Recent Alluvium Research Articles

Short term occupation surfaces in the lower Ohio River Valley: Exposing more of the late Holocene hidden record

As in other larger river valleys, Holocene alluvial deposition in the lower Ohio River Valley created a sampling bias towards certain prehistoric archaeological sites by burying them too deep to be accessed by conventional archaeological methods. Alternatively, archaeological site types that do not leave a large signature (i.e. a large sample of artifacts) may also be obscured since they are not associated with recognizable geomorphic or soil development features, such as a buried A horizon. This obscuration has led to an incomplete record of the region's prehistory. To better understand the age and type of prehistoric sites that may be buried within this alluvial landscape, it is necessary to understand the structure and history of the alluvium in the valley. This can be done by reconstructing the chronological development of alluvial deposits and the soils that formed in them. Regional models for the age and development of Ohio River Valley alluvium, and the cultural deposits they may contain, have been previously developed, but must be continuously reviewed and revised as to their applicability to all and any alluvial packages found within the lower Ohio River Valley. This study tests and expands some of these models through the investigation of an alluvial landscape near the confluence of the Ohio and Great Miami Rivers in Indiana. An age-based landscape reconstruction, which focuses on late Holocene alluvium, is presented. Cultural deposits can be linked to brief stability periods within alluvial packages, stability periods that were too brief to have formed an A horizon. This study shows that short-term or ephemeral prehistoric occupations may co-occur with periods where the surface of an alluvial landscape or landform was geomorphically stable for a brief period. Identifying these short-term stable surfaces could likely lead to the better identification of underrepresented prehistoric cultural components or archaeological site types and help to reduce sampling bias in the regional prehistoric record.

Holocene alluvial environments at Barking, Lower Thames Valley (London, UK)

Deposit modelling based on archived borehole logs supplemented by a small number of dedicated boreholes is used to reconstruct the main boundary surfaces and the thickness of the main sediment units within the succession of Holocene alluvial deposits underlying the floodplain in the Barking Reach of the Lower Thames Valley. The basis of the modelling exercise is discussed and the models are used to assess the significance of floodplain relief in determining patterns of sedimentation. This evidence is combined with the results of biostratigraphical and geochronological investigations to reconstruct the environmental conditions associated with each successive stage of floodplain aggradation. The two main factors affecting the history and spatial pattern of Holocene sedimentation are shown to be the regional behaviour of relative sea level and the pattern of relief on the surface of the sub-alluvial, Late Devensian Shepperton Gravel. As is generally the case in the Lower Thames Valley, three main stratigraphic units are recognised, the Lower Alluvium, a peat bed broadly equivalent to the Tilbury III peat of Devoy (1979) and an Upper Alluvium. There is no evidence to suggest that the floodplain was substantially re-shaped by erosion during the Holocene. Instead, the relief inherited from the Shepperton Gravel surface was gradually buried either by the accumulation of peat or by deposition of fine-grained sediment from suspension in standing or slow-moving water. The palaeoenvironmental record from Barking confirms important details of the Holocene record observed elsewhere in the Lower Thames Valley, including the presence of Taxus in the valley-floor fen carr woodland between about 5000 and 4000cal BP, and the subsequent growth of Ulmus on the peat surface.

Holocene Mississippi River floods and geoarchaeological site formation processes in the Sny Bottom, western Illinois, USA

Holocene alluvial deposits are well represented in the Sny Bottom, a reach of the Mississippi River in western Illinois characterized by the presence of a long anabranch channel (the Sny). Prior to its engineered confinement, the flood-stage Mississippi functioned as an anastomosed system comprised of many secondary landscape elements hierarchically arranged to distribute water out across a broad floodplain. Radiocarbon-dated stratigraphic sequences are used to reconstruct the geological history of this river reach as it metamorphosed from a sandy Late Pleistocene braided floodplain into a system dominated by mud. By 7400 cal BP, the Mississippi migrated to its present position and began to build the natural levee it would use for the remainder of the Holocene. Major subsequent geomorphological adjustments to the system resulted from large floods at ca. 6900, 4900, 3300 and 2000 cal BP. Valley fill is a complex arrangement of individual sedimentary bodies that accumulated at highly variable rates. Vertical accretion by sedimentation and soil upbuilding acted together to preserve numerous buried archaeological sites of all ages.

