Geomorphic Position Research Articles

Saprolite-soil transformations in the Piedmont and Mountains of North Carolina

In the Piedmont and Mountain Provinces of North Carolina average annual precipitation exceeds evapotranspiration. Soil solum thickness is usually 1 to 2 m. Saprolite thickness is variable but related to rock type and geomorphic position. Slow hydraulic conductivity in the zone between the soil and the saprolite appears to restrict vertical percolation of water, thus slowing saprolite weathering on convex slopes. In saprolite zones immediately above granitic gneiss, often about 5 m below the surface, halloysite, gibbsite and X-ray amorphous aluminosilicate clay are the initial secondary minerals formed. Halloysite contents increase upward in the saprolite, apparently from resilication of gibbsite and the amorphous aluminosilicates. In the upper zones of the saprolite the halloysite is recrystallized into kaolinite which is the predominant clay-sized mineral in the soil. Over gabbro and metagabbro rocks, the lower zones of the saprolite contain appreciable quantities of smectite, vermiculite, and where chlorite is present, regularly interstratified chlorite-smectite. Although these smectite minerals become partially interlayered with hydroxy aluminum in the overlying soil, they p persist as a substantial component of the clay-sized fraction. Saprolite thickness is less than over the granitic rocks. Increased run-off and lateral through-flow produced by low hydraulic conductives of smectite-rich argillic horizons and convex hill slopes are believed to be responsible for the thin saprolite above mafic bedrock. Soils and saprolites from biotitic gneiss on upper sideslopes in the Mountain physiographic province have mineralogical trends with depth similar to those found over the granitic gneisses of the Piedmont. Gibbsite often constitutes as much as 30% of the clay, and contents tend to increase in the deeper saprolite zones. Biotite sand, which is common throughout the soil and saprolite, alters to kaolinite sand under the acidic conditions of the saprolite. Sand-sized mica appears resistant to weathering except where there is evidence of physical transport.

Morphology, mineralogy and exchange properties as related to geomorphic position of soils in Tiko plain, coastal West Cameroon

Tiko plain, stretching out at the southeastern foot of the giant Mount Cameroun volcano (West Cameroon), is an example of an old coastal plain with a large variation in soil properties. These differences can be related to the geomorphic setting of the plain as a sequence of three fluvio-marine terraces, and to the origin of its superficial deposits. Based on the lithology, the Tiko plain can be divided into a volcanic part and a non-volcanic part. The non-volcanic soils show a clear evolution in mineralogy and profile development from the lowest to the highest terrace level. The terrace levels cut across the boundary between the non-volcanic and the volcanic part, but no sequence in mineralogy and soil development is found in the volcanic part. The mineralogical composition of the fine sand fraction is the most important indicator regarding the type of parent material (volcanic or non-volcanic). There is an overall relationship between the mineralogical composition and the cation exchange properties of the soils. These properties highlight the overestimation of CEC by classical methods (NH 4OAc, NH 4Cl and BaCl 2-TEA) where artificially high pH and ionic strength conditions are used in the determination.

Manganese Distributions in Acid Soils of the North Carolina Piedmont

AbstractManganese is a dynamic component of soils that can be present in a variety of forms. This study was initiated to examine the distribution of Mn in Ultisols and Alfisols formed in gneisses of the North Carolina Piedmont. Secondary Mn (Mnd) and Fe (Fed) depth distributions were evaluated using a citrate‐bicarbonate‐dithionite extract; the distribution of Mn among organic and various inorganic soil fractions was determined using a sequential‐extraction procedure. Results indicate that accumulation of Mnd is related to interactions between landscape position and associated redox potential (Eh)‐pH environments rather than mineralogy of soil parent material. Spatial relationships between Mnd and Fed within soils reflect Eh‐pH‐potential gradients in these acid systems. Accumulations of secondary Mn occur in well‐drained surface horizons of soils occupying lower lying landscape positions. These accumulations occur in weathered hillslope sediments and are not related to mineralogy of the underlying residuum. As much as 50% of this Mn is associated with the organic‐matter fraction and the inorganic exchange complex. Secondary accumulations of Mn also occur in B/C horizons and saprolite residuum in soils of actively down‐wearing geomorphic positions. Most of this Mn is in the crystalline Mn oxide fraction. Data indicate a significant correlation (P < 0.01) exists between quantities of Mn found in the amorphous, exchangeable, and crystalline Mn oxide fractions.

