Geologica Acta

Mineral chemistry and P-T conditions of the Karakaya volcanites at Kırka-Afyon-Isparta volcanic province, Afyon, Turkey

irem Aksoy — 2024-05-10

The Kırka-Afyon-Isparta Volcanic Province (KAIVP) is one of the best known regions in Turkey for the origin and petrological evolution of the high potassium volcanic activity. The temporal and spatial variability of volcanic rocks in the region exerts significant control over their geochemical diversity. Alkaline and ultrapotassic volcanic rocks of the Afyon volcanism are the first products of asthenospheric origin after the orogenesis in western Anatolia. We have determined the mineralogical and petrographic properties of the Karakaya volcanites surrounding Afyon with the help of microprobe analyses. Estimated thermobarometers are calculated. The Karakaya volcanites have been grouped into four different units according to their their mineralogical, petrographic and geochemical characteristics: Seydiler ignimbirite, basaltic trachyandesite, trachyandesite, trachyte and lamproite. Most samples display hypocrystalline porphyritic texture, whereas samples of lamproite unit have a holocrystalline texture. Generally, volcanic units also exhibit some textural evidence of disequilibrium crystallisation, such as sieve texture and corrosion in plagioclase phenocrysts, zoning and inclusions in clinopyroxene phenocrysts. Mineral thermobarometric estimations in all suites were tested on clinopyroxene and feldspar compositions, considering different authors’ approaches. Values of temperatures and pressure range from 1105 to 1273ºC and 5.6 to 12.2kbar, respectively. The temperature and pressure values calculated from the mineral-melt associations in the volcanics suggest that the Afyon Volcanites were affected by magma mixing processes and crystallised at different depths during the transport of magma.

Resumen

La provincia volcánica de Kırka-Afyon-Isparta es una de las regiones más conocidas de Turquía por su origen y evolución petrológica de actividad volcánica rica en potasio. La variabilidad temporal y espacial de las rocas volcánicas de la región ejerce un control significativo sobre su diversidad geoquímica. Las rocas volcánicas alcalinas y ultrapotásicas del vulcanismo de Afyon son los primeros productos de origen astenosferico después de la orogénesis en Anatolia occidental. Se han determinado las propiedades mineralógicas y petrográficas de la vulcanita de Karakaya que rodea Afyon mediante análisis de microsonda. Se calcuan los parámetros termobarometricos estimados. Las vulcanitas de Karakaya se han agrupado en cuatro unidades diferentes en función de sus características mineralógicas, petrográficas y geoquímicas: ignimbrita de Seydiler, traquiandesita basáltica, traquiandesita, traquita y lamproíta. La mayoría de muestras tienen una estructura porfídica hipocristalina mientras que, las muestras de la unidad de lamproíta tienen una textura holocristalina. Generalmente, las unidades volcánicas también presentan evidencias texturales de cristalización desordenada, como textura de tamiz y corrosión en los fenocristales de las plagioclasas y zonación e inclusiones en los fenocristales de los clinopiroxenos. Las estimaciones termobarométricas de los minerales se probaron en composiciones de clinopiroxeno y feldespato, considerando los enfoques de diferentes autores. Los valores de temperatura y presión oscilan entre los 1105 y 1273ºC y entre 5.6 y 12.2kbar, respectivamente. Los valores de presión y temperatura calculados a partir de las asociaciones de mineral-fundido en los volcanes sugieren que las vulcanitas de Afyon han estado afectadas por procesos de mezcla de magma y de cristalización a diferentes profundidades durante el transporte de magma.

Palabras clave: Química Mineral, Termobarometría, KAIVP, Volcanitas Karakaya, Turquía Occidental.

