Post-depositional processes on a buried Cambrian sequence in southern Israel, north Arabian Massif: evidence from new K–Ar dating of Mn-nodules

Abstract

AbstractThe Cambrian sedimentary sequence in Israel and adjacent countries marks the beginning of the Phanerozoic sedimentation on the Arabian–Nubian craton. The maximal burial of this sequence, in the southernmost part of Israel, was approximaly 2.5 km. Manganese nodules hosted by shales of the marine Cambrian Timna Formation, Timna Valley, were subjected to K–Ar analysis in order to date their Mn-mineral formation. In addition, the <2 μm clay fraction in the host rock was dated by K–Ar and Rb–Sr methods. The K–Ar ages (average 365 ± 4 Ma) and Rb–Sr isochron (381 ± 10 Ma) of the illitic clay fraction yielded a Middle/Late Devonian age. The results imply that K–Ar and Rb–Sr systems of <2μm illites in the Cambrian host rocks, as well as those enclosed in the Mn nodule insoluble residues, were completely resetin a Middle/Late Devonian thermo-tectonic event, coeval with the beginning of a stratigraphically recorded epeirogenic uplift. The Mn-nodules which were studied fall into two types: (1) nodules constituted by massive, well-crystallized hollandite and pyrolusite; and (2) younger nodules of poorly crystallized massive hollandite and coronadite solid-solutions. Type-1 nodules yielded a calculated Early Cretaceous age of 112 ± 11 Ma, whereas type-2 nodules yielded calculated apparent dates of 20 and 49 Ma. The first age suggests a first stage of manganese nodule formation within the Timna Formation, in Early Cretaceous time, possibly genetically connected with the shallow basic intrusions and volcanic explosive activity in the area. The much younger K–Ar dates of type-2 Mn nodules may be due to late manganese remobilization and mineralization processes. This activity is interpreted as being related to the nearby Tertiary Dead Sea rifting, which was accompanied by low temperature hydrothermal processes.