FACIES
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ERLANGEN 1999
Depositional System and Response to Sea Level Oscillations of the Senonian Rudist-bearing Carbonate Shelves. Examples from Central Mediterranean Areas Gabriele Carannante, Napoli, Roberto Graziano, Roma, Gerardo Pappone, Napoli, Daniela Ruberti, Caserta and Lucia Simone, Napoli KEYWORDS: PERI-TETHYAN CARBONATE PLATFORMS - 'FORAMOL' (TEMPERATE-TYPE) CARBONATE OPEN SHELVES AND SLOPES - RUDISTS - SEA LEVEL CHANGES - ITALY - CRETACEOUS (SENON1AN) CONTENTS
Summary 1 Introduction 1.1 Purpose Geological framework 2 2.1 Pre-depositional settings 3 The Senonian open shelves as sediment source areas 4 Senonian shelf-to-basin transition: sediment characteristics and dynamics of the depositional settings 4.1 Sardinia marginal-distal ramp successions 4.2 Apulia slope successions 4.3 Southern Apennines tectonically controlled marginal-to-slope successions 4.3.1 Matese Group 4.3.2 Alburni and Monti della Maddalena Groups 5 Results and general discussion 5.1 Senonian foramol open shelf-to-basin depositional system and facies model 5.2 Transgressive-regressive trend in the Senonian foramol depositional systems 5.3 Response of the Senonian foramol systems to relative sea level changes 6 Concluding remarks SUMMARY
In the Late Cretaceous the carbonate platforms modified the organization of their depositional systems owing to vast and complex geologic events. In this view, detailed analyses have been made on Senonian shelf-toslope rudist-bearing limestones resting on pre-Coniacian erosive surfaces or slope facies in the Nurra region (northwestern Sardinia, Italy), in the central-southern Apennines and in the Gargano area (central-southern Italy). The main characteristic of the analyzed deposits is the spreading of rudists in a context of foramol-type calcite-dominated benthonic sediment-producer communities.
The reconstructed Senonian depositional environments match a large complex of unprotected shelves that produced loose, diagenetically stable mollusc-dominated bioclastic debris which were not involved in significant in situ cementation processes. High energy episodes led to repeated and more or less total remobilization of the sedimentary sheet. On the shelves, both storm- and wind-induced currents and waves exercised a strong driving control on the sedimentary arrangement of the shifting biogenic sediments. The latter constituted large coalescing sheets of winnowed, loose, fine-to-coarse skeletal sands. Sandy sediments were easily involved in remobilization processes across the shelves toward the redepositional sites. Transport modality largely depended on the granular composition of the sediments. The early and almost continuous sweeping of the finer fraction (bioeroded-derived silt) resulted in an effective pre-sorting of the skeletal debris stored in the Senonian open shelf settings. In situ preservation potentiality of the produced skeletal material was low and huge amounts of sands may have concurred in forming slope aprons. In the studied successions a two-stage evolution is documented during the Senonian. All over the latest Turonian-early Campanian interval the rudist-bearing shallow neritic platforms retreated, with seabed opening and deepening, and an underfeeding of the slope occurred. Probably, only where rudists strongly dominated the shelf assemblages (as in the case of the southern Tethyan carbonate platforms), their relatively high rate of bioclastic sediment production and supply might partially compensate for the increased accommodation space reducing the effects of the early Senonian transgressive phase. - In the late Senonian a huge amount of foramol skeletal sands prograded over the upper slope by means of impressive -
Addresses: Prof. Dr.G.Carannante (e-mail:
[email protected]), Dr. G.Pappone (e-mail:
[email protected],na.cnr.it) and Prof. Dr.LSimone (e-maih
[email protected]), Dept. Scienze della Terra, Universita 'Federico If', Largo San Marcellino, 10, 80138 Napoli, Italy. Fax: +081/5525611; Dr.R.Graziano, Servizio Geologico d'Italia, via Curtatone, 3, 00185 Roma, Fax: +064465159; Dr.D.Ruberti (e-mail: ruberti@gmso l.geomare.na.enr.it, Dept. Scienze Ambientali, II Universit~ degli Studi di Napoli, via Arena 22, 81100 Caserta, Italy. Fax: +08231326535.
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>>> Fig. 1. Simplified tectonic and palaeogeography frame of the Italian peninsula (A)'and synthetic geologic maps of the studied regions
(B, C, D, E). A - Location map of the studied areas (B to E) in a simplified geologic sketch of Italy showing the actual distribution of the northern and southern Tethys-derived continental margin terrains; a) Northern Tethys continental margin complexes; b) oceanic remnants (ophiolites) including pelagic covers and overlying flysch deposits and melanges; c) Southern Tethys continental margin complexes; d) Austroalpine domain; e) peri-sutural basins (foredeeps and post-orogenic deposits); tO major thrust fronts. B - Schematic geologic map of the Nurra region (Sardinia): a- continental, red quartzose sandstone and conglomerate (Permian-Triassic); b- paralic deposits (Triassic) and oolitic and bioclastic shallow-water limestones and dolostones (Triassic-Early Cretaceous) showing an Urgonian facies starting from the early Valanginian; c- shallow water rudist-rich limestones locally passing to slope facies (Senonian); d- trachytic and andesitic ignimbrites (Oligocene-Miocene); e- alluvial and eolian deposits (Quarternary); f- main fault. C ~ Schematic geologic map of the southern Gargano region: a- oolitic and bioclastic shallow water limestones (Malm-Aptian); b- rudist-rich limestones of the platform-to-slope transition (Cenomanian-Turonian); c- slope limestones rich in displaced rudist debris with subordinate hemipelagic/pelagic intercalations (Senonian); d- foraminifer-rich limestones of the platform-to-slope transition laterally passing to basinal pelagites (Middle Eocene); e- alluvial deposits (Quaternary); tO main fault. D - Schematic geologic map of the Matese Group. a- oolitic and bioclastic shallow water limestones and dolostones (Early Liassic-Eafly Cretaceous); b- main bauxite outcrops; c- rudist-rich limestones of platform-to-slope transition (Senonian); d- mainly siliciclastic and carbonate deposits of the Apennines foreland and piggy-back basins (Miocene.-Eafly Pliocene); e- alluvial and lacustrine deposits (Quaternary); f- main fault; g- thrust. E - Schematic geologic map of the Alburni and Maddalena Groups. a- shallow water limestones and dolostones (Late Triassic - Early Liassic); b- pre Senonian c- rudist-rich limestones of platform-to-slope transition (Senonian); d- siliceous and carbonate, mostly pelagic, deposits of the Lagonegro Basin (Triassic - Eocene); e- siliciclastic deposits of the Apennine foreland and piggy-back basins (Miocene and Pliocene); f- alluvial and lacustrine deposits (Quaternary); g- main fault; h- thrust. gravitative flows suggesting that main depocenters moved down-slope. The persistence of healthy, producing foramol open-shelves may be inferred by the occurrence of compositionally coherent displaced skeletal sands even if reduced findings of late Campanian-Maastrichtian shallow water limestones are known characterized by a clear upward shallowing trend. A reduced accommodation space in shallow water settings may have enhanced the high off-bank sand dispersion via an increased winnowing action exerted on loose foramol-bioclastic sediments in periods in which the shelf tops were exposed to intense current winnowing. The generalized down-slope migration of the main depocenters occurred during the late Senonian regressive phase. Owing to the peculiar characteristics of the foramol-type open shelves (e.g., physiography, sediment production and composition), the sediment distribution patterns of the Senonian rudist-bearing carbonate factories and their response to sea level fluctuations were strongly modified with respect to the commonly accepted carbonate platform
chlorozoan standard model. Major progradational episodes of marginal sands occurred during both relative lowstands and terminal highstands of sea level. During transgressive phases only where the sediment production was sustained (southern Tethyan carbonate platforms), the rudist-bearing depositional systems might have dampened the typical drowning tendency of the foramol open shelves. 1 INTRODUCTION In Cretaceous times changes in climate, oceanographic circulation, sea level, tectonic and volcanic activity contributed in triggering widespread crises events that resulted among others in world-wide anoxic episodes, drastic facies variations, diffusion of bauxite deposits ( ARTHURt~ FISHER, 1977; JENKINS1980; GRACIANSKYet al. 1986; BARRON, 1987; VOGT, 1989; CARANNANTE et al., 1995; D'ARGEN10 & MINDSZENTY, 1995; PREMOLISILVA & SLITER, 1995). Such changes cannot have been ineffective in controlling the development of the depositional systems and particularly of
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the sensitive carbonate platforms which might be forced to modify their organization. Among these changes, which characterized different stratigraphic intervals during the Cretaceous, CARANNANTZet al. (1995; 1997) described a significant change in the shallow water carbonate sedimentation along the peri-Tethyan margins during the early Senonian (Coniacian-Santonian transition), a time in which minor anoxic events occurred, restricted to small areas in epeiric and marginal peri-Tethian domains (BOSELUNtet al., 1978; JENKINS,1980) and nearly euthrophic conditions seem
to have prevailed in the pelagic domains (PREMOL!SILVA SLrrER, 1995). During the early Senonian in the neritic domains, sediments characterized by assemblages dominated by rudists with variable amounts of red algae, benthonic foraminifera, bryozoans and echinoids replaced sediments with hermatypic corals, chetetids and green algae (chlorozoan association) (CARANNANTE& SIMONE, 1987; CARANNANTEet al., 1994b; 1995; 1997). This latter association was widely present in the previous carbonate-shelf contexts during the Jurassic to early Cretaceous times,
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becoming subordinated and even disappearing in younger deposits that often transgressed on previously tectonically emerged terrains. Calcite-shelled assemblages prevailed in the replacing limestones, the compositon of which does not match that of the well-known recent tropical carbonate deposits. An ongoing debate concerns the definition of similar 'unconventional' ancient carbonates. Their grain composition and sedimentary features recall some recent pure skeletal calcareous deposits characteristically present in cool and temperate seas. In these relatively cooler carbonate depositional areas ('temperate-type' carbonate platforms) carbonate sediments accumulate with peculiar characteristics which strongly differ from that of the tropical-type carbonate platforms. As a consequence, the related ancient skeletal deposits have been frequently reported as 'temperate', 'non-tropical' or 'cool-water' limestones (see also JAMES & CLARKE,1997). A good definition is still lacking and this does not strictly concern the topic of this paper. However, according to our opinion, owing to the wide distribution of these skeletal deposits (up to very low latitudes) depending on complex and interplaying ecological factors, a simple compositional definition (for terminology see LEES& BVLLER, I972; CARANNANTEet al.,I988b among others), devoid of any interpretative implication, appears, at the moment, the most objective. The studied late Cretaceous skeletal deposits mainly contain molluscs and benthonic foraminifera. Green algae and hermatypic corals (chlorozoan components in LEES & BULLER, 1972) are very rare or not significant at all. Lowlight adapted (sciaphile) organisms (red algae and bryozoans among others) are accessory sediment contributors. The environmental significance of the distinct groups may vary in relation to their abundance and characteristics. As a consequence we can define these lithofacies as foramol-type lithofacies (foramoi s e n s u lato). In late Cretaceous carbonate depositional places, the change in dominating assemblages ultimately resulted in carbonate factories with strongly modified sedimentologic characteristics. 'Temperate-type' carbonate open shelves developed v e r s u s the earlier'tropical-type' ones. The change in biologic factors triggered a modification in sediment production and availability on the shelves. Consequently a change in the supply of the sediment to the neighbouring depositional areas, characterized by different dispersal patterns, can be hypothesized, Times and modalities of the offshelf transport along these late Cretaceous carbonate shelf margins might be peculiar according to the shedding characteristics of the foramol, 'temperate-type' carbonate shelves (see CARANNANTE& StMONE, 1988; CARANNANTEet al., 1994b; 1996; BETZLERet al., 1997; JAMES,1997; JAMES& CLARKE, 1997).
