Preliminary Results of Bitumen and Kerogen Analyses of the CRP-1 Core
R.M. KRTTLIX
Department of Geosciences. University of Nebraska-Lincoln, Lincoln, NE 68588-0340 - USA Received 5 August 1998; accepted in revisedform 25 October 1998
Abstract
-
Sediments and iocks iecovei-ed in CRP-1 coiing opeiations contain ~elatively little organic mattei (aveiage 0 4% TOC) and veiy small amounts of solvent-soluble ol ~ a n i c matte~ (avei age 60 kg bitumenlg lock) The kei ogen lecovet ed fi 0111 these iocks has atomic H C iatios that I ange fioni 0.7 to1 0 and atomic O C iatios that I ange fiom 0.14-ANTARCTIC
0 22 This iange of values could be pioduced by mixing coal detutus with aquatic organic
WAIST
ICEin'iltei Coal with the 0 C iatios necessaiy to pioduce the keiogen piesent in the CRP-1 , hes,Rnta,ct,c
SHEET
winples occuis in outclops of the Penman Beacon Supeigioup ptoximal to the drillsite \\R"lsys'em
m
INTRODUCTION
The Quaternary and Miocene sediments and rocks penetrated by the CRP-1 core were deposited in environments which were variably influenced by glacial activity. Environments ranged from proximal glacimarine to shallow marine settings in which small amounts of detritus was ice-rafted to the CRP- 1 drillsite (Fig. 1) (Cape Roberts ScienceTeam, 1998a). These different depositional environments may lead to differences in the amount, type, and provenance of organic matter preserved with the sediments. Analysis of kerogen and solvent-soluble organic matter present in the CRP- 1 core was undertaken as part of the initial core characterisation effort. This effort included whole-rock measurements of elemental abundances, extraction of solvent-soluble organic matter, and measurement of the chemical composition of kerogen obtained from these sediments and rocks. The principal objective of this workis to provide preliminary information on the organic matter preserved in these sediments and rocks. This information can be used to guide more detailed studies and to make some provisional conclusions regarding the source and composition of organic matter preserved in these sediments and rocks.
METHODS
All glassware and equipment usedin sample preparation was washed in Micro solution and rinsed in purified water.
This cleaning was followed by sequential rinses with 1 % hydrochloric acid, methanol, and dichloromethane. Seven major lithostratigraphic units consisting of 18 subunits were described by Cape Roberts Science Team (1998b) (Fig. 2). Twenty five samples representative of the major lithologies penetrated by the CRP-1 hole were collected at c. 5 m intervals. While at McMurdo, the samples were
Fig. 1 - M a p of a portion of southern VictoriaLand showing the locations of exposures (diagonal shading), the CRP-1 drillsite, and a number of localities referred to in text (after Young, 1991).
freeze-dried, ground and homogenised with a mortar and pestle and stored in 15 m1 glass vials. Measurements of total organic carbon (TOC), total carbon (TC), total nitrogen (TN), and total sulphur (TS) were made using the Carlo Erba-NA 1500 at the Crary Science and Engineering Center at McMurdo. These results are presented in table 1 and the experimental procedures used are summarised in Cape Roberts Science Team ( 1 9 9 8 ~ ) .
Bitumen was extracted from the sedimentary rocks in
Shallow marine; dominance of
)pen-waten shelf-bank minor ice-rafting Shallow marine; dominated by
iceberg sedimentation in pmximat'distal settings
1
Shallow marine; dominated by gravity-flow sedimentation
with minor ice-rafting at top and bottom Ice-prox. rhythmites + dropsto
Shallow marire; dominated by gravity-flow sedimentation
Shallow marine; dominated by gravity-flow sedimentation; minor
ice-rafting in middle
Fluctuating volsof ice-rafted debris &
gravity-flow sedn.
Shallow marine: dominated by gravity-flow sedimentation
With fluctuating input of ice-rafted debris
Shallow marine;dominated by gravity-flow sedimentation
with variable input of ice-rafted debris
High-density iceberg or grounding line sedimentation,
With short-lived recession phases with mud or sand deposition
Suspended sediment settling on shelf with minor ice-rafting
l
Fig. 2 - Stratigraphic column showing lithologies penetrated by the CRP-1 core (from Cape Roberts Science Team. 1998b, Fig. 18).
a Soxhlet apparatus using dichloromethane. The dichloromethane was removed by evaporation and the extract was weighed (Tab. 1).
