LONG-TERM EVENT STRATIGRAPHY OF THE APULIA PLATFORM MARGIN (UPPER JURASSIC TO EOCENE, GARGANO, SOUTHERN ITALY)

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1 LONG-TERM EVENT STRATIGRAPHY OF THE APULIA PLATFORM MARGIN (UPPER JURASSIC TO EOCENE, GARGANO, SOUTHERN ITALY) ALFONSO BOSELLINI, MICHELE MORSILLI, AND CLAUDIO NERI Dipartimento di Scienze Geologiche e Paleontologiche, Università di Ferrara, Corso Ercole I d Este 32, Ferrara, Italy bos@dns.unife.it ABSTRACT: The Upper Jurassic to Eocene Apulia Platform margin and the eastward transition to the adjacent basinal deposits are well exposed in the Gargano Promontory (southern Italy), a carbonate block that is part of the slightly deformed foreland of the southern Apennine thrust belt. The long-term stratigraphy of this margin and slope transect is punctuated by five major dynamic phenomena that subdivide the succession into six second-order sequences. These events include (1) a Valanginian drowning unconformity, (2) an early Aptian Albian drowning and demise of the platform, (3) late Albian Cenomanian platform-margin failures, (4) a Santonian Campanian retreat of the platform margin, and (5) Eocene uplift and platform-margin collapse. The first event is documented worldwide and is probably eustatic in origin. The second is concomitant with some oceanic anoxic events (OAE). The last three processes are probably related to foreland reaction to subduction and collision in the Dinarides and Hellenides thrust belts. The ultimate cause of the Albian Cenomanian failures is more problematic. A worldwide eustatic regression is documented at this time, but regional geology seems to favor tectonic uplift. INTRODUCTION Since the first appearance of the famous Exxon cycle chart (Vail et al. 1977; Haq et al. 1987), many geologists have accepted as a dogma these eustatic curves and have tried to fit their own regional or local data to them. On the other hand, there are so many Exxon sequence-boundary events from which to choose (Miall 1992), in many cases spacing closer than any biostratigraphic resolution, that it is easy and tempting to find an ad hoc boundary. A different approach could be to elaborate local detailed stratigraphies and construct local relative sea-level curves for many regions of the world and then to compare the various charts. Only for those sequence boundaries dated accurately and precisely and occurring synchronously over large areas of the globe, some kind of eustasy could be invoked for the dominant operating mechanism. In this report we present the long-term event stratigraphy of a transect of the Apulia Platform margin and slope exposed in the Gargano Promontory of southern Italy (Fig. 1). The Apulia Platform was a relatively small carbonate bank, isolated in the middle of the western Tethys ocean, which flourished throughout the Jurassic and the Cretaceous. The importance of documenting the evolution of the Apulia Platform comes from its isolation. Because the rhythm of growth and decline in the life span of platform systems is influenced by regional environmental and tectonic conditions (Föllmi et al. 1994), it is clear that an isolated carbonate bank can easily register variations in large-scale oceanographic conditions, without any contamination from hinterland processes: the Apulia carbonate platform had a position beyond the reach of terrigenous sediments, and it was isolated and clean. However, the Apulia Platform was presumably influenced by such major geologic phenomena as eustatic sea-level rises, oceanic anoxic events, and intraplate response to distant subduction or collision processes. In this report we present for the first time the entire evolution of the platform, from the Late Jurassic to the Middle Eocene, focusing on its margin and slope. In fact, along the margin and slope of a carbonate platform, flooding or lowstand events, tectonic episodes, demise of the system, etc. are all amplified and quite often physically visible; in contrast, in the platform interior or in the deep basin floor such events are in most cases barely recorded and the sedimentary succession might appear monotonous. Finally, we document that classic sequence stratigraphic successions may be the result of episodic failure of a carbonate platform margin or of regional tectonic events. GEOLOGIC SETTING AND STRATIGRAPHIC FRAMEWORK The Apulia carbonate platform was a major paleogeographic element of the southern margin of the Mesozoic Tethys Ocean (Fig. 2). It is one of the so-called peri-adriatic platforms, which are comparable to the Bahama banks in their carbonate facies, shape, size, and subsidence rate and also in the internal architecture (D Argenio 1976; Eberli 1991; Eberli et al. 1993). The Apulia Platform, which is part of the stable and relatively undeformed foreland of the Apennine thrust belt, is bounded on both sides by basinal deposits; westward the margin is buried under the Apennine thrust sheets, to the east the adjacent paleogeographic domains are the vast Ionian Basin to the south and the Umbria Marche Basin to the north (Fig. 2). To the west, the Apulia Platform plunges downfaulted underneath the terrigenous sediments of the Apennine foredeep; to the southeast, the Jurassic Early Cretaceous margin lies km offshore from the present Apulia coastline (De Dominicis and Mazzoldi 1989; De Alteriis and Aiello 1993). The Gargano Promontory and the Maiella Mountain, which now is part of the external Apennine thrust belt (Eberli et al. 1993), are the only areas where the transition from platform facies to basin facies are exposed on land (Fig. 2). In the Gargano area this transition has been investigated extensively in the last decade (Luperto Sinni and Masse 1987; Masse and Luperto Sinni 1989; Bosellini and Ferioli 1988; Bosellini et al. 1993a, 1993b, 1994; Bosellini and Morsilli 1997; Morsilli and Bosellini 1997; among others). As a matter of fact, since the mid 1960s AGIP geologists and the Italian Geological Survey (Pavan and Pirini 1966; Martinis and Pavan 1967; Cremonini et al. 1971) recognized that the western part of the promontory is part of the shallow-water Apulia Platform, whereas the eastern part is characterized by slope and basinal deposits (Fig. 3). The backbone of the Gargano Promontory consists of a thick pile ( m) of Jurassic and Cretaceous shallow-water carbonates. A small outcrop of Upper Triassic evaporite (Anidriti di Burano) and black limestone is present on the northern seashore (Punta delle Pietre Nere) (Fig. 1). These rocks have also been encountered in wells Gargano 1 (G.1 Conoco) and Foresta Umbra 1 (F.U. Agip) (Fig. 1). The outcropping succession comprises Upper Jurassic to Eocene carbonate rocks representing platformto-basin settings (Martinis and Pavan 1967; Masse and Luperto Sinni 1989; Bosellini et al. 1993b). Minor scattered outcrops of Miocene sediments, unconformably overlying the Cretaceous and Jurassic platform, are present in many parts of the promontory, mainly along the lowland border zones (Cagnano Varano, Sannicandro, Apricena, Manfredonia), and also one site inland near S. Giovanni Rotondo (Fig. 1) (Cremonini et al. 1971). On the basis of physical stratigraphic relationships and of the presence of evident bounding surfaces, the Jurassic Eocene succession can be subdivided into six major packages of sediments, which can be classified as second-order depositional sequences (Fig. 4). The lower three sequences (Callovian to Albian) are represented by the JOURNAL OF SEDIMENTARY RESEARCH, VOL. 69, NO. 6, NOVEMBER, 1999, P Copyright 1999, SEPM (Society for Sedimentary Geology) X/99/ /$03.00