1.1 Purpose In this report we discuss the sedimentological and stratigraphical characterization of Senonian rudist-bearing deposits in platform-to-slope settings with examples from some central Mediterranean areas (Fig.I). Environmental
and palaeoecological evolution is emphasized starting from pre-Senonian times, and a new picture of relationships between platform and slope in this context is evidenced. The resulting depositional model is tested with respect to the responce of the system to sea level fluctuations with main enphasis on the ongoing debate concerning similarities and/ or peculiarities between carbonate and siliciclastic depositional systems related to relative sea level changes (SARG, 1988; SCHLACER,1991; HUNT& TUCKER,1993; SCHLABERet al., 1994, among others). Their response to sea level oscillations is sometimes considered opposite (cfr. SCHLACER, 1991; HUNT& TUCKER, 1993), but examples of important carbonate off-bank flushing and gravity-related transfers from the platforms are reported in relation to sea level lowstand episodes (cfr. BOSELLtNI, 1989; SHANMUCAN& MOIOLA, 1984; JAQUINet al., 1991; SPENCE& TUCKER,1997, among others) according to the general siliciclastic response model (cf. JERVEY, 1988; POSAMENTmRet al., 1988; JAMES, 1997). Some problems may have derived from having considered different behaviours with respect to sea level oscillation in carbonate platforms which show a different characterization (e.g.'tropical' v e r s u s 'temperate-type'). Some of these problems can be solved taking into account that temperate-type, foramol carbonate sediments display a different response to sea level changes than tropical ones do, as pointed out by some Authors (CARANNANTEet al., 1988c; 1996; CARANNANTZ& SrMONE,1988; SLMONE& CARANNANTE, 1988; SHLA~ER,1992; FEARY& JAMES,1995; B ETZLERet al., 1997 among others). In this perspective, following detailed studies focused on the Senonian shallow water, rudist-bearing limestones from the Nurra region (northwestern Sardinia, Italy) and the central-southern Apennines and on their environmental significance (CARANNANTE& SIMONE, 1987; RUBERTI, 1991; CARANNANTEet al., 1993; 1995; 1997), a comparative analysis has been made on their reworked counterpart in the transition-to-basin depositional settings preliminarly described in the Apulia region and the southern Apennines (PAPPONE, 1990; GRAZIANO, 1992; 1994; RUBERTk 1993) (Fig. 1). The sedimentary record in some of the studied regions pertaining to the undeformed or slightly deformed foreland domains (Sardinia and Apulia regions) shows lateral continuity in shelf-to-basin transition areas. On the contrary, in the trust belt domains (Apennines chain) the Mesozoic to Tertiary shelf-to-basin transitional areas have been affected by severe neogenic tectonics leading to the obliteration of original stratigraphic relationships. At any rate, a careful facies analysis supported by an improved biostratigraphic and structural analysis and event stratigraphy correlations constrained the Senonian investigated geologic records, allowing the stratigraphic reconstruction of local successions. 2 GEOLOGICAL FRAMEWORK During the Mesozoic times, the investigated depositional areas (Fig. 1) pertained to different palaeogeographic domains at the northern (Sardinia) and southern (Apennines and Gargano) Tethyan continental margins (Fig.2). Com-
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Fig. 2. Paleogeographic reconstruction of the Mediterranean Tethys at 100 Mybp (simplified after GEALEV,1988), the starting point of the carbonate platform geologic evolution discussed in the present paper, a) southern Tethys continental margins (APPA: Apulia-Pannonian Plate; AF: Africa Plate); b) northern Tethys continental margins (IB: Iberian Plate; EU: European Plate; RHO-MO: Rhodope-Moesian Plate); c) oceanic crust; d) central Turkey Plate (derived from "a" during Jurassic times); e) oceanic subduction fronts; f) active spreading ridges; g) dormant spreading ridges; 1) Nurra region; 2) Gargano region; 3) centralsouthern Apennines. mon stratigraphic and environmental evolutions in such differentiated palaeogegraphic contexts may suggest the evidence of large scale controls on the observed stratigraphic record. The studied successions correspond to areas with different post-depositional histories. Sardinia represents part of the main European foreland that, starting from the Oligocene, was affected by extensional tectonics leading to the opening of a complex rift system including the Sardinia, Valencia, Algero-Proven~al and Tyrrhenian rifts. The Algero-Provenqal and Tyrrhenian rifts finally evolved towards the oceanic floored basins of the western Mediterranean and the Tyrrhenian seas respectively. On the other hand, the Apennino-Gargano region forms the bulk of both the more internal part (Tyrrhenian side) and the external (Adriatic side) of the central-southern Apennines thrust and fold belt. The Gargano promontory pertains to the relatively undeformed southern Apennine foreland. Deformation of the central-southern Apennines carbonate platforms and related basinal areas started during the Miocene times and stopped in the early Pleistocene. The intensive shortening between the different tectonic units makes it difficult to restore the pristine palaegeographic relationships.
2.1 Pre-depositional settings Related to a'middle'-Cretaceous tectonic activity (CHERCH~ & TR~MOUgRES, 1984) and/or gentle tectonic updoming
('lthospheric bulges' s e n s u CLOETHING,1986 in D'AROENIO & Mn~DSZF~TY, 1995) which affected the peri-Tethyan areas, a major and complex stratigraphic break, accompanied by bauxite deposits occurred on both the opposing Tethyan margins ('tectonically enhanced unconformity' s e n s u JAQUIN et al., 1991). In Sardinia an angular unconformity separates the Upper Cretaceous cover from the underlying pre-bauxite deposits. These latter are Jurassic dolomitized limestones or Lower Cretaceous non-restricted shallow water limestones rich in molluscs, corals, chetetids, benthonic foraminifera and green algae ('Urgonian' facies). In the Apennine-Apulia region bauxitiferous gaps linked to longlasting exposure episodes characterize the uppermost Albian- Turonian neritic sequences at different stratigraphic intervals (CARANNANTE et al., 1988a; 1994a and references therein). The related preSenonian limestones, rich in molluscs, green algae and corals, were deposited in a more protected platform setting (cfr. PAVAN• PtRINI, 1965; LUPERTOSINNI& MASSE, 1986) and underwent multiple and complex ephemeral emersion episodes. In the Gargano Promontory good evidence of marginal to slope settings is documented in the Cretaceous limestones. There, an early Cretaceous prograding platform-tobasin system related to a low-angle depositional slope is replaced by a Cenomanian-Turonian depositional system controlled by large scale tectonic tilting triggered by transient lithospheric bulges (GRAzIANO,1992; 1994; MINDSZENTY et al., 1995). Cenomanian-?Turonian marginal sediments are characterized by high-energy rudist limestones passing downslope to grain-supported bioclastic turbidites and debris flows (GRAZIANO,1994). Transitional slope to basin settings are also documented in the central-southern Apennines where some of the studied Senoninn carbonate transitional successions appear to have formdll in complex and structurally-controlled physiographic settings. This is indicated by the widespread occurrence of angular uncontbrmities between the base of the Senonian slope deposits and their upper Triassic to Cenomanian substratum which consist of shallow water deposits. More particularly, in the Matese, the Alburni, and the Monti della Maddalena Groups slope successions are characterized by remarkable discontinuity related to both erosional and nondepositional processes and sharp lateral facies variations (PAPPONE, 1990; RUBERTI, 1993). In addition, impressive calcareous lithoclastic breccia wedges up to some hundred meters thick occur below the Senonian slope deposits. Minor breccia intercalations still occur in the Senonian limestones. All these characteristics may suggest a synsedimentary tectonic whose effects, controlling the substratum morphology, must have driven the dispersal and stacking patterns of the overcoming deposits.
