Inverse Grading Research Articles

Features and formation processes of multiple deposition layers from the 2004 Indian Ocean Tsunami at Ban Nam Kem, southern Thailand

AbstractMultiple‐layered tsunami deposits have been frequently reported from coastal stratigraphic sequences, but the formation processes of these layers remain uncertain. A terrestrial sandy deposit formed by the 2004 Indian Ocean Tsunami was investigated at Ban Nam Kem, southern Thailand. Four internal layers induced by two tsunami waves were identified in the tsunami deposit. Sedimentary structures indicated that two units were formed by run‐up currents caused by the tsunami and the other two units were deposited by the backwash flows. Graded bedding was common in the layers, but inverse grading was observed at limited intervals on the surveyed transects. The characteristics of the multiple‐layered tsunami deposit vary remarkably over a very short distance (<1 m) in response to the local topography. Remarkable asymmetries in thickness and grain‐size distribution are recognized between the run‐up and backwash flow deposits. On the basis of the interpretation of sedimentary structures, the formation process of the multiple‐layered tsunami deposit observed in this study can be explained in a schematic model as the modification of the ideal tsunami sequence by local erosion and the asymmetric hydraulic properties of tsunami waves, such as the maximum shear velocity and the heterogeneity of the flow velocity field.

Evaluation of Physical and Quality Properties of Invert Syrup from Sucrose Solution

قند انورت، مخلوطی از گلوکز و فروکتوز می باشد و از هیدرولیز اسیدی و یا آنزیمی ساکارز بدست می آید. قند انورته به علت خصوصیات خاص خود نظیر میزان شیرینی، خاصیت رطوبت پذیری، میزان کریستاله پذیری، مزه و طمع ویژه آن در صنایع مختلف غذایی، نوشابه ها و دارو سازی استفاده می گردد. میزان انورسیون ساکارز طی هیدرولیز آن تحت اثر پارامترهای زمان، دما و pH می باشد که مقدار فروکتوز – گلوکز تولید شده و ساکارز باقیمانده، نمایانگر خصوصیات فیزیکی محلول قندی و کیفیت شربت انورته تولید شده می باشد. تحقیق انجام شده با دوهدف استفاده از تغییرات خصوصیات فیزیکی محلول صنعتی ساکارز، طی انورتاسیون نظیر پارامترهای فیزیکی فعالیت نوری محلول و ویسکوزیته جهت اندازاه گیری سریع میزان درجه انورسیون در حین فرآیند صنعتی و همچنین کنترل کیفی قند انورت تولید شده با توجه به زمان و دمای انورتاسیون جهت تولید این محصول جانبی بصورت صنعتی در ایران صورت گرفته است. نتایج حاصل از این تحقیق مشخص می کند که با توجه به زمان انورسیون در دمای ثابت، مقدار درجه خلوص ساکارز باقیمانده کاهش پیدا نموده که این پارامتر به کمک روش پلاریمتری برای مشخص نمودن میزان انورسیون قابل اندازه گیری می باشد. در اثرانورسیون، میزان ویسکوزیته محلول نسبت به محلول صنعتی ساکارز پس از یک کاهش شدید اولیه، دارای تغییرات کمتری می باشد. همچنین کیفیت قند مایع و شربت انورته تولید شده از نظر رنگ، میزان قندانورت تشکیل شده، میکروبی و میزان هیدروکسی متیل فورفورال با توجه به زمان (1 ،2، و 3 ساعت) ودمای انورسیون (60، 70 و 80 درجه سانتیگراد)‌ انجام گردید که مشخص کننده تولید این محصول در دمای 60 و 70 درجه سانتیگراد با کیفیت مطلوب می باشد. واژه های کلیدی : انورسیون ساکارز، قند مایع انورته، شربت انورته، ویسکوزیته شربت انورته

