Climatic influences on sediment deposition and turbidite frequency in the Nitinat Fan, British Columbia K.P. Knudson ⁎, I.L. Hendy University of Michigan, Department of Geological Sciences, 2534 C.C. Little Building,1100 N. University Avenue, Ann Arbor, MI 48109, United States abstract article info Article history: Received 25 June 2008 Received in revised form 28 February 2009 Accepted 2 March 2009 Communicated by J.T. Wells Keywords: turbidite turbidity current glacimarine Cordilleran Ice Sheet Vancouver Margin Nitinat Fan Continental margins in regions influenced by temperate ice sheets experience climate-dependent changes in sedimentary processes. A new stratigraphy is presented for Ocean Drilling Program Hole 888B, from the Nitinat Fan, on the Vancouver Margin, in which we examine the relationship between fluctuations in glacial- sourced sediment delivered to the continental shelf and turbidite character and frequency. Glacial/ interglacial episodes are determined based on: (1) core lithology, where sandy/coarse-grained sediment and fine-grained clay/silty clay represents glacial and interglacial intervals, respectively; (2) δ 18 O of planktonic foraminifera G. bulloides, in which higher values indicate warmer sea surface temperatures and lower global ice volume; (3) magnetic susceptibility, in which higher values indicate coarser grain sizes deposited during glacials; and (4) ratios of sinistral N. pachyderma to dextral N. incompta, in which higher proportions of N. pachyderma are a sign of cooler sea surface temperatures. Finally, using radiocarbon 14 C dates, specific Marine Isotope Stages (MIS) within the top 240 m of core are assigned: MIS 2–4 (2–118 mbsf), MIS 5 (118– 157 mbsf), and MIS 6 (213–240 mbsf). Using this chronology, sedimentation rates for the Nitinat Fan were greater (187 cm/kyr) during glacial MIS 2–4 than interglacial MIS 5 (69 cm/kyr). Additionally, during glacial MIS 2–4 thicker turbidites (upwards of ~150 cm) were deposited relatively frequently (~75 year periodicity) compared with those from MIS 5, which are relatively thin (up to 27 cm) and deposited more rarely (~130 year periodicity). These results indicate that turbidite frequency and thickness are linked to climate through ice sheet extent, since transport of glacimarine sediment to the continental slope promotes turbidity currents that are responsible for the most significant amount of offshore sedimentation. This study shows that geological processes influencing turbidite deposition can fluctuate over time and may not necessarily be represented by ongoing processes within the modern depositional setting. © 2009 Elsevier B.V. All rights reserved. 1. Introduction “The present is the key to the past” is a common, simple philosophy used in the interpretation of ancient sedimentary sequences. If this approach were applied within continental margin settings, it would assume that the depositional processes on the continental slope have not changed dramatically through time. In this study, we evaluate this assumption by investigating changes in a turbidite sequence from the Nitinat Fan off the intermittently glaciated Vancouver Margin. Sequences of turbidites are often considered indicative of deposition during early stages of orogenesis, within a foreland basin with shelves sloping into deep water, in association with some degree of tectonism serving as a trigger for density-driven currents. However, as this paper will demonstrate, turbidites may also result from sedimentation processes driven by dynamic and transient phenomenon—such as climate change. It is well known that events such as earthquakes and storms trigger turbidity currents; however, high continental shelf sedimentation rates may also lead to increased turbidite frequency. At high latitudes during glacial intervals, sediment production and transport by ice sheets has the potential to deliver large sediment loads to the edge of the continental shelf, increasing the probability of slope instability that promotes turbidity currents. These currents carry sediment from the shelf and deposit it as turbidites within sediment fans. Unfortunately, our understanding of the interplay between ice sheets and turbidite frequency is currently limited, because most studies have focused on the greatly different temperate-latitude turbidite settings—which are ice-free and receive a constant influx of sediment from rivers. The limited work on high-latitude turbidites includes studies of the modern sedimentary setting of Antarctica (Wright and Anderson, 1982; Anderson et al., 1986; Anderson, 1999; Escutia et al., 2000 and references therein) and Alaska (Powell, 1983; Schwab and Lee, 1983; Powell, 1990). Regions of temperate glaciers in modern Alaska may be most similar to the Vancouver Margin during the last glacial (Powell, 1983). In Alaska, relationships between ice, ocean, and meltwater control sedimentary lithofacies, including gravity flow deposits Marine Geology 262 (2009) 29–38 ⁎ Corresponding author. Tel.: +1734 615 2844; fax: +1 734 763 4690. E-mail address: knudsonk@umich.edu (K.P. Knudson). 0025-3227/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.margeo.2009.03.002 Contents lists available at ScienceDirect Marine Geology journal homepage: www.elsevier.com/locate/margeo