Influence Of Glaciation Research Articles

The eruptive history, magmatic evolution, and influence of glacial ice at long-lived Akutan volcano, eastern Aleutian Islands, Alaska, USA

AbstractNew 40Ar/39Ar and whole-rock geochemical data are used to develop a detailed eruptive chronology for Akutan volcano, Akutan Island, Alaska, USA, in the eastern Aleutian island arc. Akutan Island (166°W, 54.1°N) is the site of long-lived volcanism and the entire island comprises volcanic rocks as old as 3.3 Ma. Our current study is on the 225 km2 western half of the island, where our results show that the focus of volcanism has shifted over the last ∼700 k.y., and that on occasion, multiple volcanic centers have been active over the same period, including within the Holocene. Incremental heating experiments resulted in 56 40Ar/39Ar plateau ages and span 2.3 Ma to 9.2 ka.Eruptive products of all units are primarily tholeiitic and medium-K, and range from basalt to dacite. Rare calc-alkaline lavas show evidence suggesting their formation via mixing of mafic and evolved magmas, not via crystallization-derived differentiation through the calc-alkaline trend. Earliest lavas are broadly dispersed and are almost exclusively mafic with high and variable La/Yb ratios that are likely the result of low degrees of partial mantle melting. Holocene lavas all fall along a single tholeiitic, basalt-to-dacite evolutionary trend and have among the lowest La/Yb ratios, which favors higher degrees of mantle melting and is consistent with the increased magma flux during this time. A suite of xenoliths, spanning a wide range of compositions, are found in the deposits of the 1.6 ka caldera-forming eruption. They are interpreted to represent completely crystallized liquids or the crystal residuum from tholeiitic fractional crystallization of the active Akutan magma system.The new geochronologic and geochemical data are used along with existing geodetic and seismic interpretations from the island to develop a conceptual model of the active Akutan magma system. Collectively, these data are consistent with hot, dry magmas that are likely stored at 5–10 km depth prior to eruption. The prolonged eruptive activity at Akutan has also allowed us to evaluate patterns in lava-ice interactions through time as our new data and observations suggest that the influence of glaciation on eruptive activity, and possible magma composition, is more pronounced at Akutan than has been observed for other well-studied Aleutian volcanoes to the west.

Influence of glaciations on North Sea petroleum systems

Abstract Even in tectonically inactive areas/times, the vertical motions of the Earth's interior may be significant due to glaciation. The most recent ice age massively changed the surface of northern Europe, leading to isostatic re-equilibration. We quantify the vertical motions resulting from three glacial-related mass redistribution mechanisms using, as an example, the North Sea throughout the Quaternary: (1) ice-sheet loading, (2) erosion, including glacial carving of fjords; (3) and sediment deposition. These processes yielded up to 1 km of vertical displacement of the lithosphere across the North Sea, and the corresponding sediment-tilting changed the geometry of petroleum systems and hydrocarbon migration routes. Using the Base Cretaceous Unconformity as a top seal proxy, we analyse the consequences in the Norwegian North Sea. Comparing well data to models, we suggest that tilting the Troll Field back towards its early Quaternary position flattens the palaeo-oil–water contact (palaeo-OWC), which today is tilted by up to 70 m. The Johan Sverdrup Field shows a more complex history. Hints of a palaeo-OWC tilted can be seen in permeable reservoirs, whereas deeper sporadic oil shows cannot be explained by simple tilt models. Our study illustrates how glacial-related processes may influence the development of giant oil and gas accumulations.

