Embed Size (px)
Citation preview
Abstracts / Quaternary International 279-280 (2012) 346–461 381
the ephemeral Rio San Pedro valley North of San Pedro de Atacama andhalite caves and their deposits in the nearby Cordillera de la Sal allowedreconstructing the pluviometric and hydrometric regime in past periodsadding new data to the increasing palaeoclimate record of the region.River terrace fill and locally their loess cover were dated by OSL, allowingto estimate the time of increased discharge of the river, whose head rea-ches the Pacific – Atlantic watershed and receives moisture from theAmazon basin through trade wind. These landforms are locally uplifted byanticline activity, forming a flight of five orders of terraces. The sedimentvolume of each terrace fill was roughly turned into a gross estimate of theannual river discharge, providing a maximum around 50 ky. This recordallows us to correlate fairly well the high discharge periods with the wetperiods registered in other climate proxies in the same area.The radiocarbon dating of cave deposits documents a Middle Holocene agefor speleogenesis in the Cordillera de la Sal, basically formed after an earlyHolocene hyperarid period. Some debris flow infillings in the caves weredated and provide a record for extreme events in the area. In theassumption that the debris flow was triggered, in a threshold-like mech-anism, by intense rainfall events, the frequency of the extreme precipita-tion values in the last 4 ky has been estimated.
THE DEGLACIAL TO POSTGLACIAL ENVIRONMENTS OF CENTRAL PARRYCHANNEL, CANADIAN ARCTIC ARCHIPELAGO
Anna J. Pienkowski. University of Alberta, CanadaE-mail address: [email protected]
The wealth of our knowledge of late Quaternary environments in theCanadian Arctic Archipelago (CAA) has been terrestrially based, althoughthis area is characterized by extensive inter-island marine channels. Herewe present three long marine cores from central Parry Channel extendingto the last glaciation (Lancaster Sound/Barrow Strait: core 86027-154;southeastern Barrow Strait: 86027-144; western Barrow Strait: 97022-04),investigated for sedimentological characteristics, dinocysts, non-pollenpalynomorphs, foraminifera, and stable isotope ratios. Our data suggestgrounded glacial ice in Barrow Strait, followed by rapid deglaciation, witha progression from ice-proximal to ice-distal conditions interrupted by aninterval of pervasive landfast sea-ice. The timing of deglaciation is difficultto determine due to the absence of dateable materials at the diamict/glaciomarine transition. Moreover, the Portlandia Effect, the appropriate Rvalue for calibration, and potential deglacial deep-water effects on R mustbe incorporated into the chronologies. Age model extrapolations suggestdeglaciation at w10.3 cal ka BP in central Parry Channel. Noticeable bio-logical activity commences in the early Holocene, a prominent signal ofplanktonic foraminifera being recorded at w9.7-9.2 cal ka BP. This marksthe penetration of deeper Atlantic waters into the archipelago followingdeglaciation, likely facilitated by higher sea-levels permitting increasedflow across inter-channel sills. Postglacial amelioration (open-waterseason greater than present) is subsequently recorded at w9-7.7 cal ka BP,corresponding to a possible regional “Holocene Thermal Optimum”. Theexclusion of deep Atlantic water due to glacioisostatic shallowing, coupledwith a generally cooling climate, eventually leads to increased sea-ice andmodern microfossil assemblages, with analogous conditions commencingat w6 cal ka BP.
