Alluvial Debris Research Articles

Analysis of the origin, formation and development of sand ramps on the Eastern slopes of Shirkouh, Yazd, Central Iran

The purpose of this study is to examine the sand ramps in the margin of Ernan playa located in Yazd Province, central Iran. The region is marked with several sand ramps, many of which are not observable as they are buried under colluvial and alluvial sediments or dense vegetation. Field studies indicated at least 18 fairly large sand ramps in the region in the form of both climbing and falling dunes. These sand ramps were formed mostly in the past and are stable and inactive now. However, in some parts of the region in question, these landforms are still forming and developing. The results indicated that the sediment, especially those of the sand ramps on windward slopes, have large grains. Also, over 50 percent of the sediments generally have grains with a diameter of more than 1mm. The presence of such minerals as Alkali Feldspar, Plagioclase, Quartz, Biotite, Muscovite, Amphibole, and Apatite, respectively in terms of quantity and frequency, in the sand ramp sediments indicates that the origin of sand ramp sediments is the monzogranites of the eastern slope of Shirkouh Mountain with the same texture and frequency. The very fact that the above-mentioned minerals are intact, i.e. they have not been rounded or eroded, suggests that these sediments have not been displaced a lot. The study of the developing sand ramps proved that such structures form at the height of more than 2400m with two months of frost annually, over 100mm of precipitation (periglacier conditions), and granite outcrops. The reconstruction of the past climate conditions indicated that the temperature in the cold Quaternary glacial age was 13 degrees lower than present, with glacier and periglacier conditions dominating. Under such conditions, the region’s granites were extremely weathered, hence producing a large quantity of grain sediments. The surface run-offs or ice tongues drifted these sediments toward Lake Ernan (i.e. the present Ernan playa) and deposited them at its shoreline. After the lake and the main river dried up, southwest winds led the sediments of the lakeshore and the Tang-e-Chenar River upward to the top of the mountains, where sand ramps were, thus, formed. Due to the short formation duration and steady climate, no colluvial, alluvial material, or even soil (despite the large quantity of feldspars in the sand ramps) was traced amid the sediment layers of the sand ramps in the studied region. The only features traced there were slopes, alluvial debris and vegetation, indicating the dominance of warmer and moister climate as compared to the conditions at the time of formation. The directions of the past and developing sand ramps are similar but opposed to the prevailing and secondary wind of the region, indicating that it is the local winds which have formed those ramps.

Diplurans of subsurface terrestrial habitats in the Iberian Peninsula, with a new species description (Diplura: Campodeidae)

Although Iberian subsurface terrestrial habitats have been sampled for a half century, they remain poorly known. During the last five years much more sampling of these subsurface habitats has been made, mainly in scree slopes (also called colluvial Mesovoid Shallow Substratum habitats, MSS) but also in alluvial debris of temporal watercourses (alluvial MSS). In our study, diplurans, a basal hexapod group, were extracted from two hundred traps installed in 69 locations in the mountain ranges of six different regions of the Iberian Peninsula, from north to south: Cantabrian, Pyrenees, Iberic System, Central System, Prebaetic and Penibaetic Mountains. A total of 1251 specimens in fifteen dipluran species: thirteen described Campodeidae, one described Japygidae and one new Campodea species inhabiting the alluvial MSS habitats of the watercourses of Prebaetic Mountains. A few populations of these dipluran species show troglobiomorphic features as a consequence of the medium-sized voids of the MSS habitats, such as Campodea grassii Silvestri, 1912, collected in a scree slope connected with a deep subterranean system in Penyas Roset, Prebaetic Mountains. Most species found in MSS habitats are endogean or epiedaphic species living in the area, but this is not the case in Sierra de Guadarrama, where three species (Campodea propinqua Silvestri, 1932, Campodea neusae Sendra & Moreno, 2006 and Campodea zuluetai Silvestri, 1932) unknown in the soil of these mountains have appeared in these subsurface terrestrial habitats.

