Trilobite and acritarch assemblages from the Lower-Middle Cambrian boundary interval in the Holy Cross Mountains (Poland)

Integrated analysis of trilobite and acritarch assemblages across the traditional Lower-Middle Cambrian boundary in the Holy Cross Mountains (Poland) has documented the development of both groups in this interval. Trilobite assemblages, comprising 31 taxa (13 are revised herein) dominated by the Ellipsocephalidae, change from the protolenoid-dominated in the Lower Cambrian to the kingaspidoid-ornamentaspidoid-dominated in the Middle Cambrian, and correlate well with the Agdzian Stage of West Gondwana (Geyer and Landing 2004). Correspondence to West Gondwana and Avalonia is also evident from the presence of the associated trilobite genera, Palaeolenus, Myopsolenites, Latikingaspis, Kingaspis, Latoucheia and Orodes. The acritarch assemblages, comprising 77 taxa, indicate that their main taxonomic turnover was gradual and preceded the earliest occurrence of Paradoxides spp., as in the Spanish sections. The geological succession studied in the HCM represents part of the Cambrian strata that are generally missing in Baltica.