Tectonogeomorphological and satellite image analysis of the Red Sea passive margin at the latitude of Wadi Siatin, Northern Quseir, Egypt

Remote sensing has become an essential tool to improve data
collection and spatial analysis in the geosciences. Identification
of passive margin structures that are exposed along the Egyptian
coast of the Red Sea, and their control on landforms has been
hampered by limited data resolution and restricted access to this
arid and inaccessible region. A major challenge lies in
distinguishing features in the landscape that formed due to
long-term tectonic activity and erosion from those features that
modified the landscape recently. The goals of this thesis were to
determine to what degree the study area is currently tectonically
active, and what major hazards might affect the touristically
developing coastal region. This study deals with the structural and
geomorphological evolution of the rift-related structures and their
impact on the sediment distribution and landforms variation in the
northern Quseir area. In such a remote desert area, field and
remote morphostructural analysis are needed to understand the
structural and geomorphological evolution. The current study is
mainly based on high-resolution QuickBird image analysis and field
investigation. Field mapping was limited to one season, owing to
acute safety concerns in the Eastern Desert. In the study area, the
pre-rift stratigraphy includes Pan-African basement rocks overlain
by pre-rift clastic and carbonate successions that range in age
from Cambrian to Eocene. Syn-rift clastic and carbonate rocks range
in age from Late Oligocene to recent and show depositional patterns
controlled by fault systems. The field area exposes a section of a
tectonically uplifted, amagmatic sedimentary sequence, which formed
due to passive-margin-related rifting of the Red Sea: the Mesozoic
and Tertiary sedimentary units that fill the 7-km wide coastal
strip are perfectly exposed as tilted fault blocks. The results of
my field mapping and structural analysis show that the fault
architecture of the area is dominated by a large NW-SE-striking
fault system. A series of SE-dipping normal faults are consistent
in cross-section with listric fault geometry, rooting into an
E-dipping detachment at depth. Our mapping also revealed that
left-steps in at least one of the major NS- striking faults are
accommodated by a flower structure, but not by SW-NE-oriented cross
faults as previously proposed in a neighboring area. Thus seismic
activity is more likely to occur on the large NW-striking normal
faults, leading to potentially larger Magnitude earthquakes than
previously recognized in the area. The left-step may act as a
barrier to rupture propagation and should be examined in more
detail. The northwestern Red Sea coast is part of the straight
coastal segment that is generally characterized as seismically
inactive. However, during the geological field mapping, I found
evidence for Plio-/Pleistocene vertical coastal uplift, likely due
to earthquake-related coastal and offshore faulting. Pliocene
marine deposits emerged recently due to sea level-drop and
earthquake-related uplift. Even the presence of up to five distinct
Pleistocene coral terraces implies that at least some of the
coastal uplift was seismogenic, because terraces of the same age
can be found at different elevations along strike. Presumably, some
of the seawarddipping, N-S-striking normal faults are active today,
despite the lack of recent instrumental seismicity. These findings
imply long recurrence intervals for active faults in the northern
Quseir area. These results differ from previously published results
for the adjacent Quseir-Um Gheig sub-basin area, were E-W-striking
strike-slip faults were mapped to offset the N-Sstriking faults,
and had been inferred as earthquake-generating faults by Abd
El-Wahed et al. (2010). Based on our mapping, we postulate that the
large rift-parallel normal faults are seismogenic. Drainage network
evolution within the study area is often structurally controlled
and the nature of these controls was examined in this study. The
Wadi Siatin stream channel network is classified in a relatively
simple way, based on the high-resolution satellite data, with
dendritic, and rectangular considered the most fundamental channel
geometries. It was possible to distinguish the different
morphological elements of the network, as well as the anomalies
that affect the patterns. This analysis revealed, in the northern
Red Sea area basins, the existence of old structures whose
successive reactivations have left their mark on the drainage
network. Comparison of joint systems direction with the directions
of the main trunk stream channel of Wadi Siatin shows that the
channel is highly affected by tectonic jointing. First-order
channels follow easily erodable faults. Investigations concerning
the relationship of stream-flow orientation with geological
structure in the Wadi Siatin Basin shows that, generally, the least
influenced flows are those of first-order which are governed simply
by the valley side slopes on which they developed. However, in
certain geological and geomorphological situations, there are clear
exceptions to this generalization. Certainly, locally, geological
control of these small streams may be even higher than in many
streams of higher order. In the peripheral parts of the Basin,
expansion of drainage into the available space has obviously been
easiest along lines of weakness and, as a consequence of this,
streams of the first order come to exhibit a high degree of
adjustment to the underlying structure. The maximum structural
control is reached by the streams of the third order. Towards the
higher orders, the influence of local structure becomes weaker.