Types Of Soft-sediment Deformation Structures Research Articles

Soft-sediment deformation structures in the Miocene deposits in the Luoyanshan area of the Qaidam basin, China: Implications for paleogeomorphology

Based on well cores, nine types of lithofacies were identified in the deposits of the Miocene Lower Youshashan Formation in the Luoyanshan area of the Qaidam Basin. The preliminary interpretation of the sedimentary environment indicates that these deposits were formed in a shoreface to a deep lake and a delta environment. Soft-sediment deformation structures (SSDSs) within multiple layers were observed in five cores. These SSDSs can be divided into four categories: (1) load structures, (2) sand injections, (3) fault-graded beds, and (4) slumps. The detailed descriptions of these SSDSs allowed us to analyze and interpret the deformation mechanisms and driving forces. The deformation mechanisms reflected by most of the SSDSs in the cores are liquefaction and fluidization (load structures and sand injections). The remaining SSDSs exhibit plastic and/or brittle behavior (fault-graded beds and slumps). The corresponding driving forces are mainly unstable density gradients and gravitational body forces. The driving forces essentially reflect the original paleogeomorphological setting (i.e., the topographic slope gradient), the initial sedimentary column, and the biological, chemical, and/or physical processes acting on the sediments. After eliminating the interfering factors, the relationship between the different types of SSDSs and the paleogeomorphological settings were established using the driving forces as the intermediary between them. The formation of the symmetric load cast and flame structures was driven by the unstable density gradient of the sediments, indicating a flat topography. In contrast, the asymmetric load cast and flame structures, the fault-graded beds, and the slumps were driven by the gravitational body force, implying a sloping topography. Furthermore, the proportions of these four types of SSDSs in each well were statistically analyzed to qualitatively determine the paleogeomorphological setting of each well during the penecontemporaneous period and to support and refine the sedimentary analysis. The results show that the five cores contain sediments deposited in five types of lacustrine sub-environments: (1) a flat platform on a subaqueous beach-bar, (2) a flat shallow to deep lake, (3) the edge of a subaqueous beach-bar, (4) a position near and below the delta slope, and (5) a steep delta slope. The results of this study illustrate that there is a strong coupling relationship between the morphologies of the SSDSs and the penecontemporaneous paleogeomorphological setting. This correlation provides a new perspective for interpreting sedimentary environments.

Processes and evolution of the Pleistocene coastal sedimentary succession of Es Codolar (Southern Eivissa, Balearic Islands, Western Mediterranean): insights from soft-sediment deformation structures

We analyze the evolution of the undeformed Middle to Late Pleistocene deposits of Es Codolar (Southern Eivissa, Western Mediterranean). The outcrop records a succession characterized by the alternation of aeolian, colluvial and alluvial fan deposits and palaeosols that result in a complex stratigraphic architecture. In this area, aeolian beds, colluvial deposits and palaeosols are exposed along sea-cliffs for almost 500 m, allowing detailed descriptions both of the general sedimentological and geomorphological features of the Middle to Late Pleistocene deposits. Several different types of soft-sediment deformation structures are described (load-casts structures, injection structures, water-scape structures, rizoconcretions), which will help us in the understanding of the climatic evolution and the syn- post-depositional processes. In this way, main processes triggering the formation of these structures seem to be sea level changes together with a wetter environment during warmer climatic episodes.

Soft-sediment deformation structures (SSDS) in the Ediacaran and lower Cambrian succession of the Aksu area, NW Tarim Basin, and their implications

