ABSTRACT In the northern Marche area of central Italy, the analysis of land- forms and stream terraces indicates a generalised Quaternary uplift, as well as differential vertical uplift (of a few tens of metres at most) in different sectors of the foothills area. Moreover, uplift rates appear to have dramatically increased in late Pleistocene-Holocene times, as shown by geomorphologic features (e.g. narrowing of valley terraces and steepening of hillslopes). Within this context, a major issue is represented by establishing the possible occurrence of Quaternary faulting, its kinematics and relationships with the processes above. Based on geomorphologic, stratigraphic and structural studies, sev- eral recent (i.e. post-thrusting) faults have been identified, both in Quaternary deposits (upper Pleistocene terrace alluvium, upper Plei- stocene-Holocene slope deposits) and in bedrock, in the Metauro River Basin area. Our analyses were focused on two main sites, the first in the Fossombrone village area, and the second downstream along the Metauro River, on the right bank (Pian di Rose). The ana- lysed brittle structures appear to form part of a hard-linked fault system mostly including roughly N-S trending normal faults and NE- SW striking sinistral oblique-slip transfer faults. Our results suggest that this fault system controlled the Quaternary geomorphologic evo- lution of the study area, at least in the middle Pleistocene and in the lower part of the upper Pleistocene. Furthermore, the occurrence of upper Pleistocene-Holocene faulted deposits suggests that active WSW-ENE (260°N) extension might characterise the study area. KEY WORDS : Um bria-Marche Apennines, geom orphology, structural geology, active faults, Quaternary uplift. RIASSUNTO Faglie quaternarie nel bacino del Fiume Metauro (Appen- nino Umbro-Marchigiano Settentrionale). L’analisi delle forme del paesaggio e dei terrazzi alluvionali nel- le Marche settentrionali indica un sollevamento generalizzato du- rante il Quaternario, accompagnato da sollevamenti differenziali in diverse aree esterne della catena. I caratteri geomorfologici, fra i quali il progressivo confinamento dei terrazzi e i profili convessi di molti versanti, indicano inoltre un aumento del tasso di sollevamen- to durante il tardo Pleistocene-Olocene. In questo contesto si inqua- dra il presente studio delle faglie quaternarie in quest’area e delle loro possibili relazioni con i suddetti processi. I nostri studi a carat- tere geomorfologico, stratigrafico e strutturale, hanno permesso di riconoscere e caratterizzare faglie recenti sia nei depositi quaterna- ri (Pleistocene superiore-Olocene), sia nel substrato pre-Quaternario. Le nostre analisi si sono concentrate su due siti principali, uno nei pressi di Fossombrone, l’altro a valle di tale abitato in destra oro- grafica del Fiume Metauro (Pian di Rose). Le faglie recenti (post- thrusting) osservate in tali siti fanno parte di un sistema di faglie consistente in segmenti orientati circa nord-sud (distensivi) e faglie di trasferimento con rigetto obliquo (sinistro-trastensivo) orienta- te nordest-sudovest. Alcuni segmenti di faglia appartenenti a questo sistema appaiono non essere state attivi negli ultimi 150.000 anni, essendo gli stessi suturati da depositi alluvionali terrazzati attribui- bili approssimativamente a tale età. Tuttavia, il sistema di faglie nel suo insieme appare avere esercitato un importante controllo sull’evo- luzione geomorfologica quaternaria dell’area, almeno nel Pleistoce- ne medio ed in parte di quello superiore. Inoltre, l’osservazione di depositi tardo-pleistocenici e olocenici fagliati suggerisce che la distensione orientata WSW-ENE (260°N), associata al sistema di faglie di cui sopra, possa essere attiva all’interno dell’area di studio. TERMINI CHIAVE : Appennino Umbro-Marchigiano, geo- morfologia, geologia strutturale, faglie attive, solleva- mento quaternario. INTRODUCTION The Marche-Romagna sector of the Apennines is drai- ned by north-eastward flowing rivers, displaying a gener- alised sub-parallel to trellis pattern of the hydrographic net, characterised by northeastward extending trunk-val- leys, generally cross-cutting fold and thrust structures. The analysis of landforms and stream terraces indi- cates a generalised Quaternary uplift of the Marche- Romagna area ( cf . F ANUCCI et alii , 1996). Differential ver- tical uplift of limited magnitude (<20 m) and a few tens of kilometres wavelength in different sectors of the foot- hill areas is also pointed out by the vertical and areal arrangement of valley terraces (e.g. NESCI et alii , 1990). Moreover, based on: (i) the areal and vertical distribution of valley terraces (ii) the occurrence of large mass-move- ments, and (iii) the convex shape of slope profiles, a late Pleistocene-Holocene enhancement of uplift rates can be inferred. Within this context, a major issue is represented by the possible occurrence of Quaternary faulting asso- ciated with the above-mentioned processes. Ongoing geomorphologic, stratigraphic and structural studies, allowed us to recognise and characterise several brittle features in both Quaternary deposits (upper Pleistocene terrace alluvium, upper Pleistocene-Holocene slope deposits) and bedrock in the Metauro River Basin area. As suggested by geologic and geomorphologic data, these features represent evidence for recent faulting. We wish to emphasise, however, that at the current stage we are not in the position of establishing a definite correlation between recent faults and differential uplift within the study area. The aim of this paper is to provide a first account of Quaternary faults in the Metauro River Basin area, within the framework of the geomorphologic and Quaternary evolution of the study area. Boll. Soc. Geol. It., Volume speciale n. 1 (2002), 931-937, 6 ff. Evidence for Quaternary Faulting in the Metauro River Basin (Northern Marche Apennines) DANIELE S AVELLI (*), MAURO DE DONATIS (**), S TEFANO MAZZOLI (**), OLIVIA NESCI (*), MARIO TRAMONTANA (***) & F RANCESCO VENERI (****) (*) Istituto di Geologia, Università degli Studi, Campus Scien- tifico, Loc. Crocicchia, 61029 Urbino. E-mail: d.savelli@uniurb.it. (**) Istituto di Dinamica Ambientale, Università degli Studi, Campus Scientifico, Loc. Crocicchia, 61029 Urbino. (***) Istituto di Geodinamica e Sedimentologia, Università de- gli Studi, Campus Scientifico, Loc. Crocicchia, 61029 Urbino. (****) Istituto di Geologia Applicata; Università degli Studi, Campus Scientifico, Loc. Crocicchia, 61029 Urbino.