Lower Jurassic Rocks Research Articles

Structural and geomorphological study of Bradost, Chinara, Shireen and Sare Musa anticlines, Iraqi Kurdistan Region

The Bradost and Chinara mountains are two well-known geomorphic features in the Iraqi Kurdistan Region (IKR), forming two anticlines, besides Shireen and Sare Musa anticlines, which are located north of the Bradost anticline, all four anticlines trend NW – SE. The four anticlines are dissected by the Greater Zab River that swings along its course within the anticlines due to tens of very old landslides and/or plunges. The four studied anticlines are dissected by different thrust faults, which extend for a few kilometers. The thrust faults trend NW – SE; however, locally they deflect from the main trend. The Lower Jurassic rocks are the oldest exposed rocks in the studied area, whereas the rocks of the Bekhme Formation form the carapace of the Bradost and Chinara anticlines. Different structural and geomorphological features were interpreted from satellite images and those which are accessible were checked in the field, all of them indicate the four anticlines exhibit lateral growth. We have measured different aspects to elucidate the type of folds. The four anticlines are Detachment folds, with shallow decollement, which ranges in depth between (100–250) m.

<i>Squaloraja</i> Riley 1833 (Holocephala: Squalorajidae) from the Lower Jurassic of Osteno Konservat-Lagerstätte (Como, NW Italy)

A remarkable, complete specimen of a squalorajid holocephalian is described for the first time from the Lower Jurassic (lower Sinemurian) rocks of Osteno (Como, NW Italy). It is the only such specimen known from the locality and belongs to a (possibly juvenile) female. The Italian specimen is assigned to Squaloraja sp., and has a large dorsoventrally flattened head, long rostrum, a single mandibular tooth plate on each lower jaw, a well-developed synarcual, thick notochordal sheath calcifications, and only slightly reduced squamation comprising distinctive placoid scales with stellate bases. There is no ethmoid canal, dorsal fin or fin spine. The Lower Jurassic succession (‘Lower Lias’) of Lyme Regis (Dorset, UK) has yielded only two incomplete purported female specimens of the type species of the genus, Squaloraja polyspondyla, thus restricting potential comparison with the Italian specimen. This new record of the genus expands the known palaeogeographical distribution of this rare holocephalian.

Long duration of benthic ecological recovery from the early Toarcian (Early Jurassic) mass extinction event in the Cleveland Basin, UK

The Cleveland Basin of Yorkshire, UK hosts one of the most iconic Lower Jurassic rock successions for studying the Toarcian oceanic anoxic event and the associated mass extinction, yet our understanding of the subsequent ecological recovery is limited. This study documents for the first time the full extent and nature of benthic macrofaunal recovery from the early Toarcian mass extinction event within the Cleveland Basin. Benthic oxygen levels remained low following the extinction event, allowing specialist communities that were tolerant to low oxygen levels to dominate. Recovery began properly once the seafloor ventilation had begun to improve and was first expressed by an expanded ecological tiering structure. Recovery progressed slowly thereafter with the possible return to oxygen-restricted environments. As sea-levels fell and sand-dominated deposition again occurred within the basin, the recovery accelerated, with ecological and species richness being reattained and even exceeding pre-extinction levels. Full recovery occurred, at the latest, c. 7 myr after the extinction event; this duration is on par with estimates of recovery rates from the largest mass extinction event of the Phanerozoic (the end-Permian mass extinction event). Recovery within the Cleveland Basin was likely to have been strongly influenced by local sea-levels and the continuation of challenging environmental conditions after the extinction event. Supplementary material: Benthic fossil occurrence data are available at https://doi.org/10.6084/m9.figshare.c.6332986

Исследование компонентного состава органического вещества отложений Восточно-Предкавказской нефтегазоносной области по результатам литолого-петрофизических и геохимических исследований

