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1. Data report: revised Pleistocene sediment splice for Site U1457, IODP Expedition 355

   https://doi.org/10.14379/iodp.proc.355.202.2019  

   Lyle, M.; Saraswat, R. (February 2019, Proceedings of the International Ocean Discovery Program)

   null (Ed.)

   Sediment cores from adjacent holes at a drill site are typically spliced to make a continuous sediment record that spans sediment gaps that occur between sediment cores within each hole. The splice also provides a template for later sampling. During International Ocean Discovery Program Expedition 355, we made such a splice for both Sites U1456 and U1457 using shipboard Whole-Round Multisensor Logger and Section Half Multisensor Logger data. The shipboard-spliced sediment section at Site U1457 was constructed for the advanced piston corer interval to an age of about 1.5 Ma. Additional postexpedition planktonic foraminifer stable isotope data (Globigerinoides ruber δ18O) show that the shipboard stratigraphic tie between Cores 355-U1457B-1H and 355-U1457A-1H was wrong. This paper describes a revised splice that appends Core 355-U1457A-1H to the base of Core 355-U1457B-1H. The core composite depth below seafloor depths of the remaining splice have been revised because of this change. The revised splice interval is also longer by 1.2 m to accommodate the lower part of Core 355-U1457B-1H. In addition, a break of unknown thickness is present between Cores 355-U1457B-1H and 355-U1457A-1H. The revised splice interval table is included in this report. 

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2. FACIES AND ICHNOFABRICS IN THE PALEOCENE OF CHICXULUB: A RECORD OF THE RECOVERY OF LIFE POST-IMPACT

   Whalen, M; O’Malley, K; Lowery, C; Rodriguez-Tovar, F; Morgan, J; Gulick, S. (January 2017, Lunar and planetary science conference abstracts)

