Shelf sedimentation across Precambrian-Cambrian boundary: Chapel Island Formation, southeastern Newfoundland
The upper Precambrian-Lower Cambrian Chapel Island Formation consists of medium- and fine-grained siliciclastics and minor limestones that record the early evolution of shelly fossils and complex trace fossils. Deposition of these Avalonian sediments occurred in a variety of shelf environments. Temporal and spatial changes in the conditions of sedimentation during the deposition of this sequence resulted in a wide spectrum of sedimentary and biogenic structures. Facies transitional with underlying terrestrial and shallow-marine red beds were deposited in foreshore and upper-shoreface settings under tidal influence and display tidal channels, shrinkage cracks (desiccation and synaersis), abundant current ripples (bimodal-bipolar current distribution), and phosphatic nodules. Sandstones and siltstones deposited in shoreface to outer-shelf settings contain evidence of storm and wave reworking. Features present include: gutter casts, thin granule lag zones, phosphate nodules, slump-fold zones, hummocky cross-stratified beds,and thin to medium-grained sandstones with sharp bases and gradational tops, wave-rippled upper surfaces, climbing wave ripple laminations, and draping laminations. These features indicate deposition on a storm- and wave-dominated shelf with locally variable topography. Thick massive siltstone beds and pebbly mudstones are interpreted as debris flows formed on a gentle slope. Red and green mudstones, nodular limestones, and medium to thick (up to 60 cm) limestones were deposited during periods of low siliciclastic input. The limestone beds - micrites to packed biomicrites - contain oncolitic and planar stromatolites, sheet-crack cavities (containing the oldest known coelobiontic fauna), iron-manganese encrusted surfaces, authigenic barite, mudcracks, intraformational and extraformational conglomerate layers, and small channels. These are interpreted as intertidal and supratidal deposits.
- Research Organization:
- Memorial Univ. of Newfoundland, St. John's
- OSTI ID:
- 5700901
- Report Number(s):
- CONF-850322-
- Journal Information:
- Am. Assoc. Pet. Geol., Bull.; (United States), Journal Name: Am. Assoc. Pet. Geol., Bull.; (United States) Vol. 69:2; ISSN AAPGB
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
020200* -- Petroleum-- Reserves
Geology
& Exploration
CAMBRIAN PERIOD
CANADA
CARBONATE ROCKS
CONTINENTAL MARGIN
CONTINENTAL SHELF
DEPOSITION
GEOLOGIC AGES
GEOLOGIC FORMATIONS
ISLANDS
LIMESTONE
NEWFOUNDLAND
NORTH AMERICA
PALEOZOIC ERA
PRECAMBRIAN ERA
ROCKS
SEDIMENTARY ROCKS
SEDIMENTATION