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Tertiary orthoquartzites occur along the Potomac and Patuxent rivers and were a favored lithic material of the Paleoindians and Early Archaic people. The samples that I found from the Paleocene (Aquia Fmt) and the Eocene (Nanjemoy Fmt), of indurated sandstone contained abundant, dark green, glauconite minerals; which aren’t seen in the worked lithics.
Dr. Zac Singer pointing at slumped over Bed 2 OQ (white blocks)
Points & Comparison
However the Miocene, (Fairhaven Mbr) orthoquartzite matches up fairly well with some points dating to early Archaic usage. With its angular sand grains, lack of glauconite, and tan opaline matrix it’s a good match.
E. Archaic Point and Comparison
This lense occurs as Bed 2 in the Fairhaven Member; of the Miocene age Calvert Formation, along the Patuxent. In historical times the diatomaceous sediment above this OQ ledge, and the glauconitic Eocene sands below it, were both quarried for different purposes.
Pecten humphreysii E. Miocene Index Fossil
The Bed 2 layer has the Miocene scallop, age indicator fossil Pecten humphreysii, which confirms it is of early Miocene age. After meeting archeologists, Dr. Singer, A. Chisholm, S. Sharpe & M. Johnson who share a fascination with the OQ, I put a lot more foot and boat work into mapping its extent. It ranges from about Lower Marlboro on the Patuxent River upstream to about Lyon’s Creek. On the Potomac River it did not show up at the Miocene age equivalent outcrops at Pope’s Creek. If time allows, hopefully the pros will be able to further map out the geographic distribution of curated points made from this Fairhaxen Mbr. Orthoquartzite.
Missing Outcrop
So far I haven’t found an outcrop of the OQ variant that perfectly matches the Paleo used material, which has a creamy white matrix and larger angular sand grains, and sometimes even small pebbles within it. Some samples even lean towards a breccia with chunks of sandstone contained in them. My thinking is this material has a source near Fredericksburg, VA, an area of high energy faults and volcanism in the distant past.
(Three of the better pictures are from Dr. Singer)
Dr. Zac Singer pointing at slumped over Bed 2 OQ (white blocks)
Points & Comparison
However the Miocene, (Fairhaven Mbr) orthoquartzite matches up fairly well with some points dating to early Archaic usage. With its angular sand grains, lack of glauconite, and tan opaline matrix it’s a good match.
E. Archaic Point and Comparison
This lense occurs as Bed 2 in the Fairhaven Member; of the Miocene age Calvert Formation, along the Patuxent. In historical times the diatomaceous sediment above this OQ ledge, and the glauconitic Eocene sands below it, were both quarried for different purposes.
Pecten humphreysii E. Miocene Index Fossil
The Bed 2 layer has the Miocene scallop, age indicator fossil Pecten humphreysii, which confirms it is of early Miocene age. After meeting archeologists, Dr. Singer, A. Chisholm, S. Sharpe & M. Johnson who share a fascination with the OQ, I put a lot more foot and boat work into mapping its extent. It ranges from about Lower Marlboro on the Patuxent River upstream to about Lyon’s Creek. On the Potomac River it did not show up at the Miocene age equivalent outcrops at Pope’s Creek. If time allows, hopefully the pros will be able to further map out the geographic distribution of curated points made from this Fairhaxen Mbr. Orthoquartzite.
Missing Outcrop
So far I haven’t found an outcrop of the OQ variant that perfectly matches the Paleo used material, which has a creamy white matrix and larger angular sand grains, and sometimes even small pebbles within it. Some samples even lean towards a breccia with chunks of sandstone contained in them. My thinking is this material has a source near Fredericksburg, VA, an area of high energy faults and volcanism in the distant past.
(Three of the better pictures are from Dr. Singer)
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