Cleavage in Triassic rocks of southern New Brunswick, Canada

Abstract

Cleavage is sporadically developed in Late Triassic redbeds of the Lepreau Formation in folds and in areas of uniform northwestward dip in the lower Lepreau River -Lepreau Harbour half-graben. The cleavage in shaly siltstone beds is a composite incipient fabric defined by patchily developed crenulated bedding laminae, pressure solution planes, and mineral orientation parallel to the cleavage direction; cleavage in sandstone beds is defined by alignment of submicroscopic cracks inferred from laboratory tests. The cleavage fabrics are subvertical trending northeast-southwest, and resulted from horizontal northwest-southeast compression. Closely spaced fractures subparallel to the cleavage fabric in both shaly siltstones and sandstones are interpreted as later structures formed during relaxation of tectonic stresses. The cleavage fabrics and fractures are also present in intraforrnational clasts of shaly siltstone and rare sandstone clasts within conglomerate beds. A distinct shape orientation of the shaly siltstone clasts parallel to their cleavage within relatively undeformed conglomerate is attributed to compression during folding of unconsolidated conglomerate beds. The mean cleavage orientation varies from coplanar to noncoplanar with fold axial surfaces. The folds and cleavage formed during lateral compression probably related to wrench faulting which postdates the formation of the Triassic grabens.Un clivage s'est developpe de f a~o n sporadique dans les lits rouges de la formation de Lepreau, datant de la fin du Trias, dans les plis et les regions de pendage uniforrne vers le nord-ouest dans la partie inferieure du demi-graben de la riviere et du port de Lepreau. Le clivage dans les lits de siltstones schisteux forrne une structure composite rudirnentaire, definie par des laminae de stratification plissotees qui se developpent par endroits, des plans de solution sous pression et par l'orientation de mineraux parallele a la direction du clivage; le clivage dans les gres est defini par l'alignement de fissures infra-microscopiques dont on soupGonne la presence a partir d'essais en laboratoire. L'orientation du clivage est subverticale avec une direction nord-est a sud-ouest et resulte d'une compression horizontale du nord-ouest vers le sud-est. On interprete les fractures rapprochees subparalltles a la direction du clivage dans les siltstones et les grts cornme des structures plus recentes formees durant la rellche des contraintes tectoniques. Les orientations du clivage et des fractures se retrouvent dans des fragments de siltstone schisteux a I'interieur de la formation et dans de rares fragments de gres dans les lits de conglornerat. On attribue I'orientation de forme distincte des fragments de siltstone schisteux parallele a leur clivage dans un conglomerat relativement peu deforme a la compression durant le plissement des lits de conglomerat non consolides. L'orientation moyenne du clivage vane de coplanaire a oblique par rapport aux surfaces axiales des plis. Les plis et le clivage se sont formes durant ...

Remnants of Early Mesozoic basalt of the Central Atlantic Magmatic Province in Cape Breton Island, Nova Scotia, Canada

“…These younger ages have been attributed to (1) complications in the argon systematics (Jourdan et al 2009), (2) a younger intrusive (crystallization) event (Jourdan et al 2009), or (3) a younger hydrothermal event coincident with zeolite formation in the North Mountain Basalt (Kontak and Archibald 2003) and sulphide mineralization related to the Caraquet Dyke in central New Brunswick (Crosby et al 1990). The younger hydrothermal hypothesis is consistent with the observation that zeolites is associated with NE-SW-trending breccia zones that parallel the Mesozoic faults bordering the Mesozoic Fundy Basin which were active up the Cenozoic (Stringer and Lajtai 1979;Crosby et al 1990). Hence, hydrothermal activity post-dated eruption and cooling of the basaltic sequence and deposition of the overlying Jurassic sediments.…”

Cleavages developed in mudstone during early diagenesis and deformation: Weldon Formation, Carboniferous (Tournaisian), south-eastern New Brunswick, Canada.

“…Morphology of these cleavages is very similar to those described in the Mabou Group or slightly younger (Visean or possibly Serpukhovian) mudstone-siltstone in southwestern New Brunswick (Stringer and Lajtai 1979: note that these authors considered the rocks in question to be Triassic, but subsequent workers have ascribed them to the Carboniferous following the discovery of Windsor Group at the bottom of the succession, see Park et al 1994 and references therein).…”

A Review of Proterozoic to Early Paleozoic Lithotectonic Terranes in New Brunswick, Canada and their Tectonic Evolution during Penobscot, Taconic, Salinic and Acadian Orogenesis

“…2). However, sedimentary rocks in the lower part of the stratigraphic section are exposed in several small fault blocks along the New Brunswick coast, where they consist mainly of Upper Triassic (Carnian) terrestrial, red alluvial and fluvial conglomerate and sandstone (Sarjeant and Stringer 1978;Stringer and Lajtai 1979;Nadon and Middleton 1985;MacNaughton and Pickerill 1995;Wade et al 1996). The upper part of the succession comprises columnar-jointed tholeiitic basalt encountered in an offshore borehole and underlying the western half of Grand Manan Island (inset in Fig.…”