Long-chain n-alkanes and alkenones were analyzed in sediments from Dabusu Lake, northeastern China, from ca. 7.2–4.5 kyr BP (the Holocene Optimum) and the present. Long-chain n-alkanes are derived from leaf waxes of terrestrial vascular plants and aquatic macrophytes. Using n-alkane proxies such as Paq and average chain length (ACL) indices, variations in paleovegetation were reconstructed. The Paq values were generally low, indicating that aquatic macrophytes were a minor floral component in Dabusu Lake. The ACL data indicated that forest/grassland mixed vegetation occurred around the lake. From the alkenone distribution patterns (C37/C38, C40/C37, and %C37:4 ratios), the main alkenone producers were inferred to be Group II producers, especially Ruttnera lamellosa. We estimated water temperatures based on alkenone unsaturation indices (UK37 and UK’’37) using the temperature calibrations obtained from culture strains of R. lamellosa. The variation pattern of the UK’’37-based water temperatures was almost similar to that of the UK37-based pattern, although some spikes differed between the temperatures based on the two indices. The UK’’37-based water temperatures were lower from 7.2 to 6.2 kyr BP, and subsequently increased after 6.2 kyr BP. The alkenone-based temperatures were highest from 5.5 to 5.3 kyr BP, indicating that this maximal stage was the Holocene Thermal Maximum in the Dabusu region. The markedly decreasing spikes of UK’’37-based water temperatures in our study likely corresponded to the cooling events during the Holocene Optimum, as previously reported, especially Asian monsoon events (AM) 1 and Bond event 4 (BE4). Also, the increasing spike (7.2 kyr BP) in temperatures was possibly associated with the warming regime just after AM2. Moreover, the rapid increasing spikes of alkenone-based temperatures corresponded to those of Paq at 7.2 kyr BP (just after AM2) and 6.4 kyr BP. These results imply that the rapid warming reconstructed using alkenone-based temperatures might have resulted in increased precipitation around the lake at these ages, especially just after the AM2 cooling.
Identifying the lacustrine haptophyte species that produce long-chain alkenones (LCAs) is essential for using alkenone unsaturation ratios to create lake water temperature reconstructions. We discovered LCAs in the brackish Lake Takahoko in northern Japan. The identity of LCA-producing species was investigated using 18S ribosomal DNA (rDNA) and organic geochemical analysis. Two distinct genetic groups, termed as Tak-A and Tak-B, were identified within the Group II haptophyte phylotype. Tak-A was closely related to Hap-A, which was obtained from Lake George, USA; and Tak-B was identified as Isochrysis galbana. Because Hap-A and Isochrysis galbana have similar temperature calibrations, Tak-A and Tak-B were also expected to share similar calibrations. Therefore, the changes of their relative abundances in the lake should not significantly disturb paleotemperature reconstructions. The alkenone temperature recorded in the surface sediment corresponded to the lake temperature in early to late summer. This is likely related to the haptophyte bloom season in Lake Takahoko suggesting that this lake may be a viable location for creating an lacustrine alkenone paleotemperature record.
Triterpenoids and their derivatives are ubiquitous in sediment samples. Land plants are major sources of non-hopanoid triterpenoids; these terpenoids comprise a vast number of chemotaxonomically distinct biomolecules. Hence, geologically occurring plant-derived triterpenoids (geoterpenoids) potentially record unique characteristics of paleovegetation and sedimentary environments, and serve as source-specific markers for studying paleoenvironments. This review is aimed at explaining the origin of triterpenoids and their use as biomarkers in elucidating paleoenvironments. Herein, application of plant-derived triterpenoids is discussed in terms of: (i) their biosynthetic pathways. These compounds are primarily synthesized via oxidosqualene cyclase (OSCs) and serve as precursors for a variety of membrane sterols and steroid hormones. Studies on OSCs and resulting compounds have helped elucidate the diversity and origin of the parent terpenoids. (ii) their chemotaxonomic significance. Geochemically important classes of triterpenoid skeletons are useful in gathering and substantiating information on botanical origin of these compounds, evolution and diversification of angiosperms, and organic matter preservation during different periods in geological history. (iii) current knowledge on their transformation into geoterpenoids via diagenetic alterations. This knowledge helped in paleoenvironmental reconstructions from the local depositional environments to paleoclimatic variations. This review focuses on triterpenoids as paleoenvironmental biomarkers, and consolidates relevant literature that can form the basis for developing tools and techniques for improved paleoenvironment reconstruction. Future investigations should focus on detecting as yet unknown classes of triterpenoids and their biosynthetic pathways, inclusion of this information in automated databases, and identification of geoterpenoids as potential biomarkers to further our understanding of paleoenvironments and paleoclimate.
