Subtidal Lithofacies Research Articles

Rare earth element geochemistry of shallow carbonate outcropping strata in Saudi Arabia: Application for depositional environments prediction

The interpretation of depositional environments provides important information to understand facies distribution and geometry. The classical approach to interpret depositional environments principally relies on the analysis of lithofacies, biofacies and stratigraphic data, among others. An alternative method, based on geochemical data (chemical element data), is advantageous because it can simply, reproducibly and efficiently interpret and refine the interpretation of the depositional environment of carbonate strata.Here we geochemically analyze and statistically model carbonate samples (n=156) from seven sections of the Arab-D reservoir outcrop analog of central Saudi Arabia, to determine whether the elemental signatures (major, trace and rare earth elements [REEs]) can be effectively used to predict depositional environments. We find that lithofacies associations of the studied outcrop (peritidal to open marine depositional environments) possess altered REE signatures, and that this trend increases stratigraphically from bottom-to-top, which corresponds to an upward shallowing of depositional environments. The relationship between REEs and major, minor and trace elements indicates that contamination by detrital materials is the principal source of REEs, whereas redox condition, marine and diagenetic processes have minimal impact on the relative distribution of REEs in the lithofacies.In a statistical model (factor analysis and logistic regression), REEs, major and trace elements cluster together and serve as markers to differentiate between peritidal and open marine facies and to differentiate between intertidal and subtidal lithofacies within the peritidal facies. The results indicate that statistical modelling of the elemental composition of carbonate strata can be used as a quantitative method to predict depositional environments and regional paleogeography. The significance of this study lies in offering new assessments of the relationships between lithofacies and geochemical elements by using advanced statistical analysis, a method that could be used elsewhere to interpret depositional environment and refine facies models.

Stratigraphic Completeness of Carbonate-Dominated Records From Continental Interiors Versus Continental Margins: Stratigraphic Thinning Occurs Via Condensation and Omission At Multiple Scales

Abstract Over Phanerozoic time scales, stratigraphic records from continental interiors, or cratons, are dramatically thinner and are generally assumed to be relatively incomplete, with more numerous and longer-duration hiatuses, compared to records from more rapidly subsiding continental margins. However, this assumption need not be true for the shorter time scales (i.e., several 106 years and shorter) over which accumulation of the preserved stratigraphic record on the continental interior actually takes place. This study compares carbonate-dominated sedimentary records from the Devonian continental interior (Iowa) and continental margin (Nevada) to evaluate whether the continental-interior record is (1) miniaturized, i.e., thinner, but equally complete; (2) comparable in thickness and quality where the sedimentary record is preserved, but certain portions of the record are notably absent, i.e., omitted or truncated; or (3) so invariably preserved that equivalent stratigraphic packages cannot be recognized compared to the continental-margin record. This study finds that fourth- to fifth-order cycles in Iowa are, on average, approximately half as thick and half as numerous compared to the continental margin of Nevada. Moreover, the stratigraphic record on the continental margin of Nevada is dominated by cycles that are composed of tidal-flat and shallow subtidal lithofacies, capped by simple flooding surfaces, and exhibit catch-up or keep-up depositional styles. The continental-interior record in Iowa is dominated by cycles that are composed of subtidal lithofacies, capped by a range of bounding surfaces, and exhibit catch-down or give-up depositional styles. These findings suggest that the thin record in Iowa is largely a result of low sedimentation rates associated with suppressed carbonate production in this epeiric-sea setting, rather than minimal subsidence rates and an increased potential for subaerial exposure and associated loss of record.

Unravelling the influence of water depth and wave energy on the facies diversity of shelf carbonates

