Early Cretaceous Research Articles

Petrogenesis of the Weideshan Pluton in Jiaodong and Its Implications for Gold Polymetallic Mineralization: Constraints from Zircon U-Pb-Hf Isotopes, Petrogeochemistry, and Whole-Rock Sr-Nd Isotopes

The Early Cretaceous Weideshan granites are associated with large-scale Au and polymetallic Cu-Mo-Pb-Zn mineralization. To investigate the petrogenesis of the Weideshan granite and constrain its tectonic setting during the Early Cretaceous, we conducted a zircon U-Pb-Hf isotope and whole-rock geochemical and Sr-Nd isotopic study of the granite. In situ zircon U-Pb dating of three granite samples yielded Early Cretaceous ages of 112.83 ± 0.80, 112.64 ± 0.91, and 111.82 ± 0.78 Ma. The samples had high-K calc-alkaline compositions and were enriched in the light rare earth and large-ion lithophile elements (e.g., K, Rb, Ba, Th, and U) and depleted in high-field-strength elements (e.g., Nb, Ti, and P). The samples had small negative Eu anomalies and initial 87Sr/86Sr and εNd(t) values of 0.70853–0.71029 and –18 to –14, respectively. The zircon εHf(t) values varied between −16 and −12, with corresponding two-stage model ages (tDM2) of 2180–2000 Ma. These characteristics indicated that the Weideshan pluton was formed in a back-arc extensional environment caused by subduction of the Paleo-Pacific Plate toward the Asian continent during the early Cretaceous. The magma was generated by crust–mantle interaction during lithospheric thinning. The diagenetic age of the Weideshan granites was the same as the formation age of gold and polymetallic ores in the Jiaodong area. The extensive fluid circulation induced by the magma emplacement may be the main source of ore-forming materials for the gold and polymetallic Cu-Mo-Pb-Zn deposits.

Landscape inversion episodes in SE China during the Mesozoic−early Cenozoic: Constrained by trace-element contents, Nd isotope geochemistry, and detrital zircon U-Pb geochronology of sedimentary basins

The tectonics and landscape of SE China experienced significant changes throughout the Mesozoic and early Cenozoic, largely in response to variations in the slab dynamics of the paleo-Pacific plate, which was subducting beneath continental Asia. We investigated the Mesozoic Yong’an basin in western Fujian Province of SE China in comparison to the sedimentary records of coeval basins in the region to document how its clastic sediment types and their provenance varied through time during the Mesozoic and what regional geologic processes may have controlled these variations. The average εNd value of samples from the Middle Jurassic Zhangping Formation is −16.6, and its detrital zircons are dominated by 1800 Ma and 2000 Ma grains, sourced from the northern Wuyishan Mountains. These mountains underwent significant rock and surface uplift by the Middle Jurassic and became the main source of clastic sediments in SE China. The Lower Cretaceous Bantou Formation contains pyroclastic rocks and represents fluvial-lacustrine deposits with εNd values of −14.8 to −12.4 and abundant 160−120 Ma detrital zircons, sourced from Late Jurassic granitoid rocks, which were widely exposed at the surface in SE China by this time. The upper Lower and lower Upper Cretaceous Shaxian Formation contains coarse-grained and poorly sorted sandstones-conglomerates with volcanic and granitic rock fragments, and it rests unconformably on the Bantou Formation. The Shaxian Formation represents fluvial- to alluvial-fan deposits, and its formation marks the timing of a rapid uplift of the paleo−Coastal Mountains. The Upper Cretaceous Chong’an Formation (>2000 m thick) contains abundant volcanic and granitic rock clasts and represents alluvial-fan and fluvial deposits. The average εNd values of the Shaxian and Chong’an Formations range between −9.3 and −7.5, and their most abundant detrital zircon ages are between 120 Ma and 80 Ma. By the end of the Late Cretaceous, the paleo−Coastal Mountains constituted a nearly 4-km-high magmatic belt, with much of SE China situated in its rain shadow at a lower elevation to the north. Eocene−Oligocene sedimentary basin rocks in Taiwan have an average εNd value of −10.9 and abundant Phanerozoic detrital zircons. The sediment source for these rocks was the paleo−Coastal Mountains. The Miocene basinal strata in Taiwan have more negative εNd values (−13.0) and contain Jurassic−Cretaceous as well as abundant Paleoproterozoic and Neoproterozoic zircons, indicating that the Wuyishan Mountains were again the main sediment source later in the Cenozoic. Denudation rates in the SE margin of South China were high (0.12−0.10 km/yr) during the Cretaceous (140−60 Ma), while they were very low in SW China and in the interior of South China during the same period. These differences confirm the existence of high coastal mountains in SE China until the Late Cretaceous. Denudation rates in eastern South China, particularly the coastal areas, were very low (0.06−0.02 km/yr) during the late Cenozoic (30−0 Ma), whereas they were the fastest (0.14−0.16 km/yr) in the northern Nanling belt and the Yangtze block farther inland to the north, indicating the surface elevation became higher in the western part of South China but lower in its eastern part in the late Cenozoic. This dynamic landscape evolution of SE China through multiple and major shifts throughout the Mesozoic and early Cenozoic was driven by the subducting slab dynamics and the tectonics of the Tibetan Plateau.