“Inverse grading” A facies structure of flood deposits in meandering rivers

“Inverse grading” A facies structure of flood deposits in meandering rivers

The forgotten slaves of Tromelin (Indian Ocean): new geoarchaeological data

Here we present geoarchaeological results from Tromelin, a small 1-km 2 atoll in the Indian Ocean, looking to elucidate human–environment interactions following the wrecking of the l'Utile in 1761. Abandoned by their French crew, around 60 Madagascans were enforced to form a micro-society on this remote island for a 15-year period. Little, however, is known about the cultural and environmental adaptations the population made during their stay. This study focuses on sediment archives from Site 5, where GRAN/INRAP archaeological work in 2008 brought to light three rooms attributed to the survivor's living quarters. Particular emphasis is placed on the impacts of cyclonic storm surges, natural hazards that presented serious environmental risks to the long-term survival of the slaves. The small size of Tromelin renders it a particularly discrete unit of analysis for such a study. We have identified four chronostratigraphic units at the site. (1) Unit 4 constitutes coarse white sand incorporating rounded gravels and reworked head and branch corals. No anthropogenic material is attested. We attribute this unit to a storm layer preceding the 1761 occupation of Tromelin. (2) Unit 3 yielded a multiplicity of archaeological material and corresponds to the 18th century cultural layer. The unit varies in thickness from 10 to 40 cm. (3) Unit 2 constitutes a 20 to 40 cm sand sheet across much of Site 5 that we attribute to a powerful cyclone event. It forms an unconformable contact above unit 3 and can be divided into two distinct sub-units, 2a and 2b. Sub-unit 2a is characterised by an inverse grading of the sediments, constituting coarse sands at the base grading into rounded biogenic gravels in the upper part. This sedimentology is typical of increasing flow velocity and is diagnostic of a storm setup flow. The transition to sub-unit 2b marks the onset of the waning flow, characterised by a sharp fall in relative flow velocities. These overwash deposits buried much of the archaeological remains and have been critical to the preservation of the vestiges through to present-day. (4) Unit 1 corresponds to a layer of infill incorporating blocks of coral and cultural objects dating from the 19th to 20th centuries.

Sedimentology and hydrodynamic implications of a coarse-grained hurricane sequence in a carbonate reef setting

Storms and associated surges are major coast-shaping processes. Nevertheless, no typical sequences for storm surge deposits in different coastal settings have been established. This study interprets a coarse-grained hurricane ridge deposit on the island of Bonaire, Netherlands Antilles. The sequence was deposited during Hurricane Lenny in November 1999. Insight is gained into the hydrodynamics of surge fl ow by interpreting textural trends, particle imbrication, and deposit geometry. Vertical textural variations, caused by time-dependent hydrodynamic changes, were used to subdivide the deposit into depositional units that correspond to different stages of the surge, such as setup, peak, and return fl ow. Particle size and imbrication trends and geometry of the units refl ect landward bed-load transport of components during the setup, a nondirectional fl ow with sediment falling out of suspension during the peak, and a seaward bedload transport during the return fl ow. Formation of a ridge during setup affected the texture of the return fl ow unit. Changing angles of imbrication refl ect alternating fl ow velocities during each phase. Normal grading during setup and inverse grading during return fl ow are caused by decelerating and accelerating fl ow, respectively. Hence, the interpreted deposit seems to represent the fi rst described complete hurricane surge sequence from a carbonate environment.

Sedimentação coluvial pleistocênica na região de Presidente Figueiredo, nordeste do estado do Amazonas

This paper describe Upper Pleistocene colluvial deposits in the Presidente Figueiredo region, northestern State of Amazonas, Brazil. Outcrop-based sedimentologic and stratigraphic study, integrated with geomorphologic analysis and optically stimulated luminescence dating, allowed to characterize the architecture and lithofacies of these sedimentary successions and provided information about the denudation history and landscape changes in the central Amazonian region during the Pleistocene. The colluvial deposits consist of sands and mainly matrix-suppported gravels with massive beddding, locally with inverse grading, suggestive of deposition by gravitaty and torrential flows. Two types of colluvial deposits were identified: Colluvial deposits 1, dated at 57.000±5.000 years BP, constituted of gravels and sands with fragments of pelite, lateritic crusts and ferruginous sandstone, overlying Early Paleozoic rocks; and Colluvial deposits 2, yielding 22.100±2.600 years BP, consisting of gravels with fragments of semi-flint kaolin and lateritic crust, overlying Cretaceous kaolinic silciclastic deposits of the Alter do Chao Formation. The types of fragments indicate as sources Phanerozoic weathered rocks and lateritic bauxitic and ferruginous laterites which were removed during denudation of plateau. The two colluvial events described here seem to confirm that the main phases of geomorphogenesis are correlated with periods of forest retreat related to the two dry climatic events recorded during the Upper Pleistocene in Amazonia.

