Lowland Plains Research Articles

Flow field stratigraphy surrounding Sekmet Mons Volcano, Kawelu Planitia, Venus

Detailed mapping has revealed several stratigraphic components among lobate plains in the vicinity of Sekmet Mons volcano (44.5°N. lat., 240.5° long.), located on the northern lowland plains of Kawelu Planitia on Venus. Volcanic effusion events produced discrete lobate plains throughout the area. Superposition of flow margins between adjacent lobate plains components indicate that the effusive activity generally progressed from southwest to northeast across the Sekmet Mons area, leading to a cumulative total of 1.5 million km2 covered by adjacent lobate plains components. Source areas for the effusion responsible for the lobate plains components occur primarily along fracture zones or from concentrations of low volcanic domes (“shield fields”) instead of from single constructs. Magellan radar backscatter values from a mixture of both radar bright and radar dark flow components within the flow fields are well below values typical of clinkery a′a lava flows on Earth, but they are consistent with values from terrestrial pahoehoe flows. Detailed mapping of Strenia Fluctus (centered on 41.5° N. lat., 251.0° long.), one of the latest lobate plains units in the area, does not show a systematic trend among effusive centers that contributed to the generation of this flow field. Instead, the Strenia Fluctus flow field is a complex mixture of flows that emanated from a shield field along Mist Chasma and that flowed down a very gentle (>0.1°) regional slope to the east. A 4‐km‐diameter cone north of Strenia Fluctus was the source of a flow complex traceable for more than 200 km over a slope of only 0.03°. Individual flows within Strenia Fluctus are composed of intermixed lobes, similar to relationships observed on the distal portion of the 75‐km‐long Carrizozo basalt flow in New Mexico, which also displays abundant inflation features and a predominant pahoehoe surface texture. If the Venusian lobate plains consist of pahoehoe flows comparable to the Carrizozo flow, they were most likely emplaced at modest effusion rates (∼50 to 500 m3/s), and even with inflation the flows are likely ≤15 m in thickness. Under these conditions all of the lobate plains surrounding Sekmet Mons could have been emplaced in ∼14,000 to 1400 Earth years, assuming continuous effusion with only one source vent active at a time. At similar rates all of the lowland plains in the northern hemisphere of Venus could have been resurfaced by 15‐m‐thick flows through continuous single‐vent effusion in ∼1.4 million to ∼140 thousand Earth years.

沖積低平地に立地する城下町都市佐賀における水路の空間特性に関する考察

This study aims to clarify the specific situation of waterways in the castle town Saga, focussing on their sustainable development. The results are as follows: 1) Waterways are specific fundamentals entirely necessary to the development of the town in lowland alluvial plains. 2) Existing waterways are built in the former castle town area with the basic and sustainable network repeating the pattern of waterway-road. 3) Existing waterways serving only as the enclosure of the social settlement unit can be divided into two types of meanings for the town life; the communal and personal availability. 4) Visibility to waterways essential for the future development will be obtained from two types of place; view from spots and linear view.

Ancient lowlands on Mars

Mars Orbiter Laser Altimeter (MOLA) data provide compelling evidence that the martian lowlands, below the smooth and sparsely cratered northern plains, are extremely old, far older than the plains which cover them. The evidence is in the form of a very large population of “Quasi‐Circular Depressions” (QCDs), many of which are very evident in the MOLA elevation data but generally not visible in available imagery. We interpret these “invisible” QCDs to be buried impact basins. Cumulative number versus diameter curves for lowland QCDs suggests the buried lowland surface is older than the visible highland surface and that the lowland plains are a relatively thin (1–2 km) veneer overlying this much older surface. We conclude that the martian lowlands have been low and stable for nearly all of martian history.

Spectral evidence for weathered basalt as an alternative to andesite in the northern lowlands of Mars.

