Print this pageInfluence of an Early Paleozoic Cratonic Arch on Dolomitization in Upper Ordovician Viola Formation, South-Central Kansas, USA
NEWELL, K. DAVID
The Upper Ordovician Viola Fm., a shelf carbonate, is eroded over the broad Chautauqua arch, and is dolomitized on its flanks. This dolomitization is reduced beneath outliers of the Upper Ordovician Maquoketa Shale; this pattern suggests dolomitization after deposition of the Maquoketa.
Cathodoluminescence indicates the dolomite near the crest of the arch has a complex internal texture ("collage") that is indicative of recrystallization, but down dip, a concentric texture predominates. Collage and associated mimetic dolomites are stoichiometric, but the concentric dolomite is calcian.
The dolomitization occurred before Late-Mississippian deep burial because dolomitic units in the Viola are brecciated by karstic processes associated with the unconformity beneath the Upper Devonian-Lower Mississippian Chattanooga Shale. Fluid inclusions indicate that dolomitization occurred at temperatures less than about 50 degrees C.
Strontium isotopes of the concentric dolomite are consistent with dolomitization during the Late Ordovician, whereas those of the collage and mimetic dolomites are consistent with a Silurian event. Primary(?) fluid inclusions in the collage dolomite are hypersaline, and may indicate seepage-reflux of brines entering the Viola where it is truncated on top of the arch. Isotopically negative oxygen in the mimetic and collage dolomites are not consistent with hypersalinity, but recrystallization may have altered the original isotopic signature. Primary(?) fluid inclusions and oxygen isotopes in the concentric dolomite indicate generally lower but variable salinities during precipitation, compatible with a mixing-zone environment.