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[EN] Deserts are stressful environments where the living beings must acquire different strategies to survive due to the water stress conditions. From the late Albian to the early Cenomanian, the northern and eastern parts of Iberia were the location of the desert system represented by deposits assigned to the Utrillas Group, which bear abundant amber with numerous bioinclusions, including diverse arthropods and vertebrate remains. In the Maestrazgo Basin (E Spain), the late Albian to early Cenomanian sedimentary succession represents the most distal part of the desert system (fore-erg) that was characterised by an alternation of aeolian and shallow marine sedimentary environments in the proximity of the Western Tethys palaeo-coast, with rare to frequent dinoflagellate cysts. The terrestrial ecosystems from this area were biodiverse, and comprised plant communities whose fossils are associated with sedimentological indicators of aridity. The palynoflora dominated by wind-transported conifer pollen is interpreted to reflect various types of xerophytic woodlands from the hinterlands and the coastal settings. Therefore, fern and angiosperm communities abundantly grew in wet interdunes and coastal wetlands (temporary to semi-permanent freshwater/salt marshes and water bodies). In addition, the occurrence of low-diversity megafloral assemblages reflects the existence of coastal salt-influenced settings. The palaeobotanical study carried out in this paper which is an integrative work on palynology and palaeobotany, does not only allow the reconstruction of the vegetation that developed in the mid-Cretaceous fore-erg from the eastern Iberia, in addition, provides new biostratigraphic and palaeogeographic data considering the context of angiosperm radiation as well as the biota inferred in the amber-bearing outcrops of San Just, Arroyo de la Pascueta and La Hoya (within Cortes de Arenoso succesion). Importantly, the studied assemblages include Afropollis, Dichastopollenites

This Ph.D. thesis presents a high‐resolution palaeogeographical study of the onset and evolution of the largest ever recorded marine transgression, the “mid” Cretaceous transgression, in an exceptional setting located in the Western Tethys, at the eastern margin of Iberia: the Cuenca Basin (Spain). The study of the Cuenca Basin allows the accurate reconstruction of the time‐space evolution of the transgressive event due to:(1) The Albian to early Cenomanian sedimentary succession represents the sedimentary record of that major transgressive event. This succession is composed of the siliciclastic deposits of the Utrillas Gr, interpreted as an arid braidplain system, and the mixed shallow marine deposits of the La Bicuerca Mb (Aras de Alpuente Fm).(2) The basin is located at the interface between those areas entirely dominated by marine sedimentation during the “mid” and Late Cretaceous, and the areas that were dominated mainly by continental sedimentation until the transgression reached its climax during the Cenomanian‐Turonian boundary. Additionally, the Albian to early Cenomanian time in Iberia was characterised by: (a) representing the transition from the Late Jurassic‐Early Cretaceous syn‐rift stage to the Late Cretaceous post‐rift stage, and (b) being an extremely prolific time span regarding the deposit of amber‐bearing successions..., Esta tesis doctoral presenta un estudio de alta resolución sobre el comienzo y evolución de la mayor transgresión marina del Mesozoico, la transgresión del Cretácico “medio”, en un contexto privilegiado, localizado al oeste del Océano del Tethys, en el margen este de Iberia: La Serranía de Cuenca (España). El estudio de esta cuenca sedimentaria ha permitido realizar una reconstrucción espacio‐temporal precisa y pormenorizada del registro geológico de la transgresión debido a dos factores:(1) La sucesión sedimentaria Albiense ‐ Cenomaniense inferior representa el registro de la transgresión del Cretácico “medio”. Esta sucesión comprende un cambio lateral de facies entre los depósitos siliciclásticos del Gr. Utrillas, interpretados como una llanura alluvial de tipo braided, y los mixtos del Mb. La Bicuerca (Fm. Aras de Alpuente), interpretados como depositados en un ambiente marino somero.(2) La cuenca sedimentaria está localizada en una zona de transición entre las areas dominadas por sedimentación marina durante el Cretácico “medio” y Superior (hacia el SE de la zona de estudio), y la sáreas que estuvieron dominadas por sedimentación continental (localizadas al NO de la zona estudiada)hasta que tuvo lugar el máximo de la transgresión durante el límite Cenomaniense‐Turoniense. Además, cabe destacar que el intervalo Albiense ‐ Cenomaniense inferior en Iberia estuvo caracterizado por: (a) registrar la transición de la etapa sin‐rift del Jurásico Superior ‐ Cretácico Inferior a la etapa postrift del Cretácico Superior, y (b) ser un periodo en cuyos depósitos se han descubierto numerosos yacimientos ambarígenos...