Mineral abundances derived from the analysis of remotely sensed thermal emission data from Mars have been interpreted to indicate that the surface is composed of basalt (Surface Type 1) and andesite (Surface Type 2). The global distribution of these rock types is divided roughly along the planetary dichotomy which separates ancient, heavily cratered crust in the southern hemisphere (basalt) from younger lowland plains in the north (andesite). But the existence of such a large volume of andesite is difficult to reconcile with our present understanding of the geological evolution of Mars. Here we reinterpret martian surface rock lithologies using mineral abundances from previous work and new mineralogies derived from a spectral end-member set representing minerals common in unaltered and low-temperature aqueously altered basalts. Our results continue to indicate the dominance of unaltered basalt in the southern highlands, but reveal that the northern lowlands can be interpreted as weathered basalt as an alternative to andesite. The coincidence between locations of such altered basalt and a suggested northern ocean basin implies that lowland plains material may be composed of basalts weathered under submarine conditions or weathered basaltic sediments transported into this depocentre.

Mapping successional boreal forests in interior central Alaska

It is necessary to develop new satellite methods to monitor boreal forests responses to climate warming. Remotely sensed maps derived from hyperspectral Advanced Visible/Infrared Imaging Spectrometer (AVIRIS) data were developed and compared for the four conifer forest ecosystems at the Bonanza Creek Experimental Forest, a long-term ecological research site on the Tanana River flood plain near Fairbanks, Alaska. The site was first stratified into montane, lowland alluvial plain, and flood plain zones based on topography. A classification of six forest and three non-forest types was created from AVIRIS images and compared on a pixel-by-pixel basis to a published vegetation map, a classified SPOT (Satellite Pour l'Observation de la Terre) image, and a hybrid SPOT image and digital elevation model classification. A comparison of AVIRIS with SPOT results showed that the AVIRIS classification was consistently more accurate (74, 43, and 43% overall accuracy, respectively). Hyperspectral classification methods have promise for mapping forest ecosystems in other boreal regions when little or no ground data are available for validation. The time difference between the creation of these maps show that substantial ecosystem changes have occurred over the past 15 years, demonstrating the need for developing a capability to obtain cost-effective landscape characterization.

Variability in sediment delivery and storage along river courses in Bega catchment, NSW, Australia: implications for geomorphic river recovery

In many catchments in southeastern Australia, alluvial stores have been the dominant source of sediments mobilised in the period since European settlement. In Bega catchment, on the South Coast of New South Wales (NSW), this has been reflected by dramatic changes to river morphology. Extensive volumes of material have been released and efficiently flushed to the lowland plain, with a sediment delivery ratio of almost 70%. However, only 16% of these alluvial sediments have been flushed through to the estuary, as antecedent controls on valley width have resulted in the lowland plain acting as a large sediment sink. The changing nature of sediment source, transfer and accumulation zones has varied markedly from subcatchment to subcatchment. The volume of material supplied to the lowland plain from differing subcatchments is not related to subcatchment area. Rather, the pattern of river types dictates the spatial variability in storage and transfer. Over 67% of sediment released has been sourced from just 25% of the catchment, from subcatchments characterised by large valley fills (cut and fill River Style) that previously stored extensive volumes of material at the base of the escarpment. These parts of Bega catchment were especially sensitive to disturbance. Sediment exhaustion from these parts of the catchment, and from river courses elsewhere, has major implications for the geomorphic recovery potential of rivers, constraining what can be realistically achieved in terms of river rehabilitation.

