Calabrian Arc Project - InfoTerre

Calabrian Arc Project Quaternary uplift of Calabria

from geomorphological evidence

Final Report

BRGM/RP-61399-FR July, 2012

Calabrian Arc Project Quaternary uplift of Calabria

from geomorphological evidence

Final Report

BRGM/RP-61399-FR July, 2012

T. Dewez with the contributions of:

C. Stark, S. Huot, A Vivien and C. Fehr

Checked by:

Name: G. Grandjean

Date: 13/12/12

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Keywords: Calabria, Crati valley, Sibari plain, subduction, uplift, marine deposits, gilbert-type delta, marine terraces, OSL, IRSL, Optically Stimulated Luminescence, feldspar absolute dating, close-range photogrammetry, ground-based photogrammetry, Photomodeler. In bibliography, this report should be cited as follows: Dewez T., Stark C., Huot C.P., Vivien S., Fehr A. (2012) - Calabrian Arc Project: Quaternary uplift of Calabria from geomorphological indicators. Final Report. BRGM/RP-61399-FR, 64 p., 33 fig., 2 tabl. © BRGM, 2012. No part of this document may be reproduced without the prior permission of BRGM.

Calabrian Arc Project: Uplift from geomorphology

BRGM/RP-61399-FR – Final report 3

Synopsis

The Calabrian Arc Project - nicknamed CALARCO - is an interdisciplinary research project funded by the Continental Dynamics program of the United States National Science Foundation (NSF). CALARCO is concerned with the geodynamic evolution of a subduction zone for the last 10 million year. The case study is that of Calabria (southern Italy) which rifted from Sardinia and was pulled across the Tyrrhenian Sea by the subducting Ionian oceanic plate rolling back on itself. The Calabrian micro-plate is now located between Sicily and Southern Italy.

The reason why the CALARCO consortium is interested in Calabria is because it appears that subduction may have stopped. Indeed, there is no seismic evidence of compression earthquakes below Calabria, and hardly any relative motion between Calabria, Sicily and Sardinia. Has the Ionian oceanic crust really stopped subducting under Calabria is the question at stake.

In Calabria’s Quaternary geological history, the most striking feature is a series of raised marine terraces etched all around the peninsula. This testifies for an uplift sustained for the last 1 million years. The cause of this uplift is unknown and its regional pattern poorly constrained though literature contains sporadic terrace studies. Geomorphological observations hold a possible key to untangling the dynamical pattern of relative regional vertical motion. The purpose of the geomorphology work package was to collect evidence of uplift across Calabria.

The task thus consisted in identifying geomorphic markers of constrained palaeo-elevation, precisely measuring their present-day elevation and dating them in chronostratigraphic order and in absolute age.

In parallel, we explored the potential of ground-based photogrammetry combined with differential GPS controls to measure precise geomorphic feature elevation remotely. It is a pioneering work started in 2006 and carried out by trials and errors as very few earth science teams had any experience with the technique. At hindsight (in 2012), with accumulated knowledge and improved software solutions, some discussions may seem naïve and obsolete. This report nevertheless evokes them as they provide context to understand the limitations of the results presented here.

The CALARCO project at BRGM was performed under National Science Foundation subaward grant EAR-06-07687 Steckler/Dewez which ran from 01 August 2006 until 31 July 2102. The subaward budget was complemented at equal amount by BRGM’s directorate of research under project PDR06ARN44 to complete for personal expenses of Thomas Dewez. The geomorphology work package was coordinated by Colin Stark from Lamont-Doherty Earth Observatory and absolute OSL dating done by Sébastien Huot and Michel Lamothe from the University of Québec at Montréal, Canada. Antoine Vivien and Cécile Fehr were graduate students who provided help in processing photogrammetric data and geological photo interpretation.



Contents

1. Project background ...................................................................................... 9

2. Ground-based photogrammetry ................................................................ 13

2.1. INTRODUCTION .......................................................................................... 13

2.1.1. Photogrammetric considerations ............................................................ 13

2.1.2. Software considerations ......................................................................... 14

2.2. PHOTOGRAMMETRIC PROJECT ............................................................... 15

2.2.1. Internal orientation.................................................................................. 15

2.2.2. Planar target calibration remarks ............................................................ 16

2.3. SHOOTING PHOTOGRAPHS FOR PHOTOGRAMMETRIC USE ................ 18

2.3.1. Viewing angles ....................................................................................... 18

2.3.2. Distance to the outcrop and scale .......................................................... 20

2.3.3. Photometry ............................................................................................. 22

2.3.4. Lighting conditions and exposure ........................................................... 23

2.4. GEOREFERENCING .................................................................................... 25

2.5. CONCLUSIONS ............................................................................................ 27

3. Geomorphological evidence of marine inundation in the Crati-Sibari plain ............................................................................................................. 29

3.1. INTRODUCTION .......................................................................................... 29

3.2. PHYSIOGRAPHY OF THE CRATI/SIBARI REGION .................................... 29

3.3. BISIGNANO .................................................................................................. 32

3.3.1. Bisignano above town level .................................................................... 32

3.3.2. Bisigano town plaza level ....................................................................... 33

3.3.3. Bisignano main quarry level ................................................................... 35

3.3.4. Bisignano main quarry ............................................................................ 37

3.3.5. La Pieta quarry ....................................................................................... 40

3.3.6. Bisignano Old Quarry ............................................................................. 40

3.3.7. Via Muccone road section ...................................................................... 41


6 BRGM/RP-61339-FR –Final report

3.3.8. Conclusion of the Bisignano sequence ................................................... 42

3.4. CATALDO ..................................................................................................... 43

3.5. TARSIA RIDGE ............................................................................................. 45

3.6. PANTANO ..................................................................................................... 46

3.7. DISCUSSION AND CONCLUSION ............................................................... 50

4. Chronostratigraphy of the Crati valley ..................................................... 53

4.1. WORKING HYPOTHESIS ............................................................................. 53

4.2. STAGE 11 (HIGH-STAND) ............................................................................ 53

4.3. STAGE 10 (LOW STAND) ............................................................................. 53

4.4. STAGE 9.3 (HIGH-STAND) ........................................................................... 56

4.5. STAGE 9.2 (LOW-STAND) AND 9.1 (HIGH-STAND) .................................... 56

4.6. TRANSITION 9.1 (HIGH-STAND) TO 8.5 (RELATIVE HIGH-STAND) .......... 56

4.7. STAGE 8.5 (RELATIVE HIGH-STAND) ......................................................... 56

4.8. STAGE 7.3 (HIGH-STAND) ........................................................................... 56

4.9. STAGE 7.1 (HIGH-STAND) ........................................................................... 56

4.10. STAGE 6.3 (RELATIVE HIGH-STAND) AND 6.1 (RELATIVE HIGH-STAND) ......................................................................................................... 58

4.11. STAGE 5.5 .................................................................................................... 58

4.12. CONCLUSION .............................................................................................. 58

5. Conclusions ................................................................................................ 59

6. References .................................................................................................. 61

List of illustrations

Figure 1: Setting of the central mediterranean subduction zones. ............................................. 9

Figure 2: Tectonic uplift pattern of the Italian peninsula (from Ferranti et al., 2005). ............... 10

Figure 3: Flight of three marine terrace levels (broad benches) in Falerna (16.14°E; 39.01°N) along the Tyrhenian coast of central Calabria. (Photo T. Dewez, Sept. 2008). ......................................................................................................................... 11



Figure 4: Photomodeler calibration procedure. ......................................................................... 16

Figure 5: Example of photogrammetric project in Bisignano main quarry. ............................... 19

Figure 6: Orthophoto of the clinoforms found at the base of Gilbert-type delta deposits in Bisignano main quarry. .............................................................................................. 19

Figure 7: Example of Bisignano overview photo shot at 24 mm, 220 m away from the outcrop face. .............................................................................................................. 20

Figure 8: Extract at scale 1:1 of the overview photo (Figure 7). Despite the distance to the outcrop, sedimentary beds can easily be discerned. ........................................... 22

Figure 9: Two views of the Bisignano clinoforms shot at different moments times (left: 13 sept 2006 at 11h37AM; right: 28 sept 2006 at 06:51PM). ......................................... 24

Figure 10: Second example of lighting conditions on the Bisignano clinoforms. Left same photo as Figure 9. Right: Oblique lighting morning conditions reveal some protruding beds (18 sept 2006 at 13h23). Lighting conditions on this image are visually more pleasing. Shot from a longer distance it is not as detailed. ................. 25

Figure 11: Physiographic map of Calabria. .................................................................................. 30

Figure 12: Location map of Gilbert-type fan delta deposits found around the Crati valley hill slopes. ........................................................................................................................ 31

Figure 13: Close-up view of Bisignano 5 (lat: 39.505726°; long: 16.301074°) site above town at 417 m asl. ...................................................................................................... 33

Figure 14: Bisignano town plaza reef fragment (site BISI02-2006) located at 16.285962131°E, 39.513418°N; 374.70 m +/- 0.30 m. .............................................. 34

Figure 15: Well-sorted marine sands visible below the foundations of a house on Bisignano Plaza leve, via Simone da Bisignano (site BISI01-2006; 16.286°E, 39.513°N, 379.15 m +/- 7.60 m). ................................................................................................. 35

Figure 16: Outcrop locations around Bisignano town (town plaza at 16.285°E, 39.513°N). ....... 36

Figure 17: Synthesis of Bisignano quarry outcrops at elevations between 260 m and 320 m which contain Gilbert-type delta deposits. ................................................................. 36

Figure 18: Bisignano main quarry overview (view to the NNE)(16.275278°E, 39.516671°N). .... 37

Figure 19: A. Clinoform exposure in the NW of Bisignano main quarry site (see Figure 18 for location). ............................................................................................................... 38

Figure 20: Pecten-familly marine shell found in Bisignano main quarry top section (16.2762°E, 39.516615°N). ........................................................................................ 39

Figure 21: Bisignano La Pieta quarry (BISI01.2007, 16.275304°E; 39.512332°N) exhibiting a gilbert-type fan delta sequence 500 m due south of Bisignano main quarry. ......... 40

Figure 22: Via Muccone outcrop in Bisignano town (16.28778°E, 39.5099°N, 308 m). .............. 42

Figure 23: Cataldo fan delta outcrop CATA03 located below GPS point n° 24927 (16.196°E, 39.553°N, 208.3 ± 0.1 m). ........................................................................ 43

Figure 24 : OSL sampling site CATA1 in the Cataldo delta sequence (see detailed view in Figure 25). .................................................................................................................. 44

Figure 25: Detailed view of OSL sample CATA1 in Cataldo delta sequence (see context in Figure 24). .................................................................................................................. 45



