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Internat ional Jo urnal o f Coal Geology16 ( 1990 ) 13 1-1 36 131E l s e v i e r S c i e n c e P u b l i s h e rs B . V., A m s t e r d a m

O n th e u s e o f m o d e r n t r o p i ca l d o m e d p e a ts a sana logues fo r pe t rog raph ic va r i a t i on in

C a r b o n i f e r o u s c o a l b e d s

J.S. Ester le and J .C. FermCoal Research Group University of Kentucky Department of Geological Sciences

Lexington KY 40506-0059 U.S.A.

( Re ce iv ed A pr i l 23 , 1990 )

A B S T R A C T

A s e r ie s o f p e a t c o r e s w e r e c o l l e c t e d a l o n g f o u r t ra n s e c t s i n I n d o n e s i a a n dM a l a y s ia f o r t h e p u r p o s e o f d e v e l o p i n g m o d e r n a n a l og u e s f or th e d e v e l o p -m e n t o f b r i g h t a n d d u l l li t h o f a c ie s i n c o a l ( F ig . 1 ) . E a c h d e p o s i t c o n s i st s o f an u m b e r o f w e l l - d e f i n e d z o n e s o f p e a t w h i c h r e f le c t t h e o r i g i n a l p l a n t t y p e sa n d t h e d e g r e e o f d e g r a d a t i o n . T h e s e c o m p o n e n t s v a r y w i th r e s p e c t t o t h e i rp o s i t io n w i t h i n t h e p e a t b o d y. F o r e x a m p l e , t h e S u m a t r a n d e p o s i t c on s is ts o fp r e d o m i n a n t l y o f m o d e r a t e l y d e c o m p o s e d w o o d y p e a t w i th t h i n i n t e rb e d s o fc o a r s e r p e a t w h i c h b e c o m e t h i c k e r i n th e c e n t r a l u p p e r p o r t i o n o f t h e d e p o s i t( F i g . 2. ) . I n c o n t r a s t , t h e c r o ss s e c t i o n s f r o m t h e M a l y a s i a n t r a n s e c t s s h o wm o r e d i s t i n c t s t r a ti f i c a ti o n i n p e a t t y p e s a n d t h i c k e r c o a r s e p e a t z o n e s i n t h ec e n t e r o f t h e d e p o s i t ( F i g . 3 ) . P r e s u m a b l y, a s th e c o a s t p r o g ra d e s , t h e n e a r-c o a s t a l p e a ts a r e b e i n g p r o g r e s s iv e l y o v e r l a i n b y i n l a n d f o re s t p e a t s a s e v i -d e n c e d i n t h e m o r e m a t u r e d e p o s it s la n d w a r d ( A n d e r s o n , 1 9 6 4 ) .

A l t h o u g h c o m p a r i s o n s o f b r i g h t t o d u l l t re n d s i n c o a l ( i. e ., d e c r e a s i n g v i-t r a in b a n d t h i c k n e s s a n d / o r v i t ri n i te c o n t e n t ) h a v e b e e n m a d e t o t h e in t e r n a l

s t ra t a o f t h e p e a t o n t h e b a s i s o f th e d e c r e a s i n g d i s t r i b u t i o n o f la rge w o o df r a g m e n t s u p w a r d s w i t h i n t h e d e p o s i t s ( E s t e r le a n d F e r m , 1 98 6; E s t e rl e a n dTi e , i n p r e ss ) t h e p r e m a c e r a l c o m p o s i t i o n o f t h e s e p e a t s h a s n o t b e e n f u ll ye s t a b l is h e d . F o r t h i s p u r p o s e , a s e r ie s o f s a m p l e s f r o m e a c h d e p o s i t w a s s e -l e c t e d f o r p e t r o g r a p h i c e x a m i n a t i o n i n r e f l e c t e d l i g h t u s i n g c o a l p e t r o l o g i cm e t h o d s . We t p e a t s a m p l e s w e r e f i r s t f r o z e n i n l i q u i d n i t r o g e n , l y o p h i l i z e da n d f in a ll y v a c u u m - i m p r e g n a t e d w i t h a l o w - t e m p e r a t u r e b i o p la s ti c . I m p r e g -n a t e d s a m p l e s w e r e t h e n s e t u p a s b l o c k s , g r o u n d a n d p o l i s h e d f o r p e t r o -g r a p h ic e x a m i n a t i o n u s i n g b r o w n - c o a l te r m i n o l o g y.

