MARCO QUINTAVALLE, MARCO TONGIORGI & MAURIZIO GAETANI

Abstract. The lower Vidiakot section (Chitral, Pakistan) comprises the lower part (Yarkhun Formation and the base of the Vidiakot Formation) of the terrigenous complex transgressively overlying the crystalline basement of Northern Karakorum. From this section, 8 of 15 samples contain moderately abundant and poorly preserved acritarchs and rare, badly preserved chitinozoans. Three different palynological assemblages have been distinguished which are referable to the chronological interval early Arenig-earliest Llanvirn.

The presence of Arbusculidium, Coryphidium, and Striatotheca in most samples confirms the paleogeographic attribution of the Northern Karakorum Terrane to the northern Gondwana margin (Lower to Middle Ordovician Mediterranean acritarch Palaeoprovince). Refined correlation with other areas and with the previously studied Ishkarwaz section (upper Yarkhun Valley, Chitral) enables the authors the Yarkun Formation to be dated as early Arenig (British lower nitidus graptolite Zone) to latest Arenig (uppermost graptolite hirundo Zone). The base of the overlying Vidiakot Formation is here correlated with the uppermost hirundo- lowermost artus graptolite Zones (latest Arenig-earliest Llanvirn).

MARCO BALINI, DANIELA GERMANI, ALDA NICORA & EUGENIO RIZZI

Abstract. This area played a key role in defining Middle Triassic stratigraphy. In the nineteenth century the study of several ammonoids collected in the Wengen Formation served as a basis for the definition of the Longobardian substage of the Ladinian. Moreover, during the 1960’s the modern Triassic Lithostratigraphy of Lombardy was founded on sections from this area.

The present study represents the first bed-by-bed sampling of this area and is focused mainly on the Wengen Formation and Pratotondo Limestone. In particular, conodonts were found in both units for the first time.

The age of some Middle Triassic formations is revised:

-the top of the Wengen Formation belongs definitively to the Lower Carnian in a sizeable portion of the study area. The overlying carbonate platform, previously attributed to the Upper Ladinian Esino Limestone, is instead Carnian and is coeval to the Breno Formation in the Southern Camonica Valley.

-the Pratotondo Limestone is dated Late Ladinian/Early Carnian, while the overlying Lozio shale is Carnian.

These new data contradict the equivalence "Wengener Schichten" = Archelaus Zone = Longobardian so common in the literature. We demonstrate that the Regoledanus Zone represents a great part of the Wengen Formation. Moreover, at the top of the Wengen Formation the ammonoid and conodont fauna represents the early Carnian Daxatina or Aon Zone.

The biochronostratigraphic revision of the basinal formations requires modification of both the chronostratigraphic schemes and the paleogeographic history of the lombardian Southern Alps during Ladinian-Carnian time.

ALAN MORO & VLASTA COSOVIC

Abstract. Rudist bivalves thrived commonly in the shallow carbonate platforms of the Cretaceous Tethyan realm. The presence of two vertically separated Rudist assemblages along two well preserved Upper Cretaceous sections of cape Mrlera (southern part of the Istrian peninsula) is interpreted as environmentally induced faunal replacement.

The first succession begins with pelagic limestones, followed by a mixed radiolitid-hippuritid assemblage, and by monogeneric floatstones-biostromes of radioliotids. The lower pelagic unit represents relatively open marine conditions while the uppermost radiolitid unit originated under more restricted marine conditions.

Radiolitid floatstones with rare Gorjanovicia bouquets represent the beginning of the second succession. A mixed radiolitid-hippuritid assemblage, characterised by radiolitid floatstones where rare large Vaccinites individuals occur, replaces the radiolitid assemblages in vertical succession.

In both sections, sea level changes were the most important factor causing the replacement of rudist assemblages. Slight differences between the two successions could be attributed to differences in submarine topography. Radiolitids and hippuritids might have occupied different biotopes within subtidal environments of the Adriatic carbonate platform. Hippuritids preferred more stable and deeper subtidal environments. By contrast, radiolitids preferred the shallowest parts of subtidal areas.

