Impacts of Pleistocene glaciation on large‐scale groundwater flow and salinity in the Michigan Basin

Pleistocene melting of kilometer‐thick continental ice sheets significantly impacted regional‐scale groundwater flow in the low‐lying stable interiors of the North American and Eurasian cratons. Glacial meltwaters penetrated hundreds of meters into the underlying sedimentary basins and fractured crystalline bedrock, disrupting relatively stagnant saline fluids and creating a strong disequilibrium pattern in fluid salinity. To constrain the impact of continental glaciation on variable density fluid flow, heat and solute transport in the Michigan Basin, we constructed a transient two‐dimensional finite‐element model of the northern half of the basin and imposed modern versus Pleistocene recharge conditions. The sag‐type basin contains up to approximately 5 km of Paleozoic strata (carbonates, siliciclastics, and bedded evaporites) overlain by a thick veneer (up to 300 m) of glacial deposits. Formation water salinity increases exponentially from <0.5 g l^?1 total dissolved solids (TDS) near the surface to >350 g l^?1 TDS at over 800 m depth. Model simulations show that modern groundwater flow is primarily restricted to shallow glacial drift aquifers with discharge to the Great Lakes. During the Pleistocene, however, high hydraulic heads from melting of the Laurentide Ice Sheet reversed regional flow patterns and focused recharge into Paleozoic carbonate and siliciclastic aquifers. Dilute waters (<20 g l^?1 TDS) migrated approximately 110 km laterally into the Devonian carbonate aquifers, significantly depressing the freshwater‐saline water mixing zones. These results are consistent with ¹⁴C ages and oxygen isotope values of confined groundwaters in Devonian carbonates along the basin margin, which reflect past recharge beneath the Laurentide Ice Sheet (14–50 ka). Constraining the paleohydrology of glaciated sedimentary basins, such as the Michigan Basin, is important for determining the source and residence times of groundwater resources, in addition to resolving geologic forces responsible for basinal‐scale fluid and solute migration.     

Late Weichselian deglaciation and sea level history of St Jonsfjorden,Spitsbergen: A contribution to ice sheet reconstruction

The elevation and age of surveyed shorelines in St Jonsfjorden, western Spitsbergen, provide a chronology for Late Weichselian deglaciation and a proxy for former ice thickness. Support is provided for previous reports of two sets of shorelines on NW Spitsbergen, the oldest (at 60 m in St Jonsfjorden) dating to a pre‐late Weichselian glaciation and the youngest documenting postglacial rebound. The remarkable survival of the older shorelines suggests that a large area of NW Spitsbergen was either covered by protective, cold‐based ice or was subject to only local glaciation during the late Weichselian even though glacier ice extended to the shelf edge in the Isfjorden Trough. A marine limit of 46 m at the mouth of St Jonsfjorden is compatible with the regional late Weichselian marine limit (LWML) dated to ～13 ka BP. A partial relative sea level curve and equidistant shoreline diagram are produced for St Jonsfjorden and used in conjunction with relative sea level curves based on data from previous studies to produce an isobase map for 9 ka BP. The curves indicate that western sites were subject to initial slow emergence followed by rapid emergence between 10 ka and 8.2 ka BP, trends characteristic of areas affected by a full glacial sea or at least subject to early break up of a thin or discontinuous glacier ice cover. A step in the 9 ka BP shoreline long profile over the western end of the peninsula separating Isfjorden and van Mijenfjorden suggests that Holocene neotectonics may have produced anomalously high rebound rates in that area.     

Late Glacial and Holocene Vegetation History at Dublin Bog North-Central Tasmania