Resum

La província volcànica de Kırka-Afyon-Isparta és una de les regions més conegudes de Turquia per l’origen i evolució petrològica d’activitat volcànica rica en potassi. La variabilitat temporal i espacial de les roques volcàniques de la regió exerceix un control significatiu sobre la seva diversitat geoquímica. Les roques volcàniques alcalines i ultrapotàssiques del vulcanisme d’Afyon són els primers productes d’origen astenosfèric després de l’orogènesi a Anatòlia occidental. S’han determinat les propietats mineralògiques i petrogràfiques de la vulcanita de Karakaya que envolta Afyon amb l’ajuda d’anàlisis de microsonda. Es calculen els paràmetres termobaromètrics estimats. Les vulcanites de Karakaya s’han agrupat en quatre unitats diferents segons les seves característiques mineralògiques, petrogràfiques i geoquímiques: ignimbrita de Seydiler, traquiandesita basàltica, traquiandesita, traquita i lamproïta. La majoria de mostres tenen una textura porfírica hipocristal·lina mentre que, les mostres de la unitat de lamproïta tenen una textura holocristal·lina. Generalment, les unitats volcàniques també presenten evidències texturals de cristal·lització desordenada, com ara textura de tamís i corrosió als fenocristalls de les plagiòclasis i zonació i inclusions als fenocristalls dels clinopiroxens. Les estimacions termobaromètriques dels minerals es van provar en composicions de clinopiroxè i feldspat, considerant els enfocaments de diferents autors. Els valors de temperatura i pressió oscil·len entre 1105 i 1273ºC i entre 5.6 i 12.2kbar, respectivament. Els valors de pressió i temperatura calculats a partir de associacions de mineral-fos en els volcans suggereixen que els vulcanites d’Afyon han estat afectades per processos de barreja de magma i de cristal·lització a diferents profunditats durant el transport del magma.

Paraules clau: Química Mineral, Termobarometria, KAIVP, Volcanites Karakaya, Turquia Occidental.

Petrogenesis of the late Miocene Chenar volcanism in the southeast Urumieh-Dokhtar magmatic belt, Kerman, Iran: evidence from geochemical, U-Pb geochronologic, and Hf isotopic constraints

Hamideh Salehi Nejard — 2024-01-29

The Chenar volcanic cone intruded the southeastern part of the Dehaj-Sarduiyeh volcano-sedimentary belt, in the southeast Urumieh-Dokhtar magmatic arc in Iran. The adakitic rocks, with porphyritic texture, mainly consist of rhyodacites and dacites,commonly comprised of phenocrysts of plagioclase, hornblende and biotite, with rare K-feldspar in a groundmass composed of plagioclase, K-feldspar and quartz. They yielded U-Pb zircon ages of 5.52±0.099Ma, 5.46±0.12Ma, and 6.44±0.12Ma, and radiogenic ɛHf(t) values ranging from +3.1 to +12.7. The whole-rock geochemical analysis of these rocks reveals transitional calc-alkaline to shoshonitic characteristics.

The geochemical characteristics of the study rocks, particularly their high Sr/Y (⁓51.6-136.8) at low Y (⁓4.43–16.2ppm) and high La/Yb (⁓28.4–118.4ppm) at low Yb (⁓0.2–1.3ppm), are coherent with a high silica adakitic signature. The whole-rock positive Eu/Eu* anomaly and zircon Ce/Ce* anomaly reflect the effects of an oxidized magmatic signature where the rocks of the study area originated from a mantle source. The high silica adakite geochemical characteristics of the Chenar volcanic cone support formation by partial melting of the modified mantle under the influence of metasomatized subducted oceanic slab in a post-collisional environment.

Resumen

El cono volcánico de Chenar intruyó la parte sudoriental del cinturón volcano-sedimentario de Dehaj-Sarduiyeh, en el arco magmático sudoriental de Urumieh-Dokhtar, en Irán. Las rocas adacíticas, con textura porfídica, consisten principalmente en riodacitas y dacitas, comúnmente compuestas por fenocristales de plagioclasa, hornblenda y biotita, con poco feldespato K, en una masa de fondo compuesta por plagioclasa, feldespato K y cuarzo. Se obtuvieron edades de circón U-Pb de 5,52±0,099Ma, 5,46±0,12Ma, y 6,44±0,12Ma, y valores radiogénicos de ɛHf(t) que oscilan entre +3,1 y +12,7. El análisis geoquímico de toda la roca revela características transicionales de calcoalcalinas a shoshoníticas.

