TECTONIC CONTROL ON FLUVIAL VALLEY-FILL

Scuola di Dottorato in Scienze della Terra,
Dipartimento di Geoscienze, Università degli Studi di Padova – A.A. 2012-2013
TECTONIC CONTROL ON FLUVIAL VALLEY-FILL:
FIELD INFERENCES AND NUMERICAL MODELING
Ph.D. candidate: VALERIA BIANCHI, III course
Tutor: Dr. MASSIMILIANO GHINASSI
Co-Tutor: Dr. TRISTAN SALLES
Cycle: XXVI
Abstract
This PhD project aims at unravel the role of tectonic control on fluvial sedimentation within upstream reaches of incised
valleys, specifically looking at aggradational and degradational phases and variations in sedimentological and architectural
features of fluvial deposits. The selected study case is an outstanding example of fluvial-valley fill deposited beyond any sealevel influences. It concerns of Plio-Pleistocene deposits of the Ambra River valley (Tuscany, Italy), where the sedimentation
was controlled by a tectonically-induced modification of vallive profile, influencing the river transport capability. The present
study was carried out through field techniques and geophysical analysis, aimed at defining river response to tectonic
deformation. A numerical reconstruction has been performed to validate and verify our geological interpretation and to
quantify the tectonic role on valley-fill aggradation. This reconstruction provided the reference parameters for generic models,
aimed to monitor the effects of variation in fluvial mass balance, tectonic uplift and uplift dynamics.
Introduction
In the last decades, the interest for incised-valleys increased in the frame of petroleum industrial
research and sequence stratigraphy, as a result of the preservation of their infill in fossil record.
Although most of the valley-fills record the influence of downstream relative sea-level changes
(Dalrymple et al., 1994; Allen & Posamentier, 1993), only few authors highlight the importance of
tectonic and climatic upstream control on valley-fill aggradation (Shanley and McCabe, 1991; Holbrook,
2001; Blum and Tornqvist, 2000) which occurred through fluvial deposits accumulation, and beyond any
influence of relative sea-level. Syn-sedimentary tectonic deformation in upstream reaches of valleys can
upset the fluvial patterns, with consequent development of heterogeneous valley-fill architectures. The
effects of syn-sedimentary tectonics are known in modern settings (Schumm, 1986) or laboratory
experiments (Ouchi, 1985), whereas study cases from fossil record are almost missing.
In order to investigate the role of tectonic on fluvial aggradation in valley settings, the Ambra River
valley succession (Northern Apennines, Italy) was investigated.
The modern Ambra River is located along the Southern margin of the Chianti Ridge (Central
Tuscany) and drains toward NE, whereas, during the Early Pleistocene, the paleo-Ambra drained toward
SW accumulating a 60-70 m thick fluvial valley-fill succession (Aldinucci et al., 2007; Bianchi et al.,
2013). The valley fill forms a NS-oriented sedimentary body and consists of two intervals separated by an
erosive surface. The lower interval has been the focus of a previous study (Aldinucci et al., 2007), which
emphasized the role of tectonic and climate during the accumulation of the alluvial deposits. Whereas the
upper interval deposits (main focus of this PhD project) show a strong along-valley facies heterogeneity
(Bianchi et al., 2013) mainly developed across a syn-sedimentary fault zone. These deposits have been
studied through outcrop (geological survey, facies analysis and paleohydraulic studies) and underground
methods (Electrical Resistivity Tomography and passive seismic data). Numerical modeling has been
performed in order to assess the geological interpretation and to provide reference parameters for running
simplified generic models. These last ones helped to understand and predict the cumulative effects of the
interplay between fluvial and tectonic variables.
Methods
1
Scuola di Dottorato in Scienze della Terra,
Dipartimento di Geoscienze, Università degli Studi di Padova – A.A. 2012-2013
The goal of this research is to understand the variations in sedimentological and architectural features
of fluvial deposits across an area affected by a syn-sedimentary tectonic disturbance, which is represented
by a normal fault crossing the studied valley. During the last three-years a high-resolution map (1:10.000
scale) of the valley-fill deposits (~20 km2) was completed, allowing to identify spatial distribution of
different depositional environments (Bianchi et al., 2013). This sedimentological approach has been
carried out through a bed-by-bed logging, outcrop linedrawing and paleocurrents measurements.
