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

Summary 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.     

Maastrichtian facies succession and sea-level history of the Hossein-Abad,Neyriz area,Zagros Basin

The Maastrichtian shallow-water carbonate platform (Tarbur Formation) is described from outcrop in southwest Iran. It is characterised by eight microfacies types, which are dominated by larger foraminifera, rudist debris and dasycladacean algae. They are grouped into four distinct depositional settings: tidal flat, lagoon, barrier and open marine. The depositional settings include stromatolitic boundstone of tidal flat, peloidal dasycladacean miliolids wackestone and peloid bioclastic imperforate foraminifera wackestone of restricted lagoon, Omphalocyclus miliolids bioclast packstone–grainstone and miliolids intraclast bioclast packstone–grainstone of open lagoon, rudist bioclast grainstone of inner-platform shoals and rudist bioclast floatstone–rudstone and bioclastic wackestone of open-marine environments.

The facies and faunal characters are typical of a ramp-like open shelf. The lack of reef-constructing organisms resulted in a gently dipping ramp morphology for the margin and slope. On the basis of facies analysis, three depositional sequences (third order) are defined.     

Platform configuration, microfacies and cyclicities of the upper Albian to Turonian of west-central Jordan

We present a comprehensive facies scheme for west-central Jordan platform deposits of upper Albian to Turonian age, discuss Cenomanian and Turonian carbonate cycles, and reconstruct the paleogeographic evolution of the platform. Comparisons with adjacent shelf areas (Israel, Sinai) emphasize local characteristics as well as the regional platform development. Platform deposits are subdivided into fifteen microfacies types that define eight environments of deposition of three facies belts. Main facies differences between Cenomanian and Turonian platforms are: rudist-bearing packstones that characterise the higher-energy shallow subtidal (transition zone) during the Cenomanian, and fossiliferous (commonly with diverse foraminifer assemblages) wackestones and packstones of an open shallow subtidal environment. On Turonian platforms high-energy environments are predominantly characterised by oolithic or bioclastic grainstones and packstones, whereas peritidal facies are indicated by dolomitic wackestones with thin, wavy (cryptmicrobial) lamination. Rhythmic facies changes define peritidal or subtidal shallowing-up carbonate cycles in several Cenomanian and Turonian platform intervals. Cyclicities are also analysed on the base of accommodation plots (Fischer Plots). High-frequency accommodation changes within lower Cenomanian cyclic bedded limestones of the central and southern area exhibit two major cyclic sets (set I and II) each containing regionally comparable peaks. Accommodation patterns within cyclic set II coincide with the sequence boundary zone of CeJo1. The lateral and vertical facies distributions on the inner shelf allow the reconstruction of paleogeographic conditions during five time intervals (Interval A to E). An increased subsidence is assumed for the central study area, locally (area of Wadi Al Karak) persisting from middle Cenomanian to middle Turonian times. In contrast, inversion and the development of a paleo-high have been postulated for an adjacent area (Wadi Mujib) during late Cenomanian to early Turonian times, while small-scale sub-basins with an occasionally dysoxic facies developed northwards and further south during this time interval. A connection between these structural elements in Jordan with basins and uplift areas in Egypt and Israel during equivalent time intervals is assumed. This emphasises the mostly concordant development of that Levant Platform segment.     

The mid-Cretaceous Debarsu Formation (Upper Albian–Middle Turonian) of Central Iran: depositional environment,palaeogeography, and sequence stratigraphic significance

The Upper Albian–Turonian Debarsu Formation in its type area around Haftoman, south of Khur (Central Iran) has been investigated using an integrated approach of high-resolution logging, bio- and sequence stratigraphic dating, and facies analysis based on field observations and detailed microfacies studies. The up to 500-m-thick Debarsu Formation consists of stacked, several 10- to?~?100-m-thick, essentially asymmetric shallowing-upward cycles from grey offshore marl via skeletal and intraclastic limestone with large-scale clinoformed foresets to thick-bedded bioclastic, locally rudist-bearing shallow-marine topset strata capped by palaeokarst surfaces. The diverse (micro)facies inventory (29 facies types) is dominated by skeletal carbonates (bioclastic pack-, grain-, float- and rudstone) that reflect deposition on a carbonate ramp with a lagoonal shoreline that was attached to an elevated area in the west and southwest. The outer ramp facies association of the Debarsu ramp contains predominantly microbioclastic marl with open-marine microfossils (planktic foraminifera) and fine-grained bioturbated packstone. The transition into the mid-ramp facies association, dominated by bioclastic pack- and grainstone (foreset strata), is commonly gradational. The inner-ramp facies association is very diverse, mainly consisting of high-energy (well-washed and cross-bedded) grainstone as well as back-ramp or inter-shoal bioclastic float- and rudist bafflestone. The Debarsu Formation occurs in an area of more than 2500 km² to the west, southwest, and south of Khur but had its depocenter with maximum thicknesses and thick offshore marl intervals in the type area. The large-scale shallowing-upward cycles correspond to third-order depositional sequences. The chronostratigraphic positions of the sequence-bounding unconformities in the Upper Albian to Lower Cenomanian match equivalent surfaces known from other Cretaceous basins on different tectonic plates. However, a large-scale intraformational stratigraphic gap (Middle Cenomanian to lowermost Turonian) at a major palaeokarstic surface in the upper part of the formation must be related to tectonic uplift. The Debarsu Formation shows similarities in (sequence) stratigraphic stacking patterns to hydrocarbon-bearing formations of the southern Tethyan margin (Arabian Plate).     

