Linking a Late Miocene–Pliocene Hiatus in the Deep-Sea Bounty Fan Off South Island, New Zealand, to Onshore Tectonism and Lacustrine Sediment Storage

Exploring the Deep Sea and Beyond themed issue

Linking a late Miocene–Pliocene hiatus in the deep-sea Bounty Fan off South Island, New Zealand, to onshore tectonism and lacustrine sediment storage

Kathleen M. Marsaglia1, Candace E. Martin2, Christopher Q. Kautz2, Shawn A. Shapiro1, and Lionel Carter3 1Department of Geological Sciences, 18111 Nordhoff Street, California State University, Northridge, California 91330-8266, USA 2Department of Geology, University of Otago, P.O. Box 56, Dunedin, 9054, New Zealand 3Antarctic Research Centre, Victoria University Wellington, P.O. Box 600, Wellington 6140, New Zealand

ABSTRACT and tectonic events that affect fl uvial-deltaic some extent in the source region, above the slope systems within their source areas and can be (e.g., Normark et al., 2009). So it is very fi tting The cored record at Ocean Drilling Pro- used to reconstruct rates of continental erosion that our Bounty Fan example be included in a gram Site 1122, located on the levee of the (e.g., Burbank et al., 1993; Clift, 2006; Clift volume dedicated to his memory and research. Bounty Fan off southeastern New Zealand, and Blusztajn, 2005; Hoorn et al., 1995). This shows a major late Miocene to Pliocene potential is often not realized. For example, con- BOUNTY TROUGH AND FAN SYSTEM (11.0–3.5 Ma) hiatus in sedimentation. This cerns about autogenic switching of submarine hiatus straddles a period of major uplift in fan lobes and stratigraphic completeness on the The Cenozoic Bounty Channel (Fig. 1) devel- the Southern Alps where the rivers that feed Indus Fan west of India forced Clift et al. (2002) oped in a Late Cretaceous continental rift, the sediment to the Bounty Fan are ultimately to focus instead on the shelf-margin stratigraphic Bounty Trough (Carter et al., 1994). This aban- sourced. There are no signifi cant changes record to address sediment budgets. In contrast, doned rift is currently proximal to or within a in sediment provenance across this inter- on the Bengal Fan east of India, no pronounced zone of transpressional deformation originat- val. We link this hiatus to a combination of breaks in sedimentation were observed (Cochran ing at the Alpine fault plate margin near the rift decreased sediment supply owing to tectonic et al., 1989). Intraplate submarine fan systems apex in southern South Island. Source river(s) disruption of fl uvial drainage and a roughly on Atlantic-style passive margins, where eustatic draining this transpressional tectonic highland simultaneous increase in bottom-current and climatic processes are thought to dominate, feed sediment across a wave-dominated shore- strength. Evidence for this scenario includes are not immune to tectonic signals in that they line onto a wave-dominated continental margin the distribution of current-generated struc- can be created or infl uenced by distant plate- where Neogene deposition has been strongly tures in the core, the relative timing of an marginal tectonic events that reorganize drainage controlled by eustatic fl uctuations of sea level onshore transition from fl uvial to lacustrine patterns (e.g., Hoorn et al., 1995) or affect sedi- (e.g., Carter et al., 1985). Seismic profi les across sedimentation, and a potential post-hiatus ment provenance (e.g., Potter, 1986). the shelf show it to be covered by thin sediment pulse of more weathered sediment into the The Bounty Fan system off South Island, wedges that pinch out landward (Carter et al., Bounty Fan. This sediment pulse was pos- New Zealand, combines aspects of both oro- 1986). Shelf sediments include modern, relict- sibly associated with the reestablishment of genic and passive systems. Like the Bengal sys- palimpsest terrigenous sand and gravel, as well throughgoing drainage and the erosion and tem mentioned above, the Bounty system exhib- as bioclastic sediments (Carter et al., 1985, 1986). fl ushing of stored alluvial to lacustrine sedi- its a major temporal disconnect from source to During highstands, bedload and coarse suspended ments through the system. Thus the Bounty sink, with a period of tectonism in the source load contribute to the inner shelf prism with fi ne Fan provides an excellent example of how the orogen (Southern Alps) correlating to a major suspended load moving along and across shelf complex interplay between tectonic and pale- submarine hiatus on the passive-margin Bounty to contribute to local shelf depocenters in the lee oceanographic forces can affect the sedimen- Fan instead of a major sediment pulse as might of major promontories and a proximal slope-fan tary record in deep-marine systems. be expected. To fully understand the implication complex (Otago fan, Fig. 2A) (Carter and Carter, of a major hiatus in Bounty Fan sedimentation 1993). During lowstands, sediment was dispersed INTRODUCTION documented at Ocean Drilling Program Site mainly across the shelf to contribute directly to 1122, we evaluated the entire source-to-sink the proximal Otago slope-fan complex, a series In determining budgets for sediment fl ux to the system, combining previously published petro- of coalescing fans fed by nine major submarine deep sea, all parts of the system must be exam- logical, sedimentological, and stratigraphic data canyons along the Otago continental slope (Carter ined (Clift, 2006) rather than just proximal (e.g., sets from onshore and offshore segments with and Carter, 1988), or to long distant transport via Burbank et al., 1993) or distal (e.g., Rea, 1992) some new geochemical data. a series of three submarine feeder channels that segments. This is the source-to-sink approach William Normark also embraced such a merge into the 900-km-long Bounty Channel promoted by Driscoll and Nittrouer (2000) that holistic approach to deep-sea fan formation (Figs. 1and 2; Carter and Carter, 1988). Note that has been successfully applied on margins across and evolution. As his work on deep-sea fans the Otago fan complex has not been drilled, but the globe including North Island, New Zealand evolved (e.g., Normark, 1970, 1974; Normark Carter and Carter (1993) infer it to potentially be (Carter et al., 2010). Large submarine fan sys- et al., 1984; Piper and Normark, 2001), so did of late Pliocene or younger age. tems associated with major orogens such as the his reali zation that the answers to submarine The Bounty Channel follows the Bounty Himalayas potentially record climatic, eustatic, fan evolution, the ultimate sediment sink, lay to Trough axis for 670 km and empties out onto

