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The AAPG/Datapages Combined Publications Database

AAPG Bulletin

Abstract


Volume: 55 (1971)

Issue: 2. (February)

First Page: 367

Last Page: 367

Title: Uniquely Rounded Desiccation Columns Near Euphrates River, Northwestern Iraq--Produced by Prolonged Erosion in Arid Climate: ABSTRACT

Author(s): James R. Underwood, Jr., Y. Y. Youash, George Philip

Article Type: Meeting abstract

Abstract:

During a reconnaissance in northwestern Iraq distinctive, much eroded, polygonal mudstone desiccation columns averaging 2 ft in diameter and ranging in height from 2 to 4 ft were seen in the bed of a wadi 200 yd upstream from its intersection with the Euphrates River between the villages of Haditha and Ana. These columns were unique because of their well-rounded upper terminations and because of their discreteness, emphasized by enlarged bounding fractures which ranged in width from 3 to 6 in. The key to the origin of such columns must lie in prolonged preservation and exposure--perhaps over a period of several years--to erosion, largely by weathering (including spheroidal weathering) and by wind and perhaps to a lesser extent by water.

At this locality the blanket of sediment in which the desiccation columns developed was deposited during floodstage of the Euphrates. If this same height of flood was not reached again for several years and if the columns were not destroyed by local rainfall or wadi flow, prolonged erosion would result. Regionally, rainfall averages only about 4 in. per year, but local areas may receive little or no rainfall for extended periods.

Thus if preserved in ancient rock such extremely eroded and rounded columns, or the casts produced by filling of their bounding fractures, would be suggestive of a more arid environment than is indicated by many occurrences of "ordinary" mudcracks or mudcrack casts and associated columns with noneroded planar or only slightly curvilinear upper surfaces.

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