Neap–spring tide sequences of intertidal shoal deposits in a mesotidal estuary

Abstract

In the mesotidal (tidal range 3·5–4·9 m) Westerschelde estuary (The Netherlands) the intertidal part of a sandbank was the subject of systematic observations of: (1) hydrographic properties, (2) the distribution and response pattern of various types of bedforms, and (3) the sedimentary structures produced. Ebb and flood usually differ considerably in strength, giving rise to a clear dominance of one over the other, which may change over the neap‐spring tide period. Parallel, long‐crested sand‐waves and irregular, short‐crested dunes have a different response to the neap‐spring variation in current velocity. Because one tide (usually the flood in our area) predominated over the other, the internal structure largely consists of unidirectional cross‐bedding, separated into a succession of tidal bundles, each formed during one tide. The tidal bundles are arranged in a lateral sequence reflecting neap‐spring tide periods and differing in character with location. Within the tidal bundle, reactivation, full vortex and slackening structures reflect acceleration, full stage and deceleration of flow respectively in the dominant tide. The full vortex structures tend to be well developed around spring tide but disappear towards neap tide. The subordinate tide carves ‘pause planes’ which enclose the tidal bundles. These pause planes are either erosional or depositional (mud).

A cretaceous ‐ early tertiary Macrotidal estuarine‐fluvial succession: Puponga coal measures in Whanganui inlet, onshore Pakawau sub‐basin, Northwest Nelson, New Zealand

“…during slack high tide and slack low tide). The architecture of the more complex compound cross-bedding is most consistent with low-activity sandwaves, as described by Boersma & Terwindt (1981) on an intertidal sandy shoal. The smiles probably represent scour pits filled by suspended material during slack tide.…”

“…Foresets, dipping (17°) in opposing directions, fill theerosional cut. Dalrymple (1984), Boersma & Terwindt (1981), andde Mowbray & Visser (1984) described similar features in modern-day migrating sand waves. According to these authors, two elements make up a sand wave: (i) an accretion bundle, which develops and migrates in the dominant current direction, and (ii) an overlying ebb cap.…”

Late Quaternary drainage dynamics in northern Brazil based on the study of a large paleochannel from southwestern Marajó Island

“…Although not diagnostic, the cross sets with abundant reactivation surfaces marked by mud drapes, which are particularly developed in the lower parts of the fining upward successions, lead to suggest possible sediment reworking by tidal currents, similarly to what has been recorded in many tidal channel successions (e.g., Boersma and Terwindt 1981, Mowbray and Visser 1984, Yang and Nio 1985, Leckie and Singh 1991, Shanley et al 1992, Hori et al 2001, Plink-Bjorklund 2005. In particular, the double mud drapes separating alternating thicker and thinner foreset packages their imprint in these sediments, which is probably due to the influence of strong fluvial inflow.…”

Dynamics of intertidal gravel dunes

“…[2] Past studies of tidal dunes have neglected dunes developed on gravel substrates and have generally focused upon bed forms developed on sandy sediments [e.g., Mclean and Smith, 1979;Boersma and Terwindt, 1981;Kostaschuk and Villard, 1996;Hughes and Weir, 2003]. Only Klein [1970] makes brief reference to intertidal gravelsand dunes and there are no studies of intertidal dunes developed in predominately gravel fractions.…”