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P-2 ROLE OF MESOZOIC PALEOGRAPHY AND TELTONICS ON THE EVOLUTION OF THE NEOGt~NE C4MPRESSIONAL STRUCTURE AND `PM-QUAT.ERNARY EXTENSIONAL BASINS, CENTRAL GIANPAOLO CAVI NATO' and MASSIMO DALLASTAZ 'CNR 2EIf Explorafion Production, CSTJF, Avenue Larribau, 64000 Pau, France

The study of various outcropping sequences in the central Apennines (Fig . 1), located in the tentral area of the Lazio-Abruzzii carbonate platform (Simbruini-Ernici Mt. and western ), has allowed to make further remarks about the role of the Jurassic-Cretaceous synsedimentary tectonics on the paleogeographic and geodynamic evoIution of the study area during Neogene and Quaternary times . The analysis has been developed, firstly, by determining the chronostratigraphic intervals characterised by general homogeneity in the facies associations and, secondly, by evaluating the area extension of the different litho-bio-facies, to aim at reconstructing the lateral and vertical facies evolutions . In this way, some events of instability have been recognized, controlled by tectono-eustatic phenomena, which conditioned the sedimentary history of this area of the Lazio-Abruzzii carbonate platform. For some of these events the horizontal disposition and vertical evolution of the Mesozoic litho-bio-facies allow to determine paleotectonics lineaments, which can have played an important role during the Neogene to Quaternary tectonics phases . The kinematics interpretation of the different tectonic elements visible on the outcrop is rather complex, because they have certainly experienced different reactivation phenomena .

It seems clear, hoorever, that the Late Miocene compressional tectonics' occurred in a region already involved in repeated tectonics and erosional events, responsible for the carbonate platform structuration in well differentiated units since Mesozoic times . In the Simbruini-Ernici Mt. the development of Mesozoic litho-bio-facies is evenly arranged from SE to NW, with restricted facies (often inter -supratidal) diffused in the South-Eastern part, and transitional-marginal facies located in Central and Northern areas .

The paleogeographic trends appear for this reason ranging from NE-SW to N-S, from the Lower Jurassic to the Upper Cretaceous . Furthermore, the Mesozoic sequences are not complete upwards at different levels from the Upper Santonian to the Lower Maastrichtian ; the more complete successions outcrop in the North-Western area of the range, whereas those characterised by longen Paleogenic hiatus are located in the South-Eastern areas . Comparing these data with the main tectonic directions, mainly oriented NW-SE in this area, it seems clean that no concordante is found between the main tectonics directions and the Mesozoic paleogeography; the formation of tectonic thrust-sheets of different volume between the South-Eastern and North-Western areas, the reduction from South-West towards North-East of the number of outcropping tectonic thrust-sheets and the increase of the stratigraphic interval seem to be in part due to the physiographic differentiation of the platform in terms of presente, location and frequency of potential local detachment levels .

SAGE Conference on Geology and Petroleum Geology - St . Julians, Malta, 1 - 4 October 2000 2

On the contrary, the numerus transvérse accïdents (rangmg ;frói iN-S and NE-SW in direction), which acted as lateral ramps during the thrust-folds structuration and which veere reactivated in a second time as extensional elements during the Plio-Quaternary extensional phase, seem to be related to paleotectonic lineaments inherited by the Mesozoic platform paleogeography .

