Convolute Lamination Research Articles

Synsedimentary Deformation in Fossil Accretionary Prism, Greece: ABSTRACT

End_Page 740------------------------------Structural and stratigraphic evidence demonstrates that Paleogene turbidites of the Politses Formation were progressively deformed during sedimentation. The Politses Formation is preserved in internally undeformed thrust sheets that are tectonically intercalated with sheets of severely deformed blocks of the formation. This imbricate stack is interpreted as a fossil accretionary prism. The Politses Formation typically consists of hemipelagic red shales and limestones (basin-plain facies association) followed by thin-bedded terrigenous turbidites (fan fringe, interlobe and distal depositional lobe facies associations) which are overlain then by predominantly thick-bedded turbidites (depositional lobe facies association). This normal progradational sequence is interrupted by incised channel complexes which lie above basin-plain sediments and beneath fan-fringe deposits in some thrust sheets. Atypical facies organization suggests tectonic activity during sedimentation. Small-scale soft sediment deformation in the form of convolute lamination exists in about 20% of turbidite sandstone beds. Assuming that the deformation resulted from seismic activity, sedimentation ra es and the distribution of structures indicate that seismic shocks affected the depositional area every 10 to 100 years on the average. The most important evidence for synsedimentary deformation lies in the distribution of marl marker beds among thrust sheets. The stratigraphic distribution of marls corresponds uniquely to individual thrust sheets. This and other sedimentological relations demonstrate that marl and turbidite accumulation was controlled by progressive tectonic removal of thrust sheets from active deposition. The absence of unconformities within thrust sheets suggests that the deep sea fans represented in the Politses Formation were deposited in a trench. End_of_Article - Last_Page 741------------

Convolute lamination in modern sands of the estuary of the Oosterschelde, the Netherlands, formed as the result of entrapped air*

ABSTRACTSoft‐sediment deformation structures similar to convolute lamination were found at the sandy rim of an intertidal shoal in the Oosterschelde estuary, the Netherlands. Abundant air filled cavities within upward penetrated domes suggest that reversed density stratification resulting from trapped air in some sand layers plays a role in the deformational process.Field observations show that air‐filled cavities are formed within fine‐grained sand; at rising tide the ground water level does not rise quickly enough to replace the interstitial air before flood water covers the sediment surface. Thus, air is trapped in the sand between the ground water level and the sediment‐water interface. Because of the weight of the overlying water column and the slow downward movement of water due to capillary action, the entrapped air is compressed and eventually may attain a pressure which enables it to lift the overlying sediment. At this time bubbles are formed, often to a depth of 20 cm. Observation and experiments show that, in layers of fine sand, bubbles develop preferentially in better sorted and coarser zones. This is probably because capillary forces are greater in finer‐grained and less sorted sand. Thus, water will penetrate by preference into the latter, pressing the interstitial air into the better sorted and coarser sand. The high content of air cavities in certain layers then provides the density instability responsible for the deformational process leading to the formation of convolute lamination. In the intertidal zone this appears to be a slow process that covers a number of ebb and flood cycles.Convolute lamination has been described from a number of ancient sandstones that are thought to have been deposited in shallow water, near‐shore environments. In many of these cases sand size compares with that found in the Oosterschelde. Air entrapment might have played a role in the formation of certain of these occurrences of convolute lamination.