Moreover, structural data concerning the syn-sedimentary fault have been also collected in collaboration
with the Earth Science Department of University of Bari (Dr. A. Brogi). The buried part of the valley fill
succession has been investigated through Electrical Resistivity Tomography (ERT) and passive seismic
data (HSVR). The integration of subsurface and outcrop methods led to a scenario of syn-tectonic
sedimentation. Paleomagnetic analyses and paleo-hydraulic calculation have been carried out in the frame
of scientific collaborations with University of München (Dr. E. Dallanave) and University of Ferrara
(Prof. P. Billi) respectively.
Once the tectono-stratigraphic frame was depicted, it was analyzed in the frame of a collaboration
with CSIRO of Sydney (Dr. T. Salles & Dr. G. Duclaux) using LECODE (Landscape Evolution Climate
Ocean and Dynamic Earth), a new geomorphic and stratigraphic forward modelling code capable of
simulating surface evolution and clastic sedimentary processes in 3D through geological times. A
numerical reconstruction of the inferred depositional dynamics was carried out, along with development
of generic models, applicable to a wider spectrum of cases (Whipple, 2004). The Ambra Valley numerical
reconstruction was performed giving basal layers to the model as topography (DEM), substratum geology
and a sediment-supply source, and then playing with changes in valley profile (i.e. tectonics) and water
discharge (i.e. climate). Generic models allowed investigating the interplay between variations in mass
balance and tectonics in several combinations.
Results and discussions
The Plio-Pleistocene Ambra Valley: depositional evolution
The coupling of outcrop methods and subsurface ones allowed depicting spatial distribution and
stratigraphic relationships between the two main intervals forming the valley-fill succession. In the
northern sector of the study area the intervals are conformable stacked, as confirmed by ERT, HSVR and
boreholes data, whereas in the southern sector they are offset and locally separated by an erosive surface,
as attested by field mapping and HSVR. This scenario reveals a bi-phasic evolution of the valley, where
deposition of the upper interval documents a lateral shift of the valley axis and the development of
marked along-valley facies heterogeneity. The hinge of valley shift is located where the valley is crossed
by the syn-sedimentary fault. This fault allows dividing the upper interval in two portions. In the northern
portion (i.e. upstream of the fault zone), the upper interval is about 30 m thick and consists of organicrich mud containing isolated channelized sand bodies. In the southern portion (i.e. downstream of the
fault zone), the upper interval is almost 25 m thick and consists of cross-stratified fluvial gravels passing
downstream into sandy deposits. Lateral tributaries fed gravelly alluvial fans along the valley flanks in
both portions.
Structural analyses highlight that the syn-sedimentary fault is EW oriented (i.e. normally to the valley
axis) and shows a dominant normal component, subsiding the upstream part of the valley. The fault zone
is still characterized by natural CO2 emissions. Evidence of tectonics affecting the lower valley-fill
interval agrees with a fault activity during accumulation of the upper valley fill interval.
Paleo-magnetism analysis along with regional constraints, allow to ascribe the valley fill succession to
the Late Pliocene – Middle Plestocene time, with a magnetic inversion within the lower interval, which
could be ascribed to the Matuyama-Brunes (0.78 Ma) or Matuyama-Olduvai (1.9 Ma) boundary.
Paleo-hydraulic investigations allowed estimating a paleo-discharge (average of bankfull discharge),
which is 280 m3/s.
The change in fluvial dynamics across the fault zone is ascribed to a syn-depositional activity of the
normal fault during accumulation of the upper interval deposits. The fault activity is thought to be the
main cause of the shift of the valley axis, which produced the offset of lower and upper valley-fill
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Scuola di Dottorato in Scienze della Terra,
Dipartimento di Geoscienze, Università degli Studi di Padova – A.A. 2012-2013
deposits in the central part of the study area. In particular, the change in fluvial transport capability
recorded by the upper valley-fill interval across the fault zone represents the response of the river systems
to tectonic movements. Specifically, tectonic upwarping caused a decrease in transport capability in the
upstream reaches of the paleovalley, manifested by the aggradation of poorly-drained floodplain deposits.
