Showing papers in "Journal of Sedimentary Research in 2012"

Seasonal Controls on the Development and Character of Inclined Heterolithic Stratification in a Tide-Influenced, Fluvially Dominated Channel: Fraser River, Canada

Abstract: Inclined heterolithic stratification (interbedded sand and mud with depositional dip; IHS) is developed on an in-channel bar in the tide-influenced, fluvially dominated (brackish water) reach of the Fraser River, British Columbia, Canada. The vertical bar succession is characterized by a fining-upward profile with an increase in mud content and mud-bed thickness from the shallow subtidal zone to the upper intertidal zone. There is also an increase in the number and lateral continuity of mud beds from the upstream side to the downstream side of the bar. Sand beds are dominated by current ripples in the intertidal zone, and by current ripples and trough cross-beds in the shallow subtidal zone. The channel base is mantled by downstream (ebb)-oriented dune-scale bedforms. Mud beds are dominantly parallel laminated, although current ripples may develop in silt-rich and sand-rich mud beds. Current-generated bedforms are predominantly ebb-oriented. Sediment deposition is seasonally controlled. Sand deposition occurs during periods of high discharge (snowmelt-induced freshet), and mud is deposited during waning freshet flow and low discharge (base flow). In mud-dominated deposits, current ripples may develop in sand-rich mud beds deposited during the freshet. Seasonal cyclicity in sediment deposition is also recorded in the ichnological characteristics of the IHS. Bioturbation is significantly more common in base-flow deposits (mud beds) than freshet deposits (sand beds). Burrows in sand beds typically subtend from overlying mud beds. Diminutive, vertical burrows dominate the trace suite, reflecting a very low diversity of infauna. Bioturbation is more common on the downstream side of the bar, associated with the thicker and more laterally contiguous mud beds. Based on these observations, seasonal cyclicity in channel-bar deposits, formed in tide-influenced, fluvially dominated channels, can be identified using a combination of sedimentological and ichnological characteristics, particularly in mud-dominated successions and in IHS. In mud-dominated deposits, seasonal controls are best-expressed ichnologically through the interbedding of bioturbated and unbioturbated intervals. The dominance of a low-diversity suite of mainly vertical traces can also be considered indicative of brackish-water conditions in the channel. In IHS successions, interbedded sand and mud beds are the best indicators of seasonal cyclicity: sand beds are typically unburrowed, and mud beds are burrowed. In sand-dominated successions that lack mud interbeds, it is difficult to recognize seasonal cyclicity.

Shelf-Edge Delta Regime As A Predictor of Deep-Water Deposition

Abstract: Shelf-edge delta depositional style and particularly the presence of river-dominated shelf-edge deltas is a reliable indicator of deep-water sand delivery, as documented by a dataset of some 29 shelf-margin clinoforms. Shelf-edge delta regime, defined as the sum of the effects of fluvial, tidal, wave, and other oceanographic currents impacting deltas as they arrive at the shelf edge is a key predictor for likelihood of sand transport off the shelf edge to deep water. Conventional sequence-stratigraphic concepts assume that delivery of sand to the deep water occurs primarily during falling and lowstand of relative sea level, and that basinward transport is associated with shelf-edge incision and sediment bypass. Recent analysis of outcrop and subsurface datasets has shown that sediment can also be transported to the deep water during rising and highstand of sea level provided sediment flux is high. In addition, some examples with documented shelf-edge entrenchment associated with sea-level fall did not deliver significant sand volumes to the deep water. In contrast to the emphasis given to sea level and supply, the role of the shelf-edge delta itself, and especially its process regime, has received relatively little attention. The data suggest that the behavior and process regime of the delta at the shelf edge is critical, except where shelf width is minimal.

Geochemical Constraints on the Provenance and Depositional Setting of the Devonian Liuling Group, East Qinling Mountains, Central China: Implications for the Tectonic Evolution of the Qinling Orogenic Belt

Abstract: The Qinling orogenic belt of Central China is one of the largest collision orogens in eastern Asia and is considered to mark the site where the eastern part of the Paleotethyan ocean, which separated the North and South China plates, was consumed. Many researchers have described the major units and tectonic framework of the Qinling orogenic belt, but there is little agreement over its Paleozoic history, particularly the tectonic setting of the Devonian assemblages. In this paper geochemistry is used to constrain the provenance and depositional setting of the Middle–Upper Devonian Liuling Group clastic sedimentary rocks from the East Qinling Mountains. Chondrite-normalized REE patterns are uniform with light REE enrichment (LaN/YbN c. 9.6), negative Eu anomalies (Eu/Eu* c. 0.62), and flat heavy REE patterns (GdN/YbN c. 1.6), indicating an upper-continental-crustal source and/or juvenile differentiated arc material. Trace-element discriminant diagrams also suggest a continental arc setting, albeit major-element chemistry can show some characters of passive-margin sandstones. Chemical index of alteration and A-CN-K relations, Nb-Ta negative anomalies (PAAS-normalized data), and high Cr-Ni-V-Ti anomalies all suggest that the source area was dominated by non-steady-state weathering regimes indicative of active uplift along an active continental convergent plate boundary, and not a passive margin. This indicates that the Liuling Group was probably related to subduction accretion with rapid uplift of its source areas. The minor recycling of older sedimentary components and oceanic-crust-related mafic inputs could be derived from the basement of the North Qinling arc and ophiolites or an accretionary complex, respectively. We conclude that the Middle to Upper Devonian Liuling Group was deposited at an active continental margin at the southern edge of the North China plate, and hence closure of eastern Paleotethys was post-Devonian.

