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.
Highlights
It has long been argued that landscapes are archives of spatial and temporal trends in tectonic activity (Davis, 1899; Penck and Penck, 1924)
Most studies that seek to extract tectonic and climate signals from fluvial landscapes rely on river profile analysis; the interpretation of the geometry of river longitudinal profiles, mostly in the context of the detachment-limited river incision model (Howard, 1994; Whipple and Tucker, 1999)
Derivation of coastal uplift rates is from data reported in Gallen et al (2014), who used optically stimulated luminescence dating of the lowest elevation marine terraces to anchor the sequences to the mid-to-late Quaternary sea level curve
Summary
It has long been argued that landscapes are archives of spatial and temporal trends in tectonic activity (Davis, 1899; Penck and Penck, 1924). Theoretical advances and empirical datasets have furthered our understanding of how rivers react to changing boundary conditions (Howard, 1994; Whipple and Tucker, 1999; Tucker and Whipple, 2002) Through these studies it has been shown that landscapes adjust to tectonic, climatic, or topological (e.g., stream capture) perturbations over 104–106 yr timescales (Snyder et al, 2000; Crosby and Whipple, 2006; Berlin and Anderson, 2007; Hilley and Arrowsmith, 2008; Val et al, 2014; Willett et al, 2014). Bedrock river systems have been shown to be sensitive indicators of changing boundary conditions, define the relief structure in mountains (Whipple et al, 1999), and transmit signals of base-level fall upstream throughout the landscape (Merrits and Vincient, 1989; Pazzaglia et al, 1998; Whipple and Tucker, 1999; Snyder et al, 2000). Pleistocene and Holocene paleo-shoreline markers found tens to hundreds of meters above modern sea level along the coastlines of Crete document continued uplift of the island throughout the Quaternary (Flemming, 1978; Angelier, 1979; Pirazzoli et al, 1982; Meulenkamp et al, 1994; Kelletat, 1996; Wegmann, 2008; Strasser et al, 2011; Strobl et al, 2014; Gallen et al, 2014; Tiberti et al, 2014; Mouslopoulou et al, 2015)
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