Environ Earth Sci DOI 10.1007/s12665-013-2619-1 SPECIAL ISSUE Geoheritage values in the Cat Ba islands, Vietnam Ta Hoa Phuong • Nguyen Huu Cu Tran Duc Thanh • Bui Van Dong • Received: August 2012 / Accepted: 21 June 2013 Ó Springer-Verlag Berlin Heidelberg 2013 Abstract Geological wonders have been generally known as natural wonderful products Resulted from geological processes, geological wonders are diverse in size that have geoheritage values that should be protected from damaging of substance, form and natural development In a large scale, geological wonders can be geoheritage areas, containing several geodiversity elements that are geologically important or in a smaller scale, they can be geosites of heritage values (or geoheritage sites) In the delimitation of areas, having geoheritage values and the establishment of geoparks, the first thing is to recognise them as geosites and geoheritage areas that indicate great geological values Besides the Ha Long bay, the world natural heritage with its outstanding aesthetic and geological values, the Cat Ba islands are typical and grandeur karst landscapes formed in tropical condition Based on the geodiversity elements with their own geoheritage values on aesthetics, uniqueness and grandeur in the Cat Ba islands, the authors have recognised three geoheritage areas: the south cape of the Cat Ba embayment, Tung Gau (shelter), and the Lan Ha bay Sites where Brachiopods, Crinoids and Tetracorals are exposed on the way through the island are considered as palaeontological geosites The folds of limestone layers in the northern part of Cat Co beach, with typical turbidite structures in carbonate formations are considered as a lithological geosite The Devonian-Carboniferous boundary near the Cat Co beach is regarded as a stratigraphical T H Phuong (&) Á B Van Dong VNU University of Science, Hanoi, Vietnam e-mail: tahoaphuong@gmail.com N H Cu Á T D Thanh Institute of Marine Environment and Resources, Haiphong, Vietnam geosite while Que Kem and Turtle islands, etc are considered as geomorphological geosites Keywords Geoheritage Á Karst Á Geosite Á Geopark Á Geodiversity Introduction Geological wonders have been generally known as natural marvellous products Resulted from geological processes, geological wonders are diverse in size and have geoheritage values that should be preserved In a large scale, geological wonders can be geoheritage areas, containing several geodiversity elements that are geologically important or in a smaller scale, they can be geosites of heritage values (or geoheritage sites) For the public, these special natural resources in the world have been preserved in the form of geoconservation with geoheritage areas at all levels and used sustainably through the establishment of geoparks for geotourism, which have been linked into the Global Geopark Network (GNN) (UNESCO 2006; Fig 1) In the delimitation of areas of geoheritage values and the establishment of geoparks, the first thing is to recognise them as geosites that indicate great geological values It is considered to be the pre-condition for preserving geoheritage values in a legal framework as in some case these geosites can be destroyed and their values may disappear before establishing a geopark The geoheritage sites of Ha Long bay have been presented in some works (Tran et al 2003; Waltham 2005) This paper will present values of some geoheritage areas and geosites which are medium and small in size in the Cat Ba Islands, Hai Phong Province 123 Environ Earth Sci South cape of the Cat Ba island It is the southernmost part of the Cat Ba island, southeastwards the Cat Ba embayment, where there exist three famous beaches (Cat Co 1, Cat Co and Cat Co 3) (Fig 2a) for swimming and several field sites of special geological features considered as geosites with their own geoheritage values on the karstic landscapes or the chronostratigraphical boundary The rocky shore of this area is composed of thin and medium inclined layers of limestone, some of which were deformed strongly into folds as found commonly in the north of the Cat Co beach and eroded into deep notches and karren relief in the southwest of the Cat Co beach (Fig 2b) Devonian-Carboniferous chronostratigraphical boundary Fig Position of research area a Folds at the Hien Hao field site (Fig 5d); b a fenglin karst-type limestone island in Tung Gau (Fig 4a); c the field site of Brachipod and Crinoid fossils (Fig 6a, b, c); d the field site of Tetracoral fossils (Fig 6d); e a foot cave in the Lan Ha bay (Fig 5c); f Hon Que Kem, a notable fenglin karst-type limestone island (Fig 4c); g a view of the Cat Co beach (Fig 2a); h Devonian-Carboniferous boundary section (Fig 2c, d); i Karren relief west of the Cat Co beach (Fig 2b); j typical folds in the northeast shore of the Cat Co beach (Fig 3a); k apparent turbidite structures in limestone, Crinoid and Gastropod fossils (Fig 3b, c, d) The Devonian-Carboniferous chronostratigraphical bound0 00 00 ary is situated at the point of 20°42 58 N and 107°02 55 E near the Cat Co beach or in the south of the Cat Ba embayment, in a sequence of black cherty limestone and marl layers at the lowest 40 cm part of the Pho Han formation and on the Trang Kenh formation (Ta et al 2009; Fig 2c, d) An abundant assemblage