J. R. L. Allen

Bio: J. R. L. Allen is an academic researcher from University of Reading. The author has contributed to research in topics: Parting lineation & Sedimentation (water treatment). The author has an hindex of 16, co-authored 19 publications receiving 5188 citations.

Sedimentary structures, their character and physical basis

Abstract: 1. Environmental Fluid Dynamics. 2. Entrainment and Transport of Sedimentary Particles. 3. Particle Motions at Low Concentrations: Grading in Pyroclastic-Fall Deposits. 4. Packing of Sedimentary Particles. 5. Orientation of Particles During Sedimentation: Shape-Fabrics. 6. Transition to Turbulence and the Fine Structure of Steady Turbulent Boundary Layers: Parting Lineation and Related Structures. 7. Models of Transverse Bedforms in Unidirectional Flows. 8. Empirical Character of Ripples and Dunes Formed By Unidirectional Flows. 9. Climbing Ripples and Dunes and Their Cross-Stratification Patterns. 10. Bedforms in Supercritical and Related Flows: Transverse Ribs, Rhomboid Features, and Antidunes. 11. Transverse Bedforms in Multidirectional Flows: Wave-Related Ripples Marks, Sand Waves, and Equant Dunes. 12. Ripples and Dunes in Changing Flows.

A review of the origin and characteristics of recent alluvial sediments

Abstract: SUMMARY Recent alluvial sediments are reviewed with respect to their geometrical, textural, structural and biological characteristics. These properties are related to the physiographic occurrence and hydraulic geometry of streams and to the dynamics of flowing water as controlling sediment transport-deposition and stream morphological activities. Based on this data, three-dimensional facies models are presented as an aid to the identification of ancient alluvial sediments, which are briefly reviewed also.

Principles of physical sedimentology

Abstract: 1 Concepts and rules of the game.- 1.1 Matter and influences.- 1.2 Flow rate.- 1.3 Law of continuity (conservation of mass).- 1.4 Law of conservation of Momentum.- 1.5 Law of conservation of energy.- 1.6 Energy losses during fluid flow.- 1.7 Newton's laws of motion.- 1.8 Fluid viscosity.- 1.9 Boundary layers.- 1.10 Flow separation.- 1.11 Applying the concepts and rules.- Readings.- 2 Pressed down and running over.- 2.1 Introduction.- 2.2 Particle composition and density.- 2.3 How big is a particle?.- 2.4 What form has a particle?.- 2.5 How close is a packing?.- 2.6 Kinds of packing.- 2.7 Voids.- 2.8 Controls on packing.- 2.9 How steep is a heap?.- 2.10 Building houses on sand.- Readings.- 3 Sink or swim?.- 3.1 Two introductory experiments.- 3.2 Settling of spherical particles arrayed in a stagnant fluid.- 3.3 Settling and fluidization.- 3.4 Flow in porous media.- 3.5 Controls on permeability.- 3.6 Settling of a solitary spherical particle in a stagnant fluid.- 3.7 Settling of a solitary non-spherical particle in a stagnant fluid.- Readings.- 4 Sliding, rolling, leaping and making sand waves.- 4.1 Some field observations.- 4.2 Setting particles in motion.- 4.3 Defining the rate of sediment transport.- 4.4 Physical implications of sediment transport.- 4.5 Sediment transport modes.- 4.6 Appearance and internal structure of bedforms.- 4.7 How do bedforms move?.- 4.8 Bedforms and flow conditions.- 4.9 Making wavy beds.- 4.10 A wave theory of bedforms.- Readings.- 5 Winding down to the sea.- 5.1 Introduction.- 5.2 Drag force and mean velocity of a river.- 5.3 Energy and power of channelized currents.- 5.4 Why flow in a channel?.- 5.5 Width: depth ratio of river channels.- 5.6 Long profiles of rivers.- 5.7 An experimental interlude.- 5.8 Flow in channel bends.- 5.9 Sediment particles in channel bends.- 5.10 Migration of channel bends.- 5.11 A model for river point-bar deposits.- Readings.- 6 Order in chaos.- 6.1 Introduction.- 6.2 Assessing turbulent flows - how to see and what to measure.- 6.3 Character of an ideal eddy.- 6.4 Streaks in the viscous sublayer.- 6.5 Streak bursting.- 6.6 Large eddies (macroturbulence).- 6.7 Relation of small to large coherent structures.- Readings.- 7 A matter of turbidity.- 7.1 Introduction.- 7.2 A diffusion model for transport in suspension.- 7.3 Transport in suspension across river floodplains.- 7.4 Limitations of diffusions models.- 7.5 A dynamical theory of suspension.- 7.6 A criterion for suspension.- Readings.- 8 The banks of the Limpopo River.- 8.1 Introduction.- 8.2 Clay minerals.- 8.3 Deposition of muddy sediments.- 8.4 Packing of muddy sediments.- 8.5 Coming unstuck.- 8.6 Erosion of muddy sediments.- 8.7 Drying out.- Readings.- 9 Creeping, sliding and flowing.- 9.1 Introduction.- 9.2 Mass movements in general.- 9.3 Soil creep.- 9.4 Effective stress and losses of strength.- 9.5 Sub-aerial and sub-aquatic slides.- 9.6 Debris flows.- 9.7 Mass-movement associations.- Readings.- 10 Changes of state.- 10.1 Introduction.- 10.2 An experiment.- 10.3 What causes changes of states?.- 10.4 What forces cause deformation?.- 10.5 For how long can deformation proceed?.- 10.6 Complex deformations in cross-bedded sandstones.- 10.7 Load casts.- 10.8 Convolute lamination.- 10.9 Wrinkle marks.- 10.10 Overturned cross-bedding.- Readings.- 11 Twisting and turning.- 11.1 Introduction.- 11.2 Mixing layers.- 11.3 Jets.- 11.4 Corkscrew vortices.- 11.5 Horseshoe vortices due to bluff bodies.- 11.6 Horseshoe vortices at flute marks, current ripples and dunes.- Readings.- 12 Sudden, strong and deep.- 12.1 Some experiments.- 12.2 Kinds of gravity current.- 12.3 Difficulties with gravity currents.- 12.4 Drag force and mean velocity of a uniform steady gravity current.- 12.5 Shape and speed of a gravity-current head.- 12.6 Why does the nose overhang?.- 12.7 Lobes, clefts and sole marks.- 12.8 Billows on the head.- 12.9 Gravity current heads on slopes.- 12.10 Dissipation of sediment-driven gravity currents.- 12.11 Sloshing gravity currents.- 12.12 Turbidity-current deposits.- Readings.- 13 To and fro.- 13.1 Some introductory experiments.- 13.2 Making wind waves.- 13.3 Making the tide.- 13.4 Waves in shallow water.- 13.5 Waves in deep water.- 13.6 Wave equations.- 13.7 Mass transport in progressive and standing waves.- 13.8 Sediment transport due to wind waves and tides.- 13.9 Wave ripples and plane beds.- 13.10 Sand waves in tidal currents.- 13.11 Longshore bars and troughs.- 13.12 Waves and storm surges - back to the beginning.- Readings.

