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The junction of the Dinaric and Hellenic mountain belts hosts a trans-orogenic normal fault system (Shkoder-Peja Normal Fault, SPNF) that has accommodated oroclinal bending, as well as focused basin formation and drainage of the Drin River catchment. Analysis of fluvial morphology of this catchment reveals higher values of river slope indices (
Drainage networks in orogens are sensitive to tectonics and climatic conditions (
Intramontane basins are either internally or externally drained depending on whether the river system draining the basin is connected with a lower base level (e.g., the sea). Thus, a change in the base level of a river in response to tectonic and/or climatic events can lead to the integration of river branches and landscape change (
The tectonics of the Dinaric-Hellenic mountain belt along the eastern shore of the Adriatic Sea (
Overview maps:
The junction of the Dinaric and Hellenic belts is an excellent place to study the competing effects of tectonics and climate on the fluvial network. This junction is the site of an oroclinal bend of some 20° (
The Drin River at the Dinaric-Hellenic junction in northern Albania (
The present-day boundary between active orogenic shortening and extension defined in geodetic studies (
Two basins in the hanging wall of the SPNF, the Western Kosovo Basin and Tropoja Basin, contain middle Miocene-Pliocene and Plio-Pleistocene clastic and freshwater sediments, respectively (
In this paper, we investigate tectonic and climatic processes affecting the evolution of river drainage at the Dinaric-Hellenic junction. Following an introduction to the geology and morphology of the basins and their catchments at this junction, we provide descriptions of the stratigraphy and river terraces carved into the Tropoja Basin. This is followed by an outline of the methods used to characterize and date the landscape on scales ranging from this basin to the entire orogenic bend. A description of the basin stratigraphy and its river terraces is followed by a presentation of new 36Cl exposure ages of these terraces. A morphometric analysis of the regional drainage network at the orogenic junction then lays the foundation for a discussion of how the river channel network has responded to tectonic uplift, erosion and climate since Pliocene time. We conclude with a conceptual model for the Pliocene-to-Present evolution of basins at the Dinaric-Hellenic junction. It is found that the Neogene fault system that accommodated oroclinal bending and Hellenic slab rollback is the main factor controlling morphology on the orogenic scale. Faulting and footwall uplift increased rocks’ erodibility through fracturing and hill-slope degradation, whereas terrace incision and drainage integration through river capture events after the Last Glacial Maximum (LGM) regulated basin infilling on the scale of individual basins.
The Neogene tectonics of the Dinarides-Hellenides is characterised by NE-SW shortening (e.g.,
The Western Kosovo Basin and Tropoja Basin are both located in the hanging wall of the main normal fault of the SPNF system (
Topography of the Dinaric-Hellenic junction:
The SPNF and related faults coincide with a significant jump in elevation and slope angles (
The Topoja Basin is filled with ∼400 m of Pliocene-Holocene sedimentary rock (
Overview of fluvial terraces and abandoned river channels documenting episodic incision of the Tropoja Basin (TB) sediments:
Tectonic map and stratigraphy of the Tropoja Basin:
The Tropoja Basin contains three lithostratigraphic units with subhorizontal bedding (units one to three in
Lithologies of the Tropoja Basin:
The intermediate unit (unit 2) is up to ∼150 m thick and unconformably overlies unit 1 (
Unit 3 some 30–50 m thick occurs along the northern and the southeastern margins of the Tropoja Basin (
The bedding of all units is generally sub-horizontal with local variations due to gravity sliding. Measured dip and dip-directions of the clast imbricates in bedding of the carbonaceous conglomerate of unit 2 indicate river paleocurrent directions (dotted lines of
Terraces T1 and T2 in the Tropoja Basin were sampled for cosmogenic 36Cl dating (
Results of the 36Cl cosmogenic nuclide analysis.
Profile | Level | Lat. (N) | Long. (E) | Alt. m | EARL** | Mean | Median | Mode | Lowest χ2 | Max | Min |
---|---|---|---|---|---|---|---|---|---|---|---|
asl | |||||||||||
TP1* | T1 | 42.38 | 20.08 | 283 | 12 | 10.4 ka | 9.7 ka |
|
17.3 ka | 35.1 ka | 3.7 ka |
TP2* | T2 | 42.36 | 20.10 | 286 | 56 | 14.5 ka | 13.9 ka |
|
15.5 ka | 40.2 ka | 5.8 ka |
Incision rate (mm/yr) | 10.7 | 10.4 |
|
24.4 | 8.6 | 20.9 |
*Labelled as TP1-N, TP2-S in the Supplementary Informations **EARL: Elevation above present-day river level (m)
Bold values are reported in the text.