AbstractCarbonate sequence stratigraphy is founded on the principle that changes in relative sea‐level are recorded in the rock record by the accumulation of sediment with relative water depth‐dependent attributes. While at the scale of a shelf to basin transect, facies clearly arrange by water depth, the relation blurs for depths <40 m, the most vigorous zone of carbonate production. The reason for this change in behaviour is two‐fold. Firstly, in shallow water, the intrinsic processes of storm and wave reworking influence the seabed through submarine erosion and sediment redistribution. Secondly, facies diversity tends to be greater in shallow water than deep water because of a greater diversity in grain producers. Remote sensing imagery, field observations and hydrodynamic models for two reef‐rimmed shore‐attached carbonate platforms in the Red Sea show neither water depth nor energy regime to be reliable indicators of facies type when considered in isolation. Considered together, however, the predictive power of the two variables rises significantly. The results demonstrate it to be an oversimplification to assume a direct link between palaeo‐water depth and depositional diversity of subtidal lithofacies, while highlighting the importance of hydrodynamics in directing the accumulation of carbonate sediments in the shallow photic zone. While the size distributions of facies extents in the two focus areas follow power laws, no direct relation between the lateral continuity of the facies belts and water depth or wave height is reported. The work is relevant for the interpretation of metre‐scale subtidal carbonate cycles throughout the geological record by demonstrating how caution must be applied when inferring palaeo‐water depths from depositional facies.

The upper Moscovian and basal Kasimovian (Pennsylvanian) of Central European Russia: Facies, subaerial exposures and depositional model

The type upper Moscovian-basal Kasimovian argillaceous-carbonate succession of central European Russia contains regionally traced cyclothem-bounded subaerial exposure horizons (geosols) represented mainly by rendzina-type palaeosols. Palaeokarst profiles occurrarely and grade laterally to palaeosols. Composite subaerial profiles divided by one or two thin marine beds are called ‘multiple geosols’. The biofaces structure of the studied succession is defined by brachiopod and fusulinoid biofaces. The heterogeneous Choristites biofacies characterizes openmarine intervals, which constitute the bulk of the succession, and is defined by presence of Choristites. The Meekella biofacies with monospecific concentrations of Meekella shells and extreme rarity of other brachiopods characterises restricted peritidal intervals which commonly constitute the terminal regressive parts of major cyclothems. Three fusulinoid biofacies defined by Baranova and Kabanov (2003) include restricted peritidal Biofacies 1 with only small fusulinoids Fusiella and Schubertella present, open shoal-to-subtidal Biofacies 2 with the richest fusulinoid assemblages, and the most offshore Biofacies 3 with less diverse, sometimes Hemifusulina-dominated, fusulinoid assemblages. Bioturbation patterns and ichnofossils allow recognition of deeper subtidal Zoophycos and shallower non-Zoophycos ichnofacies. Among the latter, shallowest subtidal facies are characterized by presence of thalassinoid burrows. Intertidal laminated lithofacies with suppressed bioturbation contain Skolithos burrows. Seventeen lithofacies are recognized. Terrestrial lithofacies include topclays (upper clayey palaeosol horizons) and aeolian grainstones. Restricted peritidal lithofacies include cross-stratified skeletal-peloidal grainstones, fine-grained laminated grainstones-mudstones, and lagoonal mudstones. Open shoal lithofacies include ooidal grainstones (rare, only in Podolskian) and coarse skeletal-peloidal grainstones. The open subtidal lithofacies include skeletal packstones-rudstones, shallow subtidal packstones-wackestones, deeper subtidal packstones-wackestones, Ivanovia boundstones (only in Podolskian), proximal tempestites, distal tempestites, and skeletal wackestones-mudstones. The fossiliferous shale lithofacies is a miscellaneous group of marine shales lacking distinct features of the above-listed lithofacies. Conglomerates of cyclothem bases that are regarded as early transgressive lithofacies are variable in their palaeoenvironmental position and are characterized by concentrated pebbles derived from palaeosol reworking. The shallowest subtidal lithofacies of fine packstones-grainstones is considered as transitional between open subtidal and restricted peritidal lithofacies. The origin of stratiform dolostones is shown to be early diagenetic in the subsurface. The depositional model involves a shallow and broad epicontinental ramp, where through water circulation prevented stratification of the water column and allowed large skeletal benthos to colonize the entire spectrum of depositional environments. Storms are thought to be the principal water-mixing agent. The anti-estuarine circulation carrying oxygenated waters down-ward may explain the lack of anoxic features in the deepest facies that may have formed below storm wave base.

