Lower Jurassic Deposits Research Articles

Historical and Geological Modeling of the Processes of Hydrocarbon Generation in the Hettangian–Aalenian Deposits of the Ust’-Tym Megadepression1

Abstract —Analysis of the geologic structure of the Hettangian–Aalenian deposits of the Ust’-Tym megadepression was carried out. The history of the formation of traps in the Hettangian–Aalenian complex has been reconstructed on the basis of a comprehensive interpretation of seismic materials and deep-drilling data. The oil and gas potential has been estimated. The time of the subsidence of the Togur Formation into the oil window has been determined, and the history of the generation of liquid hydrocarbons (HC) by the organic matter (OM) of the Togur Formation has been reconstructed. The Lower Jurassic and Aalenian deposits overlap the rocks of the pre-Jurassic basement with disagreement and are distributed almost over the entire study area. The complete section of the Hettangian–Aalenian deposits is in the most submerged parts of the territory. The section includes the Urman, Togur, and Salat/Peshkov Formations and the lower Tyumen Subformation. Three oil and gas subcomplexes—Hettangian–Early Toarcian (U16–17), Toarcian–Aalenian (U15), and Aalenian (U11–14) — are distinguished within the Hettangian–Aalenian sediments. Closed positive structures that can serve as hydrocarbon traps have been identified in each of the subcomplexes. Positive structures developed in the Jurassic, Berriasian–Early Aptian, and Aptian–Albian–Turonian time were inherited and finally formed at the post-Turonian stage only. The authors carried out a quantitative assessment of the total oil resources of the D0 category for all promising objects, taking into account the success rate. The heterogeneous organic matter of the Togur Formation is the main source of hydrocarbons in the Hettangian–Aalenian complex. The Togur Formation began to enter the oil window (OW) about 115–110 Ma and fully entered it about 5 Ma. The escape of rocks from the zone of the oil window began about 48 Ma and still continues. The history of the generation of liquid hydrocarbons by the organic matter of the Togur Formation has been reconstructed for types II and III of kerogen. For type II, the generation began about 94 Ma, at the beginning of the Late Cretaceous (Cenomanian), and for type III, it began in Turonian time (89.8 Ma). The most significant volumes of liquid HC were generated in the last 5 Myr. Potential hydrocarbon traps existed throughout the generation process, which allowed accumulation of the generated hydrocarbons in the Hettangian–Aalenian complex. Comparison of the estimated oil resources of the D0 category in the traps of the Hettangian–Aalenian complex with the volumes of generated hydrocarbons leads to the conclusion that the traps might have been filled. The results obtained in the course of the study suggest that the Hettangian–Aalenian complex is oil- and gas-promising and the Togur Formation is the main source of hydrocarbons.

THE GENERALIZATED STRATIGRAPHIC SCHEME OF THE JURASSIC OF WESTERN UKRAINE

In Western Ukraine the Jurassic deposits are known in the Carpathians, Transcarpathian Deep, Carpathian Foredeep and Western part of the East European platform. The Generalized stratigraphic scheme of the Lower, Middle and Upper Jurassic of these regions is represented. The current stratigraphic scheme is supplemented and detalized according to modern data, analisys and re-interpretation of many-years investigations these deposits by different specialists. The characteristics of stratigraphic units: distribution, lithological and paleontological composition, position in section, thicknesses and criteria for dating are given. The most complete and precise sequence of the Jurassic stages is determined on the territory of Carpathian Foredeep and adjacent part of the platform. In other regions these deposits are present fragmentarily. The stratigraphic units are mainly dated by the complexes of macro- and microfossils. In Precarpathians predominantly there are palynocomplexes for dating the Lower Jurassic deposits, mollusks, foraminifers and palynocomplexes for Middle Jurassic, and foraminifers, mollusks and tintinnids for Upper Jurassic. In Carpathians there are ammonites and belemnites for dating the Lower and Middle Jurassic deposits, and ammonites, tintinnids, dinocysts for Upper Jurassic. Correlation of the Jurassic stratigraphic units of the Western Ukraine is done.