The Tarim Basin, the largest continental and marine superimposed basin in the northwestern part of China, is typically viewed as a stable and uninterrupted sequence during the Ediacaran-Cambrian transition. Undeformed strata, thick shallow marine sediments and thin deep marine sediments characterize the basin. In this study, we identify various types of soft-sediment deformation structures (SSDS) and an unconformity at four localities in the Aksu area, NW Tarim Basin. SSDSs include large-scale load structures, plastic intrusions and extrusions, load casts and pillow structures, liquefied breccias, ground fissures and lateral liquefaction, boudinage-like SSDSs, mound and sag structures, slumps, and small syn-sedimentary faults. The deformed layers are sandwiched between undeformed sedimentary rocks. Deformation features are found in the (a) lower Cambrian Yuertusi Formation consisting of interbedded thin black shale and phosphorite chert layers, thick-bedded shallow gray dolomite and silicate layers; (b) upper Ediacaran Qigebulak Formation composed of dark gray to gray dolomite and grayish green mudstone layers; (c) in the brown sandstone layers of the lower Ediacaran Sugaitebulak Formation. These units contain fluvial-lacustrine, nearshore, carbonate platform, shelf, and bathyal sedimentary environments. The SSDSs and more detailed stratigraphy indicate a dynamic setting that includes the heretofore unrecognized unconformities, a sub-stratigraphic sequence interface and high magnitude seismic events. The SSDS were produced during rifting, short sub-aerial exposure and frequent seismic disturbances. Combined on the carbon and oxygen isotope records, gamma radiations and the concentrations of main and trace elements, the differences between the SSDS layers and the undeformed layers are preliminary analyzed. We propose that this sequence not reflect a stable tectonic-sedimentary environment during the Ediacaran-Cambrian transition. Therefore, these units provide a unique glimpse into paleo-tectonic activity and paleo-ecological-environmental variation in the Tarim Basin during the late period of Rodinia breakup and the assembly of Gondwana.

Soft-sediment deformation structures as indicators of tectono-volcanic activity during evolution of a lacustrine basin: A case study from the Upper Triassic Ordos Basin, China

Abstract The Ordos Basin, central China, is a large-scale Late Triassic intracratonic lacustrine basin, and in which the Upper Triassic Yanchang Formation comprises interbedded sandstones, mudstones and tuffs, representing deposits of a complete lacustrine life cycle. Based on observation of extensive well cores, various types of soft-sediment deformation structures have been identified in the lacustrine deposits of the southwest basin, including deformed lamination/bedding, load casts and flame structures, pseudonodules, microfaults, autoclastic brecciation, sand dykes, dyke-sill complexes, and sandy and muddy slumps. Liquefaction and fluidization of unconsolidated permeable sediments, together with brittle fracturing of semi-consolidated sediments, are the major deformation mechanisms that generated these structures. Both the scale and prevalence of the deformed sediments, as well as the geological setting of the lacustrine basin, suggest that seismic events (synsedimentary tectonic activity) were the main trigger to initiate deformation processes, although sedimentary overloading could also have been a minor localized trigger. Many volcanic tuffs preserved in both the primary undisturbed deposits and deformed sediments serve as support for synsedimentary tectono-volcanic activities that induced deformation in these lacustrine sediments. The deformation structures usually form vertical clusters of several different types, representing active syndepositional tectonic periods. Stratigraphic correlation shows three such deformation clusters to be widespread in the area detailed herein, and likely recorded three major tectonic periods during deposition. A thick extensive oil shale, with various deformation structures, also reveals another active tectonic period. These four intervals coincide well with the transition of the sedimentary architecture in the area, indicating four phases of most intense tectonic periods and their influence on lacustrine evolution.

Soft-sediment deformation structures induced by rapid sedimentation in Early Cretaceous turbidites, Lingshan Island, eastern China

Turbidites of the Early Cretaceous Lingshandao Formation on Lingshan Island, eastern China, show numerous soft-sediment deformation structures. The turbidites accumulated in a rift basin plain on the distal part of a low-energy fan, together with autochthonous fine-grained sediments that settled from suspension. Occasionally, sets of both types of sediments slumped down the basin slope. The turbidites were studied in two sections. Paleocurrent directions, measured from sole marks at the base of the sandy turbidites, indicate a slope from SE to NW; this is consistent with the dip direction of the axial planes of the major slump folds. Among the numerous types of soft-sediment deformation structures that are present, two types are of special interest because of their specific genesis, viz. rip-up clasts and dome structures. It appears that rapid sedimentation must be considered as the main trigger behind these deformations: the rapid accumulation of particularly the sandy turbidites resulted in overloading of the underlying beds and then consequently in an increase in their pore-water pressure that induced liquefaction and fluidization, which triggered the formation of the rip-up clasts and dome structures. The downslope movement of freshly deposited turbidites after slope failure over the inclined sedimentary surface induced shear stresses, which resulted in the complication of the rip-up clasts and the preferred orientation of some dome structures. Both the dip directions of the axial planes of some of the dome structures and microfolds within the rip-up clasts are consistent with the paleocurrent direction indicated by the sole marks and the slump folds.

