Angiogenesis - the growth of new blood vessels from a pre-existing vasculature - is key in both physiological processes and on several pathological scenarios such as cancer progression or diabetic retinopathy. For the new vascular networks to be functional, it is required that the growing sprouts merge either with an existing functional mature vessel or with another growing sprout. This process is called anastomosis. We present a systematic 2D and 3D computational study of vessel growth in a tissue to address the capability of angiogenic factor gradients to drive anastomosis formation. We consider that these growth factors are produced only by tissue cells in hypoxia, i.e. until nearby vessels merge and become capable of carrying blood and irrigating their vicinity. We demonstrate that this increased production of angiogenic factors by hypoxic cells is able to promote vessel anastomoses events in both 2D and 3D. The simulations also verify that the morphology of these networks has an increased resilience toward variations in the endothelial cell’s proliferation and chemotactic response. The distribution of tissue cells and the concentration of the growth factors they produce are the major factors in determining the final morphology of the network.
Elemental concentrations in Phanerozoic sea water are known to fluctuate both in time and space. With regard to carbonates precipitated from marine fluids, elemental concentrations in the carbonate crystal lattice are affected by a complex array of equilibrium and non-equilibrium as well as postdepositional alteration processes. To assess the potential of carbonate elemental chemostratigraphy, seven Upper Jurassic sections were investigated along a proximal to distal transect across the south-east Iberian palaeomargin. The aim was to explore stratigraphic and spatial variations in calcium, strontium, magnesium, iron and manganese elemental abundances. The epicontinental geochemical record is influenced by the combination of continental runoff and a significant diagenetic overprint. In contrast, the epioceanic geochemical record agrees with reconstructed open marine sea water values, reflecting a moderate degree of syn-depositional to early marine pore water diagenesis. Establishing a fair degree of preservation of matrix micrite, a thorough statistical approach was applied and elemental associations tested for their environmental significance. Principal component and hierarchical cluster analyses revealed a persistent relation between carbonate magnesium, iron and strontium abundances. Processes related to early diagenetic nodulation in Ammonitico Rosso facies most probably account for the incorporation of these elements in the calcium carbonate lattice. The clear decoupling of carbonate manganese abundance with respect to the remaining elements is documented and related to high sea floor spreading rates and hydrothermal activity during the Late Jurassic. The investigation of potential time-fluctuation of geochemical patterns was approached through variogram computation. The observed temporal behaviour is most likely to be forced by relative sea-level dynamics, reflecting Late Jurassic palaeoceanographic conditions and potential planetary interactions. The data obtained in this study highlight the utility of elemental data from carbonate matrix micrites as geochemical proxies for studying the influence of remote trigger factors.
Terra Nova, 24, 437–445, 2012
Abstract
The notion that diagenetic imprint on ancient carbonates significantly compromises palaeoenvironmental interpretations is revealed as an oversimplification. The enigmatic case at the core of this research is an extended, homogeneous, macrofossil‐poor deposit showing distinctive dark brown colour and very fine grain size (Aumedrá Fm., Majorca Island). This markedly contrasts with standard ammonitico rosso (AR) facies known from Jurassic epioceanic swells. Geochemical analysis of matrix micrite, carbonate cements and belemnite rostra are used to interpret the Aumedrá carbonates. Stable (Carbon and Oxygen) isotopes and elemental abundance are compared with data from under‐ and overlying deposits, and coeval sections. Conspicuously higher than expected C and O isotope signature, together with strontium enrichment and a typically low iron and manganese concentrations favour a distant, shallower, probably aragonitic sedimentary supply. Modern and ancient examples of carbonate deposition are integrated with possible hydrodynamic conditions justifying transport over the studied area. A potential NE source is envisaged
Terra Nova, 00, 1–9, 2012
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