Early Cretaceous Sediments Research Articles

Jurassic mountain building and Mesozoic-Cenozoic geodynamic evolution of the Northern Calcareous Alps as proven in the Berchtesgaden Alps (Germany)

New data from the Berchtesgaden Alps result in a reconstruction of the Mesozoic-Cenozoic geodynamic history of the Northern Calcareous Alps. The closure of the western part of the Neotethys Ocean started in the late Early Jurassic and is evidenced by the onset of thick clay-rich sediments in the outer shelf area (=Hallstatt realm). The Middle to early Late Jurassic contraction is documented by the migration of trench-like basins formed in front of a propagating thrust belt. Due to ophiolite obduction, these basins propagated from the outer shelf area, forming there the Bajocian to Oxfordian Hallstatt Melange, to the Hauptdolomit/Dachstein platform area, where the Oxfordian Rofan and Tauglboden Melanges were formed. The basins were separated by nappe fronts forming structural highs. This scenario mirrors syn-orogenic erosion and deposition in an evolving thrust belt. Active basin formation and nappe thrusting ended around the Oxfordian/Kimmeridgian boundary, which was followed by the onset of carbonate platforms on structural highs prograding towards the former basins in latest Oxfordian to Early Tithonian time. Underfilled basins remained between the platforms. Rapid deepening around the Early/Late Tithonian boundary was induced by extension due to mountain uplift and resulted in the reconfiguration of the platforms and basins related to normal and probably strike-slip faults. Erosion of the uplifted nappe stack including obducted ophiolites caused final drowning and demise of the platforms in the Berriasian. The remaining Early Cretaceous basins were filled up with molasse sediments including siliciclastics until Aptian. Around the Early/Late Cretaceous boundary again extension and strike-slip movements started, followed by Eocene thrusting and Miocene strike-slip movements with block rotations. These younger tectonic movements destroyed the Triassic to Early Cretaceous palaeogeography and arranged the modern block configuration. The described Jurassic to Early Cretaceous history corresponds with that of the Western Carpathians, the Dinarides, and the Albanides, where (1) age dating of the metamorphic soles prove late Early to Middle Jurassic inneroceanic thrusting followed by late Middle to early Late Jurassic ophiolite obduction, (2) Kimmeridgian to Tithonian shallow-water platforms formed on top of the obducted ophiolites, and (3) latest Jurassic to Early Cretaceous sediments show postorogenic character. Therefore, we correlate the Jurassic geodynamic evolution of the Northern Calcareous Alps with the closure of the western part of the Neotethys Ocean.

Climate's role in the distribution of the Cretaceous terrestrial Crocodyliformes throughout Gondwana

A high diversity of terrestrial crocodyliform species has been found in the continental Cretaceous deposits of Gondwana. They are widespread in the sedimentary basins of Brazil, Uruguay, Argentina, Bolivia, Morocco, Cameroon, Niger, Malawi, Madagascar and Pakistan, from alluvial, fluvial and lacustrine deposits. A peculiar aspect of these terrestrial crocodyliforms is that only some of them are cosmopolitan. They comprise distinct groups as the basal Notosuchia, baurusuchids, sphagesaurids and Sebecian peirosaurids. There is a distribution pattern of the terrestrial Crocodyliformes faunas throughout the Cretaceous. The oldest are composed of the small and probably omnivorous Notosuchia and Araripesuchus, found in Early Cretaceous deposits. In the Late Cretaceous this fauna was enriched by the medium-sized to large-size baurusuchids, sphagesaurids, peirosaurids and larger Araripesuchus which present specializations as active terrestrial predators. The distribution analysis of the terrestrial Crocodyliformes from Early and Late Cretaceous palaeogeographic and palaeoclimatic maps indicates that temperature was the principal influence on their Gondwanan distribution. Although expressed seasonality, aridity is a limiting factor for the distribution of extant crocodilians. The Cretaceous basal Notosuchia, baurusuchids, sphagesaurids, Araripesuchus, Sebecian peirosaurids, are found in arid climatic belts during Early and Late Cretaceous. To live in a hot and arid climate they have presumably developed ecological strategies that allowed such habits. The aridity or seasonal warm and cyclic dry and wet climate periods plays a role, that have not yet been analyzed, that may explain the domain of bizarre Crocodyliformes in Gondwana during the Cretaceous.

