Unit Name: Powers Steps Formation
Unit Type: Lithostratigraphic
Rank: Formation
Status: Formal
Usage: Currently in use
Age Interval: Early Ordovician (485.4 - 470 ma)
Age Justification: The formation contains lingulid brachiopods (van Ingen, 1914), orthocone ce-phalopods, synhomalonotid trilobites and the asaphid trilobite Ogyginus terranovicus, the graptolites Didymograptus nitidus and D. nitidus var. deflexus, acritarchs (Dean and Martin, 1978), and abundant and diverse trace fossils (Ranger et al., 1984). These fossils indicate the Powers Steps is Arenig in age.
Province/Territory: Newfoundland & Labrador
Originator: Ranger et al, 1984.
Type Locality:
Powers Steps, northwestern side of Bell Island, Conception Bay, eastern Newfoundland (47 deg 38'05"N, 52 deg 59'17"W; NTS 1 N/10).
Distribution:
The formation is about 70 m thick. It is exposed at Powers Steps, be-tween Youngsters Gulch and Upper Grebes Nest Point, on the northwestern side of Bell Island. An additional large exposure is present between Gull Island North Head and the gravel beach immediately to the east of Grebes Nest Point.
Lithology:
The basal 6 m consists of interbedded, silty shale, shale, and thin beds of phosphatic and pyritic, oolitic ironstone containing pyritized graptolites, pyrite-coated shale pebbles, and phosphatic shell fragments. The shale and silty shale also contain thin layers and stringers of pyritic and phosphatic shale pebble conglomerates. The overlying 28 m is fissile, dark, graptolitic shale containing thin, rippled siltstone and sandstone layers and lenses that increase in abundance and thickness upwards. Within the shale are several horizons, along which limey septarian nodules surrounded by cone-in-cone structures are common. In the upper 36 m, silty shale and sandy siltstone gradually replace the fissile shale. These sediments exhibit a variety of sedimentary structures. The sequence is believed to have been deposited initially in shallow subtidal conditions and latterly in an intertidal environment. Included within this formation is the Youngsters Gulch Member.
Relationship:
The Powers Steps Formation disconformably overlies the Lower Ordovi-cian Dominion Formation of the Bell Island Group with a sharp contact. The upper boundary is sharp and apparently conformable with the overlying Scotia Formation. The Wabana Group includes, in ascending order, the Powers Steps, Scotia, Grebes Nest Point, Gull Island and Gravel Head formations.
History:
The name was formally proposed by Ranger et al. (1984). It includes van Ingen's (1914) units H1-H3, of his Wabana Series. In Nautiyal's (1966) informal classification, the Youngsters Gulch Member was included in the lower member of his Wabana formation and the remainder of the Powers Steps Formation, together with the overlying Scotia Formation, were included in his middle member. King (1982) and Pickerill and Fillion (1983) used the name informally.
Other Citations:
Bergström, 1976; Dean and Martin, 1978; Hayes, 1915; King, 1982; Nautiyal, 1966, 1973; Pickerill and Fillion, 1983; Ranger, 1979; Ranger et al., 1984; Rose, 1952; van Ingen, 1914.
Source: CSPG Lexicon of Canadian Stratigraphy, Volume 6, Atlantic Canada; G.L. Williams, L.R. Fyffe, R.J. Wardle, S.P. Colman-Sadd, Boehner, R.C. (editor)
Contributor: C.F. O'Driscoll
Entry Reviewed: Yes
Name Set: Lithostratigraphic Lexicon
LastChange: 29 Apr 2003