The Gatún Formation was first defined and named as such by Howe in 1907. The formation was known before and when
William Phipps Blake traveled across Panama in 1853 on his way to California to join one of the transcontinental railroad surveying parties, he collected a few Gatún Formation fossils.[4] In the Canal Zone the contact between the formation with the underlying
Caimito Formation is covered by the waters of
Lake Gatún and even before the flooding of the lake perhaps all of the contact was concealed by swamps.[5]
Massive medium- to very fine-grained
sandstones and
siltstones are the chief constituents of the Gatún Formation. They are somewhat
calcareous, or
marly, somewhat
tuffaceous, and have a clay-like matrix. The sandstone contains numerous grains of black and greenish volcanic rocks and is practically a subgraywacke.
Conglomerates and hard brittle very fine-grained tuff make up a small part of the formation.
Basalt intrudes older formations in the Lake Gatún area, but is not known to penetrate the Gatún Formation.[5]
C. Pimiento, G. González-Barba, D. J. Ehret, B. J. MacFadden, A. J. W. Hendy and C. Jaramillo. 2013. Sharks and Rays (Chondrichthyes, Elasmobranchii) from the late Miocene Gatún Formation of Panama. Journal of Paleontology 87(5):755-774