Laterally variable development of a basin-wide transgressive unit of the North Dalmatian Foreland Basin (Eocene, Dinarides, Croatia)

摘要

The Palaeogene Promina Beds (PB), exposed in the Dinaric coastal range, is about a 2km thick heterogeneous succession representing a late sedimentary fill of the North Dalmatian foreland basin. The paper focuses on the middle part of the PB represented by a prominent transgressive unit. The study of this unit is based on field mapping, logging and facies analysis, as well as the investigation of stratigraphic surfaces and facies successions. The unit extends for more than 63km, along the entire basin. Deposition began transgressively over both alluvial deposits of the Lower PB and karstified basin basement. Along its extent the studied unit may be represented either by stacked (highfrequency), marine transgressive-regressive cycles, by lacustrine deposits, mainly limestones, or by a single, marine limestone unit. An ideal transgressive-regressive cycle includes a transgressive segment of limestones, and a regressive segment of storm-wave dominated shelf to gravelly beachface (coarsening-upward) deposits. Gravelly beaches are represented by several types. One of them included the steeply inclined, lower beachface which is situated below the intertidal zone. The cycles are separated by lower-rank discontinuity surfaces (flooding surfaces), while their two segments are separated by a lower-rank transgressive-regressive turnaround surface. Lacustrine deposits originated due to a rise in groundwater induced by a sea-level rise basinwards. The deposition of a single limestone unit resulted from a transgressive onlap over uplifted, Eocene and Cretaceous carbonates of the basin basement. The end of the transgression is marked by condensation processes indicated by glauconite, skeletal debris, planktonic foraminifera and hardgrounds, and a major transgressive-regressive turnaround. The subsequent evolution is almost uniform along the entire extent of the studied unit, and includes shelf to delta and shelf to beach cycles of the highstand. The studied allostratigraphic unit is here given a formal name: the Novigrad Alloformation.