Showing papers by "Maximiliano Bezada published in 2007"

Receiver function study of the crustal structure of the southeastern Caribbean plate boundary and Venezuela

Abstract: [1] We have investigated crustal thickness and composition across the southeastern Caribbean plate boundary with the receiver function technique. We used teleseismic data recorded by a temporary broadband array deployed under the BOLIVAR project and the permanent national seismic network of Venezuela. We used the primary P-to-S conversion and crustal reverberations to estimate crustal thickness and average crustal VP/VS ratio over the region. We observe large variations in crustal thickness and Poisson's ratio. Estimated Moho depth ranges from ∼16 km beneath the southeastern Caribbean Sea to ∼52 km beneath northeastern Venezuela and the Venezuelan Andes. There is a good correlation between crustal structure and tectonic terranes. Data from the Precambrian Guayana Shield suggest that the underlying crustal structure is relatively uniform with a moderate thickness (∼37 km) and an intermediate composition. A thick crust is found below the foreland basins. The two mountain systems in northern Venezuela, the Serrania del Interior and the Serrania del Falcon, have a thin crust with arc composition and are likely dynamically supported by elastic rebound or underthrusting of the oceanic plateau that characterizes the southern Caribbean. On the other hand, the Venezuelan Andes and Perija Range on the western side of the country are probably isostatically balanced by thick crustal roots.

Reply: Late Quaternary deglacial history of the Mérida Andes, Venezuela: response to comment

Abstract: We welcome the opportunity to respond to Mahaney et al.’s critique of our article on the deglacial history of the Venezuelan Andes (Stansell et al., 2005). The source of our disagreement appears to stem primarily from differences in research strategies and methodology. Our work in the Venezuelan Andes employs lake sediment archives that record continuous sedimentary sequences and can be dated using accelerator mass spectrometry (AMS) radiocarbon dating of identifiable terrestrial macrofossils. Mahaney et al. focus on temporally discontinuous deposits (moraines and glacial– fluvial sediments) and radiocarbon dates on refractory organic matter that are most likely to yield anomalously old results. The comment of Mahaney et al. is fraught with serious misunderstandings of the data we presented, and is thus misleading to readers who have not examined the original data. In our reply, we specifically address their claims regarding: (1) the local timing of the Last Glacial Maximum; (2) the chronology of the late Pleistocene–Holocene transition; and (3) Holocene environmental variability. Lakes in previously glaciated catchments are excellent recorders of glacial variability because these systems commonly preserve uninterrupted glacio-lacustrine sequences, and contain in situ organic matter that can be isolated for C dating. Lake sediment cores can also be analysed at high stratigraphic resolution for an array of sedimentological parameters, which in turn can be used to infer environmental changes over a range of timescales. Lithologic transitions in peat bogs that either formed within or directly adjacent to moraines can also date significant movements of a glacier margin. Combined, these types of records are advantageous for dating glacial activity because they are less susceptible to surface processes such as erosion and weathering, and provide broadened perspectives on the attendant climatic conditions prior to, during, and after a given glacial advance.