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1. Regional and Local Stratigraphic Markers in Three Hudson River Cores Taken Near Peekskill, New York: Core LWB 4-5

   Abdul, B. ; Adeghe, S. ; Diallo, M. B. ; McCann, B. ; Abbott, D. H. ; Bostick, B. C. ; Chang, C. ; Block, K. A. ( December 2018 , American Geophysical Union, Fall Meeting 2018, abstract #B53I-2167)

   We have been studying the stratigraphy of core LWB 4-5 taken in 2001 in the Hudson River 1.5 km north of the transit of the Peekskill meteorite in October 1992. We measured magnetic susceptibility and elemental composition at 1 cm intervals down to 50 cm and then at 5 cm intervals down to 108 cm. Magnetic susceptibilities are unusually high (above 20 cgs units) from 12-19 cm and again at 31 cm. The level at 31 cm contains mm-sized fragments of Fe oxide. X-Ray Fluorescence spectroscopy revealed high Ni/Cr levels concentrated from 9-11 cm and again below 97 cm. We found tektite-like spheroids, dumbbells and teardrops from 8-15 cm depth. They are glasses and they contain appreciable K, consistent with an origin as true tektites but we have not identified the source. Overall, we interpret the high susceptibility, high Ni/Cr and possibly tektite bearing layer as a resulting from the fall of one of the bodies postulated to have fallen with the Peekskill meteorite in 1992. A 1992 age for the top of the Peekskill layer at 8-9 cm depth is consistent with a uniform sedimentation rate in the core and the occurrence of the base of modern Pb at 97 cm depth. From previous work on cores from Central Park Lake, the base of modern Pb represents the year 1880 A.D. We also found other prominent horizons whose ages fit a linear sedimentation rate model. We found a step change in As/Pb ratio whose inferred age matches 1988, the year when Pb and Cu arsenide were banned as pesticides. Our core exhibits peaks in Ca and Sr content and a minor susceptibility peak at 17.5 depth that may represent the 1980 "Great Catskill Toilet Flush" Hudson River flood event. The Catskills contain abundant marine limestone that could serve as a source for Ca and Sr. A prominent susceptibility peak at 37.5 cm could represent a flood in 1955. We also found a peak in Pb at 50 cm depth whose inferred age matches that of the cessation of incinerator burning in 1938. 137Cs and 210Pb ages are in progress and may be available by the time of the meeting. The high Pb and As levels in parts of LWB 4-5 are supported by examination of the coarse fraction. We found two bright orange grains, both with carbon rich coatings. One grain analyses on the X-ray analyzer of an SEM as 8%C, 70% Pb, 17%As and 2% Cu. The second grain analyzes as 10% C, 43% Pb, 1% Ca, 2% P, 27% As, 4% Fe, 2% Ni, 1% Si, and 6% Zn. All analyses are in wt.% on an oxygen free basis. 

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2. Can We See Dust from the 1992 Fall of the Peekskill Meteorite in Hudson River Sediments and Can We Use It as a Stratigraphic Marker?(Regional and Local Stratigraphic Markers in Three Hudson River Cores Taken Near Peekskill, New York: LWB4-1)

   Diallo, M. B. ; McCann, B. ; Abdul, B. ; Adeghe, S. ; Abbott, D. H. ; Bostick, B. C. ; Chang, C. ; Block, K. A. ( December 2018 , American Geophysical Union, Fall Meeting 2018, abstract #B53I-2168)

   We have been studying the stratigraphy of core LWB4-1 taken in 2001 in the Hudson River about 100 meters north of the calculated transit path of the Peekskill meteorite in October 1992. We measured magnetic susceptibility at 1cm intervals from 0 -70 cm depth and found a layer with a magnetic susceptibility of 11 cgs units at 6 cm depth. This is the highest susceptibility in the top 40 cm of the core. Scanning X-Ray Fluorescence spectroscopy revealed the high susceptibility layer at 6 cm depth is part of a 3 cm interval with a high Ni/Cr ratio, but the depth of the peak in the Ni/Cr ratio is poorly resolved due to measurement error. We plan to dry and homogenize discreet samples for analysis on bench top XRF to reduce Ni and Cr error. Based on our identification of the base of modern Pb at 68 cm depth, the top 40 cm of the core covers the time interval from 2001 to 1930. From previous work on Central Park Lake, the base of modern Pb represents the year 1880 A.D. A uniform sedimentation rate model is supported a peak in Pb and As at 8 cm depth. The peak might represent the 1988 ban on the use of Pb arsenide and the start of use of DDT as a pesticide. We found a second peak in Pb at 37.5cm potentially from 1938, the date at which incineration was banned in New York City. We found a third peak in Pb at 50.5cm that might be from World War I around 1914. We found two deeper susceptibility peaks of 12 cgs at 43 cm and 8 cgs at 59 cm. These peaks could represent major Hudson River floods in 1927 and 1903. 137Cs and 210Pb 210 dating are in progress and will help us to determine if our age model is correct. Also, our core exhibits a distinct increase in Ca content starting at 18-25 cm depth and increasing towards the top of the core. This increase could be due to increased erosion, anthropogenic inputs or increased dissolution of CaCO3 rich rocks. We are measuring CaCO3 in the core to better determine the origin of this increase of Ca. 

