Editing Dinantian and Namurian depositional systems in the southern North Sea

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=== 3.2 The Dinantian of the Southern North Sea Basin ===
 
=== 3.2 The Dinantian of the Southern North Sea Basin ===
  
Hard data on the Dinantian of the Southern North Sea Basin are very scant. They are mainly confined to well 43/17-2, which penetrated the whole Namurian basin-fill succession and continued into Dinantian strata. Some 520 m of inferred Dinantian mudstones were penetrated, all probably falling within the Brigantian. These were referred to by Cameron (1993) as the Bowland Shale Formation and are broadly analogous with the Lower Bowland Shales of the Craven Basin (Earp et al. 1961) and with the mud-rich successions beneath the Edale Shales of Derbyshire, known from the Alport borehole (Stevenson & Gaunt 1971). These onshore examples differ from the succession in 43/17-2 in that they have interbedded turbiditic sandstones. The Lower Bowland Shales include the Pendleside Sandstone, which probably resulted from the bypassing of sand from Yoredale deltas on the Askrigg Block. The Dinantian mudstones at Alport have thin limestones, which were probably derived from the Derbyshire Massif carbonate platform to the south. Both of these onshore cases may be relevant in predicting what might occur offshore.
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Hard data on the Dinantian of the Southern North Sea Basin are very scant. They are mainly confined to well 43/17-2, which penetrated the whole Namurian basin-fill succession and continued into Dinantian strata. Some 520m of inferred Dinantian mudstones were penetrated, all probably falling within the Brigantian. These were referred to by Cameron (1993) as the Bowland Shale Formation and are broadly analogous with the Lower Bowland Shales of the Craven Basin (Earp et al. 1961) and with the mud-rich successions beneath the Edale Shales of Derbyshire, known from the Alport borehole (Stevenson & Gaunt 1971). These onshore examples differ from the succession in 43/17-2 in that they have interbedded turbiditic sandstones. The Lower Bowland Shales include the Pendleside Sandstone, which probably resulted from the bypassing of sand from Yoredale deltas on the Askrigg Block. The Dinantian mudstones at Alport have thin limestones, which were probably derived from the Derbyshire Massif carbonate platform to the south. Both of these onshore cases may be relevant in predicting what might occur offshore.
  
 
The relationship between Dinantian deltas on the Mid North Sea High and any coeval deepwater areas to the south, and the nature and history of the basin margin, remain conjectural. However, it is difficult to imagine a situation where sands did not bypass to distal deepwater areas once such a differentiated bathymetry developed. Early Namurian turbidite sandstones at well 43/17-2 (discussed in more detail in section 3.3 below) were presumably bypassed through Upper Limestone Group deltas and there may be similar Dinantian examples elsewhere in the basin. The main problem is to identify the time at which accelerated subsidence led to the development of deep water in the Southern North Sea Basin. Distal parts of the fluvial and deltaic systems, known from the early Dinantian of the Mid North Sea High, may have extended southwards in similar shallow-water facies before differential subsidence created the bathymetric contrasts inferred from available well data for the late Dinantian. These uncertainties impact on estimates of volumes of deepwater mudstones, which are potentially important source rocks in the basin. The Kirby Misperton-1 well may provide a clue to the timing of accelerated subsidence in the area. This is discussed further in Section 4.
 
The relationship between Dinantian deltas on the Mid North Sea High and any coeval deepwater areas to the south, and the nature and history of the basin margin, remain conjectural. However, it is difficult to imagine a situation where sands did not bypass to distal deepwater areas once such a differentiated bathymetry developed. Early Namurian turbidite sandstones at well 43/17-2 (discussed in more detail in section 3.3 below) were presumably bypassed through Upper Limestone Group deltas and there may be similar Dinantian examples elsewhere in the basin. The main problem is to identify the time at which accelerated subsidence led to the development of deep water in the Southern North Sea Basin. Distal parts of the fluvial and deltaic systems, known from the early Dinantian of the Mid North Sea High, may have extended southwards in similar shallow-water facies before differential subsidence created the bathymetric contrasts inferred from available well data for the late Dinantian. These uncertainties impact on estimates of volumes of deepwater mudstones, which are potentially important source rocks in the basin. The Kirby Misperton-1 well may provide a clue to the timing of accelerated subsidence in the area. This is discussed further in Section 4.

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