Abstract
A colony of macro-fossils Akouemma hemisphaeria has been described in the Paleoproterozoic sedimentary basin of Okondja, Gabon. These fossils are classified into two groups according to their spheroidal or elongated forms. The spheroidal shapes are similar, have a tripartite structure with two hemispheres and a median disc and gradually pass to the elongated forms. These elongated forms have a pronounced bipartite tendency to two “hemispheres” separated by a median surface, and often have several ovoid “pieces” attached. The elongated specimens show both lateral growth marks and signs of fission. Growth marks are characterized by unidirectional homogeneous side elongations and lateral bud-like protuberances. The signs of fission are marked by circular furrows perpendicular to the direction of elongation, called “constriction furrows” with varying depths depending on the degree of fission of the specimen and internal vertical “division planes”. All of these ovoid and elongated specimens have undergone significant initial deformations due mainly to mutual lateral compressions in tabular beds. The Akouemma hemisphaeria macro-organisms, which were primitive probably sessile organisms, lived on the seafloor. They provide the oldest known record of macro-organisms on Earth having vegetative growth and asexual reproduction by budding, lateral elongation and fission. Their mutual lateral deformations would result from their growth.
Highlights
The Paleoproterozoic is one of the most significant periods in the Earth’s history, for the environmental changes represented by Snowball Earth [1] and Great Oxidation Event [2], and for the appearance of the eukaryotic fossils [3]
The macrofossils Akouemma hemisphaeria described in the Paleoproterozoic basin of Okondja are located in the FB2b formations [7] [8] dated at 2191 ± 13 Ma [9] (Figures 1(A)-(C))
Edges and discontinuities of Akouemma hemisphaeria specimen consists of spheroidal and elongated shapes with either a “lateral budding”, (Figure 4), or a “homogeneous lateral elongation” (Figures 5-7)
Summary
The Paleoproterozoic is one of the most significant periods in the Earth’s history, for the environmental changes represented by Snowball Earth [1] and Great Oxidation Event [2], and for the appearance of the eukaryotic fossils [3]. The macrofossils Akouemma hemisphaeria described in the Paleoproterozoic basin of Okondja are located in the FB2b formations [7] [8] dated at 2191 ± 13 Ma [9] (Figures 1(A)-(C)) They are organic macrofossils of ovoid (spheroidal) shape, with 2 cm of average diameter, consisting of two hemispheres separated by a median disc (Figure 1 (D0), 3); and elongated shapes whose polar diameter is substantially similar to that of the ovoid shapes. The internal structure is fibro-radial, centrifugal upward in the upper hemisphere and centrifugal downward in the lower hemisphere, initially consisting of fibers and carbon particles [7] [8] These organisms have undergone significant deformations in tabular beds and hosted a large number of cyanobacteria, filamentous microorganisms, green alga fragments, small unicellular and multicellular organisms and other lenticular and oblong shape bodies; they are, in the history of Earth Sciences, the first Paleoproterozoic organisms described, living in association with a biodiversity of microorganisms [8]. Their fossilization is essentially siliceous to more than 80%, composed of micro-quartz, associated with EPS type calcite, oxides and iron sulphides and secondary-formed clay minerals which perfectly highlight the internal structure of these specimens [7] [8]
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