KEWEENAW FAULT 93 



OCCURRENCE OF INTRA FORM ATIONAL CONGLOMERATE AND BRECCIA 

 BY F. V. EMERSON ' 



{Abstract) 



Areas of round clay pebbles and angular masses of stratified clay appear in 

 the sands and sandy clays of Eocene age near Shreveport, Louisiana. The 

 rounded pebbles are of sandy clay, soft when wet, but fairly firm when dry. 

 and of diameters up to 3 inches. Many pebbles are incrusted with iron oxides, 

 forming concretionary masses. The clay fragments are mainly tabular, but 

 occasionally there are large masses of stratified and often well-jointed clay 

 which stand at all angles. The matrix is a rudely stratified sandy clay, in 

 places strongly cross-bedded. 



The rounded pebbles indicate weak wave action in waters of moderate depth 

 and the clay breccias with their disordered arrangements show sliding and 

 slumping. 



Presented in abstract extemporaneously. 



Brief remarks were made by Messrs. A. C. Lane and A. P. Coleman. 



KEWEENAW FAULT 



BY ALFRED C. LANE 



CONTENTS 



Page 



Summary 93 



History 93 



The primitive Keweenaw fault 95 



Primitive erosion 96 



Ifelation of Keeweenawan formation to Cambrian and Precambrian 97 



The Paleozoic invasions 97 



The Appalachian revolution 99 



Later history 100 



Summary 



The Keweenaw fault began as a block-fault in an interior basin like those 

 of the Great Basin region and was also a line of volcanic activity (figure 2). 



The Upper Keweenawan were deposited as playa beds in the trough d and 

 shade into the "Eastern'' Upper Cambrian sandstone, and that perhaps into 

 the "Trenton*' limestone. Thrice later — in Richmond, Niagara, and Mid- 

 Devonian times — the sea covered the region (figure 4), but retired at the time 

 of the Appalachian Revolution, when an overthrust fault took place (figures 

 G and 7). Erosion reduced the land to a peneplain in Keweenawan time and 

 exposes sometimes the block-fault, sometimes the thrust-fault. 



History 



The great Keweenaw fault, which bounds the south side of one of the 

 greatest copper-producing regions, has been an important one not only eco- 



1 Introduced by A. P. Brlgham. 



