Sedimentology and Depositional Setting of Alluvial Promina Beds in Northern Dalmatia, Croatia

Facies associations comparable with Scott- or Donjek-type facies associations have been recognised in the alluvium of the Promina beds in northern Dalmatia (Late Eocene to possible Early Oligocene). Scott-type facies associations prevail in the upper part of the studied succession whereas Donjek-type facies associations characterise its lower part. Vertical variations in sediment supply, stream gradient or base level are primarily related to south-westward thrustings followed by tectonic quiescence and erosion of the source area

Conglomerate Fabric and Paleocurrent Measurement in the Braided Fluvial System of the Promina Beds in Northern Dalmatia (Croatia)

In the alluvial part of the Promina beds of northern Dalmatia (Late Eocene to possible Early Oligocene age) the main, SW-ward paleocurrent pattern was determined from clast orientation measurements within massive and flat-bedded conglomerates. Preferred clast fabric, facies characteristics, and downward transition into shoreline and shallow-marine sandstone and conglomerate suggest a prograding, braid delta system

The Benkovac Stone Member of the Promina Formation: A Late Eocene Succession of Storm-Dominated Shelf Deposits

The Late Eocene Benkovac Stone Member of the Promina Formation of northern Dalmatia, Croatia, is a thinly bedded succession of alternating carbonate sandstones and calcareous mudstones, ca. 40 m thick, exposed as a narrow, SE-trending outcrop belt near the town of Benkovac. This unit occurs in the middle part of the Promina Formation, which is a spectacular calciclastic succession of deposits of late Middle Eocene to Early Oligocene age, about 2000 m thick, showing an upward trasition from deep-marine turbidites to shallow-marine and alluvial deposits. The sheet-like sandstone beds of the Benkovac Stone Member are mainly 1–25 cm thick and have been classified into 6 facies and 3 subfacies, differing in stratification or showing various internal sequences of stratification types. The thicker and most common beds show plane-parallel stratification passing upward into hummocky cross-lamination and undulatory to flat parallel lamination (Facies S1), or consist of only the latter two divisions (Facies S2). Subordinate beds show convolute stratification (Facies S3), are amalgamated (Facies S4), or are homogenized and merely graded (Facies S6). The thinner beds have more uneven boundaries and show translatory ripple cross-lamination (Subfacies S5a), climbing ripple cross-lamination (Subfacies S5b) or pinch-and-swell lamination attributed to starved and rolling-grain ripples (Subfacies S5c). The intervening mudstone beds (Facies M) are silt-streaked and bioturbated. Trace fossils indicate a combination of Zoophycos and Cruziana ichnofacies. The sedimentary succession was deposited in a microtidal offshore transition zone characterized by muddy “background” sedimentation punctuated by discrete storm events. The observed spectrum of tempestite sandstone beds represents a wide range of storm events, varying in magnitude and in the mode of sand dispersal – from the pure action of oscillatory waves to pure geostrophic currents. The majority of tempestites are attributed to a combination of these two end-member factors, with the geostrophic currents often enhanced by a high load of sediment suspension (density-modified currents). The Benkovac Stone Member is underlain by muddy offshore deposits (Debelo Brdo Member) and covered by sandy to gravelly shoreface deposits (Otavac Member), which in turn pass upwards into braidplain deltaic and alluvial deposits. This regressive succession is considered to be a parasequence deposited as a highstand systems tract during a gradual, stepwise rise of relative sea level. The thick parasequence consists of progradational and retrogradational sets of much smaller parasequences, the record of which differs markedly in the shoreface and offshore transitional part. The difference is attributed to the underlying contrast in the physical factors controlling the supply of sand to these shallow shelf zones

The Role of Palaeogene Clastics in the Tectonic Interpretation of Northern Dalmatia (Southern Croatia)