2 1242 A. BOSELLINI ET AL. FIG. 1. Location map of the Gargano Promontory with main roads. F.U. Foresta Umbra well (Agip); G.1 Gargano 1 well (Conoco) entire spectrum of sediments from platform to slope and basin, and the younger ones (Cenomanian to Lutetian) largely by slope and basin deposits. Probably the most typical and significant feature of the Gargano slope and basin setting is the presence of huge megabreccia bodies, which, in terms of sequence stratigraphic terminology, can be interpreted as typical lowstand wedges (Sarg 1988). ARCHITECTURE AND SEQUENCE STRATIGRAPHY OF THE PLATFORM MARGIN In this section, a long-term event stratigraphy as representing long-term dynamic phenomena including changes in climate, tectonics, and global sea level and a sequence stratigraphic organization of the platform margin are presented. Geometries and types of unconformities (especially on the slope) and associated lithologies will be discussed. During the last twenty years, the sequence stratigraphic approach has been used largely to subdivide sedimentary successions. However, a lively debate concerning primary causes, physical scale (thickness above all), and FIG. 2. Restored distribution of platforms and basins in central southern Italy during the Jurassic Cretaceous (from Zappaterra 1990; modified). time duration of depositional sequences still exists (Posamentier et al. 1988; Christie-Blick 1991; Schlager 1991, 1993, 1998; Bosellini et al. 1993b; Christie-Blick and Driscoll 1995). As is well known, the original definition of depositional sequences (Mitchum et al. 1977, p. 53) and their bounding surfaces does not imply any specific genetic mechanism or a time or physical scale. The same can be said for the original definition of systems tracts (Brown and Fischer 1977). However, in spite of the original definitions of depositional sequences and systems tracts, many authors (Vail et al. 1977; Haq et al. 1987; Posamentier et al. 1988; Van Wagoner et al. 1988, Jacquin et al. 1991; among others) gave to these stratigraphic units a specific genetic significance and a precise time duration for example, the depositional sequences are thirdorder cycles (2 3 Myr), and systems tracts are confined within them. Vail et al. (1991) maintain that the depositional sequences and the associated systems tracts are generated by short-term relative sea-level fluctuations. This interpretation is a possible one but, as shown by Schlager (1992), Bosellini (1993), and Bosellini et al. (1993b), other mechanisms, including ecological demise and tectonic collapse, can operate as well in carbonate systems. Various terms (megasequence, supersequence, composite sequence) have been used to designate depositional sequences involving a longer time span (Hubbard 1988; Vail et al. 1991; Mitchum and Van Wagoner 1991; Bosellini 1992). However, the distinction between different orders is largely arbitrary and often determined by goals and tools of the research (local vs. regional, seismic profile vs. outcrop analysis, etc.) (Christie-Blick 1991). According to our personal experience (e.g., Bosellini 1992), depositional sequences and systems tracts show a self-similarity at different scales (Greenlee and Moore 1988; Mitchum and Van Wagoner 1991). In conclusion, if we admit that depositional sequences, particularly in carbonate successions, can result not only from relative sea-level fluctuations but also from other mechanisms (carbonate system demise, tectonic collapse) and that their definition is independent of time, then the definition of their constituent systems tracts must also follow the same logic. In this report we use the term depositional sequence for unconformity-bounded stratigraphic units that are different in time scale with respect to the typical third-order sequences. However, they present the same internal organization, and systems tracts can be easily identified. Monte Sacro Sequence The lowermost sequence cropping out in the Gargano has been designated the Monte Sacro Sequence (Morsilli and Bosellini 1997), and its age

3 EVENT STRATIGRAPHY OF THE APULIA PLATFORM MARGIN 1243 FIG. 3. Late Jurassic Early Cretaceous facies distribution in the Gargano Promontory. 1) inner platform (Sannicandro Formation); 2) internal margin (Monte Spigno Formation); 3) external margin (Monte Sacro Limestone); 4) slope and basinal deposits (Casa Varfone Formation and Maiolica); 5) fault of regional importance (Mattinata Fault). The right-lateral displacement of the platform margin is due to Neogene strikeslip movements along the Mattinata fault (after Morsilli and Bosellini 1997). is Callovian Valanginian p.p. (the lower boundary is not exposed). The outcropping part of the sequence (only the upper part, the Tithonian Berriasian interval) shows an aggradational progradational trend, interpreted as the highstand systems tract. The sequence is composed of five lithostratigraphic units (formations with several facies associations) (Fig. 4). From the inner platform to the basin, they include the following. (1) Sannicandro Formation. This unit crops out only in the western and central sector of the Gargano (Fig. 3) and consists of a thick succession of meter-scale (1 5 m) peritidal parasequences representing lagoonal to supratidal environments. Common lithofacies include mudstone wackestone rich in dasycladacean algae, ostracods, gastropods (Nerinea sp.), and peloidal and oolitic packstone grainstone. Birdseye structures, fenestral fabric, and stromatolite layers associated with flat-pebble breccia are common at the cycle tops. (2) Monte Spigno Formation. This unit crops out in the central area of the Gargano promontory (Fig. 3) and consists mainly of oolitic and oncolitic grainstones. Sedimentary structures include current and wave ripples and low-angle planar lamination (dune scale). Meniscus cements and key- FIG. 4. Chronostratigraphic chart showing formations, second-order sequences, and systems tracts of the Gargano Promontory. 1) Inner platform facies; 2) margin facies; 3) slope and base-of-slope facies; 4) basin facies; 5) megabreccia; 6) hiatuses; 7) bauxites. Time scale after Gradstein et al. (1995).

