Late Quaternary geomorphological evolution of the ...

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Late Quaternary geomorphological evolution of the Adriatic coast reach encompassing the Metauro, Cesano and Misa river mouths (Northern Marche, Italy) GILBERTO CALDERONI1, MARTA DELLA SETA1, PAOLA FREDI1, ELVIDIO LUPIA PALMIERI1, OLIVIA NESCI2, DANIELE SAVELLI 2 and FRANCESCO TROIANI 2 1 Dipartimento di Scienze della Terra, University of Rome ``La Sapienza'', P.le Aldo Moro 5, 00185 Rome, Italy. E-mail: [email protected], [email protected]., [email protected], [email protected] 2 Dipartimento di Scienze dell'Uomo, dell'Ambiente e della Natura, University of Urbino ``Carlo Bo'', Campus Scientifico, Loc. Crocicchia, 61029 Urbino, Italy. E-mail: [email protected], [email protected], [email protected]

Abstract

This work has been carried out to gain deeper insights on the late Quaternary geomorphic evolution of the Adriatic costal area encompassing the Metauro, Cesano and Misa river mouths, in the outer sector of the northern Marche Apennines. In addition to detailed geomorphological survey, drilling logs and data from new and previously reported radiocarbon datings, a geostatistical processing of fluvial and marine terrace topography was attempted, which is finalized to reconstruct the original geometry of depositional top-surfaces. The Metauro, Cesano and Misa rivers in their most distal sectors flow orthogonally to the coastline and display wide and flared fluvial plains in the proximity of their mouths. At least four fluvial terrace levels, likely referred to Middle Pleistocene-Holocene glacial-interglacial cycles have been recognized throughout the study area. Fluvial plains generally merged into narrow relict coastal plains interconnecting the river mouths, and coastal fans affected by wave-cut scarps are the main geomorphic features of the coastal area. Close to the river mouths the bulk of geomorphic and geometric/stratigraphic features were consistent for identifying, for the first time, some typical coastal fans with well preserved Holocene wave cut scarps. Further, data indicate that the local convex-up morphology and the geometric assessment of the topography depend upon the fan location rather than tectonics. Finally, by coupling geomorphologic and stratigraphic data with the results of geostatistical analysis, it has been possible to constrain the location of shoreline and sea level during the last Interglacial. Basing on that, it has been calculated that the coastal area underwent a mean uplift rate of at least 0.15 mm yr-1, in fair agreement with previous estimations concerning the northern Marche coastal zone. Keywords: Fluvial and marine terraces, Geostatistic topographic analysis, Adriatic coast, Central Italy

Introduction The study area lies in the north Marche coastal area encompassing the lowermost Metauro, Cesano and Misa river valleys. The geomorphological setting of the area is manly characterized by gentle coastal hills joining a NW-SE striking coastline which reached its present position at the end of the Holocene sea-level rise (Elmi et al., 2002; Elmi et al., 2003; Colantoni et al., 2004). The northern Marche coastal zone is part of the piedmont sector of the Umbria-Marche fold-andthrust belt affected since Middle-Upper Pliocene by a northeast verging persistent tectonic uplift which is still active (Ambrosetti et al., 1982; D'Agostino et al., 2001). A general agreement exists with an active tectonics affecting the area (Frepoli and Amato, 2000; Di Bucci and Mazzoli, 2002 and reference Geology of the Adriatic area GeoActa, Special Publication 3 (2010), pp. 109-124.

therein; Basili and Valensise, 2001 and reference therein); nevertheless the style of the tectonic array and the amount of the tectonic-related perturbations have been the object of a meaningful debate. Namely, it has not cleared yet the role played by the blind-thrust driven anticlinal growth involving the coastal fold-and-thrust system (Di Bucci et al., 2003; Vannoli et al., 2004). Moreover, it has not been unravelled the relationships between the generalized tectonic uplift and the glacio-eustatic rise (with relative isostatic component) in constraining the present coastline siting. In this context a helpful input to enhance the knowledge of the present morphoevolutive framework of the area and to unravel the interactions between global changes (viz, eustatic sea-level rise and relative effects) and active tectonics, can arise from a geomorphological study according to pro109


