scholarly journals Hybrid turbidite-drift channel complexes: An integrated multiscale model

Geology ◽  
2020 ◽  
Vol 48 (6) ◽  
pp. 562-568 ◽  
Author(s):  
A. Fuhrmann ◽  
I.A. Kane ◽  
M.A. Clare ◽  
R.A. Ferguson ◽  
E. Schomacker ◽  
...  
Keyword(s):  
Sediment Transport ◽  
High Resolution ◽  
Large Scale ◽  
Sediment Accumulation ◽  
Multiscale Model ◽  
Transport Processes ◽  
Bottom Current ◽  
Oceanic Circulation ◽  
Bottom Currents ◽  
Gravity Flows

Abstract The interaction of deep-marine bottom currents with episodic, unsteady sediment gravity flows affects global sediment transport, forms climate archives, and controls the evolution of continental slopes. Despite their importance, contradictory hypotheses for reconstructing past flow regimes have arisen from a paucity of studies and the lack of direct monitoring of such hybrid systems. Here, we address this controversy by analyzing deposits, high-resolution seafloor data, and near-bed current measurements from two sites where eastward-flowing gravity flows interact(ed) with northward-flowing bottom currents. Extensive seismic and core data from offshore Tanzania reveal a 1650-m-thick asymmetric hybrid channel levee-drift system, deposited over a period of ∼20 m.y. (Upper Cretaceous to Paleocene). High-resolution modern seafloor data from offshore Mozambique reveal similar asymmetric channel geometries, which are related to northward-flowing near-bed currents with measured velocities of up to 1.4 m/s. Higher sediment accumulation occurs on the downstream flank of channel margins (with respect to bottom currents), with inhibited deposition or scouring on the upstream flank (where velocities are highest). Toes of the drift deposits, consisting of thick laminated muddy siltstone, which progressively step back into the channel axis over time, result in an interfingering relationship with the sandstone-dominated channel fill. Bottom-current flow directions contrast with those of previous models, which lacked direct current measurements or paleoflow indicators. We finally show how large-scale depositional architecture is built through the temporally variable coupling of these two globally important sediment transport processes. Our findings enable more-robust reconstructions of past oceanic circulation and diagnosis of ancient hybrid turbidite-drift systems.

Iceland-Faroe Ridge overflow dynamics, 55-6 ka BP

2020 ◽  
Author(s):  
Maryam Mirzaloo ◽  
Dirk Nürnberg ◽  
Markus Kienast ◽  
Jeroen van der Lubbe
Keyword(s):  
Grain Size ◽  
Ocean Circulation ◽  
Academic Career ◽  
Meridional Overturning Circulation ◽  
Bottom Current ◽  
Oceanic Circulation ◽  
Climate Conditions ◽  
Bottom Currents ◽  
The Past ◽  
Bulk Chemistry

<p>The understanding of the past changes in this critical area of oceanic circulation will be beneficial to predict future climate conditions and their related socio-economic impacts. Sediment cores recovered from the western flank of the Iceland-Faroe Ridge (IFR; P457-905 and -909) provide unique archives to reconstruct changes in the Iceland-Scotland overflow water (ISOW), an important component of the Atlantic Meridional Overturning Circulation (AMOC) over the last 55-6 ka BP. We provide high-resolution records of lithogenic grain-size and XRF bulk chemistry on millennial timescales. The age models of both cores have been constrained by radiocarbon datings of planktonic foraminifera and distinct tephra layers, which include the well-known Faroe-Marine-Ash-Zones (FMAZ) II and III. Both grain-size and XRF bulk chemistry (Zr/Rb and Ti/K) reveal prominent Dansgaard-Oeschger sedimentary cycles, which reflect considerable changes in near-bottom current strength and sediment transport/deposition. The transition between cold Greenland Stadials (GSs) and warm Greenland Interstadials (GIs) occur in typical, recurring sedimentation patterns. The GIs are characterized by relatively strong bottom currents and the transport/deposition of basaltic (Ti-rich) silts from local volcanic sources resembling the modern ocean circulation pattern. In contrast, fine grained felsic (K-rich) sediments were deposited during GSs, when the ISOW was weak. In particular, the Heinrich (like) Stadials HS1 and HS2 stand out as intervals of very fine felsic sediment deposition and hence, slackened bottom currents. The bottom currents appear to progressively strengthen throughout the GIs, and sharply decline towards the GSs. This pattern contrasts with records from north of the IFR, which might be explained by a diminishing contribution of the flow cascading over the IFR. Together, these new records show strong changes in bottom current dynamics related to the Iceland-Scotland overflow, which has a strong influence on the past and modern climate of the North Atlantic Region. However, climate change is an interdisciplinary field of research. HOSST-TOSST transatlantic interdisciplinary research program provides the unique opportunity for constructive communication and collaboration among scientists with different skills filling knowledge gaps and bridging the earth sciences with social and economic disciplines. Such interdisciplinary programs at early stages in an academic career is necessary to move and encourage the new generation of the scientific community toward a tradition of broad‐scale interactions.</p><p> </p><p> </p><p> </p><p> </p><p> </p><p> </p><p> </p><p> </p><p> </p>