Algal microfacies in the Theniet Et Temar Formation (middle Oxfordian), Central Saharan Atlas, Algeria

During the Oxfordian, sea-level rise created widespread carbonate platform deposition on the margins of Neotethys, although some areas remain poorly described. One such area is the Saharan Atlas of Algeria. Accordingly, the middle Oxfordian Theniet Et-Temar Formation at a new locality, Kef El Meleh, is described for the first time. Formed of marl/limestone cycles, 6 broad microfacies are present within the limestones, representing deposition in lagoon, shoal and nearshore environments. Whilst overall shallowing-up is evident, it is unclear if the smaller scale marl–carbonate cycles represent higher frequency shallowing-up, or allocyclic depositional patterns.The Theniet Et-Temar Formation contains an important archive of macrofossils and microfossils. Of note at Kef El Meleh is the presence of a microfacies rich in dasycladalean algae, notably Salpingoporella annulata Carozzi, 1953. The specimens conform well to the type and subsequent descriptions. The assemblage is effectively monospecific in terms of algae, although the larger foraminifera Alveosepta jaccardi (Schrodt, 1894) is present. This record extends the knowledge of the distribution of S. annulata within Neotethys, especially within the Oxfordian, for which previous records are limited in comparison to those for the later Jurassic and Early Cretaceous.

Early Cretaceous Equisetites from Slovakia

A new find of terrestrial plant Equisetites cf. lyellii is reported from the Early Cretaceous of Slovakia. It comes from the Mráznica Formation of the Rajec Basin in Fatricum, Zbyňov locality, Rajecké Teplice (Žilina district). The presence of a 53 mm long horsetail axis provides good evidence of terrestrial environments during sedimentation of the studied strata. According to our interpretation, such a plant strongly indicates a moist to wet habitat (even swampy environments) on the presumed dryland from where it was transported. This dryland could represent an isolated unknown small island(s) in the vicinity, or the Vindelician-Bohemian Massif that was active as a dryland for the entire period of time from the Triassic through the Late Cretaceous. However, the exact palaeogeographic position of the Fatricum during the Mesozoic in relation to the Vindelician Landmass is not entirely clear, and such an interpretation needs a bit of caution.

