Search for: All records

Middle and Late Holocene sediments have not been extensively sampled in Lake Tanganyika, and much remains unknown about the response of the Rift Valley’s largest lake to major environmental shifts during the Holocene, including the termination of the African Humid Period (AHP). Here, we present an integrated study (sedimentology, mineralogy, and geochemistry) of a radiocarbon-dated sediment core from the Kavala Island Ridge (KIR) that reveals paleoenvironmental variability in Lake Tanganyika since the Middle Holocene with decadal to centennial resolution. Massive blue-gray sandy silts represent sediments deposited during the terminal AHP (~5880–4640 cal yr BP), with detrital particle size, carbon concentrations, light stable isotopes, and mineralogy suggesting an influx of river-borne soil organic matter and weathered clay minerals to the lake at that time. Enhanced by the AHP’s warm and wet conditions, chemical weathering and erosion of Lake Tanganyika’s watershed appears to have promoted considerable nutrient recharge to the lake system. Following a relatively gradual termination of the AHP over the period from ~4640 cal yr BP to ~3680 cal yr BP, laminated and organic carbon-rich sediments began accumulating on the KIR. δ¹⁵N_bulk, C/N, and hydrogen index data suggest high relative primary production from a mix of algae and cyanobacteria, most likely in response to nutrient availability in the water column under a cooler and seasonally dry climate from ~3680 to 1100 cal yr BP. Sediments deposited during the Common Era show considerable variability in magnetic susceptibility, total organic carbon content, carbon isotopes, and C/N, consistent with dynamic hydroclimate conditions that affected the depositional patterns, including substantial changes around the Medieval Climate Anomaly and Little Ice Age. Data from this study highlight the importance of sedimentary records to constrain boundary conditions in hydroclimate and nutrient flux that can inform long-term ecosystem response in Lake Tanganyika. 

Cosmic Explorer is a next-generation ground-based gravitational-wave observatory that is being designed in the 2020s and is envisioned to begin operations in the 2030s together with the Einstein Telescope in Europe. The Cosmic Explorer concept currently consists of two widely separated L-shaped observatories in the United States, one with 40 km-long arms and the other with 20 km-long arms. This order of magnitude increase in scale with respect to the LIGO-Virgo-KAGRA observatories will, together with technological improvements, deliver an order of magnitude greater astronomical reach, allowing access to gravitational waves from remnants of the first stars and opening a wide discovery aperture to the novel and unknown. In addition to pushing the reach of gravitational-wave astronomy, Cosmic Explorer endeavors to approach the lifecycle of large scientific facilities in a way that prioritizes mutually beneficial relationships with local and Indigenous communities. This article describes the (scientific, cost and access, and social) criteria that will be used to identify and evaluate locations that could potentially host the Cosmic Explorer observatories. 

Abstract The oldest structures in a rift basin define incipient rift architecture, and commonly modulate the patterns of landscape evolution, sedimentation, and associated hazards in subsequent phases of rift development. However, due to deep burial beneath younger, thick syn‐rift sequences, and limited resolution of seismic imaging, critical early‐rift processes remain poorly understood. In the Tanganyika Rift, East Africa, we augment existing 2‐dimensional (2‐D) seismic reflection data with newly acquired aeromagnetic and Full‐Tensor Gradiometry data to assess the deep basin and underlying basement structure. Aeromagnetic and gravity grids show a dominance of NW‐trending long‐wavelength (>5 km) structural fabrics corresponding to the deeper basement, and dominant NW‐trending with a secondary NNE‐trending shorter‐wavelength (<3 km) fabric representing shallower, intra‐basin structures. Seismically‐constrained 2‐D forward modeling of the aeromagnetic and gravity data reveals: (a) an anomalously high‐density (2.35–2.45 g/cc) deep‐seated, fault‐bounded wedge‐shaped sedimentary unit that directly overlies the pre‐rift basement, likely of Mesozoic (Karoo) origin; (b) ∼4 km‐wide sub‐vertical low‐density (2.71 g/cc) structures within the 3.2 g/cc basement, interpreted to be inherited basement shear zones, (c) early‐rift intra‐basin faults co‐located with the modeled shear zone margins, in some places defining a persistent structurally‐controlled intra‐basin “high,” and (d) a shallow intra‐sedimentary V‐shaped zone of comparatively dense material (∼2.2 g/cc), interpreted to be a younger axial channel complex confined between the intra‐basin “high” and border fault. These results provide new insight into the earliest basin architecture of the Tanganyika Rift, controlled by inherited basement structure, and provide evidence of their persistent influence on the subsequent basin evolution. 

