Tunnel Valleys Research Articles

A cut-&-paste strategy for the 3-D inversion of helicopter-borne electromagnetic data — II. Combining regional 1-D and local 3-D inversion

As a standard procedure, multi-frequency helicopter-borne electromagnetic (HEM) data are inverted to conductivity–depth models using 1-D inversion methods, which may, however, fail in areas of strong lateral conductivity contrasts (so-called induction anomalies). Such areas require more realistic multi-dimensional modelling. Since the full 3-D inversion of an entire HEM data set is still extremely time consuming, our idea is to combine fast 1-D and accurate but numerically expensive 3-D inversion of HEM data in such a way that the full 3-D inversion is only carried out for those parts of a HEM survey which are affected by induction anomalies. For all other parts, a 1-D inversion method is sufficient. We present a newly developed algorithm for identification, selection, and extraction of induction anomalies in HEM data sets and show how the 3-D inversion model of the anomalous area is re-integrated into the quasi-1-D background. Our proposed method is demonstrated to work properly on a synthetic and a field HEM data set from the Cuxhaven tunnel valley in Germany. We show that our 1-D/3-D approach yields better results compared to 1-D inversions in areas where 3-D effects occur.

Unravelling the moisture sources of the Alpine glaciers using tunnel valleys as constraints

AbstractA lack of archives has impeded reconstructions of moisture pathways for past glaciations in the European Alps. Here, we focus on the confluence area of two palaeoglaciers in the Swiss Plateau that were sourced on the northern (Aare glacier) and southern sides (Valais glacier) of the European Alps. We mapped tunnel valleys in the region using a drilling database, based on which we inferred the relative extent of each glacier c. 270 ka ago when the valleys were formed. We then compared this situation with that of the LGM. We found that, while the Valais glacier expanded farther into the foreland than the Aare glacier during the LGM, the opposite was the case c. 270 ka ago. We also found that LGM glaciers were non‐erosive in the distal foreland. These contrasts in extents and erosional efficiencies imply differences in moisture pathways between the LGM and the time when the tunnel valleys were formed.

Three-Dimensional Geologic Model of Glacial Outwash in Mclean County, Illinois, Based on Seismic Refraction Studies

Seven two-dimensional (2-D) seismic refraction lines were used to determine the thickness and geometry of a valley train outwash deposit of the Quaternary Henry Formation near Heyworth in southern McLean County, Illinois. These refraction data were collected and processed in 2-D, then imported into a Petrel, a three-dimensional (3-D) geological modeling software package. The 3-D geologic model was built using the velocity attribute of the seismic refraction data. The 3-D velocity model was then verified manually by moving a cross-section through the velocity model at 20 m increments. These selected data points were used to create 3-D horizons, surfaces, and contacts constraining the target Henry Formation from the overlying alluvium of the Cahokia Formation and the underlying Delavan Till. Results of the 3-D model show the Henry Formation outwash trends about S10°E, which is oblique to S55°W-trending modern Kickapoo Creek valley. The Henry Formation outwash is confined to the Kickapoo valley, and consists of well-stratified sand and gravel at that is as much as 25 m in thickness in the channel. The thickness of the Henry Formation in the terrace is 8–10 m. The Cahokia Formation is everywhere about 2 m in thickness. The Henry Formation here is interpreted to be deposited in a subglacial tunnel valley that was deposited about 20,000 years ago as the Laurentide ice sheet retreated from its maximum southerly extent.

