Lower Paleozoic stratigraphic and biostratigraphic correlations in the Canadian Cordillera: implications for the tectonic evolution of the Laurentian margin

Abstract

The ancient Laurentian margin rifted in the latest Neoproterozoic to early Cambrian but appears not to have developed as a simple passive margin through a long, post-rift, drift phase. Stratigraphic and conodont biostratigraphic information from four platform-to-basin transects across the margin has advanced our knowledge of the early Paleozoic evolution of the margin. In northeastern British Columbia, two northern transects span the Macdonald Platform to Kechika Trough and Ospika Embayment, and a third transect spans the parautochthonous Cassiar Terrane. In the southern Rocky Mountains, new conodont biostratigraphic data for the Ordovician succession of the Bow Platform is correlated to coeval basinal facies of the White River Trough. In total, from 26 stratigraphic sections, over 25 km of strata were measured and > 1200 conodont samples were collected that yielded over 100 000 conodont elements. Key zonal species were used for regional correlation of uppermost Cambrian to Middle Devonian strata along the Cordillera. The biostratigraphy temporally constrains at least two periods of renewed extension along the margin, in the latest Cambrian and late Early Ordovician. Alkalic volcanics associated with abrupt facies changes across the ancient shelf break, intervals of slope debris breccia deposits, and distal turbidite flows suggest the margin was characterized by intervals of volcanism, basin foundering, and platform flooding. Siliciclastics in the succession were sourced by a reactivation of tectonic highs, such as the Peace River Arch. Prominent hiatuses punctuate the succession, including unconformities of early Late Ordovician, sub-Llandovery, possibly Early to Middle Silurian and Early Devonian ages.

U–Th–Pb geochronology of meta-carbonatites and meta-alkaline rocks in the southern Canadian Cordillera: A geodynamic perspective

“…6). However, our results are consistent with the conclusions of Pyle and Barnes (2003), based on regional biostratigraphic correlations and alkalic volcanism in the Canadian Cordillera, that at least two episodes of renewed extension affected this part of the continental margin in the late Cambrian and late Early Ordovician.…”

“…This pulse (~800-485 Ma) relates to the controversy over whether one Early Paleozoic rift-drift event, or two separate rift-drift events in the Neoproterozoic and Early Paleozoic affected the western margin of Laurentia (Colpron et al, 2002;Lund et al, 2010;Pyle and Barnes, 2003;Timmons et al, 2001). Our findings, in conjunction with existing sedimentological and geochronological constrains (e.g., Colpron et al, 2002;Goodfellow et al, 1995;Lester et al, 2001;Lund et al, 2010;Pigage and Mortensen, 2004), supplement models depicting the evolution of the western Laurentian margin that indicate a prolonged and diachronous process with multiple extensional episodes characterized by igneous activity and the formation of depositional basins during Neoproterozoic to early Palaeozoic times (Colpron et al, 2002;Harlan et al, 2003;Li et al, 2008;Lund et al, 2010;Pyle and Barnes, 2003;Timmons et al, 2001;Whitmeyer and Karlstrom, 2007).…”

“…Subsequent recurrent rifting along the continental margin led to the deposition of Paleozoic miogeoclinal strata (Fig. 1a) and the intrusion of alkalic and ultrapotassic rocks along the Canadian and U.S. miogeocline in the Late Cambrian and late Early Ordovician (Lund et al, 2010;Pyle and Barnes, 2003;this study). In addition, McMillan and McLemore (2004) report repeated extension-related intracratonic alkaline and carbonatite magmatism from the southwestern U.S. between~665 and 425 Ma in an aulacogen setting ( Fig.…”

Geometry of the Neoproterozoic and Paleozoic rift margin of western Laurentia: Implications for mineral deposit settings

“…Geochronologic data indicate that rifting began in the Cryogenian and accelerated in the Ediacaran to Cambrian (Stewart, 1972;Bond and Kominz, 1984;Thompson et al, 1987;Ross, 1991;Colpron et al, 2002). Stratigraphic data indicate that there was signifi cant younger Late Cambrian-Early Ordovician and Late Devonian extension (Thompson et al, 1987;Turner et al, 1989;Pyle and Barnes, 2003;Emsbo et al, 2006). These data document a prolonged episodic rift and basin-subsidence history for the western Laurentian margin, resulting in successive stacked passive-margin sequences (Thompson et al, 1987;Turner et al, 1989;Ross, 1991;Lund and Cheney, 2008;Pyle and Barnes, 2003).…”

“…3; Colpron et al, 2002). Related subsidence accelerated from Early Cambrian to Early Silurian time, as shown by facies compilations (Cecile, 1982;Turner et al, 1989;Gabrielse and Yorath, 1991;Stevens, 1991;Poole et al, 1992;Price and Sears, 2000;Pyle and Barnes, 2003) and subsidence calculations (Bond and Kominz, 1984;Levy and Christie-Blick, 1991).…”