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103-700: The culture is named after a tunnel valley near the village of Ahrensburg , 25 km (16 mi) northeast of Hamburg in the German state of Schleswig-Holstein , where Ahrensburg find layers were excavated in Meiendorf , Stellmoor and Borneck . While these as well as the majority of other find sites date to the Young Dryas, the Ahrensburgian find layer in Alt Duvenstedt has been dated to

206-453: A clay pit near Allerød Municipality on Zealand island and later in the drained peat deposits at Bølling Lake in Jutland peninsula (both parts of Denmark ). This provided proxy evidence for consistent warming at these sites during the last glacial period, because the temperatures were warm enough to support these trees. In contrast, the rest of the glacial period was so cold that

309-525: A recessional moraine . Tunnel valleys from successive glaciations may crosscut one another. Tunnel valleys frequently run along roughly parallel courses. They originate in and run through regions which include clear evidence of glacial erosion through abrasion and may exhibit striations and roche moutonnée . Depositional forms such as terminal moraines and outwash fans are found at their terminal end. In Michigan tunnel valley channels have been observed to diverge slightly with an average spacing between

412-653: A burial pit are present. In central Alaska up the northern foothills at the Dry Creek site c. 13,500-13,000 years ago near Nenana Valley , small bifacial points were found. People were thought to have moved into this area to hunt elk and sheep on a seasonal basis. Microblade sites typologically similar to Dyuktai appear about 13,000 years ago in central Kamchatka and throughout many parts of Alaska. The European distribution of Y-chromosome haplogroup I and various associated subclades has also been explained as resulting from male postglacial recolonization of Europe from refugia in

515-428: A channel and sustaining the discharge. Hence, combining this data and analysis with Icelandic jökulhlaup observations, there is experimental evidence that some form of the jökulhlaup hypothesis with features of the steady state model is correct. Subglacial meltwater flow is common to all theories; hence a key to understanding channel formation is an understanding of subglacial meltwater flow. Meltwater may be produced on

618-581: A comparatively warm period in Northern Europe. It is also referred to as Interstadial 1 or Dansgaard–Oeschger event 1. This interstadial followed the Oldest Dryas period, which lasted from ~18,000 to 14,700 BP. While Oldest Dryas was still significantly colder than the current epoch, the Holocene , globally it was a period of warming from the very cold Last Glacial Maximum , caused by

721-528: A dry plain between Chukotka and western Alaska . Clear skies reduced precipitation, and loess deposition promoted well-drained, nutrient-rich soils that supported diverse steppic plant communities and herds of large grazing mammals. The wet tundra soils and spruce bogs that exist today were absent. Cold temperatures and massive ice sheets covered most of Canada and the northwest coast, thus preventing human colonization of North America prior to 16,000 years ago. An "ice-free corridor" through western Canada to

824-420: A function of the glacial recession. The filled configuration is significant because filled tunnel valleys become excellent reservoirs for either water (aquifer) or for oil. This results since relatively coarse-grained sandstones are located on the valley floors and valley margins and valley floor because the coarser-grained sediments settle out more easily and accumulate preferentially in the flowing water common to

927-686: A gradual increase in CO 2 concentrations. A warming of around 2 °C (3.6 °F) had occurred during this period, nearly of half of which had taken place during its last couple of centuries. In contrast, the entire Bølling–Allerød Interstadial experienced very little change in global temperature. Instead, the rapid warming was limited to the Northern Hemisphere, while the Southern Hemipshere had experienced equivalent cooling. This "polar seesaw " pattern had occurred due to

1030-443: A more mobile lifestyle by the absence of mammoth-bone houses and storage pits, all indicators of long-term settlement. Visual art was uncommon. Fauna remained red deer, reindeer, and moose and indicate a mainly meat-oriented diet. The habitat of Siberia was far harsher than anywhere else and often did not provide enough survival opportunities for its human inhabitants. That is what forced human groups to remain dispersed and mobile, as

1133-403: A period of less than a year. As the flow subsided, the weight of ice closed the tunnel and sealed the lake again. The water flow was modeled satisfactorily with channeling in ice and in sediment. The analytic model shows that over some regions, the ice-bedrock geometry included sections which would have frozen, blocking off flow, unless erosion of the sedimentary substrate was the means of creating

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1236-601: A result, the ice-flow patterns and the debris accumulation are different in interlobate zones. Specifically, tunnel valleys and eskers indicate water flow toward the interlobate zones, which are elevated as the result of debris carried and deposited there. Glacially formed tunnel valleys have been identified on every continent. Tunnel valleys associated with the Late Ordovician glaciation have been observed in north African countries, including Libya . These large-scale channel-fill sandstone bodies (tunnel valleys) are

1339-509: A striking sedimentological feature of the glacially related deposits on the old North Gondwanaland margin. They range from 10–200 m (33–656 ft) in depth, and 500–3,000 m (1,600–9,800 ft) wide. The tunnel valleys are incised into the bedrock and can be traced for 2–30 km (1.2–18.6 mi) in length. In one example, in Mauritania , in the western Sahara , Late Ordovician siliciclastic glacial features and deposits on

