Small-sized <i>Trochammina</i> assemblages in deep-water Eocene flysch deposits (Outer Carpathians, Poland) and their palaeoecological implications

Abstract

Abstract. The global climate change in the early Eocene contributed significantly to the turnover of benthic foraminifera. A major extinction within agglutinated and calcareous forms and the occurrence of opportunistic assemblages resulted. The Trochammina material described here belongs to these post-crisis assemblages. Foraminiferal assemblages with numerous Trochammina species are identified within deep-water Eocene deposits of the Polish part of the Outer Carpathians. Trochammina reach up to 80% of the assemblages, the remainder consists of cosmopolitan agglutinated foraminifera, mainly Bathysiphon, Recurvoides, Paratrochamminoides and Trochamminoides. The low biodiversity (average number of species 24, of genera 15) and the presence of dwarf forms are the main characteristics of the assemblages. These assemblages occur predominantly in shales with numerous organic traces (lower Hieroglyphic beds), deposited in the Silesian Basin (Outer Carpathians) which was on the northern margin of the western Tethys Ocean during the early Eocene (Ypresian, c. 50 Ma). The Trochammina biofacies developed in the Silesian Basin after the Paleocene–Eocene Thermal Maximum crisis, and is dominated by opportunistic forms, mainly represented by mobile epifauna and shallow-water infauna, interpreted as a recolonizing assemblage in a low energy environment.

The Eocene Hieroglyphic Beds of the Silesian Nappe in the Western Polish Carpathians – their development and foraminiferal record

“…3, 6 and 10). In turn, in the Istebna area, the lower part of the Hi ero glyphic Beds is al most sand stone-free (Waoekowska, 2015a). Wójcik et al (1993b) noted sand stone-free green shale com plexes from the lower part of the Hi ero glyphic Beds in the Jas³o area.…”

“…These de pos its most of ten oc cur above the Ciê¿kowice Sandstone or Istebna Beds where they form a char ac ter is tic layer cake of lighter grey and/or green shales with darker ones. A large quan tity of dark shales causes them to be very sim i lar mac ro scop i cally to the shales of the Istebna Beds, es pe cially be cause the lat ter com plexes con tain spherosiderites, like the Istebna Beds (Ksi¹¿kiewicz, 1974b;Burtan, 1978;Wójcik and R¹czkowski, 1994;Waoekowska, 2015a). Lo cally, the Hi eroglyphic Beds in clude com plexes with a ma jor pro por tion of sand stones, or made up pre dom i nantly of sand stones.…”

“…4, 9 and 10). In the Hi ero glyphic Beds, the red shales are pre dom i nantly clayey de pos its, made of finer ma terial than the typ i cal grey-green shales (Waoekowska, 2015a).…”

“…Within the part of the pro file with the cos mo pol i tan fauna, there is a dis tinct se quence of de pos its con tain ing cri sis as sem blages with nu mer ous and small-sized Trochammina whose age was de ter mined to be Early Eocene, based on plank tonic and ag glu ti nated foraminifera. Within the Lower Eocene var ie gated de pos its, an in crease in the num ber of Glomospira is ob served (Waoekowska, 2015a). The foraminiferal as sem blages from the mid dle and up per parts of the thin-bed ded flysch are char ac ter is tic of the Ammodiscus (Dolgenia) latus zone ( Fig.…”

“…3). In the lower part of the Hi ero glyphic Beds, there is a dis tinct in crease in the num ber of Trochammina, and monospecific as semblages pre dom i nantly of dwarfed forms are found, de not ing crisis-fea ture as sem blages (Waoekowska, 2012(Waoekowska, , 2015a. In the lower part of the com plex with the Trochammina as sem blages, an in creased pro por tion of Glomospira is ob served, among which Glomospira charoides (Jones et Parker) pre dom i nates.…”