   Introduction: IODP/ICDP Expedition 364 recovered core from 505.7-1334.7 m below the seafloor (mbsf) at Site M0077A (21.45° N, 89.95° W) atop the peak ring in the Chicxulub impact structure. The core penetrated Paleogene sedimentary rocks, impactrelated suevite, melt rock, and granitic basement [1]. Approximately 110 m of post-impact, hemipelagic and pelagic sedimentary rocks were recovered, ranging from middle Eocene (Ypresian) to basal Paleocene (Danian) in age [1]. The transition between suevite and basal Paleocene sedimentary rocks is a remarkable succession of fining upward gravel to sand-sized suevite (Unit 2A) overlain by laminated carbonate-rich siltstone (Unit 1G, “impact boundary cocktail” [2]) that records the settling of fine-grained material postimpact [1]. This study concentrates on the carbonaterich Paleocene sedimentary rocks of overlying Unit 1F [1]. The degree of bioturbation, or ichnofabric index (II) [3, 4], provides a semiquantitative estimate of the density of burrowing within sedminentary facies. Collection of II data within the context of facies analysis thus yields insight into the initial and then continued disturbance of sediment by burrowing organisms recording the return of life to the crater (Fig. 1). Unit 1G: The unit extends from 616.58-617.33 mbsf (Fig. 1) and consists mainly of dark brown to dark grayish brown calcareous siltstone but is complex with several different lithologies and post-depositional pyrite nodules that disrupt bedding. The base of the unit is a sharp, stylolitized contact overlain by two ~1 cm thick, normally graded beds. Overlying, up to 617.17 mbsf, the siltstone contains internally finely laminated cm-scale beds that alternate between dark brown and grayish brown. Above, up to 616.97 mbsf is a package with mm bedded couplets of dark brown and grayish brown calcareous siltstone that grade upward into similarly colored cm bedded couplets that then thin upward into mm bedded couplets again. Above this interval bedding is indistinct and appears to be obscured by soft sediment deformation from 616.66- 616.97 mbsf. The upper part of the unit is slightly deformed with greenish marlstone and interbedded lighter gray siltstone displaying a distinct downwarp from 616.58-616.66 mbsf. Rare oval structures, that are potential individual burrows, occur down to 616.65 mbsf. Unit 1F: The unit records the remainder of the Paleocene and extends from 607.27-616.58 mbsf (Fig. 1). The base of the unit is a sharp contact at the base of a greenish claystone (II 2) that overlies Unit 1G [1]. It consists dominantly of interbedded light gray to light bluish gray wackestone and packstone (II 3-5) and light to dark bluish gray marlstone (II 2) at cm-dmscale. All lithologies contain wispy stylolites. The lower portion of the unit (616.58 and 607.74) is cyclic with cm-dm-scale bedding and light greenish-blue to bluish marlstone bases (II 2-3) that grade upward into light gray or light bluish gray wackestone and packstone (II 3-5). Contacts between lithologies are usually gradational due to burrowing. The upper portion of the unit from 610.25 to 607.74 mbsf is a light yellowish brown burrowed packstone (II 4) intercalated with gray marlstone (II 2). The uppermost 7.5 cm is calcite cemented with 1 cm wide burrows (II 3-4). Clasts are fine to coarse sand size and include foraminifera. The upper surface of this unit is a hardground and minor unconformity overlain by Eocene rocks [1]. Ichnofabric Index: II data provides a window onto the return of life post-impact (Fig. 1). Rare structures in the upper most sandy suevite (Unit 2A) and in Unit 1G (Core 40R-1) resemble bioturbation structures but may also represent fluid escape [1]. The first welldefined oval structures that appear to be burrows occur in the upper part of Unit 1G (Fig. 1, 616.58-616.65 mbsf). Unequivocal burrows (II 2) that disturb sedimentary facies occur just above, at 616.56 mbsf in Unit 1F (Fig. 1). II of 3-4 are reached 5-6 cm above indicating significant disruption of original sedimentary strutures. An II of 5 is first documented at 616.16 mbsf (Fig. 1). Above this level through the Paleocene succession II largely varies between 2 and 5 with rare laminated intervals (II 1). Bioturbation intensity correlates well with facies changes and more marly facies display lower levels of bioturbation than more carbonate- rich facies. This correlation implies a depth and/or paleoredox control on the distribution of bioturbating organisms. Discussion: II and the return of life: The II data indicate that burrowing organisms were likely reestablished in the crater before the end of deposition of Unit 1G. Biostratigraphic analyses document a mix of Late Cretaceous and earliest Danian taxa within Unit Lunar and Planetary Science XLVIII (2017) 1348.pdf 1G and lowermost Danian zone Pα documented in the lowermost part of Unit 1F down to 616.58 mbsf [1]. P1a taxa occur down to 616.29 mbsf with P1b-P4 recorded upward through 607.27 m [1]. Burrowing organisims were thus active by earliest Danian indicating a rapid return of life to the crater. Hydrocode modeling implies that much of the deformation and peak ring formation was completed within minutes of the impact [5]. Deposition and reworking of impact breccia by tsunami and seiches likely extended for several days [6]. More refined estimates for the return of life to the crater may be possible with more detailed analysis of the deposition of laminae within Unit 1G that records marine settling of fine-grained material that may have taken days to months. 

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3. Data report: Middle to Lower Miocene radiolarian biostratigraphy in the Western Pacific Warm Pool at IODP Expedition 363 Site U1490: preliminary results

   https://doi.org/10.14379/iodp.proc.363.206.2023  

   Matsuzaki, K.M.; Kamikuri, S.; Sagawa, T. (May 2023, Proceedings of the International Ocean Discovery Program Expedition reports)

   Because the western equatorial Pacific Ocean is famous for its calcareous oozes, various biostratigraphic studies on planktonic foraminifers and calcareous nannofossils have been conducted in this region. As a result, western equatorial Pacific Ocean–based studies have established that the tropical Pacific region drives the atmospheric circulation by high seawater temperature, strongly influencing the global climate. Based on this finding, a number of sites were cored in this region during International Ocean Discovery Program (IODP) Expedition 363. Shipboard results unexpectedly revealed that radiolarians are abundant and well preserved in sediment from Eauripik Rise Site U1490 between 220 and 350 m core depth below seafloor, Method A (CSF-A), within an interval of calcareous ooze composed primarily of calcareous nannofossils and foraminifers. Paleomagnetic reversal event and calcareous nannofossil and planktonic foraminiferal bioevents suggested that the interval from 220 to 350 m CSF-A corresponded to the Middle to Early Miocene. This study investigated radiolarian assemblages and the biostratigraphy of core catcher samples obtained from Hole U1490A between 250 and 350 m CSF-A. Notably, the last occurrence (LO) of Artophormis gracilis (Riedel) was confirmed at ~338 m CSF-A, demonstrating that the base of the site is older than 22.6 Ma in age. Additionally, the first occurrence (16.9 Ma) and LO (13.9 Ma) of Calocyclas costata Riedel were identified at 246.7 and 227.8 m CSF-A, respectively, and the LO of Didymocyrtis prismatica (Haeckel), indicating an age of 17.7 Ma, was recorded at 258.5 m CSF-A. We also calculate preliminary sedimentation rates based on the Early Miocene radiolarian biostratigraphy and provide taxonomic notes on radiolarian species. 

