Paleozoic Group Research Articles

Drifting with trilobites: The invasion of early post-embryonic trilobite stages to the pelagic realm

The Ordovician Radiation shaped Paleozoic marine ecosystems and led to an increase in the biodiversity of marine organisms. The onset of the Plankton Revolution in the late Cambrian is an important step within the Ordovician Radiation. During this revolution, various organisms invaded pelagic realms, which affected the marine trophic web through the introduction of phytoplankton, zooplankton, as well as plankton- and suspension-feeding animals. Trilobites, a main Paleozoic group of marine metazoans, played a major role during the Ordovician Radiation. Previous studies showed that some trilobites evolved planktic larvae during the Furongian and Early Ordovician. Herein, we quantify the appearance of trilobite planktic larvae by providing highly resolved Cambrian and Ordovician data on 144 trilobite species with well-known developmental sequences. We show that Cambrian trilobites were dominated by species and families with exclusively benthic early post-embryonic stages. On the contrary, Ordovician seas comprised a remarkable number of trilobites with one or more planktic stages. However, species and families with exclusively benthic early stages still constituted about half of the Ordovician trilobite diversity. The first trilobites with planktic larvae might have been present in the Miaolingian, but their earliest fossil record is from the mid-Furongian. The appearance of planktic forms was accentuated later in the Ordovician with many trilobite lineages adapting a multi-staged planktic mode of life – more than one developmental stage colonizing the water column during ontogeny. Between the Miaolingian and the Middle Ordovician, both species- and family-level data show a progressive increase in the number of taxa incorporating planktic larvae in their development, highlighting a gradual transition in the structure of marine ecosystems during the early Paleozoic.

Ecology, morphology and ontogeny of Paleolimulus kunguricus —a horseshoe crab from the Kungurian (Cisuralian) of the Cis-Urals, Russia

Paleolimulids represent a group of fossil horseshoe crabs that are morphologically comparable to the extant limulids. Recent work has highlighted that, contrary to traditional opinions, Paleolimulidae has a limited taxonomic and morphological diversity at the species and generic level. In the light of this new perspective, it is imperative that material documenting novel facets of species within this Paleozoic group be explored. Here, we revisit Paleolimulus kunguricus Naugolnykh, 2017 from the Cisuralian of Russia and illustrate distinct ontogenetic stages of the species. The so-called ‘trilobite’ stage, two juveniles and adult stages are presented. We document morphological transitions within the prosomal and opisthosomal sections, and changes to the lateral compound eye position. These shifts may reflect distinct life modes experienced during ontogeny. Documentation of Selenichnites ichnofossils associated with P. kunguricus specimens present insight into how the xiphosurid functioned during the later ontogenetic stages and illustrate the first evidence for shell-crushing in fossil xiphosurids. Finally, we demonstrate how occupation of lagoonal palaeoenvironments limited competition with other organisms and aided the survival of Xiphosurida.

An insect wing discovered in the Early Permian Taiyuan Formation (Shanxi Province, China)

Abstract. The first discovery of an insect wing from the Taiyuan Formation, near Yangquan City, Shanxi Province, China, is described. The combination of its wing venation characters makes it difficult to assign it to any known major Paleozoic group. The comparison is made among the new material, stem-Orthoptera species, and “fossil Grylloblattodea”. Further investigation on fossil insects from this locality is needed.

Cretaceous igneous-related mineralisation in the Reefton Goldfield, New Zealand

ABSTRACTThe Reefton Goldfield is well known for its orogenic style of Au mineralisation although the timing remains largely unconstrained. Here, a first unequivocal occurrence of igneous-related mineralisation is documented and it is suggested to place a lower age constraint on when orogenic Au mineralisation occurred. Emplacement of the 118.5 ± 1.3 Ma (U-Pb zircon) Blackwater granitoid dike into Early Paleozoic Greenland Group caused contact metamorphism up to hornblende hornfels facies temperatures (>500°C) at low pressures (<3.75 kbar). A hydrothermal convective system that developed during cooling led to propylitic and phyllic alteration associated with the precipitation in order of decreasing abundance of: pyrite, chalcopyrite, molybdenite, arsenopyrite-galena-sphalerite-millerite. Quartz veins and stockworks containing combinations of pyrite, chalcopyrite and molybdenite are common within several hundred metres of the dike. This igneous-related mineralisation overprints Greenland Group metasedimentary rocks displaying evidence for a phase of ductile deformation and associated with the occurrence of pyrite and ankerite-cored siderite porphyroclasts, chalcopyrite and cobaltite. Au-in-pyrite trace element data indicate that these pyrite porphyroclasts are more enriched in Au than the pyrite associated with dike emplacement. Quartz lodes containing Au occur within zones of ductile deformation elsewhere in the goldfield, and therefore Early Cretaceous emplacement of the Blackwater dike provides a lower age constraint for the ductile mineralisation event.