Sedimentação coluvial pleistocênica na região de Presidente Figueiredo, nordeste do estado do Amazonas

This paper describe Upper Pleistocene colluvial deposits in the Presidente Figueiredo region, northestern State of Amazonas, Brazil. Outcrop-based sedimentologic and stratigraphic study, integrated with geomorphologic analysis and optically stimulated luminescence dating, allowed to characterize the architecture and lithofacies of these sedimentary successions and provided information about the denudation history and landscape changes in the central Amazonian region during the Pleistocene. The colluvial deposits consist of sands and mainly matrix-suppported gravels with massive beddding, locally with inverse grading, suggestive of deposition by gravitaty and torrential flows. Two types of colluvial deposits were identified: Colluvial deposits 1, dated at 57.000±5.000 years BP, constituted of gravels and sands with fragments of pelite, lateritic crusts and ferruginous sandstone, overlying Early Paleozoic rocks; and Colluvial deposits 2, yielding 22.100±2.600 years BP, consisting of gravels with fragments of semi-flint kaolin and lateritic crust, overlying Cretaceous kaolinic silciclastic deposits of the Alter do Chão Formation. The types of fragments indicate as sources Phanerozoic weathered rocks and lateritic bauxitic and ferruginous laterites which were removed during denudation of plateau. The two colluvial events described here seem to confirm that the main phases of geomorphogenesis are correlated with periods of forest retreat related to the two dry climatic events recorded during the Upper Pleistocene in Amazonia.

Eruption and emplacement of a laterally extensive, crystal-rich, and pumice-free ignimbrite (the Cretaceous Kusandong Tuff, Korea)

The Cretaceous Kusandong Tuff, Korea, is a thin (1–5 m thick) but laterally extensive (~ 200 km) silicic ignimbrite emplaced in a fluviolacustrine basin adjacent to a continental volcanic arc. The tuff has been used as an excellent key bed because of its great lateral continuity and unique lithology, characterized by the virtual absence of juvenile clasts and an abundance of quartz and feldspar crystals (up to 55–73 vol.%). The tuff is mostly massive and ungraded and locally shows crude internal layering, basal inverse grading and near-top normal grading of crystals, either erosional or non-erosional lower surfaces, and flat-lying to imbricated grain fabrics. Fragile intraformational clasts of mudstone and tuff are also included. These features provide only ambiguous information on the properties of the responsible pyroclastic density currents: i.e. whether they were dense and laminar or dilute and turbulent. The overall lateral continuity and sheet-like geometry of the tuff suggests, however, that the transport system of the currents was highly expanded, dilute, and turbulent. A plug-flow or slab-flow model cannot explain the origin of crude internal layering, imbricated grain fabrics, and the high crystal content, which is most likely the result of vigorous sorting processes within a dilute and turbulent current. Features indicative of deposition from a dense and laminar transporting medium are locally present, suggesting that a dense and laminar depositional system could develop locally at the base of the dilute and turbulent transport system. The virtual absence of juvenile clasts in the tuff is interpreted to be due to rapid ascent, sudden decompression, and full fragmentation of silicic magma into fine glass shards and crystals. Scarcity of basement-derived accidental components together with the absence of pumiceous fallout deposits beneath the tuff is interpreted to be due to shallow-level fragmentation of magma followed by immediate generation of pyroclastic density currents from shallow-level blasts at the onset of eruption. The eruption occurred through multiple vent sites in a short period of time, producing a seemingly single but actually composite ignimbrite unit. Such an eruption was probably possible because of a regional tectonic event within the basin or in its vicinity. It is proposed that a composite ignimbrite with the characteristics of the Kusandong Tuff can be an exemplary product of syntectonic volcanism that can provide an insight into the interpretation of structural and stratigraphic evolution of a sedimentary basin.