scholarly journals The turbidite-contourite-tidalite-baroclinite-hybridite problem: orthodoxy vs. empirical evidence behind the “Bouma Sequence”

2021 ◽  
Vol 10 (1) ◽  
Author(s):  
G. Shanmugam
Keyword(s):  
Deep Water ◽  
General Term ◽  
Bottom Current ◽  
Turbidity Currents ◽  
Facies Model ◽  
Bottom Currents ◽  
Gravity Flows ◽  
Slope Flow ◽  
Baroclinic Currents ◽  
Facies Models

AbstractThe underpinning problems of deep-water facies still remain unresolved. (1) The Tb, Tc, and Td divisions of the turbidite facies model, with traction structures, are an integral part of the “Bouma Sequence” (Ta, Tb, Tc, Td, Te). However, deposits of thermohaline contour currents, wind-driven bottom currents, deep-marine tidal currents, and baroclinic currents (internal waves and tides) also develop discrete rippled units, mimicking Tc. (2) The application of “cut-out” logic of sequences, which was originally introduced for the “Bouma Sequence”, with sharp basal contacts and sandy divisions containing well-developed traction structures, to muddy contorts with gradational basal contacts and an absence of well-developed traction structures is incongruent. (3) The presence of five internal divisions and hiatus in the muddy contoured facies model is in dispute. (4) Intersection of along slope contour currents with down slope sediment-gravity flows, triggering hybrid flows, also develops traction structures. (5) The comparison of genuine hybrid flows with down slope flow transformation of gravity flows is inconsistent with etymology of the term “hybrid”. (6) A reexamination of the Annot Sandstone at the Peira Cava type locality in SE France fails to validate either the orthodoxy of five internal divisions of the “Bouma Sequence” or their origin by turbidity currents. For example, the “Ta” division is composed of amalgamated units with inverse grading and floating mudstone clasts, suggesting a mass-transport deposit (MTD). The “Tb” and “Tc” divisions are composed of double mud layers and sigmoidal cross bedding, respectively, which suggest a tidalite origin. (7) Although it was reasonable to introduce a simplistic “Bouma Sequence” in 1962, at a time of limited knowledge on deep-water processes, it is obsolete now in 2021 to apply this model to the rock record amid a wealth of new knowledge. (8) The disconnect between 12 observed, but questionable, modern turbidity currents and over 10,000 interpreted ancient turbidites defies the doctrine of uniformitarianism. This disconnect is attributed to routine application of genetic facies models, without a pragmatic interpretation of empirical data. (9) A suggested solution to these problems is to interpret traction structures in the sedimentary record pragmatically on the basis of empirical field and experimental evidence, without any built-in bias using facies models, such as the “Bouma Sequence”. (10) Until reliable criteria are developed to distinguish traction structures of each type of bottom currents based on uniformitarianism, a general term “BCRS” (i.e., bottom-current reworked sands) is appropriate for deposits of all four kinds of bottom currents.

High-resolution acoustic data revealing peri-platform sedimentary characteristics in the Xisha Archipelago, South China Sea

2021 ◽  
pp. 1-44
Author(s):  
Benjun Ma ◽  
Zhiliang Qin ◽  
Shiguo Wu ◽  
Guanqiang Cai ◽  
Xiangbo Li ◽  
...  
Keyword(s):  
High Resolution ◽  
South China Sea ◽  
South China ◽  
Transport Processes ◽  
Bottom Current ◽  
Carbonate Platforms ◽  
Sedimentary Characteristics ◽  
Acoustic Data ◽  
China Sea ◽  
Xisha Archipelago

