TY - JOUR A1 - Hülscher, Julian A1 - Sobel, Edward R. A1 - Kallnik, Niklas A1 - Hoffmann, J. Elis A1 - Millar, Ian L. A1 - Hartmann, Kai A1 - Bernhardt, Anne T1 - Apatites record sedimentary provenance change 4-5 myrs before clay in the Oligocene/Miocene Alpine molasse JF - Frontiers in Earth Science N2 - Extracting information about past tectonic or climatic environmental changes from sedimentary records is a key objective of provenance research. Interpreting the imprint of such changes remains challenging as signals might be altered in the sediment-routing system. We investigate the sedimentary provenance of the Oligocene/Miocene Upper Austrian Northern Alpine Foreland Basin and its response to the tectonically driven exhumation of the Tauern Window metamorphic dome (28 +/- 1 Ma) in the Eastern European Alps by using the unprecedented combination of Nd isotopic composition of bulk-rock clay-sized samples and partly previously published multi-proxy (Nd isotopic composition, trace-element geochemistry, U-Pb dating) sand-sized apatite single-grain analysis. The basin offers an excellent opportunity to investigate environmental signal propagation into the sedimentary record because comprehensive stratigraphic and seismic datasets can be combined with present research results. The bulk-rock clay-sized fraction epsilon Nd values of well-cutting samples from one well on the northern basin slope remained stable at similar to-9.7 from 27 to 19 Ma but increased after 19 Ma to similar to-9.1. In contrast, apatite single-grain distributions, which were extracted from 22 drill-core samples, changed significantly around 23.3 Ma from apatites dominantly from low-grade ( 8 earthquakes in ~1100, 1255, and 1344 C.E. The upstream dip of tributary valley fills and x-ray fluorescence spectrometry of their provenance rule out local sources. Instead, geomorphic and sedimentary evidence is consistent with catastrophic fluvial aggradation and debris flows that had plugged several tributaries with tens of meters of calcareous sediment from a Higher Himalayan source >60 kilometers away. Y1 - 2016 U6 - https://doi.org/10.1126/science.aac9865 SN - 0036-8075 SN - 1095-9203 VL - 351 SP - 147 EP - 150 PB - American Assoc. for the Advancement of Science CY - Washington ER - TY - JOUR A1 - Bernhardt, Anne A1 - Hebbeln, Dierk A1 - Regenberg, Marcus A1 - Lueckge, Andreas A1 - Strecker, Manfred T1 - Shelfal sediment transport by an undercurrent forces turbidity-current activity during high sea level along the Chile continental margin JF - Geology N2 - Terrigenous sediment supply, marine transport, and depositional processes along tectonically active margins are key to decoding turbidite successions as potential archives of climatic and seismic forcings. Sequence stratigraphic models predict coarse-grained sediment delivery to deep-marine sites mainly during sea-level fall and lowstand. Marine siliciclastic deposition during transgressions and highstands has been attributed to sustained connectivity between terrigenous sources and marine sinks facilitated by narrow shelves. To decipher the controls on Holocene highstand turbidite deposition, we analyzed 12 sediment cores from spatially discrete, coeval turbidite systems along the Chile margin (29 degrees-40 degrees S) with changing climatic and geomorphic characteristics but uniform changes in sea level. Sediment cores from intraslope basins in north-central Chile (29 degrees-33 degrees S) offshore a narrow to absent shelf record a shut-off of turbidite deposition during the Holocene due to postglacial aridification. In contrast, core sites in south-central Chile (36 degrees-40 degrees S) offshore a wide shelf record frequent turbidite deposition during highstand conditions. Two core sites are linked to the Biobio river-canyon system and receive sediment directly from the river mouth. However, intraslope basins are not connected via canyons to fluvial systems but yield even higher turbidite frequencies. High sediment supply combined with a wide shelf and an undercurrent moving sediment toward the shelf edge appear to control Holocene turbidite sedimentation and distribution. Shelf undercurrents may play an important role in lateral sediment transport and supply to the deep sea and need to be accounted for in sediment-mass balances. Y1 - 2016 U6 - https://doi.org/10.1130/G37594.1 SN - 0091-7613 SN - 1943-2682 VL - 44 SP - 295 EP - 298 PB - American Institute of Physics CY - Boulder ER - TY - JOUR A1 - Bernhardt, Anne A1 - Melnick, Daniel A1 - Jara-Munoz, Julius A1 - Argandona, Boris A1 - Gonzalez, Javiera A1 - Strecker, Manfred T1 - Controls on submarine canyon activity during sea-level highstands: The Biobio canyon system offshore Chile JF - Geosphere N2 - Newly acquired high-resolution bathymetric data (with 5 m and 2 m grid sizes) from the continental shelf off Concepcion (Chile), in combination with seismic reflection profiles, reveal a distinctly different evolution for the Biobio submarine canyon compared to that of one of its tributaries. Both canyons are incised into the shelf of the active margin. Whereas the inner shelf appears to be mantled with unconsolidated sediment, the outer shelf shows the influence of strong bottom currents that form drifts of loose sediment and transport -material into the Biobio submarine canyon and onto the continental slope. The main stem of the Biobio Canyon is connected to the mouth of the Biobio River and currently provides a conduit for terrestrial sediment from the continental shelf to the deep seafloor. In contrast, the head of its tributary closest to the coast is located similar to 24 km offshore of the present-day coastline at 120 m water depth, and it is subject to passive sedimentation. However, canyon activity within the study area is interpreted to be controlled not only by the direct input of fluvial sediments into the canyon head facilitated by the river-mouth to canyon-head connection, but also by input from southward-directed bottom currents and possibly longshore drift. In addition, about 24 km offshore of the present-day coastline, the main stem of the Biobio Canyon has steep canyon walls next to sites of active tectonic deformation that are prone to wall failure. Mass-failure events may also foster turbidity currents and contribute to canyon feeding. In contrast, the tributary has less steep canyon walls with limited evidence of canyon-wall failure and is located down-system of bottom currents from the Biobio Canyon. It consequently receives neither fluvial nor longshore sediments. Therefore, the canyon's connectivity to fluvial or longshore sediment delivery pathways is affected by the distance of the canyon head from the coastline and the orientation of the canyon axis relative to the direction of bottom currents. The ability of a submarine canyon to act as an active conduit for large quantities of terrestrial sediment toward the deep sea during sea-level highstands may be controlled by several different conditions simultaneously. These include bottom current direction, structural deformation of the seafloor affecting canyon location and orientation as well as canyon-wall failure, shelf gradient and associated distance from the canyon head to the coast, and fluvial networks. The complex interplay between these factors may vary even within an individual canyon system, resulting in distinct levels of canyon activity on a regional scale. Y1 - 2015 U6 - https://doi.org/10.1130/GES01063.1 SN - 1553-040X VL - 11 IS - 4 SP - 1226 EP - 1255 PB - American Institute of Physics CY - Boulder ER - TY - JOUR A1 - Bernhardt, Anne A1 - Melnick, Daniel A1 - Hebbeln, Dierk A1 - Lückge, Andreas A1 - Strecker, Manfred T1 - Turbidite paleoseismology along the active continental margin of Chile - Feasible or not? JF - Quaternary science reviews : the international multidisciplinary research and review journal N2 - Much progress has been made in estimating recurrence intervals of great and giant subduction earthquakes using terrestrial, lacustrine, and marine paleoseismic archives. Recent detailed records suggest these earthquakes may have variable recurrence periods and magnitudes forming supercycles. Understanding seismic supercycles requires long paleoseismic archives that record timing and magnitude of such events. Turbidite paleoseismic archives may potentially extend past earthquake records to the Pleistocene and can thus complement commonly shorter-term terrestrial archives. However, in order to unambiguously establish recurring seismicity as a trigger mechanism for turbidity currents, synchronous deposition of turbidites in widely spaced, isolated depocenters has to be ascertained. Furthermore, characteristics that predispose a seismically active continental margin to turbidite paleoseismology and the correct sample site selection have to be taken into account. Here we analyze 8 marine sediment cores along 950 km of the Chile margin to test for the feasibility of compiling detailed and continuous paleoseismic records based on turbidites. Our results