Baltica in the Cryogenian, 850-650 Ma

This new tectonic synthesis provides a framework for understanding the dynamic evolution of Baltica and for constraining tectonic correlations within the context of the Neoproterozoic break-up of Rodinia–Pannotia. Cryogenian Baltica is described with respect to five geographic regions: the northwest, northeast, east, south, and southwest (modern coordinates). These geographic regions define three principal Cryogenian tectonic margins: a rifting northwestern margin, a passive northeastern margin, and a poorly understood southern margin. The northwest region is characterized by Neoproterozoic to lower Ordovician sedimentary successions deposited on Archean to late Mesoproterozoic crystalline complexes, reworked during Caledonian orogenesis. Lare Neoproterozoic to lower Ordovician sedimentary strata record the change from an alluvial setting to a marine environment, and eventually to a partially starved (?) turbidite basin. They document rifting from the Rodinian-Pannotian supercontinent, which was unsuccessful until ca. 620–550 Ma when voluminous dikes and mafic/ultramafic complexes were intruded. Baltica's northeastern and eastern regions document episodic intracratonic rifting throughout the Mesoproterozoic, followed by pericontinental passive margin deposition throughout the Cryogenian. In the northeast platformal and deeper-water basin deposits are preserved, whereas the eastern region was later affected by Paleozoic rifting and preserves only shelf deposits. The northeastern and eastern regions define Baltica's Cryogenian northeastern tectonic margin, which was an ocean-facing passive margin of the Rodinia–Pannotia supercontinent. It remained a passive margin until the onset of Timanian orogenesis at ca. 615 Ma, approximately synchronous with the time of Rodinia–Pannotia rifting. Baltica's southern and southwestern regions remain enigmatic and controversial. Precambrian basement is generally hidden beneath thick successions of Ediacaran and younger platform sediments. Similarities between these regions exist, however, and suggest that they may share a similar tectonic evolution in the Cryogenian and therefore define the southern tectonic margin of Baltica at this time. Paleo- to Mesoproterozic basement was affected by Neoproterozoic and younger tectonism, including Cryogenian (?) and Ediacaran rifting. This was followed by Ediacaran (ca. 550 Ma) passive margin sediment deposition at the time of Rodinia–Pannotia break-up, until Early Paleozoic accretion of allochthonous terranes record the transition from rifting to a compressional regime. Paleomagnetic and paleontological data are consistent with Baltica and Laurentia drifting together between ca. 750 and 550 Ma, when they had similar apparent polar wander paths. Microfossil assemblages along the eastern margin of Laurentia and the western margin of Baltica (modern coordinates), suggest proximity between these two margins at this time. At ca. 550 Ma, Laurentia and Baltica separated, consistent with paleomagnetic, paleontological, and geological data, and a late break-up for Rodinia–Pannotia.Neoproterozoic microbial diversificatio