Geology of Marystown map sheet (E.2) Burin Peninsula, southeastern Newfoundland

The geology of southeastern Newfoundland is poorly understood in many respects. Marystown map-sheet (E/2) is a small part of this region but it contains many of the characteristic geological features which have been problematic. Detailed geological mapping, petrography and geochemistry were employed in the study of the map area. -- Marystown map-sheet (E/2) is divided into three segments by two northeasterly trending faults, each characterized by different rock sequences. The northwest segment is underlain by Late Precambrian rocks very similar to the volcanic rocks found elsewhere in southeast Newfoundland, being a subaerial , bimodal, slightly alkali, basalt-rhyolite suite. The rocks of this segment are interpreted to have formed as a result of high angle, block faulting. The central segment consists of a Late Precambrian (?) to Middle Cambrian sequence beginning with red and green sandstones and siltstones overlain by a red shale - pink limestone - grey siltstone - black shale unit. This sequence, fossiliferous in part and lithologically similar to rocks of equivalent age found elsewhere in the region, is interpreted to have formed firstly by erosion of a land mass and deposition of clastic sediments in an intertidal environment and secondly, by deposition of non-clastic and minor elastics in a restricted marine environment. The southeast segment is underlain by a conformable. Late Precambrian sequence beginning with the oldest rocks of the map area, ' grey, laminated, siliceous siltstones and polymictic conglomerates, which were derived from a subaerial acid volcanic - submarine sedimentary terrain and deposited in an environment with both deep- and shallow-water characteristics. These sedimentary rocks are overlain by a thick pillow basalt - tuffaceous sedimentary sequence intruded by a comagmatic layered sill. These volcanic and intrusive rocks are chemically and petrographically similar to ocean ridge tholeiites. The area was subjected to a period of northwest-southeast compression in post Middle Cambrian times. Metamorphism varies from greenschist facies in the older rocks to unmetamorphosed in the youngest rocks. \n