Hazard assessment in Eastern Taiwan

Introduction The topography of Taiwan is dominated by the Central Mountain Range, which has steep, densely vegetated slopes, deeply incised valleys and fractured, unstable rock masses. Although most of the population is located on the low-lying coastal plains, there is a need in this rapidly developing island to construct transportation links through the mountains. Unfortunately, the steep topography makes development difficult and there have been many instances in which poor terrain evaluation has led to inappropriate engineering solutions. This paper outlines how landslide hazard assessment is being used as part of the planning process for the development of infrastructure along one such road through the mountains. The physical setting of Taiwan Taiwan is located on the eastern margin of the Eurasian continental plate (Fig. 1). The island, which is approximately 385 km in length and 143 km in width, has formed as a result of the ongoing collision of the Philippine Sea (oceanic) and Eurasian (continental) plates. Damaging, shallow seismic activity is frequent. The most seismically active region is in the central portion of the east coast of the island. However, the recent ‘Chi-Chi’ earthquake of 21 September 1999 occurred in the centre of Taiwan and caused the loss of over 2100 lives and induced damage island-wide. Terrain evaluation in Taroko National Park Taroko National Park is located on the eastern margin of Taiwan 121°40′ E and 24°0′ N (Fig. 1). It is centred upon the drainage basin of the Li-Wu River, with terrain that varies from lowland plains

Mapping successional boreal forests in interior central Alaska

It is necessary to develop new satellite methods to monitor boreal forests responses to climate warming. Remotely sensed maps derived from hyperspectral Advanced Visible/Infrared Imaging Spectrometer (AVIRIS) data were developed and compared for the four conifer forest ecosystems at the Bonanza Creek Experimental Forest, a long-term ecological research site on the Tanana River flood plain near Fairbanks, Alaska. The site was first stratified into montane, lowland alluvial plain, and flood plain zones based on topography. A classification of six forest and three non-forest types was created from AVIRIS images and compared on a pixel-by-pixel basis to a published vegetation map, a classified SPOT (Satellite Pour l'Observation de la Terre) image, and a hybrid SPOT image and digital elevation model classification. A comparison of AVIRIS with SPOT results showed that the AVIRIS classification was consistently more accurate (74, 43, and 43% overall accuracy, respectively). Hyperspectral classification methods have promise for mapping forest ecosystems in other boreal regions when little or no ground data are available for validation. The time difference between the creation of these maps show that substantial ecosystem changes have occurred over the past 15 years, demonstrating the need for developing a capability to obtain cost-effective landscape characterization.

Seismic deformation structures of the post-2300 a BP muddy sediments in Kawachi lowland plain, Osaka, Japan

Deformed zones, consisting mainly of muddy sediments, deposited in palustrine environments, found during the excavations of archaeological sites, have been examined. The beds belong to the uppermost Holocene sequence, within 6 m depth from the present ground surface, in Kawachi alluvial lowland plain, Osaka Prefecture, Japan. Each deformation zone contained basically three deformation units related to fluidity and plasticity decreasing with depth beneath the fresh sedimentation surface. The units recognized were, from top to bottom: (1) a liquidized deformation unit expressed by a homogenized layer, in which the sediment and water have been mixed by turbulent flow; (2) a hydroplastic deformation unit characterized by a plumose pattern in the upper part of the unit and load structures in the lower part; and (3) a brittle deformation unit characterized by downward fissures and microfaults. The plumose pattern in the second unit may have formed where the more cohesive sediments in the lower part of the unit were dragged horizontally with repeated directional changes, and pulled upward by the movement of the sediments in the upper part. The load structures in the lower part of this unit are assumed to have been formed mainly by differential vertical and compressive forces applied to the sedimentary horizons. In the uppermost part of the liquidized deformation unit, load casts and pseudonodules with short horizontal tracks, suggesting movement while sinking, were seen locally. These features in the units are assumed to have been formed by the oscillatory and rotational force, irregular in intensity and direction, of an earthquake. The minor displacement of deformed sediments, such as mixing, truncation, intrusion, and injection, at the boundaries between the units and their internal layers suggests that the deformation process was initiated simultaneously in each unit, and was of short duration. The vertical occurrence order of the deformational features, similar to that of ‘fault-graded bedding’, especially of the plumose pattern and load structures, was recognizable in most deformation zones. By defining and separating superposed deformation zones according to the vertical order of the features, and by the relative dating of the zones based on the archaeological artifact chronology, a regional correlation of deformational event horizons may be proposed. Consequently, several synchronous seismic event horizons in prehistoric time have been recognized, and their lateral extents have been documented. Additionally, within one site, chronological correlation reveals that the ages of the post-13th century deformational event horizons are in accordance with the ages of historically recorded earthquakes.