Debris flow and glacioisostatic-induced soft-sediment deformation structures in a Pleistocene glaciolacustrine fan: The southern Baltic Sea coast, Poland

Middle Pleistocene glaciolacustrine fan sediments are exposed along a cliff at the Baltic Sea coast, where plastic and brittle soft-sediment deformation structures (SSDS) commonly occur: (1) fold structures (various types of folds and flexures); (2) load structures (load casts, pseudonodules) and flame structures; (3) water-escape structures (WES); and (4) brittle deformation structures, such as faults (medium- and small-scale reverse and normal), and fragments of broken-up laminae. The origins of the SSDS can be linked to gravitational processes promoted by shear stresses in subaqueous debris flows on the glaciolacustrine fan and by the weight of overlying sediments; and/or to the glacial rebound of Earth's crust during deglaciation because in the Pleistocene the Baltic Sea and surrounding areas were covered by ice sheets many times. The question investigated here concerns recognition of the trigger mechanisms responsible for the development of SSDS, and the criteria needed to recognize those mechanisms based on the lithological and deformational features of the sediments involved. Some types of SSDS can look similar regardless of trigger mechanisms, but some occur more often as a result of a specific mechanism. Is it possible to distinguish SSDS of seismic origin in a glaciolacustrine fan succession affected by multiple debris flows and of SSDS that evolved as a consequence of slope processes? We suggest criteria to recognize SSDS triggered by the glacioisostatic rebound as well as those which can develop as a result of the rebound and slope processes.

The seismite problem

During a period of 82 years (1931–2013), 39 genetic terms were introduced for various deposits. Of the 39 terms, only ten are meaningful in understanding the true depositional origin (e.g., turbidites), the remaining 29 are just jargons (e.g., seismites, tsunamites, etc.). The genetic term “seismites”, introduced by Seilacher (1969) for recognizing palaeoearthquakes in the sedimentary record, is a misnomer. The term was introduced in haste, based on an examination of a single exposure of the Miocene Monterey Formation (10 m) in California, without a rigorous scientific analysis. The fundamental problem is that earthquake is a triggering mechanism, not a depositional process. Type of triggers cannot be recognized in the ancient sedimentary record because evidence for triggers is not preserved by nature. Soft-sediment deformation structures (SSDS), commonly used as the criteria for interpreting seismites, are a product of liquefaction. However, liquefaction can be induced by any one of 21 triggers, which include earthquakes, meteorite impacts, tsunamis, sediment loading, among others. Brecciated clasts, typically associated with earthquake-induced deposits in the Dead Sea Basin, are also common depositional products of debris flows (i.e., synsedimentary product unrelated to earthquakes). Also, various types of SSDS, such as duplex-like structures and clastic injections, can be explained by synsedimentary processes unrelated to earthquakes. Case studies of sandstone petroleum reservoirs worldwide, which include Gulf of Mexico, North Sea, Norwegian Sea, Nigeria, Equatorial Guinea, Gabon, and Bay of Bengal, reveal that there is compelling empirical evidence for sediment loading being the primary cause of SSDS. The Krishna–Godavari Basin, located on the eastern continental margin of India, is ideal for sediment failures by multiple triggering mechanisms where overpressure and liquefaction have led to multi-origin SSDS. Because tsunamis and meteorite impacts are important phenomena in developing extensive deposits, lateral extent of SSDS cannot be used as a unique distinguishing attribute of earthquakes. For these reasons, the genetic term “seismites”, which has no redeemable scientific value, is obsolete.