Hydrogen isotope ratios of biomarkers have been shown to reflect water isotope ratios, and in some cases correlate significantly with salinity. The δ2H-salinity relationship is best studied for long-chain alkenones, biomarkers for haptophyte algae, and is known to be influenced by a number of different environmental parameters. It is not fully known why δ2H ratios of lipids retain a correlation to salinity, and whether this is a general feature for other lipids produced by haptophyte algae. Here, we analyzed δ2H ratios of three fatty acids, brassicasterol, long-chain C37 alkenones and phytol from three different haptophyte species grown over a range of salinities. Lipids synthesized in the cytosol, or relying on precursors of cytosolic origin, show a correlation between their δ2H ratios and salinity. In contrast, biosynthesis in the chloroplast, or utilizing precursors created in the chloroplast, yields lipids that do not show a correlation between δ2H ratios and salinity. This leads to the conclusion that location of metabolism is the first-order control on the salinity signal retained in δ2H ratios of certain lipids. Additionally, we found that δ2H ratios of alkenones from batch cultures of the Group II haptophyte species Tisochrysis lutea correlate positively with temperature, contrary to findings from cultures of Group III haptophytes, but retain a similar response to nutrient availability in line with other Group III haptophytes.
The Yezo Group, exposed in Hokkaido, northern Japan, is one of the few strata that recorded Cretaceous paleo-oceanographic changes in the Pacific Ocean. Although the group yields abundant marine macro- and microfossils, sporadic occurrences of age-diagnostic species in several stratigraphic intervals has prevented high-resolution international biostratigraphic correlation. The proposed integrated bio- and carbon isotope stratigraphy of the Yezo Group, which is exposed in northwest Hokkaido, enables high-resolution international stratigraphic correlation spanning from Upper Albian to Lower Campanian. The correlation of the present study identifies the detailed stratigraphic horizons of the Albian/Cenomanian, Cenomanian/Turonian, Turonian/Coniacian, Coniacian/Santonian, and Santonian/Campanian boundaries, as well as the Late Cretaceous paleo-environmental events in the Yezo Group. The Yezo Group is also important in order to complement the chronometric age of the Cretaceous geologic time scale because the group includes numerous felsic tuffs. The U-Pb zircon ages of some of these tuffs, which are interbedded near the Albian/Cenomanian, Coniacian/Santonian and the Santonian/Campanian boundaries in the Yezo Group, are dated at 99.7±0.3 Ma (Quidelleur et al. 2011), 86.87±0.60/0.67 (internal/total error) Ma and 84.7±0.7/1.8 (internal/total error) Ma, respectively. These radiometric ages are consistent with the latest age model of the Cretaceous time scale.
Aliphatic hydrocarbons were analyzed in 3 species (Cladonia vulcani, Cladonia scabriuscula, and Xanthoria sp.) of lichens collected from Hokkaido and Hyogo Prefectures, Japan. Molecular composition of n-alkanes is likely influenced by precipitation, as the long chain n-alkanes are produced under arid environments. Alkenes such as heptadecene are also detected as major components in these samples. Molecular composition of these alkanes is different between the genus Xanthoria and Cladonia, suggesting that the composition is influenced by taxonomic diversity. Molecular composition of the aliphatic hydrocarbons other than n-alkanes and alkenes detected are far different between the genera Xanthoria and Cladonia, but are almost similar in these 2 species of the genus Cladonia, potentially depending on taxonomy at the genus level. From these results, we predict that the alkenes, as well as other aliphatic hydrocarbons, can be useful as a chemotaxonomic marker, while the composition of n-alkanes can be an environmental indicator.