Development of rudist lithosomes in the Coniacian–Lower Campanian carbonate shelves of central-southern Italy: high-energy vs low-energy settings

The Late Cretaceous shallow-water depositional areas of southern Tethys were complexes of unprotected shelves occupied by foramol assemblages that produced loose, diagenetically stable bioclastic debris not involved in significant in situ cementation processes. Both storm- and wind-induced currents and waves exercised a strong control on the distribution of the shifting biogenic sediments which covered the open sea-floor, constituting large coalescing sheets of winnowed fine to coarse skeletal sands. Rudists spread over all shelf sectors, from more open and external areas to more internal ones, occupying different substrata and furnishing the bulk of the skeletal component by means of bioerosion processes. They colonised mobile sediments giving rise to complex bodies with peculiar characteristics related to environmental parameters of the different sectors of the shelf. On the basis of detailed sedimentological, taphonomic and palaeontological data, we recognised two main rudist-rich depositional settings (‘end members’) in the southern Italy Senonian rudist-bearing successions. In successions pertaining to hypothesised marginal shelf sectors, characterised by high-energy regime deposits, rudist lithosomes are metric in thickness and lateral extent and lens-like in morphology, rich in bioerosion-derived skeletal sand and silt. Rudists are highly diversified. Large elongated cylindro-conical hippuritids (mostly pertaining to the genera Hippurites and Vaccinites), thick-shelled radiolitids and plagioptychids largely dominate. Rudists clustered in life position are subordinate; they often form small bouquets. More commonly these organisms appear fallen but only barely reworked. The rudist-rich bodies laterally pass into clean bioclastic grainstone in which sedimentary structures, related to current and/or storm erosional action, are common. No evidence of significant original relief of the rudist bodies in respect of the neighbouring sediment can be recognised. The submarine erosion and/or the high-energy processes operating presumably inhibited the aggradation of the tidal sediments above the marginal ones. As a consequence the vertical facies organisation shows widespread subtidal cycles, as commonly recognised in open shelves with ramp-like morphologies. In successions pertaining to more internal and/or low-energy sectors, rudist-rich beds rhythmically alternate with finer-grained foraminiferal limestones. Small elevator radiolitids with oligospecific diversity are dominant, mostly concentrated in clumps. Rudists in growth position are abundant, although a large quantity of shells appear toppled with little reworking. They may form laterally continuous biostromal shell beds. Sedimentary structures such as cross-lamination and gradation are only occasionally present. The resulting facies are commonly arranged in peritidal/shallow subtidal cycles in which evidence of subaerial (up to pedogenic modifications on a large and small scale) and, less frequently, submarine exposure is common. Intermediate successions have been recognised, characterised by deposits of silty-sand plains, which present intercalations of graded, bioclastic, storm-related beds. Sedimentological characteristics seem to document more open conditions in which submarine erosion was intermittently prevalent. In these successions rudist species that are commonly found both in high-energy and low-energy assemblages coexist.     