Alternate child care options: Preferences of the hill community

The concept of alternative child care in traditional village societies consists of elders caring for children in the absence of mother. In many parts of the world, increasing labor force participation by women has brought growing pressure for alternate forms of care and support. There is a difference between the daily activities and life of farm women in upland rural hill areas and women in rural villages on the lowland plains. The majority of the lowland village women from middle and upper middle income groups stay at home and do household chores. Only during the peak harvest seasons do they assist with agricultural duties and, even then, only at the household level. In contrast, the hill village women perform almost all the agricultural tasks including the collection of wood, fodder, and water from the rivers. In addition; they perform routine household chores with the time they have left. Therefore, the care of young children is a “low” priority. The physical care of infants is generally left to the elder women. In this type of busy schedule, the farm hill women require alternative child care facilities.

River Styles, a Geomorphic Approach to Catchment Characterization: Implications for River Rehabilitation in Bega Catchment, New South Wales, Australia.

/ Geomorphologically derived river styles provide an integrative framework for examining the interactions of biophysical processes in rivers throughout a drainage basin. Nine styles of river character and behavior are identified in Bega catchment, on the south coast of New South Wales, Australia. Headwater streams above the escarpment drain into gorges in the escarpment zone. In different subcatchments at the base of the escarpment, there are three different river styles, namely cut-and-fill, vertically accreted floodplains, and fans. Downstream of these river styles, in the rounded foothills of the catchment, throughput and transfer river styles convey sediments to the lowland plain. In one mid-catchment setting, a floodout traps sediment. Finally, along the lowland plain of Bega River, there is a floodplain accumulation river style. Downstream patterns of river styles in differing subcatchments of the Bega River basin are differentiated into three types, reflecting river adjustments to valley width, slope, and responses to human disturbance. Analysis of the character and condition of each river style in Bega catchment, and their downstream patterns, are used to provide a biophysical basis to prioritorize river management strategies. These reach-scale strategies are prioritorized within an integrative catchment framework. Conserving near-intact sections of the catchment is the first priority. Second, those parts of the catchment that have natural recovery potential are targeted. Finally, rehabilitation priorities are considered for highly degraded reaches. At these sites, erosion and sedimentation problems may reflect irreversible changes to river structure.

Gentry's Rio Mayo Plants. The Tropical Deciduous Forest and Environs of Northwest Mexico

Along with some of my students and friends, I had the pleasure twice to visit this Rio Mayo region and adjacent areas via the kind courtesy of co-author Thomas R. Van Devender, who carefully pointed out all the major constituents of the various vegetation zones of vegetation. I hadnt felt as botanically inept and frustrated with a flora since I first set foot on the Chihuahuan Desert's Cuatro Cienegas Region in Coahuila, Mexico, in the 1960fs. These Rio Mayo trips forced me to reread Dr. Howard Scott Gentry's original book (1942). The fascination with the region is contagious. Gentry's accounts of 1933-1939 in poetic style and picturesque description are now more vividly appreciated. He was the first botanist to seriously explore the Rio Mayo drainage of desertic lowland plains and thorn forests and above. In the 27 months he was there, he collected 3200 numbers representing 1276 species and varieties. His annotated listing (Part 2) describes eight new species and one new variety, including five agaves and two cacti. Also, 66 Gentry collections have been newly described by other authors, all but 15 by Paul C. Standley. The new volume carefully updates, in the same format, Gentry's original account. The authors review and enlarge upon the vegetation and gazetteer via new description, photographs and specimens. Each entry of the burgeoning plant list includes not only the scientific name and classification, but also common names (in English, Spanish, and three native tongues, Guarijio, Mayo and Pima), local and overall distribution, representative documenting specimens, habitats and brief descriptions as to morphology, ecology, ethnology and ethnobotany. The amount of information provided accredits this book as a most valuable and comprehensive reference work. With some collections still in the hands of experts to be determined or newly described, the known flora boasts some 2825 taxa, more than doubling Gentry's original account. There are the 81 new taxa (Gentry 1 942); at least 40 additional taxa based on types and paratypes before the intensive collecting for the present book in the 1970's, many based still on Gentry's own collections; 54 more during the Rio Mayo revision; and 24 still in the process of being described, yielding a total of nearly 200 new taxa for this species rich diverse region, about 7% of the total flora. Shortcomings are few, but identification keys would greatly enhance the use of book. The pull-out map is black and white (in my copy) instead of the advertised color map. This book is a must for all students of Mexican botany, no doubt to be referred to innumerable times. It begs for another update several years from now.