Sediment in Alluvial and Lacustrine Debris Fans as an Indicator for Land Degradation Around Lake Ashenge (Ethiopia)

AbstractSediments deposited by (paleo) flash floods can hold valuable information on processes of environmental change, land degradation or desertification. In order to assess the suitability of flash flood deposits as proxies for land degradation, we monitored a representative gully segment in North Ethiopia (Ashenge catchment), investigated a sequence of alluvial debris fans downstream of this segment and dated a neighbouring subaquatic debris fan using short‐lived 210Pb isotope counting. During one rainy season (July–September 2014), we measured daily rainfall, peak discharge, bedload transport, suspended sediment load and sediment deposition rates. The data show that sediment deposition in the debris fans is significantly dependent on micro‐topography (net incision in micro‐channels) (p < 0·1) and position within the sequence (net incision farther away from the lake) (p < 0·05). As sediment transfer to the lake significantly depends on the balance between available water and sediment (ratio rainfall depth/bedload transport) (p < 0·05), we could reconstruct the hydro‐sedimentary evolution of the gully over the past half century and validate it with aerial photographs and semi‐structured interviews. The findings are consistent with the short‐lived isotope count results, indicating increased sediment supply from the 1970s onwards, when little amounts of clay were deposited in the lake (<5%), and a subrecent clear water effect that resulted in increased deposition rates of clay in the lacustrine debris fan. Overall, our analysis indicates that debris fan sediments can be used to estimate past environmental degradation rates, if the contemporary water and sediment behaviour is well understood. Copyright © 2015 John Wiley & Sons, Ltd.

What was the groundwater quality before mining in a mineralized region? Lessons from the Questa project

The U.S. Geological Survey, in cooperation with the New Mexico Environment Department and supported by Molycorp, Inc (currently Chevron Minerals), has completed a 5-year investigation (2001–2006) to determine the pre-mining groundwater quality at Molycorp’s Questa molybdenum mine in northern New Mexico. Current mine-site ground waters are often contaminated with mine-waste leachates and no data exists on pre-mining ground-water quality so that pre-mining conditions must be inferred. Ground-water quality undisturbed by mining is often worse than New Mexico standards and data are needed to help establish closure requirements. The key to determining pre-mining conditions was to study the hydrogeochemistry of a proximal natural analog site, the Straight Creek catchment. Main rock types exposed to weathering include a Tertiary andesite and the Tertiary Amalia tuff (rhyolitic composition), both hydrothermally altered to various degrees. Two types of ground water are common in mineralized areas, acidic ground waters in alluvial debris fans with pH 3–4 and bedrock ground waters with pH 6–8. Siderite, ferrihydrite, rhodochrosite, amorphous to microcrystalline Al(OH)3, calcite, gypsum, barite, and amorphous silica mineral solubilities control concentrations of Fe(II), Fe(III), Mn(II), Al, Ca, Ba, and SiO2, depending on pH and solution composition. Concentrations at low pH are governed by element abundance and mineral weathering rates. Concentrations of Zn and Cd range from detection up to about 10 and 0.05 mg/L, respectively, and are derived primarily from sphalerite dissolution. Concentrations of Ni and Co range from detection up to 1 and 0.4 mg/L, respectively, and are derived primarily from pyrite dissolution. Concentrations of Ca and SO4 are derived from secondary gypsum dissolution and weathering of calcite and pyrite. Metal:sulfate concentration ratios are relatively constant for acidic waters, suggesting consistent weathering rates, independent of catchment. These trends, combined with lithology, mineralogy, and mineral solubility controls, provide useful constraints on pre-mining ground-water quality for the mine site where the lithology is known.

Unusual disturbance: forest change following a catastrophic debris flow in the Canadian Rocky Mountains

Trees are often well adapted to periodic physical disturbances such as fires or floods. However, I investigated forest response to an extremely unusual disturbance event. Following heavy rain in June 1995 a catastrophic debris flow from Vimy Peak in the Canadian Rocky Mountains terminated as an alluvial debris fan that plowed through a trembling aspen (Populus tremuloides Michx.) grove. I analyzed the site over a decade to monitor forest response and determine whether there would be recolonization to the prior forest type. In contrast to my expectation, aspen recolonization did not occur; instead, black cottonwoods (Populus trichocarpa Torr. & Gray) colonized the site. These originated from seedlings and not through clonal propagation, and by 2004, black cottonwoods composed 99% of the saplings and were typically 0.6–1.4 m tall with a density of about 1/m2. The debris fan dramatically changed the physical environment, which partly resembled a floodplain depositional zone and was colonized by the regionally dominant riparian tree. I propose the concept of foreign disturbance to recognize an unusual disturbance that an organism would very rarely experience and thus to which it is unlikely to be adapted. In this example the disturbance produced an abrupt transition to an alternative forest type and this response may provide insight into forest response to other unusual disturbances, such as extreme weather events, that might increase with climate change.

