Algodones dune field of southeastern California: case history of a migrating modern dune field |
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| Authors: | M L SWEET JAMIE NIELSON K HAVHOLM JOHN FARRELLEY |
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| Institution: | Department of Geologic Sciences, The University of Texas at Austin, Austin, TX 78713 USA |
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| Abstract: | The Algodones dune field of southeastern California is one of the largest active dune fields in North America. The dune field is migrating in an easterly direction, oblique to the resultant sand flow direction (S 24° E). The migration of the Algodones results from an interaction between regional winds and the dune field. This interaction generates a localized secondary flow that has caused the dune field to migrate in a direction oblique to the resultant sand flow direction. Four lines of evidence suggest that the Algodones has migrated in an easterly direction: (1) A ramp, interpreted as the trailing edge of the dune field, 35 m thick and 500 m wide composed of aeolian deposits that borders the western edge of the dune field. No similar deposits are found on the eastern (leading edge) margin of the dune field. (2) Leading-edge sand-sheet deposits are exposed in interdune areas within the dune field. These deposits are west of the modern leading-edge sand sheet. (3) Across the breadth of the dune field sands are consistently coarser and more poorly sorted in the west and finer and better sorted in the east. This observation suggests that sand is transported from west to east. (4) Eastward migration of a large compound-complex crescentic dune. If the dune field continues to migrate it will deposit a vertical sequence consisting of: a basal sand-sheet deposit consisting of wind and water-ripple laminae, small-scale aeolian cross-strata, and ephemeral stream (wadi) deposits; aeolian dune deposits consisting of medium-scale aeolian compound cross-strata; small-scale simple sets of aeolian cross-strata with highly variable dip directions; a sand sheet containing low-angle wind-ripple cross-strata capped by a coarse sand lag super bounding surface. |
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