Facies evolution and sequence chronostratigraphy of a “mid”-Cretaceous shallow-water carbonate succession of the Apulia Carbonate Platform from the northern Murge area (Apulia,southern Italy)

The “mid”-Cretaceous carbonate succession of the Apulia Carbonate Platform cropping out in northern Murge area (Apulia, southern Italy) is composed of shallow-water carbonate rocks and is over 400 m in thickness. This paper focuses on the lithofacies analysis of this carbonate succession, its paleoenvironmental interpretation, and its sequence-chronostratigraphic architecture. Lithofacies analysis permitted to identify deposits which can be grouped into the following three facies belts: (1) terrestrial facies belt formed by: intraclast-supported paleosoils; solution-collapse breccias; (2) restricted facies belt made up of lithofacies deposited in protected peritidal environments; (3) normal-marine facies belt made up of lithofacies formed in moderate- to high-energy subtidal environments. The detailed study both in outcrops and in thin-sections revealed that, at the bed scale, lithofacies are cyclically arranged and form shallowing-upward small-scale depositional sequences comparable to parasequences and/or simple sequences. The following three small-scale sequence types have been distinguished: (1) subtidal sequences mostly made up of lithofacies formed in the normal-marine open subtidal domain; (2) peritidal sequences made up of lithofacies formed in the restricted peritidal domain; (3) peritidal sequences showing a cap formed by paleosoils. Small-scale sequences are not randomly arranged in the compiled succession but form discrete packages, or sets, that alternate in the sedimentary record. The repetition of such small-scale sequence packages in the succession has been the key to recognize large-scale sequences comparable to third-order depositional sequences. Although sedimentological data are often fragmentary due to late dolomitization, four large-scale sequences have been distinguished. The data support a generalized landward-backstepping of facies belts during transgression, which implies a gradual gain of accommodation culminating with the deposition of a package of small-scale sequences formed by normal-marine subtidal deposits. These mark periods of maximum accommodation space and form the maximum-flooding zones of large-scale sequences. A gradual seaward progradation of facies belts is recorded during highstand conditions, which implies a gradual loss of accommodation culminating with the deposition of a package of peritidal small-scale sequences capped by paleosoils or by solution-collapse breccias. The occurrence of terrestrial deposits marks periods of minimum accommodation on the platform and determines the sequence boundary of large-scale sequences. The large-scale sequences identified in this study fit with the main transgressive/regressive cycles published in the sequence-chronostratigraphic chart of European basins. As a consequence, it is interpreted that changes of the sea level recorded at the scale of European basins played an important role in determining the sequence-stratigraphic architecture of the studied succession. In spite of this, the occurrence of solution-collapse breccias, which implies a significant gap in carbonate sedimentation in between Early and Middle Cenomanian times, may also have an alternative interpretation. In particular, this deposit may represent the local fingerprint of the well-known tectonic phase which, during Late Albian-Early/Middle Cenomanian times, determined the subaerial exposure of large parts of Periadriatic carbonate platforms producing a marked regional unconformity.     

Carbonate facies evolution from the late albian to Middle Cenomanian in Southern Istria (Croatia): influence of synsedimentary tectonics and extensive organic carbonate production

Summary During the Late Albian, Early and Middle Cenomanian in the NW part of the Adriatic Carbonate Platform (presentday Istria) specific depositional systems characterised by frequent lateral and vertical facies variations were established within a formerly homogeneous area, ranging from peritidal and barrier bars to the offshore-transition zone. In southern Istria this period is represented by the following succession: thin-bedded peritidal peloidal and stromatolitic limestones (Upper Albian); well-bedded foreshore to shoreface packstones/grainstones with synsedimentary dliding and slumping (Vraconian-lowermost Cenomanian); shoreface to off-shore storm-generated limestones (Lower Cenomanian); massive off-shore to shoreface carbonate sand bodies (Lower Cenomanian); prograding rudist bioclastic subaqueous dunes (Lower to Middle Cenomanian); rudist biostromes (Lower to Middle Cenomanian), and high-energy rudist and ostreid coquina beds within skeletal wackestones/packstones (Middle Cenomanian). Rapid changes of depositional systems near the Albian/Cenomanian transition in Istria are mainly the result of synsedimentary tectonics and the establishment of extensive rudist colonies producing enormous quantities of bioclastic material rather than the influence of eustatic changes. Tectonism is evidenced by the occurrence of sliding scars, slumps, small-scale synsedimentary faults and conspicuous bathymetric changes in formerly corresponding environments. Consequently, during the Early Cenomanian in the region of southern Istria, a deepening of the sedimentary environments occurred towards the SE, resulting in the establishment of a carbonate ramp system. Deeper parts of the ramp were below fair-weather wave base (FWWB), while the shallower parts were characterised by high-energy environments with extensive rudist colonies, and high organic production leading to the progradation of bioclastic subaqueous dunes. This resulted in numerous shallowing- and coarsening-upwards clinostratified sequences completely infilling formerly deeper environments, and the final re-establishment of the shallow-water environments over the entire area during the Middle Cenomanian.     

