Geographic coordinates:

Latitude North: 12° 44′ 22.170264″

Longitude  East: 107° 51′ 54.74088″

Geographic location: Nha Đen hamlet, Ea Po ward, Cu Jut ward, Daknong province.

Nha Den ammonite fossils
Nha Den ammonite fossils

Ammonite fossil distributed in a wide range of thousand hectares, mostly belong to Hamlet 1 to Hamlet 5 of Dak Wil ward, Nam Tien hamlet, Nha Den hamlet, Suoi Tre hamlet of Ea Po ward, Cư Jut district. The density of distribution is thick with the diversity and rich of species and size. Fossils are universal dimension from a few cm to dozen cm, particularly up to over 50cm.

– Formation aged: sediment fossil has aged of Early Jura, approximately 201 – 174 Ma.

– Mechanism of formation: Ammonoidea and Bivalvia has hard and thick crust, mostly contained Canxi carbonat, like the shell of Tridacna gigas in South continental of Vietnam. When the creature died, the shell mouth open up, soft body start to rotten, decay and replace, filled by argillite of marine bottom. Their shape formed by the hard shell during the processing of sediment and stone changing. After a long processing of geology, the rich canxi carbonat shell is decomposed, only fossils of Ammonoidea and Bivalvia remains.

– The result of paleontology study in this area show: Sandstone under the sequence of Bad preserved ammonite belong to Arietitidae family, Sinemur aged (199-190 Ma) and Cardinia concinna, C. aff orbicularis, claystone in the sequence of Dactylioceras sp. and Cultriopsis counilloni, Goniomya fontainei, Entolium cf. partitum, Chlamys cf. textoria, v.v. Pliensbach aged (190-182 Ma), and the upper calcium claystone contains Dumortieria lantenoisi and Parvamusium donaiense, Myophorella saurini, Toar aged (182-174 Ma).

According to the ecological environment, the appearance of Ammonoidea and Bivalvia in half of North side of Cu Jut is the scientific evidence to prove:

+ 201 – 174 million years ago, here is the marine.

+ The position where created the argillite contains Ammonoidea and Bivalvia is the continental of ancient marine, water deep under 200m. Ancient geography environment was quite stable and not much changes.

+ Dimension of Ammonoidea and Bivalvia are large (dozen cm to 50-60cm), affirm the deep level of argillite isn’t intertidal zone (0-30m), it belongs to neritic zone around 50-200m deep water. The ecological environment at that time is rich of nutrition, warm weather and adapt for the development of Mollusca and other sea-shells.