2D Electrical Resistivity Tomography Survey for Shallow Environmental Study at Wastewater Valley of Southwestern Erbil City, Iraqi Kurdistan Region

The use of wastewater for irrigation in sandy soil increases the pollution risk of the soil and may infiltrate to the water table of groundwater aquifer. This is happening in an area southwest of Erbil City on both sides of the main wastewater valley outlet. Characterizing and monitoring underground conditions and the location of subsurface contaminants is a challenging and costly endeavor. Many sensors and non-invasive geophysical measurement techniques have been developed to interpret the nature of the subsurface without disturbing it. In this study the Electrical Resistivity Tomography (ERT) was used to get detailed 2D resistivity models of the shallowest parts of the subsurface on both side of the valley along eight profiles. The wenner array was employed with 1m, 3m and 5m electrode spacing. The length of each profile was 60 m. To create a model for the subsurface resistivity Res2Dinv software was used. The results showed that the shallowest parts of the ground consist of two types of materials: the first is a clayey sandy gravel soil represents the recent alluvial deposits with resistivity value of 15-167 Ω.m and thickness 1-2 m. Many pollutant zones were detected within it; the second is saturated silty clay and other clayey materials with resistivity value of 9-52 Ω.m. Again some polluted zones were detected. Moreover some fractured areas were detected at where the risk of downward infiltration is expected. The resistivity value changes randomly in both horizontal and vertical direction because of the high infiltration which transports the contaminated materials downward and sideward along in homogeneities formed by human activity in the studied area.

Characterization, Classification and Land Capability Evalution of Ndoni Meander Belt Soils in Niger Delta.

Characterization, classification and land capability evaluation of Ndoni Agroecological zone in the meander belt of the Niger Delta was done. The pedons were identified on the basis of topography, drainage, vegetation, physical, chemical and morphological characteristics. The soil textures were irregular; sandy in the moderately drained levees and recent alluvial deposits but clayey in the poorly drained terrace and backswamps. The soils were generally acid; had moderate to high organic matter, low to moderate total nitrogen, available p, and effective cation exchange capacity with generally high percentage base saturation. The soil morphological and physical characteristics were dominantly used for the land capability evaluation.These include drainage (internal and external), moisture retention capacity, slope, liability to flooding, erosion, effective soil depth and climatic variations. Chemical characteristics were considered only when necessary under effective soil depth.The study area was found to have the capability for crop production. Pedons 1&2 were classified into land capability Class IIe; pedon 3( Class IIw); pedon 4 (Class IIIw) and pedon 5 (Class IVw). Pedons 1and 2 lands were capable for supporting potatoes, yams, cassava, cowpeas, maize, melon, groundnut, fruits and vegetables. Pedons 3 and 4 had the capability to support swamp rice, sugar cane, maize, cowpea, penniaples fruits and vegetables.Pedon 5 soils were capable to support swamp rice and fishing. Soil management measures to control erosion, poor drainage and flooding were recommended. Crop yield in these soils were expected to be high with adequate application of organic fertilizers and lime The soils were classified using the USDA soil taxanomy with approximate correlations with the FAO/UNESCO Soil Map of the World Legend. Soils of pedons 1&2 were classified as Typic Eutropepts and Eutric Tropoudepts (Eutric-cambisols); pedon 3&4 were classified as Vertic and Eutric Endoaquepts (Vertic-Cambisol and Eutric-gleysols;) pedon 5 was grouped as Arenic Fluvaquents. The limitations of the soils to cultivation were predominantly poor drainage/ flooding (w) and soil erosion (e).Key words: Characterization, Classification, Land Capability, Inceptisols, Poor drainage, Erosion

Seismic Performance of Improved Ground Sites during the 2010–2011 Canterbury Earthquake Sequence