Percentage and influx pollen analyses of a 9.17 m core from Dublin Bog give a post last glaciation vegetation history (-13.6 to 0 ka BP) for the upper Mersey Valley. Herbaceous vegetation of Gramineae, Compositae and Chenopodiaceae developed rapidly after deglaciation and lasted until 13.2 ka BP. Around 13 ka BP Eucalyptus woodland and forest developed rapidly on the valley floor. At the same time Pomaderris apetala became an important understorey shrub/tree, and Phyllocladus aspleniifolius rainforest developed in the gullies on the upper slopes of the Mersey Valley and in the valleys to the west The major change in climate from late glacial cold (and probably drier conditions) to warm humid conditions similar to present occurred between 13.2 and 13 ka BP. Wet sclerophyll Eucalyptus forest occupied the valley throughout the post glacial and attained its maximum development between 11.7 and 8.4 ka BP. Rainforest never occupied the valley floor extensively. Phyllocladus aspleniifolius sattained an early maximum about 13 ka BP. The peak of Pomaderris apetala and expansion of Dicksonia antarctica suggests that the climate was warmer and wetter between 10.3 and 8.4 ka BP than at other times. Nothofagus attained its maximum development between about 10.3 and 6 ka BP. Both sclerophyll and rainforest vegetation associations in the upper Mersey Valley appear to have been very stable and similar to their present floristic compositions during the Holocene. Aborigines occupied the valley by 10 ka BP. Fire was always present in this marginal area between the wet climate of western and the dry climate of eastern Tasmania. Fire did not cause replacement of rainforest by wet sclerophyll forest on the valley floor, though it could have prevented rainforest establishment     

Geothermal fluids circulation at Caldas do Moledo area, Northern Portugal: geochemical and isotopic signatures

A hydrogeological conceptual model of the Caldas do Moledo geothermal site is proposed that shows mixing between geothermal waters and local shallow groundwaters. Stable isotope values of Caldas do Moledo geothermal waters indicate recharge areas located at relatively high altitudes (850–1250 m a.s.l.). The NW–SE Vigo–Régua shear zone plays an important role in fluid recharge and circulation towards the NNE–SSW Régua–Verin fault system, forming a path for ascent of geothermal fluids. The apparent ¹⁴C age of geothermal fluids (15.66 ± 2.86 ka BP) was estimated in the total dissolved inorganic carbon (TDIC). Geothermometer calculations indicate that, assuming a conductive temperature gradient of 32°C per kilometer for northern Portugal, the maximum depth of circulation is roughly 1.8 ± 0.4 km. The K, Ca and SO₄ concentrations found in some Caldas do Moledo geothermal spring waters show mixing between deep geothermal and shallow groundwater systems. Local shallow groundwaters showing the highest SO₄ concentrations were found at low elevation areas, originating from fertilisers and pesticides applied to the Port wine vineyards in the Douro River valley. Geothermal waters from boreholes AC1 and AC2 do not show evidences of direct pollution from the spreading of such agrochemicals.     

Diatom-inferred salinity changes in relation to Holocene sea-level fluctuations in estuarine environments of Argentina

Espinosa, M.A., Hassan, G.S. & Isla, F.I., September 2012. Diatom-inferred salinity changes in relation to Holocene sea-level fluctuations in estuarine environments of Argentina. Alcheringa 36, 377–391. ISSN 0311-5518.

The analysis of diatoms from three sedimentary sequences in the Quequén Grande River basin (Buenos Aires province, Argentina) has allowed the reconstruction of local and regional palaeosalinity changes in relation to Holocene sea level fluctuations. An established diatom-based salinity transfer function is used in combination with autecological methods to reveal a maximum sea level between ca 7000 and 6000 ¹⁴C years BP. This marine influence was recorded in deposits exposed 2 km and 12 km upstream, but not 32 km from the mouth. The fossil diatom assemblages are characteristic of an estuarine lagoon with maximum inferred salinities of 15‰. When the Holocene transgression began to flood the former valley (ca 7000 ¹⁴C years BP), brackish lagoons evolved into estuarine settings in the lower valley, but shallow freshwater ponds with salinities <4‰ persisted at 32 km from the mouth.     

Reconstruction of the Bulgobac Glacial System,Pieman River Basin,Western Tasmania

During the Early Pleistocene Bulgobac Glaciation, a piedmont glacial system extended into the valleys west of the West Coast Range of Tasmania. The ice that fed this extensive system originated mainly to the south and east on the western Central Highlands and northern Tyndall Mountains. The palaeo-equilibrium line lay to the east of the West Coast Range. Reconstruction of the palaeoglacial system indicates that ice-surface gradients reached only ~10–15 m km^-1 over much of the system to the west of the equilibrium line, although the ice fronts were steep and rapidly ablating. The nature of the piedmont glacier is consistent with the build up of ice behind the topographic barrier of the West Coast Range. This would have resulted in ice thickening, maintained and perhaps accentuated by high precipitation as well as by the location of the equilibrium line well to the west of the western Central Highlands.     

