Analyses of 3-D seismic data in predominantly basin-floor settings offshore Indonesia, Nigeria, and the Gulf of Mexico, reveal the extensive presence of gravity-flow depositional elements. Five key elements were observed: (1) turbidity-flow leveed channels, (2) channel-overbank sediment waves and levees, (3) frontal splays or distributary-channel complexes, (4) crevasse-splay complexes, and (5) debris-flow channels, lobes, and sheets. Each depositional element displays a unique morphology and seismic expression. The reservoir architecture of each of these depositional elements is a function of the interaction between sedimentary process, sea-floor morphology, and sediment grain-size distribution.

(1) Turbidity-flow leveed-channel widths range from greater than 3 km to less than 200 m. Sinuosity ranges from moderate to high, and channel meanders in most instances migrate down-system. The high-amplitude reflection character that commonly characterizes these features suggests the presence of sand within the channels. In some instances, high-sinuosity channels are associated with (2) channel-overbank sediment-wave development in proximal overbank levee settings, especially in association with outer channel bends. These sediment waves reach heights of 20 m and spacings of 2-3 km. The crests of these sediment waves are oriented normal to the inferred transport direction of turbidity flows, and the waves have migrated in an up-flow direction. Channel-margin levee thickness decreases systematically down-system. Where levee thickness can no longer be resolved seismically, high-sinuosity channels feed (3) frontal splays or low-sinuosity, distributary-channel complexes. Low-sinuosity distributary-channel complexes are expressed as lobate sheets up to 5-10 km wide and tens of kilometers long that extend to the distal edges of these systems. They likely comprise sheet-like sandstone units consisting of shallow channelized and associated sand-rich overbank deposits. Also observed are (4) crevasse-splay deposits, which form as a result of the breaching of levees, commonly at channel bends. Similar to frontal splays, but smaller in size, these deposits commonly are characterized by sheet-like turbidites. (5) Debris-flow deposits comprise low-sinuosity channel fills, narrow elongate lobes, and sheets and are characterized seismically by contorted, chaotic, low-amplitude reflection patterns. These deposits commonly overlie striated or grooved pavements that can be up to tens of kilometers long, 15 m deep, and 25 m wide. Where flows are unconfined, striation patterns suggest that divergent flow is common. Debris-flow deposits extend as far basinward as turbidites, and individual debris-flow units can reach 80 m in thickness and commonly are marked by steep edges. Transparent to chaotic seismic reflection character suggest that these deposits are mud-rich.

Stratigraphically, deep-water basin-floor successions commonly are characterized by mass-transport deposits at the base, overlain by turbidite frontal-splay deposits and subsequently by leveed-channel deposits. Capping this succession is another mass-transport unit ultimately overlain and draped by condensed-section deposits. This succession can be related to a cycle of relative sea-level change and associated events at the corresponding shelf edge. Commonly, deposition of a deep-water sequence is initiated with the onset of relative sea-level fall and ends with subsequent rapid relative sea-level rise.

http://www.zenzebra.net/posamentier/posamentier-deep-water-depositional-elements.pdf

Seismic Geomorphology and Stratigraphy of Depositional Elements in Deep-Water Settings

The mineral component of pelagic sediment is brought to the deep sea by transport in the wind. Extraction and analysis of this dust allows estimation of the past aridity of the eolian source region, via flux determinations, and of the intensity of the transporting winds, from grain size data. These two parameters, the grain size and mass flux of dust, vary independently. There are three significant sources of modern dust, eastern and central Asia, northwest Africa, and Arabia, all in the northern hemisphere. As the rainfall associated with the Intertropical Convergence Zone is an effective barrier to southerly transport of dust, the northern hemisphere is an order of magnitude more “dusty” than is the southern, an asymmetry that has characterized most of the Cenozoic. Eolian flux data show that most of the northern hemisphere was more arid during glacial maxima, with 3 to 5 times as much dust transported during glacial stages than during interglacials; only northwestern South America varied in the opposite sense. The periodicity of Quaternary variation in both eolian flux and eolian grain size data is strongly influenced by the Milankovitch cycles of orbital variability. Wind intensities vary on a shorter time scale than the general 100-kyr cycles of glaciation and general aridity. Eolian grain sizes display forcing at precessional (19 and 23 kyr), tilt (41 kyr), and at approximately 30 kyr periodicities. As a result the generalization that winds are uniformly stronger during glacial times is not valid. Whole-Cenozoic records show that the largest change in dust flux, an order of magnitude increase, occurred in the northern hemisphere and reflects continental drying associated with the late Pliocene onset of northern hemisphere glaciation. Southern hemisphere eolian records show no sign of paleoclimatic changes in the late Pliocene. The most important change in Cenozoic atmospheric circulation was a severalfold reduction in wind intensity that occurred at the time of the Paleocene-Eocene boundary. Before then, latest Cretaceous and Paleocene winds were essentially as strong as those of the late Cenozoic. This shift appears to be one of several climatic responses to a change in the nature and amount of global heat transport at about 55 Ma.