Galium aparine L.

Galiun L., Section KOLGYDA Dumort. (Section Aparine Koch). An annual herb with prostrate or, more usually, scrambling-ascending diffusely branched stems 15-300cm, stout and hairy at the nodes, the four angles very rough with downwardly directed prickles. Leaves 12-60 x 3-8 mm, in whorls of 6-9, narrowly to widely oblanceolate or elliptical, mucronate, 1-veined, glabrous or with hooked bristles above, margins rough with backward-pointing prickles. Flowers 1.5 mm diameter in 2-5-flowered axillary cymes, their peduncles topped by a whorl of 4-8 bracts; hermaphrodite, sometimes male (andromonoecious). Calyx a minute annular ridge; corolla 1.5-1.7 mm in diameter, whitish, with four acute lobes. Stamens 4, exserted; styles 2, short, connate below; stigmas capitate. Two-seeded fruits with length of longest axis 3-5 mm (excluding setae), wider than the corolla, olive or purplish, covered with white hooked setae with tuberculate bases, their stalks divaricate. Mature fruit a dry mericarp with length of longest axis 2-3 mm, and a mean airdry mass of 9.65 mg ? 0.33 (10 samples of 100 from a hedgerow population). Salisbury (1974) reports the average mass of seed from shade-tolerant woodland and hedgerow plants as 3.7 mg, and Grime et al. (1988) record a mean seed mass of 7.25mg for a hedgerow population. Galiumn iparine is a highly variable species owing to a combination of phenotypic plasticity and genecological variation. The species has different responses to the environment corresponding to different environmentally conditioned life cycles [see VI (e)]; plasticity in the timing of seed germination, productivity, growth form, freezing tolerance, and the light and temperature dependence of photosynthesis enable G. apa7ine to establish itself in a wide variety of habitats. Potential variability concealed in the higher polyploid conditions, especially in the widespread hexaploids [see VI (d)], enabling them to respond to changing environmental conditions, is probably also the basis of their success. Among plants of G. apariine raised from seed collected from various sites in continental Europe, B6cher etal. (1955) distinguished at least five different climatic ecotypes or races that either may be discrete or more probably ranges of a large clinal variation: mediterranean, summer-annual (seed germinates in the spring) with accelerated development from Portugal; mediterranean, biennial from Spain; southern, winterto summer-annual from France; northern, rather late flowering winterto summerannual from Denmark and Poland; and northern, very late flowering winter-annual (seed germinates in autumn) from Denmark and Sweden. Ecotypes of G. aparine have been demonstrated by Berkefeld (1988), differing in shape of cotyledons, hairiness of stems, colour of stem edges and length of fruit spines in plants grown under uniform garden conditions from seed collected in several different habitats. In Britain, two discrete ecotypes of G. apa7i71e exist, one found in arable fields or open situations and the other growing in hedgerows (FroudWilliams 1985); the two ecotypes are very similar morphologically but differ markedly in seed dormancy and germination requirements [see VIII (d)]. Bain & Attridge (1988) provide evidence of genotypic differences in shade strategies between hedgerow and field populations [see VI (e)]. Two forms have been recognized, the rarer G. aparine f. interimediwan Bonnet, with smooth or tuberculate fruits without spiny hairs, and the common form G. apar-ine f. apari71e with spiny fruits (Moore 1975). Variants of G. spur-ium with setose fruits, apart from the flower characters and the diploid chromosome number, are often not easy to distinguish from G. caparine and have been described as G. spuritini ssp. infestlin (Hanf 1983). Galiuiml apariine is native on maritime shingle beaches, in primary tall-herb fen communities, and in primary alderwood in natural hydrarch successions, but is also a very variable cosmopolitan weed found in hedges, waste places, drained fen peat, on limestone scree, roadside verges, river and stream banks, and is a major arable weed, especially of cereal crops. *Abbreviated references are used for standard works, see Jolurnal of Ecology (1975), 63, 335-344. Nomenclature of vascular plants follows Florca Euri0opaea and Stace (1997) for British species.

