Middle Jurassic-Early Cretaceous Research Articles

Multiple stages of continental rifting in Eastern Peninsular Malaysia: new insights from Jurassic–Cretaceous granitoids

Mesozoic granitoids in Peninsular Malaysia provide crucial information on the temporal–spatial relationship between the Tethyan and Palaeo-Pacific domains. This paper presents new ages and geochemical data for newly identified Jurassic–Cretaceous granites and meta-granites from East Malaya. These granitoids can be divided into three groups. Group 1 consists of high-K calc-alkaline granites and granodiorites (171–162 Ma) with variable ε Nd ( t ) values of −7.4–+0.5, zircon ε Hf ( t ) values of −7.4–+8.6, and high initial ratios for 206 Pb/ 204 Pb (20.04–20.65), 207 Pb/ 204 Pb (15.73–15.79) and 208 Pb/ 204 Pb (39.80–40.20). The melting of metasedimentary rocks with a juvenile mafic component formed Group 1 samples. Group 2 granite porphyries ( c. 131 Ma) with A-type affinities and Group 3 granitic gneisses ( c. 130 Ma) with I-type affinities share similar ε Nd ( t ) values (−7.2 to −5.5), zircon ε Hf ( t ) values (−10.1–+6.5), and initial ratios for 206 Pb/ 204 Pb (18.81–19.02), 207 Pb/ 204 Pb (15.71–15.77) and 208 Pb/ 204 Pb (38.95–39.59). Although Group 2 and 3 samples were derived from an ‘ancient’ meta-mafic source region, Group 2 shows evidence for the involvement of a juvenile mafic component. All these granitoids are akin to the Permian–Triassic igneous rocks in East Malaya. The Jurassic–Cretaceous igneous rocks in Eastern Peninsular Malaysia were formed during multiple stages of continental rifting in response to Palaeo-Pacific slab rollback pulses rather than by Tethyan evolutionary processes. Supplementary material : Data for the Middle Jurassic–Early Cretaceous granitoids of East Malaya are available at https://doi.org/10.6084/m9.figshare.c.6689085 Thematic collection: This article is part of the Mesozoic and Cenozoic tectonics, landscape and climate change collection available at: https://www.lyellcollection.org/topic/collections/mesozoic-and-cenozoic-tectonics-landscape-and-climate-change

Late Paleozoic–Cenozoic Tectonothermal Evolution of Transbaikalia: Thermochronology of the Angara–Vitim Granitoid Batholith

Abstract —The tectonothermal evolution of Transbaikalia is reconstructed using U/Pb, 40Ar/39Ar, and apatite fission track thermo-chronology of samples from the Late Paleozoic Angara–Vitim granitoid batholith (AVB). Successive closure of the zircon and amphibole isotope systems provides evidence that the AVB rocks cooled down rapidly soon after crystallization and 7–4 km of rocks were denuded subsequently during an extensive late Paleozoic orogeny in southern Siberia. The isotopic system of feldspar closed in the Middle Jurassic–Early Cretaceous (170–140 Ma) after a period of tectonic stability and slow closure of the biotite isotopic system in the early Permian–Middle Jurassic (295–170 Ma). The 170–140 Ma span was the time when the Mongol–Okhotsk orogen began its evolution, and the orogeny caused denudation of ~3 km of rocks. Denudation was slow in the Paleogene–Miocene (60–5 Ma) but accelerated over the past 5 million years (a ~3–2 km thick layer) during rapid cooling of rocks and activity under a far-field effect of the India–Eurasia collision.

Footwall geomorphology during necking domain evolution: A new model for the Frøya High, mid‐Norwegian rifted margin