Polychronous Zirconology of Navysh Volcanics of the Ai Formation (Southern Urals)

In order to resolve the age of Navysh volcanics (NV), which is usually attributed to the Lower Riphean of the Ai Formation, we have used geochronological, petrologic, and mineralogical methods of zirconology, apart from the SHRIMP isotopic data of single zircon grains. Moreover, TIMS isotope age analyses have been conducted, the results of which can be regarded as both controlling and providing the most correct information. The TIMS and SHRIMP data make it possible to suggest a polychronous character of the NV, which include not only Riphean, but also Paleozoic groups of volcanics. In this situation, an assessment of the scales of such polychroneity of NV and, correspondingly, of the Ai Formation as a whole becomes urgent.

Ostracods (Crustacea): Some problems of systematics

The initially established ostracod classification was based mainly on soft part anatomy of extant taxa. In the fossil record, ostracods are usually represented by shells alone, complicating the elaboration of a unified taxonomic system. A brief review of ostracod development in the Phanerozoic is outlined. Long-lived groups, such as Myodocopida, Podocopida, and Platycopida (Ordovician-Recent), display stable uniformity of the shell and soft part structures. The Paleozoic ostracod groups possess sharply different shell structures. The ostracod shell type is undoubtedly an important taxonomic feature. It is noteworthy that the points of view on the systematic position of extraordinary ostracod groups which became extinct in the Paleozoic (leperditicopids, beyrichicopids, kloedenellocopids) vary widely. It is proposed to assign all the ostracodomorphs and ostracods (bradoriamorphs, palaeocopids sensu lato, platycopids, podocopids) to the same high-rank taxon.

Study on Artificial Neural Networks to Identify Sedimentary Microfacies

Based on a number of stratigraphic sedimentary information included in log data, application of the Artificial Neural Network to identify sedimentary microfacies from well logging data can complete the series auto-interpreting. The application can improve the auto-interpreting accuracy and make us get more satisfied results. Ten parameters from the well logging curves are selected for to describing their shape characteristics when the deposition patterns of 8 in gas-bearing formation of Upper Paleozoic group, Ordos basin are studied. Effective parameters were selected on the basis of cores, and based on artificial neural network pattern recognition technique; the sedimentary microfacies of well cross section were auto-interpreted. About 300 wells and the results were interpreted by using the software. The software will be fit for the researchers who have the experiences of geological interpretation and some backgrounds of local geology.

The Soil Geochemical Abnormal Characteristics in Eastern of Luonan County in Shanxi Province

The study area is located in the north belt of Qingling latitudinal structural belt and contains well developed folds and faults directed EW and the iliceous carbonate sedimentary formations mainly in Lower Paleozoic Group and the sedimentary clastic rocks in Middle-upper Paleozoic Group. Tuyaowa anomaly belt, mainly with Au, As, Sb anomalies, is the favorable target for Au, As, Sb. Zhaizigou-Jianggou-Yujiagou anomaly belt, with Au, Ag, Cu, Zn, Mo anomalie, is the favorable target for Au, Ag, Cu, Zn, Mo. Miaowa-Houling abnomal belt, with Pb, Hg anomalies and Au, Ag, Zn, Mo weak anomalies, is the favorable target looking for Au, Ag, Zn, Mo and Pb. The abnomal belt of Shuigou-Hugou, with Au, Cu, Mo, Pb, V anomalie, is a favorable target for Au, Cu, Mo, Pb and V.