Deformation of soft sediments

In recent years there has been increasing awareness of the variety of structures formed by the deformation of unlithified sediment and of the difficulty in distinguishing these from structures produced in rock. Confusion of the two types clearly has serious implications, for example, in orogenic strain sequences where it is necessary to separate pretectonic slump structures from the results of later tectonism. Unfortunately, the features of soft sediment tend to fall within the realm of sedimentology whilst those of deformed rocks are the concern of structural geology so that the region where depositional, compactional, diagenetic and tectonic processes merge tends to be viewed from di­vergent positions and perhaps receives relatively little attention. The meeting held at Aberystwyth provided a forum for workers of differing background to assess recent progress in clarifying this difficult area. About a hundred participants heard a day of talks which made it clear that a wide diversity of phenomena on a variety of scales falls within the conference topic. The first part of the meeting was concerned with the structures and processes which are largely confined to soft sediments, beginning with large scale features such as olistostromes and moving on to the smaller structures such as convolute laminations. The later part continued through the compaction-lithification sequence, and the effects of tectonic strains became increasingly emphasised. Discussion following the talks returned repeatedly to two points. Firstly, there was the problem of defining terms and especially how to define the onset of lithification. The second recurrent topic was the apparent paucity of reliable criteria for distinguishing between penecontemporaneous and post-lithification structures.

The possible mechanics of convolute lamination in graded sand beds

Gravitationally unstable vertical gradients of bulk density can arise during the re-sedimentation of water-logged normally graded sand beds following liquidization, even though the density gradient imposed on the beds by the depositional process was originally stable. Convolute lamination, found chiefly in turbidites, is therefore capable of being formed under a wider range of circumstances than was formerly appreciated, and the presence of an unstable bulk density gradient dating from the time of deposition is not necessary for the manifestation in sediments of this type of Rayleigh–Taylor instability. Although the analysis promoting these conclusions cannot at present be tested experimentally because of practical difficulties, a laboratory study of the analogous sudden heating of a layer of viscous liquid from below affords some evidence in its support.

Sedimentation and water escape structures in some late Precambrian shallow marine sandstones from Finnmark, North Norway

ABSTRACTWater escape structures are abundant in the Grønnes Formation, a tectonically undeformed, late Precambrian shallow marine sandstone deposit in North Norway.Trough cross‐bedded sandstones of the current‐dominated shallow marine environment were frequently liquefied, presumably due to recurring seismic shocks. Subsequent dewatering resulted in deformation of the cross‐bedding and the formation of convolute lamination. A three‐fold upward vertical sequence developed where liquefaction occurred below the sediment‐water interface: convoluted bed → passively deformed bed → undeformed bed. The passively deformed bed resulted from differential subsidence of a relatively plastic bed above a liquefied bed. It is characterized by anticlinal ridges and sand volcanoes at the sites of vertical sediment extrusion, and synclinal troughs at the sites of lateral sediment movement.Liquefaction may have been induced by either tectonic (earthquake shocks) or non‐tectonic (storm‐induced microseisms) trigger mechanisms, or a combination of both. The restriction of such a high frequency of water escape structures to deposits immediately above a gentle regional unconformity lends support for a tectonic trigger mechanism.

Dish Structures Formed by Fluid Escape in Jurassic Shallow Marine Sandstones

ABSTRACT Dish structures, like convolute lamination over a decade ago, have been linked by geologists almost exclusively with flysch deposits, but, like convolute lamination, they are now being found in other settings. To previous reports of occurrences of dish structures in deltaic and alluvial deposits can be added their presence in the shallow marine Late Jurassic Canyon Springs Sandstone in the southern Black Hills, South Dakota. Proposed origin for dish structures from antidunes or grain flow in the upper flow regime are not compatible with associated structures in this occurrence. Instead, a recently proposed dewatering mechanism seems most consistent with available evidence. Fluid escape is especially clearly evidenced on a macroscopic scale in glacial lacustrine deposits near Appleton, Wisconsin. Pillar structures penetrating cross-laminated sands there suggest by analogy a larger-scale continuum with the more subtle disruptions that produced dishes.