Efficacy of bedrock erosion by subglacial water flow

Abstract. Bedrock erosion by sediment-bearing subglacial water remains little-studied; however, the process is thought to contribute to bedrock erosion rates in glaciated landscapes and is implicated in the excavation of tunnel valleys and the incision of inner gorges. We adapt physics-based models of fluvial abrasion to the subglacial environment, assembling the first model designed to quantify bedrock erosion caused by transient subglacial water flow. The subglacial drainage model consists of a one-dimensional network of cavities dynamically coupled to one or several Röthlisberger channels (R-channels). The bedrock erosion model is based on the tools and cover effect, whereby particles entrained by the flow impact exposed bedrock. We explore the dependency of glacial meltwater erosion on the structure and magnitude of water input to the system, the ice geometry, and the sediment supply. We find that erosion is not a function of water discharge alone, but also depends on channel size, water pressure, and sediment supply, as in fluvial systems. Modelled glacial meltwater erosion rates are 1 to 2 orders of magnitude lower than the expected rates of total glacial erosion required to produce the sediment supply rates we impose, suggesting that glacial meltwater erosion is negligible at the basin scale. Nevertheless, due to the extreme localization of glacial meltwater erosion (at the base of R-channels), this process can carve bedrock (Nye) channels. In fact, our simulations suggest that the incision of bedrock channels several centimetres deep and a few metres wide can occur in a single year. Modelled incision rates indicate that subglacial water flow can gradually carve a tunnel valley and enhance the relief or even initiate the carving of an inner gorge.

Assemblage of buried and seabed tunnel valleys in the central North Sea: from morphology to ice-sheet dynamics

Tunnel valleys are kilometre-scale, channel-like, incised subglacial landforms usually associated with glaciated lowlands (O Cofaigh 1996). Tunnel valleys related to the Pleistocene glaciations are present onshore and offshore of NW Europe (e.g. Huuse & Lykke-Andersen 2000; Van der Vegt et al. 2012). In the central North Sea, tunnel valleys are found buried in the Quaternary succession and as bathymetric deeps at the seabed. Three-dimensional (3D) seismic data from the central North Sea image extensive networks of buried tunnel valleys that consist of multiple generations of cross-cutting landforms (Stewart et al. 2013). Seabed tunnel valleys are identified in high-resolution bathymetric data, and form another set of younger glacial landforms. Morphological measurements of the buried and seabed tunnel valleys are compared to infer their relationship to past ice-margins and highlight the differences in ice-sheet configuration over time. In the central North Sea, over 180 buried tunnel valleys are clearly imaged within 14 overlapping 3D seismic datasets originally acquired for the hydrocarbons industry (Fig. 1a; Stewart et al. 2013). The survey area lies within 56–59° N and 1° W to 2° E, in water depths of 90–150 m. The buried tunnel valleys form part of the extensive erosive surface at the top of the Aberdeen Ground Formation, usually related to the Pleistocene glaciations of the region from the middle Quaternary onwards (Stoker et al. 1983; Graham et al. 2011). The buried valleys overlie the Bruhnes–Matuyama magnetic reversal (dated at 780±5 ka BP from boreholes in the region, Stoker et al. 1983) and are overlain by sediments dated to 30 14C ka BP (Graham et al. 2010). Fig. 1. ( a ) Location of the study area, three-dimensional (3D) seismic volumes and examples in the central North Sea. Map from GEBCO_08. WB, Witch Ground Basin. ( b ) All the tunnel valley outlines mapped within …

Pleistocene tunnel valleys in the North Sea Basin

Tunnel valleys were first described over a century ago from the glaciated lowlands of northern Europe (Jentzsch 1884). Landforms described as tunnel valleys constitute open, partially or fully buried palaeo-landforms. Over the past 40 years the proliferation of geophysical surveys has allowed almost complete mapping of tunnel valleys across the North Sea Basin (Huuse & Lykke-Andersen 2000; Van der Vegt et al. 2012). In the central and southern North Sea, 3D seismic surveys completely image tunnel valley systems at a resolution of tens of metres (Fig. 1) (Praeg 1996; Stewart et al. 2013; Moreau & Huuse 2014). Fig. 1. Buried middle/late Pleistocene tunnel valleys in the eastern North Sea Basin. ( a ) Seven generations of tunnel valleys interpreted using 3D seismic data along the Norwegian–Danish border. Also visualized are the near-base Pleistocene surface and locations of salt domes (Kristensen et al. 2007). ( b ) Location of study area (red box; map from GEBCO_08). ( c ) Vertical and ( d ) horizontal seismic expression of buried tunnel valley V01 (x–x′). ( e ) Arbitrary seismic line extracted along the long axis of tunnel valley V06 showing highly …

