Publications

Here’s a list of some hand-picked relevant scientific publications by the MOBILE team, dealing with reconstruction of ancient mountain belts, paleogeography, paleoclimate and life conditions. Some of the papers are free to download directly from their host website; if you are interested in any paper and can’t download, just send F. Caxito a message through here and he will send it to you for free. To see more of the vast bibliography of each collaborator, check out their websites.

2020

In this new article, the results of a study of high spatial precision dating using ionic microprobe of dykes of the southern São Francisco craton are presented. By studying the various swarms of each fragment of the ancient crust or cratons, we can build a “barcode” for this piece of crust and compare it with that of other pieces around the world. If the bar codes are similar, then it is possible that these fragments have been together in the past. The data collected suggests an increasingly well-defined link between the São Francisco craton of Minas Gerais and Bahia, Brazil, and the northern China craton between 2.55 billion and 900 million years ago, suggesting that Minas walked closely with China until they separated in this time. These two “lovers” may also have been part of greater supercontinents such as Columbia and Rodinia.

Recent geochronological (rock dating) data are presented by members of Project MOBILE in this publication in the Journal of South American Earth Sciences, with PhD student Fernando Pacheco as first author. These data indicate that the huge amount of carbon of the Jequitinhonha Complex was buried in a sedimentary basin developed between circa 610 and 550 million years ago, during a time when the Brasiliano mountain ranges were in the process of formation joining the ancient paleocontinents that form the South American and African basement rocks. Could the carbon sequestration be related to the Brasiliano mountains, with rapid erosion of the developing high-relief areas providing a large load of sediments which buried organic carbon?

This group of international researchers challenges the current model for Precambrian atmosphere oxygen. Two novel approaches, the measurement of trace elements in marine pyrite, combined with the measurement of oxygen in fluid inclusion gases in marine halite have led to a paradigm shift in our understanding of the rise then fall, and rise again of oxygen at the end of Precambrian.

  • Mukherjee, I and Large RR, 2020, Co-evolution of trace elements and life in the Precambrian oceans: The pyrite edition: Geology,  https://doi.org/10.1130/G47890.1 (on-line late June)

Postdoctoral fellow and colleague Indrani Mukherjee uses the chemistry of marine pyrite in black shales to track the changes in the trace element composition of the oceans through time. The resultant temporal matrix of ocean nutrients demonstrates the significance of certain trace elements in the evolution of life in deep time. The study reveals a “kangaroo hop” of trace element nutrient concentrations in the oceans approaching the Cambrian explosion of life.

A joint effort of correlation of geological features and paleocontinental reconstruction of the mountain belt that was divided in two and separated between northeastern Brazil and northwestern Africa due to the Cretaceous opening of the South Atlantic ocean. This is indeed the first major, Himalayan-style mountain belt (ca. 2,500 km-long) created by modern-style plate tectonics, recorded by ultra-high-pressure rocks that went way down in the mantle in deep continental subduction zones. Erosion of this mountain chain, formed at ca. 550 Ma ago, surely influenced the adjoining basins during the Cambrian life explosion that followed. Researchers from Brazil, Algeria and Cameroon discuss this scenario in this paper.

As important as reconstructing the ancient mountain belts is finding relics of the ancient oceans that were closed in order to form those features, much like India colliding with Asia to form the Himalayas caused the closure of the Tethys ocean in the Cenozoic. Here, the graduate student Leandro Amaral and collaborators describe and date a piece of 645 million-years old oceanic crust, a testimony of the Neoproterozoic Adamastor Ocean in eastern Brazil.

A sedimentological reconstruction of glacial-related basins in eastern Brazil at 630 million years ago, during and after one of the main Snowball Earth events. Researchers from Brazil, Belgium and from the Democratic Republic of Congo were involved.

Graduate student Ana Fonseca and collaborators use apatite fission track analysis to understand the uplift and erosion history of the Brasília mountain belt in central Brazil.

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2019

This book chapter summarizes the isotope geology scenario in Brazil during the last decades, and discusses the most important results and interpretations for Archean to Neoproterozoic sedimentary basins. A joint effort of nineteen Brazilian scientists, including three graduate students.

  • Crockford, P. W., Wing, B. A., Paytan, A., Hodgskiss, M. S., Mayfield, K. K., Hayles, J. A., Middleton, J. E., Ahm, A. S. C., Johnston, D. T., Caxito, F. A., Uhlein, G. J., Halverson, G. P., Eickmann, B., Torres, M., Horner, T. J. (2019). Barium-isotopic constraints on the origin of post-Marinoan barites. Earth and Planetary Science Letters519, 234-244.

This joint effort of scientists from various institutions around the world aims to understand the origin of ubiquitous barite layers that occur on cap carbonate successions. Samples from Canada, Norway, Brazil and China were studied, along with a Ba isotope survey of almost 100 modern and ancient additional barite measurements.

Graduate student João Pedro Hippertt along with collaborators present a comprehensive geochemical study of the Bambuí basin and points the importance of oceanic connection and ventilation for the development of complex life. In restricted basins, anoxia and geochemical constraints can hamper the development of typical Ediacaran-Cambrian ecosystems.

A comprehensive geochemical and isotopic study of the Bambuí basin, including a discussion about the enigmatic highly positive carbon isotope excursion named MIBE – Middle Bambuí Excursion.

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2018 and earlier

More on the ubiquitous barite layers in Brazil, China, Norway and Canada. They record a very specific triple oxygen isotope anomaly that indicates the ozon layer was seriously messed up after the Snowball glaciations. Could this be a global stratigraphic signal of equal importance to the Iridium anomaly that marks the Cretaceous-Paleogene boundary and could indicate another catastrophic event in Earth’s story?

A spike of oxygen in the seawater after the Marinoan Snowball glaciation seems to characterize cap carbonates deposited around 630 million years ago around the world. Could this have influenced the following appearance of complex life forms such as Cloudina sp. and Corumbella werneri?

A contribution that provided evidence that the Bambuí basin was developed over the São Francisco paleocontinent due to the loading of the Brasília mountain belt to the west. Could the erosion of the Brasília mountains have provided sufficient bionutrients and oxygen for Cloudina and Corumbella to thrive in the Bambuí waters?

A multi-proxy, multi-isotope investigation of the world-famous Quadrilátero Ferrífero iron deposits in Brazil. Besides the economic importance, those deposits seem to have recorded the acting of microorganisms that ingest and metabolize iron through a process called dissimilatory reduction, which could have been common when Earth experimented her first real taste of oxygen around 2.4 billion years ago.

More detailed studies of glacial-related sedimentary rocks in eastern Brazil.

Another piece of ancient oceanic crust, this time representing the Neoproterozoic Transnordestino-Central African ocean which crosscut through northeastern Brazil, Cameroon and Chad around 800 million years ago.

First findings of Cloudina and Corumbella shell fragments in the Bambuí Group. Those are Ediacaran index fossils that indicate deposition of the carbonatic sediments at the middle portion of the Sete Lagoas Formation around 550-540 million years ago. A possible connection with carbonates bearing similar fossils in the Paraguay Belt of western Brazil is suggested by the authors.

A review of the glacial-related deposits in eastern Brazil and a re-interpretation that those would represent Marinoan Snowball Earth-deposits.

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