Mississippian Dolomites from Lisburne Group, Killik River, Mount Bupto Region, Brooks Range, Alaska

Abstract

Allochthonous Osagian and Meramecian shelf carbonate rocks of the Lisburne Group that crop out from the Killik River west to Mount Bupto are extensively dolomitized and silicified. The carbonates were deposited as open-marine echinoderm-bryozoan wackestone, packstone, and grainstone with a thick sequence of interbedded carbonate mudstone in a shallow, restricted, marine to supratidal environment. Sequence of major diagenetic events in the dolomite is silicification of limestone to form chert nodules, followed by dolomitization of remaining limestone. Petrographic studies of the dolomites indicate that they have (1) dolomite rhombs with cloudy centers and clear rims, (2) voids formed by the partial dissolution of monocrystalline crinoid fragments, and (3) preserved organic skeletal voids. These features indicate dolomitization of limestone by hypersaline brines deficient in CO2. Field and stratigraphic relations suggest reflux dolomitization by hypersaline brines formed in a supratidal environment. The dolomite porosity, apparently not related to an ancient erosion surface or recent weathering processes, is thought to have been caused by the dolomitization process. Some pores contain anthroaxolite. Dolomite reservoir porosity may be present in the subsurface of the Brooks Range foothills and the North Slope from the Killik River to the Kiligwa River.