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PALAIOS, 2018, v. 33, 525–534 Research Article DOI: http://dx.doi.org/10.2110/palo.2018.045 EARLY FRESHWATER DIATOMS FROM THE UPPER CRETACEOUS BATTLE FORMATION IN WESTERN CANADA 1 2 2 2 PETER A. SIVER, MARIA VELEZ, MONICA CLIVETI, AND PIER BINDA 1Department of Botany, Connecticut College, New London, Connecticut 06320, USA 2Department of Geology, University of Regina, Regina, Saskatchewan, S4S 0A2, Canada email: [email protected] ABSTRACT: Despite the rise of marine diatoms in the world’s oceans throughout the Cretaceous, only a handful of fossil localities worldwide detail invasion of freshwater habitats by diatoms commencing in the Late Cretaceous. We report on the occurrence of numerous freshwater diatom specimens and species from the Battle Formation, an extensive freshwater locality in western Canada that formed in the Late Cretaceous approximately 66.5 million years ago (Ma). The formation represents one of the oldest known localities worldwide harboring definitive remains of freshwater diatoms, contains the oldest known freshwater specimens of the centric diatom genus Aulacoseira,and confirms that these early Aulacoseira colonizers formed filaments linked together with interdigitating spines. We further document a high diversity of araphid pennate diatoms belonging to the order Fragilariales. Seven pennate morphotypes were uncovered, six of which definitively lacked a raphe and whose closest modern relatives are in the genera Fragilariforma, Fragilaria,andStauroforma. Given the extensive coverage of the Battle Formation, it is possible that it represents a network of numerous smaller shallow waterbodies that collectively offered a diversity of environments for colonization, making it a unique deposit for examination of early freshwater diatoms. INTRODUCTION The Battle Formation represents an extensive freshwater environment that was deposited across much of southern Alberta and into southwestern Diatoms are photosynthetic, unicellular organisms with siliceous cell Saskatchewan, Canada, during the Late Cretaceous, approximately 66.5 walls that can dominate planktonic, periphytic, and benthic habitats in Ma (Binda 1970; Picard and High 1972; Srivastava and Binda 1984). The aquatic systems worldwide (Round et al. 1990; Medlin et al. 2000). High lake represented by the Battle Fm. is one of the largest lakes in the geologic cell abundances, often coupled with impressive species diversity, make record formed, in part, due to reduced drainage caused by a gentle tectonic diatoms integral elements of aquatic food chains and significant uplifting to the east (Binda 1970; Picard and High 1972). Whether the components of biogeochemical cycles in both freshwater and marine environment was one contiguous shallow water body, or a series of systems (Field et al. 1998; Armbrust et al. 2004; Katz et al. 2005). Diatoms interconnected smaller lakes, marshes and bogs is unknown. Remains of form a cornerstone of paleobiological research and have contributed freshwater lycopods, ferns, chrysophyte cysts and sponge gemmoscleres immensely to our understanding of environmental issues such as lake- were previously documented by Srivastava and Binda (1984). The purpose water acidification, eutrophication, and climate change (Smol and of this paper is to report on the occurrence of freshwater diatoms from the Stoermer 2010). Battle Fm. Species representing centric diatoms, araphid pennate diatoms, Current estimates yield a Mesozoic origin for the diatoms and since that and a possible raphe-bearing form, have been uncovered and are described time period the group has become one of the most successful protistan using both light and scanning electron microscopy. Early colonization of lineages in recent geologic history (Kooistra and Medlin 1996; Sims et al. freshwater environments by siliceous algae is discussed. 2006; Medlin 2016). Their radiation in the world’s oceans commenced in the early Cretaceous (ca. 145 Ma) and despite the rapid and prolific rise of SITE DESCRIPTION marine diatoms throughout the Cretaceous (Harwood and Nikolaev 1995), invasion of freshwater habitats, presumably from marine environments, The Battle Fm. outcrops in the southern part of the provinces of Alberta appears to have occurred later near the end of the Cretaceous (Chac´on- and Saskatchewan (Canada), and is stratigraphically located immediately Baca et al. 2002; Ambwani et al. 2003; Singh et al. 2006; Buatois et al. above the Maastrichtian Whitemud Fm. and below the Maastrichtian– 2016). Further, based on examination of numerous fossil sites, diatoms do Paleocene Scollard and Ravenscrag formations of Alberta (AB) and not begin to establish a prominence in freshwater environments until at Saskatchewan (SK), respectively (Binda 1970; Lerbekmo et al. 1987). The least the middle (Strelnikova and Lastivka 1999; Siver and Wolfe 2009) to Battle Fm. stretches from just south of Edmonton, AB, in a northwest to late (Lohman and Andrews 1968; Benson and Kociolek 2012) Eocene. southeast direction to the Cypress Hills region of southwestern