Geochemical Journal, Vol. 33, pp. 285 to 294, 1999

Characterization of n-, and phytane in the Cretaceous/ Tertiary boundary sediments at Kawaruppu, Hokkaido, Japan

HAJIME MITA and AKIRA SHIMOYAMA

Department of Chemistry, University of Tsukuba, Tsukuba 305-8571, Japan

(Received December 24, 1998; Accepted April 22 , 1999)

Normal alkanes from C12 to C36, pristane and phytane were identified in the Cretaceous/Tertiary (K/T) boundary sediments at Kawaruppu, Hokkaido, Japan. These compounds were found at the levels of sub to a few nmol g-1. Total concentrations of the n-alkanes within the boundary claystone were generally one third to one half of those in the sediments above and below the claystone. The smaller concentrations within the claystone were mainly due to smaller concentrations of longer chain n-alkanes (C25 to C31) than in the sediments above and below it. The longer chain n-alkanes were likely from terrestrial plants and reflected their small population at the end of Cretaceous. The concentration of longer chain n-alkanes decreased rapidly at the base of the boundary claystone, indicating the sudden cease of terrestrial n- input, continued low to the horizon at the upper two thirds of the claystone and then, started increasing toward the top of the claystone. The n-alkane concentration change indicates the period of the small input of terrestrial n-alkanes to be ca. 7,000 years at most and the recovery period to be ca. 2,000 years. The depth distribution pattern of pristane plus phytane concentrations in the K/T sediments roughly resembles that of the n-alkanes.

derived from then-living organisms. However, INTRODUCTION there are few studies of this kind. Those published The massive extinction of organisms, ranging to date report traces of microbial hydrocarbons and from dinosaurs to marine plankton at the end of fatty acids in the K/T boundary claystone and Cretaceous (approximately 65 million years ago) microbial fatty acids and additional terrestrial is one of the most significant biological events in resin acids in the sediments above and below the earth history. A global fallout of debris and dust claystone at Stevns Klint (Simoneit and Bellar, due to the impact of an extraterrestrial body or 1985, 1987; Meyers and Simoneit, 1989). bolide (Alvarez et al., 1980; Smith and Hertogen, The K/T boundary sediments at Kawaruppu, 1980) or to extensive volcanism (Officer and Hokkaido, Japan, provide a good sedimentary se Drake, 1983; McLean, 1985) is thought to be the quence to study the environmental changes at the cause of the extinction. Organic geochemical stud K/T boundary. The boundary claystone is similar ies on the Cretaceous/Tertiary (KIT) boundary in appearance to the well-known "boundary sediments aimed to find evidence for extraterres claystone" of the classical K/T boundary in Eu trial organic compounds (Zhao and Bada, 1989; rope, but is thicker (nearly 14 cm) and can be stud Mita et al., 1996, 1998) and wild fires triggered ied in detail along the depth. Other published stud by the bolide impact (Wolbach et al., 1985, 1988; ies of these sediments dealt with planktonic Venkatesan and Dahl, 1989; Heymann et al., foraminifera (Kaiho and Saito, 1986; Kaiho 1992), 1994a, b, 1996). palynomorphs (Saito et al., 1986), isotopes Studies of biological organic compounds in the (Kajiwara and Kaiho, 1992), and Ir accumulation K/T boundary sediments provide useful informa and clay minerals (Tasaki et al., 1992). We have tion on the massive extinction, because they are previously studied the organic geochemistry of

