Avifauna estuarina de El Chorro y Majahuas, Jalisco, durante la época no reproductiva

Con el fin de conocer la abundancia relativa y variación estacional de las aves estuarinas, su uso de los diferentes hábitats y el efecto de las marcas en los estuarios El Chorro y Majahuas, Jalisco, México. Realicé censos quincenales de septiembre de 1995 a abril de 1996, En El Chorro hubo 49 especies de aves migratorias (15,905 individuos) y 17 especies residentes (10,453 individuos). En Majahuas hubo 46 especies migratorias (22,007 individuos), y 25 especies residentes (14,837 individuos). En El Chorro hubo más especies en noviembre, enero y marzo cuando la barra se encontraba abierta, mientras que en Majahuas los mayores valores se presentaron en febrero y marzo. En El Chorro hubo más individuos en noviembre enero y abril, y en Majahuas en marzo y abril. La diversidad de hábitats usados por las aves migratorias fue diferentes en los dos estuarios (P<0.05). Las aves migratorias usaron una mayor diversidad de hábitats en El Chorro (H'=1.060) que en Majahuas (H’=0.8998). Por lo contrario, las aves residentes usaron una mayor diversidad de hábitats en Majahuas (H'=0.680) que en El Chorro (H´=0.599). Durante barra abierta, los buscadores aéreos, buscadores flotadores y zancuadas, utilizaron los mismos hábitats durante las dos mareas. Los buscadores aéreos prefirieron las planicies arenosas de Majahuas para descanso, y el mar, cerca de la boca del estuario para alimentarse. Los buscadores flotadores se alimentaron y descansaron por igual en el cuerpo de agua, y usaron las planicies arenosas y la boca del estuario para descansar. Las zancudas usaron los manglares para descansar y el cuerpo de agua para alimentarse. Los sondeadores somero y sondeadores profundos fueron los más influenciados por las mareas. Durante marea bajando aún muchos de los hábitats estaban cubiertos por el agua, y estas aves se alimentaron en las orillas del cuerpo de agua; en marea subiendo las áreas lodosas estaban descubiertas, y eran utilizadas para alimentarse. Estas aves descansaron generalmente en las planicies arenosas. La escasez de planicies lodosas en Majahuas, obligó a los individuos a alimentarse en la boca del estuario, la playa y la planicie arenosa. Los buscadores aéreos y buscadores flotadores usaron una mayor diversidad de hábitats en El Chorro que en Majahuas. Sin embargo, los sondeadores someros y zancudas usaron una mayor diversidad de hábitats en Majahuas que el Chorro, mientras que los sondeadores profundos usaron hábitats similares en ambos esteros.

Progressive shift of Late Mesozoic compressive regime until the actual transtension characterizes the geologic evolution of Northwestern Mexico and Southwestern United States. Continental extension and ocean spreading derived from extension overprinted by transtension during Late Cenozoic suggests Gulf of California and escarpment development. However, the understandings of northern part of the escarpment and Laguna Salada basin are not clear. This thesis proposes the geologic evolution of the northern part of the escarpment in Sierra Juárez, Baja California, and it also permits to limit the proposed models for Laguna Salada basin development. Main conclusions from this study permit to locate the area on the upper plate of low-angle fault with transport to the West. They also suggest that faulting on the edge of the sierra is discontinuous along the escarpment, and that the basin is not as deep as believed. In the northern part of the escarpment, prebatholithic rocks are equivalent to Julian Schist, metamorphosed in high amphibolite facies, and intruded by four main Cretaceous plutons. Cenozoic rocks resting on granitoids were divided into Lower Clastic Sequence, contains an arkosic horizon and lithic sandstones and conglomerates, equivalent with pre- Miocene Table Mountain Grave/s. Andesitic Basaltic Sequence with basaltic andesite flows and dikes similar to Miocene Jacumba Volcanics, with scarce andesitic pyroclastic deposits. The Upper Clastic Sequence includes a great variety of unconsolidated continental deposits, suggesting the basin evolution, from the volcanic activity to the basin filling. «L Pelitic rocks domain the metamorphic section, and suggest zoning, distributed in four sequences: two with marbles, one with amphibolites, and other with quarzites, from bottom to top. The garnet-biotite-plagioclase paragenesis showed 640°C and 3.7kb, from an unstable system subjected to retrograde metamorphism. Mean foliation strikes 201°-67°, defined by