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

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The results presented here show quite clearly that the main erosional episode on the East Midlands Shelf must have occurred after deposition of the youngest preserved Chalk and prior to deposition of the Palaeogene strata recognized by Stewart & Bailey (1996). Evidence in support of this conclusion is seen in the estimates of missing section derived by Japsen (2000) from sonic velocities, which show no evidence of any reduction in the amount of missing section in the vicinity of the outlier of Palaeogene strata, as might have been expected if the sedimentary section is more complete in that region. Instead, values of Japsen’s (2000) “burial anomaly” remain at about 0.8–1.0 km across the region of the outlier, suggesting that, even where the Palaeogene strata are preserved, an additional ~1 km or so of strata have been deposited and eroded.
 
The results presented here show quite clearly that the main erosional episode on the East Midlands Shelf must have occurred after deposition of the youngest preserved Chalk and prior to deposition of the Palaeogene strata recognized by Stewart & Bailey (1996). Evidence in support of this conclusion is seen in the estimates of missing section derived by Japsen (2000) from sonic velocities, which show no evidence of any reduction in the amount of missing section in the vicinity of the outlier of Palaeogene strata, as might have been expected if the sedimentary section is more complete in that region. Instead, values of Japsen’s (2000) “burial anomaly” remain at about 0.8–1.0 km across the region of the outlier, suggesting that, even where the Palaeogene strata are preserved, an additional ~1 km or so of strata have been deposited and eroded.
  
In fact, these observations lead to the conclusion that, at least in the vicinity of the outlier, erosional removal of the additional strata must have been complete prior to deposition of the Palaeogene strata preserved in the outlier. With the age of the oldest Palaeogene units in the outlier being of Late Palaeocene (Early Thanetian) age, the timing constraints from AFTA for the onset of cooling suggest that exhumation must have been extremely rapid, with the entire package of additional strata removed in as little as perhaps 5 Ma (taking the oldest limit on cooling from AFTA of 65 Ma and an age of ~60 Ma for Early Thanetian from Harland 1989). Erosion of sedimentary rocks of similar (Palaeogene) age to those in the outlier from adjacent regions of the shelf was probably achieved during the more recent (Miocene) episode of exhumation recognized in regional AFTA data, particularly onshore (see earlier discussion). This episode most likely correlates with the phase of Late Miocene inversion recognized in the SNS by Stewart & Bailey (1996) that they suggested represented the dominant erosional episode across the region.
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In fact, these observations lead to the conclusion that, at least in the vicinity of the outlier, erosional removal of the additional strata must have been complete prior to deposition of the Palaeogene strata preserved in the outlier. With the age of the oldest Palaeogene units in the outlier being of Late Palaeocene (Early Thanetian) age, the timing constraints from AFTA for the onset of cooling suggest that exhumation must have been extremely rapid, with the entire package of additional strata removed in as little as perhaps 5Ma (taking the oldest limit on cooling from AFTA of 65Ma and an age of ~60Ma for Early Thanetian from Harland 1989). Erosion of sedimentary rocks of similar (Palaeogene) age to those in the outlier from adjacent regions of the shelf was probably achieved during the more recent (Miocene) episode of exhumation recognized in regional AFTA data, particularly onshore (see earlier discussion). This episode most likely correlates with the phase of Late Miocene inversion recognized in the SNS by Stewart & Bailey (1996) that they suggested represented the dominant erosional episode across the region.
  
 
The foregoing discussion shows that many lines of evidence point to the conclusion that the offshore as well as the onshore EMS has undergone two major episodes of burial and subsequent exhumation during the Latest Cretaceous and Cainozoic. This is consistent with the conclusion reached by Japsen (1997), although the relative contributions of the two episodes may not vary exactly as he suggested. This aspect of the AFTA data from the southern North Sea will be discussed in detail, together with the regional dataset, elsewhere.
 
The foregoing discussion shows that many lines of evidence point to the conclusion that the offshore as well as the onshore EMS has undergone two major episodes of burial and subsequent exhumation during the Latest Cretaceous and Cainozoic. This is consistent with the conclusion reached by Japsen (1997), although the relative contributions of the two episodes may not vary exactly as he suggested. This aspect of the AFTA data from the southern North Sea will be discussed in detail, together with the regional dataset, elsewhere.

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