Amber is fossilized resin that preserves biological remains in exceptional detail, study of which has revolutionized understanding of past terrestrial organisms and habitats from the Early Cretaceous to the present day. Cretaceous amber outcrops are more abundant in the Northern Hemisphere and during an interval of about 54 million years, from the Barremian to the Campanian. The extensive resin production that generated this remarkable amber record may be attributed to the biology of coniferous resin producers, the growth of resiniferous forests in proximity to transitional sedimentary environments, and the dynamics of climate during the Cretaceous. Here we discuss the set of interrelated abiotic and biotic factors potentially involved in resin production during that time. We name this period of mass resin production by conifers during the late Mesozoic, fundamental as an archive of terrestrial life, the `Cretaceous Resinous Interval (CREI).

[EN] The development of arid climate conditions in eastern Iberia during the mid-Cretaceous (mid-Albian to earliest Cenomanian) has been postulated by several authors over the last two decades based on sedimentological and palaeobotanical datasets. In this paper, we present a combined sedimentological and paleosol study of the mid-Albian to earliest Cenomanian Utrillas Group in the Cuenca Basin of east-central Spain, to improve knowledge of palaeoclimate. Four facies associations are identified as follows: Proximal alluvial braidplain (FA I), Distal alluvial braidplain (FA II), Aeolian dunes (FA III), and Inner estuarine settings (FA IV). The succession records the development of a braidplain system under dominantly arid conditions followed by a marine transgressive phase. In contrast to the overall arid palaeoclimate interpretation, multi-proxy palaeoedaphological analyses conducted for three paleosol profiles (Spodosols) indicate the occurrence of periods of increased humidity in the basin. These findings allow us to infer the occurrence of shorter-term climatic oscillations characterised by a tropical savanna climate when the palaeosols developed, suggesting significantly more humid conditions than those inferred based on the sedimentological and previous palaeobotanical datasets. We propose a palaeoclimatic model that explains the alternation between the dominantly arid and these more humid periods based on the cyclical latitudinal shifting of the mid-Cretaceous climatic belts, shedding new light on the mid-Albian to earliest Cenomanian climate of Iberia.

[EN] Dinosaur bonebeds with amber content, yet scarce, offer a superior wealth and quality of data on ancient terrestrial ecosystems. However, the preserved palaeodiversity and/or taphonomic characteristics of these exceptional localities had hitherto limited their palaeobiological potential. Here, we describe the amber from the Lower Cretaceous dinosaur bonebed of Ariño (Teruel, Spain) using a multidisciplinary approach. Amber is found in both a root layer with amber strictly in situ and a litter layer mainly composed of aerial pieces unusually rich in bioinclusions, encompassing 11 insect orders, arachnids, and a few plant and vertebrate remains, including a feather. Additional palaeontological data-charophytes, palynomorphs, ostracods- are provided. Ariño arguably represents the most prolific and palaeobiologically diverse locality in which fossiliferous amber and a dinosaur bonebed have been found in association, and the only one known where the vast majority of the palaeontological assemblage suffered no or low-grade pre-burial transport. This has unlocked unprecedentedly complete and reliable palaeoecological data out of two complementary windows of preservation-the bonebed and the amber-from the same site.

[ES] Los desiertos son ambientes estresantes para las formas de vida que para sobrevivir deben desarrollar diferentes estrategias. El llamado Sistema Desértico Ibérico se estableció en el norte y este de la península Ibérica desde el Albiense superior hasta el Cenomaniense inferior. Concretamente, los yacimientos del Albiense tardío de la Cuenca del Maestrazgo (Grupo Utrillas, Este de España) se conocen por contener ámbar con abundantes bioinclusiones que incluyen diversos artrópodos. El Grupo Utrillas se interpreta como un sistema desértico situado en las proximidades de la costa de Tethys, y engloba una sucesión sedimentaria formada por una alternancia de depósitos marinos someros y dunas eólicas. Los ecosistemas que se desarrollaron en esta zona fueron biodiversos, y estaban integrados por comunidades vegetales cuyos fósiles se asocian con indicadores sedimentológicos de aridez. La palinoflora identificada en las secciones con ámbar está dominada por granos de polen de gimnospermas transportados por el viento y/o esporas de helecho. Adicionalmente, el polen de angiospermas primitivas muestra una gran diversidad de formas pero nunca alcanza valores numéricos significativos. Por su parte, los quistes de dinoflagelados son raros y su presencia refleja incursiones marinas en ambientes cercanos a la costa. En general, las asociaciones palinológicas estudiadas indican la existencia de bosques de Cheirolepidiaceae y Cupressaceae adaptados a ambientes áridos, entornos costeros con Araucariaceae, y comunidades de interdunas y marismas con helechos y angiospermas. La presencia de asociaciones macroflorísticas poco diversas, caracterizadas por Frenelopsis, Eretmophyllum y algunas angiospermas, también señalan la existencia de marismas. La aparición de granos de polen de Afropollis, Dichastopollenites, Cretacaeiporites, así como los poliplicados producidos por Gnetales, revelan que estos ecosistemas desérticos presentaron influencias de los del norte de Gondwana. Por el cont