Soil‐Geomorphic Relations on the Blue Ridge Front: II. Soil Characteristics and Pedogenesis

AbstractSoils along two mountain slope transects in mica gneiss and schist terrane were studied to better understand soil distribution and genesis on the Blue Ridge Front landscape in North Carolina. Soils may form entirely in residuum or colluvium, but on most slope positions they have developed in both materials. The colluvial/residual nature of soils is related to geomorphic position and has a strong influence on soil properties and the evolution of the soils. Soils on upper slopes have a significant residual component as a result of weathering into the parent rock. Low slope positions are sites of accumulation, resulting in deep soils formed in colluvium. Dystrochrepts, or very weakly expressed Hapludults, have developed entirely in colluvium, whereas soils with at least a partial component of residuum are Hapludults. Soils on landscape positions down wearing into fresh mica gneiss or schist are in the micaceous mineralogy class, whereas those in highly weathered colluvium and in very stable residuum (i.e., nearly level summit positions) have been depleted of mica and are in the oxidic class. A conceptual model relating slope processes to pedogenesis is proposed in which colluvial transport interrupts the orderly in situ progression of residual soil development. The genesis and distribution of soils are best understood when studied in landscape contexts, rather than at the level of individual pedons or classification units.

Directional saturated hydraulic conductivity and macropore morphology of a soil-saprolite sequence

The soils in the Piedmont and Mountain regions of the southeastern United States are characterized by the presence of saprolite at or near the soil surface. This study was conducted to describe the macropore network of a representative soil-saprolite sequence and to relate the directional saturated hydraulic conductivity of the soil profile to water flow through macropores. Large observation pits were constructed at three geomorphic positions (ridge top, shoulder and ridge nose). Soil-saprolite macropores and their morphology were described in the field. Triplicate intact soil cores were collected in five orientations: one vertical, two horizontals (perpendicular to one another) and two diagonals (perpendicular to one another) from the Bt, B/C and C (massive saprolite) horizons at each of the geomorphic positions. The saturated hydraulic conductivity ( K a) of each intact core sample was determined in the laboratory. In situ K a of each horizon was also determined near the three observation pits. Mean K a values for the five orientations, three horizons and three geomorphic positions ranged from 8.20×10 −8 m s −1 to 2.75×10 −6 m s −1. Mean in situ K a values ranged from 7.50×10 −8 m s −1 to 2.66×10 −6 m s −1. The results indicated that no significant differences existed among the K a values in different orientations for each horizon-landscape combination, with no exceptionally high conductivity value. The in situ K a results generally agree with the results for the core samples.

A toposequence of fine-textured soils in the hilly area of the northernmost part of Hokkaido

Abstract Morphological, micromorphological, and physico-chemical investigations were conducted on three profiles of a toposequence in the hilly area of northern Hokkaido: Profile Bf, on a relatively steep slope; Profile Pr, on a rounded top or upper convex slope; and Profile Pg, on a lower concave slope. The influences of eluviation and illuviation processes were evident in all three profiles, but the appearances of the profiles were different depending upon the geomorphic position. The soil substances accumulated in the B horizons in all three profiles were summarized as follows: sesquioxides not associated with humus and clay in Profile Bf; sesquioxides and humus in Profile Pr; and mainly clay but including sesquioxides not associated with humus in Profile Pg. Profiles Pg and Bf were identified as Aquic Glossoboralfs and Typic Haplumbrepts, respectively, according to Soil Taxonomy. Although Profile Pr had a spodic morphology, its Bhs horizon failed to meet one of the laboratory criteria of a spodic hori...

Regional significance of recurrent faulting and intracanyon volcanism at Oak Creek Canyon, southern Colorado Plateau, Arizona

Measured sections of late Miocene basalt lava flows, Tertiary gravel, and Paleozoic strata are the basis for stratigraphic reconstructions that provide evidence for pre- and post-volcanic movements on the Oak Creek fault, and for the existence of a prevolcanic ancestral Oak Creek Canyon, Arizona. Recurrent faulting, recording Laramide compression and Basin and Range extension, suggests probable control by an ancestral Oak Creek fault that would belong to a regional system of basement faults hat have controlled Colorado Plateau structures in Phanerozoic rocks. Locally derived Tertiary gravel and overlying lavas filled a canyon eroded in Paleozoic strata along the Oak Creek fault. Southward flow of ancestral Oak Creek, indicated y the lithology and geomorphic position of the gravel, valley reconstruction, and lava vents to the north, northeast, or east, requires that the regional drainage reversal on the southern Colorado Plateau occurred before late Miocene time in the Oak Creek area.

