134 



STRUCTURAL GEOLOGY OF NORTH AMERICA 



shifted more toward the northwest. Also, with the onset of faulting, fan- 

 glomerates were washed in by torrential streams from the uplifted block. 

 In the Deep River basin, with faulting on both sides, the fanglomerates 

 came from both directions. If Triassic sedimentation started before fault- 

 ing, it may have been due to one of two causes : ( 1 ) a broad syncline may 

 have developed which later broke into faults on one or both sides, or (2) 

 a change may have occurred from a warm humid climate in whch red 

 soils were developed on the surrounding lands to an arid or semiarid one 

 in which salt crystals developed in the sediments from time to time, and in 

 which torrential floods were common. 



The throw of the border faults according to the cross sections of Fig. 9.4 

 would equal the total thickness of the basin sediments, and therefore, 

 would be of the magnitude of 20,000 feet. This is twice as much as postu- 

 lated or computed for any other post-Proterozoic normal fault in North 

 America, and leads one to regard the large figure critically. Stose and 

 Bascom ( 1929 ) compute the throw at 6000 feet in the southeastern Penn- 

 sylvania area by means of their postulated origin of the Newark basin. 



The nature of the faults of the Triassic basins, both in vertical and 

 horizontal position and movement, and the general plan of the entire zone 

 of faults from the Carolinas to Nova Scotia reminded Bain ( 1941 ) of the 

 Rift Valleys of Africa, and he considers them a rift zone. 



LATE TRIASSIC PHASE (PALISADES OROGENY) 



The onset of faulting that formed the troughs in which the Triassic sedi- 

 ments accumulated marked the beginning of the Palisades orogeny. It 

 started in late Triassic time and probably ran its course before the end of 

 the period. After the border faults had become major faults and great 



thicknesses of sediments had accumulated, vast amounts of basic magma 

 entered the basins, chiefly along the border faults, and spread into the 

 sediments as numerous sills, some exceedingly thick, and as great dikes. 

 In places the dikes cut long distances into the country rock. Great amounts 

 of magma reached the surface as basalt flows, which were immediately 

 buried by the accumulating sediments. Accompanying the igneous activity 

 was an additional episode of faulting. Both strike and transverse parallel 

 faults provided avenues of ingress of the magma, and continued faulting 

 broke and offset some of the sills as well as the sediments. The great 

 border faults undoubtedly also continued active in places, dropping the 

 basins farther and inviting new floods of fanglomerate. 



The entire activity from the inception of the border faulting through 

 the intrusive and extrusive activity and additional faulting seems to have 

 been fairly continuous and hence not separable into early and late phases. 

 It will all be recognized here as the late Triassic phase, or the Palisades 

 orogeny. 



The faulting and dike intrusions spread into rocks adjacent to the 

 Triassic basins, and it is clear that at the time of maximum accumulation 

 the sediments were much more extensive than now. Their beds are bev- 

 eled on the sides opposite the border faults, and the fanglomerates still 

 bury in places the fault scarps and spread considerable distances over the 

 upthrown blocks. Whitcomb (1942) considers the Spitzenberg conglomer- 

 ate as a Triassic outlier 20 miles north of the present margin of the New- 

 ark basin. The now separate basins may easily have been confluent in 

 places, but such cannot be proved, it seems. It is also possible that, while 

 the Palisades orogeny was taking place in the Piedmont and folded Appa- 

 lachians, the continental margin lay 100 to 200 miles eastward and Triassic 

 sediments were accumulating there. 



