Early Cretaceous foraminifera from atoll environment (Márévár Valley, Mecsek Mountains, Hungary)

Szinger, Balázs (2008) Early Cretaceous foraminifera from atoll environment (Márévár Valley, Mecsek Mountains, Hungary). Hantkeniana, 6. pp. 127-143. ISSN 1219-3933

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Abstract

This paper presents the microfaunal examination of the Márévár (Eastern Mecsek) occurrence of the Hidasivölgy Marl Formation. The foraminifera-dominated microfauna clearly indicates the type of palaeoenvironment. The foraminiferal assemblage is composed of 35 taxa (frequent genera: Trocholina, Neotrocholina, Lenticulina, Dentalina, Nodosaria, Spirillina). The benthic foraminifera fauna is divided into four (A, B, C, D) morphogroups in relation to microhabitat depth in the sediments. Morphogroup A: epifaunal foraminifera (Neotrocholina, Trocholina, Patellina, Spirillina, Ammodiscus) live in up to 1 cm depth in the sediment. Morphogroup B: shallow infaunal foraminifera (Dentalina, Nodosaria, Pseudonodosaria) live in depth of less than 5 cm. Morphogroup C: shallow to deep infaunal foraminifers (Dorothia, Tritaxia, Reophax) live deeper than 5 cm depth in the sediments. Morphogroup D: epifaunal to deep infaunal foraminifers (lenticulinids) distribute within a wide range of depths in the substrate. The foraminifera assemblage of the Márévár occurrence can be characterized with low diversity and abundance but with significant ratio of morphogroup A (dominance of the trocholinids, neotrocholinids). The results of the microfauna and macrofauna observations indicate normal salinity, warm water, shallow marine environment in lagoon region. In addition, an input of large amount of volcanic material could be reconstructed for the time. Involving these facts into the presently accepted formation model, the Márévár occurrence of the Hidasivölgy Marl represents an outer part of the lagoon in between the basalt volcano and the atoll situated at the rim of the volcanic build-up during the Early Valanginian. Because of repeated volcanic activity, it is most probable that the lagoon filled up and mixture of volcanic material and sediments redeposited into the deeper slope around the volcanic cone.

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