Gilberto Calderoni, Marta Della Seta, Paola Fredi, Elvidio Lupia Palmieri, Olivia Nesci, Daniele Savelli and Francesco Troiani

cedures already highlighted by Burbank and Anderson (2001). Thus, our researches point to provide a contribute to the location of the past coastlines and would be an advance to unravel the puzzling relationships among distal alluvial plains, rivermouths, and coastal plains along a sector of the northern Marche coast. Accordingly, a first step was to analyse the correlativity of different levels of fluvial terraces, already recognised in the inner and middle sectors of the main northern Marchean river valleys (Nesci et al., 1995; Fanucci et al., 1996), heading for the coast. Namely, we pointed to recognise the shaded switchover among fluvial and marine terraces occurring close to the river mouths. Our research relies on a detailed geomorphological survey, and it is completed with log data and radiocarbon datings. Eventually, we applied a quantitative approach based on geostatistical topographic analysis of fluvial and marine terraces already tested as useful tool to reconstruct original depositional top-surfaces, as well as to detect possible tectonic perturbations affecting the depositional bodies (Della Seta et al., 2005). Since the Marine Isotope Substage (MIS) 5.5 high stand (125 ky B.P.) constitutes a crucial reference time-line for any further quantitative assessment of vertical neotectonic displacement along the coast (Lambeck et al., 2004; Antonioli et al., 2006; Ferranti et al., 2006), geostatistical topographic recostructions have also been made in order to provide some constrains to detect both locations and heights of last interglacial sea-level high stand.

Regional geological and geomorphological settings The study area lies in the outer sector of the Umbria-Marche Apennines and is a part of the Northern Apennines orogenic belt resulted from the deformation of the African±Adriatic continental margin. The Apennine chain mainly consists of a thrusted and folded belt including a 5-km thick concretionary limestone prism which upwards progressively changes into terrigenous rocks. Hemipelagic, turbiditic and evaporitic sediments deposited since the Miocene through the Lower Pleistocene generally overlay a JurassicPaleogene carbonatic and marly-carbonatic succession. Since the Lower Miocene the thrusted 110

anticlines of Meso-Cenozoic marine sequences migrated progressively towards the north-east. Since the Middle-Upper Pliocene the Adriatic side of the Apennines underwent an overall tectonic uplift which maximized at the end of Lower Pleistocene while extensive tectonics developed through the inner domains of the chain (Ambrosetti et al., 1982; Patacca et al., 1992; Centamore et al., 1996; Cavinato and De Celles, 1999). The same uplift, still in progress during the Holocene, affected the piedmont area of the UmbroMarchean Apennines (Troiani and Della Seta, 2008 and references therein) with a rate of about 0.3 ± 0.5 mm yr-1 during the last ~1 My in the inner sectors (D'Agostino et al., 2001; Molin and Fubelli, 2005); the uplift rate steadily drops along the W-E direction and minimises at the outermost margin of the chain. The most recent history of the Apennines development (viz, Upper Pliocene-Lower Pleistocene) includes the final emersion of the piedmont along with a contemporary establishment of the first rough drainage network (Mayer et al., 2003). As a general rule, the main watercourses are subparallel and SW-NE oriented (thus transversal to the most important structural grains, Figs. 1 and 5). In the inner areas the morphostructure is mainly controlled by the carbonatic anticlines which generally conform to the higher relieves and, analogously, over the littoral zone the locations of the coastal hills matches those of the thrusted anticlines (Fig. 1). Since the Middle Pleistocene, the persistent tectonic uplift forced the entrenchment, frequently more than 100 m, of the drainage network, this resulting in terraces formation, upstream network extension and captures (Mayer et al., 2003). In the Middle-Upper Pleistocene cyclic sea-level lowering ± which in the LGM amounted for c.a. -120 m - related to glacialinterglacial stages caused the emersion of the north Adriatic continental shelf and a huge twofold lengthening of the river channels (Elmi et al., 2003). In this context, during the glacial stages cold climate-driven aggradation took place over the present emerged and submerged main trunk valleys. Conversely, during the interglacials, thus under warmer climate, the previously deposited alluvial fillings underwent severe erosion recorded by the fluvial terraces along the main valleys (Fanucci et al., 1996). The most distal flood plains are capped by an up to 50 m thick upper Pleistocene alluvium lying 25-30 m below the present sea-level. In particular the alluvial sediments filled


Late Quaternary geomorphological evolution of the Adriatic coast reach encompassing the Metauro, Cesano and Misa river mouths (Northern Marche, Italy)

