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Upper Cretaceous (Maastrichtian) charophyte gyrogonites from the Lameta Formation of Jabalpur, Central India: palaeobiogeographic and palaeoecological implications

Khosla A.

Acta Geologica Polonica

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2014

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Vol. 64, no. 3

311--323

EN

A charophyte gyrogonite assemblage consisting of Platychara cf. sahnii, Nemegtichara grambastii and Microchara sp. is reported herein from two localities (Bara Simla Hill and Chui Hill sections) of the Lameta Formation at Jabalpur. The Lameta Formation locally underlying the Deccan traps has been shown to be pedogenically modified alluvial plain deposits containing one of the most extensive dinosaur nesting sites in the world. They are associated with dinosaur bones and freshwater ostracod assemblages that suggest a Late Cretaceous (Maastrichtian) age. This is the first detailed systematic account of charophyte gyrogonites from the Lameta Formation. This charophyte assemblage is compatible with the biostratigraphic attribution provided by the ostracods. From a biogeographic viewpoint, it exhibits considerable similarity to other infratrappean assemblages of the Nand, Dongargaon, and Dhamni-Pavna sections (Maharashtra), and some intertrappean assemblages of Kora in Gujarat, Rangapur in Andhra Pradesh and Gurmatkal in South India. Globally, the genus Microchara is well distributed throughout Eurasia, whereas the genus Platychara occurs richly in the Upper Cretaceous deposits of Europe, Asia, America and Africa. However, at the specific level, Platychara cf. sahnii shows close affinities with charophytes from the Maastrichtian of Iran whilst Nemegtichara grambastii shows distinct affinities with two species of Early Palaeogene deposits of China and Mongolia. The presence of charophyte gyrogonites in the Lameta sediments is attributed to local lacustrine and palustrine conditions within a flood plain environment.

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Spherules associated with the Cretaceous–Paleogene boundary in Poland

Brachaniec T., Karwowski Ł., Szopa K.

Acta Geologica Polonica

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2014

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Vol. 64, no. 1

99--108

EN

The succession of the Lechówka section near Chełm in south-eastern Poland presents the first complete record of the Cretaceous–Paleogene (K–Pg) boundary in Poland. Samples of the boundary clay were examined for microtektites and shocked minerals to confirm the impact origin of the sediment. The spheroidal fraction reveals morphological and mineralogical features, e.g., spherules, similar to material from the K–Pg boundary as described from elsewhere. The impact genesis of the spherules is confirmed by the presence of nickel-rich spinel grains on their surfaces. The spinels are considered to be primary microlites and, thus, the spherules at Lechówka can be classified as microkrystites. No shocked minerals were noted. The deposits with spherules comprise Aland Mg-rich smectite (Cheto smectite). This almost pure Mg-rich smectite, forming up to 100% of the clay fraction, derived from the weathering of the impact glass. It is proposed that the spherules isolated from the Cretaceous-Paleogene boundary clay at Lechówka come from the Chicxulub crater in Mexico.

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Sedimentary development and isotope analysis of deposits at the Cretaceous/Palaeogene transition in the Paraíba Basin, NE Brazil

Neumann Virgínio Henrique, Barbosa José Antônio, Nascimento-Silva Valberlândia Maria, Sial Alcides Nobrega, Filho Mario

Geologos

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2009

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Vol. 15, No. 2

103--113

EN

New data are presented for three formations (Itamaracá, Gramame and Maria Farinha) and two boundaries (Campanian/Maastrichtian and Maastrichtian/Danian) in the Olinda Sub-basin of the Paraíba Basin. Currently accepted facies models, sequence stratigraphy characterizations, and stable-isotope data of carbon and oxygen are reviewed. The carbonate cement of the Itamaracá Formation sandstones shows carbon- and oxygen-isotope ratios consistent with a shallow-marine depositional environment: δ18O ranges from -0.8 to -2.7‰ PDB, and δ13C ranges from +1 to +2‰ PDB. Within the Itamaracá Formation, a maximum flooding surface at the Campanian/Maastrichtian transition has been identified. During the Maastrichtian, a Highstand System Tract was deposited, which shows an increase in temperature and marine bioproductivity as recorded by stable-isotope values (δ18O from -3 to -5‰ PDB, and δ13C values of -1.2, -0.3, 0.1 and +2.3‰ PDB). Just below the K/Pg boundary, the O-isotope signal indicates three warming phases, alternating with four cooling phases.

