1. home and garden

Vol. 26
CCOP Techical Bulletin
Dece,nber 1997
STRATIGRAPHY OF THE LAMPANG GROUP IN CENTRAL
NORTH THAILAND: NEW VERSION
Pol CHAODUMRONG I and Clive F. BuRRETI' 2
I
Geological Survey Division, Dcparunc:111 of Mineral Rcsot1n:cs, Bangkok 10400, Thailand
Geology Depnrt111ent, University of Tasrnania, GPO Box 252[' flobart, Tasn1ania, Australia
7001
2
ABSTRACT
Thl! Lan1pang Group in central north Thailand, basl!d on stratigraphy, fossils, lithofacies relation­
ships and provenance, was fanned in two adjacent sub-basins, nmnely the Lan1pang in the west and
the Phrae in the east. These two sub-basins arc sirnilar in their sedin1ents and sequences, consisting
mainly of red beds, platfonn limestones and deep 1narinc turbidites, but are very different in age.
The Lainpang sub-basin was fanned during the Early Triassic to early Late Triassic and contains
Daonell ,a, Paracrachyceras, Costatoria and Claniia, while the Phrae sub-basin was fanned fron1 in
Late Triassic and contains mainly Halobia. 111is classification contrasts sharply with those of Piyasin
(1972) and Chonglakmani (198 l). The Lainpang Group proposed here consists of seven forma­
tions, in ascending order the Phra That, Pha Kan, Hong Hoi, Doi Long, Pha Daeng, Kang Pia and
Wang Chin. The firsc five fo1mations occur in the Lampang sub-basin whereas the last three fom1a­
tions arc in the Phrae sub-basin. Only the Pha Dacng Fonnation is widespread over both sub­
basins. Red bed forn1ations (Plua That and Pha Daeng) and limestone formations (Pha Kan, Doi
Long and Kang Pia) fanned in relalive!y narrow areas while 1nudstone forn1ations (Hong Hoi and
Wang Chin) occurred widely in the basins. Time equivalence ainong the formations is con1mon.
This proposed stratigraphy is consistent with collision between the Shan-Thai and Indochina ter­
ranes which was ended during Late Triassic Period.
JNTRODUCTION
Ainong three Triassic belts in 'rhailand, the sequences in central north Thailand of the
central belt display best exposure ranging in age fron1 Lower to Upper 1�riassic (Fig. 1), and have
long been used as a crucial evidence for tcrranc an1algan1ation in Thailand. These sequences
were folded and faulted during the late Mesozoic and Cenozoic Eras, resulting in complex geo­
logical structures, steep dips and oroclinal "S-shapcd" structural trends. They \verc first exa111ined by Pitakpaivan (1955) and named the Lampang Group by Piyasin ( 1972). Although stratig­
raphy of the Lampang Group was revised several times (Liengsakul, 1979; Chonglakmani, 1981;
Wolfart, 1987; see Table I), these authors considered sequences of the La,npang Group in the
Lan1pang area or "Lampang sub-basin" and in the Phrae area or "Phrae sub-basin" as having the
same stratigraphic level with ages younging eastward.
Recent detailed field studies on stratigraphy and sedin1ento!ogy, including 24 measured
sections and hundreds of reconnaissance localities, clearly shO\VS that the sequences in the Phrae
sub-basin are in fact different and younger units than those in the Lampang sub-basin. It is,
66
P.Chaodumrong and C.F.Burrett
* Rhoetlan
* Low. Norlon
..
¥- Mid.- Up. Cornlon
Low. Corn!on
"' Lodinlon Jo Mid. Triassic
• Anis Ion
0 Scyth!otJ
0
Low. Trloss!c
Up. Permlon
.
..
�
�
.,..... [;al
Measured
sec!lons
()
GI
MoITT Sludy Areo
1111
filllill
GI
Won11 Ctiln Fm,
Konq Pio An
Pho Doen,;i Fm
Ool LonQ Fm
t--k>r>Q Ho1Fm
Pho Kon Fm
Phro Tl'lo! Fm
GI
�
,::
0
0
...,
0
Volcanic� {Pm-Tr or 10l.!r-..erl
Fig. I Geological 111ap of the Lainpang Group in central north Thailand \vith distribu
tion of rock ages ob!ained from dated fossils. Note each block represents
an area of I 50,000 scale topographic 1nap sheet. Three Triassic belts in
Thailand are shown in the inset inap;west belt (I and 2), central (3 and 4),
and east belt (5).
67
STRATlGRAPHY OF THE LAM PANG GROUP
Tab!� i Slr.Higraphic 1ao1ne11claLure clcvclop1ncn1 of the La111pang Group
r----s,=�="�," --�",· =,'"',= �.o19'12
0Ch
. .-0a�m=.,=,,�,"·
K"·�O�a=��""'·-r-sw"ol�f�=
�,=.elg�
--�-----y-a�,
�,�-,��
, u�o�Y�-=
7 =
c' ;i
1979
mani
198!
1937
m.i.,i ;,.r;d
Tiyq:un
1985
--�
, �,,�,'.,�,.,-----!
