Young rifts are shaped by combined tectonic and surface processes and climate, yet few records exist to evaluate the interplay of these processes over an extended period of early rift-basin development. Here, we present the longest and highest resolution record of sediment flux and paleoenvironmental changes when a young rift connects to the global oceans. New results from International Ocean Discovery Program (IODP) Expedition 381 in the Corinth Rift show 10s–100s of kyr cyclic variations in basin paleoenvironment as eustatic sea level fluctuated with respect to sills bounding this semi-isolated basin, and reveal substantial corresponding changes in the volume and character of sediment delivered into the rift. During interglacials, when the basin was marine, sedimentation rates were lower (excepting the Holocene), and bioturbation and organic carbon concentration higher. During glacials, the basin was isolated from the ocean, and sedimentation rates were higher (~2–7 times those in interglacials). We infer that reduced vegetation cover during glacials drove higher sediment flux from the rift flanks. These orbital-timescale changes in rate and type of basin infill will likely influence early rift sedimentary and faulting processes, potentially including syn-rift stratigraphy, sediment burial rates, and organic carbon flux and preservation on deep continental margins worldwide.

No abstract

Resumo Estudos detalhados de fáceis sedimentares e empilhamento estratigráfico de 12 seções em minas e corte de estrada, ao longo de um perfil de 80,5 km, conduziram ao reconhecimento de 11 fácies sedimentares da Formação Sete Lagoas, 2 fácies do Conglomerado Carrancas e 3 fácies na porção basal da Formação Serra de Santa Helena. Essas fácies compõem 9 associações de fácies, as quais correspondem ao registro de 3 seqüências deposicionais. As seqüências estratigráficas descritas são caracterizadas por tratos de sistema transgressivo e mar alto, com preservação secundária de um trato de sistema de mar baixo. Duas das três seqüências reconhecidas estão associadas à sucessão carbonática da Formação Sete Lagoas, enquanto a última seqüência, sobreposta aos carbonatos, corresponde ao registro siliciclástico da Formação Serra de Santa Helena. A distribuição estratigráfica das associações de fácies revela uma transição de ambientes de águas rasas a Oeste da área estudada para ambientes de águas mais profundas em direção a Leste. Um modelo de rampa carbonática, mostrando os diferentes estágios de evolução das seqüências, é apresentado como proposta de interpretação para os dados faciológicos e estratigráficos obtidos para os depósitos da Formação Sete Lagoas na região homônima e proximidades.

No abstract

The interpretation of fluvial styles from the rock record is based for a significant part on the identification of different types of fluvial bars, characterized by the geometric relationship between structures indicative of palaeocurrent and surfaces interpreted as indicative of bar form and bar accretion direction. These surfaces of bar accretion are the boundaries of flood‐related bar increment elements, which are typically less abundant in outcrops than what would be desirable, particularly in large river deposits in which each flood mobilizes large volumes of sediment, causing flood‐increment boundary surfaces to be widely spaced. Cross‐strata set boundaries, on the other hand, are abundant and indirectly reflect the process of unit bar accretion, inclined due to the combined effect of the unit bar surface inclination and the individual bedform climbing angle, in turn controlled by changes in flow structure caused by local bar‐scale morphology. This work presents a new method to deduce the geometry of unit bar surfaces from measured pairs of cross‐strata and cross‐strata set boundaries. The method can be used in the absence of abundant flood‐increment bounding surfaces; the study of real cases shows that, for both downstream and laterally accreting bars, the reconstructed planes are very similar to measured bar increment surfaces.

The Ediacaran is one of the most important periods on Earth evolution, including the first appearance of soft‐bodied macrofossils, major climatic changes and a supposed rise in free oxygen. In southernmost Brazil, this period is represented by Camaquã Supergroup, including the Bom Jardim Group and the Acampamento Velho Formation, both of which record continental palaeoenvironmental changes in a more than 5000 m thick stratigraphic succession. Age constraints are given by seven Ar‐Ar and U‐Pb determinations on volcanic rocks, which bracket these units between c. 605 and 574 Ma, revealing the best dated and most continuous documented Ediacaran continental succession to date. Depositional systems evolution supports a Phanerozoic‐type glacial context during the last Neoproterozoic glacial event and presents the Picada das Graças Formation (580 ± 3.6 Ma) as the first dated non‐glacial unit coeval to the Gaskiers Formation.

No abstract

No abstract available. <br><br> doi:<a href="http://dx.doi.org/:10.2204/iodp.sd.13.07.2011" target="_blank">:10.2204/iodp.sd.13.07.2011</a>