3 T H E SENONIAN OPEN SHELVES AS SEDIMENT SOURCE AREAS Shallow water rudist-bearing sediments were laid down on the pre-existing peri-Tethyan shelves and related exposure surfaces during a significant transgressive event start-
Fig. 3. Depositional model of the Senonian rudist-bearing foramol open shelves strikingly contrasting with those deriving from chlorozoan, 'tropical'-type carbonate platforms. Labels illustrate the location and distribution of main sedimentary processes (italics) and lithofacies. The peculiar features of the foramoI benthic assemblages which patchily dwelled in loose substrata resulted in the lack of real limiting reefs at shelf margins. This enhanced the water circulation on open depositional places exerting a driving control on the sedimentary arrangement of the shifting biogenic sediments which constituted large coalescing sheets of winnowed fine-to-coarse skeletal sands. The foramol bioclastic fraction, mainly produced by intensive bioerosion acting on mainly diagenetically stable calcite-shelled organisms, blanketed most of the open shelf. This concurred to provide the shelf with a huge amount of loose, largely uncemented, silt-to-sand sized bioclastic detritus which was ready to be transported toward the deeper areas. (Based on CARANNANTEet al., 1997).
ing in late Turonian times. In the studied regions, these sediments reflect profoundly changed environmental conditions in the neritic realm (CARANNANTEet al., 1995; 1997; CaRANNANTE& SIMONE, 1987). A general progressive deepening upward trend characterizes these lower Senonian shallow water sequences. In general, transgressive restricted sediments overlie, and sometimes contain reworked clasts of, bauxite. A subsequent evolution to clean, grain-supported deposits of deeper and more open marine conditions is recognizable in the following foramol-type, rudist-bearing limestones. In these limestones with the exception of minor intraclasts and small peloids, non-skeletal grains are absent. Calcite-shelled producers were predominant. Calcified green algae were lacking. This induced a drastic reduction of the amount of the fine fraction (the originally aragonitic mud) that, when present, was essentially bioerosionPlate Fig. 1. Figs. 2-5.
!
derived calcitic silt. Rhodalgal associations (sensu CARANNANTEet al., 1988b) characterized the Sardinia foramol-type successions whereas in the southern Tethys margin foramoltype limestones, red algae and bryozoans occurred only in more marginal and/or upper slope depositional areas (RvB~'n, 1993). The rudist-bearing limestones show a clear predominance of the bioclastic fraction (over 90%) deriving from rudist shell breakdown (RUBER~n, 1991; CARANr~ANTEet al., 1993). These molluscs which did not build real reefs, grew surrounded by their own loose detritus consisting of poorlysorted, bioeroded skeletal fragments. Storm events and currents were active on the Senonian open shelves and swept away the bioerosion-derived finer fractions that accumulated in hemipelagic deposits. In addition, the high energy episodes occasionally remobilized the winnowed and presorted grains sheets resulting in contributions of skeletal
Senonian rudist-bearing carbonate shelves of the Mediterranean area: Sardinia successions. Lower Senonian neritic rudist-bearing limestones (a) passing upward in the sequence (black line) to hemipelagic marly limestones (b). (Graxioleddu area - Nurra region). Upper Santonian-lower Campanian hemipelagic marls in core (4), drilled from the Pala Reale area (Nurra region). Thin skeletal debris (fine sand up to silt in size) intercalations, bioturbation and erosional surfaces are recognizable. Details in thin section photomicrographs Figs. 2, 3, 5. Scale bars 5 mm (Figs. 2 and 5) and 1 mm (Fig. 3).
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grains which could present higher values of roundness and a better sorting. These latter are found as medium to wellrounded bioclastic grainstones intercalated in the shallow water, poorly sorted skeletal sediments. Critical analysis of various papers dealing with Upper Cretaceous shallow waterrudist-rich deposits suggests similar depositional contexts (with only minor local variations) in widely distributed neritic domains of the central Mediterranean area (cf. RlCCHE'I'n,1975; MARIOrn, 1982; ACCORDIet al,, 1987; LUPERTOSINNI & BORGOMANO, 1989; PAPVONE, 1990; Sn~A, 1991; GIovar,e~.u.I, 1992; SANDERS,1996) though locally, low-energy conditions characterized the uppermost Turonian-Campanian at the southern Tethyan margin. There the sedimentary successions are arranged in cycles in a general deepening trend from peritidal to shallow subtidal settings (LuPERTO-SINNI• BORGOMANO,1989; CARANNANTE et al., 1993; BOSELLINIt~r PARENTE,1994; CARANNANTEet al., 1997; RUBERTI,1997). Owing to the decline in the mean aragonite-shelled bioclast producers (VANDEPOEL& SCHLAGER,1994; CARANNANTEet al., 1995; 1997) important controls on the early diagenetic effects in these deposits may be expected, with significant implications for their redistribution fenomena. Early dissolution phenomena might be scarcely represented in the essentially calcite shells, the intragranular cavities of which locally show early calcite cement fillings (Ross, 1991). Owing to its stable mineralogical nature, the bioclastic fraction (fine to very coarse sands) was not or only scarcely involved in early cementation processes. As a consequence, a large availability of loose bioclastic sediments resulted, with a strong impact on sedimentary budget and dispersal patterns of sediments and contributing to produce high dispersion rates. Moreover, the almost total lack of donor
Plate Fig. 1.
Fig. 2.
Fig. 3.
Fig. 4.
Fig. 5. Fig. 6.
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biota able to supply an aragonitic detrital fraction, was to result in an essentiallly calcitic nature of the neigbouring hemipelagic deposits. Sedimentary characteristics and physiographic configuration of the peri-Tethyan Late Cretaceous carbonate platforms (Fig. 3) strongly conditioned the resulting dinamic relationships between sediment source (shelf) and sediment redeposition (slope) areas. 4 SENONIAN SHELF-TO-BASIN TRANSITION: SEDIMENT CHARACTERISTICS AND DYNAMICS OF THE DEPOSITIONAL SETTINGS In the following section, shelf-to-basin transitional successions from selected Mediterranean areas are described: 4.1 Sardinia marginal/distal ramp successions In some localities of northwestern Sardinia (Nurra region) (Fig. 1A) the deepening upward tendency of the lower Senonian, shallow water rudist-bearing limestones presumably reached maximum values. This is indicated by an upwards change to planktonic-rich sediments in marginal shelf/distal ramp sectors which locally show evidences of a synsedimentary tectonic control (CARAr~ANVZet al., 1995; 1997). Graxioleddu: The examined section (PI. 1/1) crops out north of the village of Olmedo (Fig. 1B) in the location of Graxioleddu, near an abandoned bauxite mine. Here approximately 40 m of transgressive Coniacian rudist-bearing limestones (PHILIPet al., 1978; CHERCHI8Z;SCHROEDER,1987) cover a continuous bauxite layer which rests over Berriasian paratic deposits of'Purbeckian' facies. In these limestones,
Senonian rudist-bearing carbonate shelves of the Mediterranean area: Apulia successions. Photo-panorama of the studied lower Senonian transitional succession cropping out about 2 Km south of the village of Monte S. Angelo (southern Gargano Promontory). The gentle S-SE dipping of the clinoforms (toward the right in the picture) mimics the original basinward deepening of the low-angle slope (no tectonic tilting restoration). The succession is mostly made up of well-bedded rudist bioclastic grainstones and rudstones with minor pelagic intercalations. Drowned upper Turonian proximal, low-angle slope clinoforms. The drowning event is marked by a thinly-bedded, about 7 m thick, upper Turonian-lower Coniacian 'Scaglia-type' pelagic level (b) abruptly overlying the thick intraclastic massive Turonian breccias (a). Pelagites are in turn overlain by Coniacian bioclastic mass-flow grainstones and rudstones (c l) and channelized breccias (c2). (Monte S. Angelo southern Gargano Promontory). Pelagic, 'Scaglia'-type cherty mudstones showing rhythmically-spaced thin bioclastic turbidites. This lithofacies typically occurs at the lower and upper boundaries of the wedge-shaped basinal deposits which interdigitate in the slope apron. 'Middle' Campanian limestones of Manganera (Monte S. Angelo- southern Gargano Promontory). Channelized deeply-scored rudist bioclastic breccias (fig. 5 for detaiI) about 3 m thick cutting into chalky, structureless wackestones-packstones (fig. 6 for detail). The breccia bed, in which rudist debris are largely predominant, shows a chaotic texture and a variable skeletal sandy matrix content. Detail of the basal breccia bed in which large rudist debris are recognizable. Micro facies detail of the structureless silty packstones; the fine-to-medium sized silty bioclastic particles show variable roundness hut entirely derive from rudist shell break-down. Matrix is composed of very fine silty particles seemingly derived from bioerosive processes acting on rudist-rich shelf assemblages. Scale bar 2 ram. Upper Campanian limestones of Coppa Caramanica (southern Gargano Promontory).
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10 skeletal wackestones-packstones with benthonic foraminifera, green algae and rudist fragments rapidly change upward to rudist-rich rudstones and grainstones with chetetids, coralline red algae and bryozoans. Grains appear not abraded and strongly bioeroded. Despite the evidence of intensive bioerosion, the thin bioerosive-derived fraction is lacking, being present only in very limited areas surrounding gatherings of rudists preserved in life position. Occasionally, sedimentary structures in the winnowed and partially remobilized sediment indicate storm and current activity. Upward in the succession, rare planktonic foraminifera and green glauconite grains occur in partially reworked, rudistdominated and bryozoan-rich deposits which underlie hemipelagic marls. The latter crop out with about 30 meters of gray, planktonic-rich deposits, Santonian in age on the basis of the presence of Globotruncana concavata (B ROTZ_Z~) and Sigalia deflaensis (SIGAL)(CHERCHI& SCHROED~, 1987). Oligo-Miocene ignimbrites seal the Cretaceous succession in this locality. Pala Reale: Cores drilled (PI. 1/4) in adjacent areas (Pala Reale near the village of Olmedo, Fig.lB) show a Cretaceous calcareous succession resting over an eroded Jurassic substratum and underlying about 100 m of Oligo-Miocene ignimbrites. A detailed analysis of these limestones attests for more then 150 m of Coniacian-lower Santonian neritic limestones in which rudist debris associate with abundant red coralline algae, bryozoans, echinoids, benthonic foraminifera and some Planktonic foraminifera. Grains are strongly bioeroded, poorly abraded and poorly sorted. Vinculariform bryozoa are particularly abundant in the highest bioclastic grainstones which underlie more then 100 m of blackish marls, rich in sponge spicula, planktonic foraminifera and coccoliths. A late Santonian-early Campanian age (CHERCHI, 1995 pers.comm.) is recognizable on the basis of the planktonic foraminifera among which Globotruncanids, Heterohelix reussi CUSHMAN and Hedbergella delrioensis CARSEV(CHERCHI& SCrmOEDER,1987). These dark (presumably anoxic) hemipelagic deposits show well-preserved thin lenticular bedding with intercala-
Plate Fig. I.
