THE UPPER ST. GEORGE GROUP, WESTERN PORT AU PORT PENINSULA: LITHOSTRATIGRAPHY, BIOSTRATIGRAPHY, DEPOSITIONAL ENVIRONMENTS AND REGIONAL IMPLICATIONS

• Main Authors: W. D. Boyce, I. Knight, D. M. Rohr, S. H. Williams, E. A. Measures
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Subjects: Newfoundland
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.493.7498; http://www.nr.gov.nl.ca/mines%26en/geosurvey/publications/cr2000/boyce.pdf

Shallow-water carbonate rocks of the upper part of the Early Ordovician St. George Group outcrop in several roadside exposures at the west end of the Port au Port Peninsula, western Newfoundland. The succession contains a previously undoc-umented, fairly abundant and diverse shelly fauna that includes ostracodes, trilobites, articulate brachiopods,?bryozoa, cephalopods, crinoids, gastropod shells and opercula, machaeridians, sponges and calcispheres. The fauna occurs within metre-scale parasequences of open-shelf, muddy carbonates overlain by grainy carbonates that are commonly rich in small oncolites, and which are assigned to the Costa Bay Member, Catoche Formation. Well-preserved graptolites occur in the upper 20 m of the member, an interval marked by a shoaling sequence of subtidal muddy carbonate to crossbedded, now dolomitized, grainstone. In contrast, peritidal cyclic carbonates of the overlying Aguathuna Formation yield mainly a mixed molluscan fauna of cephalopods, gastropod shells and silicified gastropod opercula although grainstone beds contain as yet indeterminate artic-ulate brachiopods and trilobites. The abundant and diverse faunas in shoaling, subtidal, limestone parasequences of the Costa Bay Member support an open-shelf, marine environment, seaward of a major grainstone barrier complex. The presence of graptolites at the top of the Costa Bay Member suggests that a significant oceanic flooding event may have marked the shelf at the transition from the