132 



STRUCTURAL GEOLOGY OF NORTH AMERICA 



EXPLANATION 



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SPRINGFIELD SECTION 



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HARTFORD SECTION 



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Fig. 9.3. Triassic basin of Connecticut and Massachusetts. Reproduced from Longwell, 1933. 



Fig. 9.4. Generalized east-west sections across the Triassic basin in Connecticut and Massa- 

 chusetts. Somewhat modified after Longwell, 1933. 



lescing alluvial fans that radiate westward from the Great Fault and thin 

 from 16,000 to 1500 feet in some 32 miles. 



The stratigraphic units are (1) Lower: New Haven arkose, up to 8550 feet, 

 relatively coarse fluvial gray and pink arkoses, conglomerates, red feldspathic 

 sandstones, and subordinate red siltstones and shales; (2) Middle: Meriden 

 formation, up to 2800 feet, fine-grained lacustrine and paludial variegated and 

 dark siltstones, shales, limestones, light feldspathic sandstones, subordinate 

 coarse elastics, and three basaltic lava flows; (3) Upper: Pordand formation, 

 up to 4000 feet, fluvial deposit similar to New Haven. 



Conglomerates form 10%, sandstones 64%, siltstones and shales 25%, red 

 color is present in 52%. Near the Great Fault sediments pass into fanglomerates. 



Two main groups of alluvial fans are present: Central Connecticut (indicolite 

 and little epidote) and Southern Connecticut (no indicolite, much epidote). 

 Almost all the sedimentary detritus is derived from a source area only 5 to 10 

 miles wide east of the steep, moderately high Great Fault, whose recurrent 

 rejuvenation controlled sedimentation. 



Four formations have been mapped on the state geologic map of Mas- 

 sachusetts (1916), but their distribution as continuous-layered units could 

 hardly be shown on cross sections. The central part of the basin at the 