285 286 H. Mita and A. Shimoyama amino acids (Mita et al., 1996) and reported aliphatic hydrocarbons. The GC was equipped dicarboxylic acids (Mita et al., 1998) in the with a DB-5ht capillary column (30 m x 0.25 mm sediments. In the present study, we analyzed n i.d.). The oven temperature was programmed to alkanes, pristane and phytane in the sediments hold at 50°C for initial 1 min, and then ramp from above, within, and below the boundary claystone, 50 to 90°C at a rate of 5°C min-1, and from 90 to compared the concentrations, ratios and molecu 300°C at a rate of 4°C min-'. Helium was used as lar distributions of those aliphatic hydrocarbons, the carrier gas with a flow rate of 1.5 ml min 1. and related their characteristics to the environmen The mass spectra were acquired every 0.5 s over tal changes of the K/T boundary sediments at m/z 40 to 510 in the electron impact ionization Kawaruppu. mode and mass fragmentograms every 0.2 s. Iden tification and quantification of n-alkanes, pristane and phytane were generally made by comparison EXPERIMENTS of peak retention times and areas, respectively, on Samples mass fragmentograms for selected ions with those The K/T boundary sediments occur near of standard compounds. These compounds used Kawaruppu Town, Tokachi District, Hokkaido were even carbon numered n-alkanes in the range (Saito et al., 1986; Kaiho and Saito, 1986). The of C 12to C24, and C28, C32 and C36 besides pristane location of Kawaruppu, the lithology and sample and phytane. horizons of the sediments were reported in our Analytical grade hexane (Wako pure chemi previous studies (Mita et al., 1996, 1998). Briefly, cals), and twice distilled methanol and benzene the sedimentary sequence at Kawaruppu consists were used. All glassware was heated at 500°C for predominantly of a marine, dark gray siltstone, at least 3 h prior to use in order to eliminate or bearing occasional calcareous concretions. The ganic contaminants. A procedural blank was car boundary claystone is grayish black and nearly 14 ried out with 0.5 g pre-ignited sand powder and it cm thick. Thirteen sediment samples from differ was found that there was no significant contami ent horizons within the boundary claystone (0 to nation during the analysis. 13.7 cm), 5 samples above (40 to 495 cm) and 6 samples below (-395 to 0 cm) the boundary RESULTS AND DISCUSSION claystone were analyzed for aliphatic hydrocar bons. Concentrations Normal alkanes ranging from C,2 to C36, Analyses pristane and phytane were identified. For exam For each analysis, 1 g of powdered sediment ple, the mass fragmentogram (m/z 57) of these was extracted three times with 5 ml of a mixture aliphatic hydrocarbons in the sediment at the mid of benzene and methanol (4:1 by vol.) by sonica dle horizon (5.5 to 6.3 cm) of the boundary tion for 30 min. The extracted solutions were com claystone is shown in Fig. 1. Concentrations of bined, concentrated under reduced pressure, and these aliphatic hydrocarbons are listed in Table 1. applied to a silica gel column (130 mm x 10 mm The total concentrations of n-alkanes within the i.d.; Keiselgel-60, Merck). Aliphatic hydrocarbons boundary claystone (0 to 13.7 cm) were in the were obtained by eluting with hexane (10 ml). This ranges of 4.7 to 18.2 nmol g-1 with the mean value hexane solution was concentrated to 50 ul under of 8.7 nmol g-1, in the ranges of 14.0 to 17.6 (mean nitrogen flow for the analysis of individual value 16.5) nmol gl in the sediments above (40 aliphatic hydrocarbons. to 495 cm) and 16.4 to 26.5 (mean value 21.7) A gas chromatograph (GC) combined with a nmol g-1 in those below (-395 to 0 cm) the bound mass spectrometer (MS) (Shimadzu GC-MS QP ary claystone. The concentrations of pristane plus 5000) was used for separation and detection of the phytane within the boundary claystone were in the K/T boundary sediments at Kawaruppu, Hokkaido 287

18 17 32 pristane 33 I/ phyphytane 10, 34 L 35 36 m/z = 57 18 19 20 21 22 23 16 17 24 25 T 15 C N 14 G I (21h28 29 12 13 3031 32

10 20 30 40 50 60 Retention time (min) Fig. 1. Mass fragmentogram (m/z 57) of n-alkanes, pristane and phytane in the KIT boundary claystone (5.5 to 6.3 cm). Peak numbers correspond to those of the carbon number of the n-alkanes.