AbstractObservations and modelling results from highly extended regions indicate that detachment fault systems recording displacements of 10 km or more become associated with footwall uplift and back‐rotation. This is commonly explained by the rolling hinge model, which predicts detachment fault back‐rotation and severe dip reduction (<20°) controlled by the amount of extension. Although detachment faults within necking domains at rifted margins often record displacements in orders consistent with those for the rolling hinge model, it is rarely invoked to explain the associated footwall configurations. Our study area encircles the necking domain of the mid‐Norwegian rifted margin, where the Middle Jurassic–Early Cretaceous Klakk Fault Complex (KFC) directly separates the Frøya High from the Rås Basin. The Frøya High represents the eroded footwall of the KFC detachment fault system which records displacements of 20–40 km. Seismic mapping and well correlation across the Frøya High reveal how three erosional unconformities correspond to three laterally extensive top basement segments which follow the strike of the sinuous KFC. The segments differ in terms of dip, basement geomorphology and the composition and age of the sediments that rest unconformably on the top of basement. We attribute the associated cross‐cutting basement unconformities across the Frøya High to footwall uplift and back‐rotation during fluctuating relative sea‐level and repeated subaerial exposure during Middle Jurassic–Early Cretaceous times. We herein introduce a revised tectono‐sedimentary model for the evolution of the Frøya High, with significant implications for sediment (re‐)routing across the high during rifting. The model indicates that spatio‐temporal sediment distribution was ultimately controlled by the process of necking and evolution of the KFC. Our findings indicate a rolling hinge‐type evolution for the KFC and further suggest that the associated mechanisms may be more common in the necking domains of rifted margins than previously assumed.

Type and evolution of the Middle Jurassic–Early Cretaceous basin at the northern margin of the Lhasa Block: constraints of sedimentary characteristics and provenance tracing based on zircon U-Pb ages

To identify its type and evolution features of the Middle Jurassic–Early Cretaceous basin at the northern margin of the Lhasa Block (NMLB) is of great significance for reconstructing its tectonic-paleogeography and assessing the petroliferous basins in the Bangong-Nujiang suture zone (BNSZ) and its adjacent area. This study conducted the sedimentary characteristic analyses and detrital zircon U-Pb dating of the Middle Jurassic–Lower Cretaceous strata exposed in the northern part of Nagqu County (NPNC), Tibet. The Middle–Upper Jurassic Lagongtang Formation was mainly deposited in a steep slope delta and its middle part is characterized by debris flows moving southeastward. The lower part of the Upper Jurassic–Lower Cretaceous Duoni Formation was characterized by molasses formation, and its middle and upper part were primarily deposited on a tidal flat-mixed shelf. The 384 detrital zircons from the debris-flow deposits of the Lagongtang Formation yielded ages of 2800∼210 Ma, except for one yielding an age of 174 Ma. The detrital zircons from the lower part of the Duoni Formation yielded ages of 2744∼152 Ma. Comprehensive research results show that the basin located at the NMLB is a peripheral foreland basin controlled by the BNSZ and had dual source supply, and around 152 Ma, the basin was accompanied by a stronger overthrust event and experienced the conversion from flysch basin to molasses one. Subsequently, a new foreland basin formed marked by the deposition of the Shamuluo Formation in the BNSZ.

Late Jurassic back‐arc extension in the Neuquén Basin (37°S): Insights from structural, sedimentological and provenance analyses

AbstractThe Middle Jurassic–Early Cretaceous evolution of the Neuquén Basin is traditionally attributed to a long phase of thermal subsidence. However, recent works have challenged this model. In view of this, we study the Late Jurassic Tordillo Formation, a non‐marine depositional unit that marks a shift to regional regression across the basin. Previous studies propose different causes for this regression, including the growth of the magmatic arc in the west, uplift in the south or extension in the north. We studied the Tordillo Formation in sections located at an intermediate position in the Neuquén Basin, in order to understand the tectonic processes active during sedimentation. We present evidence of normal faulting within the Tordillo Formation and the base of the overlying Vaca Muerta Formation. Some of these faults can be attributed as syndepositional. We characterize the Tordillo Formation as part of a distal fan‐playa lake depositional system with a contemporaneous western magmatic arc as the main source of sediment. When compared to the Late Triassic–Early Jurassic NE to NNE‐oriented rifting, which marks the opening of the Neuquén Basin, the Late Jurassic extension shows a switch in stress orientation; the latter is orthogonal to the north‐trending subduction zone. We interpret this change as a renewed phase of back‐arc extension induced by slab rollback along with minor distributed intraplate extension prior to opening of the South Atlantic Ocean.

