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Large cruzianid trace fossils in the Ordovician of the peri-Baltic area : the case of the Bukówka Formation (Holy Cross Mountains, Poland)

Stachacz M., Łaska W., Uchman A.

Geological Quarterly

2018

Vol. 62, No. 2

400--414

The Middle Ordovician Bukówka Formation, composed of fine-grained quartz sandstones with siltstone intercalations, belongs to the Kielce Region of the Holy Cross Mountains (peri-Baltic palaeogeographic position). It contains trace fossils of low diversity and poor preservation. Particularly noteworthy are the large Cruziana and Rusophycus, that are typical of peri-Gondwanan areas. They consist of casts of bilobate furrows showing diverse preservation. Other trace fossils include mostly horizontal pascichnia, cubichnia, and fodinichnia, but also vertical domichnia. The trace fossil assemblage is typical of the archetypal Cruziana and partly of the Skolithos ichnofacies. Some beds contain abundant orthid brachiopods. The trace fossils and sedimentary structures (horizontal, low-angle and wave ripple cross-laminations, hummocky cross-stratification) suggest deposition on the middle and lower shoreface with storm influence. The poor preservation and low diversity of the trace fossils are related to the homogeneous lithology, low accumulation rate, shallow burial of organic matter and strong bioturbation. Therefore, animals burrowed strongly but mostly in shallow tiers. Thus, the preservation potential of their traces was much lower than in many peri-Gondwanan sections but still higher than in Baltica sedimentary rocks. This explains the provincial differences in ichnofauna during the Ordovician, which at least partly were influenced by the preservation potential.

Trace fossil Cruziana tenella from the Furongian (Upper Cambrian) deposits of Poland

Sadlok G.

Acta Geologica Polonica

2010

Vol. 60, no. 3

349-355

A minute, bilobate ribbon-like trace fossil, assigned to the ichnospecies Cruziana tenella, is recorded for the first time from Furongian (Upper Cambrian) strata of the Wiśniówka Formation exposed in the Wiśniówka Wielka quarry, Holy Cross Mountains, central Poland. The collected material of C. tenella is interpreted as arthropod pascichnia trails. A significant gap in size distribution and morphology between C. tenella and other Cruziana trails from Wiśniówka Wielka suggests that the former cannot be regarded as produced by juveniles of the biotaxa responsible for the latter. C. tenella from Wiśniówka Wielka was most probably produced by arthropods reaching a small adult size.