Fig. 2. Fig. 3.
3
Southern Apennines successions. Bioclastic rudstone/grainstone characterized by cm-scale granulometric variations. Grading grain orientation and imbrication, and lamination are common features of such gravitative sandy mass-flows. Upper Campanian-lower Maastrichtian of the Gallo Matese (Matese Mountains). Thin section photomicrograph of the finer laminae of fig. 1. Bioturbation traces and microlaminations are evident. Scale bar 2.5 mm Breccia limestones with poorly-sorted, variously-shaped shallow-water calcareous l ithoclasts (late Turonianearly Campanian in age on the basis of Vaccinites sulcatus presence) in a skeletal matrix. Fine-grained skeletal packstone/grainstone intercalate between the breccia beds with wavy-to-cross lamination (Letino Matese Mountains). Thin section photomigrograph of the breccia matrix of fig. 3. Late Campanian-early Maastrichtian forams (Presiderolites sp.) are present. Scale bar 3 mm Breccia limestones with poorly-sorted, variously-shaped shallow water calcareous lithoclasts (early Cretaceous in age) in a matrix of bioclastic packstone-grainstone. (Brienza, Maddalena Mountains). Thin section photomicrograph of the breccia matrix of fig. 5. Late Campanian foraminifers (Orbitoides media d'ARCmAC) are present. Scale bar 3 mm. -
Fig. 4. Fig. 5. Fig. 6.
tions of fine bioclastic debris levels (PI. 1/2-4) and an abundance of glauconite grains. Erosive surfaces have been locally recognized (PI. 1/5). Core observation hindered the complete reconstruction of these thin intercalations which show distal storm layer and/or diluted microturbidite features. Intercalated between the bemipelagic sediment and the ignimbrite cover, 36 m of coarse bioclastic grainstones follow. They are rich in rudist remains with bioeroded and poorly abraded grains. On the basis of the recognized rich foraminifera association, the sediments are late Campanian in age (CHERCHI, 1995 pers.comm.). Punta Negra: Along the sea, northwest of the village of Fertilia (fig. 1B), 60-70 m of Upper Cretaceous rudist limestones lie over Jurassic (?Oxfordian-?Kimmeridgian) dolomitized limestones. In the lowermost part (8m) of the succession rudist-bearing wackestones-packstones crop out with benthonic foraminifera, green algae and coral fragments. Intensively burrowed clay-rich intervals intercalate in this interval passing occasionally to marls with indeterminable planktonic foraminifera. These limestones rapidly change upward to rudist-rich rudstones-grainstones and silty packstones. Green algae decrease and coralline red algae become episodically present in the Coniacian-Santonian transitional interval. Rudist, red algae and bryozoan fragments finally dominate in the coarse winnowed grainstones made up of poorly abraded skeletal debris which underlie fine grainstones, early Santonian in age on the basis of the foraminifera content (CHERCm& SCHROEDER,1985). A graded breccia follows with angular-subangular, up to 15 cm in diameter, clasts of Coniacian and early Santonian limestones (CHERCHI& TREMOLI~RES,1984). In the matrix, mollusc and red algae fragments, skeletal debris with intragranular green glauconitic infillings and fragments of reddish peloidal crusts are plentiful. A thin marly level with indeterminate planktonic foraminifera separates this graded breccia from a few m thick fine breccia containing in the bioclastic matrix abundant red algae, bryozoa, mollusc and poorly abraded echinoid fragments. Upward in the succession alternations
Plate
3
11
12
of fairly coarse breccias and marly intervals can be found. Finally, ?upper Santonian marls and clays end the sequence. Nannoplancton and planktonic foraminifera contents indicate relatively shallow (not more than 300 m), cold (9 ~ 11 ~ and mesotrophic-eutrophic water conditions (CARANNANTE et al., 1995). Discussion: In the studied successions of northwestern Sardinia, clear lower Senonian transgressive sequence follows the uppermost Turonian?-Coniacian flooding of the complex exposure-linked paleokarst-surface. Major drowning episodes occurred in Santonian-?early Campanian times resulting in the deposition of the planktonic-rich marls with only a minor intermittent supply of bioclastic fraction in marginal, outermost shelf sectors or in tectonized distal ramps. Only in the late Campanian do, neritic carbonate deposits newly settle down in the drowned areas, with clean skeletal sands devoid of pelagic intercalations whereas in outcrops where shallow water conditions persisted (work in progress) the presence of black clasts, microdissolution features and crystal-silt in ?uppermost Santonian-lower Campanian limestones seem to document a later (late Campanian?) fresh to brackish water influx. 4.2 Apulia slope successions Senonian shallow water deposits are present in the Gargano Promontory (Fig. 1A) only in a few, small outcrops (CRESCENTI & V~CHI, 1964; LAWANO & MARCO, 1996). Nevertheless, the widespread colonization of the shelf by foramol sensu lato assemblages can be inferred by the large amount of skeletal debris displaced in Senonian low-angle slope deposits of the southern Gargano Promontory (BoRGOMANO8z PHILIP, 1987; BOSELLINIet al., 1993; Neri, 1993; GRAZIANO,1994; LUPERTOStNNI& BORGOMANO,1994). Detailed studies of some slope successions are reported. Nevara: Along the road cut of the S.S. 89 south of the villageof Monte S. Angelo (Fig. 1C), about 100 m of wellbedded early Senonian slope deposits (PI. 2/1) crop out. Previously described by several authors (GRAZIANO, 1992, 1994; BOSELLINIet al., 1993; NERI, 1993 ; LUPERTOSINNI & BORGOMANO,1994) they have been studied here in detail in order to compare the slope and shelf responses to relative sea level oscillations. In proximal settings, the basal level of the succession is made up of about 7 m of thinly bedded, upper Turonian-lower Coniacian 'Scaglia'-like pelagic mudstones (PI. 2/2) with Dicarinella primitiva DALBIEZ,D. imbricata (MoRNOD) and nannoplancton Marthasterites surcatus in the lowermost samples (LAVIANO& MARrNO, 1996). This pelagic interval forms a recessive key-bed in the slope succession of the southern Gargano Promontory and characteristically pinches out basinward, being presumably eroded downcurrent by the overlying gravitative mass flow deposits in relation to the downdip increase of the erosional processes in a relatively distal part of the transitional areas as a response to increased competence of the flows. The following limestones are almost completely composed of displaced, rudist bioclastic fine to coarse grainstones and rudstones. These skeletal sands and gravels show a wide variability of their sedimentary characteristics. High de-
grees in roundness and sorting are generally associated with medium to coarse sands and gravels partially suggesting inherited features in high-energy, outer shelf settings. In other cases, subangular to subrounded bioclastic sands with bioeroded and poorly sorted skeletal grains may have served as a grainy matrix supporting coarser rudist and gastropod debris. Minor bioclastic components are echinoid and gastropod debris, whereas the occurrence of colonial corals is scattered and only accessory. Only sporadically do skeletal grapestones occur in the above gravitative deposits. Early cements usually consist of isopachous crusts of fibrous to bladed calcite crystals. A detectable amount of soft, usually well-rounded chips up to 2 cm in diameter made up of hemipelagic mudstone and wackestone are present at the base of many beds. Sometimes elongated chips are isoriented and parallel to bedding surfaces showing the occurrence of a laminar flow regimen. Textures and structures of these mainly bioclastic sands testify that they were transported by means of more or less concentrated mass flows. Beds are typically tabular, ranging in thickness from 10 to 150 cm (average value is 40-60 cm), but frequent amalgamation processes, mostly occurring in coarser displaced sediments, may develop thicker, apparently massive bedding. Lensoid morphologies of some beds may be genetically linked to laterally confined flows or channelling processes. In these cases a variable intraclastic fraction lead to the deposition of graded, mostly clast-supported breccias up to 3 m thick with lower erosive boundaries. In other cases, as at the base of the section, subangular to subrounded platform-derived clasts form the bulk of graded breccias filling broadly incised channels. 'Cut and fill' structures are also evident and appear to have eroded well-bedded intercalations of gravitative bioclastic deposits through irregular surfaces. Discontinuous, lenticular bedding originated either by depositional processes (coalescence of multidirectional feeding systems) or intraformational truncation surfaces. In the latter case, these structures have been interpreted as slide scars owing to the occurrence of thinly bedded pelagic/hemipelagic intercalations onlapping the erosive surfaces. The stacking pattern of these gravitative deposits is quite irregular even though a roughly cyclic arrangement of the lithofacies may be observed throughout the ConiacianSantonian (Early Campanian ?) times. NERI (1993) has recognised in this interval a mostly irregular stack of chaotic deposits as well as both coarsening and fining upward cycles whereas BOSELLL~ et al. (1993) estimated their average periodicity in 400,000 years, suggesting their correlation with the Milankovian long-term eccentricity. One of the main features of this Coniacian-Santonian succession with respect to the whole Senonian section is the scattered occurrence of pelagic mudstone-to-wackestone bearing a certain amount o f generally badly-preserved planktonic foraminifera (Marginotruncana coronata BOLU, M. gr. pseudolinneiana PESSAONO, Dicarinella imbricata (MonNOD), D. primitiva (DALBIEZ)in the lower levels and Dicarinella asymetrrica (SIOAL) and Globotruncana gr. linneiana (D'ORBtONY)in the upper ones) presumably deposited by means of a pure fall-out input. This implies that the
13
offbank transport of loose bioclastic sands was not continuous but punctuated by short term breaks. Moreover, these underfeeding (starvation) episodes seem to organize hierarchically the transitional succession in long term cycles having an overall, transgressive trend (GRAZIANO, 1994). Manganera: Along the road cut of S.S. 89, three km south of the village of Monte S. Angelo (Fig.lC), about 130 m of well-bedded upper Senonian slope and pelagic limestones crop out continuing the above-described lower Senonian section. The basal 30 m of the sampled section are composed of up to 1 m thick tabular and lenticular bodies made up of fine to coarse sand-sized white bioclastic grainstones and massive or graded bio-intraclastic rudstones showing channellike features and frequent amalgamation surfaces. All the l ram-to- 1 cm-sized intraclasts cofisist ofsubrounded, often isoriented, chalky hemipelagic mudstones and wackestones whereas bioclastic remains (up to 10 cm) are almost completely composed of rounded to angular rudist and gastropod fragments with a minor amount of echinoid debris. Textures and the almost total lack of distinctive sedimentary structures inside the displaced deposits and their grainy composition suggest the occurrence of granular, often concentrated, both confined and sheet-like mass flows. A rapid fining and thinning upward evolution characterizes the following 10 m of the section which is associated with a more regular bedding and with the occurrence of some white, locally silicified, pelagic mudstones and wackestones up to some dm thick bearing planktonic foraminifers. An early Campanian age may be inferred for them on the basis of the presence of Marginotruncana gr. pseudolinneiana PESSAONO and M. coronata BOLLt in sediments which rest over upper Santonian Dycarinella asymmetrica (StGAL)bearing deposits. Its middle part continues the previous stratigraphic trend with the onset of an almost pure pelagic fall-out sedimentation leading to the deposition of thinlybedded, white 'Scaglia'-like mudstones and wackestones with regularly spaced light brown cherty levels (PI. 2/3), Globotruncanids are represented by Globotruncana gr. linneiana. (D'ORmGNY)and, at the top of this interval, by Globotruncana ventricosa WroTE G, aft. arca (CuSUMAN) indicating on the whole a late early Campanian age. Few turbiditic, normally graded intercalations up to a few cm thick consisting of fine bioclastic sands occur at the lower and upper levels of the pelagic wedge suggesting a relatively gradual transition between feeding and starving regimes of the clinoforms. A sharp coarsening and thickening upward evolution follows, assuming different facies characteristics on the proximal and distal part of the underlying pelagic wedge. On the whole, after a few meters of slumped pelagics, very coarse intraclastic channeled debrites occur followed by coalescing lenticular bodies made up of coarse bioclastic rudstones comprising badly-sorted rudist, pelecypod, and gastropod debris; rare corals have been recognized. This interval, up to 15 m thick, is followed by at least 70 m of tabular and lensoid beds consisting of chalky, very fine-tocoarse bioclastic grainstones-to-rudstones arranged in mostly massive and more rarely normally graded beds (10 cm - 2 m). Pelagic and hemipelagic deposits are virtually lacking in the
