Reinterpretation of the Cedar Ridge section, Wind River Range, Wyoming: Implications for the glacial chronology of the Rocky Mountains

Abstract

The Cedar Ridge stratigraphic section in the escarpment north of Bull Lake, Wind River Range, Wyoming, may be the most significant section of Quaternary sediments in the Rocky Mountains. This section contains a thick sequence of Bull Lake till, but its greater significance is as the type section or a reference section for the deposits of three pre–Bull Lake glaciations: Washakie Point (oldest), Cedar Ridge, and Sacagawea Ridge (reference section, type section at Dinwoody Lakes). However, after reexamining the tills, lake sediments, and buried soils in this section, we conclude that the stratigraphic record is best interpreted as the result of two glaciations, not the four of previous investigations. Buried soils are especially useful in deciphering the stratigraphy of this section through the contrast between well-developed interglacial soils and weakly developed interstadial soils. We conclude that only the Bull Lake and Sacagawea Ridge glaciations are represented by deposits in the Cedar Ridge section. Deposits formerly called Cedar Ridge are reinterpreted as representing an early stade of the Sacagawea Ridge glaciation. A paleomagnetic study reveals that all the sediments have normal polarity and thus are probably younger than the Brunhes-Matuyama boundary of ca. 770 ka. Although the deposits of the Cedar Ridge section have been correlated with moraines and terraces, this procedure should be done only by direct tracing or with the use of all available dating control. The best record of Quaternary glaciations in the area, however, is in the river terraces of glacial outwash origin in the Wind River basin, not the moraines and stratigraphic sections along the mountain front.