A new species of Keteleeria (Pinaceae) from the Lower Cretaceous of Inner Mongolia, Northeast China, and its palaeogeographic and palaeoclimatic implications

Keteleeria Carrière (Pinaceae) is a small genus of evergreen conifer trees, with three to five extant species and six variants distributed across China, Laos, and Vietnam. A new species of conifer fossil wood, Keteleeria huolinhensis sp. nov., is described from the Lower Cretaceous Huolinhe Formation in Inner Mongolia, China. This species is characterized by a heterogeneous pith, endarch primary xylem, the presence of axial resin canals, abietinean radial tracheid pitting, mostly taxodioid and occasionally cupressoid cross-field pitting, nodular horizontal and end walls of ray parenchyma cells, and uniseriate rays of 1–15 (mainly 1–8) cell height. This newly discovered fossil wood represents the earliest record of Keteleeria wood, and sheds light on its evolutionary history and palaeogeographical distribution ranges in the geological past. Cladistic analysis based on 12 morphological characteristics supports the assignment of Protopiceoxylon as the ancestral group of Keteleerioxylon and Keteleeria, reflecting the evolution of radial tracheid pitting from the mixed to abietinean type. Quantitative analysis of the growth rings indicated that K. huolinhensis sp. nov. is an evergreen tree with a Leaf Retention Time (LRT) of 1–3 years. The growth ring patterns in the present fossil wood specimen suggest that the Huolinhe Basin experienced a temperate climate with regular seasonal fluctuations, and relatively sufficient water supply during the Early Cretaceous. Traumatic resin canals, wound scars, presumed fungal remains, and insect tracks in the stem contribute to a further understanding of the complex ecological relationships in the Early Cretaceous Huolinhe flora.

Palynological reconstruction of the habitat and diet of Iguanodon bernissartensis in the Lower Cretaceous Morella Formation, NE Iberian Peninsula

The recent discovery of iguanodontid remains from the new Palau-3 site in the Lower Cretaceous Morella Formation is the most complete non-articulated skeleton of Iguanodon bernissartensis on the NE Iberian Peninsula. To elucidate the paleoenvironment of the Palau-3 site, a palynological analysis was carried out on matrix samples collected from around the skeleton. The palynological assemblage is found to correspond to an upper Barremian age. While the assemblage is composed of bryophytes, pteridophytes, gymnosperms, freshwater algae, dinoflagellate cysts and fungal spores, the palynoflora is mostly dominated by the Cheirolepidiaceae conifer (Classopollis) and Anemiaceae fern (mainly Cicatricosisporites) families. The absence of angiosperm pollen in this flora is also noteworthy, as angiosperm remains have been recorded previously elsewhere in the Morella Formation. At the Palau-3 site, the fronds of Cyatheaceae and Anemiaceae ferns, as well as the foliage of the Cheirolepidiaceae conifers, may have been the major sources of nutrition of I. bernissartensis and other herbivorous iguanodontians. The paleobotany of the four major localities bearing I. bernissartensis remains in western Europe was surveyed to determine the habitat and feeding preferences of this styracosternan dinosaur. These localities are Bernissart (Belgium), Isle of Wight (England), Nehden (Germany), and Morella (Spain). In accordance to this survey, the habitat preferences of I. bernissartensis and association with specific plant communities show that this ornithopod species was adapted to a wide variety of paleoenvironments.

Early development of the Patagonian fold and thrust belt and the onset of foreland sedimentation in the Austral-Magallanes basin

Retroarc basins register the onset of compressional exhumation during the Cretaceous in the Andes, evidenced by sequences showing sedimentary provenance from the orogen. We present U–Pb detrital zircon geochronology from the Austral-Magallanes basin in the Southern Patagonian Andes (∼47–48°SL), where the foreland stage began in the Early Cretaceous. The littoral sandstones from basal foreland sequences of the Río Belgrano Formation yield ∼123 Ma maximum depositional ages, confirming previous studies that the basin infill is early Aptian. The detrital zircon ages showed two main clusters of 129-115 Ma and 151 -140 Ma, that are derived from the coetaneously exhumed Andean arc and earlier Jurassic magmatic sources. The zircons which overlap with ages of Upper Jurassic Andean synrift volcanics, confirms orogenic exhumation coeval with sedimentation. A sequence of retroarc volcanism dated between 119 and 97 Ma overlies the basal foreland littoral-continental deposits, and it is followed by a Late Cretaceous-Paleocene hiatus. Further analysis of detrital zircons ages distribution and geological considerations, indicates that the studied northern depocenter was a source region of sedimentary supply after its Cenomanian exhumation.