4 1244 A. BOSELLINI ET AL. stone vugs are common features in thin section. This facies suggests a shallow-water high-energy setting, such as oolitic shoals with local zones of emersion (small islands with beaches). (3) Monte Sacro Limestone. This formation occurs in a narrow and arcuate belt from Monte d Elio to Mattinata (Fig. 3) and consists of massive wackestone rich in Ellipsactinia, Sphaeractinia, and stromatoporoids. Boundstone rich in Tubiphytes, corals, and stromatactis are present in some areas (M. d Elio). This facies association is interpreted to represent a spectrum of environments from reef front to external margin (Morsilli and Bosellini 1997). The landward boundary with the Monte Spigno Formation is gradual with a zone of skeletal sands and scattered branching coral colonies (reef flat). (4) Casa Varfone Formation. This consists of thick-bedded skeletal rudstone, stromatoporoid breccias, and graded grainstones interfingering with cherty lime mudstones. Clasts are mainly fragments of Ellipsactinia, Sphaeractinia, stromatoporoids, and corals. The geometric relationships observable in the field support the interpretation that this facies association is a proximal to distal, clinostratified slope succession (dip between and ). It is the product of different types of gravity flows, from hyperconcentrated flows to high-density turbidity currents (sensu Mutti 1992). Upslope it passes into the Monte Sacro Limestone. (5) Maiolica 1. This is the well known formation of the Mediterranean basinal sediments of Late Jurassic Early Cretaceous age. It consists of white, thin-bedded, micritic limestone with cherts, rich in calpionellids and Nannoconus, and rich in slump features (intraformational folds, truncation surfaces) (Fig. 5). Upper Sequence Boundary. Near the town of Mattinata and between Foresta Umbra and Coppa dei Tre Confini, the inclined surface (20 28 ) of the platform slope is onlapped by a thick succession of white, thinbedded micritic limestones (Maiolica 2). The physical stratigraphic relationships, directly observable in the field (fig. 5 in Bosellini and Morsilli 1997), are clearly unconformable and suggest the existence of a drowning unconformity (sensu Schlager 1989). Moreover, the horizontal to subhorizontal onlap pattern of the Lower Cretaceous basinal sediments indicates that the platform margin had substantial vertical relief above the basin floor at the time of drowning. The age of the platform and of its coeval flank and basinal deposits (Monte Sacro Limestone, Casa Varfone Formation, Maiolica 1) is Late Jurassic Valanginian p.p., whereas the age of the adjacent onlapping succession (Maiolica 2) is Valanginian p.p. Hauterivian. No evidence of impregnation of authigenic minerals, like phosphate, glauconite, and Fe Mn crusts, commonly found associated with drowning surfaces in other areas of the Tethyan domain (Föllmi et al. 1994), has been observed on the Monte Sacro unconformity surface. The lack of mineralization could be related to the isolation of the Apulia Platform with respect to continental influx. Mattinata 1 Sequence FIG. 5. White basinal limestones (Maiolica) with thin chert layers. Several slump features are clearly visible (road cut east of Mattinata). This sequence, which spans in age from Valanginian p.p. to early Aptian, is represented mainly by inner-platform facies and slope-to-basin sediments (Fig. 4). Margin-bioconstructed facies (rudists and stromatoporoids) occur only at Monte degli Angeli. The progradational trend (highstand systems tract) of the sequence is documented by the superposition of the Mattinata 1 Formation (slope facies) over the Maiolica 2 (basin facies). A brief description of these different units follows. (1) San Giovanni Rotondo Limestone. This is a thick succession ( m) of shallow-water limestone that can be subdivided into three members (see Claps et al for a more detailed description). Member 1 consists of a monotonous and acyclic subtidal unit and represents (probably) the transgressive systems tract of the sequence. Member 2 is represented by a thick cyclic unit characterized by quasi-periodic alternation of loferitic beds and centimeter-thick layers of green shales, deposited in a tidal-flat setting. Member 3 displays a variety of facies including subtidal high-energy thin-bedded calcarenites at the base of parasequences and domal stromatolites in the upper peritidal units. Members 2 and 3 represent the middle and late highstand systems tract, respectively. (2) Monte degli Angeli 1 Limestone. This represents the bioconstructed margin of the platform and consists of skeletal sand and stromatoporoid boundstone and rudstone with scattered coral fragments. It is present only at the Monte degli Angeli (lower part), to the west of Monte S. Angelo (Fig. 6). (3) Mattinata 1 Formation. This is a slope and base-of-slope carbonate succession, rich in gravity-displaced deposits (calciturbidites, breccias), interbedded with cherty micritic limestone, commonly slumped (Luciani and Cobianchi 1994; Cobianchi et al. 1997). The type section is exposed near the town of Monte S. Angelo, along the road to Val Carbonara and S. Giovanni Rotondo (Fig. 6). (4) Maiolica 2. Same facies of the Maiolica 1 described above. Upper Sequence Boundary. There is a rather abrupt change in lithology in slope and basinal settings: both the Maiolica 2 and Mattinata 1 Formation are overlain by a marly and shaly succession, the so-called Scisti a Fucoidi Formation (Cobianchi et al. 1997), early Aptian late Albian in age (see a more detailed description in the following sequence). At Coppa di Pila, south of Cagnano Varano, the transgressive systems tract of the following sequence (Mattinata 2 Sequence) is exposed on the platform margin. A few meters of lower Aptian pelagic limestone disconformably onlap and overlie rudist mounds associated with oolitic grainstone of Berriasian age. These pelagics are in turn overlain by bioclastic rudstone rich in orbitolinids and large rudist fragments. From the standpoint of physical stratigraphy, the sequence boundary is clearly a drowning event: the platform and its bioclastic apron (Mattinata Formation) is abruptly backstepped some 5 10 km, suggesting that shallow deposition was terminated in a short time. Mattinata 2 Sequence This sequence spans from early Aptian to late Albian and is represented largely by slope and basin deposits. Equivalent shallow-water deposits are rare and are present only at Monte degli Angeli and Coppa di Pila and in the area between Rignano and Manfredonia. The sequence, characterized