Extinguishing a Permian World

At the end of the Permian, ca. 252 Ma ago, marine and terrestrial fauna were facing the most extensive mass extinction in Earth history (Raup and Sepkoski, 1982). 80%–95% of all species on Earth, on land and in the oceans, became extinct (Benton et al., 2004) within an estimated time interval of less than 200 k.y. to 700 k.y. (Huang et al., 2011; Shen et al., 2011). Among the prominent Paleozoic animal groups that vanished are fusulinid foraminifera, rugose and tabulate corals, and the arthropod class Trilobita. The numerous hypotheses about the causes of the mass extinction include various environmental changes, mostly related to the emplacement of the Siberian Traps large igneous province. The compilation of radiometric U/Pb ages for the mass extinction and the Siberian Traps demonstrate a temporal overlap of both events (Svensen et al., 2009). A prominent hypothesis for the mass extinction is an accentuated global climate change scenario induced by volcanic CO 2 degassing (e.g., Svensen et al., 2009) that triggered biotic responses in the sea and on land. But what do we know about the climate at this time in Earth history? The two main features of climate recorded in the geological archives are temperature and humidity i.e., the moisture that is available for plant growth, and to a certain extent rainfall patterns. Climate simulations model the general circulation patterns during Permian–Triassic times. The paleogeography was characterized by the supercontinent Pangea extending nearly from pole to pole, with large land masses in the mid-latitudes of the Northern and Southern Hemispheres, and with the Tethys Ocean in the tropics (e.g., Smith et al., 1994). Climate models and sensitivity experiments demonstrated that this paleogeography provided the preconditions for a monsoonal circulation with strong seasonality of temperatures and rainfall on the Tethyan coasts, and distinct northern and southern intertropical convergence zones (Fig. 1) (e.g., Kutzbach and Ziegler, 1993; Parrish, 1993). Moist conditions prevailed in middle and high latitudes and along the

A rhinesuchid-like temnospondyl from the Permo-Triassic of Uruguay

A new temnospondyl species, Arachana nigra, from the Permo-Triassic Buena Vista Formation of Uruguay is described. The holotypic and only known specimen consists of an almost complete skull lacking most of the snout, the tabular horns and the posterolateral corners of the skull table. As with other specimens from the same unit, Arachana shows a transitional morphology. It shares several characters with rhinesuchids, such as the large size and the general shape of the skull, orbits positioned slightly posterior to the skull roof mid-length, a coarsely pitted dermal ornamentation lacking pustules, and a smoothly convex cheek contour. The palatal ramus of the pterygoid suturing with the vomer, and excluding the palatine and ectopterygoid from the margin of the interpterygoid vacuity, and the presence of a small basioccipital, visible in both occipital and ventral view, also resemble the conditions found in rhinesuchids and other basal temnospondyls. Other characters present in Arachana, however, are commonly found in lydekkerinids, but are absent in almost all rhinesuchids: supratemporal excluded from otic notch; supraorbital and infraorbital sensory sulci encroaching the lacrimal, although lacking a step-like lacrimal flexure; otic notch not deeply incised; post-temporal fenestra large and rounded; occipital condyles well-separated from each other; palatine tooth row behind the palatine tusk reduced; pterygoid corpus slightly ornamented; and presence of an interorbital depression. This combination of primitive and derived characters is consistently present in most components of the Buena Vista fauna, which could thus be transitional between typical Permian and Triassic tetrapod communities found elsewhere. The location of the PTB in the Uruguayan sequence is controversial, mainly due to the lack of clear faunal correlations with other well-known sequences, such as those of southern Africa and Russia. Moreover, the mosaic-like character combinations in most of the recorded tetrapods ally them to both Triassic and Paleozoic groups, and this has complicated even more the possibility of age assignment. Transitional faunas associated with the PTB, such as the Russian Uppermost Permian faunas, could be equivalent to the unique Colonia Orozco fauna. If true, this scenario will substantially change estimates about survivorship rates, suggesting a speciation rate increase in temnospondyls after the Permian-Triassic event. Based on taxonomic, phylogenetic, and geochronologic data, the Buena Vista fauna allows us to quantify faunal turnover across the PTB and in the aftermath of the end Permian extinction event.