This study introduces results of lithological, petrophysical and geochemical investigation of Lower Cretaceous (K1) and Middle Jurassic (J2a-b) rocks of East Pre-Caucasian basin. According to pyrolytic and bituminological studies method of separate determination of kerogen and bitumen concentration been developed. In accordance with this method differentiation of organic matter components in different lithotypes of rocks been described. Also relationship between bitumen and kerogen concentrations been revealed. The majority of samples have poor to fair organic richness and poor source potential. Kerogen type is commonly presented by type III and stages of maturity characterized by stages PC3 to MC3. Bitumen compounds have low concentrations of asphaltenes and aromatic hydrocarbons and mainly contains light and heavy resins. Based on petrophysical and geochemical studies a close relationship between the concentration of organic carbon and the weight concentration of potassium nuclides was obtained. This relationship indicates that kerogen in the sediments under consideration is associated with clay minerals, which is also confirmed by the mineral composition of the rocks.

THE FORMATION HISTORY OF HYDROCARBON DEPOSITS IN THE UPPER PALEOZOIC AND MESOZOIC ROCKS OF THE VILYUI HEMISYNECLISE

The paper is aimed at the basin and petroleum systems modeling in the Vilyui hemisyneclise located in the Republic of Sakha (Yakutia). The Vilyui hemisyneclise is known to be the deepest depression of the Siberian Platform. The research identifies maturity and temperature history of the Permian source rock in the Mesozoic and Cenozoic, kitchen areas, accumulation balance of hydrocarbons in reservoirs, trapping of gas and gas-condensate deposits in the Upper Permian, Lower Triassic, and Lower Jurassic rocks. Funding: The reported study was funded by RFBR, project number 19-35-90039.

Early Jurassic (middle Hettangian) marine gastropods from the Pogibshi Formation (Alaska) and their paleobiogeographical significance

A middle Hettangian marine gastropod assemblage is reported from the Kenai Peninsula of south-central Alaska supplying new paleontological evidence of this group in Lower Jurassic rocks of North America. Pleurotomaria pogibshiensis sp. nov. is described from the middle Hettangian marine succession informally known as Pogibshi formation, being the first occurrence of the genus in the Kenai Peninsula and the oldest occurrence of the genus in present-day Alaska and North America. One species of the genus Lithotrochus, namely Lithotrochus humboldtii (von Buch), is also reported for the first time from the Kenai Peninsula. Lithotrochus has been considered as endemic to South America for a time range from the early Sinemurian to the late Pliensbachian. The newest occurrence of Lithotrochus in rocks of the Pogibshi formation extends the paleobiogeographical and chronostratigraphical distribution of the genus into the present-day Northern Hemisphere. However, the Southern Hemisphere affinities are consistent with the hypothetical interpretations (although supported both by paleobiogeographical and paleomagnetic data) that the Peninsular terrane of south-central Alaska is far-traveled and may have originated at much more southerly paleolatitudes than its present-day position. Two other Early Jurassic caenogastropods typical of the Andean region of South America and of the Tethyan epicontinental seas are described for the first time in the Pogibshi formation, and these are Pseudomelania sp. and Pictavia sp. The new gastropod assemblage reported here shows close affinities with coeval South American and European gastropod faunas, supplying new evidence to interpret their distribution during the Early Jurassic.

High-precision Re[sbnd]Os dating of Lower Jurassic shale packages from the Western Canadian Sedimentary Basin