Toarcian Black Shales In the Dutch Central Graben: Record of Energetic, Variable Depositional Conditions During An Oceanic Anoxic Event

Abstract: The wrong figure was printed in place of Figure 4 in the February 2012 issue of JSR, p. 114. Please …

Reactive Transport Modeling of Brine Reflux: Dolomitization, Anhydrite Precipitation, and Porosity Evolution

Abstract: Both geothermal convection and brine reflux drive circulation of sea-water- derived fluids through carbonate platforms during early burial, but dynamic interactions between heat and solute transport and resulting diagenesis are at present poorly understood. This paper describes high-resolution reactive transport model (RTM) simulations that suggest that reflux of 85 ppt brines rapidly restricts geothermal convection to the platform margin, with flow focused in the more permeable shallow carbonates. In a baseline simulation, involving an elongate, 25-km-wide grain-dominated packstone platform, brine reflux resulted in complete dolomitization beneath the 5-km-wide brine pool in 335 ky. The dolomite body then extends downward at c. 22 m/100 ky into an underlying broad area of partial dolomitization. This process enhances porosity at shallow depth, but beneath the dolomite body precipitation of anhydrite occludes porosity and limits the depth of reflux. In contrast, geothermal convection at the platform margin forms a smaller partially dolomitized body over a longer time (< 60% dolomite after 1 My), with very minor associated anhydrite cementation. Reflux diagenesis is sensitive to platform geometry, with higher rates of fluid flow increasing the depth of alteration beneath the brine pool for a circular platform compared to the linear baseline. Fluid flow across thermal gradients enhances reaction rates, and ignoring heat transport by 85 ppt brine reflux underestimates the extent of reflux dolomite by 25% and associated anhydrite by 90%. The depth and rate of anhydritization is sensitive to the geothermal heat flux, whereas platform-top temperatures affect dolomitization rate. Reflux diagenesis is also sensitive to brine density, which affects both fluid flow and reaction rates. Sediment permeability and reactive surface area (RSA) are key intrinsic controls on diagenesis. Where the permeability structure permits sufficient fluid flow, diagenesis preferentially affects more reactive fine-grained sediments. However, as flow rates decline, reactions become focused in the more permeable but less reactive sediments. Simulations thus shed light on why in some settings reflux preferentially dolomitizes muddy sediments, but elsewhere favors grainstones. Once active reflux ceases, brines continue to flow in the subsurface, but this “latent reflux” causes only minor dolomitization due to prior Mg2+ consumption at shallow depth.

Bedload Transport of Mud Across A Wide, Storm-Influenced Ramp: Cenomanian–Turonian Kaskapau Formation, Western Canada Foreland Basin

Abstract: Mudstone-dominated shallow-marine rocks of the Kaskapau Formation were deposited on a low-gradient ramp that spanned the foredeep of the Western Canada foreland basin during the late Cenomanian to middle Turonian. Organic-, clay-rich, and silt-rich mudstone accumulated on the flank of the forebulge, > 200 km from the western shoreline. Within this mudstone, a large proportion of the clay minerals are organized into silt- and very fine sand-size aggregate grains. These aggregates were produced both in the water column as marine snow and phytodetritus and also through reworking of previously deposited cohesive mud to form intraclasts. The latter, along with siliceous silt grains, form wave- and combined-flow ripples, graded beds, scour-fills, and ripple-tail lamination. Where sand-size sediment (comprising detrital siliceous, calcareous bioclastic, or phosphatic grains) is present, it is molded into combined-flow ripples, HCS, gutter casts, and lags. Thus all sediment grades indicate storm- wave and current reworking of the sea floor at a distance of > 200 km offshore. The common occurrence of clay minerals in the form of aggregate grains, organized into combined-flow ripples and parallel lamination, implies advective transport of clay minerals as bedload, driven by combined flows across a very low-gradient ramp. On the distal part of this ramp, latest Cenomanian rocks include thin tongues of SW-prograding quartz-rich sandstone that was derived from an emergent forebulge. This source was drowned during the early Turonian eustatic rise when the sediment abruptly changed to organic-rich mudstone dominated by clay-mineral aggregates. This compositional change was mainly a response to a sudden increase in distance to detrital sources in the west, rather than a dramatic increase in water depth. Throughout much of early to middle Turonian time, the sea floor in the forebulge region lay above effective storm wave base for silt, estimated at ~ 70 m. At sea-level lowstands, wave winnowing and erosion of the sea floor concentrated bioclastic lags at the top of siltier-upward sequences; lags are interpreted to correspond to falling-stage, lowstand, and early transgressive systems tract deposits on the western margin of the basin. Previous studies may have substantially overestimated water depth for organic- and clay-rich calcareous mudstones in the Western Interior Seaway.

Determining the Diagenetic Conditions of Concretion Formation: Assessing Temperatures and Pore Waters Using Clumped Isotopes

Abstract: Carbonate-δ^(18)O paleothermometry is used in many diagenetic studies to unravel the thermal history of basins. However, this approach generally requires an assumed pore-water δ^(18)O (δ^(18)O_(pw)) value, a parameter that is difficult to quantify in past regimes. In addition, many processes can change the original isotopic composition of pore water, which further complicates the assignment of an initial δ^(18)O_(pw) and can lead to erroneous temperature estimates. Here, we use clumped-isotope thermometry, a proxy based on the ^(13)C–^(18)O bond abundance in carbonate minerals, to evaluate the temperatures of concretion formation in the Miocene Monterey Formation and the Cretaceous Holz Shale, California. These temperatures are combined with established carbonate–water fractionation factors to calculate the associated δ^(18)O_(pw). Results demonstrate that diagenetic processes can modify the δ^(18)O of ancient pore water, confounding attempts to estimate diagenetic temperatures using standard approaches. Clumped-isotope-based temperature estimates for Monterey Formation concretions range from ∼ 17 to 35°C, up to ∼ 12°C higher than traditional δ^(18)O carbonate–water paleothermometry when δ^(18)O_(pw) values are assumed to equal Miocene seawater values. Calculated δ^(18)O_(pw) values range from +0.3 to +2.5‰ (VSMOW)—higher than coeval Miocene seawater, likely due to δ^(18)O_(pw) modification accompanying diagenesis of sedimentary siliceous phases. Clumped-isotope temperatures for the Holz Shale concretions range from ∼ 33 to 44°C, about 15 to 30°C lower than temperatures derived using the traditional method. Calculated δ^(18)O_(pw) values range from −5.0 to −2.9‰ and likely reflect the influx of meteoric fluids. We conclude that the use of clumped isotopes both improves the accuracy of temperature reconstructions and provides insight into the evolution of δ^(18)O_(pw) during diagenesis, addressing a longstanding conundrum in basin-evolution research.