Earthquake-related Tectonic Deformation of Soft-sediments and Its Constraints on Basin Tectonic Evolution

: The authors introduced two kinds of newly found soft-sediment deformation-syn-sedimentary extension structure and syn-sedimentary compression structure, and discuss their origins and constraints on basin tectonic evolution. One representative of the syn-sedimentary extension structure is syn-sedimentary boudinage structure, while the typical example of the syn-sedimentary compression structure is compression sand pillows or compression wrinkles. The former shows NW-SE-trending contemporaneous extension events related to earthquakes in the rift basin near a famous Fe-Nb-REE deposit in northern China during the Early Paleozoic (or Mesoproterozoic as proposed by some researches), while the latter indicates NE-SW-trending contemporaneous compression activities related to earthquakes in the Middle Triassic in the Nanpanjiang remnant basin covering south Guizhou, northwestern Guangxi and eastern Yunnan in southwestern China. The syn-sedimentary boudinage structure was found in an earthquake slump block in the lower part of the Early Paleozoic Sailinhudong Group, 20 km to the southeast of Bayan Obo, Inner Mongolia, north of China. The slump block is composed of two kinds of very thin layers—pale-gray micrite (microcrystalline limestone) of 1–2 cm thick interbedded with gray muddy micrite layers with the similar thickness. Almost every thin muddy micrite layer was cut into imbricate blocks or boudins by abundant tiny contemporaneous faults, while the interbedded micrite remain in continuity. Boudins form as a response to layer-parallel extension (and/or layer-perpendicular flattening) of stiff layers enveloped top and bottom by mechanically soft layers. In this case, the imbricate blocks cut by the tiny contemporaneous faults are the result of abrupt horizontal extension of the crust in the SE-NW direction accompanied with earthquakes. Thus, the rock block is, in fact, a kind of seismites. The syn-sedimentary boudins indicate that there was at least a strong earthquake belt on the southeast side of the basin during the early stage of the Sailinhudong Group. This may be a good constraint on the tectonic evolution of the Bayan Obo area during the Early Paleozoic time. The syn-sedimentary compression structure was found in the Middle Triassic flysch in the Nanpanjiang Basin. The typical structures are compression sand pillows and compression wrinkles. Both of them were found on the bottoms of sand units and the top surface of the underlying mud units. In other words, the structures were found only in the interfaces between the graded sand layer and the underlying mud layer of the flysch. A deformation experiment with dough was conducted, showing that the tectonic deformation must have been instantaneous one accompanied by earthquakes. The compression sand pillows or wrinkles showed uniform directions along the bottoms of the sand layer in the flysch, revealing contemporaneous horizontal compression during the time between deposition and diagenesis of the related beds. The Nanpanjiang Basin was affected, in general, with SSW-NNE compression during the Middle Triassic, according to the syn-sedimentary compression structure. The two kinds of syn-sedimentary tectonic deformation also indicate that the related basins belong to a rift basin and a remnant basin, respectively, in the model of Wilson Cycle.

EARLY MOLLUSCAN EVOLUTION: EVIDENCE FROM THE TRACE FOSSIL RECORD

Abstract Trace fossils extend the history of early molluscan evolution because they have a higher preservation potential in siliciclastic strata, where body fossils are rare or absent, and also because they better record the activities of soft-bodied animals. The earliest mollusks are recorded by fan-shaped scratch arrays associated with death masks of the Ediacaran animal Kimberella. Cambrian traces––Climactichnites, Musculopodus, Radulichnus––and fecal pellets record giant, but shell-less mollusks that intermittently left the water to graze the biofilms of intertidal sand flats. After the Cambrian, these traces become progressively restricted. Their subsequent disappearance results from closure of a taphonomic window, rather than from extinction of these animals or their grazing behavior. Other Paleozoic groups of shell-less mollusks may have responded to increasing predation pressures by becoming infaunal. Unlike surface trails, their backfilled burrows––Psammichnites, “Aulichnites-Olivellites,” Dictyo...