The Lower Jurassic rock record contains abundant organic-rich mudrocks suitable for refining Early Jurassic time using ReOs organic-rich shale (ORS) geochronometry, such as those associated with the Sinemurian–Pliensbachian boundary event or the Toarcian Ocean Anoxic Event (T-OAE). Despite this, most studies to date have failed to obtain high precision, geologically meaningful, ages for such Lower Jurassic rocks. The cause of imprecision in ReOs ORS age dates, at least for the Toarcian, has been linked to subtle chemostratigraphic variations in 187Os/188Osi values. Here, we report the first high-precision ReOs ages of organic-rich shale packages of the Gordondale and basal Poker Chip Members of the Lower Jurassic Fernie Formation of Northwestern Alberta, Canada from the Western Canadian Sedimentary Basin (WCSB). Our ReOs age results bracket sediment deposition between the late Sinemurian-early Pliensbachian (192.11 ± 0.77 Ma [2σ] and 193.83 ± 1.34 Ma [2σ]) and late Toarcian (180.10 ± 2.68 Ma [2σ]). When coupled with chemo- (87Sr/86Sr and 187Os/188Os isotopes) and bio-stratigraphy (ammonite and coccolith), our ReOs ages correlate with regional and global stratigraphic tie points corresponding to pivotal points of Early Jurassic time, such as the Sinemurian–Pliensbachian boundary event, T-OAE, and late Toarcian, that are otherwise weakly constrained by isotopic methods. This integrative approach helps to place these events in a more robust temporal framework. Based on seawater Os isotope data, we also speculate that a previously unidentified positive Os isotope excursion exists at the Sinemurian–Pliensbachian boundary - perhaps triggered by late-stage Central Atlantic Magmatic Province (CAMP) volcanism.

A revision of the early neotheropod genusSarcosaurusfrom the Early Jurassic (Hettangian–Sinemurian) of central England

AbstractNeotheropoda represents the main evolutionary radiation of predatory dinosaurs and its oldest records come from Upper Triassic rocks (c. 219 Mya). The Early Jurassic record of Neotheropoda is taxonomically richer and geographically more widespread than that of the Late Triassic. The Lower Jurassic (upper Hettangian–lower Sinemurian) rocks of central England have yielded three neotheropod specimens that have been assigned to two species within the genus Sarcosaurus, S. woodi (type species) and S. andrewsi. These species have received little attention in discussions of the early evolution of Neotheropoda and recently have been considered as nomina dubia. Here, we provide a detailed redescription of one of these specimens (WARMS G667–690) and reassess the taxonomy and phylogenetic relationships of the genus Sarcosaurus. We propose that the three neotheropod specimens from the Early Jurassic of central England represent a single valid species, S. woodi. The second species of the genus, ‘S. andrewsi’, is a subjective junior synonym of the former. A quantitative phylogenetic analysis of early theropods recovered S. woodi as one of the closest sister-taxa to Averostra and provides new information on the sequence of character state transformations in the lead up to the phylogenetic split between Ceratosauria and Tetanurae.

DEDUCING THE LATERAL GROWTH OF HANDREEN, ZOZIK AND TANOUN ANTICLINES IN KURDISTAN REGION USING GEOMORPHOLOGICAL FEATURES

Handreen, Zozik and Tanoun are three major anticlines in the northern part of Iraqi Kurdistan Region located NE of Rawandouz town. All anticlines are oriented NW-SE with a steep southwestern limb. The length and width of Handreen, Zozik and Tanoun anticlines are 20.2 km, 23 km, 27 km, and 10 km, 4.7 km and 2.5 km, respectively. The anticlines are separated by very narrow synclines. However, Tanoun anticline is thrusted over Zozik anticline causing the disappearance of the synclinal axis between the two folds. The oldest exposed rocks in Handreen anticline are the Cretaceous age, in Zozik anticline are the Upper Jurassic rocks, whereas in Tanoun anticline, the Lower Jurassic rocks are exposed. The carapace of Handreen and Zozik anticlines is built up by Bekhme and Qamchuqa formations and that of Tanoun anticline by the Qamchuqa Formation. Satellite images and geological maps were used to recognize the geomorphological and structural features which were checked and confirmed in the field. Handreen, Zozik and Tanoun anticlines show clear geomorphological and structural features which indicate their lateral growth. Among those features are water gaps, wind gaps, forked-shaped valleys, curved valleys, inclined (curved) valleys, radial valleys, abandoned alluvial fans, wale-back shape, en-echelon folds and folds with malty domes.

On the need of providing tooth morphology in descriptions of extant elasmobranch species.