The paleoclimatic record provided by eolian deposition in the deep sea: The geologic history of wind

http://basin.earth.ncu.edu.tw/download/courses/seminar_MSc/2012/1018_1_1.pdf

Marine hyperpycnal flows: initiation, behavior and related deposits. A review

/pdf/reconciling-plate-tectonic-reconstructions-of-alpine-tethys-1do3i5vm2t.pdf

Reconciling plate-tectonic reconstructions of Alpine Tethys with the geological–geophysical record of spreading and subduction in the Alps

Submarine sediment density flows are one of the most important processes for moving sediment across our planet, yet they are extremely difficult to monitor directly. The speed of long run-out submarine density flows has been measured directly in just five locations worldwide and their sediment concentration has never been measured directly. The only record of most density flows is their sediment deposit. This article summarizes the processes by which density flows deposit sediment and proposes a new single classification for the resulting types of deposit. Colloidal properties of fine cohesive mud ensure that mud deposition is complex, and large volumes of mud can sometimes pond or drain-back for long distances into basinal lows. Deposition of ungraded mud (TE-3) most probably finally results from en masse consolidation in relatively thin and dense flows, although initial size sorting of mud indicates earlier stages of dilute and expanded flow. Graded mud (TE-2) and finely laminated mud (TE-1) most probably result from floc settling at lower mud concentrations. Grain-size breaks beneath mud intervals are commonplace, and record bypass of intermediate grain sizes due to colloidal mud behaviour. Planar-laminated (TD) and ripple cross-laminated (TC) non-cohesive silt or fine sand is deposited by dilute flow, and the external deposit shape is consistent with previous models of spatial decelerating (dissipative) dilute flow. A grain-size break beneath the ripple cross-laminated (TC) interval is common, and records a period of sediment reworking (sometimes into dunes) or bypass. Finely planar-laminated sand can be deposited by low-amplitude bed waves in dilute flow (TB-1), but it is most likely to be deposited mainly by high-concentration near-bed layers beneath high-density flows (TB-2). More widely spaced planar lamination (TB-3) occurs beneath massive clean sand (TA), and is also formed by high-density turbidity currents. High-density turbidite deposits (TA, TB-2 and TB-3) have a tabular shape consistent with hindered settling, and are typically overlain by a more extensive drape of low-density turbidite (TD and TC,). This core and drape shape suggests that events sometimes comprise two distinct flow components. Massive clean sand is less commonly deposited en masse by liquefied debris flow (DCS), in which case the clean sand is ungraded or has a patchy grain-size texture. Clean-sand debrites can extend for several tens of kilometres before pinching out abruptly. Up-current transitions suggest that clean-sand debris flows sometimes form via transformation from high-density turbidity currents. Cohesive debris flows can deposit three types of ungraded muddy sand that may contain clasts. Thick cohesive debrites tend to occur in more proximal settings and extend from an initial slope failure. Thinner and highly mobile low-strength cohesive debris flows produce extensive deposits restricted to distal areas. These low-strength debris flows may contain clasts and travel long distances (DM-2), or result from more local flow transformation due to turbulence damping by cohesive mud (DM-1). Mapping of individual flow deposits (beds) emphasizes how a single event can contain several flow types, with transformations between flow types. Flow transformation may be from dilute to dense flow, as well as from dense to dilute flow. Flow state, deposit type and flow transformation are strongly dependent on the volume fraction of cohesive fine mud within a flow. Recent field observations show significant deviations from previous widely cited models, and many hypotheses linking flow type to deposit type are poorly tested. There is much still to learn about these remarkable flows.