Seismites from a well core of palustrine deposits as a tool for reconstructing the palaeoseismic history of a fault

The Concud Fault is located at the junction between the Jiloca and Teruel grabens (central-eastern Iberian Chain, Spain). The Late Pleistocene activity of this fault has been well logged from structural and palaeoseismological trench studies, but only scattered data of the Late Pliocene seismic activity exist. The Late Pliocene–Early Pleistocene syn-tectonic infill consists of an endorheic continental succession in which a75 m-long continuous well was drilled near the Concud Fault. Along the entire well core, several types of soft-sediment deformation structures with variable morphology, size and frequency have occurred including clastic dykes, load structures and slumps. The rigorous analysis of the deformation structures, their relationships with the involved sedimentary facies, and the discrimination of possible deformation mechanisms and trigger processes allow us to interpret part of them as seismically-induced structures. The recognition of 21 deformed beds (seismites) allow the Late Pliocene–Early Pleistocene seismic history of the Concud Fault to be reconstructed. Therefore, 21 seismic events (with M≥5) and an apparent recurrence period of about 45ka have been inferred.

Types of soft-sediment deformation structures in a lacustrine Ploužnice member (Stephanian, Gzhelian, Pennsylvanian, Bohemian Massif), their timing, and possible trigger mechanism

The succession of Stephanian C lacustrine and fluvial facies of the Ploužnice member (Semily Formation) paleolake in the Krkonose Piedmont Basin (northern Czech Republic) preserved in borehole Sm-1 shows five types of soft-sediment deformation structures (SSDS): (1) sediment injections (clastic dikes), (2) load structures and ball-and-pillow structures, (3) water-escape structures (discontinuous laminations, deformed wavy bedding, recumbent folding, and dish or pillar structures), (4) deformations by growth of carbonate and silica minerals during diagenesis, and (5) bioturbation. Bioturbations disturbing mechanical SSDS suggest that soft-sediment deformations may occur syndepositionally or soon after deposition. The discussed mechanical SSDS are developed in a lacustrine environment, most being in lower shoreface and offshore facies. The mechanical SSDS found in the Ploužnice lake deposits occur in all lacustrine facies associations (290 SSDS horizons in a 67-m-thick succession). The cumulative thickness in cm of mechanical SSDS horizons per meter of thickness (ratio cm SSDS/m) is the highest in lower shoreface facies where it reaches from 50 up to 59.7 cm SSDS/m. Offshore facies association reaches 44 cm SSDS/m. Upper shoreface facies associations have 25.9 and 26.0 cm SSDS/m, while nearshore/mudflat facies associations preserve from 22.5 to 20.5 cm SSDS/m, and in palustrine carbonate, 13.5 cm mechanical SSDS/m was found. SSDS in fluvial facies are rare (2.9 cm SSDS/m). The distribution of SSDS in the Sm-1 borehole shows clear relationships to sedimentary facies and processes such as density flows or fluctuation of water level. The relationships of particular structures indicate a relative timing of formation which is as follows: sediment deposition was followed by the formation of mechanical SSDS, then by bioturbation, and finally by deformations due to early diagenetic growth of carbonates and silica. The distribution of SSDS in vertical sections and their direct relationship to sedimentary facies point to endogenic rather than external trigger mechanisms such as seismic activity. The main endogenic trigger mechanisms responsible for the origin of SSDS included a Stephanian semi-humid seasonal climate, basin morphology with relatively steep gradients, and elevated source areas, which created a conducive environment for rapid and repeated deposition of sheetfloods and hyperconcentrated flows and turbidites causing syndepositional loading.

Seismites as a tool in the palaeoenvironmental reconstruction of fluvial deposits: The Cambrian Guarda Velha Formation, southern Brazil

Soft-sediment deformation (SSD) is widely described in the literature, but there is no clear consensus regarding its origin and significance. Existing models for SSD in fluvial sediments do not clearly demonstrate a relationship between the structures, preserved facies expression, and larger-scale depositional architecture. In this study several types of SSD structures are recorded in Cambrian fluvial deposits and these occur interbedded with undeformed strata throughout the entire stratigraphic interval. The random distribution of these features in relation to primary facies types and fluvial forms indicates that they have neither a direct nor indirect relationship with any depositional processes or bedform type. We propose that the relationship of SSD at the bed-set-scale to larger-scale depositional architecture, combined with tectono-stratigraphic analysis allows the determination of both short-term fluvial hydraulic conditions in ancient stream systems, such as the nature of the flow regime responsible for depositing ancient fluvial stream successions, and the long-term subsidence rates, in the form of mean recurrence interval of the seismic events responsible for triggering the generation of SSD in tectonically active basins.