Las características geoquímicas de las rocas estudiadas, particularmente su alto Sr/Y (⁓51.6-136.8) a bajo Y (⁓4.43-16.2ppm) y alto La/Yb (⁓28.4-118.4ppm) a bajo Yb (⁓0.2-1.3ppm), son coherentes con una firma adacítica de alto contenido en sílice. La anomalía positiva Eu/Eu* en toda la roca y la anomalía Ce/Ce* en el circón reflejan los efectos de una señal magmática oxidada, con las rocas de la zona de estudio procedentes de una fuente del manto. Las características geoquímicas de la adakita con alto contenido en sílice del cono volcánico de Chenar apoyan la formación por fusión parcial del manto modificado bajo la influencia de la losa oceánica subducida metasomatizada en un entorno post-colisional.

Palabras clave: arco magmático Urumieh-Dokhtar, cinturón volcano-sedimentario Dehaj-Sarduiyeh, isótopos de Hf, datación por U-Pb, Adakita, Irán.

Resum

El con volcànic Chenar va intruïr a la part sud-est del cinturó volcànic-sedimentari Dehaj-Sarduiyeh, a l'arc magmàtic sud-est d'Urumieh-Dokhtar a l'Iran. Les roques adaquítiques, de textura porfírítica, són principalment riodacites i dacites, comunament formades per fenocristalls de plagiòclasi, hornblenda i biotita, amb poc K-feldspat, en una massa de fons composta per plagiòclasi, K-feldspat i quars. Es van obtenir valors d’edats de zircó U-Pb de 5,52±0,099Ma, 5,46±0,12Ma i 6,44±0,12Ma i valors radiogènics de ɛHf(t) que van des de +3,1 fins a +12,7. L'anàlisi geoquímica de roca sencera revela característiques de transició de calc-alcalines a shoshonítiques.

Les característiques geoquímiques de les roques d'estudi, especialment el seu elevat Sr/Y (⁓51,6-136,8) a baix Y (⁓4,43-16,2 ppm) i alt La/Yb (⁓28,4-118,4 ppm) a baix Yb (⁓0,2-1,3). ppm), són coherents amb una signatura adakítica d'alta sílice. L'anomalia Eu/Eu* positiva de tota la roca i l'anomalia del zircó Ce/Ce* reflecteixen els efectes d'una signatura magmàtica oxidada, amb les roques de l'àrea d'estudi originàries d'una font del mantell. Les característiques geoquímiques d'adakita d'alta sílice del con volcànic de Chenar donen suport a la formació mitjançant la fusió parcial del mantell modificat sota la influència de la llosa oceànica subduïda metasomatitzada en un entorn posterior a la col·lisió.

Paraules clau: arc magmàtic d'Urumieh-Dokhtar, cinturó volcànic-sedimentari de Dehaj-Sarduiyeh, isòtops Hf, datació U-Pb, adakita, Iran.

A MATLAB approach for developing digital rock models of heterogeneous limestones for reactive transport modeling

Atefeh Vafaie — 2024-06-10

Porosity is a key parameter controlling the physico-chemical behavior of porous rocks. Digital rock physics offers a unique technique for imaging the inherently heterogeneous rock microstructure at fine spatial resolutions and its computational reconstruction, through which a better understanding and prediction of the rock behavior can be achieved. In this study, we propose a simple but accurate method to build a 3D porosity map of centimeter-scale carbonate rock cores from X-ray Micro Computed Tomography (XMCT) imaging data. The method consists of 3 main steps: i) decomposition of 3D volumetric XMCT data into sub-volumes, ii) processing of equidistributed 2D cross-section images in each sub-volume and iii) 2D slice-by-slice calculation of porosity and its assembly to reconstruct a 3D continuum porosity map over the whole core domain using a MATLAB code. The proposed approach significantly conserves the required memory to manipulate large image datasets. The digitized porosity representations are used to build 3D permeability maps of the cores by applying an explicit permeability-porosity relationship. The permeability maps are used as input for numerical simulation of the rock response to the percolation of reactive fluids through which the general validity of the approach is verified. The developed digital rock model paves the way for an improved understanding of reactive transport in carbonate rocks.

