Breccia-Massachusetts-Turners Falls, Folds (Geology), Geology, Structural-Massachusetts-Turners Falls
The Deerfield basin is part of an extensive northeast-southwest trending rift zone created during the Mesozoic (~180-250 Ma), as the supercontinent of Pangaea broke apart. During rifting activity, various Triassic and Jurassic-aged rocks were concurrently deposited, namely the Sugarloaf Arkose, the Deerfield Basalt, the Turners Falls Formation, and the Mt. Toby Formation. These strata were rotated due to the listric nature of the Easter Border fault of the Deerfield basin and today dip toward the fault by varying amounts (~10°-30°). As the Mid-Atlantic Ridge opened around ~170 Ma, the rifting turned to compression, folding the rocks into a regional syncline. The Turners Falls Formation contains a distinct assemblage of rock types. This study focuses on the lacustrine portion of the formation complete with several laterally extensive Van Houten cycles that cause an alternation of "wet-climate" black to gray shales and siltstones as well as "dry-climate" red siltstones and sandstones. At several locations in the Deerfield basin, some gray strata horizons contain breccia and folds. Previous studies of the area proposed slumping (Handy, 1977) or shear during flexural slip folding (Olsen et al., 1992) as the cause for the brecciated and folded horizons. Neither the slumping model nor the shear model satisfies all observational data. Data collected in this study finds past earthquakes and seismic shaking as a satisfactory mechanism to explain the brecciated and folded horizons.
Seidman, Lily Elizabeth, "Origin of the enigmatic breccia and folds in the Turners Falls formation, Deerfield Basin, Western Massachusetts" (2011). Honors Project, Smith College, Northampton, MA.
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