Figure 26: Tarsia and Pantano delta outcrops locations at the northern extremity of the Crati valley. ................................................................................................................ 46

Figure 27: Synthesis of Pantano hill gilbert-type delta outcrops prograded from SW to NE. ...... 48

Figure 28: Photointerpretation of outcrop sections in the Pantano delta front. ........................... 49

Figure 29: Elevations of sea level index points on the Pantano outcrop. Identified point match those of Figure 28. .......................................................................................... 50

Figure 30: Correspondance between sea-level markers and sea-level curve from Walbroek et al. (2002) to which an constant uplift 1.1 mm/y and 1.2 mm/yr has been applied. ...................................................................................................................... 54

Figure 31: Synthesis map of gilbert-type delta deposits in the Crati Valley. ............................... 55

Figure 32: Palaeo-shorelines and underwater areas during successive Quaternary sea level high-stands (refered to as Marine Isotopic Stages – MIS). ............................... 57

List of tables

Table 1: Synthesis of OSL sample results in the surrounding of Bisignano. ........................... 42

Table 2: Optically Stimulated Luminescence dates and elevation collected in Pantano hill quarries. ..................................................................................................................... 47



1. Project background

The Calabrian Arc Project is a geodynamics interdisciplinary research project funded by the United-States National Science Foundation and led by Dr Michael Steckler at Lamont-Doherty Earth Observatory. The project aims at understanding the behaviour of the Ionian oceanic plate subduction under the Calabrian microplate in the central Mediterranean region (Figure 1). The research interest was sparked by the suspicion that the subduction may have stopped given that most recorded earthquakes indicate extension and not compression, as expected in active subduction zones. Has the subduction really stopped? If so, when did it occur and why?

Figure 1: Setting of the central mediterranean subduction zones. The Ionian oceanic plate slips below southern Italy and the eastern tip of Sicily. This geodynamic context produced

strong uplift in Calabria, but the narrow width of the suducting slab caught between southern Italy and Sicily may have remained blocked.

In parallel, it is a well known geomorphological fact that Calabria underwent fast uplift during the Quaternary of the order of 1mm/y and locally faster. This was concluded more than a century ago from observation of raised shorelines found all around the peninsula. Ensuing research documented them all the way up to 1000m elevation in the Aspromonte region, all around the peninsula, and ascertained a few absolute ages from U/Th dating of coral fragments (e.g. synthesis in Bordoni and Valensise, 1998 or Ferranti et al., 2005) (Figure 2). The bulk of that work focussed on identifying flights of terraces and matching each level to sea level high-stands with whatever constraint



available, though usually not absolute age. Terrace elevation was obtained from contour lines of topographic maps where terrain elevation cannot be more accurate than about 10 m, while the geomorphic marker is generally some distance below the topographic surface. All this concurs for inaccurate marker elevation and poor timing constraints.

Figure 2: Tectonic uplift pattern of the Italian peninsula (from Ferranti et al., 2005).

Marine terraces are broad benches eroded by ancient sea levels in the substratum. The shore angle (junction line between the terrace platform and palaeo-cliff) is the elevation usually used as reference (Figure 3). Not all coastal settings are prone, however, to preserving them, nor even to forming such erosive landforms. In many locations, wave action is not powerful enough to incise the coastal profile and in other places, prograding shorelines will not enable marine terrace formation.

In this work, we densify observations of sea level markers in places where only few terraces are present (typically in central Northern Calabria), improve on the elevation estimation and propose absolute ages obtained from Optically Stimulated Luminescence dating of potassium-feldspar sand grains.

This report first discusses ground-based photogrammetric issues applied to measuring geological outcrops. Second we present field observations focused on the Crati valley outcrops of central Northern Calabria. And third, we discuss our findings to construct an integrated chronostratigraphic sequence.

The findings were presented to international conferences by Dewez et al. (2008), Huot et al. (2008). Scientific contributions to the broader geodynamics questions of



Calabrian Arc Project can be found on the NSF web page http://nsf.gov/awardsearch /showAward?AWD_ID=0607687.

Figure 3: Flight of three marine terrace levels (broad benches) in Falerna (16.14°E; 39.01°N) along the Tyrhenian coast of central Calabria. (Photo T. Dewez, Sept. 2008).

Their respective elevation is 140 m, 400 m and 650 m.



2. Ground-based photogrammetry

2.1. INTRODUCTION

2.1.1. Photogrammetric considerations

Ground-based photogrammetry is the technique that enables turning standard photographs into 3D information. It is very appealing from the outset as anyone with consumer-grade camera can achieve this aim. This chapter is to demonstrate how this was used in the context of geological outcrops and to provide generic, but also software specific guidelines, to produce 3D geological sections from photographs, without actually touching an outcrop.

Ground-based photogrammetry has leapt forward a great deal in the last decade. Software now accepts consumer-grade cameras for medium accuracy photogrammetric projects. This is the case of Photomodeler designed by EOS Inc. in Canada. In 2006 when CALARCO begun, Photomodeler was among the few reasonably priced and accessible software available to non-specialists.

The basic principle of photogrammetry is what is applied by our own eyes and brains. Two images of the same scene, seen from slightly different viewpoints enable perceiving the depth of a scene. Photogrammetry does this from photographs and attempts to compute accurate measurements from them. From this basic principle, a series of variations, with advantages and drawbacks can arise.

One needs a minimum of two images to reconstruct a scene in 3D. The number of view points however can increase, two is the minimum, but multiple stereo enables computing redundant measurements and checking the precision of point coordinates. This is useful for automated computer reconstruction. The relative aiming direction of the photos may change. Parallel axes imagery is a specific case that was extensively used for air-photo surveys. It is desirable because image pairs can be directly viewed in 3D with a stereo viewing device e.g. 3D television. Our brain synthesizes 3D instinctively and no computer cost. Nothing however prevents using a computer to reconstruct a scene in 3D from convergent photographs.

In the field, it is desirable to shoot convergent photographs of outcrops because it is both tricky to guarantee parallelism between views, and shooting convergent images maximizes the overlap area. The stereoscopic ability of a pair is set by the distance between view points, called baseline, and the distance to the object. The ratio between baseline and distance is called the base-to-height ratio B/H; the height is the term inherited from airborne surveys to express the distance to the object. With a small B/H, the scene depth resolution is small, but images are better suited for automated point matching because they strongly resemble one another. With a large B/H ratio, depth resolution will be much better resolved, but matched points will be scarcer and



plenty erroneous matches may occur. Finally, if one wants to make real world 3D measurements, there needs to be a scale somewhere. Orienting a scaled 3D model to a reference frame enables converting the vertical dimension into an actual vertical height. And setting a given location in the oriented scaled model will translate the model coordinate origin. We put this technique in practice to measure sea-level index points identified in unreachable Gilbert-type fan delta formation.

2.1.2. Software considerations

The way a user can apply and toy with these variations in a practical project is software dependant. Some software restricts photos to views with parallel axes, like airborne photo coverage, some others are capable of using convergent axes photos. Some software find remarkable points automatically, most don’t and require manual, imprecise and error-prone digitization. Some software, once photos are oriented relative to one another, can massively compute point clouds, but the more ancient software did not. Some software will take photograph from any cameras without prior knowledge, others require determining camera parameters with a calibration procedure before accepting photographs. Finally, some software allow matching 3D model points with control points and adding a known scale for absolute orientation, others also allow adding known camera positions for further constrains.

In this chapter, we will discuss our experience starting from Photomodeler v5.0 and v6.0, which was used from the early stages of the CALARCO project. This piece of software allows for consumer-grade camera to be used for photogrammetry so long as they are calibrated with their software-specific planar target. We will detail and discuss the procedure. Then, photos need to be registered respectively to one another by hand. This had a strong bearing on the field acquisition strategy and on the quantity of photos included in Photomodeler projects. Photomodeler accepts photos shot with convergent viewing axes, and favours those with B/H ≥ 0.3. This also has a bearing on field acquisition strategy. Absolute point referencing needs to be done with software compatible targets, visible on at least two, but preferably three photos. Scaling however can be done with just a known distance between two points visible on multiple images.

Photomodeler versions 5.0 and 6.0 were not capable of extracting dense point clouds automatically. Feature measurements needed to be done on remarkable natural points visible on several overlapping photos. This focused our geological processing on manually marking specific points (sparse for obvious practical reasons) and only retrieving their 3D coordinates. Our initial ambition was to also compute visually-pleasing orthophotographs was defeated by poor triangulation tools inside Photomodeler. The results were never quite to our standards and the exercise was not pursued. Instead, we graphically drew measurements on synthetic outcrop sections with a standard, non-metric, drawing software package.

Overall, the purpose of CALARCO requires that the present-day elevation of palaeo-sea level markers be measured with accuracy of the order of 1 meter with respect to present day sea-level. The exact absolute location of outcrop did not have a bearing on the geomorphological issues we tackled. Model scaling however was important for



measuring thicknesses and distances and to that respect, accurate control points needed centimetric to decimetric positioning precision.

2.2. PHOTOGRAMMETRIC PROJECT

In order to link a field position with a point observed in a digital photograph, one needs computing the forward and inverse transformation between the point’s pixel coordinates and real world 3D cartographic coordinates. This is usually achieved with a standard pinhole camera geometric model (Ma et al., 2006). The theory explains that a point on a photographic plane is the image of a real world point transformed by a central symmetry. The light ray passing through the object point travels in a straight line through the optical centre of the camera before impressing the digital sensor.

2.2.1. Internal orientation

The operation known as internal orientation consists in establishing a 3D transformation between pixel coordinates and metric coordinates. Internal orientation thus transforms lines and columns coordinates of standard image into equivalent 3D metric values expressed with respect to the geometric centre of the photograph. The operation known as external orientation consists in establishing the transformation between 3D image-space coordinates and 3D object-space coordinates.

Camera calibration is the operation that solves the internal orientation. It iteratively inverses a set of parameters relating a series of point positions on the image plane with their respective field position. Photomodeler does this with a dotted flat planar target (Figure 4).

From those measurements, the calibration algorithm computes the image centre position and the metric dimensions of the image.

The pinhole camera geometric model would be simple if camera lenses were built perfectly orthogonal to the image plane and light rays were not refracted by glass. The parameters one needs defining is the position of the optical in the image plane, the metric size of the image, the radial and tangential distortion parameters and the exact focal length of the lens.

The calibration procedure performed on the Canon EOS1DsMarkII used during CALARCO fieldwork is described with many technical details in Dewez (2007). The important point to recall is that Photomodeler needs a camera calibration procedure to operate in stereoscopy. Calibration can be achieved with two sorts of photographs: a set of photos of a software-specific planar target or a set of photos containing a large number of points otherwise known in 3D coordinates.