subparallel minerals and composicional/segregation layering, containing stretching Iineation 65° toward 298°. This section develops an isoclinal fold verging east, with axial plane cleavage 194°-63° (So = S1) and mesofolds indicate shear toward 305°. This shortening event was probably related to subduction, so the metamorphic section shows ductile sinkinematic deformation, probably closely related with the metamorphism and accretion stages. Granitoid rocks show nine varieties, distributed in two compositional belts, granodioritic to the West and tonalitic to the East. Aligned hornblende, biotite, subparallel dioritic enclaves and schlieren layering from melanocratic tonalites develop magmatic foliation. Deformed sphene-bearing spots in dike, and cleavage represent solid-state foliation. Magmatic activity produced two magmatic cycles with third derivative granitoids, equivalent to La Posta and pre La Posta plutons. The ascent and emplacement of these two magmatic cycles were around 10- 12km, under mechanisms dominated by diapirism, ballooning and fracture exploitation. A discordant arkosic horizon rests on granitoids and underlies sandstones, diamectite and conglomerate interbedings from a fluvial system with seasonal overflows. Pumice horizons cover the arkose, and are included in the upper part of the fluvial section. Pumice timing and provenance are hard to decipher, but could correlate with pre-Miocene andesitic-dacitic tuff. Basaltic andesite is in dikes, flows and breccias, unconformable to underlying sediments, and granitoids. Dikes were the vents for a gentle volcanic activity. The texture and the olivine-augite glomerocrysts suggest a deep source for these magmas, which got granitoid xenoliths (crustal contamination) in its quick ascent and they were extruded in a low to moderate relief. Breccias were developed during the flow. Deformation in these two sequences is consistent: bedding dips E and is fault-controlled on hanging walls from normal west-dipping faults; faulted flow patterns depict dike structure, suggesting the same deformational environment. Deformation in UpperClastic Sequence is moderate, and it suggests normal-dextral movements, with old-fault planes reactivation, which seem to depict the basin growth and filling evolution. This work proposes nine deformation events to depict the evolution of the northern part of the escarpment in Sierra Juarez, three ductile and six brittle. Ductile deformation involves Sevier Orogeny compression, metamorphism and intrusion during Late Mesozoic. The first two brittle events should be closely related to postorogenic compression-waning, but the low angle faulting from the third one is in between postorogenic and Basin and Range deformations. The fourth and fifth events are related to Basin and Range deformation, with the Laguna Salada basin and the escarpment in Sierra Juárez being developed and growing 9The last event in the area reflects the San Andreas deformation. The structural interpretation for the northern part of the escarpment in Sierra Juárez and Laguna Salada shows the volcanic and sedimentary layers clipping to the East. This attitude should be related by west-dipping faulting, and does not reflect laterally continuous faults along the edge of the escarpment, but discrete faulting dipping east and west. Incorporating these results to the regional geology, and having in mind especially the low-angle faulting showed at Yuha Desert and Cañada David, it seems likely that Laguna Salada area, and the escarpment in Sierra Juárez are located on the upper plate of a detachment with transport to the West. This anastomosed detachment complex system-should root Sierra Juarez. The escarpment depicts the edge of a half-graben, where the west-dipping faulting is synthetic to the detachment, and the east-dipping faulting is antithetic to the main movement, both reactivated by normal-dextral faulting. The timing is probably related to the Basin and Range evolution, characterized by brittle extension toward 275° (Event G) before basic vulcanism, which probably shifted toward 260° (Event H) after flows, and finally was replaced by transtention toward 280° (Event I) similar to San Andreas. Accordingly, faulting in the northern part of the escarpment in Sierra Juárez should relate less than 100m of vertical displacement on faults dipping West, and the bigger steps (< 600m(?)) on faults dipping East. Then the escarpment is not controlled by a master east- dipping fault system, and the Laguna Salada basin is not as deep as was believed.