Shelf Genesis Revisited

Abstract: Shelves have previously been classified according to a wide range of criteria, such as tectonic, morphological, climatic, and process-based classifications. Here, the formation of shelves is discussed in the context of conditioning from sedimentary and tectonic processes. A three-fold division of shelves is proposed: sedimentary shelves, combined structural–sedimentary shelves, and structural shelves. With a definition of a shelf as a shallow-marine surface of large areal extent located around the margin of a deeper basin (relief hundreds to thousands of meters), most cases of shelf formation can be explained by means of sedimentation, with the only contribution from tectonics being long-term accommodation provided by basinal subsidence. These sedimentary shelves are formed by virtue of differential sediment deposition basinwards in combination with nucleation and propagation of a break in slope around or close to the shoreline. Additional conditions for the formation of sedimentary shelves include (1) deep frontal waters; (2) a hinterland that can deliver a sediment budget large enough to prograde the margin; and (3) transgressions that periodically flood back across the low-gradient coastal and alluvial plains. A structural shelf is a shelf where the shelf edge is a subaqueous structural feature (e.g., a fault escarpment), not propagated by sedimentation, usually sediment starved. Commonly, sediment has draped and infilled smaller-scale topography. Combined structural–sedimentary shelves have a direct structural nucleation of the shelf–slope break. This initial break is then blanketed and propagated by sediments retaining a shelf–slope-break topography which is displaced relative to its structural heritage.

Pliocene-Pleistocene Climate Change at the NE Tibetan Plateau Deduced from Lithofacies Variation in the Drill Core SG-1, Western Qaidam Basin, China

Abstract: The Pliocene–Pleistocene sedimentologic evolution of the western Qaidam Basin at the NE Tibetan Plateau was studied on the nearly thousand-meter-deep drill core SG-1 (spanning ca. 2.8–0.1 Ma), recovered from the Chahansilatu sub-depression with an average recovery rate of 95%. Lithofacies variation records the regional climatic change in relation to Asian drying and Tibetan Plateau uplift. Sedimentary textures and structures demonstrate a continuous slight coarsening and an increase of evaporites upward. We recognized five lithofacies: (1) gray-black laminated mudstone, (2) gray massive mudstone and siltstone, (3) bedded halite, (4) loose muddy halite, and (5) brownish-yellowish saliferous siltstone and mudstone, representing (1) semi-deep fresh to semi-brackish lake, (2) shallow brackish lake, (3) perennial saline lake, (4) playa saline lake, and (5) saline mudflat conditions, respectively. Variation of the lithofacies through the core demonstrates a clear trend of lake shrinkage since the late Pliocene and the final termination of the Chahansilatu paleolake. Accelerations of lake shrinkages are observed at ca. 2.5 Ma, 2.2 Ma, 1.6 Ma, 1.2 Ma, 0.9 Ma, 0.6 Ma, and 0.1 Ma. Our results suggest that the long-term stepwise drying of the Asian inland may have been forced by the change of the global ice volume.

Milankovitch-Scale Sequence Stratigraphy and Stepped Forced Regressions of the Turonian Ferron Notom Deltaic Complex, South-Central Utah, U.S.A.

Abstract: Laterally extensive outcrops in south-central Utah of the Turonian Ferron Notom Delta Complex and its bounding shales contain numerous chronometrically age-dated bentonite beds. The chronometry enables estimation of rates of accommodation and accumulation change. Integration of 56 measured sections and walking and tracing of beds allowed rigorous application of the concept of shoreline trajectory, using the lower bentonites as stratigraphic datums. Geometric stratal relationships along with facies dislocations were used to define high-frequency sequences and systems tracts. Forty-three parasequences were grouped into 18 parasequence sets, five simple sequences, and one sequence set. Parasequence sets show repeated, aggradational–progradational, degradational, progradational–aggradational, and retrogradational stacking patterns, which match the recently developed accommodation succession model. The chronometric analysis shows that the high-frequency sequences are Milankovitch-scale (approximately 100,000 yr), and record sea-level falls of up to 50 meters. The most complete sequence set, sequence set 3, shows clear evidence of a prolonged and stepped forced regression, with two additional higher-frequency sequences (possibly 40 kyr cycles), forming a forced regressive sequence set. This matches previous observations that valley systems, associated with the sequence boundaries, are compound, and also record higher-frequency cut-and-fill cycles. Among the various controlling factors causing cyclicity, such as shoreline autoretreat, delta-lobe switching, and allogenic controls such as climate, tectonics, and eustasy, we hypothesize that glacio-eustasy is the most likely control on the cyclicity of Ferron deposition, overprinted on a tectonically active basin. Gradual build-up of glaciers are hypothesized as a possible explanation of the punctuated downsteps observed in the forced regressive sequence set 3.

Quantifying the Hierarchical Organization of Compensation in Submarine Fans Using Surface Statistics

Abstract: Stratigraphy is often interpreted within hierarchical, or scale-dependent, frameworks that subdivide deposits based on distinct jumps in characteristics such as duration of deposition or scale. While the interpretation is logically valid, few studies quantitatively demonstrate that the jumps exist. Rather, recent work has quantitatively shown some characteristics of stratigraphy to be fractal, or scale invariant. Compensational stacking, the tendency for sediment-transport systems to preferentially fill topographic lows, is a concept widely used in stratigraphic interpretation. Here we use the compensation index, a metric that quantifies the strength of compensational stacking in sedimentary deposits, to describe the architecture of stratigraphy exposed in outcrops of submarine-fan strata in the Carboniferous Ross Sandstone representing contrasting architectural styles: (1) predominantly lobe elements and (2) predominantly channel elements. In both datasets, the stratigraphic architecture is classified into hierarchical classes of beds, stories, and elements. Results are the following. First, at both sites we document statistically significant increases in the strength of compensation across larger hierarchical levels supporting the use of hierarchical interpretations of stratigraphy. It is therefore plausible for some characteristics of sedimentary systems to be hierarchical and others to be fractal. Second, we document that lobe elements stack more compensationally than channel elements. We interpret this pattern to document that compensation increases along a longitudinal transect through this distributive submarine fan.

Flow-Depth Scaling in Alluvial Architecture and Nonmarine Sequence Stratigraphy: Example from the Castlegate Sandstone, Central Utah, U.S.A.

