Depositional Environments of Buried‐Valley Aquifers in North Dakota

Abstract

ABSTRACTMany buried‐valley aquifers in North Dakota occupy narrow, trench‐like valleys incised through glacial sediment into bedrock. By analogy with nonburied valleys of similar size, shape, and geomorphic characteristics, the buried valleys are interpreted to be glacial‐lake spillways formed during glaciations prior to the last advance and retreat. Water‐bearing sediments that fill these buried valleys, although traditionally interpreted as glacial outwash, are commonly composed of nonglacial fluvial sediments deposited between glaciations. Interglacial fluvial systems that occupied the glacial‐lake spillways include major trunk streams draining the Rocky Mountains as well as sluggish, underfit streams with small drainage areas. Deposits associated with the latter type consist of fine‐grained fluvial and lacustrine sediments in the valley centers grading into coarser sediments of alluvial‐fan origin along the valley sides. Thus, in some buried valleys, the most productive aquifers may lie along the valley sides rather than in the valley centers.