FACIES 36 37-56 PI. 11-16 4 Figs. ERLANGEN 1997 Platform Margins, Microbial/Serpulids Bioconstructions and Slope-to-basin Sediments in the Upper Triassic of the 'Verbicaro Unit' (Lucania and Calabria, Southern Italy) Anna Climaco, Maria Boni, Alessandro lannace and Valeria Zamparelli, Napoli KEYWORDS: PLATFORMCARBONATES - INTRAPLATFORMBASIN - TURBIDITIC CARBONATES - ORGANIC RICH FACIES - REEFS - MICROBIALITES- SERPULIDS - CALABRIA(SOUTHERN ITALY) - UPPER TRIASSIC SUMMARY margin with buildups and related basinal sediments exists. These sedimentary and paleoecological features match The Upper Triassic carbonates of the area comprised well with those found in the intraplatform basins of the between Maratea (Lucania) and Praia a Mare (Calabria) Dolomia Principale, as well as with other coeval facies in have been studied. They have been grouped into six Southern Apennines, Central Apennines, Southern Alps facies assemblages which, in turn, define two depositional and in Southern Spain. Altogether, this evidence suggests systems: that in the Norian time both Southern Alps and Apennines 1) a platform margin depositional system, compris- experienced a very similar tectonic evolution and compara- ing algae- bivalves- bearing dolomites (A1), Megalo- ble paleoceanographic conditions, characterised by the for- dontid-bearing limestones and dolomites (A2), dololutites mation of numerous intraplatform throughs with restricted and stromatolitic/bioclastic dolomites. (A3); circulation, the latter influencing the bottom conditions as 2) a slope to basin depositional system comprising: well as the marginal communities. The margins of these buildup-facies, talus breccia and coarse to fine doloarenites restricted basins, differently from the typical Dachstein (B1), coarse to fine doloarenites and dark laminated reefs of the Upper Triassic Tethys, were dominated by dololutites (B2), dark laminated dololutites (B3). microbial-serpulid communities. The algal and bivalve dolomites represent typical peritidal platform sediments arranged in cyclical pat- 1 INTRODUCTION terns formed as shoal barrier and back-reef deposits periodically emerged and deformed in tepee structures. In the present paper we will concentrate in detail on the The outer margin of the platform was colonised by subject of the Upper Triassic platform to basin transition in peculiar bioconstructions dominated by microbialites Northern Calabria and Lucania. This subject was firstly and serpulids; little sponges occur less frequently, whereas raised by our research group after the recent discovery of rare corals have been found only in some turbiditic beds. slope facies in these regions (IANNACE et al., 1993), and Along the slope, in a distance that can be estimated shortly accounted for in a previous contribution (IA~rnACEet in 5 or 6 km, the coarse breccias give way to coarse al., 1994). This paper, mainly based on the Ph.D. thesis of turbidites, then finer turbidites and finally to dark, A. CuraACO (1996), gives a complete description of the organic-rich micrites. Most of the floatstone and associ- Upper Triassic of the area comprised between Maratea ated turbidites imply a fault- controlled slope. The (Lucania) and Praia a Mare (Calabria). laminated texture and the high O.M. (Organic Matter) Despite the strong tectonic disturbance and the low bio- content of the latter facies quite obviously point to a stratigraphic resolution, a highly diversified depositional basin with poorly oxygenated bottom waters. system has been put into evidence in the whole area, which In the uppermost Triassic there is an indication of a changes radically theprevious simplepaleogeographic models regressive trend, evidenced by the progradation of the based, during Upper Triassic, on a monotonous, long last- platform facies. At that time a back-reef area was char- ing history of peritidal sedimentation. acterised by Megalodontid prairies alternated to areas of A similar evolution of thoughts has already occurred in sandy bioclastic transport. However, due to the poor the geological knowledge of Upper Triassic of Southern biostratigraphic record and intense cataclasis, no defi- Alias and Central Apennines, where the formerly believed nite evidence of a well-structured Rhaetian platform peritidal dolomites of Upper Triassic age (Dolomia Principale) Address: Dr. A. Climaco, Prof. Dr. M. Boni, Dr. A. Iannace, Prof. Dr. V. Zamparelli, Dipartimento di Scienze della Terra, Largo San Marcellino, 10, 1-80138 Napoli; Fax. 39 - 81 - 552 56 11 38 have been demonstrated to contain also sediments depos- authors in several areas and interpreted as bioherms, but ited in tectonically controlled basins (JADOULet al., 1992). the bulk of the dolomites was generally referred to shal- Therefore, with the data