Quantitative Stratigraphy of Sedimentary Sequences
BRITISH
BALTIC
SERIES
SERIES, STAGES
=>
PORKUNI
ASHGILL
-,
PIRGU
0::
« VORMSI
I
NABALA
RAKVERE
CARADOC
OANDU
KEILA
=>
0::
HALJALA
>
KUKRUSE
LLA NDEIL 0
UHAKU
LASNAMAGI
LLANVIRN
ASERI
KUNDA
Cl
VOLKHOV
ARENIG
z
« BILLINGEN
-I
HUNNEBERG
w
0
VARANGU
TREMADOC
PAKERORT
277
Fig.2 Ordovician stratigraphy of the East Baltic region.
Correlation with British series according to Mannil and
Meidla (1994).
The correlation along the confacies belts is based on an extensive biostratigraphical data set (for reviews, see Kaljo and Nestor 1990; Mannil and Meidla
1994) and is well elaborated in the East Baltic. However, the correlation along the
facies gradient remains problematic in several particular stratigraphic levels, including the upper Viruan.
3
The Oandu Event
A pivotal moment in the development of the Baltoscandian Palaeobasin was recognized by numerous palaeontologists in late Viruan. A remarkable extinction
event at the end of the Keilan age and a subsequent short-term (about 1 rna) episode of extremely low microfaunal diversity is documented in North Estonia
(Hints et al. 1989; Kaljo et al. 1995, 1996). It is expressed as an interval containing
remarkably few taxa, followed by the appearance of a new, presumably, immigrated fauna (Mannil 1966; Jaanusson 1976). Such a turnover was named after
the regional stage the Oandu crisis (Kaljo et al. 1995, 1996).