STRATIGRAPHY AND STRUCTURAL GEOLOGY OF BALD MOUNTAIN, WILTON-WELD AREA, WEST-CENTRAL MAINE

Bald Mountain hosts one of the most extensive outcrops of metasedimentary rocks in west-central Maine. The large ~1-km × 150-m exposure of Day Mountain Formation lies within the disputed Rumford allochthon (Moench and Pankiwskij, 1988) of the Central Maine trough. The Rumford strata were presumed to be fault-bounded and deposited in a Devonian foreland basin with southeastern provenance. An alternative model proposed by Solar and Brown (2001) shows the strata to be continuous with the surrounding Silurian formations thought to be derived from the northwest. The schists and graywackes exhibit cyclically graded beds, locally cross-laminated, and are interpreted as distal turbidites. The purpose of this study was to document the orientations of the early tectonic and sedimentary structures and then remove the effects of later Devonian deformation. Bald Mountain is dominated by large-scale open folds (F2) with vertical limbs that commonly top to the southeast, and shallow-dipping horizontal limbs. The major fold axis is 210, 10 and schistosity appears to be axial planar with a fairly consistent orientation of 023, 80 NW. A small number of early isoclinal folds (F1) are truncated by the schistosity and commonly have one attenuated limb. One of these F1 folds trends ~100 and plunges ~75. By removing the later F2 deformation, F1 shows sense of shear from the NE to SW. Analysis of several cross-laminated beds suggests that paleocurrents flowed very approximately from NE to SW. With the preliminary results suggesting NE to SW paleocurrents and SW-dipping paleoslope, we are unable to discriminate between Devonian Seboomook Group and Silurian Perry Mountain Formation using this strategy. However, the lithologic resemblance between the Day Mountain Formation and dated Devonian units casts doubt on the proposed correlation with the Perry Mountain Formation.