Fig. 1 - Geological sketch of the northern Marche coastal zone enclosing the Metauro, Cesano and Misa river mouths. Legend: 1) Schlier Formation (Serravallian-Tortonian); 2) Gessoso-Solfifera Formation (Lower Messinian); 3) Miocene siliciclastic Formations (Middle-Upper Messinian); 4) Argille Azzurre Formation (Lower Pliocene p.p.- Lower Pleistocene p.p.): pelitic (a), pelitic-arenitic (b), and arenitic (c) lithofacies; 5) Terrace alluvium (Middle Pleistocene); 6) Terrace alluvium (end of Middle Pleistocene); 7) Terrace alluvium (Upper Pleistocene-Holocene p.p.); 8) Terrace alluvium (Holocene); 9) Present floodplain deposits; 10) Holocene coastal deposits and present beach; 11) Fault; 12) Anticline axis; 13) Holocene paleocliff.

those valleys deeply incised in the course of an early cold stage erosion cycle under relative marine low-stand. According to the general classification, the alluvial terraces exposed along the main UmbroMarchean river valleys belong to four distinct orders (named, from the highest to the lowermost, T1 through 4), ranging in age from Middle Pleistocene to Holocene (Selli, 1954). However, recent accounts (Nesci and Savelli, 1990, 1991a, 1991b;

Nesci et al., 1995; Fanucci et al., 1996) pointed out that such modeling is not fully satisfactory in that it does not include both the higher and the older (Middle Pleistocene) strath terraces. Further, following detailed survey, it has been found that the youngest fill terraces, cut in the Holocene alluvium and so far referred to as T4, as a matter of fact frequently consist of complex successions of cut-and-fill episodes (Nesci et al., 1995). As a result of up to date studies, Di Bucci et al. (2003) 111



Fig. 2 - Idealized cross sections depicting the arrangement of the Upper Pleistocene-Holocene alluvial fills in the Metauro and Cesano river valleys. The numbers refer to 14C readings (yr BP) for the main alluvial fills (Elmi et al., 2003, modified). Both vertical and horizontal scales are only indicative. A) sector close to the present coastline; B) downstream flood-plain reach, some 5 km inland from the river mouth; C) upstream area, about 10-15 km inland from the river mouth.

claimed that the fluvial terraces along the lower reaches of the main Umbro-Marchean river valleys are distributed according to at least ten main levels. The highest, older Middle Pleistocene strath terraces are likely of tectonic origin, whereas the younger alluvial analogues resulted from climatic-driven sedimentation on a gradually 112

uplifting and tilting thrust-belt border (Nesci et al., 1995). Regarding the origin of the alluvial terraces, along the final 10-15 km of the valley reaches it appears that the tectonic deformation did not play a significant role at least over the last 30.000 years (Elmi et al., 2003). Rather, because of their



landforms, deposits and geometric/stratigraphic arrangement, both origin and evolution of the northern Marchean valley-floors can be accounted for a sequence of events, climatic changes included (Nesci et al., 1995; Elmi et al., 2003 and references therein). The proposed evolution pattern is as follows: 1st phase: erosion of the former alluvial fills and valley deepening with down-cutting of bedrock. Since the valleys incised in this phase lie beneath the present sea-level, there is evidence that they deepened during a marine low-stand. The first aggradation phase, likely occurred by the end of this stage, is generally recorded by low-energy deposits (multi-channel/anastomosed? rivers) still of undefined age because 14C dating could only provide the ante quem terminus of > 44 ky BP (Fig. 2). 2nd phase: alluvial filling of the formerly incised valleys with subsequent formation of wide alluvial plains. The vegetal debris in the alluvial fills (matching the T3 alluvium according to the general classification) yielded 14C readings usually less than 37-32 ky BP. Gravels and sands of braided river environment and gravels and clays of alluvial fans (respectively the Fb and Fc sequences after Nesci and Savelli, 1991a) characterize this depositional stage (Fig. 2). 3rd phase: partial re-incision of the former deposits along with recurrent episodes of alluvial fillings progressively more important towards the river mouth. Based on 14C dating the aggradation phases lasted from the Lower (10-8 ky BP) to the Middle Holocene (4.25 ± 3.9 ky BP). Gravels and sands of meandering and braided rivers are the most typical deposits (Fig .2).

