Cambrian to Middle Devonian Assemblages

Fritz, W H; Cecile, M. P.; Norford, B S; Morrow, D.W.; Geldsetzer, H. H. J.

doi:10.1130/dnag-gna-g2.151

Cited by 29 publications

(11 citation statements)

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“…The strata were deposited on a prograding passive continental margin that faced the proto-Pacific ocean to the west (Ross, 1991). The shelf margin trended NW-SE (present-day orientation) and was located east (landward) of the study area during deposition of the underlying Neoproterozoic Windermere Supergroup (Narbonne & Aitken, 1995;Dalrymple & Narbonne, 1996) and only a few tens of kilometres west of the study area throughout the Lower Cambrian (Fritz et al, 1991). In the Mackenzie Mountains the sub-Cambrian unconformity is expressed as a pronounced erosional unconformity of regional extent that caps the Windermere Supergroup (Narbonne & Aitken, 1995).…”

Section: Geological Settingmentioning

confidence: 99%

Early Cambrian braid‐delta deposits, MacKenzie Mountains, north‐western Canada

MacNaughton¹,

Dalrymple²,

Narbonne³

1997

Sedimentology

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Latest Neoproterozoic to earliest Cambrian strata in north‐western Canada provide an example of a pre‐vegetation braid‐delta depositional system. Depositional environments represented in the succession include braided fluvial and braid‐delta distributary channels, aeolian dune fields and interdistributary lagoons/bays, as well as mouth bar, beach to shoreface, and prodelta to distal shelf settings. Three formations have been investigated: the Ingta Formation formed in wave‐dominated nearshore to offshore shelf environments with little or no apparent deltaic influence, whereas the overlying Backbone Ranges and Vampire formations contain an extensive record of braid‐delta deposits ranging from braidplain to distal prodelta facies. On the braid‐plain, river channels reached widths of up to several kilometres. Such channels terminated seaward in braid deltas that showed some shoreline protuberance and were characterized by fluvial‐dominated mouth‐bar deposition with lesser wave influence; wave‐dominated deltaic successions are rare in the succession. Interdeltaic areas were characterized by wave‐dominated prograding shorelines. Interdistributary lagoons probably formed primarily in abandoned distributary channels. Delta‐front/prodelta deposits are silt‐rich and contain abundant soft‐sediment deformation, including slumps. The deposits in these formations illustrate the significantly different nature of sedimentation prior to the advent of land plants. This is illustrated in the dominance of braided fluvial deposition and of silt‐rich offshore facies that may have resulted from enhanced aeolian transport of loess. The non‐actualistic effects of limited bioturbation and extensive microbial binding apparently exerted relatively little control on the distribution of facies. However, the absence of extensive bioturbation is manifest in pristine preservation of primary sedimentary structures, while the hypothesized latest Proterozoic‐earliest Cambrian decline in microbial binding may be reflected in the upward increase in the abundance of sole marks in the succession.

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Section: Geological Settingmentioning

confidence: 99%

Early Cambrian braid‐delta deposits, MacKenzie Mountains, north‐western Canada

MacNaughton¹,

Dalrymple²,

Narbonne³

1997

Sedimentology

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“…On a broader scale, the upper Stephen Formation of the southern Canadian Rockies is coeval with the mixed unit in the Great Basin (Robison, 1976) and records the seaward migration of a low-energy, terrigenous 'inshore basin' across underlying carbonate lithofacies (Aitken, , 1993. Near the Cathedral escarpment in eastern British Columbia, a thin interval of the upper member of the Stephen Formation (Ehmaniella burgessensis faunule) disconformably overlies thick massive carbonate of the Cathedral Formation comprising the near-vertical shelf-margin (McIlreath, 1977;Fritz et al, 1991;Aitken, 1993). It is tempting to speculate that this disconformity and the Ehmaniella-age disconformity of the southern Great Basin are coeval features.…”

Section: Continent-scale Correlationsmentioning

confidence: 99%

Cross‐platform architecture of a sequence boundary in mixed siliciclastic‐carbonate lithofacies, Middle Cambrian, southern Great Basin, USA

