IMPACT CRATER EXPLORATIONS
by: Charles O'Dale
MEREWETHER (Possible Impact Structure)
The Merewether structure is located north of the tree-line in Labrador approximately 93 kilometres south-west of the Saglek Fiord. I initiated my study of the Merewether structure based on an article in the February 1975 issue of the Journal of the Royal Astronomical Society of Canada. The authors classified this structure as “Probable Meteorite Crater”, an almost perfectly circular steep-walled crater, 0.2 km in diameter, in ground moraine (Grieve 1975). Meen found no evidence of meteoritic material or brecciation at this site and there has been no reported scientific investigation since. It remains on the list of probable impact sites because of its striking, crater-like form.
In the summer of 2005 I had the opportunity to over-fly the structure on one of my aerial exploration trips to the northern part of Labrador. I noted during my short stay over the structure that there are actually three small craters formed in a line (suggesting a crater "string"?). Merewether has been on the “list of suspected impact craters” for at least 50 years but it remains an enigma. There are no known natural geological causes to explain the formation of the structures and irrefutable evidence to indicate an impact event has not been discovered to this date (April 2006).
Pingualuit crater in shape and his expedition was initiated to document any impact evidence. During the short time allowed with the season, Dr. Meen documented a substantial amount of geologic data (quoted in this article). To my knowledge there has not been any other ground research performed here.
A generalized geologic sketch of the area by Dr. Meen (left) illustrates that the “grain” of the glacial moraine plateau forms north-south ridges. The moraine consists of coarse boulders bound together with sands and clays. The two smaller bowl shaped structures on each side of the prime structure are indicated by numbers 6 (north) & 14 (south). The south-west facing image (right) highlights the “three craters” of the Merewether structure that Dr. Meen sketched. The two smaller structures are positioned on each side and in a roughly north-south line through the prime structure. The water’s green colour is due to suspended silt (rock flour) which reflects the incident light before the longer wave-lengths have been absorbed by the water.
- the banding of the sediments was caused by annual fluctuations in the deposition, - the rate of deposition has decreased or remained constant since the structure was formed, and - the rock basin of the lake was originally conical.
Since there were 30 varves in one foot (0.3048 metre) of sediment and the maximum depth of sediment was estimated to be less than 29 feet (8.8392 metres), the maximum age of the structure would be less than 870 years.
This image of the prime structure (right), looking to the east, further illustrates its almost circular shape and steep walls. There is no bedrock uptilted to form a rim. Around the north, east and south the rim merges with the adjacent hills. On the west the rim is definitely higher than the adjacent terrain. The “long” diameter of its slight elliptical shape is at right angles to the past directional movement of the glaciers.
Irrefutable evidence for a meteorite impact at the Merewether structures is still lacking. Drilling in the craters for evidence of planar deformation features has not been performed and no shattercones, impact melt or meteorite fragments have been found at this site. This may be explained by the existence and movement of glaciers over the structure at the time of impact causing a smoothing of the rims and removal of any fragments of the impactor.
Samples of vegetation were collected at various points and distances about the structure. This dried material was submitted to the Chemistry Division of Science Service, Canada Department of Agriculture, for analysis. The analyses were determined colorimetrically for iron and polarographically for nickel, by Dr. Claude Sirois. The results were inconclusive but pointed to a trend toward higher nickel-iron content in plant material collected in the vicinity of the structure than in that collected further away from it (Gillett 1960).
The geologic study of the Merewether structure has eliminated the following possible causes for the shape aspects of the structure:
The following features of the prime structure taken individually would not be conclusive, but together suggest that the Merewether structure may be impact related (meteorite crater remnant):
Hypothesis by the author: The Merewether structure may have been caused by an impactor that split into at least three parts upon its collision with the earth’s atmosphere. The parts then impacted the earth (at less than their original cosmic velocity) at a position covered by glaciers and penetrated the ice to the underlying moraine material. The glacier removed any trace of the impactor and eroded the craters.
Recent research has indicated that the Merewether structure may be related to the Younger Dryas Extinction.
Grieve R.A.F., Robertson P.B., IMPACT STRUCTURES IN CANADA, the Journal of the Royal Astronomical Society of Canada, February 1975
Meen V.B., MEREWETHER CRATER – A POSSIBLE METEORITE CRATER,the Proceedings of the Geological Association Canada 1957 pp 49-67. (unless otherwise noted, the Merewether data quoted above is from this paper).
Ian SPOONER, George STEVENS, Jared MORROW, Peir PUFAHL, Richard GRIEVE, Rob RAESIDE, Jean PILON, Cliff STANLEY, Sandra BARR, and David MCMULLIN, Identification of the Bloody Creek structure, a possible impact crater in southwestern Nova Scotia, Canada. Meteoritics & Planetary Science 44, Nr 8, 1193–1202 (2009)
Haynes, C. V., Younger Dryas ‘‘black mats’’ and the Rancholabrean termination in North America Departments of Anthropology and Geosciences, Arizona, January 23, 2008.
Isabel Israde-Alcántara, James L. Bischoff, Gabriela Domínguez-Vázquez, Hong-Chun Li, Paul S. DeCarli, Ted E. Bunch, James H. Wittke, James C. Weaver, Richard B. Firestone, Allen West, James P. Kennett, Chris Mercer, Sujing Xie, Eric K. Richman, Charles R. Kinzie, and Wendy S. Wolbach, Evidence from central Mexico supporting the Younger Dryas extraterrestrial impact hypothesis, University of Hawaii, Honolulu, HI, January 31, 2012
Younger Dryas Extinction Impact Related? (Bloody Creek @ 29:30).
- PHOTOGRAPHIC IMAGES: Eric Kujala and Charles O’Dale.