Paleoenvironmental changes across the Cretaceous/Tertiary ...

New Zealand Journal of Geology and Geophysics

ISSN: 0028-8306 (Print) 1175-8791 (Online) Journal homepage: http://www.tandfonline.com/loi/tnzg20

Paleoenvironmental changes across the Cretaceous/Tertiary boundary in the northern Clarence valley, southeastern Marlborough, New Zealand C. J. Hollis , K. A. Rodgers , C. P. Strong , B. D. Field & K. M. Rogers To cite this article: C. J. Hollis , K. A. Rodgers , C. P. Strong , B. D. Field & K. M. Rogers (2003) Paleoenvironmental changes across the Cretaceous/Tertiary boundary in the northern Clarence valley, southeastern Marlborough, New Zealand, New Zealand Journal of Geology and Geophysics, 46:2, 209-234, DOI: 10.1080/00288306.2003.9515005 To link to this article: http://dx.doi.org/10.1080/00288306.2003.9515005

Published online: 21 Sep 2010.

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2003, Vol. 46: 2 0 9 - 2 3 4

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© The Royal Society of New Zealand 2003

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

1

C. J. HOLLIS 2 K. A. RODGERS 1 C. P. STRONG 1 B. D. FIELD 1 K. M. ROGERS 1

Downloaded by [183.111.169.204] at 04:23 29 January 2016

Institute of Geological & Nuclear Sciences P.O. Box 30 368 Lower Hutt, New Zealand email: [email protected]

2

Australian Museum College St Sydney, NSW, Australia

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,

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10 m of Cretaceous siliceous limestone overlain by 50 m of lower Paleocene mudstone, chert, and siliceous limestone. The top of the section is truncated by a fault. Overlying rocks are micritic limestones of late early Paleocene age (Radiolarian Zone RP4) at base (see Table 2). In ascending stratigraphic order, six lithologic units are identified in the K/T boundary section (Fig. 2): A. Uppermost Cretaceous, light grey, decimetre-bedded, siliceous limestone with dark grey chert nodules; >10 m thick B. Basal Paleocene, dark grey, centimetre-bedded, calcareous clay-rich chert and siliceous mudstone; 0.2 m C. Dark grey, decimetre-bedded, nodular, and dolomitised chert; 5.5 m D1. Dark grey to black, decimetre-bedded chert with centimetre-bedded mudstone interbeds; 12.6 m D2. Medium grey, decimetre-bedded, calcareous porcellanite; 6.2 m D3. Dark grey to black, decimetre-metre-bedded chert with centimetre-bedded siliceous mudstone interbeds, grading up into decimetre-bedded, siliceous limestone; 25 m As well as providing insight into the nature of the K/T boundary event, anomalously high concentrations of Ir, Cr, Ni, and Zn provide a valuable geochemical fingerprint for the boundary layer (Strong et al. 1987; Gilmour & Anders 1989). We did not analyse for Ir in this section but the boundary fingerprint is well expressed by high

concentrations of Ni and Cr (Fig. 2). A small enrichment in Zn in the boundary clay disappears when normalised against Al, using the equation of Schmitz et al. (1991): Y* = Y[sample]/Al2O3[sample] x Al2O3[MBKT] where Y = the element considered and Al2O3[MBKT] = 12%, which is the highest concentration of Al 2 O 3 in the Marlborough K/T boundary sections (in fact in Branch Stream sample O30/f346, 12.7 m above the K/T boundary; Hollis et al. 2003b). MEAD STREAM The section studied is the main (southern) tributary of Mead Stream (Fig. 1; grid ref: P30/76051607). Overall, Upper Cretaceous to middle Eocene stratigraphy was described by Strong et al. (1995). The K/T boundary is c. 170 m above the base of Mead Hill Formation and is overlain by 160 m of Paleocene strata (Hollis et al. 2000, 2002). The K/T boundary section has been subdivided into six lithologic units (Fig. 3): A. Upper Cretaceous, light grey, decimetre-bedded siliceous limestone with dark grey chert nodules; distinctive 0.02 m thick, laminated, dark grey chert caps uppermost limestone bed; c. 170 m B. Basal Paleocene, dark grey, centimetre-bedded, calcareous, clay-rich laminated chert; 2 claystone beds (0-0.02 and 0.26-0.3 m above the base of the unit); 0.36 m C. Dark grey, decimetre-bedded, partially dolomitised, nodular chert and calcareous porcellanite; 2.2 m

213

Hollis et al.—K/T boundary in northern Clarence valley

Si[eKc], &TRG 100


0 4

-

0.3 -r

0.2-

-0.1-

Fig. 4 The K/T boundary at Mead Stream. The stratigraphic succession from upper unit A to lower unit D (a) and close-up of the K/ T boundary transition (b), showing that enrichment of Ni* is directly below the boundary clay, within a thin layer of bioturbated chert or porcellanite that contains an earliest Paleocene foraminiferal assemblage (Zone P0?). Si[exc], Ca[exc], and TRG = excess SiO2, excess CaCO3, and terrigenous sediment concentrations, respectively.

