OCR Text |
Show abstract from Oviatt, C. G., 1997, Lake Bonneville fluctuations and global climate change: Geology 25: 155- 158, to accompany figure B " Lake Bonneville, the largest late Pleistocene closed- basin lake in the North American Great Basin, fluctuated widely in response to changes in climate. The geochemistry and mineralogy of endogenic calcium carbonate deposited in deep water, and stratigraphic studies of shore- zone deposits, provide evidence of millennial- scale lake- level fluctuations that had amplitudes of about 50 m between 30 and 10 ka. Falling- lake events occurred at 21, 18.5- 19, 17.5, 16- 15.5,14- 13, and 10 ka ( radiocarbon years) synchronously with the terminations of Heinrich events HI and H2 and other smaller scale iceberg- rafting events ( a, b, c, and Younger Dryas) in the North Atlantic Ocean. The Lake Bonneville results thus support other climate records that suggest that late Pleistocene millennial- scale climate change was global in extent. The size and shape of the Northern Hemisphere ice sheets, which determined the mean positions of storm tracks, may have been the primary control on late Pleistocene water budgets of Great Basin lakes." figure captions: Figure A. Generalized stratigraphic column of the white marl ( the fine- grained offshore facies of Lake Bonneville) showing stratigraphic units that are likely to be encountered at a typical low- elevation site in the main body of Lake Bonneville ( modified from Oviatt et al., 1994, Fig. 3, and Oviatt and Miller, 1997). Typical ostracodes in the three main facies are as follows. Post- Bonneville flood ( Provo deep- water marl): Cytherissa lacustris, Candona caudata, Candona adunca, Limnocythere ceriotuberosa, Candona eriensis (?); Deepest- water phase ( deep- water massive marl): Candona adunca, Limnocythere ceriotuberosa, Candona caudata; Early transgressive phase ( transgressive- phase laminated marl): Limnocythere staplini, Candona caudata. Basaltic ashes and their ages ( in radiocarbon years) and shown on the left; the Pahvant Butte and Pony Express ashes are found in the Sevier basin, and the Hansel Valley ash is found in the northeastern part of the main body of Lake Bonneville. Figure B. Lake Bonneville time- altitude curve modified from Oviatt et al. ( 1992, Fig. 3), Oviatt ( 1997, Fig. 2), and Oviatt and Miller ( 1997). Elevations are adjusted for the effects of isostatic rebound in the basin ( Oviatt et al., 1992), and ages are in radiocarbon years. Open circles are carbonate radiocarbon samples ( shell, tufa), solid circles are disseminated organic carbon samples, solid squares are wood or charcoal samples, and open triangles are basaltic ashes. Ul, U2, and U3 are unnamed transgressive- phase fluctuations. |