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increased uplift (Walcott, 1998). Tectonic uplift 35°S (topography), glacial development, eustatic change, and enhanced sediment supply were Australian likely linked (Carter and Carter, 1996; Carter, Taupo Plate North R.M., et al., 2004). Maximum sedimentation rates Volcanic Island on the margin and in the trough were attained Zone in late Pliocene to Pleistocene glacial periods with intervening interglacials characterized 40° by pelagic deposition in the trough as it was Transform Alpine Fault Pacific bypassed by establishment of high-stand, along- South Plate Island shelf sediment transport regimes (Carter et al., 1990). Furthermore, as outlined in Carter, L., et al. 500 km (2004), fan sedimentation was variably affected by the Paciﬁ c Deep Western Boundary Current Site 1119 Chatham Rise Chatham Is (DWBC), part of the global thermohaline cir- 45° 4000 m culation, and the mainly wind-driven Antarctic Site 594 Circumpolar Current (ACC), which initiated in Southern Alps Bounty Trough the region during the early Oligocene (Fig. 1). Here we focus on results of drilling of the Bounty Channel Site 1122 1000 m Bounty Channel at Ocean Drilling Program Bounty Fan Site 1122 (Carter et al., 1999) where a 617.8 m succession of lower Miocene to upper Pleisto- Solander Trough cene turbidites, pelagic to hemipelagic sedi- Site 1120 1000 m ments and contour current-modiﬁ ed deposits 50° Site 1121 were recovered from the channel levee (Figs. 2 Solander Channel and 3). Sandy laminae and beds represent over- Campbell Plateau S.W. Pacific bank deposits from turbidity currents that tra- Campbell “Skin” Drift Basin versed and overspilled the Bounty Channel in the process, building up the channel levees (see discussion of processes in Carter et al., 1999).

