Age and significance of fossil white spruce (Picea glauca), Tunica Hills, Louisiana-Mississippi

Radiocarbon dates indicate a Farmdalian through Woodfordian age for fossil white spruce (Picea glauca) in the Tunica Hills, a greater time span than previously documented. These dates, furthermore, require revision of the ages of fluvial terrace deposits in the region. Spruce-bearing Terrace 1 sediments, previously regarded as late Woodfordian to Holocene age, are of Farmdalian to late Holocene age. Terrace 2 sediments, previously assigned a Sangamonian or Farmdalian age, are of probable Altonian age. Plant fossils in Terrace 1 sediments represent two climatically and temporally distinct assemblages: a cool-temperate, Farmdalian-Woodfordian assemblage dominated by white spruce but including deciduous hardwoods suggestive of an oak-hickory association; and a warm-temperate Holocene assemblage composed of southern hardwoods and nonarboreal species representative of the modern flora of the Tunica Hills. Locally, fossils of white spruce have been reworked into younger Terrace 1 sediments containing the warm-temperate plant assemblage. The transition from the cool-temperate flora to the modern warm-temperate flora in the Tunica Hills probably occurred around 12,000 yr B.P.     

Late glacial and holocene 10Be production rates for western Norway

We present a new regional calibration of the ¹⁰Be production rate from two well‐dated surfaces in southern Norway: a rock avalanche with ¹⁴C‐dated wood and a precisely dated Younger Dryas moraine. Calculated ¹⁰Be production rates are 4.26 ± 0.13 and 4.65 ± 0.14 at g^?1 a^?1 for the Lal/Stone and Lifton scaling models, respectively. Our regional production rate for southern Norway is 5% lower than the canonical global ¹⁰Be production rate with lower uncertainties. Our ¹⁰Be production rate agrees with regional ¹⁰Be production rates from north‐eastern North America and New Zealand. The ¹⁰Be production rate estimate presented here can be used to improve the precision and accuracy of exposure‐dated ice‐marginal features, as well as other surfaces, in northern Europe. Copyright © 2011 John Wiley & Sons, Ltd.     

Late Wisconsin glacial advance and retreat patterns in southwestern Ohio, USA

Despite the application of radiocarbon dating for more than three decades along the southern margin of the Laurentide Ice Sheet, fundamental questions about the timing of glacial advances remain. For one of its sublobes, the Miami, we undertook areal mapping, detailed lithostratigraphic analysis, and radiocarbon dating to interpret four pulses of ice advance. On top of the undated sediments deposited during the first advance is a major unconformity. The second advance occurred about 20,000 BP and marks the beginning of the late Wisconsin glaciation. A minor recession (more than 30 km) ensued, but plants did not reoccupy the landscape. A third advance of the ice margin produced a stone-rich lodgement till to within 20 km of the late Wisconsin maximum. The final ice motion only occurred in the northern part of the study area and may be of local extent. Large accumulations of supraglacial gravity flowtills and outwash mark the final ice-margin retreat. Of these. only the second advance is well dated. This study implies that the number of advances of the ice margin is fewer than previously suggested. Consequently we argue that several of the sublobes across the southern margin of the Laurentide Ice Sheet acted in unison for the interval of 22.000 to 18.000 BP implying ice-sheet external forcing.     

Late glacial and holocene lake level fluctuations in Lake Biel,western Switzerland

Cores and outcrops from the southern shore of Lake Biel were studied to reconstruct the nearshore environment of the lake between ca. 12000 and 5000 yr BP. Core correlations were established by lithostratigraphical and pollen analytical correlations. From the Allerød to the Preboreal time quiet hydrodynamic conditions favoured the deposition of lake marl in the littoral zone and peat on the shore. Between the Preboreal(?) and the Atlantic the littoral zone shows a higher hydrodynamic environment with allochthonous material, whereas peat and clay layers are recorded from the shore. During the Older Atlantic severe erosional episodes caused the erosion of Boreal, Preboreal and Younger Atlantic layers. The previously described long hiatus between the Allerød and the Boreal time can now be connected with these erosional episodes. From Younger Atlantic to Subboreal time the littoral zone displays quiet conditions again with sedimentation of lake marl. On the basis of these results a lake level curve for Lake Biel is proposed: high lake level stands can be traced during the Allerød, Boreal, Older Atlantic and Younger Atlantic biozones; low lake level stands are found during the Allerød, Younger Dryas, Preboreal and Older Atlantic biozones.     