D. Dark grey to black, metre-bedded chert with thin siliceous mudstone partings; 18 m E. Medium green-grey, decimetre-bedded, siliceous limestone, 1.2 m F. Light grey, decimetre-bedded, siliceous limestone with dark chert stringers ("ribbon chert" of Strong et al. 1995), 40 m On lithostratigraphic and biostratigraphic criteria, Strong et al. (1995) adopted the base of unit B as the K/T boundary.

They also reported a small Ir anomaly of 0.82 ppb (8 times crustal average) from a single analysis of the boundary clay. Our study shows that while the boundary clay is rich in elements typical of the K/T geochemical anomaly worldwide (e.g., Ni, Cr, and Zn; Gilmour & Anders 1989), these elements are not anomalously rich when normalised against Al (Fig. 3). The normalised concentration of Zn is high in all samples examined from the upper 4 m of the Cretaceous and decreases rapidly in the basal Paleocene. A similar trend

214

New Zealand Journal of Geology and Geophysics, 2003, Vol. 46

is seen at Branch Stream (Fig. 2). In contrast to Branch Stream, normalised concentrations of Ni and Cr (Ni*, Cr*) are highest in the uppermost Cretaceous sample rather than in the boundary clay (Fig. 4). For reasons discussed in more detail below, the K/T boundary is inferred to be a disconformity. Earliest Paleocene sediment, including impact-derived material, appears to have been downworked into the uppermost Cretaceous prior to a diastem-scale erosional event. Subsequent deposition began with a thin

clay layer that has the superficial appearance of a typical K/T boundary clay, but has a composition equivalent to normal Paleocene mudstone beds. BIOSTRATIGRAPHY Biozones referred to here follow the definitions of Berggren et al. (1995) for foraminifera and Hollis (1993, 1997) for radiolarians. The distribution of foraminiferal and radiolarian


Table 1 Foraminifera from uppermost Cretaceous and lower Paleocene strata at Branch Stream. Abundance: A = abundant, F = few, R = Rare. Preservation: M = moderate, P = poor, VP = very poor. Occurrence: x = present, ? = uncertain identification. Age NZ Stage Foraminiferal Zone NZ fossil record no. O30/ Depth Abundance Preservation Benthics Alabamina creta Allomorphina cretacea Ammobaculites sp. Ammodiscus cretaceus Anomalinoides eoglabra Anomalinoides piripaua Anomalinoides rubiginosus Bathysiphon sp. Bolivina incrassata Bolivinopsis compta Budashavaella multicamerata Bulimina spp. Cibicides spp. Citharina sp. Clavulina anglica Cyclammina sp. Frondicularia rakauroana Gaudryina healyi Gaudryina whangaia Gavelinella beccariiformis Glomospira charoides Gyroidinoides globosus Gyroidinoides spp. Haplophragmoides suborbicularis Haplophragmoides spp. Karreriella spp. Lagena sp. Lenticulina spp. Loxostomum limonense Marginulina sp. Melonis pacimaoricum Nodosaria spp. Nuttallides carinotruempyi Oridorsalis umbonatus Osangularia navarroensis Osangularia spp. Planorotalites sp. Planulina rakauroa Pullenia coryelli Quadrimorphina allomorphinoides Rzehakina epigona Planktics Abathomphalus mayaroensis Acarinina soldadoensis Chiloguembelina spp. Eoglobigerina cf. eobulloides Hedbergella sp. % Planktics

LateK Early Paleocene Paleocene Mh lower Teurian (Dt) Teurian (Dt) P0-P1b unassigned A. may. P0 P a f172 f 1 f338 f346 f170 f351 f371 f376 f378 f379 f381 f384 -2.00 0.10 7.84 12.69 c. 15 15.63 23.03 36.47 41.45 43.02 47.92 50.93 A R R R R R R F F R F R P P P P P P M P P P VP VP

x x x x x xx

x x

x x x

X X

X X

X

X

X

X X

X

X

X

X

X

X

X X X X X

X X

x X

X

X

X

X

x X

x

X

x

35

x x 0

X X

X


Table 2 Radiolaria from uppermost Cretaceous and lower Paleocene strata at Branch Stream. Abundance: A = abundant, C = common, F = few, R = Rare. Preservation: M = moderate, P = poor. Occurrence: relative abundance expressed as percentages (1-65), where + 90

>90

0

90

>90 75-90 75-90

?