400 a b c

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0 20 40 0 5 10 0.0 0.4 0.8 1.2 Total n-alkanes Pristane plus phytane Total organic carbon (nmol g-t -rock) (nmolg-I -rock) (%) Fig. 2. Depth distributions of a: total concentrations of n-alkanes (C12 to C36),b: concentrations of pristane plus phytane, and c: total organic carbon content (Mita et al., 1996) in the KIT boundary sediments at Kawaruppu.

ranges of 0.24 to 1.6 (mean value 0.59) nmol g 1, claystone from those in the sediments below the in the ranges of 1.8 to 3.1 (mean value 2.6) nmol boundary claystone. The decreased concentration g-1 in the sediments above and 2.1 to 3.1 (mean of n-alkanes continued over the lower two thirds value 2.7) nmol g-1 below the boundary claystone. portion (0 to 10.6 cm) of the boundary claystone Concentrations of the total n-alkanes and pristane and then sharply increased in the upper one third plus phytane at each sample horizon are shown in (10.6-13.7 cm) of the claystone. The concentra Fig. 2, together with the total organic carbon con tion increase ceased at the top of the boundary tents (Mita et al., 1996). claystone, and remained rather constant in the Total concentration of n-alkanes decreased sig sediments above the claystone. Total concentra nificantly at the lowest horizon in the boundary tions of n-alkanes in the sediments above the 288 H. Mita and A. Shimoyama

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U - K/T boundary sediments at Kawaruppu, Hokkaido 289

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i 290 H. Mita and A. Shimoyama

boundary claystone were about two thirds of those above and below it were mainly due to lower con in the sediments below the claystone; therefore, centrations of the longer chain n-alkanes. the recovery of the n-alkane input to the sediments The concentrations of shorter chain n-alkanes above did not come back to the input level to the (from n-C 15to n-C 19)and longer chain n-alkanes sediments below the claystone. The depth distri (from n-C27 to n-C31) are shown in Fig. 4a. The bution pattern of pristane plus phytane content mean value of the shorter chain n-alkanes within roughly resembles that of the n-alkanes. These ,two the boundary claystone was 2.4 nmol g-1, two patterns do not coincide with that of total organic thirds of the values in the sediments above and carbon contents, showing that the aliphatic hydro below (mean values 3.6 and 3.5 nmol g -l' respec carbons were rather depleted relative to total C tively) the boundary claystone. These values are within the boundary claystone. not so different considering the sources (marine or terrestrial) of the shorter chain n-alkanes. The Molecular distribution patterns and carbon pref source throughout the K/T sediments was likely erence indices of n-alkanes marine organisms as discussed in the carbon pref Molecular distribution patterns of n-alkanes erence index (CPI) section below. On the other are shown in Fig. 3. Concentrations of n-alkanes hand, the mean value of the longer chain n-alkanes (C12 to C36) in most of the sediments within the within the boundary claystone was 1.7 nmol g 1, boundary claystone were roughly similar to each one third of that in the sediments above it (mean other. In the sediments above and below the value 4.6 nmol g-1) and one fifth of that in the boundary claystone, longer chain n-alkanes (>C25) sediments below it (mean value 7.8 nmol g-1). It were more abundant than shorter ones (

3 3 a above the boundary claystone c within the boundary claystone (>40cm) W (0-6.3cm) C C C C 2 C C 2 Relative depth (cm) Relative depth (cm) C O 495 C 0 -e 5.5-6.3 E! y -~ 225 -* -4 .3-5.5 c i -a 120 a C 1 [3 2.8-4.3 U O 0 Q 0 1.8-2.8 .- 60 0 0 0.8-1.8 U n-~.tl O 40 --*--0 -0 .8 0 0 12 16 20 24 28 32 36 12 16 20 24 28 32 36 Carbon number Carbon number

3 3 b within the boundary claystone d below the boundary claystone (6.3 13.7 cm) (< 0 cm) 00 C E C 2 2 Relative depth (cm) Relative depth (cm) 0 1 12.7 13.7 9 -3-0 -. -11.7-12.7 -•--10 )• 16J&AI. -3 -85 1 -a -10 1 .6-11.7 0 f rm... C 0 -•- 8.7 10.6 C -165 OO ElLi~~p~`~L71 U0 U ~i O -235 U 0 7.5 8.7 -~ 6 .3 7.5 5 ~0e'r -~ -395 0 0 12 16 20 24 28 32 36 12 16 20 24 28 32 36 Carbon number Carbon number Fig. 3. Molecular distribution patterns of n-alkanes in the sediments a: above (40 to 495 cm), b: within (6.3 to 13.7 cm), c: within (0 to 6.3 cm), and d: below (-395 to 0 cm) the KIT boundary claystone.

