English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools annual

Global: Zendy Free Plan

Global: Zendy Tools monthly

Global: Zendy Plus monthly

This reconnaissance study was undertaken to determine whether the mass extinctions and faunal successions that mark the Cretaceous/Tertiary (K/T) boundary left a discernible molecular fossil record in the sediments of this period. Lipid signatures of sediments taken from above and below the K/T boundary were compared in core and outcrop samples taken from two locations: the U.S. east coast continental margin (western Atlantic Ocean, DSDP Site 605) and Stevns Klint, Denmark. Four calcareous sediments taken from above and below the K/T boundary in DSDP Hole 605, Section 605-66-1, revealed changing lipid signatures between above and below that are characterized by a large component of unresolved naphthenic hydrocarbons and a homologous series of n-alkanes ranging from Ci6 to C33. These lipid signatures are attributed to an influx of a terrestrial higher plant component and to bacterial reworking of the sediments under partially anoxic depositional and/or diagenetic conditions. The outcrop samples from Stevns Klint had extremely low concentrations of indigenous lipids. The fish clay at the K/T boundary contained traces of microbial hydrocarbons and fatty acids, whereas the carbonates above and below had only microbial fatty acids and additional terrestrial resin acids. The data from both sites indicate a perturbation in the deposition of lipid compound classes across the K/T boundary. INTRODUCTION The Cretaceous/Tertiary (K/T) boundary is marked by major extinctions of both marine and terrestrial species. These extinctions may have been caused by extensive volcanic activity or by the impact of a massive extraterrestrial body (Alvarez et al., 1980, 1984), possibly of meteoritic origin according to current data on Ir and Os anomalies (Alvarez et al., 1982, 1984; Luck and Turekian, 1983). A major meteoritic impact could have had extensive biogeochemical consequences, such as the cessation or dramatic reduction of photosynthetic biomass production on a regional to global scale, possibly caused by wildfires and/or the scouring of continents by tidal waves (e. g., Wolbach et al., 1985). Presumably, a reduction of biogenesis, a possible hiatus or facies change at the K/T boundary, and a subsequent, gradual buildup of extant and new species should have left a molecular fossil record in the sediments. The purpose of this preliminary analysis is to evaluate such a possibility. The samples for this study are from Hole 605, Core 66, located on the U.S. east coast continental rise (38° 43.08'N, 72°33.64'W, 2338 m water depth) (van Hinte, Wise, et al., 1984, 1985) and from the Stevns Klint section exposed in an outcrop at Hrijerup, Denmark (Christensen et al., 1973). The sediment of Core 66, Section 1, consists of silt and foraminifer-rich clayey nannofossil limestone (greenish gray, 5G 5/1) above the K/T boundary and clay-rich nannofossil limestone with some quartz and foraminifers (gray, 5Y 5.5/1) below (Site 604/605 chapter, this volume). The K/T boundary was assigned 1 van Hinte, J. E., Wise, S. W., Jr., et al., Init. Repts. DSDP, 93: Washington (U.S. Govt. Printing Office). 2 Address: Biogeochemistry and Chemical Evolution Group, College of Oceanography, Oregon State University, Corvallis, OR 97331. within an erosional feature at about 72 cm in Core 66, Section 1 (43-75 cm), although Habib and Drugg (this volume) identify the K/T boundary between 64 and 78 cm in Section 605-66-1 based on dinoflagellate microfossils. They find good agreement with the Stevns Klint record. The Stevns Klint section is the type locality of the Danian (Christensen et al., 1973) and was sampled 15 cm above and below and in the fish clay at the K/T boundary. The upper Maestrichtian sample (2-10) is a gray Bryozoan chalk and the basal Danian sample (2-12) is a limestone with Thalassinoides and hardground facies (S. Gartner, private communication). The sample of fish clay (2-11) is a laminated marl, and the clay fraction has been found to consist of pure smectite with >95% expandable layers (Kastner et al., 1984). This was interpreted as in situ clay formation by alteration of impact glass, which was further supported by the high content of Ir and major element chemistry. EXPERIMENTAL The DSDP Hole 605 samples were freeze-dried and exhaustively extracted with azeotropic toluene:methanol in a Soxhlet apparatus; each extract was concentrated by rotary evaporation and was subjected to thin-layer chromatography (6.5% ethyl ether:hexane). The elution region corresponding to hydrocarbons was analyzed by gas chromatography (GC) and gas chromatography-mass spectrometry (GC-MS). The Stevns Klint samples were dissolved in 17V HC1, and the aqueous, acidic solutions were exhaustively extracted with hexane in a separatory funnel. Undissolved sediment residues were extracted by ultrasonic agitation; both organic extracts for each sample were combined and concentrated on a rotary evaporator. The concentrated extracts were treated with diazomethane in diethyl ether to derivatize free fatty acids. These total extracts were then subjected directly to GC and GCMS. Given the expected low concentrations of lipids to be measured, the following normal precautions of good laboratory practice were carried out to reduce potential contamination. All solvents were of distilled-in-glass (nanno grade) quality, glassware was acid-cleaned prior to use, and procedural blanks were monitored to preclude problems.

Lipid Geochemistry of Cretaceous/Tertiary Boundary Sediments, Hole 605, Deep Sea Drilling Project Leg 93 and Stevns Klint, Denmark