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Palaeokarst in the Ordovician of the southern Great Basin, USA: implications for sea‐level history
Author(s) -
Cooper John D.,
Keller Martin
Publication year - 2001
Publication title -
sedimentology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.494
H-Index - 108
eISSN - 1365-3091
pISSN - 0037-0746
DOI - 10.1046/j.1365-3091.2001.00393.x
Subject(s) - geology , dolostone , breccia , paleontology , facies , sedimentary depositional environment , ordovician , lithology , laurentia , clastic rock , carbonate platform , sedimentary rock , geochemistry , carbonate rock , structural basin
Abundant and regionally unique dolostone lithoclast breccias occur throughout the shallow‐marine, Lower to Middle Ordovician Pogonip Group in the Nopah Range and adjacent ranges in eastern California and southern Nevada. Breccia bodies display sharply cross‐cutting relationships with host dolostone bedrock stratigraphy. They also show stratigraphic variability in size, shape and dolostone clast composition, but similarity in breccia matrix composition and framework texture and fabric. These characteristics are consistent with a palaeokarst origin. Upsection changes in breccia clast lithology as well as multiple occurrences of associated quartz sand‐filled grikes (solution‐widened fissures) indicate multiple episodes of carbonate platform exposure and karstification. Repeated karstification is also indicated by stratiform bodies of quartz sand and thin terra rossa palaeosols that locally truncate breccias and grike systems, thus bracketing karstified exposure surfaces. Facies successions and stacking patterns between recognized exposure surfaces are developed as transgressive–regressive cycles and thus show depositional sequence architecture. Hence, these breccias and other associated palaeokarst features are related to a succession of disconformities that provide a sequence‐stratigraphic framework for assessing Ordovician relative sea‐level history of the south‐western Cordilleran margin of Laurentia.