Post‐European changes to the fluvial geomorphology of Bega catchment, Australia: implications for river ecology

1. Within a few decades of European disturbance in the mid‐nineteenth century, river character and behaviour were transformed in Bega catchment on the south coast of New South Wales, Australia. Ecological impacts of geomorphic changes to river structure and function throughout the catchment are assessed.2. At the time of European settlement, many water courses in Bega catchment were discontinuous, with extensive swamps along middle and upper courses. Following a series of direct and indirect human impacts, channels became continuous in the middle and upper parts of the catchment, as extensive valley fills at the base of the escarpment were incised. Along the lowland plain, the channel widened by over 300%, fundamentally altering the relationship between the channel and its adjacent floodplain.3. Geomorphic changes to river structure have modified habitat availability throughout Bega catchment. The impacts have been least pronounced in headwater streams, but have been dramatic along virtually all river courses beyond the base of the escarpment.4. Changes in river structure have been directly related to altered riparian vegetation cover, and vice versa. As a consequence of changes to river structure, bed substrate calibre (and supply volume/rate) has been modified along most streams.5. A series of indirect, secondary impacts have modified habitat viability along river courses. Lateral, longitudinal and vertical linkages within the river system have been altered, affecting the transfer of water, sediment, organic matter, nutrients and other biotic interactions.6. These direct and indirect consequences of geomorphic changes in river structure suggest that ecologists need to adopt a longer‐term, catchment‐framed view of human disturbance to river ecosystems.7. Effective, sustainable ecological rehabilitation of river courses is dependent on an understanding of geomorphic processes and determination of appropriate river structure at differing positions in catchments.

Earliest Triassic (Induan) spores and pollen from the Junggar Basin, Xinjiang, northwestern China

Permian–Triassic boundary strata cropping out in the southern Junggar Basin contain a continuous and varied fossil record, making this fluvio-lacustrine succession a potential candidate for a non-marine boundary stratotype. Abundant, diverse and well preserved miospores are recorded and illustrated from the upper part of the Guodikeng Formation and the basal part of the Jiucaiyuan Formation, comprising 92 species and 48 genera, as well as some acritarchs. Seven new species ( Anapiculatisporites decorus Ouyang et Norris, sp. nov., Baculatisporites uniformis Ouyang et Norris, sp. nov., Kraeuselisporites varius Ouyang et Norris, sp. nov., Lapposisporites echinatus Ouyang et Norris, sp. nov., Klausipollenites angustus Shu et Norris, sp. nov., Alisporites exilis Ouyang et Norris, sp. nov., Pilasporites perreticulatus Ouyang et Norris, sp. nov.) and 8 new combinations are proposed. Pteridophytic spores and gymnospermous pollen are almost equally diverse, comprising 45 species in 20 genera, and 43 species in 25 genera, respectively. Pteridophytes are numerically more important, notably Limatulasporites, Kraeuselisporites, Lundbladispora, Anapiculatisporites and Verrucosisporites, but also prominent are bisaccate pollen of Falcisporites, Klausipollenites and Alisporites. Less abundant taeniate pollen are largely bisaccate. These palynofloras are grouped together as the Lundbladispora– Lunatisporites– Aratrisporites Assemblage, argued to be Early Triassic (early Induan), and comprising both newly evolved Mesozoic taxa (herbaceous and shrubby lycopsids, coniferous trees, pteridosperms) and relict Paleozoic taxa (sphenophyllids, cordaitaleans and possibly Paleozoic lycopods). The lower boundary of the Triassic in the section is redrawn somewhat lower than by previous authors. The transitional nature of the Permian–Triassic palynofloras and of the paleophytoprovinces is discussed; neither indicates a sudden catastrophic event affecting terrestrial floras at the P–T boundary on a global scale. The Early Triassic vegetation appears to have grown under humid sub-tropical conditions in lowland flood plains and marshes dominated by hydrophilous and mesophilous pteridophytes and pteridosperms, but with locally drier upland environments supporting xerophilous and mesophilous conifers and pteridosperms. The Induan vegetation is closely comparable to that of the Angara, especially the Subangara Province, although it contains some elements of the Euramerican Province in association with a few Gondwanan, Cathaysian and cosmopolitan taxa.