Geomorphological outlines of the study area The northern Marchean littoral zone stretches mainly NW-SE between the Metauro and Misa river mouths and to E-SE is confined by the outermost sectors of the northern Marche Apennines from where the main rivers originate. The bedrock (Fig. 1) consists of Plio-Pleistocene arenitic and pelitic marine deposits overlaying Late Miocene marly, siliciclastic and evaporitic formations belonging to the external part of the central Apennines foredeep (Colantoni et al., 2004). A NW-SE oriented thrusted anticline, almost parallel to the present coastline (Fig. 1) is the main morphostructure. In general the Metauro, Cesano and

Misa rivers flow orthogonally to the coastline and therefore transversally cross-cut the most important structures. The wide and flared fluvial plains around the mouths of the main rivers merge into a 0.2-0.5 km wide coastal plain which interconnects the river mouths (Figs. 1 and 3). In conclusion, the main geomorphic features of the coastal area, hereafter showed in detail, are: i) fluvial plains and coastal plain; ii) coastal fans and wave-cut scarps. Fluvial plains and coastal plain

The northern Marche coast is dominated by sandy and gravel beaches interconnected to a narrow coastal plain bounded landwards by remnants of wave-cut scarps. The coastal plain locally merge into the Upper Pleistocene-Lower Holocene alluvial plains. Notably, a paleo-channel, immediately to the south of the present Metauro river mouth (Fig. 3), witnesses a northwards diversion of the watercourse in the uppermost Pleistocene-lowermost Holocene (Nesci et al., 2008). In general the subsurface data strongly supports the widespread occurrence of buried valleys close to the present watercourse. This peculiarity is particularly evident at the Metauro river mouth (Fig. 4) where the availability of conspicuous log data has allowed to draw the local bedrock topography. Such a finding is of great concern since confirms the Upper Pleistocene seaward extension up to the mid-Adriatic shelf of the local drainage system (i.e., incised valleys) in response to the last glacial eustatic low-stand stages. Coastal and fluvial terraces characterize the coastal slopes and the river valley sides, respectively. However, the classical four orders of alluvial terraces are well recognizable along the Cesano river valley whereas, by contrast, in the lower Metauro river valley only those referred to Upper Pleistocene-Holocene p.p. are preserved (Fig. 1). Alluvial bodies referred to the end of Middle Pleistocene and Upper Pleistocene-Lower Holocene spread up to, sometimes merging with, the coeval coastal deposits. Since several terrace treads and escarpments parallel to the present shoreline sharply deflect when approaching the fluvial valleys in proximity of the river mouths, it is reasonably inferred a strict genetic relationship between some coastal terraced deposits and the correlated Late Pleistocene-Early Holocene fluvial terraces. An akin relationship, also shown by 113



Fig. 3 - Digital Terrain Model (kriging GRID, 25 m resolution) of the northern Marche coastal zone enclosing the lower reach of the Metauro and Cesano river valleys. The main geomorphological features discussed in the text are shown.

the fluvial and marine terraces referred to the end of Middle Pleistocene, could provide a valuable marker for the location of both the ancient river mouth and the shoreline during the last interglacial.

Coastal fans and wave-cut scarps

The downstream sectors of the Metauro and Cesano rivers valley-floors match the Upper Pleistocene-Lower Holocene alluvial terraces and show a well-formed, high relief fan shape with ty-

Fig. 4 - Contour map (kriging GRID, 5 m resolution) showing the reconstructed bedrock topography beneath the alluvial and coastal deposits at the Metauro river mouth.

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Fig. 5 - A) Geological sketch of the northern Marche Apennines with the location of the main river basins; the coastal fans at the Cesano and Metauro river mouths are shown. B) Distribution (%) of easily degradable and weathering-resistant bedrock throughout the basins of the main northern Marche rivers cited in the text. The higher percentage of resistant rocks (i.e., carbonates and cherty carbonates) in the Metauro and Cesano river basins account for the relatively high-relief and pronounced convexity of the coastal fans.