English

The U.S. Geological Survey, in cooperation with the New Mexico Environment Department, has completed a 4-year investigation (2001-2005) to determine the pre-mining ground-water quality at Molycorp's Questa molybdenum mine in northern New Mexico. Current mine-site ground waters are often contaminated with mine-waste leachates and no data exists on pre-minng ground-water quality so that pre-mining conditions must be inferred. Ground- water quality undisturbed by mining is often worse than New Mexico standards and data are needed to help establish closure requirements. The key to determining pre-mining conditions was to study the hydrogeochemistry of a proximal natural analog. Main rock types exposed to weathering include a Tertiary andesite and the Tertiary Amalia tuff (rhyolitic composition), both hydrothermally altered to various degrees. Two types of ground water are common in mineralized areas, acidic ground waters in alluvial debris fans with pH 3-4 and bedrock ground waters with pH 6-8. Siderite, ferrihydrite, rhodochrosite, amorphous to microcrystalline Al(OH)3, calcite, gypsum, barite, and amorphous silica mineral solubilities control concentrations of Fe(II), Fe(III), Mn(II), Al, Ca, Ba, and SiO2, depending on pH and solution composition. Concentrations at low pH are governed by element abundance and mineral weathering rates. Concentrations of Zn and Cd range from detection up to about 10 and 0.05 mg/L, respectively, and are derived primarily from sphalerite dissolution. Concentrations of Ni and Co range from detection up to 1 and 0.4 mg/L, respectively, and are derived primarily from pyrite dissolution. Concentrations of Ca and SO4 -2 are derived from secondary gypsum dissolution and weathering of calcite and pyrite. Metal:sulfate concentration ratios are relatively constant for acidic waters, suggesting consistent weathering rates. These trends, combined with lithology, mineralogy, and mineral solubility controls, provide useful constraints on pre-mining ground-water quality for the mine site where the lithology is known.

Assessing the Influence of Mountain Slope Morphology on Pediment Form, South-Central Arizona

Pediments are common desert landforms. While the term "pediment" is used to describe subaerial bedrock platforms (here called "bedrock pediments"), it is frequently used to describe the hybrid suballuvial bedrock platforms (here called alluvial slopes) as well. Important distinctions exist between these landforms. For example, whereas bedrock pediments are mantled with a thin layer of in situ and perhaps alluvial debris, alluvial slopes tend to imitate alluvial fans, cone-shaped deposits of alluvium made by ephemeral mountain streams depositing sediment on piedmonts. Mountain slopes backing bedrock pediments and alluvial slopes located in the Phoenix, Arizona, region exhibit disparate morphologies that allow a distinction to be made between bedrock pediments and alluvial slopes developed at their base. Mountain slopes above bedrock pediments tend to exhibit larger clast sizes mantling the slope, less vegetation, steeper slopes, more abrupt piedmont angles, and fewer joints in bedrock outcrops. Mountain slopes above alluvial slopes, in contrast, exhibit smaller clasts, greater vegetation, gentler slopes and piedmont angles (i.e., more concave), and increased joint density in outcrops. Drainage areas feeding bedrock pediments also tend to be smaller compared to drainage areas feeding alluvial slopes. These results suggest that backing mountain slope morphology discriminates the occurrence of bedrock pediments and alluvial slopes in the study area, and further analyses of field data provide an indication of controls on the development of these landforms.

