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Environmental Earth Sciences ISSN 1866-6280 Environ Earth SciDOI 10.1007/s12665-013-2619-1

Geoheritage values in the Cat Ba islands,Vietnam

Ta Hoa Phuong, Nguyen Huu Cu, TranDuc Thanh & Bui Van Dong

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SPECIAL ISSUE

Geoheritage values in the Cat Ba islands, Vietnam

Ta Hoa Phuong • Nguyen Huu Cu •

Tran Duc Thanh • Bui Van Dong

Received: 3 August 2012 / Accepted: 21 June 2013

� Springer-Verlag Berlin Heidelberg 2013

Abstract Geological wonders have been generally

known as natural wonderful products. Resulted from geo-

logical 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 geologi-

cally 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 palaeon-

tological geosites. The folds of limestone layers in the

northern part of Cat Co 3 beach, with typical turbidite

structures in carbonate formations are considered as a

lithological geosite. The Devonian-Carboniferous bound-

ary near the Cat Co 3 beach is regarded as a stratigraphical

geosite while Que Kem and Turtle islands, etc. are con-

sidered as geomorphological geosites.

Keywords Geoheritage � Karst � Geosite � Geopark �Geodiversity

Introduction

Geological wonders have been generally known as natural

marvellous products. Resulted from geological processes,

geological wonders are diverse in size and have geoheri-

tage values that should be preserved. In a large scale,

geological wonders can be geoheritage areas, containing

several geodiversity elements that are geologically impor-

tant 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 geoheri-

tage 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 pre-

sented 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.

T. H. Phuong (&) � B. Van Dong

VNU University of Science, Hanoi, Vietnam

e-mail: tahoaphuong@gmail.com

N. H. Cu � T. D. Thanh

Institute of Marine Environment and Resources,

Haiphong, Vietnam

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DOI 10.1007/s12665-013-2619-1

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Geoheritage areas

A geoheritage area is defined as a distinct part of the ge-

osphere of outstanding geological and geomorphological

interest that needs to be protected against influences which

could damage their substance, form and natural develop-

ment. According to the concept above, three areas of spe-

cial 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).

South cape of the Cat Ba island

It is the southernmost part of the Cat Ba island, south-

eastwards the Cat Ba embayment, where there exist three

famous beaches (Cat Co 1, Cat Co 2 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 chro-

nostratigraphical 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 3 beach and eroded into deep notches

and karren relief in the southwest of the Cat Co 3 beach

(Fig. 2b).

Devonian-Carboniferous chronostratigraphical boundary

The Devonian-Carboniferous chronostratigraphical bound-

ary is situated at the point of 20�420580 0N and 107�02

0550 0E near

the Cat Co 3 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, con-

sisting of Uralinella bicamerata, Bisphaera malevkensis,

Septabrunsiina sp., Eoendothyra communis, Quasien-

dothyra 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 3 beach

It is about 100-m long with the coordinates of 20�420560 0N

and 107�030010 0E. 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).

At the point of 20�420550 0N and 107�03

0040 0E of the shore

on the way to the Cat Co 1 beach, turbidite structures are

the most apparent and fossils of Tetracorals, Tabulates,

Crinoids, Pelecypods and Gastropods are also commonly

found (Fig. 3b, d).

Fig. 1 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 2 beach (Fig. 2a);

h Devonian-Carboniferous boundary section (Fig. 2c, d); i Karren

relief west of the Cat Co 3 beach (Fig. 2b); j typical folds in the

northeast shore of the Cat Co 3 beach (Fig. 3a); k apparent turbidite

structures in limestone, Crinoid and Gastropod fossils (Fig. 3b, c, d)

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Tung Gau

Tung Gau, a narrow shelter generated from submerging

a karst valley during the Holocene transgression, is

a northwest-southeastern elongate body of salt water

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. Com-

pared to a short river, Tung Gau has appealed to visitors

on boats with deep impressions for the clean salt water

Fig. 2 A view of the Cat Co 2 beach (a); Karren relief west of the

Cat Co 3 beach (b); the section showing the Devonian-Carboniferous

boundary west of the Cat Co 3 beach (c); black cherty limestone and

marl layers at the Devonian-Carboniferous boundary west of the Cat

Co 3 beach (d)

Fig. 3 Typical folds in the northeast shore of the Cat Co 3 beach (a);

early Carbonifeous fossils of Crinoids in the northeast shore of the

Cat Co 3 beach (b); apparent turbidite structures in limestone in the

northeast shore of the Cat Co 3 beach (c); early Carboniferous fossils

of Gastropods in the northeast shore of the Cat Co 3 beach (d)

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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).

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

Fig. 4 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. 5 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)

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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 stick-

like 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 prop-

erties of morphology, chronology and formation condi-

tions, 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 geologi-

cal site of special geological significance can be designated

as a geosite.

Fig. 6 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)

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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

point of 20�440490 0N and 107�01

0510 0E (Fig. 6a). It is com-

posed 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 2 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

central point of 20�450200 0N and 107�01

0410 0E. It is com-

posed 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

The fold site is at the point of 20�460550 0N and 106�57

0440 0E

on the way from the Cai Vieng Harbour to the Cat Ba

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 geoheri-

tage 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 investi-

gation and evaluation of spatial resources, ecological and geological

wonders in Vietnam’s sea and islands’’.

References

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Ta HP, Tran TH, Tran DT, Nguyen HC (2009) Geodoversity in the

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