Kerogen separates were obtained from the extracted samples by reacting them with 6N HC1 overnight and
rinsing them with p11rifici.l water. The residues were tlwn
readed wi 111 coiicentriiled HI7. The spent I-11.: was t k ~ i : ; i ~ ~ ~ t - ~ l and rcpl:icd d:iily. Completedissolution ofthcsecIini~~iit;~~~y rock samples was clilTicult owing to the prescno.' of significant amounts ol'mal'ic minerals and sidcritc a n d tlic conscclucnt f'ormation of' Fe and Mg f'luoridc precipit;iti.'s, Nco-formed fluoi~idcs were removed using a 1M solution ol' AlCI, in AN 1-ICI. Pyrite was removed with a 1 M iicklic cliro~iious chloride solution. Although c h r o m o ~ ~ s clilorklc reduction is not believed to affect carbon-bonded sulphur
i i i the kerogcn (Canficlclct al.. 1986), theriskof"lahorii~ory-
induced diagccnesis" attends all procedures l'or dc.
mineralising rocks The separates were washed will1 ;I
large amount of purified water and dried at 40°C' I'yrite removal was not complete and thus the ash content of tlii.'
kerogen separates is high (Tab. 1). The elemental ratios presented in table 1 should not be affected howcvcr.
Elemental analysis of the kerogen separates was carried out using a Carlo-Erba EA-1108. CHNS analyses were carried out by combustion whereas the 0 analyses were performed by pyrolysis. These data were converted to atomic elemental ratios and are displayed in table l .
RESULTS AND DISCUSSION
The sediments and rocks penetrated by the CRP-1 drillhole contain little organic matter: the T O C values measured at the Crary Laboratory average 0.4% (Tab. I ).
The C:N ratios measured at the Crary Laboratory arc high and range from 10 to 700. C:N ratios must be interpreted with caution in rocks that contain very little organic carbon. Although the presence of inorganic N is typically cited as the reason that caution is warranted (Stein, 199 1 ), the presence of siderite or other refractory carbonate minerals can produce erroneously high C:N ratios. The analytical techniques typically used to quantify the inorganic and organic carbon contents of marine sediments and rocks (e.g. Hedges & Stem, 1984; Muller & Gastner.
197 1) rely on low-temperature acidification of all carbonate phases. Siderite is much more refractory than calcite or dolomite and complete dissolution at low temperature may require weeks or months (Rosenbaum & Sheppard.
1986). Although the high C:N ratios obtained in this work should be interpreted cautiously, two mutually consistent interpretations are possible. (1) Organic matter produced in the water column experienced extensive remineralization and only the most resistant fraction of the aquatic organic matter was preserved. (2) A significant fraction of the preserved organic matter comprises largely detrital coal or fragments of higher land plants. The extraordinarily high C:N ratios (e.g. 200-700) are more consistent with the presence of detrital coal than tessigenous plant debris:
terrigenous plant debris typically has C:N ratios ranging from 12 to 37 (Stein, 1991).
These rocks and sediments contain little solvent-soluble organic matter. The dichloromethane-bitumen solutions obtained by the Soxhlet extractions are colourless. The mass of bitumen extracted is low and averages 60 pg bitumenlgrock. The bitumen ratios (mg bitumenlg organic
Preliminiiry Results of Bitumen i i i u l Kesogcc Analyses of' CRP- l
t i l l ) 1 - Oiganic geochemical data fbi samples obtiiinci1 liom CR1'- I
.-
Depth (lnbsf) Whole-~ ock Bilumm
M'is-1' B i f u m c n Ratio'
-
l to 100
l 60 X0
l 70 40
0 94 30
l 50 10
0 90 1 0
0 56 10
0 t I 10
0 71 10
0'31 10
0 80 10
0 17 5
l 10 100
0 17 1
1 0 20
1 20 30
0 74 20
061 20
1 1 0 10
0 14 2
l SO 40
0 46 7
0 72 6
l 80 20
1 10 10
Note: "Total Organic Carbon (TOC). 'Â¥Mas ratio of organic Carbon:total Nitrogen. 'Total Sulphur. "Elemental atomic ratios.