Late Pleistocene and Holocene glacial history of James Ross Island, Antarctic Peninsula

Studies of Quaternary glacial stratigraphy and morphology around the Antarctic Peninsula have shown that James Ross Island in the western Weddell Sea probably has the best occurrences of stratigraphic sections with dateable material in the region. The stratigraphy includes sections with indefinite radiocarbon age, and three separate aminozones can be recognized. Except for indications of an early deglaciation around c . 10,000 BP, the field evidence from northern James Ross Island suggests a glacial readvance around 7000 BP. It is concluded that the readvance reflects the combined effects of eustatic sea level rise and Holocene warming, leading to increased precipitation and a positive mass balance. The most recent large-scale deglaciation in the area took place around 6000–5000 BP. This confirms the evidence from lake sediments and moss banks in other parts of the Antarctic Peninsula region, which shows that, in most cases, the initiation of organic deposition took place after c . 6000 BP. The literature on the Holocene glacial and environmental history of the region is reviewed in light of the new field evidence.     

Late glacial and late Holocene moraines in the Cerros Cuchpanga, central Peru

Small ice fields on the western cordillera northeast of Lima were expanded to three times their present size in the recent past, and the regional snow line was probably about 100 m lower than it is today. Outwash from the expanded glaciers formed deltas of silt in valley-bottom lakes. When the ice lobes retreated, the reduced outwash was trapped behind recessional moraines, and the clear meltwater infiltrated into the limestone bedrock and emerged at the heads of the deltas in spring pools. The delta surfaces then became covered with peat, and radiocarbon dates for the base of the peat (1100 ± 70 and 430 ± 70 yr B.P. for two different deltas) indicate that the maximum ice advance was older than those dates and, thus, older than the Little Ice Age of many north-temperate regions. Much older moraines date from expansion of the same local summit glaciers to even lower levels in the main valleys, which had previously been inundated by the cordilleran ice field. The cordilleran deglaciation and this expansion of local glaciers probably occurred between 12,000 and 10,000 yr ago, on the basis of slightly contradictory radiocarbon dates.     

Sedimentology and history of a Late Wisconsinan glacial lake, Grande Prairie, Alberta, Canada

The Grande Prairie region of northwestern Alberta was partially covered by glacial Lake Peace, which was dammed against the retreating Laurentide ice sheet. Two levels of glacial Lake Peace are identified in the study are by closely spaced groups of strandlines and minor deltas lying at 805 to 840 m a. s. l., and 655 to 710 m a.s.l. Sedimentation associated with the upper of the two lake levels is marked by rhythmites of silt and clay deposited by turbid underflow, interbedded with diamicton deposited by debris flow. Dropstones and dump structures indicate common ice-rafting. Thick sequences are only found on the axes of major valleys, where sediment gravity flows were concertrated. Thin sequences of ice proximal glaciolacustrine sediments reflect topographic setting and do not indicate a short-lived lake. Retreat of the ice front resulted in a decrease in ice-rafted material and diamicton in sediments. The fall in lake level to the second stage resulted in deposition of sequences of vaguely laminated silt and clay close to the modern Beaverlodge River. These sediments were deposited by suspension settling from interflow or overflow of the Beaverlodge River as it entered the lake. Lake sedimentation was dominated by inflow from unglaciated areas, rather than the ice front.     

