Gomez Et Al (07 BGSA).Pdf

A 2400 yr record of natural events and anthropogenic impacts in intercorrelated terrestrial and marine sediment cores: Waipaoa sedimentary system, New Zealand Basil Gomez† Geomorphology Laboratory, Indiana State University, Terre Haute, Indiana 47809, USA Lionel Carter‡ National Institute of Water & Atmospheric Research, P.O. Box 14901, Wellington, New Zealand Noel A. Trustrum Institute of Geological and Nuclear Sciences, P.O. Box 30368, Lower Hutt, New Zealand ABSTRACT temporally sensitive phenomena, the impacts and Sternberg, 1981; Leithold, 1989; Sommer- of which are conditioned by frequency and fi eld et al., 1999). For these reasons, depocenters The Waipaoa sedimentary system spans magnitude. By contrast, vegetation distur- on active margins have the potential to register ~100 km from terrestrial upland to continen- bance is a spatially sensitive phenomenon variations in sediment discharge that are forced tal rise. Alluvial buffering has little effect on that directly impacts sediment source areas by changes in climate, geology, and land use, as sediment fl ux at the outlet of this mesoscale and lowers the threshold of landscape sensi- well as oceanographic regime (cf. Wheatcroft dispersal system, and hinterland-to-margin tivity to erosion. For this reason, the Taupo et al., 1996; Sommerfi eld and Nittrouer, 1999; transport is accomplished rapidly. Because eruption of 1.718 ka and the piecemeal Carter et al., 2002; Gomez et al., 2004a). of this synergy, the fl oodplain and shelf dep- vegetation changes that occurred after the The generation, dispersal, and accumulation ocenters are sensitive to changes in sediment arrival of Polynesian settlers also generated of riverine particulate matter on active continen- production in the hinterland, and natural and strong depositional signals. After European tal margins are relevant to understanding bio- anthropogenically forced changes in sediment colonization, deforestation of the hinterland geochemical cycling (Leithold and Blair, 2001; source dynamics that occur at several tempo- altered landscape sensitivity and precipitated Gomez et al., 2003; Komada et al., 2004; Leithold ral and spatial scales leave distinctive signals the transition to an erosional regime that et al., 2006), as well as to the creation of mar- in the stratigraphic record. Manifested as impacted sediment production and dispersal gin stratigraphic records (Nittrouer and Wright, variations in sediment properties, these sig- across the entire magnitude-frequency spec- 1994; Wiberg et al., 1996). Investigations under- nals appear in intercorrelated sediment cores trum of events, regulating sediment delivery taken on the river-fed California-Oregon-Wash- from a headwater riparian storage area and to and transport in stream channels. No other ington continental margin highlight the impor- the major terrestrial and marine reposito- perturbation had such a profound impact on tance of short-duration, large-magnitude storm ries for sediment discharged during the past the Late Holocene depositional record. events to the land-ocean transfer of terrigenous 2.4 k.y. The signals represent the landscape sediment (e.g., Wheatcroft et al., 1996, 1997). response to vegetation and land-use change, Keywords: sediment dispersal, sediment cores, Simulations also suggest that changes in the riv- short-term fl uctuations in climate that source to sink, depositional signals, environ- erine input to the ocean, manifest as variations affect surface properties and processes, and mental change. in particle size, that occur over time scales of extreme storms and subduction-thrust earth- decades to centuries may be preserved in shelf quakes. Extreme storms are the minimum INTRODUCTION sedimentary records (Syvitski and Morehead, geomorphologically effective event preserved 1999; Morehead et al., 2001). To date, how- in the sediment records. Lower-magnitude Unlike their larger counterparts that discharge ever, investigations of fl ood-dominated marine storms that are integral components of the to the ocean across passive margins through del- depositional environments have focused on the prevailing hydrometeorological regime cre- taic depocenters (cf. Nittrouer et al., 1996), the dispersal and accumulation of modern sediment ate high-frequency fl uctuations in sediment high-yield rivers that discharge onto active con- (Sommerfi eld et al., 1999; Sommerfi eld and Nit- properties and collectively contribute to tinental margins have smaller catchments, and trouer, 1999; Mulder et al., 2001). event sequences of >100 yr duration. Events much of their sediment load escapes to the ocean Here, we examine the cause of variations in and event sequences comprise a hierarchy of (Milliman and Syvitski, 1992). Dispersal systems particle size and sediment (bio)geochemistry, traversing active margins thus constitute a trace- in three intercorrelated cores from the Waikohu able continuum from source to sink, wherein River fl oodplain, the Poverty Bay Flats, and †E-mail: [email protected]. ‡Present address: Antarctic Research Centre, Vic- the links among terrestrial sediment produc- the adjacent Poverty Shelf depocenter of toria University of Wellington, P.O. Box 600, Wel- tion, transport, and accumulation in the marine the Waipaoa sedimentary system, New Zea- lington, New Zealand. environment may be preserved (e.g., Nittrouer land (Fig. 1). The fi rst site is representative of GSA Bulletin; November/December 2007; v. 119; no. 11/12; p. 1415–1432; doi: 10.1130/B25996.1; 11 fi gures; 1 table. For permission to copy, contact [email protected] 1415 © 2007 Geological Society of America Gomez et al. riparian storage areas along headwater tributar- A 174°E 178°E B ies, while the latter sites characterize the major repositories of fl uvial sediment discharged dur- ′ ing the middle and late Holocene (Pullar and Australian Penhale, 1970; Foster and Carter, 1997; Gomez 38°40 et al., 2004a). Our focus is on the past 2.4 k. 36°S Plate 10 y., during which time erosion processes were infl uenced by a well-documented sequence of natural events and anthropogenic activities, and North 20 40 Island MD972122 for which there is a proxy record of storm activ- ′ + ity from nearby Lake Tutira (Eden and Page, 0 +LT 606 1998; Trustrum et al., 1999). First, we identify ARIELA ANTICLINE 38°50 the sediment sources and sinks and defi ne the E 40°S Hikurangi Trench 80 parameters used to unravel the history of hill- Pacific 100 slope erosion in the Waipaoa sedimentary sys- Plate tem. We then examine the nature of the signals preserved in the shelf record and correlate them Shelf Break with those in the terrestrial record. Finally, we D show how these signals can be linked to changes 0 2 km N ANTICLIN N 39°S in sediment source dynamics and how they can McPhail's HLA be used to determine how stratigraphy records Bend natural events and anthropogenic activity. LAC Mahia 178°E 178°10′ 178°20′ STUDY AREA Extent Peninsula of 1948 178°E Along with the adjacent shelf, the 2205 km2 Flood 700 C 2 6000 Waipaoa River and 312 km Turanganui basins W4 0 - + are located within the zone of active deforma- Waipaoa tion at the boundary of the Australian and Pacifi c River Taruheru plates, on the east coast continental margin of River New Zealand’s North Island (Fig. 1A). The rate 5000 of uplift in the hinterland of the Waipaoa sedimentary system is ~4 mm yr–1, but slight subsid- Waikohu S River + K ′ ence occurs near the coast, and, although two 3000 P11 fault-controlled anticlines are growing on the outer shelf (Fig. 1B), the middle shelf is sub- 38°30 Waimata siding at a rate of ~2 mm yr–1 (Brown, 1995; Te Arai W4 River Berryman et al., 2000; Foster and Carter, 1997; River + Poverty Rocks of the Barnes et al., 2002). Moderate to large earth- Bay East Coast quakes occur frequently, and there have been Allochthon Elevation four magnitude >7 subduction-thrust earth- 5 quakes at the northern end of Ariel anticline in 15 25 the past 2500 yr (Berryman et al., 1989; Ota et >35m Young Nick's al., 1991; Reyners and McGinty, 1999). 0 10 20 km MD972122 + Head Rocks in the Waipaoa sedimentary system Figure 1. Maps showing sites and localities referred to in the text. (A) Physiography of New include: (1) a structurally complex suite of Cre- Zealand’s North Island and the adjacent ocean fl oor, the location of the Australian-Pacifi c taceous and early Tertiary sandstone, argillite, plate boundary (dashed line), and Lake Tutira (LT). Dashed box indicates the area covered mudstone, marl, and limestone; and (2) a cover in B, which shows the structure and bathymetry of Poverty Bay and the Poverty Shelf dep- sequence of poorly consolidated Miocene and ocenter (after Foster and Carter, 1997), the 10 m isopach to the refl ector on the shelf dated Pliocene sandstone, siltstone, mudstone, and at ca. 8000 14C yr B.P. (solid gray line), and the location of Calypso core MD972122. (C) The limestone (Mazengarb and Speden, 2000). In Waipaoa and Turanganui basins, showing the distribution of gully-prone terrain underlain the north-northwestern sector of the hinterland, by the rocks of the East Coast allochthon (after Mazengarb and Speden, 2000), the location Cretaceous and early Tertiary rocks form thrust of the gauging station at Kanakanaia (K; solid dot), and the location of drill core P11 in rela- sheets of the East Coast allochthon (Fig. 1C), tion to those of cores MD972122 and W4. Dashed box indicates the area covered in D, which which are more indurated but have a lower rock shows relief of the Poverty Bay Flats, the maximum inland extent of the Holocene transgres- mass strength than the Neogene cover beds that sion, and the subsequent positions of progradational shorelines (dashed lines; after Brown, underlie the rest of the Waipaoa sedimentary 1995), the extent of inundation during the last major fl ood prior to the construction of the system. No part of the Waipaoa sedimentary fl ood-control leveés (solid gray line; after Pullar, 1962), and the location of drill core W4.

Load more