The soils and ages of the “raña” surfaces related to the Villuercas and Altamira mountain ranges (Western Spain)

Summary The soils of “rana” surfaces related to the “Sierra de las Villuercas” and the “Sierra de Altamira” (Western Spain) were studied with reference to vegetation cover and geomorphic position. These soils were highly weathered, with kaolinite dominant in the clay fraction and almost no weatherable minerals in the sand fraction. Iron oxides were segregated in some of the horizons giving a formation of “pseudoplinthite”. This high degree of weathering and the patina of their quartzite stones are comparable to those of soils developed on the oldest ran˜a surfaces studied in Central Spain. The soils classified as Palehumults and Palexerults are given, tentatively, a Middle-Upper Pliocene age.

Anhydromorphic and hydromorphic saline soils

Anhydromorphic and hydromorphic saline soils resemble the surface water and the ground water type of soil formation, thus differ fundamentally in geomorphic position, geochemical accumulations and ecological properties and should be differentiated accordingly.

Topographic control of soil moisture, vegetation cover and land degradation in a moisture stressed mediterranean environment

An erosion-vegetation competition model (THORNES 1985) assumes that surface litter, soil organic matter and soil moisture are positively correlated and that these in turn are correlated with topographic conditions on a uniform soil in a moisture-stressed environment. These relationships are tested for an experimental site in Mediterranean Spain. The results show that while these relationships are statistically significant, but rather weak, when all the data are used or when they are grouped according to geomorphic position (interfluve, hollow or slope), the correlations become stronger when considered in relationship to transects and when the data are subject to a low level of spatial smoothing. Even then, the relationships are rather complex, reflecting local features, the stage of vegetal development and, perhaps, the status of competition between erosion and vegetation.

The geomorphology and stratigraphy of the Lizard Loess in south Cornwall, England

The Quaternary deposits of south Cornwall are described with an emphasis placed on the loess component. A formal lithostratigraphic name – the Lizard Loess – is proposed for the loess formation with a holostratotype designated from the Lizard Peninsula. Two environments of loess deposition are distinguished on the basis of geomorphic position and degree of solifluction activity.

Relative dating techniques to distinguish late Pleistocene-Holocene continental sediments

Radiometric dating, particularly with 14C, provides ages for those Late Pleistocene and Holocene sediments that contain datable materials. Standard stratigraphic and morphostratigraphic techniques of superposition, geomorphic position, partial overlap, and offlap provide relative chronology in many situations. The use of multiple relative dating (RD) techniques, developed for the study of glacial deposits, makes use of these techniques where possible, but depends heavily on the additional comparison of the results of surface processes that act continuously and more or less uniformly after accumulation is complete. For sediments at the surface that have not been buried, the most important of these processes are weathering and morphological alteration. Soil profile development is progressive; careful field description plus laboratory analysis provide data to distinguish soils of differing maturity, hence, of different ages. Clasts at the surface and within the soil profile weather continuously, and quantification of the degree of their decay permits recognition of age differences. In mountains adjacent to deserts, a veneer of loess accumulates slowly, and is thicker on older alpine deposits. Quantification of gully development provides still another morphometric approach to dating young sediments. These RD methods have been effective in distinguishing relative ages of continental sediments from 10 2 to 10 7 yr. old in the western U.S.A. mountains and in the Central Andes.

Characteristics of soil profiles affected by smelting of nickel and copper at Coniston, Ontario, Canada

Soil profiles were examined, described and sampled by horizons in various geomorphic positions along a transect originating at the Coniston smelter and extending in a southeasterly direction for approximately 12 km. The samples were then analyzed to determine particle-size distribution, pH, organic carbon and five heavy metals. Within the study area, elevated levels of nickel, copper and iron were found with maximum total concentrations of 1.2, 0.97 and 20.0%, respectively. Manganese and zinc did not occur in above-normal concentrations. The pH values of the soils were depressed with levels as low as 2.4. Near the smelter, erosion from soils on slopes has transferred materials into lower lying areas, thereby rearranging the areal distribution of nickel, copper and iron. Although the surface soil horizons along the entire transect have above-normal concentrations of these elements, only within the eroded area is there marked variability in their vertical distribution.