Dead bellerophontids walking — The short Mesozoic history of the Bellerophontoidea (Gastropoda)

The bilaterally symmetrical gastropods grouped in the extinct superfamily Bellerophontoidea are considered as a typical Early Triassic example of Dead Clade Walking. They survived the Permian–Triassic extinction but disappeared in the Early Triassic. We analysed all Triassic occurrences of bellerophontoideans known from the literature and revised their taxonomic assignment and stratigraphic occurrence. We confirm eight Early Triassic species of Bellerophontoidea representing three genera ( Dicellonema, Retispira, and Warthia) from two families (Bellerophontidae and Euphemitidae). Bellerophontoideans were globally distributed in the Griesbachian, Dienerian, and Smithian (early-to-mid-Early Triassic) and at some localities they formed mass accumulations. Due to their relatively high diversity and abundance in the Early Triassic, they apparently had a good chance to recover from the Permian–Triassic extinction but finally became extinct at the Smithian/Spathian boundary. We could not confirm any bellerophontoidean occurrence from Spathian and younger strata. The end-Smithian extinction event was previously found for conodonts and ammonoids. Thus, a double phased extinction at the end-Permian and end-Smithian extinction events finally removed the important Paleozoic group Bellerophontoidea. We raise Dicellonema (which has been earlier proposed as subgenus of Bellerophon) to genus level. It is represented by two species: D. dicellonemata Yü and Wang in Yü (1975) and D. abrekensis ( Kaim, 2009). Two other species that may represent nomina dubia are included only tentatively: D. panxianensis (Yü) in Wang and Xi (1980) and D. granatricarinata (Wang) in Wang and Xi (1980). Two other species are transferred from Bellerophon to Warthia: Warthia vaceki (Bittner, 1899a) and W. borealis ( Spath, 1930). Euphemites guizhouensis Pan, 1982 belongs actually to Retispira and might be a synonym of R. asiatica (Wirth, 1936). We could not confirm the presence of Bellerophon (sensu stricto) and Euphemites in the Early Triassic.

Note of the executive editor

This is a collection of papers on paleontological topics presented at the International Conference “Development of Early Paleozoic Biodiversity: Role of Biotic and Abiotic Factors and Event Correlation” (Moscow, Russia, June 26‐28, 2008). The conference was organized by A.A. Borissiak Paleontological Institute, Russian Academy of Sciences, as a contribution to the International Geoscience Programme (IGCP) 503, “Ordovician Palaeogeography and Palaeoclimate” and Basic Research Programs 18 and 11 “Origin and Evolution of the Biosphere” and “Biodiversity and Gene Pool Dynamics,” Russian Academy of Sciences. The 12 articles of the collection combine several contemporary issues in paleontology of the Early Paleozoic. The first aspect is related to the reconstruction of the trophic structure of marine communities. There are three articles focused on this issue. The article by S.V. Rozhnov seeks to reconstruct and compare the trophic structures of the Vendian, Cambrian, and Ordovician marine communities. G.A. Afanasjeva considers the effect of the evolution of the filter system on the succession of the Paleozoic brachiopod communities. R.V. Gorjunova has shown the relationship between the evolution of the colonial growth habit of Ordovician moss animals of the class Stenolaemata and feeding adaptation. Several articles deal with some details of the morphology of important Paleozoic groups of invertebrates that are important both for taxonomic classification and for reconstruction of biotic relationships. R. Parsley’ paper presents some unique data on the morphology and ontogeny of gogiids, the most widespread family of the Lower and Middle Cambrian eocrinoids (echinoderms); it is based on the extremely well-preserved material from Guizhou, China. A.N. Solovjev provides an overview of the morphology, distribution, and different viewpoints on the systematic position of bothriocidaroid echinoids, the most ancient sea urchins. Modern and fossil animals often display micromorphic features; in his paper A.V. Pakhnevich describes the causes of this phenomenon in the modern and fossil brachiopods. A.A. Madison studies the shell structure of the first-formed shell of the Middle Ordovician orthid-like brachiopods from the Leningrad Region, Russia. Three papers deal with the paleobiogeography of various animal groups of the Ordovician. In her paper Ya. Ariunchimeg discusses the biogeographic and biostratigraphic significance of the Ordovician moss animals of Mongolia. In their paper Rozhnov and coauthors deal with the first records of Rhombifera echinoderms from Mongolia and discuss their biogeographic significance. O.B. Bondarenko and L.M. Ulitina compare the Ordovician corals of the Siberian and Mongolian basins. Based on their study of the Late Ordovician conodonts of the cherty rocks of central Kazakhstan, T.Yu. Tolmacheva and her collaborators reach some major biogeographic and biostratigraphic conclusions. In his extensive article A.V. Dronov compares eustatic and biotic events in the Ordovician paleobasins of the Russian and Siberian platforms.