The city of Christchurch and the surrounding region on the South Island of New Zealand are underlain by large areas of recent alluvial sediments and fills that are highly susceptible to liquefaction and seismic ground failure. Thus, the widespread liquefaction that occurred following the successive large-scale earth-quakes, with moment magnitudes (MW) ranging from 6.0 to 7.1 that struck the Canterbury region in 2010–2011 was expected. Prior to the series of earthquakes, soil improvement had been used at several sites to mitigate the anticipated damage. This paper reviews the performance of improved sites during the Canterbury earthquake sequence. The existing soil conditions at each site and the design of the ground improvement are discussed, together with descriptions of the post-earthquake damage observed. Moreover, liquefaction assessment within and surrounding a selection of the ground improvement zones is presented.

Temporal variations in Holocene slip rate along the central Garlock fault, Pilot Knob Valley, California

Average geologic slip rates along the central Garlock fault, in eastern California, are thought to have been relatively steady at 5–7 mm/yr since at least the Late Pleistocene, yet present-day rates inferred from geodetic velocity fields are indistinguishable from zero. We evaluate the possibility of non-steady slip over millennial timescales using displaced Late Holocene alluvium along the central Garlock fault in Pilot Knob Valley. Truncation of a Late Holocene alluvial fan deposit against a shutter ridge requires a minimum of 30–37 m of displacement since deposition of the fan; maximum allowable displacement is 43–50 m. The extent of soil development atop the fan surface and optically stimulated luminescence ages bracket fan deposition between 3.5 and 4.5 ka. Together, these data require that slip rates during the Late Holocene were ∼7–14 mm/yr, with a preferred rate of ∼11–13 mm/yr. Our results, in conjunction with previous estimates of displacement over the past ∼15 ka, require significant temporal variations in strain release along the Garlock fault and confirm previous suggestions that interactions among fault systems in eastern California give rise to alternating periods of fault activity and quiescence.

An assessment of the erodibility of Holocene lithounits comprising streambanks in northeastern Kansas, USA

Streambanks are the primary source of sediment for watersheds in the Midwestern USA. In much of this region, deposits of fine-grained Holocene alluvium comprising streambanks have been assigned to a single lithostratigraphic unit, the DeForest Formation. This study examines the stratigraphic relationships and measures the erodibility of the different members of the DeForest Formation in three watersheds in northeastern Kansas.Distinct differences in erodibility, measured in terms of critical shear stress (τc) by a submerged jet-test device, were observed between the different members of the DeForest Formation. The most erodible member is the Camp Creek Member (average τc=1.0Pa) while the most resistant is the Gunder Member (average τc=10.4Pa). Variability in erodibility between and within the members of the DeForest Formation is attributed to the magnitude of post-depositional soil-forming processes, including the presence of buried soils, as well as the inherent natural variability in the different parent materials. A weak positive correlation was found between percent clay and τc. Resistance to erosion by fluid flow was found to be significantly greater where clay contents exceed 28%.Although the Camp Creek Member was found to be the most erodible, it always occurs, stratigraphically, as the uppermost member. Available bankfull stage indicators suggest that bankfull discharges rarely attain elevations sufficient to erode Camp Creek Member deposits. Therefore, other members of the DeForest Formation are able to exert some control on the rate of bank erosion by hydraulic flow. Furthermore, given the observed differences in lithology, soil development and erodibility, the susceptibility to mass wasting processes is also likely to vary between the different members. Therefore, lithostratigraphic and soil-stratigraphic relationships have important implications for streambank erodibility and are crucial for accurately determining areas prone to streambank erosion in alluvial settings.