L"==,��, �",.=.
=
1-- -"S,-p"P:-,,�.cch,"-, l!o'--m-.
r.iani
t:env,sed
Ngao· t1:1aYao- C11angRii Long • W:u.gCi\;,_
198? a.b
"l..:im .nr. Subta:s,n"
"Phr�e
Subb:.sfa'
Pr.� Tlp
;;.d
l :· .::Tem
L' ?.1a D�ong
Pl,� :).a;ni;
'
,A
,,
'
G
Pll> Cacag, Tiung !..\le
t:-c, Chang L Doi Cha�g! L Doi Long
.
i'�
/7iJa(
Hong J-:c-i M Hong_ Hoi M Hong Hoi
P11a Ka
P!lri T�a1
A,
N
G
?�a K:n
"
Doi Cb�e�
PhraTha!
G
Phra Toa,
A
A
N�
G
Case
f'ba Ka"
Mia
L,l:/.1<11'1
I
Temple
,..,,..,, n,,,1
Siwu;
F1>1
therei"ore, the purpose of this p3pc-r to clarify and Jcv1sc the iithosu-atigraphic classification or
the group.
PREVIOUS STRATIGRAPHIC NOMENCLATURE: SYNTHESIS
The traditional lithostraugraphic nomeuclalural sche1nes used for the Lampang Group are
thos� of Piyasin( l 972) and Chonglak1nani(1981 ). (-Iov,•cvcr. non1cncl.aLure of the tv10 carbonate
fonnations within the Lan1pang Group in the Lan1pang sub-basin is in a very confusing state
with the nan1es Pha Kan, Doi Chang, and Doi Long being used in a variety of v,:ays(Tablc l).
The "Doi Chang" is a name of mountain on the easte111 flank of the Nlae Nloh lignite pit. Piyasin
( 1972) mapped the rocks at "Doi Chang" as Pha Kan Formation. However, he also used Doi
Chang for Lhe name of another, younger, !in1t.:sto11c fonnation. Chonglaktnani (1981) substi­
tuted the names Doi Chang and Pha Kan Fonnations of Piyasin (1972) for Doi Long and Doi
Chang Fonnations respectively. Because of the conrusion surrounding the n.arnc Doi Chang and
in accordance \vith the interna[ional stratigraphic guide (Hedberg,1976, p. 19,40) this nan1e is
abandoned in this study. It is emphasized that u�agc of lhese fonnation nan1es should be re�
strictcd to only in the Larnpang sub�basin \vhere they \vcn; originally 1nappc<l and defini.::d.
Licngsakul (1979) and Chongl.akmani (198 l) separated the Pha Daeng Fonnation from tht:
Lan1pang Group(Tablc l). Their reasons ,vcrc based 111n.inly on the red coloration and the
unconforn1ily at the base of the Pl1a Daeng Fonnation. I-lowt:.vcr. the unconformity is considered
here as local rather than regional as evidenced by local occurrence of limestone conglon1erate.
Besides, the Pha Daeng Forn1ation has lithology sin1il.ar to the Phra That Formation. In this
study, therefore, the Pha Daeng FormaLion is considered as belonging to the La,npn.ng Group.
68
P.Chaodumrong and C.F.Burrett
PROPOSED STRATIGRAPIDC CLASSIFICATION OF TIIB LAMPANG GROUP
Nev1!y proposed stratigraphy of the Lampang Group is sho\vn in Figure 2. The Lampang
Group in central north Thailand was formed in two adjacent sub-basins nan1ely the Lan1pang in
the west and the Phrae in the east. The former was formed much earlier during Early Triassic
(Griesbachian) to early Late Triassic (middle Carnian) and contains Daonella, Posidonia,
Paralrachyccras, Costatoria and Claraia, \Vhereas the latter contains rnainly Halobia, Posidonia
and Pa/acocardiw (Chonglakmani, 1981) indicating early Late Triassic (middle Camian) to Late
'friassic (early Norian). The Lampang Group consists of seven fonnations, in ascending order
the Phra That, Pha Kan, Hong Hoi, Doi Long, Pha Daeng, Kang Pia and Wang Chin. The first
five forn1ations occur in the Lampang sub-basin \vhereas the last three formations are in the
Phrae sub-basin. Only the Pha Daeng Formation is widespread over both sub-basins. In most
areas, the group unconformably overlies inferred Fermo-Triassic volcanics and both
unconforn1ably and conformably overlies the Permian strata. The confonnable contacts occur
particularly in the Lampang sub-basin. It is both conformably and unconformably overlain by
red beds of possibly Jurassic age. The maximu1n thickness is estimated at 3000 111 and 2000 m in
the Lampang and Phrae sub-basins, respectively.
PHRA THAT FORMATION
The Phra That Formation takes its name from Phra That Muang Kham temple, 12 km
southeast of the town of Lampang. This formation occurs only in the Lampang sub-basin.
Synonym : Phra That Formation (Piyasin, 1972; and Chonglakmani, 1981) and Phra That
Muang Kham Formation (Bunopas,1981), but only in the Lampang sub-basin.
