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Tectonic and Climatic Influence on the Evolution of the Surveyor Fan And Exploring the Deep Sea and Beyond themed issue Tectonic and climatic infl uence on the evolution of the Surveyor Fan and Channel system, Gulf of Alaska Robert S. Reece1, Sean P. S. Gulick1, Brian K. Horton1, Gail L. Christeson1, and Lindsay L. Worthington2 1Jackson School of Geosciences, The University of Texas at Austin, J.J. Pickle Research Campus, Building 196, 10100 Burnet Road, Austin, Texas 78758-4445, USA 2Department of Geology and Geophysics, Halbouty Building, Texas A&M University, College Station, Texas 77843, USA ABSTRACT INTRODUCTION BACKGROUND Present-day seafl oor morphology and sedi- Many studies have used accumulation rates Tectonic and Climatic Setting ment distribution in the deep-water Surveyor and sediment provenance derived from subma- Fan, Gulf of Alaska, is dominated by the rine fan sediment cores worldwide to describe The Yakutat terrane in the northern Gulf of >700-km-long Surveyor Channel, an anomaly the tectonic growth and erosion on land that Alaska is a 15–25-km-thick mafi c terrane that in a system with no major fl uvial input or shelf provided the source material for the marine originated as an oceanic plateau (Christeson et canyons. The sediment supply instead has record (e.g., Figueiredo et al., 2009; Hebbeln al., 2010; Eberhart-Philips et al., 2006). At least been provided by glacial erosion in the still- et al., 2007; Rea and Snoeckx, 1995; Ullrich, 600 km of Yakutat terrane has subducted at a active Chugach–St. Elias orogen, and glacial 2010). The terrigenous component of marine low angle beneath North America since ~10 Ma transport across the shelf. Glaciation has peri- sediment accumulation rates serves as a proxy (Fig. 1) (Eberhart-Philips et al., 2006; Gulick et odically increased in the St. Elias Range since for changes in erosion rates on land, and there- al., 2007; Plafker et al., 1994; Rea and Snoeckx, the Miocene, but began dominating erosion fore changes in either orogenic exhumation 1995). This fl at-slab subduction has resulted and spurred enhanced exhumation since the rates or climate. Burbank et al. (2003) showed in the still-active Chugach–St. Elias orogen, mid-Pleistocene transition, at ~1 Ma. Ice asso- that Himalayan erosion is dominated by tec- which exhibits the highest coastal relief and ciated with this glacial intensifi cation carved tonic uplift in spite of large variations in pre- greatest glacial infl uence of any active orogen cross-shelf sea valleys that connect the St. cipitation, but other studies demonstrate that globally (Pavlis et al., 2004). Varying degrees of Elias Range to the Surveyor Fan. The direct climate can dominate erosion in glacial orogens glacial erosion and rock exhumation in the St. deposition of newly increased terrigenous sed- at glacial maxima (Berger et al., 2008; Hebbeln Elias Range since the Miocene (Enkelmann et iment fl ux into the fan triggered the formation et al., 2007). al., 2010; Lagoe et al., 1993; Rea and Snoeckx, of the Surveyor Channel and its growth across Much work has been done to constrain the 1995; Spotila and Berger, 2010) have distrib- the Surveyor Fan. Through the formation of relationship between tectonics and climate in uted sediment into the Gulf of Alaska, leading the Surveyor Channel, climate events created the glacial St. Elias orogen in southern Alaska to periodic signifi cant increases in growth of three major differentiable sequences across the (Berger et al., 2008; Rea and Snoeckx, 1995), the Surveyor Fan (Lagoe et al., 1993; Rea and Surveyor Fan that we mapped using seismic- but this study fi lls in a key additional compo- Snoeckx, 1995; Stevenson and Embley, 1987), refl ection profi les. The change in morphology nent. The proximity of the St. Elias Mountains the terrigenous outwash body that comprises observed throughout the sequences allows to the coastline assures that the majority of gla- the majority of the Alaska Abyssal Plain (Fig. us to characterize the infl uence that a glaci- cially eroded sediment is deposited in the Gulf 1). Fan sediment as old as ~20 Ma varies in ated orogen can have in shaping margin pro- of Alaska, much of it in the deep-water Surveyor provenance, quantity, and content as a result of cesses and the sediment pathway from source Fan. A long-offset 2D seismic-refl ection study, changes in onshore exhumation rates and glacial to sink. We show that the large variation in acquired in 2008, linked to previous studies of extent (Berger et al., 2008; Enkelmann et al., sediment fl ux between glacial- interglacial Surveyor Fan sediment cores yields information 2010; Ingle, 1973; Spotila and Berger, 2010). cycles together with sea valley formation on margin processes, erosion, climate events, These changes are likely represented in fan leads to a glacial shelf transport process not orogenesis, and exhumation. The results