Depositional facies and cyclic patterns in a subtidal-dominated ramp during the Early-Middle Ordovician in the western Tarim Basin (NW China)

Due to a long-term transgression since the Early Cambrian, an extensive shallow-water carbonate platform was developed in the entire Tarim Basin (NW China). During the deposition of the Yingshan Formation (Early-Middle Ordovician), a carbonate ramp system was formed in the intrashelf basin in the Bachu-Keping area of the western basin. Four well-exposed outcrop sections were selected to investigate their depositional facies, cycles, and sequences, as well as the depositional evolution. Detailed facies analyses permit the recognition of three depositional facies associations, including peritidal, semi-restricted subtidal, and open-marine subtidal facies, and eleven types of lithofacies. These are vertically arranged into meter-scale, shallowing-upward peritidal, semi-restricted subtidal, and open-marine subtidal cycles, in the span of Milankovitch frequency bands, suggesting a dominant control of Earth’s orbital forcing on the cyclic sedimentation on the platform. On the basis of vertical facies (or lithofacies) and cycle stacking patterns, as well as accommodation changes illustrated graphically by Fischer plots at all studied sections, six third-order depositional sequences are recognized and consist of lower transgressive and upper regressive parts. In shallow depositional settings, the transgressive packages are dominated by thicker-than-average, shallow subtidal cycles, whereas the regressive parts are mainly represented by thinner-than-average, relatively shallow subtidal to peritidal cycles. In relatively deep environments, however, the transgressive and regressive successions display the opposite trends of cycle stacking patterns, i.e., thinner-than-average subtidal cycles of transgressive packages. Sequence boundaries are mainly characterized by laterally traceable, transitional zones without apparent subaerial exposure features. Good correlation of the long-term changes in accommodation space inferred from vertical facies and cycle stacking patterns with sea-level fluctuations elsewhere around the world suggests an overriding eustatic control on cycle origination, platform building-up and evolution during the Early-Middle Ordovician, although with localized influences of syndepositional faulting and depositional settings.     

Late Cretaceous sedimentary evolution of a northern sector of the Adriatic Carbonate Platform (Matarsko Podolje,SW Slovenia)

Cretaceous shallow-marine carbonate rocks of SW Slovenia were deposited in the northern part of the Adriatic Carbonate Platform. A 560-m-thick continuous Upper Cenomanian to Santonian carbonate succession has been studied near Hru?ica Village in Matarsko Podolje. With regard to lithological, sedimentological, and stratigraphical characteristics, the succession has been divided into nine lithostratigraphic units, mainly reflecting regressive and transgressive intervals of larger scale. During the latest Cenomanian and Early Turonian, hemipelagic limestones were deposited on top of shallow-marine lagoon and peritidal Upper Cenomanian deposits indicating relative sea-level rise. Subsequently, the deeper marine depositional setting was gradually filled by clinoform bioclastic sand bodies overlain by peritidal and shallow-marine low-energy mainly lagoonal lithofacies. Similar lithofacies of predominately inner ramp/shelf depositional settings prevail over the upper part (i.e., Coniacian to Santonian) of the succession. In the area, the Upper Cetaceous carbonate rocks are separated from the overlying Lower Eocene (Upper Paleocene?) carbonate sequence by regional unconformity denoted by distinct paleokarstic features. On the Adriatic Carbonate Platform the deeper marine carbonate setting, developed at the Cenomanian/Turonian boundary, is usually correlated with OAE2 and related eustatic sea-level rise. Similarly, subsequent reestablished shallow-marine conditions are related to Late Turonian long- and short-term sea-level fall. However, we are suggesting that deeper marine deposits were deposited in a tectonically induced intraplatform basin formed simultaneously with the uplift of the northern and northeastern marginal parts of the Adriatic Carbonate Platform.     

Sequence boundary and related sedimentary and diagenetic facies formed on Middle Permian mid-oceanic carbonate platform: Core observation of Akiyoshi Limestone,Southwest Japan

Detailed core observation of the Akiyoshi Limestone, Southwest Japan, reveals a sequence boundary and related sedimentary and diagenetic facies formed on a late Murgabian (Middle Permian) mid-oceanic carbonate platform. The sequence boundary lies upon karstified bioclastic grainstone and is overlain by peritidal lime- and dolo-mudstone. The karstified bioclastic grainstone, which had been affected by subaerial exposure and early diagenetic processes, is characterized by crystal silts, prismatic, bladed and dogtooth cements, blackened limestone features, and alveolar textures. The overlying peritidal lime- and dolo-mudstone is 8 m thick and exhibits fenestrae, fissures, laminations, black pebbles, and low-diversity biota composed exclusively of ostracodes and calcispherids. The sequence boundary almost coincides with a major fusulinoidean biostratigraphic boundary. A sea-level fall in the late Murgabian resulted in a biotic turnover and formed the sequence boundary and the karst textures. The following relatively slow transgression resulted in the deposition of the thick transgressive peritidal unit.     

