Road cut section, K98-30A through the Costa Bay Member, Route 463 section

Detailed stratigraphic studies of coeval Early Ordovician carbonates of western Newfoundland and North-East Greenland have been ongoing for several years. Part of this work includes the study of pioneering collections of fossils from North-East Greenland by John W. Cowie and Peter J. Adams of Bristol University from 1950 to 1953 (see Cowie and Adams, 1957); these are now housed at the National Museum of Wales, and are the subject of several studies by the authors under the leadership of Dr. Lucy McCobb. Independently, detailed stratigraphic studies of the succession in North-East Greenland by Knight and Boyce in 2000 and 2001, as part of a collaborative GEUS expedition (Stouge et al., 2001, 2002), has led to the redefinition of the Ordovician carbonate stratigraphy there (Stouge et al., in press) and has enabled fairly accurate stratigraphic location of the Cowie and Adams collections. In western Newfoundland, stratigraphic studies in the St. George Group have been ongoing (see Knight et al., 2007, 2008; Boyce and Knight, 2010). It has been long understood that the rocks of the two disparate parts of the Laurentian paleocontinent were coeval and in part lithologically similar. Nonetheless, it has been the melding of these various research projects that has highlighted that the trilobite faunas in early (Gasconadian/Skullrockian to basal Demingian/Stairsian) and late (Jeffersonian/Tulean to Cassinian/Blackhillsian) Early Ordovician strata in western Newfoundland and North-East Greenland have common characteristics, and encouraged the present study in western Newfoundland.

The Gasconadian/Skullrockian to basal Demingian/Stairsian Watts Bight Formation

The Watts Bight Formation on the Port au Port Peninsula is best known from the section at Isthmus Bay, made famous by description of microbial mounds of the Green Head complex (Pratt and James, 1982; see Knight et al., 2008) and the conodont monograph of Ji and Barnes (1994). However, work over the last few years has indicated that the lithostratigraphy of this section is unique and not replicated when the formation is traced 20 km to the west. Complex mounds are no longer dominant — the succession instead consists of monotonous, thickly bedded, stylonodular lime mudstone and wackestone with frequent thin sheets and lenses of grainstone and rudstone; mound complexes are only sporadic at the base of the formation. This appear to supports a more open, subtidal shelf setting in the west of the peninsula. A number of sections from 30 to 60 m thick were measured in detail through the lower part of the formation between Lower Cove and Ship Cove. Trilobites were newly discovered in the Ship Cove section, together with ostracodes, brachiopods, gastropods and cephalopods. This and other sections also prove to be rich in conodonts correlative with the Cordylodus lindstromi to C. angulatus zones (Ji and Barnes, 1994, figures 18, 19 and 20). Species of the following trilobite genera have so far been identified – Millardicurus, Symphysurina and Bellefontia. In particular, Millardicurus sp. cf. M. armatus (Poulsen, 1937), Symphysurina myopia Westrop in Landing et al., 2003, and Bellefontia gyracantha (Raymond, 1910)? provide a faunal linkage with the Tribes Hill Formation (Westrop et al., 1993; Landing and Westrop, 2006) of New York State, U.S.A.Millardicurus armatus (Poulsen, 1937) and Bellefontia sp.cf. B. gyracantha (Raymond, 1910) occur in the coeval Antiklinalbugt Formation of the Fimbulfjeld Group of North-East Greenland, where they figure prominently in the Cowie and Adams collection as well as the collections made in 2000 by Boyce and Knight.

