CIG   05423
CENTRO DE INVESTIGACIONES GEOLOGICAS
Unidad Ejecutora - UE
artículos
Título:
Introduction to “Comparison between intracratonic and active margin basins: examples from the Late Palaeozoic of Western Gondwana”.
Autor/es:
SPALLETTI, L.; LIMARINO, C.O.
Revista:
JOURNAL OF SOUTH AMERICAN EARTH SCIENCES
Editorial:
Elsevier
Referencias:
Lugar: Amsterdam; Año: 2006 vol. 22 p. 131 - 133
ISSN:
0895-9811
Resumen:
Western Gondwana basins are keys to understanding the evolution of the Gondwana supercontinent during the Late Paleozoic. The western margin of Gondwana underwent a complex tectonic history with continuous paleogeographic changes, including the formation of orogenic belts and basins. This has been discussed by López Gamundí et al. (1994) and Veevers and Powell (1994) in “Permian-Triassic Pangea Basins and Fold belts along the Panthalassan Margin of Gondwanaland”. Recent information has led to a better interpretation of the relationships between tectonism, magmatism, subsidence and basin type. This new evidence suggests a more complicated pattern for the evolution of western Gondwana and poses several questions about the global significance of major tectonic-magmatic events (Ramos et al., 2001). For instance, the existence of Early Carboniferous orogenic activity along the western basins of southern South America has been frequently overlooked. Nevertheless, over the last years, Early Carboniferous orogenic activity has been reported from the Andean region of Argentina, Bolivia and probably Perú (Sempere, 1996; López Gamundí and Breitkreuz, 1997). This fact clearly demonstrates that orogeny did not finish in the Late Devonian, as it is commonly assumed, but that it extended at least over the Early Carboniferous. The geodynamic significance of these movements has not been investigated yet. Thick Early Carboniferous successions occurring in western Gondwana basins are not included in the previous syntheses. These rocks contain a complete stratigraphic record, particularly in the Andean region, where thousand-meter thick sequences reveal important biostratigraphic information (for a review see Archangelsky et al., 1996). These deposits provice critical information for paleogeographic and paleoenvironmental reconstructions of Early Carboniferous times, the least known time interval in Gondwana. Since the Early Carboniferous is a time of free marine communication between paleo-Thethys and Panthalassa shelves (Davydov et al., 2004), western Gondwana marine faunas are important not only in regional scale correlation models but also for the evaluation of latitudinal versus longitudinal controls in the Mississippian marine faunas distribution (Ross and Ross, 1988). Western Gondwana basins provide significant information about the paleoclimatic evolution of Gondwana in space and time. In particular, the well preserved glacial deposits in Late Paleozoic basins provide data for the reconstruction of the Gondwanian glaciation. Early Carboniferous and Late Devonian glacial deposits as described in the Andean basins by Díaz Martínez et al. (1993) and Isaacson et al (1999) have rarely been found in the rest of Gondwana. The role of Early Carboniferous-Late Devonian glacial deposits should be carefully considered in the future since Western Gondwana might have occupied a high latitudinal position during part of the Early Carboniferous and the Late Devonian. Glacial deposits of the western region could represent a stratigraphic record for the glacial conditions deduced from isotopic composition of brachiopod shells from the Russian platform (Mii et al., 2001). The paleoclimatic information provided by the western Gondwana basins is not restricted to glacial conditions. For example, the existence of semiarid and arid climates during the Middle (and Late ?) Permian seems to have been a common feature of many basins and they seem to have been connected with global-scale increase in temperatures for both the southern and northern hemispheres (Oyarzun et al., 1999; Veizer et al., 2000).    Late Carboniferous to Late Triassic magmatic activity along the western margin of Gondwana is one of the most important magmatic events registered throughout Gondwana. It produced several thousand meters of volcanic rocks and volcaniclastic sequences in the Andean region of Argentina, Chile, Bolivia and Peru. The geotectonic significance and global-scale effect of the magmatism remains to be evaluated. Due to extensive glacial conditions in Gondwana, transgressive-regressive cycles are generally considered to be glacio-eustatic and, consequently, global in distribution (Davydov et al., 2004). Therefore, sequence stratigraphic analyses in South American basins permit more accurate local and global correlation models. There is a deficit in regional scale studies which compare the western Gondwana basins of South America