Glaciofluvial Deposits Research Articles

Late Quaternary glacial chronology on the eastern slope of Gongga Mountain, eastern Tibetan Plateau, China

The Gongga Mountain is the largest area of modern glaciation in the Hengduan Mountains and, with a summit elevation of 7556 m, is the highest mountain on the eastern margin of the Tibetan Plateau. During the Quaternary glacial-interglacial cycles the Gongga Mountain was extensively and repeatedly glaciated, and glacial landforms and outwash deposits from multiple glaciations are well-preserved in valleys, in basins, and on piedmonts. To constrain the glacial chronology of the eastern slope of Gongga Mountain, sample sites were selected based on the distribution and weathering of glacial tills, relationships among glacial deposits, and soil development on moraines. Dating of the tills and glaciofluvial deposits was undertaken with electron spin resonance (ESR) and optically stimulated luminescence (OSL). The ages of the glacial deposits can be divided into four clusters: 2.2±0.5, 11.9±0.6, 35.9±2.7-58.0±6.3 and 119.2±15.9-194.2±32.8 ka. Five glacial advances in this region have been identified, which are equivalent in age to the Little Ice Age (LIA), Neoglaciation, marine oxygen isotope stage (MIS) 2, mid-MIS3, and MIS6. The largest local last glacial maximum (LGML) occurred on Gongga Mountain during mid-MIS3, characterized by a cold-humid climate, rather than the global Last Glacial Maximum (LGMG) of MIS2. The Gongga, Nanmenguangou (NMGG) and Yajiageng Glaciations occurred during the late part of the last glacial cycle, the middle of the last glacial cycle and the penultimate glacial cycle, respectively. On the basis of geomorphological, sedimentological, and compositional characteristics, landforms of the Moxi Platform and terraces can be grouped by facies and geochronology. In combination with the dating results, this analysis indicates the basal part of the Moxi Platform between Xinxin and the Moxi Hotel is correlative with the till of the Nanguanmen Glaciation (mid-MIS3). This basal unit has occasional lenses of glaciofluvial sandy gravel and lacustrine sediments. The remainder of the Moxi Platform and the terraces beside the platform are glaciofluvial deposits occasionally mixed with debris flow deposits and range in age from MIS3 to Holocene.

The importance of weathering for the Quaternary as well as the Engineering Geology – Results of the investigations at the glaciofluvial gravel deposits in the area of Memmingen (Bavaria/Germany)

The importance of weathering for the Quaternary as well as the Engineering Geology – Results of the investigations at the glaciofluvial gravel deposits in the area of Memmingen (Bavaria/Germany)

Specific erosional and depositional processes in a pleistocene subglacial tunnel in the wielkopolska region, poland

The Pleistocene Cieśle succession accumulated in a subglacial tunnel and shows three sedimentological units: (1) trough cross‐stratified sand with granules deposited in deep channels up to 5.4 m, (2) trough stratified and massive gravels deposited in a very deep channel up to 6.2 m eroded by a catastrophic hyperconcentrated flow, and (3) a massive diamicton, interpreted as a basal till of melt‐out type. We focus on angular and deformed sandy clasts that occur in the second unit. It appears that thermal erosion, short transport in a sediment‐laden current and sudden sedimentation were responsible for the oversized sandy clasts that occur in the gravel glaciofluvial deposits. The deposits are characterized by large‐scale erosional scours, massive structure, and fluid‐escape deformations. This combination of features can be used as a key tool for the interpretation of hyperconcentrated‐flow conditions beneath Pleistocene ice sheets.