The late Cassinian/Blackhillsian Costa Bay Member, Catoche Formation, Route 463

This section through the Costa Bay Member is unique to the western end of Port au Port Peninsula and was described in some detail following its 1998 discovery (Boyce et al., 2000). The rock types include recessive and rubbly weathering, dolomitic and argillaceous, stylonodular lime mudstones to packstones capped by massive weathering, clean, oncolitic and fossiliferous, peloidal and intraclastic packstone to rudstones. This contrasts with fenestral-peloidal grainstones that make up the type section on eastern Port au Port Peninsula and with other sections logged and described briefly by Knight et al. (2008), elsewhere in western Newfoundland.Trilobites from the Route 463 section are characterized by Cybelopsis, Goniotelina/Acidiphorus and Benthamaspis amongst others, a fauna correlative with those of the Pseudocybele nasuta Zone (J) in western USA and the 'Ostracod Limestone' of the Nunatami Formation (Poulsen, 1927) of western North Greenland and similar to a rich fauna collected by Cowie and Adams (1957) from the 'Black Limestones' interval of the Cape Weber Formation of North-East Greenland. This fauna transcends a range of different lithofacies, depending on the disparate geographic location in which it is found in Newfoundland and Greenland, supporting a common event in which the shelf margins in the two areas and elsewhere in Laurentia experienced eustatic sea level rise, i.e., a deepening event. This event, noted also in the Fort Cassin Formation of New York State, was recently called the Laignet Point highstand by Landing and Westrop (2006) after the type locality at Port au Choix, where distinctive rocks were first noted and informally defined as a member by Knight (1977). Systematic sampling through the Route 463 section this summer yielded several new collections and extended the range of several trilobite species, most notably Cybelopsis speciosa Poulsen, 1927. The trilobites are accompanied by abundant brachiopods, gastropods, cephalopods, ostracodes, crinoids, oncolites, graptolites and machaeridian annelid plates.

ACKNOWLEDGEMENTS

Dr Lucy McCobb traveled to western Newfoundland with permission of the National Museum of Wales. Ruth Gingrich is thanked for finding important trilobite fossils in the Watts Bight Formation. Tony Paltanavage is thanked for his drafting skills.

Lithostratigraphy of the Watts Bight Formation

Cranidium of C. speciosa, head is about 1.6 cm across

Geology of the Port au Port Peninsula and location of sections studied in the St George Group, 2010

A graphic log of the Costa Bay Member, Catoche Formation, Route 463, Port au Port Peninsula showing range of zone J trilobites

A, rare, complete specimen of Cybelopsis speciosa

Trilobites of theCosta Bay Member

G e o l o g y o f w e s t e r n N e w f o u n d l a n d t e r r a i n s showing study area, 2010

Stratigraphy of the St. George Group, Port au Port Peninsula showing stratigraphic intervals logged in measured sections

Brachiopod, trilobite free check and crinoid ossicle from a F012, Costa Bay member, Route 463. Brachiopod about 1 cm across

Typical limestone cycle of the Costa Bay Member, route 463. Recessively and rubbly weathering, stylonodular, dolomitic and shaly skeletal mudstone are capped by more massive weathering, fossiliferous and oncolitic, peloidal packstone and grainstone. Measuring stick 1.5 m

Acidiphorus pygidium, note the robust tail spine

Strotactinus pygidium

Acidiphorus cranidium

Stratigraphic studies of the Watts Bight Formation and the Costa Bay Member (Catoche Formation),

St. George Group on the Port au Port Peninsula, western Newfoundland1 1 2W. Douglas Boyce , Ian Knight and Lucy McCobb

1 2 Geological Survey of Newfoundland and Labrador; National Museum of Wales, Cardiff, Wales, UK

Lithostratigraphy of the Costa Bay Member

Simpl i f ied geologica l map of Greenland showing the location of lower Paleozoic sections studied at Ella Ø and Albert Heims Bjerge

Stratified limestones onlap and erosionally overlie a large complex of thrombolitic boundstone mounds just west of the main Ship Cove section

Limestone section through the lower Watts Bight Formation measured near Ship Cove. The well stratified, stylobedded, lime mudstone to grainstone yielded scattered fossils including newly discovered trilobites

Detailed graphic logs of sections through the lower Watts Bight Formation at Ship Cove and Lower Cove, Port au Port Peninsula

Trilobites of the Watts Bight Formation

Bel le fon t ia c ran id ium f rom the Antiklinalbugt Formation, North-East Greenland. Cowie and Adams collection, National Museum of Wales

Bellefontia cranidium, Watts Bight Formation

Negative of Millardicurus cephalon about 1 cm across

Cranidium of Symphysurina myopia

Pygidium of Symphysurina sp.