Meso-cenozoic tectonic evolution of the ziyun-luodian fault in SW China

Regional-scale fault systems are important in adjusting intracontinental deformation. Closure of the Paleo-Tethys, Paleo-Pacific subduction, and India-continent-continent collision have all interacted to shape the Meso-Cenozoic tectonics of South China. The Ziyun-Luodian fault (ZLF) straddles across the Guizhou region in southwestern China. New petrographic and structural studies were conducted to reveal the structural evolution of the ZLF and regional deformation. At least three distinct deformation events are identified within the fault zone: During the Indosinian orogeny, dextral thrusting occurred along the ZLF, accompanied by moderate regional uplift in Guizhou, as evidenced by the Upper Triassic-Lower Jurassic disconformity. The main tectonic framework across Guizhou was established during the Yanshanian orogeny. Driven by the west-dipping Paleo-Pacific subduction (Middle Jurassic-Early Cretaceous), sinistral transpression occurred along the ZLF and NE-to N-S-trending fold belts in central-eastern Guizhou, and the NW-striking folds west of the ZLF were developed in under nearly E-W-directed compression. In the late Cenozoic, the ZLF may have undergone sinistral strike-slip movement, similar to the sinistral Ailaoshan-Red River shear zone. The Ziyun-Luodian fault plays an important role in accommodating the Meso-Cenozoic regional deformation in SW South China.

Age of the Tuchengzi Formation in Western Liaoning Province and the Jurassic–Cretaceous Boundary from the Continuous Core Records of Well YD1, Jinyang Basin

The Tuchengzi Formation is widely distributed in western Liaoning Province with a clear top and bottom. It is the focal area for the delineation of the terrestrial Jurassic–Cretaceous boundary in China. Based on continuous core samples taken from well YD1, detailed lithostratigraphic sequences and zircon uranium–lead (U-Pb) dating WERE used to investigate the Tuchengzi Formation. The zircon U-Pb ages of the tuff samples taken from the First and Third Members of the Tuchengzi Formation ranged from 153.8 to 137.16 Ma, indicating that they were formed in the late Middle Jurassic–Early Cretaceous. Dating results from the bottom of the Second Member of the Tuchengzi Formation indicate that the sedimentary time of the stratum is no later than 145.7 ± 2.1 Ma. We concluded that the Jurassic–Cretaceous boundary of the Jinyang Basin in western Liaoning province may be located at the interface at a depth of 464 m in well YD1. This conclusion is consistent with the Jurassic–Cretaceous boundary that has been presumed by other researchers based on paleontological assemblage features found in recent years, and can provide useful geological marker beds for the future study of the terrestrial Jurassic–Cretaceous boundary. In addition, the authors also systematically sorted the potential development areas and layers of the terrestrial Jurassic–Cretaceous boundary line, which may also provide useful geological marker beds for the future study of the terrestrial Jurassic–Cretaceous boundary.

Mineralogy and Origin of the Manganese Deposit in the Sulaimani Province, Kurdistan Region of Iraq: Insight to Serpentinization-Induced Manganese Production Scenario

The Manganese deposits in Sulaimani metallogenic province mainly occur within the top Qulqula Radiolarite chert unit of the Penjween ophiolite complex as strata bound type deposits near Kani Saif village, 15 km south of the Penjween district within the Imbricated zone, Kurdistan Region of Iraq. A restricted occurrence of massive manganese boulders was identified, 1 km north to the Mawat District, associated with the Oligocene Merga Red beds Group. The Qulqula Radiolarite represents the Middle Jurassic-Early Cretaceous sedimentary cover of Neo-Tethys oceanic crust deposits throughout the early to mature stages of the Neo-Tethys ocean opening along the northern and eastern margins of the Afro-Arabian plate. The field and petrographical data indicated that the nature of manganese mineralization in the area is of various forms including veins, brecciated, micronodules, banded and massive types. Reflected light microscopy, high resolution scanning electron microscope and X-ray diffraction reveal that the mineral assemblages are dominated by barunite, rhodinite, hematite, quartz and carbonate for the massive metamorphosed type deposit in the Mawat area. Meanwhile, the mineralogy of the vein, micronodule and banded types are simple and dominated by pyrolusite, hollandite minerals close to Kain Saif village. Combinations of the modal manganese minerals, filed and textural observations, a paragenetic-time model suggests that the manganese deposit in the area formed via a sequence of multiple processes (1) serpentinization of the upper mantle at mid oceanic ridge during the Cretaceous period, (2) deposition from diluted hydrothermal fluids in the Neo-Tethys mature oceanic basin, (3) the diagenetic modification of the manganese bearing sediment and (4) metamorphism of sediment a combing Zagros orogeny in Paleogene. Overall data suggest that the manganese deposits in the Kurdistan region of Iraq are cogenetic and spatially related to those which occur along the entire margin of the Arabian plates from Oman to Turkey associated with the radiolarite facies.