A review of the Mesozoic turtles of the Junggar Basin (Xinjiang, Northwest China) and the paleobiogeography of Jurassic to Early Cretaceous Asian testudinates

Middle Jurassic to Early Cretaceous sediments exposed in the Junggar Basin have yielded a rich turtle assemblage. Jurassic taxa include the purportedly basal turtle Sichuanchelys sp. and at least six basal eucryptodires, which are currently united in the likely paraphyletic taxon “Xinjiangchelyidae.” Early Cretaceous assemblages, by contrast, include a single “xinjiangchelyid” and a single potential pantrionychian, but are otherwise dominated by more derived eucryptodires, currently grouped in the paraphyletic taxon “Sinemydidae”/“Macrobaenidae.” Comparison of the Junggar turtle assemblage with those of coeval Asian localities reveals that Jurassic turtle assemblages were rather homogenous throughout the Jurassic, but split in the Early Cretaceous. In particular, the Early Cretaceous Junggar turtle assemblage resembles those of other northern Chinese provinces, Mongolia and the Lake Baikal region of Russia in their retention of rather basal turtles, whereas all other Asian localities are dominated by more derived eucryptodires, particularly pantrionychians. This chasm may be the result of biogeographic, ecological and climatic conditions, where dry conditions in isolated inland basins created an ephemeral lake habitat optimal for basal eucryptodires, whereas the river environments typical of the surrounding coastal areas were favourable for more derived eucryptodires.

Malargüe Group (Maastrichtian–Danian) deposits in the Neuquén Andes, Argentina: Implications for the onset of the first Atlantic transgression related to Western Gondwana break-up

The discovery of marine to brackish and fresh-water carbonates in the inner Agrio fold-and-thrust belt at Pichaihue, Neuquén, Argentina, located to the west of the Andean orogenic front, imposes important constraints on the paleogeography of the first Atlantic transgression in the Neuquén Basin related to the break-up of Western Gondwana. The constraints on the timing and areal extent of these deposits shed light on the early uplift history of the southern Andes. These limestones are part of the Maastrichtian–Danian Malargüe Group, which was previously only known from its exposures in the extra-Andean area, representing foreland basin deposits. The presence of stromatolites, oncoids, serpulids, bivalves and gastropods as well as silicified stems of macrophytes indicates a shallow marine, partially brackish environment associated with non-marine deposits. These strata are interfingered with and overlie distal tuffs and proximal pyroclastic flows, whose geochemical characteristics point to a magmatic arc source. SHRIMP U–Pb dating of volcanic zircons of these tuffs yielded an age of 64.3 ± 0.9 Ma that confirms the correlation to the Maastrichtian–Paleocene marine transgression from the Atlantic Ocean. The change in the paleoslope of the basin from Pacific Ocean transgressions to this Atlantic transgression is related to the uplift and deformation of the Agrio fold-and-thrust belt. The Pichaihue Limestone is unconformably deposited on volcanic agglomerates which in turn unconformably overlie Early Cretaceous deposits. Based on these data, it is confirmed that the Cretaceous uplift of the Andes was episodic at these latitudes, with a first pulse in the Cenomanian and a second one in pre-Maastrichtian times. The episodic uplift is also related to an eastward migration of the thrust front and the volcanic arc, related to a previously proposed shallowing of the subduction zone. These episodes were controlled by the Western Gondwana break-up and the beginning of absolute motion of South America toward the west.

