Lithology and biostratigraphy of Upper Cretaceous marine deposits from the Ha?eg region (Romania): Palaeoenvironmental implications

摘要

This paper presents the lithological and biostratigraphical (mainly based on calcareous nannofossils) record of the marine sediments which crop out in the NW and SE Ha?eg regions. Upper Cretaceous marine deposition starts in these two regions in the Early Cenomanian (both in the CC9 calcareous nannofossil zone, and within UC1-UC2 biozones, respectively). In NW Ha?eg, a hemipelagic sequence composed of red shales and marlstones, followed by white marlstones, probably associated with a deep-water paleoenvironment, marked the beginning of Upper Cretaceous marine sedimentation. In the SE, marine deposition started with sandstones and calcarenites, interlayered with Actaeonella and Ytruvia coquina, indicating an infralittoral paleoenvironment. From the Cenomanian up to the Coniacian, the marine setting becomes progressively shallower in the two Upper Cretaceous marine depositional Ha?eg areas; this change is marked by the occurrence of outer shelf deposits in the NW and inner shelf sediments up to infralittoral ones in the SE. These deposits are followed by lower Santonian-upper Campanian turbidites in the NW, and by Lower Santonian-Campanian pro parte red marlstones and Upper Campanian turbidites, in the SE. The marine sedimentation ends, in NW Ha?seg, with distal turbidites, Late Campanian in age (placed in the CC22 calcareous nannofossil zone, in the UC15d subzone respectively, slightly above the first occurrence of the nannofossil Uniplanarius trifidus). Towards the end of the Campanian, conglomerates and sandstones with Actaeonella and Ytruvia coquina, yielding reworked nannofloras (including Late Campanian taxa), occur in SE Ha?eg. Associated with the paroxysmal Laramian tectonic phase, continental deposition started, probably within the Campanian/Maastrichtian boundary interval, both in the NW and SE parts of the Ha?eg region. During the Late Cretaceous interval, different paleoenvironmental settings may be distinguished in the NW Ha?eg (where a deep marine basin developed for most of the Early Cenomanian up to the Late Campanian interval), and in the SE Ha?eg (characterised by an outer oscillating basin with an episodic shallow-water deposition in the same interval). Despite the various backgrounds of the two regions, some common regional events, such as the Early-Middle Cenomanian and the Early Santonian-Early Late Campanian sea level highstand, as well as the Late Cenomanian-Coniacian sea-level lowstand were recognised in both investigated areas.