Facies architecture and sequence stratigraphy of the Ordovician Bromide Formation (Oklahoma): a new perspective on a mixed carbonate-siliciclastic ramp

The Upper Ordovician (Sandbian; late Whiterockian to Mohawkian) Bromide Formation of south-central Oklahoma was deposited along a distally steepened ramp that descended into the Southern Oklahoma Aulacogen (SOA). It provides an unparalleled opportunity to examine a spectrum of marine facies that extended from back ramp peritidal settings to the center of the basin. The depositional history and environmental context of the unit are reconsidered using lithofacies analysis and the characterization of sequence stratigraphic patterns at a variety of hierarchical scales. Inner-ramp (above fair weather wavebase; FWWB) lithofacies suggest deposition in a range of environments: tidal flat, lagoon, shoreface, semi-restricted shallow subtidal, and bioclastic shoal. Middle-ramp environments between FWWB and storm wavebase (SWB) are thick and faunally diverse, and consist of rhythmically bedded marls, wackestone, packstone, and shales. Outer-ramp environments (below SWB) are represented by either fissile tan-green shale or thin-bedded carbonate mudstone and shale. Ramp stratigraphy, facies associations, and bounding surfaces suggest that three third-order depositional sequences are present in the Bromide. They demonstrate the transition from a clastic-dominated ramp in the late Whiterockian to a carbonate-dominated ramp in the Mohawkian, and show that the deposition of the Bromide was considerably more complex than the simple transgressive–regressive cycle traditionally used to describe accommodation dynamics in the basin. Meter and decameter-scale cycles (high-frequency sequences) are a common motif within the depositional sequences, and the Corbin Ranch Submember records an important peritidal succession prior to a major sequence boundary with the overlying Viola Springs Formation. New correlations based on measured sections, outcrop gamma-ray profiles, and subsurface well-logs document a novel pattern where the middle Bromide depositional sequence 2 (Mountain Lake Member) expanded down-ramp, whereas the succeeding carbonate-dominated sequence 3 (Pooleville Member) was progressively removed down-ramp. This demonstrates the existence of a major, regionally angular unconformity at the base of the Viola Springs Formation that has implications for basin evolution. Other implications include the validation of high-frequency sequences as a model for elementary cycles in mixed carbonate-siliciclastic systems and, more regionally, documentation of a new depositional sequence at the Turinian–Chatfieldian stage boundary.     

Microfacies of a Permian calcisponge reef in Lichuan,western Hubei,South China

The Lichuan Jiantianba reef is located at the platform margin between the carbonate platform and the marine trough in western Hubei, China. The water depth of this area became shallow in the late Permian Changhsingian Age, and a huge aggradation-progradation platform marginal reef developed. Based on precise field measurements and microscopic observation, this paper describes the petrological characteristics and biological assemblages of the reef in detail and distinguishes 10 microfacies: small echinoderm wackestone, sponge floatstone, bound sponge bioliestone, bound sponge framestone, large echinoderm wackestone, red algal limestone, bioclastic grainstone, dasycladales wackestone, shelly wackestone, and microbialites. Sponge floatstone and bound sponge bioliestone are defined as toppled sponge limestone. Comparisons of the petrological characteristics and biotic association of toppled sponge limestone, bound sponge framestone and bioclastic wackestone and grainstone revealed that the toppled sponge limestone and the bound sponge framestone are similar in sponge content in terms of the types and contents of reef-dwellers, except that the sponge content is slightly lower, and the preservation state is mainly toppled for the former and upright or inclined for the latter. The toppled sponge limestone is dominated by tabular calcite, and the bound sponge framestone is dominated by fibrous calcite. The bioclastic wackestone and grainstone do not contain reef-building sponge organisms, and the bioclast content is very high and often dominated by a certain class, such as echinoderms, foraminifers, green algae or shells. The toppled sponge limestone below the framework, which was classified as fore-reef breccia or bioherm bafflestone-bindstone in previous studies, should be defined as reef-core sponge limestone deposited in situ that experienced serious post-karstification. The vertical evolution of the sedimentary facies of the reef is analyzed based on the microfacies and sedimentary environment. The toppled sponge limestone and the bound sponge framestone should be classified as reef core, which is the only subfacies of the reef facies. The underlying small echinoderm wackestone should be classified as the shelf facies, whereas the overlying bioclastic wackestone and grainstone should be classified as the open platform facies. These classifications represent a modification of the sedimentary facies subdivision of the Jiantianba reef in Lichuan, Hubei Province, South China, and provide a new reference model for the subdivision of the Permian calcisponge reefs on platform margin.     

