No abstract

The Ma river delta located in the North Central of VietNam is the third largest ones in Vietnam following the Mekong Delta and the Red River Delta. However, there are not many researches on sedimentary. This study aims to determine the Characteristics of the Holocene sedimentary facies in coastal plain of the Song Ma Delta based on observation of sedimentary structure and analysis of grain size, diatom, flora, pollen and 14C dating collected for the drill core (LKTH2 borehole) from the coastal plain of the Song Ma river delta. Research results identify 08 facies consisting 02 facies of transgression period and 06 facies of regression period. During transgression period, 02 facies of tidal flat clayish silt and bay silty clay facies were formed. Of which, tidal flat clayish silt face was formed in 7,883 ± 43 14C yr BP. After the maximum flooding of the sea, the delta was initiated and 06 facies were formed during the regression period i.e. prodelta silty clay, delta front clayish silt, tidal flat sandy - silty clay, sand ridge, lagoonal sandy silty clay, and flood plain silty clay facies. The tidal flat sandy - silty clay facies occurred in 6.951± 38 14Cyr BP caused by sea level fall and the coastline was identified around the LKTH2 bore hole at that time. Integration of sedimentary facies of the sand ridge and lagoonal sandy silty clay facies shows that the Song Ma Delta was dominated by wave process during its evolution.

Located on the northern Vietnam onshore/offshore transition, the Hoanh Bo Trough is an excellently exposed terrestrial Palaeogene sedimentary sequence that may be treated as an analogue for regional interpretations of the sedimentary and structural evolution of the northern Song Hong Basin. The Hoanh Bo Trough lies to the north of the northern Song Hong Basin and to the west of the Beibuwan Basin, the origin and evolution of which are linked with Palaeogene South China Sea rifting. Field and archival well sedimentological observations were made throughout the Palaeogene succession of the Hoanh Bo Trough, and samples were collected for palynological, petrographical, and geochemical analysis. Based on the coexistence of particular lithofacies, proximal alluvial fan, distal alluvial fan, fluvial alluvial plain with channels, alluvial plain and/or lake margin, and lacustrine facies associations were distinguished. Palynological analyses suggest the sedimentary infill of the Hoanh Bo Trough is of the Late Eocene-Early Oligocene age and was deposited in a very warm tropical/subtropical climate. In turn, geochemical results demonstrate that the deposits have intermediate chemical maturity and were probably reworked from older sedimentary rock sources. Moreover, it is suggested to combine the Dong Ho and Tieu Giao formations and synonymize them as the Dong Ho Formation. The sedimentary pattern, age, climatic conditions, and structural evolution of the Hoanh Bo Trough align well with the rift initiation, rift development, and rift termination tectonic system tracts. Moreover, the Hoanh Bo Trough could be treated as a landward keyhole for the offshore basins: for instance, the Kien An Basin in the northern Song

During the Miocene-Pleistocene, generally sub-tropical to tropical warm and humid paleoclimate prevailed in Southeast Asia with a gradual cooling trend. The Truc Thon clay (TTC) mine presents interesting outcrops for sedimentological and provenance analysis. The present study uses results of geological investigation in 16 outcrops and wells at the clay mine Truc Thon. The TTC has lens-shaped geometry, filled with two clay bodies, including grey-white clay and multicolor clay. Bulk mineralogy indicates the predominance of quartz and a relatively high amount of pyrophyllite. Clay mineralogy shows the presence of main kaolinite, followed by illite and mixed-layer illite-smectite. These may interpret a warm, humid paleoclimatic condition in the source areas. Illite may be inherited from basement rocks. The bulk rock geochemistry supports intense chemical weathering with the Chemical Index of Alteration (CIA) in the TTC ranged ca. 80.6-98 (average = 90.4). In combination with the geochemical proxies and the mineralogical composition of the TTC, the chemical weathering intensity indicated warm/hot, semi-humid/humid tropical paleoclimate in the source area. A combination of mineralogical and geochemical analyses with regional geological features show that the Hon Gai Triassic rocks are the main source for the TTC. Source materials are originally related to silicic rocks of granitic-granodioritic composition. Paleoclimatic conditions favored intense chemical weathering of the Hon Gai Triassic rocks and surrounding rocks, creating a ceramic mine of great industrial value.

Kim Son coastal plain is a part of the Red River Delta located between Day and Can rivers. Over the past 55 years, Kim Son coastal plain has been the region with the highest accretion rate in the Red River Delta. This study aims to clarify the sediment characteristics of Kim Son coastal plain. It has the structure of a typical tidal flat and a relatively straightforward tide-influenced sedimentary structure evidenced by the field observation, sampling 70 hand-drilled boreholes, borehole logging and analyzing 177 samples of grain size. There are three tidal sedimentary zones to be identified, including sand flat, mixed flat, and mudflat. The history of topographic changes is also presented over six periods from 1965 to 2020 based on analyzing and interpreting multi-time satellite images. The total accretion area of Kim Son coastal plain over 55 years was 4,081.2 ha.