Structural and textural response to dynamics of fluvioglacial processes of the Rzymsko esker sediments, Central Poland

The study was conducted in the Rzymsko esker, in the Eastern part of the Turek Upland Plain, within the range of the Warta Glaciation (Saalian II). The form was accumulated in a tunnel valley, which was partially filled with esker sediments. Lithofacies analysis, extended by a detailed analysis of clasts, made it possible to identify a considerable variability of sedimentation conditions. At the initial stage, transport and accumulation of sediments took place in the conditions of high energy hydraulic flows or hyperconcentrated flows. The flow energy rose cyclically, which was recorded as sediments coarsening. Deposits of boulders as well as massive and cross-bedded gravels were identified, a record of catastrophic glacial floods. During the later stage of esker formation, sandy and gravelly sediments were accumulated in an open crevasse. The strong erosional force of subglacial water is confirmed by an extremely high content of local rocks in the gravelly fraction (30–87%) and its very good roundness. Zingg shape analysis (1935) revealed a clear predominance of oblate forms among local clasts and equant fennoscandian erratics. A dependency was also found between the processing method and petrographic characteristics.

Seismic character of possible buried grounding-zone wedges in the Late Ordovician glacial rocks of Algeria

A relatively brief ice age in the Late Ordovician, about 445 Ma ago, when North Africa was located near the South Pole led to the deposition of terrestrial and marine glacial sediments across northern Africa (e.g. Le Heron & Craig 2008). Several types of glacial landforms have been identified previously in these glacial rocks, including sedimentary features interpreted as ice-proximal fans and tunnel valleys produced by subglacial meltwater flow (e.g. Hirst 2012). These glacigenic rocks had been buried beneath about 2000 m of overlying sediment and have been deformed subsequently by multiple orogenic phases. A number of asymmetrical depocentres have been identified in three-dimensional (3D) reflection-seismic records from Illizi Basin, Algeria (Fig. 1). They are interpreted as grounding-zone wedges (GZWs), by analogy with similar features in Quaternary sediments on the Greenland margin (Dowdeswell & Fugelli 2012). Fig. 1. ( a , c , d ) Seismic profiles through the long axes of three Late Ordovician buried grounding-zone wedges (GZWs, blue lines mark upper surfaces) in Illizi Basin, Algeria. VE×25, ×10 and ×10, respectively. Time sections from ISS™ (Independent Simultaneous Sources). 3D survey shot in 2009. We acknowledge Sonatrach, BP's partner in Algeria, for its part in …

The Hirnantian glacial landsystem of the Sahara: a meltwater-dominated system

During the Hirnantian (443 Ma), ice sheets expanded towards the present-day north over North Africa and the Arabian Peninsula when the western part of the Gondwana supercontinent straddled the South Pole. A glacigenic succession is exposed around the flanks of several Saharan cratonic basins, including Murzuq and Al Kufrah basins in Libya. As a result of the present-day hyper-arid context of the outcrops, a suite of palaeo-glacial landforms has been identified and, in some cases, mapped. These landforms occur along glacial erosion surfaces, defined as unconformities derived through direct ice sculpting, meltwater erosion or a combination of these processes. Unconformities, mostly resulting from ice sculpting and including glacially striated pavements and mega-scale glacial lineations (MSGLs), are identified at a number of locations along these erosion surfaces, in association with drumlinized features. The majority of reported examples are of ‘soft sediment character’; that is, generated through the deformation of unconsolidated sediment. Features mainly associated with meltwater erosion include tunnel valleys which occur in swarm-like belts, defining palaeo-grounding-line positions as the ice fronts retreated. A ‘smeared’ series of palaeo-ice-stream footprints, resulting from multiple advance–retreat cycles, is characteristic of the landsystem. Deformation of sediments into a series of push moraines, expressed as kilometre-scale fold–thrust belts, allows the locations of the former ice front to be identified. The Hirnantian glacial record of North Africa is a classic example of a continent-scale archive of an ancient palaeo-ice sheet. Expeditions to the Sahara during the late 1960s, focusing on the Algerian record, revealed a full suite of glacial indicators including striated pavements, pingos, roches moutonnees and a variety of meltwater channels (Beuf et al. 1971). Subsequently, largely as a result of their significance as hydrocarbon reservoirs, more recent studies re-evaluated these outcrops from a sedimentological perspective. Much effort focused on unravelling the glacial stratigraphy in neighbouring …

