preserve the complex geometry of the underlying fretted terrain. Sediment deposition in either a liquid or ice-covered sea could produce the draped appearance of the fretted terrain. Outflow channels along the lowland/upland boundary, particularly those of the circum-Chryse and west Elysium regions, may have flooded the northern lowlands to depths of tens to hundreds of meters. The gradational unit contacts may represent the shorelines of such a sea. The scale of characteristic morphologies along these contacts may require an unfrozen condition of sufficient duration to allow lacustrine-style wave erosion and redistribution of material along the contacts. Our limited understanding of the Martian paleoclimate and H 2O inventories allows the possibility of clement periods in the past, and other geological evidence (e.g., small valley networks and outflow channels) strongly suggests an extensive role of liquid water.

Volcano-tectonic control on sedimentation in the Koobi Fora sedimentary basin, Lake Turkana

Summary It has previously been considered that the sedimentary rocks of the Koobi Fora basin, NE of Lake Turkana, lie disconformably upon older volcanic strata, local volcanism and sedimentation being separated in time. Volcanic and sediment relationships observed at the boundary of the basin reveal that major Pliocene tholeiitic flood volcanism took place after the initiation of proto-Lake Turkana. Significant lacustrine and fluviatile deposits lie beneath lavas in the upland margin of the northern part of the basin. These are lithologically similar, and may be laterally equivalent, to strata outcropping along the northern edge of the basin and on the southeastern flank of the Kokoi upland. The fine-grained lacustrine rocks formed during an extended period of slow sedimentation. The age of Lake Turkana, therefore, may be significantly greater than 4.3 Ma, which is recorded from the lowermost tuff bed within the Koobi Fora basin (McDougall 1985). Further lacustrine sediments form thin but laterally persistent intercalations between flood lavas. Concurrence of large scale subaerial eruptions and lacustrine sedimentation is explained by a model of volcano-tumescence and deflation. The early Pliocene lake was relatively shallow and of greater extent than present-day Lake Turkana. Swellings of the land surface preceding volcanic eruptions E of the lake produced significant withdrawals of the shoreline westwards. Subsidence, following lava outpourings, allowed transgression of the lake towards the former shorelines.

The character and interpretation of some pediment mantles

Some pediment mantles provide crucial evidence concerning the processes responsible for the shaping of the cut bedrock surfaces, or pediments, upon which they rest. On the western side of the Flinders Ranges, the mantles on the dissected Brachina pediments consist of 2–3 m of limestone and quartzite boulders and cobbles set in a silt matrix. The cobbles are derived from the uplands to the east and have been transported by rivers. Comparisons with contemporary stream channels suggest deposition by divaricating streams emerging from the uplands on to the desert plains. No palaeosol intervenes between the mantle above and the cut bedrock surface below, and the latter is ascribed to planation by laterally migrating distributary streams. Similar deposits occur, and similar interpretations can be applied, to several other dissected pediments located at the upland margins, and to some within the Ranges. But the most prominent old valley floors, or pediment remnants, in intermontane situations are capped and preserved by coarse angular blocks of quartzite. Many of the remnants are quite steeply inclined (up to 7°) compared to the 3°–4° that is normal for the pediments proper. The cappings are interpreted as slump deposits laid down either on the toes of slopes or on the heads of pediments; they are related to scarps that have since retreated (partly through slumping). But on granite pediments (e.g. on Eyre Peninsula, in northern Queensland; and on dacite and rhyolite in the Gawler Ranges) the fine textured mantles are thin, and mineralogically indicate nothing but derivation from the underlying bedrock; there is no unequivocal evidence of downslope transport. Yet, after rains, there is evidence of rillwash and sheetwash; surely these pediment surfaces are surfaces of transportation like those of the Flinders Ranges. The crucial upper layer of sediment that may provide clues to the processes active appears to have been eroded away, possibly as a consequence of European settlement and land use.

Projections for British Agriculture

While the 1947 Agriculture Act expresses general support for the farming industry, governments tend to take short-term views, while farmers need longterm indications of government intentions. The White Paper, Food from our own resources, attempts to provide such an indication, which must be viewed in the context of the country's dependence on imported food and of increasing home production from a declining area of agricultural land. Changes in govern? ment policies and the state of the economy suggest a lower rate of transfer of farmland to other uses in the future and the government expects the post-war rise in agricultural production to continue at much the same rate. The pro? jections of output for 1980 also have regional implications within the United Kingdom. Any increase in land under tillage is unlikely to come from eastern England, though there may be exceptions for particular crops. Great improvements in grassland productivity are possible, and an increase in dairy cattle, probably in the main dairying areas, should provide most of the addi? tional beef; but there are likely to be increases in numbers of both sheep and beef cattle on the uplands and upland margins respectively. In the longer run, the role of agriculture may well change in a European context; in the short run, much will depend on farmers' confidence. Since the outbreak of the Second World War, governments have played a major role in British agriculture, in the interests both of safeguarding supplies of homegrown food and of reducing the fluctuations in income which are a characteristic feature of farming. The 1947 Agriculture Act gave formal expression to that in? tention, for its purpose was to promote and maintain 'a stable and efficient agricul? tural industry, capable of producing such part of the nation's food supply and other agricultural produce as in the national interest it is desirable to produce in the United Kingdom and of producing it at minimum prices consistent with proper remuneration and living conditions for farmers and workers in agriculture and an adequate return on capital invested in agriculture'. Since 1947, this aim has been pursued by the publication of an annual review of the agricultural industry and, until the United Kingdom became a member of the European Economic Com?