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3. Expedition 397 Preliminary Report: Iberian Margin Paleoclimate

   Hodell, D.A. ; Abrantes, F. ; Alvarez Zarikian, C.A. ( February 2023 , Preliminary report)

   During International Ocean Discovery Program Expedition 397, we recovered a total of 6176.7 m of core (104.2% recovery) at four sites (U1586, U1587, U1385, and U1588) from the Promontório dos Principes de Avis (PPA) (Figure F1), a plateau located on the Portuguese continental slope that is elevated above the Tagus Abyssal Plain and isolated from the influence of turbidites. The drill sites are arranged along a bathymetric transect (4691, 3479, 2590, and 1339 meters below sea level [mbsl], respectively) to intersect each of the major subsurface water masses of the eastern North Atlantic (Figures F2, F7). Multiple holes were drilled at each site to ensure complete spliced composite sections (Figure F3; Table T1), which will be further refined postcruise by a campaign of X-ray fluorescence core scanning. At Site U1586 (4691 mbsl), the deepest and farthest from shore, a 350 m sequence was recovered in four holes that extend as far back as the middle Miocene (14 Ma), which is nearly twice as old as initially predicted from seismic stratigraphy. Sedimentation rates are lower (averaging 5 cm/ky in the Quaternary) at Site U1586 than other Expedition 397 sites (Figure F4), and a few slumped intervals were encountered in the stratigraphic sequence. Despite these limitations, Site U1586 anchors the deep end-member of the bathymetric transect and provides an important reference section to study deepwater circulation, ventilation and carbon storage in the deep eastern North Atlantic. At Site U1587 (3479 mbsl), the second deepest site along the depth transect, we recovered a 567 m sequence of late Miocene to Holocene sediments that accumulated at rates between 6.5 and 11 cm/ky (Figure F4). The high sedimentation rates and long continuous record at this site will permit climate reconstruction at high temporal resolution (e.g., millennial) for the past 7.8 My. A complete Messinian Stage (7.246–5.333 Ma) was recovered, which provides a valuable opportunity to study the Messinian Salinity Crisis in an open marine setting adjacent to the Mediterranean. Site U1385 (Shackleton site) was a reoccupation of a position previously drilled during Integrated Ocean Drilling Program Expedition 339. Expedition 339 Site U1385 has yielded a remarkable record of millennial-scale climate change for the past 1.45 My (Marine Isotope Stage [MIS] 47) (Figure F6). During Expedition 397, we deepened the site from 156 to 400 meters below seafloor (mbsf), extending the basal age into the early Pliocene (4.5 Ma). Sedimentation rates remained high, averaging between 11 and 9 cm/ky throughout the sequence (Figure F4). The newly recovered cores at Expedition 397 Site U1385 will permit the study of millennial climate variability through the entire Quaternary and into the Pliocene, prior to the intensification of Northern Hemisphere glaciation. Site U1588 is the shallowest, closest to shore, and youngest site drilled during Expedition 397 and is also the one with the highest sedimentation rate (20 cm/ky). The base of the 412.5 m sequence is 2.2 Ma, providing an expanded Pleistocene sequence of sediment deposited under the influence of the lower core of the Mediterranean Outflow Water (MOW). Together with other Expedition 339 sites, Site U1588 will be important for determining how the depth and intensity of the MOW has varied on orbital and millennial timescales. In addition, it also provides a marine reference section for studying Quaternary climate variability at very high temporal resolution (millennial to submillennial). A highlight of the expedition is that sediment at all sites shows very strong cyclicity in bulk sediment properties (color, magnetic susceptibility, and natural gamma radiation). Particularly notable are the precession cycles of the Pliocene that can be correlated peak-for-peak among sites (Figure F10). These cyclic variations will be used to derive an orbitally tuned timescale for Expedition 397 sites and correlate them into classic Mediterranean cyclostratigraphy. The cores recovered during Expedition 397 will form the basis of collaborative postcruise research to produce benchmark paleoclimate records for the late Miocene through Quaternary using the widest range of proxy measurements. It will take many years to complete these analyses, but the records will lead to major advances in our understanding of millennial and orbital climate changes and their underlying causes and evolving contextuality. Outreach during Expedition 397 was highly productive, reaching a record number of students and the general public across the world through several diverse platforms, including live ship-to-shore events, webinars, social media, videos, radio pieces, blog posts, and in-person activities. 