NEW GIS AND ITERATED PHASE MODEL OF THE SAALIAN GLACIATIONIN THE NETHERLANDS AND NW-GERMANY
Harm Jan Pierik. Utrecht University – Earth Sciences graduate school,NetherlandsE-mail address: [email protected]
Some 170,000-150,000 years ago (during MIS 6), large ice masses lastcovered the Netherlands and NW Germany (Saalian Drenthe Substage).This left many geomorphological features in the landscape. Throughoutthe 20th century extensive research has revealed the geomorphologicalassemblage of ice-pushed ridges, sandurs and glacial basins and dissectiveice-marginal and deglacation river systems. From the assemblage,sequences of glacial events, known as glaciation phase models have beenconstructed. The successive competing phase models of the 1960ies to the
1990ies each appear biased to specific features, subregions and types-of-data. New data exists and additional insights have risen since these formerphase models became established. In this research the sequence of eventswas newly reconstructed, aiming to unify the evidence in NW Germanywith that in the Netherlands. In a GIS of dedicated design, we collectedgeological-geomorphological evidence from literature and (re)mappedfeatures using new high-resolution elevation data. Importantly, we includesubglacial, ice-marginal, proglacial-drainage and deglaciation drainagefeatures. The GIS was used to store and review existing phase models, andto iterate to an updated phase model across in the entire 300�200 sq. kmof study area. Many elements of 'classic' phase models are retained andexpanded, but inconsistent elements are dropped and new lines ofexplanatory reasoning replace them. We now recognise 3 phases towardsmaximum ice-sheet extent (Drenthe advance), 1 tipping-point phase(Hondsrug ice stream) and 2 deglaciation phases (ending at the Warthereadvance). Improved structuring of observational data and, through GIS-design, forcing oneself to produce continuous maps without gaps for eachsuccessive phase, greatly facilitates the construction of self-consistentphase models. The GIS and new-iterated phase model provides valuableinput to subregional studies on past ice/bed interaction and present geo-hydrology.
MESOLITHIC LANDSCAPE AND VEGETATION DEVELOPMENT IN THEPRESENT DAY IJSSEL VALLEY, THE NETHERLANDS
Harm Jan Pierik. Utrecht University – Earth Sciences graduate school,NetherlandsE-mail address: [email protected]
During the Mesolithic period (10-6 14C ka BP w Early Holocene, first partof the Middle Holocene) hunter-gatherer groups lived in the region ofDeventer-Zutphen in the east-central Netherlands. Geomorphologicalconditions remained largely constant during this period. Major palae-oenvironmental developments occurred, that were driven by changes ingroundwater level and vegetation succession. Most likely, these changesaffected the behavioral choices, land usage and external living conditionsof Mesolithic people. This poster offers a palaeo-hydrological and palaeo-vegetational reconstruction of the Deventer-Zutphen area for the Meso-lithic period. The reconstruction was based on knowledge from pollendiagrams and current groundwater class, soil and geomorphologicalmaps. Due to the uncertainties involved in the groundwater levelreconstruction, several scenarios are outlined for the palaeo-hydrologicaldevelopment of the region. In most of the scenarios, succession causedthe vegetation to become very dense during the Mesolithic, witha subsequent rise in the groundwater level. These factors all had impli-cations for vegetation development, as well as the richness and diversityof food resources and accessibility of the area. It is possible that theamount of resources decreased and the landscape became more chal-lenging to cross for Mesolithic hunter-gatherers. The preferred scenario,together with other scenarios, will serve as input for studies of behavioralchoices and land use, which are intended to improve understandings ofthe relationship between palaeo-landscape and the archaeologicalrecord.
