This is a postprint, published version here: http://dx.doi.org/10.1144/petgeo2014-015 AbstractFacies models for wave-dominated shorelines include an "offshore transition zone" between shelfal mudstones and nearshore shoreface sandstones. Offshore transition zone deposits are commonly tabular sandstone beds interbedded with continuous mudstone beds. However, observations from the Blackhawk Formation show that the offshore transition zone locally consists of erosive-based sandstone beds with "pinch-and-swell" geometries containing steep-walled gutter-casts, in areas larger than 6 x 2 km along strike and dip. This increases the amount of sand-on-sand-contacts, and leads to improved vertical permeability. Predicting the distribution of erosive offshore transition within the subsurface is therefore desirable.In this study, offshore transition zone deposits have been studied using virtual outcrops. Tabular offshore transition zone deposits have continuous sandstone and mudstone beds much longer than 500 m, and erosive offshore transition zone deposits have discontinuous shales on average 60 m long. Reservoir modelling shows a 10-3 times increase in vertical permeability in erosive compared to tabular offshore transition deposits, the magnitude decreasing with increasing fraction of shale.Erosive offshore transition deposits occur near distributary channels, subaqueous channels and abrupt bathymetric breaks. A regional study shows that erosive offshore transition zone deposits are mainly developed where parasequences prograde into deeper water offshore the platform break of the preceding parasequence, are commonly associated with basinal turbidites, and may be related to erosion by bypassing turbidity currents.2
19Application of 3D-seismic reflection-data to igneous systems in sedimentary basins has led to 20 a revolution in the understanding of mafic sill-complexes. However, there is considerable 21 uncertainty on how geometries and architecture of sill complexes within the subsurface 22 relates those imaged in seismic reflection-data. To provide constraints on how sill complexes 23 in seismic data should be interpreted, we present synthetic seismograms generated from a 24 seismic-scale (22x0.25 km) outcrop in East Greenland constrained by abundant field-data. 25This study highlights how overlying igneous rocks adversely affect imaging of 26 underlying intrusions and rocks by decreasing seismic amplitude, frequency and making 27 steeply dipping features near-impossible to image. Furthermore, seismic modelling shows 28 that because of the high impedance contrast between siliciclastic host rock and dolerites, 29 thin (< 5m) intrusions should in principle be imaged at relatively high amplitudes. This is 30 contrary to many published 'rules of thumb' for seismic detectability of sill intrusions. 31However, actual seismic data combined with well-data shows significant amounts of un-32 imaged sill intrusions, and this is likely due to limited resolution, overburden complexity, 33 poor velocity-models, and interference between closely spaced sill-splays. Significant 34 improvements could be made by better predicting occurrence and geometry of sill intrusions 35 and including these in velocity models. 36 37
Deposits of wave-dominated shorelines are typically considered to act as relatively simple hydrocarbon reservoirs and are commonly modeled as "tanks of sand". However, important heterogeneities that can act as barriers to fluid flow occur at the parasequence, bedset and bed scales, especially in viscous oil or low permeability oil fields. Heterogeneities at the parasequence and bedset scale have been well-studied, but discontinuous mudstone-beds occurring within the shoreface have received little attention.The Book Cliffs and Wasatch Plateau are among the best exposed and most well-studied deposits of wave-dominated shallow-marine systems in the world. Two parasequences within these outcrops have been studied in detail to investigate the distributions of intrashoreface shales and to propose models for the controls on their distribution. A dataset consisting of 30 km of virtual outcrops derived from oblique helicopter-mounted lidar scanning with supporting stratigraphic sections makes it possible to collect a large quantity of accurate geometric data of depositional elements from inaccessible cliffs.A total of 921 discontinuous mudstone beds were measured. These occur as ellipses with long axes oriented normal to the paleoshoreline. Lengths and widths of these mudstone beds exhibit a lognormal distribution, with means of 21.9 and 13.8 m respectively. Within the shoreface succession, the number of mudstone beds increases downwards while size does not vary significantly with stratigraphic height. There is an average of 100 m cumulative length of shale per 100m of horizontal outcrop; this increases threefold near both wave-dominated deltas and bedset boundaries that reflect minor sea-level fluctuations during progradation.
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