Fossil Biodiversity in the Limestones of Thailand: a Cornucopia of Information About the History of Life
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NAT. NAT. HIST. BUL L. SIAM Soc. 53 (1): 33-70 ，2005 FOSSIL BIODIVERSITY IN THE LIMESTONES OF THAILAND: A CORNUCOPIA OF INFORMATION ABOUT THE HISTORY OF LIFE Henri Henri Fontaine 1， Sirot Salyapongstl and Varavudh Suteethorn 3 ABSTRACT In In Th ailand ，foss iI s are common and diverse. 百 ey come from bo 血 terrestri aI and m 紅泊E environments.τ 'h ey belong to many t泊施 periods beginning with the Cambrian ，血 us spann 泊g more 血an 500 m iII ion years (白 e Phanerozoic eon). 明lis rich past emerges 台。 m extensive pub Ii shed data and is st iII very in 加 esting to explore. 明lis pub Ii cation concems only foss iI s included in Ii mestone deposited in 白巴 seas of the pas t. Li m 巴stone is widespread 泊百ailand and of various 格的. Marine floras (aI gae) and faunas 釘宮 in abundance at many Ii mestone exposures 飢 d their skeletons ar 草加 impo 此釦I component component of 血.e limestone. 百ley give a deep-time perspective on the evolution of the Ii fe in 出e seas of 血 .e past. τ'h e Ii mestones of Th aiI and are not res 町icted to 出 e widespread exposures visible on th 巴 land. land. Th ey have been found by hydrocarbon exploration at varjed depths and in different are 鎚. Permian Permian Ii mestone has been reached by we Il s under the Kh orat Plateau and its extent has been determined determined by seismic interpretation; it is widespread (for instance ， see MOURET ， 1994). Th is pub Ii cation is concemed only wi 出 l加 estones exposed at ground surface. Limestone is a gene raI term for diverse types of rocks ，deposited in different environments. Before describing their their biodiversity ，we discuss the orig 泊。f 出e Ii mestones of τ'h a iI and. Key words: Diversity ，foss iI s，limestone ，m 悩 sextinctions ，paI eog ωgraphy， ，s回 .tigraphy ，百 lailand L Th庄 ESTONES OF THAILAND In Th ailand ，limestone (Hi n Pun in 百lai language) is a rock very widespread at the surface surface of the land all over 血e country. It makes up small to very large hills ，which are locally locally numerous ， for instance north of Saraburi between Lopburi and Muak Lek. Beautiful landscapes have been carved by erosion ，producing a marvellous castellated topography. Caves 紅 .e common. In addition to the prominent hills ，smalllimestone outcrops 釘 e scattered at at ground surface.τ 'h ey are not visible in the topography ，but easily seen in the banks of the the rivers as well as in ponds or other holes dug by f，創 mers. Li mestone is known by everybody and m 佃 y hills 紅 e called Kh ao Hin Pun or simply Kh ao pun (= Limestone Hi ll). In other places ， the names show the imagination of the local peοple; they describe the peculi 釘 topography of the limestone (k 紅 st topography; see Figs. 1，4 to 6). Many hills are called Kh ao 百lam or Kh ao Kh uha (= Hill with a Cave). A qualifier qualifier may be added because of 組 underground river (Khao 百四n Nam Lot) ，a peculi 釘 18 18 aIl ee de la Chape Il e，92140 Clamart France 2143 2143 Moo 6， Soi Pinnakom 4，Borommaratchachonnari Road ， Bangkok 10170 ，Th aiI and 30 eo log ic aI Survey ，Dep 釘飢lent of Mi ner aI Resources ，Rama IV Road ， Bangkok 10400 ，τ'h aiI and Received Received 8 November 2004; accepted 16 May 2005. 33 33 34 HENRI FONTAINE ，SIROT SAL Y APONGSE AND V ARA VUDH SUTEETHORN feature feature (Kh ao Suwana Kh uha = Hill of the Gold Cave) ， or the size (Kh ao Th am Yai or Khao Th am Luang = Hill of the Large Cave). Kh ao Laem indicates a pointed hill. Phu Tum means a bud shape; it is a common name in Loei Province. Doi Sam Sao (Hill of the 百rree Triangles) ， between Chiang Dao and Phrao ，displays 3 angular points of limestone standing standing out from its top. Li mestone hills are commonly steep-sided; Khao Pha Daeng is a hill with a red cliff ，Khao Pha Dam is a hill with a black cliff ，Khao Pha Lat is a hill with with an inclined cliff ，Kh ao Lak is a hill surrounded by cliffs and showing a milestone shape. shape. Khao Wong is a hill with a sinkhole at its centre. Wh en the limestone is clearly bedded ，it is compared to a pile of folded clothes (Khao Phap Pha). Kh ao Phap