Foss. Rec., 21, 183–205, 2018 https://doi.org/10.5194/fr-21-183-2018 © Author(s) 2018. This work is distributed under the Creative Commons Attribution 4.0 License. The Paleocene record of marine diatoms in deep-sea sediments Johan Renaudie1, Effi-Laura Drews1,2, and Simon Böhne1,2 1Museum für Naturkunde, Leibniz-Institut für Evolutions- und Biodiversitätsforschung, Berlin, Germany 2Rheinische Friedrich-Wilhelms-Universität, Bonn, Germany Correspondence: Johan Renaudie ([email protected]) Received: 27 March 2018 – Revised: 5 August 2018 – Accepted: 8 August 2018 – Published: 20 August 2018 Abstract. Marine planktonic diatoms, as today’s ocean main with two pulses of increased diversification: a short-term one carbon and silicon exporters, are central to developing an un- near the Eocene–Oligocene transition (Rabosky and Sorhan- derstanding of the interplay between the evolution of marine nus, 2009; Lazarus et al., 2014; Cermeño et al., 2015) and life and climate change. The diatom fossil record extends as a second, larger one after the beginning of the Miocene far as the Early Cretaceous, and the late Paleogene to Recent (Lazarus et al., 2014; Cermeño et al., 2015). interval is relatively complete and well documented. Their Despite initial colonization of the open ocean in the ear- early Paleogene record, when diatoms first expanded sub- lier Late Cretaceous (Harwood and Nikolaev, 1995; Har- stantially in the marine plankton, is hampered by decreased wood et al., 2007), they are, in the literature, only found preservation (notably an episode of intense chertification in in this setting worldwide, consistently well preserved and in the early Eocene) as well as by observation bias. In this arti- significant amounts, only at the end of the middle Eocene cle, we attempt to correct for the latter by collecting diatom (e.g. Baldauf and Barron, 1990; Barron et al., 2015; Re- data in various Paleocene samples from legacy Deep Sea naudie, 2016). Paleocene diatoms, in particular, are under- Drilling Project and Ocean Drilling Program deep-sea sedi- studied. While diatom-bearing land sections are known from ment sections. The results show a different picture from what this time period (Harwood, 1988; Homann, 1991; Fenner, previous analyses concluded, in that the Paleocene deep-sea 1994; Hollis et al., 2017), in particular on the Russian plat- diatoms seem in fact to have been as diverse and abundant form (e.g. Jousé, 1949, 1955; Oreshkina and Aleksandrova, as in the later Eocene, while exhibiting very substantial sur- 2007; Aleksandrova et al., 2012; Radionova et al., 2003; Ore- vivorship of Cretaceous species up until the Eocene. shkina and Radionova, 2014), then an epicontinental shallow sea, few diatom-bearing Paleocene sediments have been re- trieved or studied from the deep sea (Mukhina, 1976; Gom- bos Jr., 1977, 1984; Fenner, 1991, 2015; Fourtanier, 1991). 1 Introduction This scarcity of Paleocene data seriously hinders our abil- ity to reliably reconstruct the early Cenozoic macroevolu- Diatoms are known from the fossil record as early as in tionary history of marine planktonic diatoms (Cervato and the Early Cretaceous (Harwood et al., 2004, 2007), although Burckle, 2003; Lazarus et al., 2014; Renaudie, 2016) and molecular phylogenies tend to place their origin some- with it our ability to understand the relation between their time between the Permian and the early Jurassic (Sorhan- evolution, the evolution of other planktonic forms and the nus, 2007; Medlin, 2015). They supposedly originated from evolution of climate and the oceans. In this paper, we attempt freshwater forms (Medlin, 2002; Harwood et al., 2004, 2007; to fill that gap in our knowledge by exploring various Pale- Medlin, 2016) and invaded the oceans first with benthic and ocene Deep Sea Drilling Project (DSDP) and Ocean Drilling littoral forms in the earliest part of the Cretaceous and then Program (ODP) sites in order to get a better sense of how this with properly pelagic forms at the end of the Early Creta- group became one of the ocean’s main carbon (Smetacek, ceous, which began radiation in the Late Cretaceous (Har- 1999) and silica sinks (Tréguer et al., 1995). wood and Nikolaev, 1995; Harwood et al., 2007). From that point, they are currently thought to have slowly diversified continuously through the later Cretaceous and the Cenozoic, Published by Copernicus Publications on behalf of the Museum für Naturkunde Berlin. 184 J. Renaudie et al.: Paleocene diatoms in the deep-sea record 86 ● ● 1051A 384 ●● 96 524 208 761B ● ● ● 1121B 327A 752A ● ● ● 700B ● Figure 1. Paleocene map of studied sites. The red dots represent sites for which both the abundance and the taxonomic composition of diatoms were studied; blue is sites at which only the abundance was studied and green is sites at which only the taxonomic composition was studied. The palaeogeographic map was produced using Gplates (Boyden et al., 2011) along with the Wright et al.