EROSION RATES OF ROCK SURFACES ASSOCIATED WITH ABORIGINALROCK ART, BURRUP PENINSULA, WESTERN AUSTRALIA
Brad Pillans. Australian National University, AustraliaE-mail address: [email protected]
The Burrup Peninsula and surrounding Dampier Archipelago, near Karra-tha, Western Australia, contain the world's largest known gallery of rockart engravings (petroglyphs), estimated to number up to 1 million images.The peninsula is also the site of major industrial development, associatedwith the port ofDampier, and there are concerns that industrial emissionsmay adversely affect the stability and longevity of the rock art. The rockson which the petroglyphs occur are dominantly granophyre and gabbro ofArchean age, characterised by surface weathering rinds up to 1 cm thick.The petroglyphs were carved into the weathering rinds by pecking,scratching, rubbing and pounding using a variety of stone tools. Rock
Abstracts / Quaternary International 279-280 (2012) 346–461382
surfaces are coated by a thin (less than 1 mm), dark coloured, discontin-uous veneer of rock varnish, principally composed of oxides of Fe, Mn, Si, Aland P. The dark coloured rock varnish contrasts with the generally palercolour of the weathered rock exposed in the petroglyphs, enhancing thevisual impact of the rock art. Field observations suggest that the rockvarnish may no longer be forming and that it predates most of thepetroglyphs. We have studied the processes and rates of weathering anderosion, including the effects of fire, that affect the stability of rock surfacesand hence the longevity of the rock art, using cosmogenic nuclides. Theconcentration of 10Be in quartz yields erosion rates ofw0.2mm/1000 yearson horizontal rock surfaces and w1 mm/1000 years on vertical rock faces.The former, largely caused by mm-scale surface flaking, are amongst thelowest erosion rates measured by cosmogenic nuclides anywhere in theworld. The latter are inferred to represent a combination of mm-scaleflaking and very rare centimetre- to metre-scale block falls, controlled byfailure along joint planes. Such low erosion rates result from a combinationof resistant rocks, low relief and low rainfall, favouring long-term preser-vation of the petroglyphs.
FROM THE EEMIAN TO THE LAST LATE GLACIAL: A CONTINUOUS LAKERECORD FROM N-ITALY
Roberta Pini. CNR - IDPA, ItalyE-mail address: [email protected]
Hosted in a wide depression within the Berici Hills (Venetian Prealps),outside the maximum extent reached by LGM glaciers, Lake Fimonpreserves an almost continuous archive of landscape and climate changesfrom the penultimate glacial maximum onwards. The stratigraphicsuccession deposited at the lake bottom has been investigated in threedeep cores by means of pollen analysis, sand petrography, magneticsusceptibility, LOI, and geochronology. Tephra layers have been identifiedand are currently under study.Pollen data provide the first continuous vegetation record in northern Italyfor the last 150 ky. Terrestrial vegetation varied from interglacial warm-temperate broad leafed to oceanic mixed forests, from boreal coniferforests to open forest-steppes of colder climate. Phases of major forestexpansion and reduction have been correlated to isotopic events describedin ice (NGRIP), stalagmite (Antro del Corchia) and marine records. Persis-tent afforestation recorded in northern Italy even during cold phases of thefull pleniglacial is consistent with mesoscale paleoclimate simulationssuggesting that a sharp rainfall gradient across the Alps enabled thesurvival of woody species in the southern alpine foreland.Integrating litho- and biostratigraphical data, we identified sedimentationregìmes, accumulation rates, sediment sources and supply both for the LakeFimon cores and the adjacent Venetian Plain, allowing a direct comparisonwith major glacial advances in the Alpine area, deglaciation pulses, andglacio-eustatic displacements of the northern Adriatic shoreline.
GROUNDWATER FLOW UNDER PAST ICE SHEETS: INFERENCES FROMNUMERICAL MODELLING AND GEOLOGICAL RECORD
Jan Piotrowski. University of Aarhus, University of Sheffield, DenmarkE-mail address: [email protected]
During the Quaternary glacial/interglacial cycles in areas affected bywaxing and waning ice sheets the upper lithosphere experienced repeatedand profound re-organization of groundwater flow systems. Relativelysmall, topographically controlled groundwater catchments typical for theinterglacials changed to continental-scale groundwater flow systemscontrolled by ice sheet configuration and thickness. Under the ice sheets,pressurized groundwater circulated deeper and faster than in non-glacialtimes. In several major sedimentary basins the groundwater flow directionreversed in glacial/interglacial cycles. Glacially-fed groundwater can stillbe found in deep aquitards hundreds of kilometres away from modern icemargins. Subglacial groundwater flow had a profound influence on icesheet behaviour and the formation of specific glacial landforms. Typically,only a fraction of meltwater generated at the ice/bed interface or enteringthe subglacial system from the ice surface could have been evacuated fromthe ice sole as groundwater flow. The rest was drained through subglacial
channels that acted as discharge conduits for groundwater in the subgla-cial aquifers. In areas of low hydraulic permeability of the bed basalde-coupling by pressurized water was likely, which could have led to de-stabilizing the ice sheet. Using examples from different areas of theScandinavian Ice Sheet we can demonstrate how past glaciers interactedwith and were influenced by the subglacial hydrogeology in a complexsystem of feedback loops affecting the processes of glacial landformgeneration, sediment transfer, and ice flow mechanisms.
