Susan B. Marriott

The sequence stratigraphy of fluvial depositional systems: the role of floodplain sediment storage

Abstract The currently used model for alluvial sequence stratigraphy has been criticised (Miall, 1991) and an alternative model is offered here. In this model alluviation mainly takes place during transgressive and not highstand phases, when accommodation space allows sediment storage. The high capacity for some river systems to store floodplain sediments is a critical consideration. The effects of climatic and intrinsic geomorphic changes during fluvial deposition are likely to greatly complicate simple, base-level controlled sequence models, and recognising higher-order, fourth- and fifth-order cycles will be particularly difficult.

Arthropod trackways from the Early Devonian of South Wales: a functional analysis of producers and their behaviour

Abundant arthropod trackways, assigned to Diplichnites gouldi , are described from the Lower Old Red Sandstone (Early Devonian; Lochkovian) of Pant-y-Maes quarry, Brecon Beacons, South Wales. The trackways are preserved on bedding planes of finely laminated planar and rippled siltstones. The sedimentology of the succession indicates that these units represent bar top and marginal deposits in a braided fluvial setting. Two trackway types are recognized (Type A and B); comparisons with contemporaneous myriapodous producers favour kampecarid and eoarthropleurid myriapods, respectively. Functional analysis of the trackways indicates that the producers were not using the most efficient, stable, walking techniques, but instead utilized in-phase ‘swimming stroke’-like gaits. Together with their occurrence on rippled surfaces, and lateral displacement of some trackways (attributed to currents), this indicates that they were produced sub-aqueously.

Holocene sea-level change in the Severn Estuary, southwest England: a diatom-based sea-level transfer function for macrotidal settings

The recent growth in the use of microfossil-based transfer functions in late-Quaternary sea-level reconstructions reflects their potential to accurately quantify palaeo sea-level changes. This study details the development of a diatom-based sea-level transfer function for the Severn Estuary, southwest England, a macrotidal setting that experiences the second highest tidal range in the world. This setting presents difficulties in representing the full tidal range from mean sea level (MSL) to highest astronomical tide (HAT). However, two separate transects were merged successfully and a statistically significant relationship between contemporary diatom assemblages and altitude (m O.D.) was established. A diatom-based transfer function for palaeoaltitude was developed using weighted averaging (WA), tolerance downweighted weighted averaging (WA-Tol) and weighted averaging partial least squares (WA-PLS). WA-Tol produced the lowest prediction errors for altitude and the transfer function was applied to a fossil diatom data set from Gordano Valley, a site adjacent to the Severn Estuary.