Factors controlling the sedimentary evolution of the Kimmeridgian ramp in the north Iberian Basin (NE Spain)

The aim of this paper is to summarize the present knowledge reached by the authors on the carbonate ramp which developed in the iberian basin during Kimmeridgian times. Our results were obtained from a combined field analysis and computer modelling carried out in the north Iberian Chain (NE Spain). Extensive field analysis in the Ricia area (Zaragoza, NE Spain), resulted in a detailed mapping of the transition from inner to outerramp facies on this carbonate rampo Three facies belts may be distinguished in this rampo The outer ramp facies consists of marls and mudstones rhythmic facies. The inner ramp facies, located aboye fair-weather wave base, are dominated by coral patch reef growing. The middle ramp facies are represented by marls and micrites bearing skeletal and oolitic tempestite levels which sharply grade into high-amplitude o'olitic sandwave. Factors such as resedimentation by storms, carbonate production and relative variation of sea level acting in the Kimmeridgian ramp are also quantiphied and discussed. Most of the mud accumulated in outer-ramp areas was produced in the coral «carbonate factory» located in inner areas. Off-shore resedimentation by storm was the main agent of basinward transport of this mudo The deduced accommodation curve consists of three elements: a linear rise which satisfactorily matches the normal subsidence figures observed in intracratonic basins; a third-order cycle, that may have a regional cause and higher order cycles in the Milanckovich band, that may be eustatic in origin.La sedimentación en la cuenca ibérica septentrional durante el Kimmeridgiense tuvo lugar en una extensa rampa carbonatada de bajo ángulo. Las facies de rampa externa, acumuladas por debajo del nivel de base del oleaje debido a tormentas (i.e., C. 50 to 80 m de profundidad), están formadas por una ritmita de margas y calizas (i.e., Fm Loriguilla). Las facies de rampa interna, localizadas por encima del nivel de base del oleaje de buen tiempo (i.e., hasta 10 m de profundidad), están dominadas por bioconstrucciones de corales (i.e .. Fm Torrecilla). Las facies de rampa media están representadas por margas y micritas con niveles de tempestitas bioclásticas y oolíticas que pasan lateral y verticalmente a sandwaves oolíticos de gran amplitud (i.e., Mb. Ricia). La modelización por ordenador ha permitido cuantificar algunos aspectos de esta rampa. Así, la distancia de resedimentación mar adentro del sedimento de grano fino producido en las zonas internas de la rampa, por el efecto de tormentas, puede ser de hasta 40 Km. La producción de carbonato oscilaría entre 8 y 2 cm/l.000 años. en función de la profundidad. Por otra parte, la curva de la variación de la acomodación deducida para el Kimmeridgiense está compuesta por tres elementos: un ascenso lineal de 4 cm/l.000 años. un ciclo de tercer orden de baja amplitud y ciclos de mayor orden. de 20.000 y 100.000 años respectivamente. Tanto el ascenso lineal como el ciclo de tercer orden se han relacionado con causas regionales, mientras que los ciclos de mayor orden se encuentran en la banda de Milanckovich y pueden ser por tanto de origen eustático

A mud-dominated coastal plain to lagoon with emerged carbonate mudbanks: The imprint of low-amplitude sea level cycles (mid-Upper Cretaceous, South Iberian Ramp)

