Maine Geological Survey

Geologists have been aware of the Aroostook County manganese district in northern Maine for over 150 years, but the last mapping and exploration campaigns were completed 70 years ago, well before modern geological theories were developed. (Photo: Typical banded manganese ironstone of the main deposit at Maple Mountain, Number Nine Lake quadrangle. Additional project photos are linked below.)

The current project collected data on select areas around the City of Presque Isle and Maple and Hovey mountains southwest of Mars Hill. The work was spearheaded by Dr. Chunzeng Wang, a geology professor at the University of Maine at Presque Isle and resulted in three bulletins (detailed reports and maps) for the Presque Isle, Mapleton, and Number Nine Lake 1:24,000-scale map quadrangles.

The project also supported training the next generation of geoscientists by funding the Master's degree of co-author Lauren Madsen at the University of Maine and providing internships for five undergraduate students. The research benefited from the collaboration of international geologists and paleontologists from six countries, who assisted with fossil identification and consultation. The work was made possible by generous access from local landowners.

The project achieved several major research breakthroughs:

• The origin of manganese deposits in northern Maine:
  • The studied deposits formed in similar ways, which was precipitation of manganese from seawater on a continental shelf in Silurian time
• Discovery of the Number Nine Mountain tectonic terrane, which is a distinct piece of an ancient tectonic plate that includes three newly defined rock units:
  • Arc volcanic rocks of the Middle Ordovician Moorehouse Brook Formation (470 Ma)
  • Tectonic mélange of the lower Silurian Nine Lake Formation
  • A complete ophiolite sequence at Nineteen Mountain
• Revised the age order (stratigraphy) of rocks that formed during the Silurian and Devonian geologic time periods through the study of a variety of fossils preserved in the rocks (megafossils, conodonts, and pollen) and radiometric age determination (zircon U-Pb dating).
• Characterized regional rock structures created during the Acadian mountain-building event (orogeny) in the Devonian geologic time period. These structures provide evidence of regional compression and deformation:
  • Tight folding of rock layers deposited during the Silurian
  • Northeast-striking reverse-thrust faults.

The three-year mapping effort was funded by the U.S. Geological Survey’s Earth Mapping Resources Initiative (Earth MRI), a national program dedicated to modernizing geologic data about the United States’ critical mineral resources. These commodities are essential to the nation’s economy, clean energy transition, and national defense, yet their supply chains remain vulnerable to global disruption.

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