(2013) rotation model. 2 Material and method performed until there were at least 1000 specimens (when possible) on at least two tracks (see Supplement for more de- × Siliceous microfossils (diatoms, radiolarians, sponge tails) at 200 magnification. A species occurrence table can spicules, silicoflagellates and others) were counted on be found in Table S1 and the taxonomic list, with comments strewn slides from DSDP sites 86, 208, 327A, 384, 524 and synonymies, in AppendixA. Family assignments of di- and ODP sites 700B, 761B, 1051A and 1121B, and diatom atom genera in the text follow Nikolaev et al.(2001). occurrences were observed and identified at the species The age models of all sites come either from the NSB level in strewn slides from DSDP sites 96, 208, 327A, 384 database (Lazarus, 1994) or were made for this study using and ODP sites 700B, 752A, 761B, 1051A and 1121B (see NSB_ADP_wx (available at https://github.com/plannapus/ Fig.1). nsb_adp_wx/releases, version 0.6.1, last access: 1 Decem- These slides all belong to the Micropaleontological Refer- ber 2017, and based on the ADP software; Lazarus, 1992; ence Center (MRC, Lazarus, 2006) hosted in Berlin, a work- Bohling, 2005) and are given, with details on the biostrati- ing collection of slides from the DSDP and ODP campaign, graphic data used to produce them, as a Supplement. All ages made for radiolarian research. The studied sites were thus are calibrated to the Gradstein et al.(2012) geomagnetic po- selected based on sample availability in the MRC collection. larity timescale. The DSDP slides were produced at the Scripps Institution of The diversity (i.e. species richness) curve shown in Fig.4 Oceanography with 63 µm sieves, while the ODP slides were was produced using the same methodology as in Lazarus produced in part at the Museum für Naturkunde in Berlin and et al.(2014) – updated in Wiese et al.(2016) – using in part at Utsunomiya University, in both cases with 45 µm Shareholder Quorum Subsampling (SQS; Alroy, 2010) with sieves. Because of the use of relatively large-sized sieves, the a quota of 0.7 repeated on 500 trials, corrected using the smallest fraction of diatoms is thus unlikely to be present on D80 metrics (Lazarus et al., 2014), and time bins of 1 mil- the slides, making the reported abundance and diversity of di- lion years. Diversity curves subsampled in half-a-million- atoms a strict minimum. To avoid complications arising from year time bins are also available in the Supplement to al- the variety of methods used to produce these slides (random low direct comparison with Lazarus et al.(2014). Two vs. non-random settling, unknown amount of material used), curves are shown: the red one shows the diversity calcu- only the diatom=radiolarian ratio is reported here, instead of lated in Wiese et al.(2016) using data from the Neptune absolute abundances (see Fig.2), which tells us what propor- NSB database (Lazarus, 1994, http://nsb-mfn-berlin.de, last tion of biogenic opal is composed of diatoms. Counts were access: 27 March 2018) and the black one shows the data Foss. Rec., 21, 183–205, 2018 www.foss-rec.net/21/183/2018/ J. Renaudie et al.: Paleocene diatoms in the deep-sea record 185 54 Early Eocene 56 58 Thanetian 60 Age (Ma) Selandian Paleocene 62 64 Danian 86 327A 208 384 700B 1121 1051A 524 752A 66 0 25 50 75 % 0 10 20 30 40 % 1 2 3 δ13 (a) D/(D+R) (b) Diatoms (% smear slides) (c) Ccibicidoides Figure 2. Paleocene diatom relative abundance record. (a) shows diatom abundance relative to radiolarian abundance (expressed as a per- centage) measured in samples from the MRC collection slides (this study). Panel (b) shows absolute diatom abundance as a percentage of the components of the sediment, as estimated in smear slides by the Leg scientific staff (from the Inital Reports, as synthesized in National Geophysical Data Center, 2000, 2001). Nine sites are shown in both panels: three from the Southern Ocean (Pacific and Indian Ocean sectors, in black), three in the Southern Atlantic (red) and three in the North Atlantic (blue). Panel (c) shows δ13C trends as reported in Cramer et al. (2009) for the Southern Ocean (black), the South (red) and North (blue) Atlantic. from the NSB database as it stands in 2018 and the addition ber of species originating in the Cenozoic for the Paleocene of the occurrence data from this study. Open-nomenclature to earliest Eocene time interval. In this graph, the diversity taxa from NSB or from this study were both discarded from of each age cohort is shown on the left, and the individual the diversity analysis. The small differences outside of the species ranges on which the diversity is calculated is shown early Paleogene that can be seen between the two species di- on the right.