Print this pageControl of Paleotopography and Exposure Duration on Meteoric Calcite Cementation: Carboniferous Lisburne Group, Northeast Alaska
GOLDSTEIN, ROBERT H, RANDALL C. CARLSON, and PAUL ENOS
The Carboniferous Lisburne Group in the Sadlerochit, Shublik, and Fourth Range mountains (northeastern Brooks Range) preserves carbonate strata of the Alapah and Wahoo Limestones from the Sadlerochit "high" to paleotopographically lower areas 65 km to the southwest. The southward paleoslope is documented from on lapping geometries, erosional topography, and lateral facies variation. Twelve surfaces of subaerial exposure were identified in the Alapah and seven in the Wahoo; many can be traced across significant paleotopography. Cross-cutting relationships show that cathodoluminescence (CL) banded calcite cement was precipitated during subaerial exposure events; thus it is meteoric in origin. Vertical correlation of CL zones illustrates that meteoric calcite occluded much of the porosity. Low Mg and Sr contents, and depleted delta{18}O (mean of -6o/oo) support the meteoric interpretation. Isotopic compositions of meteoric calcites in upslope areas are the same as in downslope areas, and the proportion of porosity reduced by meteoric calcites is higher in upslope areas than in downslope areas, indicating that duration of exposure rather than climate is the primary control. cements commonly increase in abundance upward towards the subaerial surfaces. The Lisburne Group shows two significant trends that should apply to other units: Meteoric calcite cementation increases vertically approaching subaerial surfaces. Meteoric calcite cementation decreases down paleoslope as a function of duration of subaerial exposure rather than climate change. This indicates that more porosity in carbonate rocks should be found downdip on seaward flanks of paleo-highs, a novel model for petroleum exploration.