The Ketavik Formation: A new stratigraphic unit and its implications for the Paleogene paleogeography and paleoclimate of southwestern Alaska

Palaeogeography, Palaeoclimatology, Palaeoecology 295 (2010) 348–362

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Palaeogeography, Palaeoclimatology, Palaeoecology j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / p a l a e o

The Ketavik Formation: A new stratigraphic unit and its implications for the Paleogene paleogeography and paleoclimate of southwestern Alaska Judith Totman Parrish a,⁎, Anthony R. Fiorillo b, Bonnie F. Jacobs c, Ellen D. Currano d, Elisabeth A. Wheeler e a

Department of Geological Sciences, P.O. Box 443022, University of Idaho, Moscow, ID 83844-3022, USA Museum of Nature and Science, P.O. Box 151469, Dallas, TX 75315, USA Roy M. Huffington Department of Earth Sciences, P.O. Box 750395, Southern Methodist University, Dallas TX 75275-0395, USA d Department of Geology, 114 Shideler, Miami University, Oxford, OH 45056, USA e North Carolina Museum of Natural Sciences, 11 West Jones St., Raleigh, NC 27601, USA b c

a r t i c l e

i n f o

Article history: Received 27 May 2009 Received in revised form 4 September 2009 Accepted 10 September 2009 Available online 28 September 2009 Keywords: Alaska Paleogene paleobotany stratigraphy paleoclimate

a b s t r a c t A new formation, the Ketavik Formation, is proposed for Paleogene rocks of Katmai National Park near Brooks Camp. The type section is in an area previously mapped as the Jurassic Talkeetna Formation. The proposed formation was deposited in a fluvial environment. It is distinct from the coeval Copper Lake Formation on the southeast side of the Alaska Peninsula volcanic arc and was deposited in a different river system. The Ketavik Formation may include previously mapped, undifferentiated Tertiary rocks, at least some of which are similar in age, that are scattered along a belt parallel to and northwest of the present magmatic arc. The Ketavik Formation contains dicot and coniferous leaf and wood fossils that indicate a warm temperate climate. © 2009 Elsevier B.V. All rights reserved.

1. Introduction The purpose of this paper is to propose a new formation for the Alaska Peninsula, the Ketavik Formation, and to report on its fossils and depositional environment. The proposed formation is Paleogene in age, based on fossil leaves and wood and minimum 40Ar/39Ar dates from intruding diorite dikes. At the type locality near Brooks Camp, Katmai National Park (Fig. 1), the formation consists of a valley-fill deposit that we hypothesize was reincised during the glacial event that formed Naknek Lake. 1.1. Geologic setting and previous work The eastern Alaska Peninsula consists of the Peninsular Terrane (e.g., Colpron et al., 2007). This terrane accreted to North America in the Jurassic (e.g., Detterman et al., 1996; Colpron et al., 2007), and became the foundation upon which the volcanic arc that is still active was built. Sedimentary rocks from Jurassic through Quaternary age have been mapped throughout the eastern Alaska Peninsula (Riehle et al., 1993; Houston, 1994; Detterman et al., 1996). The stratigraphy is

⁎ Corresponding author. Fax: +1 208 885 5724. E-mail address: [email protected] (J.T. Parrish). 0031-0182/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.palaeo.2009.09.008

discussed in these publications and will be summarized briefly here. In reading the following, the reader should know that, because of publication delays, the information in Riehle et al. (1993) actually postdates that presented in Detterman et al. (1996). Riehle et al. (1993) mapped the Katmai Quadrangle and adjacent areas, and their map included Tertiary sedimentary formations described by Detterman et al. (1996), namely the Copper Lake Formation and Hemlock Conglomerate. The Copper Lake Formation was reassigned from the West Foreland Formation by Detterman et al. (1996). Another Tertiary sedimentary formation of the region, not mapped by Riehle et al. (1993) because it fell outside their map area, is the Tolstoi Formation. In addition, Riehle et al. (1993) mapped four isolated outcrops of “Tertiary sedimentary rocks” (Ts on their map) that were not mentioned by Detterman et al. (1996). We will review these rock units in the following paragraphs. Tertiary rocks in the western portion of the Alaska Peninsula consist of the Tolstoi Formation and the disconformably overlying Stepovak Formation (Detterman et al., 1996). The Tolstoi Formation is the oldest Tertiary sedimentary rock formation on the peninsula (Detterman et al., 1996). It is mostly non-marine and consists of conglomerate, sandstone, siltstone, and shale. It was dated by invertebrate fossils and leaves (see Detterman et al., 1996) as late Paleocene to middle Eocene. Significantly, volcaniclastic rocks are an important constituent of the formation, and it contains tuffs and some tuffaceous sandstone. The Stepovak Formation