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[ 34 J.S. ESTERLE AND J.( . FERM

B A R A M R I V E R T R A N S E C T S

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THE USE OF MODERN TROPICAL DOMED PEATS 135

Sumatra. Although the composition of both deposits is domin ate d by macer-als of the huminite group which show relative decreases in the amount ofstructured textinite and humotelinite downhole and towards the margins ofthe deposit, internite contents vary differently. In the Sarawak domed de-

posit, ine rtinite macerals are virtually absent throughout and only occur inlow percentages ( < 3%) on the thin margin. In Jambi, inertin ite contents arelow ( < 1%) at the base of the deposit an d increase upwards to 18% on thecut-bank margin that is overlain by levee sediments, to 5% in the central up-per reaches of the deposit, and to 10% of the thinned margin. These differ-ences in inertinite composition suggest that the domed peat deposit is notpresently undergoing oxidative decay and remains anoxic due to constant sat-uration from high humidity and a perched water table; whereas the Jambideposit, which may or may not have previously been domed, is being oxi-dized at the surface, perhaps due to drainage and inundation by the BatangHari River.

The results of preliminary petrographic examin ation suggest that modifi-cations are need ed for the usage of mode rn dom ed peat deposits as analoguesfor petrographic variation in Car boniferous coal beds. Although the decreasein the size and amount of wood fragments in modern domed peat depositssupports a dulling-up, or decreas ing vitra in-ba nd thickness model for coal ona megascopic scale, the petrographic d ata show contradict ory evidence.

REFERENCES

Anders on, J.A.R., 1964. The struc ture and de velo pment of the peat swamps of Sarawak andBrunei. Trop. Geogr., 18: 7-16.,

Esterle, J.S. a nd Ferm, J.C., 1986. Rela tionship between petrographic and chemical propertiesand coal seam geometry, Hance Seam, Breathitt Formation, Southeastern Kentucky. Int. J.Coal Geol., 6: 199-214.

Esterle, J.S. and Tie, Y.L., in press. A test for the analogy of tropical domed peat deposit s to'dulling up sequences in coal beds - prel imin ary results: Org. Geochem.

DISCUSSION

L. Ruppert (U.S. Geol. Survey)Question Did you do base-level surveys in Sarawak to dete rmine the heightof your peat domes?

Response Yes, all of the peat transects were surveyed relative to mean sealevel (be nch mar ked ). The peats at the coast are at the coast are at or only afew cm above mea n sea level (MSL) . The surface of the thicker deposits fur-ther inland are 10 meters above river level which at Marudi (appro ximatel y60 km in land) is only 0.93 m above sea level.

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136 J.S. ESTERLE AND J.C, FERM

R . L i t t k e ( J u l i c h , F. R . G e r m a n y )Question W h a t k i n d s o f m i n e r a l m a t t e r o c c u r i n t h e d o m e d p e a t s o f I n d o n e -s ia a n d M a y l a s i a ? A r e t h e i r s i l ic i c l a st i c l a y e rs d e r i v e d f r o m f l o o d i n g o f t h ep e a t a n d a r e t h e r e e a r ly d i a g e n e t i c s u l p h i d e s?

Response T h e m i n e r a l m a t t e r i n b o t h t h e d o m e d p e a t in t h e B a r a m R i v e r,S a r a w a k a n d i n J a m b i P r o v i n c e , S u m a t r a , i s d i s t r i b u t e d a l o n g t h e b a s e a n dm a rg i n s o f t h e d e p o s i t s. O n l y t h e f l o o d e d m a rg i n o f t h e B a r a m ( < 2 m t h i c k )c o n t a i n s i l i c i c l a s t i c s . I n t h e J a m b i d e p o s i t , s i l i c i c l a s t i c s o v e r l i e t h e p e a t o nt h e s o u t h e a s t e r n c u t b a n k m a r g i n i n t h e f o r m o f l ev e es a n d t h e a s h c o n t e n t o ft h e p e at is h i g h ( 2 0 - 5 0 % a s h ) b u t v e ry lo w in su l fu r ( < 0 . 5 % ) . I n t h e B a r a md e p o s i t , o n l y t h e b a s e o f t h e d e p o s i t i s h i g h i n to t a l s u l f u r ( u p t o 5 % ) a n d i s p r i-m a r i l y f r a m b o i d a l p y r i t e . We h a v e n o t l o o k e d a t th e m i n e r a l o g y o f t h e a s hyet .

P.C . Ly o n s ( U . S . G e o l . S u r v e y )Comment I t is i m p o r t a n t t o f o l l o w t h e l o g i c o f p r e - m a c e r a l s a n d u s e th e t e r m sp r e - t e x t in i t e , p r e - h u m i n i t e f o r p r e c u r so r s o f m a c e r a l s .

Response P e r h a p s , b u t t h e f a ct r e m a i n s t h a t i n r e f le c t e d w h i t e l i g h t u n d e r o i li m m e r s i o n , a ll o f t h e b r o w n - c o a l m a c e r a l s a r e p r e s e n t a n d t h e i r r a n k re fl ec -t a n c e v a r ie s b e t w e e n 0 . 2 a n d 0 .5 , t h e r e f o r e j u s t i f y i n g t h e m a c e r a l t e r m s . P r e -m a c e r a l t e r m i n o l o g y w a s d e v e l o p e d f o r i n f e r e n c e s m a d e f r o m p e a t t h i n s ec -t i o n s i n t r a n s m i t t e d l ig h t. W i t h r e f le c t e d li g ht , t h e c o m p a r i s o n i s m o r e d i re c t;

t h e re f o re , t h e s a m e t e r m i n o l o g y c o u l d be u s e d t o a v o i d r e d u n d a n c y a n dc o n f u s i o n .

T. G . C a l l c o t t ( A u s t r a l i a )Question W h y r e l a te t o C a r b o n i f e r o u s c o al s r a t h e r t h a n s ay C r e t a c e o u s ?

Response B a s ic a ll y b e c a u s e m y e x p e r i e n c e is i n C a r b o n i f e r o u s c o a ls a n d t h e ya r e t h o u g h t t o h a v e f o r m e d i n t r o p i c a l c l im a t e s ; t h e re f o r e , w e c h o s e a tr o p i c a la n a lo g u e . T h e r e i s a m a j o r h o l e in t h e c o m p a r i s o n b e t w e e n p e a t a n d c o al ( a n db e t w e e n C a r b o n i f e r o u s a n d C r e t a c e o u s f lo r a s) b e c a u se o f th e e v o l u t i o n o f

a n g i os p e rm s d u r i n g th e C r e ta c e ou s , b u t m a n y o f t h e N o r t h A m e r i ca n K / Tc o a ls a re t h o u g h t t o b e t e m p e r a t e . B u t o n e o f o u r o b j e c t iv e s is to d e v e l o p ag e n e r i c sy s t e m o f p e a t d e s c r i p t i o n , e i t h e r b a se d o n m a c e r a l a s s e m b l a g e s o r o nm e g a s c o p i c a t t r ib u t e s s u c h a s p a rt i c le s i ze o r w o o d c o n t e n t i n p e a t, t h a t c a nb e a p p l i e d t o a n y r a n k o f c o al . A s D r. C a m e r o n p o i n t e d o u t , t h e s e q u e n c e s o fp e a t t y p e s i n b o g s a r e s i m i l a r, r e g a rd l e s s o f l a t i t u d e a n d v e g e t a t i o n t y p e , b u ti t is th e i r t e x t u r e t h a t b e g i n s to v a r y b e c a u s e o f c h a n g e s fr o m h e r b a c e o u s t oa r b o r e s c e n t p l a n t i n p u t . I n C r e t a c e o u s c o a ls , w e h a v e a b e t t e r c h a n g e a t d e -c i p h e r i n g th e s e q u e n c e b e c a u s e o f t e n w e c a n s e e t h e w o o d d e b r i s ( s ee p a p e rb y Wa r w i c k a n d S t a n t o n , 1 98 8 ) w h e r e a s i n b i t u m i n o u s C a r b o n i f e r o u s c oa ls ,w e o n l y h a v e b a n d i n g .