Industrial seismic profiles across the Fucino basin (Fig . 2) give a clear picture of its subsurface geometry, showing a stroeg asymmetry towards North and East and a network of faults trendmg NW-SE. The thickness of the Plio-Quaternary continental deposits (more than 1000 m .) increases steadily towards the main fault zones that dip south-eastward (Serrone-Villavallelonga Faults (VF and VF; Fig. 2) and southwards (Tremonti Fault (TF ; Fig. 2), conformably to their surficial traces, while displaying a slightly listric geometry . The various combined approaches (field geology vs. seismic interpretation) to the research into the Fucino basin allows different views of the present extensional structures. The bottom of the basin is well recognized along the seismic Tines by a good and continupus signal of the top pof Meso-Cenozoic carbonate rocks . The shape of sedimentary bodies indicates that the basin .,infilling was mainly controlled by normal slip along these faults. In fact, continental depo'sits are frequently in on-lap contact on to the carbonate bedrock, several disconformable contacts occurred during the sedimentary evolution of the basin . The main faults planes (with antithetic and synthetic faults) cut the wholè sedimentary sequence up to the surface indicating a recent faults activity, allo attested by the` surface ruptures of the 1915 earthquake (Ms= 7 .0 where more than 30 .000 people'wére trilled) . The stratigraphic and tectonic setting of the Fucino basin and neighbouring areas indicates that the extensional tectonic events played an important rose in driving the structural-sedimentary evolution of the Plio-Quaternary deposits . The geometry of the depositional bodies, of the faults planes and their relationships suggest that the Fucino basin evolution can be related to an half-gratien type structure, witti some internat complexities, probably related to the preceding fold-and-thrust structures of the Apenninic orogeny (Late Messinian, in this area) . The main boundary faults are: the E-W striking Tremonti--S. Vittorino and Magnola Faults, and S.Potito-Celano Fault (striking NNW-SSE) in the north ; the Parasano, Serrone and Villavallelonga Faults (NW-SE striking) in the South-East (Fig . 2) . Geometry and kinematics indicators of these faults show that their movements have been mainly normal (along the NW-SE faults) and/or oblique slip (along the E-W to NE-SW faults), thus suggesting that extensional tectonics has been the main responsible for the evolution of the Fucino basin .

In the Western Marska range the greater homogeneity of the Mesozoic litho-bio-facies does not allow to identify accurately the isopic belts . Evidences of a Mesozoic paleotectonic (mainly Cretaceous) are given by the vertical width of the stratigraphic hiatus in the sampled successions . The following reconstruction of the depositional setting allows to imagine the presente of NE- SW tectonic elements, responsible for an important dislocation in this area of the carbonate platform. These elements could have subsequently acted, firstly as drag faults and thee as extensional faults disring the orogenic belt structuration . In addition, the NW-SE tectonic elements in this area of the Lazio-Abruzzi Appennines don't leem clearly related to a main paleotectonic Mesozoic-lineament except the fault that bounds the North-Eastern slope of the Vallelonga depression. In the northemmost areas (immediately southward of the Fucino plain), this fault connects .an almost complete Cretaceous succession (Aptian to Lower Maastrichtian, Luco of Marsi-Villavallelonga range) witti another one showing gaps from tha Upper Aptian ( Mt .); this faalt seems to show clear characteristics of an extensional palaeo-fault, active at least disring thé Upper Cretaceous . 42 3~, N QUATERNARY VOLGANK CO MPL E XES

a PLIO QUATERNARY MARINE b - CONTINENTAL

MI O CENE-P L IO CFNE TURBIDITE S

Ifi IASSIG-MIOGENE CAHBONA7E 1~z„ PLA T FORM DEPDSITS b) BASIN CARBONATE QEP4SITS l

PLEISTOCENE INTgAPENNINIC \ 1 ~~r n ~j, I AVA FLOW S

. FAULT ROMA

SUBSURFACE

~~ \ ::T:L::ULT

NORMAL FAU L T

N ~y ABS J

, N 41 15 Fig . 1 - Generalised geologie and tectonic map of the te ntral Apenni nes. Thrust 5ystems refèrred to i n teat are abbreviated as fol lows : MT, Maiel la thrust; GST, Gra n Sasso thrust ; MM T, Marsica-Morrone t hrust; ST, Simbruini thrust; OAT, O[evano-Antrodoco thrust ; LT, Lepini t hrust .

EAGE Conference on Geology and Petroleum Geology - St . Julians , Malta, 1 - 4 October 2000 Fig . ? - Geological map of the Fucino basin and surrounding area showing allo the position of the studiecí 5ci5rnic lines . I) a- Recent alluvial duosits ; b- recent lacustrine deposits (Upper Pleistocene-Holocene) ; 2) Ancient alluvial fan and ]acustrine deposits (Middle Pleistocene- Uppcr Pliocene) ; 3) "Lage-Marc'" lacustrine-lagoonal deposits (Up per Messinian) 4) Lazio- Abruzzi flysch deposits (Lower Messinian) ; 5) Marine Carbonate ramp (Eocenc Lower Miocene); 6) Hinner carbc>natc platform (Upper Cretaceouti; 7) Hirnner carbonate platform ( Middlc Jt►rassic-Luwer Cretaceous-) ; 8) Marginal Latium-Abruzzi carhonate platform (Midfile Jurassic- Upper Cretaccous) 9) Slope related to Latium-Abruzzi carbonate platf`órrn (Lower .iurassic-Eaccne) 10) Normai fault ;l l) Tht•ust fault ; 12) Backtllrust.