1000 m 1000 The Miocene section extends from 617.8 to DSDP Site 490 meters below sea fl oor (mbsf), ranges in ODP Site age from ~16 to 11 Ma, and accumulated at 55° Terrigenous supply via turbidity current an average rate of ~20 m/m.y. It is unconform- ably overlain at ~490 mbsf by lower Pliocene N DWBC + NZ sediments ~3.5 Ma in age (Fig. 3). Sediment Sediment accumulation was apparently continuous from the late Pliocene into the Pleistocene with accu- 165°E 170° 175° DWBC + ACC mulation rates reaching ~400 m/m.y. Carter et al. (1999) attributed this sedimentation pat- Figure 1. Location map with details of New Zealand plate boundaries (insert), surround- tern to uplift of the Southern Alps, but they ing bathymetry, Bounty system elements and currents mentioned in the text, and drill sites did not address the cause of the major hiatus (modifi ed from Carter et al., 1999). Abbreviations: ACC—Antarctic Circumpolar Current; and/or unconformity at 490 mbsf. Rather than DSDP—Deep Sea Drilling Project; DWBC—Deep Western Boundary Current; NZ—New an angular unconformity, the hiatus at Site 1122 Zealand; ODP—Ocean Drilling Program; S.W.—Southwest. is more accurately described as a para con- formity unrelated to plate boundary deformation (Carter et al., 1999). This is evidenced by the Southwest Pacifi c Basin to form the abyssal development of pronounced sediment waves in lack of pre-hiatus deformation on seismic data Bounty Fan (Carter and Carter, 1996). Seismic the Bounty levee in seismic Unit A (Fig. 2C) to (Carter et al., 1999; Fig. 2). In a later publica- facies and their ages, as determined by biostratig- a sea-level lowstand at ~3 Ma when there was tion, Carter, L., et al. (2004) attributed the hiatus raphy and magnetostratigraphy at Site 1122, sug- direct fl uvial input to the feeder channels at the to a strengthened ACC and correspondingly gest that the channel has been active since at least shelf edge and a concomitant rapid input of large intensifi ed bottom fl ow. They favored the ACC 16 Ma (see Shapiro et al., 2007). Specifi cally, volumes of sediment to the levee system. over the DWBC because of the timing of the Carter et al. (1994) contend that the steady north- The continental Campbell Plateau and hiatus and the relatively weak energy of the ward migration of axial sandy channel facies (see Chatham Rise, submerged since at least the DWBC as compared to the overriding ACC as arrow in purple box in Fig. 2) indicates that the Oligocene, fl ank the trough, therefore the main supported by the modern oceanography (Carter channel facies are linked to adjacent units and not post-Oligocene terrigenous sediment source has and Wilkin, 1999). We examine the composi- a younger, superimposed feature. The character been the narrow, plate-collision zone in southern tion and provenance of these sediments for of the seismic units (A, B, C, Fig. 2C) associ- South Island (Carter et al., 1994). This strike- clues as to the origin of the ~11–3.5 Ma gap in ated with the fan have, however, changed through slip dominant zone became more compressive sedimentation and discuss the possible mecha- time. For example, Carter et al. (1990) relate the at 6.4 Ma resulting in crustal shortening and nisms for this signifi cant hiatus.

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Downloaded from http://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/7/2/305/3714555/305.pdf by guest on 26 September 2021 Bounty Fan hiatus A N 10 km B A D1 D2 Site 1122 Site 1122 Basement R7 R9 R3 R11 R5 R10 C ed from Carter et al., 1999). Boundary between seismic units A and B (R5) A et al., 1999). Boundary between seismic units Carter ed from Bounty Channel Bounty Channel ectors (modiﬁ ectors NZOI 2023 Southwest Hiatus

ed from New Zealand Geological Survey, 1972). Note that Miocene basins are indicated only where patchy indicated only where 1972). Note that Miocene basins are New Zealand Geological Survey, ed from 7 Two-way traveltime (s) traveltime Two-way system (image 2. On top (A) is a topographic and bathymetric image of the Bounty source-to-sink Figure to abyssal depths in with colors progressing is shelf areas CANZ, 1996). Gray scale is subaerial; red from is detailed below in (B), which shows Boxed area marks general location of Site 1122. dark blue. Red star (simpli- region Bounty Fan sediment source and geology for drainage, structure, of onshore selected features ﬁ may distribution (and associated lacustrine environments) and their today, present are outcrops erosional image on right (C) is part of seismic section NZOI 2023 showing Site 1122 extensive. Lower have been more seismic units and R3, R5, R7, R9, R10, A, B, C, D1, and D2 are to the Bounty Channel where in relation seismic reﬂ are R11 corresponds to ~470 m at Site 1122, which is the approximate level of the hiatus. See Shapiro et al. (2007) for et al. (2007) for level of the hiatus. See Shapiro which is the approximate to ~470 m at Site 1122, corresponds outlined in purple box. channel facies in area discussion of probable 6 C Site 594 N 171°E 50 km Pacific Ocean v Waitaki River v v ) Isolated outcrop ) Isolated v v v v ( v (DV) Dunedin volcano v sediment remnants sediment Miocene basalt Miocene Major fault Major river terrestrial Miocene Otago Schist outcrop v v D V v v v v v v v v v v v v v v v v v v v v v

Taieri Taieri River

v v 170°E Otago fan Otago Clutha River 40 km B 45°S 46°S

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Leg 181 Site 1122

1122 B 1122 C 1122 C 1122 C

Depth Re- Re- Generalized Depth Re- Generalized Depth Re- Generalized (mbsf) Core cov- Core cov- Lithology (mbsf) Core cov- Lithology (mbsf) Core cov- Lithology Subunit

ery ery Epoch Epoch ery ery Subunit Epoch Age (Ma) Age (Ma) Subunit Age (Ma)

24X 45X 1H 2H

25X 10 3H Thin IA 210 410 turbidites 46X 1.7

4H 26X 20 220 Thin 420 47X (<10 cm) Pelagic 5H 27X fine sand mud and 30 230 430 48X and silt IC laminated turbidites fine sand 6H IIA

