Zlinská A., 2013: First described microfauna in the Biely Potok Formation's Chrenovec Member in the Handlovská kotlina Basin. Acta Geologica Slovaca, 5, 1, 69–82. (in Slovak with English summary)

Prvý nález mikrofauny z chrenoveckých vrstiev bielopotockého súvrstvia v Handlovskej kotline

First described microfauna in the Biely Potok Formation's Chrenovec Member in the Handlovská kotlina Basin

Adriena Zlinská

Štátny geologický ústav Dionýza Štúra, Mlynská dolina 1, 817 04 Bratislava; adriena.zlinska@geology.sk

Abstract

At the stratotype Brusno-Chrenovec locality in the Handlovská kotlina Basin, the microfauna from the Oligocene sandy Chrenovec Beds were studied. In the past, this locality was studied micropaleontologically for several times, but with negative results. From several places of the Brusno sandpit we succeeded to obtain foraminifers, to document them and to justify the age of these strata as Upper Oligocene – Egerian (Chattian), belonging to the O5–O6 biozones. The following key taxons of planctonic foraminifers were determined: Paragloborotalia opima (Bolli), Tenuitella munda (Jenkins), Chiloguembelina gracillima (Andreae), and Globigerinoides trilobus (Reuss) appearing from the Late Oligocene. At the same time, the older results of the microfaunistic studies of the Palaeogene deposits in the Handlovská kotlina Basin were revised with the following results. The previous Eocene deposits, were reclassified to the Oligocene, based on the planctonic foraminifers as Chiloguembelina gracillima (Andreae), Tenuitella clemenciae (Bermudez), and Turborotalia ampliapertura (Bolli). Similarly in the depth interval of 74–235 m in the ČČ–4 well and further on, the whole ČČ–1 well log (9–105 m), ČČ–2 (60–105 m) and ČČ–3 (308–327.2 m) were reclassified as the Oligocene. Lithostratigraphically, the revised taxons belong to the Huty and Zuberec Formations. By the revision of the microfauna, it was found out, that the lower boundary of occurrence (FAD) of the Tenuitellinata pseudoedita (Subbotina) taxon which was introduced in the surface samples from the Lower Oligocene Huty and Zuberec Formations in the Handlová area, is located as high as in Egerian, while the upper one (LAD) is in the lowermost Ottnangian. Based on the presented data, the upper part of these deposits should be younger, thus Egerian (Chattian) in age.

Key words: Handlovská kotlina Basin, Oligocene, Egerian, Biely Potok Formation, Chrenovec Beds, foraminifers

Manuscript received: 2012-02-28

Revised version accepted: 2013-02-22