upper part of the studied section and the finer sediments observed are composed of silt leading to the identification of some silty packstones. At the very base of these displaced deposits downlapping the pelagic wedge, a thin bentonitic level is present in a pelagic intercalation (GRAZtANO & ADABBO,1996) bearing Globotruncana (Globotruncanita) calcarata (CusHMAN)and G lobotruncana ( Globotruncanita ) conica W m ~ suggesting a late Campanian age. Further biostratigraphic data are lacking but a Maastrichtian age may be inferred by the overlying displaced bioclastic deposits. Discussion: The incipient flooding of the Turonian clinoforms by the upper Turonian-lower Coniacian pelagic intercalation could seemingly be correlated with the flooding of the longlasting exposure-linked paleokarst surface which characterizes the Turonian unconformity in the neritic sequences of the Apulia-Gargano area (GRAZIANO,1992; 1994). Overlying gravitative deposits show a transgressive trend entirely covering the Coniacian-lower Campanian interval. Slope facies characterization seems to be controlled mainly by an intermittent supply of bioclastic fraction which tends to reduce and finally stops with a deposition of'Scaglia'-like pelagic sediments in the (early?) middle Campanian when a sharp increase in the previous transgressive trend characterized some sectors of the Apulia region with partial drowning of the platform-to-basin transition (LuPERTOSINNI et al., 1988; LUPERTOSINNIt~ BORGOMANO,1989; GRAZIANO,1994; LUPERTOS~NI & BORGOMANO,1994). According to GRAZIANO (1994) this flooding seems to represent the response to a regional tectonic stress-field in a main Senonian-Thanetian transgressive-regressive cycle. The following regressive upper Campanian-Maastrichtian phase is testified by prograding slope facies sharply downlapping cherty pelagites ('Scaglia') deposited on the slope during the previous middleCampanian flooding. Displaced sediments (P1.2/4-6) totally lack pelagic intercalations and show a distinct coarsening and thickening upward evolution.
4.3 Southern Apennines tectonicaily-controlled marginal to slope successions The selected upper Cretaceous southern Apennines (Fig. IA) calcareous successions seem to be deposited in complex synsedimentary tectonically-controlled settings. In the related depositional systems, steeper, locally by-pass margins bordered shallow foramol-type carbonate factories (CARANNAN~ et al. 1997). A complex array of Miocene to Quaternary tectonic contacts frequently mask the pristine stratigraphic relationships between shallow water sectors and the related marginal-to-slope ones originally supposed to be adjacent. Two areas will be illustrated where resedimented rudist-rich deposits document marginal to slope settings in areas actually tectonically joined to areas in which rudist-bearing shallow water deposits crop out. 4.3.1 Matese Group The nortwestern sectors of the Matese Group (Fig. 1D) show well-developed Senonian margin-to-slope facies
14
(PESCATORE,1965; Izrro, 1970; ACCORD!et al., 1982). These latter are skeletal limestones rich in rudist fragments that lie on shallow water Triassic and Jurassic limestones/dolostones through the intercalation of discontinuous calcareous breccia bodies in rock fall/debris flow sedimentary facies (RtrBER~, 1993; VEROE, 1997). The breccias mainly contain Triassic up to Cenomanian shallow water calcareous clasts and seemingly pinch-out northward. Rock-fall related megabreccias, composed of larger platform blocks, have been recognized in a narrow area and lie as a coarse talus zone close to the platform margin that is well exposed in the tectonically-joined outcrops of the northeastern sector of the Matese Group. Gallo Matese area: On the southern side of M. Alto, 1 Km north of the village of Gallo Matese (Fig. I D), about 200 m of Senonian skeletal limestones are well exposed, directly resting over Triassic shallow water dolostones. The analyzed succession is characterized by skeletal rudstones/ grainstones and subordinated silty-packestones in which rudist fragments are abundant; other bivalve and gastropod remains are subordinated. Bryozoan and echinoid fragments are also present with micritized red algae debris and badlypreserved benthonic foraminifera among which Lepidorbitoides sp., Orbitoides sp. and Presiderolites sp. Based on their occurrence, a late Campanian - Maastrichtian age may be hypothesized. Skeletal grains are commonly bioeroded, sometimes rounded, graded and close-packed. They appear oriented and locally imbricated. Bed thickness ranges between l0 and 50 cm. In the first few meters of the succession a coarser skeletal fraction prevails together with some shallow water calcareous lithoclasts. Upward in the succession the coarser bioclastic fraction tends to reduce. Beds show an increased silt-sized fraction organized both in thin laminae and discrete layers. Micrograded beds are common. Parallel and subordinate cross lamination is recognized only on a small scale (PI. 3/1,2). Bioturbation traces may locally occur. A main unconformity surface separates the analyzed upper Cretaceous succession from the overlying Eocene (lowermost Cuisian; PIGNATrl,1996 pers. comm.) bioclastic calcarenites with chert layers and nodules. Similar features characterize coeval limestones outcropping in a wide area between the villages of Gallo and Fontegreca with minor local variations. Toward SW (north of Fontegreca), the rudist bioclastic limestones rest over a wedge-shaped breccia and do not excede 60 m in thickness; beds reach 40 cm. Angular and poorly-sorted skeletal grains are more common. Grain orientation, imbrication and lamination are lacking as well as any evidence of finer fraction. Calcareous lithoclasts are periodically present in the lowermost interval of the succession. Toward SE, coarser (up to 15 cm in diameter) calcareous lithoclast-rich layers are repeatedly intercalated in the first I0 meters of the rudist bioclastic succession. Among the lithoclasts the coarser fraction is made up of rudist-rich limestones (rudist shells are fragmented beyond taxonomic recognition) while the smaller ones (no more than 5 cm in diameter) are represented by shallow water limestones early Cretaceous in age. Coarse to medium sized skeletal sands
characterize the following 50 m with minor fine-grained intercalations. The lower Eocene bioclastic calcarenites seal the rudist-bearing limestones in these outcrops. Gravitative mass-flows of clean presorted sands presumably controlled the accumulation of these deposits in a slope setting. The observed differences across the area may reflect variations in the morphology of the paleo-slope, in the distance from the source area, in the sediment supply and in the characteristics of the depositional processes. Letino : In the more eastern sector, 2 km away from the village of Letino (Fig. 1D), along the southern side of Mt. Acerone, about 70 meters of Upper Cretaceous limestones, resting over breccia deposits, are well exposed. They are made up of fining upward breccia beds, 2-3 m thick on the average, with lower erosive boundaries. The multishaped breccia elements are poorly-sorted and rarely subrounded. The smaller (less than 10 cm) calcareous lithoclasts, very similar to the elements recognized in the first few meters of the M.Croce limestones, are Neocomian to Cenomanian shallow water limestones. The coarser lithoclasts (up to 30 cm in diameter) are rudist floatstones in which rudists are often grouped in small bouquets. The presence of Hippurites fortisi (CATULLO),Vaccinites sulcatus (DEFRANCE), Biradiolites angulosus (o'ORBXGNY),indicate a Turonian- early Campanian age for the lithoclasts (PI. 3/3). Coarse to medium sand-sized rudist shell fragments are the bulk of the breccia matrix, with minor bryozoan, echinoid, red algae debris and small micritized lithoclasts. Finer fractions in the matrix are scarce. Orbitoids (mostly Orbitoides media o'ARCHIAC, Presiderolites sp., Lepidorbitoides sp.) in the matrix suggest a late Campanian- Maastrichtian age for these deposits (P1.3/4). The graded breccia beds are overlain by about 10 cm of fine-grained skeletal packstone/grainstone in which wavy- or cross-lamination is common. Collapses of older cemented substrata and their own loose bioclastic cover gave rise to the coarse deposits described above. Discussion: Both depositional characteristics and the lateral thickness variability of the upper Senonian skeletal rudist-rich debrites concur to identify a clear deepening of the slope toward the north where a tectonically joined basinal sequence occurs (Frosolone area). This interpretation is in good agreement with the coherent northward pinching out of the underlying wedge-shaped lithic megabreccia beds which were seemingly grafted on the tectonically controlled, pre-Senonian platform-to-slope transition. On the whole, the bioclastic sediments may represent the result of a huge late Campanian-Maastrichtian off-bank transport constructing a base-of-slope apron settled down along a steep shelf margin (according to a WRIGHT & BURCHE'rTE, 1996 concept) which appear to have been tectonically controlled. The more northern and western successions (the Gallo Matese area) may represent more distal basinal facies with respect to the more proximal facies cropping out in the Letino area (Fig. 4). To date, neither direct evidences of a late Turonian-early Senonian gravitative sedimentation have been found at the very base of the upper Senonian bio-, lithoclastic apron, nor
15
continuous layers) made up of rudist-rich skeletal sands with orbitolinids. A significant planktonic content
(Marginotruncana coronata BOLLI, Marginotruncana pseudolinneiana PESSAGNO,Marginotruncana sigali RZlCHER, Marginotruncana marginata REUSS, Marginotruncana cfmariano-si DOUGLASS,Praeglobotruncana gibba KLAUS Dicarinella imbricata MOgNOD plus forms referable to Helvetoglobotruncana helvetica BOLUand Heteroelicidids)
Fig. 4. Stratigraphic correlations among the Western Matese slope facies deriving from mass-flow trasport processes in a base-of-slope apron setting. The depositional characteristics and the lateral thickness variability of the upper Senonian rudist-rich sandy debrites identify deeper slope conditions toward the north and the southwest in good agreement with the fining out of the underlying megabreccia beds. a) Shallow water limestonesdolostones (Triassic-Early Cretaceous); b) calcareous breccia and megabreccia (pre-Senonian-earliest Senonian?); c) marginto-slope rudist bioclastic limestones (late CampanianMaastrichtian); d) skeletal rudist-rich debrites (late CampanianMaastrichtian); e) bioclastic calcarenites with chert layers and nodules (Eocene); f) unconformity surface.