An elasmobranch assemblage from the terrestrial-marine transitional Lethbridge Coal Zone (Dinosaur Park Formation: Upper Campanian), Alberta, Canada

The change in depositional environments observed in the Cretaceous (Upper Campanian) strata in the region of Dinosaur Provincial Park, Alberta, from the proximal coastal plain deposits of the Oldman Formation to the lowland coastal plain deposits of the Dinosaur Park Formation, reveals an associated change in faunal composition. An assemblage collected from a microvertebrate site in the paralic deposits of the Lethbridge Coal Zone (uppermost Dinosaur Park Formation) reflects an increasing marine influence. Elasmobranch (sharks and rays) remains are the most abundant, both in terms of number of overall taxa and number of elements, and they are the best-preserved specimens. However, several brackish-water-tolerant osteichthyan taxa, and four reptile taxa (two marine and two terrestrial), were also recovered, although they exhibited evidence of extensive taphonomic reworking.The elasmobranch fauna collected from the Dinosaur Park locality is uncommon for vertebrate microfossil assemblages in the Dinosaur Park Formation of Alberta and in equivalent beds in Montana. Seven of the 10 taxa collected from this site [Cretorectolobus olsoni Case, 1978; Eucrossorhinus microcuspidatus Case, 1978; Odontaspis aculeatus (Cappetta and Case, 1975); Archaeolamna kopingensis judithensis Siverson, 1992; Protoplatyrhina renae Case, 1978; Ischyrhiza mira Leidy, 1856; and Ptychotrygon blainensis Case, 1978] are recorded for the first time from the uppermost section of the Judith River Group in Alberta; Carcharias steineri (Case, 1987), represents the first occurrence within the upper Judith River Group from either Alberta or Montana.

Crustal analysis of Venus from Magellan satellite observations at Atalanta Planitia, Beta Regio, and Thetis Regio

We investigated an improved quantitative method for interpreting attributes of the Venusian crust from Magellan spacecraft imagery and spherical harmonic topographic and gravity models. We used spectral correlation theory to compare gravity effects of topography against free‐air gravity anomalies for three tectonically disparate crustal regions. Adjusting terrain gravity effects for correlated free‐air anomalies yields compensated effects that we used to estimate the Moho and crustal thickness variations. For Atalanta Planitia, the crust may be less than 10 km thick, but thickened peripherally at concentric ridge belts and tessera terrain. Crustal thickness may increase rapidly between the interior of this lowland plain and the peripheral ridge belts. For Beta Regio, the crustal thickness may exceed 40 km. Of the three regions considered, the crust of Beta Regio may be the most poorly compensated because its free‐air anomalies are largest relative to corresponding terrain gravity effects. For Thetis Regio, crustal thicknesses may exceed 50 km. The thickened crust of Thetis Regio may also have been rifted and embayed by plains forming lavas. The lavas appear to embay and cover complexly ridged areas except where these units remained above the reach of the plains forming lavas. Crosscutting relationships, which are evident from Magellan imagery, together with our crustal thickness estimates, suggest that the complexly ridged terrain (or tesserae) may be the oldest crustal units within the three study regions. Hence these units may represent relict surfaces that predate emplacement of the plains.

