TITLE:
A Review of the Lithostratigraphy of the Early Cretaceous Sao Khua Formation, Khorat Group in Northeastern Thailand
AUTHORS:
Pradit Nulay, Rungroj Arjwech
KEYWORDS:
Khorat Group, Sao Khua Formation, Lithostratigraphy, Non-Marine Cretaceous
JOURNAL NAME:
Open Journal of Geology,
Vol.11 No.9,
September
7,
2021
ABSTRACT: Non-marine Cretaceous rocks are widespread in
northeastern Thailand and is well known as “the red bed” Khorat Group. The Sao
Khua Formation is in the upper half of the Khorat Group which is comprised of
six formations. This formation was named and defined at the type section for
the rocks between the restricted PhraWihan Formation and the Phu Phan Formation
in the drainage area of the Huai Sao Khua, an intermittent stream that flows
westward parallel to the highway between Nong Bua Lamphu and UdonThani
Provinces. It contains richest and most diverse vertebrate and invertebrate
Mesozoic fossils in Thailand. The Sao Khua Formation is characterized by the
sequence of the fining-upward successions of at least 4-5 megacycles
throughout the formation with the total thickness ranging between 400-700
meters. Each cycle starts with a channel lag conglomerate which the clasts
consist totally of re-worked calcrete nodules. The conglomerates were overlain
by fine-to medium-grained sandstones of point bar deposit. Finally, the top
part of each cycle was covered by a succession of fine-grained floodplain
deposit that makes up 60%-70% of the formation. Paleosols are commonly found
in the Sao Khua Formation within the floodplain sequence and their geochemistry
indicates a semi-arid paleoclimate. Based on lithostratigraphy, the Sao Khua
Formation is interpreted to have been deposited by a meandering river system
under a semi-arid climate condition. The age of the formation is assigned as
the Hauterivian-Late Barremian based on vertebrate and bivalves fossils.