Recognition of alkenones in a lower Aptian porcellanite from the west-central Pacific Simon C. Brassell*, Mirela Dumitrescu, the ODP Leg 198 Shipboard Scientific Party 1 Biogeochemical Laboratories, Department of Geological Sciences, Indiana University, Bloomington, IN 47405-1403, USA Received 2 August 2002; accepted 23 September 2003 (returned to author for revision 4 August 2003) Abstract ODPLeg198drillingonShatskyRiserecoveredalowerAptianporcellanite(  120.5 Ma) deposited during oceanic anoxic event (OAE) 1a that contains C 36 –C 39 alkadienones: C 37:2 and C 39:2 alkadien-2-ones and C 36:2 and C 38:2 alkadien-3-ones.Thisalkenonedistributiondiffersfromthattypicalofcontemporarysedimentsandhaptophytealgae, but resembles that of Cretaceous sediments from the Blake-Bahama basin. The discovery of alkenones in the early Aptian extends their sedimentary record by 15 M.y. to 120.5 M.y. and demonstrates the potential for long-term survival of these diagnostic functional lipids under favorable depositional conditions and subsequent shallow burial. It also contributes to the understanding and reconstruction of evolutionary developments in alkenone distributions and biosynthesis over geologic time. # 2003 Elsevier Ltd. All rights reserved. 1. Introduction Among sedimentary biomarkers, alkenones perhaps provide the best direct connection of specific molecules to defined biological sources. The distinctive and diag- nostic structural elements of alkenones are their long- carbon chains (C 36 –C 41 )andunsaturationatC 7 spacing with Z rather than E configuation (Brassell, 1993). The biosynthesis of alkenones is restricted to a few extant species of the Haptophyta, primarily Emiliania huxleyi and Gephyrocapsa oceanica (reviewed in Conte et al., 1994; Volkman, 2000). Series of related alkenes and alkyl alkenoates also occur in these organisms and in sediments (Volkman et al., 1980; Marlowe et al., 1984, 1990; Brassell, 1993). The only organism known to contain similar lipids is Chloroflexus, which produces alkenes(C 37:3 )ofcomparablechainlengthwithidentical positions ( 8,15,22 ) of unsaturation, albeit with the biosynthetically prevalent E configuration (Shiea et al., 1991;Zengetal.,1992;vanderMeeretal.,1999). An understanding of the origins of alkenone bio- synthesis requires further evidence of temporal patterns of alkenone occurrences. Alkenone phylogeny has been explored by assessment of their co-occurrence with calcareous nannoplankton, a consistency in these associations prompted the supposition that alkenones were biosynthesized by species of Reticulofenestra during the Tertiary (Marlowe et al., 1990). The search for alkenones in ancient sediments that exhibit excep- tional preservation of biolipids provides the best oppor- tunity to achieve this objective, especially where the concentrations of functional lipids significantly exceed those of hydrocarbons. 0146-6380/$ - see front matter # 2003 Elsevier Ltd. All rights reserved. doi:10.1016/j.orggeochem.2003.09.003 Organic Geochemistry 35 (2004) 181–188 www.elsevier.com/locate/orggeochem * Corresponding author. Tel.: +1-812-855-3786; fax: +1- 812-855-7961. E-mail address: simon@indiana.edu (S.C. Brassell). 1 ODP Leg 198 Shipboard Scientific Party: T.J. Bralower, I. Premoli-Silva,M.J.Malone,M.A.Arthur,K.Averyt,P.Bown, J.E.T. Channell, L.J. Clarke, A.L. Dutton, J.W. Eleson, T.D. Frank, S. Gylesjo¨, H. Hancock, H. Kano, R.M. Leckie, K.M. Marsaglia,J.McGuire,K.T.Moe,M.R.Petrizzo,S.Robinson, U. Ro¨hl, W.W. Sager, K. Takeda, D. Thomas, T. Williams, and J.C. Zachos.