In contrast, a significant increase in bedload grain-size and fine-sediment bypass is recorded by the
gravelly rivers downstream of the fault zone, where aggradation was promoted by the increase in
sediment supply from erosion of the uplifted area.
Numerical modeling
Using hydraulic, geologic and sedimentological field data to constrain the numerical experiment, we
successfully reproduce with LECODE the sedimentological pattern for the upper and lower units. Firstly,
the experiment monitored the progressive steps of valley-fill aggradation, achieving the steady-state with
sediment bypass; secondly, the simulation checked the facies heterogeneities in the framework of a syndepositional tectonics, controlling avulsion, fluvial architectural changes and grain-size variations;
thirdly, the model quantified the fault activity required to obtain both sedimentary thickness and trend
observed in the outcrops, calculating the instantaneous sedimentation rate for each time step. This
approach revealed that fault-induced aggradation did not occur synchronously in the upstream and
downstream reach of the valley probably as consequence of the different time of reaction of the fluvial
system to tectonic damming (Ouchi, 1985). Furthermore, since fluvial response to uplift disturbance is
less known in comparison with subsidence control on fluvial deposition, predictive simulations were
elaborated and calibrated with field data, combining fluvial mass balance with tectonic parameters. In
response to different uplift rate, the fluvial system behaves with (i) aggradation of different fluvial pattern
deposits, (ii) developing of intensely amalgamated successions, (iii) changes of grain-size and (iv)
triggering of localized degradation.
Conclusions
-
Ambra valley-fill aggradation was forced by a syn-depositional tectonics manifested by an
upstream-dipping, normal fault striking transverse to the valley axis.
Two different successions aggraded as consequence of fault activity: fine material aggraded
upstream of the fault, coarse material downstream of the fault.
This facies heterogeneity was driven by: i) changes in fluvial transport capability, ii) comprising of
valley slope; iii) alteration of the water and bedload discharge and bedload grain-size.
The use of LECODE validated our geological interpretation of a natural case and allowed to have
a geomorphic and stratigraphic monitoring during the overall evolution of the valley.
From the numerical reconstruction, the two aggradations of succession located upstream and
downstream of the fault were time shifted.
Simplified generic models contribute to unravel the interplay between changes of fluvial mass
balance and tectonic activity.
References
ALDINUCCI M., GHINASSI M. & SANDRELLI F. (2007). Climatic and tectonic signature in the fluvial infill of a late
Pliocene valley (Siena Basin, Northern Apennines, Italy). SEPM, Journal of Sedimentary Research, 77, 398-414.
ALLEN, G., & POSAMENTIER, H. (1993). Sequence stratigraphy and facies model of an incised valley fill: the
Gironde estuary, France. Journal of Sedimentary Research, 63(3), 378.
BIANCHI V., GHINASSI M., ALDINUCCI M., BOSCAINI N., MARTINI I., MOSCON G. & RONER M. (2013). Geological
Map of Plio-Pleistocene fluvial incised valley of Ambra Valley. Journal of Maps, 9-4, 573-583.
DOI:10.1080/17445647.2013.829412
DALRYMPLE, R. W., BOYD, R., & ZAITLIN, B. A. (1994). History of research, types and internal organization of
incised-valley systems: Introduction to the volume. Incised-Valley Systems: Origin and Sedimentary Sequences:
SEPM, Special Publication, 51, 3–10.
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Scuola di Dottorato in Scienze della Terra,
Dipartimento di Geoscienze, Università degli Studi di Padova – A.A. 2012-2013
WHIPPLE K. X., (2004) Bedrock rivers and the geomorphology of active orogens. Annual Reviews of Earth
Platenary Sciences, 32, 151-185.
OUCHI S., (1985). Response of alluvial rivers to slow active tectonic movement. Geological Society of America
Bulletin, 96, April 1985, 504-515.
SCHUMM, S. A. (1986). Alluvial river response to active tectonics. Active Tectonics, 80–94.