Origin and internal organization of widespread composite soft-sediment deformation units in a deep-water forearc basin: The lower Pleistocene Kazusa Group on the Boso Peninsula, Japan

Three main types of soft-sediment deformation structures were identified in a base-of-slope and basin-plain succession (the upper Kiwada Formation) and its age-equivalent submarine slope succession (the lower Takamizo Formation) in the early Pleistocene Kazusa forearc basin on the Boso Peninsula, Japan. The three main types are (1) folded muddy deposits, (2) chaotic muddy deposits, and (3) injected sandy deposits. Chaotic muddy deposits are dominant and are intruded by sandy deposits that locally contain abundant mudstone clasts, which are poorly sorted, and are lithologically similar to debris-flow deposits. Chaotic muddy deposits in the upper Kiwada Formation are interpreted to have formed in response to downslope movements of unconsolidated surface and shallow subsurface muddy deposits, and are locally associated with folded muddy deposits in their basal part. In contrast, chaotic muddy deposits in the lower Takamizo Formation locally show a diapir-like geometry indicative of vertical intrusion, and are laterally associated with muddy deposits that are folded as a result of dragging of the host muddy sediments. In sequence-stratigraphic terms, the development of the soft-sediment deformation structures is interpreted to have occurred during a lowstand to early rise in glacioeuatatic sea-level cycles during the early Pleistocene. Although we cannot confirm which factor was the most effective triggering mechanism for the generation of the soft-sediment deformation structures in the studied successions, the interplay between (1) the seepage of methane and fossil brine, and (2) seismic shaking during the lowstand and early rise in relative sea level is interpreted to have been important in the Kazusa forearc basin during the early Pleistocene.

3-D geometry and luminescence chronology of Quaternary soft-sediment deformation structures in gravels, northeastern Brazil

This paper reports and describes soft-sediment deformation in gravels and gravelly sediments in Quaternary alluvial deposits of the Potiguar Basin, northeastern Brazil. Deformation structures were measured in terms of geometry, size, and relationship with sedimentary bedding using geological mapping and ground penetrating radar. TL and OSL/IRSL methods following MAR and SAR protocols were used to date sediments and soft-sediment deformation events. Our results indicate that soft-sediment deformation structures are widely distributed in several stratigraphic intervals of alluvial-channel deposits in a low-lying topographic valley. Depending on their geometry and composition, two types of soft-sediment deformation structures occur: pockets and dome-like load structures. These structures resulted from the shaking of sediments with a reverse density gradient system, which caused collapse and realignment of pebbles. These features are similar in morphology and size to modern examples of seismically-induced soft-sediment deformation in coarse sediments. TL and OSL ages indicate that sediment deposition and associated soft-sediment deformation occurred at least six times from ~ 352 ka to ~ 9 ka.

Soft-sediment deformation produced by tides in a meizoseismic area, Turnagain Arm, Alaska

Turnagain Arm is a semidiurnal hypertidal estuary in southeastern Alaska with a recorded tidal range of 9 m. Contorted bedding and flow rolls preserved in tidal sediments within the estuary have previously been interpreted as resulting from the Mw 9.2 Great Alaskan earthquake of 1964. Horizons of flow rolls between undeformed beds in sediments and rock strata have been used to infer ancient earthquakes in other areas. Although many types of soft-sediment deformation structures can be formed by earthquakes, observations of sedimentation on tidal flats in the inner parts of Turnagain Arm in the summers of 2003 and 2004 show that a wide range of soft-sediment deformation structures, similar to those inferred to have been formed by earthquakes, can form in macrotidal estuaries in the absence of seismic shock. During sedimentation rate measurements in 2004, soft-sediment deformation structures were recorded that formed during one day's tide, either in response to overpressurization of tidal flats during rapid tidal drawdown or by shear stress exerted on the bed by the passage of a 1.8 m tidal bore. Structures consisted of flow rolls, dish structures, flames, and small dewatering pipes in a bed 17 cm thick. In the future, if the flow rolls in Turnagain Arm were found in isolated outcrops across an area 11 km in length, in an estuary known to have been influenced by large-magnitude earthquakes, would they be interpreted as seismites? These examples show that caution is needed when using horizons of flow rolls to infer paleoseismicity in estuarine deposits because many of the mechanisms (tidal flux, tidal bores, slumping, flooding) that can cause deformation in rapidly deposited, unconsolidated silts and sands, are orders of magnitude more common than great earthquakes.

