Fluvial Research Group

Current Activities

Fluvial response to base-level change in a low-relief shoreline setting

The Pennsylvanian-Permian Lower Cutler Beds of Utah and Arizona record a series of repeated transgressive-regressive events that reflect a complex tripartite interplay between fluvial, shallow marine and aeolian sedimentary systems, which occupied a broad coastal plain. Fluvial response to base level change includes down-cutting and incised valley generation during periods of regression and complex stacking of fluvial channel elements in a retrogradational pattern in response to transgressive events. This project provides is examining the both link between fluvial systems behaviour and base-level change and fluvial system interaction within an arid coastal plain depositional setting.

Detailed analysis has involved the construction of over 80 1D sedimentary logs, the correlation of fluvial architectural elements with surrounding shallow marine and aeolian elements, the tracing of key stratal surfaces over distances of many tens of kilometres, the erection of a completely new and detailed sequence stratigraphic framework and the production of an initial static reservoir model using Petrel. Ongoing work is identifying criteria by which autocyclic fluvial activity may be discerned from allocyclic activity. Key to this approach has been the recognition of a parasequence architecture in which sets are arranged into progradational and retrogradational stacking patterns that record longer-term trends in shoreline position.

Project details (PDF)

Fluvial-aeolian system interaction and response to climatic cyclicity

The predominantly fluvial Cutler Group of the Paradox foreland basin, Utah exhibits a variety of styles of interaction with aeolian dune-dominated parts of the succession. In places, large-scale channelised fluvial deposits demonstrate evidence for multiple fluvial incursions into the margins of a range of types of aeolian dune fields and in some instances demonstrate fluvial penetration for distances of several tens of kilometres into dune-field centres. Elsewhere, fluvial sheet-flood deposits occupy broad interdune corridors and are indicative of unconfined flash-flooding in marginal dune-field regions. A range of styles of fluvial-aeolian interaction are indicative of coeval system activity and have resulted in a complex interdigitation of a variety of facies types with subtly varying porosity-permeability characteristics. Results from this ongoing project are being used to develop reservoir models for marginal plays in the Southern and Northern Permian basins of the North Sea.

Detailed analysis has involved the construction of over 100 1D logs, the assembly of many tens of kilometres of architectural panels, the development of a series of detailed 3D semi-quantitative facies models that depict styles of facies interaction on a range of scales, the construction of a series of sequence stratigraphic models to demonstrate system response to periodic changes in regional climate, and the development of a series of numerical forward stratigraphic models with which to account for the variety of styles of fluvial-aeolian system interaction identified.

Project details (PDF)

A multi-scale approach to characterising terminal fluvial fan systems

Although facies models have been proposed previously for terminal fluvial fan systems, their wider applicability and scope has hitherto been limited and recent debate in the literature has shown them to be inappropriate or unjustified for many applications. This project seeks to present a brand new series of facies and sequence stratigraphic models with which to better understand the behaviour of terminal fluvial systems. This has been achieved through analysis of the well exposed Organ Rock Formation, a Permian succession exposed across much of southern Utah and part of northern Arizona.

Detailed analysis of basin-scale architecture has involved the recording of over 100 1D sedimentary logs from which the internal stratigraphy of the Organ Rock Formation has been established. Regional key-surface tracing has been employed to determination the nature of proximal to distal changes in preserved sedimentary style. The construction of 2D architectural panels has enabled the style of fluvial behaviour to be determined such that the relationship between fluvial processes and the resultant geometry of preserved architectural elements can be demonstrated. A series of facies models account for complex spatial and temporal complexity within the system.

Project details (PDF)

Reservoir character of the Permo-Triassic Sherwood Sandstone Group, UK

The predominantly fluvial Sherwood Sandstone Group is exposed across much of Central and NW England and forms an important reservoir succession in the Southern North Sea and East Irish Sea basins. Fluvial facies present vary from coarse-grained channelised conglomerates to fine-grained unconfined sheet-flood sandstones, with mud-prone facies present in places. Additionally, fluvial facies exhibit a variety of styles of interaction with aeolian, sabkha and lacustrine facies, all of which has resulted in an overall succession with reservoir properties that are difficult to predict. This project is developing models that characterise the various styles of stratigraphic and diagenetic heterogeneity present within the Sherwood Sandstone Group in order to produce quantitative estimates of sand-body geometry and degree of interconnectivity that can be used as input to reservoir models in an attempt to determine the reservoir behaviour of marginal 'tight gas' plays.

Detailed analysis of basin-scale architecture has involved the recording of over 80 1D sedimentary logs from which the internal stratigraphy of various formations in the Sherwood Sandstone has been established. Regional key-surface tracing has been employed to determination the nature of spatial changes in preserved sedimentary style. The construction of 2D architectural panels has enabled the style of fluvial behaviour to be determined such that the geometry of preserved architectural elements can be used to reconstruct the likely style of the fluvial system and the nature of the processes that acted therein. A series of dynamic facies models account for complex spatial and temporal complexity within the system.

