Tectonics and paleogeography along the Amazon river

The main structural and geomorphological features along the Amazon River are closely associated with Mesozoic and Cenozoic tectonic events. The Mesozoic tectonic setting is characterised by the Amazonas and Marajó Basins, two distinct extensional segments. The Amazonas Basin is formed by NNE-SSW normal faults, which control the emplacement of dolerite dykes and deposition of the sedimentary pile. In the more intense tectonic phase (mid-Late Cretaceous), the depocentres were filled with fluvial sequences associated with axial drainage systems, which diverge from the Lower Tapajós Arch. During the next subsidence phase, probably in the Early Tertiary, and under low rate extension, much of the drainage systems reversed, directing the paleo-Amazon River to flow eastwards. The Marajó Basin encompasses NW-SE normal faults and NE-SW strike-slip faults, with the latter running almost parallel to the extensional axes. The normal faults controlled the deposition of thick rift and post-rift sequences and the emplacement of dolerite dykes. During the evolution of the basin, the shoulder (Gurupá Arch) became distinct, having been modelled by drainage systems strongly controlled by the trend of the strike-slip faults. The Arari Lineament, which marks the northwest boundary of the Marajó Basin, has been working as a linkage corridor between the paleo and modern Amazon River with the Atlantic Ocean. The neotectonic evolution since the Miocene comprises two sets of structural and geomorphological features. The older set (Miocene-Pliocene) encompasses two NE-trending transpressive domains and one NW-trending transtensive domain, which are linked to E-W and NE-SW right-lateral strike-slip systems. The transpressive domains display aligned hills controlled by reverse faults and folds, and are separated by large plains associated with pull-apart basins along clockwise strike-slip systems (e.g. Tupinambarana Lineament). Many changes were introduced in the landscape by the transpressive and transtensive structures, such as the blockage of major rivers, which evolved to river-lakes, transgression of the sea over a large area in the Marajó region, and uplift of long and narrow blocks that are oblique to the trend of the main channel. The younger set (Pliocene-Holocene) refers to two triple-arm systems of rift/rift/strike-slip and strike-slip/strike-slip/rift types, and two large transtensive segments, which have controlled the orientation of the modern drainage patterns. © 2001 Elsevier Science Ltd. All rights reserved.

Morphology and histoenzymology of eosinophilic granulocytes in the circulating blood of the turtle (Chrysemys dorbignih)

The studies on the characterization of eosinophils and neutrophils/ heterophils of turtles are contradictory. Some authors have pointed out the existence of two distinct cell types: eosinophils and heterophils. Other authors have proposed that eosinophils and heterophils may be the same cells in different stages of maturation. These interpretations are based only on a morphological analysis. In the blood of the turtle (Chrysemys dorbignih), a South American freshwater species, there are two types of granulocytes with eosinophilic staining pattern: the first with round cytoplasmic granules and the second with ellipsoidal cytoplasmic granules. In the present study by using histoenzymological methods for the analyses of enzymological cellular content, we found that the cells with round cytoplasmic granules were positive for nonspecific esterase and the cells with ellipsoidal granules were positives for acid phosphatase, alkaline phosphatase, nonspecific esterase and peroxidase. The results show that these cells are distinct cells and that the cells with ellipsoidal cytoplasmic granules have the same histoenzymological characteristics as the neutrophils/heterophils of mammalians and other vertebrates.

The thrombocyte aggregation process in the turtle Phrynopys hilarii (Chelonia). An ultrastructural study

This study investigates the thrombocyte aggregation process in the South American fresh water turtle (Phrynopys hilarii) using electron microscopy. Blood was taken from surgically exposed lateral neck vessels often turtles Phrynopys hilarii during the spring and summer seasons, when the mean temperature is 37°C. Blood samples were fixed with Karnovsky solution for processing by transmission electron microscopy. The turtle thrombocytes were spindle-shaped with lobulated nuclei. Prominent vesicles and canaliculi were found throughout the cytoplasm. The cytoplasm organelles showed an agranular endoplasmatic reticulum, Golgi complex near the centrioles and scattered free ribosomes. These cells are similar to bird thrombocytes but distinct from fish and frog thrombocytes. Blood clotting time was 5 min ± 30 sec measured by the Lee and White method. Structural alterations resulting from the aggregation process occurred after activation. Thrombocytes developed numerous filopodial projections, an increased number of vacuoles and changed from spindle to spherical shape. P. hilarii thrombocytes have different morphologic characteristics compared to other non-mammalian vertebrate cells. These cells can participate in the aggregation process, as observed in birds.