Abstract Petroleum systems within rifted margin basins affected by volcanism continue to remain challenging for the exploration of hydrocarbons, most notably owing to the volume of intrusions that pose imaging, drilling and exploration problems. Typically, intrusions possess small thermal aureoles, but despite this, there is evidence that intrusions could none the less be responsible for the generation of commercial volumes of hydrocarbons. Here we shed new light on this petroleum systems challenge by integrating organic geochemical and Raman spectroscopic techniques to produce potential volumetric data for hydrocarbons generated as a result of igneous intrusion. The results indicate that, in areas with immature source rock intervals, it may be possible for intrusions to generate volumes of oil that would be capable of comfortably filling likely known oil reservoirs. This is a critical step forward in integrating several analytical techniques, indicating that under the right conditions there is the potential for hydrocarbon generation as a result of igneous intrusion.

We review the extensive record of plant fossils before, at, and after the Cretaceous-Paleogene event horizons, recognizing that key differences between plants and other organisms have important implications for understanding the patterns of environmental change associated with the Cretaceous-Paleogene event. Examples are given of the breadth of prior environmental conditions and ecosystem states to place Cretaceous-Paleogene events in context. Floral change data across the Cretaceous-Paleogene are reviewed with new data from North America and New Zealand. Latest Cretaceous global terrestrial ecology was fire prone and likely to have been adapted to fire. Environmental stress was exacerbated by frequent climate variations, and near-polar vegetation tolerated cold dark winters. Numerous floristic studies across Cretaceous-Paleogene event horizons in North America attest to continent-wide ecological trauma, but elsewhere greater floral turnover is sometimes seen well before the Cretaceous-Paleogene boundary rather than at it. Data from the Teapot Dome site (Wyoming) indicate continued photosynthesis, but during or immediately after the Cretaceous-Paleogene event, growth was restricted sufficiently to curtail normal plant reproductive cycles. After the Cretaceous-Paleogene transition in New Zealand, leaf form appears to have been filtered for leaves adapted to extreme cold, but at other high-southern-latitude sites, as in the Arctic, little change in floral composition is observed. Although lacking high-resolution (millimeter level) stratigraphy and Cretaceous-Paleogene event horizons, gradual floral turnover in India, and survival there of normally environmentally sensitive taxa, suggests that Deccan volcanism was unlikely to have caused the short-term trauma so characteristic elsewhere but may have played a role in driving global environmental change and ecosystem sensitivity prior to and after the Cretaceous-Paleogene boundary.

We examined 1,065 shock-deformed quartz grains from five Cretaceous/Tertiary (K/T) boundary sites in the Raton Basin, Colorado, and New Mexico, with cathodolum-inescence (CL) petrography. When grouped into general CL color categories, Raton Basin grains were 37.4 percent brown and 62.6 percent blue. Brown CL is thought to be associated with quartz from low-grade metamorphic rocks, so more than one third of the shocked grains were from this rock type. Almost all the blue CL quartz was medium to dark blue, broadly corresponding to quartz derived from intrusive igneous and high-grade metamorphic rocks. These data support the conclusions of a study by Owen and Anders (1988) which found no significant volcanic contribution to the shocked quartz at the K/T boundary. The proportions of brown- and blue-luminescing quartz in the present study differ from those of the previous study probably because of different sample preparation procedures and operator judgment.