Sub–ice shelf ironstone deposition during the Neoproterozoic Sturtian glaciation

Abstract The Neoproterozoic Sturtian glaciation is considered to be among the most severe glaciations in Earth history, possibly encompassing the entire planet and lasting for more than 50 m.y. Iron formations are globally associated with Sturtian glacial successions, although the influence of glaciation on the genesis of these iron formations remains contentious. Here we examine the Sturtian iron formations of Namibia and Australia that feature finely laminated ironstones containing up to 55% total iron. These ironstones are repeatedly interbedded with massive diamictites, yet dropstones and other clastic input are nearly absent in the laminated ironstone facies. Intercalated diamictites are variably ferruginous and characterized by a strong glacial influence with evidence of glaciotectonism. The ferruginous facies are laterally discontinuous and commonly occupy paleobathymetric depressions. Rare earth element signatures from these iron formations are similar to those from modern seawater but lack cerium anomalies. The paradox of dropstone-free, laminated sediments intimately interlaminated with massive ice-proximal diamictites can be resolved by deposition under an ice shelf. Polynya activity and the mixing of cold, oxygenated glacial fluids with ferruginous seawater via an ice pump mechanism may explain the deposition of these iron formations and their restriction to Sturtian glacial successions globally.

Influence of glaciation on mechanisms of mineral weathering in two high Arctic catchments

In order to investigate the effect of glaciation on mineral weathering, the stream water chemistry and the bacterial community composition were analysed in two catchments containing nominally identical sedimentary formations but which differed in the extent of glaciation. The stream waters were analysed for major ions, δ34S, δ18OSO4 and δ18OH2O and associated stream sediments were analysed by 16S rRNA gene tagged sequencing.Sulphate comprised 72–86% and 35–45% of the summer anion budget (in meq) in the unglaciated and glaciated catchments respectively. This indicates that sulfuric acid generated from pyrite weathering is a significant weathering agent in both catchments. Based on the relative proportions of cations, sulphate and bicarbonate, the stream water chemistry of the unglaciated catchment was found to be consistent with a sulphide oxidation coupled to silicate dissolution weathering process whereas in the glaciated catchment both carbonates and silicates weathered via both sulfuric and carbonic acids.Stable isotope measurements of sulphate, together with inferences of metabolic processes catalysed by resident microbial communities, revealed that the pyrite oxidation reaction differed between the two catchments. No δ34S fractionation relative to pyrite was observed in the unglaciated catchment and this was interpreted to reflect pyrite oxidation under oxic conditions. In contrast, δ34S and δ18OSO4 values were positively correlated in the glaciated catchment and were positively offset from pyrite. This was interpreted to reflect pyrite oxidation under anoxic conditions with loss of S intermediates.This study suggests that glaciation may alter stream water chemistry and the mechanism of pyrite oxidation through an interplay of biological, physical and chemical factors.

Unraveling sea-level variations and tectonic uplift in wave-built marine terraces, Santa María Island, Chile

The architecture of coastal sequences in tectonically-active regions results mostly from a combination of sea-level and land-level changes. The objective of this study is to unravel these signals by combining sequence stratigraphy and sedimentology of near-shore sedimentary sequences in wave-built terraces. We focus on Santa María Island at the south-central Chile margin, which hosts excellent exposures of coastal sediments from Marine Isotope Stage 3. A novel method based on statistical analysis of grain-size distributions coupled with facies descriptions provided a detailed account of transgressive–regressive cycles. Radiocarbon ages from paleosols constrain the chronology between >53 and ~31calkaBP. Because the influence of glaciations can be neglected, we calculated relative sea-level curves by tying the onset of deposition on a bedrock abrasion platform to a global sea-level curve. The observed depositional cycles match those predicted for uplift rates between 1.2 and 1.8m/ka. The studied sedimentary units represent depositional cycles that resulted in reoccupation events of an existing marine terrace. Our study demonstrates wave-built marine terrace deposits along clastic shorelines in temperate regions can be used to distinguish between tectonic uplift and climate-induced sea-level changes.

The Tindouf Basin, a marine refuge during the Serpukhovian (Carboniferous) mass extinction in the northwestern Gondwana platform