Elasmobranchii is a clade of chondrichthyans (cartilaginous fishes) that comprises sharks, skates and rays represented today by approximately 1,200 species. Chondrichthyans have a long evolutionary history dating back to the Late Ordovician (ca. 450 million years ago [Mya]) based on isolated dermal denticles (Janvier 1996). Other remains such as articulated skeletons and teeth are known from the Lower Devonian (ca. 410 Mya: Mader 1986; Miller et al. 2003). The fossil record of modern elasmobranchs (Neoselachii) can be traced back to the Early Permian (ca. 290 Mya) and is represented by isolated teeth (Ivanov 2005), with fossils of crown group sharks and rays appearing in Lower Jurassic (ca. 200 Mya) rocks (e.g., Cappetta 2012). Since their appearance in the geological record, elasmobranchs are mainly represented by isolated teeth, whereas articulated skeletons are very rare and restricted to a small number of fossil localities (e.g., Cappetta 2012). The scarcity of skeletal remains in their fossil record is due to their poorly mineralized cartilaginous skeleton that requires special taphonomical conditions to be preserved. Elasmobranch teeth, in contrast, are composed of highly mineralized tissues (hydroxyapatite) that have a strong preservation potential (Shimada 2006). In addition, elasmobranchs replace their teeth continuously over the course of their life span (polyphyodonty) and therefore shed thousands of teeth in their lifetime (Reif et al. 1978; Schnetz et al. 2016) leading to large numbers of potential fossils. These morphologically highly diverse isolated teeth constitute much of the rich fossil record of elasmobranchs, and largely form the basis of our understanding of elasmobranch diversity and evolution through geological time.

Extraordinary diversity of feather stars (Echinodermata: Crinoidea: Comatulida) from a Lower Jurassic (Pliensbachian–Toarcian) rock reef of Feuguerolles (Normandy, France)

Comatulid feather stars are rare fossils in the Early Jurassic, providing only patchy insights into the early evolution of the group. Here, we describe new finds of comatulids from the late Pliensbachian to late Toarcian of Feuguerolles, Calvados, France. They include new species belonging to four superfamilies. The dominant genus is Palaeocomaster, with P. structus n. sp. represented by centrodorsals. For Palaeocomaster, the family Palaeocomasteridae n. fam. is proposed; it is placed in the Superfamily Comatuloidea. Solanocrinites is represented by S. jagti n. sp. The new taxa Andymetra toarcensis n. sp. and Spinimetra chesnieri n. g. et n. sp. are Family incertae sedis. The diagnoses of Comatuloidea and Solanocrinitoidea are modified based on the new material. The paracomatulid Singillatimetra truncata n. sp. is represented by a columnal, as is Forcipicrinus normannicus n. g. et n. sp. tentatively assigned to Pentacrinitina, Family incertae sedis. The material indicates that an important early comatulid radiation took place prior to the Toarcian Oceanic Anoxic Event, creating some basic types of these free-living crinoids. Along with the stratigraphic distribution patterns of the co-occurring stalked crinoids including the isocrinids Pentacrinites collenoti, Isocrinus (Chladocrinus) basaltiformis, the millericrinid Amaltheocrinus amalthei, and the cyrtocrinids Cotylederma docens, Eudesicrinus mayalis, Praetetracrinus inornatus, Sacariacrinus n. sp. and Tetracrinus n. sp., the new feather star finds suggest that the Toarcian Oceanic Anoxic Event was not of major influence to crinoid diversity.

