Abstract

Ice ages have occurred a number of times in Earth's history, and are important in understanding changes in long-term climate. However, it is difficult to demonstrate the presence of ice sheets in the ancient record because their sedimentary products can resemble those from nonglacial processes (e.g., debris flows). Diagnostic large-scale glacial landforms, produced beneath ice sheets and preserved on continental shelves after deglaciation, can establish a glacial origin. Three-dimensional seismic evidence from the 2.7 Ma Naust Formation, Norwegian margin, illustrates several glacial landforms that are also commonly occurring features on modern high-latitude shelves: (1) streamlined mega-scale lineations produced by fast-flowing ice streams; (2) ploughmarks formed by iceberg keels; and (3) regularly spaced transverse ridges or push moraines formed during ice retreat. We have found, for example, buried ice-keel ploughmarks on a paleoshelf dating to ca. 2 Ma. Norwegian margin seismic stratigraphy data show that ice advanced and retreated many times, and some paleoshelf surfaces were preserved. Such paleosurfaces must survive ocean basin destruction for glacial landforms to be useful in identification of ancient depositional environments.

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