Ordovician conodonts and the Tornquist Lineament

Abstract

The Holy Cross Mts. in southern Poland are generally believed to be split by a tectonic dislocation into two separate parts, a NE one being a part of the Baltic Craton and a SW part belonging to the Małopolska Terrane of a complex geotectonic history connected with the Trans-European Suture Zone (Tornquist Lineament). Unexpectedly, conodont assemblages of earliest Middle Ordovician (early Darriwilian) age from Pobroszyn in the northeastern Łysogóry region and from Szumsko in the southwestern Kielce region show virtually identical species composition. One of the dominant species both in Pobroszyn and Szumsko, Trapezognathus pectinatus sp. n., characterized by denticulated M elements, occurs elsewhere only on the northern margin of Gondwana. Separation of the Małopolska microcontinent from Baltica continued after the disappearance of Trapezognathus and an apparently allopatric speciation process was initiated by a population of Baltoniodus. Also in this case, denticulation developed in the M elements of the apparatus but the process of speciation of B. norrlandicus denticulatus ssp. n. was truncated by re-appearance of the Baltic lineage of Baltoniodus. Later conodont faunas from the region are of Baltic affinities, but remain distinct in showing a relatively high contribution from exotic species of Sagittodontina, Phragmodus, and Complexodus. The periodic North American Midcontinent tropical influences observable in the Baltic region did not reach the Holy Cross Mts. The Ordovician conodont faunas from the Holy Cross Mts. can be fit into a transect extending from Baltica to Gondwana, with several intermediate terranes. This new evidence disproves the long-held concept that the Łysogóry and Kielce regions had separate early Palaeozoic fates and that the Małopolska Terrane was unified with Baltica already in the earliest Ordovician. The Trans-European Suture Zone truly marks the presence of a wide Tornquist Sea in the early Palaeozoic.