The middle Santonian-lower Campanian carbonate-mud dominated succession deposited in the northeastern margin of the South Iberian Ramp (La Cañadilla Fm, NE Spain) shows a complex set of interfingered facies developed in a low-energy and low-gradient shallow-marine to coastal environment. Three facies belts characterize the environment reconstructed in this work: (1) a low-energy shallow marine lagoon dominated by radiolitid rudist limestones and miliolid-rich facies with variable carbonate-mud content; (2) a transitional belt with a patchy distribution of ponds and mudbanks. This belt mostly consists of miliolid-rich limestones with variable amount of fenestral porosity, which are interfingered with charophytes and gastropod marls and limestones usually mixed with miliolids; (3) a coastal plain with strong freshwater influence characterized by the sedimentation of marls and limestones with charophytes, gastropods and root traces and intraclastic/black pebble limestones. The studied succession is arranged in high-frequency sequences, including meter-scale parasequences bounded by widespread flooding surfaces, which stack in five larger-scale shallowing-upward sequences (6–20 m thick). The time calibration of these sequences obtained from strontium isotopes and biostratigraphic data (benthic foraminifera) suggests a major control in the sedimentation by climate-driven low-amplitude sea level oscillations formed in tune with the long- and short-eccentricity orbital cycles. Cyclic sea level rises controlled the existence of widespread flooding events in the low-gradient carbonate ramp at the onset of parasequences, which in the studied marginal areas of the South Iberian Ramp were mostly sourced from the southern Tethyan realm. Therefore, the La Cañadilla Fm provides an example of a complex shallow marine to coastal system giving rise to a mosaic distribution of carbonate-mud dominated facies, with sedimentation mostly influenced by external factors resulting in a well-defined stratigraphic architecture. The similarities with modern analogous systems such as the Ten Thousand Islands of the Florida Bay are discussed in this paper. © 2022 Elsevier B.V

A New Calcareous Nannofossil Record from the Lower Jurassic of Kermanshah, Western Iran: Implications for Biostratigraphy and Evolutionary Reconstructions

Calcareous nannofossils are used here for the first time in order to establish a precise biostratigraphic framework for the Kermanshah Radiolarite Formation, an outcropping in Western Iran. The new data presented here challenge the previous tentative age interpretations (Pliensbachian to early Toarcian) based upon radiolarians. Calcareous nannofossil assemblages and events unequivocally indicated that the pelagic limestones and marls are late Sinemurian in age (NJT 3b nannofossil subzone), and that these are thrusted over shales and cherts dated as uppermost Sinemurian (NJT 3b-c nannofossil subzone) and lowermost Pliensbachian (NJT 4 nannofossil zone). This result leads not only to reconsideration of the age of the radiolarite formations, which are widespread in the Zagros orogenic system, but also a better understanding of the stratigraphic relationships between the various lithological units known in the area. Besides these new stratigraphic inferences, the calcareous nannofossil assemblages of the uppermost Sinemurian– lowermost Pliensbachian successions revealed the common presence of new morphologies of the Mitrolithus genus, never described before. These findings allow for the description of three new species, M. montgolfieri, M. pseudonannoconus, and M. tethysiensis, and reveal the existence of homeomorphy between the spine structure of conical Lower Jurassic coccoliths and the widespread Cretaceous nannoconids. © 2022 by the authors. Licensee MDPI, Basel, Switzerland

Facies mosaic in the inner areas of a shallow carbonate ramp (Upper Jurassic, Higueruelas Fm, NE Spain)

The internal facies and sedimentary architecture of an Upper Jurassic inner carbonate ramp were reconstructed after the analysis and correlation of 14 logs in a 1 × 2 km outcrop area around the Mezalocha locality (south of Zaragoza, NE Spain). The studied interval is 10–16 m thick and belongs to the upper part of the uppermost Kimmeridgian–lower Tithonian Higueruelas Fm. On the basis of texture and relative proportion of the main skeletal and non-skeletal components, 6 facies and 12 subfacies were differentiated, which record subtidal (backshoal/washover, sheltered lagoon and pond/restricted lagoon) to intertidal subenvironments. The backshoal/washover subenvironment is characterized by peloidal wackestone–packstone and grainstone. The lagoon subenvironment includes oncolitic, stromatoporoid, and oncolitic-stromatoporoid (wackestone and packstone) facies. The intertidal subenvironment is represented by peloidal mudstone and packstone–grainstone with fenestral porosity. Gastropod-oncolitic (wackestone–packstone and grainstone) facies with intercalated marl may reflect local ponds in the intertidal or restricted lagoon subenvironments. Detailed facies mapping allowed us to document 7 sedimentary units within a general shallowing-upward trend, which reflect a mosaic distribution, especially for stromatoporoid and fenestral facies, with facies patches locally more than 500 m in lateral extent. External and internal factors controlled this heterogeneity, including resedimentation, topographic relief and substrate stability, combined with variations in sea-level. This mosaic facies distribution provides useful tools for more precise reconstructions of depositional heterogeneities, and this variability must be taken into account in order to obtain a solid sedimentary framework at the kilometer scale.

