Editing Shawhead, Crocketford - an excursion

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==== 7 Ewe Brae: folding, Cairnharrow Formation and Turner's Monument  ====
 
==== 7 Ewe Brae: folding, Cairnharrow Formation and Turner's Monument  ====
 
Follow the farm track to a quarry at the crest of Ewe Brae (NX 835 758) where medium-to thick-bedded turbidites of the Cairnharrow Form at ion we reworked.  
 
Follow the farm track to a quarry at the crest of Ewe Brae (NX 835 758) where medium-to thick-bedded turbidites of the Cairnharrow Form at ion we reworked.  
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Steeply dipping strata, with beds grading from sandstone through siltstone to mudstone clearly young to the NW. Cleavage is well developed in the mudstones, where it is steeply inclined, and is also evident, though refracted, in the finer-grained sandstones. Both cleavage and bedding have been affected by shallow open folds with gently inclined axial planes and hinges that plunge a few degrees toward the SW; fold wavelength is about 4 cm and amplitude is about 2 cm. The folds are obvious on the quarry faces as open crenulations of the first cleavage. This folding is evidence for a second deformation episode (D2) imposed on the thrust-related deformation (D1) that produced the main cleavage. Slickensides on bedding plunge steeply to the SW and are probably associated with movement on the Laurieston Fault.  
 
Steeply dipping strata, with beds grading from sandstone through siltstone to mudstone clearly young to the NW. Cleavage is well developed in the mudstones, where it is steeply inclined, and is also evident, though refracted, in the finer-grained sandstones. Both cleavage and bedding have been affected by shallow open folds with gently inclined axial planes and hinges that plunge a few degrees toward the SW; fold wavelength is about 4 cm and amplitude is about 2 cm. The folds are obvious on the quarry faces as open crenulations of the first cleavage. This folding is evidence for a second deformation episode (D2) imposed on the thrust-related deformation (D1) that produced the main cleavage. Slickensides on bedding plunge steeply to the SW and are probably associated with movement on the Laurieston Fault.  
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Approximately 150 m due east of the spring, towards the crest of Larglanglee Hill, turbidites of the Cairnharrow Formation exposed in a small quarry (NX 820 745) comprise thickly bedded, sandstone-dominated units interbedded with thinly bedded mudstone-dominated units. There has been some tectonic disturbance and cleavage is very well developed, perhaps due to the proximity of the Laurieston Fault.  
 
Approximately 150 m due east of the spring, towards the crest of Larglanglee Hill, turbidites of the Cairnharrow Formation exposed in a small quarry (NX 820 745) comprise thickly bedded, sandstone-dominated units interbedded with thinly bedded mudstone-dominated units. There has been some tectonic disturbance and cleavage is very well developed, perhaps due to the proximity of the Laurieston Fault.  
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From the quarry walk south to the cluster of trees on the crest of Larglanglee Hill (NX 819 744). In the SW corner of the plantation, turbidites of the Cairnharrow Formation can be seen in a series of exposures. Younging is towards the NW The lowest beds comprise a thinning-and fining-upward sequence, over an interval of approximately 8 m. Thickly bedded turbidite units dominated by sandstone form the base and are overlain by medium to thinly bedded units of slightly finer-grained sandstone. The top of the sequence is of thinly bedded units of fine-grained sandstone grading into siltstone and mudstone. Such thinning-and fining-upward sequences in submarine fan deposits are thought to record the gradual abandonment of a distributary channel in a mid-fan setting (Walker and Mutti, 1973). Cleavage is only weakly developed in the mudstone tops of the turbidite units but is non-axial planar to the S1 fold structures. The strike of cleavage is rotated about 10° clockwise from the strike of bedding typical of the incongruent relationship between bedding and first cleavage seen in many Southern Uplands turbidite sequences. Cleavage formation may well have postdated the initial phase of folding; if so the relationship between cleavage and bedding cannot reliably be used to determine fold geometry or the way up of the bedding. A futher complexity here is the folding of bedding about small, open sub­horizontal D2 hinges.  
 
From the quarry walk south to the cluster of trees on the crest of Larglanglee Hill (NX 819 744). In the SW corner of the plantation, turbidites of the Cairnharrow Formation can be seen in a series of exposures. Younging is towards the NW The lowest beds comprise a thinning-and fining-upward sequence, over an interval of approximately 8 m. Thickly bedded turbidite units dominated by sandstone form the base and are overlain by medium to thinly bedded units of slightly finer-grained sandstone. The top of the sequence is of thinly bedded units of fine-grained sandstone grading into siltstone and mudstone. Such thinning-and fining-upward sequences in submarine fan deposits are thought to record the gradual abandonment of a distributary channel in a mid-fan setting (Walker and Mutti, 1973). Cleavage is only weakly developed in the mudstone tops of the turbidite units but is non-axial planar to the S1 fold structures. The strike of cleavage is rotated about 10° clockwise from the strike of bedding typical of the incongruent relationship between bedding and first cleavage seen in many Southern Uplands turbidite sequences. Cleavage formation may well have postdated the initial phase of folding; if so the relationship between cleavage and bedding cannot reliably be used to determine fold geometry or the way up of the bedding. A futher complexity here is the folding of bedding about small, open sub­horizontal D2 hinges.  

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