Kevin Righter, NASA-JSC
This newsletter reports 123 new meteorites from the 2010, 2011, and 2012 ANSMET seasons from the La Paz Icefield (LAP10), Dominion Range (DOM10), Miller Range (MIL11), Larkman Nunatak (LAR12) and Szabo Bluff (SZA12) areas. Diversity rules again, as this newsletter includes detailed descriptions for 5 new irons, a mesosiderite, a eucrite, an EL6 chondrite, and 10 carbonaceous chondrites (1 CM2, 1 CK5, 1 CH3, and 7 paired CO3s).
This newsletter includes the last remaining samples to be classified from the 2011-2012 season in the Miller Range. Notable samples from the 2011 season include: an unusual hornblende- and biotite-bearing R6 chondrite (MIL 11207), 1 iron meteorite (IIIAB), EH3 and an EL6 chondrites, 16 HEDs (3 howardites, 5 eucrites and 8 diogenite), and 51 carbonaceous chondrites including 1 CR2, 1 CH3, 2 CV3, 4 CM2, and 35 CO3 that are part of a large CO3 pairing group from the Miller Range.
Book about the US Antarctic Meteorite Program
The past several years, the staff of the US Antarctic meteorite collection has been working on a book project with "AGU and Wiley. The book, entitled 35 Seasons of U.S. Antarctic Meteorites: A Pictorial Guide to the Collection (editors K. Righter, C.M. Corrigan, T.J. McCoy, and R.P. Harvey), released in December 2014, is now available through Wiley. The book covers the history, field operations, curation and statistical aspects of the collection, and contains feature articles on primitive chondrites, achondrites, lunar and martian meteorites, unusual meteorites (misfits), and exposure histories. At the center of the book there are color plates dedicated to 80 of the more influential samples in the collection. This book has been long in the making and should be of interest to a wide range of people from undergraduates to graduates to advanced scholars in the field. We hope it is a valuable resource for the meteorite community.
MIL 11149 was classified as a L6 in the September 2014 (vol.37 No. 2) newsletter.
Microprobe analyses of this sample have yielded Fa18 olivine and Fs16 pyroxene, indicating that this sample is instead an H chondrite and it is here re-classified as an H5. The magnetic susceptibility also indicates an H chondrite (χ = 5.32 and 5.34 x 10-9 m3/kg)
A summary of the 2014-2015 ANSMET field season at the Davis-Ward Icefields
Ralph Harvey, Jim Karner and John Schutt, Case Western Reserve University
After our 2013-2014 field season was impacted by a government shutdown, logistical shortages and a broken ice-dock, we were looking forward to a “normal” Antarctic field season for 2014-2015. Our target, the icefields surrounding the Davis Nunataks and Mount Ward (affectionately known as the “Davis-Ward” site) had been visited four times previously, including two reconnaissance visits (in 1984-85 and 2003-04) and two systematic search visits (in 2008-09 and 2010-11). All our leadership personnel have spent significant time at the site previously and so we feel that we know it pretty well. The site is relatively compact, about 10 km across, shaped roughly like the state of Michigan with nunataks playing the role of the Great Lakes, surrounding and separating the “mitten” icefield from the UP. On the bad side, confusing terrestrial rocks are abundant; but on the good side, we hadn't seen any extreme weather in the past (the site seems somewhat protected) and the logistics of getting there duplicate many previous ANSMET season in the Beardmore Glacier region. In a nutshell, we felt we understood what we were getting into, barring any surprise developments. We also had a good mix of experienced and new personnel on our team (including Devon Burr, Shannon Walker, Ryan Zeigler, Brian Rougeux, Vinciane DeBaille, Christine Floss and the authors) and our preparations all went smoothly during the pre-season.