Late Pleistocene glacial chronology of the Taylor Valley,Antarctica, and the global climate

Carbonate-rich lacustrine and deltaic deposits, containing thin beds of finely laminated carbonates and thick beds of silt, crop out at several sites in the Taylor Valley and have been encountered in cores obtained by the Dry Valley Drilling Project (DVDP). Fragments of the more indurated carbonate beds have widespread occurrence as part of the desert “lag gravel” which covers much of the valley floor. Analysis of the carbonates suggests that they were deposited as algal limestones from waters derived from the East Antarctic Ice Sheet via the Taylor Glacier at times which correspond to the previous three global interglacial periods, as evidenced by the ice volumes deduced from oxygen-isotopic analysis of oceanic cores. The lacustrine carbonates have been found up to 30 km beyond the present terminus of the Taylor Glacier, and up to 100 m above the level of Lake Bonney, into which the Taylor Glacier at present discharges. It is concluded that the Taylor Glacier has advanced during each of the previous three interglaciations, and it is suggested that this has been caused by a thickening of the East Antarctic Ice Sheet during the interglaciations.     

Late quaternary glacial and vegetation changes,Little Cottonwood Canyon area,Wasatch mountains,Utah

Glacial geology and ¹⁴C dating in the central Wasatch Mountains indicate: an early canyon-mouth glaciation (Dry Creek till), probably during isotope stage 6; on that till, a paleosol (Majestic Canyon soil) dated at about 26,000 yr B.P.; overriding that soil, a later canyon-mouth glaciation (Bells Canyon till) probably beginning prior to about 19,000 yr B.P.; a midcanyon deglacial pause (Hogum Fork till) prior to 12,300 yr B.P.; an upper-canyon deglacial pause (Devils Castle till) prior to 7500 yr B.P.; and late Holocene periglaciation. Pollen ratios from bog profiles in the mid to upper reaches of the canyon suggest that temperatures cooler than the Holocene average occurred until after about 8000 yr B.P. Warmer and dryer than average conditions were initiated about 8000 to 7500 yr B.P. During the later portion of this Altithermal period conditions became relatively warm and wet. Two subsequent episodes of cooler than average temperatures correspond chronologically to the initial stades of Neoglaciation elsewhere in the Rocky Mountains. However, there is no geomorphic evidence of corresponding glacial activity in the canyon area. Relative moisture during these two periods differs significantly, suggesting that Neoglacial conditions were controlled primarily by changes in summer temperature.     

Late Quaternary glacial chronology on Nevado Illimani, Bolivia, and the implications for paleoclimatic reconstructions across the Andes

¹⁰Be terrestrial cosmogenic nuclide surface exposure ages from moraines on Nevado Illimani, Cordillera Real, Bolivia suggest that glaciers retreated from moraines during the periods 15.5-13.0 ka, 10.0-8.5 ka, and 3.5-2.0 ka. Late glacial moraines at Illimani are associated with an ELA depression of 400-600 m, which is consistent with other local reconstructions of late glacial ELAs in the Eastern Cordillera of the central Andes. A comparison of late glacial ELAs between the Eastern Cordillera and Western Cordillera indicates a marked change toward flattening of the east-to-west regional ELA gradient. This flattening is consistent with increased precipitation from the Pacific during the late glacial period.     

Late quaternary glacial stades in the Cordillera Central,Colombia, based on glacial geomorphology,tephra–soil stratigraphy,palynology, and radiocarbon dating

Using data from glacial geomorphology, tephra–soil stratigraphy and mineralogy, palynology, and radiocarbon dating, a sequence of glacial and bioclimatic stades and interstades has been identified for the last ca. 50000 yr in the Ruiz-Tolima massif, Cordillera Central, Colombia. Six Pleistocene cold stades separated by warmer interstades occurred: before 48000, between 48000 and 33000, between 28000 and 21000, from ≥16000 to ca. 14000, ca. 13000–12400, and ca. 11000–10000 yr BP. Although these radiocarbon ages are minimum-limiting ages obtained from tephra layers on top of tills, the tills are not significantly older because most are bracketed by dated tephra sets in measured stratigraphic sections. Two minor moraine stages likely reflect glacier standstill during cold intervals ca. 7400 yr BP and slightly earlier. Finally, glaciers readvanced between the seventeenth and nineteenth centuries. In contrast to the ice-clad volcanoes of the massif, ca. 34 km² in area above an altitude of ca. 4800 m, the ice cover expanded to 1200 km² during the Last Glacial Maximum (LGM) and was still 800 km² during Late-glacial time (LGT). Glacier reconstructions based on the moraines suggest depression of the equilibrium line altitude (ELA) by ca. 1100 m during the LGM and 500–600 m during LGT relative to the modern ELA, which lies at ca. 5100 m in the Cordillera Central. Glaciers in this region apparently reached their greatest extent when the climate was cold and wet, e.g. during stades corresponding to Oxygen Isotope Stage 3; glaciers were still expanding during the LGM ca. 28000–21000 yr BP, but they shrank considerably after 21000 yr BP because of greatly reduced precipitation. © 1997 John Wiley & Sons, Ltd.     