Record of Early Cretaceous dinoflagellate cysts from well JM-A, Dhansiri Valley of Upper Assam Shelf, India

A palynological study on subsurface Early Cretaceous sediments (1550–1860 m) in well JM-A located in Dhansiri Valley, Upper Assam Shelf has been carried out for determination of age and depositional environment. The palynological investigations resulted into the identification of the characteristic and diversified occurrence of Early Cretaceous dinoflagellate cysts comprising Batioladinium micropodum, Achomosphaera? neptuni, Batiacasphaera asperata, Lagenorhytis sp. cf. L. delicatula, Mendicodinium caperatum and Canningia sp. along with associated dinoflagellate cysts. The significant assemblage of spore-pollen assemblage represented by Cicatricosisporites australiensis, Ceratosporites equalis, Gleicheniidites circinidites, Contignisporites cooksonii, Microcachryidites antarcticus, Podosporites tripakshii and Callialasporites trilobatus has also been recorded. The Early Cretaceous sediments are regarded as Bamangaon Formation in Dhansiri Valley. The occurrence of dinoflagellate cysts suggests marginal marine environment for Bamangaon Formation deposited during the Early Cretaceous period corresponding to the Rift Phase. The Formation overlies the Metamorphic Basement Complex, and it is unconformably overlain by the sediments of Tura Formation of Ypresian (Early Eocene) age, deposited under subtidal to inner shelf environment during the Passive Margin Tectonic Phase.

The problem of isolation and freshening of the Jurassic–Early Cretaceous Middle Russian Sea: A new 87Sr/86Sr, δ18O and δ13C record from the Saratov Volga region

We provide the first strontium isotope data on molluscs from the lowermost Bathonian (Besnosovi Zone) and lower Aptian (Tenuicostatus and Volgensis zones) of the Saratov Volga region and some new O- and C-isotope results on early Aptian fossils from this region. Despite minor diagenetic changes in the earliest Bathonian bivalve shells from the Besnosovi Zone, they show 87Sr/86Sr values very close to that (0.70706) of a well-preserved belemnite rostrum from the same zone. New data on the Sr-isotopic composition of the Jurassic and Early Cretaceous (early Aptian) molluscs from the Saratov Volga region, combined with information on the stable isotope content of these molluscs, suggest that the isolation and partial freshening of the Middle Russian Sea occurred both in the late Oxfordian-Kimmeridgian, as has recently been reported, and in the early Aptian (during the Volgensis, to a lesser extent the Tenuicostatus chrons). This information on the lower Aptian is consistent with the available stable isotope, palynological and palaeoecological data. The pronounced early Aptian 87Sr/86Sr value deviation detected in many well-preserved fossils mainly from the Volgensis Zone seems to have contributed to the active input of radiogenic strontium into the basin during a series of repetitive events associated with some episodic isolations and partial freshening of the Middle Russian Sea, starting at the Tenuicostatus Chron and intensifying at the onset of the Volgensis Chron associated with the Oceanic Anoxic Event 1a (OAE 1a). New isotope data, collected from certain molluscs residing in the lower Aptian Tenuicostatus Zone of the Saratov Volga region and living in normal seawater salinity conditions, when combined with literature evidence sourced from other locations such as Ulyanovsk Volga region, Central Pacific and Germany suggest the presence of early Aptian climatic optimum. Further molluscs from the lower Aptian Volgensis Zone of the study area offer insight into the habitat conditions of Mesozoic ammonoids.