Palaeoclimatic conditions in the Late Triassic-Early Jurassic of southern Africa: A geochemical assessment of the Elliot Formation

The Triassic-Jurassic boundary marks a global faunal turnover event that is generally considered as the third largest of five major biological crises in the Phanerozoic geological record of Earth. Determining the controlling factors of this event and their relative contributions to the biotic turnover associated with it is on-going globally. The Upper Triassic and Lower Jurassic rock record of southern Africa presents a unique opportunity for better constraining how and why the biosphere was affected at this time not only because the succession is richly fossiliferous, but also because it contains important palaeoenvironmental clues. Using mainly sedimentary geochemical proxies (i.e., major, trace and rare earth elements), our study is the first quantitative assessment of the palaeoclimatic conditions during the deposition of the Elliot Formation, a continental red bed succession that straddles the Triassic-Jurassic boundary in southern Africa. Employing clay mineralogy as well as the indices of chemical alteration and compositional variability, our results confirm earlier qualitative sedimentological studies and indicate that the deposition of the Upper Triassic and Lower Jurassic Elliot Formation occurred under increasingly dry environmental conditions that inhibited chemical weathering in this southern part of Pangea. Moreover, the study questions the universal validity of those studies that suggest a sudden increase in humidity for the Lower Jurassic record and supports predictions of long-term global warming after continental flood basalt emplacement.

Old and juvenile source of Paleozoic and Mesozoic basaltic magmas in the Acatlán and Ayú complexes, Southern Mexico: Nd isotopic constraints

The Neoproterozoic–Paleozoic Acatlán Complex and the Mesozoic Ayú Complex of southern Mexico consist of clastic rocks and rift-related igneous rocks inferred to have originated along a rifted passive margin in southwestern Mexico, either in an inactive (Neoproterozoic–Ordovician) or an active (Devonian–Carboniferous and Triassic–Early Jurassic) tectonic setting. The latter formed on the inner margin of a backarc basin. These passive margin rocks were partly underthrust beneath the Acatlán Complex, into which they were subsequently extruded: extrusion was synchronous with the backarc basin development. Thus, (i) the Neoproterozoic–Ordovician rocks underwent underthrusting, high-pressure metamorphism, and extrusion during the Late Devonian–Carboniferous (365–330Ma); (ii) the Carboniferous rocks underwent underthrusting, amphibolite facies metamorphism, and extrusion during the Permian and Triassic; and (iii) the Triassic–Lower Jurassic rocks underwent underthrusting, amphibolite facies metamorphism, and extrusion during the Jurassic. Nd isotopic data from tholeiitic mafic rocks on either side of the HP extrusion zone reveal that both were underlain by similar peri-Rodinian subcontinental lithospheric mantle in the Neoproterozoic–Ordovician, which was supplemented in the Devonian–Carboniferous and Triassic–Early Jurassic by a juvenile depleted mantle source. The alternation of underthrusting and backarc rifting accompanied by extrusion may be related to flattening and steepening of the Beniof zone, respectively.

Episodic burial and exhumation of the southern Baltic Shield: Epeirogenic uplifts during and after break-up of Pangaea

Cratons are conventionally assumed to be areas of long-term stability. However, whereas Precambrian basement crops out across most of the Baltic Shield, Palaeozoic and Mesozoic sediments rest on basement in southern Sweden, and thus testify to a complex history of exhumation and burial. Our synthesis of published stratigraphic landscape analysis and new apatite fission-track analysis data reveals a history involving five steps after formation of the extremely flat, Sub-Cambrian Peneplain. (1) Cambrian to Lower Triassic rocks accumulated on the peneplain, interrupted by late Carboniferous uplift and exhumation. (2) Middle Triassic uplift removed the Palaeozoic cover along the south-western margin of the shield, leading to formation of a Triassic peneplain with a predominantly flat relief followed by deposition of Upper Triassic to Lower Jurassic rocks. (3) Uplift that began during the Middle Jurassic to earliest Cretaceous caused denudation leading to deep weathering that shaped an undulating, hilly relief that was buried below Upper Cretaceous to Oligocene sediments. (4) Early Miocene uplift and erosion produced the South Småland Peneplain with scattered hills. (5) Early Pliocene uplift raised the Miocene peneplain to its present elevation leading to reexposure of the sub-Cretaceous hilly relief near the coast. Our results thus provide constraints on the magnitude and timing of episodes of deposition and removal of significant volumes of Phanerozoic rocks across the southern portion of the Baltic Shield. Late Carboniferous, Middle Triassic and mid-Jurassic events of uplift and exhumation affected wide areas beyond the Baltic Shield, and we interpret them as epeirogenic uplifts accompanying fragmentation of Pangaea, caused by accumulation of mantle heat beneath the supercontinent. Early Miocene uplift affected north-west Europe but not East Greenland, and thus likely resulted from compressive stresses from an orogeny on the Eurasian plate. Early Pliocene uplift related to changes in mantle convection and plate motion affected wide areas beyond North-East Atlantic margins.