There was one pre-season question for which our answers diverged, however — how long it would take to finish our searches at the Davis-Ward site? Barring delays due to weather or logistics, this would be directly related to how many meteorites we might find during systematic searching and more specifically how many of those meteorites would be found in the moraines and nearby blue ice regions where terrestrial rocks are scattered by the millions, requiring slow and methodical foot searching. Without disclosing who held what opinion, one of us (who I shall call “The Optimist”) estimated it would take no more than part of a season to finish up Davis-Ward. Thus our plans included a possible camp move to the nearby Dominion Range Icefield late in the season. Another of us (“The Pessimist”) believed it would take this season and maybe one or two more. The third individual (“The Politician”) agreed and disagreed with both depending on who he had last talked to. The origin of this diversity of opinions was prior test-sampling of the moraines. We routinely do test searches; a few field party members will conduct a quick, limited search of a previously unvisited part of the icefield or moraine, and then we use the results to guide our workplan for the future. At Davis-Ward, these tests had produced bimodal results; some visits produced little in hours of searching, while others resulted in finds within the first minute. Our individual opinions on the meteorite potential of the Davis-Ward moraines was utterly dependent on which test you were a part of. That said, we were uniformly eager to see which opinion would hold true, and of one mind in regards to the value of the meteorites themselves.
The season got underway with only modest delays in mid-December, a very welcome change from last year. The transition from McMurdo Station to Davis-Ward (via the old CTAM site) took only a few days. Given the high density of terrestrial rock on and around these icefields we dedicated several days to searching previously visited locales, with veterans aiding newbies and all of us training or retraining our eyes to distinguish meteorites from native lithologies. Both foot-searching and icefield traverses were conducted, but by the end of the training period it was clear moraine searches were going to be a big part of the season. Moraine Mania reached a climax in the last week of the season, when the team encountered a region containing one of the densest meteorite concentrations we've ever seen, affectionately called “Meteorite Beach”. Individual specimens were often found within a meter or two of each other and during one phenomenal day the team found, surveyed and collected over 170 specimens (a new record). There were the inevitable delays due to weather and snowmobile problems, and the season ended a little early due to logistical constraints. Despite these limits on our field time, at season's end the team had recovered a total of 562 specimens; nearly 60% of these came from the moraines and most of the remainder came from ice within a few hundred meters of the moraine. With the 2013-2014 meteorites (returning after storage in Antarctica for a year) there will be nearly 900 new meteorites arriving at JSC this spring.
A view of “Meteorite Beach”, one of many segments of moraine at the Davis-Ward icefields exhibiting a very dense meteorite concentration. Each flag marks the location of at least one meteorite. (Photo by Ryan Zeigler)
And at season's end there is no longer any disagreement about the future workload at Davis-Ward; we'll be going back there for at least one full season and maybe more than once. Any region of these icefields, moraine or not, has the potential to surprise us with significant meteorite concentrations. While reconnaissance generally gives us an idea of the potential for meteorite recovery, there is no way to predict where amazing concentrations or occurrences might be, and clearly Davis-Ward is a place we can't afford to trust our instincts; we simply have to put our boots on the ice and go have a look.
Report from the Smithsonian
Cari Corrigan, Geologist (Dept. of Mineral Sci.)
This newsletter announces the description of 123 meteorites from the DOM, MIL, LAR, LAP and SZA field areas and effectively closes out the 2010 and 2011 seasons. Included in this newsletter are interesting new iron meteorites, a new mesosiderite, a CH chondrite, a brecciated eucrite and more of the MIL CO3 pairing group, in addition to others.
We are currently without a Collections Manager after Linda Welzenbach relocated to Texas this past fall. Please bear with us as we navigate the waters of hiring a replacement and as we work to get that new person trained. Please watch for the job ad to come out and spread the word if you, or anyone you know, may be interested, but please keep in mind that the position will not include research as part of its performance description.
The Smithsonian is continuing its work on investigating new ways of classifying the equilibrated ordinary chondrites, including attempting to optimize the use of the EDS system on our FEG-SEM to analyze the compositions of the olivine and pyroxene grains. The ability to obtain mineral analyses from each meteorite give us a lasting record for each stone, and a dataset that can be used in the future to understand the distribution of compositions among the ordinary chondrite groups.
We eagerly await the arrival of both the 2013 and 2014 season samples later this spring and to reporting on them in the Fall newsletter!