Topographic and bioclimatic controls on soil/paleosol morphogenesis in the Norra Storfjället Mountains, Sweden

Retreat of the Stabre Glacier in the Norra Storfjället Mountains of northern Sweden led to the emplacement of a broad expanse of glaciofluvial sediment, a virtual blanket of debris interspersed with recessional and push moraines. Episodic mass wasting of the glaciofluvial, moraine and loessic deposits yielded a pedostratigraphic succession of 14C-dated sub-Boreal and sub-Atlantic Cryosols in soliflucted sediment that provide weathering data related to Neoglacial perturbations, whereas weathering within polygonal complexes yielded single profile, one event, Cryosolic Gleysols of similar age. Both provide a database of paleosol extremes controlled by topography and bioclimate. Together, the paleosols provide a database of weathering of mixed amphibolitic gneiss, trachytic lavas and granite weathering under two variable redox conditions, one (soliflucted sediment) fully or partially aerated and free draining under a subaerial atmosphere with high redox potential; the other (polygonal soil) partly reduced under the influence of an active layer of sporadic permafrost. Paleosols dated to the Early Neoglacial (~3600–4200cal14CyrBP) have variable horizon development dependent upon landform associations, and provide maximum ages for the second oldest moraine stillstand of ice retreat into the highlands on the Arctic Circle of Sweden. The Cryosolic Gleysol yields surprisingly high extractable Fe and Al suggestive of considerable redox fluctuations over the time of morphogenesis.

Dark gray soils on two-layered deposits in the north of Tambov Plain: Agroecology, properties, and diagnostics

Dark gray soils in the Tambov Plain are developed from the light-textured glaciofluvial deposits underlain by the calcareous loam. Their morphology, water regime, and productivity are determined by the depth of the slightly permeable calcareous loamy layer, relief, and the degree of gleyzation. The light texture of the upper layer is responsible for its weak structure, high density, the low content of productive moisture, and the low water-holding capacity. If the calcareous loam is at a depth of 100–130 cm, dark gray soils are formed; if it lies at a depth of 40–70 cm, temporary perched water appears in the profile, and dark gray contact-gleyed soils are formed. Their characteristic pedofeatures are skeletans in the upper layers, calcareous nodules in the loamy clay layer, and iron nodules in the podzolized humus and podzolic horizons. The appearance of Fe-Mn concretions is related to gleyzation. The high yield of winter cereals is shown to be produced on the dark gray soils; the yields of spring crops are less stable. Spring cereals should not be grown on the contact-gleyed dark gray soils.

Provenance and depositional environment of epi-shelf lake sediment from Schirmacher Oasis, East Antarctica, vis-à-vis scanning electron microscopy of quartz grain, size distribution and chemical parameters

The scientific study of quartz grains is a powerful tool in deciphering the depositional environment and mode of transportation of sediments, and ultimately the origin and classification of sediments. Surface microfeatures, angularity, chemical features, and grain-size analysis of quartz grains, collectively reveal the sedimentary and physicochemical processes that acted on the grains during different stages of their geological history. Here, we apply scanning electron microscopic (SEM) analysis to evaluating the sedimentary provenance, modes of transport, weathering characteristics, alteration, and sedimentary environment of selected detrital quartz grains from the peripheral part of two epi-shelf lakes (ESL-1 and ESL-2) of the Schirmacher Oasis of East Antarctica. Our study reveals that different styles of physical weathering, erosive signatures, and chemical precipitation variably affected these quartz grains before final deposition as lake sediments. Statistical analysis (central tendencies, sorting, skewness, and kurtosis) indicates that these quartz-bearing sediments are poorly sorted glaciofluvial sediments. Saltation and suspension seem to have been the two dominant modes of transportation, and chemical analysis of these sediments indicates a gneissic provenance.

Grain Size Distribution and its Influence on Biological Productivity During Holocene in a Fresh Water Lake in Larsemann Hills, Antarctica

A 78 cm sediment core from one of the fresh water lake in Larsemann Hills, Antarctica was analyzed to compare the relationship between grain size and biological productivity as total organic carbon (TOC) and biogenic silica (BSi). The sediment core represented the time period of ~8.3 cal ka BP as ascertained by C14 radiocarbon dates. High sand indicates glacio-fluvial deposition from ~8.3 to ~5 cal ka BP. The increased silt marks the ice melt water, aeolian flux sediment deposition from ~5 to recent. Interestingly, TOC showed negligible variation during ~8.3 to ~4 cal ka BP and is relatively high in the upper ~10 cm (~4 cal ka BP) of the core. The increased TOC in the upper part of the core indicates good preservation of algal mat and incorporates with decrease in sand and increase in silt. The BSi showed positive correlation with sand content during ~8.3 to ~5 cal ka BP and negative correlation from ~5 to recent and this can be explained with the high and low ratio of Al:SiO2.