Several macrofaunas and microfossils of the Carboniferous Saharan basins have longer stratigraphic ranges than those of other basins in the western Palaeotethys realm, particularly in the Tindouf Basin (Morocco–Algeria). Foraminifers are particularly abundant and diverse in the Serpukhovian and basal Bashkirian compared to coeval basins, and some taxa have longer ranges than in the neighbouring Reggan and Béchar basins, although this effect is more marked compared to the western Palaeotethyan assemblages in Europe. Several rugose coral species are recorded from the early Bashkirian that previously were considered to have disappeared in the Serpukhovian. The Tindouf Basin, as one of the most western Saharan basins in North Africa, shows the greatest stratigraphic ranges of taxa which diminish eastwards. Evidence for a mass extinction event during the Serpukhovian in the Tindouf Basin has not been clearly recognized, although a possible influence of glaciation is observed in the faunal diversity. Eustatic sea-level changes were experienced in Tindouf with the cyclic pattern of sedimentation, but warm water ocean currents from the palaeoequator were able to maintain tropical conditions on the platform. Tectonics in the area, led to emerging land masses and barriers, and created a partly isolated basin in this sector of the western part of the Sahara Platform in northern Gondwana. The combination of those factors controlled the environmental conditions in the area, allowing the persistence of the fauna for longer stratigraphic ranges than its equivalent counterparts in the western Palaeotethys.

Linking present environment and the segregation of reproductive modes (geographical parthenogenesis) in Eucypris virens (Crustacea: Ostracoda)

AbstractAimGeographical parthenogenesis – in which parthenogenetic populations are more widely distributed than sexually reproducing populations – is observed in many plant and animal species. Many hypotheses have been proposed to account for this biogeographical pattern, and these often invoke historical processes such as the influence of glaciation. However, there are relatively few empirical studies of the contemporary factors associated with geographical parthenogenesis. The aim of this study was to understand its causes by linking contemporary environmental gradients with reproductive modes in the freshwater ostracod Eucypris virens.LocationEurope and North Africa.MethodsWe sampled populations of E. virens from 147 sites in 20 countries from Estonia to Morocco and from Portugal to Turkey. At each site we measured aspects of pond geography (latitude, longitude, elevation, pond area and depth), water chemistry (temperature, pH, conductivity, oxygen and ion concentrations) and macroinvertebrate assemblages. We used principal components and logistic regression analyses to test for the associations between environmental variables and the presence of males, indicating sexual reproduction, in a population.ResultsSexual populations were restricted to the Mediterranean, whereas parthenogenetic populations extended into the Baltic and Ponto‐Caspian areas. Significant environmental features were not only latitude, but also elevation, aridity and principal components summarizing water chemistry and invertebrate communities: sexual populations were more common at high elevations, in arid regions, and in turbid ponds. Ponds harbouring exclusively parthenogenetic populations were also characterized by having longer‐hydroperiod biological communities.Main conclusionsThe link between current environmental conditions and the reproductive modes of E. virens suggests a contemporary adaptation besides historical factors such as climatic cycles or the differential colonization success of sexual and asexual lineages. We propose that the pattern of geographical parthenogenesis in E. virens reflects the ability of asexual populations to colonize rapidly, and the higher adaptability of sexual populations to unpredictable hydroperiods.

Morphometric evaluation of the two mink subspecies in Illinois

The 2 subspecies of mink (Neovison vison letifera and N. v. mink) in Illinois were characterized early in the 20th century; however, quantifiable morphological distinctions between the 2 subspecies remain unclear. Illinois biogeography, and the influence of glaciations on animal populations, might explain the distinctions between the 2 mink subspecies. We evaluated sexual dimorphism within each subspecies and morphologic variation between subspecific populations. Oral, facial, and braincase regions were defined by 22 dimensions. Sexual dimorphism was present in both subspecies of mink. Data were adjusted for sex differences and tested for differences between subspecies using analysis of variance and multivariate analysis of variance. Cranial dimensions differed significantly between N. v. letifera and N. v. mink. Cranial dimensions distinguish individuals of the 2 geographically distinct subspecies; however, an intergradation zone might be present. The results are consistent with population response to glaciations and subsequent expansion, however, further genetic testing is necessary to test this historical biogeography of N. vison.

