Silurian microbial associations from the Alexander terrane, Alaska

1993 ◽  
Vol 67 (5) ◽  
pp. 728-738 ◽  
Author(s):  
Constance M. Soja ◽  
Robert Riding
Keyword(s):  
Debris Flows ◽  
Turbidity Currents ◽  
Diverse Population ◽  
Microbial Assemblage ◽  
Microbial Associations ◽  
Transport And Mixing ◽  
Shelf Margin ◽  
Water Carbonate ◽  
Carbonate Deposits ◽  
Alexander Terrane

Silurian calcareous algae, cyanobacteria, and microproblematica are abundantly preserved in the Alexander terrane of southeastern Alaska. They represent a diverse population of calcified microbes that contributed to the formation of a variety of shallow- and deep-water carbonate deposits. Five associations are recognized on the basis of recurring groups of microbial taxa. These include a Girvanella-Tuxekanella association that formed oncoids and thick encrustations on skeletal grains in shelf environments. A Renalcis association predominated in a stromatoporoid-coral reef that developed at the incipient shelf margin on a crinoid-solenoporid shoal (“Solenopora” association). Other organic buildups are characterized by a Ludlovia association, which constructed skeletal stromatolite reefs, and by an Epiphyton-Sphaerina association that contributed to the formation of a stromatolitic mud mound. A mixed microbial assemblage reflects transport and mixing of shallow-water microbial biotas that were deposited by turbidity currents, debris flows, and slumps in a slope environment.

scholarly journals Triassic metasediments in the internal Dinarides (Kopaonik area, southern Serbia): stratigraphy, paleogeographic and tectonic significance

2010 ◽  
Vol 61 (2) ◽  
pp. 89-109 ◽  
Author(s):  
Senecio Schefer ◽  
Daniel Egli ◽  
Sigrid Missoni ◽  
Daniel Bernoulli ◽  
Bernhard Fügenschuh ◽  
...  
Keyword(s):  
Shallow Water ◽  
Lower Triassic ◽  
Turbidity Currents ◽  
Distal Margin ◽  
Carbonate Platforms ◽  
Carbonate Production ◽  
Tectonic Significance ◽  
Internal Dinarides ◽  
Water Carbonate ◽  
Shallow Water Carbonate

Triassic metasediments in the internal Dinarides (Kopaonik area, southern Serbia): stratigraphy, paleogeographic and tectonic significanceStrongly deformed and metamorphosed sediments in the Studenica Valley and Kopaonik area in southern Serbia expose the easternmost occurrences of Triassic sediments in the Dinarides. In these areas, Upper Paleozoic terrigenous sediments are overlain by Lower Triassic siliciclastics and limestones and by Anisian shallow-water carbonates. A pronounced facies change to hemipelagic and distal turbiditic, cherty metalimestones (Kopaonik Formation) testifies a Late Anisian drowning of the former shallow-water carbonate shelf. Sedimentation of the Kopaonik Formation was contemporaneous with shallow-water carbonate production on nearby carbonate platforms that were the source areas of diluted turbidity currents reaching the depositional area of this formation. The Kopaonik Formation was dated by conodont faunas as Late Anisian to Norian and possibly extends into the Early Jurassic. It is therefore considered an equivalent of the grey Hallstatt facies of the Eastern Alps, the Western Carpathians, and the Albanides-Hellenides. The coeval carbonate platforms were generally situated in more proximal areas of the Adriatic margin, whereas the distal margin was dominated by hemipelagic/pelagic and distal turbiditic sedimentation, facing the evolving Neotethys Ocean to the east. A similar arrangement of Triassic facies belts can be recognized all along the evolving Meliata-Maliac-Vardar branch of Neotethys, which is in line with a ‘one-ocean-hypothesis’ for the Dinarides: all the ophiolites presently located southwest of the Drina-Ivanjica and Kopaonik thrust sheets are derived from an area to the east, and the Drina-Ivanjica and Kopaonik units emerge in tectonic windows from below this ophiolite nappe. On the base of the Triassic facies distribution we see neither argument for an independent Dinaridic Ocean nor evidence for isolated terranes or blocks.

scholarly journals Toe-of-slope facies of the Eocene limestones in Aghioi Pantes sequence (Zakynthos island, Western Greece)

