Paleoenvironmental changes across the Cretaceous/Tertiary boundary in the northern Clarence valley, southeastern Marlborough, New Zealand

Abstract

Strata outcropping in Mead and Branch Streams, northern Clarence valley, provide important records of pelagic-hemipelagic sedimentation through the CretaceousPaleocene transition in a southern high-latitude, upwelling system flanking a carbonate platform. The two stream sections, <10 km apart along-strike, comprise similar stratigraphic successions with differences mainly due to Branch Stream being situated closer to land (outer shelf to upper bathyal) than the mid-bathyal Mead Stream section. Age control is based on foraminiferal and radiolarian biostratigraphy.A Cretaceous/Tertiary (K/T) boundary clay is not preserved in either section. The siliceous microfossil record indicates that basal Paleocene sediments at Branch Stream, although slightly enriched in Ni and Cr, were deposited after a significant relative sea-level fall. A basal Paleocene claystone at Mead Stream is not enriched in K/T impactderived elements and was probably deposited after sea-level fall. Earliest Paleocene sediment may be preserved as burrow fill in an uppermost Cretaceous bioturbated zone, which is enriched in Ni and Cr and contains a foraminiferal assemblage indicative of Paleocene Zone P0. Zone PO-Pα foraminiferal assemblages within the basal Paleocene sediments in both sections indicate that sea level fell within 100 000 yr of the K/T boundary event.The K/T boundary at both sites coincides with an abrupt change in lithofacies from calcareous to siliceous ooze. pulse at c. 64.5 Ma, followed by prolonged transgression from 5-50 m above the K/T boundary, is inferred from an initial increase in the frequency of mudstone beds, followed by a similar trend from diatom-poor to radiolarian-rich microfossil assemblages. Within the upper part of this interval, an increase in carbonate marks a return to lithofacies, and probably also paleodepth, equivalent to the underlying Cretaceous.In the deeper Mead Stream section, variation in diatom and radiolarian assemblages is mainly due to variable preservation in highly recrystallised lithologies. High overall abundance and little change in paleoproductivity indicators (Ba, δ 13 C) indicate that high biological productivity continued across the K/T boundary and through the biosiliceous episode.Siliceous plankton thrived in the Marlborough upwelling zone during the early Paleocene. Fluctuations in abundance and lithofacies can be related to significant changes in sea level, which may be the result of local tectonic or global climate changes. The delayed recovery of calcareous plankton after mass extinction at the K/T boundary, in both outer neritic and bathyal settings, indicates a relatively cool oceanic regime for the first 1.5 m.y. of the Paleocene.

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

“…4). Although some of the bioevents are poorly constrained and others are not reliably dated in the South Pacific region, these age models aid comparisons between paleoenvironmental trends in these two sections as well as other local K/T boundary sections (Hollis & Strong 2003;Hollis et al 2003a). The age models are also useful for examining trends in sediment accumulation rate and for estimating the frequency of sedimentary cycles (Field & Hollis 2003, this issue).…”

“…Possible explanations are: (1) the Flaxbourne marl is a localised facies; (2) fallout from the K/T asteroid impact was preceded by an erosional event, either due to a coincidental change in sea level or a megatsunami generated by the impact; or (3) the boundary clay is not primary fallout but instead was redeposited following a Paleocene erosional event. While none of these explanations can be ruled out, the suggestion that a megatsunami may have removed the marl from shallower sections, such as Woodside Creek and the Clarence valley sections (Hollis et al 2003a), warrants further consideration. Probable proximal tsunami deposits have been identified in the Gulf of Mexico (Claeys et al 2002), and it is conceivable that the distal effects of a Pacific-crossing tsunami would be preserved in New Zealand.…”

“…Hence, Tinormalised values may be underestimated in these intervals. Sc is not used in this study as a terrigenous proxy (Schmitz et al 1991) (Hollis et al 2003a). In contrast, to avoid the possibility of overestimating biogenic silica content, we conservatively adopt the rounded, highest minimum value (70%) for SiO 2 [MBKT].…”

“…The shallowest Marlborough sections are exposed in the southern tributaries of the Clarence valley (Reay 1993;Hollis et al 2003a, this issue). These depositional relationships are supported by palinspastic reconstructions for southeastern Marlborough (Crampton et al 2003), which further indicate that the depth transect formed part of the eastern margin of a broad embayment within an otherwise linear ENE-trending margin of the East Coast Basin and Chatham Rise.…”

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…”