Cyclic sedimentation across a Middle Ordovician carbonate ramp (Duwibong Formation), Korea

The Middle Ordovician Duwibong Formation (about 100 m thick), Korea, comprises various lithotypes deposited across a carbonate ramp. Their stacking patterns constitute several kinds of meter-scale, shallowing-upward carbonate cycles. Lithofacies associations are grouped into four depositional facies: deep- to mid-ramp, shoal-complex, lagoonal, and tidal-flat facies. These facies are composed of distinctive depositional cycles: deep subtidal, shallow subtidal, restricted marine, and peritidal cycles, respectively. The subtidal cycles are capped by subtidal lithofacies and indicate incomplete shallowing to the peritidal zone. The restricted marine and peritidal cycles are capped by tidal flat lithofacies and show evidence of subaerial exposure. These cycles were formed by higher frequency sea-level fluctuations with durations of 120 ky (fifth order), which were superimposed on the longer term sea-level events, and by sediment redistribution by storm-induced currents and waves. The stratigraphic succession of the Duwibong Formation represents a general regressive trend. The vertical facies change records the transition from a deep- to mid-ramp to shoal, to lagoon, into a peritidal zone. The depositional system of the Duwibong Formation was influenced by frequent storms, especially on the deep ramp to mid-ramp seaward of ooid shoals. The storm deposits comprise about 20% of the Duwibong sequence.

Depositional cyclicity of the Middle Ordovician Yeongheung Formation, Korea

The Middle Ordovician Yeongheung Formation consists of numerous meter-scale, shallowing-upward cycles, which were deposited on a shallow-marine carbonate platform. Two types of shallowing-upward cycles, peritidal and shallow subtidal cycles, are recognized in the Yeongheung Formation. The peritidal cycles are composed of shallow subtidal lithofacies capped by tidal-flat lithofacies, whereas the shallow subtidal cycles are entirely subtidal lithofacies with no tidal-flat caps or subaerial exposure features. Stacking of shallow subtidal cycles, the similtaneous development of peritidal and subtidal cycles on different parts of the carbonate platform, and persistent vertical stacking of meter-scale, shallowing-upward cycles suggest that most of the cycles were formed in response to high-frequency eustatic sea level oscillations.

Possible seismic origin of molar tooth structures in Neoproterozoic carbonate ramp deposits, north China

ABSTRACTThe Xinmincun Formation forms the uppermost unit of a thick Neoproterozoic section which accumulated near the east margin of the North China Block and is overlain by two thin nearshore to continental formations below fossiliferous Lower Cambrian sediments. Although tectonically deformed, sedimentary structures are preserved undeformed on cleavage‐parallel surfaces, and an 80 m section has been reconstructed by correlation across minor folds and faults in the Golden Stone beach area, 50 km NE of the city of Dalian, southern Liaoning province.The measured section shows 65 m of storm‐dominated deposits, consisting of alternations of micrites and sharp‐based graded intraclastic grainstone beds (tempestites), some with rudaceous, commonly erosional or guttered, bases. The top 15 m of section shows three alternations of similar subtidal lithofacies with partly to completely dolomitized peritidal deposits (laminated, sometimes fenestral and desiccated, micrite beds, and intraclastic rudite and grainstone beds). Tempestite beds become thinner and less abundant upwards towards a muddy upper shoreface zone. This environment was characterized in part by the occurrence of micrite with thin or streaky lamination (probable storm‐resuspended sediment), interbedded tempestites, numerous erosion surfaces, and evidence of liquidization and sediment slumping into hollows.Molar tooth structures are widespread in micrite beds of the Xinmincun Formation and are present in lesser abundance in tempestites and liquefied channel‐fills. Originally the structures were sub‐vertical cracks, 1–20 cm long, tapering upwards and downwards. Subsequently they became filled with microspar cement and buckled rigidly during compaction of surrounding sediment during burial. Evidence of repeated episodes of cracking, presence of brecciated cracks and localization of cracking within beds, together with variable degree of development and variation of preferential alignment in plan indicates a mechanical origin. Crack generation may have been by seismic surface waves generated by movement along faults defining either the basin's margins or its internal structure, or possibly by wave action during storms. A seismic origin for molar tooth structure is consistent with other Neoproterozoic occurrences. Their preferential occurrence in Precambrian deposits arises from the relative rigidity of micritic sediment at this time related to lack of bioturbation, incipient cementation and possibly microbial binding.