Therefore, these two major rudist groups may be used for determination of different paleoecological conditions.

LUCA BARUFFINI, FABIO LOTTAROLI, STEFANO TORRICELLI & DARIO LAZZARI

Abstract. Original biostratigraphic and sedimentologic data concerning the type-section of the Albidona Formation (Liguride Complex, Southern Apennines, Italy) are presented and discussed. Since its definition in 1962, this lithostratigraphic unit has been the object of controversial interpretations in terms of age attribution and paleotectonic significance. Based on cross-observations performed on calcareous nannofossils and palynomorphs, we conclude that the Albidona Formation must be assigned to the Eocene and, based on these evidences, we make a review of the previous biostratigraphic literature. We further recognise four different turbidite systems (named A to D), bounded by minor stratigraphic hiatuses, that are characterised by different sedimentary facies assemblages and petrofacies. The overall vertical arrangement demonstrates that the Albidona Formation was deposited in a tectonically mobile basin during a phase of deformation that is older than the apenninic deformation and must be likely referred to the alpine tectonics of the Calabrian arc. Moreover, the relationship with the underlying folded unit suggests for the Albidona Formation the significance of an episutural deposit relevant to a Paleogene deformation that affected the older units of the Liguride Complex. By considering stratigraphic and sedimentological features, we suggest a correlation of the Albidona Formation with analogue turbidite suites cropping out in the Apennines, discussing their significance in the context of the Eocene tectonic paroxysm in the Mediterranean area.

DAVIDE BASSI & JAMES H. NEBELSICK

Abstract. This paper presents the first systematic account of calcareous algae from the limestones of the Lower Oligocene Gornji Grad beds of northern Slovenia. These bioclastic limestones are dominated by different coralline algal assemblages as well as corals, large and small benthic foraminifera as well as bivalves. The taxonomy and growth-forms of eleven species of seven non-geniculate coralline algal genera are described: Lithoporella, Neogoniolithon, Spongites, Lithothamnion, Mesophyllum, Sporolithon, Subterraniphyllum,. Additionally, the genera Polystrata (Peyssonneliaceae) Halimeda (Halimedaceae), and Cymopolia (Dasycladaceae) are present.

The taxonomic interpretation of fossil coralline material in a manner consistent with generic and specific concepts currently in use for Recent material is, at present, difficult. In the absence of comparative studies on type material, only limited comparisons are possible, and in most cases definitive taxonomic conclusions cannot be reached. Most of the species designations are thus made following and open nomenclature, pending the rigorous taxonomic revision of historically established, fossil coralline algal species. The present study reveals a considerable variation of growth-form morphologies at both genus and species levels. This demonstrates the difficulties in using this feature as a diagnostic character in the identification of fossil coralline red algal taxa.

LORENZ KEIM & VOLKMAR STINGL

Abstract. The only occurrence of Tertiary (Oligocene) sediments in the Dolomites at Monte Parei results from a complex tectonic and sedimentary history. The Tertiary marine clastic succession is sealing the Dinaric (Late Cretaceous to Paleogene) deformed basement. The basin-fill can be differentiated into four lithofacies which show extensive lateral interfingering: ,local scarp breccias with giant blocks (facies A), chaotic breccias of debris flow origin (facies B), balanid and shell coquina beds (facies C) and conglomeratic grain and debris flows with sandstone intercalations (facies D). Transport directions (imbricate clasts and cross bedding) and petrographic composition indicate two different source areas. Sediments of facies B were shed from a structural high in the SW, while carbonate-siliciclastic debris of facies C and D originated from a pebbly or rocky shore in the N. Lithofacies and facies interrelationships clearly indicate the control by synsedimentary tectonic activity. Neoalpine closure of the basin by overthrusting lead to the preservation of the sediments.