Paleokarst Evolution of the Ordovician Pogonip Group near Beatty, NV

Kervin, Robert J.¹, Dr. Adam Woods¹ (1) California State University, Fullerton, Fullerton, CA

The lower to mid-Ordovician Pogonip Group (Upper Ibexian-Lower Whiterockian) of southwestern Nevada contains an abundance of dolostone breccias that have been interpreted as the result of paleokarstification that occurred throughout southern Nevada and east-central California. The breccias occur within conduit-like cavities ranging in width from centimeters to tens of meters wide and centimeters to nearly one hundred meters thick. A paleokarst occurrence from the Pogonip Group was closely examined in the field and in thin section to determine its origin and evolution. Cathode luminescence was also incorporated to aid in the interpretation of cement paragenesis. Initial results reveal four distinct packages of paleokarst within this outcrop of subtidal sediments: (1) a large chaotically filled karst cavity that likely formed as result of dissolution at a marine-meteoric boundary; (2) chaotically filled karst conduits that formed as a result of meteoric vadose influence; (3) a paleodoline that displays evidence of growth strata and mantling breccias (due to platform exposure); and, (4) a repeated transgressive-regressive sequence that resulted in short-lived marine sediment deposition and continued meteoric karst influence. Cathode luminescence and thin section petrography display evidence of deep burial and varied geochemical influence during burial that resulted in cement growth and reduced intraclast porosity. Collectively, this paleokarst sequence does not follow the typical chaotic-mosaic-crackle brecciation sequence described by previous authors. Thus, not only do these paleokarst breccias testify to the complexity often found in paleokarst, but they may also lead to better reservoir prediction in similar settings.