28X 0.85 40 240 440 49X late Pleistocene 7H 29X 50 250 50X

0.24 450

8H 30X 51X 60 Thick 260 460 (~40 cm) 9H sand IB 31X

52X Pliocene 70 turbidites 270 470

10H 32X Approxi- 53X 3.54 80 280 480 mate 11H chlorite IIB 33X rich zone 54X UNC 90 12H 290 490

34X

13H 55X >10.4 100 300 500

14X 35X

110 middle Pleistocene Pelagic 310 56X 15X 0.95 510 mud and 36X laminated 120 57X 16X 320 Fine sand 520 sands contour- ID with 37X IIC 58X chlorite 130 ites/ 17X 330 turbidites 530

38X 59X 140 1.16 18X 340 540

Thin 39X 60X 12.34 150 19X (<10 cm) fine sand 350 1.2 550 and silt IC 40X 61X 160 20X turbidites 360 560 Coarser 13.52 41X middle Miocene 0.42 62X grained IIIA 170 21X mud and 370 570 42X sands 63X 180 22X 380 580 43X 64X 190 23X 390 590 44X 24X IIA 65X 200 45X Lithified 1.44 400 early Pleistocene 600 sediment/ IIIB Figure 3. Stratigraphic column for 66X debris Sampled Intervals flow Site 1122 modiﬁ ed from Carter et al. 610 UNC (1999); see this reference for further Sample not counted Unconformity 67X <17.4

deﬁ nition of subunits. Sample inter- 620 vals are as indicated. mbsf—meters Point-counted sand 68X early Miocene below sea ﬂ oor.

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The Miocene–Pliocene sections drilled at stained for feldspar recognition and point- the 11–3.5 Ma hiatus. This is evident in both several other Leg 181 sites (Fig. 1) provide counted using the Gazzi-Dickinson method as the sand detrital modes (Fig. 4) and bulk- no consistent trends (Carter et al., 1999). The outlined in Shapiro et al. (2007). Geochemical sediment geochemistry. The very fi ne to fi ne 500-m sedimentary section recovered at Site samples were ground for 10–15 min in an agate sand samples are micaceous and arkosic with 1119 was <3 Ma in age, younger than the hiatus ball mill before fusion according to the method grains of quartz, albite, muscovite, and chlorite, (Carter et al., 1999). Site 1120 on the Central of Norrish and Chappell (1977). Major-element and a minor metamorphic lithic component. Campbell Plateau showed a decrease in sedi- analysis was carried out on fused glasses by These are also the most abundant components ment accumulation rates at ~10 Ma, which the X-ray fl uorescence spectroscopy using a Phil- in the Otago-Haast schist and derived fl uvial shipboard scientists (Carter et al., 1999) attrib- lips PW 2400. Presented here are only chemi- sediments from the modern Clutha River (Fig. uted to current and productivity changes rather cal index of alteration (CIA) ratios. Chemical 2B; Shapiro et al., 2007). The main provenance

than tectonic events given the largely pelagic index of alteration is deﬁ ned as molar (Al2O3)/ signal in the sand fraction is that of the Clutha

nature of the sedimentary record at this site. (Al2O3 + CaO* + Na2O + K2O) (Nesbitt and River (Otago schist), and this signal remained Site 1121 to the south on the Campbell “Drift” Young, 1984), where CaO* is the calcium asso- relatively constant across the hiatus (Shapiro shows a major hiatus from 65 to 3 Ma. Deep ciated with the silicate fraction in the sediment. et al., 2007). Note that volcanic lithic fragments Sea Drilling Project Site 594, which is located at Owing to their small volume, bulk samples were are fairly rare in the Bounty sand fractions, but the head of the Bounty Trough, closer to the zone not analyzed for carbonate concentration prior there are discrete tephra-rich horizons (Shapiro of Southern Alpine deformation, has a complete to geochemical analysis. A linear (R2 = 0.9018) et al., 2007). Despite the active onshore maﬁ c stratigraphic section of calcareous ooze to cal- relationship between loss on ignition (wt%) and magmatism during the hiatus (see volcanic careous mud from the early Miocene (Kennett, CaO (wt%) was used to estimate and correct for rock distribution in Fig. 2B), there is no sig-