IN MEMORIAM: GEORGE A. SANDERSON, JR. (1926-2008)

George Sanderson (with George Verville, background) collecting fusulines at the type Derryan (Pennsylvanian) section in Sierra County, New Mexico. Photo by G. P. Wahlman, 1983. George Albert Sanderson, Jr. was born August 22, 1926 in New Haven, Connecticut. He was raised by his mother and grandparents, who emigrated from Germany at the beginning of the 20th Century. “Sandy,” as he was known to friends and colleagues, attended New Haven High School and served in the U. S. Naval Reserve from 1944 to 1946. He graduated Phi Beta Kappa from Trinity College in Hartford, Connecticut, in 1949, and received a doctorate in geology from the University of Wisconsin-Madison in 1954. Sandy’s dissertation topic was “Studies of magnesium in foraminiferal tests,” conducted under the supervision of Professor M. L. Thompson, the dean of North American fusuline specialists. It was through his association with Thompson that Sandy developed an interest in fusulines, leading to employment as a micropaleontologist with Shell Oil Company (1954–1964) and then as a research micropaleontologist and Paleozoic Group supervisor at the Amoco Production Company Research Center in Tulsa, Oklahoma, from 1964 until his retirement in 1989. While supervisor in the late 1970’s, he oversaw the unprecedented expansion of Paleozoic specialists, melding together with good humor and some cajoling raw rookies, seasoned veterans and support staff into an effective research team. His mentoring skills extended beyond company staff to the greater micropaleontological community as an outside supervisor for fusuline dissertations, including an adjunct professorship at the University of Geneva, Switzerland. Sandy made numerous contributions to the study of fusulines, especially in the areas of systematics and biostratigraphy. Perhaps his most …

Evolution of provenance in the NE Atlantic rift: The Early–Middle Jurassic succession in the Heidrun Field, Halten Terrace, offshore Mid-Norway

An integrated provenance study using provenance-sensitive heavy mineral ratios, mineral chemistry and U/Pb dating of detrital zircons has revealed significant changes in sediment provenance during deposition of the Early to Middle Jurassic succession in the Heidrun Field, offshore Mid-Norway. The variations result from the interplay of two source regions, one of which was located on the Norwegian landmass and the other on the conjugate East Greenland margin. Sediment sourced from central East Greenland is distinguished by high garnet:zircon, high rutile:zircon, low chrome spinel:zircon, garnet assemblages rich in low-Ca, high-Mg varieties, and zircon populations that include an Archean group, a diverse range of Early–Middle Proterozoic grains, and an Early Paleozoic group. These features indicate derivation from a high-grade (granulite facies) metasedimentary terrain together with Archean basement and Early Paleozoic granitoids. Norwegian-sourced sandstones differ by having lower garnet:zircon and rutile:zircon, variable chrome spinel:zircon, garnet assemblages scarce in low-Ca, high-Mg varieties, and zircon populations that lack an Archean group. Derivation from the Caledonian Nappe Domain, comprising metasediments (predominantly at amphibolite facies), ophiolites and Early Paleozoic granitoids, is indicated. Initially, during deposition of the non-marine lower part of the Åre Formation (Hettangian–Sinemurian), sediment was fed from the west, but in the upper (tidally influenced) part of the Åre Formation (Sinemurian–Pliensbachian), Norwegian-sourced material appears. Greenland-derived material disappears in the subsequent Tilje Formation (Pliensbachian), with the Tilje and subsequent Ror and Ile Formations (Toarcian–Aalenian) being predominantly sourced from the east. The regional regression at the base of the Garn Formation (Bajocian) was accompanied by a switch in provenance, with Greenland-derived material replacing sediment sourced from Norway. Variations in mineralogy offer a framework for correlation on both local and sub-regional scales.