of late Devonian microfossils (D3fm) was found at the lower part of the boundary, consisting of Uralinella bicamerata, Bisphaera malevkensis, Septabrunsiina sp., Eoendothyra communis, Quasiendothyra konensis, Q kobeitusana (Foraminifers); Renalcis ex gr nubiformis, Girvanella problematica (Algae); Palmatolepis gracilis gracilis, P gracilis sigmoidalis, P expansa (Conodonts), and early Carboniferous ones (C1t) at the upper part of the boundary: Siphonodella duplicata, Si quadruplicata, Si cooperi, Polygnathus communis communis, Pol purus purus, Pol inornatus inornatus, etc (Conodonts) The rocky shore northeast of the Cat Co beach Geoheritage areas A geoheritage area is defined as a distinct part of the geosphere of outstanding geological and geomorphological interest that needs to be protected against influences which could damage their substance, form and natural development According to the concept above, three areas of special geological significance in the Cat Ba islands, which are the South cape of the Cat Ba island (southeast of the Cat Ba embayment), Tung Gau (Gau shelter) and the Lan Ha bay, can be designated as geoheritage areas for their outstanding values (Fig 1) 123 00 It is about 100-m long with the coordinates of 20°42 56 N 00 and 107°03 01 E Limestone layers of the shore, deformed strongly into folds with turbidite structures, are attractive to so many visitors with their own inspirations, to both foreign and Vietnamese geologists and their students who want to discover these special geological values, and can be seen at no other places in Vietnam (Fig 3a, c) 00 00 At the point of 20°42 55 N and 107°03 04 E of the shore on the way to the Cat Co beach, turbidite structures are the most apparent and fossils of Tetracorals, Tabulates, Crinoids, Pelecypods and Gastropods are also commonly found (Fig 3b, d) Environ Earth Sci Fig A view of the Cat Co beach (a); Karren relief west of the Cat Co beach (b); the section showing the Devonian-Carboniferous boundary west of the Cat Co beach (c); black cherty limestone and marl layers at the Devonian-Carboniferous boundary west of the Cat Co beach (d) Fig Typical folds in the northeast shore of the Cat Co beach (a); early Carbonifeous fossils of Crinoids in the northeast shore of the Cat Co beach (b); apparent turbidite structures in limestone in the northeast shore of the Cat Co beach (c); early Carboniferous fossils of Gastropods in the northeast shore of the Cat Co beach (d) Tung Gau connecting to the Lan Ha bay in the east of the Cat Ba islands With dimensions of 5-km long and 0.5-km wide, it is the largest one in the Cat Ba—Ha Long region Compared to a short river, Tung Gau has appealed to visitors on boats with deep impressions for the clean salt water Tung Gau, a narrow shelter generated from submerging a karst valley during the Holocene transgression, is a northwest-southeastern elongate body of salt water 123 Environ Earth Sci Fig A fenglin karst-type limestone island in Tung Gau (a); a view of the Lan Ha bay (b); Hon Que Kem, a notable fenglin karst-type limestone island (c) Fig Hon Rua, a turtle-like limestone island (a); sometimes arch caves undercut through the small limestone island (b); a foot cave in the Lan Ha bay, where visitors often sail for on their kayaks (c); folds at the Hien Hao field site (d) body and well-preserved ancient and present sea-level markers engraving into the base of limestone mountains with pinnacles of diverse size Especially, there is a fenglin karst-type limestone island with high cliffs in the shelter (Fig 4a) 123 Lan Ha bay The Lan Ha bay is in the east of the Cat Ba islands and in the west of the Hang Trai and Dau Be groups of islands, and faces the open sea in the south It was at one time a part Environ Earth Sci Fig The field site of Brachipod and Crinoid fossils (a); Brachiopod fossils at the field site (b); Crinoid fossils at the field site (c); Tetracoral fossils at the field site (d) of the Cat Ba—Ha Long karst valley and then submerged in the Holocene transgression by which numerous karst pinnacles became bigger or smaller islands (Fig 4b) Limestone islands in the Lan Ha bay are diverse in size and shape, some of which are fengcong karst-type formations with summit elevations in a range of 100–200 m and fenglin karst-type ones with high cliffs At the base of the islands, sea-level markers, notches and some caves are commonly erosive forms of the relief, creating unique and beautiful landscapes surrounding the islands Some of the limestone islands in the Lan Ha bay are configured as animals, looking like a creeping tiger, a water drinking elephant or a turtle Especially, the two islands worthy of geosites are Hon Que Kem (an ice cream sticklike island, and compared to the Ha Long tower of stone) and Hon Rua (Turtle-like island), Hon Beo (Tiger-like island) Hon Que Kem Hon Que Kem is a notable fenglin karst-type limestone island with an elevation of about 100 m with high cliffs On the waterway to the Ha Long bay, visitors always admire this tapering island and feel that it seems to be gentle inclining from a certain view almost like the Pizza Tower in Italy (Fig 4c) Hon Rua Hon Rua is a crawling turtle-like limestone island on the Cat Ba–Ha Long ecotourist route that has attracted visitors’ attention to