5 EVENT STRATIGRAPHY OF THE APULIA PLATFORM MARGIN 1245 FIG. 6. Geologic profile (from photograph) between Monte degli Angeli and the town of Monte S. Angelo, The paleoslope, its connection with the platform margins (Monte degli Angeli), and the thin wedge of Aptian black mudstone (Scisti a Fucoidi), subdividing the two Mattinata sequences are clearly visible. No tectonic tilting. in the upper part by its strong progradational trend (Fig. 6), is represented by the following formations. (1) Masseria Quadrone Limestone. According to Merla et al. (1969), an inner-platform succession of Albian Cenomanian? age crops out in the southern part of Gargano. This succession consists of thick beds of mudstone wackestone with peloidal packstone grainstone intercalations. Recently, Luperto Sinni (1996b), described a thin succession (about 30 m) of mudstone packstone with late Albian orbitolinids in the same area; the top consists of a Sellialveolina vialli bearing limestone, early Cenomanian in age. (2) Monte degli Angeli 2 Limestone. This is the late Aptian to middle late Albian tract of the Lower Cretaceous margin of the Apulia Platform. It is grafted onto the underlying Hauterivian early Aptian platform margin, but, in places, there may be 1 2 m of pelagic limestone (transgressive systems tract). The Monte degli Angeli Limestone is rich in sponges, chaetetids, corals, and rudists and represents the bioconstructed margin of this sequence. The age of the outcropping part of this formation is limited to the late Aptian, whereas the Albian part is documented only in platformderived breccia occurring in the Mattinata 2 Formation. (3) Scisti a Fucoidi Formation. This lithological unit, rich in marls and black shales deposited by episodic anoxic events (Cobianchi et al. 1997), has a maximum thickness of 120 m and overlies both the Maiolica 2 and Mattinata 1 formations. It clearly represents a rather abrupt change in the basin sedimentation and is associated with a standstill in the platform evolution. The Scisti a Fucoidi wedges out against the platform slope (Fig. 6) and is absent on the platform top, where a few meters of pelagic limestone or an unconformity surface are present. (4) Mattinata 2 Formation. This is the same slope and base-of-slope succession as the Mattinata 1 Formation, previously described, from which it is separated by a wedge of pelagic limestone with thin beds of black shale (Scisti a Fucoidi Formation) (Fig. 4). The Aptian Albian Mattinata Formation, rich in graded breccias and calciturbidites, represents the highstand systems tract of the sequence. Upslope, it is physically correlatable with the shallow-water platform of Monte degli Angeli (Fig. 6). Upper Sequence Boundary. This is a major erosional unconformity of regional extent. On the platform it corresponds to well known karst and bauxite horizons developed over the entire peri-adriatic region (Crescenti and Vighi 1964; Accarie et al. 1988; D Argenio and Mindszenty 1991; Carannante et al. 1992; Mindszenty et al. 1995). In the slope and base-ofslope settings, the Mattinata and Scisti a Fucoidi formations are unconformably overlain by a huge megabreccia; the boundary is clearly erosional (Fig. 7). Monte S. Angelo 1 Sequence FIG. 7. The deeply erosional contact between the Monte S. Angelo Megabreccia and the underlying Scisti a Fucoidi formation (Superstrada road cut, near Ischitella). This sequence (late Albian Santonian) (Bosellini et al. 1993b; Neri and Luciani 1994) consists mainly of slope (Monte S. Angelo Megabreccia and Monte Acuto 1 Formation) and basinal, fully pelagic sediments (Scaglia 1) (Fig. 4). The shallow-water tract of the sequence is represented by a small outcrop in the western and southern part of the promontory. The sequence consists of the following formations. (1) Casa Lauriola Limestone. This formation consists of shallow-water, subtidal to peritidal carbonates, and crops out in two zones, near S. Giovanni Rotondo and near Apricena. It unconformably overlies the mid-cretaceous bauxite horizon (Merla et al. 1969). In the S. Giovanni Rotondo area it consists of mudstone wackestone with thin intercalations of green marls of late Turonian? Coniacian p.p. age (Luperto Sinni 1996b), whereas in the Apricena area the outcropping succession consists of meter-thick mudstone wackestone beds with scattered bouquets or clusters of rudists

6 1246 A. BOSELLINI ET AL. (radiolitids) and intercalated stromatolite layers, planar or LLH (laterally linked hemispheroids, sensu Logan et al. 1964) (late Turonian Senonian). (2) Monte S. Angelo Megabreccia. This represents the base of the sequence (lowstand systems tract) in the slope and base-of-slope settings. In the type area, it consists mainly of megabreccia lenses with boulders and clasts derived from the Lower Cretaceous carbonate platform margin. In the Ischitella Vico area (northern Gargano), graded breccias and calciturbidites are intercalated with pelagic limestones. The thickness can be as much as 200 m. This unit, late Albian Cenomanian in age (Neri and Luciani 1994), represents the slope and base-of-slope accumulation derived from large platform-margin failures. (3) Monte Acuto 1 Formation. This is a succession deposited in slope and base-of-slope settings (Neri 1993; Neri and Luciani 1994). It consists of white, chalky and cherty lime mudstones, alternating with coarse bioclastic calciturbidites, breccias, and megabreccias; clasts are both of platform and slope basin derivation. The entire M. Acuto Formation (1 and 2) has been divided into five units (Neri 1993): (a) a basal condensed pelagic interval (Unit 1), which may be interpreted as the transgressive systems tract; (b) two bodies of calciturbidites (Units 2 and 4) (highstand systems tract), separated by a Scaglia tongue (Unit 3), some 50 m thick, (Santonian early Campanian in age), and (c) a pelagic interval on top of the succession (Unit 5). Facies associations of Units 2 and 4 are representative of a system of laterally coalescing depositional lobes (Neri 1993). Only Units 1 and 2 constitute the Monte Acuto 1 Formation. (4) Scaglia 1. This is the basinal counterpart of the sequence and consists of thin-bedded, chalky and cherty white lime mudstones. Upper Sequence Boundary. Even if there is no control from the platform section, we consider the Scaglia tongue (Unit 3) as a possible transgressive systems tract of a younger depositional sequence of Santonian early Danian age (Fig. 4). Moreover, this sequence boundary has also been recognized in offshore seismic profiles, with a marine onlap that probably reflects a partial drowning of the Apulia Platform (De Alteriis and Aiello 1993). Monte S. Angelo 2 Sequence This sequence comprises only slope and basin facies. Two formations are present. (1) Monte Acuto 2 Formation. This corresponds to units 3, 4, and 5 as defined by Neri (1993). Unit 3, the Scaglia tongue previously described, consists of pelagic sediments with some breccia and turbidite layers, which seem to be more common