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Abstract Sea-level rise and settlement are investigated at Ta'ab Nuk Na, an ancient Maya salt works in Belize, by examining samples from wooden posts and marine sediment. The samples included Post 145 of Building B and the Nunavut beam, along with marine sediment columns cut from beside both wooden posts. The sediment columns were sampled at 2 cm intervals. Loss-on ignition confirmed the presence of organic material. Identifying the organic content involved removing nonorganic material from the sediment and sorting the organic material under magnification. This procedure established that most of the organic material was red mangrove (Rhizophora mangle). Red mangroves tolerate salt water, but under conditions of sea-level rise, the plants grow vertically to keep their leaves above water. Sediment, leaves, and detritus trapped in the prop roots form mangrove peat, which serves as a proxy for sea-level rise. AMS dating of fine red mangrove roots determined that the local sea levels rose at Ta'ab Nuk Na throughout the Late Classic period and continued into the Postclassic period. Radiocarbon dates obtained from the wood-post samples yielded Late Classic–period dates. Comparing the radiocarbon dates from the wooden posts and the sediment core samples determined that the site was abandoned before the rising seas flooded the area. Evidently, sea-level rise did not play a role in site abandonment.
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Data report: radiocarbon age of planktonic foraminifera collected at Site U1474, Natal Valley, IODP Expedition 361
An age model for a marine sediment core is a prerequisite for paleoenvironmental studies. Here, we report 27 radiocarbon dates of planktonic foraminifera (24 dates for Orbulina universa and 3 for Trilobatus sacculifer) collected from International Ocean Discovery Program Expedition 361 (Southern African Climates) Site U1474 in the Natal Valley. The top to the bottom of Section 361-U1474F-1H-1 was used for the analysis. The results indicate that sedimentation is almost constant, extending to 42.0 ky BP at 140 cm below the seafloor. The obtained age-depth model is consistent with that of a marine sediment core obtained from a proximate site in a previous study and was confirmed by comparing the color reflectance of the sediment cores.
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- Award ID(s):
- 1326927
- PAR ID:
- 10405104
- Date Published:
- Journal Name:
- Proceedings of the International Ocean Discovery Program
- Volume:
- 361
- Issue:
- 203
- ISSN:
- 2377-3189
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Sea-level rise and settlement are investigated at Ta'ab Nuk Na, an ancient Maya salt works in Belize, by examining samples from wooden posts and marine sediment. The samples included Post 145 of Building B and the Nunavut beam, along with marine sediment columns cut from beside both wooden posts. The sediment columns were sampled at 2 cm intervals. Loss-on ignition confirmed the presence of organic material. Identifying the organic content involved removing nonorganic material from the sediment and sorting the organic material under magnification. This procedure established that most of the organic material was red mangrove (Rhizophora mangle). Red mangroves tolerate salt water, but under conditions of sea-level rise, the plants grow vertically to keep their leaves above water. Sediment, leaves, and detritus trapped in the prop roots form mangrove peat, which serves as a proxy for sea-level rise. AMS dating of fine red mangrove roots determined that the local sea levels rose at Ta'ab Nuk Na throughout the Late Classic period and continued into the Postclassic period. Radiocarbon dates obtained from the wood-post samples yielded Late Classic–period dates. Comparing the radiocarbon dates from the wooden posts and the sediment core samples determined that the site was abandoned before the rising seas flooded the area. Evidently, sea-level rise did not play a role in site abandonment.more » « less
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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.more » « less