10-20

?

63 µm, HCl-leached residues, and the highly siliceous samples have been leached

223



5

unit C are a mixture of shallow water spongy-walled spumellarians and Cretaceous survivor nassellarians, some of which may be reworked (Table 2). For these reasons, we consider the K/T boundary at Branch Stream to be a disconformity and lowermost Paleocene sediments to represent a transgressive sequence deposited after a lower Paleocene sea-level fall. Planktic foraminifera within unit B are correlated with Zones P0Poc (65-64.9 Ma), which indicates a basal Paleocene hiatus of 63 µm) per gram of sediment Diatom/radiolarian ratio in >63 |jm HCl-leached residue Percentage of spumellarian radiolarians

Actinommids

Percentage of actinommid radiolarians

Fisher a index

Radiolarian diversity measure

Ca[exc]

Excess or biogenic CaCO3 based on TRG (see below) Excess of biogenic SiO2 based on TRG (see below) Biogenic or excess Ba based on Ti as proxy for TRG (see below) Ba normalised to Al as a clay proxy

Si[exc] Ba[exc] Ba/Al TRG Ti/Al

Terrigenous sediment component based on Ti content Guide to excess Ti or Al

TOC

Total organic carbon (%)

813C[org]

813C for total organic matter (kerogen + elemental carbon) 813C for bulk carbonate (primarily from calcareous plankton) 818O[carb] for bulk carbonate

13

8 C[carb] 818O[carb]

High value implies: High radiolarian or diatom productivity High biosiliceous and probably high general productivity Cool climatic, shallow or nutrient-rich conditions Cool climatic, shallow or nutrient-rich conditions High or low productivity, deep water High calcareous plankton productivity, warm surface water High siliceous plankton productivity, cool surface water High biological productivity

Reference Ramsay 1977; Hollis et al. 1995 Ramsay 1977; Hollis et al. 1995 Hollis 1996

High biological productivity

Zachos et al. 1989; Shimmield 1992 Schroeder et al. 1997

High input of terrigenous sediment Enhanced aoelian or hydrodynamic winnowing High preservation of marine kerogen or elemental carbon High biological production or reduced upwelling High biological production or reduced upwelling Relative cooling of surface waters (if postdepositional alteration can be ruled out)

Hollis 1996 Murray 1991 Schroeder et al. 1997 Schroeder et al. 1997 Schroeder et al. 1997

Schmitz 1987; Shimmield 1992 Wolbach et al. 1988 Hollander et al. 1993 Zachos & Arthur 1986; Corfield 1994 Zachos & Arthur 1986; Corfield 1994

225


m

Rad zone Lithology Units

Age

a. TRG & TOC

b. Si & Ca Si[exc] (wt%)

TRG (wt%)

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e. Siliceous microfossil abundance individuals/g

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65.1

A 0

0.5 TOC (%)

100 0 Ca[exc] (wt%)

0

0.05

Ba/Al

0.1

-30

-27

513C[org] CD

Fig. 6 Variation in paleoenvironmental indicators across the K/T boundary at Branch Stream (-2 to 5 m), including concentration in (a) terrigenous sediment (TRG) and total organic carbon (TOC), (b) excess SiO2 (Si[exc]) and excess CaCO3 (Ca[exc]), and (c) excess Ba (Ba[exc]), and variation in (d) bulk carbonate and total organic 813C (813C[carb], 813C[org]), (e) siliceous microfossil abundance, and (f) the diatom/radiolarian ratio.

