Biostratigraphy, phylogeny and systematics of Paleocene trochospiral planktic foraminifera

Citation:
Berggren, WA, Norris RD.  1997.  Biostratigraphy, phylogeny and systematics of Paleocene trochospiral planktic foraminifera. Micropaleontology. 43:1-116.

Keywords:

basin, equatorial pacific, isotopic composition, ocean, sea, stable isotopes

Abstract:

We present an analysis of the biostratigraphic distribution of trochospiral (sub)tropical Paleocene planktonic foraminifera at four oceanic sites located in the Atlantic (DSDP Site 384), Indian (DSDP 213 and ODP 758) and Pacific (ODP 465) together with a review of Paleocene planktic foraminiferal biostratigraphy and zonal schemes developed in the Former Soviet Union (FSU) and a revised Paleocene zonal scheme developed by one of us (WAB). We review the vicissitudes of the classification of Paleocene trochospiral planktic foraminifera at the generic level and present a detailed taxonomic and phylogenetic treatment of 43 species (including one new form, Globanomalina archaeoimitata Norris and Berggren). A significant aspect of the synonymies presented here is the inclusion of geographic location and biostratigraphic occurence data for/in each entry thereby providing information on the paleobiogeographic and biostratigraphic distribution on each taxon. Cladistic and stratophenetic phylogenies suggest that all Paleocene trochospiral planktic foraminifera are monophyletic. Three major lineages diverged in the earliest Danian and gave rise to Globanomalina, Subbotina, and founding species of the Morozovella group. All are derived from Hedbergella - a survivor of the terminal Cretaceous extinction. Use of the Cretaceous genera Globotruncanella and Rugoglobigerina as putative ancestors both produce less resolved cladograms than Hedbergella, and thus they probably were not direct founders of the Cenozoic radiation. Hence, even if there were other survivors of the extinction besides hedbergellids, they did not contribute to the subsequent radiation of trochospiral taxa. Globanomalinids remained morphologically conservative in the Danian but the lineage rapidly spun off the parasubbotinid and subbotinid groups as well as Praemurica taurica. All three lineages are present in the earliest Danian along with Globanomalina and illustrate the rapidity of the morphological diversification. The most structurally divergent groups are Parasubbotina and Subbotina which acquired inflated chambers, pitted wall texture and involute coiling compared to the globanomalinids. In addition, Subbotina acquired acicular spines similar to those of modern Globigerinoides and Globigerina. In contrast, P. taurica remained structurally reminiscent of Globanomalina but founded two major lineages, Morozovella and Igorina, in the late Danian. Praemurica is a paraphyletic group transitional between Globanomalina and the morozovellids and igorinids. Morozovella split early into two lineages: one with completely muricate walls (M. apanthesina-M. aequa) and a group with muricae concentrated on peripheral regions of the shell, such as the keel, and later the adumbilical ridges (M. angulata-M. velascoensis). Igorina is a sister group to Morozovella and itself is part of a larger group that includes the acarininids of the late Paleocene. Ecologically, each of the major Paleocene lineages developed distinct life habitats revealed by their morphology and stable isotope geochemistry. Comparisons between upper Maastrichtian planktic foraminifera show that hedbergellids consistently have some of the heaviest delta(18)O of any coexisting species and probably lived within the thermocline. The delta(18)O of Hedbergella holmdelensis is nearly identical with that of Globanomalina planocompressa and early representatives of P. taurica at DSDP Site 384 in the North Atlantic. Both Danian groups may have grown in the thermocline since both are about 0.5 parts per thousand delta(18)O more positive than coexisting Chiloguembelina. However, P. taurica appears to have become a near-surface dweller less than 1 my after the terminal Cretaceous extinction, whereas Globanomalina continued to grow in the thermocline throughout the remainder of the Paleocene. Likewise, Parasubbotina and Subbotina began as deep-water groups and remained in this habitat. Once established in the surface ocean, morozovellids acquired photosymbionts by -61.5 Ma ago. Photosymbiosis is indicated by the common occurrence of very negative delta(18)O throughout growth, and a positive, and large gradient in delta(13)C during ontogeny similar to the distinctive chemistry of extant photosymbiotic foraminifera. There is no isotopic evidence that the subbotinids ever developed photosymbiotic relationships despite their general resemblance in gross morphology and spinose wall texture to modern photosymbiotic globigerinids. The subbotinids may had a life habit analogous to modem carnivorous, non-photosymbiotic, Globigerina bulloides. The development of the Paleocene radiation shows that many of its major themes were established during the earliest Danian. The influence of the surviving hedbergellids on the ecologic and skeletal evolution of Danian species was short-lived as the subbotinid, parasubbotinid, and praemuricate lineages rapidly diverged from the conservative globanomalinid root-stock. However, some innovations, such as the acquisition of photosymbiosis in trochospiral foraminifera and keeled morphologies by Morozovella, as well as the distinctive acarininid morphology, did not appear until later in the Paleocene. The globanomalinids, too, developed keeled morphologies unknown in their Cretaceous antecedents although they retained the hedbergellid tendency to speciate slowly in a deep water habitat.

Notes:

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DOI:

10.2307/1485988