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Search Results: 1 - 10 of 676 matches for " Cretaceous "
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Late Cretaceous/Early Paleocene Biostratigraphy of the Northern Portion of the Bornu Basin, Nigeria  [PDF]
Peter S. Ola, John A. Adekoya, Solomon O. Olabode
Open Journal of Geology (OJG) , 2016, DOI: 10.4236/ojg.2016.67044
Abstract: Ditch cutting samples from Kasade-1 well were processed for microfauna, nannofossil and palynomorphs to throw more light on biostratigraphic events in the northern portion of the Bornu Basin, Nigeria. The lower section of the well within interval 990 - 1565 m yielded fairly abundant foraminifera species, while the upper section was barren. Palynomorph distribution follows the same pattern as observed for foraminifera except that few fresh-water algal species, Botryococcus braunii, were recovered from the upper section. The samples are devoid of nannofossil but contain few ostracod species, echinoid remains and fish tooth. Recognition of two planktonic foraminifera zones, Globotruncanella havanensis and Globotruncana aegyptiaca, enabled the delineation of the Campano-Maastrichtian and Maastrichtian boundary. The Cretaceous Tertiary boundary was inferred based on the top occurrence of palynomorph Dinogymnium euclaense. An abrupt truncation in the distribution of foraminifera species at a depth of about 990 m suggests unconformity, a widely reported event that followed the Santonian squeeze in the entire mega-Chad Basin.
Aptian-Late Cenomanian Fluvio-Lacustrine Lithofacies and Palynomorphs from Mamfe Basin, Southwest Cameroon, West Africa  [PDF]
Olivier A. Njoh, Miriam B. Nforsi, Junie N. Datcheu
International Journal of Geosciences (IJG) , 2015, DOI: 10.4236/ijg.2015.67064
Abstract: The sedimentary sequences in the Mamfe Basin are generally thought of as continental (fluvio-lacustrine) in origin. But the wide spread occurrence of salt springs and salt accumulations and in places gypsum, often puts to question the exclusive continentality throughout this basin’s history. The sequences studied portray a wide range of complex lithologies and lithofacies relationships and include basal and intra-formational conglomerates, sandstones, shales, carbonaceous, carbonate and halite facies respectively. All these are well exposed at several outcrop sections distributed all over the basin with some measuring up to and above 30 m in height.Sedimentary structures include: parallel aligned imbricated prismatic pebbles, plannar to trough-cross stratifications, fining upward grain size distribution and thin frequently alternating sandstone-shale beds. Palynological data have been obtained for the first time from the shally and carbonate intervals and integrated with five lithofacies associations, permitting the determination of the ages and paleo environmental reconstruction. The palynomorphs are characterized by pteridophytic spores dominated byCicatricosisporitessp.,Cyathiditessp. andDeltoidsporasp., pollen grains include gymnosperms dominated byClassopollis annulatus
Microfacies, Sedimentary Environment and Sequence Stratigraphy of Gadvan and Darian Formations in the Zagros Basin, South of Semirom, Iran  [PDF]
Mohammad Kazem Hamedanian, Seyed Hamid Vaziri, Mahnaz Amir Shakarami, Mehran Arian, Naser Arzani
Open Journal of Geology (OJG) , 2016, DOI: 10.4236/ojg.2016.69086
Abstract: Gadvan and Darian formations are in the upper part of Khami group that has been deposited in the highland Zagros zone and the southern Margin of Neotethys. These formations outcrop in the south of Semirom (Agh-Dagh Mountain) consist of Orbitolina limestones and marly limestones with a Late Barremian-Aptian age and thickness of 520 meters. Based on field characteristics, petrographic and texture of facies, these rocks consist of Oregonian facies (Urgonian facies) with 12 carbonate microfacies which are deposited in Lagoon, barrier and shallow open marine. The absence of loss and flows of turbidities indicates that carbonate platform of Gadvan and Darian formations in the studied area are (Hmoklinal) platform type. Abundance of rudist (bivalves) and Peloid markers show that there is a Photozoan collection in tropical climates. In the above sedimentary succession, from a sequence stratigraphic perspective, three sedimentary cycles were recognized which deposited in a platform model. The Gadvan Formation overlies on Fahliyan Formation disconformable and is covered by Darian Formation gradual with reducing the amount of marl and increase of limestone. The Kazhdumi Formation is exposed disconformably with hematite nodules and oxidized sediments over the Darian Formation. On the basis of petrographic studies, diagenetic process of Gadvan and Darian formations in the study area includes cementation, the physical and chemical density and replacement processes such as pyritation, ironies and silica. Porosity observed in the study area is mainly inter-granular porosity type, modular and vaggy.