Soil Fertility Dynamics after Clearing a Tropical Rainforest in Peru

AbstractThis paper describes changes in soil properties during the first 8 y after clearing a fine loamy, siliceous, isohyperthermic Typic Paleudult at Yurimaguas, Peru. Three adjacent fields under a 17‐year old secondary forest were slashed, burned, and planted to three crops per year with or without fertilization for 8 years. Ash from the burn increased soil pH, available N, P, K, Ca, Mg, and decreased exchangeable Al. Six months after burning, however, the levels of available N and K were reduced, along with sporadic S, Cu, and B deficiencies. Topsoil organic C and total N decreased at an annual rate of 25% during the first year but approached an equilibrium afterwards. The rapid organic matter decomposition probably released organic matter‐bound Al which reversed the liming effect of the ash. Phosphorus and Mg became deficient during the second year, Ca within the first 30 months and Zn and Mn during the fourth year. Molybdenum deficiencies occurred sporadically, particularly when locally produced legume seed was used. Soil chemical properties have improved with continuous cultivation because of liming and fertilizer additions. After 8 years and 21 crops, topsoil pH increased to 5.6, exchangeable Ca increased by 10 times, effective CEC doubled, available P increased from 5 to 39 mg kg−1, and Al saturation decreased from 82 to 1%. The 15‐ to 50‐cm layer of the subsoil has undergone significant increases in exchangeable Ca and Mg and a decrease in Al saturation. This should promote deeper root development. The time at which nutrient deficiencies appeared and the amounts of fertilizer or lime needed to correct them varied substantially between the three fields, despite their close proximity, same preclearing vegetation, geomorphic position, and same soil classification at the family level.

Origin of bimodal volcanism, southern Basin and Range province, west-central Arizona

Miocene volcanic rocks in the Castaneda Hills area, west-central Arizona, are interbedded with continental clastic sedimentary rocks, minor limestone, gravity glide blocks of Precambrian(?) and Paleozoic(?) rocks, and monolithologic megabreccia. The sedimentary and volcanic units dip to the southwest and are offset by northwest-trending listric and high-angle normal faults. The listric faults coalesce at the Rawhide detachment fault, which overlies mylonitic gneiss. The volcanic suite is strongly bimodal; rocks with 55 to 71 wt % SiO 2 are rare. On the basis of age, geomorphic position, and petrography, five volcanic units can be distinguished: older basalts (18.7 and 16.5 m.y. old), quartz-bearing basalts (13.7 and 12.4 m.y. old), rhyolite lavas and tuffs (15.1 to 10.3 m.y. old), mesa-forming basalts (13.1 to 9.2 m.y. old), and megacryst-bearing basalts (8.6 to 6.8 m.y. old). Most of the basalts contain groundmass olivine and titanaugite phenocrysts and are alkali-olivine basalts. Many rhyolites contain more than 75 wt % SiO 2 . The initial whole-rock Sr isotopic composition of the basalts indicates that they are partial melts of an isotopically vertically heterogenous mantle. The chemical composition of some of the megacrysts in megacryst-bearing basalts with 87 Sr/ 86 Sr i equal to .7035 and .7038 supports a high-pressure mantle origin. The low (.7034) Sr ratio and lack of evidence for mixing with young rocks indicate that the quartz-bearing basalts were also derived from the mantle. Other basalts with 87 Sr/ 86 Sr i > 0.705 probably were derived from old, lithospheric mantle with a high Rb/Sr ratio and do not appear to be contaminated with old, upper-crustal material. The rhyolites have initial Sr isotopic ratios of 0.7093 and 0.7141. These ratios indicate that the rhyolites were not differentiated from the basalts. Partial melting of 1.3-b.y.-old lower-crustal material with Rb/Sr = 0.10 to 0.19 satisfactorily explains the isotopic ratios of the rhyolites. Granulite, which may constitute the lower crust in this part of Arizona, has Rb/Sr ratios similar to those required to produce the rhyolites. K substituted for Na during cooling and devitrification in some of the rhyolites. Partial melting of upper-mantle peridotite and old lower-crustal granulite from 19 to 7 m.y. ago in the Castaneda Hills area produced the bimodal volcanic suite. The nearly contemporaneous production of basaltic and rhyolitic magma from the Earth9s crust and mantle requires extremely heterogenous source regions. Asthenospheric upwelling associated with basin-range extensional tectonism probably produced the heating event that caused partial melting and basaltic magma generation at different levels in the mantle. Partial melting in the lower crust to produce rhyolitic magmas probably was caused by the intrusion of basalt magma. The basaltic and rhyolitic magmas formed in separate source regions, rose independently, and erupted at the same time and place.