The Holocene fluvial history of the Tremithos river (south central Cyprus) and its linkage to archaeological records

This study aims to reconstruct the Holocene fluvial history of the Tremithos river, south central Cyprus and examine linkages to regional and local archaeological records. Three stratigraphic profiles (Sp1, Sp2 and Sp3) located in the lower valley have been investigated using sedimentology and magnetic parameters. The ¹⁴C dating of 10 samples reveals mid-Holocene ages for Sp1 and Sp2, while the upper most part of Sp3 can be attributed to the early to mid-Holocene. Two main phases of vertical accretion have been recognised: the first, recorded in the lower most part of Sp3, could not be dated but might relate to the late Glacial period. It is not associated with any archaeological artefacts. The second, recorded in all profiles, dating from ca. 5000 to ca. cal 2800 BC, spans the Late Neolithic Sotira (cal 4800/4000 BC) and Late Chalcolithic (cal 2900–2500 BC) cultures. The sediments of Sp1 and Sp2 are up to 8–10 m thick and mainly composed of fine material. However, an intercalated phase of coarse sediment has been identified at the beginning of the third millennium BC, indicating a sudden change in river dynamics, potentially associated with the 5.2 ka rapid climate change regional event. Typical mid-Chalcolithic (ca. cal 3300–3050 BC) ceramics found in a palaeosol in Sp2 indicate for the first time human occupation of the Tremithos river terraces. Two other palaeosols have also been recognised in Sp3 and radiocarbon dated to ca. cal 5600–4100 BC and ca. cal 2900–2600 BC, respectively. These results make it possible to propose a palaeogeographic reconstruction of the Holocene evolution in the Tremithos valley and to make a preliminary assessment of the relative roles of tectonics, climate and anthropogenic forcing.     

DATING OF THE HOMINID (HOMO NEANDERTHALENSIS) REMAINS ACCUMULATION FROM EL SIDRÓN CAVE (PILOÑA,ASTURIAS, NORTH SPAIN): AN EXAMPLE OF A MULTI‐METHODOLOGICAL APPROACH TO THE DATING OF UPPER PLEISTOCENE SITES

The age of Neanderthal remains and associated sediments from El Sidrón cave has been obtained through different dating methods (¹⁴CAMS, U/TH, OSL, ESR and AAR) and samples (charcoal debris, bone, tooth dentine, stalagmitic flowstone, carbonate‐rich sediments, sedimentary quartz grains, tooth enamel and land snail shells). Detrital Th contamination rendered Th/U dating analyses of flowstone unreliable. Recent ¹⁴C contamination produced spurious age‐values from charcoal samples as well as from inadequately pretreated tooth samples. Most consistent ¹⁴C dates are grouped into two series: one between 35 and 40 ka and the other between 48 and 49 ka. Most ESR and AAR samples yielded concordant ages, ranging between 39 and 45 ka; OSL dating results permitted adequate bracketing of the sedimentary layer that contained the human remains. Our results emphasize the value of multi‐dating approaches for the establishment of reliable chronologies of human remains.     

Carnivores and their prey in the Wezmeh Cave (Kermanshah,Iran): a Late Pleistocene refuge in the Zagros

Wezmeh Cave is located on the northeastern edge of the Islamabad plain, a high intermontane valley in the western‐central Zagros. In 1999 a disturbed but large faunal assemblage was recovered from this site. The abundant and extremely diverse faunal spectra present at Wezmeh Cave has highlighted the importance of this assemblage. Carnivore remains constitute the bulk of the assemblage; red fox (Vulpes vulpes) has the highest number of identified specimens followed by spotted hyena (Crocuta crocuta), brown bear (Ursus arctos), wolf (Canis lupus), felids (lion, leopard, lynx/caracal and wildcat), mustelids (badger, polecat, marten) and viverrids (mongoose). Artiodactyls (bovid, cervid, suid), equids, rhinoceros (Dicerorhinus sp.) and small animals (Cape hare, porcupine, tortoise, snake, birds) are also present. According to U‐series dating, the site was occupied from around 70 ka BP through to sub‐recent periods by carnivores. Amongst this rich assemblage, a human fossil tooth was also found and dated by non‐invasive spectrometry gamma dating to 20–25 ka BP. A preliminary zooarchaeological and taphonomic study shows that Wezmeh Cave was used by multiple carnivore species, a unique phenomenon in the Zagros Mountains in particular and southwest Asia in general. Copyright © 2008 John Wiley & Sons, Ltd.     