Alkenone-producing species have been recently found in diverse lacustrine environments, albeit with taxonomic information derived indirectly from environmental genomic techniques. In this study, we isolated alkenone-producing algal species from Canadian saline lakes and established unialgal cultures of individual strains to identify their taxonomical and molecular biological characteristics. Water and sediments collected from the lakes were first enriched in artificial seawater medium over a range of salinities (5–40 g/L) to cultivate taxa in vitro. Unialgal cultures of seven haptophyte strains were isolated and categorized in the Isochrysis clade using SSU and LSU rRNA gene analysis. The alkenone distributions within isolated strains were determined to be novel compared with other previously reported alkenone-producing haptophytes. While all strains produced the typical C37 and C38 range of isomers, one strain isolated from Canadian salt lakes also produced novel C41 and C42 alkenones that are temperature sensitive. In addition, we showed that all alkenone unsaturation indices (e.g., and ) are temperature-dependent in culture experiments, and that alkenoate indices (e.g., , , RIA38 and A37/A38) provide alternative options for temperature calibration based on these new lacustrine algal strains. Importantly, these indices show temperature dependence in culture experiments at temperatures below 10 °C, where traditional alkenone proxies were not as sensitive. We hypothesize that this suite of calibrations may be used for reconstructions of past water temperature in a broad range of lakes in the Canadian prairies.
Ester-bound compounds (compounds released by saponification) from the resistant macromolecules (RMMs) were analyzed in the extant and Pliocene fossil Liquidambar fruit from the Tokai Group distributed in Gifu Prefecture, central Japan. We compared the distributions of the ester-bound triterpenoids from the fossil with those of free and ester-bound triterpenoids of the extant fruits. The series of triterpenoid acids such as oleanolic and ursolic acids were identified in free compounds but hardly detected in ester-bound compounds from the extant Liquidambar samples. Most of free triterpenoids identified in the extant Liquidambar were also present in the fossil Liquidambar sample as the ester-bound compounds. These results indicate the occurrence of post-depositional incorporation of the free triterpenoids into the macromolecules such as the RMMs via ester bonds. Thus, it is suggested that the ester-bound triterpenoids in RMMs serve as excellent archives of the indigenous assemblage of triterpenoids. The class distributions of the oleanoids and ursanoids in the ester-bound compounds from the fossil sample are considerably different from those in the free polar compounds of the extant samples. Selective preservation of C-28 carboxyl group compared to C-3 oxygenated functions indicates that the triterpenoid acids were incorporated into RMM via ester-bound formed between C-28 carboxyl and hydroxyl groups of the RMM. These results indicate that the ester-bound triterpenoid acids obtained from the fossil sample are selectively preserved by incorporation into the RMM of the fruits.
Biomarker analyses for evaluating maturity of organic matter and depositional environments such as redox conditions, were performed in sediments across the Cenomanian–Turonian boundary (CTB) in the Saku Formation of the Yezo Group distributed along the Shumarinai‐gawa River and the Omagari‐zawa River, both in the Tomamae area, Hokkaido, Japan. Maturity indicators using steranes and hopanes, show that organic matter in sediments from the Shumarinai‐gawa and Omagari‐zawa sections are of lower maturity than those from the Hakkin‐gawa section (Oyubari area). Moreover, the ββ hopane ratios clearly show that the maturity of the Shumarinai‐gawa samples is lower than that of the Omagari‐zawa samples. These variations in the maturity of organic matter presumably reflect the difference in their burial histories. The results for the pristane/phytane (Pr/Ph) ratios suggest that the Shumarinai‐gawa samples were deposited under dysoxic to anoxic environments across the CTB, while the depositional environments of the Omagari‐zawa samples were relatively oxic. By another paleoredox indicator using C35 homohopanoids including a homohopene index (HHenI), higher values are observed in the Shumarinai‐gawa section, particularly in the horizons of the preceding period and an early stage of the first negative shift phase and the latest oceanic anoxic event 2 (OAE2) interval. These results suggest that the Shumarinai‐gawa samples record dysoxic to anoxic environments across the CTB. In contrast, the signals for the C35 homohopanoid index values show a relatively oxic condition in the Omagari‐zawa section. The trends of stratigraphic variations in redox conditions are different from those in the OAE2 interval in the proto‐Atlantic and Tethys regions as reported previously. Hence, the redox variations in the Tomamae area were basically related to a local environmental setting rather than global anoxia. However, the prominent anoxic emphasis observed in the HHenI profile of the Shumarinai‐gawa section can be a distinctive, and possibly global, event in the North‐West Pacific just before the OAE2.