Abstract: Changes in the proximity and arrangement of channel-belt sandstone bodies in the rock record and associated unconformities in alluvial successions (i.e., alluvial architecture and nonmarine sequence stratigraphy) are often interpreted to reflect changes in basin boundary conditions, including subsidence and sea level. Such interpretations do not often consider how the size of a depositional system influences alluvial architecture and sequence stratigraphy. We investigate how paleoflow depth scaling affects fluvial stratigraphic interpretations using the Castlegate Sandstone (Campanian) at its type section in central Utah as an example. Using LIDAR imaging, channel preservation and paleoflow depths are estimated from bar clinoforms throughout the unit, and these data are compared to scour spacing, scour continuity, and mudstone content within the study interval. Within the Castlegate Sandstone bar clinoforms are routinely close to fully preserved (i.e., rollover of the upper part of the bar is present), and an overall increase in paleoflow depth up-section is coincident with changes in other alluvial-architecture characteristics including increases in scour-surface spacing and mudstone abundance up-section. This suggests that alluvial architecture commonly ascribed to changes in accommodation may result primarily from changes in the scale and style of fluvial deposition rather than accommodation-limited reworking and amalgamation. Additionally, although sequence boundaries have previously been identified in the section, no scour surfaces deeper or more extensive than what could be produced autogenically by large rivers typical of the Castlegate system were found in the study interval. This study demonstrates that estimates of paleoriver depth can enhance studies of alluvial architecture and provide a more robust basis for correlating and interpreting fluvial deposits.

High-Frequency Cyclicity in the Mediterranean Messinian Evaporites: Evidence for Solar–Lunar Climate Forcing

Abstract: The deposition of varved sedimentary sequences is usually controlled by climate conditions. The study of two late Miocene evaporite successions (one halite and the other gypsum) consisting of annual varves has been carried out to reconstruct the paleoclimatic and paleoenvironmental conditions existing during the acme of the Messinian salinity crisis, ~ 6 Ma, when thick evaporite deposits accumulated on the floor of the Mediterranean basin. Spectral analyses of these varved evaporitic successions reveal significant periodicity peaks at around 3–5, 9, 11–13, 20–27 and 50–100 yr. A comparison with modern precipitation data in the western Mediterranean shows that during the acme of the Messinian salinity crisis the climate was not in a permanent evaporitic stage, but in a dynamic situation where evaporite deposition was controlled by quasi-periodic climate oscillations with similarity to modern analogs including Quasi-Biennial Oscillation, El Nino Southern Oscillation, and decadal to secular lunar- and solar-induced cycles. Particularly we found a significant quasi-decadal oscillation with a prominent 9-year peak that is commonly also found in modern temperature records and is present in the contemporary Atlantic Multidecadal Oscillation (AMO) index and Pacific Decadal Oscillation (PDO) index. These cyclicities are common to both ancient and modern climate records because they can be associated with solar and solar-lunar tidal cycles. During the Messinian the Mediterranean basin as well as the global ocean were characterized by different configurations than at present, in terms of continent distribution, ocean size, geography, hydrological connections, and ice-sheet volumes. The recognition of modern-style climate oscillations during the Messinian suggests that, although local geographic factors acted as pre-conditioning factors turning the Mediterranean Sea into a giant brine pool, external climate forcings, regulated by solar–lunar cycles and largely independent from local geographic factors, modulated the deposition of the evaporites.

Distinguishing Depositional Environments in Shallow-Water Mixed, Bio-Siliciclastic Deposits on the Basis of the Degree of Heterolithic Segregation (Gelasian, Southern Italy)

Abstract: A new sedimentological technique has been tested in Gelasian cross-stratified, bio-siliciclastic deposits cropping out in southern Italy (Lucanian Apennine) to disentangle paleoenvironmental and model reconstructions for shallow-water mixed sediments. The proposed method suggests the use of the bioclastic/siliciclastic ratio (bls), and the Segregation Index (S.I.) to evaluate the percentage of the dominant elastic component in a mixed deposit, and in order to estimate the degree of the heterolithic segregation between bioclastic and siliciclastic particles. The principle of this method is based on the experimental evidence that bioclasts and quartz grains reveal a different physical behavior if entrained by a hydraulic flow of a given energy. Thus, a different internal texture of bioclastic and terrigenous particles in the same sedimentary deposit is regarded as the result of the variation in the energy of a number of hydrodynamic processes that characterize shallow marine settings, including waves, currents, and tides. The studied mixed sediments, subdivided into facies associations, exhibit stratigraphic shoaling-upward successions recording repeated transitions from offshore to shoreface environments. These trends are documented through the vertical variations in the degree of heterolithic segregation between mixed clastic particles, quantified by using the S.I. introduced in the present study. The assessment of the degree of heterolithic segregation is thus proposed as a proxy to distinguish depositional environments related to different water depths in shallow-water mixed systems.

Petrological, Geochemical, and Statistical Analysis of Eocene–Oligocene Sandstones of the Western Thrace Basin, Greece and Bulgaria

Abstract: The Rhodopian Orogen developed since the Late Cretaceous–early Eocene during accretionary processes following the closure of the Vardar ocean basin, a branch of Neotethys. Through a multidisciplinary approach, including sandstone petrology and geochemistry of the clastic and volcanoclastic sediments, we reconstruct the unroofing history of the Rhodopian orogen and characterize the formation and the evolution of the western portions of the Thrace basin, in Greece and Bulgaria, between the late Eocene and Oligocene. Detrital modes of 127 sandstone samples provide evidence of three distinctive petrofacies: quartzolithic, quartzofeldspathic, and volcanoclastic. The petrographic composition gives evidence of contributions from three key source areas corresponding to the three main tectonic units: the Circum-Rhodope Belt, the Variegated Complex (ultramafic complex), and the Gneiss–Migmatite Complex. The three petrofacies reflect multiple provenance from different tectonic settings as they evolve from quartzolithic to quartzofeldspathic to volcanoclastic, corresponding to collisional orogen, crustal block uplift, and volcanic arc settings, respectively. Geochemical data on major elements and trace elements are used to discuss the efficacy of tectonic-setting discrimination diagrams and compare them to the Dickinson model as well as to distinguish and characterize (i) petrographically homogeneous gneiss-supplied subbasins and (ii) volcanic contributions to sandstone composition. Multivariate statistical techniques are used to unravel the complex web of factors controlling sediment composition. Biplot analysis highlights the influence of two independent processes: (1) mixing between carbonate and silicate phases, and (2) evolution from mafic to felsic source rocks. The latter indicates progressively increasing supply rates from deeper crustal levels. The compositional evolution of the sandstone suites of Thrace basin in NE Greece and SE Bulgaria is strictly related to various geodynamic stages of the Rhodope region. Provenance analysis of Thrace sandstones provide an example of the changing nature of orogenic belt sand associate basins through time, and may contribute to the general understanding of similar geodynamic settings.

