Magnetostratigraphic evidence from the Cold Creek bar for onset of ice-age cataclysmic floods in eastern Washington during the early pleistocene

Abstract

This study provides a detailed magnetostratigraphy of sediments composing the Cold Creek cataclysmic flood bar in the Pasco Basin, Washington. Our interpretation suggests onset of Missoula floods or similar events prior to 1.1 myr, later than previously suggested by Bjornstad et al. [Bjornstad, B.N., Fecht, K.R., Pluhar, C.J., 2001. Long history of pre-Wisconsin, Ice Age cataclysmic floods: evidence from southeastern Washington State. Journal of Geology 109 (6), 695–713]. Nonetheless these data suggest that Channeled Scabland features formed over a much longer timespan than commonly cited, that continental ice sheets of the early Pleistocene reached as far south as those of the late Pleistocene, and that similar physiography existed in eastern Washington and perhaps Montana to both generate and route Missoula-flood-like events. This study adds paleomagnetic polarity results from 213 new samples of silts and sands derived from nine new drill cores penetrating the Cold Creek cataclysmic flood bar to our previous database of 53 samples from four boreholes, resulting in a much more robust and detailed magnetostratigraphy. Rock magnetic studies on these sediments show pure magnetite to be the predominant remanence-carrying magnetic mineral, ruling out widespread remagnetization by secondary mineralization. The magnetostratigraphy at eastern Cold Creek bar is characterized by a normal polarity interval bracketed by reversed polarities. Equating the normal zone with the Jaramillo subchron (0.99–1.07 myr) affords the simplest correlation to the magnetic polarity timescale. Western Cold Creek bar was likely deposited during the Brunhes chron (0–0.78 myr) since it exhibits mainly normal polarities with only two thin reversed-polarity horizons that we interpret as magnetic excursions during the Brunhes.

Geology Data Package for the Single-Shell Tank Waste Management Areas at the Hanford Site

“…Recent studies using the magnetic polarity of the Hanford formation sediments have shown that the earliest floods may have occurred as long ago as 2 million years. Four magnetic polarity reversals have been found in sediments from core holes in the 200 East Area (Pluhar et al 2006). These polarity reversals have paleosols at the top of each reversed sequence of sediments.…”

“…Net erosion by these floods was minimal and probably associated with only the earliest floods; later floods only partially incised into older flood deposits before backfilling. Recent work on subdividing the Missoula flood deposits at the Hanford Site has shown that paleomagnetic polarity is a useful technique (Pluhar 2003;Pluhar et al 2006). In a detailed study at the 200 East Area, four magnetic polarity reversals were recognized (Figure 4.13).…”

“…Layer 3 has two paleosols, although one is not present everywhere in the IDF site. It also has two polarity reversals-a reverse polarity at the base of the sequence and a normal polarity between the surface and the top of the reverse polarity (Figure 4.13) (Pluhar et al 2006). …”

Characterization of Direct-Push Vadose Zone Sediments from the 241-B and 241-BX Tank Farms

“…Cold Creek Bar grew as sediments were episodically laid down in series of perhaps hundreds of floods spanning a million years or more (Pluhar et al 2006). A network of braided flood channels sweeping across the bar locally scoured into the pre-existing deposits and backfilled with coarse sand and gravel.…”

Geologic Descriptions for the Solid-Waste Low Level Burial Grounds

“…In general, the Hanford formation is subdivided into three principal facies associations: 1) graveldominated (GD), 2) sand-dominated (SD), and 3) interbedded sand-and silt-dominated (ISSD). The general distribution of these three facies associations is shown in Figure 2 (Pluhar et al 2006). A network of braided flood channels sweeping across the bar locally scoured into the preexisting deposits and backfilled with coarse sand and gravel.…”