The Late Paleoindian Occupation of the Western Ouachita Mountains of Southeast Oklahoma: The Archaeology of Component V at the Quince Site (34AT134)

The Quince site (34AT134) is a well-preserved and relatively deeply stratified Ouachita Mountains archaeological site in Atoka County in southeastern Oklahoma. The site’s archaeological deposits are buried in Late Pleistocene and Holocene alluvial terrace deposits of McGee Creek, a tributary to Muddy Boggy Creek, itself a southern-flowing tributary to the Red River, that cuts through the western edge of the mountains. Excavated in 1982 and 1983 prior to the creation of McGee Creek Reservoir by the Bureau of Reclamation, the 3.0 m deep archaeological deposits at the Quince site contained a record of prehistoric occupations spanning most of the Holocene period (from ca. 10,500 B.P to 1000 radiocarbon years B.P., or ca. 12,590 to 927 calibrated years B.P.) Woodland (Component I), Late Archaic (Components II and III), and Middle Archaic (Component IV) period occupational deposits are present in good stratigraphic order within the upper 1 m of McGee Creek alluvium. There are also a series of buried Late Paleoindian occupations (in what is defined as Component V) with features and chipped stone lithic tools recovered in situ that are recognized beginning from about 1.10 m to 3.0 m in depth below the surface. In this article, I discuss the archaeological evidence for use of the Western Ouachita Mountains by Late Paleoindian foragers as seen principally from the micro-scale; that is, from the perspective of this one well-preserved and stratified Late Paleoindian site. Paleoindian occupations with good stratigraphic context are apparently quite rare in the Ouachita Mountains and along the edge of the Southeastern woodlands and the Great Plains in the eastern and eastcentral part of the state of Oklahoma. Much of the archaeological research dealing with Late Paleoindian peoples in this region has dealt primarily with the description and classification of isolated temporally diagnostic projectile points (and the kinds of lithic raw materials employed in projectile point manufacture) found on the surface or in mixed and relatively shallow stratigraphic contexts. The Quince site Late Paleoindian archaeological deposits provide direct and compelling evidence for the long-term and recurrent use of the western Ouachita Mountains by hunter-gatherer groups.

Effectiveness of natural riparian buffers to reduce subsurface nutrient losses to incised streams

Perennial vegetation borders many incised, perennial streams and rivers in southern Iowa and is assumed to provide a natural riparian buffer against subsurface nutrient losses from shallow groundwater. Questions remain about the effectiveness of these systems near incised channels that cut through nutrient-rich Holocene alluvium underlying the riparian corridors. In this study, riparian groundwater nutrient concentrations were evaluated near an incised stream under four perennial land cover types common to southern Iowa with the objectives to assess how groundwater quality differed by i) distance away from an incised stream and ii) perennial land cover type. Groundwater samples were collected from riparian wells installed 1m, 20m and 40m from an incised channel under four replicated land covers (cool season grass, warm season grass, woods, pasture) on six occasions across the growing season. Results indicate that channel incision lowers water tables in the near-stream zone and maintains more aerobic conditions but did not result in enhanced nitrogen mineralization or leaching to groundwater. Average concentrations of nitrate–nitrogen, phosphorus and dissolved organic carbon were 0.3mg/l, 0.2mg/l and 6mg/l, respectively, with variations due mainly to land cover type and geomorphology. Study results suggest that nutrient losses from perennial buffers in the region do not greatly impact regional water N and P loads although average concentrations in riparian groundwater may exceed proposed stream nutrient criteria.

Water retention and availability in soils of the State of Santa Catarina-Brazil: effect of textural classes, soil classes and lithology

The retention and availability of water in the soil vary according to the soil characteristics and determine plant growth. Thus, the aim of this study was to evaluate water retention and availability in the soils of the State of Santa Catarina, Brazil, according to the textural class, soil class and lithology. The surface and subsurface horizons of 44 profiles were sampled in different regions of the State and different cover crops to determine field capacity, permanent wilting point, available water content, particle size, and organic matter content. Water retention and availability between the horizons were compared in a mixed model, considering the textural classes, the soil classes and lithology as fixed factors and profiles as random factors. It may be concluded that water retention is greater in silty or clayey soils and that the organic matter content is higher, especially in Humic Cambisols, Nitisols and Ferralsol developed from igneous or sedimentary rocks. Water availability is greater in loam-textured soils, with high organic matter content, especially in soils of humic character. It is lower in the sandy texture class, especially in Arenosols formed from recent alluvial deposits or in gravelly soils derived from granite. The greater water availability in the surface horizons, with more organic matter than in the subsurface layers, illustrates the importance of organic matter for water retention and availability.

