1,721,247 research outputs found
What the morphology and the shell structure of Permo-Carboniferous brachiopods from western Palaeotethys/Neotethys can tell us about palaeoecology and palaeoclimate
No full textZ.Q Chen e G.R. Shi, Artinskian-Kungurian (Early Permian) brachiopod faunas from the Tarim Basin, Northwest China. 1, Paleobiogeography, and systematics of orthotetida, orthida, spiriferida, spiriferinida, rhynchonellida, athyridida and terebratulida, "Palaeontographica Abteilung A", 274(2006), pp. 113-177
No full textQuantitative palaeoecology in the Pachycyrtella Bed, Early Permian of Interior Oman
No full textThe population dynamics and community structure of the Pachycyrtella Bed at the base of the Lower Permian Saiwan Formation (Interior Oman) are described. The populations of the brachiopod Pachycyrtella omanensis and the bivalve Dickinsartella pistacina are census populations, which show a stable structure, with individuals growing successfully to maturity due to fast initial growth rate. P. omanensis and D. pistacina are opportunist species that colonized a physically stressed environment, characterized by high mobility of the substrate, high energy and high nutrient influx at the end of the Gondwanan deglaciation. Both P. omanensis and D. pistacina have a large biovolume with respect to surface area and this may reflect an adaptation to cool climate conditions, whereas their thick shell substance could be the result of increasing biocalcification in the high O2/CO2 Early Permian atmosphere. Community structure records the combined effect of rich food resources and an unstable environment, as low (individuals) to very low (biovolume) diversity values and short suspension feeding chains characterize the pioneer palaeocommunities of the Pachycyrtella Bed. The slight increase in diversity in the upper part of the bed is interpreted to have resulted from a change in the environmental stability, probably connected to decreasing hydrodynamic energy during a small scale sea-level rise. More favourable conditions at the top of the bed are also suggested by the relative abundance of the newly recognized small-sized strophalosiid species Strophalosia ericinia n. sp., which spent part of its life firmly attached to P. omanensis and bivalves
Z.Q. Chen e G.R. Shi, Artinskian-Kungurian (Early Permian) brachiopod faunas from the Tarim Basin, Northwest China. 2, Biostratigraphy and systematics of productida, "Palaeontographica Abteilung A", 275(2006), pp. 1-53
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Structure and development of upper Permian brachiopod shells from North Iran
No full textThe calcareous shell of several Rhynchonelliform brachiopods from the Nesen Formation (Late Permian) of North Iran was studied under scanning electron microscopy and cathodoluminescence to define their ultrastructure and their state of preservation versus diagenetic alteration. The Strophomenata shell succession is composed of a cross-bladed laminar secondary layer crossed by pseudopunctae; a prismatic tertiary layer has been observed in a few species only. The Rhynchonellata shell succession is composed of a fibrous secondary layer and a prismatic tertiary layer in all the studied species. Specimens were classified into six morphological types based on layer fabric and the morphology of its structural units (laminae, fibres and prisms). Subsequently these morphological types were analyzed through cathodoluminescence to assess their eventual diagenetic alteration. Relative frequencies were calculated for each morphological type and for the degree of luminescence based on the different lithology of the host rocks to evaluate the main factors that affect shell preservation. Results show that diagenetic alteration depends on shell fabric, taxonomy and lithology of the host rocks, but it appears that the first and the second features are the most important factors in determining the fate of the shell and its preservation
Guadalupian (Permian) brachiopods from the Ruteh Limestone, North Iran
No full textThirty-three brachiopod species from the Guadalupian Ruteh Limestone of North Iran are here systematically described and illustrated. Brachiopods have been collected bed-by-bed along five stratigraphic sections and in one fossiliferous locality in the region between Dorud and Shirinibad in the Alborz Mountains. Four new species and one new genus are erected in the present paper: Haydenella eminens n. sp. Perigeyerella rutehiana n. sp.; Martinia bassa n. sp. and Bisolcatelasma iraniana n. gen. n. sp. Quantitative biostratigraphic analysis of the brachiopod data based on the Unitary Association method (Guex, 1991) has lead to the construction of a local sequence of three discrete biozones: The Squamularia sp. B-M. bassa Biozone at the base of the formation, the H. kiangsiensis-N. (N.) asseretoi Biozone in its middle part and the R. exile-R. gemmellaroi Biozone at its top. The latter however has been recognized only in the Shirinabad section. As already envisaged for the Carboniferous and Lower Permian brachiopod faunas from North Iran, the Guadalupian fauna is comprised mostly of cosmopolitan taxa, confirming the role of the Iranian microplate as a staging-post for most of the late Palaeozoic. When compared to the younger Lopingian faunas collected in the same regions of North Iran, the Ruteh brachiopods appear significantly different, indicating a marked biotic change in the brachiopod communities across the end- Guadalupian biotic crisis
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