MARINE VERSUS NON-MARINE ENVIRONMENTS FOR THE JIBALAH GROUP, NW ARABIAN SHIELD: A SEDIMENTOLOGIC AND GEOCHEMICAL SURVEY AND REPORT OF POSSIBLE METAZOA IN THE DHAIQA FORMATION

We report sedimentologic, geochemical, and zircon U-Pb geochronologic data for the Dhaiqa formation, a 300 m thick carbonate succession (Dhaiqa basin, NW Arabian shield) thought to represent one of Saudi Arabia fs youngest Precambrian basement exposures within the Ediacaran age Jibalah Group. The evidence supports that Dhaiqa formation deposition occurred between ≤ 600 and ~530 Ma, within an unresolved lacustrine, paralic, or marine setting. Possible metazoan trace fossils occur in the lower part of the Dhaiqa formation, below a distinct diamictite interval that bears detrital zircons as young as 599 ±4.8 (core) and 570 ± 4.6 (rim) Ma. If confirmed, the metazoan traces argue for a marine depositional setting and a marine context for interpreting isotopic signatures. Strontium isotope compositions between 0.704.0.706 demonstrate a prominent diagenetic and/or depositional influence by ensimatic Sr, which prohibits correlation with Ediacaran seawater. Carbon isotopic compositions, more resistant to diagenetic alteration by meteoric and diagenetic fluids, are predominantly positive, averaging +2.4 ± 2.3 %. If marine δ^13_Ccarb compositions are retained, the positive signatures constrain Dhaiqa formation deposition to the interval either before (~600 Ma to sometime after the Gaskiers glaciation, possibly 570.560 Ma) or after (~551 to 542 Ma) the Shuram anomaly. Earth fs greatest marine negative δ13Ccarb excursion. The former correlation is consistent with the Khufai Formation (Nafun Group) in Oman below an unconformity attributed to the Gaskiers glaciation, but this implies the oldest record of behaviorally complex Ediacaran trace fossils. The latter correlation is consistent with the burrows recognized.