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1. Milankovitch paleoclimatic, tectonic, and sedimentary signals in late Permian-Early Triassic fluvial-lacustrine records, Bogda Mountains, NW China

   Zhang, W; Yang, W (August 2025, International Meeting for Applied Geoscience and Energy)

   The stratigraphic sections in the Bogda Mountains, Xinjiang, NW China, provide detailed records of the terrestrial paleoenvironments during the late Permian to Early Triassic time at the paleo-mid-latitude of NE Pangea. The South Taodonggou (STDG), Central Taodonggou (CTDG), South Tarlong (STRL) and North Tarlong (NTRL) sections are located in the Tarlong-Taodonggou half graben at the southern foothills of Bogda Mountains (Yang et al., 2010, 2021; Guan, 2011; Peng, 2016; Obrist-Farner and Yang, 2017; Fredericks, 2017; Zheng and Yang, 2020). Lake expansion and contraction, and fluvial peneplanation and deposition, occurred repetitively in the basin (Yang et al., 2007, 2010, 2021). This study carried out gamma analysis, gamma and astronomical tuning, and spectral analysis of the lithofacies and environmental series. The thicknesses of the STDG, CTDG, STRL, and NTRL sections are 282.9 m, 539.7 m, 872.2 m, and 826.1 m, respectively. The major lithofacies are conglomerate, sandstone, mudrock, carbonate rock, and paleosols (Yang et al., 2010, 2021). Gamma analysis generates facies-dependent thickness-time conversion factors (gamma values) to construct gamma-tuned time series (Kominz and Bond, 1990; Bond et al., 1991; Kominz et al., 1991), which are more realistic than the untuned thickness series. Positive and stable gamma values suggest that the assumption of a unique sedimentation rate for each facies is not violated. The sedimentation rates of individual facies ranged from 0.18 to 1.53 m/kyr in the STDG section, 0.13 to 2.43 m/kyr in the CTDG section, 0.29 to 1.03 m/kyr in the STRL section, and 0.3 to 1.09 m/kyr in the NTRL section with average rates of 0.33 m/kyr, 0.3 m/kyr, 0.44 m/kyr and 0.46 m/kyr, respectively. The average sedimentation rates of the STRL and NTRL sections are 1.5 times greater than those of the STDG and CTDG sections. This difference can be attributed to the accommodation space, with the STRL and NTRL sections situated on the axial subsidence and depositional center of the half graben, while the STDG and CTDG sections are on the ramp margin. The stratigraphic completeness of the four sections ranges from 32% to 57% as the ratio between depositional and total durations. Astronomical tuning mitigated the long-term impact of variable sedimentation rates. The gamma and astronomical tuning enhance the spectral resolution of the environmental series. Spectral analysis of the astronomical-gamma-tuned series of STDG, CTDG, STRL and NTRL sections reveal significant peaks ranging from 14.2 to 405 kyr, corresponding to Milankovitch cycles (Figure 1). The evolutive spectrograms of the STDG, CTDG, STRL and NTRL sections contain many peaks with varying magnitude and frequency persistency throughout the entire section, with notable differences between the lower and upper parts (Figure 1). Most fluvial and lacustrine high order cycles (HCs) have durations less than 14 kyr, while some have durations same as obliquity and precession index cycle periods. The high-frequency signals, representing these HCs, in the sub-Milankovitch bands in the spectra are interpreted as combination tones of the eccentricity and precession index cycles. These results suggest that the cyclic sedimentation of the fluvial-lacustrine cycles was predominantly controlled by Milankovitch paleoclimatic forcing with variable strength evident across the entire sections. 

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2. 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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3. Western Pacific Warm Pool

   https://doi.org/10.14379/iodp.proc.363.2018  

   Rosenthal, Y.; Holbourn, A.E.; Kulhanek, D.K. (June 2018, Proceedings of the International Ocean Discovery Program)

   null (Ed.)

