Abstract

La repentina aparición de metazoos biomineralizados en las facies calcáreas del Miembro de Pockenbank (Namibia) parece reflejar un rápido cambio en el estado redox, la concentración de calcio y la alcalinidad del océano. La combinación de una importante innovación biológica con el final de una profunda excursión de isótopos de carbono respalda la idea de que la anomalía Shuram fue un fenómeno tectónico y oceanográfico, en contraposición a una “conspiración” diagenética mundial. La concordancia temporal de estos profundos acontecimientos, tal como se conservan en los estratos de Namibia meridional puede considerarse, por tanto, como marcadores geológicos excepcionales para la base del Ediacárico terminal.

Highlights

  • Given the template-directed mineralization of their funnel-in-funnel carbonate shells (Grant, 1990), the terminal Ediacaran fossil Cloudina may represent the earliest complex multicellular metazoan

  • We found the tubular fossil in a newly-recognized unconformity-bounded sequence immediately above the Mara Member in three locations south of Aus

  • Given the global distribution of the Shuram Excursion, its stratigraphically cohesive pattern of carbon, sulfur, and strontium isotope change, and its preservation in a wide range of depositional lithofacies (Grotzinger et al, 2010), the carbon isotope excursion may be understood in terms of the pulsed addition of 12C-rich alkalinity to the oceans

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Summary

Introduction

Given the template-directed mineralization of their funnel-in-funnel carbonate shells (Grant, 1990), the terminal Ediacaran fossil Cloudina may represent the earliest complex multicellular metazoan. The tubular fossil has a global distribution, but is best known from terminal Ediacaran strata of the Nama Group in southern Namibia – with a first appearance in the Mara Member (Germs, 1972), the fossil has not until recently been relocated at this level since its discovery over 50 years ago.

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