Architecture and origin of fluvial cross-bedding based on flume experiments and geological examples field case studies: Rillo de Gallo, Spain and Northumberland, UK

Cross-stratified sandstones formed by dunes and unit bars is common in the rock record. Cross-bed architecture is controlled by the size and shape of, and processes on, the original formative bedforms, and processes that truncate, deform or bury the cross-strata. This thesis reports an investigation of cross-bedded sandstones and their internal sedimentary structures formed in fluvial environments within different depositional settings at Rillo de Gallo, (Spain) and Seaton Sluice, (Northumberland). In addition, flume experiments using well-sorted fine sand were used to investigate some of the factors controlling cross-bed architecture produced by unit bars migrating downstream in a unidirectional flow under controlled conditions over pre-existing topography. New ways of classifying cross-bedding were developed to allow analyses of patterns and relationships between set geometry, flow behaviour and stratigraphic position within sedimentary sequences. The amount and variation in divergence between scour trend and scour-fill laminae dip direction is found to be potentially diagnostic of flow pattern, and should improve palaeoenvironment interpretation. A relationship between the amount of variation in bar lee-face angle with bar height was found in the flume and may be useful for inferring bedform size in the rock record. Integration of laboratory and field observations on lee-face angle, bedform superimposition, reactivation surfaces, topography development and bottomset formation helped to mitigate the issue of preservation level when interpreting rock analogue examples and led to improved interpretations of the ancient fluvial deposits. This is an approach that should help the interpretation of other ancient fluvial sequences. The mechanisms and patterns of trough scour formation and scour filling have been to a certain extent ignored to date. Herein it is highlighted the need for further research on the understanding of scour formation and fill in association with bedform development and migration leading to improved knowledge of cross-bedded sandstones.

Name dc:type.qualificationname

phd

Level dc:type.qualificationlevel

doctoral

Grantor dc:publisher.institution

University of East Anglia

Year dc:date.issued

2015

Author dc:creator

• Martinez De Alvaro, Maria

Language dc:language

en