SUMMARY
Some
interpretations of upper
Miocene sediments in the Hanoi depression
Mai Thành Tân, Đinh Văn
Thuận, Nguyễn Văn Sơn, Ngô Thị Đào,
Nguyễn Văn Tạo, Lê Đức Lương
Upper Miocene sediments in the Hanoi depression are
interpreted in terms of depositional characteristics, environments and paleoclimate, based on the analyses of grain-size, thin
section, chemistry, X-ray diffraction, foraminifera and palynology from samples
of 3 boreholes. Study result had revealed that these Upper Miocene
sedimentswere deposited mainly in coastal areas including:marshes,
tidal flats, estuaries, neritic shallow waters. They could be divided into
lower and upper parts. The lower is composed mainlyof medium-grained sandstones
with fine-or-coarse-grained sandstonesof gray and ash-gray colour, siltstones
andclaystones in similar color andcoal; weakly to moderatelyconsolidated;
formed in environments of agitated shallow water with influence of turbidity
currents, estuaries, tidal flats and coastal
marshes. The upper is characterized mainly by fine-to-medium-grained sandstones
with lesser coarse-grained sandstones in gray and ash-gray interbedded with
thin layers of gray, gray-brown and blue-gray siltstones, claystones and coal;
weakly consolidated; deposited in environments of aggitated shallow water with
influences of turbidite currents or rivers, estuaries, tidal flats and coastal
marshes. The paleoclimate in late Miocene washot and humid tropical or
subtropical, however, the hot and humid degree had temporally changed.
Keywords: Upper
Miocene, depositional environments, paleoclimate, Hanoi depression.