Deformación andina en el cordón del Hielo Azul al oeste de El Bolsón. Implicancias en la evolución tectónica de la Cordillera Norpatagónica en Río Negro, Argentina

This geological study, carried out in the Cordon del Hielo Azul, west of the town of El Bolson (Rio Negro province, Argentine), shows the different relationships between the Early Jurassic cordilleran volcano-sedimentary sequence, the Middle-Late Jurassic Cordilleran Patagonian Batholith and the Cenozoic volcanic rocks of the Ventana Fornation exposed in the Patagonian Cordillera of Rio Negro. Through structural analysis, a series of previously unknown complex deformational structures have been identified. It has been observed that the sequence of volcanic rocks that outcrop on the Cerro Lindo, just west of El Bolson, is bounded by a backthrust in the eastern side and by an out of sequence thrust to the west; two other thrusts affect the sequence, with associated folded structures. To the north, on the west side of Cerro Hielo Azul, these Lower Jurassic volcanic rocks are in tectonic contact with the Cenozoic rocks of the Ventana Formation. Based on these observations, we inferred that an extensional fault controlled deposition of the Cenozoic volcanic rocks, being subsequently inverted, superimposing these rocks on the Jurassic volcanics. The different recognized faults exerted a first order control in the building of the mountain front and are robust evidence to establish the tectonic framework and uplift history of the North Patagonian Andes. This deformation took place from the Eocene to the Late Miocene. A pre-Oligocene contractional pulse led to the development of a thin-skinned fold and thrust belt affecting the Jurassic volcanics. During the Oligocene a regional extensional event resulted in the formation of basins such as the one recognized on Cerro Silvia, where the Ventana Formation crops out. A second contractional pulse took place during the Miocene and led to the development of a thick-skinned fold and thrust belt with deep faults that built the present mountain front.

Palaeomagnetism and 40 Ar/ 39 Ar dating from Lower Jurassic rocks in Gastre, central Patagonia: further data to explore tectonomagmatic events associated with the break-up of Gondwana

New 40 Ar/ 39 Ar data indicate ages of c . 185 Ma for the Lonco Trapial volcanic field in Gastre, north–central Patagonia, implying that this andesitic unit is roughly coeval with the Marifil silicic province that crops out in the eastern part of northern Patagonia. These volcanic fields are therefore roughly coeval with the Karoo–Ferrar large igneous province, further contributing to the huge, 185–180 Ma magmatic outpouring in southern Gondwana. The comparison of palaeomagnetic results from the unit with Early Jurassic reference palaeopoles suggests that Gastre records a small, anticlockwise finite rotation with respect to stable South America. This contrasts sharply with the large clockwise rotation recorded by roughly coeval dolerites from the Falkland/Malvinas Islands, and argues against a direct relationship between the rotation of the islands and the tectonic activity in Gastre. The results support previous suggestions that the Gastre Fault System is not the locus of major strike-slip displacement activity in the Jurassic as some workers have suggested. Taken as a whole, palaeomagnetic data from Patagonia suggest a more complex than previously thought pattern of distributed and variable deformation during the early stages of Gondwana breakup. The crustal block boundaries in the region remain cryptic. Supplementary material: 40 Ar/ 39 Ar analytical procedures and expanded data are available at http://www.geolsoc.org.uk/SUP18522 .