36Cl dating was performed by the isotope dilution method (
We computed the depth profile age using Monte Carlo simulations in Mathcad (see
We analyzed the river landscape at the Dinaric-Hellenic junction with two morphological measures:
χ (Chi) has dimensions of length (m) and is defined:
In
Knickpoints are defined as points or zones (knickzones) of abrupt change in the slope of rivers (e.g.,
For the Drin River analysis in
The two sampled terrace profiles, TP1 and TP2, show an exponential decrease of 36Cl concentration with depth (
36Cl nuclide concentration vs. profile depth for the two sample profiles TP1
The interested reader is referred to Section 1.4 of the Supplementary Information for a description of the method used to calculate river incision rates. We compared the minimum, maximum, and modal ages, which resulted in a best-fit incision rate of 11.7 mm/yr (
Most of the 80 knickpoints in the Tropoja Basin (
Morphometric analysis of the rivers in the Tropoja Basin catchment:
A striking feature of the knickpoints in the Tropoja Basin is that about half of them cluster at two distinct intervals in the elevation vs.
To compare the fluvial metrics of the Tropoja Basin catchment with the regional drainage network, we identified a total of 114 knickpoints in the entire Drin River drainage basin, starting from the Drin River outlet (taken here to be the base level,
Distribution of knickpoints and relief (defined as the difference between the min and max elevations) at the Dinarides-Hellenides junction:
Overall, channel slopes are much steeper along the Adriatic coastal mountain range where shortening is ongoing than in the high-relief Dinaric hinterland where the orogen is actively extending. There, the horizontal displacement rates range from 1.5–4 mm/yr normal to the strike of the orogen (
Two features of the distribution of blue knickpoints stand out in the channel profiles in
The
Stream metrics for the Dinaric-Hellenic junction, including the MDD–main drainage divide (purple dashed line), the DDD–Drin drainage divide (thin purple line) and main faults (thin black lines), including the SPNF (thick black line):
Bright colors in
The overarching question posed when interpreting our data is: How are patterns of deposition and erosion linked on different scales? To answer this, we begin with the scale of the Drin River catchment, then progress to the smaller scale of the Tropoja Basin, where the record of sedimentation and fluvial incision is best preserved and can be assessed in the context of faulting, climatic variation, stream-capture and autogenic factors, e.g., events that occurred within the basin.
Several important points emerge from the river stream metrics at the scales of the Tropoja Basin (
Knickpoints along rivers in the Drin catchment:
A further striking feature is that the
Following
The confluence of tributary channels delineates the trunk of the Drin River (
There are no discontinuities in stream profiles and river metrics across the transition from active extension to shortening (SET in
Knickzones away from the Adriatic coast and situated east of the SET within 90 km of the Drin outlet at elevations from 300 to 1,400 m asl (
The gap in knickpoints identified in
Today, we see that the Tropoja Basin is adjusted to the current steady-state conditions (
We focus our analysis on the Tropoja Basin as is gives us the opportunity to relate incision events and knickpoint migration to dated terrace levels. This in turn provides a potential age for catchment-wide reorganization events. To do this, we first identify mobile knickpoints, defined as knickpoints that migrate upstream due to a downstream perturbation (e.g., base-level fall,
During the LGM the regional base level of the Drin was the Adriatic Sea at ∼ 120 m below present-day sea level (
We propose that a new steady-state condition was established each time the sea-level rose significantly, thus creating an incision event or knickpoint that migrated upstream to adjust the river network to the new base level. These knickpoints are seen throughout the catchment of the Drin River (
The numerous knickpoints in the Tropoja Basin that did not form a
We tentatively correlate the age of terrace T3 with the lowest base-level during the LGM. However, we were unable to date this terrace and its age and origin remain speculative.
