“Chevrons” are not mega-tsunami deposits—A sedimentologic assessment

Abstract

Since the introduction of the term “chevron” for large v- or u-shaped bed forms in Egypt and the Bahamas, others have adopted the term to describe large-scale coastal bed forms in Australia, Madagascar, and elsewhere. These authors interpret “chevron” bed forms as deposits of mega-tsunamis resulting from Holocene oceanic asteroid impacts. We reason that chevron-type bed forms are common and are present far enough from the coast to preclude tsunami genesis. Moreover, we argue that “chevrons” are not mega-tsunami deposits by modeling tsunami behavior and evaluating sediment-transport conditions under which such features formed. We model the southern Madagascar case, with an impact source in the Indian Ocean, and show that a modeled wave approach is inconsistent with “chevron” orientation. We then evaluate sediment-transport conditions under which these “chevron” bed forms could persist, i.e., bed-load transport. In our analysis, no conditions specified generate pure bed-load transport, and most result in pure suspended-load transport.