Newly collected high-resolution acoustic data are used to describe the morphologies and sedimentary characteristics along the slopes of isolated carbonate platforms in the Xisha (Paracel) Archipelago. Base on multibeam bathymetric and seismic data, we identified seven types of morphological and depositional features around the platforms, including erosive grooves, mass transport deposits (MTDs), gullies, confined channels, canyons, mounded sediments and marginal contourite depressions. The occurrence of erosive channelized features around the platforms indicate that gravity flow is a major sediment-export mechanism for the transportation of excess neritic carbonates towards the slope. Marginal contourite depressions and mounded sediments are interpreted as bottom-current reworking products, suggesting an important role of bottom current and deep-water circulation of the South China Sea in shaping the slope morphology of the carbonate platforms. Furthermore, the bottom-current products tend to develop along the slopes of the carbonate platforms at the Xisha Uplift margin, in particular, erosional features formed by bottom current frequently occur in the southern side of the carbonate platforms. By comprehensive analysis of morphological and depositional features, we establish a facies model around the carbonate platforms to interpret different sedimentary transport processes, such as off-platform and along-slope sediment transport processes. These findings highlight a notable and complex relay-style channelized transport system consisting of grooves/gullies-channels-canyons, which has implications for linking neritic carbonate platforms into deep-sea basins.

Large and medium-scale morpho-sedimentary features of the Messina Strait: insights on bottom-current controlled sedimentation and interaction with downslope processes

2021 ◽  
pp. SP523-2021-77
Author(s):  
E. Martorelli ◽  
D. Casalbore ◽  
F. Falcini ◽  
A. Bosman ◽  
F. G. Falese ◽  
...  
Keyword(s):  
Large Scale ◽  
Coarse Grained ◽  
Sand Wave ◽  
Bottom Current ◽  
Tyrrhenian Sea ◽  
Submarine Landslides ◽  
Bottom Currents ◽  
Medium Scale ◽  
Time Periods ◽  
Messina Strait

AbstractThe Messina Strait is a ∼ 3-8 km wide and 40 km-long extensional area that connects the Tyrrhenian Sea with the Ionian Sea (Mediterranean Sea), and where tectonics, oceanographic and erosive-depositional downslope processes strongly interact each other. Based on the analysis of high-resolution multibeam data, we present an updated morpho-sedimentary framework that reveals a complex seabed morphology, characterized by a variety of features linked to bottom-currents and downslope processes. In particular, we recognize a suite of large to medium-scale erosive and depositional features, related to different bottom-currents (e.g., reverse tidal flows, residual flows, internal waves) acting over diverse time periods. Large scale bottom-current features are represented by contourite drifts and channels developed over long periods (> thousands of years). Medium-scale features formed during shorter time periods and include scours, furrows, transverse ridges (pinnacles) and narrow longitudinal bodies in the sill sector, along with several sand wave fields, located at greater depths on the Ionian and Tyrrhenian sides of the Messina Strait. Downslope processes encompass channelized features originated by sedimentary gravity flows, coarse-grained aprons and fans and submarine landslides. They mostly occur along strait margins and become predominant in the southern exit where the axial Messina canyon and its tributaries are present.Overall, our study shows that the MS is a fruitful area in which to investigate the interaction between recent erosive-depositional sedimentary and oceanographic processes, also modulated by sea-level fluctuations, during the last eustatic cycle. Moreover, the observed seabed morphologies and the associated processes provide insights for interpreting similar features in modern and ancient similar straits and seaways.

scholarly journals CROSS-SHORE SEDIMENT TRANSPORT IN THE SWASH ZONE: LARGE-SCALE LABORATORY EXPERIMENTS

2020 ◽  
pp. 18
Author(s):  
Sara Dionisio Antonio ◽  
Jebbe van der Werf ◽  
Bart Vermeulen ◽  
Ivan Caceres ◽  
Jose M. Alsina ◽  
...  
Keyword(s):  
Sediment Transport ◽  
Large Scale ◽  
Surf Zone ◽  
Transport Processes ◽  
Sand Transport ◽  
Swash Zone ◽  
Flume Experiments ◽  
Wave Flume ◽  
Shoreline Evolution

The swash zone is a highly dynamic boundary between the beach and the surf zone. Swash processes determine whether sediment is either stored on the upper beach or is transported offshore, and thus strongly affect shoreline evolution. The present research focuses on the hydrodynamics, sand transport processes and net sediment transport in the swash zone through a series of large-scale wave flume experiments. This research aims to improve the understanding of swash zone sand transport processes, in particular the role of cross-shore sand advection and wave-swash interactions, and bring new detailed insights into the relation between intra-swash processes and net sand transport rates.Recorded Presentation from the vICCE (YouTube Link): https://youtu.be/tYvJ0pML-kU

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