SHANLEY K.W. AND MCCABE P.J. (1991). Predicting facies architecture through sequence stratigraphy –an
example from the Kaiparowits Plateau, Utah. Geology, 19, 742-745.
SUMMARY OF PHD-PROJECT ACTIVITIES:
Courses:
2011
W. NEMEC: “ Sedimentology and Facies Analysis”, Department of Earth Science, University of Bergen.
W. NEMEC: “ Geostatistics”, Department of Earth Science, University of Bergen.
A. TAYLOR: Short Course: “Trace Fossils”, Department of Earth Science, University of Bergen.
S. BOESSO, E. DANIELETTO: “Laboratorio di Refworks: Gestire le bibliografie con Refworks”, Dipartimento di
Goescienze, Università degli Studi di Padova.
S. BOESSO: “Introduzione alla Biblioteca” Dipartimento di Goescienze, Università degli Studi di Padova.
G. ARTIOLI, G. DI TORO, A. FIORETTI: “Corso di comunicazione scientifica.” Dipartimento di Goescienze, Università
degli Studi di Padova.
2012
W. HELLAND-HANSEN: “Sequence Stratigraphy” Workshop, Dipartimento di Geoscienze, Università degli Studi di Padova.
MILLI S. & FONNESU F. “Processes and depositional architectures of turbidite systems”, GeoSed pre-congress course,
Feltre. (July, 2, 2012)
ELENA CALANDRUCCIO: “Inglese parlato”, Dipartimento di Geoscienze, Università degli Studi di Padova.
LIDIA GULIK: “Inglese scientifico” Dipartimento di Geoscienze, Università degli Studi di Padova.
ROSS J. ANGEL: “Corso di comunicazione scientifica.” Dipartimento di Geoscienze, Università degli Studi di Padova.
2013
T. SALLES, G. DUCLAUX: “Using CSIRO-modeling code LECODE (Landscape Evolution Climatic Oceanic and Dynamic
Earth)” Workshop. CSIRO, Sydney, Australia.
VARIOUS AUTHORS: “High performance scientific computing” Workshop. Dipartimento DEI, Universita’ di Padova.
Field work:
2011
21st – 26th February 2011: explorative field work on Siena-Valdarno area.
3rd June – 2nd July 2011: sedimentological field work and geophysical investigations on the Ambra Valley area
2012
19th - 23rd March 2012: sedimentological field work on the Ambra Valley area.
4th April 2012: geophysical investigations on Ambra Valley area.
5th – 14th December 2012: passive seismic investigations (HVSR) on Ambra Valley area.
2013
1st – 5th February 2013: sedimentological field work and passive seismic investigations (HVSR) on Ambra Valley area.
______________________________________________________________________________________________________
Publications:
BIANCHI V., GHINASSI M., ALDINUCCI M., BOSCAINI N., MARTINI I., MOSCON G., RONER M. (2013). Geological Map of
Plio-Pleistocene fluvial incised valley of Ambra Valley. Journal of Maps, 9-4, 573-583.
DOI:10.1080/17445647.2013.829412
BIANCHI V., GHINASSI M., ALDINUCCI M., BOAGA J., BROGI A., DEIANA R. Effects of tectonics on fluvial aggradation: the
Plio-Pleistocene Ambra Valley-fill succession (Tuscany, Italy). (In prep. To be submitted to Sedimentology)
BIANCHI V., SALLES T., DUCLAUX G., GHINASSI M., BILLI P., DALLANAVE E. Evolution of a syn-depositional cross-valley
faulting: numerical reconstruction of the Plio-Pleistocene Ambra paleovalley (Northern Apennines, Italy). (In prep. To be
submitted to ESPL)
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Scuola di Dottorato in Scienze della Terra,
Dipartimento di Geoscienze, Università degli Studi di Padova – A.A. 2012-2013
Communications:
2011
BIANCHI V., GHINASSI M., ALDINUCCI M., BOAGA J., DEIANA R., BOSCAINI N., MOSCON G., RONER M., (2011) - The
Pleistocene non-marine valley fill of the Ambra river (Tuscany, Italy): A case of fluvial response to tectonic deformation –
Geosed, Caserta September, 26-27, 2011. Oral presentation.
