Cretaceous samples

The analysis of lignitic woods by analytical pyrolysis has shown that lignin structural units can be preserved as biomaikers in samples as old as Carboniferous age, or approximately 300 million years. At least half or more of the pyrolysis products in lignitic wood of Cretaceous age are methoxyphenols characteristic of lignin. The pn uct distributions in these Cretaceous samples indicate that the lignin is mainly altered in the 3-carbon side chains. Phenols, cresols, catechols, and other methylated phenols account for most of the remaining pyrolysis products. It is likely diat these products are also derived frx>m li in, especially lignin that has been altered by coalification reactions. 

What is, however, still unclear is whether these effects arise solely from different chemical compositions (and molecular configurations) or are also, at least in part, a consequence of the Cretaceous coals generally containing almost twice as much mineral matter as the Carboniferous samples. 

The Tb abundance in meteorites is assumed to be 0.5 ppm. Errors for the Danish Cretaceous (3 samples) and Tertiary (3 samples) HNO,-insoluble residues are root-mean-square deviations. Errors for the HNO,-insoluble residues from the Gubbio and Danish boundary layers are 1 a values of the counting errors. Key , Gubbio boundary layer residue O, Danish Cretaceous residues < >, Danish Tertiary residues and , Danish... 

Fig. 1. Physiography and bedrock geology of northwest Alberta in which the sampling survey (National Topographic System sheets 84M and 84L) was undertaken. Cretaceous bedrock units listed from oldest to youngest (after Hamilton ef al. 1998) Loon River Formation (Kl), Shaftesbury Formation (Ksh), Dunvegan Formation (Kd) and Smoky Group (Ks).

Sheilds WR, Murphy TJ, Catanzaro EJ, Garner J (1966) Absolute isotopic abundance ratios and the atomic weight of a reference sample of chromium. J Res Natl Bur Standards 70A(2) 193-197 Shukolyukov A, Lugmair GW (1998) Isotopic evidence for the Cretaceous-Tertiary impactor and its type. Science 282(5390) 927-929... 

Figure 11,21 Age spectra of hornblendes of a Paleozoic gabbro (367 Ma) intruded by a granitic body during the Cretaceous (114 Ma). Samples underwent permeation of " Ar from lower crustal portions and differential losses of radiogenic argon (32, 57, and 78% respectively), proportional to distance from contact (0.3, 1, and 2.5 km). Reprinted from T. M. Harrison and I. McDougall, Geochimica et Cosmochimica Acta, 44, 2005-2020, copyright 1980, with kind permission from Elsevier Science Ltd., The Boulevard, Langford Lane, Kidlington 0X5 1GB, UK.

In an attempt to delineate the degree of preservation of lignin in pre-Tertiary coal, we examined numerous coalified wood samples ranging in age from Carboniferous to Cretaceous. The samples were initially screened by solid-state l C nuclear magnetic resonance to detect the possible presence of methoxyl carbon. Once such carbons were detected, the samples were subjected to analytical pyrolysis to determine the relative yields of methoxyphenols which would provide an indication of the state of preservation of the lignin-derived structu units. We report here on the identification of lignin-derived methoxyphenols in the coalified wood samples selected for analytical pyrolysis. 

Figure 2a. Py/gc traces of Lower Cretaceous lignitic wood samples.

Two diamond drill cores, designated DDH-A and DDH-B were obtained from central Colorado. DDH-B is from the vicinity of Redstone, Gunnison County, and core DDH-A is from the vicinity of Somerset in Delta County. These samples were particularly interesting since there is a transition from unaltered high volatile bituminous coal to natural coke at the igneous contacts. Both cores are of Cretaceous age coal. All core samples are from depths in excess of 1500 feet below the surface. 

Another environment that has been successfully searched for nanodiamonds is the Cretaceous-Tertiary boundary layer. Carlisle Braman (1991) carried out the now time honoured acid dissolution procedure on samples from Knudsen s Farm, Alberta, Canada. They found 45 ppb of a white fraction 97 % carbon almost entirely 3-5 nm... 

In Mesozoic samples, mostly Cretaceous and Jurassic black shales, the abundance and variance of OSC is generally low. A few samples of Jurassic age show a distribution pattern of C20 isoprenoid thiophenes which may indicate increased salinity during deposition. A C20 isoprenoid thiolane is the most abundant compound in black shales from the Falkland Plateau, whereas at other locations the C35 thienylhopane dominates. In one case two C33 mid-chain 2,5-dialkylthiophenes were identified. 

In a Cretaceous slump clast from Site 547 off Morocco (E12743), recovered in the Eocene section, two coeluting C33 mid-chain thiophenes (11 m/z 490(55%), 433(15%), 419(18%), 181(92%), 167(73%), 111(100%)) were detected. Similarly high abundances of C33 mid-chain thiophenes and thiolanes were observed in a sample from the Nordlinger Ries (27) and in the Jurf ed Darawish oil shale (28). 

One of the cometary probes to have embarked is on a sample-return mission [270], and MS will certainly play a part in the analysis of the material obtained. This will not, however, be the first occasion on which cometary material has reached the Earth. One of the most intriguing, albeit contentious [271-274], reports of the last few years has been the mass-spectroscopic identification of interstellar fullerenes, such as C60, as fossil molecules in the geologic strata associated with the supposed Cretaceous/Tertiarymeteoritic [275] ( dinosaur killer ) and Permian/Triassic cometary [276] ( the Great Dying ) impacts. Similar results are also reported for the Murchison and Allende meteorites, and for material obtained from the ancient ( 2 billion-year-old) Sudbury impact feature... 

Possibly, as presumed by Frausto Da Silva and Williams (2001), some hitherto essential elements lost their biocatalytic functions altogether or are about to do so (ibid.) yet, this issue is open to speculations only because there is no way to determine former biocatalytic functions in fossil samples even if they are fully preserved, like inclusions in amber (with chitin retaining the metals) or dry mummies. Moreover, very few such samples date back beyond the Cretaceous (dinosaur xeromummies from Mongolia, Arabic amber) whereas most of the changes we consider here took place far back in the Precambrian. Changes of enviromnental conditions may also contribute to stabilization of changes by substitution of some redox-inert ion with 3 func-... 

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