Stratigraphic significance of heavy minerals in the Late Precambrian-Mesozoic clastic sequence (“Nubian Sandstone”) in the Near East

Abstract

Five heavy-mineral assemblages are recognized in the Precambrian-Mesozoic clastic sequence (“Nubian Sandstone”) of southern Israel, southern Jordan and Sinai. On their basis, eight assemblage zones of wide lateral continuity are established. These zones coincide in most cases with already-established lithostratigraphic units. Changes in the heavy-mineral assemblages can aid in recognizing paraconformities which are not always apparent otherwise. The zones are grouped into three associations representing three depositional cycles—Late Precambrian, Early Paleozoic, and Late Paleozoic-Mesozoic—separated by regional unconformities. Within the same rock, the heavy and light-mineral associations display parallel trends of maturation. The composition and vertical zonation of the heavy-mineral associations suggest the following sedimentary history: 1. (1) An association of unstables, with much chlorite, hornblende and staurolite, characterizes the Late Precambrian arkoses and conglomerates. These were derived from elevated metamorphic and magmatic terrains which underwent rapid stripping by erosion. Transport was short without intensive weathering, and burial rapid, thus preserving much of the composition of the source rocks. 2. (2) An association of ultrastables (zircon, tourmaline, rutile) and detrital apatite, which characterizes subarkoses and sometimes quartz-arenites of Early Paleozoic age. It was derived from magmatic, probably acidic terrains of moderate to low relief. The clastics underwent weathering and reworking under an epeirogenically controlled regime, by which the less stable constituents were selectively eliminated. 3. (3) An association of ultrastables—zircon, tourmaline and rutile—which characterizes the Upper Paleozoic and Mesozoic quartz-arenites. This association was derived from the recycling of earlier arkoses and subarkoses under a continued epeirogenic regime. Within the ultrastable heavy-mineral assemblage occur local admixtures of unstable heavy minerals (mostly staurolite, and lesser garnet, hornblende, epidote and chlorite), derived from local igneous outcrops which were exposed during the pre-Carboniferous pre-Permian and pre-Early Cretaceous uplifts.