Stable isotope stratigraphy across the Silurian-Devonian boundary in southern Oklahoma and subsurface west Texas
Stable isotopic ( 13C - ä 18O) analysis of carbonates from the Upper Silurian Henryhouse and Lower Devonian Haragan Formations in southern Oklahoma, and the Frame Formation (Upper Silurian-Lower Devonian) in southern Andrews County, Texas was conducted to determine if an excursion in ä 13C coincides with the shift in conodont faunal diversity that characterizes the Klonk event in Southwest Laurentia. Results show a gradual steady increase in ä13C (+ 1.0 %o) across the Henryhouse-Haragan boundary that reaches a peak value (~ + 3.0%o) in the early Lochkovian Icrodiuspostwoschmidti zone. The 5'^C signature of the Frame Formation also shows a steady increase in 5'^C (~ + 3.0 %o) from the late Pridoli that reaches a peak value (~+ 5.0 %o) in the early Lochkovian Icrodius postwoschmidti zone. The ä 13C chemostratigraphic curves do not exhibit an excursion at the level where conodont faunal diversity shifts at the Klonk event in the Henryhouse-Haragan or Frame formations. Intercontinental correlation of the data with other chemostratigraphic studies of Southern Gondwanan successions including the Global Stratotype Section and Point at Klonk in the Czech Republic, reveals no relationship between ä 13C and conodont faunal diversity as proposed by Jeppsson's (1990,1997,1998) model of Silurian Ocean cyclicity.