Rock varnish dating

Thus a Chlorine-36 date may reflect either recent exposure of a surface due to processes such as frost shattering, or an original exposure date. Professor Bowen and colleagues have obtained a date of c.

This difficulty of interpretation is why Chlorine-36 dating is normally done on boulders or lava surfaces whose erosional history is known (e.g. 14,000 years exposure time for the fragment from Stonehenge.

Looks like a bit of Chilmark stone to me -- please correct me if I'm wrong. The date apparently came out as showing that the stone was first exposed to the atmosphere around 40,000 years ago.

Even if it is a quarried surface, its relevance to Stonehenge is questionable, because the bluestones were erected there about 4000 years ago. Dating gives clue to Stonehenge riddle, British Archaeology 1 (February). Thus, even if it is considered that the bluestones were moved by human transport, the Chlorine-36 dates do not tell us at what era that movement might have taken place. Chlorine-36 dating British ice-sheets, Abstracts of the American Geophysics Union, 1994 Fall Meeting: 226. This finding was widely purported in the media to demonstrate conclusively that glaciation could not have moved the bluestones to Stonehenge. It does not even support the human transport theory.Prof Bowen's dating exercise -- also involving other dates, with two from Carn Meini, has been heavily criticised by other geologists.We then use this climatically correlated varnish layering sequence as a correlative dating tool to determine surface exposure ages for late Quaternary geomorphic features in the study region.

VML dating of alluvial fan deposits in Death Valley of eastern California indicates that, during the mid to late Pleistocene, 5–15 ky long aggradation events occurred during either wet or dry climatic periods and that major climate shifts between glacial and interglacial conditions may be the pacemaker for alteration of major episodes of fan aggradation.Other dates for rock surfaces at Carn Meini were 5,400 BP and 4,900 BP. Chosen because they looked fresh, or because they looked old? Chlorine-36 dating gives an estimate of the length of time that a rock surface has been exposed to the atmosphere, by measuring the amount of Chlorine-36 produced by exposure of the rock to cosmic radiation. If the rock or surface has been covered or buried, the date obtained will reflect the reduced time of exposure to air. The article in British Archaeology suggests that dating a monolith surface of a bluestone at Stonehenge will resolve the problem. At least some of the bluestones were dressed and the argument continues about which, and how many were altered in this way. A dressed or damaged bluestone will give a Chlorine-36 date reflecting total exposure time - for example, about 4000 years if it is dressed but not subsequently damaged. A variety of older dates could be obtained, depending on whether the bluestone was removed from Wales by a glacier as an erratic, buried for part or all of its glacial transport, or broken up by erosional processes in post-glacial times. I'm a bit confused, because there is another date (for the big sample in the picture? PLEASE will somebody do some sensible cosmogenic dating one day, to help us to understand what has gone on at Stonehenge? Bowen of the University of Wales, Cardiff and colleagues have dated a fragment of igneous rock reported as having been found at Stonehenge (exact type unknown, but not a spotted dolerite) at 14,000[ or -]1900 years, and surfaces of outcrops at Carn Menyn in Preseli at 5400[ or -]4[ or -]400 years (Bowen et al. This information has been interpreted as indicating that the bluestones of Stonehenge could not have been transported to the site of Stonehenge by ice, because the ice sheets were extensive enough only at c.