The influence of glaciations on the dynamics of mountain hydrothermal systems: numerical modeling of the La Léchère system (Savoie, France)

Abstract Although thermal waters are found in numerous Alpine valleys, the mechanisms responsible for their occurrence remain unclear. The present study used a 2-D numerical model of an Alpine hydrothermal system (La Léchère, Savoie) to investigate these mechanisms. A steady-state hydrodynamic model was calibrated using present-day observations, and then applied to predict outlet temperatures assuming steady-state conditions and the current heat flux and water flow. This simulation produced anomalously low outlet temperatures compared with present-day temperatures, indicating that water circulation within the La Léchère aquifer cannot have been constant throughout its history. Based on the suggestion that glaciations block aquifer circulation, a second simulation was carried out assuming zero water infiltration during the Würm glacial period. The outlet temperatures predicted by this second simulation were much closer to present-day temperatures. These two simulations show that the thermal anomaly at La Léchère is incompatible with the classic model of the progressive heating of thermal waters and that the current temperature of the thermal waters can be explained by changes in aquifer infiltration rates.

World ocean temperature lag time: an analysis based on glaciation data for the last two million years

¶It is postulated that before the influence of glaciation, it was the amount of cloud cover and the thermal inertia of the ocean that controlled the Earth’s temperature. The control system went into oscillation 37 myr BP when Antarctica started moving into its present position, the temperature of the ocean and that of the rest of the environment opposing each other in antisymmetric mode. Support for this theory is provided by the observation of periods of enhanced glaciation at regular intervals. The enhancement, being attributed to harmonics with the Earth’s 22,000 yr-precession and 41,000 yr-nutation cycles, allows the calculation of 23,500 yr for the period of the ocean/atmosphere-temperature cycle. The corresponding lag time between atmosphere and ocean is 11,750 yr.

Influence of glaciation on divergence patterns of the endemic minnow, Zacco pachycephalus, in Taiwan.

The genetic subdivision of the endemic minnow, Zacco pachycephalus, in 12 rivers of Taiwan was studied by allozyme electrophoresis. Among 26 loci surveyed, six were significantly differentiated among sites. Allozyme genotype frequencies within samples accord with Hardy-Weinberg expectations. A highly divergent genetic structure among sites (FST = 0.497) with low genetic variability within samples (H = 0.006-0.062, mean = 0.03) suggests that local populations originated from a small number of founders. UPGMA and Fitch trees derived from Nei's genetic distance and hierarchical analysis of FST values reveal that samples of Z. pachycephalus can be divided into northern, middle, and southern subgroups and that most genetic variation (87%) is distributed among rather than within groups. It is proposed that there were two isolated refugia during the most recent glacial period, and that populations of the southern group (Group I) originated from a southern refugium in Taiwan below the boundary of the Kaoping River, and other groups (Group II), including northern and middle subgroups, originated from a refugium located on the extinct land-bridge between Taiwan and mainland China. The postglacial division between northern and middle subgroups may be due to hydrological differences between these two regions.

The influence of glaciation on the basin temperature regime

The effect of glaciation on the temperature regime in a sedimentary basin has been estimated. Four modeling cases, representing glaciation with cold (permafrost) glaciers and temperate glaciers as well as non-glaciation, were undertaken. The thermal consequences of taking the glaciation into account can be significant. Subsurface temperatures during a cold (permafrost) glaciation were as much as 25°C lower than the subsurface temperatures in a non-glaciated case. Increased conductivities due to frozen pore water contributed significantly to the cooling of the subsurface. Given two cases of cold glaciation, the first with increased thermal conductivities due to freezing of pore water and the second with no effect of freezing, the first case results in up to 10°C lower subsurface temperatures than the second one. A temperate glacier with a temperature of 0°C at the ice/sediment boundary is, as expected, less significant compared to a cold glacier. In this case subsurface temperatures were up to 7°C lower than the subsurface temperatures in the non-glaciated case. Thus it is crucial to know which type of glacier is present at which time as well as the effect of frozen pore water on thermal conductivity in order to have a good estimation of subsurface temperatures in glaciated areas.