Project details (PDF)

Sand-body architecture within a mud-prone meandering fluvial succession

The Permian Warchha Sandstone of the Salt Range, Pakistan represents a mud-prone meandering fluvial succession in which gravel- and sand-dominated channelised elements are sporadically developed. Although depositional units within the succession are arranged into predictable fining-upward cycles, the lateral continuity and degree of interconnection of sand-prone units, which possess favourable reservoir characteristics, is difficult to predict. The preserved sedimentary architecture reflects the complex nature of meander belt evolution with sand-dominated lateral accretion elements juxtaposed against crevasse splay, levee and chute channel elements, each of which are themselves surrounded by mud-dominated floodplain sediments with abundant well developed palaeosols.

This project is characterising the detailed sedimentary architecture of the Warchha Sandstone to develop a series of facies models that account for the complex geometry of the sand-bodies preserved within this otherwise mud-dominated succession. The preserved architectural expression reflects a complex interplay between autocyclic meander-loop evolution, channel switching (avulsion and neck cut-off), style of sediment supply and climate. The available dataset consists of 1D sedimentary logs, subsurface wireline logs, architectural panels and lateral surface tracings, all of which have been used to determine 3D sand-body geometry and stacking pattern.

Project details (PDF)

Sedimentary character of braided and anastomosing fluvial systems, Iceland

Braided and anastomosing fluvial channel networks are widespread on the topographically unconfined pro-glacial outwash plains (sandar) of Iceland. These sand-dominated systems are exhibit a variety of channel forms ranging from single, moderate-sinuosity channels that are entrenched below the regional sandur surface, through braided channel networks in which flow is diverted around compound braid bars, to anastomosing, simultaneously-occupied channels that diverge to occupy distinct and separate parts of the outwash plain before re-converging further downstream. Anastomosing channel patterns on the distal parts of Skeiđarársandur (southern Iceland) are especially unusual as many of the streams exhibit downstream increases in discharge where they are fed from a shallow ground water table. Furthermore, these systems flow around and interact with aeolian dune and sandsheet complexes which are themselves undergoing active construction.

This project is investigating the sedimentary character of these complex fluvial systems and is seeking to determine how downstream changes in fluvial style are reflected in associated changes in preserved sedimentary expression. Ongoing detailed analysis has involved the construction of over 50 sedimentary logs from various sandar across Iceland, the assembly of many kilometres of architectural panels, textural analyses of clast fabrics, and the development of a series of detailed 3D semi-quantitative facies models that depict the arrangement of fluvial architectural elements on a range of scales.

Project details (PDF)

Sedimentary character and flow behaviour of catastrophic floods, Iceland

Controversy surrounds the rheological nature of many fluvial outburst flood deposits in Iceland and little is known about their mode of sedimentary preservation and the nature of the flows that generated them. This project is reconstructing the rheological properties of the 1918 Katla outburst flood (jökulhlaup) through a combined sedimentological and architectural approach, and is also investigating sedimentary successions related to previous flood events. The use of architectural analysis, rather than more traditional vertical profile analysis, in the study of high magnitude flow events and their deposits is providing greater insight into the relationship between the outburst flood events and their deposits.

Architectural analysis of the 1918 flood deposits has revealed the presence of extensive bounding surfaces and distinct bed-set geometries that represent transcritical and supercritical flow conditions. The structureless and diffusely stratified characteristics of depositional units that were previously ascribed to deposition from a hyperconcentrated flow and debris flow are now better interpreted as artefacts of rapid deposition following flow deceleration at the stoss side of major antidunes, and at hydraulic jumps. This sedimentary evidence indicates that the 1918 Katla outburst flood was a highly turbulent, sediment-charged flow.

Estimates of flow velocities obtained from this study are in relatively good agreement with flow velocities derived from eyewitness accounts of the flood. This study provides a basis for the recognition of large-scale sedimentary features related to supercritical flows in both the recent and ancient sedimentary record. This is important if assessments are to be made regarding the likely hazards posed by large-scale supercritical flow events.

Project details (PDF)

Salt-walled mini basin development as a control on fluvial drainage patterns in distal sheet flood and marginal marine successions

Distal fluvial sheet flood sandstones of the Triassic Moenkopi Formation are predominantly characterised by fine-grained, parallel laminated fluvial sheet sandstones with numerous minor single storey channels and rare multi-storey channel complexes, replete with a variety of styles of cross bedding. These fluvial elements are interbedded with a range of facies of marginal marine origin and that are themselves characterised by tidal flat and estuarine shoal sands, wave ripples, heterolithic deposits with mud drapes, intraclasts and extensive bioturbation that together represent a marine-influenced tidal flat and lagoon-bay setting. Around the Moab region of SE Utah this mixed fluvial and marginal marine succession exhibits dramatic changes in preserved thickness that are thought to have been controlled by the early onset of development of a series syn-sedimentary salt-walled mini-basins. Thus, the Moenkopi Formation bears many similarities to the hydrocarbon-bearing Triassic Skaggerak Formation of the UK Central North Sea.

