Elsevier

Cretaceous Research

Volume 124, August 2021, 104804
Cretaceous Research

Lowermost Cretaceous biostratigraphy and paleoenvironmental features of the central-western Getic Carbonate Platform (Pui-Bănița zone, Southern Carpathians, Romania): A holistic approach

https://doi.org/10.1016/j.cretres.2021.104804Get rights and content

Highlights

  • Combined micropaleontological, microfacies and multivariate statistical analyses.

  • Important biostratigraphic arguments for the Berriasian–lower Valanginian.

  • Diversity indices reflect strong facies control over species richness and the spatial distribution of species.

  • A more accurate interpretation of the paleoenvironmental/paleoecological conditions.

Abstract

We carried out combined micropaleontological, microfacies and multivariate statistical analyses of benthic foraminiferal assemblages on a previously undocumented lowermost Cretaceous carbonate succession from the western part of the Getic Carbonate Platform (Pui-Bănița zone, Southern Carpathians). The microfacies analysis and interpretations suggest that these limestones were developed under peritidal settings within different zones of a shallow-water inner platform paleoenvironment (bioclastic grainy bars, subtidal–intertidal flats and intertidal–supratidal ponds), where benthic foraminifera, microbial microstructures and calcareous algae were the main carbonate producers. The well-preserved micropaleontological content (mostly benthic foraminiferal assemblages) is important for lowermost Cretaceous Neotethyan biostratigraphy and allows the recognition of the Valanginian stage within this part of the Getic Carbonate Platform. The multivariate data processing (diversity indices, cluster analyses and principal components analyses) performed on the benthic foraminifera assemblages provide valuable information about their compositional patterns, diversity trends and spatial distribution with respect to the main facies zones. The results obtained through these analyses are extremely useful for the recognition of common/different paleoecological features and for a more precise interpretation of depositional paleoenvironments.

Introduction

Similar to the majority of pelagic microfossil assemblages, the shallow-water benthic communities of Neotethyan carbonate platforms experienced a series of events during the earliest Cretaceous that were linked to a decrease in populations, biotic changes, changes in distribution patterns and preferential adaptations (Erba et al., 2004; Grădinaru et al., 2016; Pleș et al., 2017). Most of these events can be related to the global environmental changes triggered by the onset of the Valanginian Weissert Oceanic Anoxic Event (sensu Erba et al., 2004) and to extensional tectonic activity within the Neotethyan realm (Golonka, 2002; Gawlick and Schlagintweit, 2006; Schmid et al., 2008; Gawlick et al., 2009; Missoni and Gawlick, 2010; Grădinaru et al., 2016). Following the demise of the Upper Jurassic Štramberk/Plassen-type mixed coral–sponge–microencruster bioherms, carbonate production in the Berriasian–Valanginian shallow-water paleoenvironments of the central Neotethys originated from the innermost parts (peritidal settings) of the existing carbonate platforms (Schlagintweit and Enos, 2013; Săsăran et al., 2017; Pleș et al., 2019), where the most important carbonate producers were microbial structures, algae and benthic foraminifera.

The Pui-Bănița region of the Southern Carpathians holds valuable micropaleontological arguments for the lowermost Cretaceous biostratigraphy and paleoenvironmental setting of a large carbonate platform system known in the geological literature as the Getic Carbonate Platform (GCP) (sensu Patrulius, 1976). However, compared with the other sedimentary zones of the GCP (e.g., the Reșița-Moldova Nouă zone, the Buila-Vânturarița Massif, the Piatra Craiului-Dâmbovicioara zone and the Bucegi Massif – Fig. 1A), the lowermost Cretaceous carbonates of this region are still insufficiently documented with respect to their areas of outcrop and their biotic assemblages. Dragastan (2010) and Pleș et al. (2019) reported several biostratigraphically important taxa (benthic foraminifera and dasycladalean algae), which allowed identification of the Berriasian–Valanginian interval within the carbonate sequence of the Pui-Bănița area. However, such limestones were only identified from a small area within the central parts of this region (the Lunca Ohabei Plateau; Pleș et al., 2019), where they are found in sedimentological continuity above the massive Upper Jurassic carbonate sequence. Field campaigns performed in the southeastern parts of the Pui-Bănița zone (the Taia Gorges) led to the discovery of a new outcrop, where a relatively thick sequence of lowermost Cretaceous bioclastic carbonates is unconformably developed over the crystalline rocks of the Şureanu Mountains (Fig. 1B).