has a significant pelagic fallout been evidenced. Starvation episodes on the slope correlated with the deepening episodes which characterize the lower Senonian shallow water limestones in the neighbouring outcropping areas (Eastern Matese), may be hypothesized following the ?Turonian breccia collapses. The breccia matrix (badly preserved because of dolomitization and stilolitization processes) could contain, in its upper part, reduced lower Senonian sediment contributions. 4.3.2 Alburni and Monti della Maddalena Groups The Alburni and Monti della Maddalena Groups (Fig. 1E) are part of the southern Apennines thrust and fold belt. These areas appear strongly deformed with discrete but not yet well-estimated shortening. They show well-exposed margin-to-slope carbonate sequences late Cretaceous in age. The related facies overlie shallow water limestonedolostones ranging in age from Trias to Cenomanian. Where Cenomanian-Turonian slope facies occur, they generally are rock fall/debris flow-induced calcareous breccia reaching up to 400 meters in thickness (PAPPONE,1990). Breccia clasts are generally self-supported with a matrix (plus intercalated
testify to a pelagic influx in middle-upper Turonian times. Thickness of the breccia bodies, the wide range of the lithoclast age, characteristics of the stratigraphic gaps (an increase of gaps, both in terms of frequency and width, is recognizable moving from the proximal to the more distal slope sectors, Alburni and Maddalena Mountains respectively) suggest for these areas an intensive syn-sedimentary, pre-Senonian tectonics. Senonian displaced sediments crop out in these areas with rudist-rich skeletal detritus which variously associate with debrites of pre-Senonian lithified limestones. Madonna del Carmine (Alburni Mountains): In the Alburni Mountains outcrops of post-Turonian marginal sequences are rare, limited to lower Senonian limestones of deeper open shelf settings which laterally blend to coeval shallower water limestones. Near the village of Sant'Arsenio along the Madonna del Carmine road (Fig. IE) about 210 m of upper Cretaceous neritic limestones crop out (PAPPONE, 1990). Here, 150 m of massive grainstones and subordinated packstones, the skeletal constituents of which are almost esclusively medium to fine rudist debris, underlie 40 meters of rudist-bearing limestones in which beds rich in complete rudist shells (Plagioptychus paradoxus MATHERON,Jerinella klinae PEJOVlC,Biradiolites angulosissimus D'ORBIONY, Vaccinites taburni GUlSCARm,Hippurites colliciatus WOODWARD, among other), often in growth position, intercalate. Some bed boundaries are enhanced by sharp (erosive?) surfaces and flattened lens-shaped layers are recognizable. In the sediment, mostly made up ofbioeroded, poorly-sorted rudist debris, accessory contributors are calcareous spongiae, bryozoans, red coraIline algae and benthonic foraminifera among which Dicyclina schlumbergeri MUr~mR-CHALMAS. A peloidal fraction, with variable skeletal and intraclastic content, characterizes beds of fine-grained grainstones whereas coarser skeletal grainstone intercalations have rounded, medium to well-sorted grains. Planktonic foraminifera (Hedbergella mouthensis OLSON, Globotruncana linneiana D'ORBIGNY,Globotruncanita stuartiformis DALBIEZ, Hetrohelicids among other) become significant at the top. On the basis of the above fossil content a Turonian?- early Senonian age may be inferred for these rudist-bearing limestones which reach a late Santonian-Campanian age in the last more open, planktonic-bearing interval. In adjacent areas about 20 m of neritic upper Campanian rudist-bearing limestones (on the basis of the presence of Siderolites vidali DoUvmLf~and Orbitoides cf tissoti SCHLUMBERGERamong others), devoid of planktonic foraminifera crop out. Moldic cavities geopetally filled by crystal-silt seem to indicate a fresh water diagenesis apparently related to a later shifting of the water table in a sediment which contains a few corals.
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Crocifisso di Brienza (Maddalena Mountains): In the central sector of the Maddalena Mountains near the village of Brienza (Fig. IE), in the locality of 'Monte il Crocifisso', a thick breccia succession crops out. Here, resting over the pre-Senonian breccia wedge, 130 m oflithoclastic rudstones and minor floatstones crop out. Beds are 30 to 70 cm in thickness. Calcareous lithoclasts range from 10 to 50 cm in diameter and are angular to subangular in shape: among the constituents Giurassic and lower Cretaceous shallow water limestones are common (PI. 3/5). The breccia matrix is skeletal grainstone which shows, at the base, an abundance of coarse, well-rounded Caprinid fragments. In the upper part, skeletal grains in the matrix reduce their size. They are essentially made up of rudist fragments, from subrounded to angular in shape, with a limited contribution of bryozoans, benthonic foraminifera and red algae. Orbitoides media D'ARCHIAr is present (PI. 3/6) in the sediment that locally shows a peloidal and/or silty component. 170 m of thinner stratified (from 20 to 50 cm) lithoclastic grainstones and rudstones follow. Lithoclasts may reach up to 15 cm in diameter and are included in a matrix of fine bioclastic sand. Skeletal grains are from subrounded to angular, the latter appear very poorly abraded. Small planktic wackestone clasts are sporadically present. Rudist debris prevail among the constituents which contain Stomiosphera and Siderolites calcitrapoides LAMARCK. Thin intercalations of greenish marls characterize the central part of this interval. Upward in the succession, 50 m of thin stratified (5-10 cm) bioclastic and peloidal grainstones-packestones follow. Thin levels of greenish marl showing slump deformations at the top intercalate in this interval. Bioclastic grains are scarcely bioeroded and frequently rounded. Among the constituents rudists, echinoids, bryozoans, red algae, sponge, benthonic foraminifera (among which Lepidorbidoides sp., Orbidoides cf tissoti SCHLUMBERGER,Orbidoides media d'ARcHIAC, Omphalociclus macroporus LAMARCK,and Siderolites calcitrapoides LAMARC~.A planktonic component has been also found with Globotruncanita stuartiformis DALBIEZ and Globotruncana linneana D'ORBIGNY, On the basis of the fossil content a late CampanianMaastrichtian age is inferred for the breccia limestones that originated from impressive gravitative flows. From the bottom to the top of the section, lithoclasts tend to reduce both in size and in frequency and bedding becomes thinner and thinner. 50 m of poorly stratified grainstones to rudstones, Eocene in age, end the succession. Serra Capurso (Maddalena Mountains): In the southern sector of the Maddalena Mountains, 2 km northwest of the village of Paterno (Fig. 1E), near Serra di Capurso, 270 m of Cretaceous slope sediments crop out resting on upper Triaslower Lias paralic dolostones. In the Cretaceous succession about 230 m are massive calcareous breccia with bioclastic matrix. Planktonic foraminifera associate in the upper strata (among them Helvetoglobotruncana helvetica BOLLIdocuments a middle Turonian age). On this pre-Senonian breccia wedge, a few meters (about 10-15) of bioclastic sediments follow in which breccia levels diminish until they disappear; the sediment forms graded lamines of silty packstones passing to silty wackestones and silt. Skeletal fragments are
largely rudist debris from medium to fine in size. The silty thin intervals contain planktonic foraminifera, among which Dicarinella sp. suggests a ?latest Turonian-early Senonian age. Finally 40 m of well-stratified bioclastic grainstones follow, made up essentially of rudist debris. Well-rounded, reworked grains made up of Caprinid fragments and Orbitolinids prevail in the coarse grainstones and silty rudstones characterizing the first meters of the succession which evolves to coarse bioclastic grainstones in which rudist fragments largely prevail. Skeletal grains are from subrounded (the larger ones) to subangular or angular. In the latter, bioerosion may reach significative values. No planktonic foraminifera occur and levels of breccia intercalate only sporadically. Lithoclasts do not exceed a few centimeters in diameter. On the basis of the presence of Orbitoides aft. media D'ARCmAC in the matrix, an upper CampanianMaastrichtian age may be inferred for these displaced deposits. Discussion: Gravitative mass flows displacing pre-sorted sands devoid of pelitic fraction presumably controlled the sediment accumulation in this articulated, tectonically-controlled slope setting. In spite of local variations in deposit stratigraphic architecture, probably due to local tectonic processes affecting the sediment dispersion pattern, some common features can be highlighted: - resting on a pre-Senonian debrite which shows a significant middle-late Turonian pelagic imput, a thin lower Senonian horizon occurs showing evidences of underfeeding up to starvation. This event seems to be correlative with deepening episodes in neighbouring shallow source areas (Madonna del Carmine outcrop). - the above are followed by a huge amount of upper Senonian coarse to fine displaced sediments, usually devoid of planktonic contribution. The thicker section is locally punctuated in its upper interval by marl intercalations suggesting sudden underfeeding episodes. 5 RESULTS AND G E N E R A L DISCUSSION 5.1 Senonian foramol open shelf-to-basin depositional system and facies model Complex arrangements ofunwinnowed, winnowed, partially remobilized and/or resedimented lithofacies have been recognized in the studied outcrops. The related winnowing and remobilization processes acted on shelves the margins of which, depending on the depositional, erosive and/or tectonic controls, might be more or less steep. These Senonian foramol carbonate factories were characterized by a low in situ preservation potential of the produced bioclastic debris (CAR~N,~'~ et al., 1997). As a consequence, neither aggradation above the wave base level nor progradation of the tidal fiat occurred and cohesionless gravity flows, induced by storms and increased current activity, might easely transport sediments offshore (shelf sweep) from marginal areas of the shelf. Bioclastic sands reached the slope as more or less concentrated granular mass-flows and biosilt was presumably exported off-shelf by means of more continuous downslope sinking of sediment-charged waters, similar to in the sediment-charged thermoaline waters described by
