Abstract
New ammonoid data prove an early Late Pliensbachian deepening event above the ?Late Hettangian-Sinemurian shallow-subtidal gray-reddish micro-oncoidal-foraminifera grainstone facies and the ?early Pliensbachian deeper-marine micro-oncoidal-crinoidal-ammonoid wacke- to packstone facies. Based on the presence of Fuciniceras lavinianum (Fucini), Lytoceras ovimontanum Geyer and Arieticeratinae gen. indet. from a hardground above the deeper-water micro-oncoidal limestones in the Mihajlovici section (north - eastern Montenegro) a Late Pliensbachian to early Toarcian condensation horizon is proven. The Middle Toarcian ammonoid-bearing horizon also yielded species not known from previous studies: Calliphylloceras capitanii (cATuLLo), Harpoceras subplanatum (oPPeL) and Furloceras aff. chelussii (PAriScH & ViALe), also described in the present paper. These new data prove a stepwise deepening of the depositional area during the early and the Middle Jurassic reflected in detail in four sedimentary members: 1) ?Late Hettangian to Sine - murian/?earliest Pliensbachian open-marine shallow subtital micro-oncoidal limestones; 2) ?early to Late Pliensbachian open-marine condensed limestones with few micro-oncoids and more open-marine influence; 3) Toarcian open-marine condensed red limestones with hardgrounds; and 4) condensed red nodular Bositra Limestone. These four members are separated by hard - rounds representing stratigraphic gaps in deposition. The stepwise deepening during the early-Middle Jurassic follows the general trend of deposition as known in the whole Western Tethys realm above the Late Triassic Dachstein carbonate Platform.
Highlights
The new ammonoid dating clearly improves a stepwise deepening throughout the whole early–Middle Jurassic and the stratigraphic gaps in the early Jurassic are shorter in duration as interpreted before
A Late Sinemurian brachiopod fauna was described by ALBrecHT (1924) whereas microfossil associations were assigned to the early Jurassic and to the Bajocian–Bathonian. unfortunatelly, a new ammonoid fauna is not known from this localiy, but some assumtions can be made according to species cited in published literature. except for PeTkoVić (1934) who thought that the ammonoids from the red nodular limestones were Middle Triassic in age, all other authors mention or describe early Jurassic species
LeDeBur (1941) describes from this section Lytoceras fimbriatum and Calliphylloceras cf. nilssoni, ćirić (1954) cited Calliphylloceras nilssoni and rAMPnoux (1974) mentions Lytoceras sepositum, Calliphylloceras capitanii and Harpoceras strangewaysi, all found in the red nodular limestones above the micro-oncoidal facies. one of these species (Lytoceras fimbriatum) can only be found in Pliensbachian sedimentary rocks, another (Harpoceras strangewaysi) is known only from early Toarcian, whereas the third (Lytoceras sepositum) is characteristic for Middle Toarcian
Summary
The early-Middle Jurassic depositional history in the inner Dinarides is poorly known due to the lack of available outcrops, and modern microfacies analysis in combination with exact biostratigraphic data are very rare (GAWLick et al, 2017, 2020 and references therein; HAAS et al, 2019). in contrast to the early–Middle Jurassic well known depositional history in the outer Dinarides, i.e. the Adriatic carbonate Platform Basement and the Adriatic carbonate Platform evolution (VLAHoVić et al, 2005 and references therein), the transitional zone between the early–Middle Jurassic shallow-water depositional realm of the outer Dinarides and the open shelf environment (inner Dinarides) near to the neoTethys ocean to the east (GAWLick et al, 2016; West Vardar ocean in the nomenclature of ScHMiD et al, 2008, 2020) is poorly known. early–Middle Jurassic sedimentary rocks from the outer shelf environment are practically unknown, since they were in parts removed/eroded or overthrust in the course of Middle to Late Jurassic west-directed ophiolite obduction (GAWLick et al, 2016, 2020; GAWLick & MiSSoni, 2019 and references therein). only few remains of this facies belt are known preserved either as small components in the late Middle to early Late Jurassic trench-like foreland basin fills (GAWLick et al, 2017) or are preserved as metamorphosed successions (e.g., in the kopoanik area: ScHeFer et al, 2010). in addition, due to intense erosion after mountain uplift from the kimmeridgian/Tithonian boundary onwards (GAWLick et al, 2017, 2020) most of the Jurassic outer shelf successions were eroded. especially in the areas of the Late Triassic open lagoonal facies belt (open lagoonal Dachstein Limestone: GAWLick et al, 2017, 2020) transitional to the Late Triassic reef belt, where the presence of early–Middle Jurassic condensed red nodular limestone successions could so far only be reconstructed from pebble anaylsis (GAWLick et al, 2017) early–Middle Jurassic sequences are preserved only in rare cases. The detailed deepening history of this red nodular early–Middle Jurassic limestones (Ammonitico rosso), with its well-known and in detail described facies characteristics (FLüGeL, 2004 and references therein) and the adjacent facies belts transitional to the Adriatic carbonate Platform Basement, can in the inner Dinarides only be reconstructed indirectly. In the eastern Alps or Western carpathians mainly early–Middle Jurassic deep-water limestones, often in red nodular condensed facies are known (HAAS et al, 2011 and references therein). All these areas are affected by the opening history of the Alpine Atlantic (Ligurian, Piemont, Penninic, Vah oceans in other nomenclature: MiSSoni & GAWLick, 2011) from Hettangian times onwards. Successions in the inner Dinarides may provide a possibility to filter global and overregional events and their importance
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