The Cosquer Cave on Cape Morgiou, Marseilles

The discovery of Palaeolithic wall paintings and engravings in a cave whose entrance lies below the present sea-level near Marseilles has created considerable interest – and no little controversy. The paper describes and analyses the remarkable find, with special attention to its authenticity.During the Pleistocene there were large variations in sea-level under the influence of glaciations and inter-glacial warm episodes. During the Late Wurm glaciation in the Upper Palaeolithic the sea-level dropped to 110–120 m below its present level (Lumley 1976: 311). At that time the Lerins islands, the Hyeres islands and the Frioul archipelago and the islet of Planier off Marseilles were linked with the coast, and much of the Golfe du Lion was occupied by a vast plain.

Sedimentary framework of the southern Maine inner continental shelf: Influence of glaciation and sea-level change

Although the tidally influenced shoreline of Maine is longer than that of virtually any other state, almost no research on its geology has been published. In order to go some way towards remedying this, 1500 km of high-resolution seismic reflection data and 800 km of sidescan sonar imagery have been collected. On the basis of these data and observations made during ten submersible dives, more than 800 bottom samples were collected and evaluated for texture and composition. The understanding of the sedimentary framework of the southern Maine shelf and the processes that maintain it are summarized, and future research directions to evaluate the strategic mineral potential are indicated. In the past 14,000 years, the Maine shelf has experienced a deglaciation and two marine transgressions separated by a regression. The deglaciation was accompanied by the first transgression and deposited till interbedded with up to 40 m of glaciomarine sediment (the Presumpscot Formation) across the shelf. The first transgression culminated about 12,500 yrs B.P., and its landward limit is marked by large glaciomarine deltas 50–100 km landward of the present-day coast. Sea level fell until about 9500 yrs B.P., when shorelines were cut at about the 65 m depth and some large “lowstand deltas” were deposited. Sea level has risen since then and in the general absence of modern river sediment input marine processes have reworked the older sediment. Five shelf environments have been defined in terms of their surficial sediment and stratigraphy. Nearshore ramps are sandy regions extending to about 30 m deep offshore of sandy beaches. These may be reworked lowstand deltas, and possess the thickest bodies of sand in the region. Nearshore basins are mud-filled troughs seaward of coastal areas lacking significant river input. Slumping glaciomarine deposits provide most of the Holocene mud that floors these basins. Rocky zones are extensive areas of exposed rock most common in the 30–50 m depth range. These are areas of high carbonate productivity and provide shell fragments to adjacent areas. The outer basins are muddy regions that begin at the 65 m shoreline and extend beyond the 100 m isobath to the deep Gulf of Maine. Finally, shelf valleys are former stream courses that connect nearshore ramps and basins to the outer basins. These bedrock-framed valleys are filled with sand and mud and are apparently still active conduits for the offshore movement of sediment. The mineralogy of the shelf sediment is complex, and it is not yet clear whether glacial homogenization has obliterated distinctions between river drainage basins and the adjacent shelf. Studies are continuing into northern Maine and analysis of the heavy mineralogy of the shelf sediment utilizing a 2 m Humphrey Spiral to process large grab samples and cores has begun.

