THE OUTSTANDING VALUE OF THE GEOLOGY OF HA LONG BAY Tran Duc Thanh(1) & Tony Waltham(2) (1).Haiphong Institute of Oceanology; 246 Danang Street, Haiphong city, Vietnam; (2) Nottingham Trent University, England Introduction Nature has given Ha Long Bay many precious values Ha Long bay was first recognised as a World Natural Heritage Area solely on the basis of its outstanding landscape value The beauty and aesthetic value of natural landscape of the Bay reflect the shapes and the colours of jewels However, it is geological structure and material of the bay that have created the jewels The outstanding value of Ha Long Bay’s geology and geomorphology needs to be conserved for the benefit of future generations This paper is a preliminary review of that value 1.THE VALUE OF REGIONAL GEOLOGY Ha Long Bay, the area near the shore and other area adjacent to the Bay are composed of thick beds of limestone and clastic sediments which have been aged from ancient to the present day This is the carved picture of geological processes which occurred hundreds of million of year ago Throughout this time while the colour, the ingredients and the architecture of the limestone beds were being formed, fossil relicts have been preserved between the layers These, and the nature of the sediments, contribute to a scientific record of the region Mane sedimentary rocks contain remains and traces of flora and fauna of the ancient past in many forms including those of plants and creatures that become extinct many years ago This leaves a store of information about the evolution and development of life on the Earth (Table 1) In the geological structure, Ha Long bay lies in the Duyen Hai Zone (Dovjicov, A.E et all, 1971) belonging to Caledonian-Katasia structure which suffered from orogenic movement during the early Palaeozoic era On the Caledonide folded basement, the Indosinian orogeny at the end of Triassic period formed the block faults and bearing anthracite sediments were deposited The well-known sub-latitude deepening fault system of Vietnam has developed in this zone (Can, N., et all, 1994) The series of the movement also formed the Cua Luc and Ha Long depressions, which were subsequently flooded by sea The record of the old, recent movement are clearly shown in Ha Long Bay area in the strong deformation of sedimentary layers such as gentle and returned folds, and normal and reverse faults with the tectonic breccia belts They are of Nature’s lively Sculptures preserved on the limestone cliffs normally The Ha Long Bay has a long geological history with the different paleogeographical environments commencing nearly 570 million years ago (Table 2) Between Ordovician and Silurian periods (500 to 410 million years ago), the area was the deep sea Latter, between Carboniferous and Permian periods (340 to 250 million years ago), the area fell into the sallow sae environment By the end of Paleogenic and the beginning of Neogenic periods, between 26 and 20 million years ago, the sea area had become part of a large coastal peneplain This was inundated by sea several times in the Quaternary, during million last years The present Ha Long Bay was formed around or thousand years ago by the sea invasion during Holocene transgression begun at about 17-18 thousand years ago (Thanh, T.D et all, 1997; Thanh, T D., 1998) The geological history of Ha Long bay involved three major periods of orogeny (Thanh, T Dz., 1977) The first was Caledonide epi-geosynclinal orogeny at the end of Silurian periods, about 410 million years ago The second was Indosinide epi-platform orogeny at the end of Triassic period, about 200 million years ago The last Alpide orogeny in the late Paleogene period, around 30 million years ago created the distinction between horst mountains and graben depressions which was basis of the formation of Ha Long Bay latter There existed two distinguished paleogeographical environments in Ha Long Bay area The Carboniferous periods, between 340 and 285 million years ago, was a warm period all over the planet when huge swamps created the great coal basins of Europe and America In Ha Long Bay, carbonate sediments were deposited in a shallow sea in dry, hot conditions, gradually building in to thick beds of limestone Throughout the hundred – million year period, the sea bed gradually subsided thereby allowing the limestone under the shallow sea to accumulate in thick layers eventually achieving a thickness of 1,200m eventually permitting the formation of a characteristic karst landscape By contrast, during the Triassic period between 240 and 195 million tears ago when most of the rest of the world was experiencing hot, dry climatic conditions, the Ha Long region had a hot, wet climate The decayed remains of enormous forests of tree ferns were the basis of coal deposits in the area The present Ha Long Bay is a karst plain that has been submerged by the sea and is the result of a geological history spanning more a hundred million years Prior to the formation of Ha Long Bay, 300 to 240 million years ago, there must have been an ancient sea above a 1000 m thick bed of limestone The 20 million year process of