The classification of cross‐stratified units. with notes on their origin

Abstract: A descriptive classification of cross-stratified units is proposed based on six objective criteria, and diagnoses are given for fifteen distinct kinds of cross-stratified unit recognised with their aid. The origin of each kind is discussed in the light of existing observational, experimental, and theoretical studies. A three-fold genetic classification of cross-stratified units is tentatively outlined in which apparent origin and physical properties are closely correlated.

Outline of Geology of Niger Delta

Abstract: The coastal sedimentary basin of Nigeria has been the scene of three depositional cycles. The first began with a marine incursion in the middle Cretaceous and was terminated by a mild folding phase in Santonian time. The second included the growth of a proto-Niger delta during the Late Cretaceous and ended in a major Paleocene marine transgression. The third cycle, from Eocene to Recent, marked the continuous growth of the main Niger delta. A new threefold lithostratigraphic subdivision is introduced for the Niger delta subsurface, comprising an upper sandy Benin Formation, an intervening unit of alternating sandstone and shale named the Agbada Formation, and a lower shaly Akata Formation. These three units extend across the whole delta and each ranges in age from early T rtiary to Recent. They are related to the present outcrops and environments of deposition. A separate member of the Benin Formation is recognized in the Port Harcourt area. This is the Afam Clay Member, which is interpreted to be an ancient valley fill formed in Miocene sediments. Subsurface structures are described as resulting from movement under the influence of gravity and their distribution is related to growth stages of the delta. Rollover anticlines in front of growth faults form the main objectives of oil exploration, the hydrocarbons being found in sandstone reservoirs of the Agbada Formation.

Riverine landscape diversity

Abstract: 1. This review is presented as a broad synthesis of riverine landscape diversity, beginning with an account of the variety of landscape elements contained within river corridors. Landscape dynamics within river corridors are then examined in the context of landscape evolution, ecological succession and turnover rates of landscape elements. This is followed by an overview of the role of connectivity and ends with a riverine landscape perspective of biodiversity. 2. River corridors in the natural state are characterised by a diverse array of landscape elements, including surface waters (a gradient of lotic and lentic waterbodies), the fluvial stygoscape (alluvial aquifers), riparian systems (alluvial forests, marshes, meadows) and geomorphic features (bars and islands, ridges and swales, levees and terraces, fans and deltas, fringing floodplains, wood debris deposits and channel networks). 3. Fluvial action (erosion, transport, deposition) is the predominant agent of landscape evolution and also constitutes the natural disturbance regime primarily responsible for sustaining a high level of landscape diversity in river corridors. Although individual landscape features may exhibit high turnover, largely as a function of the interactions between fluvial dynamics and successional phenomena, their relative abundance in the river corridor tends to remain constant over ecological time. 4. Hydrological connectivity, the exchange of matter, energy and biota via the aqueous medium, plays a major though poorly understood role in sustaining riverine landscape diversity. Rigorous investigations of connectivity in diverse river systems should provide considerable insight into landscape-level functional processes. 5. The species pool in riverine landscapes is derived from terrestrial and aquatic communities inhabiting diverse lotic, lentic, riparian and groundwater habitats arrayed across spatio-temporal gradients. Natural disturbance regimes are responsible for both expanding the resource gradient in riverine landscapes as well as for constraining competitive exclusion. 6. Riverine landscapes provide an ideal setting for investigating how complex interactions between disturbance and productivity structure species diversity patterns.