The timescale and mechanisms of fault sealing and water‐rock interaction after an earthquake

Hydrogeochemical monitoring of a basalt‐hosted aquifer, which contains Ice Age meteoric water and is situated at 1220 m below sea level in the Tjörnes Fracture Zone, northern Iceland, has been ongoing since July 2002. Based on hydrogeochemical changes following an earthquake of magnitude (M_w) 5.8 on 16 September 2002, we constrained the timescales of post‐seismic fault sealing and water–rock interaction. We interpret that the earthquake ruptured a hydrological barrier, permitting a rapid influx of chemically and isotopically distinct Ice Age meteoric water from a second aquifer. During the two subsequent years, we monitored a chemical and isotopic recovery towards pre‐earthquake aquifer compositions, which we interpret to have been mainly facilitated by fault‐sealing processes. This recovery was interrupted in November 2004 by a second rupturing event, which was probably induced by two minor earthquakes and which reopened the pathway to the second aquifer. We conclude that the timescale of fault sealing was approximately 2 years and that the approach to isotopic equilibrium (from global meteoric water line) was approximately 18% after >10⁴ years.     

HOLOCENE ACCUMULATION OF COLLUVIAL AND ALLUVIAL SEDIMENTS IN THE WEIßE ELSTER RIVER VALLEY IN SAXONY,GERMANY*

Geoarchaeological investigations at two archaeological excavation sites lead to new results with respect to the Holocene landscape development of an archaeologically important loess landscape of Central Europe. Colluvial and alluvial sediments were sampled during archaeological excavations on the valley edge of the Weiße Elster and dated by means of ¹⁴C, TL and dendrochronology, and on the basis of archaeological finds. Thus, for the first time, the development of a valley edge of a river in the Leipzig area, which has been continuously settled for 7300 years, can be reconstructed. The first soil erosion on the valley edge is established towards the end of the Atlantic period. During the High Middle Ages, a colluvial sediment developed. Its deposition time can be limited to between ad 1000 and 1100. The flood loam near Großstorkwitz, which can be stratified by means of the soil and colluvial deposits, originated in the late Sub‐Boreal and early Sub‐Atlantic, as well as after ad 1100. During the first millennium ad, a soil developed in the older flood loam, which indicates a phase of reduced flood loam sedimentation.     

Quaternary Organic Deposit from Newton Creek Valley,Western Tasmania

Pollen and macrofossils from an organic deposit probably 44 ka BP in age record subalpine heath with abundant local Athrotaxis cupressoides. This was succeeded by subalpine heath that included Casuarina, Phyllocladus and Eucalyptus. The pollen/vegetation assemblages are comparable with present subalpine vegetation located between 850–1050 m, though the site is at 550 m and potentially below the limit of temperate rainforest (620 m). It is inferred that the vegetation altered from upper to lower subalpine heath and that the climate became warmer and wetter. The mean temperature is estimated to have been at least 3.2°C to 1.7°C colder than today. The trend of vegetation and climate change compares closely with Late Glacial changes but does not compare with changes recorded from sites of Middle Last Glacial age in the West Coast Ranges. A radiocarbon date of 34 ka BP and a trend towards warming suggests that the deposit may represent the onset of an interstadial during the Early Last Glacial Stage.     

Optical dating and sedimentary record from the terrace depositional profile of the Warta River (Central Poland)

Results of OSL dating and sedimentary studies from the profile of the low alluvial terrace of the middle Warta River are presented. The samples were dated using the single-aliquot regenera-tive method. Dating was used to establish a timing of the Weichselian Late Glacial events in the river valley environment. Stable conditions on the floodplain are expressed by the deposition of organic-rich series radiocarbon dated at 12 900-12 600 cal BP and 11 600-10 770 cal BP. Samples for OSL dating were collected from the mineral material deposited during the intensification of flood events during the Weichselian decline. The results obtained for the alluvia range from 12.78 ± 0.62 ka b2k to 14.33 ± 0.74 ka b2k. Sedimentological criteria allowed to distinguish between particular flood events. Overestimation of OSL ages is probably a result of rapidity of environmental changes in that time.     

