Asteroids - Extreme Events: A Physical Reconstruction and Risk Assessment - page 233

Figure 9.3. The K--T boundary sequence at Raton Basin in Colorado. The K--T
boundary is marked by the light coloured unit (knife). Photograph courtesy of
Professor D. A. Kring, University of Arizona.
effects may not be recorded stratigraphically and lithologically. However, dis-
tal impact effects, often consisting of deposition of microtektites and diamic-
tites, could be expected to be preserved in the stratigraphic record (Glikson,
1993).
Impact events can also generate major oil-bearing rock reservoirs. Grajales-
Nishimura et al. (2000)analysed the lithology, biostratigraphy and mineral com-
position from the offshore wells on the sea bed near the K--T impact event
(Fig. 9.3). They found a unique stratigraphy and distribution of impact material
within the calcareous breccia of the marine platform which they assume was
generated during the impact event. Immediately following the impact, the off-
shore carbonate platform collapsed resulting in the deposition of a breccia unit.
Following this, ballistic impact ejecta was deposited and then much of this
material experienced reworking and mixing with coarser material as impact-
generated tsunamis were reflected back and forth in the Gulf of Mexico. Grajales-
Nishimura et al. (2000)suggest that these extraterrestrial impact-generated struc-
tures, seals and reservoir facies are conducive for oil production. The K--T breccia
generated during this event is now one of the best known oil-reservoir rock units
related to an impact event.