Evidence for Jurassic subduction from the Northern Calcareous Alps (Berchtesgaden; Austroalpine, Germany)

The closure of the western part of the Neotethys Ocean started in late Early Jurassic. The Middle to early Late Jurassic contraction is documented in the Berchtesgaden Alps by the migration of trench-like basins formed in front of a propagating thrust belt. Due to ophiolite obduction these basins propagated from the outer shelf area (=Hallstatt realm) to the interior continent (=Hauptdolomit/Dachstein platform realm). The basins were separated by nappe fronts forming structural highs. This scenario mirrors syn-orogenic erosion and deposition in an evolving thrust belt. Active basin formation and nappe thrusting ended around the Oxfordian/Kimmeridgian boundary, followed by the onset of carbonate platforms on structural highs. Starved basins remained between the platforms. Rapid deepening around the Early/Late Tithonian boundary was induced by extension due to mountain uplift and resulted in the reconfiguration of the platforms and basins. Erosion of the uplifted nappe stack including obducted ophiolites resulted in increased sediment supply into the basins and final drowning and demise of the platforms in the Berriasian. The remaining Early Cretaceous foreland basins were filled up by sediments including siliciclastics. The described Jurassic to Early Cretaceous history of the Northern Calcareous Alps accords with the history of the Western Carpathians, the Dinarides, and the Albanides, where (1) age dating of the metamorphic soles prove late Early to Middle Jurassic inneroceanic thrusting followed by late Middle to early Late Jurassic ophiolite obduction, (2) Kimmeridgian to Tithonian shallow-water platforms formed on top of the obducted ophiolites, and (3) latest Jurassic to Early Cretaceous sediments show postorogenic character.

A pupal caddisfly from the Early Cretaceous of China (Trichoptera)

Although caddisfly (Trichoptera) cases and adults are fairly abundant in the fossil record, fossils of the immature stages, particularly insights into the pupal stage, are exceedingly rare. Herein we report the discovery of a fossil caddisfly pupa, putatively of the family Vitimotauliidae, from Early Cretaceous deposits in northeastern China. This is the first fossil trichopteran pupa to have been described from China.

A new ornithuromorph (Aves: Ornithothoraces) bird from the Jehol Group indicative of higher-level diversity

ABSTRACT Basal Ornithuromorpha, until recently, was one of the most poorly documented segments of early avian evolution. The known species diversity of the ornithuromorph clade has increased rapidly with the addition of new discoveries from the Early Cretaceous deposits of northeastern China. Reported in this paper is the discovery of a new bird from the Lower Cretaceous Yixian Formation, Liaoning Province, China. The specimen represents a new species, Longicrusavis houi, but bears similarities to Hongshanornis longicresta from the same formation of Inner Mongolia. The two birds are comparable in size and share an unusual sigmoid mandible and elongate hindlimbs relative to their forelimbs. Together these taxa represent a clade (Hongshanornithidae, new taxon) of specialized ‘shorebirds’ whose elongate hindlimbs indicate ecological adaptations different from those of other Jehol ornithuromorphs. Phylogenetic relationships of Mesozoic birds are discussed based on the results of a comprehensive cladistic analysis. New morphological information on Ornithuromorpha is provided through the detailed description of the new taxon together with new information on Hongshanornis.

OPHIOLITES FROM THE GRAMMOS-ARRENES AREA, NORTHERN GREECE: GEOLOGICAL, PALEONTOLOGICAL AND GEOCHEMICAL DATA

The Grammos-Arrenes ophiolites crop out between the Pindos Flysch to the East and the Meso-Hellenic basin to the West and represent the northernmost exposure of the Pindos Ophiolite belt in Greece. Field work and sampling on key outcrops of the Sub-ophiolitic Melange provided new data on the oceanization age and on the geochemistry of the effusive products. The basalts samples show a N-MOR affinity and are associated with latest Bajocian-early Bathonian radiolarian cherts. Emplacement of the ophiolites onto the continental margin is preceded by mass flow deposition of ophiolitic material in the basins facing the advancing ophiolitic nappe. Ophiolite-bearing debris flow deposits and slide blocks are recognized in the Early Cretaceous deep water sediments of the Beotian Unit and in the upper portion of the Tertiary Pindos Flysch. The intercalations of ophiolitic material in the Beotian Flysch first, and in the Pindos Flysch, later, are interpreted as the forerunners of the Ophiolitic Nappe which derived from the Vardar Ocean to the east, and was emplaced westwards onto the Adria continental margin. The collected data allow consolidating the constraints for the timing and mechanism of ophiolite emplacement in the Pindos-Grammos area. In addition, taking into consideration the geometry of the tectonic stack in the Grammos-Arrenes area and the ages of the involved sedimentary deposits it is possible to reconstruct a geodynamic history comparable to that of the other zones studied along the Dinaric-Hellenic Chain.

