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70-16 Investigation of Detrital Sediment Distribution and Inter-reef Currents in McKay Bay Member Knoll Reef, Upper Peninsula, Michigan

Session: Paleontology, Biogeography/Biostratigraphy & Phylogenetic/Morphological Patterns (Posters)

Poster Booth No.: 186

Presenting Author:

Tucker Kelly

Authors:

Kelly, Tucker Lee¹, Bieker, Ross², VanHook, Matthew³, Larson, Erik⁴, Testa, Maurice⁵

(1) University of Arkansas - Fort Smith, Fort Smith, AR, USA, (2) University of Arkansas - Fort Smith, Fort Smith, AR, USA, (3) University of Arkansas - Fort Smith, Fort Smith, AR, USA, (4) Shawnee State University, Portsmouth, OH, USA, (5) University of Arkansas - Fort Smith, Fort Smith, AR, USA,

Abstract:

Research on the Michigan Basin's pinnacle reef systems began in the 1930s, but its outcropping knoll reefs have received little attention. These carbonate mounds, found in shallow waters, grow horizontally rather than vertically. The knoll reefs currently under investigation are located in the McKay Bay Member of the Bush Bay Formation, part of the early-Silurian Engadine Group, within the Eastern Hiawatha National Forest in Michigan's Upper Peninsula.

The initial phase of this project, conducted in 2023, involved the systematic collection of over 120 geological samples from three distinct knoll reefs: the primary structure designated as Reef A, and two auxiliary reefs, Reef B and Reef C, positioned south/southeast of Reef A. Samples and cores were acquired at 1-meter intervals along a transected grid, with radial transects spaced at 22.5-degree increments. Concurrently, fossil specimens were identified and cataloged for subsequent biostratigraphic analysis.

This project's primary objective is to elucidate the provenance and spatial distribution of detrital sediment incorporated within the largest knoll reef (Reef A) of the study area. For this project, 60 of the 120 samples have been analyzed. Each collected sample underwent preparation into a thin section for microscopic examination. These thin sections were then subjected to point-counting analysis to quantify the detrital sediment content originally entrapped within the reef matrix. The cumulative detrital sediment counts per thin section were subsequently utilized to construct rose diagrams, facilitating the determination of the directional influx of sediment into the main reef structure. The petrographic analysis not only delineates the direction of sediment influx but also provides evidence for the presence and orientation of inter-reef currents circulating between the primary reef and the two smaller, adjacent reefs.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-9072

Investigation of Detrital Sediment Distribution and Inter-reef Currents in McKay Bay Member Knoll Reef, Upper Peninsula, Michigan

Description

Session Format: Poster

Presentation Date: 10/19/2025

Presentation Room: HBGCC, Hall 1

Poster Booth No.: 186

Author Availability: 3:30–5:30 p.m.

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