A proposed Global Boundary Stratotype Section and Point for the base of the Middle Ordovician Series: The Niquivil section, Precordillera of San Juan, Argentina

Graphic correlation of Argentine Precordillera and North American Lower/Middle Ordovician sections

“…It is of interest to note, however, that the single level of occurrence of B. triangularis in Precordilleran sections, projects to the 599 csu-level in the Ibexian-Whiterockian composite section assembled graphically by Sweet, Ethington and Harris (2005). Thus, the conodont-based framework reported here includes the potential for recognition of the Whiterock Canyon-based GSSP proposed many years ago by Ross and Ething-(Continued) ton (1991), the Cooperignathus aranda -based GSSP proposed by Albanesi et al (2003Albanesi et al ( , 2004, and, possibly, the Baltoniodus triangularis -based GSSP proposed recently by Stouge et al (2005). College, 1950;M.S., Ph.D., 1952, 54, University of Iowa.…”

“…Using range data abstracted from the literature for the Niquivil, Peña Sombría, and Yanso sections (Albanesi et al, 1998, Albanesi et al, 2003, 2004 a Precordilleran composite section was compiled, with the Niquivil section serving as SRS (= standard reference section). This essentially straightforward procedure yielded the correlations shown in Figure 1.…”

The Global Stratotype Section and Point for the base of the Middle Ordovician Series and the Third Stage (Dapingian)

“…The occurrence of M. flabellum in the Huanghuachang section demonstrates that the boundary coincides with the base of the T. leavis Biozone in type localities for the North American Whiterockian and the Ibexian sections (Ethington & Clark, 1982, Ross et al, 1997. It also correlates with the base of the T. leavis Biozone in the upper San Juan Limestone of Precordillera, San Juan, Argentina (Albanesi et al, 2003(Albanesi et al, , 2006 based on the presence of diagnostic fossils typical of the underlying Oepikodus evae Biozone, e.g. Reutterodus andinus, Oepikodus intermedius and Microzarkodina sp.…”

“…leavis. In the Niquivil section near San Juan, Argentina the FAD of Cooperignathus aranda basically coincides with the boundary between the O. evae and O. intermedius Biozones as these biozones have been defined by Albanesi et al (2006). This level should be a little below the top of the lower O. evae Biozone in the Huanghuachang section (Wang et al 2005).…”

“…The two GSSP proposals (Wang et al, 2004(Wang et al, , 2005Albanesi et al, 2006), were discussed and debated at length on the Ordovician Subcommission website. A postal ballot completed in October 2006, 75% of the votes favored the Huanghuachang proposal over the Niquivil proposal, and 94% of the voting members then approved the Huanghuachang GSSP in a ballot completed in December 2006.…”