Hyperpycnal Rivers and Prodeltaic Shelves in the Cretaceous Seaway of North America

Abstract Despite the historical assumption that the bulk of marine “shelf” mud is deposited by gradual fallout from suspension in quiet water, recent studies of modern muddy shelves and their associated rivers show that they are dominated by hyperpycnal fluid mud. This has not been widely applied to the interpretation of ancient sedimentary fluvio-deltaic systems, such as dominate the mud-rich Cretaceous Western Interior Seaway of North America. We analyze two such systems, the Turonian Ferron Sandstone Member of the Mancos Shale Formation, in Utah, and the Cenomanian Dunvegan Formation in Alberta. Paleodischarge estimates of trunk rivers show that they fall within the predicted limits of rivers that are capable of generating hyperpycnal plumes. The associated prodeltaic mudstones match modern hyperpycnite facies models, and suggest a correspondingly hyperpycnal character. Physical sedimentary structures include diffusely stratified beds that show both normal and inverse grading, indicating sustained flows that waxed and waned. They also display low intensities of bioturbation, which reflect the high physical and chemical stresses of hyperpycnal environments. Distinct “mantle and swirl” biogenic structures indicate soupground conditions, typical of the fluid muds that represent the earliest stages of deposition in a hyperpycnal plume. Hyperpycnal conditions are ameliorated by the fact that these rivers were relatively small, dirty systems that drained an active orogenic belt during humid temperate (Dunvegan Formation) to subtropical (Ferron Sandstone Member) “greenhouse” conditions. During sustained periods of flooding, such as during monsoons, the initial river flood may lower salinities within the inshore area, effectively “prepping” the area and allowing subsequent floods to become hyperpycnal much more easily. Although shelf slopes were too low to allow long-run-out hyperpycnal flows, the storm-dominated nature of the seaway likely allowed fluid mud to be transported for significant distances across and along the paleo-shelf. Rapidly deposited prodeltaic hyperpycnites are thus considered to form a significant component of the muddy shelf successions that comprise the thick shale formations of the Cretaceous Western Interior Seaway.

Paleo-mud-volcanoes of the Lower Miocene Tanabe Group on the Southern Kii Peninsula, Southwest Japan

The Lower Miocene Tanabe Group, exposed on the southern Kii Peninsula, is a thick pile of fore-arc basin sediments, which clino-unconformably covers the Paleogene Shimanto accretionary complex. Many mud diapirs and mud dykes intrude into the Tanabe Group. Several thick sequences of bedded breccia are found at Tanoi and Fukuro in Shirahama-cho, Wakayama Prefecture. In this paper, bedded breccias with shallow-marine sediments are described. The facies analysis shows that the bedded breccias are mud-volcanic deposits, and that two submarine mud volcanoes were involved in the southern Tanabe Group. The Tanoi sequences, which reach a thickness of 490 m, are mainly composed of sand-matrix, bedded breccia associated with mud-matrix, and bedded breccia. The bedded breccias range from 5 to 150 cm in thickness. They contain angular to sub-rounded clasts consisting of sandstone and mudstone from granule to cobble in size. The bedded breccia is matrix-supported with scattered clasts, which develop with inverse grading. It is considered to be a subaqueous debris flow deposit. The Fukuro sequences are mainly composed of mud-matrix, bedded breccias associated with clast-bearing sandstone of 1-15 cm thickness, which have turbidite-like sedimentary structures. The bedded breccias range from 5 to 150 cm in thickness. They contain angular to sub-rounded clasts consisting of mudstone and sandstone from granule to cobble in size. The bedded breccias are matrix-supported with scattered clasts, which develop with inverse grading. It is considered that the cause is a subaqueous debris flow deposit. The upper part of the clast-bearing sandstone is likely to have been reworked later by storm waves and tidal currents. The paleocurrent deduced from the sole marks of mud-matrix, bedded breccia flowed from northeast and east. The shallow-marine sediments develop wave ripple, planar cross-stratification, trough-type cross-stratification, chevron structure, off-shooting foreset, and hummocky cross-stratification, which indicate that the Fukuro mud-volcanic products were deposited at a depth near the lower limit of the storm wave base from the lower shoreface to the shelf. During the Early Miocene, submarine mud volcanism took place at Tanoi and Fukuro in the southern Tanabe Group. It is believed that the Tanoi mud volcano caused the Tanoi mud-volcanic deposits to erupt from the Tanoi mud diapir, and that the Fukuro mud volcano caused the Fukuro mud-volcanic deposits to erupt from the Migusagawa-Hirukawadani mud diapir.

