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Alegret, Ortiz & Kaminski (eds.), 2012. Ninth International Workshop on Agglutinated Foraminifera, Abstract Volume
The Cenomanian/Turonian Boundary Event in the Sawin-19 borehole (SE
Poland): restructuring of agglutinated foraminifera assemblages
Danuta PERYT
Institute of Paleobiology, Polish Academy of Sciences, 00-818 Warszawa, Poland.
e-mail: d.peryt@twarda.pan.pl
A major paleoceanographic event, often referred to as the Oceanic Anoxic Event II or the
Cenomanian/Turonian Boundary Event (CTBE), took place in the latest Cenomanian-earliest
Turonian. The CTBE involved among others a significant faunal turnover.
The agglutinated foraminiferal response to the CTBE was studied from a 30-m-thick
section in the Sawin-19 borehole, SE Poland, representing the Rotalipora cushmani,
Whiteinella archaeocretacea and Helvetoglobotruncana helvetica Zones.
Foraminiferal assemblages from the Rotalipora cushmani Zone yield both planktonic
and benthic taxa. Planktonic foraminifera form 10-30% of the assemblages. The benthic
assemblage is relatively high diverse and is typical of the late Cenomanian; calcareous forms
dominate assemblages. Upward the Rotalipora cushmani Zone agglutinated component
gradually increases. Tritaxia spp., presumed infaunal species, form up to 40% of benthic
foraminiferal assemblages in the upper part of the Zone and in that interval rare species such
as Arenobulimina sabulosa, A. conoidea, A. frankei, A. advena, Pseudotextulariella cretosa,
Ataxophragmium depressum, Gaudryinopsis gradata, Verneuilinoides gorzoviensis, Plectina
cenomana underwent gradual extinction.
At the boundary between Rotalipora cushmani and Whiteinella archaeocretacea
Zones, Tritaxia spp. completely disappear. Tritaxia pyramidata, T. macfadyeni and T.
plummerae become extinct. Tritaxia tricarinata temporarily disappears.
At the base of the Whiteinella archaeocretacea Zone, a rapid increase in the
percentage of planktonic foraminifera is recorded, and a high P/B ratio (60-90%) continues
upwards. Low species diversity and domination by two to four species are recorded in the
assemblages of benthic foraminifera in the lower part of Whiteinella archaeocretacea Zone.
Arenobulimina preslii and Marssonella oxycona are immigrants which replaced Tritaxia spp.;
they are main agglutinated components of benthic foraminifera assemblages in the very basal
part of the zone. Higher up, Tritaxia tricarinata re-appear and a slow upward increase in a
diversity of agglutinated foraminiferal assemblages is recorded.
The pattern of change from diverse foraminiferal communities of the middle
Rotalipora cushmani Zone to high dominance, low diversity communities at the base of the
Whiteinella archaeocretacea Zone suggests that changes occurred in the lower part of the
water column which was related, in part, to benthic oxygenation and trophic resources.
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