Name: Tlayúa Location: Mexico Age: Early Cretaceous (100 mya)

Tlayua Quarry is from the Early Cretaceous (100 million years old) when it was a coral reef barrier that had double-monsoon influences from both hemispheres and with an average rock accumulation of 19 mm/year. It is mainly made of micritic limestones. The geology of Tlayua has been the subject of several studies. The oldest rocks in the region are from the Acatlan Complex of Early Palaeozoic age. In some parts, the continental Upper Jurassic and Early Cretaceous may be seen. Above this sequence are layers that formed the carbonate unit described by Pantoja-Alor et al. (1992), as the Tlayua Formation, which is divided into three subunits:

1. Lower Member- Made of grey-blue limestone with rudists (e. g. Toucasia polygyra) and bivalves (e.g. Chondrodonta) among other species of invertebrates.
2. Middle Member- Characterized by its reddish limestones with several layers where some of the fossils came from. This sequence is 30 m high, and can yielded around 200 species of invertebrates and vertebrates fossils.
3. Upper Member- Comprises medium layers of dolomite and dolomitic limestones. There are no fossils here.

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