Climate is a factor that can control the river network as expressed by river metrics (e.g.,
Fluvial terraces contain information about climatic fluctuations (
In comparing our estimated incision rates for the Tropoja Basin (
To summarize this chapter, the combination of 36Cl ages of the fluvial terraces and geomorphic metric analysis show that river incision and sedimentation after the LGM was episodic. Prior to that, in the Early Pleistocene, a change from an internally to an externally drained system for the Drin River must have occurred as indicated by widespread lake sediments and relict topographic features mimicking former lake geometries. A tectonically controlled difference in base-level along the SPNF initially led to the formation of internally drained basins and lakes in the internal Dinarides which, like the Western Kosovo Basin and Tropoja Basin, lasted until Pliocene-to-Early Pleistocene time (
In the preceding chapters, we have documented how Cenozoic normal faults acted as a template upon which the last ice age substantially modified the landscape in this domain of tectonic bending at the Dinaric-Hellenic junction. Here, we present a conceptual model of how the post-Miocene rivers and lakes evolved in this structurally complex area (
Post-Miocene evolution of drainage in the vicinity of the Tropoja Basin (TB) and WesternKosovo Basin (WKB) at the Dinaric-Hellenic junction. Sketches are not to scale:
During stage 1 (Late Pliocene,
We estimate an approximate accumulation rate of 0.1–0.2 mm/yr for stage 1 based on the 200–300 m thickness of Pliocene Late-Pleistocene lacustrine sediments in the southwestern part of the Western Kosovo Basin (
Stage 2 (Pleistocene) was presaged in the Tropoja Basin by the deposition of sandstone in Unit 1 and the unconformable deposition of grey conglomerates of unit 2 (
The main drainage divide is depicted in
In this paper, we show that the landscape at the Dinaric-Hellenic junction has undergone dramatic changes long after the cessation of the main Neogene activity of the normal faults of the SPNF that transect the mountain range. In particular, the most recent ice age enhanced depositional and erosional events in its aftermath that used the Cenozoic normal faults as a template for a strong morphological imprint. The first-order modification of the landscape during Pleistocene to Holocene time is perhaps best exemplified by the arcuate shape of the present drainage divide around the SPNF at the junction of Dinaric and Hellenic segments of the mountain belt. This fault and its related extensional structures helped localise Pleistocene to Holocene precipitation, erosion and deposition. The reorganization of fluvial drainage patterns leading to the formation and partial demise of lakes and basins.
Regarded at the scale of individual basins, the landscape reflects a subtle feedback between tectonic and climate-induced processes. Differential erosion fostered by the fault-induced juxtaposition of lithologies with contrasting erodibilities and possibly triggered by seismicity set the stage. But it was climatic variation, especially glaciation and subsequent melting, that increased erosion rates and changed the erosional base-level, facilitating a switch from internal to external drainage of lakes and basins into the Drin River. Our data show that river integration increased after the Last Glacial Maximum (LGM) when the Drin River drainage expanded its upstream drainage area, leading to a top-down incision of the river system.
Overall, our data support the idea that rollback subduction in the Hellenides and associated extension, both parallel- and normal to the orogen, affected landscape formation. This happened because crustal extension accommodating slab steepening and bending localized faulting and induced basin subsidence. Normal faults like the SPNF control erodibility and provide river paths that focus erosion and sediment transport (e.g.,
The original contributions presented in the study are included in the article/
LG lead the study and wrote the manuscript, which was supplemented by substantial written contributions from MH, AR and JG, in consultation with KH, BM, MG and AB. Basic project funding was acquired by JG and MH with additional funding for cosmogenic dating obtained by LG and KH. BM, DS and MG conducted fieldwork and data analysis in the TB Basin supervised by LG, JG, MH and MG. BM performed the 36CL nuclides analysis and incision rates modelling supervised by LG and KH. LG and BM analysed the geomorphology and interpretated it with input from AR and MH. AB aided in the sedimentological analysis of the basins.
Funding for our research came from the German Science Foundation in the form of Grants Gi 825/4-1 and Ha 2403/21-1, respectively, to co-authors JG and MH. This grant also supported the work of the first author, as well as the MSc work of co-authors DS and BM, and the PhD of MG. The TCN ages were made possible by a grant from RADIATE (Grant Agreement No. 19001937) to LG.
The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.
All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article, or claim that may be made by its manufacturer, is not guaranteed or endorsed by the publisher.
We thank Naki Akçar (Univ. Bern), Jan Pleuger (FU-Berlin), Eline Le Breton (FU-Berlin), Dirk Scherler (GFZ/FU-Berlin) and Kujtim Onuzi (Univ. Tirana) for engaging discussions during the course of our work. Lab work was assisted by Philipp Hoelzmann and Frank Kutz (both FU-Berlin, major element compositions), Jessica A. Stammeier (ICP-MS trace element composition analysis), C. Vockenhuber (36Cl research, support of MSc students at the Ion Beam Physics, Physics-LIP, Zurich), Olivia Steinemann-Kronig (support with terrestrial cosmogenic nuclides lab work), we acknowledge the remarks of the associated editor Gang Rao and reviewers Xianyan Wang and Huiping Zhang.
The Supplementary Material for this article can be found online at: