TITLE:
Growth, Duplication and Lateral Mutual Compressive Deformation of Akouemma hemisphaeria on the Seafloor of Okondja Basin at 2.2 Ga (Gabon)
AUTHORS:
Ambroise Edou-Minko, Mathieu Moussavou, Tomohiko Sato, Yusuke Sawaki, Simplice Ndong Ondo, Richard Maire, Guillaume Fleury, Michel Mbina Mounguengui, Anders Kaestner, Richard Ortega, Stéphane Roudeau, Asuncion Carmona, Makaya Mvoubou, Benjamin Musavu Moussavou, Osamu Sasaki, Shigenori Maruyama
KEYWORDS:
Paleoproterozoic, Francevillian Group, Okondja Basin, Akouemma hemisphaeria, Growth, Duplication
JOURNAL NAME:
International Journal of Geosciences,
Vol.8 No.9,
September
28,
2017
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.