Meso-Cenozoic growth of the eastern Qilian Shan, northeastern Tibetan Plateau margin: Insight from borehole apatite fission-track thermochronology in the Xiji Basin

The surface uplift of the Tibetan Plateau (TP) is among the most important geological events in Earth's history, but the growth of the eastern TP margin that yielded the thickened crust and abrupt topography remains controversial. In this paper, six sample apatite fission-track (AFT) analyses of three boreholes in the Xiji Basin are applied to constrain the Mesozoic-Cenozoic uplift and exhumation history of the eastern Qilian Shan, northeastern TP. Most of the AFT ages range from 134 ± 8 Ma to 117 ± 6 Ma, except for the shallowest sample, with a younger age of 65.9 ± 3.2 Ma. Thermal history modeling indicates that the eastern Qilian Shan experienced a three-phase differential cooling history: (1) widespread rapid cooling during the Middle Jurassic-Early Cretaceous (ca. 174-120 Ma, Stage 1), (2) regional cooling during the Late Cretaceous-Paleocene (ca. 80-60 Ma, Stage 2) and (3) widespread cooling during the Eocene-early Miocene (ca. 40-20 Ma, Stage 3). We conclude that the Middle Jurassic-Early Cretaceous was the main stage of the growth and thickening of the northeastern TP, which was related to the upper-crustal horizontal shortening of the eastern Qilian Shan. Thermal history modeling of the youngest sample and seismic profile analysis imply significant reactivation of the Liupanshan fault zone during ca. 80-60 Ma. This locally intense uplift and deformation on the eastern margin of the Qilian Shan during the Late Cretaceous was likely induced by the closure of the Neo-Tethys and the continued shortening of the Lhasa-Qiangtang block. Late Eocene-Early Miocene (ca. 40-20 Ma) cooling of the eastern margin of the Qilian Shan records the coeval crustal extension and exhumation of the northeastern margin of the TP as the far-field effect of subduction of the western Pacific plate. Our AFT data detect no intense late Cenozoic reactivation information for the Xiji region, which indicates that the ca. 15-7 Ma rapid uplift triggered by fault reactivation was only located in the Haiyuan-Liupanshan fault zone, along the eastern margin of the Qilian Shan, northeastern TP. This multi-phase exhumation history is not beneficial for regional hydrocarbon exploration.

Late paleozoic–mesozoic subduction and accretion of the paleo-pacific plate: insights from the ocean plate stratigraphy of the wandashan accretionary complex, NE China

ABSTRACT The Wandashan accretionary complex (AC) is located in the easternmost part of Northeast China and consists of the Raohe complex in the east and Yuejinshan complex in the west. It represents an excellent location for insights into Paleo-Pacific subduction and accretion processes. However, the protolith (mainly contains Ocean Plate Stratigraphy ‘OPS’ and ophiolite) nature and tectonic evolution of the Wandashan AC are under debate. This contribution reports three representative geological sections, conducts the OPS reconstruction, compares the reconstructed Wandashan OPS with the adjacent Bikin OPS in Russia and Inuyama–Mino–Neo OPS in Japan, and re-accessed detrital zircon U-Pb age data of the Wandashan area. The results show that the protolith of the Yuejinshan complex is consistent with the OPS formed on a back-arc basin. This back-arc basin formed in the Early Permian and eventually closed after ~216 Ma, and the basin materials emplaced and metamorphosed at ~210–180 Ma to form the metasedimentary rocks and greenschists. The Raohe complex has a relatively complete OPS, which mainly includes Carboniferous–Permian coastal- to shallow-sea- limestones, Middle Triassic–Early Jurassic pelagic cherts, Middle Jurassic hemipelagic siliceous shales/mudstones and slates, and a Middle Jurassic–Early Cretaceous turbidite sequence. The provenances of the trench fill (turbidites) include the widespread Precambrian basement in NE China, the Yuejinshan complex, seamounts and seafloor sediments on the subducted slab, and the adjacent Jiamusi, Khanka, and Songnen massifs. The Raohe OPS experienced decollement, submarine sliding, diapirism, offscraping, underplating, out-of-sequence thrusting, and progressive disruption during the process of accretion, forming the Raohe complex in the Middle Jurassic–Early Cretaceous (~169–133 Ma). Together, the Raohe and Yuejinshan complexes form the Wandashan AC.