Field Study of Subsurface Heterogeneity with Steady‐State Hydraulic Tomography

Remediation of subsurface contamination requires an understanding of the contaminant (history, source location, plume extent and concentration, etc.), and, knowledge of the spatial distribution of hydraulic conductivity (K) that governs groundwater flow and solute transport. Many methods exist for characterizing K heterogeneity, but most if not all methods require the collection of a large number of small-scale data and its interpolation. In this study, we conduct a hydraulic tomography survey at a highly heterogeneous glaciofluvial deposit at the North Campus Research Site (NCRS) located at the University of Waterloo, Waterloo, Ontario, Canada to sequentially interpret four pumping tests using the steady-state form of the Sequential Successive Linear Estimator (SSLE) (Yeh and Liu 2000). The resulting three-dimensional (3D) K distribution (or K-tomogram) is compared against: (1) K distributions obtained through the inverse modeling of individual pumping tests using SSLE, and (2) effective hydraulic conductivity (K(eff) ) estimates obtained by automatically calibrating a groundwater flow model while treating the medium to be homogeneous. Such a K(eff) is often used for designing remediation operations, and thus is used as the basis for comparison with the K-tomogram. Our results clearly show that hydraulic tomography is superior to the inversions of single pumping tests or K(eff) estimates. This is particularly significant for contaminated sites where an accurate representation of the flow field is critical for simulating contaminant transport and injection of chemical and biological agents used for active remediation of contaminant source zones and plumes.

Physical, Chemical, and Thermal Properties of Soils across a Forest-Meadow Ecotone in the Uinta Mountains, Northeastern Utah, U.S.A.

Physical, chemical and thermal properties of five pedons in the Uinta Mountains of northeastern Utah were studied to determine how soils and microclimates vary across the ecotone between subalpine forest and dry meadow. All five profiles have developed in the same parent materials, from base upward: basal till, glaciofluvial sediment, and coarse supraglacial debris with infilled eolian silt. Temperatures were measured at the soil surface and at depths of 10 and 50 cm for 420 days. Meadow soils (Typic Humicryepts) are warmer, have Bw horizons, and contain more Ca, organic carbon, and clay in the A horizon. Forest soils (Inceptic Haplocryalfs) have Bt horizons, higher B/A horizon clay ratios, are more acidic, and contain more exchangeable Mg and total exchangeable cations than meadow soils. Although subzero temperatures were never recorded at the surface of the forest soil in the summers of 1998 and 1999, those at the surface of the meadow soil fell below 0 °C on ∼35% of the nights. Mean 4:00 a.m. temperatures in the meadow during the summer are significantly colder than those in the forest (2.2 °C vs. 5.2 °C). The meadow formed following an initial forest clearing event, possibly fire or an insect infestation. Since that time, forest encroachment has been slow because seedling establishment in the meadow is inhibited by a combination of frequent summer freezing events, moisture stresses resulting from textural discontinuities between soil parent materials, and competition between tree seedlings and meadow vegetation.