17
McGPo~IL& CANNES,(1983) and WltSON & ROBERTS(1992) and variously termed as 'lutite flow' or 'cold-water cascade'. It is interesting to note that this process is particularly favoured in temperate to cold climate and/or conditions thus constituting a coherent conceptual link according to the temperate-type characterization of the Senonian open shelves. More recently, WiLsON& ROBERTS(1995) defined as'density cascading' all these hyperpycnal (high density) off-shelf waters flows. With respect to gravitative mass-flows, perhaps there actually exists too proliferating nomenclature about both deposits and processes. In addition, little effort has probably been made in order to delineate the peculiarity of carbonate sandy mass-flows. Both the particular hydrodynamic behaviour of skeletal grains (induced by porosity, bulk density and variable morphology) and the low cohesive strength of lime fine fractions (NAYLOR, 1980; KEm'ER & SCHLAGER,1989) suggest that a particular caution is necessary and a rearrangment should be attempted regarding carbonate mass-flows. Recentely 'sandy debris flow' has been used for a wide range of problematic massive submarine sands (SHANMUGAN, 1996; 1997). Even though introduced for siliciclastic mass-flows having cohesive, very low matrix content, this term could help to define the massive carbonate sands which evidence having been transported by laminar fluxes and not sustained by turbolence. These Senonian rudist-dominated shelves were characterized by a low aggradation rate despite quantitative calculations about rudist growth rate carried out on Senonian Radiolitidae of the Mediterranean Tethys (up to more than 5 cm per year according to STEUBER,1996) which state that a significant sediment production is to be expected for those Senonian shelves in which rudists were largely dominant in the benthonic assemblages (see also SCHUMANN, 1995). From this view point, a differentiation can be made between the studied Senonian limestones of Sardinia and the Apennines-Apulia ones. Sardinia foramol sequences are characterized by abundant coralline red algae and bryozoans and show rhodalgal assemblages (sensu CARANNANTEet al., 1988). Rudists, even if abundant, did not reach total dominance. Thus the Santonian drowning of peripheral sectors of the Nurra carbonate platform may have resulted from the slow growth rate of this carbonate factory that, like many similar carbonate open shelves, showed a drowning attitude (StMoNE & CARANNANTE, 1988). On the contrary, in the southern Tethys margin the coralline red algae and the bryozoans were only subordinate sediment contributors and were limited to the outermost sectors of the shelf. In these southern Tethyan carbonate platforms very peculiar foramol assemblages may be recognized related to the ubiquitous dominance of the rudists. The high production rates of these molluscs presumably reduced the tendency of the open foramol factory to drown, resulting in a more significant skeletal sand availability. Apart from some compositional peculiarities of the sediment, the various Senonian open shelves, suffering different boundary conditions, gave rise to similar shallow water sedimentary lithosomes with coherent internal organization and sediment characterizations. Only the basinward dispersal patterns of the reworked sediments seem to have
suffered the peculiarities of local tectonically-controiled physiographic features. Owing to their physiography (e.g. presence of depositional low-angle slopes and/or distally steepened ramps vs erosive and/or tectonically-controlled steep margins) and sedimentary balance (e.g. more or less high production rate of neritic sediments with a relatively scarce aggradation in shelf setting) an overfeeding of the clinoforms might locally occur, resulting in rapid migration of these carbonate 'foramol' factories toward the basin. Where and when ramp-like slopes persisted, together with a high production rate (Apulia-Gargano Region), slope aprons could easily develop, supported by the occurrence of a continuous linear source of sediment supply. Where complex and tectonically-controlled margins were present in the same high production conditions (southern Apennines), discontinuous successions deposited in by-pass slope setting could develop. Based on sedimentary characteristics of the Senonian Mediterranean Tethys depositional systems (Fig. 5), a depositional model (Fig. 6) has been constructed also taking into account sedimentary as well as stratigraphic features available in the literature for coeval, well-exposed depositional systems of neighbouring areas (CAMOINet al., 1983; Gus~c & JELASKA, 1990; EBERLI et al., 1993; Mtrrn et al., 1996; SANDERS, 1996; SANDERS& BARoN-SZABO, 1997). 5.2 Transgressive - regressive trend in the Senonian foramol depositionai systems The latest Turonian-early Senonian flooding of the previously emerging platform areas reestablished neritic conditions rapidly evolving to open shelf settings during the early Senonian interval. All over the latest Coniacian-early Campanian interval, the rudist-bearing shallow neritic platforms retreated, with sea bed opening and deepening, and an underfeeding of the slope occurred. Only where rudists largely dominated the shelf assemblages (e.g. southern Tethyan margin) their relatively high rate of bioclastic sediment production and supply might have partially compensated for the increased accomodation space reducing the effects of the early Senonian transgressive phase on the sedimentary balance. In some cases, the sediment availability resulted on the slope in stacked piles of reworked sediments with both unorganized or cyclic patterns in a main transgressive trend (see Apulia-Gargano outcrops). In all the marginal shelf-to-slope sectors the early Senonian vacuity or reduced sedimentation was followed by impressive bioclastic supply starting from the middle?-late Campanian when a huge amount of skeletal sands was displaced basinward and prograded over the upper slope by means of repeated and significant gravitative flows in an overall regressive phase. A reduced accomodation space in shallow water settings may have enhanced the high off-bank sand dispersion via an increased winnowing action exerted on loose foramol-bioclastic sediments by water currents in a period in which the shelf tops were exposed to intense current winnowing. Only minor occurrences of late Campanian-Maastrichtian shallow water facies may be found within the Mediterranean carbonate geologic record. They
18
Fig. 5. Composite scheme resuming the overall sedimentary characteristics of the studied shelf-to-basin Senonian 'foramol' depositional systems (in the hypothetical assumption of a stationary configuration): a) qualitative cumulative frequences of the main acting sedimentary processes; b) sedimentary textures of the most diffused lithotypes (in decreasing order); c) main physiographic domains; d) large-scale sedimentary organization of the characterizing lithofacies across the depositional profile. Note that, unlike a given chlorozoan 'tropical-type' platform, the maximum of the neritic sediment productivity curve (1) is located in the shelf core (sites B) and does not correspond to the maximum of the sediment accumulation curve (2). The latter, in fact, is located on the inner/mid ramp (site D) in response to the intense off-bank sediment shedding plus the open physiography of the factory. This sediment budget peculiarity represents one of the major sedimentary and stratigraphic variations with respect to the chtorozoan 'tropical-type' rimmed shelves. Nontheless, it supports the extremely important role of the winnowing/redepositional processes in this open depositional setting (based on CARANNANTEet al., 1994).
19
Fig. 6. Depositional model of the shelf-to-basin transition in the Senonian foramol-type depositional systems. a) off-shelf sweeping and fall-out of shelf-derived fine fractions; b) off-shelf transport of coarse bioclastic sediments (sand-to-cobble sizes) by means of mass-flows. are locally restricted inner shelfdeposits (e.g. Apulia region in RZtNA & LtrezaTo-S~Nz, 1993; Central Apennines in SmNA, 1991). Nevertheless the persistence of healthy foramolproducing open sea beds may be inferred by the occurrence of the compositionally coherent displaced skeletal debris found both in sandy slope sheets and as a matrix in breccia beds. Where steep, tectonic-controlled margins existed, as documented in some Maastrichtian southern Apennines outcrops (e.g., Maddalena Mountains ), presumably they locally precluded the carbonate factory downslope shifting and its related survival. As a consequence, during the terminal relative lowstand, starvation episodes occurred on the slope, resulting in Maastrichtian planktonic-bearing marly limestones which intercalate and succeed to the previous gravitative skeletal ones. Briefly a two-stage evolution has been documented in the sucessions of the studied areas. A general transgressive trend, with a low aggradational-retrogradational tendenc3, characterized the carbonate factories during the late Turonianearly Campanian times (CARANNANTEet al., 1995; 1997) as well as the above-described, related transitional-to-slope areas. Differently a late Campanian-Maastrichtian regressive trend seems to have interested the studied sections in which we can recognize a sharp slope progradation which coherently occured with a shallowing upward evolution in the shelf settings. Similar stratigraphic trends seem to characterize many other areas in the peri-Mediterranean region. Some papers dealing with facies characterization, sediment typology and composition and/or stratigraphic evolution of late Cretaceous successions from the central Apennines (Maiella Mts. in F.BERLI et al., 1993; Marsica Mts. in
GIOVANNELLI,1992), Apulia (Murge region in LUPERTOStNN1 et al., 1988; LUPERTOSrNNI& BORGOMANO,1989) and Dalmatia (Guslc & JELASKA,1990), among others, allow us to recognize some surprising similitudes with the ones discussed above.