Tectonic thermal history and its significance on the formation of oil and gas accumulation and mineral deposit in Ordos Basin

The analyzing data on stratigraphic temperature measurement, thermal conductivity of the strata and radioactive heat production rate show that the present average geothermal gradient in the Ordos Basin is 2.93 °C/100 m, and the average heat flow value is 61.78 mW/m2, which belongs to the mesothermal basin, and the value of the present geothermal gradient and heat flow in the east is higher than that in the west. The sandstone radioactive heat production rate of Zhiluo Group in Dongsheng Uranium deposits of Yimeng uplift is obviously higher in the mudstone, indicating that there exists a uranium anomaly. Based on studies of the present thermal field of the basin, the late-Mesozoic paleotemperature and paleogeothermal gradient are determined by using different kinds of paleotemperature methods. According to the anomaly of the late-Mesozoic paleotemperature gradient and magmatic event age, there was a tectonic thermal event in the early Cretaceous epoch of late-Mesozoic. This article rebuilds tectonic thermal history of different tectonic units by thermal history simulation using basin simulating software. The evolution of oil-gas and coal, and accumulation (mineralization) of mineral uranium are all controlled by the tectonic thermal history in the Ordos basin, especially by the tectonic thermal event that happened in the late Mesozoic. For both the gas source rocks of upper Paleozoic group and lower paleozoic group, the gas was largely generated in the early Cretaceous epoch of the late Mesozoic. The main petroleum generation period for Yanchang Group in Triassic system is the early Cretaceous epoch too, and the highest thermal maturity of the coal of Permo-Carboniferous, Triassic, and Jurassic reaches is the early Cretaceous epoch also. Early Cretaceous epoch is still one of the most important mineralizing periods of uranium.

Diversification of atypical Paleozoic echinoderms: a quantitative survey of patterns of stylophoran disparity, diversity, and geography

The analysis of morphological disparity and of morphospace occupation through the macroevolutionary history of clades is now a major research program in paleobiology, and increasingly so in organismal and comparative biology. Most studies have focused on the relationship between taxonomic diversity and morphological disparity, and on ecological or developmental controls. However, the geographic context of diversification has remained understudied. Here we address geography quantitatively. Diversity, disparity, and paleogeographic dispersion are used to describe the evolutionary history of an extinct echinoderm clade, the class Stylophora (cornutes, mitrates), from the Middle Cambrian to the Middle Devonian (about 128 Myr subdivided into 12 stratigraphic intervals). Taxonomic diversity is estimated from a representative sample including 73.3% of described species and 92.4% of described genera. Stylophoran morphology is quantified on the basis of seven morphometric parameters derived from image analysis of homologous skeletal regions. Three separate principal coordinates analyses (PCO) are performed for thecal outlines, plates from the lower thecal surface, and plates from the upper thecal surface, respectively. PCO scores from these three separate analyses are then used as variables for a single, global, meta-PCO. For each time interval, disparity is calculated as the sum of variance in the multidimensional morphospace defined by the meta-PCO axes. For each time interval, a semiquantitative index of paleogeographic dispersion is calculated, reflecting both global (continental) and local (regional) aspects of dispersion.Morphospace occupation of cornutes and mitrates is partly overlapping, suggesting some morphologic convergences between the two main stylophoran clades, probably correlated to similar modes of life (e.g., symmetrical cornutes and primitive mitrocystitids). Hierarchical clustering allowed the identification of three main morphological sets (subdivided into 11 subsets) within the global stylophoran morphospace. These morphological sets are used to analyze the spatiotemporal variations of disparity. The initial radiation of stylophorans is characterized by a low diversity and a rapid increase in disparity (Middle Cambrian–Tremadocian). The subsequent diversification involved filling and little expansion of morphospace (Arenig–Middle Ordovician). Finally, both stylophoran diversity and disparity decreased relatively steadily from the Late Ordovician to the Middle Devonian, with the exception of a second (lower) peak in the Early Devonian. Such a pattern is comparable to that of other Paleozoic marine invertebrates such as blastozoans and orthid brachiopods. During the Lower to Middle Ordovician, the most dramatic diversification of stylophorans took place with a paleogeographic dispersion essentially limited to the periphery of Gondwana. In the Late Ordovician, stylophorans steadily extended toward lower paleolatitudes, and new environmental conditions, where some of them radiated, and finally survived the end-Ordovician mass extinction (e.g., anomalocystitids). This pattern of paleobiogeographic dispersion is comparable to that of other examples of Paleozoic groups of marine invertebrates, such as bivalve mollusks.

