The Raman microprobe spectra of natural brookite crystals from Switzerland and Brazil and a synthetic brookite powder exhibit a characteristic intense band at 153 cm-'. In contrast, anatase has a band of similar intensity at 144 cm-' and rutile lacks a strong band in this region. Polarization experiments with the Brazilian crystal permit 17 out of a predicted 36 vibrational bands to be readily assigned as A,, (127, 154, 194, 247, 412, 640 cm-I), B,, (133,159,215,320,415,502 cm-'), B,, (366,395,463,584 cm-') and B,, (452 cm-I). Eight weaker bands and component subbands resolved at 172, 287, 545, 618 cm-', 254, 329, 476 cm-' and 497 cm-I are tentatively assigned to B,, , B,, and A & , modes respectively. Traces of Si and Fe in the Brazilian crystal and Si, Fe, A1 and S in the Swiss sample are indicated by spot electron microprobe analysis. Electron spin resonance spectra suggest small amounts of Fe3+ are substituting for Ti4+ in the structure. Concomitant protonation of oxygens to maintain charge balance yields OH groups which give rise to three sharp, low-intensity absorption bands near 3360, 3380and 3404 cm-' in the infrared spectra. X-ray photoelectron spectroscopy shows that surface-bound OH/H,O species exist in both crystals but no detectable Ti3+.

No abstract

No abstract

No abstract

An integrated study of variation in siliceous microfossils, lithofacies, and other geochemical guides to environmental conditions through the Cretaceous/Tertiary (K/T) boundary transition at Flaxbourne River and Woodside Creek, coastal eastern Marlborough, indicates that the K/T impact disrupted oceanic conditions along the continental margin of eastern New Zealand for c. 1 m.y. Initial effects of the K/T event were a major reduction in carbonate production, associated with calcareous plankton extinctions, and significant increases in terrigenous clay and biogenic silica content. An absence of radiolarian extinctions or significant negative excursions in paleo-productivity indicators (Ba, d 13 C) at the boundary, followed by rapid increases in the abundance of diatoms and spumellarian radiolarians, indicate that biogenic silica production partly compensated for the collapse in calcareous plankton.The earliest Paleocene recovery of calcareous plankton was short-lived, giving way to a progressive increase in siliceous plankton abundance over c. 500 000 yr, which culminated in a c. 400 000 yr episode of peak biogenic silica production. The dominance of siliceous facies, coupled with the abundance of diatoms and spumellarian radiolarians, indicates climatic or oceanic conditions were significantly cooler than in the Late Cretaceous. Stepped increases in biogenic silica production show c. 100 000 yr periodicity, suggesting that early Paleocene lithofacies changes were influenced by climate forcing agents at the eccentricity bandwidth.