Origin of Chaotic Structures on New World Island, Newfoundland
Colleen G. Elliott
Previous workers interpreted complex folds in Upper Ordovician turbiditic sandstone at Farmer Head, southwestern New World Island, to result from slumping in unlithified sediments. This interpretation is based on (1) the presence of various outcrop-scale ductile structures combined with the absence of brittle structures, (2) the presence of "welded contacts," (3) the apparent disharmonic and chaotic nature of the folds, and (4) the absence of tectonic cleavage. However, recent investigations indicate that the folds are tectonic in origin. Ductile deformation structures are common, but they are not diagnostic of penecontemporaneous deformation. Moreover, brittle deformation structures associated with folding are visible in thin section. The folds on Farmer Head are not dis armonic, and the complex outcrop patterns can be explained in terms of noncoaxial overprinting of two fold generations that both fold an older tectonic cleavage. These folds can be correlated with F3 and F4 folds in adjacent areas. F1 folds on New World Island probably formed in unlithified sediments, but where they are associated with olistostromal horizons, they are probably tectonic in origin. Elsewhere, F1 folds may be slump structures; however, because of at least three subsequent stages of tectonic deformation, F1 folds are difficult, if not impossible, to distinguish from tectonic folds.
AAPG Search and Discovery Article #91043©1986 AAPG Annual Convention, Atlanta, Georgia, June 15-18, 1986.