suggest that the deposition of areally widespread, synchronous turbidites triggered by seismicity is largely controlled by sediment supply and, hence, the climatic and geomorphic conditions of the adjacent subaerial setting. The feasibility of compiling a turbidite paleoseismic record depends on the delicate balance between sufficient sediment supply providing material to fail frequently during seismic shaking and sufficiently low sedimentation rates to allow for coeval accumulation of planktonic foraminifera for high-resolution radiocarbon dating. We conclude that offshore northern central Chile (29-32.5 degrees S) Holocene turbidite paleoseismology is not feasible, because sediment supply from the semi-arid mainland is low and almost no Holocene turbidity-current deposits are found in the cores. In contrast, in the humid region between 36 and 38 degrees S frequent Holocene turbidite deposition may generally correspond to paleoseismic events. However, high terrigenous sedimentation rates prevent high-resolution radiocarbon dating. The climatic transition region between 32.5 and 36 degrees S appears to be best suited for turbidite paleoseismology. (C) 2015 Elsevier Ltd. All rights reserved. KW - Turbidite paleoseismology KW - Chile convergent margin KW - Earthquake KW - Seismoturbidites Y1 - 2015 U6 - https://doi.org/10.1016/j.quascirev.2015.04.001 SN - 0277-3791 VL - 120 SP - 71 EP - 92 PB - Elsevier CY - Oxford ER - TY - JOUR A1 - Stright, Lisa A1 - Bernhardt, Anne A1 - Boucher, Alexandre T1 - DFTopoSim modeling topographically-controlled deposition of subseismic scale sandstone packages within a mass transport dominated deep-water channel belt JF - Mathematical geosciences : the official journal of the International Association for Mathematical Geosciences N2 - Facies bodies in geostatistical models of deep-water depositional environments generally represent channel-levee-overbank-lobe morphologies. Such models adequately capture one set of the erosional and depositional processes resulting from turbidity currents traveling downslope to the ocean basin floor. However, depositional morphologies diverge from the straight forward channel-levee-overbank-lobe paradigm when the topography of the slope or the shape of the basin impacts the timing and magnitude of turbidity current deposition. Subaqueous mass-transport-deposits (MTDs) present the need for an exception to the channel-levee-overbank-lobe archetype. Irregular surface topography of subaqueous MTDs can play a primary role in controlling sand deposition from turbidity currents. MTD topography creates mini-basins in which sand accumulates in irregularly-shaped deposits. These accumulations are difficult to laterally correlate using well-log data due to their variable and unpredictable shape and size. Prediction is further complicated because sandstone bodies typical of this setting are difficult to resolve in seismic-reflection data. An event-based model is presented, called DFTopoSim, which simulates debris flows and turbidity currents. The accommodation space on top of and between debris flow lobes is filled in by sand from turbidity currents. When applied to a subsurface case in the Molasse Basin of Upper Austria, DFTopoSim predicts sand packages consistent with observations from core, well, and seismic data and the interpretation of the sedimentologic processes. DFTopoSim expands the set of available geostatistical deep-water depositional models beyond the standard channel-levee-overbank-lobe model. KW - Geostatistics KW - Event-based modeling KW - Facies modeling KW - Deep-marine sedimentology KW - Submarine channel Y1 - 2013 U6 - https://doi.org/10.1007/s11004-013-9444-7 SN - 1874-8961 VL - 45 IS - 3 SP - 277 EP - 296 PB - Springer CY - Heidelberg ER - TY - JOUR A1 - Bernhardt, Anne A1 - Stright, Lisa A1 - Lowe, Donald R. T1 - Channelized debris-flow deposits and their impact on turbidity currents: The Puchkirchen axial channel belt in the Austrian Molasse Basin JF - Sedimentology : the journal of the International Association of Sedimentologists N2 - Deposits of submarine debris flows can build up substantial topography on the sea floor. The resulting sea floor morphology can strongly influence the pathways of and deposition from subsequent turbidity currents. Map views of sea floor morphology are available for parts of the modern sea floor and from high-resolution seismic-reflection data. However, these data sets usually lack lithological information. In contrast, outcrops provide cross-sectional