Early Cretaceous flysch from Betic-Maghrebian and Europe Alpine Chains (Gibraltar Strait to the Balkans): comparison and palaeotectonic implications

Early Cretaceous flysch crops out along all the Alpine Chains of the western, central and eastern Europe for more than 7000 km from the Gibraltar Arc to the Balkans. In the different sectors of the Alpine Chain (Maghrebides, Apennines, Alps, Dinarides, Hellenides, Carpathians and Balkans) these flysch deposits, characterized by calcareous turbidites grading upwards into arenaceous turbidites, mark the contact between the internal and external areas. They show a provenance linked to internal areas and are made up by crystalline sources and locally by ophiolitic complexes. Due to the Cretaceous re-organization of the plates, all these successions experienced a Late Cretaceous tectonics, with the only exception of the Maghrebian flysch deposits. In this area, similar tectonic events have never been recorded but only suspected and aged to slightly later times. This paper aims to show the stratigraphic, geological and structural similarities of all these Early Cretaceous flysch sediments by emphasizing the difficulties to imagine that only the Maghrebian sector of the Alpine Tethys escaped the Mid- to Late-Cretaceous tectonics widely recognized in all the other segments of the Alpine Chain. In fact the Late Cretaceous or post-Cretaceous tectonics connected with a “mesoalpine” stage, has been hypothesized for the Maghrebian chain at the beginning of the nineties and recently it has been supported by the presence of Alpine metamorphic overprints recognized within the Hercynian crystalline units of the Calabria- Peloritani Arc (southern Italy). This tectonics seems to be linked to an early segmentation and deformation of the Maghrebian Early Cretaceous flysch with local underthrusting beneath the southern European margin.

Biogeographic implications of Albian Mohria-like spores (Family Anemiaceae) in SW Gondwana (Patagonia)

The schizaeaceous extant genus Mohria has a distribution restricted to South Africa and Madagascar area. Its cicatricose spores are characterised by their large size and muri with hollow longitudinal channels unknown in other schizaeaceous genera. Fossil spores that sometimes have been referred to Mohria lack this typical character and therefore the determinations were discarded. Early Cretaceous (Albian) sediments from Patagonia, referred to the Piedra Clavada Formation of the Austral Basin, contain spores that have the characters now found in Mohria. These fossils are hereby assigned to the new genus Palaeomohria that includes several morphological types. The paleogeographical proximity of South Africa and Patagonia in Southwestern Gondwana persisted from the Permian to the Early Cretaceous, during a time when floras of both regions had significant similarities. In this context, the finding of Mohria-like spores in Patagonia suggests that the distribution of this fern was more extended in the past and became restricted while the continents shifted apart during the Cretaceous/Tertiary. The two living Mohria species may then represent relict taxa of a much more varied and rich group that flourished during the Early Cretaceous in SW Gondwana.

A NEW LATE CRETACEOUS MACROSEMIID FISH (NEOPTERYGII, HALECOSTOMI) FROM MOROCCO, WITH TEMPORAL AND GEOGRAPHICAL RANGE EXTENSIONS FOR THE FAMILY

Abstract: A recent collection of actinopterygian fossil fishes from a previously unreported locality in the Cenomanian or Turonian of southeastern Morocco includes a single specimen of a macrosemiid fish. Macrosemiids are more common in Jurassic and Early Cretaceous deposits, with the previously known range of the family being Late Triassic through Aptian or Albian. This discovery therefore extends the temporal range of the family into the Late Cretaceous. Moreover, macrosemiids had not previously been reported from northern Africa or the Moroccan area of the Tethys basin; therefore, this fossil also increases the geographical range of the family. The Moroccan macrosemiid is described in a new genus and species, Agoultichthys chattertoni. A phylogenetic analysis places it basal to all other genera of the family with the exception of Notagogus. Diagnostic characters of the new species include the high number of scales laterally along the body and the greater number of dorsal fin rays than in other members of the family.