Long-chain alkenones and related compounds were analyzed in Miocene and Pliocene sediments from the Gulf of Cadiz (GoC) in the eastern North Atlantic, which were obtained by Integrated Ocean Drilling Project (IODP) Expedition 339. Both GC and GC–MS analyses using non- and mid-polar columns were performed on the sediments. Isomeric cis-C37 alkenones were identified along with common trans-C37–C39 alkenones. The use of a mid-polar column resulted in the complete separation of the trans-C37 tri-unsaturated alkenone and the cis-C37 di-unsaturated alkenone and thus contributed to a more precise estimation of the alkenone-based paleotemperature. The reconstructed SSTs range from 26 to 28 °C during ca. 6–3 Ma in the GoC. These variations are concordant with global climate change during the period, particularly the Pliocene Climatic Optimum and the onset of sustained ice sheet growth in the northern hemisphere. The concentrations of C37–C39 alkenones and the C37/C38 alkenone ratios are lower during the late Miocene to early Pliocene and increase after ca. 4.2 Ma, which corresponds to the taxonomic change of the plausible alkenone producers from the genus Reticulofenestra to genera Gephyrocapsa and Reticulofenestra. Moreover, a C38 di-unsaturated alkene-2,36-dione was tentatively identified. Variations in the concentrations of a tentatively identified alkenedione are almost synchronous with those of other alkenones, and their relative abundances decrease after ca. 4.2 Ma. These results suggest that the alkenedione originated from the ancient alkenone producers such as the genus Reticulofenestra.
We investigated the compositions of long chain alkenones and alkenoates in cultured strains of the marine haptophyte Tisochrysis lutea CCMP463 and T. lutea NIES-2590 (formerly classified as Isochrysis galbana). Both T. lutea strains grown at various temperatures of 15–35 °C could be characterized by the lack of tetraunsaturated alkenones and alkenoates in comparison with strains in other genera Isochrysis and Ruttnera, which are classified in the same family Isochrysidaceae and order Isochrysidales that contain alkenone-producing haptophytes. We found that T. lutea has a distinct alkenone response to temperature, which is characterized by high -temperature sensitivity at 15–30 °C and continuing sensitivity at warm-end temperatures over 30 °C, where the other species fail to adapt. Both strains showed similar trends in alkenone compositions and alkenone unsaturation index-temperature calibrations. In addition, both strains CCMP463 and NIES-2590 showed notably close phylogenetic relationships, even those that were collected from remote regions of the Atlantic Ocean, namely the Caribbean Sea and English Channel, where their habitats, particularly the sea surface temperature, are notably different. Considering previous published datasets, three genera, Isochrysis, Ruttnera and Tisochrysis, showed very different trends in the alkenone unsaturation index-temperature calibration. These results suggest that the lack of tetraunsaturated alkenones, warm-water oriented growth and the high sensitivity to growth temperature serve as distinct chemotaxonomic characteristics of T. lutea in the Isochrysidaceae family.