Dating the Trollesgave site and the Bromme culture – chronological fix-points for the Lateglacial settlement of Southern Scandinavia

The Bromme culture belongs to the Lateglacial, the period when people settled in the recently deglaciated Southern Scandinavia. Until now there have been only a few imprecise fix-points relating to the chronological position of this archaeological culture. This situation can now be improved with the aid of research results from a Bromme culture settlement at Trollesgave in SE Denmark. Using pollen and plant macrofossil data, Lateglacial lacustrine deposits containing waste material from the settlement can be assigned to the end of the climatically mild Allerød period. A series of ¹⁴C dates establishes the age of the settlement as c. 10 826 ± 49 ¹⁴C years BP (12 871–12 590 cal yr BP). By correlation with climate data from the Greenland ice cores, the occupation can be assigned to the early part of the cold climatic zone GS-1, thus demonstrating that the global ice-core climate zones are not absolutely synchronous with the regional division into biozones.     

First 230Th/U date of Middle Pleistocene peat bog in Siberia (key section Krivosheino, Western Siberia)

A ¹⁴C date older than 53900 yrs BP was obtained for the uppermost part of the buried peat bog in Krivosheino section (Middle Pleistocene of Western Siberia). These sediments also yielded ²³⁰Th/U dates of 195 _?9.1 ^+10.8 ka using the leachate alone (L/L) and 204 _?13 ⁺¹⁷ ka using total sample dissolution (TSD) models. Peculiarities of ²³⁰Th/U dating are discussed. Palynological investigation of the buried peat bog together with underlying and overlaying sediments, and comparison with palynological data from Baikal and Elgygytgyn lakes revealed that the peat layer in Krivosheino section was formed at the end of Shirta Interglacial (Marine Isotopic-Oxygenous stages MIS-7), when climate conditions at all studied sites were more severe compared to the modern ones.     

The reflection of human activity in the sediments of Iwankowskie Lake from Subatlantic Phase (Polish Outer Carpathians)

The paper presents the analysis of organic and mineral sediments filling the depression, which developed over the landslide located at the slope (767–773 m a.s.l.) of Lubań ridge decscending to the Ochotnica river valley in the Polish Flysch Carpathians. The landslide formed in an early stage of the Subatlantic Phase (2490 ± 35 BP). The top of peat is dated at 1360 ± 50 years BP and is covered by 72 cm of clayey silts with some sandy intercalations, which indicate slopewash after deforestation. The pollen of ruderal plants and Cerealia (undiff.) reflect agricultural activity in the surroundings. The fragments of charcoal indicate the age of the forest clearance to the first half of the 17^th century. The late forest clearance at the elevated north exposed slopes followed 200–300 years later in relation to the foundation of the village at the valley floor.     

Mitochondrial DNA haplotypes of Devensian hyaenas from Creswell Crags,England

Spotted hyaena (Crocuta crocuta) remains have been recovered from British Middle and Upper Pleistocene sites at intervals within the period 700–730 ka BP. Morphological studies have suggested that hyaenas of the Last Interglacial sensu stricto (Ipswichian: Marine Isotope Stage [MIS] 5e, 130–115 ka BP) and Last Glacial (Devensian: MIS 3, 61–24 ka BP) were two distinct populations, the Ipswichian hyaenas becoming extinct in Britain during MIS 5 and the Devensian ones arriving via a subsequent migration from continental Europe. However, the apparent presence of hyaenas in later MIS 5 deposits has led to the alternative suggestion that there was a southern relict population from which the Devensian hyaenas originated. We obtained ancient DNA (aDNA) sequences from four Devensian hyaena specimens from Creswell Crags, Derbyshire, dated to around 45 ka ¹⁴C BP. Each of these four specimens belonged to the mitochondrial DNA (mtDNA) clade A. This clade is not thought to have been present in Europe until ~360 ka BP, after the initial arrival of hyaenas in Britain. The DNA results, therefore, suggest that there were at least two waves of hyaena dispersals into Britain. The results are consistent with the repeated dispersals into Britain of another Pleistocene social carnivore, Homo sapiens.     

