Glaciations in North and South America from the Miocene to the Last Glacial Maximum: comparisons, linkages and uncertainties

RUTTER, N.; CORONATO, A.M; HELMENS, K.; RABASSA, J.; ZÁRATE, M.

Springer Verlag

Lugar: Dordretch; Año: 2012 p. 67

978-94-007-4398-4

Improved dating methods have increased our ability to more precisely determine 148 the timing and durations of glaciations. Utilizing glacial and loess deposits, we 149 have compared glaciations that occurred in North and South America in order to 150 determine whether events are synchronous or not, to explore forcing mechanisms, 151 and to compare glaciations with cold periods of the Marine Oxygen Isotope stages 152 and the loess/paleosol records of China. Stratigraphic sections containing a variety 153 of glacial deposits, some with interbedded volcanics, as well as loess deposits, 154 were used in reconstructing the glacial history. The major problems included 155 fragmentary sections, missing evidence, and limited detailed age estimates. Dating 156 methods utilized included radiocarbon, K?Ar, 40Ar?39Ar, fission track, paleo- 157 magnetic polarity interpretation, and luminescence techniques (China). In North 158 America, the best evidence for Late Cenozoic glaciations is in southeastern 159 Alaska, the Pacific Coastal Mountains, and northwestern Canada, in South 160 America, in the Patagonian Andes and forelands of Argentina, and in the Bogotá 161 basin of Colombia. Four Miocene-Pliocene (Gilbert and Gauss Chrons) and Pli- 162 ocene?Pleistocene (Gauss/Matuyama Chrons) glaciations have been identified in 163 southern South America, whereas only one mountain Pliocene and one Pliocene? 164 Pleistocene glaciations have been identified in northwest America. This may be the 165 result of the near-coeval volcanic activity which preserved till deposits under 166 basaltic lava flows. Major tectonic uplift in the northern Andes suggests the 167 absence of terrain high enough to support glaciers in the Bogotá mountains during 168 the Miocene-Pliocene. During the Early and Late Pleistocene (Matuyama Chron) 169 there are ten glacial advances recognized in either North or South America. Five 170 appear to be roughly synchronous. During the Jaramillo Chron the greatest 171 glaciation occurred in Patagonia whereas the Jaramillo glaciation in northwestern 172 Canada was not a major event. At least three Middle Pleistocene (Brunhes Chron) 173 glaciations are represented in both North and South America. In southern South 174 America, subsequent glaciations are less extensive than the previous. The opposite 175 is true in northern South America and North America where younger glaciations 176 appear to be more extensive. This may indicate the impact of local factors such as Layout: T1 Standard SC Book ID: 303393_1_En Book ISBN: 978-94-007-4398-4 Chapter No.: FM Date: 12-5-2012 Page: 9/14 ix Author Proof UNCORRECTED PROOF 177 tectonism, glacial overdeepining, and/or precipitation gradient increase acting over 178 global forces. The Late Pleistocene (Brunhes Chron) Last Glacial Maximum is 179 recognized in mountain and continental areas of North America but only in the 180 mountains of South America. Commonly, our comparisons indicate roughly syn- 181 chronous glaciations on the two continents, whereas other glaciations are more 182 elusive and difficult to compare. Although our comparisons are at low resolutions, 183 the results suggest that Milankovitch forcing is most likely the dominant trigger for 184 hemispheric glaciation modified by local factors.