'Mass (mg) of bitumen. 'mg of bitumen extractedlg organic carbon. q a t i o not determined (n.d.) because sufficient kerogen could not be isolated for analysis.
carbon) obtained (Tab. 1) are exceedingly low, and average less than 30 mg bitumenlg organic carbon. It is unlikely that Rock-Eval pyrolysis of these or other CRP-1 samples would yield useful data because Rock-Eval pyrolysis data are very difficult to interpret when the samples analyzed have very low TOC and bitumen contents (Peters, 1986).
That the Quaternary samples have slightly higher bitumen ratios (Tab. 1) is to be expected: in the classical view of kerogen formation (e.g. Durand, 1980), lipids, alcohols, and organic acids present in sediment may undergo polymerisation over geologic time and contribute to the kerogen fraction. The molecular composition of the small amounts of extractable organic matter in these rocks could have been affected significantly by contamination at the drillsite or during the initial stages of core processing. Any conclusions drawn from molecular analyses would probably be equivocal; thus, molecular characterisation of the bitumen was not undertaken.
Although the H:C and O:C ratios of the kerogen separates plot along and above the evolution curve for Type I11 organic matter (Fig. 3), higher land plant detritus need not have comprised a significant fraction of the organic matter deposited at Cape Roberts. All organic matter present in sedimentary rocks is amixtureof materials derived from aquatic and terrigenous sources. Among the possible sources of terrigenous organic matter at Cape Roberts are outcrops of coal-bearing rocks in the Permian Beacon Supergroup that are exposed in the Transantarctic Mountains. Coates et al. (1990) have compiled the results of numerous analyses of coal from the Beacon Supergroup in the Transantarctic Mountains. These data have been converted to atomic O:C and H:C ratios and, when plotted
on figure 3, define a trend that is grossly parallel to the evolution curve for Type I11 organic matter but displaced to lower HIC values. Such displacement to lower HIC values is typical for organic matter that has been weathered (Jones, 1987). Although the C:N data are suggestive that little aquatic organic matter was preserved, the most refractory portion of the aquatic material may have been
0 CRP-1 kerogen
,o Beacon coal (Coates et al., 1990)
1
Fig. 3 - Van Krevelen diagram showing the composition of kerogen present in CRP-l samples and coals from the Transantarctic Mountains.
CONCLUSIONS
The rocks and s e d i m e n t s p e n e t r a t e d by t h e CRP-1
c o n t a i n l i t t l e s o l v e n t - s o l u b l e o r g a n i c m a t t e r or k e r o g e i i . I'lic d a t i i c o l l e c t c t i in t h i s i n i t i a l c o r e c l i a r r i c t e r i s : i t i o n eff'ort s u p p o r t s s t r o n g l y t h e conclusion m a d e in t h e I n i t i a l R e p o r t (Cape R o b e r t s S c i e n c e Team. 1 9 9 8 ~ ) t h a t much of
t h e organic m a t t e r in t h e s e r o c k s and s e d i m e n t s i s a m i x t u r e of d e t r i t a l c o a l and a q u a t i c o r g c i n i c m a t t e r . The
e l e m e n t a l c o m p o s i t i o n of the kerogcn and the w h o l e - r o c k
C:N r a t i o s a r e c o n s i s t e n t w i t h ( b u t c l o n o t r e q u i r e ) d e r i v a t i o n
of t h e coal d e t r i t u s from o u t c r o p s in the drainage area of
t h e Mackay Glacier.
(';illr ~<l)l-u'lis ~ r i e l l ~ v ' ~ ' ~ ~ ; l i l l . ll)')s;l, ~ l l i l l i l l i l l ) 111 l < i ' ~ l l l \ I t t 1111 l l < [ ' 1 (';I~L' I<ohi'ii\ P l l l l i ' ~ ~ . ~ \ l i ~ ; i l ~ ' ~ l l ' i i . Ii'ili! \ i l / t i i / i c d . 51 1 ) 1 ' 1 1 1 (';ili(- R ~ i h r i ~ s Si.'iriier. IOOSb I ~ ; I ~ ~ ~ ~ ~ I ~ I I I I I ~ ~ in C K I ' 1 . ( ' i i t i i K u l i r i ~ , .
I'ro1~'ri. A i ~ l ; u c i n ' i i . Trim . \ i i / i i i / i r n . 51 11. I U).