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Fig. 6 - The Metauro coastal fan sediments outcropping in a quarry wall close to the river mouth.

pical convex-up topography. This morphology, the stratigraphy and the sedimentological data (Fig. 2) are consistent to infer the occurrence, over the river mouths areas, of typical coastal fans (Fig. 3). These latter characterize the Upper PleistoceneLower Holocene alluvial deposits and, a few km inland, partially merge into the Upper Pleistocene alluvial body (Figs. 2 and 3) (Nesci et al., 2008). At first glance it is striking that the well-formed high relief costal fans reported from the Metauro and Cesano river mouths are poorly evident along the lower reach of the Foglia and Misa river valleys (Fig. 5). The coastal fans in the downstream sector of Metauro and Cesano rivers are, according to an indirect evaluation, some 10-20 m thick. The coastal fans exposed on a quarry walls not far from the Metauro river mouth provided us with some lithologic data and organic remnants suitable for 14C dating (Fig. 3). The lithology of the bodies is dominated by gravels and sandygravels with the festoon-like cross-stratification of the gravels that indicates a braided river environment (Fig. 6). Moreover, some sporadic episodes of epsilon cross-stratification imply local phases of fluvial bends. The blackish organic matter-bearing horizons from two silty-clay levels 116

intercalated within the gravels at ca. 7 m (ca. 4 m a.s.l.) in depth have been dated at 10.70095 and 10.88095 yr BP (calibrated dating), respectively (Fig. 7). Well developed fluviatile sandy facies also occur. However, it is noted that similar facies reported from nearby the Metauro river mouth are puzzling in that they could be of littoral environment (i.e., back-shore). Finally, it is noted that comparable facies are also known in the coastal fan deposits occasionally outcropping at the Cesano river mouth. The wave-cut scarps parallel to the modern coastline (Fig. 3) at the seaward ending of the main valley mouths are noteworthy landforms of the northern Marche coastal area (Elmi et al., 2002). At the mouths of the Metauro and Cesano river valleys the scarps are sharp and evident (Figs. 1, 3 and 8), whereas, nearby the Foglia and Misa river mouths, they are smoothed and partly overshadowed by urbanization. These scarps, already interpreted as relics of a ``Roman'' shoreline (Elmi et al., 2002; Dell'Aglio and Nesci, 2004), represent the maximum inland marine ingression during the Holocene, accounting for a landwards migration of the ancient coastline of some 200-500 m (Nesci et al., 2008).



Fig. 7 - Cross-sections based on log data located southernward the Metauro river mouth, with the location of two 14C dated samples. The section traces are drawn in fig. 3. The Holocene wave-cut scarps at the Metauro and Cesano river mouths could form because of the pronounced convex shape of the Upper Pleistocene-Lower Holocene coastal fans: both the longitudinal variations in cliff height and its local disappearance account for the occurrence of coastal fans.

The distribution of scarps and their relative height clearly mirror the pristine relief (viz, before the landward-migrating marine erosion) of the Upper Pleistocene-Lower Holocene coastal fans around the river mouths (Fig. 3), and therefore that the higher the scarp-relief, the higher the upward convexity of the coastal fan. The development of coastal fans affected by wave-cut scarps depended on an adequate gravel load significantly supplied by the most resistant rocks exposed throughout the catchment area (Fig. 5).

Geostatistical analysis of fluvial and marine terrace topography The geostatistical topographic analysis is effective for reconstructing the river terrace surfaces from the surveyed remnants (Della Seta et al., 2005): when the analysis is used to obtain surface grids it requires the interpolation of three-dimensional topographic data. In the present application the data come from 1:10,000 vector topographic maps and the interpolation complies to 117



Fig. 8 - Inactive wave-cut scarp about 2 km southernward the Metauro river mouth.

the ordinary kriging method (Cressie, 1990). This latter has been chosen among the many proposed and despite the criticisms (Burrough and McDonnell, 1998; Chaplot et al., 2006; Weber and Englund, 1992; Weber and Englund, 1994; Wilson and Gallant, 2000 and references therein), because in many case studies it has been tested its better performance (Zimmerman et al., 1999). Moreover, it has been reported (Chaplot et al., 2006) that the kriging interpolator is the best choice when dealing with poor data sampling density and little altitude variation, thus, the most common conditions to be faced in river terraces and coastal plains topography analysis. According to the above outlined procedure we generated a 10 m grid sized digital terrain model (DTM) of the study area, then, to implement the topographic database for the individual terraces, the remnants of the original top-surfaces of the alluvial to coastal plain deposits were isolated. The pattern of the surface shape for the investigated alluvial bodies was gained through a stepwise process of interpolation which yielded individual contour maps (Fig. 9). The morphology was refined by expanding the grid surfaces over the supposed boundary of the deposits, e.g., beyond the contact with the bedrock on the valley sides. Finally, the alluvium top-surfaces contour maps were blanked according to their real borders (Fig. 10). 118