Lithology : Lo\ver part the Phra That Formation is characterized mainly by alternating beds of
feldspathic sandstone, conglomerate, siltstone and mudstone. These are mainly red, thin to thick
and nonparallel hcds with normal graded beds. Fining-upward sequences, cross-stratifications
and mottled texture are common. In general, fine-grained elastics increase up the sequence.
Conglomerate clasts are 1nainly volcanics. The upper parl of the formation generally consists
n1ainly of gray 1nudstone and rare thin- to thick-bedded gray sandstone and limestone. Fossils.
particularly bivalves, often occur in this upper part.
Thickness : 1'hc thickness ranges from 90 to about 650 m. The 1neasured sections at Phra That
Muang Kham temple and km post 31.6 to 31.9 on the Lampang-Denchai highway are 90 and 87
111 thick, respectively (Figs. 2). In the Ban Tha Si area the thicknesses measured by various
authors are different, 200 m by Piyasin(l972), 650 m by Chonglakmani (1981), and 383.5 m by
Liengsakul( 1979).
Paleontology and age : The age ranges fro,n early Scythian to early Anisian. At Ban Tha Si, the
limestone beds in the lo\ver part of the forn1ation contain Eumorphotis 111ultifon11is of Scythian
age while rnudstone in the 1niddle part contains a Costatoria assemblage of early Anisian age
STRATIGRAPHY OF Tl IE LAMPA'.'l"G GR{)UP
Lampang Sub-basin
69
Phrae Sub-basin
[[g Kang Pia Fm.
E] Pha Daeng Fm.
EJ Doi Long Fm.
III] Hong Hoi Fm
� Pb.a Kar. Fm.
;:] Ptlfa That Fm.
� Strati. Erealc
Fig.2 Si1nplified stnltigraphic J\.'."!J;lonships \Vithin the L<unpting Group
(Chonglak1nani, I 98 1 ). The conodont Neospalhodu.•,; p;Jkist.1nensis of Early Triassic age
(latest Dienerian- earliest S1nithian) has beer1 t:xtracted fro1n interbedded lin1estone cropping out
on the gravel road just a fe'.V n1eters \vest of the Phra Thu Pha li1nestone quarry (Carey et al.,
1995).
Reference locality : The sequences at the type locality, Phra That Muang Kha1n temple, are
poorly exposed . .A.n additional reference locality ls proposed here at km 3 1 .6 to 3 1 .9 on the
La1npang-Denchai high\vay.
PHA KAN FORMATION
The Pha Kan Fonnation takes its. nan1e fro1n Doi Pha Kan north of Ban Tha Si and \\las
proposed by Piyasin ( 1 972). This fonnation occurs only in the La111pang sub�basin.
S) nony1n : Pha Kan Fonnation ( Nhich occurs only in the La1npang sub-basin) of Piyzisin
( l 972), Bunopas (l 981) and Wolfart (1987): Doi Chang Formation (only in the Lampang sub­
basin) of Chonglakn1ani (198 1), and Chonglak111ani and Kcnvised ( 1987 a, b). It is possibly
synonyn1ous \vith tht:: t'I unit or Bau,n and 1-Iahn (1977) Lo the \Vest of the Phayao Jrca.
1
1
Lifholog�v : The Pha Kan Forn1ation consists of three lin1csconc n1crnbers and one intervening
elastic n1en1ber: \\1iang Sa ...van, Cbang Garb, Cave Temple. and Muang Kham Men1be.rs. In
some areas, the forn1ation is JTiade up ahnost entirely ur lin1L::stonc: in the other it has an interven­
ing elastic member (Table I and Fig. 3).
Wiang S.:nvan lvfe.n1l>er : This takes its name fron1 the \Viang Sav,,an temple ln lv1ac Moh vilta_g�.
It is char3cterized by n.I1c111ating beds ofo11coli1ic packstonc to v.'.ackcstone a11d \Vackeslone rviih
n1inor intcrbcdded shale. In son1e areas, al!ochcins such as da�y-cladaccans, bioclasts, ooids or
70
P.Chaoduinrong and C.f.Burrett
A
F
Ternpy
/
Gorb
Chong
0
Phro
T hat
Fm.
r:'";l
ig�
Fig. 3 Lithostratigraphic correlations fron1 the ineasurcd sections of'l'he Plua That and
Pha Kan Fonnations. c and e on the Larnpang-Denchai highway.
A) Phra 1l1at Muang Khan1 temple, B) Nopawong quarry, C) km 22.8, D) Doi
Chang sections, E) kin 3 1 .6-3 1 .9, F) Doi Pha Khan quarry, and G) Pha Thu Pha
quarry and sacred place.
intraclasts prcdo1ninate. Most limestones are dark gray to gray, thin- to thick-bedded of \vavy­
and nonparallel-bed type but in some places \Vavy and parallel beds occur. Lateral facies changes
arc co1nn1cH1. The upper boundary is taken as the top of the thick oolitc unit exposed at Phra 1'hat
Muang Khan1 tc1nple or as the top of the thick oncolite unit (base of thick elastic unit) exposed
at Doi Chang.