THE FIRST RECORD OF A REPRESENTATIVE OF THE TOARCIAN-EARLY AALENIAN BELEMNITES IN KIMBERLITES OF THE OBNAZHENNAYA PIPE (NORTHEASTERN SIBERIAN PLATFORM)

Berlites of the Obnazhennaya pipe of the Kuoika kimberlite field (northeastern Siberian Platform, Olenyok uplift), a rostrum fragment of a representative of Toarcian–Early Aalenian (latest Early Jurassic–earliest Middle Jurassic) belemnites was found for the first time, namely Arcobelus cf. krimholzi (Sachs, 1970). It is shown that belemnite records previously known from here and dated to the Late Jurassic or Early Cretaceous, may be of Bajocian–Bathonian (Middle Jurassic) age. The stage of kimberlite magmatism of 177 ± 1.5 Ma, recently established in the northeastern part of the Siberian craton according to U–Pb geochronological data, falls on the time of the existence of belemnites of the genus Arcobelus. The estimated Late Bajocian–Early Bathonian age of the representative of the genus Pachyteuthis previously found in kimberlites of the Obnazhennaya pipe is consistent with the 40Ar/39Ar age (167 Ma) as well as with the age based on some paleomagnetic data (168 ± 11 Ma) reported for the pipe. In the paleogeographic schemes of the northeastern part of the Siberian Platform during the Toarcian–Early Bathonian interval, the inner part of the shelf should be extended to the territory of the Kuoika kimberlite field, taking into account the new data on belemnites.

Deposition in the Northwest Porcupine Basin During the Cretaceous

The paper details the sedimentary infill of the northwest part of the Porcupine Basin, offshore west Ireland, during the Cretaceous. This is a critical area for understanding the sediment input and incremental infilling of the basin, particularly during the early Cretaceous. Late Jurassic rifting and early Berriasian erosion produced a northward narrowing valley on the Base Cretaceous unconformity surface, which provided an entry point for sediment into the basin and also constrained the lateral extent of initial sedimentation. Following Berriasian marine transgression, the first deposits in the Porcupine Basin were turbidites located in localised depressions on the unconformity surface (named here informally as Basal Deposits 1–4). As the unconformity surface became smoother, the succeeding layers were more widespread (Sequences 1–3, the top being of probable Barremian age). Several features, interpreted as mounded fans sourced from the basin flanks, are developed in the Valanginian-Barremian section. Where drilled, the Berriasian to Barremian section is predominantly fine-grained. The rifted marginal horsts were covered in late Barremian time, and Aptian and later sediments onlapped the flanks of the Porcupine High to the west. The ‘Near Base Aptian’ is a well-defined prograding surface and the ‘Near Top Aptian’ horizon is a marked unconformity. The Aptian section is comprised predominantly of deep-water mudrocks and siltstones, although a distinctive, possibly shallower, erosive Intra-Aptian event was also mapped. A renewed sediment influx, comprising of sand prone deltaics, occurred at the northern margin of the basin during the Albian. Sand content decreases southwards into the basin. Sedimentation in the late Cretaceous was dominated by the basinwide deposition of the Chalk Group (Cenomanian-Selandian) deposited in a stable thermal subsidence setting. At the northern basin margin Upper Cretaceous deposits are thin and lithologically variable. The well-defined ‘Top Chalk’ reflector, which shows mounded features, is overlain unconformably by Paleocene clastics.

The early fossil record of Caturoidea (Halecomorphi: Amiiformes): biogeographic implications