Resumen

La porosidad es un parámetro clave que controla el comportamiento físico-químico de las rocas porosas. La física digital de rocas ofrece una técnica única para obtener imágenes de la microestructura rocosa, inherentemente heterogénea, a resoluciones espaciales finas y su posterior reconstrucción computacional. En este estudio, proponemos un método simple pero preciso para construir mapas de porosidad 3D de muestras de roca carbonatada a escala centimétrica a partir de datos de imágenes de Microtomografía de Rayos X (XMCT). El método, que usa un programa escrito en MATLAB, consta de 3 pasos principales: i) descomposición de los datos volumétricos 3D (XMCT) en subvolúmenes, ii) procesamiento de imágenes 2D (cortes transversales), equidistribuidas en cada subvolumen, y iii) cálculo de porosidad corte a corte, con su posterior ensamblaje para reconstruir un mapa de porosidad 3D continuo sobre todo el dominio de la muestra. El enfoque propuesto permite un aprovechamiento eficaz de la memoria necesaria para manipular grandes conjuntos de datos de imágenes. Las porosidades digitalizadas se utilizan para construir mapas de permeabilidad 3D de las muestras, aplicando una relación explícita de permeabilidad-porosidad. Estos mapas se utilizan como entrada para la simulación numérica de la respuesta de la roca a la percolación de fluidos reactivos, a través de la cual se verifica la validez general del enfoque. El modelo digital de la roca facilita el camino hacia una mejor comprensión del transporte reactivo en rocas carbonatadas.

Palabras clave: Tomografía computarizada. Física digital de rocas. Heterogeneidad de rocas. Reconstrucción de porosidad. Modelado de transporte reactivo.

Resum

La porositat és un paràmetre clau que controla el comportament fisicoquímic de les roques poroses. La física digital de roques ofereix una tècnica única per a la imatge de la microestructura de la roca, inherentment heterogènia, a resolucions espacials fines, i la seva reconstrucció computacional. En aquest estudi, proposem un mètode senzill però precís per construir mapes de porositat 3D de mostres de roca carbonatada a escala centimètrica a partir de dades d'imatges de Microtomografia de raigs X (XMCT). El mètode, que fa servir in programa escrit en MATLAB, consta de 3 passos principals: i) descomposició de dades volumètriques 3D (XCMT) en subvolums, ii) processament d'imatges 2D (seccions transversals), equidistribuïdes a cada subvolum, i iii) càlcul de porositat tall a tall i el seu muntatge per reconstruir un mapa de porositat continu en 3D sobre tot el domini de la mostra. L'enfocament permet un ús eficaç de la memòria necessària per manipular grans conjunts de dades d'imatge. Les porositats digitalitzades s'utilitzen per construir mapes de permeabilitat 3D de les mostres aplicant una relació explícita permeabilitat-porositat. Els mapes de permeabilitat s'utilitzen com a entrada per a la simulació numèrica de la resposta de la roca a la percolació de fluids reactius, mitjançant la qual es verifica la validesa general de l'enfocament. El model de roca digital facilita el camí per a una millor comprensió del transport reactiu en roques carbonatades.

Paraules clau: Tomografia computada. Física digital de roques. Heterogeneïtat de roques. Reconstrucció de porositat. Modelització de transport reactiu.

Mass occurrence of planktic dendroid graptolite synrhabdosomes (Calyxdendrum) from the Early Ordovician Fezouata biota of Morocco

Juan Carlos Gutiérrez-Marco — 2024-07-04

The genus Calyxdendrum is here revised to include planktic dendroid graptolites from the Ordovician (Tremadocian to Sandbian). The mass occurrence of Calyxdendrum amicabilis n. sp. from the Fezouata biota represents one of the few occurrences of synrhabdosomes of dendroid morphology that have ever been discovered. Composite structures, formed from about four to six slender, conical tubaria of the species appear as umbrella-shaped synrhabdosomes. In these, the individual tubaria are connected by their short nemata forming an irregularly shaped proximal membrane. The species is found in the late Tremadocian Sagenograptus murrayi Biozone of the Bou Izargane section in the Ternata plain north of Zagora, Morocco. The mass occurrence is interpreted to represent planktic dendroid colonies transported by low velocity currents or moving actively into different water regions on a wide shallow shelf region. They settled in the “soupy” soft sediment, where they were subsequently compacted in the now lithified mudstone. Planktic dendroids of the genus Calyxdendrum are so far known exclusively from the peri-Gondwana region, but may prove to show a wider biogeographical distribution when better known.

