Truuver, K.; Meidla, T. (2015). A Hirnantian deep-water refuge for warm-water ostracods in Baltoscandia. Geological Quarterly. 59(4).

221099

10.7306/gq.1258 [view]

Truuver, K.; Meidla, T.

2015

59(4)

Publication

Available for editors  

The lat est Or do vi cian is marked by a se vere cli mate change, the Hirnantian gla ci ation. This cli ma tic event af fected many ma - rine taxa in clud ing ostracods. Rich and abun dant ostracod as sem blages of the Bal tic Palaeobasin were severely im pov er ished. Many of the typ i cal pre-Hirnatian warm-wa ter ostracod spe cies died out, but also some dis tinct, cold-wa ter spe cies ap peared. Two very dif fer ent but likely co eval lat est Or do vi cian ostracod as sem blages are re corded in the Bal tic coun tries and north east ern Po land. The lat est Or do vi cian Es to nian Shelf (in ner ramp) is char ac ter ized by the Medianella aequa as so ci a tion whilst sec tions in the Livonian Ba sin (mid dle to outer ramp) re veal the Harpabollia harparum as so ci a tion that is thought to rep re sent a cold-wa ter as sem blage be long ing to the Dalmanitina–Hirnantia Fauna sensu lato. A tran si tional as sem blage com posed of a “spe cies mix ture” of typ i cal Hirnantian cold-wa ter and some pre-Hirnantian warm-wa ter ostracod spe cies is de scribed for the first time from the Kêtrzyn IG 1 bore hole, north east ern Po land. The as sem blage is dom i nated by Cryptophyllus pius sp. n. The ge nus Cryptophyllus is rare in the two other well-known as sem blages. The dis cov ery sug gests that mar ginal parts of the Bal tic Palaeobasin could serve as a kind of ref uge for the last rep re sen ta tives of the ostracod fau - nas of the in ner shelf of Bal tic Palaeobasin. The Hirnantian as sem blage is re placed by the low-di ver sity re cov ery as sem - blage that is dated as late Hirnantian–Si lu rian in Es to nia and other ar eas. This sug gests that the po si tion of the sys temic bound ary in the Kêtrzyn bore hole and else where in north east ern Po land should be re-eval u ated.

Ostracoda

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