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Fig. 1. Map of the Brooks Camp area, southwestern Alaska, showing distribution of outcrops of Jurassic Talkeetna Formation as mapped by Riehle et al. (1993), with the exception of the Brooks Camp area.

is divided into a sandstone member and a siltstone member. The sandstone member consists in part of tuffaceous sandstone and tuff, along with conglomerate with volcanic clasts. The siltstone contains sandstone beds with pumice fragments and chert pebbles, as well as thin-bedded, dark siltstone and shale. The formation contains marine fossils throughout, and is dated as Eocene or early Oligocene based on the fossils and early Oligocene or younger based on radiometric ages of volcanic rocks that were the source for the volcaniclastic rocks in the upper part of the formation. The middle portion of the Alaska Peninsula contains no mapped lower Tertiary sedimentary rocks (Detterman et al., 1996). In the northeastern portion of the peninsula, lower Tertiary rocks consist of the Copper Lake Formation. The Copper Lake Formation comprises conglomerate and sandstone, with minor siltstone and coal (Detterman et al., 1996) and is interpreted to be predominantly braid-plain fluvial deposits (Houston, 1994). Detterman et al. (1996) described minor siltstone and coal, but these do not appear in Houston's (1994) section, possibly because Houston's (1994) does not encompass the entire distribution of the formation. The clasts in the conglomerate are volcanic, plutonic, metamorphic, and limestone. Based on plant fossils, the formation is dated as Ypresian (early Eocene), and Detterman et al.

(1996) suggested it might extend into the upper Paleocene based on field relations. Thus, the Copper Lake Formation is wholly or partially equivalent to the Tolstoi Formation. Houston (1994) measured both planar and trough crossbeds and clast imbrication to obtain a mean paleocurrent direction to the southeast, although modes showing flow to the northeast (crossbeds) and west (clast imbrication) are also present. He interpreted the Copper Lake (West Foreland) Formation in the Katmai area to indicate short-distance, high-gradient transport. The Copper Lake Formation is disconformably overlain by the Hemlock Conglomerate (Detterman et al., 1996). This formation consists of fluvial sandstone and conglomerate with minor siltstone, shale, and coal, with a few tuff beds (Detterman et al., 1996) deposited in high-sinuosity streams and adjacent floodplains (Houston, 1994). The sandstone is commonly carbonaceous and sometimes tuffaceous; the conglomerate clasts consist of volcanic rock, chert, and granitic rocks. The formation contains wood fragments and abundant leaves in coaly layers (Houston, 1994; Detterman et al., 1996). The Hemlock Conglomerate has been dated by plants to be late Oligocene or, possibly, earliest Miocene (Detterman et al., 1996). Palynological determinations were poorly constrained, yielding “possibly” Eocene or Paleocene/Eocene ages (Houston, 1994). Fission track dates

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Fig. 2. Geologic map of part of the Katmai Quadrangle, simplified from Riehle et al. (1993), showing the distribution of unnamed Tertiary outcrops (see text for discussion). JPz, Paleozoic–Jurassic metamorphic rocks; Ji, Jurassic igneous rocks; Js, Jurassic and Cretaceous sedimentary rocks, excluding the Talkeetna Formation; Jt, Jurassic Talkeetna Formation; Ti, Tertiary and Quaternary igneous rocks; Ts (bold), unnamed Tertiary sedimentary rocks, including the proposed Ketavik Formation (see Fig. 3); Q, Quaternary sediments and sedimentary rocks; stars, Quaternary to present volcanic vents. Thin lines, contacts, lake shores, and glacial margins; thick plain lines, unspecified or vertical faults, dashed where inferred; thick line with tick marks, thrust fault, dashed where inferred.