3D geological modelling of a buried-valley network based on AEM and borehole data

In former glaciated areas buried tunnel valleys can often be found. These buried erosional structures can be highly decisive for groundwater recharge and groundwater flow. Delineation of the architecture and infill of the structures are therefore very important in relation to groundwater mapping. The dense data coverage offered by airborne electromagnetic methods makes it possible to map and model the buried valley structures with a high degree of detail. The delineation of the individual valleys and the mapping of the internal cross-cutting relationships are dependent on the geological interpretation, which is founded on the knowledge about geological processes and the regional geology. In this study, we have investigated a relatively small study area in Denmark with SkyTEM and lithological log data as the main data sources. The area is characterised by a network of cross-cutting buried tunnel valleys, which have been incised into impermeable Paleogene clay deposits. The geological interpretation of the SkyTEM data resulted in modelling of 21 buried valleys belonging to at least 7 different generations. Manual voxel modelling of the infill of these valleys, as well as the surroundings, resulted in a geological 3D model consisting of 43 different units. Most of the valleys show heterogeneous infill, characterized by a predominant lithology (for instance meltwater sand) with local occurrences of secondary lithologies (for instance clay till). In the majority of the valleys, meltwater sand is the main lithology, but clay till and meltwater clay deposits are also commonly found. Due to the heterogeneity of the infill, proper modelling of this type of geology requires voxel modelling instead of layer modelling.

3D geological modelling of a complex buried-valley network delineated from borehole and AEM data

Buried tunnel valleys are common features in formerly glaciated areas, and where present, they are very important for the groundwater recharge and flow. Delineation of the structures and modelling of the infill is therefore very important in relation to groundwater mapping. Typically, borehole information is too sparse to enable a detailed delineation of the structures, whereas densely covering airborne electromagnetic data have proven to be very useful for this. In the last decades, the mapping approach has been studied carefully, but the 3D modelling of the valley structures has not been described to the same degree yet. In this study, we create a 3D geological model of an area that is characterised by a complex network of buried valleys mapped with a spatially dense airborne electromagnetic survey. Due to the comprehensive dataset, the modelling requires formulation of an advanced strategy. This contains a number of steps, where the AEM-derived resistivity data are initially interpreted based on the geological background knowledge to identify the buried valleys and build a conceptual geological model. Secondly, the age relationships between the valleys are established from the valley orientations and their internal cross-cut relationships. Thirdly, the deep erosional surfaces are modelled. Subsequently, the interpreted age relationships are utilised to trim the valley floor surfaces, such that younger valleys cut older. Finally, a voxel model is built and populated with lithofacies and stratigraphical units. The model is constructed as a combined layer-based and voxel model in order to map both the overall structures as well as the lithological variations within the 3D model domain. The final model contains 20 buried valleys that show a complex cross-cut setting that indicate the presence of at least eight valley generations. Most of the valley infills show lithological variations, and the final voxel model thus contains 42 different geological units.

Differentiation of the concentration of heavy metals and persistent organic pollutants in lake sediments depending on the catchment management (Lake Gopło case study)