REDOXIMORPHIC FEATURES IN SOILS OF THE TRIASSIC CULPEPER BASIN1

Conflicting observations have been reported about redoximorphic features in soils derived from red Triassic sediments. Previous laboratory research has shown that development of redoximorphic features is sometimes inhibited in these sediments. Soil morphological descriptions made under the auspices of The National Cooperative Soil Survey, however, include redoximorphic features consistent with their drainage status. The objective of this study was to examine the relationship between soil characteristics and development of redoximorphic features in these soils. Eleven pedons located along two topohydrosequences in the Triassic Culpeper Basin of Maryland were described and characterized. In addition, water table depths were measured biweekly over a 2-year period at each pedon during the wet season. Similarly drained, yet morphologically different pedons were observed occupying the lower backslope, footslope, and toeslope positions of both topohydrosequences. Differences in organic carbon content and soil temperature did not explain the observed morphological differences among these similarly drained soils. The nature of the parent material, however, appears to control the development of redoximorphic features in the soils of the Triassic Culpeper Basin of Maryland. Lithological discontinuities were observed at the boundary between horizons with yellow and red hues (i.e., 5YR) in soils that occupy the footslope and toeslope positions. These discontinuities are believed to represent the incorporation of alluvial debris in these soils. Within pedons whose upper sola were influenced by alluvial additions and a persistent seasonally high water table, substantial development of redoximorphic features was observed. Within hydrologically-similar pedons derived mainly from Triassic residuum, redoximorphic features were weakly expressed. Hydromorphological features are formed by redox processes, but the particular expression may be affected by the nature of the parent materials. These results may be useful to field soil scientists for their assessment of the correct drainage class of these soils.

Origins and environments of pediments

Abstract Three types of pediment have been recognised. The first are cut bedrock surfaces, veneered (and hence smoothed and protected) by coarse alluvial debris. Characteristically developed in the Brachina area of South Australia, they form in the piedmont zone in areas of mixed sedimentary outcrop and in areas where there are large variations in river and stream discharge, including occasional high floods. They are not restricted to any conventionally defined climatic region or regions, though their development is favoured by stream regimes characteristic of arid and semiarid lands. The second and third types are typical of granite regions. The debris veneer of the second form, well developed around Ucontitchie Hill, mainly consists of weathered rock in situ, though in places there is also a thin discontinuous veneer of transported material. The mantis consists of grus and is readily eroded, exposing the weathering front as a rock platform or pediment, such as that found adjacent to Corrobinnie Hill. Th...

Structural Geology of the Sierra de la Gavia, Coahuila, Mexico

Sierra de la Gavia, in east-central Coahuila, Mexico, is one of a number of northwesterly aligned, mountain-forming anticlinal structures which constitute part of the Coahuila Marginal Folded province of northeastern Mexico. This province, an uplifted segment of the southwestern limb of the Rio Grande Embayment, lies north and east of the folds of the Sierra Madre Oriental. It includes several geologic elements: the Parras and Sabinas Basins, the paleogeographic Coahuila and Tamaulipas Peninsulas, and fold belts east of the Coahuila Platform and north of the Tamaulipas Arch. The fold, roughly 60 miles in length, rises abruptly out of bolson plains which border its northeast and southwest flanks. Lower-Upper Cretaceous-Quaternary rocks exposed within the Sierra include several thousand feet of detrital and chemico-detrital sedimentary rocks. Lower Cretaceous formations (Barril Viejo, Patula, La Mula, Taraises-Cupido, La Pena, Aurora-Cuesta del Cura), which are more than 7000 feet thick, form the major part of the mountain mass. Upper Cretaceous rocks (Indidura) and alluvial debris, together more than 500 feet thick, constitute minor mappable units. Younger Cretaceous units (Parras, Difunta), largely obscured by alluvium, form flanking outcrops, and generally occupy synclinal areas between Gavia and adjacent structural highs. In gross aspect, the axis of the structure is doubly inclined, striking generally northwest-southeast and plunging in both these directions. Areal mapping, however, discloses the presence of five separate areas of closure. Inclinations of the axial plane vary markedly along strike. Large-scale drag folding modifies both northeast and southwest limbs of the structure in certain areas. Minor en echelon normal (?) faults, thought to be shear fractures, occur at the structural culmination of the fold. It is suggested that Sierra de la Gavia and similarly aligned structures in the Coahuila Marginal Folded province owe their origin initially to movement of recurrent nature occurring along a suggested wrench fault of regional magnitude—a fault expressed at the surface in the abrupt change in strike and character of the frontal folds of the Sierra Madre Oriental between Monterrey, Nuevo Leon, and Torreon, Coahuila. Local northeast overturning on the southwest flank of Gavia, near its northwest end, is thought to be a surface reflection of the buttressing mass of the northeast edge of the Coahuila Peninsula.

