Dinoflagellate cysts from neptunian dykes in the Middle Jurassic of Poland — A stratigraphical approach

Dinoflagellate cysts are of use in determining the age of allochthonous sediments within host rocks. Due to the high durability of the cyst walls they are able to persist in difficult environmental and synsedimentary conditions. This case study focuses on palynological analysis of neptunian dykes cutting through Middle Jurassic clays with siderite concretions exposed in three sites in Central Poland. Within the fissures, intense mixing of palynodebris from the host rock with the infilling sediments took place. Palynological analysis of the internal sediments from the fissure infillings revealed well-preserved mixed assemblages of Middle and Late Jurassic taxa enabling the age of the process to be constrained. The analysis of the infillings of neptunian dykes is of particular importance as sometimes this provides the only proof of eroded sediments, and the fissure systems are usually evidence of regional extensional tectonic activities.

► Dinoflagellate cysts are of use in determining the age of neptunian dykes.
► Palynological analysis revealed mixed assemblages of Middle and Late Jurassic taxa.
► The Early–Late Kimmeridgian neptunian stage of dyke development is confirmed.
► These stratigraphic data constrain the age of the regional extensional tectonics.