The Palaeogene coarse-grained clastics of Northern Dalmatia (Jelar breccia, Promina deposits and Flysch) are syntectonic deposits related to the structural evolution of the Dinaride Thrust Belt. The Jelar breccia is a proximal sedimentary unit deposited in response to early compression of the carbonate platform (Lutetian to Bartonian). Flysch deposits are considered as their distal equivalents. The Early Jelar breccia displays a blended clast composition related to the simultaneous erosion of various carbonate stratigraphic units along the Early Velebit Fault. The Late Jelar breccia, the next tectonically generated deposit, has an inverted clast composition related to the erosion of the faulted Velebit anticline. The next tectonic phase (Bartonian to possibly Oligocene) caused folding and thrusting of underlying platform carbonates and tectonic transport, cannibalisation and reworking of the existing Flysch, Early and Late Jelar breccias. Continuing compression created a new elongated foreland basin with NW-SE extension, filled with about 2000 m of prograding Promina deposits. The final structural setting of Northern Dalmatia was the result of thrusting of the northeast edge of the Promina deposits. This produced duplexing of internal thrusts, uplift of the Promina deposits on the highest topographic position and significant erosion. This polyphase and complex tectonism can be described by a thin skin tectonic model in which Upper Jurassic - Lower Cretaceous platform anhydrites acted as a perfect gliding surface

Stable isotope and trace element stratigraphy across the Permian-Triassic transition: A redefinition of the boundary in the Velebit Mountain, Croatia

Stable isotopes of carbonates (delta(13)C(carb), delta(18)O(carb)), organic matter (delta(13)C(org), delta(15)N(org)) and major, trace and rare earth element (REE) compositions of marine carbonate rocks of Late Permian to Early Triassic age were used to establish the position of the Permian-Triassic boundary (PTB) at two continuous sections in the Velebit Mountain, Croatia. The chosen sections - Rizvanusa and Brezimenjaca - are composed of two lithostratigraphic units, the Upper Permian Transitional Dolomite and the overlying Sandy Dolomite. The contact between these units, characterized by the erosional features and sudden occurrence of ooids and siliciclastic grains, was previously considered as the chronostratigraphic PTB. The Sandy Dolomite is characterized by high content of non-carbonate material (up to similar to 30 wt.% insoluble residue), originated from erosion of the uplifted hinterland. A relatively rich assemblage of Permian fossils (including Geinitzina, Globivalvulina, Hemigordius, bioclasts of gastropods, ostracods and brachiopods) was found for the first time in Sandy Dolomite, 5 m above the lithologic boundary in the Rizvanusa section. A rather abrupt negative delta(13)C(carb) excursion in both sections appears in rocks showing no recognizable facies change within the Sandy Dolomite, -2 parts per thousand at Rizvanusa and -1.2 parts per thousand at Brezimenjaca, 11 m and 0.2 m above the lithologic contact, respectively. This level within the lower part of the Sandy Dolomite is proposed as the chemostratigraphic PTB. In the Rizvanusa section, the delta(13)C(org) values decline gradually from similar to-25 parts per thousand in the Upper Permian to similar to-29 parts per thousand in the Lower Triassic. The first negative delta(13)C(org) excursion occurs above the lithologic contact, within the uppermost Permian deposits, and appears to be related to the input of terrigenous material. The release of isotopically light microbial soil-biomass into the shallow-marine water may explain this sudden decrease of delta(13)C(org) values below the PTB. This would support the hypothesis that in the western Tethyan realm the land extinction, triggering a sudden drop of woody vegetation and related land erosion, preceded the marine extinction. The relatively low delta(15)N(org) values at the Permian-Triassic (P-Tr) transition level, close to approximate to 0 parts per thousand, and a secondary negative delta(13)C(org) excursion of -0.5 parts per thousand point to significant terrestrial input and primary contribution of cyanobacteria. The profiles of the concentrations of redox-sensitive elements (Ce, Mn, Fe, V), biogenic or biogenic-scavenged elements (P, Ba, Zn, V), Ce/Ce* values, and normalized trace elements, including Ba/Al, Ba/Fe, Ti/Al, Al/(Al + Fe + Mn) and Mn/Ti show clear excursions at the Transitional Dolomite-Sandy Dolomite lithologic boundary and the chemostratigraphic P-Tr boundary. The stratigraphic variations indicate a major regression phase marking the lithologic boundary, transgressive phases in the latest Permian and a gradual change into shallow/stagnant anoxic marine environment towards the P-Tr boundary level and during the earliest Triassic. (C) 2010 Elsevier B.V. All rights reserved