et al., 1986). This range of marine records CaCO3 (wt%) allotting a proportion for phos- niﬁ cant increase in maﬁ c volcanic lithic con- emphasizes that the response to tectonic events phatic Ca. This technique could be used because tent in the post-hiatus section. This is not may differ across the region depending on the of the low CaO concentrations of the Bounty surprising because the weathering of basaltic depositional setting. minerals (e.g., albitic feldspar). Removing this volcanic rocks produces mainly clay minerals eustatic biogenic signal (Carter and Carter, as opposed to sand-sized detritus (see discus- METHODS 1993) was important in being able to decipher sion in Marsaglia, 1993). In addition, because detrital mineral provenance. the volcanism was concentrated in the north- Representative unconsolidated sandy sam- east segment of the study area (Fig. 2B), any ples taken from cores recovered at Site 1122 SEDIMENT COMPOSITION AND epiclastic signal may have been preferentially (Fig. 3) were split into two equal portions for PROVENANCE ACROSS HIATUS translated to the northeast along the shelf and geochemical and petrographic analyses sum- slope north of the Dunedin volcanic complex. marized here. For petrographic analyses, Sediment composition is relatively uniform Major- and trace-element compositions of sample splits were sieved for the sand fraction within the cored section at Site 1122 with no Bounty Fan sediments are also consistent with and thin sections prepared from the sand were distinct changes in sediment provenance across a mainly Clutha River (schist) source (Kautz

Figure 4. Sediment accumulation plot for Site 1122 (Hole C) A B modified from Carter et al. (1999) on right (B) and geochemical data on left (A) keyed

to shipboard subunit designa- Sed. Rate ~400 m/m.y. tions (I–III, A–D). The latter Key to Site 1122 is a plot of chemical index of Sample Intervals (CIA) by Subunit alteration (CIA) versus core depth. Modern Clutha river sediment data from Kautz and C Martin (2007) and remainder (unweathered Otago schist, Sed. Rate Otago Miocene sediments, and ~100 m/m.y. weathering proﬁ le on Otago schist) from Corcoran (2005). Ternary plot of proportions of total quartz (Q) versus total Unit feldspar (F) versus total lithic Sed. Rate average ~20 fragments (L) for Ocean Drill- m/m.y. ing Program Site 1122 (C) and potential river sources illus- trating that the Clutha River most closely matches Bounty Fan sand composition (from Less weathering More weathering Shapiro et al., 2007). mbsf— meters below sea ﬂ oor.