The rich and well-preserved biotic components of this outcrop (mainly benthic foraminifera) are of great biostratigraphic importance for the lowermost Cretaceous interval of the Neotethyan realm. These assemblages, together with the identified facies traits, can also provide useful information about the paleoenvironments and paleoecological conditions. For these reasons, the main objective of this study is to combine biostratigraphic, microfacies and statistical analyses to clarify the existing uncertainties about the age of the studied carbonates and to reconstruct the paleoenvironmental setting of the central-western parts of the GCP during the earliest Cretaceous. This study also highlights the importance of statistical analyses in micropaleontological studies in giving more precise paleoenvironmental/paleoecological interpretations.

Section snippets

Geological setting

The studied deposits, together with other synchronous carbonates from this region (the Pui zone sensu Stillă, 1971 or the Hațeg zone sensu Săndulescu, 1984), represent a fragment of the sedimentary cover of the Getic Nappe (the Median Dacidic Nappe System; Săndulescu, 1984). In addition to scarce Permian terrigenous deposits that can be observed in several locations (Stillă, 1985; Stilla and Luță, 1986), the sedimentary sequence of this region consists of mainly marine Mesozoic deposits (Fig. 2

Outcrop description and field observations

The studied outcrop is located in the Taia Gorges Natural Reserve in the northeastern part of the Petroșani Depression along the Taia River (GPS coordinates: 45° 28′ 27.7″ N, 23° 24′ 59.1″ E). This gorge sector is part of the Piatra Leșului limestone structure with a length of about 8 km. Massive white to gray carbonates crop out along the Taia River. The sampled section consists exclusively of such limestones, which are generally defined by granular micritic facies. In the lower part of the

Materials and methods

This study is based on thin section analyses of 68 limestone samples collected from one outcrop belonging to the Pui-Bănița zone (Southern Carpathians). The methodology used within this study encompasses paleontological and sedimentological investigations, microfacies analyses and statistical data processing. The microfacies classification and interpretation follows Dunham (1962), Embry and Klovan (1971) and Flügel (2010). The systematic hierarchy of the benthic foraminifera species are based

Biotic components

The sampled carbonates contain a relatively rich micropaleontological assemblage represented by benthic foraminifera, calcareous green algae (Fig. 3A–B; mainly protohalimedacean fragments – Carpathocodium anae, Fig. 3G–H), Rivularia-type cyanobacteria (Fig. 3C–E) and other cyanophyceans, small mollusks (mainly gastropods) and microorganisms of problematic biological affiliations (bacinellid mesh works, Fig. 3F; Crescentiella-type microstructures, Fig. 3I; Thaumatoporella “ladders”, Fig. 3J).

Biostratigraphy

With respect to the biostratigraphic significance of the present biotic association, the most relevant species for age establishment are the benthic foraminifera (especially the orbitolinids). Based on their known stratigraphic range, the identified foraminiferal species can be divided in four categories (Fig. 8).

Conclusions

  • 1.

    The combined sedimentological/paleontological investigations, microfacies study and statistical data analyses of the benthic foraminiferal assemblages (diversity indices, cluster and PCA) from the Taia Gorges carbonates (the Pui-Bănița region, Southern Carpathians) provide new biostratigraphic, paleoecological and paleoenvironmental data that represent important arguments in understanding the evolution of the central-western part of the GCP during the earliest Cretaceous.

  • 2.

    Among the present

Acknowledgments

The authors thank the two reviewers Felix Schlagintweit (Munich) and Bruno Granier (Brest) for helpful suggestions that improved this paper. We gratefully acknowledge the Administration of Grădiştea Muncelului–Cioclovina Natural Park for providing access to the study region. Last but not least, G. P. gratefully acknowledges the suggestions by Eduardo Koutsoukos that enhanced the final version of the manuscript.

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      sp., are considered by numerous authors to be key indicators for the Berriasian–Valanginian in shallow-water carbonates of the Neotethys Ocean (Altiner, 1991; Bucur et al., 1995; Neagu, 2000; Husinec and Socač, 2006; Krajewski and Olszewska, 2007; Ivanova and Kołodziej, 2010; Catincuț et al., 2011; Ivanova et al., 2015; Ungureanu et al., 2015, 2017; Granier, 2019; Bucur et al., 2020; Oprișa et al., 2021). Moreover, numerous occurrences of Bulbobaculites felixi, Coscinophragma cribrosum, Charentia cuvillieri, Nautiloculina bronnimanni, Pseudolituonella gavonensis, Coscinoconus cf. alpinus and Salpingoporella annulata were recorded from Berriasian–Valanginian deposits (Arnaud-Vanneau, 1980; Arnaud-Vanneau et al., 1988; Ivanova and Kołodziej, 2010; Mircescu et al., 2019; Oprișa et al., 2021). It is worth mentioning that many of the Cribellopsis specimens identified in MFT4–5 (Fig. 6A–E) resemble some Berriasian–Valanginian Cribellopsis species described by Schlagintweit and Bucur (2021).

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