Abstract
AbstractThis study is a reconstruction of the Coniacian palaeogeographic and palaeoenvironmental development in the North Sudetic Basin, a synclinal trough within the Late Cretaceous Central European seaway linking the Boreal and Tethyan marine provinces. The basin formed as an early side effect of the Alpine orogeny combined with the mid‐Cretaceous eustasy, and crucial stages of its evolution occurred during the Coniacian. The basin in the early Coniacian was a long and narrow shallow‐marine embayment with a hypothetical (non‐preserved) bayhead strait funnelling tidal currents. Coalescing tidal sand ridges formed a littoral platform that prograded from the bayhead zone along the basin axis, impinged on laterally by the basin‐margin shoreface and local river deltas. A mid‐Coniacian forced marine regression and closure of the bayhead strait, attributed to the Alpine tectonism combined with eustasy, brought about a dramatic change in the basin, whereby the basin‐wide littoral sand platform emerged and turned briefly into a denudated coastal plain. The late Coniacian eustatic marine transgression formed an in‐place growing coastal sand barrier at the outer edge of the former littoral platform, sheltering a paralic limno‐lagoonal plain with peat‐forming mires. The coastal barrier was eventually drowned by the sea and maximum marine flooding occurred, followed by a normal regression recorded as a rapidly upwards‐shallowing succession of offshore‐transition to fluvio‐deltaic deposits. This case study of the sedimentation pattern in an evolving, tectonically controlled marine embayment contributes to the existing facies models for estuarine embayments formed by a passive marine drowning of large fluvial or glacial valleys.
Highlights
The vast majority of reported case studies on sedimentation in long and relatively narrow marine embayments are from drowned fluvial or glacial valleys with bayhead river deltas, falling broadly into the category of estuaries (Boyd et al, 1992; Dalrymple et al, 1994, 2006; Perillo, 1995; Dalrymple, 2010; Gilbert et al, 2018)
The present study is a significant contribution to an understanding of the sedimentary environment and palaeogeographic development in the Late Cretaceous North Sudetic Basin, which was a main component of the Central European seaway linking the Boreal and Tethyan provinces and was eventually inverted by Alpine tectonism into the present‐day North Sudetic Synclinorium (Figure 1B)
The present study focuses on the Coniacian stage of evolution of the North Sudetic Basin (Figure 2), when a combination of tectonic and eustatic forcing resulted in a dramatic change in the basin palaeogeography and sedimentary environment
Summary
The vast majority of reported case studies on sedimentation in long and relatively narrow marine embayments are from drowned fluvial or glacial valleys with bayhead river deltas, falling broadly into the category of estuaries (Boyd et al, 1992; Dalrymple et al, 1994, 2006; Perillo, 1995; Dalrymple, 2010; Gilbert et al, 2018). The present‐day North Sudetic Synclinorium is a well‐preserved axial relic of the Cretaceous North Sudetic Basin—one of the epicontinental shallow‐marine basins that formed in the mid‐Cretaceous within and around the Bohemian Massif (Figure 1A) as a side effect of the Alpine orogeny. The Cretaceous deposits in the North Sudetic Synclinorium overlie a discontinuous succession of Carboniferous to Middle Triassic sedimentary rocks (Figure 1B) These Cenomanian to Santonian deposits are nearly 1,000 m thick (Bossowski et al, 1976; Bossowski, 1991a) and include sandstones, mudstones, claystones and marlstones, with subordinate limestone. (uppermost Rakowice Wielkie Fm.) overlain by coal‐bearing muddy to sandy deposits of the lowermost Czerna Fm. Active quarry operated by Kopalnie Piaskowca S.A. Bolesławiec. Sandstones of the Żerkowice Mb. (uppermost Rakowice Wielkie Fm.) overlain by lowermost Czerna Fm
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