2.2.2. Planar target calibration remarks

The planar target calibration is relatively easy to perform (Figure 4). Photos need to be shot with B/H = 1 for accuracy considerations. Thus with the planar target (ca. 1mx1m) laid flat on the ground, the camera needs to be set as high as it is far from the target centre. This is to form a view angle on the target of ca. 45°. The target need not filling entirely single every frame but the sum of the photos should cover the frame entirely (Figure 4). The target is turned around with respect to the camera, so that points are viewed from all 4 sides of the target. This is important for minimizing light rays intersection errors. Targets dots should come close to all sides of the photo frame. To fit dots along the top of the camera frame, roll the camera to shoot portrait-oriented photographs. In total, target points should appear everywhere in the frame, and every photo should contain all four corner markers.

Figure 4: Photomodeler calibration procedure. Shoot six photos of the Photomodeler target in the sequence described above. Make sure the camera is setup at about

45° with respect to the target. Target dots should come as close to the frame edge as possible to maximize overall coverage. Remember to roll the camera in landscape and protrait orientation. Camera setting should be in sharp focus

and aperture set on f/16 to maximize depth of field.



Photomodeler automatically computes relative photo orientations using radial coded targets (Figure 4) and automatically finds matching points (Dewez, 2007). It may happen that Photomodeler fails to recognize some points close to the edges of the photo frame. Manual editing needs carrying out to complete point marking and matching. Photomodeler may indeed have marked them on some photographs but not all. The sub-pixel marking tool will mark the centroïde of an elliptic object, while manual referencing will tell Photomodeler which marks are homologous among the set of photos. Adding a few more points to the calibration will not dramatically improve internal orientation parameters but it will extend the calibrated zone closer to the photo edge. Outside of this zone, Photomodeler will not consider points for 3D computation

The planar target of Photomodeler is software specific (note the four radial coded dots on Figure 4). All photogrammetric software exploiting flat targets rely on matching a set of sparse points on multiple views. Photomodeler is particular because it uses black dots, as opposed to corners of a chessboard pattern. It also uses numbered radial coded targets in order to determine the target corner positions with respect to the camera. Bouguet’s calibration procedure implemented in the popular Matlab Calib toolbox and in the open source OpenCV C++ library cannot be used with Photomodeler (for details, see http://www.vision.caltech.edu/bouguetj/calib_doc/ and http://opencv. willowgarage.com/wiki/). OpenCV added a new procedure for dotted target recently.

Photomodeler will not accept calibration parameters computed elsewhere. It needs to compute them internally to be valid. That means that one cannot calibrate a camera with Bouguet’s procedure and force Photomodeler to ingest it.

Planar target calibration has a limited accuracy because it is quasi impossible to print an A0 poster that will remain planar over time. Paper distorts with ink, air humidity, temperature variations. Even when the poster is glued on a rigid board (e.g. PVC, foam board, aluminium-framed strong cardboard or even Dibond®, all of these were tested) the board will end up bending curving the supposedly flat reference. The only practical solution we found was to put heavy weights on the board to flatten it when shooting the photos.

The alternative to planar target calibration is field calibration, which is recommended by EOS Inc. for highest accuracy computation. It has the advantage that it is closer to the scale of the object to survey later on. The difficulty is to dispose of a large size calibration field equipped with Photomodeler sub-pixel targets and where viewing conditions are sufficiently large to enable large enough B/H ratio. This solution was tested in Dewez (2007) but not put in practice.

All in all, constraining camera parameters is what will ultimately impede photogrammetric accuracy but Photomodeler software is set in its proprietary conventions and cannot be easily tweaked. Use field calibration if at all possible. Otherwise, use as flat a target as possible and check the extent of the automatic calibration results. Resulting point accuracy tested elsewhere was above 1 part in 1000, which corresponds to a positioning error of the order of 1m at a distance of 1000m. This is plenty for our needs.

http://www.vision.caltech.edu/bouguetj/calib_doc/

http://opencv.willowgarage.com/wiki/

http://opencv.willowgarage.com/wiki/



2.3. SHOOTING PHOTOGRAPHS FOR PHOTOGRAMMETRIC USE

Shooting photographs that are amenable to photogrammetric processing are not as trivial as one would think. Making them acceptable for specific software is even more complicated. In this section a series of shooting parameters are reviewed. They were tested during fieldwork to formulate recommendations. This discussion addresses first geometric concerns, and then photometric considerations.

2.3.1. Viewing angles

As evoked above, Photomodeler v5.0 and 6.0 used relied on on-screen manual point marking. It requires finding remarkable homologous points on at least two, but preferably three or more photographs. This is tedious imprecise and error-prone. Anymore photographs represent additional work that operators are reluctant to incur, unless they provide a means of seeing a poorly defined part of an outcrop. A good rule of thumb is to limit the number of photographs to a minimum.

Photomodeler is happy computing 3D points from convergent photographs which makes shooting more practical in the field as they maximize the overlap area between photos.

Convergence between photographs should account for the following limit case. Viewing angles must satisfy a B/H strictly larger than 3° (B/H>0.05 i.e. 1/20) and preferably larger than 10° (B/H > 0.17, i.e. 1/6) (e.g. Figure 5). This practically means that for an outcrop 100 m away. Shooting positions should be about 17m apart along an axis parallel to the outcrop front, i.e. in a sideways direction; stepping back 17m will not provide stereoscopy. If multiple views are taken, try to fan around the outcrop (Figure 5) so that photos from both ends of the series span a large angle (i.e. 45° to 60°), even if the angle between adjacent photos is small. Note also that with increasing B/H, homologous points become increasingly more difficult to recognize. A practical cut-off limit is around B/H = 1, but already from B/H = 0.4-0.5 finding homologous points by eye becomes tricky.

Finally, to build a visually appealing orthophotograph (Figure 6) or simply a synthetic photo to report the geological interpretation, do not forget to shoot a view encompassing the entire outcrop and orthogonal to the outcrop plane. A single view will be more practical to handle (Figure 6), but a set of photos can also be assembled in a panorama.



Figure 5: Example of photogrammetric project in Bisignano main quarry. The project combines four distant overviews for building the geometric framework of the entire outcrop, a series of

detailed views (see thumbnails in the left). This is one of the most significant outcrop in our study area, which justified shooting and computing relief from so many photos. Overall B/H>1(B = 370 m; H = 203 m; B/H = 1.8 ) from left to right,

by increments of 0.25 < B/H < 0.4.

Figure 6: Orthophoto of the clinoforms found at the base of Gilbert-type delta deposits in Bisignano main quarry.

This view is taken in a direction normal to the main outcrop planeand allows for measuring the thickness and dip of sandy units. This outcrop is sufficiently planar for the image to be understandable although the upper left part of the

outcrop is unreasonnably stretched towards the sky.



2.3.2. Distance to the outcrop and scale

The distance between the point of view and the outcrop is determined by several factors: safety and accessibility, size of the outcrop, field of view of the camera and desired scale or resolution.

First, accessibility and safety are an issue. Photos can only be shot from where it is safe and accessible to stand (e.g. Figure 7). In many field sites, this was a major constraint which obliged us to choose viewing conditions which were more difficult to work with. Using the zoom is by far the least desirable solution for photogrammetric applications but we nevertheless sometimes resorted to it. Some imperfect data is better than none. We calibrated our camera with a Canon EF 24-105 mm f/2.8 IS lens at each zoom graduation 24, 35, 50, 70 and 105 mm. When zooming we were careful to set the lens label strictly in front of the focal length label mark so that the EXIF tag written in the photo file was correct. Photomodeler uses this tag for matching calibration files automatically. Most of the time however we shot at the minimal zoom setting of 24mm to stay reasonably close to the calibrated value.

Figure 7: Example of Bisignano overview photo shot at 24 mm, 220 m away from the outcrop face.

The photo was shot from the opposite side of the valley to have a clear view of the outcrop front.

Second, the size of the outcrop will determine how far to step back to fit all important features in the frame. We usually tried to maximize the area covered by the photographs, stepping back enough to see the entire height of the outcrop (e.g. Figure



7). We do not recommend shooting panoramas with the camera rolled in portrait mode. This certainly improves the photo resolution but multiplies the number of photos to process and limits their extent. Recent software, like 123DCatch or Visual SFM, do not mind processing large number of photographs automatically but do not appreciate the camera being rolled. Photomodeler did not mind much except for the tedious, imprecise and error-prone manual processing involved.

The camera field of view (FOV) determines the dimensions of the objects that will fit in the frame. One determines the field of view (α) with:

Equation 1

x

f2tan 1

Where f is the focal length in mm and x is either the sensor width (w) or the sensor height (h) expressed in mm. Typically for a 24 mm lens mounted on the EOS Canon 1DsMkII, with sensor width = 36 mm and height = 24 mm, the field of view is 53.1° (0.92 radian) by 63.4° (1.1 radian). The FOV expressed in radian multiplied by the distance to the object directly gives the frame dimensions. At 100m, the frame covered 92 m x 110 m. Figure 7 was shot from 220m away. Its effective field of view is thus 242 x 202 m on the outcrop plane.

The scale of the photographs should be considered especially when trying to map small objects on large outcrops. The scale is tied to the focal length and the distance to the object pixel resolution on the outcrop. This scale is resolved by s = Z/f, where s is the unitless scale (i.e. the denominator of the expression e.g. 1/25.000), Z is the distance to the outcrop expressed in meters, and f is the focal length expressed in meters. For an outcrop located 100 m away (Z), shot with a 0.024 m lens (f), the scale (s) is 4166. A pixel, which has a physical size on the digital camera sensor of 7.2 µm (case of Canon EOS1DsMkII), will represent an outcrop object of 0.03 m. Recall that to see an object you need to be able to discern the edge of it (Nyquist theorem). The minimum object size discernable in a photo will be twice the sampling rate. So in the worked example above, only pebbles of 6cm will be discernable, smaller won’t systematically.

Note that the pixel size also has a bearing on the digitizing precision and thus on 3D reconstruction quality (see later section).

In the example presented on Figure 7 and Figure 8, shooting conditions are satisfactory. The photos were shot from a safe and accessible place. The entire outcrop fits in the frame with a 24 mm lens field of view. One may have liked a closer point of view to improve slightly the scale even though pixels represent about 6.6cm on the outcrop. Major structures of interest are well visible from afar and closer views were added to locally improve the resolution.



Figure 8: Extract at scale 1:1 of the overview photo (Figure 7). Despite the distance to the outcrop, sedimentary beds can easily be discerned.

At this photo scale (232 m/0.024 m = 9666), a 7.2 µm pixel is 6.9 cm on the outcrop. It appears sufficiently resolved to see the structure of the clinoforms but not to discern whether beds are pebble-rich or sand-rich.

