Paleoenvironmental changes across the Cretaceous/Tertiary boundary at Flaxbourne River and Woodside Creek, eastern Marlborough, New Zealand

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.

The Cretaceous/Tertiary boundary event in New Zealand: Profiling mass extinction

“…Similar Cretaceous lithofacies at Branch and Mead Streams contain abundant diatoms, consistent within locations within the core of the upwelling zone (Hollis et al 2003b). An intermediate diatom-bearing lithofacies at Woodside Creek is consistent with an uppermost bathyal location at the lateral margin of the upwelling zone (Hollis et al 2003a). …”

“…Flaxbourne River contains the most complete earliest Paleocene foraminiferal succession in the South Pacific, including Zones P0, Pa, and P1a-b (Strong 2000). The apparent juxtaposition of an impact fallout layer and Zone Poc-Pla foraminifera in the boundary claystone at Woodside Creek (Strong 1977;Hollis et al 2003a) indicates that the unit contains a hiatus of >30 000 yr (i.e., the duration of Berggren et al (1995), showing correlation of low-mid-latitude foraminiferal and nannoplankton zones with South Pacific radiolarian zones (Hollis 1997(Hollis , 2002 and New Zealand dinoflagellate zones (Wilson 1984 Fig. 1), as basal Paleocene sediments lack a well-defined fallout layer and definitive Zone P0 foraminiferal assemblages (Hollis et al 2003b).…”

“…There is no evidence for a latest Cretaceous cooling episode in the Marlborough K/T sections. Indeed, the thin marl bed that underlies the K/T boundary at Flaxbourne River is thought to represent warmer oceanic conditions than underlying limestone beds (Hollis et al 2003a). …”

“…Facies variations between the sections are consistent with a depth transect across a continental margin upwelling zone (Ramsay 1977;Hollis et al 2003b). Cretaceous lithofacies at Flaxbourne River, within the mid-bathyal distal margin of the upwelling zone, is radiolarian-bearing calcareous ooze (Hollis et al 2003a). Diatoms are absent or rare.…”

“…The sections and inferred depositional settings are: Flaxbourne River (pelagic, upper to mid-slope), Woodside Creek (pelagic, uppermost slope), Mead Stream (pelagichemipelagic, upper slope), Branch Stream (pelagichemipelagic, outer shelf), mid-Waipara River (siliciclastic, mid-shelf), and Moody Creek Mine (mire, non-marine). The primary aim of this article is to review evidence for paleoenvironmental changes through the K-T transition in the four pelagic-hemipelagic Marlborough sections (Hollis et al , 2000(Hollis et al , 2003a(Hollis et al this issue, 2003bHollis 1996;Crampton et al 2003, this issue;Field & Hollis 2003, this issue;Su et al 2003, this issue). In addressing this aim, the Marlborough record is compared with studies of the shallower, siliciclastic mid-Waipara section (Hollis & Strong 2003, this issue;Vajda & Raine 2003, this issue), the non-marine Moody Creek Mine section (Vajda et al 2001), paleoclimate indicators in the regional vegetation record (Kennedy 2003, this issue), and regional studies of the K-T transition (e.g., Laird et al 2003, this issue).…”