( ' i t [ i c l Rohcr!\ .Seieiiet.' Teiim. 101lSi.-, M i i i t ~ 1 1 1 1 S I I ~ I I ~ I 111 ('l-:l' l ( ' , I I W
I < o h r i i s PI'O~CVI. Anl;irc~tii.~;i. /;,ii<i , \ i n n i ' ~ i i i i . 5( I I. (13 l ' I (':ilie I<ol'irils Sciciiee'l'c;iiii. lO1)SiI. (,)ii:ilni~:iiv S l i i i t ; ~ i i i ('[.;I' I ( ',illi-
RobciIs I'i'oji'ei. A ~ i i ; i n . ' i ~ ~ ; i , / < Â ¥ / , \ i i / ~ n / i t ~ i . 5( I ) . { l ( X l ( ' i i u l ~ i - l ~ l D.I;.. K : i i s \ \ ~ - I I R , . \\irs~~,ic'li .l.'l'.. I < r ; m , s ( '.M. c<' I i r i i ~ r i l< \
19S(i. I lie use o f ~ ~ ~ I I I ~ I I ~ I I I I ~ I i ~ ~ i l ~ i r i i o ~ ~ III ilu' iiii;il\sis -1 ti'din r d i ~ i o r g ; t i ~ i e s i ~ I l i i r i ~ ~ s c ~ i . l i ~ ~ i ~ ~ ~ i s ; ~ i i ~ l sliiik~s. ( ' / i ~ i i ~ i ~ ~ / t K ' i r ~ ~ / { i \ ' \ ~ . 5-1 I 1'1 l V,
('o;ilrs D.!\.. S l i i e k e ~ ~ (;.I). it l.iiiidis ];,l< . l 0 0 0 . C<i;il !;<-I ~ l n v \ . C n.11 t111:iIil). am1 co;il irsdiirccs i n ilic I ' e i ~ i i i i i i i lo c k s o l l l n - I~V.IIIIII S i i ~ ~ ' i ~ i ' o i i ~ i . ' l ' r ; i i i s ; i i i t ; ~ i ~ i . ' ~ i c M o i i i i ~ i i i i i s , Aiit;ii't'lie;i. 111: S p l r i ~ ~ , i o i ~ ~ , ~ . r i S.l", it l)i'cseIioI'l' d,!\.M. ( r i l s , ). ~ \ / i i n ' i ' n l !'!c\i~iiri 1"i / ' 0 / , 11iii11 , I /
A i ~ a i ' i /;(.(I, , \ ( i ! ' A a / i i r d u . / < t ' \ < ' t i i ' < I t .S(,/'I(Y, 51. l H I(, (lc I.ex'u\\ .I.V\'. X I .;II~G;III('.. I W \ . A l:<'\ icy\\ 111 ~ ~ i ; i c i o i i i ~ i l c ~ t . ' i ~ 1,1i 1 1 1 ~ . 1 1 1 1 ,
c o i i i ~ i o u ~ i i l s iIi;il coiiiprisc l i \ in" o s ~ i ~ i i ~ s n i s iind llic'ii i o k ' I 11 I \ ~ - I ~ , ~ , < , I I , co;il.;iii~l pni~oI~-11111 I'oi 111:iimii. In: Miic'koS.;\, & l < i i ~ e l M I I I n I , . I,
O/.xiill;i' (;i'Oi /ll'ili;\if'\: /'/'//!l ;/>/i'\ cllli/Af)f>/ii ( ~ t i f l \ . ~ ' ~ t ' l l 1 l i l l , Ni'\\
Y o r k . 23-72.
l)iir;~n(l 13.. I W O . Sc~linicnt;n'\ o i y i t n i ~ HI;III~'I" iind ILe'ropeii. l II~~IIIIIII~II
; ~ ~ ~ ~ l t ~ ~ ~ ; ~ ~ ~ l i l ; i l i \ c i ~ ~ i p c n l ; ~ ~ ~ c c o I ' l ~ ~ i o ~ i ~ ~ ~ , I n : l)m;iiid l i . ( c d . ) , h r i < y r n l i i ^ o / i i h h ' O ~ i i n i c i \ ' ! ~ i n c r j i o i ! ~ , S i ' i l i i ~ i i ~ ~ i l ~ i i Y/T'(JC/~\, l - . d i ~ i o ~ I\ I ' r r l i m p , 1). .HIS. : 13-3.1.