1442-486: A subglacial lake. The hydraulic head of the water collected in a basal lake will increase as water drains through the ice until the pressure grows high enough to either develop a path through the ice or to float the ice above it. Sources of water and water drainage routes through and below temperate and sub-polar glaciers are reasonably well understood and provide a basis for understanding tunnel valleys. For these glaciers, supraglacial water ponds or moves in rivers across

1545-823: A surface area of 351 km (136 sq mi). Northern Idaho and Montana show evidence of tunnel valley formation under the Purcell lobe and the Flathead Lobe of the Cordilleran Ice Sheet. Tunnel valleys in southeast Alberta form an interconnected, anabranching network comprising Sage Creek, the Lost River and the Milk River and generally drain southeast. Tunnel valleys have been observed in Minnesota , Wisconsin and Michigan at

1648-505: A tradition persisting from preceding Upper Paleolithic archaeological horizons. Fur-bearing small mammal remains abound such as Arctic fox and paw bones of hares , reflecting pelt removal. Large and diverse inventories of bone, antler , and ivory implements are common, and ornamentation and art are associated with all major industries. Insights into the technology of the time can also be seen in features such as structures, pits, and hearths mapped on open-air occupation areas scattered across

1751-826: A tunnel valley may go uphill: water can flow uphill if it is under pressure in an enclosed pipe: for example in Doggerland (submerged land which is now part of the bed of the North Sea ) are some infilled tunnel valleys that flowed from north to south across the hollow of the Outer Silver Pit . They vary in channel depth and width; Danish examples run from 0.5–4 km (0.31–2.49 mi) wide and from 50–350 m (160–1,150 ft) deep. They vary in depth along their course, exhibiting overdeepening ; overdeepened sections cut into bedrock and typically are significantly deeper than either upstream or downstream sections of

1854-661: Is an indicator of the presence of oil in these areas. Tunnel valleys represent a substantial fraction of all meltwater drainage from glaciers. Meltwater drainage influences the flow of glacial ice, which is important in understanding of the duration of glacial–interglacial periods, and aids in identifying glacial cyclicity, a problem that is important to palaeoenvironmental investigations. Tunnel valleys are typically eroded into bedrock and filled with glacial debris of varying sizes. This configuration makes them excellent at capturing and storing water. Hence they serve an important role as aquifers across much of Northern Europe, Canada and

1957-691: Is commonly accepted that the Hamburgian , featured by "Shouldered Point" lithics, is a techno-complex closely related to the Creswellian and rooted in the Magdalenian . Within the Hamburgian techno-complex, a younger dating is found for the Havelte phase, sometimes interpreted as a northwestern phenomenon, perhaps oriented towards the former coastline. The Hamburgian culture existed during

2060-474: Is commonly divided into three stages. The initial Bølling stage had the largest hemispheric temperature change, and it is also the stage when Meltwater Pulse 1A had occurred. The beginning of the Bølling is also end of the Oldest Dryas at approximately 14,600 years BP . The Oxygen isotope record from Greenland ice indicates that the Bølling stage lasted approximately 600 years. It was then interrupted by

2163-682: Is considered to prelude the techno-complex of the Ahrensburg culture and would point to the provenience of Ahrensburg from Bromme culture. As such, the Grensk culture in Bromme territory at the source of the Dnieper River was proposed to be the direct originator of Ahrensburgian culture. However, the exact typological chronology of this culture is still unclear. Though associated with the Bromme complex, Grensk culture has its roots more defined in

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2266-490: Is evidence of ice erosion such as linear striations in the bedrock, these are observed only in the widest valleys, and are believed to have played a secondary role. The subglacial layout of valley tunnels is predominantly oriented parallel to glacial ice flow lines – essentially they stretch from areas of thicker sheet ice toward areas of thinner sheet ice. They can exhibit reverse gradients, which result when pressurized meltwater flows over obstacles such as ridges or hills along

2369-695: Is located in Northern Germany and Poland to south Lithuania. Fish-hooks were discovered in Allerød layers and emphasize the importance of fishing in the Late Palaeolithic. A certain survival of late Upper Palaeolithic traditions similar to contemporary Azilian (France, Spain) becomes apparent, such as the amber elk from Weitsche that can be considered as a link to the Mesolithic, amber animal sculptures. Bromme culture sites are found in

2472-592: Is located in the southern Southern Patagonian Ice Field , terminating in Lake Argentino . It divides Lake Argentino into the Los Témpanos channel, and the Rico branch, blocking the channel and forming an ice dam. Lake Argentino periodically breaks through in outburst floods with drainage initially through a tunnel with subsequent roof collapse to form an open channel. There have been five known ice ages in

2575-402: Is lower in areas of thinner ice; hence subglacial water tends to converge on the interlobate joint. The separate lobes move at different speeds, generating friction at the ice boundary; the heat released melts ice to release additional water. The surface of the interlobate area is crevassed, allowing surface meltwater, which runs down the ice surface to the lower area, to penetrate into the ice. As

2678-416: Is reflected in the lithic technology, as tiny blades were typically manufactured, often termed microblades less than 8 mm wide with unusually sharp edges indicating frugality from low resource levels. They were fixed into grooves along one or both edges of a sharpened bone or antler point. Specimens of complete microblade-inset points have been recovered from both Kokorevo and Chernoozer'e. At Kokorevo, one