The hydrocarbons in cultures of marine haptophytes Emiliania huxleyi NIES837 and Gephyrocapsa oceanica NIES1315 were analyzed, and nonacosadienes and hentriacontadienes were detected as the major compounds in both strains. C29 and C31 monoenes and di-, tri- and tetra-unsaturated C33 alkenes were also detected as minor compounds but not C37 and C38 alkenes. The positions of the double bonds in the C29 and C31 alkenes were determined by mass spectrometry of their dimethyl disulfide (DMDS) adducts. Among the four C29 alkenes identified, the most abundant isomer was 2,20-nonacosadiene, and the other three compounds were 1,20-nonacosadiene, 3,20-nonacosadiene and 9-nonacosene, respectively. Hitherto, 2,20-nonacosadiene and 3,20-nonacosadiene were unknown to be natural products. The double bond at the n-9 (ω9) position in these C29 alkenes is hypothesized to be derived from precursors of unsaturated fatty acids possessing an n-9 double bond, such as (9Z)-9-octadecenoic acid. Nonacosadienes have the potential for being used as distinct haptophyte biomarkers.
The stable carbon isotope ratio (δ13C) values of sedimentary long chain (> C20) n-alkanoic acids from the equatorial Pacific (IODP Sites U1331–1338) were measured for historical reconstruction of C4 plant contribution from South America over the last 40 Ma. The values for C30 and C32 acids ranged between −36.9‰ and −25.4‰, suggesting that they likely originated from higher plant wax associated with C3-dominated vegetation. The molecular distribution of alkanoic acids in the sediments showed a marked change across the Intertropical Convergence Zone (ITCZ), indicating a potential contribution from the Northern Hemisphere to the sediments located at > 10°N. In contrast, the abundances of n-alkanoic acids significantly decreased in the sediments at < 10°N. The results suggest that the ITCZ may have acted as an effective barrier for the atmospheric transport of terrigenous biomarkers from the Northern Hemisphere, and the records presumably reflect the plant wax signal from the northern part of South America. The latitudinal variation in the δ13C values suggest that the differences in the core locations possibly caused north- and southward shifts of ca. −1.0‰/°N and ca. +0.5‰/°S from the equator, respectively. The corrected δ13C values of C30 and C32 acids did not cross the C3 end member threshold until 1.7 Ma, despite the onset of C4 plants in central South America at ca. 7 Ma. This implies that vegetation in the low latitudes of South America was less affected by hydrological changes induced by the uplift of the Andes during the late Miocene.
Cultured Chrysotila lamellosa CCMP1307 produced high proportion of C37:4 alkenones.
C. lamellosa values reproduced the typical values for C37:4-rich lakes.
calibration showed a better fit with temperature than calibration.
The unsaturation degree of C31 alkenes was also controlled by growth temperature.
The compositions of long chain alkenes, alkenones and alkenoates in a cultured strain of the haptophyte Chrysotila lamellosa CCMP1307, isolated from a salt marsh, were investigated. The biomarker patterns were distinctive and showed a high proportion of tetraunsaturated alkenones and alkenoates, with a pronounced proportion of C40 alkenones and a lack of C38 methyl and C39 ethyl alkenones. Linear regression of the alkenone unsaturation degree with growth temperature (T) was obtained over the range of possible CCMP1307 growth temperature values (4–20 °C): = 0.045 × T (°C) − 1.016, (n = 13, r2 0.96), while the values were weakly correlated with T: = 0.0035T (°C) + 0.0511 (n = 18, r2 0.70). The calibration exhibited a low y-intercept in comparison with that of a Chinese inland lake strain reported previously. The data show significant intraspecific variation in for C. lamellosa between strains from different geographic origins. C. lamellosa CCMP1307 reproduced typical values observed in C37:4 rich lakes, especially at lower temperature (< 15 °C). In addition, we identified C29:2, C31:1, C31:2 and C31:3 alkenes, and found that the unsaturation degree of C31 alkenes (), calculated with C31:1 and C31:2 alkenes, might also be a useful index of growth temperature for the haptophyte C. lamellosa.