Abstract This paper presents the results of the study on the concentration of heavy metals and persistent organic pollutants (POPs), including PAHs and PCBs, in the bottom sediments of Lake Gopło. This lake is significantly elongated (about 25 km); its longitudinal profile is diversified, and there are deeps and thresholds impeding the flow of water. The shoreline is varied, which is characteristic of tunnel valley lakes. The catchment has a typical agricultural character with a point arrangement of industrial centres. The analysis of the diversity of the concentration of heavy metals and POPs was based on 37 samples from two representative cores: one collected in the northern part of the lake, the catchment of which shows an industrial character, and the second one in the southern part where the catchment is agricultural in character. In the sediments, the content of the following heavy metals was analysed: Cu, Pb, Cd, Zn, Ni, Cr, Hg and As, as well as PAHs and PCBs. The sediment age was determined by the 210Pb dating method. In order to assess the contamination level of the bottom sediments with heavy metals, the contamination factor (CF) and degree of contamination (DC) were calculated. Moreover, the impact of the changes in the catchment’s land use over the past 100 years was determined. The results showed that the sediments from the industrial part of the lake significantly exceed the geochemical background for both the heavy metals from the group identified as industrial pollution and from the group of agricultural pollutants. The southern core shows only a slight increase in the amount of pollution from the agricultural group, lack of industrial pollution and a low degree of contamination. A slight increase in persistent organic pollutants is also recorded, without any apparent effect on the state of the deposited sediment. The 210PB dating enabled the main stages of human impact to be determined: the pre-industrial revolution, from the beginning of industrialisation to the 1950s, intensive human impact from the 1960s to the 1980s, and a gradual decrease in the human impact starting from the 1990s. In addition, attention was paid to the changing sedimentation rate.

Bryozoan fauna of the Upper Ordovician (Katian) of Alnif, Morocco

Bryozoan fauna was discovered within the glaciogenic sediments of an Ordovician (Hirnantian) tunnel valley infill near Alnif, Morocco where it had been redeposited from the upper Tiouririne Formation (Ktaoa Group, Katian). This fauna contains four species—one esthonioporine, two trepostomes and one rhabdomesine cryptostome—of which three are new: Revalotrypa ramosa sp. nov., Radiotrypa alnifensis sp. nov. and Heminematopora gaetula sp. nov. The fourth species, Monotrypa sp., is described using open nomenclature. Branched colonies of R. alnifensis sp. nov. are the most abundant element of the bryozoan-rich floatstones of the upper Tiouririne Formation in which bryozoans were deposited after being transported for a short distance. The genus Radiotrypa was previously known exclusively from the Hirnantian of Sweden, and the genus Heminematopora was known from the Upper Ordovician of North America and Europe. Study of the internal morphology of Heminematopora confirmed the presence of heterozooecia in this genus.

Differentiation of the concentration of heavy metals and persistent organic pollutants in lake sediments depending on the catchment management (Lake Gopło case study)

This paper presents the results of the study on the concentration of heavy metals and persistent organic pollutants (POPs), including PAHs and PCBs, in the bottom sediments of Lake Goplo. This lake is significantly elongated (about 25 km); its longitudinal profile is diversified, and there are deeps and thresholds impeding the flow of water. The shoreline is varied, which is characteristic of tunnel valley lakes. The catchment has a typical agricultural character with a point arrangement of industrial centres. The analysis of the diversity of the concentration of heavy metals and POPs was based on 37 samples from two representative cores: one collected in the northern part of the lake, the catchment of which shows an industrial character, and the second one in the southern part where the catchment is agricultural in character. In the sediments, the content of the following heavy metals was analysed: Cu, Pb, Cd, Zn, Ni, Cr, Hg and As, as well as PAHs and PCBs. The sediment age was determined by the 210Pb dating method. In order to assess the contamination level of the bottom sediments with heavy metals, the contamination factor (CF) and degree of contamination (DC) were calculated. Moreover, the impact of the changes in the catchment’s land use over the past 100 years was determined. The results showed that the sediments from the industrial part of the lake significantly exceed the geochemical background for both the heavy metals from the group identified as industrial pollution and from the group of agricultural pollutants. The southern core shows only a slight increase in the amount of pollution from the agricultural group, lack of industrial pollution and a low degree of contamination. A slight increase in persistent organic pollutants is also recorded, without any apparent effect on the state of the deposited sediment. The 210PB dating enabled the main stages of human impact to be determined: the pre-industrial revolution, from the beginning of industrialisation to the 1950s, intensive human impact from the 1960s to the 1980s, and a gradual decrease in the human impact starting from the 1990s. In addition, attention was paid to the changing sedimentation rate.