Stratigraphy and macrofauna of the Lower Jurassic (Toarcian) Marrat Formation, central Saudi Arabia

The stratigraphy and macrofaunal content of the Lower Jurassic (Toarcian) Marrat Formation was studied at Khashm adh Dhibi, central Saudi Arabia. The studied succession is dominated by limestones and dolomites, with subordinate occurrences of sandstones, siltstones and claystones. The formation is highly fossiliferous with brachiopods, gastropods, bivalves, ammonites and echinoids, particularly the lower and upper members. Twenty nine species are identified, they include 7 species of brachiopods, 8 gastropods, 8 bivalves, 4 ammonites and 2 echinoids. Many of the identified fauna are correlated with Jurassic equivalents in Jordan, Italy, Morocco, Egypt and India. Three gastropod species: Globularia subumbilicata, Ampullospira sp., Purpuroidea peristriata and seven bivalve species: Palaeonucula lateralis, Chlamys (Radulopecten) fibrosa, Eligmus weiri, E.integer, E. asiaticus, Musculus somaliensis and Pholadomya orientalis were recognized for the first time in the Lower Jurassic deposits of Saudi Arabia.

A new leptonectid ichthyosaur from the Lower Jurassic (Hettangian) of Nottinghamshire, England, UK, and the taxonomic usefulness of the ichthyosaurian coracoid

Thousands of ichthyosaurs have been discovered from the rich Lower Jurassic deposits of the UK, with the majority collected from along the Lyme Regis-Charmouth area of the Dorset coast. Here, I describe a new leptonectid ichthyosaur, Wahlisaurus massarae gen. et sp. nov., based on a partial skull and an incomplete skeleton collected from the Lower Jurassic (Hettangian) of Nottinghamshire, England. Wahlisaurus can be referred to the Leptonectidae through the possession of an extremely slender and delicate snout, and a mandible shorter than the snout which produces an overbite. This referral is supported by a phylogenetic analysis. The new taxon is distinguished from other ichthyosaurs through a unique combination of characters and autapomorphies of the pectoral girdle including the presence of both a scapular-coracoid foramen and a large and roughly ovoid coracoid foramen. A coracoid foramen has only previously been reported in the Triassic ichthyosaur Cymbospondylus. The peculiar coracoid morphology further highlights the taxonomic utility of coracoids in ichthyosaurs. The aforementioned features demonstrate that W. massarae cannot be referred to any currently recognized leptonectid. Wahlisaurus is the ninth Lower Jurassic ichthyosaur genus to be recognized worldwide, and the fifth documented in the Lower Lias Group.http://zoobank.org/urn:lsid:zoobank.org:pub:EE500E11-66AB-43C8-BB59-F21654763241

Basin geodynamics and sequence stratigraphy of Upper Triassic to Lower Jurassic deposits of Southern Tunisia

Aims of this paper are to propose a geodynamic and sequential framework for the late Triassic and early Jurassic of and south Tunisia and to evidence the impact of local tectonics on the stratigraphic architecture. Facies of the Upper Triassic to Lower Jurassic of Southern Tunisia have been interpreted in terms of depositional environments. A sequential framework and correlation schemes are proposed for outcrops and subsurface transects. Nineteen middle frequency sequences inserted in three and a half low frequency transgression/regression cycles were evidenced. Despite some datation uncertainties and the unknown durations of Lower Jurassic cycles, middle frequency sequences appear to be controlled by eustasy. In contrast the tectonics acted as an important control on low frequency cycles. The Carnian flooding was certainly favored by the last stages of a rifting episode which started during the Permian. The regression accompanied by the formation of stacked angular unconformities and the deposition of lowstand deposits during the late Carnian and Norian occured during the uplift and tilting of the northern basin margins. The transpressional activity of the Jeffara fault system generated the uplift of the Tebaga of Medenine high from the late Carnian and led to the Rhaetian regional angular Sidi Stout Unconformity. Facies analysis and well-log correlations permitted to evidence that Rhaetian to Lower Jurassic Messaoudi dolomites correspond to brecciated dolomites present on the Sidi Stout unconformity in the North Dahar area. The Early-cimmerian compressional event is a possible origin for the global uplift of the northern African margin and Western Europe during the late Carnian and the Norian. During the Rhaetian and the early Jurassic a new episode of normal faulting occured during the third low frequency flooding. This tectonosedimentary evolution ranges within the general geodynamic framework of the north Gondwana margin controlled by the opening of both Neotethys and Atlantic oceans.