showed well-constrained ages of late Oligocene and Miocene (Houston, 1994), more consistent with the plant age dates, suggesting that the pollen were reworked from older rocks. Riehle et al. (1993) mapped four outcrops of unnamed and undifferentiated rocks (Ts) in the Mt. Katmai Quadrangle and adjacent areas (Fig. 2). Although the rocks in some ways resemble the Copper Lake Formation, Riehle et al. (1993) declined to map them as such, limiting the use of “Copper Lake Formation” to established units southeast of the arc, along the coast. To our knowledge, no one has followed up on these unnamed rocks. The unnamed rocks are described as “poorly to moderately well indurated, pale- to dark-gray or brown fluvial sandstone, siltstone, conglomerate, and volcaniclastic tuff and breccia. Conglomerate clasts are chiefly plutonic and (or) altered volcanic rocks, and lesser metamorphic and sedimentary rocks. The unit consists of local deposits, some of which lithologically resemble lower (altered volcanic clasts) and upper (fresh volcanic clasts) conglomerate members of Copper Lake Formation” (Riehle et al., 1993). An age determination of 42.5 ± 1.5 Ma, or late middle Eocene (Walker and

Geissman, 2009), was based on radiometric dating of an intercalated basaltic andesite flow in the largest outcrop, northeast of Naknek Lake, by Shew and Lanphere (1992). Two of the outcrops of unnamed Tertiary rocks mapped by Riehle et al. (1993) lie in a northeast–southwest belt that is congruent with the outcrop we discovered and mapped, and one is south–southeast of the outcrop described in this paper (Fig. 2). All lie northwest of the Bruin Bay Fault and northwest of the volcanic centers marking the arc edifice, which separates the outcrops from the named formations, which are exposed along the coast. The fourth outcrop of Ts mapped by Riehle et al. (1993) is a small one that lies right at the crest of the range (Fig. 2, near lower right-hand corner). The geology of the Katmai area northwest of the mountains is dominated by Triassic and Jurassic metamorphic rocks, Jurassic igneous and sedimentary rocks, and Tertiary igneous rocks; no other Tertiary sedimentary rocks besides the unnamed rocks have been mapped. The unnamed rocks overlie or are intercalated with Tertiary intrusive or volcanic (Shew and Wilson, 1981) rocks or Jurassic intrusive rocks.

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Fig. 3. Detailed geologic map of the outcrop of Ketavik Formation measured and reported in this paper. Diorite dikes excluded for clarity.

2. The Ketavik Formation 2.1. Description and justification The Ketavik Formation consists of interbedded quartz feldspathic and quartz lithic sandstone and conglomerate with rare, very thin interbeds of silty sandstone or mudstone. Several diorite dikes penetrate the formation at the type section. The section is in inferred disconformable contact with the Jurassic Talkeetna Formation and with Quaternary surficial sediments (Fig. 3). The Ketavik Formation is a mappable unit that is dissimilar in composition and age from the units with which it is in contact. The proposed Ketavik Formation was probably not mapped previously because it is not extensive in area and is exposed only along the shoreline of Naknek Lake north and east of Brooks Camp. It is partially obscured by vegetation and by water when the lake level is high. The formation is named for Ketavik Falls, the previous name for what is now Brooks Falls, along the Brooks River between Naknek Lake and Lake Brooks (D. Dumond, personal communication).

2.2. Type and reference sections The type section and a reference section of the Ketavik Formation (Fig. 4) are located on the southern shore of Naknek Lake, Alaska, and extend from approximately 0.7 km north to 5.2 km northwest of Brooks Camp (Fig. 3). The outcrop is divided by a fault, and the type section is east of the fault and the reference section west of the fault (Fig. 3). In 2002, we explored most of the rocky outcrops along the margins of both the North and Iliuk arms of Naknek Lake (Fig. 1) but did not locate additional outcrops of the Ketavik Formation. Weather

and time constraints prevented us from exploring the rest of Naknek Lake or other areas that might have outcrops of this formation. Thus, the type and reference sections are currently the only known sections (but see Discussion and conclusions). The sections are illustrated in Fig. 4. The type section is approximately 48.4 m thick (the uncertainty is because of the lack of continuity where the section was moved, but is probably no more than 1 m). Neither the base nor the top of the section is exposed, as the lake shore is heavily vegetated (Fig. 5), and much of the section is covered. The base of the section is placed at the base of a 1.7 m-thick bed of sandstone that outcrops on the east side of a gully approximately 10 m from the shoreline (the distance varies with lake level). The top of the section is the last exposure to the east. The strike and dip of the beds vary slightly, with strikes 90° to 124° and dips 6° to 11° to the northeast (Fig. 3). Three dikes intrude the section; they are excluded from Fig. 3. The reference section is 18.7 m thick (Fig. 4). The lower contact is in fault contact with the type section, as revealed by a pronounced change in the strikes of the beds. The upper contact is covered. The strikes are 52° to 84° and the dips 8° to 27° (Fig. 3). The sections comprise two facies of sedimentary rock: conglomerate and sandstone with minor mudstone. These will be described below.