STRATIGRAPHY OF THE LAMPANG GROUP
71
Chang Garb Mernbcr : The 1nen1ber takes its na1ne fron1 Huai Chang Garb at Doi Chang and is
characterized by alternating beds of sandstone, siltstone and nu1dstone vvith minor limestone
beds (Fig. 3). Sandstone and siltstone are gray, laminated to thick-bedded and medium to coarse­
grained. Mudstone is gray to greenish-gray with conchoidal fracture. Li1nestonc is 1nainly thin­
to medium bedded packstone and grainstone and consists n1ostly of ooids with sonic oncoids
and pe!oids. Cross-stratification is co1n1non in the sandstones, siltstoncs and oolites, and in
some instances it is represented by oriented fossils. Bivalves as well as a benthic fauna are
common and arc aggregated as lenticular beds within sornc sandstone successions. These bivalves
con1monly occur convex-side up. 1'his 1nc1nber n1ay h1,; \Videly distribuled in the area bet\vccn
Phra That Muang Kham te1nple and Doi Chang, and sho\vs no significant exposure in Ban Tha
Si and Phra Thu Pha areas. Its upper boundary is taken as the base of the first tnassive limestone
unit.
Cave Temple Men1bcr : This 111cmber is named after the Nera1nil Cave Ten1ple east of Mae
Moh. It is distinguished from the other two limestone members by its physical appearance of
massive and light gray color. It consists of packstonc, grainstone, wackestone and boundstone,
containing mainly allochems of bioclasts such as bivalves, coral, algae and echinoderms, and
intraclasts. Karst is extensively developed. The Cave Ternple Men1ber is widely distributed in
Doi Chang, Neran1it Cave temple, Doi Wiang I-Io, south\varcl to kin post 19 on the Lan1pang­
Denchai highway, and at Ban 'fha Si north\vard to Pha Thai Cave.
Muang Kham Member : This member takes its name from Huai Muang Kham situated on the
eastern side of the Phra That Muang Kha111 tc1nple. It is characterized by alternating beds of
oncolitic packstone to \Vackestone, peloida !-skeletal packstone to grainstone, wackestone and
lime mudstone (Fig. 3). Shallo\ving-upward sequences are com1non. It is gray to dark gray,
having thin to thick beds of \vavy and nonparallel bed type. Fossils consist of foran1inifera,
echinoderms, ostracods, gastropods and bivalves. Oncoids are generally large ( l -3 cm in diameter)
but small oncoids (<I cm) also occur locally. Lithologically, this member is similar to the
Wiang Sawan Member but can be easily distinguished by its stratigraphic position; this me1nber
overlies the Chang Garb Men1bcr. In the area studied this rncn1hcr crops out n1ainly in Phra That
Muang Kham te1nple and adjacent areas.
Thickness : The formation thickness ranges from 400 to 640 m. A thickness of 640 m was
1neasured at the Phra That Muang Kham temple, 465 m at the Doi Chang section and 400 m at
the Phra Thu Pha section.
Paleontology and ,1ge : Lin1estone of the Wiang Savvan Men1bcr at km 9.6 on Lan1pang- Denchai
highway contains the conodont Ncospathodus pakistanensis of the Early Triassic (Carey et al.,
1995 ). The fossils collected by Pitakpai van ( 1955) in Mac Moh area and identified by
Chonglakmani (1981) as the floll:.111di1cs-B;1/ntonitcs zone , and Spirigcra sp. of late Anisian age
may be correlated to the Chang Garb Men1ber. The Chang Garb 1nudstones at Phra That M uang
Kham ten1ple section also contain Pteria, Pccten, Eleganti:.i, Euniorphotis, Entoliurn, Costatoria
of Anisian age.
Reference section : The n1easurcd sections al the Phra ·rhat Muang Khan1 tc,nplc, Doi Chang
and the Phra Thu Pha li1ncstone quany are rcgarthxi as retCrcncc sections (hypostratotypcs) of
the Pha Kan Formation.
72
P. Chao<lumrong and C.F.Burrcll
HONG HOI FORMATION
With regard to Pitakpaivan (1955) who proposed the name " Hong Hoi Shale and Sand­
stone" to represent sandstone and grayish-green shale containing an1monoids and bivalves in
the Mae Moh area, Piyasin ( 1972) named it the Hong Hoi Formation. This formation occurs
only in the Lan1pang sub-basin (Fig. l ).
Synonym : Hong Hoi Formation (only in the Lampang sub-basin) of Piyasin ( 197 2 ) .
Chonglakmani ( 198 1 ), Liengsakul ( 1979) and Bunopas ( 198 1 ); Hong Hoi Shale and Sandstone
(Pitakpaivan, 1955; and Keereevat and Suensilpong, 1965).
Lithology : The Hong Hai Fonnation is that sequence generally lying between the limestones of
the overlying Doi Long Formation and the underlying Pha Kan Fonnation. However, in some
places it ,nay be confonnably overlain by the Pha Daeng Formation, conforn1ably underlain by
the Phra That Forn1ation or Permian strata. It consists mainly of fine-grained turbidites that can
be subdivided into three rncrnbers: the Tha Si, Mae Duin Sandstone and 1-Iuai Muang (Fig. 4A,
B).
