A viagem da U. S. Astronomical Expedition (1849-1852): observar estrelas e relatar a América do Sul

O trabalho analisa a expedição astronômica realizada pela Marinha norteamericana ao Chile, durante os anos de 1849 a 1852, comandada pelo oficial e também astrônomo James Melville Gilliss. O objetivo foi compreender os interesses científicos, políticos, geopolíticos e comerciais que motivaram a viagem, bem como as imagens e representações sobre a América do Sul, especialmente do Panamá, Peru, Chile e Argentina, construídas e divulgadas através do relatório oficial da expedição, com o título \"The U.S. Naval Astronomical Expedition to the Southern Hemisphere during the years (1849- 1852). Esta pesquisa também procura examinar os diferentes dispositivos discursivos utilizados pelos oficiais que escreveram o relatório, James Gilliss e Archibald MacRae, discutindo dissensões e diferentes visões sobre o modo de veicular dados científicos, e também modos distintos de relatar a América do Sul.

Astronomical time scale for Paleocene and early Eocene sediments

The astronomical-tuned time scale is rapidly extended into the Paleogene but, due to the existence of an Eocene gap, different tuning options had to be presented for the Paleocene. These options differ both in number and tuning of ~405-kyr eccentricity related cycles and are only partially consistent with recalculated 40Ar/39Ar constraints for the Cretaceous/Paleogene (K/Pg) and Paleocene/Eocene (P/E) boundaries. In this paper, we evaluate the cyclostratigraphic interpretation of records from ODP Leg 198 and 208 sites, and the Zumaia section to solve the problem of the different tuning options. We found that the interval between the K/Pg boundary and the early Late Paleocene biotic event (ELPE) comprises 17 instead of 16 * ~405-kyr eccentricity related cycles as previously proposed, while the entire Paleocene contains 25 * ~405-kyr cycles. Starting from 40Ar/39Ar age constraints for the K/Pg boundary, a new tuning to 405-kyr eccentricity is presented for the Paleocene and earliest Eocene, which results in ages of ~66.0 and ~ 56.0 Ma for the K/Pg and P/E boundaries, respectively. This tuning introduces considerable differences in age for a number of nannofossil events at ODP Sites 1209 and 1262 in the interval between 61 and 63 Ma, but eliminates large and abrupt changes in the seafloor spreading rate. The tuning seems further consistent with recalculated 40Ar/39Ar ages for ash layer -17 of early Eocene age. However, despite this apparent consistency with existing radio-isotopic constraints, an alternative 405-kyr younger or, less likely, older tuning cannot be excluded at this stage.