New constraints on sediment-flux–dependent river incision: Implications for extracting tectonic signals from river profiles

Patience A. Cowie; Alexander C. Whittaker; Mikaël Attal; Gerald Roberts; Greg E. Tucker; Athanassios Ganas

doi:10.1130/g24681a.1

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

Earth Surface Dynamics ◽

10.5194/esurf-5-161-2017 ◽

2017 ◽

Vol 5 (1) ◽

pp. 161-186 ◽

Cited By ~ 30

Author(s):

Sean F. Gallen ◽

Karl W. Wegmann

Keyword(s):

Profile Analysis ◽

Normal Fault ◽

Drainage Area ◽

Uplift Rate ◽

Stream Power ◽

River Incision ◽

South Central ◽

History Of ◽

River Profiles ◽

Fault Growth

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.

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Valley downcutting in the Ardennes (W Europe): Interplay between tectonically triggered regressive erosion and climatic cyclicity

Netherlands Journal of Geosciences – Geologie en Mijnbouw ◽

10.1017/s0016774600001517 ◽

2012 ◽

Vol 91 (1-2) ◽

pp. 79-90 ◽

Cited By ~ 7

Author(s):

A. Demoulin ◽

A. Becker ◽

G. Rixhon ◽

R. Braucher ◽

D. Bourlès ◽

...

Keyword(s):

Common Belief ◽

Migration Rates ◽

Base Level ◽

River Incision ◽

New Findings ◽

Starting Point ◽

Middle Europe ◽

The Common ◽

Vertical Spacing ◽

River Profiles

AbstractWhile climatic models of valley downcutting discuss the origin of terrace staircases in valleys of middle Europe within the frame of alternating cold and temperate periods of the Quaternary, other models, starting from a base level fall imposed by an initial tectonic signal, describe the response of the drainage network mainly as the propagation of an erosion wave from the place of base level fall (the margin of the uplifted region) toward the headwaters, the two types of model being rarely confronted. In the Ardennes (West Europe), cosmogenic 10Be and 26Al ages have recently been calculated for the abandonment of the Younger Main Terrace (YMT) level, a prominent feature at mid-height of the valleysides marking the starting point of the mid-Pleistocene phase of deep river incision in the massif. These ages show that the terrace has been abandoned diachronically as the result of a migrating erosion wave that started at 0.73 Ma in the Meuse catchment just north of the massif, soon entered the latter, and is still visible in the current long profiles of the Ardennian Ourthe tributaries as knickpoints disturbing their upper reaches. At first glance, these new findings are incompatible with the common belief that the terraces of the Ardennian rivers were generated by a climatically triggered stepwise general incision of the river profiles. However, several details of the terrace staircases (larger than average vertical spacing between the YMT and the next younger terrace, varying number of post-YMT terraces in trunk stream, tributaries and subtributaries) show that a combination of the climatic and tectonic models of river incision is able to satisfactorily account for all available data. The cosmogenic ages of the YMT also point out a particular behaviour of the migrating knickpoints, which apparently propagated on average more slowly in the main rivers than in the tributaries, in contradiction with the relation that makes knickpoint celerity depend directly on drainage area. We tentatively suggest a process accounting for such anomalies in migration rates.

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