karts erosion took place during the Neogenic and Anthropogenic periods the much later marine invasion is related to a warmer climate all over the planet over ten thousand years ago The Quaternary and the marine geological values The Ha Long Bay area has many valuable features of the Quaternary period The Quaternary sediment players, the upper sea bed with a plain surface conserving ancient rivers, systems of caves and deposits of sediments, traces of ancient marine action forming distinctive notches are important evidence of geological events and processes taking place at a time when human beings inhabited the earth Particularly from the Holocene time, from about 11,000 years ago when modern, intelligent humans had developed, Ha Long Bay has much archaeological evidence connecting variations in sea levels with the development of ancient cultures such as the Soi Nhu and Ha Long cultures Unfortunately, this aspect has not yet been researches or evaluated in detail In terms of marine geology, Ha Long is recorded as a modern sedimentary basin, a bay created by a system of boundary islands The Bay has strong tidal currents, but weak ware In the alkaline environment, the chemical denudation process of calcium carbonate proceeds rapidly, creating wide, strangely shaped marine notches This appears to be an active process, concerning CO2 supplied from respiration of algae and plants living in Ha Long Bay Karst geomorphic value Ha Long Bay is a mature karst landscape developed during a warm, wet, tropical climate The sequence of stages in the evolution of a karst landscape over a period of 20 million years requires a combination of several distinct elements including a massive thickness of limestone, a hot wet climate and slow overall tectonic up lift Waltham T 1998 According to Chinese scientists, the process of karst formation is divided into five stage is the formation of the distinctive line karst This is followed by the development of fengcong karst can be seen in the groups of hills on Bo Hon and Dau Be Inland These cones with sloping side average 100m in height with the tallest exceeding 200m Fenglin karst is characterised by steep separate towers The hundreds of rocky islands with form the beautiful and famous landscape of the Bay are the individual towers of a classic Fenglin landscape where the intervening plains have been submerged by the sea Most towers reach a height of between 50 and 100m with a height to width ratio of about The karst dolines were flooded by the sea becoming the abundance of lakes that lie within the limestone islands For example, Dau Be island at the mouth of the Bay has six enclosed lakes including those of the Ba Ham lakes lying within its fencong karst The Bay contains examples of the landscape elements of fengcong, fenglin and karst plain These are not separate evolutionary stages but the result of natural non – uniform processes in the denudation of a large mass of limestone Marine erosion created the notches which in some places have been enlarged into caves The marine notch is a feature of limestone coastline but, in Ha Long Bay, it has created the mature landscape Table 1: The geological history of Ha Long Bay (Thanh, T.D.,1998) Era Period Holocene Events Marine transgression, after world's glaciations, overran the coastal areas to form the modern Ha Long Cainozoic Bay This is mainly a land environment, with development of karst landscapes and river systems Systems of caves formed at heights of 10-15 m, 20-30 m and 40-60 m Anthropogene Pleistocene Neogene Mesozoic Tectonic downwarpings of Cua Luc Bay and Ha Long Bay Uplift tectonic movements on Dong Trieu Arc Paleogene The East Sea is formed River erosion and alluvial deposition formed a large peneplain Cretaceous Jurassic A continental environment with orogenic movements Erosion processes are strong Triassic A land environment, where tectonic downwarping created a coal swamp basin is followed by strong movements of the Indosinian orogeny Permian Downwarping disturbed the coastline creating a land environment Carboniferous Paleozoic A marine transgression formed the ancient Ha Long Bay Previously the sea-level had been 100-120 m lower than today and well outside the modern coast during the cold stages of the glacial Ages Devonian A shallow warm sea enlarged from the west, rich in sea creatures, including coral, foraminifera, brachiopods and crinoids Limestone, over a thousand metres thick, is formed Ha Long Bay is a land area Nearby the Quan Lan archipelago, Trang Kenh, Do Son and Cat Ba were downwarpings invaded by the sea Silurian Ordovician Open sea with deep water in the Katazia geosyncline The sea extended to the west, but the East Sea was a landmass Cambrian Land Proterozoic and Archean Unknown Table Sediment formations and fossils in Ha Long Bay and its surrounding areas (Dovjicob, A E et all, 1971, Luong, N C et all, 1980 and Toan, N Q et all 1993) Or Name of der formation Sight Thick ness Sediment ingredients Fossils Geological period Location Cô Tô 03 – S1ct 2500 Clastic Graptolites mixed with volcanic ash early ordovicianSilurian Cô Tô, Thanh Lân Con Ngựa Dưỡng động D1 – 2dd ≅ 500 Raw clastic Coral, Brachiopada Middle Devonian Ngọc Vừng, Vạn Cảnh Lỗ Sơn D2els 300 Limestone, lime-clay, lime-silica old coral Middle Devonian Trà Bản, Cái Lim Đồ Sơn D3đs 350 Clastic Brachiopada in Do Son Late Devonian Đông Kho, Quán Lạn, Trà Bản Phố Hàn D3C1ph 400650 Limestone and clastic Coral, Late Brachiopada, DevonianForaminifera early Cát Bà carboniferou s Cát Bà C1cb 450 Limestone Coral, Early Brachiopada, carboniferou Foraminifera, s Crinoids Ha Long Bay, Cát Bà Quang Hanh C2-Pqh 750 Clean limestone Coral, carboniferou Brachiopada, s-Permian Boraminifera Ha Long Bay, Cát Bà, Quang Hanh, Đèo Bụt Bãi Cháy P2bc 300 Silica Coral, Foraminifera Late Permian Bãi Cháy, Cửa Lục Hòn Gai T3n-nhg ≈ 200 Clastic with coal Swamp plants Late Triassic Hòn GaiCẩm Phả 10 Đồng Ho N1dh 140 Clastic with bearing oil Swamp plants Early Neogenic Cửa Lục Bay 11 Tiêu Giao N2tg 100200 Clastic Plants, mollusks Early Neogenic Cửa Lục Bay 12 Các Hệ tầng Đệ Tứ Q 1-10 Clastic, carbonate Before modern creature, mordern creature Quaternary Widle Within Ha Long Bay, the main accessible caves are the older passages that survive from the time when the karst was evolving though its various stages of fengcong and fenglin Three main types of caves can be recognized in the limestone islands (Waltham, T 1998): 1- Remnants of old phreatic caves 2- Old karstic foot caves 3- Marine notch caves The first group of caves is old phreatic caves which include Sung Sot, Tam Cung, Lau Dai, Thien Cung, Dau Go, Hoang Long, Thien Long Nowadays, these caves lie at various high levels Sung Sot cave is on Bo Hon island From its truncated entrance chambers on aledge high on the cliff, a passage of more that 10m high and wide descends to the south Tam Cung is a large phreatic fissure cave that developed in the bedding planes of the limestone dividing the fissure cave into three chambers Lau Dai is a cave with a complex of passages extending over 300m opening on the south side of Con Ngua island Thien Cung and Dau Go are remnants of the same old cave system They both survive in the northern part of Dau Go island at between 20 and 50m above sea level Thien Cung has one large chamber more that 100m long, blocked at its ends and almost subdivided into smaller chambers by massive wall of stalactites and stalagmites Dau Go is a single large tunnel descending along a major set of fractures to a massive choke The second group of caves is the old karstic foot caves which include Trinh Lu, Bo Nau, Tien Ong and Trong caves Foot caves are a ubiquitous feature of karst landscapes which have reached a stage of widespread lateral undercutting at base level They may extend back into maze caves of stream caves draining from larger cave systems within the limestone They are distinguished by the main elements of their passages being close to the horizontal and are commonly related to denuded or accumulated terraces at the old base levels Trinh Nu, which is one of the larger foot caves in Ha Long Bay with its ceiling at about 12m above sea level and about 80m in length, was developed in multiple stages Bo Nau, a horizontal cave containing old stalactite deposits, cuts across the 25 o dip of the bedding plane The third group is the marine notch caves that are a special feature of the karst of Ha Long Bay The dissolution process of sea water acting on the limestone and erosion by wave action crates notches at the base of the cliffs In advantageous conditions, dissolution of the limestone allows the cliff notches to be steadily deepened and extended into caves Many of these at sea level extend right though the limestone hills into drowned dolines which are now tidal lakes A distinguishing feature of marine notch caves is an absolutely smooth and horizontal ceiling cut through the limestone Some marine notch caves had been not formed at present sea level, but old sea levels related to sea level changes in Holocene transgression, event to Pleistocene sea levels Some of them passed preserved the development of old karstic foot cave in mainland environment or preserved the remnants of older phreatic caves One of the most unusual features of Ha Long Bay is the Bo Ham lake group of hidden lakes and their connecting tunnel – notch caves in Dau Be island From the island’s perimeter cliff a cave, 10m wide at water level and curving so that it is almost completely dark, extends about 150m to Lake Luon cave is on Bo Hon island and extends 50m though to an enclosed tidal lake It has a massive stalactite hanging 2m down and truncated at the modern tidal level It has passed though many stages in its formation The karst landscape of Ha Long Bay is of international significance and of fundamental importance to the science of geomorphology The fenglin tower karst, which is the type present in much of Ha Long Bay, is the most extreme form of limestone landscape development If these karst landscapes are broadly compared in terms of their height, steepness and number of their limestone towers, Ha Long Bay is probably second in the entire world only to Yangshou, in China However, Ha Long Bay also been invaded by the sea so that the geomorphology of its