OSL ages revealing the glacier retreat in the Dangzi valley in the eastern Tibetan Plateau during the Last Glacial Maximum

Mountain glaciers are highly sensitive to temperature and precipitation fluctuations and, thus, the deposits of glacier growth and retreat constrain climatic variables. The Dangzi valley, located on the northern slope of Queer Shan Mountain, eastern Tibetan Plateau, is influenced by Indian monsoon and has preserved four integrated sets of moraines and associated glacial sediments. Numerical ages are scarce in this area, even though the moraines have been investigated for decades. In this study, dating of the glacial tills and glaciofluvial deposits was undertaken using quartz optically stimulated luminescence (OSL). We conclude that: (1) OSL ages show good agreement with geomorphological features. The samples should have been well-bleached before deposition, otherwise it is rather impossibly that all the ages in the former three sets are overestimated to a similar degree due to poor beaching as the spatial and temporal dynamics vary within glaciated valley. (2) Mountain glaciers have reached the maximum extent at about 25–22 ka in Dangzi valley during the Last Glacial Maximum (LGM). Then the glaciers retreated several times and formed the last terminal moraine at about 16.5 ka, which may indicate the termination of LGM on the eastern Tibetan Plateau. (3) The age of DZ307 (54.0 ± 4.7 ka) demonstrates that the glacial advance also occurred at Marine Isotope Stage (MIS) 3, and that the glacial advance was larger in MIS 3 than in LGM, which is in agreement with previous results in the adjacent Yingpu valley. (4) The glacial evolution during the LGM in the study area was possibly controlled by the temperature changes, which could response to the summer solar insolation in northern hemisphere.

Arsenic mobilization in a freshening groundwater system formed within glaciomarine deposits

Abstract Arsenic release to groundwater and conditions favoring As mobility are investigated in a system of aquifers formed within unconsolidated Quaternary sediments. The studied groundwater system is comprised of unconfined aquifers formed in glaciofluvial sediments with Ca–Mg–HCO3 groundwater, and confined aquifers formed within glaciomarine sediments with high As (above 10 μg/L) Na–HCO3 or Na–Cl groundwater. A positive relationship of As concentrations with the Na/(Ca + Mg) ratio of groundwater indicates that As release occurs in glaciomarine sediments concurrent to cation exchange reactions related to groundwater freshening. Arsenic is mobile in confined aquifers as a result of groundwater basic pH which prevents arsenate from adsorbing to mineral surfaces, and reducing conditions that favor speciation to arsenite. Selected extractions applied to sediment core samples indicate that As occurs in sediments predominantly in sulfide minerals and in Mn oxides and/or Fe oxyhydroxides. General positive relationships between As and the reduced species Fe2+, NH3 and dissolved S2− suggest that As release occurs at increasingly reducing conditions. Despite likely As release via Fe oxyhydroxide reductive dissolution, Fe remains at relatively low concentrations in groundwater (up to 0.37 mg/L) as a result of possible Fe adsorption and Fe reprecipitation as carbonate minerals favored by basic pH and high alkalinity. The presence of S2− in some samples, a negative relationship between δ34S of SO4 and SO 4 2 - concentrations, and a positive relationship between δ34S and δ18O of SO4 indicate that groundwater in confined aquifers is undergoing bacterial SO4 reduction.

A buried glaciofluvial channel in the Anděl Col, Northern Bohemia: new evidence for the Middle Pleistocene ice sheets extent in Western Sudetes

This study presents a new finding of glaciofluvial sediments filling a buried channel in the Anděl Col (522 m a.s.l.) in the Jizera Mts., on the Czech-Polish border. At least 550 m long and 55–100 m wide channel filled by glaciofluvial sediments was determined by geophysical methods in the lowermost part of the col. The base of the channel was found at a depth of 14–19 m under the present ground surface, descending from east to west draining the ice sheet front in the same direction. The channel is incised in the bedrock representing thus a Nye channel and is filled by >13 m of glaciofluvial sand, gravel and mud, which is covered by 1–2 m thick colluvial deposits. The large part of the glaciofluvial package was deposited in subglacial environment reflecting the ice sheet decay events of higher release of the material from the ice sheet. The upper glaciofluvial part of sediments was deposited in front of the slowly decaying ice sheet front. No subglacial tills have been found in the col area, which is not unusual for such an exposed site. We reconstruct the maximum altitude limit of the ice sheet in the col as being at least at ~540 m and the ice thickness in the Anděl Col being few tens of metres. The Anděl Col is the highest known area in Northern Bohemia covered by an ice sheet and improves thus our knowledge about the maximum vertical extent of Middle Pleistocene ice sheets in Western Sudetes.