2781-569: The Great Barrier Reef , the Bølling–Allerød period is associated with a substantial accumulation of calcium carbonate , which is consistent with the modelled cooling of the region. A 2017 study attributed the second Weichselian Icelandic ice sheet collapse, onshore (est. net wastage 221 gigatons of ice per year over 750 years) and similar to today's Greenland rates of mass loss, to atmospheric Bølling–Allerød warming. The melting of

2884-514: The Gulf of Alaska show abrupt sea-surface warming of about 3 °C (in less than 90 years), matching ice-core records that register this transition as occurring within decades. Antarctic Intermediate Water (AAIW) cooled slightly during this interstadial. The Meltwater pulse 1A event coincides with or closely follows the abrupt onset of the Bølling–Allerød (BA), when global sea level rose about 16 m during this event at rates of 26–53 mm/yr. In

2987-718: The Late Paleozoic Pilbara ice sheet . Tunnel valleys and related glacial impacts have been identified in Russia, Belarus, Ukraine, Poland, Germany, Northern France, the Netherlands, Belgium, Great Britain, Finland, Sweden, Denmark and Norway. They have been studied in detail in Denmark, north Germany and north Poland where the thick ice sheet of the Weichsel and earlier Glaciations , having flowed down from

3090-624: The Magdalenian . As the Fennoscandian ice sheet continued to shrink, plants and people began to repopulate the freshly deglaciated areas of southern Scandinavia. Prey favored by European hunters included reindeer , wild boar , European fallow deer , red deer , and European wild ass . Periglacial loess - steppe environments prevailed across the East European Plain , but climates improved slightly during several brief interstadials and began to warm significantly after

3193-789: The Middle East , the pre-agricultural Natufian settled around the Eastern Mediterranean coast to exploit wild cereals, such as emmer and two-row barley . By the time of the Allerød, the Natufians may have started to domesticate grain, bake bread, and ferment alcohol. Over the land between the Lena Basin and northwest Canada , increased aridity occurred during the Last Glacial Maximum. Sea level fell to about 120 m below its present position, exposing

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3296-678: The Niagara Escarpment flowed through tunnel valleys beneath the ice expanded to form a west-to-east passage between the main Laurentide Ice Sheet and a mass of ice in the Lake Ontario basin. Cedar Creek Canyon is a tunnel valley located in Allen County, Indiana . It is a very straight, narrow gorge about 50 to 100 ft (15 to 30 m) deep that contains part of the lower segment of Cedar Creek ,

3399-507: The North European Plain c. 16,000-15,000 years ago. The environmental landscape became increasingly boreal , except in the far north, where conditions remained arctic . Sites of human occupation reappeared in northern France, Belgium, northwest Germany, and southern Britain between 15,500 and 14,000 years ago. Many of these sites are classified as Magdalenian . In Britain, the Creswellian culture developed as an offshoot of

3502-913: The Ruppiner See (a lake in Ostprignitz-Ruppin , Brandenburg ), the Werbellinsee , and the Schwielochsee , all in Germany. Okanagan Lake is a large, deep ribbon lake in the Okanagan Valley of British Columbia which formed in a tunnel valley from the Okanogan lobe of the Cordilleran Ice Sheet . The lake is 135 km (84 mi) long, between 4 and 5 km (2.5 and 3.1 mi) wide, and has

3605-562: The Younger Dryas , which was followed by the present warm Holocene . The interstadial stage abruptly with a decline in temperatures within a decade and the onset of the glacial Younger Dryas . Global temperatures declined only slightly during YD, and they had steadily climbed alongside the CO 2 concentrations once that period had transitioned to Holocene. There may have also been another brief cold stage during Allerød. In regions where

3708-936: The glacial ice near the margin of continental ice sheets such as that now covering Antarctica and formerly covering portions of all continents during past glacial ages . They can be as long as 100 km (62 mi), 4 km (2.5 mi) wide, and 400 m (1,300 ft) deep. Tunnel valleys were formed by subglacial erosion by water and served as subglacial drainage pathways carrying large volumes of meltwater. Their cross-sections often exhibit steep-sided flanks similar to fjord walls. They presently appear as dry valleys, lakes, seabed depressions, and as areas filled with sediment. If they are filled with sediment, their lower layers are filled primarily with glacial, glaciofluvial or glaciolacustrine sediment, supplemented by upper layers of temperate infill. They can be found in areas formerly covered by glacial ice sheets including Africa, Asia, North America, Europe, Australia and offshore in

3811-540: The Antarctic. Piotrowski's model predicts a cycle as follows: Tunnel valleys have similar characteristics, irrespective of whether they are formed on land or in a submerged environment. This is because they are formed by high pressure water under a thick ice sheet – in a submerged environment they still have sufficient pressure to erode tunnel valleys into configurations comparable to those generated on land. Tunnel valleys may remain open, partially filled or filled, as

3914-710: The Balkans, Iberia, and the Ukraine/Central Russian Plain. Males possessing haplogroup Q are postulated as representing a significant portion of the population who crossed Beringia and populated North America for the first time. The distribution of mtDNA haplogroup H has been postulated as representing the major female repopulating of Europe from the Franco-Cantabrian region after the Last Glacial Maximum. mtDNA haplogroups A, B, C, D and X are interpreted according to some as supporting