presented in this paper we would low water, lagoonal environment. A distinction between like to stress that a common tectonic and paleogeographic darker and lighter carbonate facies was also observed history was experienced during Upper Triassic in most (BURTON, 1971, p. 53), butno interpretation was proposed sedimentary domains now represented in many Italian for the fact. carbonate successions. The presence of marginal stromatolitic bioconstructions was also indicated by D'ARGE~aO (1966) but this first 2 GEOLOGICAL SETTING mention, based on limited outcrops, was never followed by extensive research. According to the "Structural Model of Italy" (B~GI et Subsequent research works in the area only dealt with al., 1991), the following tectonic units can be recognised regional or applied geology aspects (A~ODIO-MORELtJet in the Miocenic Apenninic nappes of northern Calabria al, 1976; IE~O et al., 1992), never paying more than a and Lucania (from bottom to top): cursory attention to the sedimentology of Upper Triassic - San Donato Unit; dolomites. - Alburno-Cervati Unit; Only very recently, following the work of IAN~CE - Verbicaro Unit. (1991) in the Lattari Mountains, where many different - Frido Unit types of Norian-Rhaetian platform marginal facies have The Frido Unit consists of metasediments of oceanic been described, was proposed that margin-to-slope facies affinity. The first three units mostly consist of carbonate had eventually to occur also in the Verbicaro succession successions deposited on the Apulian passive continental of Northern Calabria (IAr~ACE, 1993): in fact, this as- margin during Meso-Cenozoic. sumption was confirmed shortly later (IANNACE et al. The San Donato and Alburno-Cervati Units, separated 1993, 1994). by a normal fault (BARBIERI et al., 1984), consist of Triassic to Miocene sediments deposited in a carbonate 4 METHODOLOGICAL REMARKS platform environment (BOUSQUET& GRANDJACQUET,1969; D'ARGF.~aO et al., 1973; AMODto-MORELLIet al., 1976). The stratigraphic and sedimentologic investigation of The Verbicaro Unit rests tectonically over both the the Upper Triassic facies in Calabria has been limited San Donato Unit and the Alburno-Cervati Unit (Fig. 1). It quite significantly by the effects of the strong tectonic was defined by BOUSQUET• GRANDJACQUET(1969), and activity characterising most of these successions, coupled comprises the dcaille de Praia a Mare, (recognised by with the traditionally poor biostratigraphic content of the GRANDJACQUET, 1961) and other similar successions more platform carbonates of this age. to the south, formerly believed to be parautochthonous. In fact, thick, continuos successions are rare through- This unit has been interpreted as resulting from the defor- out the whole area and generally limited to platform mation of transitional domain between a carbonate plat- facies. In these kind of facies, the fossil content only form to a basin, unknown in outcrop (D'ARGEr~O et al., allows a very broad differentiation between Lower-Mid- 1973). However, this conclusion has been based only on dle Norian and Upper Norian-Rhaetian, the latter marked the Jurassic to Paleogene part of the succession because by the appearance of Triasina hantkeni (see below). No the significance of the Triassic sediments was never local marker has been found to allow a correlation based addressed in detail. on purely lithologic or 'event stratigraphy' criteria. The situation is even worse for the slope facies. The 3 PREVIOUS STUDIES well bedded nature of these carbonate facies made them highly susceptible to be affected by numerous shear planes The widespread occurrence of Upper Triassic (Norian- and pervasive brittle fracturing. In fact, many extensive Rhaetian) dolomites, comparable to the Hauptdolomit outcrop areas consist of cataclastic, deeply eroded, dark (Dolomia Principale) of the Alps, has been known in dolomites, sometimes developing calanchi features. northern Calabria (Southern Italy) since the end of the last For these reasons, the field investigations have been century (CORTESE, 1895). conducted with different degrees of detail in distinct Particularly, the papers of CORTESE (1895) and DI areas: hundreds of m of platform successions have been Sa'EFANO (1904), despite some stratigraphic discrepancies, measured at m scale, whereas fragments of slope facies and related disagreement between the two authors, are the successions have been surveyed at a dm scale (Fig. 2). first source of objective descriptions and sound data, Total thickness evaluations in the platform facies can be which can still be successfully used in modem research. only affected by the presence of normal faults; on the The extensive geological mapping performed in the contrary, an exact evaluation of the thicknesses