and lateral stratigraphic details of deep-water strata with superb lithological control but provide little information on sea floor morphology. Here, a methodology is presented that extracts fundamental lithological information from sediment core and well logs with a novel calibration between core, well-logs and seismic attributes within a large submarine axial channel belt in the Tertiary Molasse foreland basin, Austria. This channel belt was the course of multiple debris-flow and turbidity current events, and the fill consists of interbedded layers deposited by both of these processes. Using the core-well-seismic calibration, three-dimensional lithofacies proportion volumes were created. These volumes enable the interpretation of the three-dimensional distribution of the important lithofacies and thus the investigation of sea floor morphology produced by debris-flow events and its impact on succeeding turbidite deposition. These results show that the distribution of debris-flow deposits follows a relatively regular pattern of levees and lobes. When subsequent high-density turbidity currents encountered this mounded debris-flow topography, they slowed and deposited a portion of their sandy high-density loads just upstream of morphological highs. Understanding the depositional patterns of debris flows is key to understanding and predicting the location and character of associated sandstone accumulations. This detailed model of the filling style and the resulting stratigraphic architecture of a debris-flow dominated deep-marine depositional system can be used as an analogue for similar modern and ancient systems. KW - Basin axial submarine channel KW - debris-flow topography KW - deep-marine sedimentary processes KW - foreland basin KW - lithofacies proportion modeling KW - Molasse Basin KW - multi-attribute KW - multi-scale (MA-MS) proportion calibration KW - sea floor morphology KW - turbidites Y1 - 2012 U6 - https://doi.org/10.1111/j.1365-3091.2012.01334.x SN - 0037-0746 VL - 59 IS - 7 SP - 2042 EP - 2070 PB - Wiley-Blackwell CY - Hoboken ER - TY - JOUR A1 - Bernhardt, Anne A1 - Jobe, Zane R. A1 - Grove, Marty A1 - Lowe, Donald R. T1 - Palaeogeography and diachronous infill of an ancient deep-marine foreland basin, Upper Cretaceous Cerro Toro Formation, Magallanes Basin JF - Basin research N2 - The details of how narrow, orogen-parallel ocean basins are filled with sediment by large axial submarine channels is important to understand because these depositional systems commonly form in through-like basins in various tectonic settings. The Magallanes foreland basin is an excellent location to study an orogen-parallel deep-marine system. Conglomerate lenses of the Upper Cretaceous Cerro Toro Formation have been previously interpreted to represent the fill of a single submarine channel (48 km wide, >100 km long) that funneled coarse detritus southward along the basin axis. This interpretation was based on lithologic correlations. New U/Pb dating of zircons from volcanic ashes and sandstones, coupled with strontium isotope stratigraphy, refine the controls on depositional ages and provenance. Results demonstrate that north-south oriented conglomerate lenses are contemporaneous within error limits (ca. 8482 Ma) supporting that they represent parts of an axial channel belt. Channel deposits 20 km west of the axial location are 8782 Ma in age. These channels are partly contemporaneous with the ones within the axial channel belt, making it likely that they represent feeders to the axial channel system. The northern Cerro Toro Formation spans a Turonian to Campanian interval (ca. 9082 Ma) whereas the formation top, 70 km to the south, is as young as ca. 76 Ma. KolmogorovSmirnoff statistical analysis on detrital zircon age distributions shows that the northern uppermost Cerro Toro Formation yields a statistically different age distribution than other samples from the same formation but shows no difference relative to the overlying Tres Pasos Formation. These results suggest the partly coeval deposition of both formations. Integration of previously acquired geochronologic and stratigraphic data with new data show a pronounced southward younging pattern in all four marine formations in the Magallanes Basin. Highly diachronous infilling may be an important depositional pattern for narrow, orogen-parallel ocean basins. Y1 - 2012 U6 - https://doi.org/10.1111/j.1365-2117.2011.00528.x SN - 0950-091X VL - 24 IS - 3 SP - 269 EP - 294 PB - Wiley-Blackwell CY - Hoboken ER -