宮崎県日南海岸沿いに分布する新第三系宮崎層群青島層の重力流堆積物とその層序パターンの特異性

The Neogene Aoshima Formation of the Miyazaki Group, well exposed along the Nichinan coast, has been considered to be a turbidite succession deposited at a forearc basin, although the thickness-frequency distributions and the sedimentary facies of the formation are in disagreement with those of typical turbidite successions. In this study, we investigated the depositional system and the sedimentary environments of the formation, on the basis of the facies of sediment-gravity flow deposits and stratigraphic variations of bed-thickness distributions. From the results, we can classify the sediment-gravity flow deposits of the formation into the following types; Type G: sedimentary structures containing grading beds, whose wavelength is in the range of 0.5-5m; Type I: inverse grading structures composed of a finer lower unit with climbing-ripple cross lamination or HCS-mimics, and a coarser upper unit with massive sandstones; and Type M: massive structureless sandstones. Individual sediment-gravity flow deposits can be correlated over 10 km using key-tuff markers along palaeocurrent directions. Stratigraphic fluctuations of the hemipelagic-mudstone thickness and sediment-gravity flow thickness show that the formation along the Aoshima Island consists of a lower progradational system indicated by a thinning-upward trend of hemipelagic mudstones and an upper system dominated by lobate sand bodies characterized by the cyclic sedimentation of thick-sediment-gravity flow deposits. These results indicate that the depositional setting of the formation is a deep-offshore basin of a fandelta along the south-east coast of the Kyushu Island.

Deposit Structure and Processes of Sand Deposition from Decelerating Sediment Suspensions

Turbidity currents are notoriously difficult to monitor directly, therefore interpretation of their deposits forms the basis for much of our understanding of these flows. The deceleration rate of a flow is a potentially important yet poorly understood control on depositional processes. A series of experiments were conducted in an annular flume, in which fast (up to 3.5 m/s) and highly turbulent flows of sand (up to 250 µm) and water were decelerated at different rates and processes of deposition and deposit character analyzed. Previously poorly documented depositional processes were observed in the experiments. This is because the flows were initially unusually fast and of prolonged duration, with sustained periods of sediment fallout as the flow slowed down. The conditions in these flows are thus likely to be closer to those at the base of a waning turbidity current than is achieved in other relatively slow experimental flows. The collapse of high-concentration, moving, thin (< 5 mm) near-bed layers (laminar sheared layers) were an important mechanism by which the bed aggraded beneath these unsteady flows. At bed aggradation rates in excess of 0.44 mm/s the sequential collapse of laminar sheared layers produced a structureless, poorly graded and poorly sorted deposit (Bouma Ta). When bed aggradation rates fell below 0.44 mm/s the collapsing laminar sheared layers were reworked by turbulence to form planar laminae (Bouma Tb). These laminae are formed in a very different manner than the planar laminae attributed to bedwaves in previous open-channel flow experiments. Collapse of laminar sheared layers is therefore an alternative process for generating the Bouma Tb division. Inverse grading developed at the base of the deposits of slowly decelerated flows. This inverse grading was probably a result of grain sorting in a high-concentration layer that persisted at the base of the flow for many minutes prior to the onset of deposition.