U K/T boundary sediments at Kawaruppu, Hokkaido 291

Simoneit, 1978). Therefore, the substantially below, within and above the claystone were ap smaller concentrations of the longer chain n proximately 2.3, 1.7 and 2.1, respectively. The alkanes within the boundary claystone were prob values 2.3 and 2.1 are not significantly different ably related to smaller inputs of terrestrial organic and indicate that no major diagenetic effect to the matter than into the sediments above and below n-alkanes in the sediments below the boundary it. claystone occurred during the deposition of the Carbon preference indices (CPIs) of the shorter claystone. The CPI decrease at the bottom of the chain n-alkanes (from n-C 15 to n-C 19) were ap claystone was likely due to a small input of ter proximately one throughout all the sample hori restrial organic matter. zons at Kawaruppu (Fig. 4b); therefore the major source of those n-alkanes was likely marine al Pristane to phytane ratios gae. It was reported that shorter chain n-alkanes Pristane to phytane (Pr/Ph) ratios were in the (from n-C 14to n-C20) with no odd or even carbon range of 2.5 to 3.5 (mean value 3.0) throughout number preference were derived from marine al all the sample horizons (Fig. 4c). The ratios indi gae even when a strong odd carbon number pref cate that the Kawaruppu sediments were depos erence of longer chain ones (>n-C24) was observed ited under an oxic environment, assuming that the (Simoneit, 1986). CPIs of the longer chain n Pr/Ph ratio can be used as an indicator of redox alkanes (from n-C27 to n-C31) in the sediments potential in sedimentary environment. The higher

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N -400 U 1 I Q I 4P I I I C) I . I I I v I 0 5 10 0 1 2 3 0 3 6 Concentrations of CPIs of Pristane/phytane ratios n-C15-19(o) and n-C27-29(.) n-C15_19(o) and n-C27-29(.) (nmol g -1 rock) Fig. 4. Depth distributions of a: concentrations of shorter chain n-alkanes (C15 to C19) and longer ones (C27 to C31),b: carbon preference indices (CPIs) of shorter chain n-alkanes (C15 to C19)and longer ones (C27 to C31),and c: ratios of pristane to phytane in the KIT boundary sediments at Kawaruppu. CPIs for the shorter and longer chain n-alkanes are calculated by the equation,

1 Cn + Cn+2+ 2 Cn+4 CPI= 2 C.+1 + Cn+3 where C„ is the concentration of n-alkane with n carbon atoms, and n is 15 for the shorter and 27 for the longer chain n-alkanes.

