Figure 6. Satellite image analyses of the study area from west of the Rusayl Embayment to the Batain area. The study area is divided into eight sub-areas to potentially reveal local/regional variations in orientation of the lineamentary features (areas 1-8, separated by the red dashed lines). The orientations of the lineaments (light blue lines) from the satellite image are plotted in the rose diagrams (Jenness, 2014), with a bin size of 5°. All measurements are plotted in the rose diagram at the upper right. N=number of measured linear features; Maximum Values is the total length (in meters) of all measured lineaments.
4.3 Map analysis
This section summarizes previously mapped ~N/S-oriented compressive structures, ~E/W-oriented normal faults and ~NW-striking sinistral faults within eastern Oman (Figs. 7 and 8; Table 1). These structures affect mostly Paleocene/mid-Eocene sedimentary rocks but also some Miocene rocks, especially near the Qalhat Fault. Besides the mappable features, Wyns et al. (1992) measured sub-horizontal stylolite axes within Cenozoic carbonates, including those of the Oligocene Shama Formation near the Qalhat Fault. Stylolite axes are oriented ENE-WSE and interpret as axes of maximum compression during the Miocene (Wyns et al., 1992).
4.3.1. Folds
N/S to NW/SE-oriented folds within the post-obductional formation in the Muscat-Seeb area and the Permian rocks of the Saih Hatat Dome have been reported by Le Métour et al. (1986a), Villey et al. (1986a, 1986b), Mann et al. (1990), Miller et al. (2002), Kajima et al. (2012a, 2021b, 2021c), Scharf et al. (2016), Searle et al. (2019), Hansman et al. (2021) and Levell et al. (2021), and are summarized in Table 1. Traces of fold axes are shown in Figure 7. The respective folds deform stratigraphic units up to the mid-Eocene limestone of the Seeb Formation. Mapped folds are open to tight and display sub-vertical fold axial planes. Fold axes plunge gently towards the north to NW or are sub-horizontally. The interlimb angle of individual folds within the Rusayl Embayment varies. Towards the South, the same fold elements (synclines/anticlines) are tighter then in the North, where the folds open (Mann et al., 1990). Interlimb angles are homogeneous along individual folds outside the Rusayl Embayment.
Ninkabou et al. (2021) and Levell et al. (2021) presented seismic and well data from offshore northereastern Oman. A pre-late Eocene NNE-trending major fold has been spotted by Levell et al. (2021). This fold occurs in the NNE-ward projected extension of the Jabal Akhdar/Jabal Nakhl. Further ~N/S-trending folds extend from the Rusayl Embayment into the Sea of Oman and near Muscat. Rabu et al. (1986) and Coffield et al. (1990) mapped several Cenozoic ~N/S to NNW/SSE-trending faults in the Fanja area between the Jabal Akhdar and Saih Hatat domes as well as along the Frontal Range Fault and the Wadi Mansah Fault (Fig. 7).
Approximately N/S-oriented open to tight folds have been mapped within Paleocene to Miocene formations near Quriyat, in the Salma Plateau and Batain area (Le Métour et al., 1986a, 1986b; Roger et al., 1991; Wyns et al. 1992; Peters et al., 2001). Further ~N/S-oriented open asymmetric folds and monoclines deformed Maastrichtian to Eocene rocks at Jabal Ja’alan (Filbrandt et al., 1990). The traces of some of these folds are depicted in Figure 8.
4.3.2 Faults
Fournier et al. (2006) mapped sets of conjugate strike-slip faults within the Jafnayn Formation in the Muscat area (Figs. 7 and 8). Dextral and sinistral faults strike NE/SW and E/W, respectively (Fournier et al., 2006). The computed maximum horizontal stress trends ENE/WSW (between N54°E and N85°E; Fournier et al., 2006).
A segment of the Paleogene rocks, including the Jafnayn, Rusayl and Seeb formations at the “Tertiary Ridge” at Al Khod Village represents a WNW-striking transpressive sinistral shear zone with ~N/S-oriented compressive structures (folds and reverse faults) and ~E/W-striking normal faults (Scharf et al., 2016). The horizontal shorting direction was ENE/WSW (Scharf et al., 2016).
In the Sunub area of the Rusayl Embayment and near the Frontal Range Fault, the well-exposed WNW-striking sinistral transtensional Sunub Shear Zone associated with ~E/W-striking normal faults exists. It has been interpreted as a negative flower structure with a shale dike (Mattern et al., 2018c).
The southwestern margin of the Saih Hatat Dome and the Fanja area is characterized by the Wadi Mansah Fault Zone (Bailey et al., 2019; Scharf et al., 2019a). This major extensional shear zone has a throw of ≤7 km and a sinistral shear component. It has been interpreted as active during doming of the Jabal Akhdar and Saih Hatat domes during the late Eocene to Miocene (Scharf et al., 2019a). The southeastern extend of the Wadi Mansah Fault Zone is parallel to the margin of the Saih Hatat Dome and merges with the extensional Wadi Tayin Fault of Searle (2007). The latter has a throw of ~2 km (Searle, 2007). Numerous ~WNW-striking faults in the Fanja area affected autochthonous and allochthonous rocks (Stanger, 1985).
Within the Semail Ophiolite, parallelly orientated to the Wadi Mansah Fault Zone and near the Wadi Tayin Fault, a further sinistral transtensional fault zone is present – the Issmaiya Fault Zone (Callegari et al., 2020). This ~NW-striking shear zone is ~30 km long and ~3 km wide. Activity along this fault zone occurred first during the Maastrichtian to early Eocene and then following the mid-Eocene (Callegari et al., 2020).
The Salma Plateau, including mid-Eocene limestones, has been affected by numerous faults of the NW-striking sinistral transpressive Coastal Parallel Shear Zone (Wyns et al., 1992; Moraetis et al., 2018). Sinsitral slip was determined by Roger et al. (1991) and Wyns et al. (1992).
In the southeastern prolongation of the Issmaiya Fault Zone, the NW-striking Ja’alan Fault is exposed (Roger et al., 1991; Wyns et al., 1992; Fig. 8). This fault is a present-day major reverse fault with a sinistral component (Filbrandt et al., 1990; Wyns et al., 1992). The throw amounts to a few kilometers. The Ja’alan Fault marks the southwestern limit of the Salma Plateau (Fig. 2).
The ~N/S-striking Qalhat Fault is located near Sur and defines the eastern margin of the Salma Plateau (Fig. 2). The throw along the major fault amounts to a few to several kilometers, where the Neoproterozoic crystalline basement was thrust onto Oligocene/Miocene sedimentary rocks (Wyns et al., 1992). Adjacent to the Qalhat Fault are several ~N/S-oriented folds (Roger et al., 2001). The rocks east of the Qalhat Fault were not uplifted, while the same Cenozoic rocks to the West have been uplifted to an elevation of >2000 m.