Luminescence dating ancient pluvial lake shorelines in the Lake Lahontan basin using.... tufa?

Well, we know we can determine the age of sand using luminescence dating here at DRILL. But can we date tufa?? We’re gonna try! Many ancient shorelines in the Lahontan basin are cemented in carbonates (tufa) that precipitated out of lacustrine waters.

The Jessup embayment preserves shoreline features mainly dating to the last (Sehoo) lake cycle in the Late Pleistocene. The sampled lithoid terrace at 1339 m asl, with tufa coated beach cobbles, may have started to form during the penultimate (Eetza) lake cycle ~100,000 years earlier (Adams & Wesnousky 1998; 1999).

As it turns out, these carbonates contain silt and sand that would have been exposed to sunlight in the nearshore environment, making them interesting candidates for luminescence dating. We’ve sampled tufa from a cobble beach deposit associated with a former pluvial lake highstand in the Jessup embayment to determine its potential for dating.

TOP. The sampled lithoid terrace in the Jessup embayment. Person for scale. BOTTOM LEFT. Lithoid tufa. BOTTOM CENTER. The IRSL signal from silt (<32 um) extracted from the tufa. BOTTOM RIGHT. A fading plot showing a moderate to high fading rate.

Results so far show that i) up to ~13% of this tufa consists of sediment, ii) this sediment has a sufficiently bright IRSL signal for dating, and iii) the IRSL signal has a moderate to high fading rate. Future work will explore the potential of other luminescence signals that will depend less heavily on fading corrections.