2.3.3. Photometry

Photometry concerns the light contents recorded by the photograph. Several issues enter in this field: file format and colour rendering among others. The exposure and lighting conditions will be covered in the next section.

During the CALARCO project, we initially shot native JPEG files in 2006, then switched to RAW files in the 2007 campaign. The advantage of JPEG files is that they are small, ca. 5 Mb for JPEG versus ca. 16 Mb RAW files, and readily viewable with any image viewer at a small computing cost. They also directly enter in Photomodeler. On the other hand, JPEG files are lossy and contain a limited dynamic range for correcting possible exposure defects.

JPEG files are not perfect for photogrammetric applications. First the compression algorithm is lossy. Codec processing works in several steps: colour space conversion, discrete cosine transforms applied to a quadtree decomposed image separated into colour bands and finally truncation of precision terms (Russ, 1999). That means that the original digital image is decomposed in patches of uniform colours, defined by a tolerance. This effectively lumps adjacent look-alike pixels and erases fine textures. This reduces the light dynamic range recorded which is then compressed to 8 bits channels. Both conduct to a loss in texture.

JPEG compression may not be as bad as it sounds at first because colours are not coded as distinct RGB channels but rather converted into video-based YUV channels of luminance (Y) and chrominance (U and V). Each band is compressed with separate compression rates to preserve the most detail in luminance. This is because the human eye is mostly sensitive to greyscale variations and much less to subtle hue variations.



Knowing that photogrammetric software only extract texture from the luminance band, which is that best preserved by JPEG encoding, is reassuring. Nevertheless, the light dynamics is only coded on 256 grey levels which is rather limiting under harsh lighting conditions (e.g. bright sun shine at mid-day on a rough white sand outcrop).

Instead, RAW files record direct numerical counts from the digital sensor in a proprietary format (CR2 format for Canon cameras). They code the light dynamics over 10 to 14 bits which preserves a lot more detail levels and thus texture information. The down side of using RAW files is that they are about 3 times larger than JPEG, they need specific software for converting RAW to legible JPEG and require post-processing to convert the photos into JPEG file in order to use it in photogrammetric software. Using RAW files multiplies the number of files and versions to handle with additional third party software. And finally it saturates hard disk space, which remains always tricky in the field and in the office.

A last point in photometry concerns colour rendering. Our eyes are extremely tolerant to the coloured light illuminating objects and compensates for so-called colour casts. We’ve all seen photos of a bright sunny day coming out as extremely blue or bright orange scenes lit-up by a candle. This is because the light source has that colour. What we actually want in geological applications is to replicate colours that are close enough to the actual rock colour. This parameter can be controlled by the white balance setting. In RAW files, white balance is a soft-coded parameter, so it can easily be changed for a different custom set value. In JPEG files, colours are what they are. It is possible to modify the tones by software but at the expense of squeezing some colour values.

It is possible to measure the white balance in the field with devices like a light diffusing filter (e.g. ExpoDisk White Balance, from ExpoImaging) and set the camera to the measured light. Alternatively it is possible to modify colour rendering after the fact. For this, find an object which ought to have been neutral grey in the photo (not always possible) and measure the ratio between RGB values. Third party software such as Adobe Photoshop Lightroom enables this correction. This is a further case in favour of RAW files.

2.3.4. Lighting conditions and exposure

Shooting a photo is and always will be a matter of exposing a light-sensitive medium to photons. To make our geological interpretation, we need properly exposed photographs in which we can pick all the desired details with enough contrast. Shooting digital makes it easier to improve contrasts digitally after the fact, but some lighting conditions produce better results than others.

A camera light-meter is designed to compute the correct exposure, i.e. choose an appropriate triplet of Aperture, Speed and Sensitivity, to replicate an 18 % grey patch in the field as an 18% grey patch. It is the reason why some photos may become over- (too clear and washed out) or under-exposed (too dark and dirty). This is because the point on which light was measured by the light-meter was not a real 18 % grey patch,



but was either a darker (leading to over-exposure of the scene) or brighter object (leading to under-exposure of the scene; Figure 9). Light-metering can be either done on spot measurement, i.e. on a very specific point in the camera frame, or weighted with some clever algorithms aboard the camera. The bottom line is this, light-meters can be fooled which will result in low contrast images. Check the exposure with the histogram screen display. All important pixels must be exposed in the middle of the range. Burning the sky, does not matter, only outcrop pixels matter. Shooting RAW photos may help salvage a situation because light is not crammed into a tiny 3 x 256 levels space, as in JPEG, but rather in a 3 x 4096 levels (12bits) space.

Figure 9: Two views of the Bisignano clinoforms shot at different moments times (left: 13 sept 2006 at 11h37AM; right: 28 sept 2006 at 06:51PM).

On the left, the outcrop in the the morning shade. Bed composition seems to be linked to humidity. On the right, full-face lighting reveals sedimentary composition based on redening. The face has dried and less details are visible. Note that

the right view is under-exposed due to the light colour of the sediment.

Lighting conditions are very difficult to control when doing geological fieldwork. Usually, one shoots photos of an outcrop whenever one stumbles upon it, no matter where the sun is in the sky. So always focus attention on what is to be seen and accept to loose some non-critical information if need be.

For sedimentological application, what matters is to see the nature of beds, reflected by the change in colours (e.g. Figure 9 right or Figure 10 right). One can sometimes see the grain size when clasts are large enough with respect to the pixel resolution. For this the best lighting ought to be uniform, either fully in the sun, or totally shaded from it. Shadows cast on Figure 10 right preserve details because sun light is slightly diffused by haze and high clouds.



Figure 10: Second example of lighting conditions on the Bisignano clinoforms. Left same photo as Figure 9. Right: Oblique lighting morning conditions reveal some protruding beds (18 sept

2006 at 13h23). Lighting conditions on this image are visually more pleasing. Shot from a longer distance it is not as detailed.

For structural mapping, where discontinuities (stratification, diaclases, faults…) are important, it is best to seek some amount of oblique lighting (Figure 9 left). Fringing lighting (very shallow angle with respect to the general outcrop plane – e.g. Figure 9 left) will enhance fine details, but may also produce very long shadows. These situations are difficult to expose properly because one wants to see textural details in highlights and in shadows at once. In these situations, prefer shooting RAW photos or even possibly in high dynamic range (HDR). This will help expand the sensitivity, but shooting in HDR requires using a tripod, which is a nuisance for easily moving around and involves adding yet another kind of specific processing software like Microsoft Image Composite Editor (freeware from Microsoft Labs).

2.4. GEOREFERENCING

Once a 3D model has been assembled by intersecting series of homologous points among overlapping photographs, it is necessary to establish geometrical constraints for extracting useful geometric information. In the field, one does not want to be burdened by a lot of technical equipment. We went for what seemed the best balance between survey time, equipment weight and strict necessity. This is the reason why we did not place many remarkable targets all around our field sites, nor did we use an EDM-total-station. It was deemed impractical. The strict necessity in our view was to set the exact height of a point, establish the vertical axis and scale the project. This is not to say that this is the best way to achieve good results, but it seemed to do the trick. We sought to achieve better-than-a-meter point elevation positioning.



Photomodeler has three methods for georeferencing a projet: (i) set a position, a reference distance and at least one axis; (ii) set X,Y,Z coordinates of 3 marked points; (iii) import a set of external coordinates and reference them to digitized 3D points. The first two methods presume that measurements are exact and precise. The third performs a least-square bundle adjustment, which tolerates that imprecision exists in the dataset.

In the field we practiced one of the three following options.

Option 1: Use an object of set length (e.g. levelling rod), a survey pole setup vertically and a recognizable point. This option is only really applicable in small sites (10-20m). Both ends of the scale should be well visible from several well-spread camera stations. The survey pole should be set and held vertically with a lightweight tripod. The circular section of the pole makes it easy to compute its axis from all directions. One extremity of the scale was surveyed with dGPS. Additional constrains on reference-frame direction may be gained if the azimuth of the scale placed on the ground is measured with a compass. Typical point positioning error on both ends of the scale is around 1cm, over a length of 2-4m. It is therefore best to restrict processing to a small site where imprecision will not eventually cause large sea level index point errors by abusive extrapolation.

Option 2: Survey each camera position with dGPS and shoot from at least three non collinear stations. This solution will establish the project scale as well as reference a frame. In general however, camera positions tend to be co-linear along an axis parallel to the outcrop plane, instead of being fully in 3D. Surveying camera stations with dGPS required time to record enough GPS epochs to solve the position accurately (typically 10-20 minutes per camera position). It was used but was not our preferred option.

Option 3: Establish a set of at least 3 tripods visible on more than two photographs and survey them with d-GPS for a few minutes (maximum 20 minutes). This gave us the minimum constrain for locating the site in 3D in the cartographic space. This solution was accepted by Photomodeler where photo points were digitized on each photo and then associated with UTM33-ED50 coordinates via the Import Explorer. The trouble was the large size of the tripod heads and non-symmetrical shape of them when looked at from different directions. This induced a location error of the order of 10cm. This is the same size as the dGPS precision. To limit scaling errors, it is a good idea to spread the tripods and set them up in a non collinear fashion. Tripods too far apart however come out of the camera frame and require more photos.

At hindsight, using well recognizable targets is desirable, if practical. They should be sufficiently large so that pointing their centre is easy, but also accommodate for scale changes from close and far views. A target seen as 10-15 pixels-wide is probably a reasonable minimum size for the furthest photograph. Target colour should stand out on the surrounding background (avoid black and white, they become grey in the shade and are difficult to recognize in partially shaded outcrops). The pattern of the target should be circular so that Photomodeler’s sub-pixel marking tool can be used. It is opposed to quadrant targets, which Photomodeler did not use to recognize for sub-



pixel marking. Photomodeler recommends using retro-reflective surface (like road signs) as the most precise target solution.

Referencing ought to rely on at least 10 control targets, and account for a few more, in order to validate the 3D model quality. Their disposition should encompass the entire 3D site. Making flat targets may also cause issues with fringing views, a suggestion, which ought to work, is to use a reflective band on a large diameter pole.

2.5. CONCLUSIONS

This chapter was concerned with the technicalities of processing outcrop photographs to reconstruct them in 3D and enable feature measurements. We specifically used a Canon 1Ds MarkII digital SLR camera equipped with a Canon 24-105 mm f/4 IS zoom lens and Photomodeler v5.0 and 6.0 software.

Camera calibration was discussed at length in Dewez (2007). Here we reviewed the practicalities of organizing a photo session on natural outcrops to reconstruct them in 3D.

