Isalo III Formation

Isalo III Formation
Stratigraphic range: Bajocian-Bathonian
~168–165 Ma
TypeGeological formation
Sub-unitsIsalo IIIa or Beronono Formation
Isalo IIIb or Sakaraha Formation
OverliesIsalo II Formation (unconformity)
Lithology
PrimarySandstone
OtherClaystone, marl
Location
Coordinates16°36′S 47°00′E / 16.6°S 47.0°E / -16.6; 47.0
Approximate paleocoordinates23°54′S 25°06′E / 23.9°S 25.1°E / -23.9; 25.1
RegionMahajanga & Fianarantsoa Provinces
Country Madagascar
ExtentMahajanga Basin
Isalo III Formation is located in Madagascar
Isalo III Formation
Isalo III Formation
Isalo III Formation
Isalo III Formation
Isalo III Formation

The Isalo III Formation is a geological formation in Madagascar, off the eastern coast of Africa. It dates back to the Middle Jurassic.[1] The use of the term "Isalo III" is somewhat controversial as the two prior units Isalo I and II are Triassic cross-bedded sandstone units that form a continuous depositional sequence, while the "Isalo III" sandstones are not part of the same depositional sequence, and were deposited considerably later. and are perhaps better treated as part of several separate formations.[2] It is traditionally divided into two subunits the lower, Bajocian aged Isalo IIIa unit also known as the Beronono Formation and the upper, Bathonian aged Isalo IIIb unit also known as the Sakaraha Formation or Sakahara Formation.[3] The Sakaraha Formation consists of sandstones, marls and carbonates and represents a coastal plain environment, and is laterally equivalent to the predominantly carbonate Bemaraha Formation, which represents a coastal barrier lagoon complex.[2] The formation is found in the northwest and in the southeast of the country and has provided a variety of fossils.

  1. ^ Weishampel et al., 2004, pp.542-543
  2. ^ a b Geiger et al., 2004
  3. ^ Cite error: The named reference :0 was invoked but never defined (see the help page).