Temporo‐spatial Coordinates of Evolution of the Ordos Basin and Its Mineralization Responses

Abstract: The Ordos basin was developed from Mid‐Late Triassic to Early Cretaceous, and then entered into its later reformation period since the Late Cretaceous. Its main body bears the features of an intra‐cratonic basin. The basin also belongs to a multi‐superposed basin which has overlapped on the large‐scale basins of the Early and Late Paleozoic. Currently, Ordos basin has become a residual basin experienced reformation of various styles since the Late Cretaceous. It's suggested that there were at least four obvious stages of tectonic deformations existing during the basin's evolution, dividing the evolution and sedimentation into four stages. The prior two stages were of the most prosperous, during which the lake basin was broad, the deposition range was more than twice larger than the current residual basin, resulting in major oil‐ and coal‐bearing strata. The two stages were separated by regional uplift fluctuations in the area. At the end of the Yan'an Stage, the depositional interruption and erosion were lasting for a short period of time. The third one is the Mid‐ Jurassic Zhiluo‐Anding stage, in which the sedimentation extent was still broad but the lake area was obviously reduced. In the Late Jurassic tectonic deformation was intensive. A thrust‐nappe belt was formed on the basin's western margin while conglomerate of different thickness were accumulated within the foredeep of the eastern side. The central and eastern parts of the basin were subject to erosion and reformation. A regional framework with “uplift in the east and depression in the west” took shape in the area west of the Yellow River. In the Early Cretaceous sediments were widely distributed, unconformably overlapping the former western margin thrust belt and the ridges on the northern and southern borders. There are abundant energy resources such as oil, natural gas, coal and uranium deposits formed in Ordos Basin. The main stages of generation, mineralization and positioning of the multiple energy resources have obvious responding connection and close coupling relationships with those of the Mesozoic and Cenozoic evolution and reformation in Ordos Basin.

Intrabasement reflections of the Ontong Java Plateau: Implications for plateau construction

The Early Cretaceous Ontong Java Plateau (OJP) in the western equatorial Pacific, Earth's most voluminous large igneous province (LIP), is characterized by intrabasement seismic reflections. To investigate the nature of such reflections, we have analyzed new and all older multichannel seismic (MCS) reflection data from the OJP using an instantaneous phase velocity analysis technique and synthetic seismograms. Intrabasement reflections are most prevalent on the main OJP, especially on its crest. On MCS data, the reflections (1) are semicontinuous and subparallel to the top of igneous basement; (2) in places, have the opposite phase of seafloor reflections; and (3) have an average frequency of ∼20 Hz. We calculate synthetic seismograms using impedance contrasts between massive lava and pillow lava flows obtained from downhole logs at OJP scientific drill sites and show that these lithologies can produce intrabasement reflections similar to those observed in the MCS data. Alternatively, to evaluate the possibility of sediment/sedimentary rock interbeds causing the intrabasement reflections, we use published Early Cretaceous sedimentation rates determined from OJP drill sites and published estimates for the duration of massive OJP volcanism to calculate a range of possible sedimentary interbed thicknesses. The range proves to be below the detection limit of the MCS data. Therefore, we conclude that the intrabasement reflections arise from alternating relatively thin lava flows produced at low effusion rates and relatively thick massive flows generated at high effusion rates, both originating from vents and fissures on the OJP, probably on its crest.

