ORIGINAL PAPER Types and nature of fracture associated with Late Ordovician paleochannels of glaciofluvial Sarah Formation, Qasim region, Central Saudi Arabia Jarrah Mohammed Ahmed Babiker 1 & Mustafa Mohammed Hariri 1 & Osman Abdullatif 1 & Gabor Korvin 1 Received: 20 March 2016 /Accepted: 16 February 2017 /Published online: 20 March 2017 # Saudi Society for Geosciences 2017 Abstract This study evaluates the Late Ordovician glaciofluvial deposits of the Sarah Formation and equivalent outcroppings in north, central, and southwestern Saudi Arabia. The Sarah Formation also covers a wide area in the subsurface and is considered as an important target for uncon- ventional tight gas reservoir. Defining the fracture types, na- ture, and distribution in outcrop scale might help to establish a successful fracture simulation model and behavior for the Sarah tight gas reservoir in the subsurface. This study inves- tigates fracture characteristics for the Sarah Formation at Sarah paleochannel outcrops. The study revealed three sets of fractures, which have EW, NS, and SE-NW directions, and these fractures vary from open, resistive, and filled to resistive fractures. The closed fractures are filled with ferruginated iron oxides and gypsum. The filled fractures (the thrust boundary) are found in the study area at the SE- NW strike fracture set, while open and resistive fractures are found mainly at S-N and E-W fracture sets, respectively. The syn-depositional filled fractures (iron oxides) are considered as the younger fracture sets while the open and resistive frac- tures are post-depositional fractures which may have resulted from uplift or tectonic movement. A general model representing the fracture pattern and the thrusting boundaries due to glacial movement was constructed. It has been noticed that the systematic occurrence of filled fractures (thrust boundaries) described the boundaries between different gla- cial events, which act as a fluid barrier (filled fractures) and decrease the reservoir quality. The finding of this study might be utilized as a guide and lead for exploration in the subsur- face Sarah glacial deposits. It will also help to understand and speculate the nature pattern and distribution of fractures with the Sarah Formation. Keywords Sarah formation . Fracture types . Glaciofluvial deposits . Tight reservoir . Fracture model Introduction The Late Ordovician glaciofluvial deposits of the Sarah Formation were distributed along central and NW Saudi Arabia (Vaslet 1989; McGillivray and Husseini 1992; Clark- Lowes 2005) as a first glaciofluvial event in the Arabian Peninsula. The deposition of Late Ordovician sediments cor- responding to the Ordovician-Cambrian first-order retrogradational sequence set is characterized by 200-m- thick glacial sediments, extending from Oman to Spain and from Mauritania to Saudi Arabia (Ghienne 2011). The Sarah Formation was cropped out in central and NW Saudi Arabia as an incised paleovalley and covers wide areas in the subsurface. Regionally, Saudi Arabia is considered as a part of the North Gondwana platform with Libya, Mauritania, Niger, and Algeria. Most of the Middle East and North Africa were subjected to Hirnantian glaciation (Le Heron et al. 2009). The North Gondwana platform is considered the proximal ice zone, and most of the glaciation features can be found * Jarrah Mohammed Ahmed Babiker jarra72012@hotmail.com Mustafa Mohammed Hariri mmhariri@kfupm.edu.sa Osman Abdullatif osmanabd@kfupm.edu.sa Gabor Korvin gabor@kfupm.edu.sa 1 King Fahd University of Petroleum and Minerals, Dhahran, Saudi Arabia Arab J Geosci (2017) 10: 146 DOI 10.1007/s12517-017-2922-3