Sedimentary and Tectonic History of Cretaceous Flysch in Southwestern Alaska: ABSTRACT

Cretaceous deep-water sedimentary rocks are discontinuously exposed or have been dredged, along 1,700 km of the outer continental margin of the Alaska Peninsula-Bering Sea shelf. In the Shumagin and Sanak Islands, on the continental shelf near the southwestern end of the Alaska Peninsula, the deep-sea sediments are comprised of monotonous sections of thin (4 cm) to thick (10 m) bedded sandstone and mudstone, showing grading, convolute lamination, groove and flute casts. The sandstone beds are lithic arenite with more than 40% volcanic-derived framework grains. Over 500 measurements of sole marking in the Shumagin and Sanak Islands show maxima End_Page 795------------------------------ toward the southwest and west-northwest respectively, with minor lateral feed from the north. This flysch sequence was deposited primarily by turbidity currents in an elongate trough supplied from a northerly volcanic source area. In the absence of a confining basement seaward of the flysch deposits, the original depositional basin is interpreted as an oceanic trench. These trench deposits were deformed initially in a semilithified state with the development of axial-plane salty cleavage. Fold axes parallel the existing continental shelf edge, trending northeast and west-northwest in the outer Shumagin and Sanak Islands, respectively. Folds are overturned seaward predominantly, axial surfaces dipping landward. Locally units may be described as broken formations, though no melanges are observed. The style of this early folding is consistent with, but not diagnostic of, gravity liding. Alternatively, the rocks may have been deformed by underthrusting at the trench inner wall. At rates of 10-13 to 10-14/sec (calculated assuming underthrusting), the trench sediments may have undergone strain hardening from increasing internal grain friction and cementation during dewatering. End_of_Article - Last_Page 796------------

Sedimentary structures formed by flash floods in southern Israel

During the rainy season the ephemeral streamcourses of southern Israel are swept by flash floods of low volume and short duration, which produce meander bars, megaripples and ripples, harrow marks, current lineations, obstacle marks, washouts and remnant bars, rhomboid marks, rill marks, rare convolute lamination, imbrication, mud pebbles and polygonal desiccation patterns. The rapid abatement of floods results in a variety of coexisting, interfering and superimposed associations of bed forms, which shed light on some aspects of provenance and origin of alluvial bed forms.

Transport and Deposition of Coarse Clastics in Turbidite Basin in French Alps: ABSTRACT

Marine breccias of Jurassic to Early Cretaceous ages are present in the Breccia Nappe of the French Prealps. Breccia types Ia and Ib are restricted to the lower part of the sequence in the Lower Shale, Lower Breccia, and Upper Shale formations. Type Ia breccias occur in beds from a few centimeters to tens of meters thick. They contain clasts up to more than 1 m in diameter, and are sometimes graded. Sole markings occur but are not common. Tops of some beds have large scale cross-stratification or parallel bedding, usually in granule-pebble grade material. Individual beds are of limited lateral extent--of the order of 1-2 km along the depositional strike and in places up to 7-8 km across it. The breccias have a clast framework and interstitial material is usually pebble or granule size. There is a continuous spectrum, with change in relative proportions of gravel and sand, from the breccias to pebbly turbidite sandstones. Type Ib is much less common than Ia. It has clasts of the same composition and size but it is characterized End_Page 342------------------------------ by more than 50% sand-grade matrix. Beds are less than 200 cm thick, parallel-sided, and have an uppermost sand-silt layer with convolute lamination. Type Ia is interpreted as a deposit from mass flow of coarse granular debris where internal shear was extensive enough to allow development of grading. For the transport of Type Ib beds, a slide mechanism is favored. End_of_Article - Last_Page 343------------

On the convolute lamination occurring in the flysch-type sandstones

On the convolute lamination occurring in the flysch-type sandstones

Cleavage and Penecontemporaneous Deformation Structures in Sedimentary Rocks

An occurrence of convolute laminations is described from Devonian sediments exposed along the south coast of New South Wales, Australia. In many of the folds there is an axial plane cleavage which developed prior to consolidation of the sediment and closely resembles the cleavage commonly found in tectonites of low metamorphic grade. The style of individual folds, even to their fabric, is indistinguishable from that of many tectonic folds. From a discussion of the criteria used for distinguishing between penecontemporaneous and tectonic deformation structures, it is concluded that the folds are convolute laminations formed by load deformation of a semifluid sediment. The axial plane cleavage has probably developed by rotation of preexisting inequant grains, rather than by recrystallization of layer silicate minerals in a stress field.

