4 Geohazards of the Rocky Mountain West and Beyond (Posters)

Monday, 4 May 2020
8:30 AM - 4:30 PM
Ballroom A

REDEFINITION OF THE UNCONFORMITY BETWEEN THE MOENKOPI FORMATION AND THE CHINLE FORMATION IN SOUTHERN UTAH FOR GEOLOGICAL ENGINEERING PURPOSES

Paper number: 4-14
Program: Theme Sessions
Time: 8:30 AM – 4:30 PM

Authors

  • Hugo Angeles Presenting Author
    Southern Utah University, St George, UT

Abstract

The Upper Red Member of the Moenkopi Formation generally consists of siltstone and sandstones and is in direct contact with the Chinle Formation through an unconformity. Several studies have defined a thin layer of mudstone in the Upper Red Member with properties more alike the Chinle Formation. Stewart (1972) defines that if this happens then the boundary should be lowered for stratigraphic purposes. I will be testing the hypothesis that several areas that have been defined as the Upper Red Member of the Moenkopi Formation, due specifically to the unconformity with the Chinle Formation, belong to this formation and are expansive mudstones. This research will help to broaden the level of understanding of the nature of geohazards such as expansive mudstones in the construction industry. The recognition of this knowledge in preparation for exploratory operations is key to avoid future problems regarding the possibility of distress due to heaving.

This study will provide better detailed definition of the stratigraphy of this specific area that can help to recognize this type of material to elevate of understanding of the unconformity and its effects. The main question to answer is if the Cedar City stratigraphy includes this thin unit mudstone layer as the Lower Member of the Chinle Formation, why it is not recognized in the Southern Utah Area. Few homes built around this area have shown signs of distress defining the presence of expansive mudstones that are characteristic of the Chinle Formation. Geological engineers rely on stratigraphic maps to develop exploration for construction purposes.

I will produce stratigraphic columns on the areas where these types of claystone have been observed to take samples and provide evidence that they belong to the Chinle Formation. This evidence will happen through comparison of materials from the Moenkopi and Chinle formation known characteristics as measurements parameters. These parameters include plasticity through Atterberg Analysis and oedometer test methods to measure the expansive potential due to the montmorillonite content. Field costs can be done personally at no preparation cost other than basic lab supplies. All laboratory materials and supplies for sample preparation have already been acquired.

Geological Society of America Abstracts with Programs. Vol. 52, No. 3

doi: 10.1130/abs/2020RM-346745

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