Pha is a common name in Surat 官 lani Province (see Fig. 3). Th e names of other hills are focussed on the flora or the fauna of the hills: Kh ao Ruak (Hill (Hill of a small kind of bamboo) ，Kh ao P耐ik (Hill of the Red Pepper) ，Khao Pha Fai (Hill with with a cliff and cotton) ，Kh ao K wang (Hill of the Deer) ，Kh ao Th am Ik ea (Hill of the Cave of of the Bats) ，Kh ao Lan (Bald Hill ，without vegetation). Many species live in karst topography at at the surface of the hills or in the caves which are common in limestone hills. Types of Limestone Li mestone is commonly grey to black ， but locally it may be white ， yellow or red. It is is massive or thinly to thickly bedded (Figs. 1 to 6). is It fine- to coarse-grained. From a chemical chemical point of view ，it is almost pure carbonate of calcium deposited in a clean environment; environment; this is the case at many localities of Th ailand. However ，this is not the rule; clay clay and even sand locally occur in the limestone ，occasionally in such a quantity that the appropriate appropriate names of the rocks become calcareous shale or calcareous sandstone. Limestones are are polygenetic; they were deposited in differing environments which will be described below. below. In these different types of rocks ，fossils are commonly well preserved. Their abundance abundance dis 佐ibutions and their diversities reflect the images of ancient living communities ， with with some fidelity. After After its deposition ，limestone has been transformed by different diagenetic processes which were destructive or constructive. It may have been dolomitized; then ，it displays a fair fair content of magnesium. In the field ，dolomitic limestone is easy to recognize because its its surface is not smooth ， but looks like elephant skin. Dolomitization commonly destroys the the fossils and precise identifications are impossible. Wh en limestone has been heated by intrusion intrusion of igneous rocks ，it is recrystallized and the fossils 紅 e again largely or entirely destroyed. destroyed. In dolomitized and recrystallized limestones ， the original characters 訂 'e obscured or or erased. Th ese rocks are not helpful in reconstructing life of the past and they are locally difficult difficult to date. They are fortunately restricted to small areas of Thailand. Depositional Depositional Environments Limestone Limestone has been deposited almost everywhere in τbailand 加 marine environments ， and commonly in distinct subenvironments of shallow seas. An exception has been recognized recognized (IW AI ， 1972 and 1973) ，a few limestone beds at the base of the Kh orat Group in in Northeast Th ailand have been considered lake deposits; they 紅 'e thin ，less 由加 10 cm thick ， with the exception of a bed reaching 2m in thickness. Th is limestone is practically barren barren of fossils. Lacustrine faunas ぽ e commonly of low diversity. Such deposits are FOSS IL BI OD IVERS ITY IN T H E L1 MESTONES OF TH A IL AND 35 Figll re 1. Lim es ton e hill s nea r Na ll1 Pi ya ng Din Wa ter fa ll sO lllh 01' Wa ng Sa phll ng in Lo巴iPro vi nce パlorlh eaS lell1 T hail a nd. Th e li ll1 eS l0ne，Ea rl y Permi an in age ，co nl a ins ll1 any fo rall1 ini fe ra (s ll1 all erf oramini fe raa ncl fu sulin ace an s). It is al so ri ch in ca Ic isph er es a nd T ll bip /り刊 s frag ll1 enl s; co rals are ral 巴 (FON Tfl INE ti AL. ，2002 ，a nd in pl 巴parati on) Fig ur e 2. B edd ed lim 巴stone atK oS iC hang nea rV as hir av lll Brid ge. K oS i C hang is an isla nd 01' lh 巴 north easlel 日 part part of th e Gul f0 1' Th ail and . Th 巴 li ll1 es lone is part ly rec rys talli ze d ancl poo r in foss il s (Sfl LYfl PONGSE ET A L.， 20 02); it is co nsid erecl O rdov i cian in ag 巴 36 HE NR IF ONTA IN E，SIR OT SALY AP O NGSE AN D V A RAVUDH SUTEETI -IORN Fi gllr es 3. 8 edded lim es ton巴s at two diff ere l1l hill s. a: a: Permian li l1l es ton e hill of S lI rat T ha ni Pr ovin ce in Penin s ular Th ail and . T he lim es ton e is c1 ea rl y bedd e d. II is cO l1l par ed to to a pil 巴 of fold ed c1 01h es (Phap Pha ) and ca ll ed Kha o Phap Pha (Hill of th 巴 Fo lded C loth 巴s) . lt is loca ll y ri ch in f oss il s ，blll of of a low di ve rsil y .