Oligo-Miocene fluvial-dominated deltas on the shelf of the South Caspian Sea (Paratethys)

The Oligo-Miocene Zivah Formation forms the principal reservoir unit in the Moghan area of northwest Iran. Characterization of the constituent facies of the formation and their spatial distribution represent a major aspect of this investigation. The combination of results from the field and laboratory studies lead to the determination of 18 lithofacies and 13 petrofacies (petrographic lithofacies). Three major types of sedimentary cycles (small-, medium-, and large-scale cycles) of variable thickness (few meters, few tens of meters, few hundreds of meters, respectively) are recognized on the basis of facies association properties. Depositional environments representing each facies and facies association are defined and interpreted on the basis of their sedimentological characteristics. The major depositional systems of the Zivah Formation are interpreted as fluvial-dominated deltas on the shelf of the South Caspian Sea (or Paratethys). The principal controls on sedimentation are discussed in terms of lithofacies/petrofacies characteristics and the nature of sedimentary cycles. Development of large-scale cycles is related to world-wide sea-level change (eustasy), medium-scale cycles to tectonism along the basin margin, and small-scale cycles to the rate of sediment supply and local environmental conditions. Active tectonism seems to be the main cause for high sediment supply to the Zivah Basin.     

Platform environments, microfacies and systems tracts of the upper Cenomanian-lower Santonian of Sinai, Egypt

Summary Factors controlling grain composition and depositional environments of upper Cenomanian—Santonian limestones of Sinai are discussed. The mainly shallow-water, inner-platform setting investigated is subdivided into five major facies belts, each represented by several microfacies types (MFTs). Their lateral distribution patterns and their composition underline aclear relation between depositional environment and platform position. The facies belts include sandstones and quartzose packstones of siliciclastic shorefaces, mudstones and bioclastic wackestones of restricted lagoons, shallow-subtidal packstones with diverse benthic foraminifera and calcareous algae, bioclastic and/or oolitic grainstones of inner-platform shoals, and wackestones of deep open-marine environments. The microfacies distribution patterns of the Cenomanian-Santonian strata are evaluated with respect to local and regional large-scale environmental changes. While protected shallow-subtidal environments with only subordinate ooids and oncoids prevail during the late Cenomanian, high-energy oolithic shoals and carbonate sands occur locally during the middle and late Turonian. They were probably related to a change of the platform morphology and a reorganisation of the platform after a late Cenomanian drowning. In the Coniacian-Santonian, the lack of ooids, oncoids, and the decrease of calcareous algae versus an increase in siliciclastics indicate a shift to lower water temperature and to a more humid climate. Especially in the Turonian, the interplay between sea-level changes, accommodation, hydrodynamics, and siliciclastic input is reflected by lithofacies and biofacies interrelation-ships that are elaborated within individual systems tracts. In particular, increasing accommodation intensified circulation and wave-agitation and controlled the distribution of high-energy environments of the middle and upper Turonian trans-gressive systems tracts. During highstands protected innerplatform environments prevailed.     

Facies pattern and sea-level dynamics of the early Late Cretaceous transgression: a case study from the lower Danubian Cretaceous Group (Bavaria,southern Germany)