upslope. Unit 4 is a thick calciturbidite body, like unit 2. The last unit is represented by pelagic sediments with some thin bioclastic turbidite of Danian age (M. trinidanensis zone) (Bosellini et al. 1993b). (2) Scaglia 2. Lithologically, this succession is the same as Scaglia 1 and crops out extensively along the northeastern part of the Gargano. Upper Sequence Boundary. The Monte Acuto 2 and Scaglia 2 formations are overlain by the Grottone Megabreccia or by laterally equivalent calciturbidites of the Peschici Formation (Bosellini et al. 1993a, 1993b) of Middle Eocene age. The contact is everywhere unconformable and deeply erosional. Monte Saraceno Sequence FIG. 8. The marine onlap of the Peschici Formation (Lutetian) over the deeply eroded Scaglia (left) of late Turonian early Coniacian age (Vieste sea-cliff). The youngest depositional sequence of the Gargano succession is m thick and entirely Middle Eocene (Lutetian) in age (Bosellini et al. 1993a, 1993b) (Fig. 4). The Monte Saraceno Sequence is separated from the underlying Upper Cretaceous and Paleocene substratum (Monte Acuto Formation and Scaglia) by a pronounced unconformity, and is represented almost entirely by slope and base-of-slope deposits. It is the result of the margin collapse of an Early Eocene carbonate platform and of its Cretaceous Paleocene basement, followed by the installation and progradation of a nummulite platform over the adjacent basinal deposits. It consists of the following formations. (1) Grottone Megabreccia. The basal lowstand systems tract is a m thick megabreccia consisting of several channelized bodies separated by amalgamation surfaces. The Grottone Megabreccia records a series of catastrophic debris-flow episodes resulting from the dismantling of a Cretaceous and Early Eocene platform (lowstand systems tract). (2) Peschici Formation. This is a thick succession (350 m) of graded breccias and calciturbidites alternating with pelagic marlstone onlapping (marine onlap) a huge scar on the underlying Scaglia (Fig. 8), deeply eroded into the late Turonian early Campanian strata (Bosellini et al. 1993b). This large hiatus has also been recognized offshore (De Alteriis and Aiello 1993). (3) Punta Rossa Limestone. This is the Eocene basinal (proximal) facies, consisting of chalky, whitish and thin-bedded lime mudstone. There are several m thick calciturbidites within the succession, which appears to be characterized by frequent truncation surfaces and discordances (slump scars). (4) Monte Saraceno Limestone. This is the uppermost unit of the sequence and is represented by clinostratified, coarse calcarenites and rudstones, consisting entirely of Nummulites and Dyscociclinidae. In places, floatstones rich in branching corals, gastropods, and bivalves occur. This unit can be interpreted as a proximal slope with small patch reefs growing on the deeper margin and is probably related to a forced regression (lowstand shelf edge); in fact, no progradation of the system is observed, as it should be in case of depositional regression. PROCESSES AND EVENTS CONTROLLING MARGIN ARCHITECTURE: DISCUSSION In this section, the various geological processes and events (Fig. 9) that punctuated and gave rise to the sequence stratigraphic architecture of the platform margin will be analyzed and discussed. The Valanginian Drowning Unconformity Physical relationships and age determination of the sedimentary succession clearly document that the Apulia Platform, moderately prograding during the Late Jurassic Valanginian p.p. interval, was stopped in its evolution in the early Valanginian and then onlapped by basinal sediments (Maiolica 2) (Bosellini and Morsilli 1997). According to all available paleontological data (Chiocchini 1987; Barattolo and Pugliese 1987; De Castro 1987; Parente, personal communication), the age of the uppermost part of the shallow-water carbonate platform in Apulia and southern Apennines is Berriasian earliest Valanginian, whereas the Gargano onlapping basinal succession is early Valanginan at the toe of the slope (Calpionellites Zone) and

7 EVENT STRATIGRAPHY OF THE APULIA PLATFORM MARGIN 1247 FIG. 9. The various events that controlled the sequence stratigraphic architecture of the Apulia Platform margin along the Gargano transect. O.A.E. column after Jenkyns (1991). progressively younger upward (latest Valanginian early Hauterivian; subzone NC4a of Bralower 1987). We can therefore infer a hiatus from a minimum of less than 1 Myr at the slope toe to a maximum of 6 Myr toward the top of the platform. The Late Jurassic was a time of rapid subsidence and widespread platform growth on the margins of the central North Atlantic and of the Ligurian Ocean (western Tethys). However, these carbonate platforms were drowned and their growth suddenly interrupted during the Valanginian. This phenomenon and the associated drowning unconformities are well known in a large part of world, from the Caribbean to eastern Arabia. The Valanginian drowning is documented (see references in Bosellini and Morsilli 1997) in: (1) the western continental margin of the Atlantic Ocean (Scotian Shelf, Baltimore Canyon, Caribbean); (2) the eastern continental margin of the Atlantic Ocean (Iberia, Morocco); (3) the western peri-alpine domain, i.e., the northern and western continental margin of the Ligurian Ocean and the margin of Iberia (southern France, Helvetic Alps, Estremadura, eastern Prebetic and Betic areas); and (4) the margins of the Adria Plate (Apulia Platform). Recently, additional data have been presented by Stoll and Schrag (1996). According to these authors, strontium-isotope data from the deep ocean (Blake Bahama Basin, off the eastern coast of United States) from an interval spanning 7 million years in the Berriasian Valanginian would imply that global sea level fluctuated about 50 meters over time scales of 200,000 to 500,000 years. Interpretation of widespread episodic synchroneity in carbonate platform ecologic behavior is controversial (Föllmi et al. 1994). Besides eustasy, proposed mechanisms include widespread eutrophism (Hallock and Schlager 1986), globally increased tectonic movements (Eberli 1991), large-scale oceanic anoxia (Vogt 1989; Schlager and Philip 1990; Jenkyns 1991; among others), and pulses in ocean-crust formation (Mullins et al. 1991). As documented in other carbonate platform during the same time (Schlager 1991, 1998; Erlich et al. 1993; Föllmi et al. 1994), the Valanginian relative sea-level rise was associated with an environmental crisis that reduced the potential growth of the previously healthy platform. However, the Apulia carbonate platform had a position beyond the reach of terrigenous sediments; it was isolated and clean, at least during Valanginian time. In conclusion, the worldwide Valanginian