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4. Rhyolite volcanism in the Marie Byrd Land volcanic province, Antarctica: New evidence for pyroclastic eruptions during latest Pliocene icesheet expansion

   https://doi.org/10.5194/egusphere-egu21-9003  

   Iverson, Nels ; Siddoway, Christine S. ; Zimmerer, Matt ; Smellie, John ; Dunbar, Nelia ; Gohl, Karsten ; Scientists, IODP Exp379 ( April 2021 , vEGU21, the 23rd EGU General Assembly)

   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). 

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5. Expedition 391 summary

   Sager, W. ; Hoernle, K. ; Höfig, T.W. ; Avery, A.J. ; Bhutani, R. ; Buchs, D.M. ; Carvallo, C.A. ; Class, C. ; Dai, Y. ; Dalla Valle, G. ; et al ( October 2023 , Proceedings of the International Ocean Discovery Program Expedition reports)

   Hotspot tracks (chains of seamounts, ridges, and other volcanic structures) provide important records of plate motions, as well as mantle geodynamics, magma flux, and mantle source compositions. The Tristan-Gough-Walvis Ridge (TGW) hotspot track, extending from the active volcanic islands of Tristan da Cunha and Gough through a province of guyots and then along Walvis Ridge to the Etendeka flood basalt province, forms one of the most prominent and complex global hotspot tracks. The TGW hotspot track displays a tight linear age progression in which ages increase from the islands to the flood basalts (covering ~135 My). Unlike Pacific tracks, which are often simple, nearly linear chains of seamounts, the TGW track is alternately a steep-sided narrow ridge, an oceanic plateau, subparallel linear ridges and chains of seamounts (most are flat-topped guyots). The track displays isotopic zonation over the last ~70 My. The zonation appears near the middle of the track just before it splits into two to three chains of ridge- and guyot-type seamounts. Walvis Ridge, forming the older part of the track, is also overprinted with age-progressive late-stage volcanism, which was emplaced ~30–40 My after the initial eruptions and has a distinct isotopic composition. The plan for Expedition 391 was to drill at six sites, three along Walvis Ridge and three in the seamounts of the Guyot Province, to collect igneous rocks to better understand the formation of volcanic edifices, the temporal and geochemical evolution of the hotspot, and the variation in paleolatitudes at which the volcanic edifices formed. After a delay of 18 days to address a shipboard Coronavirus (COVID-19) outbreak, Expedition 391 proceeded to drill at four of the proposed sites: three sites on Walvis Ridge around Valdivia Bank, an ocean plateau within the ridge, and one site on the lower flank of a guyot in the Center track of the Guyot Province, a ridge located between the Tristan subtrack (which extends from the end of Walvis Ridge to the islands of Tristan da Cunha) and the Gough subtrack (which extends from Walvis Ridge to Gough Island). The first hole was drilled at Site U1575, located on a low portion of the northeastern Walvis Ridge just north of Valdivia Bank. At this location, 209.9 m of sediments and 122.4 m of igneous basement were cored. The sediments ranged in age from Late Pleistocene (~0.43–1.24 Ma) to Late Cretaceous (Campanian; 72–78 Ma). The igneous basement comprised 10 submarine lava units consisting of pillow, lobate, sheet, and massive lava flows, the thickest of which was ~21 m. Most lavas are tholeiitic, but some alkalic basalts were recovered. A portion of the igneous succession consists of low-Ti basalts, which are unusual because they appear in the Etendeka flood basalts but have not been previously found on Walvis Ridge. Two holes were drilled at Site U1576 on the west flank of Valdivia Bank. The first of these holes was terminated because a bit jammed shortly after entering the igneous basement. Hole U1576A recovered a remarkable ~380 m thick sedimentary section consisting mostly of chalk covering a nearly complete sequence from Late Pleistocene (~0.43–1.24 Ma) to Late Cretaceous (Campanian; ~79–81.38 Ma). These sediments display short and long cyclic color changes that imply astronomically forced and longer term paleoenvironmental changes. The igneous basement recovered in Hole U1576B yielded 11 submarine lava units (total thickness = ~65 m). The flows range from pillows to massive flows with compositions