Chronology of discontinuities and petrology of speleothems as paleoclimatic indicators of the Klamath Moutains, Southwest Oregon, USA
Speleothems from Oregon Caves National Monument, a dissolutional cave system located in the Klamath Mountains of southwest Oregon, are composed mainly (>90%) of columnar calcite crystals. Columnar calcites form through syndepositional lateral coalescence of crystallites and precipitate under stable hydrodynamic conditions in humid, temperate climates. Numerous discontinuities from short-lived events (<100 years) punctuate the calcites. Minor fabrics, such as transitional- and randomly-oriented elongate calcites are seeded on these discontinuities and detrital layers. Columnar calcites eventually overrun sub-horizontally oriented crystals as a result of competitive growth. Large (≈750 μm) crystal terminations indicate growth under increased water film resulting from greater flow and/or ponding. 14 U- series dates provide mean growth rates of 5.6 to 27.9 mm/ka during interglacial periods (marine isotope stages 11 through 9, substage 5e, and late stage 2 through stage 1), and indicate short growth intervals during early-to mid-interglacial periods. Several outcrop-scale discontinuities represent periods of prolonged growth stoppage. Growth cessation occurred during the colder phases of stages 8-9 and 6-7, which translate into hiatuses of 77.5 and 99 ka respectively. Given the sensitivity of alpine regions to climate change and the lack of evidence for continental or alpine glaciation, the hiatuses are presumed to be caused by groundwater freezing during extended periglacial conditions, triggered by the lowering of periglacial thresholds by as much as 1800 m during glacial periods.
|Journal||Carbonates and Evaporites|
Turgeon, S. (Steven), & Lundberg, J. (2001). Chronology of discontinuities and petrology of speleothems as paleoclimatic indicators of the Klamath Moutains, Southwest Oregon, USA. Carbonates and Evaporites, 16(2), 153–167.