Spatio-temporal position of the Ediacaran Thalbah Basin in the Najd Fault System, Arabian Shield

Abstract

ABSTRACT This paper starts with a bibliographic review of the lithostratigraphy and radiometric dating of the Ediacaran Thalbah Group in the northwestern Arabian Shield, Saudi Arabia. It seeks to establish the spatio-temporal position of the group in the ongoing compilation and correlation of Ediacaran–Cambrian sedimentary time-rock units in the Middle East Geologic Time Scale (Al-Husseini, 2010, 2011, 2014). The group is defined and described in the Thalbah Basin, which crops out in the Al Wajh Quadrangle, and is approximately 100 km (NW-SE) by 40 km (SW-NE) in extent (Davies, 1985). The basin is situated within the approximately (ca.) 300 km-long, NW-trending Qazaz Fault Zone of the Najd Fault System. The Thalbah Group consists of three siliciclastic units: Hashim Formation (ca. 1,050–1,300 m thick) and likely coeval Zhufar Formation (ca. 600–1,400 m thick), and the younger Ridam Formation (ca. 1,000 m thick). Recently published U-Pb dating of detrital zircons gave ages of ≤ 596 ± 10 Ma for the Hashim Formation, and ≤ 612 ± 7 Ma for the Zhufar Formation (Bezenjani et al., 2014). The maximum depositional ages of the Hashim and Zhufar formations indicate they are approximately coeval to the lower part of the sedimentary and volcanic rocks of the Jibalah Group (≤ 605 ± 5 and ≥ 525 ± 5 Ma). The latter group was deposited in pull-apart basins along the ca. 600 km-long Rika and several other extensive fault zones of the NW-trending Najd Fault System in the northern and eastern parts of the Arabian Shield. The Qazaz Fault Zone left-laterally dislocated ophiolites of the NE-trending Yanbu Suture Zone (≥ 700 Ma) by about 100 km. The strike of the Qazaz Fault Zone projects into the Rika Fault Zone, along which five major pull-apart basins contain the Jibalah Group. The Rika Fault Zone dislocated by about 100 km the NS-trending ophiolite outcrop belts of the Ad Dafinah and Hulayfah fault zones (sometimes interpreted as parts the Nabitah Suture Zone, 680–640 Ma). Based on the time correlation of the Thalbah and Jibalah groups, and the highlighted structural features, the Rika and Qazaz fault zones are interpreted as a continuous 30 km-wide, 1,200 km-long, N63°W-striking fault zone, the “Rika-Qazaz Fault Zone”, which left-laterally dislocated the Arabian Shield by approximately 100 km after 605 ± 5 Ma and before 525 ± 5 Ma.