V.H. Garduño-Monroy

A reexamination of human-induced environmental change within the Lake Pátzcuaro Basin, Michoacán, Mexico

This paper presents 2,000 years of settlement and land use within the Lake Pátzcuaro Basin, Mexico. Three findings challenge the conclusions of previous research. We show (i) that initial land degradation was caused by settlement, not by agriculture; (ii) that population density inversely correlates with erosion; and (iii) that land degradation was associated with European Conquest but not from the introduction of the Euro-agro suite. Instead, demographic collapse caused by European-introduced disease prevented human-generated landscapes from being maintained, resulting in widespread degradation. These findings support the use of indigenous landscape technology for modern conservation if past failings can be resolved.

Lacustrine record in a volcanic intra-arc setting: the evolution of the Late Neogene Cuitzeo basin system (central-western Mexico, Michoacán)

Abstract Late Miocene to Quaternary lacustrine and alluvial–lacustrine sequences were deposited in the Charo–Morelia sub-basin, to the south of the recent Cuitzeo lacustrine depocentre (central-western Mexico), where deposition was largely controlled by widespread faulting and block tilting. Moreover, pyroclastic and epiclastic deposits occur throughout the terrigenous and biogenic sequence, which indicates intense synchronous volcanic activity, directly linked to the faulting. The Charo alluvial–lacustrine sequences crop out extensively to the south of the present Cuitzeo Lake and their exposures record the development and spreading of Late Miocene and Pliocene alluvial–lacustrine zones. The resulting sequences are up to 40 m thick and record four major evolutionary stages related with specific tectonic and volcanic events, which caused changes in the basin morphometry and the palaeodrainage conditions. The first of these stages (Late Miocene) caused the generation of small, NE–SW-oriented shallow lacustrine and swampy zones, which resulted from the activity of strike-slip faults with the same orientation. Alluvial deposits and shallow lacustrine diatomaceous horizons were deposited during this stage. The second stage (Early Pliocene) gave rise to the formation of NE–SW-trending basins related to the extensional reactivation of the earlier NE–SW strike-slip faults. Within this second stage the Charo–Morelia lacustrine depocentre became a larger, deeper tropical lake. The planktonic and planktonic-facultative lacustrine diatom floral assemblages record the development during this stage of a major lake transgression, which could be caused both by wetter climate and tectonic watershed and drainage rearrangement. The third and fourth stages (Quaternary) were related to widespread block tilting processes, which were linked to the generation of E–W-oriented extensional faults and which resulted in the shifting and restriction of the larger, perennial, steadier lacustrine zones to the present Cuitzeo Lake. To the south of this lake the sedimentary record of this stage started with widespread fluvial sequences, which erosively overlaid the diatomitic deposits. The lacustrine zones developed during this alluvial-dominated stage were restricted to small depressions and consisted of small lakes and pond-related environments, which were fed by ephemeral fluvial currents. These minor water bodies were infilled and overlain by acidic pyroclastic fall deposits developed during a major volcanic episode which affected the Charo–Morelia sub-basin (fourth stage). The Cuitzeo and other ancient to recent lacustrine systems (i.e. Chapala Lake) evolved in the Trans-Mexican Volcanic Belt as a result of its tectono-volcanic evolution, which largely influenced the highly sensitive lacustrine systems. Therefore, the analysis of the development, sedimentary evolution and shifting of the lacustrine zones may help us to understand the structural evolution of the central Mexican igneous arc complex and the ongoing processes developed along the related major subduction zone which is oblique to the Middle American Trench in the Pacific margin.

Integration of InSAR and GIS in the Study of Surface Faults Caused by Subsidence-Creep-Fault Processes in Celaya, Guanajuato, Mexico

In Celaya city, Subsidence‐Creep‐Fault Processes (SCFP) began to become visible at the beginning of the 1980s with the sprouting of the crackings that gave rise to the surface faults “Oriente” and “Poniente”. At the present time, the city is being affected by five surface faults that display a preferential NNW‐SSE direction, parallel to the regional faulting system “Taxco‐San Miguel de Allende”. In order to study the SCFP in the city, the first step was to obtain a map of surface faults, by integrating in a GIS field survey and an urban city plan. The following step was to create a map of the current phreatic level decline in city with the information of deep wells and using the “kriging” method in order to obtain a continuous surface. Finally the interferograms maps resulted of an InSAR analysis of 9 SAR images covering the time interval between July 12 of 2003 and May 27 of 2006 were integrated to a GIS. All the maps generated, show how the surface faults divide the city from North to South, in two zone...