Data report: radiolarians from the latest Cenomanian and Turonian, Holes U1512A and U1516C, IODP Expedition 369

A total of 47 samples from the Albian to Turonian at three sites from International Ocean Discovery Program (IODP) Expedition 369 were investigated for radiolarian faunas. With a few exceptions, the preservation of radiolarian tests did not allow for a taxonomically sophisticated and proper determination. Consequently, radiolarian assemblages from only three samples from the uppermost Cenomanian in Hole U1516C, the lower Turonian in Hole U1516C, and the upper Turonian in Hole U1512A are described and illustrated here. The three faunas described include faunal elements reported from time equivalent successions in the Tethys as well as the western Pacific.


Introduction
International Ocean Discovery Program (IODP) Expedition 369 recovered sediments from the Great Australian Bight and Mentelle Basin in the southeast Indian Ocean ( Figure F1). One of the main reasons for drilling the Expedition 369 sites was their high paleolatitude (60°-62°S) position, which allowed the sampling of high-latitude successions that are important for a reconstruction of the dynamics of the Cretaceous greenhouse climate system (Huber et al., 2019). Cenomanian to Turonian radiolarians from this part of the Cretaceous world have only been described in a single study so far that documented some specimens from Deep Sea Drilling Project (DSDP) Site 258 (Riedel and Sanfilippo, 1974). For this reason, documentation of new radiolarian records from Expedition 369 sediments is warranted. Note that because of their moderate to poor preservation, the three assemblages described here do not represent the entire taxonomic spectrum of radiolarians from this stratigraphic interval and area.

Material and methods
All samples were crushed into small pieces (approximately 1 cm in diameter), dried, and gently disaggregated using a 90% water and 10% hydrochloric acid solution. After soaking and reacting, the samples were washed with warm water over a 40 μm mesh sieve and dried at 50°C. The fraction >40 μm was then dry-sieved into fractions >125 μm and >63 μm. From each fraction, radiolarians were picked in slides. Scanning electron microscope (SEM) images were acquired at the laboratories of the Federal Institute for Geosciences and Natural Resources (BGR) in Hannover (Germany) using an FEI Sirion 200.

Results
The estimated abundance and preservation of the samples investigated is documented in Table T1. With very few exceptions, radiolarians are rare in the Turonian in Hole U1512A. The abundance, preservation, and species diversity increase upsection. No radiolarians were found in samples from Hole U1513A. The residue, however, consists of siliceous chalks and some faint ghost structures of organisms. The latter might have been radiolarian tests leaving the impression that the absence of radiolarians is not caused by ecological but diagenetic reasons. The diagenetic overprint of the samples investigated from the Cenomanian/Turonian Boundary interval in Hole U1516C is less severe, resulting in comparably well-preserved faunas. The number of species in each sample listed here correlates with the preservation of faunas; the higher the species diversity, the better the preservation:

Stratigraphic implications
The reported stratigraphic ranges of some of the radiolarian species identified allow for summary age estimates of the two samples from Hole U1516C. A. praegallowayi, D. squama, P. clavata, S. conicus, and P. vielseitigus described here from Sample 369-U1516C-28R-4, 26-30 cm, are species typical in younger Late Cretaceous strata. They have not been reported from successions older than early Turonian in age. In contrast, H. barbui and T. pulchra, which are both present in Sample 33R-4, 56-60 cm, have not been reported from strata younger than latest Cenomanian in age. This confirms the presence of the Cenomanian-Turonian transition in Hole U1516C. Another species that hasn't been described in sediments younger than latest Cenomanian in age is N. mclaughlini. In this study, however, it is documented in the late Turonian in Hole U1512A with a little doubt because the preservation is rather poor.

Acknowledgments
This research used samples and/or data provided by the International Ocean Discovery Program (IODP). I would like to thank IODP for making the samples available. Thanks also to Brian Huber and Maria Rose Petrizzo for making me aware of the presence of radiolarians in the Cenomanian and Turonian at the IODP Expedition 369 sites and thus making me enter a kind of time warp resulting in my first (and probably last) involvement in radiolarian research in 20 y. Gabriele Grützner and Sabine Stäger, both at BGR, are thanked for SEM imaging, sample preparation, and production of plates. Finally, I thank Chris Hollis for his constructive review, which greatly improved this manuscript.