The sediment-fill of Pago Pago Bay (Tutuila Island,American Samoa): New insights on the sediment record of past tsunamis     

Brieuc Riou  Eric Chaumillon  Jean-Luc Schneider  Thierry Corrège  Catherine Chagué 《Sedimentology》2020,67(3):1577-1600

Extensive bathymetric and two-dimensional seismic surveys have been carried out and cores collected in Pago Pago Bay (Tutuila, American Samoa) in order to describe and gain a better understanding of the sediment fill of the bay, which was affected by the 2009 South Pacific Tsunami. Eight sedimentary units were identified over the volcanic bedrock. The basal transgressive unit displays retrograding onlaps towards the shore, whereas the overlying seven aggradational layers alternate between four draping units and three pinching out seaward units. ‘Core to seismic’ correlation reveals that draping units are composed of homogeneous silts, while pinching out units are dominated by very coarse coral fragments showing fresh cuts, mixed with Halimeda plates. The basal unit is attributed to transgressive sedimentation in response to flooding of the bay after the last glacial maximum, followed by the upper aggradational units corresponding to highstand sedimentation. The changeovers in these upper units indicate an alternation between low-energy silt units and high-energy coral debris units interpreted as tsunami-induced deposits. The ¹⁴C dating reveals that high-energy sedimentation units can last up to approximately 2000 years while low-energy sedimentation units can last up to approximately 1000 years. This alternation, deposited during the last highstand, may be explained by cycles of tectonic activity and quiescence of the Tonga Trench subduction, which is the main source of tsunamigenic earthquakes impacting the Samoan archipelago. In the uppermost silt unit, only the geochemical signature of the terrestrial input of the 2009 SPT backwash deposits was detected between 7 cm and 9 cm depth. Hence, Pago Pago Bay offers a unique sediment record of Holocene bay-fill under the impact of past tsunamis intermittently during the last 7000 years.  相似文献   

Rock magnetics of carbonate systems–investigating palaeodune archives on Fuerteventura (Canary Islands)     

Florian Schneider  Christopher-Bastian Roettig  Daniel Wolf  Philipp Baumgart  Ulrich Hambach  Dominik Faust 《第四纪科学杂志》2020,35(4):594-606

The mineral magnetic properties of Pleistocene aeolian dune sands from the island of Fuerteventura (Canary Islands, Spain) were studied in order to reconstruct the palaeoenvironmental evolution of Pleistocene climates during their formation. The palaeodunes on Fuerteventura mainly consist of carbonate sands admixed with dust and material of volcanic origin. Due to the low magnetic background caused by the diamagnetic character of carbonate sands, these archives offer a lot of potential for environmental magnetic studies to detect the imprint of dust, volcanic material and paedogenesis. Four sections of alternating palaeosurface–aeolianite sequences in palaeodune fields have been analysed by means of extensive rock magnetic measurements. These Quaternary archives consist of deposits originating from different sources. I. material blown from the shallow shelf, II. material of volcanic origin, and III. long-range transported dust. The rock magnetic findings enable a more detailed interpretation of the palaeosurfaces within the sequences. We are able to differentiate semiquantitatively between the different source materials on one hand and to distinguish on the other hand those from soil-forming processes. Soil formation is only weakly developed in the dust imprints in the palaeosol aeolianite sequences, linked to sparse vegetation cover during the Pleistocene on Fuerteventura.  相似文献   

High-Resolution Characterization of a Chlorinated Solvent Impacted Aquifer Using a Passive Profiler     

Haley A. Schneider  W. Andrew Jackson Ph.D.  P.E.  Paul B. Hatzinger Ph.D  Charles E. Schaefer Ph.D 《Ground Water Monitoring & Remediation》2020,40(4):27-43

A direct-drive high-resolution passive profiler (HRPP) was developed to quantify and delineate concentrations of chlorinated volatile organic compounds (CVOCs), geochemical indicators and CVOC-degrading microorganisms/genes, as well as to perform compound-specific stable isotope analysis (CSIA) of CVOCs and estimate interstitial velocity at <30-cm resolution. The profilers can be coupled together to provide a continuous sample interval and advanced to depths up to approximately 9 m below-ground surface (bgs) within saturated media where direct-push techniques are feasible. The HRPP was field tested in a previous dense nonaqueous phase liquid (DNAPL) source zone at the former Naval Air Station in Alameda, CA. HRPP data sets were compared to the following traditional groundwater data sets: CVOC and anion concentrations in standard and multilevel monitoring well water samples, CVOC concentrations in soil core samples, qualitative contaminant profiles delineated with a membrane interface probe (MIP), microbial community and CSIA profiles from Bio-Traps® deployed in wells, groundwater velocity from passive flux meters (PFMs), lithologic profiles correlated with MIP electrical conductivity (EC), and velocity estimates based on permeability profiles measured with a Geoprobe hydraulic profiling tool (HPT). In some cases, the HRPP data were equivalent to traditional techniques and, in other cases, the HRPP data were more representative of local variability rather than bulk aquifer conditions. Overall the results support the use of the HRPP to provide high-resolution data on concentrations, velocity, and microbial activity in temporary direct-push deployments without well installation, providing a new tool to better assess source zones and contaminated groundwater plumes, even in low permeability media, and to increase the fidelity of site transport models.  相似文献   