The facies development and onlap pattern of the lower Danubian Cretaceous Group (Bavaria, southern Germany) have been evaluated based on detailed logging, subdivision, and correlation of four key sections using an integrated stratigraphic approach as well as litho-, bio-, and microfacies analyses. Contrary to statements in the literature, the transgressive onlap of the Regensburg Formation started in the Regensburg–Kelheim area already in the early Early Cenomanian Mantelliceras mantelli ammonite Zone and not in the Late Cenomanian. In the Early Cenomanian, nearshore glauconitic-bioclastic sandstones prevailed (Saal Member), followed by Middle to lower Upper Cenomanian mid-shelf siliceous carbonates intercalated with fine-sandy to silty marls (Bad Abbach Member). Starting in the mid-Late Cenomanian (Metoicoceras geslinianum ammonite Zone), a considerable deepening pulse during the Cenomanian–Turonian Boundary Event (CTBE) initiated the deposition of the deeper shelf silty marls of the Eibrunn Formation, which range into the early Early Turonian. During the CTBE transgression, also the proximal Bodenwöhrer Senke (ca. 40 km NE of Regensburg) was flooded, indicated by the onlap of the Regensburg Formation onto Variscan granites of the Bohemian Massif, overlain by a thin tongue of lowermost Turonian Eibrunn Formation. A detailed record of the positive δ¹³C excursion of the global Oceanic Anoxic Event (OAE) 2 has been retrieved from this shallow-water setting. An integrated approach of bio-, event-, carbon stable isotope and sequence stratigraphy was applied to correlate the sections and to decipher the dynamics of this overall transgressive depositional system. The Cenomanian successions show five prominent unconformities, which correlate with those being known from basins in Europe and elsewhere, indicating their eustatic origin. The rate of sea-level rise during the CTBE suggests glacio-eustasy as a driving mechanism for Late Cenomanian sea-level changes. The Regensburg and Eibrunn formations of the lower Danubian Cretaceous Group are highly diachronous lithostratigraphic units. Their regional distribution and northeast-directed onlap pattern onto the southwestern margin of the Bohemian Massif can readily be explained by the lateral movements of roughly coast-parallel (i.e., NW/SE-trending) facies belts of a graded shelf system transgressing on a northeastward-rising substrate. It took the Cenomanian coastline ca. 6 Ma to transgress from southwest of Regensburg to the topographically elevated granite cliffs southeast of Roding in the Bodenwöhrer Senke (=60 km distance).     

Re-interpretation of a Lower–Middle Cambrian West Gondwanan ramp depositional system: a case study from the Cantabrian Zone (NW Spain)

Detailed litho- and biofacies investigations of the Lower–Middle Cambrian carbonate Láncara Formation resulted in its subdivision into nine lithofacies types: (1) claystone, (2) recrystallized mudstone, (3) laminated mudstone with laminoid-fenestral fabrics, (4) stromatolite, (5) laminated aggregate grainstone, (6) non-laminated aggregate grainstone, (7) oolitic-bioclastic floatstone, (8) echinodermal packstone, and (9) bioclastic grainstone. The thicknesses of lithofacies 1–7 (lower member of the Láncara Formation) decrease from south to north. Lithofacies types 8–9 (upper member of the Láncara Formation) are characterized by similar thicknesses and low facies and faunal gradients and are thus indicative of deposition on a carbonate ramp. From palaeoecological, palaeo(bio)geographical, palaeomagnetic, and tectonic considerations, the depositional environment of the Láncara Formation is re-interpreted as an eastward/north-eastward sloping, low morphology carbonate ramp. The Cantabrian Zone, with a primary lateral extension of about 300 km, is further construed to be an element of a widespread and connected, discontinuous drowned Perigondwanan depositional system.     

Biostratigraphy and paleoecology of the Oligo-Miocene succession in Fars and Khuzestan areas (Zagros Basin,SW Iran)

Paleontological and biostratigraphical studies on carbonate platform succession from southwest Iran documented a great diversity of shallow-water benthic foraminifera during the Oligocene–Miocene. Larger foraminifera are the main means for the stratigraphic zonation of carbonate sediments. The distributions of larger benthic foraminifera in two outcrop sections (Abolhayat and Lali) in the Zagros Basin, Iran, are used to determine the age of the Asmari Formation. Four assemblage zones have been recognized by distribution of the larger benthic foraminifera in the study areas. Assemblage 3 (Aquitanian age) and 4 (Burdigalian age) have not been recognized in the Abolhayat section (Fars area), due to sea-level fall. The end Chattian sea-level fall restricted marine deposition in the Abolhayat section and Asmari Formation replaced laterally by the Gachsaran Formation. This suggests that the Miocene part of the formation as recognized in the Lali section (Khuzestan area) of the Zagros foreland basin is not present in the Abolhayat outcrop. The distribution of the Oligocene larger benthic foraminifera indicates that shallow marine carbonate sediments of the Asmari Formation at the study areas have been deposited in the photic zone of tropical to subtropical oceans. Based on analysis of larger benthic foraminiferal assemblages and microfacies features, three major depositional environments are identified. These include inner shelf, middle shelf and outer shelf. The inner shelf facies is characterized by wackestone–packstone, dominated by various taxa of imperforate foraminifera. The middle shelf is represented by packstone–grainstone to floatstone with a diverse assemblage of larger foraminifera with perforate wall. Basinwards is dominated by argillaceous wackestone characterized by planktonic foraminifera and large and flat nummulitidae and lepidocyclinidae. Planktonic foraminifera wackestone is the dominant facies in the outer shelf.     

