7 D1. Caves, Karst, and the Hydrogeology of Fractured Bedrock Aquifers (Posters)

Monday, 18 May 2020
8:30 AM - 5:30 PM
Lake Superior Ballroom KJ

GRIKES OF THE HIAWATHA NATIONAL FOREST: DISSOLUTIONALLY ENLARGED JOINTS OF MICHIGAN’S UPPER PENINSULA

Paper number: 7-3
Program: Technical Sessions
Time: 8:30 AM – 5:30 PM

Authors

Abstract

The St. Ignace District of the Hiawatha National Forest (HNF) is located on the eastern end of Michigan’s Upper Peninsula. This area has been studied the last several years due to its abundance of karst features. Sink holes, springs, sinking streams, and grike fields are found throughout the area, the latter being the subject of this study. These features form in the Engadine Group which is made of mid-Silurian-aged dolostones and in part forms the Niagara Escarpment. The karst of the area is believed to be post-glacial, as no evidence suggests the features could have survived the last glaciation of the area.

Grikes are dissolutionally enlarged joints, a surficial karst feature of the HNF. They range from few to dozens of cm in width and often intersect each other. Orientations of the grikes follow three major trends: ~5°, ~75°, and ~135°. Regional joints sets in the Michigan Basin are: ~1°, ~52°, ~91°, and ~134°.

Grikes of the Rockview Formation are associated with the lakeshore of Glacial Lake Algonquin (11.7 ka) and have an average width of 14.8cm with a dissolution rate of 6.72mm / 1000yr. The grikes of the Bush Bay Formation are associated with the lakeshore of Glacial Lake Nipissing (4ka) and have an average width of 14.2cm with a dissolution rate of 17.71mm / 1000yr. Both of these rates assume the karst of the area is post-glacial.

Drummond Island, a location east of our main study, will be investigated again to continue our efforts in cataloguing the grikes and joints of the alvar formed in limestone and dolostone of the Ordovician Queenston Shale. In 2019, orientations of 293 joints were collected across six 1m2 sections. Width was recorded where possible as they only averaged ~1cm. These grikes are oriented at ~35° and ~130°.

In May of 2020, we will continue to expand on the data collected in the past while additionally focusing on recording grike depth, and utilizing aerial imagery from drones to better map the distribution of the grikes. Excavation of the loose sediment between grikes may give insight to the terminating habits of the features, the degree of organic loading, and the likelihood of grikes being preferential flow paths for groundwater.

Geological Society of America Abstracts with Programs. Vol. 52, No. 5

doi: 10.1130/abs/2020NC-347959

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