Foods Consumed by Breeding Mallards on Wetlands of South-Central North Dakota

Foods consumed by 117 mallards (Anas platyrhynchos) collected on the breeding grounds of south-central North Dakota during spring and summer 1974-80 were examined. Animal foods accounted for 38 and 37% of the diet of paired males and nonlaying females, respectively (N = 80). The diet of laying females consisted of 72% animal foods, which differed significantly from that of paired males and nonlaying females. Insects, gastropods, crustaceans, annelids, and seeds made up 27.1, 16.4, 12.9, 12.8, and 24.8% of the diet, respectively, of laying females (N = 37). J. WILDL. MANAGE. 49(1):197-203 The prairie pothole region of North America contains a high density of shallow wetland basins with biotic communities that have developed under the influence of glaciation and a semiarid climate. Annual moisture deficits vary in magnitude and are accompanied by changes in water levels and dissolved salts (Stewart and Kantrud 1971, Swanson et al. 1974b). Plant and animal communities continually change in response to fluctuations in water level and salt content, and periodic droughts produce major changes in wetland biotic communities (Swanson and Meyer 1977). The dynamic nature of this water regime, and the periodic changes in the biota that it produces, is a dominant factor influencing the food base available to breeding waterfowl. Superimposed on the dynamic water regime of the prairie pothole region are tillage practices that can alter seasonally flooded wetlands annually and semipermanent wetlands during drought years. Tillage alters the food base of low prairie, wet meadow, and shallow marsh zones and is a major factor interacting with hydrology to influence biotic succession and, consequently, food availability. The high rate of nest destruction experienced by ground-nesting ducks in the prairie pothole region (Kirsch 1969, Higgins 1977) requires persistent renesting by mallard females if they are to achieve reproductive success. With each renesting effort and subsequent loss in body reserves, the food base available to breeding females increases in importance (Swanson et al. 1979). Foods consumed by laying mallards on the breeding grounds have not been identified. Perret (1962) described foods consumed by mallard females, but the reproductive status of the birds was not reported. Some preliminary results of foods consumed by laying mallards were discussed by Swanson et al. (1979). Studies of wetland ecology, mallard feeding ecology, and mallard renesting characteristics were undertaken concurrently in the prairie pothole region of south-central North Dakota to assess the ecological relation between breeding birds and their aquatic habitats. The purpose of the present paper is to describe foods consumed by laying female mallards on the breeding grounds of south-central North Dakota and compare these with foods of paired nonlaying females, paired males, and birds in

Quaternary Sedimentary Facies on Continental Shelf, Northeast Gulf of Alaska: ABSTRACT

The complex Quaternary history of the northeast Gulf of Alaska has resulted in a variety of sedimentary deposits ranging from glacially derived marine silt and clay to coarse glacial ice-contact moraines and tills. Four major sedimentary units crop out on the continental End_Page 446------------------------------ shelf. These units, defined on the basis of seismic reflection and sedimentologic data, are (1) Holocene glacial-marine sediments, (2) Holocene end morainal deposits, (3) Holocene (neoglacial) and Pleistocene glacial sediments, and (4) Pleistocene and older lithified sedimentary rocks. Each of these four units is divisible into facies on the basis of depositional environment. Each of the units was derived either totally or in part as a result of glaciation, hence each unit is a chronofacies or lithofacies of the overall glacial and glacial-marine depositional picture of the northeast Gulf of Alaska during the Quaternary. The Holocene glacial-marine sedimentary unit contains sediment originally glacially eroded and transported that was (and is) deposited in the marine environment through glacial-fluvial, eolian, or ice-transported mechanisms. Facies in this unit vary from unimodal clayey silt to bimodal pebbly silt and clay with large percentages of ice-rafted components. The end moraine unit, which contains deposits representing the farthest penetration onto the shelf of fiord-filling piedmont and valley glaciers, contains facies ranging from massive boulder and cobble accumulations to fine-grained silt and clay that accumulated in basins within the lobes of the moraine. The Holocene (neoglacial) and Pleistocene sedimentary unit is the most variable of the four units as it contains sediment ranging fr m multi-modal ablation and lodgment tills, to recessional glacial-lacustrine and outwash facies, to marine pebbly mud. Post-depositional winnowing has further modified the textural and compositional nature of this unit. The lithified sedimentary rock unit, typified by submarine outcrops of the Yakataga Formation, contains components of each of the three other units. The lithified unit, however, represents glacial and glacial marine events predating Holocene time. Stratigraphic and paleontological evidence suggests that the depositional environments producing the facies present in the Quaternary sedimentary units have changed little since middle Miocene time, and the influence of glaciation has been the primary controlling factor in the shaping of upper Tertiary and Quaternary depositional sequences. End_of_Article - Last_Page 447------------

Drainage Density, Length Ratios, and Lithology in a Glaciated Area of Southern Connecticut

Twenty-five third order basins in the Mount Carmel quadrangle, Connecticut, were analyzed morphometrically with emphasis on drainage density and length ratios. Drainage density and maximum summit altitude are adjusted to lithology, indicating that the landscape is in dynamic equilibrium, despite the influence of glaciation and possible past erosion cycles. Total length ratio correlates with lithology, but mean length ratio does not. The latter is a function of the bifurcation ratio, and hence has an important environmentally independent stochastic component.