PALEOCLIMATIC SIGNIFICANCE OF CALCRETES IN THE DINANTIAN OF THE COCKBURNSPATH OUTLIER (EAST LOTHIAN NORTH BERWICKSHIRE)

Calcretes are present at two horizons in the Dinantian Inverclyde and Strathclyde Groups of the Cockburnspath Outlier. The lower calcrete, p robably uppermost Courceyan to Chadian in age (at the top of the Hurke r Member, Ballagan Formation), was formerly interpreted as a tectonic breccia. Petrology shows that the bed is a calcrete with associated ro ot casts. Pyrite within this calcrete suggests that it underwent marin e hydromorphism, probably caused by rising marine groundwater associat ed with relative sealevel rise. The upper calcrete, probably Asbian in age (in the Cove Harbour Member, Aberlady Formation), is mature (stag e 3) and has undergone in situ grainification caused by desiccation an d shrinkage. The Hurker Member calcrete (and other palaeoclimatic indi cators) suggest that semi-arid climatic conditions prevailed in Scotla nd throughout the Lower Carboniferous until Chadian times. This is con sistent with palaeoclimatic indicators elsewhere in Euramerican rocks. The Cove Harbour Member calcrete probably correlates with calcretes i n the Sandy Craig Formation in Fife. However, it occurs in a rock Sequ ence dominated by humid climatic indicators (coals, sideritic mudstone palaeosols and oil-shales), implying a regionally significant semiari d period, during otherwise humid conditions. This finding is consisten t with fluctuating humid to semi-arid palaeoclimatic phases proposed f or the Dinantian of England and Wales.