The Holocene vegetation history of the Khibiny Mountains: implications for the post‐glacial expansion of spruce and alder on the Kola Peninsula,northwestern Russia

Pollen and peat botanical investigations of the Lutnermayok peat bog, Kola Peninsula, northwestern Russia, were carried out, and 21 surface pollen samples were studied. Combined with previous studies our data form the basis for the vegetation history over the last 7000 yr of the Khibiny Mountains. Pinus sylvestris was the dominant species between 7000 and 5000 yr BP and Picea obovata penetrated to the Khibiny Mountains ca. 5500/5300 yr BP. Since 4500 yr BP, Picea replaced Pinus in major parts of the area and dominated the forest cover. Picea immigrated to the Kola Peninsula after 7000 yr BP. There were two paths of spruce migration: from the southeast and the southwest. Grey alder, Alnusincana, immigrated to the Kola Peninsula from the southwest and northwest about ca. 8000 yr BP. Grey alder has been restricted to its modern range since 4000 yr BP. The range of vertical movement of the treeline in Khibiny Mountains during the last 700 yr was 240–260 m, which corresponds to an amplitude of summer temperature change of 2°C. Copyright © 1999 John Wiley & Sons, Ltd.     

Late glacial and postglacial pollen and plant macrofossils from Lake West Okoboji, Northwestern Iowa

Pollen and plant macrofossils preserved in lake sediment from Lake West Okoboji, Dickinson County, Iowa, indicate how the vegetation of that area changed during the late glacial and postglacial. A closed coniferous forest, dominated by spruce and larch trees, produced the Picea-Larix pollen assemblage zone. Fir trees were a minor constituent of this forest; pine trees were probably absent. Black ash trees increased in abundance at Lake West Okoboji and by 13,500 yr ago were an important constituent of the forest. The sediment accumulation rate and the pollen influx were low throughout this time. Birch and alder pollen peaked in abundance approximately 11,800 yr ago. Pollen influx increased rapidly as birch and alder replaced coniferous trees on the uplands. A deciduous forest, containing abundant oak and elm trees, replaced the birch-alder-coniferous forest. This forest inhabited northwestern Iowa from approximately 11,000 to 9000 yr B.P. Nonarboreal species became prevalent between approximately 9000 and 7700 yr B.P. as prairie began to replace deciduous forest on the uplands. Charred remains of Amorpha canescens and other upland species attest to the presence of prairie fires as an aid in establishing prairie and destroying the forest. The pollen influx declined. The warmest, driest part of the postglacial occurred in northwestern Iowa from approximately 7700 to 3200 yr ago. Lake level fell 9 to 10 m, and prairie extended to the edge of the lake. Wet-ground weeds inhabited areas near lake level which were alternately flooded, then dry. Pollen influx was approximately 100 grains/cm²/yr during the driest time in this dry interval.Deciduous trees, particularly oaks, returned after approximately 3200 yr B.P. Prairie continued to occupy the uplands but trees were more common in the lowlying wet areas. Settlement by Europeans in northwestern Iowa about 1865 is marked by an increase in weed pollen. Macrofossil deposition changed in 1910 in response to the stabilization of lake level.     

