Sistema Regional de Información
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Certain physical, chemical and biological characteristics of Lake Tequesquitengo in the State of Morelos, are presented to enlighten on such a phenomenon as the mortality of the fish species, which occasionally occurs there. The electric conductivity, (2.46 mmhos/cm3) and the total solid residue of its wáter (2.8‰) allow to classify it as being oligohaline. The total cation and anion analyses indicate a high Mg/Ca relation as well as concentration of sodium, sulphates and strontium; the later in concentrations of 1.0 ppm. Values of dissolved O2 are eminently good in most localities sampled to a depth of 8 m (from 5.13 to 8.71 ml/l); from this depth downwards it tends to be anoxic... In order to continue, download the full paper in PDF.

The geochemical analisis by X-ray fluorescence of rocks and minerals dissolved in lithium teraborate is presented. XRF, when applied to mineral samples fused in the borate, thus limiting matrix effects, produces results within twice the standard deviation, quite satisfactory for geological exploration and mineral deposits evaluation. Algorithms intensity, concentration for SiO2, Al2O3, Fe2O3, CaO, K2O, TiO2, Cu, Pb, Zn, Ag, Mo, and Mn are computed. The analytical procedure is specified, including correction for volatil components and sample preparation. The technique is qualified as rapid, requiring analytical times in the order of seconds. The concentration covered are those normally accepted for rocks with metallic mineralizations up to 18%.  

The Playa San Bartolo is 20 km to the north of Babia Kino, Sonora and represents a good example of a playa or sebkha with its dunes sculptured my the dominant northwest winds, with its flat floor covered by mudcracked surface and bordered by the Sierra Seri and its piedmont. The Playa San Bartolo is considered to be of tectonic origin. The sedimentological and geomorphological studies allow to propose a hypothesis whereby a lacustrine and fluvial period was followed by a dry period, during the recent Quaternary.

The presence of Pseudotissotia (Pseudotissotia) galliennei (D'Orbigny). Coilopoceras colleti Hyatt, Coilopoceras requieni (D'Orbigny), Forresteria (Forresteria) alluaudi (Boule, Lemoine and Thevenin) and Texasia dentatocarinata (Römer) has been determined in samples collected from the Mexcala Formation at Llanos de Tehuitzingo and Pochutla, in the northeast part of the State of Guerrero. The age of the fossils is Turonian-Coniacian.

A new method for handling petrographic data is introduced. The method is based on "tree diagrams", commonly used in Probability Theory and Numerical Taxonomy. The method can be applied to a set of rock specimens, representative of a particular geological unit, for which relative mineral abundances have been determined. The particular case of the andesitic "Calixtlahuaca" volcanics, Mexico, is used as an example. Petrographic tree diagrams can be used as a support for the more time consuming modal analyses. However, it is "relative mineral abundances" that forms the basis for tree diagrams and hence must be considered separate from diagrams based on modal analyses, which deal with exact percentages of minerals. Tree diagrams are of great help for presenting every single mineral assemblage whilst highlighting the most important ones.

A small marine fauna of pelecypods, gastropods and brachiopods, is described, and its age as Kimmeridgian-Portlandian is established, on the basis of its similarity to the Tethyan european faunas of this age. The material comes from the San Ricardo Formation, and was collected in western Chiapas, about 20 km to the east of Cintalapa. This fauna was vaguely known only and was considered to be Neocomian. This is the first desicription of Upper Jurassic macro-invertebrates of Chiapas.

The present paper describes a faunal association, consisting of the crinoids Cylindrocausliscus fiski? Moore and Jeffords and Lamprosterigma mirificum Moore and Jeffords with the pelecypods Aviculopecten and Palaeolima, collected in indurated slaty, black shales of Pennsylvanian age. The fossils proceed from the Santa Rosa Inferior Formation of southeastern Chiapas State.

La Comisión Americana de Nomenclatura Estratigráfica está integrada por representantes de instituciones y sociedades geológicas del Canadá, Estados Unidos de América y México. Esta Comisión en su 32a. Reunión Anual, celebrada en la Ciudad de Seattle, Washington, el 8 de noviembre de 1977, acordó avocarse a una extensa revisión del Código, que incorpore las numerosas enmiendas, adiciones y modificaciones que ha sufrido el actual Código de Nomenclatura Estratigráfica (versión publicada en 1970) y lo armonice con la International Stratigraphic Guide (H. D. Hedberg, Ed., 1975), publicación que ha tenido gran impacto en la práctica estratigráfica mundial. Esta revisión constituye una tarea muy importante y de enorme envergadura. La Comisión designó un Comité ad hoc de cinco miembros, quienes trabajarán y coordinarán la labor de Sub-comités especializados en las distintas clases de unidades estratigráficasy se asesorarán por expertos en cuestiones particulares tales como unidades glaciológicas, magneto-estratigráficas, submarinas, de rocas ígneas y metamórficas, etc. In order to continue, download the full paper in PDF.

A system of Upper Cretaceous planktonic foraminiferal zonation is presented. The Upper Cretaceous is subdivided into 14 foraminiferal zones. When possible, the elaborated zonal scheme is calibrated with the ammonites zonation. The following boundaries are established based on the distribution of planktonic foraminífera: The Albian/Cenomanian boumdary is placed at the base of Zone CS-1; corresponding to the first stratigraphic appearance of Thalmanninella evoluta (Sigal). The Cenomanian/Truronian boundary, is defined at the Base of Zone CS-4, corresponding to the first evolutiouary appearance of double-keeled Hedbergelloidea. The Santonian/Campanian bonndary is defined at the base of Zone CS-8, corresponding to the first evolutionary appearance of single keeled globotruncanids. The Campanian/Maestrichtian boundary is placed at the top of Zone CS-1 O, corresponding to the last stratigraphic occurrence of Globotruncanita calcarata. The Maestrichtian/Danian boundary is established at the top of the Zone CS-14, and corresponds to the first appearance of Globigerina eugubina.

Important advances have taken place in different fields of investigation. It is worthwhile revising once more the interesting subject of tridimensional projection, now under new technological basis. The main purpose is to support those areas as in photogeology where the use of volumetric images are irreplaceable. The elementary principies of stereoscopy are briefly outlined together with the description of an adjustable mirrordevice capable of: a) fitted into a photographic camera, providing on the same print or slide a stereoscopic pair; and b) coupled to a conventional projector, superimpose the considered stereoscopic pair on a screen.