5.3 Response of the Senonian foramol carbonate systems to relative sea level changes
The transgressive-regressive characteristics of the above Senonian rudist-bearing limestones both in shelf and slope settings also recall the foramol (temperate-type) open shelf behaviour for what concerns their responses to sea level oscillations. Like foramol-type deposits (see StMONE & CARANNANTE, 1985; CARANNANTE(:~ SIMONE, 1988; NELSON, 1988 and references therein; JAMES& VANDERBORCH, 199 I; JAMES • CLARKE, 1997 and references therein), they built open-shelf settings where sediment source areas gradually merged into the redepositional ones through a ramp-like morphology if no particularly steep margin (tectonically or erosionally induced) existed. On the contrary, chlorozoantype deposits tend to build rimmed shelves with preferentially high angle, well-cemented slopes (WtLsON, 1975; /AMES, I983 among others). These shelves generally evolve according to a drop-off model showing a sharp distinction between source areas (factory) of sediments and their redepositional places. - During the very early transgressive phase both the foramol and chlorozoan carbonate systems may have difficulty in keeping pace with the rapid rise of relative sea levels as demonstrated by various records in space and time by
20
SIMONE(~ CARANNANTE(1988), GRAMMER(~ GtNSBURG(1992), HANDFORD& LOUCKS(1993) and CARANNANTEet al. (1994b). The lagging behind of sedimentation seems to be particularly critical for foramol depositional systems owing to their relatively low growth rate deriving both from a relative reduced productivity and high dispersion rate (CARANNANTE & SL~ONE,1987; StMONE& CARANNANTE,1988; JAMES& VON DER BORCH, 1991; JAMES & BONE, 1994). Drowning events may thus easily occur in wide shelf sectors, as in the case of the Sardinia shelf successions, the related slopes of which underwent significant starvation episodes. When and where foramol platforms succeeded in surviving the incipient drowning, as in the case of Upper Cretaceous rudist-dominated southern Tethyan platforms, they could infill the increasing accomodation space upbuilding with a limited sediment supply only a stack of generally retreating sequences. In some cases higher productive assemblage-related sedimentation could provide the still increasing accomodation space of the late transgressive phase with a fairly increased supply able to upbuild aggradational sequences. On the contrary, it is undoubtedly true that chlorozoan factories tend to aggrade and may sustain a marked progradation, at least along leeward margins, as soon as platform tops are flooded, becoming sites of huge shallow water sediment production and an adequate oceanic circulation occurs (GRAMMER& GINSBURG,1992; HINE& NEUMANN, 1977; HINEet al., I98 l; HANDFORD(~ZLOUCKS,1993). - As is well-known, in both recent and fossil tropical chlorozoan carbonate platforms, sediments accumulate on platform tops as well as on deeper periplatform areas mainly during relative highstands of sea level when off-bank transport of excess sediments assumes greater relevance. The 'highstand shedding' concept of KIER& PILKEY(197 l) which has recently been critically reviewed by Schlager et al. (1994) (see also HINE et al., 1981; KENDALL~(~ SCHLAGER, 1981; BOARDMAN~(~NEUMANN,1984; DROXLER(~ SCHLAGER, 1985; HAAK& SCHLAGER,1989; WILBERet al., 1990; REUMER et al., 1991; GRAMMER& GINSBURG,1992; among others) constitutes one of the most distinct peculiarities of the carbonate depositional system with respect to the siliciclastic one and their responses to sea level fluctuations. On the contrary, a reduced 'highstand shedding' may be expected for the wide and deeper foramol carbonate platforms (NELSON et a1.,1982; CARANNANTE(~ SLMONE,1988; CARANNANTEet a1.,1996; JAMES, 1997). Nevertheless pronounced flushing of sediment might characterize areas with a small or zero subsidence (terminal highstand stages) or with relatively higher productive organic assemblages, as in the case of the Upper Cretaceous rudist-dominated southern Tethyan plat-
forms. Finally, during relative sea level lowstands a subaerial exposure easily occurs on the shallower chlorozoan banks inducing meteoric dissolution and cementation in the aragonite-dominated shallow water lithofacies. Little carbonate sediment is produced by the narrow shallow water belt grafting as a lowstand wedge on older steep platform slopes, and a reduced off-bank sediment contribution may be expected (SARG, 1988; SCHLAGER,1991 ; HANDFORD& LOUCKS, 1993; HUNT& TUCKER,1992). Few reports of sandy lowstand -
shedding exist in current literature (e.g.: SCHLANGERt~ PREMOLI-SILVA,1981; SHANMUGAN• MOIOLA, 1984; Jaquin et al., 1991) being the megabreccia counterparts more often described and probably more diffused (e.g., SANG, 1988; BOSELLINI,1984 among others) as margin collapse and slope failure products (see SPENCE(~ TUCKER,1997 for an updated review). On the contrary, the wide and deeper foramoi carbonate platforms may show evidences of emersion during sea level lowstands only in their shallower inner sectors with only reduced early meteoric dissolution and cementation of the calcite-dominated lithofacies. The usual occurence in 'temperate-to-cool water' foramol depositional systems of gentle slope margins, allows a pronounced basinward shifting across the outer shelf of the bathymetric interval compatible with life of the sediment-donor foramol benthonic assemblages. In such conditions the loose neritic sediments may be more easily remobilized and involved in off-shelf transport episodes to build the gravitative counterparts of possibly large autochtonous lowstand prograding complexes as in the cases of the Sardinia and Gargano regions. This calls for a net 'lowstand shedding' feature providing a clear alternative to the well known 'highstand shedding' concept in carbonate sequence stratigraphy (cf. SCHLAOERet al., 1994 for a detailed discussion). However, an important pecularity should be reported. The foramol factories are generally deeper than the chlorozoan ones. As a consequence, they may result less sensitive to minor sea level oscillations (see also PASSLOW,1997). The generalized late Senonian-Maastrichtian down-slope migration of the main depocenters which characterize the studied foramol sequences is in good agreement with the uppermost Campanian-Maastrichtian restricted deposits gradually replacing open shelfrudist-rich sediments in shallow water settings as well as with the early fresh water diagenetic imprintingon pre-Maastrichtian open shelf neritic deposits (e.g. Nurra Region and Alburni Mountains). From the above, it derives that according to the foramol carbonate system behaviour, the Senonian, rudist-bearing limestones prograded in different contexts. At any rate, major progradational episodes of marginal sands seem to have occurred during the terminal relative highstand and the following relative Iowstand of the sea level according to a general siliciclastic response model. During the transgressive phase, only in areas characterized by relatively high production rates of skeletal particles, these latter partially filled the increasing accomodation space, dampening the typical drowning tendency of the foramol open shelves; neverthless low aggradation and/or retrogradation occurred in these cases, and starvation episodes characterized the neighbouring slopes and basins. This late Cretaceous example emphasizes that the factory ecological features and the resulting sediment composition and dispersal pattern constitute another main factor controlling carbonate depositional systems. As a consequence, they are to be taken into account when using sequence stratigraphy procedures in addition to the well established controlling factors such as sediment supply, eustasy, subsidence and initial depositional profile.
21
6
CONCLUDING
REMARKS
Once the original sequence stratigraphy model as defined by VAlE et al. (1991) and following variations (Haq et al., 1988; VAN WAGONERet al., 1988) had been subdued by diffused criticism and integrations (BURTONet al., 1987; SCHLAGER, 1991, 1993; MIAEE, 1996 among others) a wide sequence stratigraphy nomenclature and models proliferated in order to furnish the most diverse geologic records and large scale stratal geometries with more adeguate descriptions and modelizations by sequential procedures (e.g.: GALLOWAY,1989; HUNT& TUCKER, 1992; POSAMENTIER et al., 1992; POSAMENTIER& ALLEN, 1993; JAQU~ & VAIL, 1995). In recent years various parameters controlling the building of depositional sequences have been discussed and evaluated within the ongoing debate on sequence stratigraphic modelling (e.g.: environmental bias and sediment supply in SCHLAfiER, 199 1, 1993; initial sedimentary profile in JAQU|N & VAIL, 1995, among others). In spite of the fact that several papers predicate a basically similarresponse of both carbonate and siliciclastic depositional systems to relative sea-level fluctuations (e.g.: VAIL et al., 1991 ; JAQUINet al., 199 l, among others) some workers stated that certain peculiarities within them allowed for the construction of different and distinctive sequences and system tracts models foreseeing carbonate facies architectures (e.g.: SCHEAGER, 1991; HANDFORD& LOOCKS, 1993; SCHEAGER et al., 1994; among others). Obviously we do share the conviction that carbonate and siliciclastic systems are intrinsically quite different depositional realms in respect of their inception and sediment production, composition and dispersal. Nevertheless we state that the implications provided to sequence stratigraphy by the carbonate sediment composition resulting from the factory ecological parameters appear to be highly underestimated in current studies. Carbonate sediment composition may be indicative of different scenarios which modern sequence stratigraphy has to face. Similarity or difference in the response to sea level changes between the carbonate and the siliciclastic depositional systems result difficult to understand by using a single standard carbonate model of reference: the chlorozoan tropical model. This latter arises from well-known and documented, but peculiar, depositional settings; as a consequence it cannot be considered completely suitable to represent the variety, complexity and dynamics of different carbonate-producing and depositional areas. On the basis of previous assumptions, it is limiting not to consider, in interpreting ancient calcareous sequences, the occurrence of different types of carbonate factories (e.g. foramol vs chlorozoan) the characteristics of which differ not only in terms of sediment type and production, but also in the related sediment distribution pattern in response to sea level oscillations. ACKNOWLEDGEMENTS We are indebited with A. Cherchi, R. Radoicic, J.S. Pignatti and G. Sirna for their help on stratigraphic analy-
sis. We thank D. Fiorentino who prepared the photographic materials and M. Cardas who helped with the English text. The manuscript greatly benefited from constructive comments by C. Betzler who kindly reviewed the text. Field work and facies analysis of the studies outcrops were provided respectively by G. Carannante and L. Simone (Nurra Region, Sardinia), R. Graziano (Gargano Peninsula, Apulia), D. Ruberti (Matese Group, Southern Apennines), G. Pappone and G. Carannante (Monti della Maddalena and Alburni Groups, Southern Apennines). Financial support was provided by the C.N.R. (Italy) and by M.P.I.40% grants to G. Carannante and L. Simone respectively. REFERENCES
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