2.2.1. Conglomerate The conglomerate beds occur throughout the section but are concentrated in the lower part (Fig. 4). In addition, the conglomerates tend to be coarser in the lower part of the section. The conglomerate beds are matrix supported and poorly bedded to massive. The clasts are subrounded to rounded volcanic rock and some appear to be second-

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Fig. 4. Type and reference sections of the Ketavik Formation. The reference section is east of the fault in Fig. 3; the type section is west of the fault.

cycle conglomerate clasts. The clasts are consistent in composition, texture, and color with volcanic and volcaniclastic rocks of the adjacent Talkeetna Formation. 2.2.2. Sandstone The sandstone is lithic arkose in composition. Grain size is mostly fine to medium, although coarse sandstone is interbedded with conglomerate and fine sandstone is found immediately adjacent to the silty sandstone facies. The grains are subrounded to rounded. The sandstone is generally thin- to medium-bedded, unevenly and poorly bedded to massive. The color is light olive gray. Sedimentary structures include trough crossbeds and ripples. The upper portions of some sandstone beds are muddy, and plant fossils tend to occur in these muddier intervals. These intervals are

sometimes stained with iron oxides and appear to be more nodular, consistent with very early stages of pedogenesis. Root traces are present, including large traces consistent with woody plants (Fig. 6). We were able to obtain one paleocurrent measurement from a bedding-plane exposure of a trough of 349° (uncorrected; this is nearly parallel to the dip). 2.3. Boundaries No contacts of the Ketavik Formation and adjacent rocks were observed directly. The only mapped unit in the area of the Ketavik Formation is the Talkeetna Formation. Contact with the Talkeetna Formation, which is exposed on the hillside above the type section, is inferred from a pronounced break in the topography of the hillside

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Fig. 5. Photograph looking to the northeast from Brooks Camp showing the distinct break in slope (arrow) marking the boundary between the Ketavik Formation and the Talkeetna Formation. The slope to the left is the lower slope of Dumpling Mountain, which consists entirely of Talkeetna Formation that is well exposed above the vegetation line out of the picture.

adjacent to the lake (Figs. 3 and 5), but is completely obscured by vegetation. We interpret this contact to be unconformable (see Discussion and conclusions). This contact is perpendicular to the strike of beds in the Ketavik. The Talkeetna Formation does crop out northwest of the upper part of the exposed Ketavik, but modern shore deposits obscure the relationships. The Ketavik–Talkeetna contact is most likely an erosional unconformity (see Discussion and conclusions), but the exposures do not allow confirmation of what underlies or what, if anything, overlay the Ketavik. 2.4. Fossils Fossil leaves and wood are common in the Ketavik Formation. The fossil leaves are generally poorly preserved dicot and conifer leaves. The fossil wood occurs almost exclusively as float, although some pieces were in situ. These specimens are identical in preservation to the float specimens, and the lack of wood in the adjacent formation upslope makes it extremely unlikely that the fossil wood in float is derived from another unit. 2.4.1. Leaves The leaves are generally isolated and flat lying, although a few are preserved in a rolled orientation, indicating some transport before burial. The leaves are impressions and occur as small fragments to nearly complete leaves. In some cases, tertiary venation is visible, but for the most part only primary and secondary veins are preserved. Nevertheless, we were able to distinguish 12 broad-leaved dicot morphotypes and one gymnosperm morphotype among the 45 specimens, based upon key morphological characters (Appendix A). Of these, the gymnosperm and six dicot morphotypes are identifiable to the species level, two of the dicots are assigned to existing genera, and two to plant families. The remaining two morphotypes have distinct morphological characteristics that separate them from the other leaf specimens, but they lack sufficient detail for taxonomic placement. The identified taxa are typical of other Paleogene floras from Alaska and western North America (e.g., Hollick, 1936; Brown, 1962; Wolfe, 1975; Hickey and Wolfe, 1975; Hickey, 1977; Manchester, 1987; Crane et al., 1991), but also include Platimeliphyllum, a genus known from the Kamchatka Peninsula and Sakhalin Island and previously undocumented from North America (Maslova, 2002; Kodrul and Maslova, 2007). Representative specimens of better-preserved leaves are illustrated in Fig. 7; descriptions are in Appendix A. 2.4.2. Wood The fossil woods are usually well preserved and are mostly coniferous wood with distinct growth rings. The coniferous woods