Holocene and modern sediment budgets for the Ganges-Brahmaputra river system: Evidence for highstand dispersal to flood-plain, shelf, and deep-sea depocenters

The partitioning of fluvial sediment load across continental margins is an important control on strata formation and sequence development; however, few quantitative sediment budgets that encompass entire dispersal systems exist. For the Ganges-Brahmaputra river system, sediment discharge is estimated to be 10 9 t/yr at gauging stations ~300 km inland of the coast, but little has been known of the downstream fate of this material. Geochronological, geophysical, and stratigraphic investigations of the lowland flood plain, delta plain, and shelf help to delineate the extent of Holocene fill and allow calculation of a first-order sediment budget. Results reveal that 1500 ◊ 10 9 m 3 of sediment fill has been sequestered within the flood plain and delta plain since ca. 7000 yr B.P., or about one-third of the annual discharge. The remaining load appears to be apportioned between the prograding subaqueous delta (1970 ◊ 10 9 m 3 ) and transport to the deep-sea Bengal fan via a nearshore canyon. Modern (<100 yr) budget estimates based on short-term accretion rates indicate a similar dispersal pattern and show that contemporaneous deposition continues within these disparate depocenters. The roughly equal partitioning of sediment among flood-plain, shelf, and deep-sea settings reflects the respective influence of an inland tectonic basin, a wide shelf, and a deeply incised canyon system. The findings also support new sequence stratigraphic models for these settings and indicate the important insight that modern river deltas can provide for ancient margin systems. Furthermore, results affirm that values of riverine sediment flux to the oceans may be considerably overestimated by not accounting for loss to the flood plains downstream of the gauging stations.

The MOLA Topographic signature at the crustal dichotomy boundary zone on Mars

MOLA data collected during the aerobraking hiatus provide good longitudinal sampling of the crustal dichotomy boundary zone in eastern Mars and reveal a significant topographic signature associated with the transition from cratered highlands to lowland plains. Total relief between the two major units is always &gt;2.5 km and sometimes &gt;6 km; median elevation differences are about 4 km. Regional slopes are very low (&lt;0.02°) in both cratered terrain south and in lowland plains north of the boundary. Within the transition zone where cratered terrain changes to detached plateaus, mesas and knobby terrain, slopes are 50–100 times steeper and over a few hundred kilometers average about 1°. The topographic signature of the boundary zone is best described as a 2–4 km step function between two nearly flat surfaces, similar in slope and amplitude to some terrestrial passive margins. This supports previous conclusions of a significant difference in crustal properties (thickness, composition, or both) between the lowland plains and cratered terrain, and suggests this difference occurs over a relatively short distance of a few to several hundred kilometers.

Adoption of Agroforestry for Soil Conservation in Akwa Ibom State, Nigeria

ABSTRACT By its location on a lowland coastal plain, Akwa Ibom State should not be menaced by soil degradation through erosion. But some of its component areas are characterised with hill ranges which are intensively cultivated. With a high mean annual rainfall of 4020 mm and its attendant impact on the generally sandy loam soils, these areas have become victims of environmental degradation and require soil conservation. The age old techniques of soil conservation such as earth works and mechanically constructed waterways are known to be of high initial outlay with little or no return to investment capital through crop yield. On the contrary, agroforestry is looked upon as inexpensive but with the potential to achieve more than mechanical structures in erosion control, maintenance of soil organic matter and physical properties as well as in the promotion of efficient nutrient cycling and high yield. It is also seen as an important farming package for sloping lands and an easily adaptable innovation in soil conservation. A change in soil conservation policy is recommended.