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Interplay of orbital forcing and tectonic pulses in the Cambrian Iberian platform, NE Spain (2000)

Álvaro, J. J. ; Vennin, E. ; Muñoz, A. ; [et al.]

Springer

International journal of earth sciences 89 (2000), S. 366-376

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ISSN: 1437-3262

Keywords: Key words Cyclicity ; Tectonism ; Palaeogeography ; Iberian Chains ; Cambrian

Source: Springer Online Journal Archives 1860-2000

Topics: Geosciences

Notes: Abstract The stratigraphy of carbonate/shale couplets, cycles and cycle-stacking patterns in a Cambrian shallow water platform (Iberian Chains, NE Spain) are related to sea-level changes driven by orbital forcing and by tectonic pulses. The interplay of both effects can be discriminated in the Iberian fault-controlled platform, in which the tectonic activity can be analysed by accurate and detailed biostratigraphic correlations based on trilobite zonation. The stratigraphic hierarchy of rhythmically interbedded limestones and shales, in two coeval but structurally separated geodynamic settings, yields cycle ratios of 1.44 :1. This ratio is supported by time thickness and spectral analysis, which is based on a graphic method of analysis: the Map of Grey Lines. The cycle ratio seems to be evidence for orbital forcing by obliquity and precession cycles predicted for early Paleozoic time. Carbonate/shale couplets, the smallest rhythmic units recognisable in the field, represent short-term, periodic fluctuations in supply of terrigenous sediments and carbonate productivity of uncertain origin, which could be associated with one of several harmonics of the former orbital cycles. The pulsating tectonic activity was approximated by using a quantitative analysis of tectonically induced subsidence (Shaw method). Recurrence frequencies of tectonic pulses were estimated and dated by biostratigraphy. As a result, tectonic disturbances in the Cambrian Iberian platform show an episodic periodicity comparable to that of orbital eccentricity cycles, which could mask their recognition.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/s005310000091

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Cell death during detachment of the lens rudiment from ectoderm in the chick embryoA preliminary report of some of the results presented in this paper were presented to the Fourth European Anatomical Congress. Basle ('77). (1979)

Garcia-Porrero, J. A. ; Colladoand, J. A. ; Ojeda, J. L.

New York, NY [u.a.] : Wiley-Blackwell

The @Anatomical Record 193 (1979), S. 791-803

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ISSN: 0003-276X

Keywords: Life and Medical Sciences ; Cell & Developmental Biology

Source: Wiley InterScience Backfile Collection 1832-2000

Topics: Medicine

Notes: The distribution and cytological characters of physiological cell death associated with formation of the lens vesicle in the chick embryo was studied by means of vital staining, light and electron microscopy.We have established a constant pattern of cell death which differs in some aspects from that reported for mammals and amphibians. The necrotic process is observed initially in the dorsal part of the lens cup (stage 15). The necrotic area progressively surrounds the lens pore as invagination proceeds (stage 16) and at stage 17 is located in the zone of fusion of the invaginated lens. After detachment of the lens (stages 18, 19 and 20) dead cells appear in the ectoderm, in the superficial epithelium of the lens vesicle and in the space between both structures.Ultrastructurally we observe isolated dead cells in different stages of degeneration and in phagocytosed cells. Phagocytosis is carried out by the neighboring healthy epithelial cells. Phagocytic activity was detected concomitant with the beginning of the necrotic process. Cell fragments were occasionally detected within the lens cavity.