Sediment budgeting of short-term backfilling processes: The erosional collapse of a Carolingian canal construction     

Johannes Schmidt  Lukas Werther  Johannes Rabiger-Völlmer  Franz Herzig  Birgit Schneider  Ulrike Werban  Peter Dietrich  Stefanie Berg  Sven Linzen  Peter Ettel  Christoph Zielhofer 《地球表面变化过程与地形》2020,45(14):3449-3462

Sediment budgeting concepts serve as quantification tools to decipher the erosion and accumulation processes within a catchment and help to understand these relocation processes through time. While sediment budgets are widely used in geomorphological catchment-based studies, such quantification approaches are rarely applied in geoarchaeological studies. The case of Charlemagne's summit canal (also known as Fossa Carolina) and its erosional collapse provides an example for which we can use this geomorphological concept and understand the abandonment of the Carolingian construction site. The Fossa Carolina is one of the largest hydro-engineering projects in Medieval Europe. It is situated in Southern Franconia (48.9876°N, 10.9267°E; Bavaria, southern Germany) between the Altmühl and Swabian Rezat rivers. It should have bridged the Central European watershed and connected the Rhine–Main and Danube river systems. According to our dendrochronological analyses and historical sources, the excavation and construction of the Carolingian canal took place in AD 792 and 793. Contemporary written sources describe an intense backfill of excavated sediment in autumn AD 793. This short-term erosion event has been proposed as the principal reason for the collapse and abandonment of the hydro-engineering project. We use subsurface data (drillings, archaeological excavations, and direct-push sensing) and geospatial data (a LiDAR digital terrain model (DTM), a pre-modern DTM, and a 3D model of the Fossa Carolina] for the identification and sediment budgeting of the backfills. Dendrochronological findings and radiocarbon ages of macro remains within the backfills give clear evidence for the erosional collapse of the canal project during or directly after the construction period. Moreover, our quantification approach allows the detection of the major sedimentary collapse zone. The exceedance of the manpower tipping point may have caused the abandonment of the entire construction site. The spatial distribution of the dendrochronological results indicates a north–south direction of the early medieval construction progress. © 2020 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd  相似文献   

A 6000 year water level history of Europe Lake, Wisconsin, USA     

Barry B. Miller  Allan F. Schneider  Alison J. Smith  Donald F. Palmer 《Journal of Paleolimnology》2000,23(2):175-183

Europe Lake occupies a small, closed, basin that would have been an embayment in Lake Michigan during the high water level events in the larger lake. Cores recovered from the lake reveal late Holocene water level fluctuations in the basin that are inferred from changes in taxa and abundance of molluscs, ostracodes, magnetic susceptibility, organic carbon, and oxygen isotopes.Non-glacial, Holocene lacustrine/paludal sedimentation in this portion of the Europe Lake basin started after 6600 RCYBP and was probably initiated by a rise in the water table of the deep bedrock aquifer, during the Nipissing transgression in Lake Michigan. Isotopically light ground water from this source was probably a major contributor during this phase to the negative ¹⁸O spikes in Valvata tricarinata and Amnicola limosa.The start of stable lacustrine conditions is marked by maximum diversity of ostracode and mollusc taxa and a shift toward much more positive ¹⁸O values. The Europe Lake basin at this time became an embayment of Lake Michigan. This event was probably coeval with the peak of the Nipissing transgression, when the water plane reached an altitude of about 183 m.The isolation of Europe Lake from Lake Michigan started at about 2390 RCYBP and is probably due to a drop in water level in Lake Michigan and/or to isostatic uplift of the Door Peninsula. Since isolation from Lake Michigan, water levels in Europe lake have been controlled primarily by fluctuations in local precipitation, evaporation and ground water discharge.  相似文献