Stratigraphy of the Jo-Mary Mountain area: with emphasis on the sedimentary facies and tectonic interpretation of the Carrabassett Formation
Hanson, Lindley S.
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The sedimentary facies of the Upper Silurian and Lower Devonian Madrid, Carrabassett, and Seboomook Formations, exposed on the northwestern limb of the Kearsarge-Central Maine Synclinorium, belong the following facies categories: (1) sandstone-rich turbidites, (2) pelitic turbidites and related hemipelagites, and (3) disrupted facies. Lithofacies within each formation are organized into one or more descriptive facies associations--these are the: (1) massive sandstone, (2) thickbedded turbidite, (3) thin-bedded turbidite, (4} chaotic, (5) massive-pelite, and (6) laminated-pelite facies associations. Where strata are well exposed, and sedimentary structures and bed geometries are discernible, these descriptive facies can be discussed in terms of one or more interpretive associations (e .g. channel and channel-margin facies associations.) The Devonian Carrabassett Formation is the youngest widespread formation exposed in the Kearsarge - Central Maine Synclinorium. In the Jo-Mary Mountain quadrangle and surrounding area, the Carrabassett Formation is a complex facies assemblage dominated by fine-grained turbidite and chaotic facies. The underlying Upper Silurian Madrid Formation is composed largely of sandstone- and siltstone-rich turbidites. The younger Seboomook Formation is characterized by pelitic turbidite and related hemipelagic facies. A facies analysis of the Carrabassett and underlying Madrid Formations indicates that sediments were derived from eastern sources and deposited in northwesterly-migrating slope and foredeep environments during the Late Silurian and Early Devonian. Sedimentation is believed to have been partly diachronous, becoming progressively younger toward the northwest. Short term penecontemporaneous deposition probably occurred in different settings, such as along the axis of the foredeep basin (Madrid Fm.) and lower- to base-of-slope environment (Carrabassett Fm.). Olistostromes, shed from the lower slope, and thir bedded turbidites dominated later stages of basin sedimentation when the source of coarse clastics, supplied from the northeast, was shut off during the Early Devonian. These environments are interpreted in terms of an accretionary complex contemporaneous with initial stages of compression during the Acadian orogeny.
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