Corcoran & Dore(eの頭に´)(2005)による〔『A review of techniques for the estimation of magnitude and timing of exhumation in offshore basins』(129p)から〕


 Exhumation, the removal of overburden resulting from the vertical displacement of rocks from maximum burial depth, occurs at both regional and local scales in offshore sedimentary basins and has important implications for the prospectivity of petroliferous basins. In these basins, issues to be addressed by the petroleum geologist include, the timing of thermal ‘switch-off’ of source rock units, the compactional and diagenetic constraints imposed by the maximum burial depth of reservoirs (prior to uplift), the physical and mechanical characteristics of cap-rocks during and post-exhumation events, estimate their magnitude and deduce their timing. A variety of individual techniques is available to assess the exhumation of sedimentary successions, but generic categorisation indicates that ‘point’ measurements of rock displacement, in the offshore arena, are made with respect to four frames of reference - tectonic, thermal, compactional or stratigraphic. These techniques are critically reviewed in the context of some of the exhumed offshore sedimentary basins peripheral to the Irish landmass. This review confirms that large uncertainty is associated with estimates from individual techniques but that the integration of seismic interpretation and regional stratigraphic data provides valuable constraints on estimates from the more indirect tectonic, thermal and compactional methods.

Keywords: exhumation; techniques; magnitude; timing; offshore basins』

1. Introduction and definition of exhumation
2. Why measuring exhumation is important
3. Irish landmass and offshore basins - an exhumation laboratory
4. Techniques for assessment of exhumation
5. Tectonic based techniques
6. Thermal history-based techniques
7. Compaction-based techniques
8. Stratigraphic correlation-based techniques
9. Comparison of exhumation estimates derived from different methods, illustrated using wells drilled in basins offshore Ireland
 9.1. Celtic Sea Basins
 9.2. Kish Bank, Central Irish Sea and St. George's Channel basins
 9.3. Porcupine Basin
 9.4. Slyne/Erris Basins
 9.5. East Irish Sea Basin
10. Discussion and conclusions

Table 1 Exhumation/uplift lexicon - summary definitions. The preferred terms used in this paper, net exhumation and gross exhumation are shown in italics at bottom of Table

Term Summary definition Frame of reference Spatial-wavelength
Uplift Non specific term referring to displacements “opposite to the gravity vector”
(England and Molnar, 1990)
Object displaced and/or reference frame not specified Not specified
Surface uplift Displacement of Earth's surface averaged over area>103-104km2
(England and Molnar, 1990)
Geoid or mean sea level Long
Crustal uplift Also ‘uplift of rocks’ - vertical displacement of rock column
(England and Molnar, 1990: Dore (eの頭に´)et al., 2002a)
Geoid or mean sea level Short
Net uplifta Present elevation of a marker bed above its maximum burial depth
(Riis and Jensen, 1992; Dore(eの頭に´) and Jensen, 1996)
Ground level or seabed Short
Epeirogeny Broad regional uplift of continental interiors driven by thermal, isostatic or intra-plate stress fields
(Turner and Williams, 2004)
Geoid Long
Inversion Compressional reactivation of formerly extensional fault systems leading ultimately to extrusion of synrift fill
(Cooper and Williams, 1989)
Pre-extensional regional elevation Short and/or long
Erosion Local subaerial or submarine removal of material by both mechanical and chemical processes
(Ring et al., 1999; Riis, 1996)
Fixed subsurface coordinates Short
Denudation Loss of mass from both surface and subsurface parts of a drainage basin or regional landscape by all types of weathering, physical and chemical
(Leeder, 1999)
Fixed internal reference axes within bedrock Long
Exhumation Descriptive term describing removal of overburden material such that previously buried rocks are exposed
(Dore (eの頭に´)et al., 2002a)
Ground level Short and/or long
Net exhumation Difference between present-day burial depth of a reference unit and its maximum burial depth prior to exhumation
(this paper)
Tectonic, thermal, compactional, stratigraphic (relative to seabed, ground-level, or stratigraphic marker) Short
Gross exhumationb Magnitude of erosion which must have occurred at a particular unconformity prior to post-exhumation re-burial
(this paper)
Thermal, compactional, stratigraphic (relative to seabed, ground-level, or stratigraphic marker) Short
a Other terms used in the literature which are synonymous with Net Uplift are: Apparent uplift (Scherbaum, 1982; Bulat and Stoker, 1987); Apparent exhumation (Hillis, 1995a,b); Negative burial anomaly (Japsen, 1998; Japsen et al., 2002); Net exhumation (this paper).
b Term Gross exhumation (this paper) is synonymous with: Total exhumation or exhumation at time of denudation (Hills, 1995a,b); Lost cover (Cope, 1997); Removed section (Bray et al., 1992; Green et al., 2002)