Abstract Ice streams are sites of ice-sheet drainage and together with other processes, such as calving, have an impact on deglaciation rates and ice-sheet mass balance. Proglacial lake deposits provide records of ice-sheet deglaciation and have the potential to supplement other paleoclimate records. Oneida Lake, northeastern USA, contains a thick proglacial lake sequence that buries evidence of ice streaming and a paleo-calving margin that developed during retreat of the Laurentide Ice Sheet. Previous high-resolution digital elevation models identified the Oneida Ice Stream from glacial landforms northwest of the lake. In this study, we utilize seismic refractions from a multichannel seismic (MCS) reflection dataset to estimate the thickness of glacial deposits using seismic tomography. With this method we constrain the depth to top of Paleozoic strata, especially in areas where the reflection data yielded poor outcomes and validate our reflection data in regions of good coverage. We demonstrate that where long offset seismic data are available, the first-arrival tomography method is useful in studies of formerly glaciated basins. Our study identifies a ~108 m thick sedimentary section and potentially long paleoclimate record in Oneida Lake, and identifies a paleotopographic low that likely encouraged formation of the Oneida Ice Stream. 

In July 2019, approximately 217 km of 2-D multichannel seismic reflection data were collected along 27 profiles on Oneida Lake, New York using a 120 channel Seamux™ solid-towed array marine streamer with a 3.125 m group interval and a maximum offset of ~400 meters. Data were originally recorded in SEG-D format on a NTRS2 recording system. Navigational data and ancillary data (ship speed, depth, etc.) were fed into the external header of each field file. The seismic source was a 4x10 in3 Bolt 2800 LLX airgun array and was towed at ~1 meter depth to allow for venting of seismic source air bubbles. Gun pressures varied from 1500 to 2000 PSI. Air guns were fired every 6.25 m distance using two high resolution (Trimble) GPS receivers for navigation. This geometry provided 30-fold seismic coverage with a common midpoint (CMP) interval of 1.56 m. Record length is 2 seconds and the sample rate is 0.25 ms. The following processing steps were applied to the dataset using SeisSpace/ProMAX Software. Data were initially reviewed in shot mode and noisy traces were edited. Geometry was applied using source and receiver offsets with group and shot intervals, and data were sorted into the CMP domain. Stacking velocities were picked using a combination of velocity semblance plots and constant velocity stacks applied to CMP supergathers. For the constant velocity stacks, supergathers were constructed from 51 CMPs and analyzed in increments of 100 CMPs. Once time-velocity pairs were selected, normal moveout was applied to the full profile data set and the data were stacked.Nested Ormsby bandpass filters of 110-135-1500-1700 Hz and 40-70-1100-1300 Hz were applied to the stacked datasets. Ormsby filter frequencies were picked by executing a careful parameter test where frequencies were altered incrementally until the ideal filter was produced. A post-stack F-K filter was applied to remove steeply dipping noise, and a careful comparison of F-K filtered profiles and raw profiles was conducted. A post-stack Kirchhoff time migration with a 200 ms bottom taper was applied using the RMS stacking velocities picked for each seismic profile. The data files are in SEG-Y format and were generated as part of a project called P2C2: A High Resolution Paleoclimate Archive of Termination I in Oneida Lake and Glacial Lake Iroquois Sediments. Funding was provided through NSF grant EAR18-04460 to Syracuse University. 

In July 2019, approximately 217 km of 2-D multichannel seismic reflection data were collected along 27 profiles on Oneida Lake, New York using a 120 channel Seamux™ solid-towed array marine streamer with a 3.125 m group interval and a maximum offset of ~400 meters. Data were recorded in SEG-D format on a NTRS2 recording system. The seismic source was a 4x10 in3 Bolt 2800 LLX airgun array and was towed at ~1 meter depth to allow for venting of seismic source air bubbles. Gun pressures varied from 1500 to 2000 PSI. Air guns were fired every 6.25 m distance using two high resolution (Trimble) GPS receivers for navigation. This geometry provided 30-fold seismic coverage with a common midpoint (CMP) interval of 1.56 m. Record length is 2 seconds and the sample rate is 0.25 ms. These raw field shot data files are in SEG-D format, bundled by seismic line. The files were acquired as part of a project called P2C2: A High Resolution Paleoclimate Archive of Termination I in Oneida Lake and Glacial Lake Iroquois Sediments. Funding was provided through NSF grant EAR18-04460 to Syracuse University.