The basaltic volcanic rocks in the Tuyon Basin, NW China: Petrogenesis and tectonic implications

The Tuyon basin is located near the crossing of the Tien Shan orogenic belt, the Western Kunlun fold system and the TarimAlashan blocks. The crossing of two lithospheric scale fault, the Talas-Ferghana dextral strike-slip fault and the NE extended South Tien Shan strike-slip fault, is just at the southern margin of the Tuyon basin. Therefore, many geoscientists all over the world have been attracted to petrogenesis of the Cenozoic basaltic volcanic rocks in the Tuyon basin and their tectonic implications. According to previous researches, the basalts emplaced within the Tuyon basin are of two units, the lower basalts and the upper basalts, aged 120~110 Ma and 70.4~36.6 Ma respectively. All these basalts are classified as alkali series, enriched in potassium, and considered as a result of a small plume probably rooted at a shallow level in the asthenosphere. Our new works on the igneous rocks in the Tuyon basin suggest that the so-called lower basalts are preserved as a series of cone dikes, which are emplaced in Jurassic-Lower Cretaceous sedimentary rocks; the upper basalts are formed as a series of volcanic eruptions, including calderas, ring dikes, necks and volcanic cones. For example, there are three volcanic cones in the line between the Kuvt cone and Bilebluk cone. We have discovered basaltic intrusive units in Jurassic sandstone and conglomerate strata. The basaltic extrusive units have the same occurrence with the early Cretaceous sediments, but uncomfortably overlain by the Paleogene sedimentary rocks. Therefore, the Tuyon basin is a compound volcanic basin, including series of volcanic eruptions with lavas and subvolcanic rocks, rather than it has two-layer structure consisted of two igneous units. Our investigations indicate that the basaltic rocks are mainly of dark gray, massive structure and porphyritic texture. The basaltic extrusive rocks are developed as columnar joint structure, vesicular structure and amygdaloidal structure. Most of volcanic rocks within Tuyon basin contain phenocrysts such as olivine, clinopyroxene and plagioclase, and occasionally phlogopite, amphibole and apatite. Olivine belongs to chrysolite circled by fine-grained aggregate of magnetite and talc. Most of olivine phenocrysts have been altered into iddingsite and talc. The clinopyroxene mainly belongs to augite, which characterize hourglass structure and zoned texture. The plagioclase phenocrysts have more content of anorthite. They are mainly andesine and occasional labradorite, but rare in zoned texture. The matrix minerals are clinopyroxene, plagioclase, magnetite and volcanic glass, and mainly formed tholeiitic texture, occasionally intergranular texture and vitrophyric. Therefore, the Cenozoic volcanic rocks in the Tuyon basin show characteristics of alkali series, and suggest that the region may was at extensional condition. In the Arhesaiordy volcanic-sedimentary sequences there are five basaltic sills intruded into the Jurassic sedimentary deposits. Many megacrysts have been found in the lowest basaltic layer, such as augite, phlogopite, amphibole and anorthoclasite. From the same layer we have collected lots of the deep-seated xenoliths including peridotite, granulite, pyroxenite, gneiss and so on. In the other four layers, the number of megacrysts and deep-seated xenoliths has been decreased quickly. There are also lots of deep-seated xenoliths in the Tasgeler caldera. Therefore, basaltic magma has the characteristics of rapid ascent. Consequently, the basaltic volcanic rocks in the Tuyon basin are formed direct from primary magma, which is rare affected by fractional crystallization.

Erdtmanispermum juncalense sp. nov., a new species of the extinct order Erdtmanithecales from the Early Cretaceous (probably Berriasian) of Portugal

Well-preserved lignitic seeds are described from Early Cretaceous sediments (probably Berriasian) exposed in the Vale Painho clay pit complex near the small village of Juncal in the Estremadura region, Western Portugal. The seeds are small, weakly triangular in transverse section, about 1.05–1.5 mm long and 0.75–1.1 mm broad, with elongated distinctly pointed micropylar area at the apex and rounded base. The seeds have clear affinity with the extinct Erdtmanispermum (Erdtmanithecales) and are assigned to a new species Erdtmanispermum juncalense based on the distinct rugulate outer envelope and the ovoid to guttiform outline. The description of the mesofossils provided here is the first report of Erdtmanithecales seeds from the Early Cretaceous of Portugal and adds to our knowledge of the diversity and geographic distribution of Cretaceous Eucommiidites-producing plants.

