David Alt

Land-based evidence for Tertiary climatic variations: Northern Rockies

Paleoclimatic interpretations of sedimentation patterns, paleosol mineralogy, and vertebrate faunal assemblages of extensive Tertiary continental clastic sediments of Montana and Idaho indicate four major changes in precipitation in this area during Tertiary time: wet to dry in late Eocene, dry to wet in late early Miocene, wet to dry in early middle Miocene, and dry to wet in late Miocene–Pliocene time. This climate pattern is synchronous with similar climatic changes inferred from deep-ocean sedimentation rates for the Indian, Pacific, and Atlantic Oceans, and to oxygen isotope paleo-temperature data for the North Pacific Ocean and New Zealand. Other paleoclimatic evidence supports the pattern. The evidence suggests widespread synchronous Tertiary climate changes that may provide useful time-stratigraphic markers.