4017-663: The Earth's history; the Earth is experiencing the Quaternary Ice Age during the present time. Tunnel valleys formed during four of the five have been identified. Aller%C3%B8d Oscillation Dansgaard-Oeschger event 1 The Bølling–Allerød Interstadial ( Danish: [ˈpøle̝ŋ ˈæləˌʁœðˀ] ), also called the Late Glacial Interstadial (LGI), was an interstadial period which occurred from 14,690 to c. 12,890 years Before Present , during

4120-732: The East European Plain. Mammoths were typically hunted for fur , bone shelter, and bone fuel. In the southwest region around the middle Dnestr Valley, sites are dominated by reindeer and horse , accounting for 80 to 90% of the identifiable large mammal remains. Mammoth is less common, typically 15% or less, as the availability of wood eliminated the need for heavy consumption of bone fuel and collection of large bones for construction. Mammoth remains may have been collected for other raw material, namely ivory. Other large mammals in modest numbers include steppe bison and red deer . Plant foods more likely played an increasing role in

4223-608: The Hamburgian and the Brommean. This corresponds with the notion that "tanged point cultures" such as "Brommian" or " Bromme - Lyngby " appear to be based on the Magdalenian , during the Allerød and were closely associated with reindeer hunting. Stellmoor was a seasonal settlement inhabited primarily during October, and bones from 650 reindeer have been found there. The hunting tool was bow and arrow . From Stellmoor there are also well-preserved arrow shafts of pine intended for

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4326-688: The Last Glacial Maximum on the eastern edge of the Central Russian Upland , along the Don River . Epigravettian archaeological sites, similar to Eastern Gravettian sites, are common in the southwest, central, and southern regions of the East European Plain about 17,000 to 10,000 years BP and are also present in the Crimea and Northern Caucasus . The time of the Epigravettian also reveals evidence for tailored clothing production,

4429-491: The North Gondwana continental shelf include incised channels identified as tunnel valleys. The filled tunnel valley are several kilometers long and several hundred meters wide. Reconstructions conclude that these structures were located in glacier ice-margin regions; the cross-sections of the valleys are comparable to those confirmed to have formed glacially, the valleys end in outwash fans similar to tunnel valleys, and

4532-638: The North Sea, the Atlantic and in waters near Antarctica. Tunnel valleys appear in the technical literature under several terms, including tunnel channels, subglacial valleys, iceways , snake coils and linear incisions. Tunnel valleys play a role in identifying oil-rich areas in Arabia and North Africa. The Upper Ordovician –Lower Silurian materials there contain a roughly 20 m (66 ft) thick, carbon-rich layer of black shale. Approximately 30% of

4635-469: The Nye channel formation which has been observed in sediments, a weakness of the steady state theory is that it requires that tunnel valleys be excavated in unconsolidated sediment, in which meltwater is initially forced through an initially narrow subglacial conduit. With progressive sediment erosion by the meltwater, ice deforms under its own weight into the cavity to creating an ever-larger tunnel valley. However

4738-702: The Older Dryas is not detected in climatological evidence, the Bølling–Allerød is considered a single interstadial period. The strengthening of the Atlantic meridional overturning circulation is considered to be the primary cause for the Bølling–Allerød warming of the Northern Hemisphere, while its weakening is considered responsible for the inverse pattern during the Older and Younger Dryas. While CO 2 increase had also occurred during this interstadial, it

4841-602: The Pomeranian ice margin. The younger Havelte phase has been proven for the area beyond the Pomeranian ice margin and on the Danish Isles after c. 12,300 BCE. The "Backed Point" lithics of Federmesser culture are usually dated in the Allerød Interstadial. Early Federmesser finds follows shortly or are contemporary to Havelte. The culture lasted approximately 1200 years from 11,900 to 10,700 BCE., and

4944-674: The Southern Hemisphere, the weakened Southern Ocean overturning circulation caused the expansion of Antarctic Intermediate Water , which sequesters CO 2 less effectively than the Antarctic bottom water , and this was likely the main reason for the increase in CO 2 concentrations during the interstadial. The Bølling–Allerød was almost completely synchronous across the Northern Hemisphere . The climate began to improve rapidly throughout Western Europe and

5047-526: The Tanana Valley sites contain artifacts similar to the Siberian Dyuktai culture. At Swan Point, these comprise microblades, burins, and flakes struck from bifacial tools. Artifacts at the nearby site of Broken Mammoth are few, but include several rods of mammoth ivory. The diet was of large mammals and birds, as indicated by faunal remains. Earliest site occupation at Ushki sites of central Kamchatka (about 13,000 years ago) display evidence of small oval houses and bifacial points. Stone pendants, beads, and

5150-433: The United States. Examples include Oak Ridges Moraine Aquifer , Spokane Valley-Rathdrum Prairie Aquifer, Mahomet Aquifer , the Saginaw Lobe Aquifer, and the Corning Aquifer. Tunnel valleys have been observed as open valleys and as partially or totally buried valleys. If buried they may be partially or totally filled with glacial outwash or other debris. The valleys may be incised in bedrock, sand, silt, or clay. A part of

