Thread by @GeoBrentatlarge

Back from fieldwork so time to tweet about the boulder hunting. This is the central portion of the Ruby Range, SW Yukon. Follow thread for more info. #SFUglacialgeology #YukonGeologicalSurvey

We are dating deglaciation, both the Cordilleran Ice Sheet (CIS) and local alpine glaciers. These small cirques would have supported glaciers during the last glaciation (MIS 2). #SFUglacialgeology #YukonGeologicalSurvey

We use the accumulation of Terrestrial Cosmogenic Nuclides from glacially transported boulders to date deglaciation. Good boulder selection is crucial. These large boulders are from the CIS, most of these are saw worthy! #SFUglacialgeology #YukonGeologicalSurvey

Derek Cronmiller (MSc student) using a cut out saw to take a uniform sample in the upper 2.5-3 cm of a boulder. Some people just use chisels, but that is way more work! And does not always provide a uniform sample. #SFUglacialgeology #YukonGeologicalSurvey

We then use a chisel to get sample with uniform thickness. TCN dating is based on the accumulation of rare isotopes (10Be in this case) formed by bombardment by high energy cosmogenic particles. #SFUglacialgeology #YukonGeologicalSurvey

By measuring the amount of 10Be and knowing the production rate, when the boulders melted out of the glacier can be calculated. We sampled three boulders on this moraine in Albert creek that may predate the last glaciation and be MIS 4. #SFUglacialgeology #YukonGeologicalSurvey

This is the Late Wisconsinan (MIS 2) moraine in Albert Creek. Four boulders were sampled just inside this limit. We can compare this age to that of the CIS to understand forcing mechanisms. Derek's initial findings are local ice deglaciation later than the CIS #SFUglacialgeology

Jeff Bond using the cut out saw and Derek spraying water and lubricating the blade. #SFUglacialgeology #YukonGeologicalSurvey

Experimenting with a Makita angle iron with a diamond blade on it. Worked well and is much lighter for hiking! But having enough batteries are an issue. #SFUglacialgeology #YukonGeologicalSurvey

The glacial history of Ruby Range is complex. These Tors (periglacial features) indicate a long period of weathering. These surfaces have likely not been glaciated, unless it was cold based ice. #SFUglacialgeology #YukonGeologicalSurvey

One of the finding of Derek’s thesis is that there are much larger areas of the uplands that have never been glaciated compared to previous studies. #SFUglacialgeology #YukonGeologicalSurvey

Beautiful colluvial cones in a small cirque valley. #SFUglacialgeology #YukonGeologicalSurvey

Flew by some Mountain sheep. Look carefully.

The boulder hunting team, from left to right, Jeff Bond (YGS), Dion Parker (TRK Helicopters), Derek Cronmiller (SFU). Was a fantastic day both weather wise and geologic! We took a record 10 samples! #SFUglacialgeology #YukonGeologicalSurvey

Got dropped off first thing and Dion had to go set out some other people. As it leaves you always wonder if it will come back. But he did! #SFUglacialgeology #YukonGeologicalSurvey