Caturoidea is a clade of Mesozoic predatory ray-finned fishes which lived mainly in the Jurassic. The clade has a few records in the earliest Cretaceous and only two in the Triassic. Among the latter, specimen MPCA 632 Caturus sp. doubtfully from continental Early Triassic of Argentina, i.e., outside Europe, was particularly problematic in the light of the known fossil record of the group, which suggested their origin in the Western Tethys. The micropaleontological and geochemical analysis of bulk-rock samples of MPCA 632 allowed us to correct the provenance of the specimen which corresponds to Tithonian marine outcrops of the Vaca Muerta Formation, Neuquén, Argentina. Specimen MPCA 632 is excluded from Caturus and reclassified as Caturoidea sp. MPCA 632 might be a specimen of Catutoichthys olsacheri, the only caturoid known from the Vaca Muerta Formation (Los Catutos Member), but the fossils are not comparable and, thus, this hypothesis needs further study. Additionally, the first-hand study of the type material of the only other alleged Triassic caturoid, Furo insignis, in the Norian of Seefeld, Austria, led to the exclusion of this taxon from the Caturoidea. Consequently, the clade Caturoidea is restricted to the Jurassic–Lowest Cretaceous. After a modest evolution during the Early Jurassic, the group had its initial radiation and westward dispersion across the Hispanic Corridor during the Middle Jurassic and reached its maximal diversity during the Kimmeridgian and Tithonian.

First Articulated Rhamphorhynchoid Pterosaur from the Early Cretaceous of the Democratic People’s Republic of Korea

First Articulated Rhamphorhynchoid Pterosaur from the Early Cretaceous of the Democratic People’s Republic of Korea

Lower Cretaceous (Aptian-Albian) Bisbee Group, Arizpe area, northern Sonora, Mexico: Integrated biostratigraphy, age and provenance from U-Pb and Hf isotopes

New data on the stratigraphy, biostratigraphy, detrital zircon U-Pb, and Hf isotope geochronology of a Lower Cretaceous succession of the Bisbee Group in northern Sonora, Mexico that accumulated in the Altar-Cucurpe sub-basin help to constrain ages of their formations and documents the detrital provenance. These tectonically shortened strata, studied in the Arizpe area, crop out in the Cerro La Ceja block (CCB) composed of the upper Morita Formation, the complete Mural Limestone, and Cintura Formations, and the lower part of La Juana Formation. The Sierra Los Azulitos block (SAB), composed of the Mural Limestone, is thrust eastward over the CCB. A measured section of the Mural Limestone in the SAB block includes the upper Tuape Shale, Los Coyotes, Cerro La Puerta, and part of the Cerro La Espina members whose age is constrained as upper Aptian to lower Albian based on benthic and planktonic foraminifera, bivalves and echinoderms. The age of the boundary between the Morita and Tuape Shale Member is constrained by detrital zircon maximum depositional ages (MDA) of 115.8 ± 1.1 Ma and 113.9 ± 0.8 Ma, respectively. The MDA of the upper Mural is 111.6 ± 1.6 Ma and the MDA of basal Cintura Formation is 108.8 ± 1.1 Ma. The La Juana Formation has upper Albian bivalves and echinoderms.
 About one-quarter of the detrital zircon grains dated from the five sandstone samples have Proterozoic ages with age peaks that clearly indicate provenance from basement rocks of southwestern Laurentia. More than two-thirds of the grains are of Jurassic and Early Cretaceous age in about the same proportions, and have main peaks at 166, 150, and 118 Ma. The Jurassic grains may have sources in rocks of the Jurassic Cordilleran continental magmatic arc of southwestern North America, and the most probable sources for the Cretaceous grains are arcs of the Peninsular Ranges batholith that by that time were located adjacent to coastal Sonora. Jurassic and the Early Cretaceous zircons dated from 195.3 to 106.8 Ma both have mixed εHf(t) values that range from 9.53 to -21.28, and TDM model ages between 0.4 to 0.8 Ga for the primitive grains, and 0.8 to 1.3 Ga for the more evolved zircons. The probable source for the Jurassic grains with negative εHf values might be local granites of that age in northern Sonora that have Neoproterozoic TDM model ages. In contrast, sources for the Jurassic zircon with positive Hf values may be Jurassic igneous and metaigneous rocks of the Peninsular Ranges Batholith of the Californias, although data reported are scarce. Similarly, the Early Cretaceous detrital zircon grains with mixed positive and negative εHf values may have provenance from igneous rocks of the Peninsular Ranges Batholith-Sierra Nevada magmatic arc.

Angiosperm flowers reached their highest morphological diversity early in their evolutionary history.