5253-585: The amounts of ice accumulated through precipitation and lost through ablation . The increased gradient increases the shear stress on a glacier until it begins to flow. The flow velocity and deformation are also affected by the slope of the ice, the ice thickness and temperature. Punkari identified that continental ice sheets typically flow in fan-shaped lobes, which converge from separate sources and move at differing speeds. Lobes are separated by interlobate zones, which have thinner ice coverage. Water collects in this interlobate area. The hydraulic head (pressure)

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5356-530: The annual production of water from one typical catchment of 642,000,000 m (2.27 × 10  cu ft) would normally drain through its associated tunnel valley in less than 48 hours. The debris found in tunnels and at the mouth of tunnels tends to be coarse rocks and boulders – this is indicative of high flow velocities and an extremely erosive environment. This erosive environment is consistent with creation of tunnels over 400 m (1,300 ft) deep and 2.5 km (1.6 mi) wide, as have been observed in

5459-411: The beginning of the Late Glacial Maximum. Pollen profiles for this time indicate a pine - birch woodland interspersed with the steppe in the deglaciated northern plain, birch-pine forest with some broadleaf trees in the central region, and steppe in the south. The pattern reflects the reemergence of a marked zonation of biomes with the decline of glacial conditions. Human site occupation density

5562-418: The beginning of the Meiendorf Interstadial around 12,700 BCE. Palynological results demonstrate a close connection between the prominent temperature rise at the beginning of the Interstadial and the expansion of the hunter-gatherers into the northern Lowlands. The existence of a primary “pioneer phase” in the re-colonisation is contradicted by proof of e.g. an early Central European Magdalenian in Poland. Today it

5665-438: The beginning of the Mesolithic, the discovery of deposited bones and new dating indicate that there was no (significant) break in settlement continuity. New knowledge provides aspects for a further autochthonous development, with a rapid climatic change stimulating a swift cultural change. Fertile Crescent : Europe : Africa : Siberia : Tunnel valley A tunnel valley is a U-shaped valley originally cut under

5768-633: The channels of 6 km (3.7 mi) and a standard deviation of 2.7 km (1.7 mi). Tunnel valley channels often start or stop abruptly. They have convex-up longitudinal profiles. They are often occupied by elongated lakes of underfit streams. They frequently show signs of subsequent depositions such as eskers. Evidence suggests that erosion in a tunnel valley is primarily the result of water flow. They erode by meltwater, which it has been argued, episodically drains in repeated jökulhlaups from subglacial lakes and reservoirs; examples of such motion have been observed in Antarctica . Although there

5871-481: The colder surface freshwater in the North Atlantic, generated ocean convective available potential energy (OCAPE) over decades at the end of HS1. According to fluid modelling, at one point the accumulation of OCAPE was released abruptly (c. 1 month) into kinetic energy of thermobaric cabbeling convection (TCC), resulting in the warmer salty waters getting to the surface and subsequently warming the sea surface by approximately 2 °C (3.6 °F). Records obtained from

5974-429: The culture's characteristic skaftunge arrowheads of flint . A number of intact reindeer skeletons, with arrowheads in the chest, has been found, and they were probably sacrifices to higher powers. At the settlements, archaeologists have found circles of stone, which probably were the foundations of hide teepees . The earliest reliable traces of habitation in the northern territories of Norway and western Sweden date to

6077-540: The deglaciation following the LGM, which has been hypothesised to be the result of sluggish meridional overturning circulation or due to a release of volcanic carbon or methane clathrates into abyssal waters. The Eastern Tropical Pacific Oxygen Minimum Zone (ETP-OMZ) witnessed high oxygen depletion during the early stages of the deglaciation following the LGM, most likely as a result of a weakened Atlantic meridional overturning circulation (AMOC) and an increased influx of nutrient-rich waters due to intensified upwelling. In

6180-538: The dominant plant in the area was a small, cold-adapted flower called Dryas octopetala . Thus, the cold period which preceded this interstadial is known as the Oldest Dryas , and the two subsequent cold periods as the Older and Younger Dryas . Additional evidence for this period involves the gathering of oxygen isotope stages (OIS) from stratified deep-sea sediment cores . Samples are gathered and measured for change in isotope levels to determine temperature fluctuation for given periods of time. This interstadial

6283-414: The early Brommean artefact inventory. Still, Federmesser types are also often found in close association with Hamburgian assemblages (e.g. at Slotseng and Sølbjerg) and tentative, dating from northern Germany shows some degree of contemporaneity between the late Hamburgian Havelte sites and the Federmesser ones. Therefore, in southern Scandinavia the Federmesser may represent a brief transitory phase between

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6386-523: The eastern Scotian Shelf off Nova Scotia . They originate from the Laurentian Channel south of the Cabot Strait . Additionally, seismic profiles show deeply buried post-Miocene channels, some of which lie 1,100 m (3,600 ft) below modern sea level, cutting across the eastern part of the outer Laurentian Channel which have also tentatively been determined to be tunnel valleys. Seismic profiles have also mapped large tunnel valleys on Banquereau Bank and Sable Island Bank . The Perito Moreno Glacier

