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Sedimentary structures gerenated on the foreshore by migrating ridge and runnel systems on microtidal and mesotidal coasts of S. Spain

Dabrio, Cristino J. (1982) Sedimentary structures gerenated on the foreshore by migrating ridge and runnel systems on microtidal and mesotidal coasts of S. Spain. Sedimentary Geology, 32 (1-2). pp. 141-151. ISSN 0037-0738

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Abstract

The migration of ridge and runnel systems on mícrotidal coasts is a rather simple process
starting with the formation of a rídge at the uppcr shoreface after storms and its
mígration landwards until it welds onto fue berm. This results in an ideal sequence of
structures which ineludes (from bottom to top): cross-laminated sands (runnel facies);
cross-bedded sands with local discontinuity surfaces (ridge facies); and even-laminated
sands (berm facies). Larger tidal tange and higher wave activity on mesotidal coasts
induce a mote differentiated pattern. At early stages of accretion, the ridge is covered
at high tide and éxposed at low tide. Swash accumulates a secondary bar of coarse sediment during low water that is removed snd incorporated in the slip face of the ridge by
avalanching during rising tídes. At high tide, large amounts of finer sedíment are brought
by waves and deposíted on top of the rídge and in the slip face, generating fining-upward
sequences. Erosional low-angle discontinuity surfaces develop during falling tides. Within
the runnel, longshore currents are strong enough to build up small megaripples with crests
roughly normal to the shoreline and waves induce wave ripples with crests more or less
parallel to the shoreline. At later stages of accretion, the ridge is submerged mainly during
spring high tide. After the runnel has been filled up, a vertical growth of the new berm
occurs associated with finíng-upward sequences due to decreasing energy and shoreward
shíftíng of swash zones, during the transition from neap to spring tides. The resulting
ideal sequence of sedimentay structures is larger and better differentiated than those
described for microtidal and tideless coasts.

Item Type:Article
Uncontrolled Keywords:Microtidal coasts, Mesotidal coasts, Sedimentology, Spain
Subjects:Sciences > Geology > Stratigraphic geology
ID Code:10620
Deposited On:07 May 2010 09:01
Last Modified:07 May 2010 09:01

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