Punctuated Deep-Water Channel Migration: High-Resolution Subsurface Data from the Lucia Chica Channel System, Offshore California, U.S.A.

Abstract: High-resolution Autonomous Underwater Vehicle (AUV) multibeam bathymetry and chirp subsurface profiles from a portion of the Lucia Chica channel system, offshore central California, provide imaging of small-scale morphologies associated with deep-water channel migration. From ~ 950 m to ~ 1250 m water depth, the Lucia Chica channel system contains a complicated pattern of channels and scours. The quality and resolution of the subsurface chirp profiles reveals sediment packages on the same scale as geometries from outcrop strata. Detailed mapping and measurements along channels, here numbered from oldest (1) to youngest (4), indicate that the sinuous Channel 2 shifted position in discrete lateral steps, typically associated with erosion and new channel incision. Where channel fill was not removed by incision, a bench, morphologically defined as a relatively flat, higher area adjacent to the axial channel, resulted from each lateral shift. Innerbend levees were deposited on each bench and draped over the previous levees as flows travelled through the new channel position. Using the dense grid of high-resolution AUV-collected images from Channel 2 as an example, we propose a conceptual model of punctuated lateral migration, associated with inner-bend benches formed during axial-channel and outer-bend erosion, instead of point bars, associated with gradual lateral accretion. Greater erosion during punctuated migration as compared to lateral accretion has important implications for reservoir distribution and connectivity.

Prediction of Permeability in Quartz-Rich Sandstones: Examples from the Norwegian Continental Shelf and the Fontainebleau Sandstone

Abstract: Correctly predicting sandstone permeability from variables such as porosity, composition, and texture is one of the major problems of petroleum geology and hydrology. Using data sets comprising composition, texture, porosity, and permeability for sandstone samples from the Norwegian continental shelf and the Fontainebleau Sandstone, we have tested several previously suggested methods for permeability prediction, and also suggest a new method for sandstones containing significant volumes of clay. Our results indicate that permeability is successfully predicted from porosity and mean grain size by the Kozeny equation for most sandstones with clay contents less than 3% when porosities exceed 6–14%, with the lowest threshold values of porosity tending to occur in the sandstones containing least clay. The Kozeny equation also seems to enable calculation of the probable maximum possible permeabilities for sandstones with given porosities and grain sizes. For clay contents above 3%, the Kozeny equation typically overpredicts permeability. Including a percolation threshold in the Kozeny equation, using estimated macroporosity rather than total porosity, or applying a form of the equation where internal surface area is used as input instead of grain size does not provide generally acceptable permeability estimates. However, a modified Kozeny equation which includes a parameter reflecting the type of pore system often provides useful permeability estimates even for clay-rich samples. This parameter can often be regarded as a constant for a specific formation or sandstone unit when porosity variations are not excessive. Mercury-injection data suggest that its value is controlled by the width and connectivity of the dominant flow paths through the system, which in turn are probably determined by factors such as volume and distribution of clay.

Mass-Balance Effects in Depositional Systems

Abstract: Net deposition is necessarily accompanied by overall loss of sediment mass from the transport system; on long time scales the deposition compensates for subsidence and creates the stratigraphic record Although its spatial pattern changes and it can be locally stopped or reversed, depositional mass loss is a fundamental driving influence on the morphology and behavior of depositional systems Mass extraction to deposition leads directly to facies changes as sediment flux declines; indirectly it usually leads to down-channel sediment fining as deposition preferentially removes coarser particles Laboratory experiments illustrate the effects of systematic mass extraction on fluvial channel stacking and deposit grain size, and show how a mass-balance framework allows consistent comparison of facies despite major shifts in depocenter location Mass-balance analysis of experimental fluvial and turbidite systems, and a turbidite mini-basin from the Gulf of Mexico, show a change from channel-dominated to lobe-dominated deposits at about 80% total mass extraction Experimental and field studies also show a close connection between rate of mass loss and rate of downstream grain-size fining, as predicted by a mechanistic theory based on mass balance These are first steps towards a framework for quantitative basin analysis based on mass extraction A mass-balance framework allows for consistent, quantitative comparison across basins of varying scale and shape Mass-balance frameworks can account for overall and/or generic mass-balance effects, and help separate them from local effects One way to use such generalized models effectively is to view the results as reference cases of down-transport change resulting from the basic interplay of spatial mass-extraction pattern and sediment supply Where such reference cases do not provide detailed predictions of specific field cases, they can still provide a baseline to separate local, case-specific features from generic system behavior The approach is analogous to the way the geoid serves as a reference case against which to measure gravity anomalies

Occurrence of Hyperpycnal Flows and Hybrid Event Beds Related To Glacial Outburst Events In A Late Ordovician Proglacial Delta (Murzuq Basin, SW Libya)

Abstract: A Late Ordovician glacially related delta is documented based on architecture and facies from outcrops in the western Murzuq Basin (Libya). Sandstone megabeds highlight clinoform geometries of a proglacial, low-angle, shallow-water delta. The progradational wedge extends over 25 km from the SSE to the NNW and is about 100 m thick. Two types of clinothems have been distinguished, and eleven facies sequences are characterized in relation with their along-slope positions. Sand-prone facies sequences in type 1 clinothems relate to high-magnitude–low-frequency glacial outburst floods generating a freshwater, highly concentrated plunging hyperpycnal flow at the river mouth. During the waxing stage, the slope adjustment of an out-of-grade profile causes significant erosion. The resulting additional sediment charge involves along foresets a downslope flow transformation into a co-genetic sandy debris flow and high-density turbidity flow. Hybrid event beds including linked debrites and turbidites are the resulting deposits. In the lower slope, decreasing sediment concentration of the high-density turbidity flow leads to sediment lofting and to a second flow transformation resulting in a lower-density turbidity flow and a concomitant rising sediment plume. Deposition results in crude ripple cross-stratification. Debrite deposition is temporally restricted to an early segment of the rising limb of the flood hydrograph. During the ensuing waxing stage, uninterrupted, sustained-flow conditions maintain up to the peak flow, permitting the aggradation of thick sandstone successions with crude ripple cross-stratification. During the waning stage, backstepping of the whole depositional system leads to prevailing sedimentation in the delta-plain setting. Mouth-bar development and channel plugs are characterized by climbing-dune cross-stratification (CDCS). Shale-prone sedimentation in type 2 clinothems essentially corresponds to background ablation-related sedimentation but also includes minor, debrite-bearing, outburst-related event beds. This study documents the links between glacial outbursts, hyperpycnal flows, and hybrid beds in low-angle delta settings and illustrates a type of proximal, sand-dominated hyperpycnite. Dam failure of subglacial lakes is inferred for the outburst generation. Comparison with modern and Pleistocene examples may suggest that outburst events were days to several years in duration (type 1 clinothem), with a 1–40 ky recurrence period (type 2 clinothem).