the marvellous configuration of nature (Fig 5a) Karstic caves Karstic caves in limestone islands are common and can be distinguished into three types with their own properties of morphology, chronology and formation conditions, which are phreatic caves, foot caves and marine notch caves The accessible phreatic caves at all levels (at least 10 m higher than the present sea level) in limestone islands are now bigger or smaller remnants of the very old caves that were segmented and then uplifted in the past stages The foot caves are common karst landscapes that have reached a stage of widespread erosion at the base level higher than the present sea level (Fig 5c) The marine notch caves are common and diversiform, created by the marine erosion They are often cliff notches, sometimes arch caves by undercutting into or through the small limestone island (Fig 5b) Geosites A geosite is known as a geological site that provides information on the evolution, structure properties of the Earth’s crust (Rohling and Thomes 2004) Every geological site of special geological significance can be designated as a geosite 123 Environ Earth Sci The field site of Brachipoda and Crinoidea fossils The field site is 80-m long and 8-m high, and 5.2-km distance from the Beo Harbour on the way through the Cat Ba islands, at the Tran Chau commune with the central 00 00 point of 20°44 49 N and 107°01 51 E (Fig 6a) It is composed alternately of weathered cherty limestone and marl layers of the Pho Han formation (D3-C1 ph) Especially, grey, sloping and thin-bedded cherty limestone contains numerous 1–15 mm long kidney-shaped pockets of marl, which sometimes are aggregated into layers with an extraordinary kidney-type structure At the field site, Brachiopoda fossils (Cyrtospirifer chaoi, C aff whitneyi, C triplisinosus, Rugosochonetes sp., Spinocyrtina sp., Camarotoechia aff baitalensis, Atrypinae gen indet.) with an individual length up to cm are exposed on the surface of layers (Figs 6b) Besides Brachiopods, smaller and larger crowds of Crinoids are found on the surface, all of which serve as an open museum for research, education and geotourism (Fig 6c) The field site of Coral fossils The site is about 30-m long and 10-m high, and 16 km from Gia Luan, in the Tran Chau commune and at the 00 00 central point of 20°45 20 N and 107°01 41 E It is composed mainly of black and thin to thick-bedded limestone containing shell debris of the upper part of the Pho Han formation (D3-C1 ph), in which colonies of Tabulates (belonging to the Order Syringoporids) and Tetracorals indicating the early Carboniferous period have been recorded for the first time by Doan Nhat Truong, Nguyen Dinh Huu (Institute of Geology and Mineral Resources of Vietnam) and the authors These coral fossils (Fig 6d) at the site are white, serving as adornments on the surface of black limestone layers, for which it can be selected for visiting and research in the field The field site of folds in Hien Hao 00 00 The fold site is at the point of 20°46 55 N and 106°57 44 E on the way from the Cai Vieng Harbour to the Cat Ba 123 National Park The site consists of limestone and cherty limestone layers, and thin-bedded marl of the upper part of the Pho Han formation (D3-C1 ph) On the wall of a cave of the site, these layers were deformed strongly into complex folds of all kinds as a painting, for which the site can be considered as a good example for the structure of carbonate formations (Fig 5d) Conclusion Besides famous values on the biodiversity, the Cat Ba islands contain special natural resources of the geodiversity with elements forming geotopes and geosites of geoheritage values The designation of geotopes and geosites in the Cat Ba islands is an initiative result for further studies towards the establishment of a geopark at the national level and a member of the GGN Acknowledgments Two of the authors, Tran Duc Thanh and Nguyen Huu Cu are grateful to the Project No 14 ‘‘Basic investigation and evaluation of spatial resources, ecological and geological wonders in Vietnam’s sea and islands’’ References Rohling H-G, Thomes MS (2004) Geosciences for the public: geotopes and national geoparks in Germany Episodes 27(4): 279–283 Ta HP, Tran TH, Tran DT, Nguyen HC (2009) Geodoversity in the Cat Ba islands—a base establishing a geopark J Sci Earth 31(3):13–21 (In Vietnamese) Tran VT, Le DA, Lai HA, Tran DT, Waltham T (2003) The Ha Long world heritage: outstanding geological values J Geol 277:6–20 (In Vietnamese) UNESCO (2006) Guidelines and criteria for national geoparks seeking UNESCO’s assistance to join the Global Geoparks Network Waltham T (2005) Karst and caves of Ha Long bay Int Caver 2000:24–31 ... South cape of the Cat Ba island It is the southernmost part of the Cat Ba island, southeastwards the Cat Ba embayment, where there exist three famous beaches (Cat Co 1, Cat Co and Cat Co 3) (Fig... development According to the concept above, three areas of special geological significance in the Cat Ba islands, which are the South cape of the Cat Ba island (southeast of the Cat Ba embayment), Tung... ary is situated at the point of 20°42 58 N and 107°02 55 E near the Cat Co beach or in the south of the Cat Ba embayment, in a sequence of black cherty limestone and marl layers at the lowest