Uma Se o Tipo para o Limite Cretáceo-Terciário
Ignácio Machado Brito
Anuário do Instituto de Geociências , 1988,
A new palm trunk from the Upper Cretaceous of Argentina
Ottone,Eduardo G.;
Ameghiniana , 2007,
Abstract: a new morphospecies of palm trunk, palmoxylon pichaihuensis sp. nov., is proposed on the basis of several specimens recovered from a succession of tuffs and breccias at pichaihue, neuquén province, argentina. the specimens comprise atactosteles that display densely crowded fibrovascular bundles in the peripheral zone, and less congested fibrovascular bundles, randomly scattered or arranged in irregular circles in the central zone; sclerenchyma reniform; xylem with 1-4 large metaxylem vessels and 6-12 smaller protoxylem elements in the central zone, and an f/v ratio of 1.3-2:1. the pichaihue fossil assemblage is similar to, and probably coeval with the flora of bajo de santa rosa, río negro province, reflecting a warm and relatively humid climate, at ca. 40- 45o s, in southern south america during the late cretaceous.
Controles estratigráficos en la preservación de restos de vertebrados en la formación Cerro Barcino (Cenomaniano), provincia del Chubut
Cladera,G; Limarino,C. O; Alonso,M. S; Rauhut,O;
Revista de la Asociaci?3n Argentina de Sedimentolog?-a , 2004,
Abstract: the factors that controlled the differential concentration of vertebrates remains in specific stratigraphic intervals of cerro casta?o member are considered in this paper (fig. 1). the finding of vertebrates is only limited to pebbly sandstone beds that form fluvial channels with non erosive bases and tabular geometry. the closely associated alluvial plains, and other types of channels intercalated in the sequence, have not yielded significant paleontological remains. in order to analyze the origin of the differential concentration of vertebrates, the sequence was divided in six sedimentary facies (figs. 2 and 4, table 1), including different kinds of channel (chmt, chsl y chsw) and flood plain (pd, pp y pc) deposits. chmt facies is composed of cross-bedded sandstones and conglomerates forming tabular multistorey channel complex bounded by non erosive bases (fig. 4). sandstones comprise lithoarenites and feldslithoarenites with low matrix percentage (less than 4 %), high quantities of cement (up to 21 %), open fabric, scarce diagenetic alteration and almost absent porosity. three different types of cements have been distinguished in these rocks: 1) rim-type zeolite cement, 2) poikilitic calcite and 3) microcristalline and poikilitic analcime (fig. 5d,e). chsw facies forms simple lenticular channels with erosive bases deeply incised into floodplain deposits (fig. 4). the lowermost part of each channel shows lenses of intraformational conglomerates covered by massive and cross-bedded medium- and fine-grained sandstones. chsw facies is dominated by lithoarenites showing moderate to high matrix content (up to 20 %), mainly zeolitic cement and frequent formation of pseudomatrix (fig. 5f). the last type of channel deposits correspond to chsl facies that form thin lentiform channels (up to 0.5 m thick) encapsulated into floodplain facies (fig. 4). these channels comprise coarse-grained sandstones showing low proportions of matrix, relatively open fabric and scarce diagenet
Magnetostratigraphic study of Cretaceous depositional succession in the northern Kuqa Depression, Northwest China
Shoutao Peng,Zhong Li,Baochun Huang,Tao Liu,Qingchen Wang
Chinese Science Bulletin , 2006, DOI: 10.1007/s11434-005-0340-5