Glaciodynamic sequence stratigraphy

Abstract The glaciofluvial deposits are by volume and permeability the most important unit in the terrestrial glacial successions, and they are the obvious target for groundwater as well as hydrocarbon reservoir exploration. The dominant glaciofluvial units are related to the proglacial setting in the foreland of an advancing ice margin, which results in a coarsening-upwards sequence with fine-grained beds at the base and glaciofluvial gravel at the top. In a complete sequence a till caps the unit, and at its base a glacitectonite is formed by shearing related to the development of the deformational layer below the ice. The glacial deposits laid down during the same glacial advance represent a glaciodynamic sequence. An important feature added to this is the proglacial glaciotectonic deformation. The glaciotectonic architectural elements comprise thrust faulting, folding of hanging-wall anticlines, thrust-sheet duplexes, hydrodynamic breccias and mud diapirs, the structural style of which define the glaciotectonic complex. The glaciodynamic sequence corresponds to the glaciodynamic event related to one major ice advance. The glaciodynamic processes representing the event comprise deposition as well as deformation, creating a glaciogenic sedimentary succession and a set of glaciotectonic structures. These constitute the elements to be recognized for defining a glaciodynamic sequence.

Crosshole traveltime tomography using particle swarm optimization: A near-surface field example

Particle swarm optimization (PSO) is a relatively new global optimization approach inspired by the social behavior of bird flocking and fish schooling. Although this approach has proven to provide excellent convergence rates in different optimization problems, it has seldom been applied to inverse geophysical problems. Until today, published geophysical applications mainly focus on finding an optimum solution for simple, 1D inverse problems. We have applied PSO-based optimization strategies to reconstruct 2D P-wave velocity fields from crosshole traveltime data sets. Our inversion strategy also includes generating and analyzing a representative ensemble of acceptable models, which allows us to appraise uncertainty and nonuniqueness issues. The potential of our strategy was tested on field data collected at a well-constrained test site in Horstwalde, Germany. At this field site, the shallow subsurface mainly consists of sand- and gravel-dominated glaciofluvial sediments, which, as known from several boreholes and other geophysical experiments, exhibit some well-defined layering at the scale of our crosshole seismic data. Thus, we have implemented a flexible, layer-based model parameterization, which, compared with standard cell-based parameterizations, allows for significantly reducing the number of unknown model parameters and for efficiently implementing a priori model constraints. Comparing the 2D velocity fields resulting from our PSO strategy to independent borehole and direct-push data illustrated the benefits of choosing an efficient global optimization approach. These include a straightforward and understandable appraisal of nonuniqueness issues as well as the possibility of an improved and also more objective interpretation.

Optically stimulated luminescence dating of glaciofluvial sediments on the Canterbury Plains, South Island, New Zealand

New Zealand is a key location for investigating the geomorphic response of fluvial systems over glacial–interglacial timescales, and as such provides a potentially rich archive of Quaternary climate change. Identification of the climatic response of fluvial systems requires the application of a reliable geochronological method to place the sedimentary record within the context of the regional climate history. Optically stimulated luminescence (OSL) dating offers the opportunity to generate ages from quartz in glaciofluvial sediments, and so has many possible applications in South Island. However, in applying this method, previous studies have encountered problems of low OSL signal intensities in quartz. This has limited the application of quartz OSL in South Island; most geochronological studies have instead used feldspar for luminescence dating, but have been affected by problems such as weathering. In this study, we found that although the OSL signal levels from quartz are low, a useable OSL signal can be observed from medium-sized aliquots containing ∼500 grains of quartz separated from samples from eastern South Island. Mathematical component separation of the quartz OSL signal indicated that the signal is dominated by a fast component. Ages produced using the central age model range from 18.2±1.3 to 36.7±2.9ka, are in stratigraphic order, and agree with independent age control from two 14C ages. This study demonstrates the successful application of quartz OSL to glaciofluvial sediments from Canterbury, and its potential to provide a chronology for sedimentary records of climate change in this region.