Geotechnical map of Holocene alluvial soil deposits in the metropolitan area of Granada (Spain): a GIS approach

The results of a geotechnical research on Holocene alluvial deposits in 14 municipalities of the Granada basin are presented, and a procedure to draw a geotechnical map of foundation conditions, using ArcGIS 9.3 (ESRI 2009) is described. Three different alluvial soil units were distinguished: (1) cohesive soils; (2) cohesive and fine granular soil; (3) coarse granular soil, based on their properties concerning grain size, bulk density, cohesion, internal friction angle, and NSPT value. The actual building structures have predominantly shallow foundations. The definition of the minimum depth to actual foundation level was based on the analysis of thickness of disturbed soils, man-made fillings, depth to the water table and bearing capacity. The depth to actual foundation levels varies from 0.5 to 4 m in the study area. Concerning the ground, the geotechnical data compiled on foundation conditions show a high heterogeneity expressed by the spatial distribution of the basic properties in the three distinguished units of cohesive, cohesive and fine-granular, and coarse granular soils, respectively. The fine-grained alluvial soil units (cohesive) have a low bearing capacity varying between 40 and 100 kPa and are associated with a shallow water table appearing near the surface. In contrast, across the wide extension of the coarse-grained alluvial soil unit, a bearing capacity ranging from 60 to 300 kPa is determined; this unit is associated with a deep water table appearing at more than 40 m below the surface. The usefulness of the obtained geotechnical map of foundation conditions extends to the analysis of further alternatives of urban expansion and for the delimitation of future trends for of land-use-development processes in the metropolitan area of Granada, mainly at local and regional scales.

Influence of Assumed Groundwater Depth on Mapping Liquefaction Potential

Groundwater depth is a critical parameter in assessing regional liquefaction potential. Uncertainties associated with groundwater depth are usually pervasive because of natural variability and spatial separation between data points. These uncertainties often lead to erroneous or doubtful assessments of liquefaction potential. In an attempt to provide more credible estimates of liquefaction potential across a sizable urban area, this study sought to estimate the threshold groundwater depths that could be expected to trigger liquefaction in the St. Louis, MO, metro area, which was damaged by the 1811–1812 New Madrid earthquakes. We used liquefaction potential indexes (LPIs) > 5 and > 15 as the thresholds for moderate and severe liquefaction risks, respectively. The threshold groundwater depth for triggering liquefaction was evaluated using standard penetration test data and a scenario involving an M7.5 earthquake with a peak ground acceleration of 0.20 g. The threshold groundwater depths then were geostatistically contoured and compared with accepted groundwater level scenarios to map the corresponding liquefaction risk. This study revealed that Holocene alluvium in East St. Louis generally exhibits deeper threshold groundwater depths than do the mean groundwater levels and appears to be more prone to liquefaction.

Assessment of Aquifer Salinization Beneath an Offshore Industrial Park Based on Solute Transport Calculation

The purpose of this study is to assess aquifer salinization in the coastal area of an Offshore Industrial Park in Taiwan. Study area belongs to the new Delta Holocene alluvium, which is composed of clay, silt, sand, gravel and their mixture. Groundwater quality measurements including electrical conductivity, total dissolved solids, chloride and sulfate were used as indicator to evaluate aquifer salinization. Regional groundwater flows from the middle of study area to the embracing beach, which is the typical island-type-like distribution of groundwater lens. Temporal variations of chloride concentrations in monitoring wells were simulated based on the calculation of solute transport. The simulation result matched with the observation that rainfall leaching could cause dilution of chloride concentration and lessen aquifer salinization. Solute exchange at the interface of fresh water and saline water strongly affected desalinization rate in groundwater, and thus desalinization rate was dependent on its distance from the seashore. According to the calculation of solute transport, it might take about 14 years for complete desalinization through continual rainfall leaching.