Tha Si Men1ber : ·rakes its name from Ban Tha Si and is characterized by mudstone and minor
intercalated sandstone, conglomerate and limestone. Mudstone is gray to greenish-gray and
laminated or structureless, and commonly displays conchoidal fractures. 'fhe lan1ination is formed
by interbedding of mudstone and la,ninated siltstone. Sandstone is thin- to medium bedded,
fine- to coarse-grained and often normally graded, and frequently contains feldspar and fossil
wood fragments. This member is exposed along the Lampang-Ngao (Phaholyothin) highway.
Its upper boundary is taken as the base of a thick sandstone bed.
Mae Durn Sandstone Me1nber : This takes its nan1e from Huai Mae Dum where good exposure
occurs. It consists mainly of thin- to n1assively bedded, gray feldspathic sandstone and n1inor
conglomerate and mudstone. Sandstones display sharp contact with the underlying mudstones.
Fossil wood fragn1ents are co1nn1on in the lower part of sandstone beds. Graded beds are con1rnon but flute and channel structures are rare. Conglon1erates are both clast-supported and ma­
trix-supported and clasts are made up n1ainly of volcanics and in some cases, limestones. Mud­
stoncs arc generally thin units, but can be thick and are interbeddcd \Vith laminated to thin­
bedded sandstone to siltstone, and fossils of the a1nmonoids Paratrachyceras and the bivalves
Posidoni.1 and DaoncJJa are usually cornn1on. Upper boundary of the n1c111ber is taken as the
base of the first overlying limestone bed.
Huai Muang Men1ber : Its nan1e is borro\ved from Huai Muang where good rock exposures
occur. It is characterized by n1ainly gray to greenish-gray n1udstone and shale with intercalation
of lirncstone beds or nodules siltstone in the upper part of the sequence \vhcre it is overlain by
limestones of the Doi Long Fonnation. In thin section, lin1estones com1nonly contain thin-shelled
fossils. There arc also so,nc papery clayshale, sandstone and pebbly sandstone beds.
Thickness : 'fllickncss of the fonnation at type locality along Huai Mae Dum through Huai
73
STRATIGRAPHY OF THE LAM PANG GROUP
"'
,
,�
�
"
,
0
A
Jj
5
"
:,
>
m'4 <n<>,
di,h<<l'<d 1><,J,
.,.,,..,cs,or..:,.;00
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m.d"J "'"1.,ct no.uc
<IJp,cl.,tJr,,o,c
uJtt>ln,c'
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.:
-
-
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e
\
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Fig.4 Lithostratigraphic column of the Hong Ooi (A-B) and Wang Chin Fonnations
(C-F). C,E and F on the Lan1pang-denchai highway.
A)Hnai Mae dum to Huai Muang, B) km4.2 on the canal road of lhe Mac Chang
Dam, C) krn 45.5- 46.5, D) km 35-33.9 on Rong kwang - Ngao highway,
E) km 54.8-55.9, F)km 66.3-66.7.
2
74
P.Chaodumrong and C.F.Burrett
<..,1MPANG
0
100 m
E
0
Fig. S Lilhostraligraphic correlations fro1n the n1easurcd sections of the Doi Long Fonnation.
A) Ban Pang La, B) Doi Pha Bong, C} Doi Long, D) Doi Huai Long, and E) Doi Nok.
Muang section is 700 n1.(Fig. 4A),\vherc the lo\vcr boundary of the formation was not seen.
Paleontology and age : The formation ranges in ages from lov1ermost Triassic to lower Upper
Triassic. According to Chonglakn1ani (1981), the Claraia-Ophiceras fauna, such as Claraia
stachei, C!araia concentrica, of late Griesbachian age occur in Ban Bon \vest of Sop Parp, in Ban
I--Iuat \Vest of Ngao, and Huai Or Dong \vest of Mae Wang Dam. The Daonella indica zone of
late Ladinian age occurs in Ban Pang La, and Huai Khok Chang of Ko Kha District. Lo\ver
Camian fauna dominated by the a1nn1onoids Paratrachyccr,1s and bivalves Daonella and Posidonia
occurs in the Ban Tha Si, Mae Moh and Chae Hom areas (Chonglakmani, 1981 ). At Chae Hom
District, Baum ct al. ( l 970) reported the upper Scythian conodonts, Hadrodontina anceps and
Puchyc/adina synunetrica, in the basal conglon1erate of the Hong Hoi Formation.
Type /ocalit)' : A good exposure or the Hong Hoi Fonnation crops out from Huai Mae Duin to
Huai Muang NE of Ban rfha Si \Vhich is regarded as the type locality.
DOI LONG FORMATION
'J'hc l)oi Long Fonnation \vas nan1cd aflcr the Doi Huai Long situated 40 krn NE of the lO\vn
or Lan1pang by Chong!akmani ( 198 l ).