A porphyritic copper (gold) ore-forming model for the Shaxi-Changpushan district, Lower Yangtze metallogenic belt, China: geological and geochemical constraints

Ore-forming P-T-X conditions and the nature of gold occurrence in the Shaxi-Changpushan porphyry copper deposit, central Anhui Province, eastern China, were investigated employing a wide range of geological and geochemical methods. Our results document liquid-vapour conditions and show that abundant fluid inclusions occur in quartz veins accompanied by pyrite-chalcopyrite-gold mineralization. Most economic deposits involved coexisting liquid and gas phases, whereas a few formed in equilibrium with a homogeneous aqueous liquid. The ore-forming temperature lies between 230 and 350°C. Isotope studies show that the δ34 S values are between –0.20 and 3.00‰ for most of the sulphides; δ34 S values of chalcopyrite are somewhat more homogenous than those of pyrite. Ore-forming fluids and materials were mainly derived from magmatic sources. Meteoric water played a small role in the ore-forming process, judging by the oxygen and hydrogen isotope data for fluid inclusions measured by the explosion method (δ18 O values ranging from 3.51 to 5.52‰, and δD ranging from −59.8‰ to −82.4‰). In the ore deposit, the gold occurs as micro-inclusions heterogeneously distributed in chalcopyrite and pyrite. Gold mineralization is positively correlated with As in chalcopyrite, pyrite, and some Cu-bearing ores. Igneous rocks and sedimentary rock distributions in the Shaxi-Changpushan ore district were strictly controlled by the regional fault system since the Jurassic period, especially the Tan-Lu fault system in east China. Intrusive bodies comprising porphyritic quartz dioritoid, biotite-quartz dioritoid, and fine-grained dioritoid are ore-bearing, cutting sedimentary rocks of the Upper Jurassic and Middle–Lower Silurian series. Sediments exposed in the ore district consist of Upper Devonian–Middle Silurian clastic rocks, Middle and Lower Jurassic and Upper Cretaceous terrestrial clastic rock series. Petrologic data show that formation of Cu-Au ore bodies was related to adakitic intrusives in the Shaxi-Changpushan area. Based on geochemical exploration and the tectonic background of the southern part of Tan-Lu fault zone, we propose a porphyric copper (gold) ore-forming model for the Lower Yangtze metallogenic belt: ore bodies were controlled by structural shielding in the core of the regional anticline. Combined geological and geochemical evidence suggests that a super-large porphyry (gold) deposit may be present in the region.

Textural-structural, mineralogical, isotopic, and age characteristics of Jurassic terrigenous rocks of the northwestern Caucasus (the Belaya River section)

Results of the comprehensive study of structural, lithological, mineralogical, and isotopic characteristics of Lower Jurassic rocks exposed in the Belaya River valley (Adygeya) in meganticlinorium of the Greater Caucasus are presented. Deformation microstructures were studied. Lithological and textural-structural changes in sequences related to intense secondary transformations should affect the state of isotopic systems of rocks. To reveal basic trends in the evolution of isotopic systems, investigation using the K-Ar method was carried out. Clay fraction (less than 1 μm) separated from rocks and bulk samples were analyzed. Cleavage development, approximate value of rock contraction, and isotopic characteristics are compared with the available data on alteration of clay mineral assemblages. Relationship between the degree of rock deformation at the microlevel and calculated K-Ar ages has been established. K-Ar systems of clayey rocks indicate the age of cleavage formation and correspond to the Bajocian-Bathonian contraction period.

