A reappraisal of the terrane concept in the Holy Cross Mountains (Polish segment of the Trans-European Suture Zone) based on the Furongian (upper Cambrian) stratigraphy and facies in the Lenarczyce PIG 1 well

A wide stratigraphic gap spanning the middle Miaolingian to early Tremadocian in the succession of the northern Małopolska Block, exposed in the southern Kielce Region of the Holy Cross Mountains in south-central Poland, was hitherto indicated as the key argument for its different tectonic evolution compared to the adjacent northern Łysogóry Block. As these two blocks form part of the Trans-European Suture Zone, deciphering their early Palaeozoic history has profound impact on our understanding of the evolution of this major Central European tectonic domain. Based on data from the Lenarczyce PIG 1 well (Kielce Region), we analyse here the stratigraphy and sedimentary record of the upper Cambrian in the Holy Cross Mountains. Rich acritarch assemblages coupled with rare macrofossil specimens from this well indicate the presence of a Miaolingian and Furongian succession showing different tectonic styles and separated by a stratigraphic gap. The stratigraphic gap separating these successions spans the middle to late Miaolingian and the early to middle Furongian, and it has proved to be much narrower than previously considered. The upper Furongian siliciclastic succession recognised here can be defined as a shallow-water flood-dominated delta system, developed after the tectonic event responsible for the intense deformation of the lower and middle Cambrian strata. In the latest Furongian, this sedimentary system passed rapidly upwards into an offshore mud belt produced by a relative sea-level rise (transgressive event). The unconformity at the Cambrian–Ordovician boundary in the southern Holy Cross Mountains is shown to be of a complex nature resulting from pre-Furongian folding and thrusting, and post-Furongian changes of relative sea-level/accommodation space.