PLINK-BJORKLUND, PIRET and LENNART BJORKLUND
Goteborg University, Sweden

Abstract: Sedimentary Response in the Baltic Devonian Basin to Post-Collisional Events in the Scandinavian Caledonides

The Baltic basin was an epicontinental sea, dominated by marine carbonate deposition during Ordovician and Silurian times. In the Early Devonian, episodic continental siliciclastic sedimentation started. The main phase of siliciclastic deposition was from the Emsian until the end of the Middle Devonian. We have studied deposits of this phase in outcrops in Estonia.

The siliciclastic deposition throughout the whole Middle Devonian was dominated by deltaic sedimentation on braid plains in channels and interchannel areas, and in minor mouth bars. Fine-grained overbanks and lagoonal deposits are also present. The Middle Devonian siliciclastic succession becomes texturally and mineralogically more mature upwards. The sediment influx was from the NW sector throughout the whole period.

The field results in conjunction with previous works suggest that the Emsian to early Frasnian main phase of siliciclastic deposition occurred in response to the extensional collapse and uplift in the Scandinavian Caledonides. This followed the Scandian collision of Baltica and Laurentia during the Scandinavian orogeny ("main" collision ca 425 Ma in Wenlockian) resulting in extreme crustal thickening in the Caledonian Belt. The Caledonian foreland basin was uplifted in the Wenlockian and turbitidic sedimentation changed into continental. The Emsian uplift resulted in high sediment influx southwards along the basin axis. The Emsian uplift caused (1) direct input into the Baltic basin from the Caledonides, toward SE across the foreland, and (2) a later cannibalisation of the foreland material as suggested by upwards distinctly increasing textural and mineralogical maturity of the Baltic Basin infill.

AAPG Search and Discovery Article #90928©1999 AAPG Annual Convention, San Antonio, Texas