This project will test whether the distribution of preserved facies and the style of interaction between fluvial and marginal marine facies within the Moenkopi Formation were controlled by the early movement of salt buried within the evolving Paradox Basin. Salt movement is known to have exerted a strong control on the deposition of the younger Middle Triassic Chinle Formation but little is known about its role in controlling development of the Lower Triassic Moenkopi Formation. In particular, what combinations of fluvial sediment deliver and salt-influenced mini-basin development will likely lead to the best reservoir development in terms of sandbody interconnectivity.

Project details (PDF)

Characterisation of distal fluvial sheet flood successions: implications for reservoir characterisation and evaluation

Distal fluvial sheet flood sandstones of the Permian Organ Rock Formation reflect deposition in an unconfined basin plain setting. Facies are characterised by a range of fine- to very fine-grained sandstones interbedded with siltstone and rare claystones. Minor channels, which are typically filled with intrabasinal rip-up clasts and reworked calcrete nodules, are present within the otherwise sheet dominated succession. The cyclic arrangement of subtle coarsening- or fining-upward cycles may represent the episodic progradation of channel-dominated systems into the distal parts of the basin, in response to either tectonic or climatic variation. Subtle variations in drainage pattern across the region, as revealed by palaeocurrent data, may reflect the early onset of uplift of the Monument Upwarp, which could have acted to control intrabasinal drainage patterns. Alternatively, multiple stream sources may have converged within the central part of the basin, as suggested by subtly differing grain populations within neighbouring parts of the succession. The Organ Rock Formation has received relatively little attention from sedimentologists to date, despite its close match in terms of facies architecture with several important hydrocarbon-bearing reservoir intervals including the Triassic of the Central North Sea (e.g. Skaggerak Formation) and the East Irish Sea (e.g. Ormskirk Sandstone and the transition into the overlying Mercia Mudstone Group). This project will determine how the rate of accommodation creation within the developing basin acted to control the distribution of sheet-like sand bodies and how subtle tectonic uplift may have acted to divert drainage patterns within the interior of the basin. One primary project objective is to determine whether such effects can be differentiated from the influence of multiple sediment entry points. A second primary objective is to ascertain whether climatic and/or tectonic controls on sedimentation can be effectively discerned from intrinsic sedimentary behaviour within these fine-grained systems.

Project details (PDF)

Deciphering the effects of climate change from autocyclic (intrinsic) behaviour in fluvial successions

Climate is widely cited as a primary control on the morphology and behaviour of a broad range of fluvial systems and the effects of past climatic changes are commonly considered to be expressed as distinctive stratigraphic signatures within resultant preserved deposits. However, unequivocally demonstrating a climatic origin for many of these preserved stratigraphic trends is not straightforward and alternative explanations are possible in many cases. For example, facies arrangements indicative of fluvial system shutdown and abandonment and which show an apparently drying-upward trend can sometimes be alternatively interpreted in terms of autocyclic (intrinsic) fluvial behaviour, whereby meander loop cut-off, lobe switching or nodal avulsion can result in abandonment of a fluvial reach without the need for a change in an external controlling parameter such as climate. Many fluvial sedimentary successions are known to record the preserved stratigraphic signature of a mix of both autocyclic and allocyclic controls (including climate) and these can be shown to operate on a variety of spatial and temporal scales, such that together they account for the complex stratigraphic architectures typical of most fluvial successions.

This studentship will combine outcrop-based field data collection (e.g. Utah and Arizona) with numerical stratigraphic modelling techniques to develop a suite of quantitative predictive facies and sequence stratigraphic models that account for the combined effects of climatic and autocyclic controls on fluvial system evolution and preservation. Field data will be collected from a range of fluvial successions that accumulated under the influence of a varied semi-arid climate regime. Field methods will include high-resolution sedimentary logging, facies and architectural element analysis, and sequence stratigraphic correlation. Field results will be used to guide development of a numerical (computer) model for the prediction of fluvial stratigraphic architecture. Modelling results will be employed to assess the likely significance of competing climatic versus autocyclic controls on sedimentation. Such models are important for better understanding fluvial system behaviour and for predicting subsurface fluvial stratigraphic architectures in hydrocarbon reservoirs and in saline aquifers currently being considered as sites for long-term underground CO2 storage.

Interested applicants should have experience of field-based data collection and should be willing to learn a computer programming language such as C++ or Java. The successful applicant will join a dynamic and active team of researchers within the Fluvial Research Group at Leeds.

Project details (PDF)

Additional projects underway within the FRG

  • Carboniferous, Europe (including North Sea)
  • Mesozoic braided fluvial successions, Southern Africa
  • Modern arid-climate braided alluvial systems, Namibia