A 3 Ga old polythermal ice sheet in Isidis Planitia, Mars: Dynamics and thermal regime inferred from numerical modeling

Isidis Planitia is a 1350 km wide impact crater located close to the martian equator. To test the hypothesis that the 2.8 to 3.4 Ga old Thumbprint Terrain preserved on the floor of this basin is a glacial landform assemblage, we perform a numerical simulation of glaciation with a thermo-mechanically coupled model of ice sheet dynamics. As model inputs, we use surface temperatures and ice accumulation patterns predicted by a General Circulation Model based on the present-day atmospheric characteristics, and values of the geothermal heat flux provided by a global model of planetary thermal evolution. We find that, under favorable orbital conditions, an ice sheet covering the entire basin can develop in 2 to 5 Ma, with a maximum thickness of 4.9 km. The modeled ice sheet is polythermal: it is permanently cold-based in the periphery and, due to a negative heat-flux anomaly, also in the center, while the pressure melting point is reached in an intermediate ring. Our simulation is consistent with the interpretation that the Thumbprint Terrain is a martian equivalent of terrestrial ribbed moraines and has formed below a wet-based ice sheet. It supports also the interpretation that sinuous ridges and linear valleys observed at the periphery of the basin are parts of a subglacial network of eskers and tunnel valleys that drained the glacial meltwater outwards, across the cold-based periphery of the ice sheet. This work strengthens the hypothesis that glaciers thick as much as several km may have existed on Mars several Ga ago and that glacial basal melting may have contributed to the production and flow of surface liquid water at that time, under an atmosphere no thicker than the present-day one.

History of Development and Terrestrialization of Lake Starowlany in the Eemian Interglacial Based on Cladocera Analysis (Sokόłka Hills, Ne Poland)

Abstract This paper presents development of the paleolake Starowlany existing in the Eemian Interglacial (MIS 5e) in north - eastern Poland. The lake history is based on Cladocera analysis. The paleolake Starowlany is located in the central part of the Sokółka Hills, approximately 9 km north of the town of Sokółka in the North Podlasie Lowland. The sediments studied filled a southern part of a tunnel valley formed during the Warta Glaciation. The coring was carried out with a geological drilling and constituted a part of the frame work aimed at preparing the Sokółka sheet for the Detailed Geological Map of Poland in scale 1:50000. The core was 7 m long. Peaty silt, peats and organic silt were present at the depth of 4.0-6.6 m, under deluvial sands, tills and silt. Organic series was over lain by a clayey silt with no glacial cover. Cladocera analysis was conducted with 20 samples from a depth interval 6.6-4.1 m. Remains of 17 species of Cladocera were found, representing the families: Chydoridae, Sididae and Bosminidae. A vast majority of them were the littoral species. In the paleolake Starowlany four development zones were distinguished that reflected changes as regards temperature, trophic levels and changes of water level in the lake. The paleolake existed from the early until the middle Eemian. The high est water level and the most favorable conditions for zooplankton development occurred in zones SCZ I and II. The highest trophic level took place in SCZ III (middle Eemian). In the late Eemian the water level dropped and the paleolake was transformed into a wetland. At certain points, the higher water level enabled existence of a few Cladocera species. The reasons for disappearance of the paleolake Starowlany included a local decrease in ground water levels as well as morphometric and geological characteristics of the lake.

A simplified algorithm for the design of piled raft foundations applied for the case study of a building erected within Żoliborz-Szczęśliwice glacial tunnel valley

Abstract A common engineering solution for excessive settlement with raft foundation (s) is the use of piles in order to reduce the vertical displacements, in this method, the whole structural load is transferred to the piles. This is an overly cautious approach, and there remains a need to find an optimal design method for a building’s foundations. Such a solution may be the piled raft foundation, which allows a reduction of the number of piles due to the integration of the raft in the bearing capacity of the foundation. The aim of the article is to estimate the contribution of foundation elements such as the raft and the piles in the bearing capacity of a residential building located in Warsaw, where the geological conditions are characterized by organic soil layers, principally of gyttja.

