THE RECORD OF DEXTRAL STRIKE/SLIP MOTION IN THE LIMESTONE MEMBER OF THE WATERVILLE FORMATION, MAINE

We investigated the extent of dextral kinematic indicators in the Limestone Member of the Waterville Formation in Kennebec County, Maine. The Waterville Formation is composed of interbedded pelite and limestone, and was deformed multiple times during the late Paleozoic. It can be separated into two facies: the western facies, and the eastern facies. The western facies is more thickly bedded with abundant quartz wacke, while the western facies is dominated by phyllite. Short and Johnson (2006) documented dextral transpression in one outcrop of the Limestone Member in the eastern facies. This indicates that the Limestone Member may comprise a dextral shear zone related to the Norumbega Fault system. But the extent of the dextral transpressional deformation in the surrounding area is still not known, therefore, we mapped the extent of dextral shear sense indicators in the Limestone Member over an area of 12 km across strike and 21 km along strike using the 1968 geological map of the Waterville-Vassalboro area as a base map. Dextral motion is recorded by structures in limestone beds such as asymmetric boudinage of synkinematic veins and asymmetric folding. Generally, the eastern facies exhibits dextral shear sense indicators, and the western facies does not. However, there is a range of abundance of shear-sense indicators within the eastern facies. Outcrops along the far eastern edge of the Waterville Formation contain fewer shear-sense indicators. Pelite beds are much less deformed than adjacent limestone beds throughout the eastern-facies outcrops. Veins within pelite beds exhibit clockwise rotation, yet rarely show complete boudinage or significant elongation like those visible in the limestone beds. These observations may help us understand the weakening mechanisms that enabled strike slip motion to localize in this region and will help reevaluate the structural geology of the area.