6489-484: The end of the Last Glacial Maximum (LGM). The cold had previously forced them into refuge areas , but the warming of the interstadial enabled them to begin repopulating the Eurasian landmass. The abrupt Northern cooling of the subsequent Younger Dryas may have triggered the Neolithic Revolution , with the adoption of agriculture in the Levant . In 1901, Danish geologists Nikolaj Hartz (1867–1937) and Vilhelm Milthers (1865–1962) found deposits of birch trees in

6592-550: The entire southern and southeastern Baltic, and are dated to the second half of Allerød and the early cold Dryas III period. The "classical" Brommian complex is typified by simple and fast, but uneconomical, flint processing using unipolar (single-platform) cores. A new development noticed in Lithuania introduced both massive and smaller "tanged Points" . In Bromme culture this technology is proposed to be an innovation derived from tanged Havelte groups. As such, derivation of Bromme culture and even migration of its representatives from

6695-464: The final stages of the Last Glacial Period . It was defined by abrupt warming in the Northern Hemisphere , and a corresponding cooling in the Southern Hemisphere , as well as a period of major ice sheet collapse and corresponding sea level rise known as Meltwater pulse 1A . This period was named after two sites in Denmark where paleoclimate evidence for it was first found, in the form of vegetation fossils that could have only survived during

6798-444: The glacial ice (called Rothlisberger channels), eventually flowing out at the ice margin. On the simplest level, the tunnel valley can be considered a larger-scale version of these phenomena. Tunnel valleys or tunnel channels are produced by meltwater flows beneath glacial ice. Tunnel valleys are often buried or partially buried by sediment accumulation during periods of ice advance and retreat. Although attractive since it scales up

6901-406: The glacier bed. Tunnel valleys can be formed under extremely thick glacial ice – examples have been observed on the bottom of Lake Superior and in the oceans offshore in Antarctica. The course of a tunnel valley typically runs from thickest glacial ice to the glacier margin; as a result the glacial ice pressurizes the water such that it runs uphill toward its end. Although there is agreement on

7004-427: The glacier surface (supraglacially), below the glacier (basally) or both. Meltwater may flow either supraglacially or basally as well; the signatures of supraglacial and basal water flow differ with the passage zone. Supraglacial flow is similar to stream flow in all surface environments – water flows from higher areas to lower areas under the influence of gravity. Basal flow exhibits significant differences. In basal flow

7107-560: The glaciers of Hardangerfjord began during this interstadial. Boknafjord had already begun to deglaciate before the onset of the Bølling–Allerød interstadial. Some research suggests that isostatic rebound in response to glacier retreat (unloading) and an increase in local salinity (i.e., δ Osw) was associated with increased volcanic activity at the onset of Bølling–Allerød. Notably, volcanic ash fallout on glacier surfaces could have had enhanced their melting through ice-albedo feedback . The deep oceans were depleted in radiocarbon during

7210-418: The increased biomass led to a marked intensification in foraging by all groups, the development of inter-group contacts, and ultimately, the initiation of agriculture. The different technolithic complexes are chronologically associated with the climatic chronozones. The re-colonisation of Northern Germany is connected to the onset of the late Glacial Interstadial between Weichsel and the Dryas I glaciation, at

7313-653: The infill is post-glacial typical of that observed for tunnel valleys. In southern Africa a Permo-Carboniferous tunnel valley system has been identified in northern Cape Province, South Africa. The active formation of tunnel valleys is observed in the present period beneath the Antarctic ice. During the late Ordovician , eastern Gondwana was covered with ice sheets. As a consequence, Jordan and Saudi Arabia exhibit regionally-extensive filled tunnel valley structures. Open-pit gold mines near Kalgoorlie , Western Australia, expose an extensive network of glacially-eroded valleys filled with tillite and shale cut below

7416-660: The largest tributary of the St. Joseph River . In the Laurentian Channel offshore eastern Canada, numerous tunnel valleys have been identified originating from the submerged valley of the St. Lawrence River , which is also of glacial origin. Seismic reflection profiles of the fill of tunnel valleys suggest that they are of various ages, with the youngest dating from shortly after the Late Glacial Maximum . They result from erosion by sub-glacial water crossing

7519-502: The largest cross-sectional area in the center of the course and terminate over a relatively short distance in elevated outwash fans at the ice-margin. Tunnel valleys are found to cross the regional gradient – as a result they may be crosscut by modern stream networks. In one example, tributaries of the Kalamazoo River cut at nearly right angles across buried tunnel channel filled with ice and debris. They frequently terminate at

7622-652: The late Dryas period is contradicted by new information that the Ahrensburgian techno-complex probably already started before the Younger Dryas, strengthening proposals to a direct derivation from the Havelte stage of the Hamburg culture. Some recent finds, such as the Hintersee 24 site in southern Landkreis Vorpommern-Greifswald, would contribute to the argument of an early Ahrensburgian in northern Germany. Alternatively, flint artefacts of Bromme tanged-point groups

7725-518: The local Mammoth Hunters' culture. Another possibility derives from the observation that on a regional scale, the Hamburgian culture is succeeded geographically as well as chronologically by the Federmesser culture , or Arch-Backed Piece Complex. The existence of a genuine Federmesser occupation in southern Scandinavia is highly controversial, and there is wide, though not unanimous, agreement that some Federmesser types constitute an integral part of