Patterns of Sedimentation in the Contemporary Red Sea as an Analog for Ancient Carbonates in Rift Settings

Abstract: Patterns of sedimentation in the Red Sea offer a contemporary analog for carbonate deposition in marine rift settings. Covering 20° of latitude, the sea is sufficiently long to display pronounced climate differences and the clear tropical waters support vigorous coral reef growth and associated production of carbonate sediment. Six focus areas within the Red Sea, each covering exactly 1,600 sq. km, illustrate the variability of spatial patterns in reefal and other carbonates in this rift setting. Five of the focus areas are located on a north–south transect along the western margin of the sea: (1) Gubal Straits (Egypt), (2) Shalatayn (Egypt), (3) Trinkitat (Sudan), (4) Dahlak (Eritrea), and (5) Halib (Eritrea); and one is from the eastern margin: (6) Farasan Banks (Saudi Arabia). Using Landsat imagery, water depth and two marine facies classes, “reefal frameworks” and “sediments,” were mapped. Lumping these two classes define “carbonate bodies” that were analyzed for trends in orientation, relation to local fault networks, and size-frequency distribution. Fault lineaments digitized from the literature are closely related to the orientation of carbonate bodies with areas exceeding 5 sq. km. Smaller bodies do not preferentially align with fault trends. Water depth and the occurrence of reefal frameworks and sediments for the six focus areas are not systematically related. Used as an analog, these data from the contemporary Red Sea may provide insight into the orientation and scale of accumulation of carbonates in subsurface marine rift settings.

Sequence Stratigraphic Evolution and Cyclicity of an Ancient Coastal Desert System: The Pennsylvanian–Permian Lower Cutler Beds, Paradox Basin, Utah, U.S.A.

Abstract: The lower Cutler beds comprise a 200-m-thick succession of at least 12 repeating cyclic packages of strata, each 10–18 m thick, that are of mixed eolian, fluvial, and shallow marine origin. These accumulated during the latest Pennsylvanian to early Permian in the Paradox foreland basin of southeast Utah. Each depositional cycle comprises a lower unit composed of a bioclastic wackestone or a bioclastic sandy calcarenite facies, both of shallow marine origin. The upper units in each cycle are of nonmarine eolian (dune and interdune) and fluvial (channel and floodplain) origin. The mixed nonmarine and shallow marine nature of the inferred paleoenvironments of the lower Cutler beds is significant because the preserved expression of the nonmarine eolian and fluvial units in each cycle demonstrates an external climatic control on system development, whereas the marine units in each cycle (together with associated transgressive and regressive surfaces) demonstrate repeated episodes of relative sea-level change. Key stratigraphic surfaces have been traced from the continentally dominated northeastern portion of the basin into apparently contemporaneous, shallow-marine dominated sections in the southwest of the basin. Interdependent changes in both climate and relative sea-level change are shown to have generated the preserved cycles, which are interpreted to represent high-frequency sequences that are bounded by erosional unconformities (sequence boundaries) and paraconformities (diastems). Relative sea-level lowstand was coincident with climatic aridity at which time exposure of a broad, low-relief coastal plain enabled the generation of a substantial eolian sediment supply that was available for transport by a paleowind aligned parallel to the trend of the paleocoastline, resulting in dune-field construction and accumulation along a coastal belt. Episodes of relative sea-level rise were coincident with a transition to a more humid paleoclimate, during which the eolian sediment supply was greatly reduced, resulting in dune-field deflation and associated expansion of the fluvial system across the deflated former dune-field surface. Marine transgression occurred first in a series of estuarine embayments via the back-flooding of broad but shallow fluvially incised valley systems. Later transgression culminated in marine incursion over the former low-relief floodplain. Episodes of relative sea-level highstand were coincident with maximum climatic humidity. The high-frequency sequences make up a composite sequence set, which itself records a longer-term relative sea-level cycle. At this larger scale, a lowstand systems tract is recorded in the lower part of the studied lower Cutler beds succession, whereas a substantial transgressive systems tract is developed in the upper part. A regionally extensive maximum flooding surface defines the top of the lower Cutler beds. The preserved thickness and number of high-frequency cycles, together with their relation to the long-term subsidence trend of the Paradox Basin, records a periodic switching of both climate and relative sea level, the temporally linked nature of which demonstrates that glacio-eustasy exerted a dominant control on the origin of the preserved succession. The lower Cutler beds preserve evidence for the linkage and feedback between combined climatic and eustatic allogenic controls on sedimentation, and their role in generating high-frequency Milankovitch-style cycles in mixed clastic–carbonate successions.

Influence of Climate and Dolomite Composition on Dedolomitization: Insights from a Multi-Proxy Study in the Central Oman Mountains

Abstract: Dedolomitization is an important diagenetic process that can yield information on the history of paleo-fluids in a given aquifer or outcrop, and by extension it offers a window into past hydrologic conditions. Dedolomitization is also relevant economically as it can alter the porosity and permeability of carbonates, thus affecting reservoir quality. Despite considerable research, the process of dedolomitization is still not entirely understood. Here, new findings from the central Oman Mountains highlight the importance of dolomite chemistry and fluctuating climate on dedolomitization. Petrographic, mineralogical, and geochemical data from both altered and pristine dolomite hosted in Jurassic carbonate rocks from the Sahtan Group and outcropping at Wadi Mistal in the Jebel Akhdar tectonic window reveal two dolomite bodies with different characteristics, stratabound and fault-related dolostone. The (ferroan) dolomite crystals are larger in the fault-related dolostone, whereas the (non-ferroan) dolomite crystals are smaller in the stratabound dolostone. Petrography reveals a complex suite of alteration textures, including pristine dolomite, recrystallized dolomite, and calcitized dolomite (dedolomite). Iron oxides are present pervasively in the altered rocks, and different alteration textures co-occur in the same sample. Relative to unaltered dolomite in this outcrop, the recrystallized dolomite is characterized by similar positive carbon isotope values but less negative oxygen isotope values, and the calcitized dolomite is characterized by even less negative oxygen isotope values and more negative carbon isotope values. Based on field data and petrography, two phases of alteration are evident, an earlier dedolomitization event affecting the stratabound dolomite only, and a more pervasive Pleistocene-Holocene alteration phase associated with surface weathering that affected both the fault-related dolomite and to a lesser extent the stratabound dolomite. Stable isotope results further suggest that the more recent subaerial weathering phase happened under two alternating climate regimes: dedolomitization was triggered by meteoric fluids that interacted with soil-related carbon during humid climatic period(s), whereas recrystallization of ferroan fault-related dolomite happened during more arid climatic period(s) with less developed soils and lower fluid–rock interaction. These results suggest that weathering of ferroan fault-related dolomite can lead to formation of goethite and recrystallized, non-stoichiometric dolomite (with a reset stable oxygen isotope signature), and sometimes to dedolomitization.