by actinommids or other spumellarians, but a restricted group of Paleocene nassellarians become increasingly common in upper unit D3 (Fig. 7f). These assemblages are similar to the low diversity early Paleocene assemblages at Flaxbourne River and Mead Stream (Hollis 1996, 1997; Hollis et al. 2003a; Table 4). They are distinct from the diverse early Paleocene assemblages, with relatively high numbers of Cretaceous survivors, found at Woodside Creek. On the basis of such differences, Hollis (1996) argued for a different depositional setting for Woodside Creek, shallower and outside the core of the main upwelling system. Given that Branch Stream paleodepth was probably shallower than Woodside Creek, the upwelling setting and nutrient availability may have had more influence on these radiolarian assemblage differences than depth. Paleoenvironmental changes through the K-T transition at Mead Stream Geochemical analyses of Mead Stream section were targeted to complement rather than duplicate the record at Branch

Stream. Because of 100% fresh exposure across the K/T boundary, it was possible to sample regularly through 6 m of uppermost Cretaceous strata and to collect closely spaced samples through the first 1.5 m of the Paleocene, except for a highly dolomitised interval within the sample gap between 0.6 and 1.2 m (Fig. 8). Placement of a single microfossil sample (P30/f447,1.0 m) within this dolomitised interval is uncertain as the sample was collected before detailed logging of the section. Lithofacies variation through the K/T boundary transition (Fig. 3) is similar to Branch Stream. The K/T boundary coincides with an abrupt change from siliceous carbonate ooze (unit A) to clay-rich, calcareous siliceous ooze (unit B). An expanded transition zone (unit C), in which carbonate content gradually declines, is followed by a relatively condensed interval of peak biosiliceous sedimentation (unit D). The return to siliceous carbonate ooze (units E-F) is abrupt, suggesting that the contact between units D and E may be faulted or disconformable. In detail, paleoenvironmental indicators are remarkably stable through the uppermost 5 m of Cretaceous strata (Fig. 8a-d).

226

New Zealand Journal of Geology and Geophysics, 2003, Vol. 46 d . 8 13 C & 1 3

c. Ba Si[exc] (wt%) 0

100

d13C[org] (/)ooo

Ba[exc] (ppm) 2

10

10

3

4

10

-30

-27

e. Siliceous microfossil abundance D/R ratio 2

10-

1

10-

100

101

f. Radiolaria % Spumellaria 0

50

100


D/R ratio o 3 pt moving t average

0.02

0.06 Ti/Al

0.04

100 50 0 Ca[exc] (wt%)

10

10 Ba/Al

10

0

1.5 TOC (%)

10

10 Individuals/gram

10

0

6 12 Fisher a index

65.3

Fig. 7 Variation in paleoenvironmental indicators in uppermost Cretaceous and lower Paleocene strata at Branch Stream (-3 to 50 m), including concentration in (a) terrigenous sediment (TRG), (b) excess SiO2 (Si[exc]) and excess CaCO3 (Ca[exc]), and (c) excess Ba (Ba[exc]), and variation in (d) total organic 813C (813C[org]) and total organic carbon (TOC), (e) siliceous microfossil abundance, and (f) spumellarian radiolarian abundance and radiolarian diversity.

Through most of this interval, TRG, Si[exc], and Ca[exc] concentrations are stable around respective means of 6, 26, and 65%. A small decrease in Si[exc] in the upper 3 m of Cretaceous strata may be due to reduced productivity as a similar decrease occurs in Ba[exc], and 813C[carb] exhibits a weak negative trend. Variation in siliceous microfossil abundance in the uppermost Cretaceous is largely due to variable preservation (Fig. 8e). Preservation is relatively poor throughout this interval and extreme recrystallisation probably accounts for barren or sparse assemblages in 7 of the 12 samples examined. A high D/R ratio in four rich assemblages implies relatively high productivity. The K/T boundary at Mead Stream The uppermost Cretaceous sample in unit A is anomalously rich in Ni and Cr and contains what appears to be an earliest Paleocene foraminiferal assemblage. The bulk composition differs markedly from underlying samples, with high Si[exc] and TRG content and low Ca[exc] (Fig. 4, 8a-c). The sample represents a 20 mm thick layer of finely bioturbated, slightly

calcareous, clay-rich chert or porcellanite that caps a thick siliceous limestone bed. It is distinguished from chert nodules within this bed by its pale colour and planar lower and upper contacts (Fig. 4). The layer provides evidence for mixing of Cretaceous and Paleocene sediment, apparently by bioturbation, following deposition of a Ni- and Cr-rich impact ejecta layer. The siliceous microfossil assemblage indicates that the Cretaceous facies was similar to underlying sediments. Bulk and trace element composition indicates that the downworked Paleocene sediment was similar to basal Paleocene sediment at Branch Stream (being a rich in silica, terrigenous clay) and impact-derived fallout. In contrast, the basal Paleocene clay layer at Mead Stream is normal terrigenous clay with a similar composition, including very low Si[exc], to clay layers higher in unit B (Fig. 4, 8a,b) and in Branch Stream unit D1 (Fig. 7a,b). Therefore, the K/T boundary at Mead Stream appears to be a disconformity, as it is in many oceanic records (MacLeod & Keller 1991; Bralower et al. 2002). After deposition of earliest Paleocene sediment rich in impactderived material, some sediment was downworked into the