Dating North America's oldest petroglyphs,Winnemucca Lake subbasin,Nevada

On the west side of the Winnemucca Lake subbasin, Nevada, distinctive deeply carved meter-scale petroglyphs are closely spaced, forming panels on boulder-sized surfaces of a partially collapsed tufa mound. The large, complex motifs at this side are formed by deeply carved lines and cupules. A carbonate crust deposited between 10 200 and 9800 calibrated years B.P. (ka) coats petroglyphs at the base of the mound between elevations of 1202 and 1206 m. Petroglyphs above the carbonate crust are carved into a branching form of carbonate that dates to 14.8 ka. Radiocarbon dates on a multiple-layered algal tufa on the east side of the basin, which formed at an elevation of 1205 m, as well as a sediment-core-based total inorganic carbon record for the period 17.0–9.5 ka indicate that water level in the Winnemucca Lake subbasin was constrained by spill over the Emerson Pass Sill (1207 m) for most of the time between 12.9 ± 0.3 and ≥9.2 ka. These and other data indicate that the lake in the Winnemucca Lake subbasin fell beneath its spill point between 14.8 and 13.2 ka and also between 11.3 and 10.5 ka (or between 11.5 and 11.1 ka), exposing the base of the collapsed tufa mound to petroglyph carving. The tufa-based ¹⁴C record supports decreased lake levels between 14.8–13.2 ka and 11.3–10.5 ka. Native American artifacts found in the Lahontan Basin date to the latter time interval. This does not rule out the possibility that petroglyph carving occurred between 14.8 and 13.2 ka when Pyramid Lake was relatively shallow and Winnemucca Lake had desiccated.     

Spatial–temporal distribution and geographic context of Neolithic cultural sites in the Hanjiang River Basin,Southern Shaanxi,China

Understanding how to live successfully within our environment is among the most pressing challenges facing contemporary society. This paper probes the problem based on comparative analysis and discusses the relationship between the spatial–temporal distribution of the Neolithic cultural sites and the geographic context in the Hanjiang River Basin in the south of Shaanxi Province, China. Archaeological studies have identified 175 Neolithic cultural sites in the study area, with a sequence of Laoguantai (¹⁴C age 8–7 ka BP), Yangshao (¹⁴C age 7–5 ka BP) and the late period of the Neolithic Age (¹⁴C age 5–4 ka BP). The total number of archaeological sites, the distribution area and the density all showed an early ascending and later descending trend, but the proportion of the number of archaeological sites in the study area to the corresponding value of the entire Shaanxi Province declined sharply. Spatially, these sites were concentrated on the terraces of the Hanjiang River and its main tributaries with an altitude of 400–800 m. Multiple data were integrated to clarify the critical effects of tectonic and geomorphologic conditions on the distribution of the Neolithic sites. Further comparisons revealed the correlation of Holocene climate change and environmental evolution with the Neolithic cultural succession in the study area that ameliorated conditions to generally promote the development of the primitive culture while degeneration coincided with the culture's transition or interruption. The discussion on the origin of the primitive culture and the temporal–spatial distribution corresponding to the regional culture differentiation sheds light on the complex and dynamic human–nature interaction system during the Neolithic Age, thus emphasising the wider field-based investigation and high-resolution reconstruction works of the palaeoclimate and palaeoenvironment in the future.     

New Data on the Relief Development of the South Shetland Islands,Antarctica

Abstract

During several expeditions to the Antarctic Peninsula and the neighbouring islands, samples were collected from different sediments which contained datable materials or which were datable with new techniques. Thus it became possible to develop, together with our geomorphic field data, some new ideas on relief development at the rim of the Antarctic continent as well as on the glacial history of the area studied.

Planation surfaces in this area seem to be fairly old. For example, the prominent marine erosion surface on Fildes Peninsula, 35–45 m above mean sea level, is probably older than 85 000 years – older than the last interglacial period and the penultimate glaciation. All Holocene beaches, which are situated between 20 m and the present coastline, were formed during the last 6000 years.

Before 6000 BP the islands were still completely glaciated. The breakdown of the ice cover to nearly the present extent must have been extremely abrupt, taking no more than 1000 years (6000 to 5000 BP). Between 3000 and 1000 BP there were at least two re-advances. These advances were restricted to the prominent outlet glaciers, which followed pre-existing valleys.