Revision of Platte River Alluvial Facies Model Through Observations of Extant Channels and Barforms, and Subsurface Alluvial Valley Fills

Abstract: The Platte River of Nebraska, central USA, has been used by sedimentologists as a type example of a sandy, braided river system for some forty years. Despite this designation, however, the details of the river’s subsurface stratigraphy have never been evaluated, and so the extant facies model for the Platte River remains unvalidated. This paper analyzes the Holocene stratigraphy of the central and lower Platte River. It utilizes newly acquired data from wireline logs, sediment cores, aerial photography, and ground-penetrating radar (GPR) traverses to characterize subsurface geology, in addition to surface sediment and geomorphic mapping, sampling, and analysis of serial aerial imagery. Cores and GPR profiles show that the lithosome of the active Platte is 6–8 m in thickness and consists predominantly of medium sand. Although macroform features are common on the surface of the modern (active) central and lower Platte River in Nebraska, the shallow subsurface stratigraphy is dominated by mesoform cross-bedding and planar stratification overlying channel scour fills. This differs markedly from the vertical succession predicted by the Platte River facies model of Miall (1977). Data from inactive portions of the central and lower Platte River, however, show macroform cross-bedding indicative of the downstream and cross-stream migration of linguoid and transverse bars, which would be predicted by the published model. The typical architecture of the Holocene channel-belt sand body in the areas studied thus comprises a lower unit dominated by macroform-scale cross-bedding, overlain by an upper unit dominated by mesoform-scale cross-bedding and scour fills. Furthermore, time-series analysis of aerial photography of the river in the vicinity of Grand Island, Nebraska, shows that: (1) the river has become dominated by aggressively vegetated subaerially exposed channel-bed domains (termed “vegetated channel islands”) that superficially resemble bars; and (2) that this stretch is no longer dominated by downstream-accreting macroform bars, which were abundant in the 1960s and 1970s. Contraction of the active channel in this region has accompanied these changes, somewhat independently of discharge variation. New vertical sequence facies models are presented to account for these differences. Our data show the futility of seeking to characterize a fluvial system by means of a single vertical sequence model, and furthermore indicate that the Holocene facies architecture of the sandy, braided Platte River varies both in space and in time. The dominance of mesoform-scale structure in the shallow subsurface of the central and lower Platte River likely reflects the ongoing process of gradual abandonment of the system. It further highlights the need for caution in interpreting subsurface structure from surface geomorphology in fluvial systems.

Origin of Siderite Concretions in Microenvironments of Methanogenesis Developed in a Sulfate Reduction Zone: An Exception or a Rule?

Abstract: The Mississippian shales from Wardie (Scotland) were deposited in a large normally brackish-water basin. They host siderite concretions with δ13C values ranging from −3.5 to 12.1‰ which show that sulfate reduction and methanogenesis contributed to the production of bicarbonate. Fossils are found within each of the concretions, suggesting that the decay of these organic remains provided a catalyst for concretionary growth. The pore water was freshened, which is indicated by the very negative δ18O values (from −12.8 to −4.7%). Many features indicate that the concretions are very early-diagenetic, precompactional precipitates. The concretions are mostly homogeneous; only a few exhibit complex concentric zoning. The microstructure of the homogeneous concretions indicates a pervasive growth. However, their isotopic composition reveals a clear trend towards lighter δ13C and δ18O values from the center to the edge. It is proposed that the concretions grew due to methanogenesis in microenvironments around large organic remains, which acted as nuclei. We suggest that this process may be one of the reasons for the very common occurrence of cements as mineral concretions, not as disseminated precipitates along beds. These microenvironments developed entirely within the sulfate reduction zone, which resulted in the establishment of isotopic gradients in bicarbonate dissolved in the pore water across these microenvironments. These gradients were caused by fast consumption of sulfate by the intensive oxidation of organic remains. This resulted in the isotopic trends preserved in the homogeneous concretions. The formation of the zoned concretions proceeded generally concentrically, but detailed observations suggest that pervasive growth also contributed to their formation. Afterwards, all the concretions were deeply buried, probably within the oil window, where late-diagenetic phases crystallized (mainly kaolinite, quartz, and sulfides).

Depths of Modern Coastal Sand Clinoforms

Abstract: Clinoforms are classical geological features. Examples in the rock record or in seismic reflection data that originally formed in shallow water can potentially help to locate paleo–sea level, but their precise links with sea level need to be established using modern examples before such inferences can be made accurately. Some near-shore areas of high wave energy and steep coasts host sand bodies with upwards-convex surfaces. These clinoforms have been suggested to have been created from sand exported from the upper shoreface during stormy conditions, and deposited at depths where wave action diminishes below the threshold of motion (Field and Roy 1984; Hernandez-Molina et al. 2000). We have compiled the shapes of these bodies in a variety of wave environments in order to test this idea. The interpreted depths at which the sand surface steepens (i.e., the clinoform rollover) vary from 21 m off southern California to deeper than 50 m off SE Australia. To assess the link with wave action, rollover depths were compared with adjacent deep-water wave properties over the period 1992–2001 in the ERA-40 reanalysis dataset. Rollover bed shear stresses were computed from properties representing average wave conditions and from properties associated with upper–percentile conditions. Stresses were found to reach 0.1–0.5 Pa during upper 5-percentile wave conditions, exceeding the sediment threshold of motion estimated from reported grain-size data. Sediment to below the rollover is therefore mobile during extreme wave conditions.