Synony1n : Doi Chang Forn1ation of Piyasin (1972), Bunopas ( l 981 ); and Doi Long Fonnation
of Chonglakmani (1981 ), Chonglakmani and Kenviscd ( 1987 a ) but excluding limestone-con­
glo1ncratc.
Liihology 'fhc Doi Long Fonnation is characterized by n1assivc bedded, light gray to gray
packstonc to grains tone of peloids, oncoids and algal debris with 1ninor bioclasts, oolite and
stroinato!itc beds or lenses (Fig. S ). Macrofossils arc scarce but ,nay be abundant locally, espe-
STRATIGRAPHY OFT!iE LAtv1PANG GROUP
A
H
�
f!.- � n ;
! ....
:-_--- !'1
;;
Q
SS.
; : : ! .....-
�--- ,'
c
'"
Fig. 6 Lithostraligraphic correlations fro1n the 1ncasurcd sections of the Pha Daeng Formal ion:
A} Hual Ting Tue, B) Huai Or-Huai Nain Lon, C) km 50.5 - 5 1 .5, D) km 45 - 45.6,
E) kn1 69, F) Huai Bong, G) Huai Chan. and H) kn1 34 - 36.3.
ciaHy in rhe upper part of the fonnation. Late diagenctic dolon1jtes v;c.::ithefJng light brown are
common. The upper part of the fonnation is ,g�nerally ln!crbcdd�d wilh red to pink wackestonc
as at the Doi Huai Lon_g Jnd Doi Ph:i Bong sections. It i s suggesled that in the absence of fossil
and stratigraphic control, the Doi Long Forn1ation 1nay be distinguished froin the Cave Temple
1\1ember, on the basis of their liLhL}]ogy in \Vhich the Cc1nncr is don1inatcd by peloids, type C
oncoids (Chaodumrong, 1992) and algal dcbri.s..
Thickness : 1'he fnn11ation n1ay tie iensoic:.td. ll is 1hlckcs1 (230 n1,1 at 1h� Doi Huai Long area.
Paleornojogy and age ' fhe 1nlddle Carnian Trigonodus costarus collccLe.d froin reddish gray
argillac.:cous li1ncstoni: clasl in lh� I3an l'ha Si area ((:hnng!ak1nani, ! 98 ! ) i,-; prohably equivalent
to the upper part of this fOnnation.
76
P. C haodu1nrong and C.F. B urrett
Type locality ; The Doi Huai Long (Fig. 50) east of Ban Tha Si is the type locality proposed by
Chonglakmani ( 198 1 ). The exposures al the Doi Pha Bong and at the Doi Nok are also good and
are here proposed as reference localities.
PHA DAENG FORMATION
The Pl1a Dacng Fonnation was na1ncd after Doi Pha Dacng by Piyasin (1972). Limestone
conglon1erates occurring 1,vithin the red beds in the lower pan of the sequences are considered in
this study as part of the Pha Daeng Formation \Vhich was contrast to the original proposed. This
fom1ation occurs in both Lainpang and Phra-e sub-basins.
Synonym ; Tlie Pila Dacng Formation (Piyasin. 1972; Clionglakmani, 198 1 ; Liengsakul, 1979;
Bunopas, 1981 ); Thung Po Fom1ation and lower part of the Mae Thang Formation (Chonglakmani
and Tiyapun, 1985); Unit ms 1, h and h2's, particularly in Ngao area, of Baum and Hahn ( 1 977);
Phra That Formation (only in the Phrae sub-basin) of Piyasin ( 1972), Chonglakmani (1981), and
Bunopas (1981 ).
Lithoiogy : This fonnation consists 1nainly of red to maroon sandstone. siltstone and mudstone
\Yith subordinate conglomerate(Fig. 6). Fining-upward sequences are characteristic. Gray mud­
stone, minor gray sandstones and li1ncstones occur locally in the upper part of ihe formation,
\1,1here foss1ls such as bivalves, and am1nonoids 1nay be common, \vhile limestone conglomerate
presents locally in lhe Jon,cr parL
The conglomerate is both stratified and unstratified and contains mainly volcanics, vein-quartz
and red sandstone clasls. Sandstone is mainly feidspathic. red to brov.-·nish red and grayish·
green, fine- to coarse-grained and medlun1 to thick-bedded with wavy to parallel bedding. Small
scale cross-beddings and rfpple marks are common in siltstones and fine-gr ained sandstones.
Channel structures and bioturb.ation occur locally. 1\1ud cracks have a rare occurrence.
Thickness : l'bc fonnation's thickness ranges rron1 200 to 700 m and possibly, in places, up to
1000 n1 thick. ...\.t the type locality along Doi Pha Dacng to Huai Ting Tue section the formation
is 700 m thick. At km 35+950 m to 36+295 m and at km 45+020 m to 45.4 on the Rong Kwang1\- gao highway, the thicknesses are 123 m and 206 m , respectively.
