Quantitative biostratigraphy of Middle Jurassic – Early Cretaceous foraminiferal events from the Arctic - 25/10/19
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Abstract |
Arctic foraminiferal events are of great interest for biostratigraphical understanding of the Boreal Realm, but Greenland, Svalbard, Barents Sea and Siberia have limited published studies in the Middle Jurassic – Early Cretaceous. Selected foraminiferal events data have been compiled and entered into a database. This database has been subjected to quantitative analysis with the help of the RASC program (RAnking and SCaling). In total, 740 foraminiferal events from 13 outcrops and wells were used to build a large-scale zonation for the Arctic with seven tentative zones, using the probabilistic zonation feature of RASC. Published foraminiferal zones, lithostratigraphic units, and palaeoenvironmental interpretations for each area are compared and discussed, and their correlations to the calculated ranked and scaled optimum sequences of events contrasted. The chosen marker species in the literature and their correlative reliability over the Boreal Realm is investigated, and foraminiferal event arrangement in the ranked optimum sequence is compared to the published age ranges for the taxa. These investigations have highlighted foraminiferal events, which are reliable and traceable through more than one basin, such as the first and last occurrences of Recurvoides obskiensis and Schleiferella emeljanzevi, the first occurrence of Recurvoides scherkalyensis, and the last occurrence of Trochammina septentrionalis. Statistical tests performed by the RASC program have revealed other events, which could be unreliable, for example the first occurrences of Cribrostomoides subretusus and Ammoglobigerina canningensis, and the last occurrence of Eomarssonella paraconica. The reliability of published zones on a local scale depends on various factors, and they can prove to be too detailed if the goal is to correlate foraminiferal events to other areas. The ranking and scaling of the RASC program is an extremely valuable tool in quantitative stratigraphy, and with its help the first step has been taken towards building a biostratigraphic zonation for the Arctic. The zonation presented herein is the first published zonation of Arctic foraminiferal events.
Le texte complet de cet article est disponible en PDF.Keywords : RASC, Biostratigraphy, Foraminifera, Arctic, Jurassic, Early Cretaceous
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