In short, combine overview shots and close-ups of details. Shoot photos by increments of B/H=0.1-0.2, circling around the outcrop so that the full coverage spans B/H=1 or more. Shoot quickly so that shadows do not change too much between photo positions. Watch out for exposure conditions; always try to preserve the maximum contrast to record outcrop rocks arrangement. Record RAW files. They are less practical than shooting JPEG, but can salvage poorly exposed photographs. Organize georeferencing so that is it practical given the scale of the outcrop with unambiguous information. Ideally use well-visible total-station-surveyed targets. If unavailable, dGPS may be used to survey camera position, specific points and even measure a set distance. A vertical reference is simple to implement.

Manual processing, forced by Photomodeler versions used during CALARCO, limited the number of photographs in each project. This constraint is much less necessary in 2012 with automated point cloud extraction and automated relative orientation solutions becoming available.



3. Geomorphological evidence of marine inundation in the Crati-Sibari plain

3.1. INTRODUCTION

This chapter describes evidences collected in the field for deciphering Quaternary sea level fluctuations and uplift in the Crati-Sibari region. Reaching that aim required constraining precisely the present-day elevation of key sea level markers and their absolute age. Elevation was measured with ground-based photogrammetry combined to differential GPS surveys while absolute ages were constrained with Optically Stimulated Luminescence dating methods.

The Crati-Sibari region is known for two geological and geomorphological features which were not related in the literature before this work: classical gilbert-type fan deltas outcrops of some unconstrained age (Colella et al., 2007 and Colella, 1988) and Quaternary marine terraces etched around the Sibari –bounding hillslopes (Cucci et al., 2004). On the one hand, sedimentologists were interested in gilbert-type fan delta architecture to explain their formation processes. They needed normal faults to be active for creating a steep accommodations space to build and store the pile of river-driven sediments (Colella, 1988). No attention was paid to possible glacio-eustatic components in this story because they had not found any datable material in them to relate them to Quaternary eustatic fluctuations. On the other hand, geomorphologists often used air-photos without field validations for mapping flat expenses of land and assigned sequences of terraces to glacio-eustatic Quaternary oscillations. They were aware of potential active faulting but ignored the presence of massive sedimentary packages lying conformably below some of the terraces. Neither groups had age constraints nor were they examined together to unravel the uplift history of Calabria.

Our first concern was thus to tie gilbert-type fan delta chronology to Quaternary sea level oscillations, and then reconstruct a coherent uplift history of this region of Calabria.

This chapter reviews a series of key sites to understand the evolution of the Crati Sibari plain. Figure 12 synthesises their relative disposition in the Crati-Sibari region.

3.2. PHYSIOGRAPHY OF THE CRATI/SIBARI REGION

Calabria can be divided in 3 domains from north to south (Figure 11). (i) Northern Calabria is the transition between the southern Apennines and Calabrian micro-plate to the north and to the Catanzaro basin to the south. (ii) Central Calabria comprises the Catanzaro basin and Serre Massif. (iii) Southern Calabria bounds the Messinia straight, the southern limit of the Calabrian micro-plate and comprises the Aspromonte Massif.



Although we visited all of these domains, we gathered most uplift field evidence from Northern Calabria (Figure 11).

Figure 11: Physiographic map of Calabria. The tectonic micro-plate of Calabria is pinched between the southern Apenines in the North, and Straight of Messina in

the South. Although field work was carried out in most the the territory we focused our attention in Northern Calabria and particllarly in the Crati valley and Sibary plains.

Northern Calabria is made of two major reliefs (Figure 11), the Catena Costeria in the West, which bounds the Tyrrhenian Sea and culminates at 1541 m, and the Sila massif to the East which culminates at 1928m. The Crati valley divides northern Calabria from south to north, and flows between the Catena Costiera and the Sila (Figure 11). It drains both highlands northward into the Sibari plain via the Crati gorges and into the Ionian Sea. The Crati gorges are carved into the metamorphic basement of the Sila.



Figure 12: Location map of Gilbert-type fan delta deposits found around the Crati valley hill slopes.

Brown labels correspond to field site identifiers. This chapter will discuss the Bisignano site on the eastern flank of the valley, Cataldo, on the western flank, Tarsia and Pantano.



The Crati valley floor elevation goes from ca. 200 m near Cosenza, in the south, to 100 m prior to entering the Crati Gorge and flowing into the Sibari Plain A fold and thrust belt bounds the eastern flank of the Sila massif. All seaward flanks of Northern Calabria are etched with marine terraces reported in the literature. Tectonically, the Catena Costiera and Sila are made of hercynian rocks (granit in the Sila, sandstones and limestones in the Catena Costiera). The eastern flank of the Sila, known as the Crotone Basin (Figure 11), is made of uplifted Tertiary (Mio-Pliocene) marine sediments. It corresponds to the emerging part of the accretionnary wedge above the subducting plate. Marine sediments are faulted, folded and carved by Quaternary marine terraces.

The Crati valley (Figure 12) focused our attention as both valley flanks preserved marine sediments of so far unconstrained age. Key outcrops are described below as indicators of marine presence in the valley. They range from South to North, from eldest to youngest features.

3.3. BISIGNANO

The town of Bisignano is located on the eastern flank of the Crati valley, ca. 3 kilometres north of the confluence of the Mucone river in the Crati valley (Figure 12). We extensively surveyed this area as it concealed a lot of sedimentary outcrops at different elevations. They cluster in three topographic levels.

Above town, at an elevation around 415 m-420 m, we found the highest presumably marine sediments abutting Sila crystalline basement. They lie a few meters from the basement contact and enable setting an age for the basal sediment/basement unconformity.

Bisignano town plazza is the second topographic level. The town plaza is built on top a flat topped hill at an elevation of 374 m with reef boulders and marine sand outcrops.

Finally, the third, and lower, level culminates around 320 m elevation. This is the level below which Gilbert-type fan delta deposit exhibit clear topset/foreset transitions (Figure 17). These transitions can serve as sea level proxies as they usually lie just a few meters below sea level in modern analogues.

3.3.1. Bisignano above town level

Along the road going from Bisignano to Acri via road SS660 (lat: 39.505726°; long: 16.301074°), at an elevation of 417 m (unprocessed GPS elevation), a 1-m-high outcrop at the back of a private field exhibits a sequence of 50-cm-thick bed of fine well-sorted sands, covered by 10-cm-thick of sandy clay, followed by another bed of fine sands. The sand contains shelly macrofauna. The outcrop is located very close to the bedrock unconformity, only a few meters away from the Sila crystalline basement. This sediment deposited under uncertain water depth.

OSL samples (Figure 13) collected in the lower massif sand layer, produced a fading-corrected age of 328 ± 24 ka. This age, put in the context of other Bisignano outcrop



seems odd. Specific analysis of BISI5 sand grains revealed the presence of sodium-rich feldspar, in addition to targeted potassium-rich feldspars (Huot & Lamothe, 2012). Sodium-rich feldspar contents may have biased dating procedures and lead to an apparent younger age (see details in Huot & Lamothe, 2012).

Figure 13: Close-up view of Bisignano 5 (lat: 39.505726°; long: 16.301074°) site above town at 417 m asl.

OSL samples (visible in the scraped part) were collected in a ca. 50-cm-thick massive fine sand unit below a more clayey 10-cm-thick level. This translates into a quiet sedimentary environment which we think was shallow marine, but

of unknown palaeodepth.

3.3.2. Bisigano town plaza level

On the main square of Bisignano town plaza, a 2.5 x 3 x 3 m3 block of marine sediments is preserved at an elevation of 374.70 ± 0.30 m (site BISI02-2006) (Figure 14). One cannot be certain that the block lies in situ though it is unlikely that it has been moved from a long distance on a truck given the fragility of the rock. It contains abundant shallow marine fauna with bivalves and coral fragments typical of a reef. The deposition environment was probably quiet.

A second outcrop at the base of a wall, Via Simone da Bisignano (16.286348916°E, 39.513674482°N), at 379.15 ± 7.6 m (site BISI01-2006, Figure 15) showed well sorted beach sands. Palaeo-depth was probably at or very near sea-level. OSL samples were collected there but not processed.



Figure 14: Bisignano town plaza reef fragment (site BISI02-2006) located at 16.285962131°E, 39.513418°N; 374.70 m +/- 0.30 m.

It is unclear whether this block staid in-situ when the pavement was installed. Given the fragility of such rock, we assume that it cannot have been imported there with a truck. The detritic material is positively marine with bivalves and

coral fragments.

Bisignano Plaza morphologically has a flat hill top which dominates the surrounding landscape at an elevation ca. 375-380 m. The horizontal surface is probably inherited from its underlying sediment and is a relict topographic surface. The presence of marine sediments on it and below its surface indicates its marine origin. It must relate to a marine high-stand posterior to Bisignano 5 upper level, but older than subsequent formation found further. We suppose that this level relates to MIS 9.3, 330 ka ago.



Figure 15: Well-sorted marine sands visible below the foundations of a house on Bisignano Plaza leve, via Simone da Bisignano (site BISI01-2006; 16.286°E, 39.513°N, 379.15 m +/- 7.60

m).

3.3.3. Bisignano main quarry level

Hilltops surrounding Bisignano town plaza only reach elevations ca. 320 m-325 m. That is 60 m below town level. Below these hills, many quarries exploit sands and gravels. Bisignano main quarry, La Pieta and Bisignano old quarry were examined in detail and surveyed photogrammetrically (Figure 17). The sedimentary section of via Mucone was also surveyed and described. All these outcrops are detailed below.



Figure 16: Outcrop locations around Bisignano town (town plaza at 16.285°E, 39.513°N). Yellow wedges indicate the view points of the different figures presented for the Bisignano fan delta complex.

Outcrop names are identical in the following text.

Figure 17: Synthesis of Bisignano quarry outcrops at elevations between 260 m and 320 m which contain Gilbert-type delta deposits.

A: overview of quarried hills from Bisignano town plazza level. B,C,D, E: details of individual quarries. Topset-foreset transitions are all located around 280 m elevation and are capped by a marine-fluvial sequence. OSL sample BIS1 was

collected in outcrop E (left) and BIS2 in outcrop C (top right).



3.3.4. Bisignano main quarry

Bisignano main quarry (Figure 17C) is one of the key sites described by Colella et al. (1987) as a classic example of Gilbert-type fan delta deposit. The outcrops have changed since the original paper was published 25 years ago, but the delta deposit features have remained.

The outcrop is located at the site named La Pietà to the west of town. What we termed Main Quarry the northernmost of three sites along Via Pieta that are exploited for gravels and sands (Figure 16).

Figure 18: Bisignano main quarry overview (view to the NNE)(16.275278°E, 39.516671°N). This outcrop is a section through a gilbert-type fan delta deposit with topset (horizontal) and foreset (oblique) beds. Note

the lorry on the left side for scale. Next to it is the clinoform outcrop (in detail on Figure 19). Topset/foreset transitions are exposed on the right part of the quarry, at elevations between 281 m and 285 m. Low angle stratified sands and gravels terminate in shallow quiet environment, with marine bivalves.The upper section of the outcrop may turn into

fluvial sands.The diagram on the right details the different sedimentary packages and interpretations.