2018 ◽  
Vol 34 (2) ◽  
pp. 699
Author(s):  
Μ. ΚΑΤΗ
Keyword(s):  
Shallow Water ◽  
Debris Flows ◽  
Depositional Environment ◽  
Facies Analysis ◽  
Facies Association ◽  
Gravity Flows ◽  
Carbonate Sequence ◽  
Western Greece ◽  
Water Carbonate ◽  
Water Facies

The facies analysis of the Eocene limestones in the Aghioi Pantes section in central Zakynthos, part of the Preapulian carbonate sequence in the greater area, showed three megafacies types: a) graded beds, in which two main subtypes have been recognized, medium- to thin-bedded calcarenites-calcilutites and thick-bedded ruditic calcarenites, consisting mainly of redeposited shallow-water carbonate sands (mostly bioclasts of nummulites and echinoids); based on their sedimentary structures they have been interpreted as low density turbidite and high density turbidite (or sandy debris flows) deposits correspondingly, b) calcareous conglomerates consisting of shallow-water facies lithoclasts and abundant pelagic intraclasts all of which have been interpreted as debris flow deposits and c) folded strata of pelagic-hemipelagic composition that have been interpreted as slumps. Subsequently, the studied limestones constitute exclusively deep-water resedimented facies having been deposited mainly through sediment gravity flows, carrying significant amounts of shallow-water bio- lithoclastic material. The distribution and the organization of this facies association, with the dominance in particular of the base cut-out turbidites, suggest as depositional environment of the studied Eocene limestones a "low" in the outer slope connecting the Preapulian platform with the adjacent Ionian basin.

Sedimentary facies on the rises and slopes of passive continental margins

1980 ◽  
Vol 294 (1409) ◽  
pp. 169-176 ◽  
Keyword(s):  
Sediment Transport ◽  
Debris Flows ◽  
Thermohaline Circulation ◽  
Dominant Role ◽  
Sedimentary Facies ◽  
Turbidity Currents ◽  
Continental Margins ◽  
Passive Margins ◽  
New Evidence

JOIDES drilling results provide new evidence concerning facies patterns on evolving passive margins that strengthens and extends hypotheses constructed from studies of morphology, seismic reflexion data and shallow samples on modern margins, and from field geologic studies of uplifted ancient margins. On the slopes and rise, gravity-controlled mechanisms - turbidity currents, debris flows, slides and the like - play the dominant role in sediment transport over the long term, but when clastic supplies are reduced, as for example during rapid transgressions, then oceanic sedimentation and the effects of thermohaline circulation become important. Sedimentary facies models used as the basis of unravelling tectonic complexities of some deformed margins, for example in the Mesozoic Tethys, may be too simplistic in the light of available data from modern continental margins.

Slow build-up of turbid currents triggered by a moderate earthquake in the Sea of Marmara

2020 ◽  
Author(s):  
Pierre Henry ◽  
M Sinan Özeren ◽  
Nurettin Yakupoğlu ◽  
Ziyadin Çakir ◽  
Emmanuel de Saint-Léger ◽  
...  
Keyword(s):  
Pressure Sensor ◽  
Debris Flows ◽  
Background Level ◽  
Signal Strength ◽  
Normal Operation ◽  
Turbidity Currents ◽  
Central Basin ◽  
Sea Of Marmara ◽  
Moderate Earthquake ◽  
Mud Flow

