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♣ Dipartimento di Scienze della Terra – Università di Pisa – Italy

River profiles in the Northern Apennines: differential tectonics, or rock-type? Matteo Spagnolo ♣ & Frank J. Pazzaglia ♠. ♣ Dipartimento di Scienze della Terra – Università di Pisa – Italy ♠ Earth and Environmental Sciences – Lehigh University - USA.

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♣ Dipartimento di Scienze della Terra – Università di Pisa – Italy

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  1. River profiles in the Northern Apennines: differential tectonics,or rock-type?Matteo Spagnolo♣ & Frank J. Pazzaglia♠ ♣ Dipartimento di Scienze della Terra – Università di Pisa – Italy ♠ Earth and Environmental Sciences – Lehigh University - USA S. Anna, la Madonna e il bambino con l’agnello Leonardo da Vinci Grande Galerie du Louvre

  2. River longitudinal profiles have long been used to interpret active tectonics because the profile shape is traditionally viewed as a reflection of the rate and location of channel incision in response to base level fall….however, many studies (Hack, 1957; Flint, 1974; Moglen and Bras, 1995; Slingerland et al., 1998; Hurtrez et al., 1999; Snyder et al., 2000 and Kirby and Whipple, 2001) correctly point out thatchannel slope is inversely proportional to discharge (drainage area is typically used as a proxy), resulting in a general concave-up shape. In logS-logA space, this concave-up shape takes the form of a straight line: • S = ks A-θ • with θ being the concavity index and ks the steepness index. Recent studies (Hurtrez et al., 1999; Snyder et al., 2000; Kirby and Whipple, 2001) argue that q is relatively insensitive to tectonics (or climate), but that ks is correlated with the rate of rock uplift. There are few data on the effects of variable rock type. long profile area

  3. Examples of log-slope, log-area plots Ks = - 0.49 r² = 0.85 θ = - 0.6 S = ks A-θ areas dominated by debris-flows and/or landslides where channel slope does not vary accordingly with increasing draining area

  4. Goals • A slope-area analysis of the rivers on the northeastern flank of the northern Apennines was carried out, focusing on two main goals: • to perform a sensitivity analysis using different methods of sampling a DEM • to investigate the spatial correlation of variations in profile steepness (Ks) with perceived or demonstrated differences in the rate of rock uplift.

  5. Monte Cimone (2165 m slm) The study area - geography • 11,000 km2 • mean elevation of 500 m • mean slope gradient of 12.3°

  6. The study area – geology (rock type) • Emila: the Cenozoic turbidites remain buried beneath a largely intact structural lid called the Ligurian nappe which is composed of ophiolite basement, Mesozoic marine siliciclastics and carbonates, and epi-Ligurian shelf-slope basins Sillaroline Feroni et al., 2001argue that the Ligurianlid has been rapidlyand recently beenstripped off theRomagna Apennines…that is, MORE AND RECENT UPLIFTeast of the Sillaro line • Romagna: the Ligurian nappe has been removed by erosion (Messinian to now?), revealing the underlying Miocene foredeep deposits of the Marnoso-Arenacea Formation made of turbiditic siliciclastics thinly bedded, stratigraphically and structurally coherent, and locally containing resistant units. The Romagna rocks are generally characterized by finer grains and less grade of tectonizations

  7. The study area – geology (shallow seismicity) • Note the greater density of seismicity on the Romagna Apennines

  8. The study area - climate • From a climatic point of view, the Emilia Romagna Region is characterized by three distinct sections with their characteristic micro-climate: the mountain portion, the Po plain, and the area nearby the Adriatic Sea. In the Apennines area mean annual temperature decrease of approximately of 0.6°C every 100 m in elevation, while mean annual precipitation increases of about 50 mm every 100 m in elevation. • Because all the studied rivers cut perpendicularly the mountain chain from SW to NE, climate should have played approximately the same influence on the evolution of these rivers and on their profiles…..that is, WE DO NOT EXPECT TO BE MEASURING A CLIMATIC SIGNAL OR EFFECT.

  9. Methods – three nested levels of analysis • (1) to one single river (the Secchia River), central in the study area and with a distinctive profile, good for testing the methodology of the study • to the main 14 rivers in the study area, mainly bedrock channels of order equal to or higher than six; from SE to NW, the Savio, Bidente, Rabbi, Montone, Lamone, Santerno, Savena, Reno, Panaro, Secchia, Parma, Baganza, Taro and Ceno rivers • (3) to 14 selected bedrock streams with distinct lithology (seven in the Liguridi and seven in the Marnosa Arenacea) of order equal to or lower than 4 in the upper portion of the mountain flank.

  10. Secchia River analysis 500 km2 1000 km2 200 km2 Summary:………(you enter the summary here)…………..

  11. Results – sensitivity test • sampling method affects river profile analysis • The Secchia River was studied with different sampling intervals of 0.1, 0.2 and 0.4 km. Although θ does not vary much, Ks seems to be quite sensitive, expecially when moving from the 0.2 to the 0.4 intervals (Ks from 0.32 to 0.65 respectively). • The same river was also tested with different downhill draining area thresholds of 200, 500 and 1000 km2. This time both θ and Ks vary with different draining area thresholds. • thus is not possible to generalize conclusions obtained from a river profile analysis, neither is possible to compare values obtained by using different sampling methods I would summarize this in one sentence on the previous slide

  12. 14 main stem rivers analysis

  13. Results – 14 main stem rivers analysis • θ and Ks vary consistently throughout the region but it is recognizable a geographical pattern with higher θ (mean value of 0.83) and lower Ks (0.30) in the eastern section of the study area and lower θ (0.73) and higher Ks (0.51) in the western one. • Considering that climate does not show such a east-west geographical pattern, it is likely that the variation in θ and Ks is connected to rock uplift and/or roch type, both showing a east-west differential distribution

  14. 14 upstream channels analysis

  15. Results – 14 upstream channels analysis • The 14 upstream channels were selected specifically in dependence on rock type, 7 in the Ligurian units area (west) and 7 in the Marnosa Arenacea Formation (east). • The results show again that both θ and Ks varies from the east to the western sections, with a higher Ks mean value in the western area. • Thus confirming the importance of rock uplift and/or rock type in the development of river profiles.

  16. ks is consistently LARGER (steeper channels) for the Emilia Apennines, underlain by Ligurian rocks, than for the Romagna Apennines, underlain by Marnosa Arenacea. (1) Uplift is HIGHER in Emilia, contradictingseismicity and results of Feroni et al. Romagna Apennines Emilia Apennines (2) Uplift is the same for Emilia and Romagna; difference in ks is because of rock-type (3) Uplift is faster in Romagna, but rock-type has a strongover-riding influence on long profile steepness.

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