The Whately thrust: a structural solution to the stratigraphic dilemma of the Erving Formation

Compilation for the bedrock geologic map of Messachusetts demonstrated apparent incompatibilities between the Silurian and Lower Devonian stratigraphic sequences east and west of the Mesozoic basins in Massachusetts. Various stratigraphic "solutions' to the enigma all require that one or more of the observed rock types appear twice in the stratigraphic sequence. Difficulties with all such resolutions are severe. The resolution followed on the State bedrock map and the one we find least objectionable, though far from flawless, proposes that the sequence east of the Mesozoic basins is the "true' sequence and that the relations west of the basins are explained by a thrust, the Whately thrust, that carried the Littleton Formation westward at least 20km from the vicinity of the Bronson Hill anticlinorium onto the Gile Mountain-Waits River and Erving Formations. Acceptance of the Whately thrust model implies that the Merrimack and the Connecticut Valley belts were probably a single Silurian and Devonian sedimentary trough in which sedimentation spread westward through time. -Authors