drowning unconformities and sea-level fluctuations suggest some kind of eustatic mechanism (glacioeustatic, geoidal eustasy, pulses in ocean-crust formation, etc.), which can also be invoked for the onlap geometry and associated drowning unconformity observed in the Gargano. The Aptian Albian Anoxia The Apulia Platform and the adjacent slope suddenly became inactivate during the early Aptian (Figs 4, 6). This event coincides with a relatively abrupt change in open marine sedimentation: the pelagic (and cherty) coccolith-rich, white lime mudstones of the Maiolica 2 Formation are overlain by marly and shaly sediments, the so-called Scisti a Fucoidi Formation. This pelagic unit is widespread along the southern continental margin of the Tethys ocean and is characterized by a well developed cyclicity expressed by limestone marlstone couplets and by redox rhythms (Erba 1992; Tornaghi et al. 1989; among others). In the Gargano, the Scisti a Fucoidi Formation has a thickness of m and consists mainly of marls and marly limestone. Two organic-carbon-rich black shales are scattered within the Albian tract of this unit (Cobianchi et al. 1997; Cobianchi et al. 1999). Because the base of the Scisti a Fucoidi Formation is early Aptian, there seems to be no hiatus in the slope-to-basin setting. The hiatus shown in Figure 4 on the platform top is inferred and not really detectable on a biostratigraphic basis. The onset of deposition of the Scisti a Fucoidi Formation, so rich in marls and with episodic organic-carbon-rich black shales, was clearly not related to the sedimentary dynamics of the Apulia Platform. Aptian Albian units equivalent to the Gargano Scisti a Fucoidi are well known from the southern Alps to the Apennines (the Umbria Marche basin is the type locality) (Arthur and Fischer 1977; Cresta et al. 1989; Bersezio 1992), and Greece (Skourtsis-Coroneou et al. 1995) and Cretaceous anoxia events occurred on a global scale, related to worldwide oceanographic and climatic conditions (Schlanger and Jenkyns 1976; Jenkyns 1980, 1991; Arthur et al. 1990; Bralower et al. 1994). During the Cretaceous five anoxic events took place in the ocean (Jenkyns 1991). Oceanic Anoxic Event 1 (O.A.E. 1), subdivided into OAE 1A, 1B, and 1C, occurred during the late Barremian interval and continued through the Albian, O.A.E. 2 during the Cenomanian Turonian transition and O.A.E. 3 during the Coniacian Santonian interval (Arthur and Schlanger 1979; Jenkyns 1980, 1991; Bralower et al.

8 1248 A. BOSELLINI ET AL. FIG. 10. The amphitheater-like contact between the Monte S. Angelo Megabreccia and the adjacent Lower Cretaceous platform carbonates. 1) Monte Spigno Formation; 2) Monte Sacro Formation; 3) Monte degli Angeli Formation; 4) Mattinata Formation; 5) Scisti a Fucoidi Formation; 6) Monte S. Angelo Megabreccia; 7) Monte Acuto Formation; 8) Monte Saraceno Sequence; 9) Quaternary deposits; 10) erosional unconformities; 11) paraconformable sequence boundary; 12) faults. 1994). Large amounts of organic carbon were deposited and preserved in the marine sediments as the result of the development of poorly oxygenated waters and the expansion of the oxygen-minimum zones. As suggested by Jenkyns (1991), a particularly thick column of deoxygenated water developed in the Umbria Marche Ionian deep-water basin and was carried onto the adjacent carbonate platforms during the various Cretaceous transgressions. This water lapped onto the Apulia Platform and fostered regional deposition of carbon-rich facies (Scisti a Fucoidi Formation). Causal mechanisms of changes in atmospheric CO 2 concentrations and greenhouse intensity, globally increased carbon transfer rates into the sedimentary reservoirs, global positive 13 C excursion, rise in nutrient input into the oceans etc., and concomitant sea-level rise are extensively discussed by Föllmi et al. (1994) and Drzewiecki and Simo (1997). However, exact relationships between rising sea level and anoxia, and the source of oxygen-depleted waters, remain problematic (Jenkyns 1991). It is not our intention to solve this problem here: we present only data and it is reasonable to infer that the early Aptian drowning and retreat of the Apulia Platform might be associated with the deposition of the Scisti a Fucoidi Formation. Because this unit appears to be the result of specific worldwide oceanographic and climatic conditions, we suggest a causal link between the platform standstill and the Aptian Albian poorly oxygenated marine waters. The Late Albian Cenomanian Collapses According to our field observations (Bosellini et al. 1993a, 1993b), the Monte S. Angelo Megabreccia is the result of major collapses of the platform margin that occurred in the late Albian Cenomanian interval during a time span of about 6 Myr (Neri and Luciani 1994). At least three superimposed megabreccia bodies can be distinguished in the northern Gargano area, whereas to the south there is a single amalgamated megabreccia unit. As visible in plan view (Fig. 10), the geometry of the contact between the megabreccia and the adjacent Lower Cretaceous platform carbonates is an amphitheater-like feature, and this rules out the presence of a paleofault as suggested by previous authors. But this is not the only indentation observed along the edge of the Apulia carbonate platform; there are several other scalloped features (Bosellini et al. 1993b, fig. 13). For example, a large scallop that incises the almost rectilinear Apulia Platform margin, has recently been identified by Bosellini and Morsilli (1994). This reentrant, which grossly corresponds to the present-day Lake of Varano (Fig. 11), is in part sutured by Cretaceous breccias and megabreccias and by a thick Miocene succession. Supported by detailed geologic mapping and by several stratigraphic data, Bosellini and Morsilli (1994) believe that the depression that accommodates the Lake of Varano originally was a submarine slide scar of Cretaceous age resulting from a large-scale platform collapse. It is well known (Crescenti and Vighi 1964; D Argenio and Mindszenty 1991, 1992; Mindszenty et al. 1995) that pronounced exposures of the shallow-water platforms occurred over the entire southern Apennines and Apulia during the mid-cretaceous. Accarie et al. (1988) document a Cenomanian unconformity in the Maiella Mountain, some 150 km northwest of Gargano, with karst cavities penetrating into the Lower Cretaceous substratum for about 50 meters; hiatuses associated with the bauxite horizons are included within the late Albian early Cenomanian interval. In the Matese mountains, Ruberti (1993) documents two gaps, the lower one extending from the middle Albian to the Cenomanian p.p., the upper one corresponding to the lower middle Turonian. Hiatuses extending from the Albian p.p. to the