On the formation of couplet-style stratifications

Couplet-style stratifications refer to the sedimentary sequences that consist of alternating coarse-grain-dominated bed and fine-grain-dominated bed, with or without a sandwiched middle-sized bed. The formation mechanism is complicated due to the interplays of varying driving force (s), sediment supply & transport and topographic configurations. This paper presents a comprehensive overview of such characteristic bedforms, which emerge during the transport and deposition of non-uniform sediments. The leading formative models include water-stage variation, gravel-overpassing process, superimposition of bedload sheets and avalanching process (inverse grading). Each process might produce similar or distinct sedimentological features with respect to grading, matrix content, grain attitude, bounding faces between beds and internal longitudinal/transverse geometry. The couplet-style stratified strata might play an active role in landscape evolution.

Breaking size segregation waves and particle recirculation in granular avalanches

Particle-size segregation is a common feature of dense gravity-driven granular free-surface flows, where sliding and frictional grain–grain interactions dominate. Provided that the diameter ratio of the particles is not too large, the grains segregate by a process called kinetic sieving, which, on average, causes the large particles to rise to the surface and the small grains to sink to the base of the avalanche. When the flowing layer is brought to rest this stratification is often preserved in the deposit and is known by geologists as inverse grading. Idealized experiments with bi-disperse mixtures of differently sized grains have shown that inverse grading can be extremely sharp on rough beds at low inclination angles, and may be modelled as a concentration jump or shock. Several authors have developed hyperbolic conservation laws for segregation that naturally lead to a perfectly inversely graded state, with a pure phase of coarse particles separated from a pure phase of fines below, by a sharp concentration jump. A generic feature of these models is that monotonically decreasing sections of this concentration shock steepen and eventually break when the layer is sheared. In this paper, we investigate the structure of the subsequent breaking, which is important for large-particle recirculation at the bouldery margins of debris flows and for fingering instabilities of dry granular flows. We develop an exact quasi-steady travelling wave solution for the structure of the breaking/recirculation zone, which consists of two shocks and two expansion fans that are arranged in a ‘lens’-like structure. A high-resolution shock-capturing numerical scheme is used to investigate the temporal evolution of a linearly decreasing shock towards a steady-state lens, as well as the interaction of two recirculation zones that travel at different speeds and eventually coalesce to form a single zone. Movies are available with the online version of the paper.

Sedimentology and geochemistry of extensive very coarse deepwater submarine fan sediments in the Middle Jurassic of Oman, emplaced by giant tsunami triggered by submarine mass flows

Unusual fining upwards coarse conglomerates overlain by sandstones, thin cherts and green shales occur at the top of the deep-water submarine fan deposits of the Oolitic Limestone Member of the Jurassic Guwayza Formation of Oman. They separate the dominantly submarine fan deposits of the Guwayza Formation from the pelagic shales, fine-grained limestones and cherts of the overlying Sidr Formation. The cross-bedded and graded framework conglomerates occur in extensive, tabular units and are dominated by earlier Mesozoic carbonate clasts with sandy oolitic and peloidal grains derived from fault escarpments and shelf sediments far to the southwest. Subordinate inverse grading, very thick beds, very large floating clasts (up to 100 m long in places) indicate deposition from catastrophic debris flows. Though most palaeocurrents indicate flow from off the platform to the southwest, hummocky cross-bedding shows divergent palaeocurrents suggesting movement in part by deep-water waves. The beds are too coarse for antidune formation and the conglomerate to sand hummocks indicate decelerating flow. There are no nearby large objects to deflect turbidity currents to form divergent flows. We consider that the hummocky cross-stratification, like that in shallow water, was formed by interfering waves. That such coarse, tabular conglomerates affected by wave action occur over extensive areas across deep submarine fan environments, suggests deposition by high-velocity seaward-moving debris and grain flows followed by reworking by waves large enough to redistribute coarse sediment in deep water. The only waves large enough are those of giant tsunami. Petrology and geochemistry show no impact or explosive volcanic constituents in the finer units and the waves involved are too large for generation directly by submarine fault displacements. We suggest that the top Guwayza conglomerates were deposited by very large submarine slides which were then reworked by the tsunami generated by them. Such contemporary massive slope failure deposits are present on the adjacent slope and shelf margin.