Record of very high energy events in Plio-Pleistocene marine deposits of the Gulf of Cadiz (SW Spain): facies and processes

The depositional conditions that characterized the sedimentary filling in the southern sector of the Guadalquivir Basin during the late post-orogenic Neogene have been established through the sedimentological study of the Plio-Pleistocene outcrops along the Cadiz coast (SW Spain). The study has contributed to a better interpretation of the regional stratigraphy and helped to establish both depositional mechanisms and processes. Deposits show different lithofacies according to the dominant climatic and prevailing environmental conditions. Pliocene deposits show bioclastic lithofacies with abundant warm-water fossils, whereas Pleistocene sediments have a low fossil content. Stratigraphic sections indicate important depositional changes: sandstone and grainstone were deposited under a seasonal regime, whereas accumulations of large boulders and bioclasts are interpreted as event deposits, the product of episodic oceanographic processes, such as huge storms or tsunamis. These deposits do not have a seasonal character; however, given their relative frequency in the stratigraphic sections, they were probably associated with neo-tectonic activity in the Guadalquivir Foreland Basin, which was an important controlling factor in this basin. The proximity to the Africa-Eurasia plate boundary together with several historically documented earthquakes and tsunamis in the study area, suggest that these processes could explain the origin of these deposits. The seismic-tectonic activity was more intense between the late Pliocene and early Pleistocene, as shown by the presence of a well-marked angular unconformity, as well as by a higher frequency of the very high energy clastic and bioclastic accumulations.     

Lateral variability of shallow-water facies and high-frequency cycles in foreland basin carbonate platforms (Pennsylvanian,NW Spain)

The kilometer-sized and 100-meter-thick carbonate platforms of the Escalada Fm. I and II (Middle Pennsylvanian) accumulated in the foredeep of a marine foreland basin during the transgressive phases of 3rd-order sequences and were buried by prograding siliciclastic deltaic systems in the course of the subsequent highstand. The carbonate successions show a general upward trend from grain- to mud-supported carbonates, interfingering landwards with siliciclastic deposits of a mixed siliciclastic-carbonate shelf (Fito Fm.) adjacent to deltaic systems. The spatial variability of the carbonate facies and the high-frequency (4th–5th order) cycles, from the platform margin-outer platform to the deltaic systems, has been interpreted from basin reconstruction. Carbonate facies include skeletal grainstone to packstone, ooidal grainstone, burrowed skeletal wackestone, microbial and algal boundstone to wackestone forming mounds, various algal bafflestone and coral biostromes in areas with siliciclastic input. These high-frequency transgressive–regressive cycles are interpreted to record allocyclic forcing of high-amplitude glacioeustasy because they show characteristic features of icehouse cycles: thickness >5 m, absence of peritidal facies, and in some cases, subaerial exposure surfaces capping the cycles. In the mixed cycles, siliciclastics are interpreted as late highstand to lowstand regressive deposits, whereas carbonates as transgressive-early highstand deposition. The lateral and vertical variability of the facies in the glacioeustatic cycles was a response to deposition in a rapidly subsiding, active foreland basin subjected to siliciclastic input, conditions that might be detrimental to the growth of high-relief carbonate systems.     

Microfacies and cycle stacking pattern in Liassic peritidal carbonate platform strata, Gavrovo-Tripolitza platform, Peloponnesus, Greece

Platform carbonate sediments of Liassic age cropping out in the area of the Pigadi-Fokianos Gulf (SE of Leonidion, Peloponnesus) have been investigated in order to determine their depositional environment. Facies analysis allowed the recognition of several microfacies types and their cyclic stacking pattern. The carbonates were deposited in a restricted inner platform environment (lagoon-peritidal domain) and are arranged into small-scale shallowing-upward cycles. Palaeosol horizons containing typical pedogenic features are developed on the top of the peritidal facies or are directly superimposed on subtidal deposits, forming diagenetic caps. This implies repeated sea-level fluctuations and periodic emersion episodes. The presence of orbitally forced cyclicity though is mostly probable, cannot be clearly documented by the available data. The studied carbonates are comparable with other coeval analogous peritidal cycles of the same age along the southern margin of the Tethys.