227


Unit

m

Rad zone

Age

a. TRG & TOC

b. Si & Ca

d. 6 13 C & 6 18 O

c. Ba

[carb] Si[exc] (wt%) 50

wt%

100 0

100

Ba[exc] (ppm) d13C[carb] (/) 0 1500 -1 0

e. Siliceous microfossils D/R ratio 10°

J1 \\

c. Ma

0.5 -

RP2

1.0

XX

[carb] • [org] o

XX XX[ —

64.5

?

C RP1

Early Paleocene

' °

\ |

64.6

B

_

_ -4 _

A

A

i

A A

i

•

65.0

•

65.1

A

A A

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i

A

65.2

i

A A

i

A A

i

65.3

A A

-

I

i

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Late Cretaceous


t

A

i

A

-6

0.5 TOC (%)

100

50 Ca[exc] (wt%)

0.15 Ba/Al

-30

-26 10 d13C[org] ( / )

Individuals/g

Fig. 8 Variation in paleoenvironmental indicators across the K/T boundary at Mead Stream (-6 to 1.5 m), including concentration in (a) terrigenous sediment (TRG) and total organic carbon (TOC), (b) excess SiO2 (Si[exc]) and excess CaCO3 (Ca[exc]), and (c) excess Ba (Ba[exc]), and variation in (d) bulk carbonate and total organic 813C (813C[carb], 813C[org]), and (e) siliceous microfossil abundance and the diatom/radiolarian ratio.

Cretaceous by burrowing organisms, or perhaps filled existing burrows, before the Paleocene sediment was removed by an erosional event. This event is likely to be the sea-level fall inferred for basal Paleocene at Branch Stream. As at Branch Stream, foraminifera indicate that basal Paleocene sediments are within Zones PO-Poc and, consequently, the sea-level fall occurred within the first 100 000 yr of the Paleocene. The basal Paleocene units at Mead and Branch Streams are similar in general characteristics but significantly different in detail. Both units are dark grey, finely bedded or laminated, calcareous, clay-rich chert. However, the strong covariance between TRG, TOC, Si[exc], Ca[exc], Ba, and 813C in unit B at Branch Stream is not evident in these variables at Mead Stream. Apart from sharp increases in the two clay beds, TRG is stable through units B and C at Mead Stream, whereas TOC decreases sharply in basal unit C (Fig. 8a). Si[exc] and Ca[exc] are also relatively stable in unit B, with Si[exc] increasing gradually relative to Ca[exc] through unit C (Fig. 8b). On balance, the Ba[exc] and Ba/Al trends indicate little change in productivity across the boundary and a weak increase through unit B (Fig. 8c). Stable 813C[carb] values through units A and B also indicate little change in productivity across the K/T boundary, whereas a

negative trend through unit C parallels declining Ca[exc] concentration and is inferred to be a diagenetic artefact (Fig. 8d). A negative 813C[org] excursion in the basal Paleocene is not linked to other paleoproductivity indicators and its significance is uncertain (Fig. 8d). A subsequent positive 813C[org] trend is correlated with Ba[exc] and may indicate increasing productivity. However, an accompanying decrease in TOC suggests that increases in the two paleoproductivity indicators are more likely diagenetic artefacts. Decreasing TOC implies less diagenetic reduction of biogenic Ba and may also cause a positive 813C[org] trend as the abundance of isotopically heavy inorganic carbon increases relative to organic carbon. From the base of unit C, Ba[exc] and 813C[org] values are similar to the Cretaceous and therefore indicate high productivity. Unlike Branch Stream, siliceous microfossils are abundant from the basal Paleocene in this section, with sporadic barren samples in unit B and basal unit C probably due to recrystallisation rather than low original abundance (Fig. 8e). Five consecutive barren samples in upper unit C reflect pervasive recrystallisation in this unit, which is also evident through much of unit D (Table 4; Hollis et al. 2003b). In summary, earliest Paleocene sediments appear to be preserved only as burrow fills within the uppermost 0.02 m

228 Fig. 9 Paleogeographic reconstruction for the New Zealand region in the latest Cretaceous (after King et al. 1999). Location of Marlborough sections (BR = Branch, MD = Mead, FX = Flaxbourne, WO = Woodside) is based on the palinspastic reconstruction of Crampton et al. (2003). Ocean circulation is based on the Paleogene general circulation models of Huber & Sloan (2001) and Bice & Marotzke (2002).

