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

Abstract

Of over 20 known Cretaceous/Tertiary (K/T) boundary sections in the New Zealand region, 6 in the northern South Island were selected for detailed biostratigraphic and paleoenvironmental study because of their apparent stratigraphic completeness and the range of depositional environments represented. These sections represent the only known southern high-latitude (55-60°S) transect of the K/T boundary transition from continental slope to terrestrial mire.The K/T boundary is marked by deposition of an impact fallout layer in four of these sections, and a disconformity representing a hiatus of < 100 000 yr in the remaining two sections (Mead and Branch Streams). In the terrestrial Moody Creek Mine and shallow marine mid-Waipara sections, rapid and widespread destruction of forests is shown by abrupt replacement of mixed forest pollen and spore assemblages by assemblages dominated by few species of ground ferns. Foraminiferal and radiolarian biostratigraphy indicates that within 100 000 yr these ferns were replaced by a cool-temperate conifer-dominated assemblage that persisted until c. 63.5 Ma. In the marine sections, an abrupt decrease in carbonate content reflects a major decline in carbonate production associated with mass extinction of calcareous plankton, although several smaller species of planktic foraminifera persist for c. 100 000 yr into the Paleocene.In four sections in Marlborough (Flaxbourne, Woodside, Mead, and Branch), which represent a transect across a coastal upwelling zone, paleoproductivity proxies (excess SiO 2 , excess Ba, Ba/Al, δ 13 C) indicate that the decline in calcareous plankton was partly offset by sustained siliceous plankton productivity. Extinctions of thermophilic foraminifera, survival of cosmopolitan foraminifera, and expansion of diatoms and spumellarian radiolarians indicate that pronounced cooling occurred across the K/T boundary. A subsequent decline in planktic foraminifera and in carbonate content, associated with a progressive increase in siliceous plankton productivity, indicates that further cooling resulted in dominantly biosiliceous sediment being deposited in the core of the Marlborough upwelling zone from c. 64.9 to 63.5 Ma. The onset of this biosiliceous event at c. 64. Ma and a later major increase in biogenic silica in the deepwater sections (Flaxbourne, Woodside) at c. 64.6 Ma are correlated with sea-level falls in the shelf section (Branch) and are also linked to eustatic events recorded in Europe and North and Central America.These early Paleocene regressive events within a cool climatic regime are the probable cause of incomplete K/T boundary records in most of New Zealand. It remains uncertain if they are directly related to the K/T bolide impact, the short-term effects of which may have disrupted the global climate system for millions of years, or are related to other factors such as tectonism or fluctuating CO 2 emissions from Deccan volcanism.

South Pacific evidence for the long-term climate impact of the Cretaceous/Paleogene boundary event

“…For the southwest Pacific, a pattern of short-lived climate instability followed by prolonged climatic cooling over ~1 Myrs has been inferred from both marine and terrestrial K/Pg boundary records (Vajda et al, 2001;Hollis, 2003;Vajda and Raine, 2003). Prolonged cooling has been invoked to explain both a delayed recovery of calcareous plankton and the abundance of diatoms and radiolarians in the basal Paleocene pelagic sediments of northeastern South Island, New Zealand (Hollis et al, 1995(Hollis et al, , 2003a.…”

“…1) contains the most complete known K/Pg transition in a neritic setting in the South Pacific region (Hollis and Strong, 2003). It provides an important link between bathyal marine and terrestrial sections in New Zealand (Hollis, 2003) and is one of only two neritic K/Pg boundary record in the Southern Hemisphere, the other being on Seymour Island, Antarctic Peninsula (Elliot et al, 1994;Bowman et al, 2012;Kemp et al, 2014;Petersen et al, 2016;Witts et al, 2016). The mid-Waipara section contains abundant and diverse palynomorphs, including dinoflagellates Willumsen, 2004;2006;2012;Ferrow et al, 2011) and terrestrial palynomorphs (Vadja et al, 2001;Vadja and Raine, 2003;Ferrow et al, 2011), which provide qualitative indications of climatic and environmental variability.…”

Biostratigraphy and carbon isotope stratigraphy of uppermost Cretaceous‐lower Cenozoic Muzzle Group in middle Clarence valley, New Zealand

“…Lithologies such as organic-rich mudstone and soft calcareous mudstone or marl tend to yield slightly to strongly negative bulk carbonate δ 13 C values , which result from diagenetic interaction with isotopically light organic matter, either in situ or carried in pore waters (Marshall 1992;Schmitz et al 1997a). In all Muzzle Group lithologies examined so far, bulk carbonate δ 18 O bears a diagenetic overprint that makes paleoenvironmental interpretation very difficult to impossible (Hollis 2003;Hollis et al 2003). Bulk carbonate δ…”

“…Previous stratigraphic studies of Muzzle Group lithologies (Hancock et al 2003;Hollis et al 2003 have shown that stable isotope analysis of bulk carbonate from indurated limestone yields δ 13 C profiles that can be correlated with some confidence to global deep sea δ 13 C records (e.g., Zachos et al 2001). Lithologies such as organic-rich mudstone and soft calcareous mudstone or marl tend to yield slightly to strongly negative bulk carbonate δ 13 C values , which result from diagenetic interaction with isotopically light organic matter, either in situ or carried in pore waters (Marshall 1992;Schmitz et al 1997a).…”

Detection of Late Cretaceous eustatic signatures using quantitative biostratigraphy

“…Secondly, apparent turnover may be exaggerated by monographic effects inasmuch as many studies have tended to extend up to, but not across, the boundary (e.g., Roncaglia et al, 1999; but see Willumsen, 2000). Thirdly, the Cretaceous-Paleocene boundary is known to correspond to an unconformity in many or most New Zealand sections (Hollis, 2003). Finally, event levels in the composite are relatively widely spaced around the Cretaceous-Paleocene boundary, and, thus, for the reasons outlined above, the size of the cluster is likely to be exaggerated (compare Figs.…”