Solution‐collapse breccias of the Minkinfjellet and Wordiekammen Formations, Central Spitsbergen, Svalbard: a large gypsum palaeokarst system

AbstractLarge volumes of carbonate breccia occur in the late syn‐rift and early post‐rift deposits of the Billefjorden Trough, Central Spitsbergen. Breccias are developed throughout the Moscovian Minkinfjellet Formation and in basal parts of the Kazimovian Wordiekammen Formation. Breccias can be divided into two categories: (i) thick, cross‐cutting breccia‐bodies up to 200 m thick that are associated with breccia pipes and large V‐structures, and (ii) horizontal stratabound breccia beds interbedded with undeformed carbonate and siliciclastic rocks. The thick breccias occur in the central part of the basin, whereas the stratabound breccia beds have a much wider areal extent towards the basin margins. The breccias were formed by gravitational collapse into cavities formed by dissolution of gypsum and anhydrite beds in the Minkinfjellet Formation. Several dissolution fronts have been discovered, demonstrating the genetic relationship between dissolution of gypsum and brecciation. Textures and structures typical of collapse breccias such as inverse grading, a sharp flat base, breccia pipes (collapse dolines) and V‐structures (cave roof collapse) are also observed. The breccias are cemented by calcite cements of pre‐compaction, shallow burial origin. Primary fluid inclusions in the calcite are dominantly single phase containing fresh water (final melting points are ca 0 °C), suggesting that breccia diagenesis occurred in meteoric waters. Cathodoluminescence (CL) zoning of the cements shows a consistent pattern of three cement stages, but the abundance of each stage varies stratigraphically and laterally. δ18O values of breccia cements are more negative relative to marine limestones and meteoric cements developed in unbrecciated Minkinfjellet limestones. There is a clear relationship between δ18O values and the abundance of the different cement generations detected by CL. Paragenetically, later cements have lower δ18O values recording increased temperatures during their precipitation. Carbon isotope values of the cements are primarily rock‐buffered although a weak trend towards more negative values with increasing burial depth is observed. The timing of gypsum dissolution and brecciation was most likely related to major intervals of exposure of the carbonate platform during Gzhelian and/or Asselian/Sakmarian times. These intervals of exposure occurred shortly after deposition of the brecciated units and before deep burial of the sediments.

Comparison of spatio–temporal evolution of experimental particulate gravity flows at two different initial concentrations, based on velocity, grain size and density data

Flume experiments were conducted to investigate the spatio–temporal structure of subaqueous particulate gravity flows with an initial concentration of 14% by volume. Time series of downstream flow velocity and its calculated degree of turbulence, median grain size and sediment concentration at different positions along the path of nominally identical flows are analysed and combined to constrain the spatio–temporal evolution of a single idealised flow. Comparison of the 14% flow with a flow of 5% initial concentration reveals similarities in the basic spatio–temporal structure of velocity, turbulence, grain size and concentration. Both flow types exhibit a velocity maximum at about 1 / 3 of the flow height above the flume floor. At that level, velocity decreases slowly in the flows' body and more rapidly in their tails. Moreover, turbulence intensity is highest in the head and at the base of the flows, whereas the level of maximum velocity and the tail of the flows typically are weakly turbulent. The zones of high turbulence are associated with shear at the front and base of the gravity flows. The flow of 5% and 14% initial concentration also agree in stratification patterns of median grain size and concentration. Grain populations are relatively well mixed in the head, show normal grading in the main part of the body and normal to inverse grading in the rear of the body and tail. The inverse grading is thought to originate from particles transported from the head upward and backward into the body of the flows, where they subsequently settle. The main difference between the flow of 5% and 14% initial concentration is that the higher-density flows appear to develop from a jet into a turbidity current closer to the inception point than the lower-density flow. This difference is interpreted from dimensionless vertical profiles of the flow parameters: horizontal velocity, concentration and grain size distribution. In the turbidity current phase of both flows, the dimensionless variables collapse well. This indicates that the flows behave in a dynamically similar manner and inspires confidence that the dimensionless variables can be used to predict the dynamic behaviour of particulate gravity flows across the measured concentration range in the flume, which due to dilution/sedimentation effects, was from ∼7 to < 1 vol.% concentration.