Sedimentary architecture of a prograding oolitic-siliciclastic wedge: Response to changes in wave-base oscillation (Kimmeridgian, Iberian Basin)

A detailed facies and sequential architectural analysis has been carried out along the wedge-shaped shallow marine cross-bedded oolitic-siliciclastic Ricla Member (Kimmeridgian, Northern Iberian Basin). The obtained results are based on fieldwork along the 4 × 1 km continuous outcrops with the use of high-resolution photomosaics and drone-made videos, which have led to a precise and extensive facies reconstruction. Three main facies that are laterally related (A to B to C) in down-dip direction have been differentiated, which correspond to the topset, foreset and bottomset parts of a sloping depositional surface. Sedimentation was controlled by sweeping drift and downwelling storm-induced currents causing avalanching processes, with the deep action of oscillatory currents. The sedimentary architecture consists in 5 successive units composed by several sub-units, arranged according to different stacking patterns, which reflect the sedimentary response to wave-base oscillations superimposed to the regressive part of a third-order transgressive-regressive cycle. The sedimentological features indicate that this unit, which has been previously interpreted as a dune complex fit with an infralittoral prograding wedge model, as it is observed in geographically close and stratigraphically similar units. The Ricla Member is therefore regarded as an example of a well-exposed grain-supported unit with broad potential application to other prograding grain-dominated lithosomes that do not conform to the traditional sand shoal model

El Jurásico superior de la Sierra de Aralar (Guipuzcoa y Navarra): caracterizacion sedimentológica y paleogeográfica

Facies analysis carried out in the Upper Jurassic of the Sierra de Aralar (Eastern Basc-Cantabric Basin), give new information on the sedimentary evolution and palaeogeographic distribution of the sedimentary domains. Two depositional sequences are defined. The Lower Sequence is Oxfordian in age and ineludes two types of facies, developed in middle ramp areas. The more proximal peloidal and skeletal packstones grades to the SW into the more distal sponge, ammonite and belemnite wackestones. The Upper Sequence expands from Late Oxfordian to Kimmeridgian and consists of four types of facies. Both the sandy and the oolithic, skeletal and intraelastic facies were developed in the inner ramp areas (delta front and associated subtidal shoals). In the middle ramp areas, sedimentation was dominated by both the oolithic and peloidal and the coraline facies. The carbonate ramp was opened to the SE. The source for the elastic material, located to the N, were the elevated areas of the Ebro Massif. The Lower Sequence shows a progradational facies arrangernent, which has been interpreted as a highstand systems tract. The Upper Sequence display a retrogradationalprogradational evolution, which would define both a transgressive and highstand systems tract. The comparison of these sequences to the ones previously defined in the Iberian basin allows to state that the driving mechanism creating the accommodation in the basin was related to regional, tectono-eustatic changes.El análisis de facies realizado en el Jurásico superior de la Sierra de Aralar (Cuenca Vasco-Cantábrica oriental) ha permitido establecer nuevas precisiones en tomo a la evolución sedimentaria y a la distribución paleogeográfica de los dominios de sedimentación. Se han reconocido dos secuencias deposicionales. La Secuencia inferior, de edad Oxfordiense, está constituida por packstone de peloides y bioelastos que hacia los dominios más distales pasan a wackestone de esponjas, ammonites y belemnites. Estas facies se depositaron en la zona media de una rampa que presentó sus dominios distales abiertos hacia el SW. La Secuencia superior, de edad Oxfordiense superior-Kimmeridgiense, está formada por cuatro tipos de facies. Las facies arenosas y facies de ooídes, bioelastos e intraelastos corresponden al desarrollo de un delta y de barras submareales someras situadas en los dominios internos de la rampa. Las facies de ooides y peloides y las facies coralinas se interpretan como bajíos y arrecifes desarrollados en las zonas medias de la rampa. Esta rampa presentó sus dominios distales abiertos hacia el SE. El área fuente del material detrítico correspondería a un paleorrelieve situado al N, que formó parte del denominado Macizo del Ebro. La Secuencia inferior presenta un dispositivo progradante de facies, que se ha interpretado como correspondiente al cortejo de alto nivel del mar. La Secuencia superior muestra un dispositivo retrogradante-progradante , que constituyen respectivamente los cortejos transgresivo y de alto nivel del mar. La comparación de estas secuencias con las definidas en la cuenca ibérica permite establecer un posible control tectono-eustático en la evolución sedimentaria de las facies en las cuencas del E de Iberia

