Dating Lake Mohave Artifacts and Beaches

1964 ◽  
Vol 30 (2Part1) ◽  
pp. 206-209 ◽  
Author(s):  
Claude N. Warren ◽  
John de Costa

AbstractIt is generally accepted that Lake Mohave artifacts date from the closing phase of the last deglaciation when the lake stood at its highest level. A re-evaluation of published data shows that Lake Mohave artifacts date from the overflow period, but only after the lake had abandoned the highest or 946-foot beach. A radiocarbon date of 9640 ± 240 years has been obtained from Anodonta shells at levels between 925 and 930 feet. These shells have been interpreted as remains of animals stranded en masse during the final recession of the Pluvial lake. No evidence for such a catastrophic event has been presented, and there is some evidence which suggests the opposite. The Anodonta shells appear to represent remains of dead animals deposited when the lake stood somewhat higher than 930 feet. It is apparent that an interdisciplinary approach, involving geology, paleolimnology, and palynology, as well as archaeology, is needed if man's place in the history of Lake Mohave is to be understood.

2013 ◽  
Vol 80 (3) ◽  
pp. 482-494 ◽  
Author(s):  
Julien Carcaillet ◽  
Isandra Angel ◽  
Eduardo Carrillo ◽  
Franck A. Audemard ◽  
Christian Beck

In the tropical Mérida Andes (northwestern Venezuela), glacial landforms were found at altitudes between 2600 and 5000 m, corresponding to 600 km2 of ice cover during the maximum glacial extension. However, the lack of sufficient absolute age data prevents detailed reconstruction of the timing of the last deglaciation. On the northwestern flank of the Mucuñuque Massif, successive moraines and striated eroded basement surfaces were sampled for cosmogenic 10Be investigation. Their compilation with published data allows the establishment of a detailed chronology of the post-LGM glacier history. The oldest moraines (18.1 and 16.8 ka) correspond to the Oldest Dryas. Successive moraine ridges indicate stops in the overall retreat between the LGM and the Younger Dryas. The cold and short Older Dryas stadial has been identified. Results indicate that most of the ice withdrew during the Pleistocene. The dataset supports an intensification of the vertical retreat rate from ~ 25 m/ka during the late Pleistocene to ~ 310 m/ka during the Pleistocene/Holocene. Afterwards, the glacier was confined and located in the higher altitude zones. The altitude difference of the Younger Dryas moraines in the Mucubají, La Victoria and Los Zerpa valleys indicates a strong effect of valley orientation on the altitude of moraine development.


2010 ◽  
Vol 36 (-1) ◽  
pp. 47-54 ◽  
Author(s):  
Anto Raukas ◽  
Wojciech Stankowski ◽  
Vitālijs Zelčs ◽  
Petras Šinkunas

Chronology of the Last Deglaciation in the Southeastern Baltic Region on the Basis of Recent OSL DatesThe study of the deglaciation chronology in the south-eastern Baltic Region belonging to the outer zone of the last Pleistocene glaciation has a long history. The Finnish investigator H. Hausen (1913) who worked in the north-western portion of the East-European Plain at the beginning of the 20thcentury was the first to attempt a reconstruction of the course of glacial retreat during the last glaciation. At that time investigators had no physical dating methods and the time scale based on varvometric method, introduced by the Swedish geologist G. de Geer (1912) who divided the deglaciation history of Scandinavia into Daniglacial, Gotiglacial and Finiglacial, each of which had different palaeoglaciological conditions. During last decades different dating methods, including14C, ESR, luminescence methods and10Be techniques have been used, but they could not help essentially improve the existing stratigraphical charts and many problems of topical interest in the history of deglaciation have not been solved yet. During last years the first two authors have studied the suitability of OSL method for the geochronological purposes, paying the most attention to the waterlaid sediments. In the first step they have found the most promising genetical varieties of glaciofluvial sediments (glaciofluvial deltas and sandurs) and in this paper they widened the study area to all three Baltic states with close cooperation with Latvian and Lithuanian colleagues. The obtained results demonstrated, that not all mineral grains in the uppermost glaciofluvial and glaciolacustrine sediments were fully bleached during the last deglaciation. Probably the older sediments also influenced to the luminescence results. It means, that stratigraphic conclusions based on single dates or their small sets are inadmissible and in each case luminiscence dating requires a verification using other methods.


Author(s):  
Ángel Rodés

Cosmogenic nuclides are widely used to constrain the landscape history of glaciated areas. At nunataks in continental polar regions with extremely arid conditions, cosmogenic nuclides are often the only method available to date the ice thinning history of the glacier. However, the amount of cosmogenic isotopes accumulated at the surface of nunataks depends not only on the length of time that rock has been exposed since the last deglaciation, but on the full history of the surface, including muon production under ice, exposure during previous interglacials, subaerial weathering rate, glacial erosion rate, and uplift rate of the nunatak. The NUNAtak Ice Thinning model (NUNAIT) simulates the cosmonuclide accumulation on vertical profiles, fitting the aforementioned parameters to a set of multi-isotope apparent ages from samples taken at different elevations over the ice-sheet surface. The NUNAIT calculator is an easy-to-use tool that constrains parameters that describe the geological history of a nunatak from a set of surface exposure ages.


2017 ◽  
Author(s):  
Maureen H. Walczak ◽  
◽  
Heather D. Bervid ◽  
Anders E. Carlson ◽  
Alyson N. Churchill ◽  
...  

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