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Abstract. We present a global atlas of downcore foraminiferal oxygen and carbon isotope ratios available at https://doi.org/10.1594/PANGAEA.936747(Mulitza et al., 2021a). The database contains 2106 published and previously unpublished stable isotope downcore records with 361 949 stable isotopevalues of various planktic and benthic species of Foraminifera from 1265 sediment cores. Age constraints are provided by 6153 uncalibratedradiocarbon ages from 598 (47 %) of the cores. Each stable isotope and radiocarbon series is provided in a separate netCDF file containingfundamental metadata as attributes. The data set can be managed and explored with the free software tool PaleoDataView. The atlas will provideimportant data for paleoceanographic analyses and compilations, site surveys, or for teaching marine stratigraphy. The database can be updated withnew records as they are generated, providing a live ongoing resource into the future.more » « less
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IODP Expedition 379 deep-sea drilling in 2019 (Gohl et al. 2021, doi:10.14379/iodp.proc.379.2021), offered an opportunity to obtain chronostratigraphic control for seismic reflection data for Amundsen Sea shelf and slope deposits that record Miocene to Present fluctuations in volume of the West Antarctic ice sheet. Here we report the age and interpret the provenance of a volcanic ash bed recovered at/near the Plio-Pleistocene boundary at 31.51 meters below sea level in Hole U1533B and 33.94 mbsf in Hole U1533D. With distinctive geochemistry and inferred wide regional distribution, the bed may serve as a reliable age marker. In Hole 1533B, the fresh tephra forms a discrete layer interstratified within uniform brown marine mud. The layer has a sharp base and upper boundary that is gradational over 5 cm into overlying mud. Color reflectance and density data aided identification of the tephra horizon (diffuse) in Hole 1533D, ~1000m away. A possible on-land source for ash is the Miocene to Pleistocene Marie Byrd Land volcanic province, comprising 18 large alkaline volcanoes dominated by effusive lavas. Products of pyroclastic eruptions are uncommon, mainly occurring as distal englacial, and probably marine, tephra. We undertook an offshore-onshore comparison by first characterizing samples of Site U1533 tephra from a petrographic and geochemical standpoint, using thin section observations, EMPA-WDS glass compositions, and 40Ar/39Ar dating. We then identified onshore exposures with similar characteristics. The offshore tephra are composed of coarse (50-300µm) cuspate glass shards with elongated vesicles. The glass composition is rhyolite, with 75-79wt.% SiO2, ~4wt.% FeO and 0.0wt.% MgO. Single-crystal feldspar 40Ar/39Ar dates are 2.55±0.12 and 2.92±0.02 Ma for U1533B and 2.87 ±0.45 Ma for U1533D. The geochemistry, shard morphology, discrete bed expression, and lateral continuity between Holes U1533B-U1533D indicate that the rhyolite tephra formed as airfall settled to the deep seabed. The ca. 2.55 Ma age based on youngest feldspar grains differs slightly from the 2.1 to 2.2 Ma result obtained from in-progress core bio-magnetostratigraphy. Rare exposures of rhyolite are found in the Chang Peak/Mt. Waesche centers, 1080 km from Site U1533. We obtained pumice sample MB.7.3 (prior-published age of 1.6±0.2 Ma), which displays elevated FeO and F content, and MB.8.1, a specimen of porphyritic cryptocrystalline lava. Single-crystal sanidine 40Ar/39Ar dates are 1.315±0.007 Ma (MB.7.3) and 1.385±0.003 Ma (MB.8.1). Site U1533 samples share a geochemical affinity with these on-land rhyolites, expressed as similar SiO2, CaO, TiO2, MgO and FeO content, suggesting an origin for Site U1533 tephra in the Chang-Waesche volcanoes. A possible explanation for the distinctly greater age, and observed contrasts in Al2O3, Na2O and F percentages, is that Site U1533 tephra are older and erupted from a source entirely concealed beneath subsequent eruptions and the ice sheet. Our results suggest that rhyolite volcanism initiated earlier, was of longer duration than previously known (2.92 to 1.315 Ma), and dispersed tephra far offshore. The finding is significant because ash and aerosols produced by large eruptions may influence regional climate. Antarctica cooled significantly and ice sheets expanded in latest Pliocene time (McKay et al. 2012, doi:10.1073/pnas.1112248109).more » « less
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Accepted Manuscript1.0
- Book Chapter:
- https://doi.org/10.14379/iodp.proc.361.203.2023