Evolución sedimentaria y paleogeografía del Jurásico Superior (Kimmeridgiense superior-Titónico) en la Sierra de Arcos (Cordillera Ibérica)

Facies analysis of the upper Kimmeridgian-Tithonian of the Sierra de Arcos (Iberian Chain) allowed the reconstruction of the sedimentary evolution during the deposition of two sequences, the so called J3.6 and J3.7 sequences defined by Aurell et al. (2000). Both sequences display a thin or even condensed transgressive systems tract, and a thick highstand and forced regressive systems tracts. Development of shallover facies in the distal part of the ramp was controlled by the so-called Montalbán-Ejulve High. Peloidal and oncolitic shoals were present during deposition of sequence J3.6, whereas peloidal shoals and coralgal patch reefs developed during the highstand of sequence J3.7. These set of shallow facies prograded over outer ramp facies (i.e., lime mudstone and marls). The influence of the sedimentary high is not obvious during deposition of the forced regressive systems tract of sequence J3.7, when the overall southeast progradation of the oolitic shoals and associated restricted environments took place

Cyclostratigraphy and chemostratigraphy of a bioclastic storm-dominated carbonate ramp (late Pliensbachian, Iberian Basin)

Deposition of regressive successions and coeval positive trend in the oxygen stable isotope record in relatively deep marine successions of the upper Pliensbachian of western European basins have been related to a cooling interlude within the warm greenhouse conditions of the Pliensbachian. Sedimentological, cyclostratigraphic and chemostratigraphic analyses carried out in two upper Pliensbachian successions exposed in the Iberian Chain (Obón and San Pedro localities, Spain) allowed the characterization of the imprint of this cooling interlude on the relatively shallow areas of the Iberian carbonate ramp. The upper Pliensbachian succession is characterized by skeletal limestones and encompasses proximal mid-ramp to proximal outer-ramp facies, in which resedimentation and reworking by storm-induced flows controlled the accumulation of bioclastic debris. Two orders of high-frequency, metre-scale sequences have been identified: bundles of beds, and deepening-shallowing sets of bundles. According to the age calibration (previous biostratigraphic data and new strontium isotopes data) and correlation with nearby sections, these sequences are suggested as formed in tune with the short-term and long-term eccentricity Milankovitch cycles. The isotopic data from brachiopod shells and belemnite rostra indicate progressively increasing d18O and slightly decreasing d13C trends for the uppermost Pliensbachian Spinatum Zone, reflecting the influence of cooling conditions. However, facies analysis reflects that the expected coeval long-term regression was interrupted by a tectonically driven transgressive event in the uppermost part of the Spinatum Zone

Estratigrafía secuencial y sedimentologÍa del Jurásico superior del noreste de Albacete