Sedimentology and palynology of Middle Wisconsinan deposits in the Pecatonica River valley, Wisconsin and Illinois

The bedrock valley of the Pecatonica River north of Freeport, Illinois, contains a thick valley-fill complex of alluvium and drift. Within the valley, loess-capped benches surround hills of silty Illinoian drift. Beneath these benches lie thick deposits of poorly sorted stony silt interbedded with thin lenses of silt, sand, and organic-rich loam. Channel deposits and peat cap the diamicton in places. We interpret the stony silts as solifluction debris shed from silty slopes within the valley-fill during the Early or Middle Wisconsinan (Altonian). Top and bottom radiocarbon dates from a 2.5-m section of peat overlying the diamicton are 26,820 ± 200 and 40,500 ± 1700 yr B.P., respectively. We informally refer to the stony silts, channel sediments, and peat as the “Martintown unit.” Geomorphic position, sediment input, and macrofossils suggest that the dated peat was deposited in a floodplain pond (oxbow?). The pollen record from the peat indicates that a boreal forest dominated this area during the Middle Wisconsinan (late Altonian and Farmdalian). Two pollen zones are recognized: a basal Zone I with Pinus slightly more abundant than Picea and with few herbs and shrubs, and an upper Zone II dominated by Picea and with a larger representation of herbaceous and shrub taxa. Little displacement of vegetation zones is indicated, even though ice advanced to within 100 km of the site during the time of peat accumulation. Because of the problems involved in clearly defining Middle Wisconsinan forest-tundra in mid-latitudes by using analogs of Holocene forest-tundra in high latitudes, caution is required in making geomorphic inferences solely from vegetation data. Together, though, pollen and sediment data indicate that during the Middle Wisconsinan, Pecatonica hillslopes progressed through a sequence of instability-stability-instability related to climatic fluctuations.

Carolina Bays on the Eastern Shore of Virginia

AbstractCarolina bays were analyzed on the Eastern Shore of Virginia utilizing infrared imagery and pedologic techniques. Over 160 bays were delineated thus indicating they are major landforms in the area. Bays differed from those reported in other regions by being less elliptical, more westerly oriented, and lacking well‐developed rims in any specific quadrant. Bay location and size are apparently controlled by landscape and sandy parent materials as evidenced by association with less distinct natural depressions with similar orientation as the related geomorphic urface. Soils on bays of recent surfaces have weaker profile development compared to Pleistocene upland bays. More than one period of bay formation is suggested by differential pedogenic development and geomorphic positions. Data indicate Carolina bays were formed by the alteration of poorly drained areas on undissected Coastal Plain interfluves. Wind and waves are suggested as factors in bay formation based on well‐sorted sands of elevated rims, “dune‐like” character, and silt content of possible aeolian origin.

Native-induced secondary plant succession in the Mackenzie River delta, Northwest Territories, Canada

Plants introduced by man play a very minor role in the flora of the Mackenzie River, delta and are primarily restricted to centres of habitation such as Inuvik, Aklavik, and Reindeer Station (Map 1) (Cody, 1965; Gill, 1971). Within the delta itself, however, a number of introduced species are recurringly present on one geomorphic position, the point bar, which forms the convex section of a meander bend in flood plains and deltas (Fig 1). The Mackenzie delta supports a northerly extension of the boreal forest, and most of the higher levees are occupied by trees, particularly White SprucePicea glauca. Point bars are constructed of coarser alluvium than other delta landforms, thus they have a drier and warmer soil environment than other locations (Gill, 1972a); vegetation response to this locally ameliorated environment has been such that virtually every point bar in the Mackenzie delta is occupied by a discrete plant community dominated by Balsam PoplarPopulus balsamifera(Gill, 1972b). The poplar stands are surprisingly well developed for such a northerly latitude, 68°45′N (Fig 2).

A parametric approach to land system classification

Progress in land system analysis needs distinct, preferably genetic and quantitative or semi-quantitative descriptions and classification. In an attempt to fulfil this need, the following parameters are used to classify land systems: process, altitute, relief, dominant geology, drainage pattern, stream frequency, characteristic plan-profile, geomorphic position, dominant facet, characteristic facet, characteristic variant and land zone.