Cycles of sand-flat sandstone and playa–lacustrine mudstone in theTriassic–Jurassic Blomidon redbeds, Fundy rift basin, Nova Scotia: implications for tectonic and climatic controls

Abstract

The redbeds of the 220 m Blomidon Formation comprise more than 100 pairs of (i) sand-flat sandstone (distal alluvial fan) and (ii) playa sandy mudstone and (or) lacustrine claystone. These pairs are tectonic autocycles generated by rift-basin subsidence and sagging along the Glooscap fault zone that shifted loci of active fan sedimentation toward and away from the playa surface as fan lobes migrated into topographically low areas.Intervals of intense and prolonged aridity are recorded in many of the sand-flat sandstones and playa sandy mudstones by evaporite minerals, principally gypsum, precipitated by subsurface evolution of a CaS04-NaCI brine. Aridity is further demonstrated by intense disruption of sediment fabrics beneath evaporite crusts, deep mudcracks, eolian-sandstone layers and patches, and the presence of authigenic Ca-Mg-rich illite-smectite and analcime. During relatively wetter intervals, claystone beds accumulated in shallow lakes that filled the playa depression, lapping onto the sand flats. The claystones lack evaporite minerals and textures, and many are partially bioturbated.The long-term climate became progressively wetter from latest Triassic to earliest Jurassic time, as evidenced by an increase upsection in the ratio of lacustrine claystone to playa sandy mudstone and by less evaporite mineralization in the sand-flat sandstones.Les lits rouges de la Formation de Blomidon d'une puissance de 220 m incluent plus de 100 paires de bancs de (i) grks de platier tidal (cBne alluvial distal) et de (ii) mudstones grkseux de playa et (ou) d'argilite lacustre. Ces paires de bancs skdimentaires reprksentent des autocycles tectoniques crtks par la subsidence d'un bassin dans une zone de rift et par un flkchissement le long de la zone de failles de Glooscap; le jeu de ces failles a fait osciller le centre de la skdimentation active du cBne alluvial en directions convergente et divergente de la playa, au fur et i mesure que migraient les lobes des cBnes alluviaux dans les regions de faible relief.Les mintraux d'tvaporites, particulikrement le gypse prkcipitt par les changements en subsurface de la saumure CaS04-NaCI, prksents dans plusieurs lits de grks de platier tidal et de mudstones grtseux de playa sont les tkmoins d'intervalles d'une ariditk intense et prolongke. Le climat aride est corrobork par la fabrique skdimentaire kclatee des lits sous-jacents aux crofites d'kvaporites, par les fissures de desiccation profondes, par les lits et plages de grks kolien et par la prksence d'illite-smectite authigknique riche en Ca-Mg et de I'analcime. Durant les intervalles relativement plus humides, les lits d'argilite se sont accumulks dans des lacs peu profonds et ont comb16 la dkpression de la playa, chevauchant les grks de platier tidal. Les argilites ne contiennent pas d'kvaporites et n'exhibent pas de textures et plusieurs lits sont bioturbts.Entre la fin du Trias et le dkbut du Jurassique, la longue pkriode d'ariditk a ctdt la place h un climat progressivement plus humide, comme en tkmoignent I'augmentation...

The Upper Triassic Chedabucto Formation, Guysborough County, Nova Scotia: depositional and tectonic context

“…The Chedabucto Formation more closely resembles the coarse clastic units of the Wolfville Formation cropping out to the west in the Minas subbasin, whereas the upper Eurydice Formation is lithologically and temporally similar to the Norian-Hettangian Blomidon Formation which overlies the Wolfville Formation. In the Minas subbasin, the Wolfville and Blomidon Formations constitute a major finingupward megasequence of alluvial-fan to braided-stream to sandflat/playa deposition resulting from basin enlargement (Olsen et al 1989;Mertz and Hubert 1990;Schlische and Olsen 1990). A similar sequence may exist in the Eurydice Formation o f the nearby Orpheus basin, consisting o f a coarse, lower member equivalent to the Chedabucto and Wolfville Formations, and a finer-grained upper member, similar to the Blomidon Formation.…”

Triassic Basin Stratigraphy at Grand Manan, New Brunswick, Canada

“…10). Minerals that have been eroded to form the open spaces are also unidentified but may be described in other studies of the Blomidon Formation (Mertz and Hubert 1990;Olsen and Et-Touhami 2008). Alcock (1948) noted the presence of "minor amounts of reddish and brownish sandstone and conglomerate" a few km to the southwest of Grand Harbour, which he mapped beneath the basalt along the western side of the Red Point Fault.…”

“…It might be produced by a local playa or ephemeral lake in a semi-arid climate, as in the sedimentary environment described by Mertz and Hubert (1990) for the Blomidon Formation. Wade and Jansa (1994, p. 228) reported that this lithology is not known in the Blomidon Formation beneath the basalt elsewhere around the Bay of Fundy.…”

“…More common in the Blomidon Formation is "redbed" sandstone (Mertz and Hubert 1990). This appears to be true for the Dwellys Cove Formation as well, and light red, finegrained sandstone makes up most of the clastic part of the core on display in the Grand Manan Museum, which is missing the clay-rich contact member directly beneath the basalt.…”

Stratigraphic trapping potential in the Carboniferous of North Africa: developing new play concepts based on integrated outcrop sedimentology and regional sequence stratigraphy (Morocco, Algeria, Libya)

“…Leleu et al 2009) and subordinate aeolian dune deposits (Hubert & Mertz 1980 and alluvial fan sediments (Hubert & Mertz 1984). The contact between the formations corresponds to a major change in facies architecture to mud-rich playa margin deposits containing evaporites and ephemeral fluvial sheetsandstones (Hubert & Hyde 1982;Mertz & Hubert 1990;Gould 2001). The extensive North Mountain Basalt, part of the Central Atlantic Magmatic Province event (McHone 2000), overlies the Blomidon Formation, and straddles the Triassic-Jurassic boundary (Olsen et al 1989;Olsen 1997).…”