So-called turbidite structures

The term 9turbidite structures9 recently used by Sen (1967) is better avoided, because only a combination of features together with the absence of others can be diagnostic. The distinctions in meaning between the terms 9turbidites9 and 9fluviatile deposits9 should not be confused. The explanation of convolute lamination by exaggeration of ripple mark is supported by experimental results.

Distribution of Minor Structures in Gulf of Mexico Sediments: ABSTRACT

Minor sedimentary structures are studied by means of X-ray radiography from cores collected from various physiographic provinces of the Gulf of Mexico. The Gulf can be divided into two large petrographic provinces meeting at DeSoto Canyon and Campeche Canyon. The western part is a terrigenous clastic province and the eastern is a carbonate province. For a study of the sedimentary structures it is necessary to divide both petrographic areas into their proper physiographic provinces. The sedimentary structures and characteristics distinguished are: thin bedding (regular, irregular, lenticular), lamination (parallel, lenticular, irregular), coarse-grained laminae, turbidites (single, multiple, vague), convolute lamination, load casts, degassing structures, mottled, slump, homogeneous, burrowing, mycelium, shells, and shell fragments. Several of these characteristics can be found in almost any area but some of them are of restricted occurrence. Cores collected from one province reveal only slight variations in their content of sedimentary structures. End_of_Article - Last_Page 1830------------

Dish Structure, a Primary Sedimentary Structure in Coarse Turbidites: ABSTRACT

Some clean but poorly sorted sandstone beds in California contain vertical progressions of thin lens-shaped structures, here termed dish structures. Individuals are 4-50 centimeters long, 1 to a few centimeters thick, oval in plan, and are oriented parallel with bedding. Each dish has a fine-grained, slightly clayey lower surface that is concave-up, and from which clay content decreases and sand size increases upward to a coarse, clay-free top. The size of the structures decreases and the concavity of their bottoms increases higher in the bed. The margins of each dish are truncated by adjacent and overlying dishes, except where they occur along individual horizons with their joined margins forming upward-pointing peaks. Steeply oriented elutriation columns lacking clay an finer sand commonly accompany dish structure. They disrupt or turn up dish surfaces through which they pass, and terminate beneath overlying dishes. Typical sandstone beds containing dish structure are about 1 meter thick and progress upward from a base of coarse, structureless sand (interval a of Bouma, 1962) through flat lamination, dish structure, and overlying flat lamination (b), to a top of very fine-grained sand containing convolute lamination (c). Dish structure also occurs as a central interval within an otherwise nearly structureless, very thick bed. Antidunes may produce simple dish structure by alternate scour, and by breaking and deposition in the troughs during aggrading suspension flow in a turbidity current that has declined from dispersion flow (after Bagnold). Middleton (1965) reports structures similar to some dish structures in size and shape resulting from antidune flow. Some characteristics, possibly including clay distribution, may result from sporadic water expulsion, related sediment flowage, and general de-watering of the bed. Dish structure between structureless intervals would require dispersion flow to progress to antidune flow, then revert to dispersion flow. End_of_Article - Last_Page 485------------

Modification of the Model for Internal Structures in Graded Beds to include a Dune Division

AN important recent advance in our understanding of sedimentation in flysch basins is the discovery that the internal structures of most graded sandstones and limestones follow a fixed sequence. Proceeding upwards in a graded bed, the model-sequence described by Bouma1 consists of five structures: (A) graded division; (B) lower division of horizontal lamination; (C) division of current ripple lamination, often deformed into convolute lamination; (D) upper division of horizontal lamination; (E) pelite division (Fig. 1). This sequence, or partial sequences with base, middle, and/or top truncation of one or more of the divisions, characterizes graded sandstones and limestones in many flysch basins in North America and Europe.