Early and Middle Holocene Hunter-Gatherer Occupations in Western Amazonia: The Hidden Shell Middens

We report on previously unknown early archaeological sites in the Bolivian lowlands, demonstrating for the first time early and middle Holocene human presence in western Amazonia. Multidisciplinary research in forest islands situated in seasonally-inundated savannahs has revealed stratified shell middens produced by human foragers as early as 10,000 years ago, making them the oldest archaeological sites in the region. The absence of stone resources and partial burial by recent alluvial sediments has meant that these kinds of deposits have, until now, remained unidentified. We conducted core sampling, archaeological excavations and an interdisciplinary study of the stratigraphy and recovered materials from three shell midden mounds. Based on multiple lines of evidence, including radiocarbon dating, sedimentary proxies (elements, steroids and black carbon), micromorphology and faunal analysis, we demonstrate the anthropogenic origin and antiquity of these sites. In a tropical and geomorphologically active landscape often considered challenging both for early human occupation and for the preservation of hunter-gatherer sites, the newly discovered shell middens provide evidence for early to middle Holocene occupation and illustrate the potential for identifying and interpreting early open-air archaeological sites in western Amazonia. The existence of early hunter-gatherer sites in the Bolivian lowlands sheds new light on the region’s past and offers a new context within which the late Holocene “Earthmovers” of the Llanos de Moxos could have emerged.

Letting Wet Spots be Wet: Restoring Natural Bioreactors in the Dissected Glacial Landscape

In this paper, we argue that there is tremendous potential for nitrate-N reductions to occur throughout the Corn Belt region of the USA if we simply let naturally occurring wet spots on the landscape be wet. Geologic and hydrologic data gathered in the Walnut Creek watershed located in south-central Iowa provides compelling evidence that substantial nutrient-processing capacity exists in this dissected glacial landscape. Self-similarity of stratigraphy, sedimentology and hydrology observed at all spatial scales in the watershed suggests that Holocene alluvial fill deposits provide a natural bioreactor for denitrification of upland groundwater nitrate-N; the occurrence of such deposits can be mapped to identify potential nitrogen sinks across the landscape. This approach to identifying potential nitrogen sinks is geology focused and extends potential locations for nutrient processing upstream into the headwater catchments of individual fields.

Mercuriferous gold and amalgams in Mesozoic-Cenozoic rocks of the Vyatka-Kama depression

Mercuriferous gold and amalgams of two types have been detected in the Lower Triassic, Middle Jurassic, and Holocene alluvial deposits in the sedimentary cover of the Vyatka-Kama depression. Electron microscopic studies revealed that some of these aggregates represent intergrowths of individual segregations (globules) ranging in size from 1 to 300 μm. At high magnifications (up to 100 000 times or more), electron photomicrographs show that the smallest globules include tiny (up to nanoscale) gold particles. Microprobe analysis made it possible to detect significant chemical variations in the globules mainly due to alterations in the Hg content (from 0 to 58.25 wt %). The major part of such aggregates belongs to solid Au-Hg solid solutions. Amalgams with Hg >19.8 at % are represented by several phases: (Au,Ag)3Hg and (Au,Ag)2Hg prevail; (Au,Ag)3Hg2, (Au,Ag)5Hg4, and (Au,Ag)Hg are subordinate. In terms of composition, some globules correspond to argentiferous gold (without Hg), mercuriferous electrum, and Au-Pb intermetallides with Hg, Ag and Cu. Another, more widespread type is represented by lumpy massive grains (with mercuriferous gold shell) and porous amalgam. Their formation is related to natural amalgamation initiated by the Early Mesozoic tectonomagmatic activation of the platform and adjacent deep faults. The results obtained can be used in prospecting for Au-Hg mineralization in the sedimentary cover of the Vyatka-Kama depression.