LOWER JURASSIC DEPOSITS STRATIFICATION IN THE SECTION OF TOTA-YAKHINSKAYA 25 WELL AND OIL AND GAS PROSPECTS ON GYDAN PENINSULA

A new option of stratigraphic disjunction of the Lower Jurassic deposits in the section of Tota-Yakhinskaya 25 well is offered. A substantiation of the proposed stratification option is presented and its comparison with other researchers’ works is made. A conclusion is drawn about a significant influence of the Kiterbyuit horizon position variation upon the estimation of oil-and-gas content in the entire Lower Jurassic series within the Gydan peninsula.

A new fern from Lower Jurassi sediments of the Irkutsk coal basin (Eastern Siberia)

The paper describes a new fern species Lobifolia nana A. Frolov et Mashchuk from the Lower Jurassic deposits of the Irkutsk coal basin. The fern is characterized by small measurements of fronds and pinnae and by the absence of well-developed aphlebia-like basal pinnae. The material comes from an open-pit mine of the Mugun lignite deposit that exposes the Cheremkhovskaya Formation.

Oil potential of the Lower Mesozoic deposits of the Khapchagai megaswell of the Vilyui syneclise

Analysis of all available geological, geophysical, and field data on some gas condensate fields discovered within the Khapchagai megaswell (Vilyui syneclise of the Siberian Platform) as early as the 1960s shows the presence of oil rims in Lower Triassic (horizon T1-III in the Srednevilyuiskoe and Tolonskoe gas condensate fields and horizon T1-Kh in the Mastakhskoe gas condensate field) and Lower Jurassic (horizons J1-I and J1-II in the Mastakhskoe gas condensate field) deposits. The C3 oil reserves in these rims are estimated at several tens of millions of tons of oil. The results are indicative of the oil potential of the Lower Mesozoic deposits not only of the Vilyui syneclise but also of the Lena–Vilyui petroliferous province as a whole, which was always characterized as a gas-bearing province in summary reports.

Comprehensive database on Induan (Lower Triassic) to Sinemurian (Lower Jurassic) marine bivalve genera and their paleobiogeographic record

Fil: Ros Franch, Sonia. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - La Plata; Argentina. Universidad de Valencia; Espana. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Division Paleozoologia Invertebrados; Argentina

A mysterious giant ichthyosaur from the lowermost Jurassic of Wales

Ichthyosaurs rapidly diversified and colonised a wide range of ecological niches during the Early and Middle Triassic period, but experienced a major decline in diversity near the end of the Triassic. Timing and causes of this demise and the subsequent rapid radiation of the diverse, but less disparate, parvipelvian ichthyosaurs are still unknown, notably because of inadequate sampling in strata of latest Triassic age. Here, we describe an exceptionally large radius from Lower Jurassic deposits at Penarth near Cardiff, south Wales (UK) the morphology of which places it within the giant Triassic shastasaurids. A tentative total body size estimate, based on a regression analysis of various complete ichthyosaur skeletons, yields a value of 12–15 m. The specimen is substantially younger than any previously reported last known occurrences of shastasaurids and implies a Lazarus range in the lowermost Jurassic for this ichthyosaur morphotype.

Middle Jurassic theropod trackways from the Panxi region, Southwest China and a consideration of their geologic age

Theropod footprints from the Middle Jurassic Xincun Formation in the Panxi region (Sichuan Province, Southwest China) show strong similarities to the ichnogenus Kayentapus. They are characterized by slender digits, wide digit divarication, and a characteristic pad configuration that is different from other Jurassic theropod ichnotaxa. At the Shansong tracksite, three trackways are present, each consisting of four consecutive tracks (stride and pes lengths up to 200cm and 36cm, respectively). The speed of the trackmakers has been calculated with values between 1.1 and 1.4m/s. The assemblage is a further document of a Middle Jurassic occurrence of this morphotype that is basically known from the Lower Jurassic deposits elsewhere. This could be due to peculiarities of theropod communities in this region, reflecting a different paleobiogeographic distribution pattern in the Middle Jurassic. Biostratigraphically, ostracods lend support to a Middle Jurassic age of the trackbearing unit. This corresponds partly with data from the Shangshaximiao Formation that is considered to be of Middle Jurassic age based on ostracods but Late Jurassic age based on vertebrate skeletons. The ichnological record and the presence of Kayentapus-like footprints in both units support a Lower–Middle Jurassic age.