Bed geometry used to test recognition criteria of turbidites and (sandy) debrites

The origin of thick-bedded deep-water sandstones has generated much controversy in recent years. Two fundamentally different models have been proposed for beds with the same internal sedimentary characteristics: (1) progressive particle settling from the base of a turbulent flow—the “turbidity current” model and (2) en-masse freezing of a higher-concentration flow—the “sandy debris flow” model. These models predict beds with very different geometries; turbidites thin gradually whereas debrites have abrupt terminations. Previous studies have relied upon sedimentary recognition criteria (i.e., sedimentary features in small-scale outcrop or core) to interpret depositional mechanism. In this study, depositional mechanism is deduced from bed geometry gained from extensive correlations of individual sandstones preserved in a classic turbidite system (Marnoso-arenacea Formation, Italy). This approach allows recognition criteria for turbidites and submarine debrites to be independently tested. We find that tabular and tapered sandstones (turbidites) have distinctly different internal characteristics to beds with abrupt margins (debrites). Turbidites are relatively well sorted, often exhibit grading and traction structures and have relatively low matrix mud contents. They may also contain massive division, floating clasts and inverse grading. Debrites are moderate-to-poorly sorted, ungraded, structureless, contain floating clasts and have elevated matrix mud contents. These findings have implications for the assessment of submarine gravity flows deposits and reservoir rock characterization.

Progressive assembly of a massive layer of ignimbrite with a normal-to-reverse compositional zoning: the Zaragoza ignimbrite of central Mexico

The Zaragoza ignimbrite and two enclosing rhyodacite pumice fall layers were emplaced during the 15 km3 (DRE), ∼0.1 Ma Zaragoza eruption from Los Humeros volcanic centre, 180 km east of Mexico City. The ignimbrite comprises several massive flow-units, the largest of which locally exceeds 20 m in thickness and is regionally traceable. It comprises massive lapilli-ash with vertical elutriation pipes, and has a fine-grained inverse-graded base and a pumice concentration zone at the top. It also exhibits an unusual gradational ‘double’ vertical compositional zonation that is widely traceable. A basal rhyodacitic (67.6–69 wt% SiO2) zone grades up via a mixed zone into a central andesitic (58–62 wt% SiO2) zone, which, in turn, grades up into an upper rhyodacitic (67.6–69 wt% SiO2) zone. Zoning is also defined by vertical variations in lithic clast populations. We infer that pyroclastic fountaining fed initially rhyodacite pumice clasts to a sustained granular fluid-based pyroclastic density current. The composition of the pumice clasts supplied to the current then gradually changed, first to andesite and then back to rhyodacite. Inverse grading at the base of the massive layer may reflect initial waxing flow competence. The pumice concentration at the top of the massive layer is entirely rhyodacitic and was probably deposited during waning stages of the current, when the supply of andesitic pumice clasts had ceased. The return to rhyodacitic composition may have been the result of eruption-conduit modification during collapse of Los Potreros caldera, marked in the ignimbrite by a widespread influx of hydrothermally altered lithic blocks, and/or a decrease in draw-up depth from a compositionally stratified magma chamber as the eruptive mass flux waned. The massive layer of ignimbrite thins locally to less than 2 m, yet it still shows the double zonation. Correlation of the zoning suggests that the thin massive layer is stratigraphically condensed, and aggraded relatively slowly during the same time interval as did the much thicker (≤50 m) massive layer.

Stochastic analysis of single particle segregational dynamics

Inverse grading in hard sphere granular flow is described by an effective stochastic process for the vertical displacement of particles in time. By pure, parameter-free data analysis, we extract an underlying stochastic Langevin equation for the heights dynamics of large and small particles. Fixed points of the deterministic vertical dynamics of individual particles are determined and show that within this macroscopic description of a granular flow, inverse grading of large particles is due to a deterministic effect. These results may be used as an efficient alternative to time consuming direct numerical modelling of inverse grading.