Blackford 'sinkhole', Douglas Lake (Ordovician of the United States)

Where: Tennessee (36.0° N, 83.5° W: paleocoordinates 30.0° S, 69.7° W)

• coordinate estimated from map

• outcrop-level geographic resolution

When: Blackford Formation, Llanvirnian (468.1 - 460.9 Ma)

• Whiterockian; All from Unit B; most from upper 8 feet of this unit

• formation-level stratigraphic resolution

Environment/lithology: peritidal; lithified dolomite and lithified, volcaniclastic conglomerate

• ... is a sequence of laminated, massive deposits. Concentrations of organic material at the top of the varvelike graded beds emphasize the laminated appearance. There are 1 to 20 laminations per inch. This lithologic member, designated as Unit B, does not have shale partings. IT is massive when fresh but weathers rapidly. The weathered material splits readily at the carbonaceous plane at the top of each "varve".

•Layers and lenses of conglomerate and breccia are recurrent throughout this unit. These beds and lenses, usually 1/8 to 2 inches in thickness, contain angular to subrounded pebbles up to 2 1/2 inches in diameter. Most of the graded beds have a basal zone of angular pyroclastic granules. The breccia fragments are predominantly of volcanic origin whereas the subrounded pebbles are of a wide variety of lithologic types, some unknown in this vicinity.

•In many places the laminations of this unit have been contorted by the soft rock deformational processes of sediment flowage and slumping. Laurence (1944, fig. 6A and 6B) figured contorted laminations between undisturbed beds and an angular unconformity within a sequence of conglomeratic beds.

Size class: macrofossils

Preservation: mold/impression

Reposited in the USNM

Primary reference: K.E. Caster and H.K. Brooks. 1956. New fossils from the Canadian-Chazyan (Ordovician) hiatus in Tennessee. Bulletins of American Paleontology 36(157):157-199 [S. Holland/S. Holland/S. Holland]more details

Purpose of describing collection: taxonomic analysis

PaleoDB collection 37450: authorized by Steven Holland, entered by Steven Holland on 15.03.2004

Creative Commons license: CC BY (attribution)

Taxonomic list

 Xiphosurida -