Bisignano main quarry shows a section through a sedimentrary sequence comprising stratified sandy formations at the base, clinoforms, rising gilbert-type fan delta topset/foreset deposits, sub-horizontal shallowing marine layers capped by fluvial sands (Figure 18).

Below the clinoforms, the lower part of the outcrop exhibits cross-stratified sandy units containing meter-thick cobble lenses (Figure 19A) at elevations between 257 m and 265 m. Sands and cobble samples were collected for cosmogenic radio-nucleides burial age measurements by Joerg Schaeffer at Lamont Doherty-Earth Observatory (yellow dots CAL06.01, CAL06.02 and CAL07.03 Figure 19A). Dating results are not finalized. This sand and cobbles layer is nevertheless at the same elevation as OSL sample BIS1 collected 50 m to the north-west (Figure 19B and C). The OSL fading corrected age of BIS1 comes at 335 ± 21 ka.

Above this, a 7m-thick clinoform unit progrades unconformably from South-East to North-West. The clinoforms’s basal unconformity has an apparent down dip of 10° to



the NW, indicating current in this direction. The clinoforms appear to be the lateral prolongation of Gilbert-type delta foresets seen further to the south-east (Figure 18), although lateral continuity with foresets is obscured by vegetation. Clinoforms are cross sections through prograding underwater dunes requiring some unknown water depth.

Coming back to the main quarry outcrop (Figure 18), forest/topset transitions can be clearly seen on at elevation between 280 m and 285 m. This typical deltaic feature is a reliable sea level indicator as topset/foreset form just a few meters below sea level where the sediment plume carried by a river enters deep water. The main outcrop front is oriented N300°E, the apparent flow has a north-westerly direction.

Figure 19: A. Clinoform exposure in the NW of Bisignano main quarry site (see Figure 18 for location).

Sand and cobble samples (at yellow marls labelled CAL06.01, CAL06.02,CAL06.03,) were collected for cosmogenic radio-nucleides burial age absolute dating. B: Context view of sand sample OSL BIS1 collected below the base of the

clinoforms for absolute dating. C:Close-up view of BIS1. The absolute burrial age of this OSL sample comes at 335 ± 21 ka. No substancial hyatus is noticeable in the sequence except perhaps the channel base underlined in red in pannel A.

White dots indicate local elevation above sea-level reconstructed from photogrammetry.



Delta topset-forsets grade into sub-horizontally-bedded fine sands with occasional pebbly beds. This unit has a thickness of ca. 30 m from 285 m to 315 m. OSL sample BIS2 collected at 312 m was dated at 256 ± 17 ka. Just above this massive fine sand unit, a layer of clayey fine sands, rich in marine macro-fauna, is found at 315 m. Pecten shells (Figure 20) deposited in a quiet, sub-aerial environment. Such environment must not have been very far from sea level.

Figure 20: Pecten-familly marine shell found in Bisignano main quarry top section (16.2762°E, 39.516615°N).

It is distinctive of shallow marine waters, note the delicate ornementation of the ribs testifying how little transport it suffered after deposition. Elevation of the scallop is ~310-320 m. OSL sample BIS2 taken 2-5 m below this layer is

dated 256 ± 17 ka. Our preferred age for this layer is MIS8.5 ca. 285 ka.

The last 10m of sediments go all the way to the hill top, at around 320 m-325 m (Figure 18). They progressively grade from marine to fluvial sands indicating a transition between shallow marine environments to continental environment. An OSL sample was collected in fine sands in a small lane (16.278392°E, 39.516424°N, ~322 m) but was not processed by Sebastien Huot at UQAM.

Bisignano main quarry thus shows a complete deltaic sequence from distal clinoforms climbing all the way to fluvial sands in a 70m-thick sediment pile. This sequence is continuous, which is a strong feature for absolute dating.



3.3.5. La Pieta quarry

Figure 21: Bisignano La Pieta quarry (BISI01.2007, 16.275304°E; 39.512332°N) exhibiting a gilbert-type fan delta sequence 500 m due south of Bisignano main quarry.

The quarry we named La Pieta is the second active quarry west of Via La Pieta, 500 m to the south of Bisignano main quarry. Its entrance is located just a few meters below Bisignano main quarry. The topset-foreset transitions exhibited toward the top of the hill are correlative with those of the main quarry (Figure 21). D-GPS data were not processed making it impossible to orient the 3D photogrammetric model properly. Nevertheless, a scaled model was build and relative elevations of inflexions points were measured (Figure 21). Uncorrected GPS coordinates, however, suggest that these transitions are at elevations of about 275 m. Since the corrections could bring up to 10 m of vertical correction, topset/foreset transitions in this outcrop are at compatible elevations with that of Bisignano main quarry.

Flow directions in this outcrop are clearly oriented to the North, with an easterly component. This implies that the river mouth was located further to the south of this outcrop. At present, the feeder system of Bisignano gilbert-type fan delta has not been recognised yet but is likely to be an ancestor of Mucone River.

One should note that topset/foreset transitions are rising (Figure 21) which may be an indication for relative dating.

3.3.6. Bisignano Old Quarry

The old quarry section is located to the east of La Pieta quarry (16.278924°E, 39.510674°N) (Figure 16). The section is the last remnant of a sandy sequence also exhibiting topset/foreset transitions. The outcrop was processed to produce a 3D model



but was not set to scale nor oriented. Uncorrected GPS points suggest that topset/foreset transitions are at an elevation of about 270 m, with a vertical uncertainty of about 10 m.

Again, this sea level indicator is at the same elevation as those of the main quarry and of the La Pieta quarry.

3.3.7. Via Muccone road section

The via Mucone sedimentary section (16.28778°E, 39.5099°N, 308 m) is located about 1.3 km to the west of Bisignano main quarry along a road section inside of Bisignano town. Its DGPS-controlled elevation is comprised between 304.4 m and 318.2 m (a,b,c,d yellow marks on Figure 22). It corresponds to the uppermost sequence of Bisigano main quarry outcrop, where shallow marine strata grade into fluvial. Here the deposit is rather made of coarse clastic and sands fluvial channels with hints of sedimentary dip toward the base of the outcrop. The vertical extent of the outcrop does not permit to be sure about this interpretation.

With respect to Bisignano main quarry, this outcrop is located upstream of the fan’s feeder system. If one assumes that the steepened beds located in the lower section of the outcrop (Figure 22, close to “a” control point label) are akin to foresets, this transition is at an elevation of 305 m. This elevation is identical to the massive marine



sand beds found at the top of the main quarry. Similar elevation suggests that both levels could be contemporaneous, one being the continental counter-part of the other.

Figure 22: Via Muccone outcrop in Bisignano town (16.28778°E, 39.5099°N, 308 m).

3.3.8. Conclusion of the Bisignano sequence

The first, presumably marine, shallow water deposit found above Bisigano town was found at 417 m elevation and was OSL-dated to 328 ± 24 ka (BIS5) and then questioned by Huot & Lamothe (2012). The outcrop’s palaeo-depth however is not well constrained. This sample, taken only a few meters away from the Sila basements is very close to the basal unconformity where marine formations encroach onto the granitic substratum.

Table 1: Synthesis of OSL sample results in the surrounding of Bisignano. Sample ID Quarry ID Sample

elevation asl (m)

Fading-corrected age (ka)

Sedimentological context

BIS 1 La Pietà 258 m 335 ± 21 1m-thick sandy layer below clinoforms

BIS 2 La Pietà 312 m 256 ± 17 Sandy horizontal layer just below pecten level at quarry top

BIS 3 La Pietà 322 m Not processed Dirt road above La Pietà quarry, fine sands, possibly not marine

BIS 4 Via Mucone

308.7 m Not processed Nearshore marine coarse clastics laterally and vertically very close to

shoreline BIS 5 Above

town ~417 m 328 ± 24 Contact between sands and Sila

granitic basement note discussion in Huot and Lamothe (2012)

BIS 6 Below town

Not processed Non-marine sandsclose to likely faulted contact with Sila basement



The lack of any faulting in the sediments throughout all visited outcrops around Bisignano town implies that the Crati trough already existed when the delta sequence was deposited. Active faulting is therefore not a precondition to depositing Gilbert-type deltas as classically assumed by Collela et al. (2007) or Colella (1988). The precondition is the existence of a sufficient accommodation space where sediment plumes can collapse in deep water.

The base of Bisignano main quarry was dated at 335 ± 21 ka at 258.5 m elevation, below the clinoforms while the top sample, above topset/foreset transition dates it to 256 ± 17 ka, at 312 m elevation. Such ages are stratigraphically consistent, the older being at the bottom and the younger at the top. From this we may suppose that progradation of the Gilbert delta deposit took place in the time interval probably during MIS 8.5, 285 ka ago.

The via Mucone coarse clastic fluvial deposit at 305 m-315 m is correlative with the continental formation capping Bisignano main quarry. We interpret it as the final deposit of stage 8.5 before a major marine regression and total abandonment of Bisigano surroundings.

3.4. CATALDO

The second key site in understanding the Crati Quaternary evolution is located on the western flank of the Crati valley (Figure 12) at an elevation of about 220 m. Cataldo fan delta drained the Catena Costiera into the Crati river. The fan delta is confined at a lower elevation than the Tarsia ridge (Figure 12). In Cataldo, a series of quarries are exploited there for sands and gravels. The quarry identified as CATA03 (16.196°E, 39.553°N, 208.3 ± 0.1 m) (Figure 23) faces SW and exhibits rising topset/foreset transitions turning into truncated foresets. This transition measured by photogrammetry is comprised between 196 m and 201m (Figure 23).

Figure 23: Cataldo fan delta outcrop CATA03 located below GPS point n° 24927 (16.196°E, 39.553°N, 208.3 ± 0.1 m).

Transitions measured by photogrammetry between topset/foreset numbered 1 to 5 range between 196 and 201 m. Note that transition points 4 and 5 are truncated contacts.



An OSL sand sample was collected at site CATA01 (16.193°E, 39.553°N) at an elevation of 202.4 m ± 1.2 m (Figure 24), 300 m due west of CATA03. Sand was collected for OSL dating from the foreset sequence, some meters below the topsets, probably within 10-20 m of the topset/foreset transition. Its OSL estimated age is 203 ± 18 ka. Palaeo-sealevel ought to have lied around 210-220 m elevation at the time of deposition. Absolute age suggests that this marine delta sequence relates to Marine Isotope Stage 7.1.

Figure 24 : OSL sampling site CATA1 in the Cataldo delta sequence (see detailed view in Figure 25).

