Dazhang Formation

The Dazhang Formation is a geologic formation in China. It preserves fossils dating back to the late Paleocene, including those of plants and mammals. The formation is primarily composed of interbedded marl, oil shale, claystone and glutenite. Depending on the section, the color of the mudstone may vary from green, red-brown or gray-black.

Dating
Comprehensive comparison of the lithology and stratigraphy suggests the Dazhang Formation was deposited during the late Paleocene. This dating is further supported by fossil evidence, as standard Paleocene fossils such as those of the snails Parhydrobia xiaohegouensis and Opeas guangdongensis, and anagalid mammals. Palynological evidence based on large amounts of Paleocene palynomorphs (including Proteaceae and Ulmaceae) also supports a late Paleocene age for this formation.

Depositional environment
Judging from the lithology and absence of evaporative salt debris, the Dazhang Formation is believed to have represented delta and semi-deep lake environments, with a mild and humid climate during deposition. Palynology indicates the vegetation of the Dazhang Formation was primarily a mixed forest of coniferous and broadleaf deciduous trees within warm and temperate conditions, with broadleaf deciduous trees being dominant. Using the coexistence approach, the mean annual temperature has been estimated at 11.8–19.6 °C, with the mean temperatures of the warmest and coldest months at 19.8–28 °C and 3.9–5.9 °C respectively. Mean annual precipitation is believed to be 793.9–1389.4 mm.