Palynology in action: faults

Palynology is usually associated with simple dating or palaeoenvironmental and climate studies, but it can be used to solve larger regional geological problems. One example relates to the origin and history of the Dead Sea Fault famous for its destruction of Jericho. The Dead Sea Fault extends for around 1,000 km, and produced more than 100 km of displacement between the Negev and Jordan. Although the fault in its present form is Miocene in age, an older pre-existing deformed zone was also probably present. Here palynology analysis shows that a precursor to the fault was probably active during the Permian.

The fault

The Dead Sea Fault is a major tectonic element in the Middle East which extends from the Red Sea to Turkey, and contains evidence indicating ca. 107 km of strike-slip left-offset across the Negev-Jordan segment since the early to middle Miocene (e.g. Kohn et al., 2019). Although the Dead Sea Fault and its sinistral movements are widely accepted as Miocene in age, evidence suggests it may relate to an older pre-existing deformed zone as revealed from Eocene – Oligocene successions (see Avni et al., 2012), the early Cretaceous (Weissbrod, 2002), and the Precambrian (Avni, 2010). The fault is associated with intense folding close to the Dead Sea coast in Jordan (Fig. 1).

Fig. 1. Folding associated with the Dead Sea fault in Jordan. The beds in the cliff at centre and right are horizontal. The yellowish-brown beds to the right are vertical.

The palynology

Evidence from palynology shows that the fault or its precursor was also likely to have been active during the Permian. This is because it is possible to show through the occurrence of stratigraphically important fossil pollen species, that strata of the same age either side of the precursor are of very different thickness, and that a large part of the Permian succession is missing on  the Jordanian side. On the Negev side, the key formations are the Saad and Arqov formations  which vary in thickness across the Negev with the lower Saad Formation being thickest in the southern Negev and in the east adjacent to the Dead Sea Fault.

On the Jordanian side of the Dead Sea, the Permian succession is limited to the Umm Irna Formation. Palynology shows that the formation is likely of latest Permian age (Changhsingian) because it contains the pollen Pretricolpipollenites bharadwajii (Stephenson and Powell 2013, 2014). Cored sections of the Arqov Formation in the Negev boreholes Avdat-1 and Makhtesh Qatan-2 (Stephenson and Korngreen 2020, 2021) also contain Pretricolpipollenites bharadwajii. This indicates that the Umm Irna Formation is at least in part equivalent to the Arqov Formation (Fig. 2). However palynology also indicates that the Saad Formation does not occur to the east of the present day fault in the Dead Sea area of Jordan (Fig. 2).

Fig. 2. Lithostratigraphy, palynology and biozones of Makhtesh Qatan-2; Ramon-1, Boqer-1, Avdat-1 and Jordanian Dead Sea outcrops; solid star indicates Permian-Triassic boundary depth, blank star indicates approximate depth of the Permian-Triassic boundary

A possible mechanism for the fault’s influence is shown in Fig. 3. Here Permian fault movements allow for accommodation space to be created basinward (west), whereas this was restricted on the landward (east side).

Fig. 3. Possible mechanism for the fault’s influence

In this example palynology is shown as being very powerful in being able to differentiate the character of strata either side of the fault. This would be very difficult using other palaeontological groups because macrofossil and other microfossils are very rare in these Permian beds, whereas fossil pollen are very abundant in the Negev and Jordanian rocks at outcrop and in borehole cores.

References

Avni, Y. 2010. Evidence for early activity along faults sub-parallel to the Dead Sea transform in the eastern Negev.  In: Ryb, O., Edelman-Furstenberg, Y., Matmon, A., Nahmias, Y., Peleg, N., Avigad, D., (Eds.) Annual Meeting Abstract: Eilot, Israel, Israel Geological Society, 31.

Avni, Y., Segev, A., Ginat, H., 2012. Oligocene regional denudation of the northern Afar dome: Pre- and syn-breakup stages of the Afro-Arabian plate. Geological Society of America Bulletin, 124, 1871–1897, doi:10.1130/B30634.1.

Kohn, B., Weissbrod, T., Chung, L., Farley, K., Bodorkos, S. 2019. Low‐temperature thermochronology of francolite: Insights into timing of Dead Sea Transform motion. Terra Nova 31(3), 205-219.

Stephenson Michael H, Dorit Korngreen 2021. Palynology of the Permian of the Makhtesh Qatan-2, Ramon-1 and Boqer-1 boreholes Arqov Formation, Negev, Israel. Rivista Italiana di Paleontologia e Stratigrafia, V. 127 NO. 3 (2021)

Stephenson Michael H, Dorit Korngreen, 2020. Palynological correlation of the Arqov and Saad formations of the Negev, Israel, with the Umm Irna Formation of the eastern Dead Sea, Jordan, Review of Palaeobotany and Palynology, 274, 104153

Stephenson, M H, and Powell, J H. 2013. Palynology and alluvial architecture in the Permian Umm Irna Formation, Dead Sea, Jordan. GeoArabia, 18, 3, 17-60.

Stephenson, M H, and Powell, J H. 2014. Selected spores and pollen from the Permian Umm Irna Formation, Jordan, and their stratigraphic utility in the Middle East and North Africa. Rivista Italiana di Paleontologia e Stratigrafia, 120, 145-156

Weissbrod, T., 2002, Stratigraphy and correlation of the Lower Cretaceous exposures across the Dead Sea Transform with emphasis on tracing the Amir Formation in Jordan. Israel Journal of Earth Sciences 51, 55–78, doi:10.1560/XMAF-ED4A-7HVE-CB1J.

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