The early Jurassic fauna from the Gurumdy and Mynhajir zones of the East Pamirs

The Southeast Pamirs is a unique region with a wide development of Jurassic marine sediments that are characterized by complete different-facies sections and diverse fossils. Of particular interest are Early Jurassic corals, which represent the first finds in mountainous Central Asia and the entire eastern Mediterranean belt. Finds of such fossils are extremely rare in other regions of the world so far. According to [1], Jurassic sediments in the Southeast Pamirs can be divided into three (Gurumdy, Mynhajir, and Istyk) structural‐facies zones. Upper Jurassic fossils are confined to the Gurumdy and Mynhajir zones, which occupy marginal parts of the Southeast Pamirs and make up a horseshoe-shaped framing around the Inner Istyk zone (Istyk Uplift), where sedimentation commenced in the terminal-Early-initialMiddle Jurassic (Toarcian‐Aalenian). The Gurumdy and Mynhajir zones constitute the southwestern and northeastern segments of this horseshoe-shaped zone, respectively (figure). In the Jurassic, both zones were elements of a single trough located along the periphery of the Istyk Uplift inside a sea basin. The Gurumdy segment of the trough experienced intense subsidence and accumulated thick sediments, while the Mynhajir segment subsided less significantly to accumulate thinner sediments of variable composition. The present communication is dedicated to the characteristic of distribution, lithology, age, and fossils of the Lower Jurassic sediments developed in the Gurumdy and Mynhajir zones of the Southeast Pamirs. Different fossil groups from Lower Jurassic sediments have been determined and described by many paleontologists, including G.K. Melnikova (corals); V.P. Makridin, S.A. Melnikova, and A.S. Dagys (brachiopods); L.D. Kiparisova, L.V. Sibiryakova, and T.F. Andreeva (bivalves); and G.Ya. Krymgol’ts, V.I. Dronov, and Yu.S. Repin (ammonites). In the present-day structure of the Gurumdy zone, Jurassic sediments are developed in the river basins draining the Vahan Ridge beginning from upper reaches of the Beik River to the Zorkul Depression. Farther northwestward, they are widespread in the basins of the Mashale, Gurumdy, Irikyak, Alichur, Karademur, Kattamarjanai, and Vatasaif rivers that drain the eastern part of the South Alichur and western part of the North Alichur ridges. In the zone under consideration, the Jurassic rocks are unconformably sandwiched between upon Permian‐Triassic strata and Tertiary sediments. The zone is characterized by the continuous Jurassic section that includes sediments ranging from the basal part of the system to upper Callovian layers. Its lower series is very thick because of the development of reeflike sequences in some areas. The total thickness of the Lower Jurassic rocks amounts to 700 m. The Jurassic sediments of the Mynhajir zone are developed in the East and West Mynhajir mountains separated by the Aksu River and along the northern foothill of the Zougan Ridge, in the Karasu River basin, and at the estuary of the North Boztere, Kaindy, and other rivers. They are unconformably sandwiched between Permian‐Triassic and Tertiary layers. The Mynhajir zone also includes a complete section extending from the basal Jurassic to the Bathonian‐Lower Callovian strata, although the Mynhajir zone differs from the previous zone in more diverse lithology and two times lower thickness of the Lower Jurassic sequence (220‐285 m). Following below is a description of the Jurassic type sections of the Gurumdy and Mynhajir zones with Early Jurassic faunal assemblages. The integral Lower Jurassic section of the Gurumdy zone is compiled on the basis of outcrops on the watershed between the Sedek and Irikyak rivers. The author of the present communication studied it first together with V.P. Novikov (in 1969), E.V. Boiko (1970), and V.I. Dronov (1970s‐1980s).

Bushmen Cave Paintings of Ornithopod Dinosaurs: Paleolithic Trackers Interpret Early Jurassic Footprints

Remnants of Bushmen cave paintings showing representations of dinosaurs evidently reconstructed from footprints, trackways and skeletal remains have been found in Lesotho. This is a region of prolific dinosaur trackways preserved in Lower Jurassic sedimentary rocks, and the Bushman culture is renowned for extraordinary skill in the tracking of modern animals. It is probable that the track and trackmaker representations depict ornithopod dinosaurs. The track drawings are accurate, and the trackmaker representations show that Bushman artists anticipated modern reconstructions of bipedal dinosaurs and produced depictions that are more realistic than many paleontological reconstructions that endured until quite recently.