Characteristics and age of an uplift signal in the Biga Peninsula (NW Turkey) from a mix of geomorphic indices

Situated in the area where the western end of the North Anatolian Fault Zone meets the extensional domain of
the North Aegean Sea, the Kazdag Mountain range (Biga Peninsula, NW Turkey) is known to have undergone
Plio-Quaternary uplift. However, no detailed chronology of this presumably ongoing uplift phase was so far
available. In order to obtain a first-order estimate of the time of the last tectonic perturbation (uplift rate change) in
the region, we performed a morphometric study of the fluvial landscape at the scale of the Biga Peninsula, coupling
the recently developed R/SR analysis of the drainage network with concavity and steepness measures of a set of
29 rivers of all sizes. Defined as the ratio of two-by-two differences between hypsometric integrals describing
respectively a catchment’s topography, its drainage network "composite profile" and the trunk stream profile, the
R metric is a measure of the catchment’s incision response to a relative base level lowering. The SR index is then
simply the slope of the regional relation R = f(ln A), a feature characteristic of the time elapsed since uplift caused
an erosion wave to propagate in the drainage system. We obtained a SR value of 0.324±0.035 that, according to
the t = f(SR) relation established by Demoulin (2012), yields an age range of 0.54-1.29 Ma and a most probable
value of 0.82 Ma for the time of the last uplift signal in the Biga Peninsula. We also carried out an analysis of
knickpoint migration in a subset of rivers, modelling their propagation by the stream power law under different
assumed ages so as to compare the obtained values of the K coefficient with values mentioned in the literature. The
positive results of this analysis, yielding realistic K values for ages around 0.8 Ma, lend independent support to
our morphometric estimate of the uplift time, moreover corroborated by published observations suggesting basin
inversion of the Bayramiç and Çanakkale depressions at the same epoch. We relate this episode of increased uplift
rate to the early-to-mid Pleistocene tectonic transition identified in the Eastern Mediterranean realm by Schattner
(2010) and marked by a brief compressional episode. Finally, while the dependence of river profile concavity on
basin size confirms that the landscape of the peninsula is still in a transient state, the spatial distribution of profile
steepness values characterized by higher values for streams flowing down from the Kazdag massif shows that the
latter undergoes higher uplift rates than the rest of the peninsula. This indicates that, after the regional Middle
Pleistocene episode of accelerated uplift had come to an end, a local component of uplift persisted associated with
either transpressive conditions along SW-trending segments of the North Anatolian Shear Zone or normal faulting
along the southern border of the massif.
References
Demoulin A., 2012. Morphometric dating of the fluvial landscape response to a tectonic perturbation. Geoph. Res.
Lett. 39, L15402, doi:10.1029/2012GL052201.
Schattner U., 2010. What triggered the early-to-mid Pleistocene tectonic transition across the entire eastern
Mediterranean? Earth Planet. Sci. Lett. 289, 539-548.