292 H. Mita and A. Shimoyama

Pr/Ph ratio (>1) indicates oxic conditions (Didyk Estimated accumulation rates from et al., 1978). However, the sulfur isotopic record paleomagnetic study were 1.5 cm kyr 1 and 0.9 in the K/T boundary sediments at Kawaruppu cm kyr 1 in the sediments above and below the showed anoxic conditions for sediments from 0 boundary claystone, respectively (Kajiwara and to 60 cm (Kajiwara and Kaiho, 1992). On the other Kaiho, 1992). Rather more rapid sedimentation of hand, a foraminifera study suggested that oxygenic the boundary claystone than of the sediments conditions at Kawaruppu were. relatively high for above and below it was proposed from concentra the sediments below the -300 cm horizon and tions of benthic foraminifera (Saito et al., 1986). above the boundary claystone, low in the Therefore, the duration of a low input of terres sediments between -300 and -10 cm, and medium trial n-alkanes to the boundary claystone (0 to 10.6 for the rest of sediments including the boundary cm) was 7,000 years at most. On the same basis, claystone (Kaiho, 1992). Therefore, it is not ap it took about 2,000 years (10.6 to 13.7 cm) for the propriate to judge whether oxic or anoxic condi recovery of the n-alkane input to the level found tions prevailed in the sedimentary environment at in the sediments above the boundary claystone. Kawaruppu based on the present information. The input recovery time of the longer n-alkanes was much shorter than the period of the sulfur iso Implications for the biomass extinction event tope anomaly (ca. 70,000 years) (Kajiwara and Kawaruppu is located on the western continen Kaiho, 1992) and the period of the shallowing (ca. tal slope of "Eastern Hokkaido Island" riding on 70,000 years) (Kaiho, 1992). It is apparent that the North American Plate (Maruyama and Seno, the n-alkane record in those sediments shows a 1985) and "Eastern Hokkaido Island" did not un more rapid response to the environmental change dergo a distinct vertical tectonic movement near which took place at the end of the Cretaceous. the K/T boundary time (Kaiho, 1983). Further more, a eustatic sea-level drop at the end of the CONCLUSIONS Cretaceous (Ekdale and Bromley, 1984; Hallam, 1987) was observed at Kawaruppu by the study Analysis of aliphatic hydrocarbons in the K/T of foraminifera (Kaiho, 1992). Sediments at -0.5 boundary claystone and the sediments above and m accumulated in the lower part of the upper below it at Kawaruppu found n-alkanes (C12 to bathyal zone (depth: 300-600 m). Sea bottom C36), pristane and phytane. Examination of their shallowing started at -0.5 m and stopped at 0.4 characteristics led the following conclusions: m. Sediments at 0.4 m accumulated in the upper (1) Concentrations of the individual com part of the upper-bathyal zone (depth: 150 to 300 pounds were mostly at the level of sub-nmol g-1 m). The shallowing suggests that rather higher except for longer chain n-alkanes (C21 to C31) in concentrations of longer n-alkanes could have the sediments above and below the boundary been found in the sediments above the -0.5 m claystone which were present in amounts up to horizon than in the sediments below the -0.5 m 2.9 nmol g 1. horizon. However, the concentrations of longer n (2) Total concentrations of the n-alkanes within alkanes within the boundary claystone were lower the claystone were one third to one half of those than expected. Therefore, the lower concentrations in sediments above and below it. These smaller might have been caused by the devastation of vas concentrations were mainly due to lower concen cular plants at the time the K/T boundary claystone trations of the longer n-alkanes within the bound was deposited. Palynological study also suggested ary claystone than in the sediments above and the devastation of vascular plants at the K/T below it. boundary time at Kawaruppu (Saito, et al., 1986), (3) CPIs of shorter chain n-alkanes (C15 to C19) similar to the situation in the interior of western and longer chain n-alkanes (C25 to C31) suggested North America (Tschudy et al., 1984). that they originated in marine and terres K/T boundary sediments at Kawaruppu, Hokkaido 293 trial plants, respectively. Heymann, D., Wolbach, W. S., Chibante, L. P. F., Brooks, R. R. and Smalley, R. E. (1994b) Search for (4) Depth distribution of the total concentra extractable fullerens in clays from the Cretaceous/ tions of n-alkanes and their molecular distribu Tertiary boundary of the Woodside Creek and tions suggest a much smaller input from terres Flaxbourne River sites, New Zealand. Geochim. trial plants to the boundary claystone than to the Cosmochim. Acta 58, 3531-3534. sediments above and below it. Heymann, D., Chibante, L. P. F., Brooks, R. P., Wolbach, W. S., Smit, J., Korochantsev, A., Nazarov, (5) A large concentration decrease of the longer M. A. and Smalley, R. E. (1996) Fullerenes of possi chain n-alkanes at the K/T boundary was likely ble wildfire origin in Cretaceous-Tertiary boundary due to a rapid devastation of terrestrial plants, a sediments. The Cretaceous-Tertiary Event and Other part of the large biomass extinction at the time. Catastrophes in Earth History (Ryder, G. et al., eds.), The n-alkane concentration change within the Geol. Soc. Amer. Spec. Paper 307, 453-464. boundary claystone indicates the period of the Hunt, J. M. (1968) How gas and oil form and migrate. devastation to be ca. 7,000 years at most and the World Oil 167, 140-150. Kaiho, K. (1983) Geologic ages of the Paleogene of recovery period to the normal level in lower Ter Hokkaido, Japan based upon planktonic foraminifera: tiary to be ca. 2,000 years. The relationship between the hiatuses and sea-level movements. Kaseki (Fossils) 34, 41-49 (in Japanese Acknowledgments-We thank Y. Kajiwara, University with English abstract). of Tsukuba, for samples of the K/T boundary sediments Kaiho, K. (1992) A low extinction rate of intermedi at Kawaruppu. We are grateful to J. R. Cronin, Arizona ate-water benthic foraminifera at Cretaceous/Terti State University, who read an earlier version of this ary boundary. Mar. 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