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Otwornice bentosowe a granica kreda/paleogen (K/P) w profilu Ain Settara, Tunezja

Peryt D., Alegret L., Molina E.

Przegląd Geologiczny

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2003

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Vol. 51, nr 12

1069-1074

PL

Z odsłonięcia Ain Settara (północna Tunezja) zbadano ponad 12-metrowy profil osadów najwyższego mastrychtu (2,5 m) i dolnego paleogenu (9.6 m) reprezentujący następujące poziomy otwornicowe: Plummerita hantkeninoides, Guembelitria cretacea, Parvularugoglobigerina eugubina i Parasubbotina pseudobulloides . W osadach najwyższego mastrychtu zespoły otwornic bentosowych są zróżnicowane pod względem taksonomicznym z podobnym udziałem form infaunalnych i epifaunalnych. Dramatyczna zmiana w strukturze zespołów otwornic bentosowych jest równoczesna z tworzeniem się warstewki z anomaliami geochemicznymi, tj. w spągu poziomu Guembelitria cretacea, gdzie zróżnicowane i o niskiej dominacji zespoły otwornicowe zostają zastąpione przez zespoły zubożone pod względem taksonomicznym a zdominowane przez epifaunalne morfogrupy. W tym momencie 14 rodzajów zanika. Niektóre z nich wymierają, podczas gdy inne pojawiają się ponownie w dolnym danie jako taksony Łazarza. Naszym zdaniem gwałtowny spadek dopływu pokarmu będący skutkiem załamania produkcji pierwotnej i równoczesnej zmiany w składzie fitoplanktonu (z przewagi nanoplanktonu wapiennego na przewagę bruzdnic) mogły być bezpośrednią przyczyną restrukturyzacji zespołów otwornic bentosowych. Globalne załamanie produkcji pierwotnej było prawdopodobnie skutkiem impaktu asteroidu na półwyspie Jukatan.

EN

The outer shelf-upper bathyal section across the Cretaceous/Paleogene (K/P) boundary at Am Settara (Central Tunisia) has been studied for quantitative changes in benthic foraminiferal assemblages. The studied interval extends from 2.5 m below to 9.6 m above the Cretaceous/Paleogene (K/P) boundary and encompasses the uppermost Plummerita hantkeninoides, Guembelitria cretacea, Parvularugoglobigerina eugubina and Parasubbotina pseudobulloides planktonie foraminiferal zones. In the uppermost Maastrichtian benthic foraminiferal assemblages are highly diversified and composed of mixed epifaunal and infaunal morphogroups. The dramatic change in the structure of benthic foraminiferal assemblages corresponds to the layer with the impact evidence, i.e., at the base of the Guembelitria cretacea Zone where highly diversified, low-dominance Upper Maastrichtian assemblages with infaunal and epifaunal morphogroups were suddenly replaced by taxonomically impoverished assemblages, strongly dominated by epifaunal morphogroups. At this level several species with inferred infaunal mode of life disappeared. Some of them went extinct, whereas others reappeared in the Lower Danian as Lazarus taxa. We interpret that a sudden breakdown of the food supply as a consequence of a collapse in primary productivity and simultaneous changes in the phytoplankton composition (from calcareous nannoplankton to dinoflagellates) resulted in extinction or temporary emigration of most infaunal morphogroups. The sudden collapse of primary productivity probably resulted from the impact of the K/P asteroid.