[pt] Este trabalho apresenta minuciosa pesquisa sobre atributos geomorfológicos, de geodiversidade e da geoconservação do Astroblema da Serra da Cangalha/TO, uma cratera de impacto a hipervelocidade em avançado estado de erosão. A delimitação da área de estudo se deu com base na configuração geomorfológica e geológica local, abrangendo a área interna da cratera e as principais bacias de drenagem que dela nascem. O primeiro objetivo do trabalho foi analisar a transformação desta paisagem para o estágio em que se observa atualmente e verificar em que medida um evento extraordinário tal qual um impacto meteorítico a hipervelocidade condiciona a forma do relevo e a rede de drenagem local mesmo ainda milhões de anos depois. Discute-se como a exumação de camadas estratigráficas ocorrida durante o impacto direcionou o modelamento da estrutura erodida ao longo do tempo geológico e apresentam-se as principais bacias hidrográficas da área de estudo, além de uma análise fenomenológica da experiência de vivenciar o encontro in loco com este astroblema de proporções quilométricas. Dada a raridade e demais valores de geodiversidade deste tipo de feição, este trabalho tem como segundo objetivo investigar as ações pretéritas e presentes no sentido da preservação ambiental deste patrimônio geomorfológico-geológico e astronômico em confluência com a possibilidade de um desenvolvimento sustentável da região. Os métodos utilizados constaram de uma visita de campo, análises SIG e descrições fenomenológicas. É apresentada, por fim, a partir das experiências do Ries UNESCO Global Geopark (um geoparque alemão criado a partir do maior astroblema da Europa, a Nördlinger Ries Krater) e do Parque Estadual do Desengano/RJ (primeira Unidade de Conservação da América do Sul a receber o selo Dark Sky Park da International Dark Sky Association) - uma proposta de um Geoastroparque para a região do Astroblema da Serra da Cangalha, de acordo com as premissas de sustentabilidade e geoturismo da rede mundial UNESCO Global Geopark e em prol de uma preservação e uso astroturístico de sua baixa poluição luminosa, com a possiblidade de atividades diurnas (geologia, geomorfologia, meteorítica) e noturnas (observação do céu) observando sempre os limites para um turismo sustentável com uma preocupação continuada de respeito ao meio ambiente e à população local. / [en] This paper presents a thorough research on geomorphological attributes, geodiversity and geoconservation of the Serra da Cangalha/TO Astroblem, a hypervelocity impact crater in an advanced state of erosion. The delimitation of the study area was based on the local geomorphological and geological configuration, covering the inner area of the crater and the main drainage basins that originate from it. The first objective of the work was to analyze the transformation of this landscape to the stage where it is observed today and to verify to what extent an extraordinary event such as a meteorite impact at hypervelocity conditions the shape of the relief and the local drainage network even millions of years later. We discuss how the exhumation of stratigraphic layers that occurred during the impact directed the modeling of the eroded structure throughout geological time, and we present the main watersheds of the study area, in addition to a phenomenological analysis of the experience of living the encounter in loco with this astroblem of kilometer proportions. Given the rarity and other geodiversity values of this type of feature, the second objective of this work is to investigate the past and present actions towards the environmental preservation of this geomorphological-geological and astronomical heritage in confluence with the possibility of a sustainable development of the region. The methods used consisted of a field visit, GIS analysis and phenomenological descriptions. Finally, based on the experiences of the Ries UNESCO Global Geopark (a German geopark created from the largest astroblem in Europe, the Nördlinger Ries Krater) and the Desengano State Park/RJ (the first South American Conservation Unit to receive the label Dark Sky Park from the International Dark Sky Association) a proposal for an Astrogeopark for the region of the Serra da Cangalha Astroblem is presented, in accordance with the premises of sustainability and geotourism of the world network UNESCO Global Geopark and in favor of a preservation and astro-tourism use of its low light pollution, with the possibility of daytime activities (geology, geomorphology, meteoritics) and nighttime activities (sky observation) always observing the limits for a sustainable tourism with a continued concern for the respect of the environment and the local population.

