Print this pageArchitecture of an Aggrading, Sandy Braided River, Northeast Nebraska
SKELLY, RAYMOND L.; FRANK G. ETHRIDGE, and CHARLIE S. BRISTOW
Vibracores and profiles from a ground penetrating radar (GPR) survey delineate the lithofacies architecture of recent channel-belt deposits of the lower Niobrara River, northeastern Nebraska. Rapid aggradation has occurred in the Niobrara River channel, near its confluence with the Missouri River, since the mid 1950s. The vibracores and GPR profiles provide data for development of a three-dimensional, architectural model of this sandy braided river.
Radar facies are characterized by parallel/planar, hummocky, inclined (high and low angle), parabolic, and curved truncated reflectors. Few large-scale, continuous reflectors are present and radar facies are distributed in a complex manner throughout the channel-belt deposits. These facies resulted from sedimentary processes observable in present-day environments. Actively migrating macroforms (bars) and bedforms (dunes) of the channel belt are represented by planar, hummocky, and inclined reflectors in the GPR profiles. Dissection of larger scale bar complexes by minor channels is represented by the curved, truncated reflectors. Wood debris prevalent on bar surfaces and in channels is identified as parabolic reflectors in the GPR profiles.
The overall architecture of the radar facies is discontinuous, with many truncated reflectors, which suggests that a complex series of depositional and erosional events occurred during the recent channel-belt aggradation. Channel fill and cross-channel accretion from minor, secondary channels are recognized but there is no evidence of large-scale, systematic, downstream or cross-channel accretion of the channel-belt in the GPR profiles.