Facies Analyses and Depositional Environments of the Carbonates and Ironstones-Bearing Succession of Um Himar Formation, Turabah Area, Saudi Arabia

Ali A. Mesaed; Rushdi J. Taj; Mohamed Gameil; Ahmad S. Tayeb; Mohamed I. Matsah

doi:10.48084/etasr.18651

Authors

Ali A. Mesaed Geo-Exploration Techniques Department, Faculty of Earth Sciences, King Abdulaziz University, Jeddah, Saudi Arabia | Geology Department, Faculty of Sciences, Cairo University, Giza, Egypt
Rushdi J. Taj Petroleum Geology and Sedimentology Department, Faculty of Earth Sciences, King Abdulaziz University, Jeddah, Saudi Arabia
Mohamed Gameil Petroleum Geology and Sedimentology Department, Faculty of Earth Sciences, King Abdulaziz University, Jeddah, Saudi Arabia | Geology Department, Faculty of Sciences, Cairo University, Giza, Egypt
Ahmad S. Tayeb Petroleum Geology and Sedimentology Department, Faculty of Earth Sciences, King Abdulaziz University, Jeddah, Saudi Arabia
Mohamed I. Matsah Structural Geology and Remote Sensing Department, Faculty of Earth Sciences, King Abdulaziz University, Jeddah, Saudi Arabia

Volume: 16 | Issue: 3 | Pages: 36659-36671 | June 2026 | https://doi.org/10.48084/etasr.18651

Received: 10 March 2026 | Revised: 18 April 2026 and 8 May 2026 | Accepted: 9 May 2026 | Online: 19 May 2026

Corresponding author: Ali A. Mesaed

Abstract

The present study investigates facies analysis and depositional environments of the carbonate- and ironstone-bearing succession of the Um Himar Formation in the Turabah area. The study area is located in the southwestern part of the Arabian Shield of Saudi Arabia. Geologically, the area includes Arabian shield rocks that are overlain by the studied tertiary sedimentary succession of the Um Himar Formation. Tertiary basaltic flows are present and terminate the Tertiary succession. The Um Himar Formation is composed of four main units: Unit 1: Metavolcanics-Silicified Carbonate; Unit 2: Glauconitic Yellow Clays-Dolostone; Unit 3: Green Clays-Iron Ore; and Unit 4: Tertiary basic volcanic flows (Harrat). Field and microscopic investigations of these units revealed nine facies and related subfacies. Unit 1 is composed of andesitic tuffs and silicified dolostone and represents part of the greenstone belt of the Bidah Group to the west of the study area. It is composed of successive cycles of green glauconitic clays that grade into yellow dolomitic mudstones and dolostones. The cyclic pattern indicates the beginning of deposition in slightly deeper (dysaerobic) conditions. During the progressive shoaling of the depositional environments and a decrease in the volcaniclastic input, the silicified carbonates were deposited, which indicates restriction of the depositional environment and an increase in the alkalinity and formation of evaporitic cherty bands. Unit 2 represents a new transgressive cycle that begins with green celadonitic clays that were formed during the synsedimentary authigenesis instead of the deposited basic tuffs during transgressive time. During the progressive shoaling, thinly bedded dolostones were deposited in restricted environments. Unit 3 represents reddish brown to black massive ironstones, just terminated by oxidized green celadonitic clays. These ironstones were formed by diagenetic devitrification and hematitization of the underlying green clays and formation of reddish brown silicified hematitic iron ore horizon. Basaltic volcanic flows led to the formation of the topmost Unit 4 of the succession.

Keywords:

Um Himar Formation, carbonates, ironstones, volcaniclastics

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