Accurate estimates of the spatial pattern of denudation by inversion of stacking velocity data: An example from the British Isles

Abstract

[1] Accurate measurement of the temporal and spatial variation of uplift and denudation would improve our understanding of the way in which mountain building and mantle convection modify the Earth's surface. Here, we show that inverse modeling of stacking velocity data from seismic reflection data sets is a potentially useful tool for obtaining spatially resolved denudation estimates along and across continental shelves. Unlike many techniques for measuring denudation, our approach is not restricted to outcrop or borehole locations, although it is important to calibrate results with other measurements of denudation. We have inverted 2200 stacking velocity analyses from a dense network of two-dimensional seismic reflection lines which surround the British Isles. This region was chosen because there is a well-known signal of Cenozoic uplift and denudation which is big enough to be detectable using our approach. Despite simplified assumptions about the way in which porosity varies with depth, our offshore denudation estimates are consistent with outcrop patterns and accord with published denudation measurements. Furthermore, stacking velocity estimates agree with measurements obtained by analyzing sonic velocity logs from selected boreholes. A region encompassing the British Isles has evidently undergone variable amounts of denudation during Cenozoic times. However, significant denudation (>1.5 km) is concentrated in discrete areas, such as off NW Scotland and parts of the Irish Sea. The magnitude of denudation changes significantly over short ($10 km) distances, implying that differential uplift and erosion have been important factors in creating the present-day denudation pattern.

Signature of cryptic sedimentary basin inversion revealed by shale compaction data in the Irish Sea, western British Isles

“…reflection profiles. Their estimates within the EISB are restricted to the northern part of the basin and are generally <1.6 km [Mackay and White, 2006], similar to the estimates presented here (Figure 7). In section 4, we argue that the heterogeneous exhumation patterns revealed by exhumation studies in the EISB may be a signature of sedimentary basin inversion, which has been hitherto unrecognized because of the apparent absence of compressional structures in this basin.…”

“…Both Rowley and White [1998], who estimated exhumation in a tectonic reference frame by calculating the amount of expected postrift subsidence on the basis of the preserved synrift stratigraphy, and Ware and Turner [2002] in their sonic velocity study of this basin, reported higher exhumation magnitudes from wells located in hanging walls than in footwall wells. Mackay and White [2006] estimated exhumation in the EISB and other parts of the British Isles using inverse modeling of stacking velocity data from seismic Yaliz and McKim [2003] with the permission of the Geological Society of London), location given in Figure 3. The 2.87 km of removed section in exploration well 110/13-2 (which discovered the Douglas oil field), drilled into the hanging wall of the Hamilton Fault, is higher than the value of 2.31 km measured in exploration well 110/13-1, drilled into the footwall (this well led to the discovery of the Hamilton gas field).…”

“…The general absence of post-Jurassic sediments from the EISB is in marked contrast to the basins of the southern Irish and Celtic Seas, which contain thick sequences of Jurassic, Cretaceous and Cenozoic rocks [Tappin et al, 1994;Holford et al, 2008]. Various methods for estimating exhumation have been used to show that up to 3 km of postEarly Jurassic overburden has been removed from the EISB and its margins [Colter, 1978;Chadwick et al, 1994;Rowley and White, 1998;Green, 2002;Ware and Turner, 2002;Mackay and White, 2006]. In spite of this substantial exhumation, the EISB is a prolific hydrocarbon province [Doré et al, 2002b]; as of 2001, oil and gas reserves were 176 MMBO and 7.5 TCF, respectively [Department of Trade and Industry, 2001].…”

Early Cenozoic Denudation of Central West Britain in Response to Transient and Permanent Uplift Above a Mantle Plume

“…The data from Ireland and the Isle of Man are obtained from thermal models that are based on AFT data from quasi‐vertical profiles; the used values are from the top sample. Our estimates of denudation in the EISB, 1.5–2.1 km, are more than 1 km lower than the denudation estimates of Lewis et al () calculated assuming constant, present‐day geothermal gradient, and they are in good agreement with values derived from other methods, such as sonic velocity analysis, inverse modeling of stacking velocity data from seismic reflection data, and compaction studies (Holford et al, ; Jackson & Mulholland, ; Mackay & White, ; Rowley & White, ; Ware & Turner, ).…”

Reply to discussion on ‘Multiple post-Caledonian exhumation episodes across NW Scotland revealed by apatite fission-track analysis'

“…Indeed, we consider it likely that large parts of the region experienced a complicated and dynamic history of vertical motions during the Mesozoic-Cenozoic, comparable with the motions that are being increasingly documented from sedimentary basins around the British Isles (e.g. White & Lovell 1997;Holford et al 2005Holford et al , 2009aPraeg et al 2005;Mackay & White 2006;Hillis et al 2008;Shaw Champion et al 2008;Stoker et al 2010). Detailed understanding of this behaviour, which is at present only poorly understood, will emerge only through integration of constraints on upward movements from thermochronology with complementary evidence for downward movements from geological constraints provided by sedimentary cover.…”