Osleger

Montañez

1996

Sedimentology

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Stratigraphic analysis of mixed siliciclastic‐carbonate lithofacies within the Middle Cambrian Bonanza King Formation of the southern Great Basin reveals three distinct facies associations that record a range of depositional environments from semi‐arid tidal flats to deeper subtidal, restricted lagoons. Stratigraphic trends, cross‐platform facies variations and correlation of individual surfaces across 250 km of the study area suggest that these mixed lithofacies were deposited in three temporally distinct phases. (1) Extensive progradation of mixed peritidal environments culminated in a prolonged episode of subaerial exposure marked by an areally extensive intraclast breccia (0·5–1·2 m thick) that we interpret to be a major Type 1 sequence‐bounding disconformity. (2) Abrupt flooding of the exposed platform resulted in the deposition of mixed deeper subtidal lithofacies, including a condensed interval of fissile, fossiliferous shale. (3) Progressive shallowing and aggradational accumulation was accompanied by a decrease in siliciclastics and a shift to pure carbonate deposition. Deep‐water siliciclastics and megabreccias record deposition along the base‐of‐slope off the Middle Cambrian shelf‐edge, and are interpreted to represent lowstand deposits emplaced during the prolonged episode of subaerial exposure of the shallow shelf. The presence of fine siliciclastics in both peritidal facies and sharply overlying deeper subtidal facies of the study interval within the Bonanza King suggests a variable, but relatively continuous, influx of terrigenous material throughout an extended period of accommodation change, apparently asynchronous with respect to the predictive model of reciprocal sedimentation. We suggest that the primary siliciclastic source changed with relative sea‐level position. During lowered sea level, aeolian processes acting upon the unvegetated Cambrian craton transported fine siliciclastics onto peritidal and shallow‐subtidal environments. During higher sea level, coastal siliciclastic reservoirs supplied sediment that was transported for long distances by geostrophic currents flowing along the submerged platform. As opposed to many Cambro‐Ordovician grand cycles that are commonly interpreted to consist of a transgressive shaly half‐cycle grading upward into a regressive carbonate half‐cycle, the sequence boundary within this Middle Cambrian succession occurs within siliciclastic‐rich, mixed lithofacies rather than in adjoining purer carbonates, implying that some ‘grand cycles’ should not be considered synonymous with ‘sequences’. Interbasinal correlations of the Type 1 sequence boundary within the mixed unit are speculative, primarily because of the inherent imprecision of available trilobite biostratigraphy. However, there is evidence that an extended episode of subaerial exposure may have been continent‐wide during the Ehmaniella trilobite biochron.

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“…2). The tectonic setting and pattern of continental margin sedimentation changed in the Late Devonian through Early Mississippian as the Kechika Trough filled and deposition of northerly and westerly derived clastics was initiated (Gordey et al 1987;Fritz et al 1991). Associated with Devonian sedimentation are second-order sub-basins bounded to the northeast by Early and Middle Devonian reefs, such as the Kwadacha and Akie reefs (Pigage 1986;MacIntyre 1992).…”

Section: Regional and Economic Geologymentioning

confidence: 99%

“…Regionally, south of 56°N, Lower and Middle Devonian strata are preserved only locally beneath a sub-Upper Devonian unconformity (Fritz et al 1991). In the northern Cordillera, Nahanni map area, Yukon and Northwest territories, the Deserters Formation correlates to the Grizzly Bear Formation (Gabrielse et al 1973) based on the lithology and conodont fauna.…”

Section: Regional Correlationmentioning

confidence: 99%

“…This study improves the correlation of Lower to Middle Devonian units from the Ospika Embayment to the MacDonald Platform. It is also significant in describing strata that elsewhere in the Cordillera, especially south of latitude 56°N, are absent beneath a sub-Upper Devonian unconformity (Fritz et al 1991). The local preservation of strata from the Ospika Embayment (Fig.…”

Section: Introductionmentioning

confidence: 99%

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Conodont biostratigraphy of the Lower to Middle Devonian Deserters Formation (new), Road River Group, northeastern British Columbia

et al. 2003

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A new Lower to Middle Devonian basinal unit of the Road River Group, herein formally named the Deserters Formation, contains argillaceous, crinoidal limestone and black shale deposited in a linear sub-basin of the Ospika Embayment, southern Kechika Trough. The abrupt lateral facies changes in the region, facies thickness, and occurrence of volcanics indicate a period of extensional tectonism. A total of 53 (45 kg each) samples from the Deserters Formation yielded 7766 conodont elements assigned to 14 genera representing 33 species. The formation ranges from the Lochkovian (eleanorae Zone, or lower part of the delta Zone of the Cordilleran Region) to Eifelian (australis Zone). The temporal constraints established by conodont biostratigraphy allow correlation to the Grizzly Bear Formation, a regionally restricted Lower to Middle Devonian unit in the Selwyn Basin to the north.

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Cambrian to Middle Devonian Assemblages

Cited by 29 publications

References 0 publications

Early Cambrian braid‐delta deposits, MacKenzie Mountains, north‐western Canada

Early Cambrian braid‐delta deposits, MacKenzie Mountains, north‐western Canada

Cross‐platform architecture of a sequence boundary in mixed siliciclastic‐carbonate lithofacies, Middle Cambrian, southern Great Basin, USA

Conodont biostratigraphy of the Lower to Middle Devonian Deserters Formation (new), Road River Group, northeastern British Columbia

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