Petrography and major element geochemistry of the Permo-Triassic sandstones, central India: Implications for provenance in an intracratonic pull-apart basin

Detrital mode, composition of feldspars and heavy minerals, and major element chemistry of sandstones from the Permo-Triassic succession in the intracratonic Satpura Gondwana basin, central India have been used to investigate provenance. The Talchir Formation, the lowermost unit of the succession, comprises glacio-marine and glacio-fluvial deposits. The rest of the succession (base to top) comprising the Barakar, Motur, Bijori, Pachmarhi and Denwa formations, largely represent variety of fluvial depositional systems with minor fluvio-deltaic and fluvio-lacustrine sedimentation under a variety of climatic conditions including cold, warm, arid, sub-humid and semi-arid. QFL compositions of the sandstones indicate a predominantly continental block provenance and stable cratonic to fault-bounded basement uplift tectonic setting. Compositional maturity of sandstones gradually increases upwards from the Early Permian Talchir to the Middle Triassic Denwa but is punctuated by a sharp peak of increased maturity in the Barakar sandstones. This temporal change in maturity was primarily controlled by temporal variation in fault-induced basement uplift in the craton and was also influenced by climatic factors. Plots of different quartz types suggest plutonic source rocks for the Talchir sandstones and medium-to high-rank metamorphic plus plutonic source rocks for the younger sandstones. Composition of alkali feldspars in the Permo-Triassic sandstones and in different Precambrian rocks suggests sediment derivation from felsic igneous and metasedimentary rocks. Compositions of plagioclase in the Talchir and Bijori sandstones are comparable with those of granite, acid volcanic and metasedimentary rocks of the Precambrian basement suggesting the latter as possible source. Rare presence of high-K plagioclase in the Talchir sandstones, however, indicates minor contribution from volcanic source rock. Exclusively plagioclase-bearing metasedimentary rock, tonalite gneiss and mafic rocks are the probable sources of plagioclase in the Upper Denwa sandstones. Quartz-rich nature of the sandstones, predominance of K-feldspar over plagioclase and albite rich character of plagioclase in the sandstones is consistent with deposition in an intracratonic, pull-apart basin like the Satpura Gondwana basin. Composition of garnet and its comparison with that from the Precambrian basement rocks suggests mica-schist and amphibolite as possible sources. Predominance of dravite variety of tourmaline in the Permian sandstones suggests sediment supply from metasedimentary rocks. Presence of both dravite and schorl variety of tourmaline in subequal amount in the Triassic sandstones indicates sediment derivation from granitic and metasedimentary rocks. However, schorl-bearing rocks are absent in the basement complex of the study area. A–CN–K plot suggests granites, acid volcanic rock and meta-sediments of the basement as possible sources of the Talchir sandstones and metasedimentary rocks for the Barakar to Pachmarhi sandstones. The Denwa sandstones were possibly derived from K-feldspar-free, plagioclase-bearing metasediments, mafic rocks and tonalite gneiss. Chemical Index of Alteration (CIA) values suggest low intensity source rock weathering for the Talchir sandstones and higher intensity source rock weathering for the others. Various bivariate plots of major oxides composition of the sandstones suggest passive to active continental margin setting and even arc tectonic setting for a few samples.