Resumen

El género Calyxdendrum se revisa aquí para incluir graptolitos dendroides planctónicos del Ordovícico (Tremadociano a Sandbiano). La presencia masiva de Calyxdendrum amicabilis n. sp. en la biota de Fezouata representa una de las pocas apariciones de sinrabdosomas de morfología dendroide que se han descubierto. Las estructuras compuestas, formadas por alrededor de cuatro a seis tubarios cónicos delgados de la especie, aparecen como sinrabdosomas en forma de paraguas. En estos, los tubarios individuales están conectados por sus nemas cortos formando una membrana proximal de forma irregular. La especie se encuentra en la biozona de Sagenograptus murrayi del Tremadociano tardío de la sección Bou Izargane en la llanura de Ternata al norte de Zagora, Marruecos. La ocurrencia masiva se interpreta como una representación de colonias planctónicas de dendroides transportadas por corrientes de baja velocidad o moviéndose activamente hacia diferentes regiones de agua en una amplia región de plataforma poco profunda. Se asentaron en el sedimento blando "espeso", donde posteriormente se compactaron en la lutita ahora litificada. Los dendroides planctónicos del género Calyxdendrum se conocen hasta ahora exclusivamente en la región peri-Gondwana, pero podrían mostrar una distribución biogeográfica más amplia cuando se conozcan mejor.

Palabras clave: Ordovícico. Konservat-Lagerstätte. Marruecos. Dendroides planctónicos. Sinrabdosomas.

Resum

El gènere Calyxdendrum es revisa aquí per incloure graptolits dendroides planctònics de l'Ordovicià (Tremadocià a Sandbià). L'aparició massiva de Calyxdendrum amicabilis n. sp. a la biota de Fezouata representa una de les poques aparicions de sinrabosomes de morfologia dendroide que s'han descobert. Les estructures compostes, formades d'uns quatre a sis tubaris esvelts i cònics de l'espècie, apareixen com a sinrabosomes en forma de paraigua. En aquests, els tubàris individuals estan connectats per les seves nemes curtes formant una membrana proximal de forma irregular. L'espècie es troba a la biozona de Sagenograptus murrayi de la secció de Bou Izargane a la plana de Ternata al nord de Zagora, Marroc. S'interpreta que l'aparició massiva representa colònies de dendroides planctònics transportats per corrents de baixa velocitat o movent-se activament a diferents regions d'aigua en una àmplia regió de plataforma poc profunda. Es van instal·lar al sediment tou "caldós", on posteriorment es van compactar al fang ara litificat. Els dendroides planctònics del gènere Calyxdendrum es coneixen fins ara exclusivament a la regió peri-Gondwana, però podrien mostrar una distribució biogeogràfica més àmplia quan es coneixin millor.

Paraules clau: Ordovicià. Konservat-lagerstätte. El Marroc. Dendroides plànctònics. Sinrabdosomes.

Late Ediacaran carbonate production and REE+Y signatures tracing redox conditions in a Cadomian retroarc basin, Central Iberian Zone, Spain

J. Javier Alvaro — 2024-09-20

The late Ediacaran carbonate production recorded in a Cadomian retroarc basin from the Iberian Peninsula provides an excellent opportunity to evaluate the tectonic and redox factors that controlled the infill of the foredeep troughs, located between uplifted orogenic wedges and exposed forebulge transects. In the Central Iberian Zone of the Iberian massif, the carbonates of the Villarta Formation follow two geographic belts, which represent short-term mosaics of uplifted and tilted fault-bounded basement highs. These recorded the nucleation of fringing reefal (rich in Cloudina and Sinotubulites microfossils embedded in thromboid textures) and shoal and back-barrier complexes, which episodically fed slope-related megabreccia lobes and channels. REE+Y datasets from the impure carbonates reflect contamination by detrital material, hydrothermal interaction and variable redox conditions, ranging from oxic to dysoxic, the latter emphasized by the deposition of kerogenous black shales in distal parts of the foredeep trough.