<p>Earthquake-induced submarine slope destabilization is known to cause debris flows and turbidity currents. These also interact with currents caused by tsunami and seiches resulting in deposits with specific sedimentological characteristics, turbidite-homogenites being a common example. Data on the deep-sea hydrodynamic events following earthquakes are, however, limited. An instrumented frame deployed at the seafloor in the Sea of Marmara Central Basin recorded some of the consequences of a magnitude 5.8 earthquake that occurred Sept 26, 2019 at 10-12 km depth without causing any significant tsunami. The instrumentation comprises a Digiquartz® pressure sensor recording at 5 s interval and a 1.9-2 MHz Doppler recording current meter set 1.5 m above the seafloor and recording at 1-hour interval. The device was deployed at 1184 m depth on the floor of the basin near the outlet of a canyon, 5 km from the epicenter. Chirp sediment sounder profiles indicate a depositional fan or lobe is present at this location. The passing of the seismic wave was recorded by the pressure sensor, but little other perturbation is recorded until 25 minutes later when the instrument, probably hit by a mud flow, tilts by 65° in about 15 seconds. Over the following 10 hours the tilted instrument records bursts of current of variable directions. The last burst appears to be the strongest with velocities in the 20-50 cm/s range, causing enough erosion to free the device from the mud and allowing the buoyancy attached to the upper part of the frame to straighten it back to its normal operation position. Then, the current, flowing down along the canyon axis, progressively decays to background level (≈2 cm/s) in 8 hours. Doppler signal backscatter strength is a proxy for turbidity, sensitive to sand-size suspended particles. Signal strength increased to high values during the event (max -7.6 dB from a background value of -40dB) and decayed over the next three days. These observations show that even a moderate earthquake can trigger a complex response involving mud flows and turbidity currents. We infer simultaneous slope failures at various locations may produce complex current patterns and cause build-up of kinetic energy over several hours.</p>

Debris Flows vs. Turbidity Currentsa Modeling Comparison of Their Dynamics and Deposits

2000 ◽  
Author(s):  
Lincoln F. Pratson ◽  
Jasim Imran ◽  
Gary Parker ◽  
James P. M. Syvitski ◽  
Eric Hutton
Keyword(s):  
Debris Flows ◽  
Turbidity Currents

Influence of Salt Tectonics On Fault Displacements and Submarine Slope Failures from Algeria To Sardinia

2019 ◽  
Vol 25 (4) ◽  
pp. 318-330 ◽  
Author(s):  
Julia A. Yeakley ◽  
Abdul Shakoor ◽  
William Johnson
Keyword(s):  
Debris Flows ◽  
Average Rate ◽  
Plate Boundary ◽  
Western Mediterranean ◽  
Turbidity Currents ◽  
Salt Tectonics ◽  
Slope Failures ◽  
Submarine Slope ◽  
Lateral Extent ◽  
Pipeline Route

ABSTRACT We used previously obtained marine geophysical and geotechnical data for the proposed Galsi pipeline route from Algeria to Sardinia to analyze the buried salt distribution, rates of fault displacements, and frequency and lateral extent of submarine slope failures. Crossing the convergent African/Nubian–European plate boundary, the southern section of the pipeline route traverses continental shelves and slopes of Algeria and Sardinia as well as the Algerian abyssal plain of the western Mediterranean. Deeply buried Messinian-aged salt is present throughout this area. Being less dense and more buoyant than the overburden sediment, the salt tends to flow upward to form diapiric structures that, in turn, result in the formation of faults and landslides in the overlying sediment. Measured offsets from seismic profiles of different resolutions were compared with predicted sediment age at depth of each offset, yielding an average rate of fault displacement of 1.5 cm/kiloyear (ky). The highest rates of displacement are along the Cagliari slope near Sardinia (2.5-2.7 cm/ky) and near the convergent plate boundary (2.3 cm/ky). Utilizing the same geophysical data, the frequency and lateral extent of submarine slope failures in the study area can also be linked to the distribution of salt and the influence of salt tectonics. Turbidity currents and hyperpycnal flows are present within the Algerian basin, whereas local debris flows, landslide runouts, and channelized debris flows are present along the Sardinian slope. The low sedimentation rates, determined in this study, suggest that the most recent slope failures related to salt tectonics occurred more than 12,000 years ago.

Paleobiogeographical significance of the Late Silurian microproblematicum Tuxekanella Riding and Soja

2010 ◽  
Vol 84 (2) ◽  
pp. 346-351 ◽  
Author(s):  
Stanislaw Skompski
Keyword(s):  
Shallow Water ◽  
The Moment ◽  
Water Carbonate ◽  
Shallow Water Carbonate ◽  
Alexander Terrane

An enigmatic microproblematicum, Tuxekanella Riding and Soja (1993), has been identified in the shallow water carbonate succession of the Late Silurian Skala formation (Podolia, Ukraine). the newly found specimens suggest most probably the algal nature of this enigmatic microfossil. Tuxekanella is known only from two extremely distant regions at the moment: the Alexander terrane in Alaska and Podolia. the possibility of their paleobiogeographical link is discussed in the context of paleotectonic models, assuming the peri-Gondwanan origin of the Alexander Terrane.

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