Recent deformation of Quaternary sediments as inferred from GPR images and shallow P-wave velocity tomograms: Northwest Canterbury Plains, New Zealand

Prior to the recent highly damaging M 7.1 earthquake near the city of Christchurch on the South Island of New Zealand, we recorded coincident high-resolution seismic and ground-penetrating radar (GPR) data across parts of the northwest Canterbury Plains. The seismic reflection images reveal a vast network of interconnected faults and folds below a seemingly undisturbed flat surface. To complement the seismic images, which only provide limited information on the very shallow subsurface (i.e., < 20 m), we have now processed and analysed the GPR data. The migrated GPR images are dominated by complex reflection patterns characteristic of glaciofluvial sediments. Such sediments eroded from the Southern Alps are observed at the surface throughout our study site. Although it is difficult to distinguish between complexities associated with complicated sedimentation processes and disruptions and offsets of GPR reflections associated with recent movements on faults and folds, we identify a number of regions where the GPR data are consistent with tectonic deformation of Holocene sediments. Two of these regions straddle an interpolated connection between active faults mapped at the surface. In a third region, the development of river terraces imaged in the GPR data may have been affected by slip on newly discovered underlying faults. The most significant near-surface deformation, which is apparent on a coincident seismic reflection image, P-wave tomogram and GPR image, is observed on the flank of a major anticline that appears to have been thrust close to the surface along a reverse fault. Some of the faults and folds resolved in our seismic and GPR data may have been reactivated during the recent period of intense seismicity.

Holocene climate variability from lake sediment core in Larsemann Hills, Antarctica

A sediment core (L2) from Larsemann Hills, Antarctica was analyzed for Biogenic Silica (BSi), Sand (%) and Total Organic Carbon (TOC). The 78 cm core length represents the time span of ~8.3 cal ka BP. The values of BSi from the core show prominent high productivity from ~8.3 to ~6 cal ka BP in comparison to less productivity in mid-late Holocene (~6 cal ka BP to recent). Moreover, high sand (%) infers the glacio-fluvial deposition from ~8.3 to ~5 cal ka BP TOC shows little variation through out the core, except in the upper ~10 cm (~4 cal ka BP) part wherein it is comparatively high. The increased TOC in the upper part of the core possibly indicates presence of algal mat due to exposure of the lake to the ice free (glacier free) conditions.

Age of the Pomeranian ice-marginal position in northeastern Germany determined by Optically Stimulated Luminescence (OSL) dating of glaciofluvial sediments

The Pomeranian ice margin is one of the most prominent ice-marginal features of the Weichselian glaciation innorthern Europe. Previous results of surface-exposure dating (SED) of this ice margin di ...

Field Study of Hydrogeologic Characterization Methods in a Heterogeneous Aquifer

Hydraulic conductivity (K) and specific storage (S(s)) are required parameters when designing transient groundwater flow models. The purpose of this study was to evaluate the ability of commonly used hydrogeologic characterization approaches to accurately delineate the distribution of hydraulic properties in a highly heterogeneous glaciofluvial deposit. The metric used to compare the various approaches was the prediction of drawdown responses from three separate pumping tests. The study was conducted at a field site, where a 15 m × 15 m area was instrumented with four 18-m deep Continuous Multichannel Tubing (CMT) wells. Each CMT well contained seven 17 cm × 1.9 cm monitoring ports equally spaced every 2 m down each CMT system. An 18-m deep pumping well with eight separate 1-m long screens spaced every 2 m was also placed in the center of the square pattern. In each of these boreholes, cores were collected and characterized using the Unified Soil Classification System, grain size analysis, and permeameter tests. To date, 471 K estimates have been obtained through permeameter analyses and 270 K estimates from empirical relationships. Geostatistical analysis of the small-scale K data yielded strongly heterogeneous K fields in three-dimensions. Additional K estimates were obtained through slug tests in 28 ports of the four CMT wells. Several pumping tests were conducted using the multiscreen and CMT wells to obtain larger scale estimates of both K and S(s). The various K and S(s) estimates were then quantitatively evaluated by simulating transient drawdown data from three pumping tests using a 3D forward numerical model constructed using HydroGeoSphere (Therrien et al. 2005). Results showed that, while drawdown predictions generally improved as more complexity was introduced into the model, the ability to make accurate drawdown predictions at all CMT ports was inconsistent.