Cross‐platform architecture of a sequence boundary in mixed siliciclastic‐carbonate lithofacies, Middle Cambrian, southern Great Basin, USA

ABSTRACTStratigraphic analysis of mixed siliciclastic‐carbonate lithofacies within the Middle Cambrian Bonanza King Formation of the southern Great Basin reveals three distinct facies associations that record a range of depositional environments from semi‐arid tidal flats to deeper subtidal, restricted lagoons. Stratigraphic trends, cross‐platform facies variations and correlation of individual surfaces across 250 km of the study area suggest that these mixed lithofacies were deposited in three temporally distinct phases. (1) Extensive progradation of mixed peritidal environments culminated in a prolonged episode of subaerial exposure marked by an areally extensive intraclast breccia (0·5–1·2 m thick) that we interpret to be a major Type 1 sequence‐bounding disconformity. (2) Abrupt flooding of the exposed platform resulted in the deposition of mixed deeper subtidal lithofacies, including a condensed interval of fissile, fossiliferous shale. (3) Progressive shallowing and aggradational accumulation was accompanied by a decrease in siliciclastics and a shift to pure carbonate deposition. Deep‐water siliciclastics and megabreccias record deposition along the base‐of‐slope off the Middle Cambrian shelf‐edge, and are interpreted to represent lowstand deposits emplaced during the prolonged episode of subaerial exposure of the shallow shelf.The presence of fine siliciclastics in both peritidal facies and sharply overlying deeper subtidal facies of the study interval within the Bonanza King suggests a variable, but relatively continuous, influx of terrigenous material throughout an extended period of accommodation change, apparently asynchronous with respect to the predictive model of reciprocal sedimentation. We suggest that the primary siliciclastic source changed with relative sea‐level position. During lowered sea level, aeolian processes acting upon the unvegetated Cambrian craton transported fine siliciclastics onto peritidal and shallow‐subtidal environments. During higher sea level, coastal siliciclastic reservoirs supplied sediment that was transported for long distances by geostrophic currents flowing along the submerged platform.As opposed to many Cambro‐Ordovician grand cycles that are commonly interpreted to consist of a transgressive shaly half‐cycle grading upward into a regressive carbonate half‐cycle, the sequence boundary within this Middle Cambrian succession occurs within siliciclastic‐rich, mixed lithofacies rather than in adjoining purer carbonates, implying that some ‘grand cycles’ should not be considered synonymous with ‘sequences’. Interbasinal correlations of the Type 1 sequence boundary within the mixed unit are speculative, primarily because of the inherent imprecision of available trilobite biostratigraphy. However, there is evidence that an extended episode of subaerial exposure may have been continent‐wide during the Ehmaniella trilobite biochron.

Cycles in Gasperian (Mississippian) Basin-Edge Sediments of Indiana: ABSTRACT

Basin-edge sediments of the Gasperian Stage (Upper Mississippian) in southwestern Indiana consist of four limestone formations that alternate rhythmically with three terrigenous formations. Each formation exhibits an aggregate of supratidal to subtidal lithofacies having characteristic fossil assemblages and diagnostic parameters of depositional turbulence. Areal distribution patterns of lithofacies for each widely correlative stratigraphic unit have analogs in known lithotope patterns of modern inner shelf sediments. Certain Gasperian patterns were influenced by antecedent topography. Lithofacies succeed one another in predictable sequences representing distinctive regressive and transgressive lithotopes of seven principal cyclothems. Two successive, homotaxial cyclothem are represented wholly by carbonate facies. Other cyclothems maintain greater individuality and are partly or entirely terrigenous. Lithofacies of all but one cyclothem are arranged asymmetrically with either prolonged transgressive or prolonged regressive phases. Sudden lithotope shifts are discernible. Local influxes of terrigenous sediments coupled with progressive changes in strike of the contemporaneous shoreline from N25° W to N5° W effected disappearance of three cyclothems toward the north. Although Gasperian formations maintain essentially the same sequential order throughout the Illinois basin, those exposed in Indiana differ fundamentally from equivalent strata near the structural axis of the basin in thicknesses, proportion of carbonates, strike of sedimentary bodies with respect to paleoslope, and magnitude of shoreline migrations. Gasperian sediments in Indiana accumulated in a relatively stable coastal region influenced by shoreline processes. This area differs from the basin center which other authors have shown to be the locus of terrigenous deposition in an unstable deltaic regime. End_of_Article - Last_Page 727------------