CONVOLUTE LAMINATION AND OTHER STRUCTURES FROM THE LOWER COAL MEASURES OF YORKSHIRE

SUMMARYSeveral deformational sedimentary structures are recorded from the non‐marine sandstones of the Lower Coal Measures of Yorkshire. Some of these structures may be termed convolute lamination and for others the term corrugated lamination is proposed. The scope and synonyms of convolute lamination are discussed and both terms are defined and illustrated. The essential difference between convolute lamination and corrugated lamination is the absence of an overall anticline‐syncline morphology in the latter. Rupture of lamination through most of the thickness of the deformed horizons give rise to rupture structures.A petrological investigation of the sediments showed slight variations in both grain size and mineralogy within individually deformed horizons. The structures are considered to be the result of load casting, caused by heterogeneity of the sediment, and/or thixotropic behaviour.

Convolute Lamination, its Origin, Preservation, and Directional Significance

ABSTRACT Convolute lamination or convolute bedding occurs in marine and non-marine sediments deposited in many environments. Current convolute laminations found in turbidite deposits are accounted for by the forces known to exist in turbidity currents. The convolutions are a fossil record of the forces which acted upon a laminated bed during its sedimentation. The directional significance of the structure is also discussed. Other convolutions seem to be caused by loading. A variety of such convolute bedding structures is described and origins are suggested.

Convolute Lamination in Non-Graded Sequences

Convolute lamination and other sedimentary structures have been observed repeatedly in sequences characterized also by graded bedding. As a result, practically all have come to be regarded individually as proofs of turbidity-current deposition. But gravity-deformed stratification and load structures as well as flutes, grooves, current bedding, and ripple mark are already recorded in non-graded sequences representing quite varied environments. This paper records examples of convolute lamination also in diverse, non-graded deposits, leaving only repetitious graded bedding and anomalous resedimented organisms or detritus as chief evidences of ancient turbidity currents. Existing terminology and classification of the physical sedimentary structures in question mix genetic and descriptive factors, thus conceal more fundamental relations of the two chief formative processes involved-gravity-induced versus current-induced flow. Most structures involve both processes to varying degrees; however, classifications have imposed an unrealistic dichotomy between these processes. Morphologically similar contorted statification can be produced by two and probably three or more different processes. In many cases two of these have acted together simultaneously.

Sedimentation of the alternating greywacke and argillite strata in the Porirua district

Summary The Lower Mesozoic alternating greywackes and argillites in the Porirua district exhibit graded bedding, lamination, convolute lamination, cross lamination, mud flakes, and current markings. The sediments, rapidly derived from a plutonic terrain, were rapidly transported and deposited by turbidity currents in the New Zealand Geosyncline. The orientation of cross lamination and Current markings suggests that the turbidity currents flowed north-north-east, sub-parallel to the present regional tectonic trend. At Porirua, sedimentation was in deep water, a considerable distance from the supplying land mass, and not far from the axis of the geosyncline.

TURBIDITES IN FLYSCH OF THE POLISH CARPATHIAN MOUNTAINS

The Polish Carpathian Mountains are occupied for the greater part by rocks of the flysch type; in which graded bedding with the usual accompanying sole markings and other features of turbidites are ubiquitous. For several years Polish geologists have successfully applied the concept of turbidity flow to explain features formerly thought to be conflicting. This paper deals with paleogeographic problems and summarizes results so far attained by numerous measurements of current direction. A few separated troughs persisted throughout the Cretaceous and Paleogene sedimentary history. Each of these oblong basins had its separate history in which location and direction of supply varied greatly with time. Most units show a consistent system of transport. Dominantly lateral supply is obvious in some cases. In others the measurements indicate a distant supply and from thence longitudinal transport in the flysch trough with or without local coarse supply from the sides. However, evidence, mainly paleogeographic, strongly suggests that local cordilleras between or flanking these troughs acted as the main source. Continued field work may throw light on this controversial topic which occurs in many other geosynclines that contain turbidite formations. A number of sedimentological problems are examined on the basis of evidence mainly from Poland: upper margins of graded beds, suspended currents, convolute lamination, doubtful turbidites, glauconite in turbidites. A few new sole markings are named and described.