Subaqueous sediment density flows: Depositional processes and deposit types

A useful comparison of modern and ancient submarine fans can be based only on well-understood and thoroughly mapped systems. In addition, the examples selected for comparison must represent depositional systems similar in such characteristics as type of basin, size of sediment source, physical and temporal scales, and stage of development. Many fan sedimentation models presently in use do not meet these criteria.

https://link.springer.com/content/pdf/10.1007%2F978-94-009-3241-8_1.pdf

Comparing Examples of Modern and Ancient Turbidite Systems: Problems and Concepts

Deltaic, mixed and turbidite sedimentation of ancient foreland basins

The vertical and lateral stratigraphic relations of facies and facies associations, palaeocurrent directions, and geometry and internal organization of associated thick-bedded and coarse-grained bodies of sandstone provide the framework for distinguishing five thin-bedded turbidite facies in the Eocene Hecho Group, south-central Pyrenees, Spain. Each facies is characterized by a number of primary features which are palaeoenvironmental indicators by themselves. These features and their palaeoenvironmental significance are summarized below.



1
The impressive regularity and lateral persistence of bedding and depositional structures, combined with the association of thin hemipelagic intercalations are typical characteristics of the basin plain thin-bedded turbidites. Lateral variations in bed thickness, internal structures, grain size, sand: shale ratio, and amounts of hemipelagic intercalations are present in these sediments, but take place so gradually that they cannot generally be recognized at the scale of even very large exposures. The basin plain facies has a remarkable character of uniformity over great distances and considerable stratigraphic thicknesses.

2
Thickening-upward and/or symmetric cycles with individual thicknesses ranging from a few metres to a few tens of metres are typical of lobe-fringe thin-bedded turbidites. The sediments that comprise the cycles contain small but recognizable variations in bed thickness and sand: shale ratio. The diagnostic cyclic pattern can be detected in relatively small exposures. It should be noted that in absence of coarse-grained and thick-bedded sandstone of the depositional lobes the above cyclic pattern is diagnostic of fan-fringe areas.

3
An extremely irregular bedding pattern with lensing, wedding, and amalgamation of individual beds over very short distances, sharp rippled tops of many beds, and internal depositional structures indicative of mainly tractional processes without substantial fallout, are typical and exclusive characteristics of channelmouth thin-bedded turbidites.

4
Bundles of interbedded thin-bedded sandstone and mudstone as thick as a few metres that are separated in vertical sequences by mudstone units of roughly similar or greater thickness are typical of interchannel thin-bedded turbidites. The most diagnostic feature of this depositional environment is the presence of beds of sandstone filling broad shallow channels as probable crevasse-splays.

5
Thin, thoroughly rippled sandstone beds with marked divergence of the bedding attitude characterize the channel-margin facies. The divergence or expansion in thickness, is consistently toward the channel axis. Small and shallow channels filled with thin-bedded deposits, interpreted here as crevasses cut into channel edges or levees during period of severe overbanking are also characteristic.

Distinctive thin‐bedded turbidite facies and related depositional environments in the Eocene Hecho Group (South‐central Pyrenees, Spain)

(1978). Turbidites of the northern Apennines: introduction to facies analysis. International Geology Review: Vol. 20, No. 2, pp. 125-166.

Turbidites of the northern Apennines: introduction to facies analysis

Long-term global sea level variations and local tectonic control form the basic framework within which turbidite sediments develop as a response to breaks in the equilibrium between shelfal and basinal sedimentation. An understanding of the interaction of these processes and resulting types of turbidite deposition is still in its infancy and requires, as a preliminary approach, the precise framing of turbidite sediments within well defined depositional sequences.

Emiliano Mutti

Papers

Comparing Examples of Modern and Ancient Turbidite Systems: Problems and Concepts

Deltaic, mixed and turbidite sedimentation of ancient foreland basins

Distinctive thin‐bedded turbidite facies and related depositional environments in the Eocene Hecho Group (South‐central Pyrenees, Spain)

Turbidites of the northern Apennines: introduction to facies analysis

Turbidite Systems and Their Relations to Depositional Sequences