BSRG PG Fieldtrip: Skye, Scotland (2005)
A series of superb sections with well exposed Mesozoic sediments will be examined on Skye. The sediments were deposited in actively subsiding half-grabens and record brackish and shallow marine/deltaic environments with significant variations between wave and tidal-influence. The fieldtrip will focus on 1) interpretation of tidal and wave influence within shallow marine and brackish siliciclastic sediments and 2) illustration and discussion of published sequence stratigraphic interpretations.
From a petroleum geology viewpoint, at virtually all the localities it is possible to look at aspects of heterogeneity which are likely to affect fluid flow, particularly vertical and horizontal variations. At a larger scale (between outcrops) it is possible to infer variations in reservoir architecture-heterogeneity related to changes in base-level (i.e. incised valley fills cutting shoreface). In addition it is possible to illustrate changes in architecture-heterogeneity between the same stratigraphic units in different sub-basins. In other words, despite potential reservoir units being the same age, the architecture/heterogeneity and likely mechanisms of production from these reservoirs is completely different as you cross a fault. In most localities it is also possible to see the development of small-scale faults (discussion of sealing/non-sealing capacity) and the effects of igneous intrusions on cementation and fracturing of sandstones, and maturation of organic-rich mudstones.
Potential localities and aspects of interest
Camas Malag - Tertiary granite, Durness Limestone Formation, ?Triassic Broadford Beds. Illustrates marine transgression/onlap of tilted fault-block in late Triassic/early Jurassic times. Sediments are shallow marine with evidence for an initial high energy rocky shoreline followed by lower energy transgression.
Spar Cave - Bearreraig Sandstone Formation. Tidal sand wave deposits exceptional potential reservoir.
Bearreraig - Bearreraig Sandstone Formation. A section with 3 stacked coarsening upwards parasequences from offshore open marine to wave-dominated upper shoreface. Very different architecture/heterogeneity distribution compared to Spar Cave.
Invertote - Elgol Sandstone Formation, Great Estuarine Group. Incised valley-fill cutting through wave-dominated shoreface.
Kilt Rock viewpoint - Tertiary sills and Valtos Sandstone Formation, Great Estuarine Group.
Dunans, Staffin Bay - Staffin Bay Formation. Late Jurassic transgression akin to Heather Formation development in North Sea.
Dunans - Red Bole, weathered Tertiary lavas. Collection of pretty zeolite minerals!
Rubha Garbhaig - Valtos Sandstone Formation, Great Estuarine Group. Mixed carbonate/clastic sequence sandwiched between a Tertiary sill.
Elgol - Bearreraig Sandstone Formation and Great Estuarine Group. Superb section through much of the Middle Jurassic illustrating internal variations in shallow marine sandstone body architecture, faults, effects of igneous activity, transgressions, parasequence stacking patterns etc.
Drinan - Scalpay Sandstone, Raasay Ironstone and Bearreraig Sandstone Formation. Superb ichnofauna, condensed section with oolitic ironstones and subsequent development of tidal sand waves. Very variable reservoir quality/and architecture.
Leader: Adrian Hartley, Dept. of Geology, University of Aberdeen