SK, Significant diversification of the group does not occur in North America outcropping extensively in Red Deer, Drumheller and Cypress Hills until the Miocene (Bradbury and Krebs 1995), possibly correlated with (Fig.1A, 1B). The formation is a 3–12 m thick, massive, dark brown expansion of grasslands (Kidder and Gierlowski-Kordesch 2005). Despite claystone deposit (Irish 1970; Gibson 1977) situated approximately 50 m recent discoveries, the fossil record surrounding the early invasion of below the K–Pg boundary (Binda 1970). A thin silicified tuffaceous layer, freshwater habitats by diatoms, including the initial colonizing taxa, is known as the Kneehills Tuff, was deposited in the upper portion of the poor. Battle Fm. and used to estimate the age of the formation based on K/Ar Published Online: December 2018 Copyright Ó 2018, SEPM (Society for Sedimentary Geology) 0883-1351/18/033-525 Downloaded from https://pubs.geoscienceworld.org/sepm/palaios/article-pdf/33/12/525/4597907/i0883-1351-33-12-525.pdf by Kathleen Huber on 24 January 2019 526 P.A. SIVER ET AL. PALAIOS FIG. 1.—Details of the study location. A, B) Geographic location of the Gleichen locality relative to other known areas (Horseshoe Canyon, Standard and Cypress Hills) where outcrops of the Battle Formation exist. C) The Gleichen site showing the underlying Whitemud Fm. and the overlying Battle Fm. Note the chromatic contrast between the two units. D) The Kneehills Tuff layer capping the Battle Fm. (arrow). dating of sanidine and biotite minerals (Allan and Sanderson 1945; MATERIALS AND METHODS Lerbekmo et al. 1987). The chromatic contrast between the Battle and Mudstone samples from the Gleichen Pond locality were prepared for Whitemud formations is striking (Fig. 1C). microscopy and examined for microfossil remains using light (LM) and North of the town of Gleichen (AB), on Range Road 231, adjacent to the scanning electron microscopy (SEM). Although all samples contained 0 00 0 00 Hamlet of Gleichen water reservoir (50852 49.7 N/113804 21 W) there is microfossil remains and were examined as part of this project, samples an outcrop displaying 3 m of Battle Fm. (Fig. 1B). This site, referred to as GP4, GP5, GP6, and GP7, representing approximately 80 cm of the strata, GP, was sampled in September of 2017. The contact with the underlying yielded the highest number of diatom specimens. Whitemud Fm. is visible west of the reservoir (Fig. 1C); to the east, the Samples for LM observation were prepared by oxidizing 100–500 mg of outcrop is capped by a continuous indurated layer of the Kneehills Tuff mudstone fragments with 30% H2O2 under low heat for a minimum of an (Fig. 1D). The 3 m deep outcrop was systematically sampled every 20 cm hour. Two different cleaning procedures were used, both yielding similar starting at the top of the Whitemud Fm. and labeled as GP1, GP2, etc. results. In one case, 300 ml of distilled water was added to the oxidized through to the top of the Battle Fm. A minimum of 50 gm of sediments slurry and left at room temperature for 24 hours to settle. Two-hundred ml was taken from cleaned surfaces at each interval. Sediments are composed were then discarded leaving a 100 ml sample. In the second procedure, the of shale displaying the typical fracture of the formation reported in Binda oxidized slurry was washed five times with distilled water using repeated (1970) with varying degrees of organic content, from highly organic, centrifugation and the final pellet diluted to 15 ml and stored in a glass carbonaceous roots at the bottom, to coaly shale. Shale is intermixed with vial. Aliquots of each preparation were air dried onto glass coverslips, light colored silt in the top two samples. mounted onto glass slides with Naphrax, and observed with either an Downloaded from https://pubs.geoscienceworld.org/sepm/palaios/article-pdf/33/12/525/4597907/i0883-1351-33-12-525.pdf by Kathleen Huber on 24 January 2019 PALAIOS CRETACEOUS FRESHWATER DIATOMS 527 Olympus CX10 coupled with an Infinity 1-2C camera, or a Leica DMR 3.5–5 lm(n¼ 20). Valve shape resembled species in the genera coupled with a Zeiss Axiocam 506 color camera. Fragilaria, Fragilariforma,orStauroforma. For SEM observation, an aliquot of each slurry was air dried onto a Morphotype #2 (Figs. 4A–4C, 5C), also a common form in samples piece of heavy duty aluminum foil. The aluminum foil samples were GP5–GP7 with over 50 specimens observed, had linear valves with wavy trimmed and attached to aluminum stubs with Apiezont wax. Samples margins and attenuated to slightly rostrate apices. One valve type was were coated with a mixture of gold and palladium for two minutes with a slightly constricted in the center with biundulate margins (Fig. 5C), while Polaron Model E sputter coater, and examined with an FEI Nova others were slightly swollen in the center forming triundulate margins (Fig. NanoSEM 450 FESEM. Measurements of specimens were taken directly 4A–4C). Striae were mostly parallel and the axial area was narrow or from electron micrographs. unresolved.

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