Diagenesis Evolution and Pore Types in Tight Sandstone of Shanxi Formation Reservoir in Hangjinqi Area, Ordos Basin, Northern China

Diagenesis and pore evolution of tight sandstone reservoir is one of the most important issues surrounding clastic reservoirs. The tight sandstone of the Shanxi Formation is an important oil and gas producing layer of the Upper Paleozoic in Ordos Basin, and its densification process has an important impact on reservoir quality. This study determined the physical properties and diagenetic evolution of Shanxi Formation sandstones and quantitatively calculated the pore loss in the diagenetic process. Microscopic identification, cathodoluminescence, and a scanning electron microscope were used identify diagenesis, and the diagenesis evolution process was clarified along with inclusion analysis. In addition, reservoir quality was determined based on the identification of pore types and physical porosity. Results show that rock types are mainly sublitharenite and litharenite. The reservoir has numerous secondary pores after experiencing compaction, cementation, and dissolution. We obtained insight into the relationship between homogenous temperature and two hydrocarbon charges. The results indicated that there were two hydrocarbon charges in the Late Triassic–Early Jurassic (70–90 °C) and Middle Jurassic–Early Cretaceous (110–130 °C) before reservoir densification. The quantitative calculation of pore loss shows that the average apparent compaction, cementation, and dissolution rates are 67.36%, 22.24%, and 80.76%, respectively. Compaction directly affected the reservoir tightness, and intense dissolution was beneficial to improve the physical properties of the reservoir.

Sedimentary Environments and Basin Development of the Middle Jurassic–Early Cretaceous Tetori Group in Its Main Area, Central Japan

Sedimentary Environments and Basin Development of the Middle Jurassic–Early Cretaceous Tetori Group in Its Main Area, Central Japan

Post-rift extensional tectonics at the edge of a carbonate platform: insights from the Middle Jurassic-Early Cretaceous Monte Giano stratigraphic record (central Apennines, Italy)

A new interpretation of the Middle Jurassic-Early Cretaceous paleogeographic evolution of the NW sector of the Latium-Abruzzi carbonate platform facing the Umbria-Marche Basin is proposed, based on Monte Giano area (central Apennines, Italy). During Late Triassic-early Bajocian time, the area was characterized by shallow water sedimentation. Inner and marginal carbonate platform deposits are overlain by pelagic deposits (Posidonia level), early Bajocian p.p. in age. This unconformity testifying the sudden drowning of the Monte Giano area, while shallow water sedimentation persisted in the remaining sectors of the carbonate platform. The Posidonia level is paraconformably overlain by distal slope deposits of the Velino Gorge limestones Formation, Kimmeridgian p.p.-Tithonian p.p. in age. Therefore, a 12Ma gap is recorded as in the Umbria-Marche Basin pelagic carbonate platforms. An extensional Bajocian tectonic phase, possibly related to the Piemont-Ligurian Ocean opening coupled with rheologic differences at the basin/platform boundary, drastically changed the regional paleogeography causing the breakup and the drowning of the NW sector of the Latium-Abruzzi carbonate platform and the creation of a large flat-topped pelagic carbonate platform. The estimate offset of the early Bajocian fault is around 300-350m. The Velino Gorge limestones fm. pass laterally and vertically to the Upper Tithonian platform-margin reef complex of the Ellipsactinia limestones fm.; these units constitute a shallowing and coarsening upward sequence and levelled the paleobathymetric gradient created by the Bajocian extension. The progradation of the Latium-Abruzzi carbonate platform continued during Early Cretaceous time. These results have strong implications on the tectonic and paleogeographic evolution of the major domains of the central Apennines.