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4. Data report: revised composite depth scale and splice for IODP Expedition 363 Site U1483

   https://doi.org/10.14379/iodp.proc.363.201.2020  

   Gong, L.; Lübbers, J.; Beil, S.; Holbourn, A. (June 2020, Proceedings of the International Ocean Discovery Program)

   null (Ed.)

   The shipboard sediment splice of International Ocean Discovery Program Expedition 363 Site U1483, drilled in 1733 m water depth on the Scott Plateau off Northwest Australia, was primarily based on a composite of the magnetic susceptibility records at 2.5 cm resolution from three holes drilled at this site. We performed X-ray fluorescence (XRF) core scanning at 2 cm intervals with overlaps of ~1–2 m at splice tie points and used these new data to verify the tie points along the original splice from 0 to 211.53 m core composite depth below seafloor (CCSF). Based on the XRF records, we revised the position of three original tie points and present a revised composite depth scale for Site U1483. These revisions resulted in shifts of up to 94 cm relative to the original shipboard offsets and a continuous section extending down to 211.62 m revised core composite depth below seafloor (r-CCSF). 

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5. Expedition 377 Scientific Prospectus: Arctic Ocean Paleoceanography (ArcOP)

   https://doi.org/10.14379/iodp.sp.377.2021  

   Stein, R.; St. John, K.; Everest, J. (August 2021, Scientific prospectus)

   null (Ed.)

   Prior to 2004, geological sampling in the Arctic Ocean was mainly restricted to near-surface Quaternary sediments. Thus, the long-term pre-Quaternary geological history is still poorly known. With the successful completion of the Arctic Coring Expedition (ACEX) (Integrated Ocean Drilling Program Expedition 302) in 2004, a new era in Arctic research began. Employing a novel multivessel approach, the first mission-specific platform (MSP) expedition of the Integrated Ocean Drilling Program proved that drilling in permanently ice-covered regions is possible. During ACEX, 428 m of Quaternary, Neogene, Paleogene, and Campanian sediment on Lomonosov Ridge were penetrated, providing new and unique insights into Cenozoic Arctic paleoceanographic and climate history. Although it was highly successful, ACEX also had three important limitations. The ACEX sequence contains either a large hiatus spanning the time interval from late Eocene to middle Miocene (based on the original biostratigraphic age model) or an interval of strongly reduced sedimentation rates (based on a more recent Os-Re-isotope-based age model). This is a critical time interval, spanning the time when prominent changes in global climate took place during the transition from the early Cenozoic Greenhouse Earth to the late Cenozoic Icehouse Earth. Furthermore, generally poor recovery during ACEX prevented detailed and continuous reconstruction of Cenozoic climate history. Finally, a higher-resolution reconstruction of Arctic rapid climate change during Neogene and Pleistocene times could not be achieved during ACEX. Therefore, Expedition 377 (Arctic Ocean Paleoceanography [ArcOP]) will return to the Lomonosov Ridge for a second MSP-type drilling campaign with the International Ocean Discovery Program to fill these major gaps in our knowledge on Arctic Ocean paleoenvironmental history through Cenozoic times and its relationship to global climate history. The overall goal of this drilling campaign is to recover a complete stratigraphic sedimentary record of the southern Lomonosov Ridge to meet our highest priority paleoceanographic objective, the continuous long-term Cenozoic climate history of the central Arctic Ocean. Furthermore, sedimentation rates two to four times higher than those of ACEX permit higher-resolution studies of Arctic climate change. The expedition goal can be achieved through careful site selection, the use of appropriate drilling technology and ice management, and by applying multiproxy approaches to paleoceanographic, paleoclimatic, and age-model reconstructions. The expedition will complete one primary deep drill hole (proposed Site LR-11B) to 900 meters below seafloor (mbsf), supplemented by a short drill site (LR-10B) to 50 mbsf, to recover an undisturbed uppermost (Quaternary) sedimentary section. This plan should ensure complete recovery so scientists can construct a composite section that spans the full age range through the Cenozoic. 

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