include Cupressinoxylon sp., Metasequoia sp., Cedrus penhallowi, and at least one new species of Pinus of Section Parrya. One specimen of dicot wood was identified as Platanoxylon sp. Representative sections are illustrated in Figs. 8 and 9; descriptions are in Appendix B. In order to provide some general information on growth ring structure, which may have implications for paleoclimate reconstruction, we measured growth-ring width and latewood percentage in ten of the coniferous wood specimens (Table 1; Fig. 10). Measurements were made using a binocular microscope with an eyepiece that had a calibrated reticule. Growth rings are narrow in all samples examined (Table 1); the narrowest ring is 0.25 mm wide, the widest is 4.6 mm. The ring series for each sample, showing the earlywood and latewood widths, are illustrated in Fig. 10. Latewood, the wood formed during the waning or very end of the growing season, is recognized macroscopically by its darker color. In conifers, this darker color is caused by the latewood tracheids being narrow in the radial dimension and consequently having a higher cell wall-to-lumen (open space) ratio than earlywood tracheids. Previous studies on high-latitude forests have included measurements of latewood percentage, and we attempted to do likewise. Because the Ketavik woods have a gradual transition from earlywood to latewood, different observers might perceive the transition as occurring at a different position within a growth ring and thus report somewhat different latewood percentages. Nonetheless, our data indicate that some high-latitude Paleogene trees had relatively high amounts of latewood as recognized macroscopically; for the pines, average latewood percentages range from 34 to 63% (Table 1). However, in

Fig. 6. Root traces in sandstone.

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Fig. 7. Fossil leaves in the Ketavik Formation. A, Glyptostrobus europaeus (Taxodiaceae; KATM 44715). B, Ziziphoides flabella (Trochodendraceae; KATM 44721). C, Corylites sp. (Betulaceae; KATM 44725). D, Cercidiphyllum genetrix (Cercidiphyllaceae; KATM 44732, 44733). E, “Carya” antiquorum (Juglandaceae; KATM 44742). F, Platimeliphyllum sp. (Platanaceae; KATM 44731).

one of the Metasequoia samples, latewood was mostly 1–2 cells wide (see Fig. 8D). For foresters and wood scientists, latewood proportion is important as it is positively correlated with wood specific gravity, and the physical and mechanical properties of wood. There have been many studies examining the effects of growing conditions on latewood percentage and the heritability of earlywood and latewood characteristics (see summary in Zobel and Jett 1995). A latewood definition that allows comparison of results of such studies is important. According to Zobel and Jett (1995), the most universally accepted definition of latewood is Mork's (1928). Their rephrasing of Mork's definition is “cells are classified as latewood when the double wall thickness is greater than the [radial] lumen diameter.” This phrasing matches one of the interpretations of Mork that Denne (1989) made. However, as Zobel and Jett (1995) noted, Mork's (1928) definition is not without its problems. There are some instances in which the cells in a dark-colored band of latewood do not fit Mork's definition at all; this is especially true for young trees. It would seem that using Mork's definition of latewood would be advantageous for fossil wood studies as it would provide a methodology for obtaining reproducible results. However, our experience with the Ketavik woods that have a gradual transition from earlywood to latewood suggests this may not be so. We prepared digital photomicrographs of the cross sections and used Image J (Rasband, 1997–2009) to measure radial lumen diameter and double

cell wall thickness. Mork latewood percentages are lower (averages of 22–33%) than those computed from measurements made with the binocular microscope. Moreover, within a growth ring, there is variation from radial row to radial row in the first occurrence of latewood tracheids as defined by Mork (see Fig. 8G). Thus, once again there will be observer-related variability associated with choosing tracheids to measure and identification of the latewood–earlywood boundary. It is legitimate to question whether the extra time needed to do the cell measurements required by Mork for recognizing latewood tracheids provides more robust and reproducible results than measuring latewood with a binocular microscope. We do not think it does for this material, which is characterized by considerable within-ring variation in cell wall thickness. 2.5. Age The age of the paleoflora (and the Ketavik Formation) cannot be precisely determined based upon floral composition because the assemblage lacks any taxon or combination of taxa unique to either the Paleocene or Eocene Epoch. However, the genus Platimeliphyllum is currently only known from rocks of Late Paleocene to Early Eocene age, thus providing some time constraint. Although we attempted to collect pollen, all samples were barren. The fossil wood belonging to Pinus Section Parrya may be limited to the middle Eocene (see appendix).