of this stratigraphy, morphology, and shifts in acoustic typical of a fl uvial system. This glacial shelf study will add to the existing body of work on character (Ness and Kulm, 1973; Stevenson and transport along with the channel terminus in climate-dominated tectonic systems, and dem- Embley, 1987). the Aleutian Trench makes the Surveyor Fan onstrate how such a system cannot only trans- The fi rst appearance of Gulf of Alaska ice- and Channel morphologically one of the most form the orogen, but also the entire margin from rafted debris appeared in the now uplifted and unique systems in the world. source to sink. exposed marine Yakataga Formation at ~5.5 Ma. Geosphere; August 2011; v. 7; no. 4; p. 830–844; doi:10.1130/GES00654.1; 15 fi gures; 1 table. 830 For permission to copy, contact [email protected] © 2011 Geological Society of America Downloaded from http://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/7/4/830/3339594/830.pdf by guest on 23 September 2021 Surveyor Fan and Channel This alpine glaciation event is referred to as with the increase at the MPT being the largest crust (Shipboard Scientifi c Party, 1973). Pre- glacial interval A (Lagoe et al., 1993). Glacial on record. Additionally, Berger et al. (2008) vious studies divided the Surveyor Fan into activity was diminished during the mid-Pliocene showed a major increase in St. Elias orogen two major sequences (Ness and Kulm, 1973; warm interval, but returned during the onset of exhumation rates associated with glacial inter- Stevenson and Embley, 1987; von Huene and Northern Hemisphere glaciation at 2.9–2.4 Ma val C and proposed that the glacially carved Kulm, 1973). These sequences were termed (Raymo, 1994), referred to as glacial interval Bering Trough (Figs. 1 and 2) fi rst reached the upper and lower and were based on sedimen- B (Lagoe et al., 1993). Glacial interval B pro- shelf edge near the time of the MPT, providing tation rates and differences in acoustic facies vided the fi rst ice-rafted debris observed in the a sediment delivery pathway from exhumed imaged in 2-D seismic-refl ection profi les. The distal fan at Ocean Drilling Program (ODP) site orogen to shelf edge. Ultimately, due to erosion boundary between the two sequences represents 887 (Fig. 2) (Rea and Snoeckx, 1995). A fur- of sediment during repeated glacial advances a shift from a lower coarser grained facies to an ther intensifi cation of glacial activity, glacial across the shelf, the Surveyor Fan may be the upper fi ner grained facies possibly associated interval C, occurred at ~1 Ma, and could have most robust long-term record of onshore exhu- with Surveyor Channel inception and its control been a regional response to the mid-Pleistocene mation and climate events. on fan sediment distribution during deposition transition (MPT) (Berger et al., 2008), a change of the upper sequence (Ness and Kulm, 1973; in glacial-interglacial cycles from 40 k.y. to Surveyor Fan and Channel Stevenson and Embley, 1987). 100 k.y. (Clark et al., 2006). The Chirikof and Surveyor Channel systems Terrigenous sediment fl ux in the Gulf of Terrigenous turbidites, mudstone, and clay- (Fig. 1) dominate present-day Surveyor Fan Alaska at ODP 887 doubled at each of the three stone of the Surveyor Fan overlie marine chalk morphology and sediment distribution (Carl- glacial intervals (Rea and Snoeckx, 1995), and a basaltic basement of the Pacifi c plate son et al., 1996; Stevenson and Embley, 1987), 61° 7′ 51′′ N 61° 6′ 25′′ N W W ′′ ′′ 8 ′ 35 ′ Bering Glacier Icy Bay Malaspina Glacier 150° 50 Yakutat Bay KT 138° 57 BT PS North America plate Yakutat terrane YSV 50 mm/yr Transition Fault N ASV Icy West Leg Icy East LegYakutat Leg Alsek Leg Aleutian Trench Chirikof Surveyor Channel Surveyor Fan Channel Kodiak-Bowie Seamount Chain GS Alaska Pacific plate 53 mm/yr W W ′′ ′′ Patton-Murray Seamount Chain 34 57 ′ ′ Gulf of Alaska 0 150 km 138° 47 53°150° 57 18′ 3′′ N 53° 19′ 41′′ N Figure 1. Three-dimensional perspective view of the bathymetry and topography of the southern Alaska continental margin, showing tectonic boundaries, and the Surveyor Fan in high-resolution bathymetry. ASV—Alsek Sea Valley; BT—Bering Trough; GS—Giacomini Seamount; KT—Kayak Trough; PS—Pamplona Spur; YSV—Yakutat Sea Valley. Plate boundaries adapted from Gulick et al. (2007); high- resolution bathymetry (Gardner et al., 2006); remaining bathymetry (Smith and Sandwell, 1997); Yakutat terrane motion relative to North America (Elliott et al., 2010); Pacifi c plate motion (Kreemer et al., 2003). Geosphere, August 2011 831 Downloaded from http://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/7/4/830/3339594/830.pdf by guest on 23 September 2021 Reece et al. but unlike other large deep-sea channels, the This Study plex interactions between climate and tectonics Chirikof and Surveyor Channels are not associ- in glacially dominated systems.
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