Shell bed tempestites in the Chenier Plain of Louisiana: late Holocene example and modern analogue

Abstract

AbstractHurricane Ike's storm surge deposited a concentrated shell bed in the form of a series of coalescing washover fans over backshore sand and adjoining marshland in part of southwest Louisiana's Chenier Plain. The shell bed is a tempestite and has distinctive morphological, sedimentological and biogenic characteristics that provide a modern analogue to aid interpretation of older shell bed tempestites in the geological record. The shell bed has a wedge‐shaped profile that thickens landward, is about 40 m wide, up to 27 cm thick and extends several hundred metres parallel to the shore. Shells are predominantly disarticulated valves of the common bivalve Mulinia lateralis, probably reworked and transported landward from skeletal remains offshore. The shell bed has an erosional base, is bioclast supported, normally graded and has common mud rip‐up clasts. Similarities between the modern shell bed and another concentrated shell deposit, forming part of a sandy beach ridge some 1.5 km inland, suggest that the palaeo shell deposit is also a tempestite recording hurricane washover of a former shoreline 600 a ago. These findings demonstrate that the shell bed deposited by Hurricane Ike is a valuable analogue for palaeotempestological investigations and that hurricanes have likely contributed to the construction of both modern berm ridges and palaeo beach ridges on this coastal plain. Copyright © 2011 John Wiley & Sons, Ltd.