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Fig. 8. Thin sections of fossil wood from the Ketavik Formation. A–C, Cupressinoxylon sp. A, Distinct growth rings, prominent latewood. B, Ray composed of ray parenchyma only, mostly two cupressoid pits per cross-field. C, Exclusively uniseriate rays, D–F, Metasequoia sp. D, Distinct growth ring boundary with narrow latewood. E, Tall uniseriate rays. F, Earlywood with biseriate opposite pits, rays composed of ray parenchyma, with taxodioid cross-field pits in horizontal rows. D, Fusiform rays and rays commonly biseriate. E, Two fusiform rays, short uniseriate rays, and biseriate rays. G–J. Cedrus penhallowi. G, Traumatic axial resin canals tangentially arranged. H, Traumatic horizontal resin canals, I. Intertracheary pits, some biseriate and opposite, possible scalloping of tori. J. Taxodioid to cupressoid cross-field pitting. Scale: 200 µm in A, D, E, G, H; 100 µm in C, F; 50 µm in B, 20 µm in I, J.

The formation is penetrated by three diorite dikes. Samples from two dikes were sent to the laboratory of Dr. Terry Spell at the University of Nevada, Las Vegas. Both were weathered, but one yielded a usable date

of 39.63 ± 0.17 Ma, or late middle Eocene (Walker and Geissman, 2009). Thus, the formation is no younger than middle Eocene. In conclusion, we favor a late Paleocene or early Eocene age for this formation.

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Fig. 9. Thin sections of fossil wood from the Ketavik Formation. A–H, Pinus sp. Section Parrya. A, Distinct growth ring boundary, latewood with resin canals. B, Earlywood longitudinal tracheids with biseriate intertracheary pitting, longitudinal resin canal with thin-walled epithelial cells interconnecting with radial resin canal. C, Fusiform rays and rays commonly biseriate. D, Two fusiform rays, short uniseriate rays, and biseriate rays. E, Small cross-field pits. F, Smooth-walled ray tracheids at top of ray in KATM 44750. G, Distinct growth rings, with resin canals in earlywood, KATM 44750. H. KATM 44750 with fewer biseriate rays than in (C). I–L, Platanoxylon sp. I, Diffuse porous wood with indistinct growth-ring boundaries, vessels solitary and in small groups. J, Wide (> 10 cells wide) and tall (> 1 mm) rays. K, Crowded opposite intervessel pits. L, Scalariform perforation plate in side view. Scale: 200 µm in A, C, G, H, I, J; 100 µm in B, D; 50 µm in E, F, K, L.

2.6. Environments of deposition As noted previously, the clasts in the conglomerate are identical to those in the adjacent Talkeetna Formation. Thus we interpret the

conglomeratic facies to represent debris-flow deposits. The outcrop is too narrow to determine aspect ratio or any other geometrical features of the conglomerate beds. However, although we cannot rule out that these were channel deposits, the lack of sedimentary structures favors

J.T. Parrish et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 295 (2010) 348–362 Table 1 Growth-ring data for coniferous woods from the Ketavik Formation. Accession number is KATM 00298. Wood type/catalog #

Pinus/44744 Pinus/44745 Pinus/44746 Pinus/44749 Pinus/44750 Pinus/44751 Cedrus/44748 Cupressinoxylon/44743 Metasequoia/44747 Metasequoia/44752

# Rings

Ring width in mm

Latewood %

Mean (SD); min–max

Mean (SD); min–max

11 18 13 39 38 26 40 34 20 65

2.3 (0.87); 1.6–4.6 1.65 (0.44); 0.25–2.38 1.86 (0.37); 1.38–2.63 0.86 (0.56); 0.35–2.7 2.00 (0.97) 0.36–2.7 1.23 (0.73), 0.42–3.18 2.63 (0.83); 0 .56–3.8 1.35 (0.84); 0.3–4.0 1.68 (0.52); 0.75–2.5 1.81 (0.71); 0.72–4.38

37 34 47 38 63 42 48 43 31 –

(11); 22–55 (11); 14–56 (7); 40–61 (13); 13–73 (15); 33–95 (20); 10–86 (13); 25–83 (8); 26–57 (12); 8–47