Flowers are the complex and highly diverse reproductive structures of angiosperms. Because of their role in sexual reproduction, the evolution of flowers is tightly linked to angiosperm speciation and diversification. Accordingly, the quantification of floral morphological diversity (disparity) among angiosperm subgroups and through time may give important insights into the evolutionary history of angiosperms as a whole. Based on a comprehensive dataset focusing on 30 characters describing floral structure across angiosperms, we used 1201 extant and 121 fossil flowers to measure floral disparity and explore patterns of floral evolution through time and across lineages. We found that angiosperms reached their highest floral disparity in the Early Cretaceous. However, decreasing disparity toward the present likely has not precluded the innovation of other complex traits at other morphological levels, which likely played a key role in the outstanding angiosperm species richness. Angiosperms occupy specific regions of the theoretical morphospace, indicating that only a portion of the possible floral trait combinations is observed in nature. The ANA grade, the magnoliids, and the early-eudicot grade occupy large areas of the morphospace (higher disparity), whereas nested groups occupy narrower regions (lower disparity).

The oldest fossil bird-like footprints from the upper Triassic of southern Africa.

Footprint morphology reflects the anatomy of the trackmaker's foot and is direct evidence for the animal's behaviour. Consequently, fossil tracks can be used to infer ancient diversity, ethology, and evolutionary trends. This is particularly useful for deep-time intervals during which the early history of an animal group is reliant upon limited fossil skeletal material. Fossil tracks of early birds and theropods, the co-existing dinosaurian ancestors of birds, co-occur in the rock record since the Early Cretaceous. However, the evolutionary transition from dinosaur to bird and the timing of the birds' origin are still contested. Skeletal remains of the basal-most birds Aurornis, Anchiornis, Archaeopteryx and Xiaotingia are Middle to Late Jurassic, while tracks with tentative bird affinities, attributed to dinosaurs, are known from as early as the Late Triassic. Here, we present numerous, well-provenanced, Late Triassic and Early Jurassic tridactyl tracks from southern Africa, with demonstrable bird-like affinities, predating basal bird body fossils by c. 60 million years.

Tectonics and evolution of the Palmeiras and Xai-Xai Grabens, offshore southern Mozambique

The tectonic evolution of the Mozambique Basin was controlled by the break-up of Gondwana which led to the development of extensional domains along the East African margin. As a result, multiple grabens systems were formed both onshore and offshore southern Mozambique. Two of them are the Palmeiras and Xai-Xai grabens, which are discussed in greater details in this study using an extensive seismic dataset, together with regional gravity and magnetic data. The data show that the Palmeiras Graben evolved from a single extensional phase in the Middle to Late Jurassic (Kimmeridgian?). In contrast, the Xai-Xai Graben records three extensional phases. The first extensional phase occurred in the Late Jurassic (Tithonian?) to Early Cretaceous (Berriasian), the second during the Aptian-Albian and the third in the Late Miocene. The tectonic evolution of these grabens strongly controlled their sedimentary infill during Late Jurassic and Early Cretaceous rifting.Volcanism associated to these tectonic events is documented by onshore and offshore boreholes, as well as by the presence of buried volcanic bodies, lava extruded along fault planes and intrusions of Mesozoic age. Furthermore, a volcano-sedimentary sequence and dome type volcanoes were imaged in seismic data.Differences in tectonic activity impacted the oil and gas potential of both the Palmeiras and Xai-Xai grabens. The sedimentary sequences deposited in the Palmeiras Graben were preserved due to a period of relative tectonic stability predominating from the Aptian to the present day. The burial of the Palmeiras Graben during this period of tectonic stability under a thermal subsidence favoured the generation and preservation of hydrocarbons. In contrast, the Xai-Xai Graben was impacted by intense tectonics, which led to a limited or restricted deposition of strata since the Late Cretaceous to the Paleocene – Early Eocene. As a consequence of a long lasting tectonic activity in the Xai-Xai Graben, uplifting and erosion of potential reservoirs and destruction of existing traps, impacted on the prospectivity for hydrocarbons.