Results and discussion Coastal fans at the Metauro and Cesano river mouths

In agreement with geomorphological and stratigraphic/sedimentological data (Figs. 2, 3, 5, 6, 7 and 8) the results of the geostatistical topographic analysis (Fig. 9) confirms the occurrence of wellformed high-relief coastal fans, Upper Pleistocene-Lower Holocene in age, at the Metauro and Cesano river mouths, showing a particularly evident fan shape (Figs. 9a and 9b). Although the Middle Pleistocene alluvium top-surface at the lower reach of Cesano river is more severely reworked than its younger analogue, the reconstructed topography also revealed a fan-type depositional body (Fig. 9c). Contour maps point out a complex arrangement resulting from recurrent remoulding of the pristine alluvium topsurface because of rivers and streams entrenchment. Also in this case the geostatistical analysis points out the overall convex fan-shape of the former surfaces and provides for a rough location of the fan apexes. From the topographic sections crossing the Upper Pleistocene±Lower Holocene terraced coastal fans near the mouths of the Metauro and Cesano rivers (m-m' and c-c'. Figs. 10a and 10b, respectively) it results the remoulding of the fan surfaces by the main streams during the Holo-



Fig. 9 - Geostatistical contouring of the fluvial to coastal terrace surfaces

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Fig. 10 - Interpretation of the fluvial to coastal terrace surface reconstructed geometries.

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cene. We note that, by applying the 2nd order polynomial regressions for evaluating the trend of the sections, a reliable overall convex-up topography is outlined, with the location of the peaks not far from the axes of the valleys. Conclusion is drawn that the identified short-wavelength convexities are fan-related rather than of tectonic origin as previously claimed (Vannoli et al., 2004 and references therein). The longitudinal profiles of the fluvial terraces top-surfaces, referred to both end of Middle Pleistocene and Upper Pleistocene±Lower Holocene alluvium, are given in Figure 11. These features are cut across their present remnants by the profile traces l-l' (Fig. 10). Figure 11 points out the effects of the severe erosion and/or recurrent episodes of fan-head shifting and entrenchment experienced by the older top-surface. Let's stress that both wavelength and location of the topographic perturbations noticed on the top-surfaces compare well with the spacing of the tributaries (only in part noticeable in Fig. 1), this providing evidence of their role in the intensive remoulding. The reconstructed pristine depositional topsurface of the Upper Pleistocene-Lower Holocene of both fluvial and coastal terrace deposits resulted of some concern. In particular, at the Metauro and Cesano river mouths, ca. 10 km and 4 km inland from the modern coastline, two distinct knick-zones affected by pronounced bumps (see Figs. 9 and 10 and the longitudinal profiles in Fig. 11) are recognizable on the reconstructed top-surfaces. Based on this finding each of these top-surfaces can be divided into three different sectors. The first sector from 12 km to 8 km inland from the coastline, the second sector from 8 km to 4 km inland, and the third one from 4 km to the present shoreline. Our interpretation of the knickzones fits the conclusions drawn for the Metauro river mouth area by Nesci et al. (2008). In particular, it is our opinion that: i) the first sector (first knick-zone) coincides with the top-surfaces of the last glacial alluvial deposits; ii) the third and easternmost sector (second knick-zone) coincides with the convex-up morphology of the Upper Pleistocene-Lower Holocene coastal fan; iii) the slight topographic depression between the knickzones is the result of fluvial erosion occurring just before the post-glacial coastal fan construction. Such data and reconstructions compel to stress here again that the new findings hardly support any more the tectonic origin for the above mentioned morphological perturbations affecting the

Upper Pleistocene-Lower Holocene both fluvial and coastal plains within the study area. Uplift rate estimation in the coastal area