We investigated terpenoid biomarkers in muds from lignite seams, clays from porcelain clay beds that slightly contain lignite, and from a conifer cone macrofossil from the Miocene Tokiguchi Porcelain Clay Formation of the Tokai Group in central Japan, as well as extant cones. The n-alkanes, n-alkanols (suberin origin), diterpenoids (conifer origin), hopanoids (bacteria origin) and steroids were mainly present in the lignite-containing muds and clays. On the other hand, the diterpenoids, triterpenoids (angiosperm origin), hopanoids and steroids were detected as major component in the conifer cone macrofossil. In addition, the diterpenoids were mainly detected in the extant conifer cones. The low hopane isomer ratios and the detection of biosterols are confirmed to be immature in the lignite, sediment and macrofossil in the formation. The stanol/sterol ratio values of the lignite-containing muds and clays are much higher than that of the macrofossil. The higher ratios in lignite-containing muds and clays are possibly attributed to enhanced microbial reduction of organic matter under reduced condition in the swampy environments. A large amount of angiosperm-derived triterpenoids detected in the conifer cone macrofossil are considered as contaminants in the sample from sedimentary organic particles originated from detrital waxes of angiosperms. Such contamination might occur by migration of organic compounds within sediment after deposition. The angiosperm-derived polar terpenoids may be hardly affected by contamination by migration of organic matter from the adjacent sediments because these are less abundant in the conifer macrofossil. Thus, it is suggested that the polar terpenoid biomarkers are more reliable as paleochemotaxonomic and paleovegetation indicators.
► We analyze terpenoid in sediments of Miocene lignite and clay beds, and plant fossil.
► Coniferous diterpenoid is mainly detected in sediments in the lignite and clay beds.
► Low hopane isomer ratio and biosterol detection show the lignite seams are immature.
► Lower stanol/sterol ratios of lignite seams are due to microbial reduction in swamp.
► Angiosperm-derived triterpenoids are detected as contaminant in a conifer fossil.
Atmospheric carbon dioxide concentrations and climate are regulated on geological timescales by the balance between carbon input from volcanic and metamorphic outgassing and its removal by weathering feedbacks; these feedbacks involve the erosion of silicate rocks and organic-carbon-bearing rocks. The integrated effect of these processes is reflected in the calcium carbonate compensation depth, which is the oceanic depth at which calcium carbonate is dissolved. Here we present a carbonate accumulation record that covers the past 53 million years from a depth transect in the equatorial Pacific Ocean. The carbonate compensation depth tracks long-term ocean cooling, deepening from 3.0–3.5 kilometres during the early Cenozoic (approximately 55 million years ago) to 4.6 kilometres at present, consistent with an overall Cenozoic increase in weathering. We find large superimposed fluctuations in carbonate compensation depth during the middle and late Eocene. Using Earth system models, we identify changes in weathering and the mode of organic-carbon delivery as two key processes to explain these large-scale Eocene fluctuations of the carbonate compensation depth.
Terrestrial higher plant terpenoids (HPTs) occurring in ancient marine and lacustrine sediments, are more refractory and constitute a more highly diversified family of molecules than the other terrestrial higher plant biomarkers including wax compounds and lignin phenols. Therefore, this HPT biomarker can be plant biogeochemical and paleontological indicators. Triterpenes such as oleanane are derived from various biological triterpenoids synthesized by almost all angiosperms. Diterpenenes such as retene are originated from abietane-type diterpenoids, which are constituents of gymnosperm, especially conifer. In pimarane and phyllocladane type diterpenoids, their precursors, source plants, and diagenetic products have been partly known. In addition, sesquiterpenoids are derived from both angiosperm and gymnosperm biosynthesized compounds. Several researchers have suggested that the HPT distributions were useful as the paleovegetation proxies for reconstructing the relative abundance of angiosperm to gymnosperm (e.g. angiosperm/gymnosperm index; AGI). Moreover, we recently examinated applicability of the indicator for angiosperm/gymnosperm ratio by using the HPTs in ancient plant fossils. In this paper, we review such HPT biomarkers and their applicability and reliability of the indicator as plant chemotaxonomy and paleovegetation in the ancient sediments.
In March 2009, the R/V JOIDES Resolution returned to operations after its extended refit and began with a drilling program ideally suited to its drilling strengths, the Pacific Equatorial Age Transect (PEAT, IODP Exp 320/321; Fig. 1A).
