Controls on temporal & spatial distribution of organic matter in siliciclastic mudstones: implications for source rock development in Shale Gas plays

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This PhD is an exciting opportunity to contribute a rapidly expanding area of sedimentology and use innovative approaches to investigate the fundamental physical, chemical and biological controls that act upon mudstone variability. Up to 60% of future hydrocarbon production may derive from unconventional Shale Gas sources. This PhD would aid understanding of known plays and examine the potential for the UKCS Shale Gas plays. Until recently geologists have assumed that mudstone successions were largely homogenous with any inhomogeneties produced by changes in primary productivity and anoxia at the time of deposition. Recent studies utilising optical and electron optical methods reveal that these rocks are much more variable than previously assumed. Successive strata (mm and sub-mm scales) can contain very different proportions of material derived from clastic input, primary productivity and diagenetic processes. These studies also reveal that variability is systematic and can be interpreted in terms of varying detrital inputs, biological productivity and subsequent diagenesis using sequence stratigraphic principles. Therefore understanding the fundamental controls that underpin lithofacies variability at mm scales has significant implications for interpreting climate change signals preserved in these strata and for effectively exploring for unconventional shale gas plays. Lithofacies variability at these scales controls the distribution and abundance of organic matter and their hydrofracturing properties. This proposal is linked to, but distinct from, 'Lithofacies variability in mixed clastic carbonate fine-grained successions: implications for identifying Shale Gas exploration sweet spots' submitted by Dr. J. Macquaker (University of Manchester). Major aim: to investigate the variability of siliciclastic mudstone lithofacies in order to determine the fundamental controls on sedimentation and the preservation of organic matter in fine-grained successions. Key Objectives: (1) Describe the variability in mudstone character from Pennsylvanian siliciclastic successions from northern England using a multidisciplinary approach (field logging, optical, electron optical, whole rock geochemical methods). (2) Interpret this variability in terms of fundamental physical, chemical and biological controls operating at and close to the sediment water interface. (3) Investigate geochemical proxies as indicators of redox conditions during deposition that may correspond with enhanced organic matter deposition/preservation. (4) Generate integrated high-resolution sequence stratigraphic models in order to determine the temporal and spatial processes that might lead to unusual silica enrichment in specific environments. Deliverables (1) A mudstone lithofacies scheme, highlighting organic rich facies, that can be interpreted in terms of fundamental controls on mudstone deposition (Objectives 1 and 2). (2) An assessment of geochemical proxies, links to mudstone lithofacies and their significance in interpreting changing redox conditions and association with enhanced organic matter preservation (Objective 3). (3) A high-resolution sequence stratigraphic model that draws together all elements of the basin fill, and examines the temporal and spatial distribution, and preservation, of organic-rich mudstone lithofacies in a siliciclastic-dominated, shallow-marine setting. (Objective 4) The student will be trained in sedimentological and sequence stratigraphic analysis; sedimentological and palaeontological field and laboratory procedures; optical and electron microscopy, geochemical preparation, analytical and interpretation techniques (XRF, XRD and organic carbon). The student will spend between 3 and 18 months working within the company (Leatherhead and Upstream Research Company, Houston), in addition to formal meetings with ExxonMobil supervisors.