early Cenomanian are also reported by Carannante et al. (1992) from various platform sections in the Campania region. Recently, Mindszenty et al. (1995) reviewed the general problem of the mid-cretaceous emergences of the southern Apennine carbonate platforms and of the associated bauxite and paleokarst horizons and unconformities. Their conclusion is that the rather monotonous story of the Cretaceous carbonate platforms is interrupted by two major regional unconformities, one of them Albian Cenomanian, the other Turonian. According to Crescenti and Vighi (1964), the age of the Gargano bauxites is Turonian, whereas the Gargano collapses and megabreccias are late Albian to Cenomanian (Neri and Luciani 1994). Therefore, they are coeval with the older bauxite and paleokarst horizons. However, quite recently, it has been shown (Grötsch et al. 1993; Fernández-Mendiola and García-Mondéjar 1997) that a late Albian phase of global karstification is present in many carbonate platforms of the world (Slovenia, Mid-Pacific guyots, Venezuela, Basco- Cantabrian basin, etc.). It should be ultimately related to a short-term regressive transgressive cycle with an amplitude of more than 100 m. General stratigraphy and geology demonstrate that the Gargano collapse events were coeval with a general emergence of the southern Apennines and Apulia and of many carbonate platforms around the world (Grötsch et al. 1993). Therefore, it is tempting to consider a relative sea-level lowstand as the triggering mechanism. The generalized mid-cretaceous emersions of the southern Apennines and Apulia carbonate platforms have been interpreted by many authors (D Argenio et al. 1987; D Argenio and Mindszenty 1991, 1992; Bosellini 1989; Eberli 1991; Mindszenty et al. 1995) as the

9 EVENT STRATIGRAPHY OF THE APULIA PLATFORM MARGIN 1249 FIG. 12. The pelagic interval ( transgressive systems tract ) overlying the Monte S. Angelo Megabreccia and abruptly overlain by gravity-displaced debrites ( highstand system tract ). The erosional contact represents the downlap surface of the prograding depositional system of the Monte Acuto Formation (Monte S. Angelo Manfredonia road). be related to seismic shocks associated with the incipient uplift of Apulia, which culminated with its generalized emersion in Cenomanian and Turonian times. In conclusion, the result of this story is that the classic sequence stratigraphic organization of a slope-to-basin succession can simply derive from platform dismantling. In fact, margin failure interrupts carbonate production by bioconstructors or by sedimentary processes (oolite and skeletal sands). After megabreccia accumulation ( lowstand systems tract ) and before the margin is recolonized, there necessarily follows a period of starvation along the entire slope and base-of-slope tract: pelagic, thin-bedded sediment accumulates on the lowstand megabreccia, simulating the transgressive systems tract and the associated condensed section (Fig. 12). Finally, once margin deposition resumes, sediment export starts and the entire system begins to prograde again ( highstand systems tract ). FIG. 11. The Varano Lake (A) is a morphological feature inherited from a large scallop (B) of the Cretaceous Apulia Platform edge (modified from Bosellini and Morsilli, 1994). 1) Monte Spigno Formation; 2) Monte Sacro Formation; 3) slope and basin deposits; 4) depositional platform edge; 5) erosional margin. foreland reaction to distant plate collision (lithospheric bulge). We are also in favor of a tectonic origin for the Gargano megabreccias for several reasons, including: (a) no major karst or bauxite horizon seems to be present in the platform interior during the late Albian to Cenomanian; (b) it is well known that the Albian Cenomanian emergence resulted in a karstbauxite surface, and this dissolution process is not expected to generate sediment export to the basin; on the contrary, the adjacent basin should be in starved conditions (see Bosellini 1993); (c) the megabreccia boulders do not show any sign of previous exposure and karstification (vadose cements, red color, terra rossa, etc.); and (d) the Cenomanian Turonian time is a period of enhanced sea-level rise and platform drowning all over the world (Haq et al. 1987; Schlager and Philip 1990). We believe that the triggering mechanism of the Gargano collapses might Santonian Campanian Retreat of the Platform Margin The highstand deposits (coarse bioclastic calciturbidites forming progradational lobe cycles) of the Monte S. Angelo 1 Sequence of the southern Gargano area are overlain quite abruptly by pelagic cherty limestone (Scaglia 2, Fig. 4). This is a wedge-shaped unit with a maximum thickness of m, thinning upslope and inserted as a Scaglia 2 tongue within the Monte Acuto Formation. On the basis respectively of planktonic foraminifers and nannoplankton, this pelagic unit has been referred to the Santonian early Campanian by Neri and Luciani (1994) and to the late Santonian by Laviano and Marino (1996). There seems to be no hiatus between the sequences Monte S. Angelo 1 and 2 in the basin setting. Upslope, however, erosional hiatuses responsible for the omission of the whole G. elevata zone (about 3 Myr) locally occur. The pelagics are characterized upslope by 1 5-m-thick platform-derived megabreccias, commonly deeply channelized, by isolated platform olistoliths up to 4 5 m in size, by massive breccia and paraconglomerates derived from cannibalization of slope-to-basin deposits (pelagic lime mudstone, chert, and calciturbidites), and by slumpings and slump scars, resulting in significant hiatuses, recognizable biostratigraphically (Neri and Luciani 1994). The Scaglia tongue marks the base of the Monte S. Angelo 2 Sequence and is overlain by a succession of coarse calciturbidites, about 150 m thick, the base of which can be referred to the early Campanian p.p. It testifies to a retreat of the margin and a strong reduction in platform productivity, although the presence of bioclastic turbidites within the unit indicates that the carbonate factory did not stop entirely. Because impressive