Thecamoebians from the early Cretaceous of the Scotian Shelf

This study reports and describes fossil thecamoebians from early Cretaceous deposits of Cohasset A-52 well located on the Scotian Shelf. In this paper we illustrate and discuss fossil thecamoebians to provide additional data to the few published reports on this fossil group. The identified taxa are attributed to the genera Cucurbitella, Difflugia and Heleopera , showing a strong similarity with recent thecamoebians. Several other forms with an uncertain generic characterization are are described.

Variability of Habroblattula drepanoides gen. et. sp. nov. (Insecta: Blattaria: Blattulidae) from the Yixian Formation in Liaoning, China

Habroblattula drepanoides gen. et sp. nov. (Blattulidae) is described from the Late Jurassic or Early Cretaceous sediments of the Yixian Formation in Western Liaoning, China. Wing venation of Habroblattula drepanoides reveals low coefficient of variation (CV) for total number of the forewing veins (CV=5.72) which indicates active flight capability. The higher hindwing variability (CV=14.43) might suggest Habroblattula was an advanced genus, may be caused by the regulation of the vein. The asymmetry between the left and right forewing in the same individual indicates the flight was limited when comparing with the CV of the left and right forewings.

Anacoracid shark teeth (Chondrichthyes, Vertebrata) from the early Cretaceous Albian sediments of Leighton Buzzard, south-central England

Anacoracid shark teeth (Chondrichthyes, Vertebrata) from the early Cretaceous Albian sediments of Leighton Buzzard, south-central England

Late Jurassic–Early Cretaceous intra-arc sedimentation and volcanism linked to plate motion change in northern Japan

The Sorachi Group, composed of Upper Jurassic ophiolite and Lower Cretaceous island-arc volcano-sedimentary cover, provides a record of Late Jurassic–Early Cretaceous sedimentation and volcanism in an island-arc setting off the eastern margin of the Asian continent. Stratigraphic changes in the nature and volume of the Sorachi Group volcanic and volcaniclastic rocks reveal four tectonic stages. These stages resulted from changes in the subduction direction of the Pacific oceanic plate. Stage I in the Late Jurassic was characterized by extensive submarine eruptions of tholeiitic basalt from the back-arc basin. Slab roll-back caused rifting and sea-floor spreading in the supra-subduction zone along the active Asian continental margin. Stage II corresponded to the Berriasian and featured localized trachyandesitic volcanism that formed volcanic islands with typical island-arc chemical compositions. At the beginning of this stage, movement of the Pacific oceanic plate shifted from northeastward to northwestward. During Stage III, in the Valanginian, submarine basaltic volcanism was followed by subsidence. The Pacific oceanic plate motion turned clockwise, and the plate boundary between the Asian continent and the Pacific oceanic plate changed from convergent to transform. During Stage IV in the Hauterivian–Barremian, in situ volcanism ceased in the Sorachi–Yezo basin, and the volcanic front migrated west of the Sorachi–Yezo basin.

A gobiconodontid (Mammalia, Eutriconodonta) from the Early Cretaceous (Barremian) Wessex Formation of the Isle of Wight, Southern Britain

Abstract: Bulk screening of Early Cretaceous (Barremian) strata of the Wessex Formation, exposed in sections on the south‐west and south‐east coasts of the Isle of Wight, southern England, has resulted in the recovery of mammal remains, the first to be obtained from Wealden Group strata since the early 1970s. The fauna comprises at least six taxa represented by isolated teeth and in addition, in the case of an as yet undescribed spalacotheriid, a partial dentary. One of the teeth, a distal premolar, is of unique tricuspid, single‐rooted morphology and represents the first British record of the Gobiconodontidae. Discovery of a gobiconodontid mammal in Early Cretaceous deposits of Britain sheds further light on the palaeogeographical distribution of an apparently successful clade of Early Cretaceous mammals and together with the occurrence of a gobiconodontid in the earliest Cretaceous of North Africa calls into question recent hypotheses concerning the area of origin of the Gobiconodontidae and mechanisms of dispersal therefrom.