Combining 3D geological modelling techniques to address variations in geology, data type and density – An example from Southern Denmark

The very complex near-surface geology in Denmark is a big challenge when constructing 3D geological models. Borehole data alone are normally insufficient for proper 3D modelling because data are too widespread. Therefore, Airborne ElectroMagnetic (AEM) techniques are often used to obtain supplementary information on the spatial distribution and composition of the geology.A large-scale AEM survey and high-resolution seismic data along with both new and existing borehole data and seismic data from hydrocarbon exploration were available for the construction of a detailed 3D geological model in our study area. The data are unevenly distributed, and only part of the study area was covered by the AEM survey. Cross-cutting tunnel valleys, erosional unconformities, delta units and a large glaciotectonic complex are among the geological features identified in the area. The geological complexity varies significantly across the model area.A broad geological overview and understanding of the area was obtained by joint cognitive interpretation of the geophysical and the geological data. To address the geological complexity and the very high level of detail gained from the AEM data, the model was constructed as a voxel model with lithofacies attributes supplemented by a number of bounding surfaces. In areas where the geology is not too detailed and complex, the model was constructed manually, whereas automated methods were used to populate voxels in areas with a high complexity. The automated methods comprised clay fraction modelling, which was used where AEM data are available, and stochastic modelling, which was used outside the area covered by AEM data.Our study shows that it is advantageous to combine several modelling methods in areas with varying geological complexity and data density. The choice of modelling methods should depend on the character and coverage of available data and on variations in geology throughout the model area.

The Middle Pleistocene tunnel valley at Schöningen as a Paleolithic archive

Schöningen represents one of the key sites for Lower Paleolithic archaeology in central Europe, where a Middle to Late Pleistocene sedimentary succession, locally up to 45 m thick, has been preserved in an Elsterian tunnel valley. After deglaciation, the tunnel valley remained underfilled and provided the accommodation space for Holsteinian interglacial deposition and also kept the artifact-bearing strata below base level for subsequent erosion. The Holsteinian (MIS 9) succession consists of laterally and vertically stacked lacustrine delta systems, which were controlled by repeated lake-level changes. In the face of changing climatic and environmental conditions the long-lived interglacial lake provided an attractive site for animals and early humans. Artifacts were deposited on the subaerial delta plain and became embedded during lake-level rise. Although the area was considerably affected by erosion and glacitectonic deformation during the subsequent Saalian glaciation, the artifact-bearing Holsteinian strata were preserved in the deeper part of the tunnel valley.Tunnel valleys should be regarded as potential archives for interglacial deposits, which may contain important Paleolithic sites. Tunnel valleys may provide accommodation space and also have a high preservation potential. Interglacial lakes situated within underfilled tunnel valleys represented attractive sites for animals and early human hunter-gatherers.

Embayment scale assessment of submarine groundwater discharge nutrient loading and associated land use

A shoreline survey of porewater nutrient concentrations and 222Rn surface water activities was performed in Port Jefferson Harbor, NY, an embayment of Long Island Sound. Submarine groundwater discharge (SGD) was calculated for individual shoreline segments; shallow porewater nutrient concentrations were applied to calculated groundwater flux values in order to spatially depict the nutrient flux to overlying harbor water. Nitrate was the dominant form of inorganic nitrogen as porewater concentrations of ammonium were negligible. Land use analysis showed that nitrate to phosphate ratios (N:P) in SGD were positively correlated with medium to high development of inland aquifer watersheds. A multivariate regression model was developed which describes 79% of the variability in shoreline nitrate discharge. Three modes of nutrient transport were observed; 1) High SGD rates coupled with nutrient rich groundwater derived from high density development, 2) moderate SGD rates coupled with low nutrient groundwater from low density development/forested watersheds and 3) negligible SGD rates associated with recirculated seawater adjacent to low density development areas. Transport mode 1 dominated total SGD nitrate inputs primarily due to steep hydraulic gradient, a characteristic of tunnel valleys in glacial deposits, which highlights the critical role hydrogeology plays in groundwater nitrogen loading to surface water. Total nitrate inputs to the harbor from shoreline SGD alone are 980 mol d−1, similar to average daily sewage treatment plant nitrogen inputs of 870 mol d−1. The techniques used in this study represent an effective methodology for calculating SGD derived nutrient loads where a surface water nutrient source is present.