Caractéristiques sédimentologiques, volcanologiques et structurales du bassin de Granada dans la ceinture de roches vertes de l'Abitibi (Québec) /

Abstract

The Granada Basin, correspond to the stratigraphie unit known as the Granada Formation. This unit lies in the southernmost part of the Southern Volcanic Zone of the greenstone dominated Abitibi Subprovince in Quebec.Faciès analysis in the Granada Basin has identified clastic and volcaniclastic rocks deposited in an environment evolving from relatively deep marine to fluvial. The earliest sediments were mainly turbidites (faciès la and lb) deposited in extensional sub-basins. These sediments were overlain by a regressive sequence that evolved from shallow marine wave base dominated sediments (faciès 2a) to coastal deposits (faciès 2b). These deposits represent the transition between marine and continental depositional environments. The transition zone is marked by deposits of sandstoneargillites-stratified pebble conglomerate (faciès 2b) transported by waves and tides between the subtidal and intertidal zone. Faciès 3a and 3b of the felsic volcaniclastic lithofacies are interbedded with faciès la, lb and 2a.Deposits of the Granada Basin are transitional faciès separated by intra-basin unconformities, which are characteristic of sedimentary basins formed along fault margins. The volcano-sedimentary deposits of the Granada Basin have characteristics of sedimentation influenced by tectonisme such as: i) local and basinwide lateral and vertical faciès variations; ii) alternating fining and coarsening upwards sequences; iii) high rate of accumulation of sediments; iv) some conglomerate boulders are over 1 m in size and the thickness of conglomerate deposits; v) interdigitation of conglomerates and sandstones that denotes a progradation; vi) intra-basin unconformities; vii) the local source of conglomerates; and viii) associated alkaline magmatism. Tectonism would be ongoing throughout the development of the basin which would have induced several phases of source renewal areas for the sediments coupled with intra-basin unconformities. The earliest formed sedimentary deposits of the Granada Basin were affected by uplift and subsequently eroded and recycled into later basin fill along intra-basin unconformities. Gradually as the basin filled the sedimentary deposits became less and less shallower which is a characteristic of piggyback-type basins. The decrease in the depth is a consequence of an increase in topography due to repeated uplift along faults.Sedimentary rocks of the Granada Basin were intruded by alkalic mature volcanic arc-type sills, stocks and porphyritic dikes. These intrusive rocks are similar to Timiskaming-type porphyry intrusions and volcanic rocks found in the Kirkland Lake area of Ontario.The structural style of the Granada Basin, consisting of overturned southward verging tight to isoclinal folds, is characteristic of thrust basins. Two major east-west trending synclinal axial traces are distinguishable and their juxtaposition in a back to back relationship is compatible with there being an unconformity between them. This unconformity is further demonstrated by the presence of sandstone cla...

Population productivity of shovelnose rays: Inferring the potential for recovery

“…There is increasing evidence of historical and contemporary declines in landings and catch rates for wedgefishes, giant guitarfishes, guitarfishes and banjo rays (herein collectively referred to as shovelnose rays), of up to 80% throughout most of their ranges [24], including Indonesia [31], South Africa [32], Madagascar [33], Mozambique [34], Tanzania [35], Arabian Seas and surrounding region [19, 36], India [37] and Brazil [38]. Many species of shovelnose rays are facing a high to extremely high risk of extinction in the wild [24, 39, 40].…”