Regional nutrient decrease drove redox stabilisation and metazoan diversification in the late Ediacaran Nama Group,...

Area of Science:

• Paleoceanography
• Paleontology
• Geochemistry

Background:

• The late Ediacaran period saw increased metazoan diversity and ecological complexity, preceding the Cambrian Explosion.
• Understanding the environmental drivers of this diversification is crucial for reconstructing early animal evolution.

Purpose of the Study:

• To investigate the relationship between marine redox conditions, nutrient dynamics, and biotic diversification in the Nama Group, Namibia (~550 to ~538 Million years ago).
• To constrain the environmental factors that promoted or inhibited metazoan radiation during the Ediacaran-Cambrian transition.

Main Methods:

• Analysis of redox and nutrient data (including phosphorus speciation) from two shelf transects.
• Inventory of biotic diversity and distribution from the Nama Group fossil record.

Main Results:

• Unstable marine redox conditions prevailed from ~550 to 547 Million years ago (Ma), coinciding with the appearance of the first skeletal metazoans.
• A deepening of the redoxcline and reduced anoxic events occurred from ~547 Ma onwards, leading to basin ventilation by ~542 Ma.
• Initially, anoxic conditions facilitated phosphorus drawdown but allowed some recycling; decreased nutrient delivery and upwelling led to reduced recycling and promoted stable oxic conditions.

Conclusions:

• Gradual ventilation of Nama Group basins, driven by decreased nutrient input and possibly reduced upwelling, altered phosphorus cycling.
• The shift to stable oxic conditions, resulting from decreased anoxic phosphorus recycling, was a key factor in the radiation of new mobile metazoan taxa during the late Ediacaran.