Paleozoic and Mesozoic Era

II. The Paleozoic Era

From 600 million years to 250 million years ago
In Ethiopia, the major geologic (geomorphic) process was denudation followed by peneplanation.
Paleozoic is the only era that left a gap in a rock formation in Ethiopia.
No significant structural formation took place.
massive denudational activity resulted in the formation of inselbergs (residual features) in some parts of Ethiopia.
The Paleozoic era is known for the predominance of invertebrates.

III. The Mesozoic Era

From 250 million years to 70 million years ago
This era was marked by alternate slow sinking and uplifting of the landmass (Epeirogenesis) of the Horn of Africa.
The Mesozoic Era was an era of sedimentary rock formation in Ethiopia.
The Mesozoic era has three distinct periods
Triassic : 250 - 180 millions
Jurassic : 180 - 135 millions
Cretaceous :135 - 70 millions

Triassic Period

Landmass sank due to internal forces.
This event was followed by transgression of a nearby sea into the mainland of today’s Somalia and southeastern Ethiopia.
Oldest sedimentary rock Adigrat sandstone was formed.
Adigrat sandstone is the oldest in the southeast and progressively decreases in age to the northwest.

Jurassic Period
Transgression of the sea continued into the mainland in the northwest direction.
Deposited sedimentary rock known as Hintalo limestone.
Hintalo limestone is younger in the northwest
Hintalo limestone is older in the southeast.