The sand sample is collected in the foreset sequence some meters (between 10 and 20 m) below the topset/foreset transition. Elevation of the sampling site is 202.4 ± 1.2 m. OSL corrected age is 203 ± 18 ka. Corresponding sealevel

elevation is around 210-220 m.

Along the western flank of the Crati valley, the ridges of Contessa, Cozzo Carbonaro and Sartano also reach an elevation of about 220 m and all exhibit Gilbert-type foresets (Figure 12).



Figure 25: Detailed view of OSL sample CATA1 in Cataldo delta sequence (see context in Figure 24).

The sand sample is collected in the foreset sequence some meters (between 10 and 20 m) below the topset/foreset transition. Elevation of the sampling site is 202.4 ± 1.2 m. OSL corrected age is 203 ± 18 ka. Corresponding sealevel

elevation is around 210-220 m.

3.5. TARSIA RIDGE

The Tarsia ridge is the topographic high that runs across the present-day Crati valley and forces the Crati River through a narrow bedrock gorge between Lago di Tarsia reservoir and its outlet in the Sibari plain, below the town of Terra Nova da Sibari. The ridge is made of three units: marine shore-face sands containing abundant shelly fauna (83 m up to ~200 m asl), a compact grey clay unit and a fourty-meters-thick gilbert-type fan delta deposit above all this (198 m-240 m). The stratigraphic relation of the grey clay to both other layers is uncertain we could not ascertain the nature of their contact.

A sequence of Gilert-type delta topset/foreset beds was observed in a disused quarry along the road named Grotta di Santa Maria (16.241°E 39.614°N), a small road going from Tarsia to Scalo Ferroviario. The delta sequence contains clasts of granitoids and schists/gneiss mostly rounded though some were subangular. We specifically looked for limestone clasts, indicating a sediment source from the Catena Costiera but did not find any. The flow direction indicated by foresets is NW (N305°E). Both these information indicate that the delta was the outlet of a river flowing out of the Sila Massif into a trough occupied today by the Esaro River. The basal sands found at car-park level (Z = 198 m) are sub-horizontal affected by hummocky cross-stratifications. One OSL sample was collected in them. We suppose that they correspond to the bottomset



beds of the topset/foreset beds observed above and relate it to a palaeo sea level ca. 230 m to 240 m. The fading-corrected age comes to 246 ± 16 ka.

Figure 26: Tarsia and Pantano delta outcrops locations at the northern extremity of the Crati valley.

Note that the faint greydots indicate the road network used during fieldwork.

3.6. PANTANO

Located ca. 5km to the North-West of Spezzano Albanese, the Pantano fan delta complex (16.25°E 39.69°N) pertains to the Esaro fluvial system that drains into the Sibari plain (Figure 27). Delta deposits make now an isolated hill 6.5 km x 2.5 km x 80 m in size. The hill’s North slope corresponds to the delta front in the Sibari plain. Both NW and SE hill sides have been incised by rivers since the deposit occurred. The NW



hill side is a dry valley, probably formed by the piracy of Esaro River that now flows along the south-eastern side. The upstream part of the delta (SW hill slope) is bounded by an active N170°E-66°W normal fault that throws down the western compartment and uplifts the Pantano hill (Figure 27, Quarry 1).

The Pantano delta has been quarried for sands and gravels since the 1980’s. Colella’s classical San Lorenzo Del Vallo gilbert delta outcrops along the south-eastern flank of the hill, at locality Peschiera, (Colella, 1987; Figure 27, yellow box with SLV label). Since Colella’s work, four new open pit quarries were opened along the western flank of the hill (numbers 1 to 4 on Figure 27). We visited them in September 2006 and September 2007 and found a large set of gilbert delta topset/foreset. Optically Stimulated Luminescence (OSL) absolute dating was obtained for 6 samples both at the rear and front of the delta sequence but only 5 were fully processed to provide fading-corrected ages. Despite being separated by more than 2.5km, all dates are coherent with a delta formed 160 000 years ago (see Table 2) and relating to a palaeo sealevel now found around 110 m.

Photogrammetric elevation reconstruction of topset/foreset transitions in quarry 3 (Figure 28) showed that transitions were falling from ca. 104 m down to 98 m above present-day sea-level in the frontal part of the delta (Figure 28.3, Figure 29). The sedimentary pile visible in quarry 3 and 4, above topset/foreset transition grades into alluvial sands. These indicate the continental transition though these sands were not well exposed in outcrop to ascertain their origin.

OSL samples were collected in ca. 1-m thick sandy beds in all four quarries (Table 2).

Table 2: Optically Stimulated Luminescence dates and elevation collected in Pantano hill quarries.

Sample ID Quarry ID Sample elevation asl (m)

Fading-corrected age (ka)

Sedimentological context

Pan 1 1 95.4 m 162 ± 13 Sandy layer inside foresets

Pan 4 1 104.1m 156 ± 10 Sandy layer inside foresets

Pan 3 1 ~98m 155 ± 10 Sandy alluvial bed in hanging-wall of Pantano fault

Pan 2 2 ~108m 163 ± 10 At topset/foreset transition

Pan 5 3 134m 164 ± 10 In alluvial sands well above topsets

Pan 7 4 108m Not processed At topset/foreset transition Quarry ID relates to Figure 27. Samples are sorted in stratigraphic order from most upstream to downstream samples. Note that Pan1,4 and 3 are 2.6 km upstream of Pan 2, 5 and 7. They are all synchronous within measurement errors.

They all relate to a palaeo sea-level around 110 m. Pan3 collected in the hangingwall may have suffered of the order of 30m offset since deposition (0.18 mm/a fault slip rate).



Figure 27: Synthesis of Pantano hill gilbert-type delta outcrops prograded from SW to NE. Four gravel quarries revealed rising topset/foreset transitions. A set of 6 OSL dating samples and 2 cosmogenic radio-

nucleides samples were collected to complete the geometric interpretation.



Figure 28: Photointerpretation of outcrop sections in the Pantano delta front. Red and blue dots mark the position of topset/foreset transitions (see corresponding elevation on Figure 29.

The Pantano fault discovered by Nano Seeber (Lamont Doherty Earth Observatory) in quarry 1 is not well constrained (Figure 28.1). Freshwater travertines were found in the alluvial layer capping quarry 1 at elevation around 125-130 m, i.e. on the footwall. The same formation was found in the hangingwall of the normal fault nearby OSL sample Pan 3 at elevation ca. 98 m. The elevation difference amounts to ca. 30 m and imply a slip rate ca. 0.19 mm/a.

The consequence of fault motion on palaeo elevation estimates is probably of limited extent. If one assumes a slip distribution split between ¾ of subsidence vs ¼ of footwall uplift, sea level markers may be biased by only 7 m or so in 160 ka. Neither the extent of the fault nor its impact have been explored further in this work package, though Nano Seeber may have included it in his structural interpretation.



Figure 29: Elevations of sea level index points on the Pantano outcrop. Identified point match those of Figure 28.

3.7. DISCUSSION AND CONCLUSION

This chapter was concerned with the documentation of sea level markers found in northern Calabria. To the difference of current literature on late quaternary uplift of Calabria, we focused our investigations on constructive landforms (delta deposits) as opposed to erosive geomorphic features (marine terraces). These markers can be found in a protected environment such as that of the Crati valley.

Crati deltas had been recognized tow decades ago as prominent sedimentological features (see Colella 1987, 1988), but their unconstrained age was never related to Quaternary eustatic variations nor to Calabrian uplift. With the support of absolute dating by means of feldspar-based Optically Stimulated Luminescence (OSL), we make here the demonstration that delta sequences found on both sides of the Crati valley are ubiquitous. They are marine in origin and they are definitely late Quaternary in age. Elevation reconstruction by means of ground-based photogrammetry enabled precisely pinpointing the present-day elevation of such features.

The eldest dated outcrop dates back to ca. 440 ka ago. OSL sampling captured 4 marine high stand sedimentary packages.

Finally, Gilbert-type deltas need accommodation space at their outlet to form steep foresets and clear topset/foreset transition. Colella (1987, 1988) assumed that this accommodation space could only form in an active tectonics setting. In our field observations, we only ever saw faulted sediments outside the Crati basin. Yet despite



hundreds of meters of exposures, the Bisignano delta section for instance did not exhibit any faults. We are thus forced to consider that active faulting is just one possibility to create accommodation space, but that steep passive continental margins may host gilbert-type delta deposits just the same. The only requirement is to have sufficiently deep margins to enable steep angle foresets, which is the case along the Sila and Catena Costiera massifs.

The following chapter discusses an interpretation of these outcrops.



4. Chronostratigraphy of the Crati valley

In this chapter, we propose a synthesis and interpretation of field data gathered around northern Calabria.

4.1. WORKING HYPOTHESIS

For this story to fit both elevations and ages, tectonic uplift has to be around 1.1-1.2 mm/yr. One cannot discount the local effect of faulting, though it is not necessary to explain the bulk of the observations. A synthetic elevation profile (Figure 30) along with site location map (Figure 31) and palaeo flooding (Figure 32) represent the geography of this interpretation. Note that Figure 31 reproduces Figure 12 for reading convenience.

4.2. STAGE 11 (HIGH-STAND)

The story starts 420 thousands years ago with the deposition of sands above the town of Bisignano at an elevation close to 450 m (Figure 30). Huot and Lamothe 2012 acknowledged that OSL sample BIS5 turned out to be too young because of a high NA-feldspar contents and inappropriate fading correction. BIS5 may be fifty thousand older than measured (Figure 30). This deposit puts in contact marine sands with the bedrock. At the end of stage 11 a regression starts.

4.3. STAGE 10 (LOW STAND)

The end of the falling limb of stage 11 to stage 10, with sea level close to 280-290 m, induced a delta progradation into Bisignano La Pietà quarry. Sample BIS1 collected below the clinoforms is contemporaneous of this low-stand situation and is correlative to topset/foreset transitions at 280 m. Note that for sea level to be at 280 m 340 ka ago, uplift rate should rather be of the order of 1.15 mm/y.



Figure 30: Correspondance between sea-level markers and sea-level curve from Walbroek et al. (2002) to which an constant uplift 1.1 mm/y and 1.2 mm/yr has been applied.

Deposit elevation is represented by black dots, while whiskers represent OSL dating uncertainties. Sea level elevation (top of ellipse) is inferred from the type of deposit observed in the field.



Figure 31: Synthesis map of gilbert-type delta deposits in the Crati Valley.



4.4. STAGE 9.3 (HIGH-STAND)

From stage 10 to stage 9.3 sea level rises to 380 m and enables the formation of a reef at the level of Bisignano town plaza.