Investigation of numerical and analytical solutions of 1D steady and transient flow in unsaturated layered soils

Ahmed Chetti — 2024-10-31

This study presents a comprehensive numerical simulation and analytical modeling of steady and transient flow in heterogeneously saturated soils. Solving the Richards equation involves challenges due to the nonlinearity between the pressure and the water content. Two constitutive models are used to describe the complex relationships between moisture content, hydraulic head, and hydraulic conductivity namely, Gardner model and Van Genuchten-Mualem model. Through detailed simulations, four configurations are investigated, including the capillary barrier effect, bi-layered soil dynamics in paddy fields, and infiltration in multi-layered soil in both saturated and unsaturated steady-state regimes. The comparison between numerical results and the established analytical model shows a good agreement. It underscores the usefulness of the model to reproduce saturated and unsaturated seepage flow in bi-layered and multi-layered soils. Moreover, it captures the dynamic interactions between infiltration and evaporation during the transient phase. These findings offer insights for water resource management, land subsidence mitigation, and environmental sustainability.

Geometrical characterization of fracture systems using point clouds and SEFL-Software: example of the Añisclo anticline carbonate platform, Central Pyrenees

David Garcia-Sellés — 2024-09-30

Natural fracture systems contribute significantly to rock mass anisotropies. Characterizing these systems is essential for understanding processes of fluid flow, energy exploration and storage, slope stability or tectonic processes that can affect the permeability or compaction of the material, as well as reflect its temporal evolution. This work presents a set of automatic and supervised algorithms integrated into the open-access software solution SEFL, designed to characterize fracture systems using remote sensing data sets. The software implements various strategies to quantify geometrical parameters with deterministic or stochastic descriptions, facilitating a detailed characterization of the fracture system for numerical simulations. Geological outcrops provide direct access to the rock masses and discontinuities, offering analogies with materials that are otherwise inaccessible for its direct study. The digital acquisition of the terrain using high-resolution techniques, such as Terrestrial Laser Scanner (TLS) or photogrammetry to obtain point clouds, enabled post-field studies, particularly for fracture systems that are complex, inaccessible, or large in scale. Additionally, SEFL offers a tool based on the concept of fracture stratigraphy to identify mechanical units, which are essential frameworks for measuring and calculating fracture properties. This new methodology has been applied to study the fractured Eocene limestone outcrop at the hinge of the Añisclo anticline (South-Central Pyrenees, NE Iberia) which has been digitally acquired and characterized. SEFL output data interpretations revealed an outcrop characterized by over two thousand modelled fractures, five fracture sets, fourteen fracture stratigraphic units, and 1-2 fractures/m.

Fossil corals with skeletal lesions comparable to modern ones

Telm Bover-Arnal — 2024-11-19

Whereas post-mortem bioerosional features such as bivalve, sponge or worm borings are frequently preserved in ancient corals, reports of ante-mortem skeletal anomalies are rare and virtually non-existent from Mesozoic specimens. Here, we document the occurrence of fossil skeletal lesions produced during the life span of the colonies in exceptionally well-preserved Aptian (Early Cretaceous) scleractinians from the Maestrat Basin (East Iberia). These ante-mortem damage features are characterized by millimetric to centimetric areas of skeletal depression, as well as upward growth around damaged areas indicating regeneration. Depressed skeletal lesions are commonly overprinted by post-mortem lithophagid borings. Distribution of skeletal anomalies on the colonies can be focal or multifocal, and their location basal, medial and/or apical. The extent of the skeletal anomalies can be mild (occupying <10% of the colony) to extreme (occupying ≥50% of the colony). The edges of the skeletal anomalies are distinct (disk-shaped) or annular (ring-shaped), the margins are mainly smooth to uneven, and the shapes are circular, oblong, pyriform, linear, or irregular. The skeletal anomalies exhibited by the corals are comparable to tissue lesions produced in modern corals either by predation, bioerosion or disease, which may be followed by skeletal overgrowth or denudation. Although demonstrating disease in fossil colonies is challenging, there is no reason to believe that corals did not experience diseases back in the Cretaceous. This paper gives an example of the potential of coral anomalies originating from tissue lesions and skeletal damage to be preserved in the geological record, a factor that may have been often overlooked in the study of fossil coral communities.