varying from tholeiitic basalt to basaltic andesite, only the second occurrence of the latter composition recovered from the TGW track thus far. These units are separated by seven sedimentary chalk units that range 0.1–11.6 m in thickness, implying a long-term interplay of sedimentation and lava eruptions. These intercalated sediments revealed Upper Cretaceous (Campanian) ages of ~77–79 Ma for the upper two interbeds and ~79–81.38 Ma for the lower beds. Coring at Site U1577, on the extreme eastern flank of Valdivia Bank, penetrated a 154.8 m thick sedimentary section ranging from the Paleocene (Thanetian; ~58.8 Ma) to Upper Cretaceous (Campanian; ~81.43–83.20 Ma). Igneous basement coring progressed only 39.1 m below the sediment/basalt contact, recovering three massive submarine tholeiitic basalt lava flows that are 4.1, 15.5, and >19.1 m thick, respectively. Paleomagnetic data from Sites U1577 and U1576 indicate that the former volcanic basement formed just before the end of the Cretaceous Normal Superchron and the latter during Chron 33r, shortly afterward. Biostratigraphic and paleomagnetic data suggest that Valdivia Bank becomes younger from east to west. Site U1578, located on a Center track guyot, provided a long and varied igneous section. After coring through 184.3 m of pelagic carbonate sediments mainly consisting of Eocene and Paleocene chalk (~55.64–63.5 Ma), Hole U1578A cored 302.1 m of igneous basement. Basement lavas are largely pillows but are interspersed with sheet and massive flows. Lava compositions are mostly alkalic basalts with some hawaiite. Several intervals contain abundant olivine (some fresh), and some of the pillow stacks consist of basalt with remarkably high Ti content. The igneous sequence is interrupted by 10 sedimentary interbeds consisting of chalk and volcaniclastics and ranging 0.46–10.19 m in thickness. Investigations of toothpick samples from the intercalated sediments were examined, each revealing the same age range of ~63.5–64.81 Ma (lower Paleocene; Danian). Paleomagnetic data display a change in basement magnetic polarity ~100 m above the base of the hole. Combining magnetic stratigraphy with biostratigraphic data, the igneous section is inferred to span >1 My. Nearly 7 months after Expedition 391, JOIDES Resolution transited from Cape Town to the north Atlantic. During this transit (Expedition 397T), 7.9 days of ship time were used to drill two holes (U1584A and U1585A) at sites on the Gough and Tristan tracks that had been omitted because of COVID-19–related time loss on the earlier cruise. For both, coring was begun only a short distance above the igneous basement to save time. The 75.2 m thick section drilled in Hole U1584A contains two sedimentary units: clay-rich carbonate sediments overlie a pumice-dominated volcaniclastic deposit containing basalt fragments. Because the goal was to core basalt and the base of the volcaniclastic deposit was not imaged in the seismic profile, the hole was terminated early to save operation time for the next site. In Hole U1585A, coring penetrated a 273.5 m thick sediment section overlying an 81.2 m thick pile of massive basalt flows. The sediment section is divided into four units: The uppermost unit consists of nannofossil chalk; The two intermediate units contain alternating chalk and volcaniclastic sediments containing several breccia units; and The lowermost unit consists of volcanic breccia containing juvenile blocks, bombs, and accretionary lapilli. This thick sedimentary section documents a transition from shallow-water volcanism to open-ocean sedimentation as the seamount subsided. The thick underlying basalt section is made up of four sparsely to highly phyric massive flows, the thickest of which is >43 m thick. Samples of these units are mostly basalt with a few trachybasalts and one trachyandesite. Although the igneous penetration was less than planned, coring during Expeditions 391 and 397T obtained samples that clearly will lead to an improved understanding of the evolution of the TGW hotspot and its track. Reasonable recovery of fresh basalt in some holes provides ample samples for geochemical, geochronologic, and paleomagnetic studies. Good recovery of Late Cretaceous and early Cenozoic chalk successions provides samples for paleoenvironmental study. 

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