with those of the rest of Gondwana. This special issue presents regional-scale studies and illustrates some of the more prominent features of the Late Paleozoic sequences of southern South America. This issue also demonstrates the differences between basins located along the western active margin (Andean region) and those placed in more stable intracratonic areas (eastern South American basins). In this sense, the division between western active basins and eastern intracratonic ones clearly emphasizes their different tectonic, magmatic and sedimentary evolution. While intracratonic basins are characterizes by  limited tectonic activity, low subsidence rates and nearly absent magmatism during the Late Paleozoic, western active basins show several episodes of tectonic activity, together with widespread magmatism and relatively high subsidence rates.     Our contribution “Paleogeography of the Upper Paleozoic Basins of Southern South America: An Overview” is a summary of the paleogeographic evolution of southern South America during the Late Palaeozoic. Many of the paleogeographic and stratigraphic models proposed in this paper will be improved, corrected, and modified in the future; yet, this paper serves as a departure point for a regional interpretation of the western basins of South America. The problem of the transition from glacial to postglacial conditions is analysed in two papers, one which shows the transition in cratonic basins, and the other in a foreland basin. “Deglaciation sequences in the Permo-Carboniferous Itararé Group, Paraná Basin, southern Brazil” by F. F. Vesely and M. L. Assine identifies and regionally correlates cratonic deglaciation sequences. Moreover, the paper shows an interesting example where deglaciation sequences, with ice-retreat depositional tracts, do not necessarily include unconformity-bounded units. The presence of progradational coarsening-upward facies forming the top of the sequences differs from traditionally accepted models. Several Late Paleozoic glacial events are described by D. Starck and C. del Papa in “The Northwestern Argentina Tarija Basin – Stratigraphy, Depositional Systems and Controlling Factors in a Glaciated Basin”. This contribution reports recurrent advances and retreats of ice bodies in a foreland basin during the Late Carboniferous and the Early Permian. The origin of deep valley incision and changes in accommodation in the foreland area are discussed in relation to the glacial dynamics. Tectonism, sea level changes and climatic controls on the evolution of Late Paleozoic Basins are presented in two contrasting areas. Tthe effect of tectonic movements on a classical Late Palaeozoic cratonic basin (Paraná Basin) is discussed in “Hierarchy of Tectonic Control on Stratigraphic Signatures: Base-Level Changes During the Early Permian in The Paraná Basin, Southernmost Brazil” by M. Holz. Although sea level changes played a major role in the sequence stratigraphic architecture of the Paraná Basin, as is common in cratonic areas, the important stratigraphic effects of tectonic movements are discussed in this paper. The author proposes that tectonic activity influenced the nature and thickness of the depositional systems, the changes in the subsidence regime, the development of non uniform sequence boundaries and the shoreline displacement.  In the active basins of western South America the tectonic regime also played a leading role in sequence definition. An example is shown in the paper by C. Limarino, A. Tripaldi, S. Marenssi and L. Fauqué “Tectonic, Sea-Level and Climatic Controls on Late Paleozoic Sedimentation in the Western Basins of Argentina”. Two megasequences resulted from very different tectonic scenarios, and four marine transgressions subdivided each megasequence. Climatic conditions favored the formation of specific lithological assemblages, i.e. glacial and glacial-related diamictites, coal beds and aeolian sediments.    The effects of Late Paleozoic volcanism along the western proto-Pacific margin of Gondwana and the adjacent cratonic area is discussed in “Permian Plate-Margin Volcanism and Tuffs in Adjacent Basins of West Gondwana: Age Constraints and Common Characteristics” by O. López Gamundí. The paper focuses on the presence of tuffs in the Paraná Basin which serve as important correlation levels with the Permian record of the San Rafael, Sauce Grande, Paraná and Karroo basins. The paper “Applying Sandstone Petrofacies to Unravel the Upper Carboniferous Evolution of the Paganzo Basin, Northwest Argentina” by L. Net and C. Limarino demonstrates the use of modal analysis for provenance characterization in a foreland basin. Using this technique, seven petrofacies were grouped in three petrosomes. These petrosomes characterize three major morphostructural units: crystalline basement, recycled orogen and volcanic arc.