LATE HOLOCENE ALLUVIAL ARCHITECTURE OF PO AND ADIGE RIVERSREVEALED BY HIGH RESOLUTION STRATIGRAPHICAL ANDGEOMORPHOLOGICAL DATA
Silvia Piovan. Dept. of Geography - University, ItalyE-mail address: [email protected]
The sediments of Po and Adige rivers interfingered, during late Holocene,in the area behind the southern Venice lagoon. New high-resolutionsedimentological and geochronological data from cross sections allow thedefinition of an architectural model of the alluvial plain after the sedi-mentary hiatus recorded across the entire Venetian–Friulian Plain,between 14.5 and 8.0 kyr BP. Alluvial plain aggradation started asa consequence of the post-glacial sea level rise: the result is a sequence ofsilty-clay and peats, characterized by the accumulation of a laterally-continuous peat bed (up to 1.5 m thick and dated 5595-5754 to 3158-3383cal BP in Santa Margherita cross-section) that interests the whole areabehind the coastline. After peat deposition, a phase of major aggradationoccurred in the area, which resulted in the formation of alluvial ridges byboth Po and Adige paleochannels, as seen in Santa Margherita and Con-selve cross-sections. Around 3000 BP the Po River northernmost branchwas no more active; aggradation continued until Roman times due tosedimentation by the Adige alluvial system. The Po and Adige sedimentsupply, unbalanced by sea-level rise, seems to have caused the pro-gradation of a delta system in the southern Venice lagoon after 6 kyr BP,which was documented by Zecchin et al. (2009).Geomorphological evidences from high-resolution digital terrain modeland remote sensing, coupled with stratigraphic data, show prominent Poand Adige palaeochannels which run behind the southern Venice Lagoonand fed the growing delta.Thevertical aggradation in thealluvialplainandtheprogradationof thedeltais synchronous todeforestation in the catchment, especially since theBronzeAge and during the Roman Age. This timing suggests a possible influence ofman-induced soil erosion on the increase of the rivers sedimentary load.
VEGETATION CONTROLS ON THE FIRE REGIME IN THE SOUTHERNYUKON TERRITORY, CANADA DURING THE PAST 1200 YEARS
Michael Pisaric. Carleton University, CanadaE-mail address: [email protected]
Resilience theory predicts that ecosystems will tend towards a state ofstability until interrupted by some form of disturbance. The disturbancecan trigger community change in the form of shifting composition orstructure in response to the altered environmental conditions. In theboreal forest of Canada themost frequent form of disturbance that can leadto these changing states is fire. In Yukon Territory, Canada, the average areaburned is approximately 120,000 hectares per year. Here we present twomacroscopic charcoal records of fire history during the past 1200 yearsfrom compositionally and structurally different forest systems in thesouthern Yukon Territory. Buck Lake (60�180 1000N,134�460 1100W) is locatedin a lodgepole pine (Pinus contorta var. latifolia)-white spruce (Picea glauca)mixed forest and is characterized by a high frequency, low intensity fireregime. Dendrochronological studies in the region around Buck Lake havefound abundant fire-scarred lodgepole pine, with many trees havingmultiple fire scars. Burnt Bowl Pond (61�190 3500N,135�360 3400W) is locatedabout 120 km to the north in a white spruce dominated forest. Few fire-scarred trees have been located in the region around Burnt Bowl Pondowing to the lower frequency, more intense fires that characterize theregion. Macroscopic charcoal analysis indicates that 11 fires have occurredat Burnt Bowl pond during the past 1200 years while 21 fire events were