   International Ocean Discovery Program Expedition 363 sought to document the regional expression and driving mechanisms of climate variability (e.g., temperature, precipitation, and productivity) in the Indo-Pacific Warm Pool (IPWP) as it relates to the evolution of Neogene climate on millennial, orbital, and geological timescales. To achieve our objectives, we selected sites with a wide geographical distribution and variable oceanographic and depositional settings. Nine sites were cored during Expedition 363, recovering a total of 6956 m of sediment in 875–3421 m water depth with an average recovery of 101.3% during 39.6 days of on-site operations. Two moderate sedimentation rate (~3–10 cm/ky) sites are located off northwestern Australia at the southwestern maximum extent of the IPWP and span the late Miocene to present. Seven of the nine sites are situated at the heart of the Western Pacific Warm Pool (WPWP), including two sites on the northern margin of Papua New Guinea with very high sedimentation rates (>60 cm/ky) spanning the past ~450 ky, two sites in the Manus Basin (north of Papua New Guinea) with moderate sedimentation rates (~4–14 cm/ky) recovering upper Pliocene to present sequences, and three sites with low sedimentation rates (~1–3 cm/ky) on the southern and northern Eauripik Rise spanning the early Miocene to present. The wide spatial distribution of the cores, variable accumulation rates, exceptional biostratigraphic and paleomagnetic age constraints, and mostly excellent or very good foraminifer preservation will allow us to trace the evolution of the IPWP through the Neogene at different temporal resolutions, meeting the primary objectives of Expedition 363. Specifically, the high–sedimentation rate cores off Papua New Guinea will allow us to better constrain mechanisms influencing millennial-scale variability in the WPWP, their links to high-latitude climate variability, and implications for temperature and precipitation in this region under variable mean-state climate conditions. Furthermore, the high accumulation rates offer the opportunity to study climate variability during previous warm periods at a resolution similar to that of existing studies of the Holocene. With excellent recovery, Expedition 363 sites are suitable for detailed paleoceanographic reconstructions at orbital and suborbital resolution from the middle Miocene to Pleistocene and thus will be used to refine the astronomical tuning, biostratigraphy, magnetostratigraphy, and isotope stratigraphy of hitherto poorly constrained intervals within the Neogene timescale (e.g., the late Miocene) and to reconstruct the history of the Asian-Australian monsoon and the Indonesian Throughflow on orbital and tectonic timescales. Results from high-resolution interstitial water sampling at selected sites will be used to reconstruct density profiles of the western equatorial Pacific deep water during the Last Glacial Maximum. Additional geochemical analyses of interstitial water samples in this tectonically active region will be used to investigate volcanogenic mineral and carbonate weathering and their possible implications for the evolution of Neogene climate. 

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4. Expedition 363 Preliminary Report: Western Pacific Warm Pool

   https://doi.org/10.14379/iodp.pr.363.2017  

   Rosenthal, Y.; Holbourn, A.E.; Kulhanek, D.K. (February 2017, Preliminary report)

   null (Ed.)

