Halong Bay, Vietnam

Hạ Long Bay (Vietnamese: Vịnh Hạ Long, literally: "descending dragon bay") is a UNESCO World Heritage Site, and a popular travel destination, in Quảng Ninh Province, Vietnam. Administratively, the bay belongs to Hạ Long City, Cẩm Phả town, and part of Vân Đồn District. The bay features thousands of limestone karsts and isles in various sizes and shapes. Hạ Long Bay is a center of a larger zone which includes Bái Tử Long bay to the northeast, and Cát Bà islands to the southwest. These larger zones share similar geological, geographical, geomorphological, climate, and cultural characters.

Hạ Long Bay has an area of around 1,553 km², including 1,960–2,000 islets, most of which are limestone. The core of the bay has an area of 334 km² with a high density of 775 islets. The limestone in this bay has gone through 500 million years of formation in different conditions and environments. The evolution of the karst in this bay has taken 20 million years under the impact of the tropical wet climate. The geo-diversity of the environment in the area has created biodiversity, including a tropical evergreenbiosystem, oceanic and sea shore biosystem.

Hạ Long Bay is home to 14 endemic floral species and 60 endemic faunal species.

Historical research surveys have shown the presence of prehistorical human beings in this area tens of thousands years ago. The successive ancient cultures are the Soi Nhụ culture around 18,000–7000 BC, the Cái Bèo culture 7000–5000 BC and the Hạ Long culture 5,000–3,500 years ago. Hạ Long Bay also marked important events in the history of Vietnam with many artifacts found in Bài Thơ Mount, Đầu Gỗ Cave, Bãi Cháy.

500 years ago, Nguyễn Trãi praised the beauty of Hạ Long Bay in his verse Lộ nhập Vân Đồn, in which he called it "rock wonder in the sky". In 1962, the Ministry of Culture, Sports and Tourism of North Vietnam listed Hạ Long Bay in the National Relics and Landscapes publication. In 1994, the core zone of Hạ Long Bay was listed by UNESCO as a World Heritage Site according to criterion vii, and listed for a second time according to criterion viii.

In 2000, the UNESCO’s World Heritage Committee has inscribed the Hạ Long Bay in the World Heritage List according to its outstanding examples representing major stages of the Earth’s history and its original limestone karstic geomorphologic features. The Hạ Long Bay and its adjacent areas consist of a part of the Sino-Vietnamese composite terrane having its development history from pre-Cambrian up to present day. During Phanerozoic, terrigenous, volcanogenic and cherty-carbonate sediments containing in abundance graptolites, brachiopods, fishes, corals, foraminiferas, radiolarias, bivalves and flora, separated one from another by 10 stratigraphic gaps, but the boundary between Devonian and Carboniferous has been considered as continuous. The limestone karstic geomorphology of the bay was developed since Miocene, especially the cone-shaped hills (fengcong), or isolated high limestone karst towers (fenglin) with many remnants of old phreatic caves, old karstic foot caves, marine notch caves form magnificent limestone karst landforms as unique on the world. The Quaternary geology was developed through 5 cycles with the intercalation of marine and continental environments. The present Hạ Long Bay, in fact, appeared after the Middle Holocene maximum transgression, leaving ultimate zone of lateral undercutting in the limestone cliffs bearing many shells of oysters, having the 14C age as 2280 to >40,000 y. BP. Geological resources are abundant: anthracite, lignite, oil shale, petroleum, phosphate, limestone and cement additives, kaolin, silica sand, dolomite, quartzite of exogenous origin, and antimony, mercury of hydrothermal origin. Besides, there still are surface water, groundwater and thermal mineral water on the shore of the Hạ Long - Bái Tử Long Bays and other environmental resources.

In terms of marine geology, this area is recorded as an especially coastal sedimentary environment. In the alkaline seawater environment, the chemical denudation process of calcium carbonate proceeds rapidly, creating wide, strangely shaped marine notches.

The bottom surface sediments are various from clay mud to sand, however, silty mud and clay mud are dominated in distribution. Especially, the carbonate materials originated from organisms make up from 60-65% sedimentary content. The surface sediments of coral reefs are mainly sand and pebbles of which the carbonate materials occupy for more than 90%. The intertidal zone sediments are various from clay mud to sand and gravel depending to distinguished sedimentary environments such as mangrove marshes, tidal flats, beaches etc. At the small beaches, but wonderfully beautiful, the sand sediments may be dominated quartz or carbonate materials.

The sediment layers of intertidal zone, the upper sea bed with a plain surface conserving ancient rivers, systems of caves and it's sediments, traces of ancient marine action forming distinctive notches, beaches and marine terraces, mangrove swamps are important evidence of geological events and processes taking place during Quaternary.

History of tectonics

Hạ Long Bay has experienced at least 500 million years in various geological states of orogeny, marine transgression and marine regression. During the Ordovician and Silurianperiods (500-410 million years ago), Hạ Long Bay was deep sea. During the Carboniferous and Permian periods (340-250 million years ago), Hạ Long Bay was at shallow sea level.

The dominated uplift movement of neotectonic and recent tectonic influenced deeply on topography of this area, and the present landscape of sea-islands was formed around 7 or 8 thousand years ago by the sea invasion during Holocene transgression begun at about 17-18 thousand years ago. Particularly from the Holocene time, from about 11,000 years ago Cat Ba - Hạ Long area has much archaeological evidence connecting variations in sea levels with the development of ancient cultures such as the Soi Nhu and Ha Long cultures.