Microcrystalline Quartz Generation and the Preservation of Porosity in Sandstones: Evidence from the Upper Cretaceous of the Subhercynian Basin, Germany

Abstract: Formation of microcrystalline quartz formation has proven to be effective at preserving porosity in deeply buried sandstone petroleum reservoirs, typically cemented by syntaxial quartz cement. There remains much uncertainty about what controls the growth of microcrystalline quartz and how it prevents syntaxial quartz overgrowths. Here, the Cretaceous Heidelberg Formation, Germany, provides a natural laboratory to study silica polymorphs and develop an understanding of their crystallography, paragenetic relationships, and growth mechanisms, leading to a new understanding of the growth mechanisms of porosity-preserving microcrystalline quartz. Data from scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), and transmission electron microscopy (TEM) data illustrate that porosity-preserving microcrystalline quartz cement is misoriented with respect to the host grain upon which it grows. In contrast, ordinary quartz cement grows in the same orientation (epitaxially) as the host quartz sand grain, and typically fills pore spaces. EBSD and TEM observations reveal nanofilms of amorphous silica (~ 50–100 nm in thickness) between the microcrystalline quartz and the host grain. The microcrystalline quartz is interpreted to be misoriented relative to the host grain, because the amorphous silica nanofilm prevents growth of epitaxial quartz cement. Instead, the microcrystalline quartz is similar to chalcedony with perpendicular to the growth surface and c axes parallel with, but randomly distributed (rotated) on, the host quartz grain surface. Development of pore-filling quartz growing into the pore (in the fast-growing c-axis direction) is thus inhibited due to the amorphous silica nanofilm initially and, subsequently, the misoriented microcrystalline quartz that grew on the amorphous silica.

Origins of Microbial Microstructures in the Neoproterozoic Beck Spring Dolomite: Variations in Microbial Community and Timing of Lithification

Abstract: Microbialite microstructures form at the scale of microbial processes and can preserve evidence of growth, degradation, and lithification in microbial communities. Understanding how these processes are preserved in microstructures will provide insights into microbial ecosystems and how microbial communities have evolved through time. Microbialites in the Neoproterozoic Beck Spring Dolomite, southern California, U.S.A., contain microstructures that record variations in the morphology of microbial communities as well as the timing of degradation versus lithification in the communities. These processes are represented by five end-member microbial microstructures: 1) distinct laminated microstructure; 2) diffuse laminated microstructure; 3) distinct clotted microstructure; 4) diffuse and regular clotted microstructure; and 5) diffuse and irregular clotted microstructure. These microstructures are distinguished by fabrics defined by organic inclusions. In distinct microstructures, organic inclusions sharply define microbial features, such as laminae that are laterally continuous for millimeters or 50–200 micron diameter microdots. The contacts between distinct microstructures are always sharp. In diffuse microstructures, zones of organic inclusions lack distinct boundaries; neighboring laminae and clots grade into each other within tens of microns, and boundaries between microbial structures and encasing cements are indistinct. Diffuse microstructures grade into each other and into distinct microstructures in a systematic way that suggests that differences are due to variations in the timing of mineralization relative to growth and degradation of microbial communities. Sharply defined textures in distinct microstructures suggest that lithification started during growth of the microbial community, and the close spatial association but lack of intergrading between distinct laminated and distinct clotted microstructures suggests that they formed from two distinct microbial communities that lived in the same environment. By contrast, diffuse microstructures formed where lithification occurred after the onset of decay and degradation of the primary growth structure. The continuum from distinct microbial textures through more diffuse and irregular textures documents variations in the timing of lithification relative to growth and decay of the microbial community. Thus, where petrographic preservation is extremely good, such as in the Beck Spring Dolomite, sub-millimeter-scale microbial microstructures record a gradation between growth and degraded microbial structures depending on the relative timing of lithification and heterotrophic decay.

Turbidites, and the Case of the Missing Dunes

Abstract: In the deep-marine stratigraphic record classical turbidites are common and when complete comprise five vertically stacked units, which in ascending order are termed the a to e divisions. The b division consists of planar lamination, which in almost all cases is overlain by ripple cross-stratification of the c division. Conspicuously absent in this succession is dune cross-stratification, which for sediments coarser than middle fine sand in a decelerating flow should occur between the planar-stratified and ripple cross-stratified units. Here it is argued that the paucity of dune cross-stratification is the result of the deleterious effect of suspended sediment on dune inception. Specifically, high suspended-sediment concentration, and hence high density, in the bottom part of the parent turbidity current prevents the development of a sufficiently sharply defined interface between the bottom part of the current and the dense, underlying bed-load layer. This results in the absence of the necessary hydrodynamic instability whose waveform structure along the interface would otherwise mould the bed surface into the incipient bed forms from which dunes (and also ripples) grow. The almost exclusive occurrence of ripple cross-stratification above planar lamination suggests that in almost all natural turbidity currents a sufficiently well developed density interface does not become established until flow speed is in the ripple stability field.

Cathodolumenescence Spectra of Quartz As Provenance Indicators Revisited

Abstract: We present a discrimination scheme for cathodoluminescence (CL) spectra of quartz as a tool in provenance studies. We analyzed > 1000 quartz crystals from 58 samples of different plutonic, volcanic, metamorphic, and pegmatitic rocks. The technique is based on the measurement of the relative intensity of the two main emission centers in visible light at 470–490 nm and 600–640 nm. The results confirm a red, violet, or bright to medium blue luminescence for volcanic phenocrysts, mainly bright blue colors for felsic plutonic and high-temperature metamorphic quartz, as well as brown to dark blue CL for quartz of low-temperature metamorphic origin. These and additional results for mafic plutonic (dark blue) and pegmatitic quartz (bright blue) lead to a possible discrimination with the following rock grouping: (1) volcanic quartz, (2) low-temperature metamorphic and mafic plutonic quartz, and (3) felsic plutonic, high-temperature metamorphic, and pegmatitic quartz. In the proposed scheme, 87% of the spectra are classified correctly. The three quartz groups can be taken as an estimate for the amount of volcanic, metamorphic, and plutonic quartz in sediments, unless major input from plutonic, high-temperature metamorphic, or pegmatitic quartz has taken place. Hence, despite criticism within the literature during the last decades, the CL colors of detrital quartz still can be used as provenance indicators. We finally conclude that the measurement of wavelength spectra is a fast and straightforward method to determine quartz-bearing source rocks of siliciclastic sediments.