Editing Post-Carboniferous burial and exhumation histories of Carboniferous rocks of the southern North Sea and adjacent onshore UK

Jump to navigation Jump to search

Warning: You are not logged in. Your IP address will be publicly visible if you make any edits. If you log in or create an account, your edits will be attributed to your username, along with other benefits.

The edit can be undone. Please check the comparison below to verify that this is what you want to do, and then save the changes below to finish undoing the edit.

This page supports semantic in-text annotations (e.g. "[[Is specified as::World Heritage Site]]") to build structured and queryable content provided by Semantic MediaWiki. For a comprehensive description on how to use annotations or the #ask parser function, please have a look at the getting started, in-text annotation, or inline queries help pages.

Latest revision Your text
Line 35: Line 35:
 
== 1. Previous AFTA studies ==
 
== 1. Previous AFTA studies ==
  
Application of AFTA to samples from outcrops and hydrocarbon exploration wells on the East Midlands Shelf (EMS), and to samples from the UK southern North Sea (SNS) wells, has shown that the sedimentary section in this region has experienced major Cainozoic cooling (Green 1989, Bray et al. 1992, Green et al. 2001). Results in sedimentary rocks of Carboniferous to Triassic age from outcrops on the onshore EMS reveal cooling from palaeotemperatures of 70–90°C beginning some time between 65 and 55Ma (Palaeocene). Results from subsurface samples confirm this episode and also provide improved definition of the cooling history, revealing an additional subsequent cooling episode from lower peak palaeotemperatures, which began some time between 25 Ma and 5 Ma (Miocene). Vitrinite reflectance data from Carboniferous units in EMS wells are highly consistent with the Palaeocene palaeotemperatures defined by AFTA (Bray et al. 1992, Green et al. 2001), and it is clear that, in these wells, Carboniferous units cooled from their maximum postdepositional palaeotemperatures in Palaeocene times, which effectively dates the termination of active hydrocarbon generation from Carboniferous source rocks in the region.
+
Application of AFTA to samples from outcrops and hydrocarbon exploration wells on the East Midlands Shelf (EMS), and to samples from the UK southern North Sea (SNS) wells, has shown that the sedimentary section in this region has experienced major Cainozoic cooling (Green 1989, Bray et al. 1992, Green et al. 2001). Results in sedimentary rocks of Carboniferous to Triassic age from outcrops on the onshore EMS reveal cooling from palaeotemperatures of 70–90°C beginning some time between 65 and 55Ma (Palaeocene). Results from subsurface samples confirm this episode and also provide improved definition of the cooling history, revealing an additional subsequent cooling episode from lower peak palaeotemperatures, which began some time between 25Ma and 5Ma (Miocene). Vitrinite reflectance data from Carboniferous units in EMS wells are highly consistent with the Palaeocene palaeotemperatures defined by AFTA (Bray et al. 1992, Green et al. 2001), and it is clear that, in these wells, Carboniferous units cooled from their maximum postdepositional palaeotemperatures in Palaeocene times, which effectively dates the termination of active hydrocarbon generation from Carboniferous source rocks in the region.
  
Attempts to understand the mechanisms responsible for the elevated Palaeocene palaeotemperatures and subsequent Cainozoic cooling, and also the exact timing at which cooling began, have been the subject of some discussion. Green (1989) reported AFTA data from five EMS wells. He suggested that Palaeocene palaeogeothermal gradients were indistinguishable from present-day values, and that 1–2 km of section have been removed by Cainozoic uplift and erosion. Bray et al. (1992) came to a similar conclusion, on the basis of a more rigorous statistical analysis of palaeotemperatures derived from AFTA and VR data from these wells. Bray et al. (1992) also reported that similar effects had been detected in wells from the offshore (SNS) portion of the EMS.
+
Attempts to understand the mechanisms responsible for the elevated Palaeocene palaeotemperatures and subsequent Cainozoic cooling, and also the exact timing at which cooling began, have been the subject of some discussion. Green (1989) reported AFTA data from five EMS wells. He suggested that Palaeocene palaeogeothermal gradients were indistinguishable from present-day values, and that 1–2km of section have been removed by Cainozoic uplift and erosion. Bray et al. (1992) came to a similar conclusion, on the basis of a more rigorous statistical analysis of palaeotemperatures derived from AFTA and VR data from these wells. Bray et al. (1992) also reported that similar effects had been detected in wells from the offshore (SNS) portion of the EMS.
  
 
Although results of sonic velocity studies of wells in the region (Hillis 1991, 1993) supported the estimates of Cainozoic exhumation derived from AFTA and VR data, Holliday (1993) and Smith et al. (1994) considered these amounts to be unrealistically large, on the basis of regional geological trends. These concerns were echoed more recently by Holliday (1999). Specific comments included doubts about the validity of extrapolating linear palaeogeothermal gradients to estimate removed section, questions concerning the most appropriate values of palaeosurface temperature, and, on the basis of criticisms by McCulloch (1994) that were shown to be erroneous by Green et al. (1995a), the precise timing at which cooling began.
 
Although results of sonic velocity studies of wells in the region (Hillis 1991, 1993) supported the estimates of Cainozoic exhumation derived from AFTA and VR data, Holliday (1993) and Smith et al. (1994) considered these amounts to be unrealistically large, on the basis of regional geological trends. These concerns were echoed more recently by Holliday (1999). Specific comments included doubts about the validity of extrapolating linear palaeogeothermal gradients to estimate removed section, questions concerning the most appropriate values of palaeosurface temperature, and, on the basis of criticisms by McCulloch (1994) that were shown to be erroneous by Green et al. (1995a), the precise timing at which cooling began.

Please note that all contributions to Earthwise may be edited, altered, or removed by other contributors. If you do not want your writing to be edited mercilessly, then do not submit it here.
You are also promising us that you wrote this yourself, or copied it from a public domain or similar free resource (see Earthwise:Copyrights for details). Do not submit copyrighted work without permission!

Cancel Editing help (opens in new window)

  [] · [[]] · [[|]] · {{}} · · “” ‘’ «» ‹› „“ ‚‘ · ~ | °   · ± × ÷ ² ³ ½ · §
[[Category:]] · [[:File:]] · <code></code> · <syntaxhighlight></syntaxhighlight> · <includeonly></includeonly> · <noinclude></noinclude> · #REDIRECT[[]] · <translate></translate> · <languages/> · ==References== · {{reflist}} · ==Footnote== · {{reflist|group=note}} · <ref group=note> · __notoc__ · {{DEFAULTSORT:}} <div class="someclass noprint"></div> {{clear}} <br>

Template used on this page: