Abstract
The stratigraphic succession in the Cikola Canyon (part of the North Dalmatian Foreland Basin) was studied in detail to describe both the sedimentological characteristics and fossil assemblages of the Lower Eocene deposits during the initial stage of the foreland basin formation. The North Dalmatian Basin now represents a part of the Outer Dinarides, and was developed in front of the evolving Dinaric structures by tectonic deformation and marine transgression of an emerged and denuded Mesozoic Adriatic Carbonate Platform (AdCP). During the initial phase, a distal ramp of a foreland basin was formed, characterised by carbonate sedimentation, lasting until the Middle Eocene. In a studied section more than 300 m thick, porcelaneous foraminifera, Alveolina, Orbitolitesand complex miliolids (Idalina, Periloculina) prevail, associated with conical agglutinated forms, nummulitids and red algae. These samples belong to the SBZ 11–12 (Ypresian), according to occurrences of Alveolina decastroi, Alveolina cremae, Alveolina multicanalifera and Coskinolina liburnica. Two main lithological units have been described: 1) mudstones to wackestones with sporadic occurrences of ostracods and charophyceae, deposited in restricted lagoonalsettings with several episodes of freshwater influences, and 2) foraminiferal packstones to grainstones with complex miliolids, alveolinids, corallinacean algae and nummulitids, deposited within inner and middle ramp settings. Palaeogene deposition of ramp carbonates in the Outer Dinarides area was mainly controlled by the continuous compressional tectonics, and the deposits today appear in more or less discontinuous outcrops. Palaeogene transgression occurred at different times over various parts of the former carbonate platform area, and subsequent carbonate sedimentation was characterised by deposition in similar environments during different time intervals over spatially restricted carbonate ramps controlled by synsedimentary tectonics.
Highlights
The aim of this study was primarily to determine the microfacies properties of the Čikola river canyon carbonate deposits rich in Larger Benthic Foraminifera (LBF). These determined forami niferal assemblages and their ecological requirements combined with the study of other carbonate-producing biota, enabled the definition of the palaeoenvironmental settings of the Lower Eocene deposits known as the Foraminiferal limestones
The detailed studies of thin sections reveal a reduction of fossils towards the youngest Cretaceous rocks, and the presence of Microcodium sp. aggregates in over lying beds, which are typical for the early stages of palaeosol de velopment in many Peri-Tethyan sections (KOŠIR, 2004)
In the Čikola Canyon, Northern Dalmatia, during the Early Eo cene around 300 m of carbonates were deposited transgressively over the Upper Cretaceous (Campanian) rudist-bearing limestones, representing one of thicker successions of Palaeogene car bonates in the Dinarides
Summary
The aim of this study was primarily to determine the microfacies properties of the Čikola river canyon carbonate deposits rich in Larger Benthic Foraminifera (LBF). These determined forami niferal assemblages and their ecological requirements combined with the study of other carbonate-producing biota (corals, bryo zoans, echinoids, molluscs, coralline red algae), enabled the definition of the palaeoenvironmental settings of the Lower Eocene deposits known as the Foraminiferal limestones. During the Eocene the shallow-marine (neritic) carbonate succession rich in LBF, known as the Foraminiferal limestones, was deposited within carbonate ramp environments (DROBNE et al, 1991; BABIĆ & ZUPANIČ, 2016 with references therein) over either the Kozina beds or directly onto karstified Cretaceous deposits. The ramp deposits pass upward into glauconite-bearing marly Transitional beds, overlain in some areas by a turbiditic succession of flysch and/or by a thick succession of Promina beds (MRINJEK et al, 2012)
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