解説Stromatolitic metadolostone (Kona Dolomite, Paleoproterozoic, 2.2 to 2.3 Ga; Co. Rd. 480 roadcut, Ragged Hills, SW of Marquette, Upper Peninsula of Michigan, USA) 3 (15015846748).jpg |
Silicified stromatolitic metadolostone - nice stromatolite in the Kona Dolomite from the Precambrian of northern Michigan, USA.
Stratigraphy: Kona Dolomite, Chocolay Group, lower Marquette Range Supergroup, Paleoproterozoic, 2.2 to 2.3 Ga.
Locality: roadcut on northern side of County Road 480 in the Ragged Hills (= W1/2 SW1/4 Section 8, T47N, R25W, Sands 1:24,000 USGS topographic map), south-southwest of Carp River Lake, just west of gravel pits, southwest of the town of Marquette, northern Marquette County, northern Upper Peninsula of Michigan, USA.
Stromatolites are large, layered structures built up by mats of cyanobacteria. Stromatolites vary in appearance, ranging from slightly wrinkled horizontal laminations in sedimentary rocks to low mounds to prominent mounds to columnar structures and other forms.
Stromatolites are most common in the Proterozoic fossil record. They are scarce today, but famous modern examples occur at Shark Bay, Western Australia. |