limestone is lands are, at least in part, the consequence of marine erosion The marine invasion distinguishes Ha Long Bay and makes it unique in the world There are other areas of submerged karst towers which were invaded by the sea, but none is as extensive as Ha Long Bay Mineral resources and other values The value of the mineral resources of Ha Long Bay cannot be ignored, although their exploitation is another issue that needs to be considered in relation to conservation and development There is an enormous reserve of limestone in the Ha Long area, hundreds of millions of tons with a calcium carbonate content of between 96% and 100% Conservation of this area also has to take into account the maintenance of this vast carbonate Limestone formations also have a solid black silica layers, important for art material The coal deposits of Hon Gai Basin are of high grade anthracite with a calorific value of between 7000 and 8400 Kcal/kg, an ash content of between1.2% and 1.5% and a sulfur content of between 0,2% and 1,2% The Tertiary sedimentary formations onshore of Ha Long Bay have a great reserve of clay materials for bricks and tiles of which hundreds million have been manufactured a year recently Dong Ho formation with the stones bearing oil has been determined as Oligocene age shows the petroleum prospect in coastal Northeast part of Vietnam ( Trung, P.Q et all, 1999) The tourism development value of Ha Long Bay is increasingly determined by the value of the geological resource factor However, the attraction would be much greater were the geological value to be more effectively Apart from scientific tourism, if the geological value is explained through effective interpretation and representation, tourism gain not only an appreciation of the beauty of the natural landscape but also come to understand the value of the heritage - its geological history, structure, process of creation and so on As well as its close relation to the value of the natural landscape, the geology of Ha Long Bay is associated with the value of the bio – diversity of the eco – systems, such as the coral reefs and mangroves on and around the islands of Ha Long Bay In some caves, such as Sung Sot, Trinh Nu, Vung Ba Cua, Hoang Long, Dau Go and Bo Nau, there are many bats In many caves, archeologists have found remains and artefacts of the Soi Nhu culture of the late Pleistocene period and the Ha Long culture of the middle Holocene period An old picture was also found on the roof of a cave on the west bank of Vung Ba Cua island Dau Go cave is regarded as the place where the wooden stakes for the battle at the Bach Dang River in 1288 were hidden Conclusion Ha Long Bay has outstanding values of geology and geomorphology These include the scientific values of regional geology, Quaternary geology, marine geology and karstic geomorphology In addition there are the resource values of minerals and tourism and the ancillary values of archeology and bio – diversity Of these, the value of the karstic geomorphology is the most outstanding and unique, and plays a fundamental role in the science of karstic geomorphology In addition to its natural landscape value, Ha Long Bay is worthy of further recognition as a World Heritage in respect of its geological value The conservation of this heritage is, therefore, of the highest level of importance REFERENCES Can N et all 1994 Recent faulting in Hai Phong – Quang Yen area In: Marine resources and environment Sci and Tech Pub House Ha Noi p 54 - 60 Dovjicov, A E; N v Chien at all, 1971 Geology of North Viet Nam Sci and Tech Pub House Ha Noi Luong N C, et all 1980 Report on Geology of Mong Cai – Hon Gai Area Geological map scale 1/200.000 Reserved at Geological survey of Viet Nam Thanh, T Dz 1977 Geological History (development history of the Earth Crust) Publishing house of university and Professional high – school Ha Noi Thanh, T D, N Can and D D Nga 1997 Coastal development of Do Son – Ha Long Area during Holocene In: Marine Geology and Geophysics Sci and Tech Pub House Ha Noi p 199 - 212 Thanh, T D 1998 Geological History of Ha Long Bay Global Pub House and MDHB, Ha Noi p – 94 Toan, N A et all, 1993 Report on geology and mineral resources of Hai Phong City Geological map Scale 1/50.000 Reserved at Geological survey of Viet Nam Trung, P.Q et all, 1999 New palynological find in the Dong Ho formation Petrovietnam Review Vol.3 Hanoi, p.14-20 Waltham, T., 1998 Limestone karst of Ha Long Bay, Viet Nam Engineering Geology Report, No 806 Nottingham Trent University UK p.1 - 41 ... to the value of the natural landscape, the geology of Ha Long Bay is associated with the value of the bio – diversity of the eco – systems, such as the coral reefs and mangroves on and around the. .. across the 25 o dip of the bedding plane The third group is the marine notch caves that are a special feature of the karst of Ha Long Bay The dissolution process of sea water acting on the limestone... decayed remains of enormous forests of tree ferns were the basis of coal deposits in the area The present Ha Long Bay is a karst plain that has been submerged by the sea and is the result of a geological