Palynostratigraphy, Palynofacies, T-R Cycles and Paleoenvironments in the Middle Jurassic–Early Cretaceous Ramså Basin, Andøya, Northern Norway

Palynostratigraphy and palynofacies analyses are applied to identify transgressive-regressive sequences and changes in paleoenvironment through the Middle Jurassic–Early Cretaceous succession of the Ramså Basin on Andøya. The conglomerate, the succeeding lacustrine-swamp deposits of the Hestberget and Kullgrøfta members (Ramså Formation) and the overlying terrestrial to marginal marine deposits of the lower Bonteigen Member (Ramså Formation), comprise the Bajocian T-R sequence. Bathonian–Oxfordian strata appear to be missing in the studied boreholes, and the second T-R cycle spans the Kimmeridgian to Berriasian open marine deposits of the upper Bonteigen Member and the Dragneset Formation (Breisanden, Taumhølet and Ratjønna members). The overlying Nybrua Formation comprises a condensed marine succession of Valanginian–Early Barremian calcareous sandstone and marl, followed by brownish-red siltstone. The upper T-R sequence (Skarstein Formation) consists of marine transgressive Barremian dark siltstones, silty shales and mudstones, followed by dark mudstone and shale. Marine palynomorphs recovered in these stacked marine slope turbidite sediments are of Late Barremian age, but possibly the youngest T-R cycle also includes Aptian deposits elsewhere in the basin.

Geochemistry, U[sbnd]Pb geochronology, and Sr-Nd-Hf isotope systematics of a SW-NE transect in the southern Peninsular Ranges batholith, Mexico: Cretaceous magmatism developed on a juvenile island-arc crust

The Peninsular Ranges batholith (PRB) is a North American Cordillera segment with a protracted record of subduction-related magmatism (177–92 Ma). However, such a record is regionally fragmented, showing broad petrologic variations challenging to integrate into a coherent geologic evolution history. Here, we present a petrogenetic study of Cretaceous plutons in the southern PRB along the Sierra El Arco-San Francisquito transect (SW-NE) perpendicular to the paleotrench. The Middle Jurassic-Early Cretaceous (166–140 Ma) magmatism developed as an island arc with sedimentary rocks of intra-arc and oceanic marginal basins. At the Sierra El Arco, the Calmallí pluton intruded the Jurassic arc sequence. The basic to intermediate rocks of the Calmallí pluton show εSrt (average –3.6), εNdt (average +3.3), and εHft values (average +6.0) that suggest an origin from mantle-derived melts with minor contamination. These rocks display almost flat rare earth elements (REE) patterns and Eu anomalies suggesting plagioclase fractionation. East of the Calmallí pluton from the Piedra Blanca to the San Francisquito region, granodiorite and granite (100–92 Ma) are continuously exposed. The εSrt (average +3.1), εNdt (average +1.1), and εHft (average +2.6) isotopic signatures in the acid rocks suggest a mantle-derived melt genesis with increased contamination. Most granodioritic and granitic rocks display a characteristic depleted-HREE pattern without Eu anomalies, suggesting differentiation under the influence of garnet. The Jurassic-Cretaceous (166–92 Ma) magmatism displays an εSrt vs. εNdt correlation trend, indicating progressive contamination of mantle-derived magmas with a recycled crust. SrNd and NdHf isotopic mixing curves suggest the assimilation of the metasedimentary Triassic basement of NW Mexico instead of the considerably older and isotopically evolved Precambrian basement. The integration of this work with data from NW Mexico suggests a continuous magmatic activity from the Middle Jurassic to the Late Cretaceous. We consider the geochemical, isotopic, and temporal variation of the PRB indicative of natural heterogeneities along the trench axis of a long-lived arc system (crustal thickness and paleogeography) due to continuous subduction of the Farallon plate below the North American plate.

Wear patterns and dental functioning in an Early Cretaceous stegosaur from Yakutia, Eastern Russia.