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grained lithologies, which are limited to silty or muddy sandstone, suggests low aggradation rates (Blakey and Gubitosa, 1984). Abundant fossil leaves and wood indicate that the exposed lithologies represent only part of the fluvial system, because plants require stable substrates to grow. 3. Discussion and conclusions The type section and reference sections together comprise the only confirmed outcrop of the Ketavik Formation. However, the unnamed Tertiary sedimentary rocks mapped by Riehle et al. (1993) are similar, based on the descriptions provided by them, to the proposed formation. We were unable to visit those outcrops, and to our knowledge, they have never been studied since the mapping and dating of Riehle et al. (1993) and Shew and Lanphere (1992). 3.1. Paleogeography and relationships

our interpretation. The apparent second-cycle nature of the conglomerate also is consistent with mass-wasting of the adjacent Talkeetna Formation with some reworking. We tentatively interpret the sandstone facies to represent channel deposits of low-sinuosity, high bedload rivers. The paucity of fine-

The Ketavik Formation is substantially younger than the Talkeetna Formation with which it is inferred to be in contact. The age of the Talkeetna Formation is Early Jurassic, based on ammonites (Riehle et al., 1993). A block of Talkeetna rocks occurs near (but not at) the

Fig. 10. Growth-ring series for ten specimens of coniferous wood from the Ketavik Formation. All graphs are to the same scale for both the vertical and horizontal axes. Light shading, earlywood; dark shading, latewood. The latewood in KATM 44752 is no wider than 4 cells and is not illustrated; graph shows total ring width only. Ring series are numbered from the innermost to the outermost ring in each specimen. Not all ring series are actually continuous; gaps of up to 3 poorly preserved rings are excluded from the series. Raw data are available from the senior author.

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Fig. 11. Schematic geologic history proposed for the Brooks Camp area. Paleogene valley fill of the Ketavik Formation was almost completely destroyed during subsequent glacial erosion as the glaciers reincised the paleovalleys carved into the Talkeetna Formation.

fault; we interpreted this to be a large fallen block, which is consistent with our interpretation of the conglomerate as debris-flow rather than channel deposits. The Talkeetna Formation is strongly deformed. Immediately adjacent to the outcrop of the Ketavik Formation, on Dumpling Mountain, bed orientations in the Talkeetna are chaotic. Elsewhere around Naknek Lake, the bed orientations are similarly chaotic. In contrast, bed orientations in the Ketavik Formation vary little. Thus we propose that the contact between the Ketavik and the Talkeetna formations is an angular unconformity. An angular unconformity can be caused by either faulting or deposition of beds on top of deformed sedimentary rocks. The Talkeetna Formation is variable in this region, and the clasts in the Ketavik Formation are identical to those in the underlying Talkeetna Formation at that locality, so we prefer the interpretation that the Ketavik was deposited on top of folded Talkeetna. In addition, fault contact would require a fault that is oriented nearly at right angles to other vertical faults northwest of the Bruin Bay Fault (which is a thrust). Based on the geometry of the Ketavik, its young age relative to the adjacent Talkeenta Formation, and the strong possibility that the contact is an angular unconformity, we interpret the Ketavik Formation as an early Tertiary valley-fill deposit from a valley that was incised into the older Talkeetna Formation. We interpret the present geometry of the Ketavik Formation to be the result of reincision of the paleovalley by rivers and/or ice (Fig. 11). Thus it is a remnant of what was likely a much larger unit that filled the entire valley now occupied by Naknek Lake. The remaining outcrop represents the part of the valley fill closest to the valley margin, which is consistent with both the debris-flow origin of the conglomerate and the relatively low aggradation rates inferred from the sandstone beds (see above). Given the close correspondence in age and the similar lithology, we believe it is likely that the undifferentiated Tertiary outcrops mapped by Riehle et al. (1993), at least those mapped northwest of the Bruin Bay Fault, are also remnants of paleovalley-