Decapod assemblages from the Aptian-Albian transition of the eastern Maestrat Basin (Iberian Chain)

Àlex Ossó — 2024-10-24

Two decapod (Arthropoda: Malacostraca: Decapoda) assemblages from two newly discovered localities near Torreblanca (Castelló, Valencian Country, Spain), situated in the Orpesa Sub-basin of the Maestrat Basin, are described. The first assemblage exhibits a diverse fauna of lobsters, including erymoids, glypheoids and nephropoids representatives of five different genera, some of them reported for the first time in Iberia, as well as brachyuran crabs, primarily palaeocorystoids, including one new species, Paranecrocarcinus xivertensis. It is assigned to the uppermost Aptian of
the Benassal Formation. The second assemblage, found in the lower Albian Escucha Formation, showcases an exceptional richness of exquisitely preserved complete remains of a new genus and species of axiidean ghost shrimp, Cretagourretia salasi, along with some palaeocorystoids, also representatives of a new species, Joeranina tausi, within a varied community of invertebrates and plants. This work investigates the paleoenvironment in which these assemblages thrived, and explores their faunal similarities with other decapod assemblages from the nearby Garraf Basin, as well as more distant ones such as the Basque-Cantabrian Basin and the Isle of Wight. An ammonite occurrence, likely belonging to the genus Roberticeras, has been identified in the upper Aptian Benassal Formation. Additionally, the juvenile stage of the ammonite Parengonoceras bassei from the lower Albian Escucha Formation is reported and described for the first time. The study provides valuable insights into reconstructing coastal to marine environments and the associated biota that developed in the Maestrat Basin during the Aptian-Albian transition.

Linking high-frequency lacustrine sequences to orbitally-induced cyclicity (Lower Cretaceous, Iberian Basin)

Natalia Illueca — 2024-11-12

The lacustrine El Castellar Formation in the Castillo de Aliaga section (Early Cretaceous Galve sub-basin, eastern Spain) features two carbonate successions of marl and limestone, separated by a mudstone and marl interval. Sequence analysis revealed small-scale (44 elementary sequences), medium-scale (ten complete and two incomplete parasequences), and large-scale (three sets of parasequences, one incomplete), high-frequency lacustrine sequences, with an average thickness of 2.9, 12.4 and 54m, respectively. These sequences start with a sudden facies change (deepening) and exhibit a shallowing-upward trend with features of subaerial exposure (bioturbation, oxidation, or brecciation) at the top, indicating phases of climate-modulated lake expansion and retraction. The temporal framework of the lacustrine sequences is further characterized by the correlation of these sequences with sedimentary-cycle periodicities of 3.3, 13.2 and 57.3m, attributed, respectively, to the long precession cycle (22.4kyr) and the short (95kyr) and long (405kyr) eccentricity cycles of the Earth’s orbit. The hierarchical stacking of sequences aligns with orbitally driven cyclicity, with thickness variations interpreted as tectonic subsidence effects (accommodation) resulting from normal fault slip in a rift system. The three sets of parasequences (SPS-1 to SPS-3) align with stages of lake system evolution. SPS-1 represents deposition in a lowenergy shallow carbonate lake. SPS-2 indicates a significant lake expansion and deepening, linked with clastic input and a mixed lake system, and correlates with a major increase in accommodation, over ~200kyr, involving fault-induced local tilting. SPS-3 represents deposition in a high-energy carbonate lake. The parasequences identified show variations in cyclic thickness tied to a >700kyr tectonic cycle. The elementary sequences, mainly corresponding to marl-limestone bundles, exhibit thickness changes probably due to shorter-term tectonic pulses. Accelerated tectonic activity resulted in increased accommodation in shorter (40-50kyr) periods, followed by longer (>100kyr) periods of progressive deceleration.