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and Martin, 2007) displaying similar rare-earth not what one would expect if eustasy were the 1122. They describe the pre–3.5 Ma section as element (REE) concentrations and upper con- main control; in fact, it is the exact opposite. At a Bounty Channel–fed contourite succession tinental crust–normalized (McLennan, 2001) ~10.5 Ma, when there is a major global fall in that evolved into the Bounty submarine fan sys- patterns, except for some Miocene samples sea level (Haq et al., 1988), deposition ceased tem. It follows then that contour currents were that exhibit slightly lower REE concentra- on the Bounty Fan, whereas fan deposition was a secondary rather than a primary depositional tions. Note that although the Waitaki River reestablished in the early Pliocene just after a input mechanism during accumulation of Units is an apparent major sediment contributor to period of relatively high sea level (Haq et al., II and III. the upper reaches of Bounty system, the main 1988). Such out-of-phase development contra- provenance signal in the sand fraction of the dicts the paradigm of submarine fan buildup Changes in Sediment Input Bounty levee at Site 1122 is that of the Clutha during sea-level lowstands (see Covault et al., River (Otago schist), and this signal remained 2007 for discussion and additional southern Paleogene postrift thermal subsidence and relatively constant across the hiatus. No dra- California examples). Therefore something marine transgression of the Otago region were matic unroofi ng sequence is observed within other than sea-level change must have dimin- interrupted by transpressional tectonics at the the Bounty succession because at ~16 Ma ished input and/or removed sediment sometime inception of the Alpine fault (Cooper et al., (oldest sediment at Site 1122) the Otago schist between ~11 and 3.5 Ma. 1987) at ~23 Ma (Carter and Norris, 1976; had already been exposed and peneplained Kamp, 1986). Subsequent late Miocene (Kaik- (LeMasurier and Landis, 1996). Submarine Erosion and Transport ouran) deformation is linked to transpression along the Alpine transform plate boundary DISCUSSION Sediment fl ux throughout the upper and (Molnar et al., 1975) brought about by changes lower regions of the Bounty marine system in the Australia-Pacifi c instantaneous pole There are several possible causes for the may have been strongly infl uenced by abys- positions fi rst at 12 Ma and then later at 5 Ma development of a major hiatus in a Bounty sub- sal current activity. Shelf-edge–parallel trans- (Sutherland, 1995; Cande et al., 1995). This marine fan system including the following: port of sediment along the base-of-slope fan deformation produced an estimated 20-km complex has been infl uenced by a major inter- exhumation along the Alpine fault since 10 Ma Autogenic Switching of Bounty Channel mediate water fl ow as described by Lu and (Cooper, 1980) and more rapid uplift and exhu- Fulthorpe (2004). At Site 1122, sedimentary mation since 6.4 Ma (Walcott, 1998). Curray et al. (2002) show that channel avul- structures suggest likely reworked and redis- The lower age limit of the hiatus at Site sion in the Bengal Fan is limited to the upper and tributed sediments occur both above and below 1122 roughly corresponds to the onset of early upper middle fan, whereas channel migration the hiatus, with current-generated bedforms Miocene tectonism, reemergence of central on the lower fan is slower and less important . being best developed in the core that contains Otago, development of the so-called “Dun- However, the Bengal Fan is largely unconfi ned. the hiatus (Carter et al., 1999). Today, south stan” fl uvial system, and deposition in onshore In contrast, the course of the Bounty Channel of the Bounty Trough, erosion prevails under terrestrial basins (Youngson and Craw, 1996; is largely structurally (basement) controlled the infl uence of a strong and dominating ACC. Youngson et al., 1998). The Dunstan paleoriver, and confi ned to the relatively narrow Bounty The paleolatitude of the Bounty Fan would which evolved from a coarse, conglomeratic, Trough (Carter and Carter, 1996). There is place it under the infl uence of the ACC prior to braided to a fi ner-grained, sandy, meandering some evidence for slight channel migration, but 10 Ma (Carter, L., et al., 2004). As New Zealand system, was eventually transgressed by lacus- no evidence for pre-Pleistocene channel avul- drifted north to its present position, the Bounty trine deposits of the Bannockburn Formation sion and reestablishment in the vicinity of Site Fan moved to the periphery of the main path (Douglas, 1986; Youngson et al., 1998; Young- 1122. Thus the pronounced left bank, channel of the ACC, although it is likely to be affected son and Craw, 2002). The formation of this levee at Site 1122 should provide a detailed pre- during glacial periods (e.g., Crundwell et al., large lake or series of lakes at or ~11–13 Ma, Pleistocene record of sediment delivered to the 2008) and is periodically infl uenced in modern signaled the tectonic disruption of the Dun- Bounty Fan. times by ACC-generated eddies (e.g., Bryden stan paleoriver drainage, owing to reactivation and Heath, 1985). Against the background and reverse movement along Cretaceous nor- Sea-Level Change of an episodic impact of the ACC, the Fan is mal faults (e.g., Bishop and Laird, 1976). The continually bathed by the DWBC. By 1.4 Ma, lake geometry is roughly defi ned by the spatial Modern highstand sediment is transported this northward shift, coupled with the infl ux distribution of lake-deposit remnants, which if mainly along the shelf and therefore largely of sediment from a rapidly uplifting Alps connected, suggest that the lake(s) may have bypasses Bounty Trough (Carter and Carter, that were exposed to more intense glacial- been extensive (see Fig. 2B). Associated uplifts 1993). Any sediment pulse in the system would interglacial cycles, resulted in fan deposition produced clastic successions (Wedderburn For- fi rst be stored in the nearshore shelf sediment overwhelming the remaining erosional effects mation and Maniototo Conglomerate) that fed wedge or prism (Carter and Carter, 1986), of the abyssal fl ow of the DWBC and episodic into and eventually fi lled the lake (Youngson which would only supply sediment to the ACC, although the middle fan appears to be et al., 1998). From 13 to 10 Ma these faults also deeper trough when it prograded to the platform undergoing minor erosion under the present served as conduits for mafi c magma producing edge. During lowstands, therefore, a major fl ow (Carter and Carter, 1996). Such a sce- the Dunedin volcanic complex (shield volcano) part of the terrigenous sediment supply (note nario is independent of the supply of sediment and outlying mafi c intrusions (Coombs et al., that some sediment was contributed to Otago to the fan, which may not have been uniform 1986). Correlatives of these fl uvial and lacus- margin fan system) should have been distrib- throughout the span of the hiatus. trine deposits, known at the Kurow Formation uted downslope and directly fed into the feeder Shapiro et al. (2007) argue that the presence or Group, are also present in the Waitaki River channels of the base-of-slope fan complex of channel facies (purple box in Fig. 2) suggests drainage basin to the north (Fig. 2B; Youngson (Carter and Carter, 1989). The sediment pattern that there was turbidity current input through- et al., 1998) indicating that fl uvial drainage in in the Miocene–early Pliocene at Site 1122 is out deposition of the recovered section at Site this region was also affected.