Polymetallic sulfide ores hosted in Late Permian carbonate at the Alanish locality,northern Iraq: petrography and mineral chemistry

Polymetallic sulfide ores (Zn, Pb, Fe, Cu, Ag, and Cd) found in the Alanish locality of northern Iraq are hosted by dolostone in the Late Permian Chia Zairi Formation. The Alanish locality is one of several Zn–Pb deposits that are widespread in northern Iraq, situated along the northern passive margin of the Arabian plate. This paper describes the ore deposit classification, mineral chemistry, and paragenetic sequence of the area and proposes an ore formation model. We report the presence of acanthite and greenockite for the first time in Iraq. A brine solution derived from the sedimentary basin formed the primary sulfide ore minerals (sphalerite, galena, acanthite, pyrite, chalcopyrite, greenockite, and marcasite). The pre-tectonic mineralization is characterized by replacement textures including (1) high-Fe, low-Zn, dark-colored, coarse-grained sphalerite; (2) deformed anisotropic coarse-grained galena; and, (3) idiomorphic cubes of crushed pyrite. Conversely, the post-tectonic mineralization is characterized by open-space filling textures, including (1) low-Fe, high-Zn, light-colored, fine aggregated sphalerite; (2) fine-grained galena; and, (3) the existence of acanthite and marcasite. Although galena is an Ag carrier, both mineralization phases contained non-argentiferous galena. Non-sulfides (smithsonite, cerussite, and goethite) have replaced older sulfides in many areas due to supergene process. Gangue minerals present are dolomite, calcite, barite, and siderite. Open spaces and cavity filling of small paleo-karsts, replacement, veins, and veinlets are common features of the ore body. Metals were sourced from brines generated in the sedimentary basin, whereas sulfur was derived from nearby evaporates. Sediment compaction and tectonic activity, probably during Late Cretaceous, were the driving forces that squeezed and moved ore-bearing fluids derived from the sedimentary basin. Multiple stages of ore-bearing fluids were epigenetically intruded into the Late Paleozoic dolostone, forming an epigenetic strata-bound Mississippi Valley-type deposit precipitated under a temperature of 120 °C, as indicated by the cadmium fractionation in sphalerite and galena. Dolomitization and tectonic activity provided the necessary permeability for accumulating ores. The main ore body is directly connected to a fault plane and to adjacent dolostone that is frequently fractured and brecciated.     

The origin of glacial rafts: detachment, transport, deposition

Ruszczyńska-Szenajch, Hanna 1987 06 01: The origin of glacial rafts: detachment, transport, deposition. Boreas , Vol. 16, pp. 101–112. Oslo. ISSN 0300–9483.
Characteristics of the processes of detachment and transport of glacial rafts and some aspects of the process of raft deposition are considered for two main genetic groups: (1) glaciotectonic rafts, detached and transported by pure mechanical, i.e. tectonic, action of glacial ice (subdivided into (a) squeezed or pressed-out, (b) dragged, and (c) pushed rafts) and (2) glacio-erosional rafts, detached by freezing-on, transported within the ice, and deposited mostly by a melting-out process. A third group of rafts, of composite origin, is also briefly discussed and exemplified. Attention is drawn to the fact that quite a number of glacial rafts are known by other names, e.g. some of the very large ones, simply representing squeezed-up ('ice thrust') end moraines, or very minute rafts occurring within tills and often called 'soft clasts', 'substratum lenses', etc.     

Late Quaternary mollusks from glacial Lake Algonquin,Nipissing, and transitional sediments from southwestern Ontario,Canada

Mollusks were studied from six sites in Lake Algonquin deposits (12,000-10,000 yr B.P.), five transitional (Lake Stanley low stage; 10,000 – 6000 yr B.P.), and six Nipissing stage sites (6000-4000 yr B.P.) east of Lake Huron in southwestern Ontario. The sites represent a variety of near-shore, lagoonal, estuarine, and fluvial environments. Eighteen species were limited to occurrences in Algonquin stage deposits; 8 were found only in the transitional age sites; and 14 species were restricted to Nipissing stage localities. With the possible exception of Goniobasis livescens, which occurred at five of the six Nipissing stage sites, the remaining stratigraphically limited species were usually restricted to one or two localities and probably cannot be used as zone fossils. Some cold-tolerant species (e.g., Anodonta grandis simpsoniana) were very early migrants into the study area, while others arrived later, apparently from eastern, southern, and western sources. Mollusks proved useful in paleoenvironmental reconstructions and to a lesser extent in biostratigraphic zonation.