2012
BIANCHI V., GHINASSI M., ALDINUCCI M., BOAGA J., DEIANA R. (2012) - A Plio-Pleistocene fluvial succession driven by
tectonic deformation: the Ambra valley-fill (Tuscany, Italy) – Geosed, Feltre July, 2-6, 2012. Oral presentation.
BIANCHI V., GHINASSI M., ALDINUCCI M., BOAGA J., DEIANA R., BOSCAINI N., MOSCON G., RONER M., (2012) - Fluvial
response to tectonic deformation: the Ambra Plio-Pleistocene incised-valley deposits (Tuscany, Italy) – IAS, Schladming,
Austria, September, 10-13, 2012. Poster.
BIANCHI V., GHINASSI M., ALDINUCCI M., BOAGA J., DEIANA R. (2012) - The Plio-Pleistocene fluvial deposits of the
Ambra valley (Tuscany, Italy): an example of tectonically-controlled valley fill succession – SGI, Cosenza, September,
18-20, 2012. Oral presentation.
2013
BIANCHI V., GHINASSI M., ALDINUCCI M., BOAGA J., DEIANA R. (2013) - A Plio-Pleistocene fluvial succession driven by
tectonic deformation: the Ambra valley-fill (Tuscany, Italy) – ICFS, Leeds, UK. July, 15-19, 2013. Oral presentation.
BIANCHI V., SALLES T., DUCLAUX G., GHINASSI M. (2013) - Evolution of a syn-depositional cross-valley faulting:
numerical reconstruction of the Plio-Pleistocene Ambra paleovalley (Northern Apennines, Italy) – IAS, Manchester, UK.
September, 10-13, 2013. Oral presentation.
BIANCHI V., SALLES T., DUCLAUX G., GHINASSI M. (2013) – Reconstruction of syn-depositional cross-valley faulting
through numerical modelling: the Plio-Pleistocene Ambra paleovalley (Northern Apennines, Italy) – GeoSed, Roma,
September, 18-20, 2013. Oral presentation.
BIANCHI V. (2013). Sedimentary and architectural features of non-marine valley-fills. Lecture for CSIRO staff, CSIRO,
North Ryde, Sydney, Australia. May, 25, 2013. Oral presentation.
Visiting Period:
March-April 2011: fellowship at the Department of Earth Science, University of Bergen (Norway).
March-July 2013: Internship CESRE – CSIRO, North Ryde (Sydney, NSW, Australia)
Teaching Activity:
Teaching assistant: 25 hours, “Introduzione alla Geologia del Sedimentario” (Prof. C. Stefani), Laurea di primo livello in
Scienze Geologiche (2011/2012).
Teaching assistant: 21 hours, “Geologia del Sedimentario”(Dr. A. Breda), Laurea di primo livello in Scienze Geologiche
(2012/2013).
Field assistant: 15-17 January 2013, course of “Sedimentology” (Dr. M. Ghinassi), Laurea Magistrale in Geologia e
Geologia Tecnica (2012/2013).
Extra:
2011
Participation at fieldwork phase of the project “Gilbert-type deltas in the Gulf of Corinth” (Project Leader Prof. W.
Nemec, University of Bergen). May, 13-20, 2011.
2012
Partecipation at sedimentological field-work on Adwa area and stratigraphical expedition for studying Adigrat Sandstone
(Ethiopia) (Project Leader: Dr. M. Ghinassi). February, 2-22, 2012
Partecipation to geophysical investigations in Grosseto area for ERT acquisitions (Leader: Anna Breda), April, 5-10, 2012.
Editor of the Rendiconti Online della Società Geologica Italiana 20th vol., July 2012.
Organizer of the 10th GeoSed meeting, Feltre. July, 2-6, 2012.
Awarded of the travel grant for IAS meeting (Schaldming, 2012).
2013
Co-author of the Technical Report of Stratigraphic and Geomorphic Forward Modeling Framework for Earth Science and
Resource Engeneering Unit in CSIRO, Australia. August, 2013.
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