Paleontology and .age Only 1niddlc Can1ian fossils \vas reported f or the Pha Daeng Forn1ation
from both the Lampang and Phrae sub-basins. In the Lampang sub�basin, its lo\ver boundary is
situated just a fcv...· meters above the middle Carnian Trigonodus costatus collected from red­
dish-gray argillaceous limestone (Chonglakmani, 198 !). In the Phrae sub-basin, a lower middle
Camlan, assemblage including Halobia sryriaca , l-falobia cassia.na, Pafaeocardita singularis
and Cassianefl..t tcnuislri,i was reported from the upper part of the fonnation at kn1 45+350 n1
along the Rong Kwang-Ngao highway (Chonglakrnani, 198 1).
Type section : The type section is located along Doi Pha Daeng through Huai Ting Tue (Fig. 6).
An additional reference locality is situated along km 50.5 to 6 1 and km 45+020 m to 45.4 on the
Rong K,vang-Ngao high"vay.
STRATIGRAPHY OF THE LAM PANG GROUP
77
KANG PLA FORMATION
The Kang Pla Formation ,vhich takes its name fron1 Doi Kang Pia, 50 kn1 north o f Phrae
Province, was proposed by Chonglakmani and Tiyapun ( l985) but no stratigraphic details were
given. This nan1e is favored here. This formation occurs in the Phrae sub-basin.
Synonym : Pha Kan Formation (only east of Phayao, Ngao and Long areas) of Piyasin (1972),
and Chonglakmani (1981) ; Khun Huai Ri Formation (Chonglakmani and Tiyapun, 1985); Unit
t'I in Ngao and east of Phayao (Baum and Halm,1977).
Lithology : The Kang Pia Forn1ation consists 1nainly of thin to massive bedded, light to gark
gray limestone with minor intcrbeddcd clastics(Fig. 6D,E). The lithology varies laterally; in
son1c areas oolilc or skeletal grainstone is developed, in the others li111c n1udstonc and pcloidal
packstone.
Thickness : The formation varies in thickness from the type locality at km 45.5 on the Rong
Kwang-Ngao highway, where it is 76 n1 thick, to a section in the south at km 69 on the Lampang­
Denchai highway, where it is 38 m thick. These t,vo locations are possibly only the feather
edges of a large lensoidal limestone body.
Paleontology and age : The formation ranges in age fro111 ,niddle Carnian to lower Norian.
Middle Camian Halobia cornata and Spirifcrina ,vere reported fron1 gray limestone in Ban Pha
Kho, 1 5 km north of Tam Bon Ban Pin (Chonglak1nani,1981). The lower Norian conodont,
EpigondolelJa abneptis , is found in limestone at km 69 on the Lampang-Denchai highway
(Carey et al., l 995).
Type section : It is proposed here that the section al kin post 45+500 111 to 45+625 111 on the Rong
Kwang-Ngao highway is the type section of the fonnation.
Wang Chin Fonnation
According to Wolfart (1987), the Wang Chin Formation was introduced by Charoenpravat
(1968). This name is adopted in this study following Wolfart (1987). However, its definition is
different frorn that or \Vol fan (1987) who co,nparcs it to the I- long J�toi Fonnation. It is subdi­
vided here into three members as the Phu Tap, Huai Chan and Mac Lu Sandstone Members
(Table 1). 'fhis forn1ation occurs only in the Phrac sub-basin.
Synony111 : I.-J:ong I.-J:oi Fonnation (but only in the Song, Long and Wang Chin areas) of Piyasin
(1972), Bunopas (1981 ), Chonglakmani (1981), the Phra That Formation (Maneenai, et al.,1987);
the Mae \Vang Chang Fonnation (Sukvattananunt and Paksa1nut,1986); and the Wang Chin
Formation (Wolfart, 1987) but only in the W..ing Chin arca.c
78
P.Chaodumrong and C.F.Burrett
Lithology This fonnation consists n1ainly of n1uclstones with subordinate turbiditic sandstones
and allodapic limestones. It is subdivided into three me1nbers as the Huai Chan, Mae Lu Sand­
stone, and Phu Tap (Table ! ,Fig. 4C-F). Halobi,i is a typical fossil and often occurs in the Mac
Lu Sandstone and Phu Tap Mc,nbcrs
Phu Tap Member : This member takes its name from the Phra That Phu Tap temple which is
situated at km 50.6 on the Lampang-Denchai highway. It consists mainly of gray to greenish­
gray, laminated to thin- bedded to structureless mudstone with minor fine-grained sandstone and
siltstone beds or lenses. Halobia is common.
Huai Chan Mcn1bcr : 'fakes its nan1e fro1n Huai Chan where exposure is good. The Huai Chan
Member is characterized by alternating beds of gray to dark gray limestone, 1nudstone and shale
with n1inor sandstone and chert beds. Limestone is laminated and thin- to ,nedium bedded, often
displaying Bou1na sequence. Norn1ally graded beds and lainination are co1nn1on. Load, convo­
lute, and sedimentary slump structures occur locally.
Mae Lu Sandstone Me1nber : Takes its nan1e from Ban Mae Lu situated along the Lampang­
Denchai highway. It is characterized by 1nainly sandstone beds intercalated with subordinate
mudstone. The sandstone is gray to light bro\vn, fine- to coarse-grained and thin- to medium
bedded with occasional thick beds. Sandstone beds usually display planar bases and normal
grading, and cross-bedding is rare. J{alobia rnay be co,nmon to abundant in the mudstone.
