CORE AND GEOPHYSICAL ANALYSIS OF BIOGENIC TUFA DEPOSITS IN THE SPRING RIVER IN NORTHERN ARKANSAS

The Spring River is fed by Mammoth Spring, a large spring on the Missouri-Arkansas border which produces roughly 230 million gallons of water per day (MGD). These deposits appear as tufa dams that cause water to pool upstream. Aerial analysis of the dams show that there are approximately 100 of these features present in the first 45 miles downstream of Mammoth Spring. Tufa deposits in a karstic area on a spring fed river are not uncommon, but these are more frequent further down river than near the mouth of the spring. Some preliminary mapping data shows structural features in this region of Arkansas, but mapping of the area is still ongoing at a 1:24,000 (STATEMAP).

Geophysical studies using Resistivity and VLF have been performed in meander bends to determine if these deposits underlie the former river channels. The geophysical data that has been collected suggests joints/fractures under the river banks that lead up to the tufa. Imagery study of the deposits using Google Earth and ArcGIS show the dams to have similar orientations in both N to S and NE to SW trend, which suggests structural control. Preliminary map data by Arkansas State Survey also shows geologic structures to have a similar orientation.

Eight core samples have been taken from three different dam locations to understand the vertical extent of the deposits. The coreholes range in depth from two feet to nine feet. An in-depth core log was created for each core taken and a base analysis of each sample, a calculated surface porosity, along with corehole depth. Thin sections have also been made from several core pieces and show a biogenic/stromatolitic growth pattern with secondary crystal growth. Further analysis on the SEM will be done to look closer at the growth pattern/secondary crystals within the deposits. Results of these geophysical, imagery analyses, core analyses, and thin section analyses will be presented along with their interpretation relative to potential structural influences and a vertical analysis of the dams.