Editing Shawhead, Crocketford - an excursion

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=== Introduction  ===
 
=== Introduction  ===
[[File:ShawheadExcursionMap.jpg|thumbnail|Locality map and outline geology for the Shawhead excursion in the Crocketford area.]]
 
 
Major faults, components of an imbricate thrust stack, divide the Southern Uplands sequence of steeply dipping turbidites and pelagic shales into a series of tectonostratigraphical tracts (Figure 1). The fine-grained sedimentary rocks of the Moffat Shale Group are relatively soft and the tract-defining faults formed preferentially within them. Thus me line of faulting is often marked by a series of Moffat Shale inliers and in areas of poor exposure, may be expressed as a topographic low across the landscape where the softer Moffat Shales have been preferentially eroded. Where sequences of turbidites are faulted against each other, without intervening shales, the line of the fault is very much more difficult to trace.  
 
Major faults, components of an imbricate thrust stack, divide the Southern Uplands sequence of steeply dipping turbidites and pelagic shales into a series of tectonostratigraphical tracts (Figure 1). The fine-grained sedimentary rocks of the Moffat Shale Group are relatively soft and the tract-defining faults formed preferentially within them. Thus me line of faulting is often marked by a series of Moffat Shale inliers and in areas of poor exposure, may be expressed as a topographic low across the landscape where the softer Moffat Shales have been preferentially eroded. Where sequences of turbidites are faulted against each other, without intervening shales, the line of the fault is very much more difficult to trace.  
  
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Volcaniclastic grains interpreted to be from a volcanic island arc are known from Ordovician turbidite sequences within the Northern Belt (Stone et al., 1987; Styles et al., 1989), and the Moffat Shale ruffs may have come from the same source. Alternatively, they may be related ro basalts in the Moffat Shale Group, which are inferred to have been generated by back arc spreading marginal to the Iapetus Ocean or by within-plate volca nism in the Iapetus Ocean (Lambert et a1., 1981; Stone et al., 1987).  
 
Volcaniclastic grains interpreted to be from a volcanic island arc are known from Ordovician turbidite sequences within the Northern Belt (Stone et al., 1987; Styles et al., 1989), and the Moffat Shale ruffs may have come from the same source. Alternatively, they may be related ro basalts in the Moffat Shale Group, which are inferred to have been generated by back arc spreading marginal to the Iapetus Ocean or by within-plate volca nism in the Iapetus Ocean (Lambert et a1., 1981; Stone et al., 1987).  
[[File:ShawheadGraptoliteBiostratigraphy.jpg|thumbnail|Graptolite biostratigraphy for the Moffat Shale, Gala and Hawick groups in the Shawhead area.]]
 
  
 
==== 7 Ewe Brae: folding, Cairnharrow Formation and Turner's Monument  ====
 
==== 7 Ewe Brae: folding, Cairnharrow Formation and Turner's Monument  ====

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