Thickness : 'I'hcre is no single co,nplctc section. The forn1ation is estirnated to be about 600 to
over 1,000 m thick. The Huai Chan Member at the type locality is 110 m thick. The Mae Lu
Sandstone Member is about 40-230 m thick. The thickness or the Phu Tap Member is about
190-400 m.
Paleontology and age : Only n1iddle Carnian to lo\vern1ost Norian fossils have been reported
from this formation. At Ban Thung Laeng, 22 kin NE of Wang Chin, Halobia styriaca and
Halobi�i cassiana of ,niddle Carnian age were reported from gray shale and siltstone 150 m
above the base of the fonnation, possibly equivalent to the Phu Tap Me1nber. The Middle Camian
Halobia styriaca was also observed from the Mae Lu Sandstone at k m 55 + 542 m on the
Lampang-Denchai highway. Lowennost Norian bivalves were reported from Ban Dok Khan1
Tai or Ngao, Huai Puy of Song, and Ban Mae Saliam Wan of Thoen (Chonglakmani,1981 ).
Type locality : Type localities are proposed here for the 1-fuai Chan Me1nber at Huai Chan of
Song District, and for the Mac Lu Sandstone and Phu Tap Members at km 54+ 730 m to 55+930
,n and 66+350 111 1 0 66+770 111 along the La1npang-l)cnchai highway (Figs. 4E. F).
DEPOSITIONAL ENVIRONMENTS AND TECTONIC IMPLICATIONS
Depositional environ1nent and tectonic i111plication of the Lan1pang Group were detailed by
Chaodun1rong (1992): brief is given belo\v. During early Triassic time, there were two conti­
nental tcrranes, na1nely Shan-Thai tcrranc in the west and subducting Indochina tcrranc in the
cast (Fig. I ) that \Vere seperated hy deep ocean. In the forearc basin of the Shan-Thai terrane,
STRATIGRAPHY OF THE LAl\1PANG GROUP
79
there \Vas a deposition of the Lampang Group. Red beds of the Phra That Fom1ation and carbon­
ates of the Pha Kan Forn1ation were formed in continental to shallow marine areas \Vhereas
gravity flow sediments of the Hong Hai Formation \vere accu1nulated in deep sea areas. Rate of
basin subsidence \Vas probably higher than rate of carbonate precipitation, resulting a lensoidal
shape of carbonate !Onnation. During Middle 'l'riassic, dct.:p sea cnvironn1cnt still occurred \Vi<lcly
over the area. As a result of the collision bet\veen the Shan-Thai and Indochina terranes during
early Late Triassic, the Lan1pang sub-basin was relatively uplifted becoming a shallow marine
basin where carbonates of the Doi Long Fonnation were deposited. Mean\vhile to the east, a ne\V
subsiding area so called Phrae sub-basin was initiated. Red beds of Pha Daeng Formation oc­
curred over the t\VO sub-basins under fan-deltas environn1cnt. Lithofacies of the Wang Chin
F orn1ation indicated having been deposited in sub111arinc fan environment. Sanstones of the
Hong Hoi and Wang Chin Fonnations arc different in con1position, although both arc lithic
arkose to feldspathic litharenite. The Hong Hai sandstones in n1ost case contain less than <25o/o
quartz while the Wang Chin sandstones consist of 30-50o/o quartz, having n1ore rounded quartz
and less microlitic texture in volcanic fragments. High quartz content in the Wang Chin Forma­
tion may partly due to subdued tectonic allowing intense \veathering in source area and resulting
in greater concentration of stable grains. 1'hc collision probably ceased during late Triassic.
CONCLUSIONS
1 . The Lan1pang Group in central north 'l'hailand was fanned in l\VO adjacent sub-basins, the
Lampang sub-basin, to the west, occurred during the Early Triassic to early Late Triassic and
contains Daone!la, Paratrachyceras, Costatoria and Claraia, while the Phrae sub-basin, to the
east, was formed fron1 in Late Triassic and contains 1nainly Halobia.
2.
The Lampang G roup consists of seven for111ations. in ascending order as Phra That, Pha
Kan, Hong Hoi, Doi Long, Pha Dacng, Kang Pia and Wang Chin. 'fhe 'friassic sequences in the
Phrae sub-basin have been stratigraphically overlying those in the Lampang sub-basin.
3.
The limestone rorn1ations (Pha Kan, Doi Long and Kang Pia) apparently fanned in relative
narrow and lin1ited areas, \Vhcre they did not develop their contiguous forn1ations are confonn­
ably joined. Such occurrences arc sho\vn in the field by conforn1ahlc contacts between the I-long
Hoi and Pha Daeng Forrnations or the Pha Daeng and Wang Chin Formations. In such cases the
gray beds on top of the red beds belong to the overlying gray-beds forn1ation, i.e. either Hong
Hoi or Wang Chin Fonnation.
4.
The collision between Shan Thai and Indochina terranes \vas ceased during Late Triassic.
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