Early Permian silt-bed fluvial sedimentation in the Orogrande basin of the Ancestral Rocky Mountains, New Mexico, USA

The Lower Permian (Wolfcampian) Abo Formation of south-central New Mexico was deposited by a silt-dominated fluvial system along the western half of the Orogrande basin a few degrees north of the equator in western Pangaea. Fluvial channel deposits consist primarily of: (1) inclined siltstone stratasets up to 4.5 m thick and 25 m wide interpreted as point bar deposits, and (2) symmetrically infilled siltstone stratasets up to 2.4 m thick and 14 m long that may represent avulsion crevasse channels. Both types of channels are dominated by climbing ripple cross-laminae and plane bed laminae, but trough cross-beds are also present, as are several types of soft-sediment deformation structures and desiccation cracks. Red silty mudstones interpreted as floodplain deposits comprise up to 70% of the formation and are interbedded with thin (<2 m) tabular siltstone beds of crevasse-splay/levee origin, as well as rare lacustrine carbonates (∼0.5 m thick) and structureless siltstones (<1 m thick) interpreted as loessites. Common pedogenic features in floodplain strata and on the tops of some fluvial channel beds include root traces, peds, and calcic nodules/tubules, whereas gypsum, gley colour mottling, and translocated clay and/or iron oxides are rare. Also present is an ichnofauna dominated by opportunistic arthropods that colonized the moist upper surfaces of recently deposited crevasse-splay/levee beds and the uppermost surfaces of fluvial channels following avulsion. The relative abundance of channel and crevasse-splay/levee deposits increases eastward in response to moderate asymmetrical subsidence of the basin, whereas calcic paleosols are more numerous on the more slowly subsiding western margin of the basin. A semi-arid to sub-humid palaeoclimate with seasonal precipitation favoured relatively deep rivers whose point bars were seasonally exposed, the formation of calcic and vertic soils, a sparse ichnofauna and flora, periodic desiccation of small carbonate lakes, and perhaps reworking of loess from the floodplain and/or upstream catchments.

Roll-up Structures: Evidence of In situ Microbial Mats in Late Archean Deep Shelf Environments

In addition to its well-known banded iron formations, the late Archean to Paleoproterozoic Hamersley Group of Western Australia contains substantial volumes of thinly laminated carbonaceous shale and carbonate lutite. Locally, some of the laminae in these carbonates are deformed into highly distinctive folds in pockets whose cross-sections range up to about 2 cm in height and 10 cm in length. Individual folds consistently have circular hinge zones and vary in shape from simple buckles to recumbent, elastica, and even spiral geometries. Based on the strength and flexibility with which they responded to soft-sediment deformation, we infer the deformed carbonaceous laminae were bound by cohesive microbial mats. We propose the name roll-up structures for these features as they differ in subtle but important ways from most previously described soft-sediment deformation structures. Roll-up structures only occur in lutites deposited below wave base and are absent from peritidal deposits, suggesting that the microbial mats involved may not have been based on photosynthesis. Large portions of the deep sea floor could presumably have been stabilized by mats built by heterotrophic or chemoautotrophic microbes prior to the Neoproterozoic, given the lack of both predators and competing algae. Roll-up structures are potentially useful as indicators of deposition below wave base, but very few candidates have been reported anywhere else save for the coeval carbonates of the Transvaal basin of South Africa. The paucity of other examples, particularly in younger strata, means that either roll-up structures have simply not been distinguished from other types of soft-sediment deformation structures, or the microbes and/or environmental conditions required to make them are a rarity in Earth history.