Regional-Scale CO2Storage Capacity Estimation in Mesozoic Aquifers of Poland

The CO2 storage capacity estimated at the regional scale provides a preliminary recognition of as far as the possible uses of CO2 sequestration as an option of emission reduction. There has been presented the estimation of CO2 storage capacity for aquifers of Lower Cretaceous, Lower Jurassic and Lower Triassic of Polish Lowland. The Lower Jurassic deposits exhibit the greatest CO2 storage capacity of all the horizons, storage capacity of the Lower Triassic deposits is lower, the smallest capacity was estimated for the Lower Cretaceous deposits. The use of specific capacity maps for carbon dioxide in aquifers has been suggested in order to estimate the potential on national and basin scale as well as the search for prospective areas for CO2 storage.

Marine shelf to paralic biofacies of Upper Triassic to Lower Jurassic deposits in Spitsbergen

The Upper Triassic to Lower Jurassic Kapp Toscana Group of Spitsbergen consists of mudstones, sandstones and shales deposited in offshore marine to paralic conditions in an extensive shelf embayment. The study focuses on microfossil-based biofacies features (mainly foraminifera, but also palynomorphs) combined with sedimentary and selected geochemical data, in relation to transgressive–regressive developments. The analysed material includes field logs and sediment samples originating from the Juvdalskampen section, central Spitsbergen.The benthic foraminiferal succession reveals three principal associations: 1) assemblages of mixed agglutinated and calcareous components, typified by medium to high diversities, indicating offshore shelf conditions; 2) assemblages consisting dominantly or entirely of agglutinated forms with low diversity, attributed to hyposaline conditions; 3) highly impoverished agglutinated assemblages or barren samples suggesting extremely brackish to freshwater environments. The marine influence is highest in the lower and upper parts, and lowest in the middle part of the Kapp Toscana Group, as indicated both by foraminiferal and palynomorph proxies. The potential of the boron concentration as a salinity indicator is demonstrated by its co-variance with biofacies features: the boron content increases with increasing salinity.The Kapp Toscana Group consists of two depositional sequences. The Storfjorden sequence (Carnian to Early Norian) starts with a transgressive systems tract formed in offshore shelf conditions with normal marine salinity and terminates at the maximum flooding event, which is succeeded by a highstand systems tract deposited in paralic (hyposaline to freshwater), prodelta to delta plain environments. The overlying Wilhelmøya sequence (Middle Norian to Bajocian) is punctuated by several hiatuses, and was deposited in hyposaline waters on a sediment-starved, prodelta shelf platform.

Trans-border (South-Eastern Serbia/South-Western Bulgaria) correlations of the Jurassic sediments: The Getic and Supra-Getic units