7828-661: The margins of the Laurentide Ice Sheet . Examples of bedrock tunnel valleys in Minnesota include River Warren Falls and several valleys which lie deep beneath till deposited by the glaciers which created them, but can be traced in many places by the Chain of Lakes in Minneapolis and lakes and dry valleys in St. Paul . The Kawartha lakes of Ontario formed in the Late Wisconsinan glacial period. Ice melt from

7931-511: The mountains of Scandinavia , began to rise up the north-European slope, driven by the altitude of the glacial ice accumulation over Scandinavia . Their alignment indicates the direction of ice flow at the time of their formation. They are found extensively in the United Kingdom with several examples reported from Cheshire for example. They are also to be found under the North Sea. Examples of lakes formed in tunnel valleys include

8034-588: The northern plains is thought to have opened up no earlier than 13,500 years ago. However, deglaciation in the Pacific Northwest may have taken place more rapidly and a coastal route could have been available by 17,000 years ago. Rising temperatures and increased moisture accelerated environmental change after 14,000 years ago, as shrub tundra replaced dry steppe in many parts of Beringia . Camp settlement sites are found along Tanana River in central Alaska by 14,000 years ago. Earliest occupation levels at

8137-544: The older Older Dryas (after Dryas octopetala , an Arctic plant widespread during such cold periods in the Northern Hemisphere). The Older Dryas lasted approximately one century. before northern hemisphere warming returned during the Allerød stage. The Allerød stage was a warm and moist global interstadial that occurred c.13,900 to 12,900 BP . It raised temperatures in the northern Atlantic region to almost present-day levels, before they declined again in

8240-400: The pressure of the ice forces the water to areas of lower ice coverage until it emerges at a glacial face. Hence the configuration of the various tunnel valleys formed by a specific glaciation provide a general mapping of the glacier thickness when the tunnel valleys were formed, particularly if the original surface relief under the glacier was limited. Analyses by Piotrowski demonstrate that

8343-489: The role of meltwater in creation of tunnel valleys, several theories are still under consideration for the role of that meltwater: Periodic outbursts of subglacial water have been observed moving subglacial water between subglacial lakes beneath the East Antarctic Ice Sheet. Satellite data recorded a subglacial discharge totaling two km (0.48 cu mi) traveling ~260 km (160 mi) over

8446-467: The same tunnel valley. They have steep sides which are frequently asymmetric . Tunnel valleys frequently include relatively straight individual segments parallel to and independent of one another. Tunnel valley courses may be periodically interrupted; the interruption may include a stretch of elevated esker , indicating the channel ran through ice for a distance. The below-grade sections typically run 5–30 km (3.1–18.6 mi) in length; in some cases

8549-413: The sections form a larger pattern of an interrupted channel composed of strings of depressions which can extend from 70–100 km (43–62 mi). The upstream portion – that section furthest into the glacier – consists of a branching system forming a network, similar to the anastomostic branching patterns of the upper reaches of a river (as contrasted with dendritic patterns). They typically exhibit

8652-436: The southwest region than in the central and southern plains since southwest sites consistently yield grinding stones widely thought to have been used for preparation of seeds, roots, and other plant parts. During the interstadial, Siberian human occupations sites are confined to latitudes below 57°N and most are C dated from 19,000 to 14,000 years ago. Settlements differed from those of the East European Plain as they reflected

8755-417: The steady state theory appears not to account for erosion into bedrock, which has been extensively observed. There is evidence that meltwater discharges are episodic. This can result because as water continues to collect, more ice is lifted, and the water moves outward in a growing under-ice lake. Areas where the ice is most easily lifted (i.e., areas with thinner overlying ice sheets) are lifted first. Hence

8858-531: The strengthening of the Atlantic meridional overturning circulation (and the corresponding weakening of the Southern Ocean overturning circulation ). These changes in thermohaline circulation had caused far more heat to be transferred from the Southern Hemisphere to the North. For human populations of the Northern Hemisphere, Bølling–Allerød Interstadial had represented the first pronounced warming since

8961-427: The subsequent disintegration of Late Palaeolithic cultures between 15,000 and 10,000 BCE. The extinction of mammoth and other megafauna provided for an incentive to exploit other forms of subsistence that included maritime resources. Northward migrations coincided with the warm Bølling and Allerød events, but much of northern Eurasia remained inhabited during the Younger Dryas . During the holocene climatic optimum ,

9064-453: The surface of the glacier until it drops down a vertical crevice (a moulin ) in the glacier. There it joins subglacial water created by geothermal heat; some portion of the water drains into aquifers below the glacier. Excess subglacial water that cannot drain through sediment or impermeable bedrock as groundwater, moves either through channels eroded into the bed of sediment below the glacier (called Nye channels ) or through channels upward into

9167-474: The territories of Denmark and northern Germany have been proposed, although other sources hold early Bromme not to be very well defined in (late Allerød) Northern Germany, where it groups with Federmesser. Ahrensburg culture is normally associated with the Younger Dryas glacialization and the Pre-boreal period. The traditional view of the Ahrensburg culture being a direct inheritor of the Bromme culture in