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Thus the Bounty hiatus may have been pro- interesting to note that the highest CIA index ACKNOLWEDGMENTS duced when sediment input was shut off dur- (~73) is recorded in the Pliocene interval over- The manuscript benefi ted from discussions with ing onshore fault reactivation and magmatism lying the hiatus, a value suggesting signifi cant Dave Craw, Daphne Lee, Nick Mortimer, and Michael that created a “tectonic obstacle course” for the weathered input consistent with recycling of Palin and input from Peter Clift, Tim Cope, Andrea drainage that needed to be overcome before onshore Miocene sediments. This pronounced Fildani, and an anonymous reviewer. sediment could be resupplied to the Bounty peak cannot be linked to any specifi c climatic REFERENCES CITED Channel. This trapping of sediment in onshore event. However, gradual fl uctuations in the basins in the late Miocene to Pliocene may have overlying section could be climate related, e.g., Armishaw, J.E., Holmes, R.W., and Stow, D.A.V., 2000, The been similar to the effects of sediment trapping the maximum at ~290 mbsf roughly correlates Barra Fan: A bottom-current reworked, glacially fed submarine fan system: Marine and Petroleum Geol- in glacial lakes in the Waitaki River headwaters with the mid-Pleistocene transition in glacial ogy, v. 17, p. 219–238, doi: 10.1016/S0264-8172(99) during the past 10,0000 yr (Carter and Carter, and interglacial cycles, the origin of which is 00049-5. Bishop, D.G., and Laird, M.G., 1976, Stratigraphy and 1990). Breaching may have been gradual or still debated (e.g., Lisiecki and Raymo, 2007). depositional environment of the Kyeburn Formation more sudden and catastrophic, similar to that It has been linked to a major glacial event, (Cretaceous), a wedge of coarse terrestrial sediments of glacial Lake Missoula, which is known to Marine isotope stage 22 (see discussion in in central Otago: Journal of the Royal Society of New Zealand, v. 6, p. 55–71. have delivered large volumes of sand to abys- Mildenhall et al., 2004). Perhaps this second Bryden, H.L., and Heath, R.A., 1985, Energetic eddies at the sal fans in the northeast Pacifi c Ocean (Zuffa CIA maximum and high values in overlying northern edge of the Antarctic Circumpolar Current in et al., 2000; Normark and Reid, 2003; Prytulak sections represent further fl ushing of Miocene the southwest Pacifi c: Progress in Oceanography, v. 14, p. 65–87, doi: 10.1016/0079-6611(85)90006-0. et al., 2006). In the Bounty example, it may terrestrial sediments associated with enhanced Burbank, D.W., Derry, L.A., and France-Lanord, C., 1993, have taken some time for the signal to propa- glacial runoff. Reduced Himalayan sediment production 8 Myr ago despite an intensifi ed monsoon: Nature, v. 364, gate down the fan system to Site 1122, consis- p. 48–50, doi: 10.1038/364048a0. tent with Curray et al.’s (2002) fi ndings for the CONCLUSIONS Cande, S.C., Raymond, C.A., Stock, S., and Haxby, W.F., Bengal Fan, where they showed the time span 1995, Geophysics of the Pitman Fracture Zone and Pacifi c-Antarctic plate motions during the Ceno- of a signifi cant hiatus decreased up the fan. The We can eliminate autogenic channel switch- zoic: Science, v. 270, p. 947–953, doi: 10.1126/ paleogeography of the pre- and post-hiatus river ing and eustasy in creating the hiatus at Site science.270.5238.947. systems (Clutha, Waitaki, and smaller Taieri 1122. We favor a model where the system was CANZ (Charting around New Zealand), 1996, Undersea New Zealand, New Zealand region physiography, rivers) are poorly constrained and may have affected by tectonically driven changes in sedi- 1:4,000,000: National Institute of Water and Atmo- been very different, but the relatively uniform ment fl ux superimposed on the erosive effects spheric Research Chart Miscellaneous Series 74. Carter, L., and Carter, R.M., 1986, Holocene evolution of the composition of sand across the hiatus at Site of the ACC and DWBC. The sediment accu- nearshore sand wedge, south Otago continental shelf, 1122 (Shapiro et al., 2007) suggests that since mulation pattern observed at Site 1122 could New Zealand: New Zealand Journal of Geology and the Miocene the major sand-contributing rivers be produced if the sediment fl ux varied with a Geophysics, v. 29, p. 413–424. Carter, L., and Carter, R.M., 1988, Late Quaternary devel- to the Bounty Fan were largely developed on relatively sudden decrease at ~11 Ma, moder- opment of left-bank–dominant levees in the Bounty Otago schist terranes. ate input after 3.5 Ma and higher input from Trough, New Zealand: Marine Geology, v. 78, p. 185– The reestablishment of fl ow-through drain- 2 Ma onwards. The change in sediment input 197, doi: 10.1016/0025-3227(88)90108-9. Carter, L., and Carter, R.M., 1990, Lacustrine sediment