A Sequence Stratigraphic analysis carried out in the Upper Jurassic of the linking area between the Betic and Iberian Ranges (Albacete, SE Spain) has resulted in the identification of two depositional sequences (i.e., Kimmeridgian and Tithonian-Berriasian Sequences). Further division of systems tracts in the lower sequence was based on extensive facies analysis. This analysis also gave new information on the transition from inner to outer areas in the Kimmeridgian ramp. During lowstand systems tract, after a basinwards coastal shift, a deltaic prograding complex is observed in middle ramp areas. At the onset of the transgressive systems tract, flooding of the inner ramp areas was effective and fine grain carbonate deposition progressively covered the outer and middle ramp realms. Sandy and oolitic facies sharply prograded over middle ramp areas during highstand systems tracto During the Tithonian, a fast progradation of the bioclastic-peloidal facies (inner ramp) over the oncolitic- oolitic facies (middle ramp) took place. The comparison between the results reported here to others reached in previous works, allows to state that the overall evolution of the accommodation during the Late Jurassic was similar in the Iberian basin and resulted in a similar distribution of sequences and systems tracts. The driving mechanism creating the accommodation in the basin is interpreted to be related to regional, tectono-eustatic changes. Local differences observed on the facies are controlled by intra-basinal factors. In contrast to other marginal areas of the Iberian basin, which were dominated by high-amplitude oolitic sand-waves and extensive coral growing, marine restriction and larger c1astic input in the Albacete sector reduced the potential coral growing and diminished the effect of storms, as reflected by the lower amplitude of the oolitic bars.El Jurásico superior del noreste de Albacete se organiza en dos secuencias deposicionales que, por correlación con otros dominios de la cuenca Ibérica, se han denominado Kimmeridgiense y Titónico-Berriasiense. El análisis de las facies permite caracterizar el tránsito entre las zonas internas y externas de la rampa Kimmeridgiense, y reconocer tres estadios de evolución: (1) durante el cortejo de bajo nivel del mar tiene lugar la progradación de un complejo deltaico sobre dominios más externos dominados por una sedimentación margosa; (2) el cortejo transgresivo está constituido en las zonas proximales de la rampa por facies margosas y arenosas que pasan lateral y verticalmente a facies micríticas, definiendo un dispositivo retrogradante; (3) durante el cortejo de alto nivel del mar la rampa presentó un dominio sublitoral con sedimentación arenosa y oolítica, un dominio submareal somero con desarrollo de barras oolíticas y arenosas y un dominio externo con sedimentación de fango carbonatado. Durante el Titónico se produce una rápida progradación de las facies dominantemente bioclásticas y peloidales de rampa interna sobre las facies oncolíticas y 00líticas de rampa media. El emplazamiento paleogeográfico particular del sector de Albacete durante el Jurásico superior explica el tipo de facies presentes y sus diferencias respecto a otros dominios marginales de la cuenca Ibérica. Sin embargo, la evolución de la acomodación deducida es similar a la observada en el conjunto de la cuenca Ibérica. Estas observaciones demuestran que la distribución de facies, cortejos sedimentarios y secuencias estuvo controlada tanto por factores de extensión local como regional

Orbital cycles, differential subsidence and internal factors controlling the high-frequency sequence architecture in a Sinemurian shallow carbonate platform (Mallorca island, Spain)

The ~125 m thick lower to lowermost upper Sinemurian peritidal to shallow subtidal platform carbonates in the Llevant Mountains of Mallorca (Spain) have been analysed from four stratigraphic sections, to provide new data on the hierarchical stacking pattern of high-frequency depositional sequences. Due to the fact that in shallow water environments the stacking of carbonate facies can be controlled by external (allocyclic) and internal (autocyclic) processes, deciphering the dominant controls on the high-frequency sequence architecture of these platforms is a challenge. The studied carbonates encompass a high variety of facies representative of open lagoon, internal bars, restricted lagoon and tidal flats with local beach sands. Based on a detailed analysis of vertical facies trends and bounding surfaces, large-, medium- and small-scale sequences have been identified within the long-term transgressive-regressive facies cycle defined by the entire succession. Large-scale sequences (~10–30 m thick) and medium-scale sequences (~1–10 m thick) are generally shallowing-upward sequences bounded by sharp facies changes to relatively deeper facies, and have been related to sea-level variations driven by long- (~400 kyr) and short- (~100 kyr) eccentricity cycles respectively. The overprinting of differential subsidence (probably related to extensional tectonic) and carbonate production and accumulation processes varied throughout time, controlling the lateral continuity and preservation potential of the ~100 kyr medium-scale sequences. Shallowing-upward, locally aggradational, small-scale sequences (~0.3 to 5 m thick) are very variable in number and thickness and cannot be correlated between sections, pointing out that their most important controlling factor was the internal processes (hiatuses and erosion related to subaerial exposure at the peritidal caps, lateral migration of internal bars, local wave and currents patterns, depositional and erosional processes related to spring tides and storms) in the frame of a complex mosaic of facies within the studied platform