Isolated stegosaurian teeth from the Early Cretaceous high-latitude (palaeolatitude estimate of N 62°- 66.5°) Teete locality in Yakutia (Eastern Siberia, Russia) are characterized by a labiolingually compressed, slightly asymmetrical and mesiodistally denticulated (9–14 denticles) crown, a pronounced ring-like cingulum, as well as a “complex network of secondary ridges”. The 63 teeth (found during on-site excavation in 2012, 2017–2019 and screen-washing in 2017–2019) most likely belong to one species of a derived (stegosaurine) stegosaur. Most of the teeth exhibit a high degree of wear and up to three wear facets has been observed on a single tooth. The prevalence of worn teeth with up to three wear facets and the presence of different types of facets (including steeply inclined and groove-like) indicate the tooth-tooth contact and precise dental occlusion in the Teete stegosaur. The microwear pattern (mesiodistally or slightly obliquely oriented scratches; differently oriented straight and curved scratches on some wear facets) suggest a complex jaw mechanism with palinal jaw motion. Histological analysis revealed that the Teete stegosaur is characterized by relatively short tooth formation time (95 days) and the presence of a “wavy enamel pattern”. Discoveries of a “wavy enamel pattern” in the Teete stegosaur, in a Middle Jurassic stegosaur from Western Siberia, and in the basal ceratopsian Psittacosaurus, suggest that this histological feature is common for different ornithischian clades, including ornithopods, marginocephalians, and thyreophorans. A juvenile tooth in the Teete sample indicates that stegosaurs were year-round residents and reproduced in high latitudes. The combination of high degree of tooth wear with formation of multiple wear facets, complex jaw motions, relatively short tooth formation time and possibly high tooth replacement rates is interpreted as a special adaptation for a life in high-latitude conditions or, alternatively, as a common stegosaurian adaptation making stegosaurs a successful group of herbivorous dinosaurs in the Middle Jurassic–Early Cretaceous and enabeling them to live in both low- and high-latitude ecosystems.

Petrogenesis of the meta-igneous rocks of the Sierra El Arco and coeval magmatic rocks in Baja California: Middle Jurassic-Early Cretaceous (166-140 Ma) island arc magmatism of NW México

ABSTRACT The Jurassic-Early Cretaceous Vizcaíno and Alisitos terranes are juxtaposed in the central part of the Baja California Peninsula, México. The southernmost outcrops of the Alisitos terrane are located in the Sierra El Arco, which consists of greenschist-facies meta-igneous rocks. Further east in the Calmallí area, amphibolite and paragneiss dominate. The meta-igneous rocks constitute a magmatic system ranging from peridotite to granodiorite, with associated basaltic to dacitic volcanic rocks. The suite displays negative εSrt (average −8.4, n = 23) and positive εNdt values (average +5.8, n = 23), suggesting mantle-derived melts with no discernible assimilation of continental crustal material. Geochemical and isotopic data of the amphibolite suggests a protolith similar to the meta-igneous rocks. Paragneiss samples display εSrt of +166 and εNdt around −7, with Nd crustal residence ages of 1.5 Ga. The isotopic data of the paragneiss suggest provenance from continental sources. Similar to Triassic-Middle Jurassic metasedimentary rocks from the Baja California Peninsula and western México. Middle Jurassic magmatism on Cedros Island (Vizcaíno terrane) and the Sierra El Arco (Alisitos terrane) define an εSrt vs. εNdt evolutionary trend that is mostly within the mantle array, suggesting a common origin within the same island arc subduction setting. Jurassic magmatism of continental affinity, defined by positive εSrt (average +39, n = 15) and negative εNdt values (average −4.2, n = 15), is widespread in the Baja California Peninsula and western México. Our Sr-Nd isotope mixing curves suggest that the assimilation of Late Triassic metasedimentary rocks or a lower crust could explain the isotopic composition of the continental affinity Jurassic magmatism.

Deciphering the Late Paleozoic to Mesozoic tectono sedimentary evolution of the northern Bohemian Massif from detrital zircon geochronology and heavy mineral provenance

