Geo-Techno Alert: For those interested, here is the Abstract of a paper to be given at the 'Edmonton Geological Society' talk on Friday, October 16th at 4:00pm (I believe it's open to the public):
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"The Bad Heart Formation (Upper Cretaceous) of west-central Alberta: origin, paleoenvironments, and relation to kimberlite pipe swarms of the Buffalo Head and Chinchaga."
Christopher J. Collum, Royal Tyrrell Museum of Palaeontology,
Drumheller, Alberta, Canada. e-mail: cjcollum@mtroyal.ab.ca
The Bad Heart Formation (Coniacian stage: Scaphites depressus Zone) is a relatively thin (>7.0 m thick), fossiliferous, bioturbated, fine to coarse-grained sandstone, correlative to the Marshybank Member of the Wapiabi Formation. 40Ar-39Ar radiometric dating of sanidine feldspar from Scaphites depressus / Volviceramus involutus Zone bentonite suggests an age of 85.5 Ma BP for the Bad Heart Formation. Present only in the area of the Peace River Arch, facies of the Bad Heart Formation are interpreted to reflect active tectonism along major Precambrian-age basement fault trends and related horsts and grabens (Donaldson, 1997; Collum, in prep). The most notable feature of the Bad Heart Formation is the presence of abundant iron-rich ooids (composed of authigenic berthierine, nontronite and goethite), indicating marine water depth of > 30 metres and syndepositional fault-related seafloor brine seeps (Kimberley, 1994; Collum, 1997).
The nuclei of a significant portion of these phyllosilicate ooids are mineral grains not normally found in the Western Canada Sedimentary Basin. These include euhedral feldspars, quartz, eclogitic garnet and microdiamonds. Also present are chromite, olivine, and pyroxenes. These are all considered to be indicator minerals and elements of kimberlite / lamproite emplacement (Fipke et al., 1995). Their presence within these ooids require the event(s) resulting in the distribution of these xenoliths to either shortly precede or be coeval to the Bad Heart Formation. To date, approx. 25 kimberlite pipes have been discovered nearby in the region of the Buffalo Head Hills by Ashton et al. Preliminary K-Ar dates obtained from perovskite in crater facies restrict the age of these intrusions to 86.0 - 88.0 Ma BP (Carlson et al., 1998), closely matching those obtained for the Bad Heart / Marshybank clastic wedge to the southwest. Based on the paleogeographic position, relative to known Cretaceous facies belts, the Buffalo Head pipes were likely extruded into the Western Interior seaway. Active prospecting and development in the Chinchaga Hills region by Marum et al. is focused on approx. 20 anomalies visible on high-resolution aeromagnetic surveys. Petrographic studies of material from these targets have revealed the presence of kimberlitic deposits in this region of Alberta as well, although their extent, mining potential, and relation to the Buffalo Head pipes is not well known. The general distribution of marine and coastal facies in the Chinchaga region indicate that some of these pipes may have been extruded on the vegetated coastal plain of the western shoreline of the seaway. Therefore, available data support the following temporal sequence of closely spaced events:
1. progradation of shorelines in Western Canada during the Late Coniacian due to relative sea-level fall,
2. initiation of kimberlite pipe emplacement, both subaqueously and subaerially, (possible causal mechanism for such extrusive volcanism discussed below)
3. seepage of iron-saturated, saline brines and resulting production of nontronite ooids.
Finally, the most controversial aspect of the Bad Heart - Chinchaga - Buffalo Head kimberlite pipes and associated deposits and their possible origin from one or more meteorite impacts in Western Canada during the Coniacian stage. Although preliminary, this hypothesis suggests at least one small, buried impact crater (approx. 10.0 km diameter, with central uplift) present in the region of the Naylor Hills region may be causally linked to both an otherwise anomalous swarm of up to 45 kimberlite pipes and extensive brine seepage (with associated iron ooid development). This hypothesis follows recent work on the Cretaceous-Tertiary boundary (Boslough et al., 1996), connecting the meteorite impact that formed the Chixlub Crater in Yucatan, Mexico with the penecontemporaneous Deccan Trapps flood basalts of India. Although the extrusive flows resulting from the impact of a 10 km wide bolide at the K-T boundary were located on the opposite side of the Earth from the crater site, it may be possible for smaller, possibly oblique impacts to initiate less extensive volcanism (e.g. kimberlites) in heavily-faulted cratonic settings. Continuing research into this complex problem will attempt to document the occurrence of xenoliths within the Bad Heart Formation, and sedimentological evidence for seeps, pipes, and impact(s).
** Presented to the Edmonton Geological Society - October 16, 1998
REFERENCES
Boslough, M.B.; Chael, E.P.; Trucano, T.G.; Crawford, D.A., and Campbell, D.L., 1996. Axial focusing of impact energy in the Earth's interior: a possible link to flood basalts and hotspots: Geological Society of America Special Paper 307 (ed. By G. Ryder, D., Fastovsky, and S. Gartner), p. 541-550.
Collum, C.J., 1997. Stratigraphy, petrology, and geochemistry of the Bad Heart Sandstone (Smoky Group: Upper Cretaceous), Peace River Arch Region, Alberta: evidence for possible syndepositional hydrothermal seeps: Geological Society of America National Meeting, Salt Lake City, Utah, Oct 20-23, Abstracts Volume, p. n/a.
Collum., C.J., 1999 (in prog.). Systematic Paleontology, Biostratigraphy, and Paleoenvironmental Analysis of the Wapiabi Formation and Equivalents (Upper Cretaceous); Alberta and British Columbia, Western Canada: Ph.D. Dissertation, Univeristy of Calgary, Alberta, Canada, 596 p.
Donaldson, W.S., 1997. The sedimentology, stratigraphy and diagenesis of the Upper Cretaceous Bad Heart Formation, northwestern Alberta; Ph.D. Dissertation, University of Western Ontario, London, pages n/a.
Kimberley, M.M., 1994. Debate about ironstone: has solute supply been surficial weathering, hydrothermal convection, or exhalation of deep fluids?; Terra Nova, 6, p. 116-132.
Carlson, S.M.; Hiller, W.D.; Hood, C.T.; Pryde, R.P.; and Skelton, D.N., 1998. The Buffalo Hills kimberlite province, North-central Alberta, Canada: Victory Ventures World-Wide Web listing (www.victoryventures.com/vip buffart.html), April 14, 3 pages.
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Further to this:
Several more interesting follow-up comments of Marum president Richard Boulay are posted on the MMU thread, here:
Message 5971252
Regards,
-j
:>
PS, A great Thanksgiving Weekend to the Canadians!
_ Monday is a Holiday |
