Elemental chemistry as a tool of stratigraphic correlation: A case study involving lower Paleozoic Wajid, Saq, and Qasim formations in Saudi Arabia

Abstract

Separated physically by a distance of over 1250 km, two lower Paleozoic formations in Saudi Arabia, the Wajid Formation in the southwest and the Saq Formation in central and northwestern Saudi Arabia, are fairly similar in lithology (both are quartz arenite) and overall depositional environment; yet the exact stratigraphic relationship between these two formations is not adequately known. Based on seismic and well data some earlier studies suggested that these two formations are in fact a single formation, and the name Wajid Formation and its Members should be abandoned in favor of the terminology adopted for similar Paleozoic formations in the central and northern part of the country. The present study, which is first of its kind in Saudi Arabia, is an attempt to determine the stratigraphic relationship between the Dibsiyah Member of the Wajid Formation and the Risha Member of the Saq Formation based on their overall elemental chemistry. This study also included the Ordovician Kahfah Member of the Qasim Formation for ensuring validity of the approach—this younger formation is expected to show a significantly different elemental chemistry compared to the other two formations. Elemental data when subjected to multivariate cluster and factor analyses and plotted confirmed three end members corresponding to these three formations. However, based on the observation that there is considerable overlapping of the Wajid samples in both Saq and Qasim sample domains of the plots, and very little or insignificant presence of the Qasim samples in the Wajid sample domain, it was concluded that these three formations were deposited in a single basin and represent a single stratigraphic succession in which sediments of the Saq and Wajid formations are closely related. Also, based on overall similarity in lithology, substantial overlapping and mixing of the Wajid and Saq formations, and apparent absence of such relationships involving Wajid and Qasim samples, the Wajid and Saq can be considered as a single formation.