10 Aug 2023
 | 10 Aug 2023
Status: this preprint is currently under review for the journal BG.

Serpulid-microbialitic bioconstructions from the upper Sarmatian (Middle Miocene) of the Central Paratethys Sea (NW Hungary) – witnesses of a microbial sea

Mathias Harzhauser, Oleg Mandic, and Werner E. Piller

Abstract. We present so far unknown stacked bowl-shaped bioherms reaching a size of 45 cm in diameter and 40 cm in height from weakly solidified peloidal sand from the upper Sarmatian of the Paratethys Sea. The bioherms were mostly embedded in sediment and the ‘stages’ reflect a reaction on sediment accretion and sinking into the soft sediment. The bioherms are spirorbid-microclots-acicular cement boundstones with densely packed Janua tubes surrounded by microclots and acicular cement solidifying the bioherm. The surrounding sediment is a thrombolite made of peloids and polylobate particles (mesoclots) which are solidified synsedimentarily by micrite cement and dog-tooth cement in a later stage. The shape of the bioherms reflects a series of growth stages with an initial stage (‘start-up’ phase) followed by a more massive ‘keep-up stage’ which grades into a structure with a collar-like outer rim and a central protrusion and finally by a termination of growth (‘give-up stage’). The setting was a shallow subtidal environment with normal marine or hypersaline, oligotrophic conditions with an elevated alkalinity. The stacked bowl-shaped microbialites are a unique feature so far undescribed. Modern and Neogene microbialite occurrences are no direct analogues to the described structures but the marine examples, like at the Bahamas, Shark Bay and the Persian Gulf offer insight into the microbial composition and environmental parameters.

The microbialites and the surrounding sediment document a predominance of microbial activity in the shallow marine environments of the Paratethys Sea during the late Middle Miocene, which was characterized by a warm, arid climate.

Mathias Harzhauser et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on bg-2023-105', Anonymous Referee #1, 04 Sep 2023
  • RC2: 'Comment on bg-2023-105', Anonymous Referee #2, 14 Sep 2023

Mathias Harzhauser et al.

Mathias Harzhauser et al.


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Short summary
Bowl-shaped spirorbid-microbilate bioherms formed during the Late Middle Miocene (Sarmatian) in the Central Paratethys Sea under warm and arid climate. The microbialites and the surrounding sediment document a predominance of microbial activity in the shallow marine environments of the sea at that time. Modern microbialites are no analogues in for these unique structures, which reflect a series of growth stages with an initial ‘start-up’, a massive ‘keep-up stage’ and a termination of growth.