4.5. STAGE 9.2 (LOW-STAND) AND 9.1 (HIGH-STAND)

Zumpano “deep” water sediments (ZUMP) deposited with a marine sequence top at a possible elevation of 300 m (uncertain).

4.6. TRANSITION 9.1 (HIGH-STAND) TO 8.5 (RELATIVE HIGH-STAND)

Alternative age for Zumpano deep water deposit. At the northern end of the Crati, the Terra Nova da Sibari a deposition phase started with clastic material shed on the shoreface.

4.7. STAGE 8.5 (RELATIVE HIGH-STAND)

At stage 8.5, the Bisignano La Pietà main quarry finished to be filled. Undated OSL samples BIS2 et BIS3 should confirm this interpretation. At the same time, a reef started building above the Terra Nova dated clastic deposits.


During the rising limb of stage 7.3, deposition of deep shoreface storm deposit started occurring in Tarsia. Subsequent the Tarsia delta started prograding during the falling limb of 7.3. The Vaccarizzo da Sibari delta probably prograded simultaneously.

Inside the Crate valley, watersheds of the Catena Costiera deltas started pouring sediments to fill Cataldo, Sartano and Cozzo deltas.

The falling limb of stage 7.3 probably saw the occurrence of headward erosion east of Terra Nova which initiated the formation of the neo-Crati gorge. This erosion was completed by the onset of 7.1.


Confined Cataldo, Sartano and Cozzo deltas continued prograding during the falling limb of 7.1 inside ravines. They debouched inside the present-day Crati valley where scouring has created some accommodation space. The Tarsia ridge is formed and separates the Crati drainage basins from the Esaro basins.



Figure 32: Palaeo-shorelines and underwater areas during successive Quaternary sea level high-stands (refered to as Marine Isotopic Stages – MIS).

The coloured surfaces clearly show where sediments of each high-stands are expected to lie.



4.10. STAGE 6.3 (RELATIVE HIGH-STAND) AND 6.1 (RELATIVE HIGH-STAND)

By the end of stage 7.1, sea level drops. The drop entrains the confined progradation of the Pantano delta north of the Tarsia ridge and down to the present-day Pantano North quarry. Further sea level drop abandons the hill altogother

4.11. STAGE 5.5

As the last marine incursion, stage 5.5 entered the Crati gorge and enabled reef formation in the vicinity of the Lago di Tarsi reservoir (Ferramonti). Since then, eustatic marine excursions remained in the Sibari plain and never again intruded the Crati valley.

4.12. CONCLUSION

This chapter details the succession of events that took place in the Crati valley and at its northern end in the last 420 thousand years. Field evidence along with dated samples enables recounting a continuous marine story for the Crati embayment. While the story itself is only of regional interest, there are two generic facts: (i) we need not implying active tectonics in order to explain outcrop elevation which means that gilbert-type deltas do not need tectonic activity; (ii) the uplift rate in this region was very fast (1.1 to 1.2 mm/yr) compared to other uplifting regions of the world and was as high as that for the last 420 ka.



5. Conclusions

The Calabrian Arc Project is a geodynamics interdisciplinary research project funded by the United-States National Science Foundation and led by Dr Michael Steckler of the Lamont-Doherty Earth Observatory. The project aims at understanding the behaviour of the Ionian plate subduction under the Calabrian microplate in the central Mediterranean region. The interest was sparked by the suspicion that the subduction may have stopped given that most recorded earthquakes indicate extension and not compression, as expected in active subduction zones. In parallel, it is a well known geomorphological fact that Calabria underwent fast uplift during the Quaternary. It is this vertical motion, related to the subduction activity, that we tracked across the landscape to constrain the geodynamics setting.

BRGM contributed to the Geomorphology work package of the Calabrian Arc Project under sub-award agreement EAR-06-07687 Steckler/Dewez which ran from 01 August 2006 until 31 July 2102. The subaward budget was abounded at equal amount by BRGM’s directorate of research under project PDR06ARN44 to cover personal expenses.

Uplift reconstruction requires identifying geomorphic markers acting as sea level proxies in the field; measure their present-day elevation accurately and date them in order to tie them to Quaternary sea level cycles. In this work, we focused our efforts in finding little used sea level proxies in the form of gilbert-type delta deposits. The accurate elevation of the topset/foreset transitions, indicative of palaeo sea level, was measured with a combination of DGPS and ground-based photogrammetric surveys. The timing of deposition was then constrained with Optically Stimulated Luminescence technique.

The main conclusions reached by this collaborative work are:

1. Ground-based photogrammetry is a viable technique for reconstructing the geometry of unreachable outcrops. The basic technique used from the beginning of the project has now much improved with new available software.

2. Gilbert-type delta deposits found around the Crati valley in Northern Calabria, well known as sedimentological archetypes, have through this work been proven to be of Quaternary age. Some deposits were formed during sea level high-stands, but others also formed during sea-level low-stands.

3. Gilbert-type deltas do not need active faulting to develop, the only two determinants are steep underwater margins, which the Crati valley offered, and massive sediment outflow from upstream river catchments.

4. The combined interpretation of all field sites enables the reconstruction of a coherent chronostratigraphic history of sea level cycles in the central part of Northern Calabria. We found that uplift was sustained at a constant rate of 1.1 to



1.2 mm/a, for a duration of at least 400 ka. It is as fast as that along the Messina Strait in Southern Calabria and is coherent to present-day uplift rates.

5. From the uplift history, we conclude that the subduction has probably behaved in the same manner as now for the last 400 thousand years. If behaviour change has occurred, it must be older.



6. References

Antonioli F., Ferranti L., Lambeck K., Kershaw S., Verrubi V., Dai Pra G. (2006) - Late Pleistocene to Holocene record of changing rates in Southern Calabria and Northeastern Sicily (southern Italy, Central Mediterranean Sea). Tectonophysics, 422, p. 23-40.

Bordoni P., Valensise G. (1998) - Deformation of the 125 ka marine terrace in Italy: tectonic implications. In: Stewart, I.S., Vita-Finzi, C. (eds) Coastal Tectonics. Geological Society, London, Special Publications, 146, p. 71-110.

Bouillot R. (2006) - Cours de photographie numérique : principes, acquisition et stockage, Dunod ed., Paris.

Clarke T.A. and Fryer J.G. (1998) - The development of camera calibration methods and models. Photogrammetric Record. 16, p. 51-66.

Clarke T.A., Fryer J.G., Wang X. (1998) - The principal point and CCD cameras. Photogrammetric Record. 16, p. 293-312.

Colella A., De Boer P.L., Nio S.D. (1987) - Sedimentology of marin intermontane Pleistocene Gilter-type fan-delta complex in the Crati Basin, Calabria, southern Italy. Sedimentology, 34, p. 721-736.

Colella A. (1988) - Fault-controlled marine Gilbert-type fan deltas. Geology, 16, p. 1031-1034.

Cucci L. (2004) - Raised marine terraces in the Northern Calabrian Arc (Southern Italy): a ~ 600 kyr-long geological record of regional . Annals of Geophysics, 47, p. 1391- 1406.

Dewez T.J.B. (2007) - Calarco annual report year 1. Progress report, BRGM report, 40 p., BRGM/RP-55734-FR, available at: http://www.brgm.fr/publication/pubDetailRapportSP.jsp?id =RSP-BRGM/RP-55734-FR

Dewez T.J.B., Stark C.P., Huot S., Cardinali M., Lamothe M., Guzzetti F., Seeber L. (2008) - Late Quaternary uplift and coastal landscape evolution in northern Calabria. American Geophysical Union, Fall Meeting 2008, abstract #T53B-1930

Dumas B., Guérémy P., Lhénaff R., Raffy J. (2000) - Périodicités de temps long et de temps court, depuis 400 000 ans, dans l’étagement des terrasses marines en Calabre Méridionale (Italie). Géomorphologie: relief, processus, environnement, 1, p. 25-44.

Ferranti L., Antonioli F., Mauz B., Amorosi A., Dai Pra G., Mastronuzzi G., Monaco C., Orrù P., Pappalardo M., Radtke U., Renda P., Romano P., Sanso P., Verrubi V. (2006) - Markers of the last interglacial sea-level high stand along the coast of Italy: Tectonic implications. Quaternary International, 145-146, 30-54.

Fraser C.S. and Al-Ajluoni S. (2006) - Zoom-dependant camera calibration in close-range digital close-range photogrammetry. Photogrammetric Engineering and Remote Sensing. 72, p. 1017-1026.

http://www.brgm.fr/publication/pubDetailRapportSP.jsp?id=RSP-BRGM/RP-55734-FR

http://www.brgm.fr/publication/pubDetailRapportSP.jsp?id=RSP-BRGM/RP-55734-FR



Fryer J.G., Clarke T.A., Chen J. (1994) - Lens distortion for simple 'C' mount lenses. International Archives of Photogrammetry and Remote Sensing. 30, p. 97-101.

Huot S., Lamothe M., Stark C.P., Dewez T.J., Cardinali M., Guzzetti F., Seeber L. (2008) - Assessment of the Uplift Rate in the Calabrian Peninsula: Dating Deltaic Foresets by Luminescence, AGU American Geophysical Union, Fall Meeting 2008, abstract #T53B-1931

Huot S. and Lamothe M. (2012) - The implication of sodium-rich plagioclase minerals contaminating K-rich feldspars aliquots in luminescence dating. Quaternary Geochronology. 10, p. 334-339.

Remondino F. and Fraser C. (2006) - Digital camera calibration methods: considerations and comparisons. IAPRS. XXXVI, p. 266-272.

Steckler M.S., Baccheschi P., Cardinali M., Dewez T., Faccenna C., Finkel R.C., Gervasi A., Guerra I., Guzzetti F., Huot S., Kim W., Lamothe M., Lavier L.L., Malinverno A., Margheriti L., Nedimovic M.R., Agostinetti N.P., Reitz M.A., Seeber L., Stark C.P., Schaefer J.M., Thomson S.N. (2010) - Tectonics at the Transition from Subduction to Collision at the Calabrian Arc, American Geophysical Union, Fall Meeting 2010, abstract #T13G-07

Tortorici G., Bianca M., De Guidi G., Monaco C., Tortorici L. (2003) - Fault activity and marine terracing in the Capo Vaticano area (southern Calabria) during the Middle-Late Quaternary. Quaternary International, 101-102, p. 269-278.

Waelbroeck C., Labeyrie L., Michel E., Duplessy J.C., McManus J.F., Lambeck K., Balbon E., Labracherie M. (2002) - Sea-level and deep water temperature changes derived from benthic foraminifera isotopic records. Quaternary Science Reviews, 21, p. 295-305.

Westaway R. (1993) - Quaternary of Southern Italy. Journal of Geophysical Research, 98-B12, 21, 741-21, 772.

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