At about 20 sites in the Raton basin of Colorado and New Mexico and at least 10 sites in Wyoming, Montana, and western Canada, a pair of claystone units, an iridium (Ir) abundance anomaly, and a concentration of shock-metamorphosed minerals mark the palynological Cretaceous/Tertiary (K/T) boundary. The lower unit, the K/T boundary claystone bed, is generally 1 to 2 cm thick; the upper unit, the K/T boundary impact layer is, on average, 5 mm thick. This couplet is overlain by a coal bed 1 to 16 cm thick. The boundary claystone in the Raton basin consists mainly of kaolinite and small amounts of illite/smectite (I/S) mixed-layer clay; but to the north at some sites in Wyoming, Montana, and Canada, it is more smectitic. Where the boundary claystone is kaolinite rich, it is similar to tonstein layers in coal. Typically, the claystone contains deformed vitrinite laminae, root-like structures, and plant impressions. The microscopic texture of the claystone is a polygonal framework of kaolinite filled with micrometer-size kaolinite spherules. The claystone is fragmental; at some sites, particularly in Wyoming, it contains centimeter-size kaolinite pellets, some of which contain carbonaceous plant material and millimeter-size goyazite spherules. The suite of trace elements in the claystone is, in general, similar to the suite of trace elements in tonsteins and to that in average North American shale, except that the boundary claystone contains anomalous amounts of platinum-group elements, including Ir (0.07 to 0.32 ppb). The K/T boundary impact layer also consists of kaolinite and considerably more (I/S) mixed-layer clay than the boundary claystone. Commonly it is 3 to 8 mm thick, microlaminated, and contains planar laminae of vitrinite and ubiquitous kaolinite barley-shaped pellets similar to the “graupen” of tonsteins. The microscopic texture of the claystone as seen with a scanning electron microscope (SEM) generally consists of an open wavy framework similar to that of smectite and (I/S) mixed-layer clay. This texture is significantly different than the microspherulitic texture of the underlying K/T boundary claystone. The contact between the impact layer and boundary claystone is generally sharp, and locally it may be a diastem. The impact layer and boundary claystone are similar chemically, but the former has slightly more Fe, K, Ba, Cr, Co, Li, V, and Zn than the latter. Iridium is most abundant in the impact layer (1.2 to 14.6 ppb); however, anomalous amounts of this element are found in carbonaceous shale and coal below or above the impact layer (0.1 to 2.0 ppb). The fact that the boundary claystone and impact layer make up a regionally extensive unit suggests they are composed of primary air-fall impact or volcanic material. However, mineralogic and chemical evidence indicates that the K/T boundary claystone is not composed of altered impact ejecta because it essentially lacks shock-metamorphosed minerals and contains only a minor Ir anomaly. Moreover, it contains only a few parts per million of Ni; this is inconsistent with the idea that it is composed of altered impact material. Observational and chemical evidence disclosed that the shocked minerals and Pt-group elements, including Ir, are the only impact-related components in the impact layer. Seemingly, the boundary claystone and impact layers are not of volcanic origin because they essentially lack a coherent assemblage of volcanic crystals. In the Raton basin, the boundary claystone, but not the impact layer, contains two types of spherules: kaolinite and goyazite (hydrous aluminum phosphate). Spherules composed of two Fe-rich minerals—jarosite or goethite—occur in the boundary clay-stone and impact layer. Kaolinite spherules are always solid and consist of a microspherulitic core encased in a thin shell of columnar kaolinite, whereas goyazite spherules are generally hollow and consist of a microlaminated colloform shell. Kaolinite spherules are large (0.1 to 0.5 mm) and relatively common (0.1 percent); in contrast, goyazite spherules are small (<0.1 mm) and rare (<0.01 percent). Kaolinite and goyazite spherules are dispersed widely in the claystone, but inexplicably they also occur in clusters. At two Wyoming sites, the boundary claystone contains abundant (as much as 30 percent) large (0.9 mm) goyazite spherules. Evidence indicates that the spherules formed by authigenesis. Although the impact layer is mainly composed of clay, it contains a small amount, as much as 2 percent, of clastic mineral grains. About 50 percent of the grains are quartz, and about 50 percent of these contain multiple sets of shock lamellae. Quartzite and metaquartzite constitute 26 percent of the assemblage of clastic grains in the impact layer, and 30 percent of these contain multiple sets of shock lamellae. Clearly the source of the quartzite and metaquartzite grains was chiefly sedimentary, metasedimentary, and metamorphic rocks and not volcanic rocks as some have suggested. Unshocked grains of chert and chalcedony compose from 8 to 46 percent of the assemblage. Grains of shocked feldspar (oligoclase and microcline) and granite-like mixtures of quartz and feldspar are rare. The abundance of unshocked quartzite, metaquartzite, and chert in the impact layer as compared to their paucity in underlying Cretaceous rocks suggests that most of these grains were derived from continental supracrustal impact target rocks and are not locally derived material. Shock-metamorphosed mineral grains are larger (mean = 0.15 to 0.20 mm) at North American K/T boundary sites relative to boundary sites elsewhere in the world (mean = 0.09 mm). Large (0.25 to 0.64 mm) grains are found at all Western Interior North American K/T boundary sites. Moreover, shocked minerals are several orders of magnitude more abundant at these sites as compared to elsewhere in the world. This information indicates unambiguously that the K/T impact occurred in North America. The Manson, Iowa, impact structure may be the K/T impact site because of the mineralogic similarity of Manson area subsurface rocks and shocked K/T boundary minerals, the large size (36 km) of the structure, the compatible isotopic age (~66 Ma) of shocked granitic rock from the Manson structure and the K/T boundary, and the proximity of the Manson structure to North American K/T boundary sites that contain relatively abundant and large shock-metamorphosed minerals.

In many parts of the world a thin clay or marly unit marks the boundary between Cretaceous and Tertiary rocks. In marine sequences this boundary is defined by the first appearance of typically Paleocene marine plankton in the clay. In continental rocks, the boundary sediment yields the stratigraphically highest occurrence of a Cretaceous assemblage of fossil pollen. Detailed analyses of the marine boundary sediment at Caravaca, Spain, permit a three-fold subdivision: the lowest is apparently a fallout deposit of impact ejecta, preserved as a 0.5-cm lamina of red clay. The main subdivision is a black or dark gray clay or marl, containing reworked extraterrestrial debris, laid down in an oxygen-deficient environment. The uppermost boundary clay is lighter gray in color, transitional in lithology to the overlying Paleocene sediments, which were deposited after the recovery from the terminal Cretaceous convulsive event. The boundary clay unit on land, represented by a section in Raton Basin, New Mexico, consists of a lower white clay, which is apparently a fallout deposit, and an upper carbonaceous shale. Boundary sections elsewhere are similar to those sections. The sedimentology of the boundary sediment records the convulsive environmental changes at/after a terminal Cretaceous event.