2005 Salt Lake City Annual Meeting (October 16–19, 2005)

Paper No. 4
Presentation Time: 8:45 AM


HARRISON, J.B.J., Dept. of Earth and Environmental Science, New Mexico Tech, Socorro, NM 87801 and NIEMI, Tina M., bruce@nmt.edu

Soil stratigraphic relationships are an important tool for interpreting paleoseismic events in trenching studies of normal faults. A faulting event creates a topographic scarp that over time erodes depositing sediments on the hanging wall of the fault. Deposition is initially rapid and declines with time as the scarp angle decreases. As the colluvial wedge stabilizes, a soil will develop. Further faulting activity will result in burial of the soil developed on the colluvial wedge and begin the sequence again. In hyperarid environments, soil development is very slow and is initially characterized by the accumulation of soluble salts and minor amounts of dust. The salts are redistributed throughout the soil profile and the dust accumulated close to the soil surface. Fan stratigraphy is laterally variable making it difficult to correlate units over distances so soil development becomes an important correlative tool. Fan surfaces show considerable textural variation, especially between bar and swale sites. These variations can strongly influence soil development so it is important to determine the range of soil development on the same aged surface. We studied soils developed on three fan surfaces, offset by Holocene-aged faults along the Dead Sea transform fault system in Aqaba, Jordan. Soils were described on the foowall and hanging wall of three of the faults and in areas away from the faults. Soil development was measured by the accumulation of fines (silt+clay) and soluble salts including gypsum, NaCl and CaCO3. These soil features were used to correlate stratigraphic units exposed in the trenches and helped define event horizons and constrain timing of faulting events.