Earth and Planetary Sciences ETDs

Publication Date

4-9-1997

Abstract

The history of motion on splays of the Pajarito Fault Zone in the area of Cochiti Canyon in the Jemez Mountains is examined using morphometric techniques and investigations of river terrace soils and deformation. Hypsometry, sinuosity and long-profile analysis all suggest that the main splay of the Pajarito Fault has been active in the late Pleistocene and possibly Holocene, but no calibration is available that numerically constrains this activity. Terraces were mapped and correlated based on soil development and landscape position, Correlation revealed the presence of three strath terraces between 87 and 18 .5 meters above present grade and one fill terrace 14 meters above grade. Terraces are informally designated as the Ridge ( ~500-600 ka), Canada ( ~350- 240 ka), Rio ( ~ 125-175 ka), and Ash ( ~60 ka) terraces. Age estimates were derived from comparison to dated soil chronosequenses, a calibrated varnish-cation ratio age, and the presence of ash from the ~60 ka El Cajete eruption in a terrace deposit. Long profiles of terraces and the modern stream valley were constructed by surveying the modem floodplain, the upper surface of each terrace deposit (the terrace tread), and the of terrace deposits with underlying bedrock (the strath or the base of fill). Offset of terraces ranged from 5 to 110 meters. Rates of offset are between oo.3 and 0.13 mm/yr. Offset across two splays of the fault zone has been nearly constant through time, and faulting will presumably continue on these splays. Incision rates were calculated by measuring the height of terrace remnants above grade on apparently undeformed segments of terrace profiles. Incision rates have been nearly constant from 1.22 to ~60 ka, twice as high from ~60 ka to the present, and significantly higher during the period 1.61 to 1.22 Ma.

Degree Name

Earth and Planetary Sciences

Level of Degree

Masters

Department Name

Department of Earth and Planetary Sciences

First Committee Member (Chair)

Leslie D. McFadden

Second Committee Member

Frank Pazzagila

Third Committee Member

Gary A. Smith

Project Sponsors

This work was financially supported, in part, by grants from the Student Resource Academic Committee (S.R.A.C.), Sigma Xi, and the Department of Earth and PLanetary Sciences at the University of New Mexico.

Language

English

Document Type

Thesis

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