The value of fluvial and marine terraces as geomorphic markers of possible tectonic perturbations on coastal areas affected by active tectonic uplift has been previously stated (Merritts and Vincent, 1989; Merritts et al., 1994; Keller and Pinter, 1996; Burbank and Anderson, 2001). Given the availability of both geometry and age of the deposits, the evaluation of the uplift rate can be attempted. In this view many efforts were addressed towards reconstruction and understanding the landforms related to marine and fluvial terraces that, for being reliable markers for sea-level changes, could also be used for assessing the geomorphology in tectonically active areas. By applying the two following distinct methods, a rough estimation of the mean uplift rate since last interglacial maximum on the northern Marche coast has been calculated. i) The fluvial to coastal plains switch points (Fig. 10) were regarded as significant features as they are related to the coastal plain development under sea level high-stand; thus provide us with some insights on the past sea level changes and shoreline locations. Unfortunately their usefulness is hampered because of the unsatisfactory chronology. So far only the Upper Pleistocene and Holocene fluvial sediments from the northern Marche (Fig. 2) could have been profusely dated by 14C method, whereas sporadic and uncertain isotopic datings are available for the analogue features of the end of Middle Pleistocene. Given such constraint, the only viable approach to assess the timing of the geomorphologic events herein considered consists in assigning the older deposits a tentative age. Our estimation of the uplift rate at the Cesano river mouth, some 0.13 mm yr-1, results from the ca. 15 m difference in height between fluvial and coastal plains switch points (Figs. 10b and 10c) following their identification on the reconstructed top-surfaces of diachronic coastal fans. ii) To calculate the mean uplift rate at the Misa river mouth (located just south of Cesano river) the evaluation of the tectonic contribution has been accomplished by measuring the difference in height between the relics of the top-surface of the end of Middle Pleistocene marine terrace and the present fluvial to coastal plain switch point. Then, 121



Fig. 11 - Longitudinal profiles of the fluvial to coastal terrace surfaces. Location in fig. 10.

according to Burbank and Anderson (2001), we corrected the determined relative sea-level change (accounting for ca. 25 m) by assuming the value of 6 + 3 m as the absolute sea level change since the last interglacial maximum on the northern Marche coastline (Lambeck et al., 2004). It resulted that the tectonic uplift has been responsible for some 16-22 m of the apparent sea level change. Based on this new figure the mean uplift rate is bracketed between 0.13 and 0.18 mm yr-1, in fair agreement with previous estimation.

Conclusions Aimed at assessing the late Quaternary geomorphologic evolution of the northern Adriatic coastal area of Marche region, the main geomorphologic features of fluvial and marine terraces have been studied at the Metauro, Cesano and Misa river mouths. The goal has been achieved by coupling field and aerophotogrammetric geomorphological surveys with sedimentological/ stratigraphic data and geostatistical topographic analysis. The main findings were as follows: i) For the first time a convex-up morphology affecting both valley-floors and coastal plain has been identified at the mouths of the main rivers draining the Adriatic piedmont of the northern Marche Apennines. The overall morphological and geometric/stratigraphic features were effec122

tive for recognizing typical coastal fans at the main river mouths. Hence, the local convex-up arrangement of topography is fan dependent rather than resulting from tectonics. According to Nesci and Savelli (2003) these landforms mainly developed for fluvial deposition of coastal fans at the mouth of the trunk streams crossing the piedmont area. At present, only the apex-intermediate portions of the pristine coastal fans are still noticeable. They represent the relics of wider and seawards extended bodies whose intermediatedistal portions were dismantled by sea waves during the Holocene sea level high stand. The better preserved coastal fans are located at the Metauro and Cesano river mouths. They show high relief and prominent convexity owing to a relative high content of debris originated from the persistent lithotypes outcropping throughout the drainage basins. The occurrence of well-formed high relief coastal fans accounts for the location of the wellpreserved Holocene wave-cut scarps at present exposed in proximity of the Metauro and Cesano river mouths. At the Metauro and Cesano river mouths the primitive treads of alluvial and marine terraces was established by geostatistical analysis. The results confirm that a fan-related convexity affects the surface topography of Upper PleistoceneLower Holocene and end of Middle Pleistocene alluvial terraces. The uplift rate of the coastal area enclosing the



Cesano and Misa river mouths over the last 125,000 years has been evaluated with two independent procedures for improving the reliability. Both procedures yielded median values almost coincident (mean: 0.15 mm yr-1), thus proving the effectiveness of the approach to get

rid of biases. The result confirms that geostatistical analysis of topographic and geometric arrangement of fluvial and marine terraces is an effective tool for evaluating the uplift rate in tectonically active areas.

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