The Getic and Supra-Getic are palaeogeographic units in SE Serbia and SW Bulgaria. Based on the presence (in Eastern) or absence (in Western) of Lower Jurassic marine deposits, the Getic is divided into Eastern and Western. In the Eastern Getic, the Lower Jurassic sedimentation in SE Serbia is represented by the Vidlic Clastites covered by the Lukanja Coal Beds, Lukanja Quartz Sandstones, Lukanja Brachiopods Beds, Lukanja Marlstones, Lukanja Belemnitic-Gryphaean Beds and Lukanja Cephalopod Limestones; in SW Bulgaria, the sedimentation commenced with the Tuden Formation, followed by the Kostina Formation and the Ozirovo Formation with a few members. The Middle Jurassic in SE Serbia commenced with the Senokos Siltstones and Shales and the Gulenovci Beds, while in SW Bulgaria with black shales (the Etropole Formation), followed by marls and clayey limestones of the Bov Formation. The Middle Jurassic sediments are represented in the Western Getic of SE Serbia by the Kurilovo Clastites and the Kurilovo Limestones (synonym to Gumpina Limestones of KRA?TNER & KRSTIC 2003); in the Supra-Getic of SE Serbia they are formed by the Jerma Clastites and Jerma Limestones (synonym of the Gumpina Limestones). In SW Bulgaria the Middle Jurassic sediments are represented by the sandstones of the Gradets Formation and by the bioclastic limestones of the Polaten Formation. During the Callovian (Middle?) started the formation of a carbonate platform with micritic limestones. In SE Serbia, it is Basara Limestones, Vidlic Limestones, Beljanica and Zdrelo Limestones, and in SW Bulgarian, the Belediehan Formation of Callovian-Kimmeridgian p.p. age. Characteristic for the Supra- Getic is the formation of a few grabens with specific sedimentation: the Svetlya Graben (the Zhablyano and Ozirovo Formations) and the Lobosh Formation; the Treklyano Graben (the Dobridol and Sredorek Formations), and out of it - the Methohya and Sredorek Formation. During the Callovian-Kimmeridgian p.p., in the Svetlya Graben was sedimented the Lobosh Formation, horizontally passing into the Javorets and Gintsi Formations. During the latest Kimmeridgian-Tithonian commenced a big facial diversification: on the Getic in SE Serbia sedimented reef or sub-reef limestones (the Crni Vrh and Kucaj Reef Limestones), while in SW Bulgaria, the Slivnitsa Formation. On the Supra-Getic in SE Serbia formed Luznica Flysch and in SW Bulgaria pre-flysch of the Neshkovtsi Formation and siliciclastic flysch of the Kostel Formation.

Occurrence of Aninopteris (Matoniaceae) from the Middle Jurassic of East central Iran

Aninopteris Givulescu and Popa 1998, a matoniacean fern originally known from the Lower Jurassic deposits of Romania, has been recently reported from the Middle Jurassic coal bearing deposits of Mazino mine, south of Tabas region, east central Iran. This is the second record of this genus, excepting its original occurrence from the Anina region of Romania. Besides the younger age, the Iranian material differs from the type material in having a higher number of sporangia, and less branched secondary veins. Thus, Aninopteris formosa var. persica var. nov. is proposed for the studied material.

Multivariate analysis of taphonomic data in Lower Jurassic carbonate platform (northern Italy)

Taphonomical analysis on skeletal concentrations and taphofacies has been carried out in the Lower Jurassic deposits of the Trento carbonate platform (northern Italy). The interpretation of the taphonomic categories used has been refined applying three statistical processes to the semi-quantitative values of taphocharacter abundance in eight types of skeletal concentrations. Analysis of correlation allowed the taphocharacters to be subdivided into four genetic categories: (1) palaeobiological processes on shelly ground; (2) palaeobiological activity on the substrate; (3) mechanical processes induced by currents; (4) infilling processes induced by currents. Cluster analysis on the eight types of skeletal concentrations defined six genetic processes. Moreover, principal-components analysis offered three factors which explained 75% of the variance. Factor 1 shows the contribution of hydrodynamic vs. bioturbation processes in the genesis of the resulting skeletal concentration. Factor 2 displays the degree of transport undergone by bioclasts before burial. Finally, factor 3 points out the dominance of superficial taphodistortion and colonization of the substrate, or deeper colonization in the substrate. Numerical analysis on taphonomical data has been proved to be a powerful tool for palaeoenvironmental studies, thereby aiding in the understanding of the shell beds genetic processes. To cite this article: J.E. Caracuel et al., C. R. Palevol 4 (2005) .

The Jurassic of East Greenland: a sedimentary record of thermal subsidence, onset and culmination of rifting