Provenance of Late Cretaceous to Paleocene submarine fan sandstones in the Norwegian Sea: Integration of heavy mineral, mineral chemical and zircon age data

This paper describes a strategy for effective discrimination and provenance evaluation of sandstones transported by different sediment dispersal systems using an integrated programme of heavy mineral analysis, mineral chemistry and zircon age dating. Sandstones derived from different source regions are initially discriminated using provenance–sensitive heavy mineral parameters (ratios of abundances of stable, hydraulically equivalent minerals). Differences between the heavy mineral populations are reinforced by single-grain mineral chemical analysis, which also provides further information on the nature of the source terrains. Zircon age dating of representative samples places further constraints on the location of the source areas, by identifying the main crust-forming events. In addition, the validity of the mineralogical discrimination can be tested by the zircon age data. The value of this integrated approach is illustrated by a case study of deep marine Late Cretaceous–Paleocene sandstones in the Norwegian Sea. Potential sources of coarse clastic sediment lie both to the east, in mid-Norway, and the west, in East Greenland. Three main sand types (MN1, MN2 and MN3) have been identified, each of which has a unique combination of heavy mineral ratios (rutile/zircon, monazite/zircon, chrome spinel/zircon and apatite/tourmaline) and mineral chemistry (garnet and tourmaline). Sand type MN1 has a simple zircon age spectrum, with a large Early–Middle Proterozoic group and a small Early Paleozoic group, indicating derivation from northern mid-Norway. Sand type MN2 has a complex age structure including Archaean and early Proterozoic zircons. It can be divided into two subtypes, MN2a and MN2b, and can be ascribed to a source in East Greenland. Sand type MN3 has a simple age structure dominated by Middle Proterozoic zircons, and it was sourced from southern mid-Norway. Since reservoir presence is a major area of uncertainty in the deep water Norwegian Sea, the use of heavy mineral, mineral chemical and zircon age data to discriminate sandstones of eastern and western origin is crucial to hydrocarbon exploration of the area.

U-Pb SHRIMP ages recorded in the coesite-bearing zircon domains of paragneisses in the southwestern Sulu terrane, eastern China: New interpretation

Laser Raman spectroscopy and cathodoluminescence (CL) images reveal that abundant and complicated mineral inclusions occur in zoned zircon separates from paragneisses in drill holes CCSDPP2, ZK-2304, and CCSD-MH, at Donghai, southwestern Sulu terrane, China. Many low-P mineral inclusions are preserved in inherited zircon cores. Coesite + quartz within a single inclusion, and some low-P minerals (e.g., quartz and albite) are identified in zircon mantles. Textures showing the quartz to coesite transformation in zircon indicate that both core and mantle of the zircon are detrital. Inclusions of coesite, together with garnet, jadeite, and phengite, are common in zircon rims formed during ultrahigh-pressure (UHP) metamorphism. SHRIMP U-Pb analyses of these zoned zircon grains identify three discrete and meaningful age groups. Proterozoic ages of 840 to 658 Ma for zircon cores indicate that the detrital zircons have a variety of sources. An early Paleozoic group of 505 to 455 Ma ages for zircon mantles constrain neither the timing of a discrete UHP metamorphic event, nor the transformation age from quartz to coesite. The 227 ± 9 Ma (the weighted mean age) obtained from coesite-bearing zircon rims represents the UHP metamorphic age. Thus, one Late Triassic UHP metamorphic event, rather than two UHP metamorphic events, is well established in Sulu UHP terrane by the method of U-Pb SHRIMP dating for coesite-bearing zircon rims in garnet-biotite-amphibole-albite gneisses.