Impaktite des Chicxulubkraters wurden petrographisch (Polarisationsmikroskopie, REM, KL) und chemisch (RFA, TRFA, PGE, EMS) untersucht, um das Verhalten von Ejekta während des atmosphärischen Transports zu erforschen. Die proximalen Impaktite der UNAM-7 Bohrung bestehen aus einer suevitischen Brekzie (222.2 bis 384.4 m) und einer basalen, polymikten Brekzie mit geringem Silikatschmelzanteil. Letztere beinhaltet Evaporit-Megablöcke und Karbonatschmelzpartikel; Zersetzung von Kalzit und Anhydrit ist durch Entgasungsbläschen indiziert. An der distalen Kreide-Paläogen Grenze von El Guayal (520 km SW vom Kraterzentrum) beinhaltet eine 10 m mächtige suevitische Abfolge in einer oberen Untereinheit akkretionäre Lapilli und darüber eine Toneinheit. Das Auftreten von Karbonatschmelzen mit der PGE-angereicherten Impaktorkomponente in der Toneinheit belegt den Zusammenhang der K-P Grenze mit dem Chicxulub-Impakt. Die folgenden Stadien können für die Ablagerung und Alteration der Ejekta unterschieden werden: (1) Ein Hochgeschwindigkeitsauswurf beschleunigte Zersetzungsprodukte und initiierte einen Gasstrom. (2) Karbonatschmelzen wurden mit Anhydrit-Megablöcken ausgeworfen und initiierten einen lateral ausbreitenden Ejektavorhang. Kalzitrückreaktionen erhitzte das Material während des Transports. (3) Die Ejektionswolke kollabierte teilweise, wobei der zurückfallende Suevit vom Impaktormaterial, das in die Stratosphäre verteilt wurde, fraktioniert wurde. Die Kombination von Silikatschmelze mit Kalzit initiierte einen heißen, gas-angetriebenen Strom. In einer oberen, moderat temperierten, turbulenten Aschewolke kondensierte Wasserdampf, und durch Akkretion von Asche entstanden akkretionäre Lapilli. (4) Die Impaktorkomponente wurde mit den feinsten Ejektamassen für Wochen bis Jahre abgelagert. (5) Der Transport von Ejekta in der heißen Ejektionswolke induzierte Alterationsprozesse in den Ablagerungen. Es kann geschlussfolgert werden, dass ein gewisser Anteil des CO2 zu Kalzit zurückreagierte, währenddessen SOX Gase vollständig in die Atmosphäre freigesetzt wurden. Diese Beobachtungen inklusive des Auftretens von Karbonatschmelzen unterstützen die Aussage, dass der freigesetzte Anteil von CO2 in die Atmosphäre in der Vergangenheit überbewertet wurde. / Impactites of the Chicxulub crater were studied petrographically (polarisation microscopy, SEM, CL) and chemically (XRF, TXRF, PGE, EMPA) to investigate the evolution of ejecta during transit through the atmosphere. At the proximal UNAM-7 borehole, the sequence of impactites consists of a suevitic breccia (222.2 to 348.4 m) on top of a polymict silicate melt-poor breccia. The latter is intercalated with evaporite megablocks representing an analogue to the Bunte Breccia of the Nördlinger Ries crater. It contains carbonate melt particles; calcite and anhydrite decomposition is indicated by degassing vesicles. At the distal Cretaceous-Palaeogene site of El Guayal (~520 km SW of the crater centre), a ~10 m thick suevitic succession contains at its upper subunit accretionary lapilli and on top a clay unit. Intermixing of calcite with hot silicate melt resulted in recrystallisation and decomposition of calcite. In the clay unit, the presence of carbonate melt spheroids together with the PGE-enriched impactor component links the Chicxulub impact with the K-P boundary. The following stages can be distinguished for the deposition and alteration of the ejecta: (1) Jetting accelerated decomposition products and initiated a vapour flow. (2) Carbonate melts were excavated with anhydrite megablocks and initiated a lateral extending ejecta curtain. Calcite reformations heated the material during transport. (3) The expanding ejecta plume partially collapsed separating the falling suevite from impactor material that had been lifted into the stratosphere. The combination of silicate melt with calcite initiated a hot, gas-driven, basal flow. In an upper, moderately tempered, turbulent ash cloud, steam condensed and accretion of ash-sized material formed accretionary lapilli. (4) The impactor component was deposited with the finest ejecta for weeks to years. (5) The prolonged transport of ejecta in the hot ejecta plume induced alteration processes observed in the deposits. It can be concluded that a certain amount of CO2 has back-reacted to calcite, whereas SOX gases were completely liberated. These observations including the abundant presence of carbonate melts support that the amount of CO2 released to the atmosphere during the Chicxulub impact was overestimated previously.