The Late Palaeozoic – Mesozoic extensional basin complex of East Greenland contains a record of deposition during a period of Rhaetian – Early Bajocian thermal subsidence, the onset of rifting in the Late Bajocian, its growth during the Bathonian–Kimmeridgian, culmination of rifting in the Volgian – Early Ryazanian, and waning in the Late Ryazanian – Hauterivian. The area was centred over a palaeolatitude of about 45°N in the Rhaetian and drifted northwards to about 50°N in the Hauterivian. A major climate change from arid to humid subtropical conditions took place at the Norian–Rhaetian transition. Deposition was in addition governed by a long-term sea-level rise with highstands in the Toarcian–Aalenian, latest Callovian and Kimmeridgian, and lowstands in the latest Bajocian – earliest Bathonian, Middle Oxfordian and Volgian. The Rhaetian – Lower Bajocian succession is considered the upper part of a megasequence, termed J1, with its base in the upper Lower Triassic, whereas the Upper Bajocian – Hauterivian succession forms a complete, syn-rift megasequence, termed J2. The southern part of the basin complex in Jameson Land contains a relatively complete Rhaetian–Ryazanian succession and underwent only minor tilting during Middle Jurassic – earliest Cretaceous rifting. Rhaetian – Lower Jurassic deposits are absent north of Jameson Land and this region was fragmented into strongly tilted fault blocks during the protracted rift event. The syn-rift successions of the two areas accordingly show different long-term trends in sedimentary facies. In the southern area, the J2 syn-rift megasequence forms a symmetrical regressive–transgressive–regressive cycle, whereas the J2 megasequence in the northern area shows an asymmetrical, stepwise deepening trend. A total of eight tectonostratigraphic sequences are recognised in the Rhaetian–Hauterivian interval. They reflect major changes in basin configuration, drainage systems, sediment transport and distribution patterns, and in facies and depositional environments. The sequences are bounded by regional unconformities or flooding surfaces and have average durations in the order of 10 Ma. They are subdivided into conventional unconformity-bounded depositional sequences with durations ranging from tens of thousands of years, in the Milankovitch frequency band, up to several million years. Deposition was alluvial and lacustrine in the Rhaetian–Sinemurian, but almost exclusively marine during the Pliensbachian–Hauterivian time interval when a marine strait, up to 500 km wide and more than 2000 km long, developed between Greenland and Norway, connecting the Arctic Sea and the North Sea. Coal-bearing fluvial and paralic deposits occur, however, at the base of the onlapping Middle Jurassic succession in the central and northern part of the basin complex. The sedimentary development is similar to that in the Northern North Sea and on the Norwegian shelf, and East Greenland offers important onshore analogues for virtually all of the types of deeply buried Jurassic depositional systems of these areas and especially their hydrocarbon reservoirs.

Aspects of Romanian Early Jurassic palaeobotany and palynology: Part II. A new species of Pachypteris from Cristian

The Lower Jurassic (Sinemurian) deposits of Cristian (Braşov County, Romania) contain a well-preserved land flora. Pachypteris gradinarui n.sp., a new species of seed fern foliage belonging to the Corystospermales, is described, figured and analysed. The species has a bipinnate, petioled frond; secondary rachises inserted on the upper side of the primary rachis; rounded, occasionally lobed pinnules without marked abaxial thickening or folding. The material is compared with other Pachypteris species, and with Cycadopteris, a related genus characterised by marginal (cuticular) thickening and folding, as it presents transitional characters between the two genera.

99/02907 Conditions for formation and germanium content in the Lower Jurassic coal deposits in the western part of Northern Caucasus

99/02907 Conditions for formation and germanium content in the Lower Jurassic coal deposits in the western part of Northern Caucasus

Environmental implications of oncoids and associated sediments from the Remoredo Formation (Lower Jurassic) Mendoza, Argentina

Lower Jurassic deposits of the middle member (19 m) of the Remoredo Formation at Arroyo Montañesito, southwestern Mendoza Province (Neuquén Basin, Argentina), and its oncoids are described. Four lithofacies constitute the lacustrine deposits of the Remoredo Formation: (1) laminated green to gray calcareous shales; (2) laminated to massive dark gray mudstones; (3) massive to upward-coarsening dark gray oncolite wackestones; and (4) massive dark gray packstones with abundant macro-oncolites. According to layer configuration, two types of oncoids were recognized: (a) those having distinctly banded, well defined concentric and continuous lamination (Type I); and (b) those having a vertical arrangement of irregular and discontinuous laminae (Type I 3–I). The continuous micritic laminations suggest growth during agitated conditions, and the discontinuous laminations reflect short periods of non agitation or tranquility in the water mass. The oncolites are associated with a well preserved faunal assemblage of ostracods ( Darwinula sp. and possible members of the Subfamily Iliocypridinae) and some fragments of bivalves that are indicative of shallow water conditions. The facies association is a coarsening-upward sequence interpreted as the product of deposition in a shallow nearshore lacustrine environment, and a progressive infilling by pyroclastic subaereal flows.