Abstract: There are some quite different disputes about chronostratigraphic division of the Cretaceous in the Kuqa Depression, northern margin of the Tarim Basin. We then carried on a magnetostratigraphic study on Cretaceous succession in the Kuqa River and Kezilenuer Channel profiles. Detailed paleomagnetic analyses on 446 specimens from 265 sites permit a construction of a preliminary magnetic polarity sequence for the Cretaceous strata. Together with paleobiologic constraints from calcareous nannofossils, magnetostratigraphic results show that the Bashenjiqike Formation was probably deposited during the late Campanian to Maastrichtian stages of the Late Cretaceous, ranging from about 79.1 to 65.6 Ma. On the other hand, magnetozones identified from the Yageliemu, Shushanhe, and Baxigai formations may principally correlate with chrons M18r to M3 of the Geomagnetic Polarity Time Scale (GPTS). This correlation suggests that these three formations were very likely to be formed during the early-middle stage of the Early Cretaceous between the Berriasian to the early Berremian stages (141.9–124.1Ma). Therefore it is possible that the Bashenjiqike Formation contacts the underlying strata with an unconformity and there is a giant sedimentary hiatus during the period of the late Barremian to early Maastrichtian stages in the Kuqa Depression.
Early diversification of birds: Evidence from a new opposite bird
Fucheng Zhang,Zhonghe Zhou,Lianhai Hou,Gang Gu
Chinese Science Bulletin , 2001, DOI: 10.1007/BF02900473
Abstract: A new enantiornithine birdLongipteryx chaoyangensis gen. et sp. nov. is described from the Early Cretaceous Jiufotang Formation in Chaoyang, western Liaoning Province. This new bird is distinguishable from other known enantiornithines in having uncinate processes in ribs, elongate jaws, relatively long wings and short hindlimbs, and metatarsal IV longer than metatarsals II and III. This new bird had probably possessed (i) modern bird-like thorax which provides firm attachment for muscles and indicates powerful and active respiratory ability; (ii) powerful flying ability; (iii) special adaptation for feeding on aquatic preys; and (iv) trochleae of metatarsals I–IV almost on brate heterocoelous. Distal region of sternum with well developed carina and lateral processes. Uncinate processes present but not fused with ribs. At least 6 rows of gastraliae present. Carpometacarpus not completely fused, minor metacarpal longer than major one; second phalanx the same level, an adaptation for perching. The new bird represents a new ecological type different from all known members of Enantiornithes. It shows that enantiornithines had probably originated earlier than the Early Cretaceous, or this group had experienced a rapid radiation right after it first occurred in the early Early Cretaceous.

科学通报(英文版) , 1989,
The oldest elasmosaurs (Sauropterygia, Plesiosauria) from Antarctica, Santa Marta Formation (upper Coniacian? Santonian–upper Campanian) and Snow Hill Island Formation (upper Campanian–lower Maastrichtian), James Ross Island
José P. O'Gorman
Polar Research , 2012, DOI: 10.3402/polar.v31i0.11090
Abstract: Elasmosaurs are recorded for the first time in the Lachman Crags Member (Beta Member) of the Santa Marta Formation (lower Campanian) and in the Herbert Sound Member of the Snow Hill Island Formation (upper Campanian). These are the first elasmosaurids from James Ross Island, Antarctic Peninsula. These records greatly improve our knowledge of the taxonomic diversity of plesiosaurs of the Santa Marta Formation and Herbert Sound Member of the Snow Hill Island Formation, and extend the lower limit of the record of Elasmosauridae in Antarctica to the lower Campanian, making this the oldest record of an Antarctic elasmosaur.
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