   International Ocean Discovery Program Expedition 363 sought to document the regional expression and driving mechanisms of climate variability (e.g., temperature, precipitation, and productivity) in the Western Pacific Warm Pool (WPWP) as it relates to the evolution of Neogene climate on millennial, orbital, and geological timescales. To achieve our objectives, we selected sites with wide geographical distribution and variable oceanographic and depositional settings. Nine sites were cored during Expedition 363, recovering a total of 6956 m of sediment in 875–3421 m water depth with an average recovery of 101.3% during 39.6 days of on-site operations. Two sites are located off northwestern Australia at the southern extent of the WPWP and span the late Miocene to present. Seven sites are situated at the heart of the WPWP, including two sites on the northern margin of Papua New Guinea (PNG) with very high sedimentation rates spanning the past ~450 ky, two sites in the Manus Basin north of PNG with moderate sedimentation rates recovering upper Pliocene to present sequences, and three low sedimentation rate sites on the southern and northern parts of the Eauripik Rise spanning the early Miocene to present. The wide spatial distribution of the cores, variable accumulation rates, exceptional biostratigraphic and paleomagnetic age constraints, and mostly excellent foraminifer preservation will allow us to trace the evolution of the WPWP through the Neogene at different temporal resolutions, meeting the primary objectives of Expedition 363. Specifically, the high sedimentation–rate cores off PNG will allow us to better constrain mechanisms influencing millennial-scale variability in the WPWP, their links to high-latitude climate variability, and implications for temperature and precipitation variations in this region under variable climate conditions. Furthermore, these high accumulation rates offer the opportunity to study climate variability during previous warm periods at a resolution similar to existing studies of the Holocene. With excellent recovery, Expedition 363 sites are suitable for detailed paleoceanographic reconstructions at orbital and suborbital resolution from the middle Miocene to Pleistocene, and thus will be used to refine the astronomical tuning, magneto-, isotope, and biostratigraphy of hitherto poorly constrained intervals within the Neogene timescale (e.g., the late Miocene) and to reconstruct the history of the East Asian and Australian monsoon and the Indonesian Throughflow on orbital and tectonic timescales. Results from high-resolution interstitial water sampling at selected sites will be used to reconstruct density profiles of the western equatorial Pacific deep water during the Last Glacial Maximum. Additional geochemical analyses of interstitial water samples in this tectonically active region will be used to investigate volcanogenic mineral and carbonate weathering and their possible implications for the evolution of Neogene climate. 

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5. REFINING THE AGE MODEL OF THE LAKE JUNIN (PERU) DRILL CORE BY CORRELATION TO REGIONAL CAVE STALAGMITES

   https://doi.org/10.1130/abs/2023AM-395566  

   Rodbell, Donald; Olson, Elizabeth; Stoltenberg, Hailey; Parmenter, Dylan; Verheyden, Anouk; Edwards, Lawrence; Gillikin, David (January 2023, Geologic Society of America)

   Lake Junín, located in the uppermost Amazon Basin in central Peru, was drilled as part of the International Continental Drilling Program in 2015. A piston core with a composite length of ~95 m provides a continuous archive of upstream glacial activity spanning ~700,000 years. The age-depth model was established with 80 AMS 14C dates, 12 U-Th dated intervals of authigenic calcite, and 17 geomagnetic relative paleointensity tie points, and yields an age of 677±20 ka at 88 m. Four samples from near the base of the core reveal normal polarity paleomagnetic directions, consistent with an age younger than ~773 ka. The composite section comprises intervals of siliciclastic sediment intercalated with intervals dominated by authigenic calcite. The siliciclastic-rich intervals have a consistent signature, with relatively low concentrations of carbonate and organic carbon, and high values of bulk density, magnetic susceptibility and concentrations of elements derived from glacial erosion of the non-carbonate fraction of the regional bedrock. We find that tropical glaciers tracked changes in global ice volume and followed a clear ~100,000-year periodicity. Two caves, Huagapo and Pacupahuain, are located within 25 km of Lake Junín and provide a basis for testing and refining the age model of the Lake Junín drill core based on the high precision and accuracy of Uranium series dates for speleothems from these caves. The assumption here is that significant changes in regional ice volume will also be recorded in the 18O of cave drip water and thus in speleothems. Our initial target interval is the 9-8 marine isotope stage (MIS) boundary (~300 ka), which is recorded in the Junín drill core as an abrupt increase in the influx of glacigenic sediment, and in stalagmite 22-22 from Huagapo Cave as an abrupt 4.5‰ decrease in 18Ocalcite. The age of the onset of this transition in the Junín drill core is about 25 kyr older than that in Stal 22-22, and this difference is within the age model error envelope for the Junín drill core. Similar MIS boundaries provide the basis for adjustments in the Junín age model, which will improve the precision of correlation of this continuous record of tropical glaciation with paleoclimate archives in extra tropical regions. 

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