10 1250 A. BOSELLINI ET AL. gravity processes affected the slope and the platform margin, we tend to believe that a simple rise in sea level cannot completely account for them. A significant landward retreat of the margin of the Apulia platform during early Campanian times is also recorded in the Fasano Ostuni area, some 200 km to the southeast (Murge, Fig. 1) (Luperto Sinni and Borgomano 1989; Pieri and Laviano 1989; Guarnieri et al. 1990; Luperto Sinni 1996a; Luperto Sinni and Reina 1996a, 1996b) and in the Adriatic offshore (De Alteriis and Aiello 1993). The pre-campanian platform margin is located a few tens of kilometers offshore, whereas the Campanian margin is documented about 5 10 km inland of the present-day coastline. It is not clear what kind of mechanism controlled such a transgression: tectonics or eustasy. According to Simo et al. (1993), a prominent sequence boundary (seaward shift of the coastal onlap followed by fast transgression) is recorded at the Santonian Campanian transition in carbonate successions in a number of very different paleogeographic settings, such as the Caribbean, Western Europe, Adria, and North Africa, thus suggesting a primary eustatic control. However, the frequent occurrence in the discussed stratigraphic interval, both in Gargano and Murge areas, of megabreccia lenses, olistolith swarms, and significant gravity-displaced slope-to-basin deposits suggests that downfaulting and local tectonically induced collapses may have been important mechanisms in the platform retreat. Further data are required, especially from Murge, to solve the problem, but it seems reasonable that the intraplate stress controlling the Albian Cenomanian collapses was still at work during Santonian Campanian time. The Middle Eocene Collapse The last depositional sequence of the Gargano succession is the Monte Saraceno Sequence. It is separated from the underlying Upper Cretaceous and Paleocene substratum (Scaglia and Monte Acuto Formations) by a pronounced unconformity associated with a major erosional hiatus (Fig. 4). The age of Eocene catastrophic event is bracketed between the Morozovella trinidadensis zone (Danian; age of the youngest sample of the underlying sequence) and the Morozovella lehneri zone (middle Lutetian; age of upper pelagic chalk). The presence of nummulites of probable Lutetian age in the matrix of the basal megabreccia confines its age to the initial Lutetian or the top of the Ypresian, a time (between 49 and 45.5 Myr) of a major lowstand event, according to Haq et al. (1987). We must admit, however, that the timing of the Grottone Megabreccia is based on the presence of very poorly preserved nummulites. Moreover, the biostratigraphic dating by this fossil group certainly does not allow resolution at the Myr range. The extent of the associated hiatus may vary from to more than 40 Myr in the eastern Gargano (see Fig. 4), where the Peschici Formation, dated as mid-lutetian, disconformably overlies the Scaglia Formation, the uppermost part of which is Coniacian in age (Marginotruncana sigali zone) (Bosellini et al. 1993b). The Eocene was a time of general uplift and subaerial exposure of Apulia and present-day southern Adriatic Sea. A major unconformity at the top of Cretaceous carbonates is documented by outcrops, well data, and seismic data (De Dominicis and Mazzoldi 1989; Colantoni et al. 1990; De Alteriis and Aiello 1993; Argnani et al. 1993). It is worth noting that this unconformity is present in all offshore wells of the Adriatic, suggesting that the uplift was associated with the foreland bulge of the west-verging Dinarides Hellenides thrust belts (Gambini and Tozzi 1996). Once again, a classic sequence stratigraphic succession the Monte Saraceno Sequence is the result of a tectonic relative sea-level fluctuation. CONCLUSIONS The long-term event stratigraphy of the Apulia Platform margin and slope along the Gargano transect is punctuated by five major events. These events subdivide the succession into six second-order sequences and constitute the framework of its stratigraphic architecture. (1) Valanginian drowning unconformity. Physically visible as an onlap of basinal sediments onto the Jurassic Berriasian platform slope, this abrupt sea-level rise is documented worldwide, from the deep ocean to the Atlantic continental margins, Iberia, Alps, etc. It is reasonable to infer that some kind of eustatic mechanism (glacio-eustatic, geoidal eustasy, pulse in ocean crust formation, etc.) is responsible for the onlap geometry and the associated drowning unconformity observed in the Gargano. (2) Early Aptian Albian drowning and demise of the platform. This event is coeval with the onset of deposition of the Scisti a Fucoidi Formation in the basin. This unit, rich in organic deposits and black shales, records several global Cretaceous anoxia events. We suggest (cf. Jenkyns 1991) that a particularly thick column of deoxygenated water lapped onto the Apulia Platform and fostered regional deposition of carbon-rich facies. As a result, the carbonate platform factory was temporarily turned off, giving way to a substantial drowning and retreat of the platform system. (3) Late Albian Cenomanian collapse. The slope and base-of-slope settings of the Gargano are characterized by huge megabreccia bodies and other gravity-displaced deposits. According to detailed field work, these megabreccias are the result of major collapses of the platform margin and are coeval with a general emergence of the southern Apennines and Apulia and of many carbonate platforms of the world (Grötsch et al. 1993; Fernández-Mendiola and García-Mondéjar 1997). Because no data indicative of a previous exposure have been found in the megabreccia elements, however, it is suggested that the triggering mechanism of the Gargano collapses could be related to seismic shocks associated with the incipient uplift of Apulia, which culminated in its generalized emersion in Cenomanian and Turonian times. This uplift was the result of foreland reaction to distant plate collision (Mindszenty et al. 1995). (4) Santonian Campanian retreat of the platform margin. This is the less well documented event. A m-thick pelagic tongue inserted into the bioclastic calciturbidite and breccia slope succession testifies to a retreat of the margin and a strong reduction in platform productivity. A significant landward retreat of the Apulia Platform margin, both in the Adriatic offshore and in southern Apulia, is also documented. (5) Eocene uplift and platform-margin collapse. A major erosional unconformity separates the Middle Eocene (Lutetian) bioclastic turbidites from the underlying Upper Cretaceous or Paleocene pelagics. The Eocene was a time of general uplift and subaerial exposure of Apulia and the present-day southern Adriatic Sea, most probably related to the foreland arching of the west-verging Dinarides-Hellenides thrust belts. We hope that our data on the Gargano stratigraphy will be regarded as a further contribution to construct a global stratigraphic template for Cretaceous chronostratigraphic correlation. ACKNOWLEDGMENTS The authors gratefully acknowledge reviewers Karl Föllmi, Robert W. Scott, and Helmut Weissert for very helpful and constructive comments. The careful editorial work by John B. Southard is very much appreciated. Financial support was provided by grants from the Italian Consiglio Nazionale delle Ricerche (CNR Grants , , ). 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