lk'tlgcs S.I. ('2 Stern S.l1.. l0S.l. (';i~~Iion ;itid iiitiopcn (I~~E~IIIIIII.~IIIIII~~ (11
~;~rho~i;~lc-conl:iinuil; solids. l.iiiiiiii/iip ~ U K / ~ ~ ' O ~ I I I ~ I , ~ ; M ~ / I / I \ ' . 20. ii'i i' dd 4 Junes R.W.. 10S7. 0rg;inic 1':icics In: lirooks S. it \4'rlii.- 1) ( 1 ~ 1 s I,
Advances 111 /'i,ii'd/i,iiui ~/co(~/n~iniMi'i~. A c i i d c ~ ~ i i c Piess. l ,o~icIoii. L I V0 M;ii.~clis C.S.. ll;iikliid R , l . & C%;iii~oii .I.I'.. 1002. 0ri;;iiiir III.IIII~I
i i c c u ~ ~ ~ ~ ~ l i t t i o ~ ~ . r c i ~ ~ i ~ i e i ' i i l i / i i ~ i o n . ;in(i b ~ i i i ; i l in ;in ; i n c i ~ i ' (YI,I~I;I~
s c i l i ~ ~ ~ e n ! . I n : \ V l ~ e l ; i n I . K . 83 i;iiri in~!loi~.I.\\~. ( c ~ l s . ) . (h'giiiin Miiih'i Pi'oi/t<c{!\'iiy, A i ~ i ~ m a n i a i i i i n , i i i i ( i ' / ' r e ~ \ c ~ ~ i ~ a i i o i i in R e c a i / a n i l . \~I~Â¥I<,II Sediments. C'olumhia l l i i i \ e r s ~ i y Press, Nc3\v Y o r k . 8 2 - 0 s .
MiiHer C i . A: Ciastnci M , . 107 1. The "l<iirl'io~i;ii-lioiiihc ;I s i i i i p l r ( l r \ 11.c l o r the d c t e r i ~ ~ i i i i i t i o ~ ~ o f ~ h e c i i r b o i i i i ~ c contcnl i n s e i l i ~ i u ~ n ~ s . soils.
iiiui othei m a k r i i i l s . Ncuc'i . f ( i / ~ r i ~ i i i ' f i , / ~ / ' ~ ' M t i u ' i ' ( ~ l o ~ i c ~ l ~ / o n i i i \ / s r / / t ~ , 10. 4(i6-4(i1j,
Pelers K.!';.. IOSO, Gui(lcIines I o r c ' \ i i l i i a ~ i n g I ~ ' I I " ~ ~ L Y I I I I s o u n ' r i o c k using p r o i ; r i t ~ ~ ~ i ~ ~ c t l pyrolysis. American Association o/ / i ~ ~ / r i ~ / i ~ ~ i n Grii/o,qi.\/i liiillfliii. 70. 3 18-320.
Roscnhcium I? ..I. K SlieparJ S.M.I".. IOSA. A n isolopic stiitly ol s i ~ l r i 1 1 ~ s . doloiiiiles. am1 ankci-itcs a1 h i g h triiiperaliii'cs. ( i c o f l i i i i i i i . i i i'i
C o . ~ i ~ n ' h i / i i i ( . i i A r i a . 50. 1 147- 1 150.
Stein R.. 19W . A ( ~ f i i i i i i i l i i / i o n o/'Oi.,qmiiu' C i i r h o n ~ I I Marine . S ( ~ i l i n i o i i ~ \ . S p ~ ~ i n ~ r - V c r l ; i g . Ik-rlin, 2 17 p.
Tcgcl;i;ir l<.\\!.. d c l.ccnu S.\\'.. D c r c i ~ i ~ e S. 1% I,;iri;c;m c'., IOSO. A
~recippi'ais~il of kci-ogen l'o1:iii:itioii. (iciicliiiiiicii c l C i i \ i i i i ~ c l i i i i i i ( i i /lcln. 53. 3 103.3 l Oft.
You11gG.C.. 1991. Fossil fishes f r o m Anlarctica. In: T i i i g e y R.S. ( r i l . ) . The G p o l o g ~ nf'Aii/(ti'rlirii, Clarendon Press. Oxford. 53s-507.