From Permian to Late Cretaceous, the northern Bohemian Massif experienced a complex intra-plate tectono sedimentary evolution involving development of at least four generations of sedimentary basins in different settings. We examine this protracted evolution using stratigraphic changes in sediment provenance, analyzed through heavy mineral assemblages and U–Pb detrital zircon geochronology (by laser-ablation ICP–MS) in Permian, Jurassic, and Late Cretaceous successions. The provenance data point to multiple, temporally evolving sources ranging from local (e.g., the ʽWest Sudetic Islandʼ) through more distant from elsewhere in the Bohemian Massif to exotic, likely derived from Baltica. The latter is interpreted as a trace of now completely eroded Late Jurassic to Early Cretaceous basin that once covered the Lusatian (Lausitz) Block and received the Baltica-derived detritus from northerly fluvial and deltaic depositional systems. We suggest that fill of this basin was recycled into the Bohemian Cretaceous Basin during progressive unroofing of the West Sudetic Island. A time-slice reconstruction of the paleogeographic and tectono sedimentary evolution of the northern Bohemian Massif is then developed to show that periods of basin development and deposition (early Permian, late early Permian to Early Triassic, Middle Jurassic–Early Cretaceous, and Late Cretaceous) were interrupted by major depositional gaps (Middle Triassic–Early Jurassic, mid-Cretaceous, and post-early Campanian). The Mesozoic depositional episodes resulted from reactivation of major NW–SE strike-slip fault zones due to stress transfer from the North Atlantic Rift during Jurassic to Early Cretaceous, overridden by the far-field effect of convergence of Iberia, Africa, and Europe during Late Cretaceous.

Polyonyx-like tracks from Middle-?Upper Jurassic red beds of Morocco: Implications for sauropod communities on southern margins of tethys

A new dinosaur tracksite is reported from continental red beds of the Jurassic (Late Bathonian-?Callovian) Isli Formation along the northern flank of the Aït Ali ou Ikkou Syncline of the Imilchil area, Central High Atlas, Morocco. The succession was deposited in a fluvio-lacustrine environment, and contains at least fourteen track-bearing levels. The diverse dinosaur-dominated ichnofauna includes the footprints of crocodylomorphs, pterosaurs, theropods, sauropods and ornithischians, together with numerous invertebrate traces. Here, we focus on a long sauropod trackway, which comprises nine consecutive manus-pes sets preserved as concave epireliefs. The low heteropody and asymmetry of manus prints with a large digit I (pollex) impression oriented medially, and a large triangular claw trace, which is posteriorly oriented, are characteristic of the ichnogenus Polyonyx. Different from typical Polyonyx is the narrow gauge pattern compared to the wide gauge observed in the type trackway from Portugal. Additional material from Morocco, similar to Polyonyx, comprises the trackway of a very small (?juvenile) individual found close to the main trackway, as well as a short trackway from a different locality in the Isli Formation. Our data from the Moroccan High Atlas indicates the presence of basal eusauropods in the Middle Jurassic-Early Cretaceous interval in the northwestern part of Gondwana for the first time, and suggests they inhabited a lacustrine paleoenvironment.

Geochemistry, detrital zircon geochronology and Hf isotope of the clastic rocks in southern Tibet: Implications for the Jurassic-Cretaceous tectonic evolution of the Lhasa terrane

In order to reconstruct tectonic evolution history of the southern margin of Asia (i.e., Lhasa terrane) before the India-Asia collision, here we present a comprehensive study on the clastic rocks in the southern Lhasa terrane with new perspectives from sedimentary geochemistry, detrital zircon geochronology and Hf isotope. Clasts from the Jurassic-Early Cretaceous sedimentary sequences (i.e., Yeba and Chumulong Formations) display high compositional maturity and experienced moderate to high degree of chemical weathering, whereas those from the late Early-Late Cretaceous sequences (Ngamring and Shexing Formations) are characterized by low compositional maturity with insignificant chemical weathering. Our results lead to a coherent scenario for the evolution history of the Lhasa terrane. During the Early-Middle Jurassic (∼192-168Ma), the Lhasa terrane was speculated to be an isolated geological block. The Yeba Formation is best understood as being deposited in a back-arc basin induced by northward subduction of the Neo-Tethys ocean with sediments coming from the interiors of the Lhasa terrane. The Middle Jurassic-Early Cretaceous Lhasa-Qiangtang collision resulted in the formation of a composite foreland basin with southward-flowing rivers carrying clastic materials from the uplifted northern Lhasa and/or Qiangtang terranes. During the late Early-Late Cretaceous (∼104-72Ma), the Gangdese magmatic arc was uplifted rapidly above the sea level, forming turbidites (Ngamring Formation) in the Xigaze forearc basin and fluvial red beds (Shexing Formation) on the retro-arc side. At the end of Late Cretaceous, the Lhasa terrane was likely to have been uplifted to high elevation forming an Andean-type margin resembling the modern South America before the India-Asia collision.