Holocene floodplain deposition and scale effects in a typical European upland catchment: A case study from the Amblève catchment, Ardennes (Belgium)

This study quantifies Holocene alluvial sediment deposition in the Belgian Amblève catchment (1080 km2), situated in the Ardennes uplands. An extended coring data set is used for a quantitative description and a quantification of the alluvial depositions. The floodplains fall into three main types: the upper and lower floodplains and the steep reaches. Total Holocene alluvial sediment deposition amounts to 32 Tg, or 0.029 Tg/km2. Dating of sediments using iron slag as tracer shows that on average 42% of contemporary storage was accumulated during the last 600 years. Radiocarbon dating of fluvial deposits at eight sites in the catchment confirms that the majority of the sediment is relatively recent. The increased sedimentation rates for this period are related to anthropogenic land use, possibly enhanced by climatic variations. A fluvial sediment budget was constructed for this 600 yr time period and shows that export from the catchment has about the same importance as storage in the floodplains, while lateral reworking of existing floodplain deposits only affects half the quantity of sediments. Overall, floodplain sediment storage in the Amblève catchment, comparable with other upland catchments, is of lesser importance compared with catchments dominated by loess. This can mainly be explained by lower sediment supply resulting from less intense anthropogenic land use, despite the higher sediment transport efficiency through the fluvial system. Floodplain sediment storage is scale-dependent, with initially a sharp increase in catchment area-specific sediment deposition, followed by a steady decrease with increasing catchment area.

An evaluation of Mesodon and other larger terrestrial gastropod shells for dating late Holocene and historic alluvium in the Midwestern USA

Understanding the history of stream erosion and changes in channel morphology is important for managing and restoring unstable streams. One of the significant challenges in this type of research is establishing accurate dating of late Holocene and historic alluvium. Here we evaluate the potential of using 14C dating and amino acid racemization (AAR) to date large terrestrial gastropod shells that are often preserved within alluvial sediments. Many terrestrial gastropods incorporate old carbon from limestone or other carbonate rocks into their shells and therefore are unsuitable for radiocarbon dating. Recent studies, however, have shown that some taxa avoid this ‘limestone problem’ and can yield reliable 14C ages. In this study, we measured the 14C activity of specimens for the genera Mesodon, Ventridens, and Allogona collected live and from alluvial sequences dated independently by dendrochronology, 14C dating of wood, and/or 137Cs analyses. Mesodon zaletus contained old carbon in similar concentrations (up to ~30%) found in previous studies of other large taxa and should be avoided for 14C dating when possible. In contrast, shells of Ventridens ligera and Allogona profunda showed minimal limestone effects and therefore may be suitable for dating late Holocene alluvium. These results highlight the importance of taxonomic identification of gastropod taxa prior to their use for 14C dating and demonstrate that shell fragments that are not identifiable should be avoided. We also measured d/l ratios (n=17) of aspartic and glutamic acid from eight different taxa of terrestrial gastropods recovered from four late Holocene and historic stratigraphic sequences. Average d/l ratios of aspartic and glutamic acid from historic sediments <300years old are lower in shells from younger stratigraphic units, indicating that AAR can be used to differentiate between multiple historic stratigraphic units.

Deep gullies entrenchment in valley fills during the Late Holocene in the Basento basin, Basilicata (southern Italy)

Deeply entrenched channels namely badland gullies occur on the gently sloping valley floors of any alluvial basins in the semi-arid environments of Fossa Bradanica, Basilicata, southern Italy. Valley fills in this region consist of predominantly Holocene alluvium; late Pleistocene deposits occur as terraces above the present flood plain or as eroded benches buried beneath younger alluvium. Historical fluvial deposition began before 7000 a cal. BP and ended at around 120 a cal. BP. In this study, we focus on the channel entrenchment (badland gullies incision) in the last 4500 years, based on a detailed study of chronostratigraphic alluvial sequences of Basento River. Four main phases of incision have been recorded at around 4500-4350, 1500, 900-800, and 120 a cal. BP. The formation of late-Holocene badland gullies can be related to changes in climate, vegetation and groundwater conditions. Environmental history mainly derived from the high-resolution pollen record of Lago Grande di Monticchio. Badland gullies formation appears to be linked to repeated dry-wet cycles. During dry periods, water tables significantly dropped and vegetation cover decreased with increase in runoff and water discharge from rainfall, leading to deepening and widening of stream channels.