New Zealand Journal of Geology and Geophysics, 2003, Vol. 46 warm surface currents


Circulation Paleogeography Non-deposition (probable land) Terrestrial Shelf -_- Bathyal slope 1— Abyssal

of Cretaceous strata at Mead Stream. The K/T boundary disconformity is overlain by normal terrigenous clay, which is inferred to mark the base of a transgressive sequence following a sea-level fall within 100 000 yr of the K/T event. If a major decrease in overall productivity occurred at this site it must have been within this missing record, as productivity levels through units B and C appear to have been as high as in the last 400 000 yr of the Cretaceous. As at Branch Stream, carbonate production appears to have decreased relative to biogenic silica across the K/T boundary, increased slightly in unit B and then decreased to very low levels in units C and D. The truncated recovery of calcareous plankton implies that the early Paleocene transgression proceeded within a cool oceanic regime that promoted biogenic silica production and delayed the full recovery of calcareous plankton by c. 1.5 m.y. Radiolarians and diatoms continue to be common to abundant through units D-F. A relatively low D/R ratio through unit D might be due to pervasive recrystallisation, which reduces the abundance of smaller diatoms relative to radiolarians. Conversely, better preservation of assemblages in units E and F might explain a high abundance of diatoms relative to unit D. Lithologic similarities and biostratigraphy indicate that unit D may be correlated with units D1-3 at Branch Stream. The much greater thickness of these units at Branch Stream may simply reflect higher sedimentation rate. However, abrupt contacts at the base and top of unit D3 at Mead Stream raise the possibility of unidentified faulting or further disconformities. DISCUSSION This study has highlighted the importance of comparing records from different depositional settings within the Marlborough sector of the East Coast Basin. Uncertainties and stratigraphic gaps in the Mead section are partly resolved by comparison with the more expanded record at Branch Stream. The significance of the sparse siliceous microfossil

Deep current Surface current Upwelling 70S

assemblages at Branch Stream is only evident from comparison with Mead Stream, Woodside Creek, and Flaxbourne River. The two Clarence valley sections provide insight into the long-term effects of the K/T boundary event on the biota and nutrient pathways within a high-latitude upwelling system. A location within a nutrient-rich continental margin setting, such as an upwelling zone, is inferred from the abundance of diatoms and radiolarians in both uppermost Cretaceous and lower Paleocene sediments. Within the constraints of paleogeographic reconstructions (Crampton et al. 2003) and paleo-circulation models (Parrish & Curtis 1982; Huber & Sloan 2001; Bice & Marotske 2002), upwelling along the eastern margin of the Marlborough subbasin may have been driven by offshore westerly winds or longshore northwesterly currents, probably aided by the obstruction formed by the Chatham platform (Fig. 9). The Paleogene paleocirculation model of Bice & Marotske (2002; K. Bice pers. comm. 2002) indicates that the cool, deep waters that upwelled along the northeastern margin of New Zealand during the Paleogene originated from downwelling at the Antarctic margin, analogous to the modern Deep Western Boundary Current (Warren 1981). Variation in the intensity of upwelling in this region would have been controlled by climatic factors influencing the strength of prevailing winds, coastal currents, and the strength, salinity, and nutrient content of upwelling waters. Conditions of moderately high productivity in a relatively cool oceanic setting are inferred from stable lithofacies and paleoproductivity indicators for the last 300 000 yr of the Cretaceous. Relatively cool oceanic conditions are inferred from the absence or scarcity of most species of planktic foraminifera and radiolarians that form the basis of low- to mid-latitude biozonations, notably Globotruncana aegyptica, Rosita contusa, Amphipyndax tylotus, and Pseudotheocampe abschnitta (Caron 1985; Sanfilippo & Riedel 1985; Hollis & Kimura 2001). Equivalent foraminiferal and radiolarian assemblages at DSDP Site 208

229


a. 8AR