Genesis of the Yidonglinchang gold deposit, Lesser Xing’an Range, China: Insights from fluid inclusions, H-O-S-Pb isotopes, and Sm-Nd and U-Pb geochronology

The origin and evolution of the newly discovered Yidonglinchang gold deposit in the Lesser Xing’an Range, Northeast China, remain poorly understood. This article focuses on the investigations of the geological characteristics, fluid inclusions, H-O-S-Pb stable isotopes and geochronology of the deposit. The Yidonglinchang gold deposit is mainly controlled by NEE-trending faults, and the ore bodies are present in volcanic rocks of the Early Cretaceous Ningyuancun Formation (K1n). Silicification, pyritisation, and argillization zones develop sequentially from near the ore center outwards. The ore minerals mainly include electrum and argentite. The gangue minerals are mainly quartz, calcite, and a small amount of sericite, plagioclase and adularia. The main gold-bearing minerals are quartz and calcite. The primary fluid inclusion types in quartz are pure-liquid-phase, gas-rich-phase, and liquid-rich-phase inclusions. Most of the inclusions are classified as a H2O-NaCl system which were formed under low-temperature, low-salinity conditions, indicating that Yidonglinchang is an epithermal gold deposit. The occurrence of boiling fluid inclusion assemblage indicates that the fluids underwent decompression boiling. Sm-Nd dating of calcite from the main ore-forming stage yields an age of 97.5 ± 2.3 Ma, which is interpreted as the timing of mineralisation. Zircon U-Pb dating of dioritic porphyrite yields ages of 98.8 ± 1.1 and 98.0 ± 1.3 Ma, which are consistent with the mineralisation age, suggesting a potential genetic link between the intrusive rocks and the ore formation. H-O-S-Pb isotopic compositions indicate that the ore-forming fluids were magmatic water during the early mineralisation stage, with the addition of meteoric water during the late stage. These isotopic compositions are also indicative of an origin of the ore-forming materials from the mixed crustal and mantle components. The mineralisation of the Yidonglinchang gold deposit was related to the slab rollback of the subducted Palaeo-Pacific Plate in the early Late Cretaceous.

TAXONOMIC AND BIOSTRATIGRAPHIC REMARKS ON TORINOSUELLA MAYNC, 1959 AND BALKHANIA MAMONTOVA, 1966, LARGER BENTHIC FORAMINIFERA FROM THE LOWER CRETACEOUS OF IRAN (SANGESTAN, TIRGAN FORMATIONS)

The monospecific genera Torinosuella Maync [type-species T. peneropliformis (Yabe & Hanzawa)] and Balkhania Mamontova (type-species B. balkhanica Mamontova) have been reported from the Lower Cretaceous of Iran, respectively the ‘Carbonate Member’ of the Sangestan Formation (Central Iran) and the Tirgan Formation (NE Iran). The literature review reveals a range of late? Tithonian–early Barremian for Torinosuella and late Barremian–early Aptian for Balkhania. In a recent publication dealing with the ‘Taft’ Formation (Central Iran) and the Tirgan Formation (northeastern Iran), both taxa have been lumped together and described as two morphotypes of B. balkhanica based essentially on size differences. This mixing was associated with incorrect phylogenetic, taxonomic, biostratigraphic (e.g., First Appearance Datum) and palaeoecological conclusions that are herein addressed and corrected. Without clarification about the spatial and temporal distribution of individual taxa, the usefulness of larger benthic foraminifera for biostratigraphy, palaeoecology and palaeobiogeography would be distinctly reduced.

Methane adsorption effected by pore structure of overmature continental shale: Lower Cretaceous Shahezi Formation, Xujiaweizi Fault, Songliao Basin

Methane adsorption effected by pore structure of overmature continental shale: Lower Cretaceous Shahezi Formation, Xujiaweizi Fault, Songliao Basin