The PEAT drilling program was developed to understand how a major oceanic region evolved over the Cenozoic Era (65–0 Ma) and how it interacted with global climate. It specifically targeted the interval between 52 Ma and 0 Ma and drilled a series of sites that originated on the paleoequator. These sites have since been moved to the northwest by plate tectonics. The equatorial Pacific is an important target for paleocean ographic study because it is a significant ‘cog’ in the Earth’s climate machine, representing roughly half of the total tropical oceans that in turn represent roughly half of the total global ocean area. Prior drilling in both the Deep Sea Drilling Project (DSDP) and the Ocean Drilling Program (ODP) outlined the changes that have occurred through the Cenozoic (e.g., van Andel et al., 1975; Pisias et al., 1995). Not only did the earlier work fail to cover sufficient time intervals but also many of the sites were cored with ‘first-generation’ scientific drilling technology with incomplete and disturbed sediment recovery and thus cannot be used for detailed studies. ODP Legs 138 and 199 provide the best sample material from previous drilling, but each leg recovered sections spanning less than 10 million years suitable for cyclostratigraphy (the use of earths orbital cycles, recorded in sediments, as a measure of time). Up until the PEAT program it was difficult to achieve more than a reconnaissance of the environmental changes that have occurred in the equatorial Pacific. The PEAT program was designed to augment previous drilling and collect undisturbed sediments that could be spliced into a continuous, high-resolution environmental record of the eastern equatorial Pacific for the entire period from 56–0 Ma to present.
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The distributions of aliphatic and aromatic terpenoids in Cretaceous and Paleogene angiosperm fossils from Japan were investigated. Aliphatic A ring-degraded oleanane, ursane and lupane were found in all samples. In addition, aliphatic gymnosperm-derived diterpenoids were detected in significant quantities. Aromatic oleanane-type triterpenoids were the major components, with ursane- and lupane-type triterpenoids being minor compounds in all angiosperm fossils. In a Cretaceous gymnosperm fossil, major components included aliphatic labdane-, isopimarane- and abietane-type diterpenoids, aromatic abietane-type diterpenoids, and chrysene- and picene-type polyaromatic hydrocarbons (PAHs). Trace amounts of oleanane-, ursane- and lupane-type triterpenoids were also identified. It is likely that the aromatic triterpenoids were introduced to the gymnosperm fossil from the angiosperm-derived material in the sediments. We defined an angiosperm/gymnosperm index (al-AGI′) as an alternative to the aliphatic triterpenoid/diterpenoid ratio proposed in the literature. The al-AGI′ index may underestimate the angiosperm contribution, because the aliphatic angiosperm-derived triterpenoids are more readily converted to aromatic counterparts than the diterpenoids during diagenesis. An aromatic angiosperm/gymnosperm index (ar-AGI) can be calculated using aromatic diterpenoids and triterpenoids. We suggest that ar-AGI is best calculated using only the oleanane-, ursane- and lupane-type aromatic triterpenoids, and that the chrysene- and picene-type PAHs be excluded.
The chemical compositions of woody fossil fragments collected by picking manually and density centrifugation from sandstones of the Lower Cretaceous Yezo Group in Oyubari, central Hokkaido, Japan were analyzed by KOH/methanol hydrolysis (saponification) after solvent extraction. Organic compounds bound in macromolecules of the woody fragments with ester bonds, obtained by saponification, were mainly composed of short-chain (C14 to C18) fatty acids and series of n-alkanols ranging from C12 to C28 homologues. These ester bound constituents are attributed to moieties of polyester parts of selectively preserved resistant macromolecule like cutin or suberin. Even carbon-number predominance was observed in both compounds, which indicated that biological components were well preserved. The bound fatty acids showed similar distribution patterns among all samples, indicating that these moieties might have been altered by strong diagenetic processes. On the other hand, the distribution patterns of n-alkanols significantly varied. In particular, those of long-chain (>C20) n-alkanols varied possibly depending on plant taxonomy. Thus, we suggest that these parameters are strongly useful as molecular paleobiological indicators for chemotaxonomic analyses. Also, the distributions of short-chain n-alkanols and the ratios of short to long-chain homologues are presumably useful indicators for diagenesis, taphonomy and environment.