Lower–Middle Jurassic clastic formations of the Western Carpathian Klippen Belt: testimony to the rifting-breakup-drifting processes 

Abstract

<p>The Lower to early Middle Jurassic terrigenous clastic deposits witness the early breakup processes of Pangaea. Rifting and subsequent ocean-floor spreading of the Central Atlantic branch that propagated eastward into the Alpine–Carpathian realm split several continental blocks (Adria, Tisia, Dacia, Moesia), and smaller intervening fragments (such as Cervinia and Oravic), off the southern European plate margin. Alongside the ocean-faced margins of Europe and drifting blocks, the initial rifting phases are recorded by terrigenous terrestrial fluvial-limnic, deltaic to open marine clastic formations. Although showing some regional variations in composition and age, they share many common developmental characteristics.</p> <p>In the Carpathian Pieniny Klippen Belt (PKB), the Lower – early Middle Jurassic clastics are partly preserved in the Šariš (Grajcarek) Unit that was derived from the outer (northern) margin of the continental ribbon surrounded by the Pennine oceanic branches. Palaeogeographically, this continental splinter is known as the Czorsztyn Ridge and its detached Jurassic–Eocene sedimentary nappes are designated as the Oravic tectonic units (Šariš, Subpieniny and Pieniny).</p> <p>The Šariš sedimentary succession related to the incipient rifting stage begins with massive quartzitic sandstones of probably Hettangian age deposited in continental to shallow-marine environs. The mature rifting stage is represented by quartz-calcareous, partly turbiditic sandstones rich in imprints of Sinemurian ammonites intercalated by thin layers of grey shales. Overlying spotted marlstones of the Fleckenmergel facies of the Pliensbachian–Toarcian Allgäu Fm. are locally passing into black shales representing the Toarcian oceanic anoxic event. Deposition of dysoxic black shales continued to the Aalenian and early Bajocian by the Szlachtowa Fm., which is characteristic of the Šariš Unit. In addition to micaceous black shales with common imprints of pelagic bivalves of <em>Bositra buchi</em>, it comprises also beds of black turbiditic siliciclastic sandstones rich in white mica flakes and few allochthonous coal seams. Black shales with pelocarbonate nodules out of the reach of turbiditic currents are identical with the concomitant Skrzypny Fm. recognized also in the successions of the Subpieniny Nappe. Beds of calciturbiditic crinoidal limestones occurring in the upper part of the formation indicate input of shallow-marine bioclastic material derived from the adjacent Czorsztyn Ridge uplifted during the middle–late Bajocian. Subsequent latest Bajocian hiatus and drowning of the Czorsztyn Ridge, along with a sudden decline of clastic input in the Šariš Basin, are interpreted as the breakup phase of a nearby oceanic zone.</p> <p>The post-breakup pelagic succession represents the drifting stage and consists of the late Middle–Upper Jurassic dark, calcite-poor siliceous shales, red ribbon radiolarites, red marlstones and cherty limestones,  followed by the Lower Cretaceous spotted micritic limestones with cherts, mid-Cretaceous Fleckenmergel and dark silicitic shales and Upper Cretaceous red calcite-free claystones. Finally, the synorogenic phase is recorded by the Maastrichtian–Paleocene calcareous flysch with olistostrome bodies and limestone megaolistoliths derived from the overriding Subpieniny Nappe.</p>