traps age could have conceivably produced a pulse at ~11 Ma is best related to tectonic disruption and their effect on continental shelf sedimentation— of more weathered material temporarily of onshore drainage in Central Otago schist ter- South Island, New Zealand: Geo-Marine Letters, v. 10, no. 2, p. 93–100, doi: 10.1007/BF02431026. stored in the interior basin successions into rains, the main sediment source as determined Carter, L., and Carter, R.M., 1993, Sedimentary evolution the Bounty Trough. The sediment pulse would using sand detrital modes and geochemistry. of the Bounty Trough: A Cretaceous rift Basin, south- have to make its way down the Bounty system The erosive effects of the ACC and DWBC western Pacifi c Ocean, in Balance, P.F., ed., South Pacifi c Sedimentary Basins, Sedimentary Basins of the and once near Site 1122, largely exceeded the may have postponed the signal of enhanced tec- World: Volume 2: Amsterdam, Elsevier, p. 51–67. erosive capacity of the ACC and DWBC. Sand tonism at 6.4 Ma to >3.5 Ma. The CIA values Carter, L., and Wilkin, J., 1999, Abyssal circulation around detrital modes show no evidence for recy- document input of more weathered material that New Zealand—A comparison between observations and a global circulation model: Marine Geology, cling (increase in quartz) across the Miocene– could be linked to drainage development within v. 159, p. 221–239, doi: 10.1016/S0025-3227(98) Pliocene hiatus. However, there are indications the system periodically tapping into and fl ush- 00205-9. Carter, L., Carter, R.M., Nelson, C.S., Fulthorpe, C.S., and in the bulk geochemical data of changing pro- ing older terrestrial lacustrine and fl uvial depos- Neil, H.L., 1990, Evolution of Pliocene to Recent portions of weathered material through time its into the submarine system. We note that it abyssal sediment waves on Bounty Channel levees, as demonstrated in the plot of CIA versus age may be diffi cult to separate out tectonic from New Zealand: Marine Geology, v. 95, p. 97–109, doi: 10.1016/0025-3227(90)90043-J. in Figure 4. The CIA refl ects the bulk parent- paleoceanographic signals (erosive currents) in Carter, L., Carter, R.M., and McCave, I.N., 2004, Evolu- rock chemistry and relative leaching of soluble deep-sea successions, especially where the cur- tion of the sedimentary system beneath the deep Pacifi c elements (Ca, K, and Na) during weathering; rent development and strength are partly linked inflow off eastern New Zealand: Marine Geology, v. 205, p. 9–27, doi: 10.1016/S0025-3227(04)00016-7. lacustrine sediments generally undergo high to movement of tectonic plates. Carter, L., Orpin, A.R., and Kuehl, S.A., 2010, From moun- rates of chemical weathering and consequently Insights from the Bounty system, where tain source to ocean sink—The passage of sediment across an active margin, Waipaoa sedimentary system, have high CIA (~70–90; e.g., Das and Haake, tectonic-induced fl uvial drainage reorganization New Zealand: Marine Geology, v. 270, p. 1–10, doi: 2003; Selvaraj and Chen, 2006). Compara- can be directly linked to the deep-sea record, 10.1016/j.margeo.2009.12.010. tive data for unweathered versus weathered are applicable to ancient systems, particularly Carter, R.M., and Carter, L., 1996, The abyssal Bounty Fan and lower Bounty Channel evolution of a rifted-margin schist and modern Clutha River versus Mio- those potentially affected by fl uvial drainage- sedimentary system: Marine Geology, v. 130, p. 181– cene basin (fl uvial-lacustrine) sediments are disrupting tectonic events (e.g., Rio Grande 202, doi: 10.1016/0025-3227(95)00139-5. as shown, with higher indices corresponding fl uvial-deltaic system, Connell et al., 2005). Carter, R.M., and Norris, R.J., 1976, Cenozoic history of southern New Zealand: An accord between geologi- to more weathered material. For compari- Furthermore, the Bounty Fan has also been cal observations and plate-tectonic predictions: Earth son, modern Clutha River sediments exhibit infl uenced by submarine currents and so pro- and Planetary Science Letters, v. 31, p. 85–94, doi: 10.1016/0012-821X(76)90099-6. CIA values ranging from 50 to 60 depending vides insights in other systems such as the Barra Carter, R.M., Carter, L., Williams, J.J., and Landis, C.A., on grain size and distance downstream. It is Fan (Armishaw et al., 2000). 1985, Modern and relict sedimentation on the south

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MANUSCRIPT RECEIVED 3 JUNE 2010 Douglas, B.J., 1986, Lignite resources of Central Otago: Normark, W.R., and Reid, J.A., 2003, Extensive deposits on REVISED MANUSCRIPT RECEIVED 13 OCTOBER 2010 New Zealand Energy Research and Development the Pacifi c plate from Late Pleistocene North American MANUSCRIPT ACCEPTED 17 NOVEMBER 2010

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