9270-456: The tidal environment will show undertow dominated fans. The transitional environment is characterized by both mixed marine and fresh water life in a delta environment. In an essentially dry environment, the glacial flow carries sediment which accumulates much as it would in any stream bed. Ice flow within glaciers results from an increase in the surface slope of the glacier, which result from geographic features combined with an imbalance between

9373-546: The transition period from the Younger Dryas to the Preboreal. More favourable living conditions, and past experience gained through seasonal rounds, prompted increased maritime resource exploitation in the northern territories. The Hensbacka group on the west coast of Sweden exemplifies the cultural fragmentation process that took place within the Continental Ahrensburgian. Instead of new immigrations at

9476-455: The tunnel valley fill stages. The subglacial tunnel valley networks originally formed near the ice margin. Tunnel valleys are likely to fill with sediment as the result of meltwater release during glacial recession. Tunnel valleys fill in two main ways. In the first instance, debris carried by flow settles out and accumulates in the tunnel valley. Subsequently, once the ice has retreated sufficiently, marine deposits may be laid down, depending on

9579-408: The underlying materials and the overlying ice, creating a channel even as the reduced pressure allows most of the glacial ice to settle back to the underlying surface, sealing off the broad front release and channelizing the flow. The direction of the channel is defined primarily by the overlying ice thickness and secondarily by the gradient of the underlying earth, and may be observed to “run uphill” as

9682-466: The very late Allerød , thus possibly representing an early stage of Ahrensburgian which might have corresponded to the Bromme culture in the north. Artefacts with tanged points are found associated with both the Bromme and the Ahrensburg cultures. The Ahrensburg culture belongs to a Late Paleolithic and early Mesolithic (or Epipaleolithic ) cultural complex that started with the glacial recession and

9785-644: The warm Bølling period, the brief Dryas II glaciation (lasting 300 years) and in the early warmer Allerød period. However, the distribution of the Hamburgian east of the Oder River has been confirmed and Hamburgian culture can also be distinguished in Lithuania. Finds in Jutland indicates the expansion of early Hamburgian hunters and gatherers reached further north than previously expected. The Hamburgian sites with shouldered point lithics reach as far north as

9888-496: The water depth at the ice front. The tunnel valley sedimentary record is controlled by meltwater release flow rates and sediment burdens during glacial recession. The sediment found in the tunnel valley provides insight into whether it was laid down in a tidal environment, a transitional environment, or an essentially dry environment with good drainage. In the glaciomarine environment, glacially-related deposits are interbedded with to those similar to those on non-glaciated tidal areas;

9991-418: The water may move up the terrain underlying the glacier if it moves toward areas of lower overlying ice. As water collects, additional ice is lifted until a release path is created. If no preexisting channel is present, the water is initially released in a broad-front jökulhlaup which can have a flow front that is tens of kilometers wide, spreading out in a thin front. As the flow continues, it tends to erode

10094-409: The water, either produced by melting at the base or drawn downward from the surface by gravity, collects at the base of the glacier in ponds and lakes in a pocket overlain by hundreds of meters of ice. If there is no surface drainage path, water from surface melting will flow downward and collect in crevices in the ice, while water from basal melting will collect under the glacier; either source will form

10197-636: The wedge-shaped cores and microblades, along with some bifacial tools, burins, and scrapers. The site likely represents the material remains of the people who spread across the Bering Land Bridge and into the New World. δ O records from Valmiki Cave in southern India indicate extreme shifts in Indian Summer Monsoon intensity at Termination 1a, which marks the start of the Bølling–Allerød and occurred about 14,800 BP. In

10300-479: The world's oil is found in these shale deposits. Although the origin of these deposits is still under study, it has been established that the shale routinely overlies glacial and glacio-marine sediment deposited ~445 million years before the present by the Hirnantian glaciation . The shale has been linked to glacial meltwater nutrient enrichment of the shallow marine environment. Hence the presence of tunnel valleys

10403-560: Was at a rate of 20–35 ppmv within 200 years, or less than half of the increase of the recent 50 years, and role in global warming was dwarfed by the opposing hemispheric changes caused by thermohaline circulation. Some research shows that a warming of 3–5 °C (5.4–9.0 °F) had occurred at intermediate depths in the North Atlantic over the preceding several millennia during Heinrich stadial 1 (HS1). The authors postulated that this warm salty water (WSW) layer, situated beneath

10506-614: Was found embedded in a bison shoulder blade. As climates warmed further around 15,000 years ago, fish began to populate rivers, and technology used to harvest them, such as barbed harpoons, first appeared on the Upper Angara River. People expanded northwards into the Middle Lena Basin. The Dyuktai culture , near Dyuktai Cave , on the Aldan River at 59°N, is similar to southern Siberian sites and includes

10609-489: Was most prevalent in the Crimea region and increased as early as around 16,000 years ago. Reoccupation of northern territories of the East European Plain did not occur until 13,000 years ago. Generally, lithic technology is dominated by blade production and typical Upper Paleolithic tool forms such as burins and backed blades (the most persistent). Kostenki archaeological sites of multiple occupation layers persist from

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