River profile response to normal fault growth and linkage: an example from the Hellenic forearc of south-central Crete, Greece

Abstract

Abstract. Topography is a reflection of the tectonic and geodynamic processes that act to uplift the Earth's surface and the erosional processes that work to return it to base level. Numerous studies have shown that topography is a sensitive recorder of tectonic signals. A quasi-physical understanding of the relationship between river incision and rock uplift has made the analysis of fluvial topography a popular technique for deciphering relative, and some argue absolute, histories of rock uplift. Here we present results from a study of the fluvial topography from south-central Crete, demonstrating that river longitudinal profiles indeed record the relative history of uplift, but several other processes make it difficult to recover quantitative uplift histories. Prior research demonstrates that the south-central coastline of Crete is bound by a large ( ∼ 100 km long) E-W striking composite normal fault system. Marine terraces reveal that it is uplifting between 0.1 and 1.0 mm yr −1 . These studies suggest that two normal fault systems, the offshore Ptolemy and onshore South-Central Crete faults, linked together in the recent geologic past (ca. 0.4-1 My BP). Fault mechanics predict that when adjacent faults link into a single fault the uplift rate in footwalls of the linkage zone will increase rapidly. We use this natural experiment to assess the response of river profiles to a temporal jump in uplift rate and to assess the applicability of the stream power incision model to this setting. Using river profile analysis we show that rivers in south-central Crete record the relative uplift history of fault growth and linkage as theory predicts that they should. Calibration of the commonly used stream power incision model shows that the slope exponent, n, is ∼ 0.5, contrary to most studies that find n ≥ 1. Analysis of fluvial knickpoints shows that migration distances are not proportional to upstream contributing drainage area, as predicted by the stream power incision model. Maps of the transformed stream distance variable, χ, indicate that drainage basin instability, drainage divide migration, and river capture events complicate river profile analysis in south-central Crete. Waterfalls are observed in southern Crete and appear to operate under less efficient and different incision mechanics than assumed by the stream power incision model. Drainage area exchange and waterfall formation are argued to obscure linkages between empirically derived metrics and quasi-physical descriptions of river incision, making it difficult to quantitatively interpret rock uplift histories from river profiles in this setting. Karst hydrology, break down of assumed drainage area discharge scaling, and chemical weathering might also contribute to the failure of the stream power incision model to adequately predict the behavior of the fluvial system in south-central Crete.

Temporally Constant Quaternary Uplift Rates and Their Relationship With Extensional Upper‐Plate Faults in South Crete (Greece), Constrained With36Cl Cosmogenic Exposure Dating

“…Analysis of bathymetry defines the approximate offshore extent of this fault as~2.5 km south of the coastline (Figure 3a; Alves et al, 2014;Kokinou et al, 2012). This interpretation contrasts with the suggestion by Gallen and Wegmann (2016) where the SCCF represents the onshore extension of the Ptolemy fault, which they suggest has a normal motion, implying in an intraplate normal fault, which is~124 km in length. This length is at odds with the notion that maximum fault length is about twice the depth of the seismogenic layer of 12-15 km (Jackson & White, 1989), so we prefer our interpretation, which defines a~45-km fault.…”

“…The hangingwall subsidence is counteracted by uplift, presumably related to the subduction interface and/or thrust faults in the overlying wedge and/or footwall uplift from offshore, E-W striking normal faults. Uplift in the hangingwall of normal faults is observed along the south coast of Crete, namely, the Sfakia fault, SW Crete (Skourtsos et al, 2007;Tsimi et al, 2007), the Ierapetra fault, SE Crete (Gaki-Papanastassiou et al, 2009), and the SCCF (Angelier, 1979b;Gallen et al, 2014;Gallen & Wegmann, 2016).…”

“…The Ptolemy fault trends NE to NNE (Angelier et al, 1982) and extends~90 km along strike ( Figure 1). The motion on this fault has been the subject of much debate with earlier studies suggesting that it either accommodates convergence as a transform/thrust fault (Mascle et al, 1982;McKenzie, 1978;Taymaz et al, 1990), is a strike-slip fault (Chaumillon & Mascle, 1997;Huguen et al, 2001;le Pichon & Angelier, 1979), or is a normal fault (Gallen et al, 2014;Gallen & Wegmann, 2016). However, evidence from microseismicity, bathymetry, and seismic reflection and analysis of fault-plane solutions suggest that the active fault cuts through the entire upper plate; is south dipping, near vertical (85 o ); and records sinistral transtensional motion that has resulted in the development of a wedge-shaped sedimentary basin approximately 4 km thick (Becker et al, 2006;Bohnhoff et al, 2001;Kokinou et al, 2012;Meier et al, 2004).…”

“…These studies show that thrust faulting occurs as a result of forearcnormal compression at depths linked to subduction to the south of Crete; additionally, Shaw et al (2008) suggested that reverse (high-angle) splay faults may cut the upper crust in western Crete; however, their existence was debated by Ganas and Parsons (2009) on the basis of a lack of compatible seismological data. The E-W and N-S trending normal faults accommodate arc-normal and arc-parallel extension (Angelier, 1979a;Armijo et al, 1992;Caputo et al, 2006;Caputo et al, 2010;Fassoulas, 2000;Floyd et al, 2010;Gallen et al, 2014;Gallen & Wegmann, 2016;Ganas et al, 2017;Howell et al, 2017;Kokinou et al, 2012;Peterek & Schwarze, 2004;Snopek et al, 2007), which is also reflected in Eurasian (upper) plate GPS motions that increase toward the southern edge of the plate in the location of Crete (Floyd et al, 2010;McClusky et al, 2000) and are quantified by Nocquet (2012) as~10 mm/year. Pleistocene uplift is visible in sequences of preserved marine terraces seen throughout the eastern and southern coasts of Crete (Angelier, 1979b;Gaki-Papanastassiou et al, 2009;Gallen et al, 2014;Peterek & Schwarze, 2004;Pirazzoli et al, 1982;Strobl et al, 2014).…”

“…Investigations using uplifted hangingwall and footwall marine terraces, 2-D viscoelastic modeling, and sedimentary correlations have led to a large variety of uplift estimates along the south coast of Crete from 0.2 to 7.7 mm/year over timescales since the late Quaternary (~600 ka) to the present day (Gaki-Papanastassiou et al, 2009;Gallen et al, 2014;Gallen & Wegmann, 2016;Meulenkamp et al, 1994;Mouslopoulou et al, 2017;Shaw et al, 2008;Skourtsos et al, 2007;Strasser et al, 2011;Strobl et al, 2014;Tiberti et al, 2014). Additionally, some authors propose that uplift rates have significantly varied over time (Gallen et al, 2014;Tiberti et al, 2014).…”