Miocene of Caliente Range and Environs, California

Caliente Range and environs furnishes what is believed to be the best Miocene record for California. Approximately 180 molluscan and echinoderm faunas representing 47 nearly consecutive horizons from that of Turritella inezana var. hoffmani upward to well above that of Astrodapsis tumidus have been obtained from a Miocene succession locally about 13,800 feet in thickness. At Caliente Mountain a homoclinal section exposes, upward, successively about 1,100 feet of upper Oligocene(?), 4,500 feet of Vaqueros (lower Miocene), 4,700 feet of Temblor (middle Miocene), and 4,600 feet of Monterey (upper Miocene) strata. The marine Miocene series locally grades on the one hand to fine facies yielding foraminifers, and on the other to coarse continental facies yielding terrestrial ve tebrates. The district lies at the junction of the three largest Miocene provinces of the state, linking their histories. The area discussed formed the pivotal part of a peculiarly long, narrow, and deep upper Oligocene and Miocene trough about 300 miles in length and 20 in width which seemingly extended from the Santa Cruz region southeast to Caliente Range. At this latter place the trough forked, sending a branch east into what is now the San Emigdio foothill region of southern San Joaquin Basin, with the original strike continuing southeast to intersect and die out in Ventura Basin. A thick marine succession along the axis of the trough grades on the flanks to thin wedges separated by unconformities that appear and grow strandward. Near its heads the succession locally passes into continental deposits with similar areal relations. The trough was pinched out and strongly deformed and eroded by post-Miocene diastrophism. Its strata were steeply tilted, locally overturned and overthrust, and in places largely removed. Thrusts, erosion, slides, and alluvial debris have obliterated or hidden stretches near its mouth, both heads, and intermittently between these points. Evidence secured in Caliente Range and environs, in combination with state-wide data, suggests the following history. In the lower Oligocene California seems to have been completely emergent, with continental deposits being locally laid down near the present coast. In the upper Oligocene the sea invaded the state as a narrow inlet occupying the newly initiated Caliente trough, continental deposition continuing in most former areas of that nature. The marine Miocene of California is a transgressive series, essentially conformable basinward, but revealing, strandward, the occurrence of two oscillations which respectively inaugurate and divide its upper third. It comprises three End_Page 193------------------------------ nearly equal major natural divisions, the Vaqueros, Temblor, and Monterey stages, which approximate lower, middle, and upper Miocene. Each of these has a more or less distinctive epeirogenic history, fauna, and average physical aspect. The sea transgressed throughout the Vaqueros stage, hesitated without receding, and then advanced more widely during the Temblor. Moderate regression accompanying diastrophism of locally prominent to locally imperceptible intensity and a widespread quickening of vulcanism then caused strandward unconformity. In early lower Monterey (Briones) time the sea again advanced widely. Its boundaries remained more or less static during the late lower Monterey (Cierbo). Moderate regression and diastrophism then again caused strandward unconformity. In upper Monterey (Neroly) time the sea once more advanced, reaching its widest extent during the epoch. The Miocene series records progressively cooler waters, the tropical Vaqueros fauna giving way to the subtropical fauna of the Temblor, and this n turn to the slightly hardier fauna of the Monterey. Each fauna changed relatively slowly during its stage, with hardier forms of the succeeding dynasty encroaching as an admixture in open, cooler waters, and then gave way to a new fauna with relative rapidity during a short transitional interval corresponding to one of the epeirogenic movements that divide the Miocene series of California into approximately equal thirds as regards major physical and coincident faunal units. Wide regression resulting in almost or quite complete emergence of California separates the Miocene series from the markedly different and more restricted Pliocene series.