fill deposits. To date we have been unable to examine them due to their remoteness. Consideration must be given to the possibility that these represent upstream equivalents of the Copper Lake Formation and, therefore, the proposal of a new formation is not warranted on that basis. There are two lines of evidence that argue against this hypothesis. First, the paleocurrent direction obtained from the Ketavik Formation is to the northwest, whereas the Copper Lake Rivers flowed generally southeast; we acknowledge that one paleocurrent direction does not provide strong evidence. Second, the magmatic arc had already begun building in the Eocene (Wilson, 1985). The paleocurrent direction in the Ketavik and the ones in the Copper Lake Formation, then, are exactly what would be expected from rivers draining opposite sides of the arc. Although the Ketavik was certainly contemporaneous with the Copper Lake Formation, it was deposited in a different river system. 3.2. Paleoclimate The flora is very similar to other Paleogene floras described from Alaska, and most of the identifiable species are abundant throughout both Alaska and the Western Interior of the United States during the Paleogene (e.g. Cercidiphyllum genetrix, Glyptostrobus europaeus, and Platanus raynoldsi). Although only 45 leaf specimens were collected, they represent 12 distinct morphotypes. This number seems especially high, but it may be due to transport of leaves, as described earlier. The plant species found here are deciduous and typical of warm temperate to subtropical climates (Wolfe, 1966, 1977). There are not enough species for quantitative physiognomic climate analyses. Although the growth rings in the dicot wood are indistinct, those in the coniferous woods are distinct, a phenomenon seen in other Eocene wood assemblages (e.g., fossil forest of Yellowstone National Park (Fritz et al., 1991). Although growth rings cannot be confidently used to quantitatively reconstruct paleoclimate in older fossil floras

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except under unusual circumstances (Brison et al., 2001; Falcon-Lang, 2005; Williams, 2007), the occurrence of a dicot with indistinct growth rings and conifers with distinct growth rings is consistent with a warm temperate climate, including summers that cool toward the end of the growing season before the plant goes dormant. 3.3. Conclusions The Ketavik Formation is a new formation that was deposited in a paleovalley that had been incised into the Jurassic Talkeetna Formation. The Ketavik is a remnant of that valley fill, representing the valleymargin deposits, and much of the formation was eroded away by water and/or ice during subsequent reincision of the paleovalley to form the valley now filled by Naknek Lake. The climate at the time of deposition of the Ketavik was warm temperate. We propose that isolated and unnamed Tertiary outcrops farther to the northeast represent similar remnant valley fills and thus may be included in the Ketavik Formation, but this proposal must remain tentative until those outcrops are better studied. Acknowledgements We thank the National Park Service, Alaska Region, particularly Russell Kucinski and Peter Armato, for funding and logistical support. We also thank Vincent Santucci and Roland Gangloff for initial field assistance. Adam Hicks did the growth-ring measurements in six of the fossil wood specimens. Thanks to Don Dumond (University of Oregon) for calling the name “Ketavik” to our attention. Appendix A Leaves, including descriptions, identified in the Ketavik Formation. If a genus is in quotes, we suspect that, although the name is valid, the generic assignment is incorrect. Division Coniferophyta Family Taxodiaceae Glyptostrobus europaeus (Brongniart) Heer Description. Alternately arranged needles Reference. Hickey (1977) Catalog numbers. KATM 44715, 44722, 44729, 44735, 44737, 44741 Division Dicotyledon Family Platanaceae Platanus raynoldsi Newberry Description. Incomplete leaves, at least mesophyll in size, most likely palmately lobed, with platinoid teeth (rounded sinus, concave distal flank, straight proximal flank). Palinactinodromous primary venation, craspedodromous secondaries, and opposite percurrent tertiary veins. Comments. The teeth and venation are characteristic of Plantanaceae, and these specimens compare favorably with published accounts of P. raynoldsi Newberry. References. Brown (1962); Hickey and Wolfe (1975) Catalog numbers. KATM 44713, 44717, 44723 Platimeliphyllum sp. Maslova Description. Mesophyll leaves with spinose concave–concave teeth and a cordate base. Venation is pinnate, with craspedodromous secondary veins, and compound agrophics. Tertiary veins are strongly impressed, regularly spaced, and opposite percurrent. Comments. The venation and tooth characters are similar to both Platanaceae and Hamamelidaceae, but not unique to either family. However, our specimens compare favorably with Platimeliphyllum, a genus recently erected to accommodate this leaf morphology. Reference. Maslova (2002) Catalog numbers. KATM 44712, 44714, 44731

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Family Trochodendraceae Zizyphoides flabella (Heer) Crane, Manchester & Dilcher Description. Elliptic microphyllous leaf with decurrent base, actinodromous lateral primary veins and irregular reticulate tertiary veins. Leaf margin mostly untoothed with irregular crenations. Comments. The primary venation, base and margin characters compare favorably with Z. flabella, which has been reported widely from the Paleocene and Eocene of North America and the Arctic. Reference. Crane et al. (1991) Catalog number. KATM 44721 Family Ulmaceae Chaetoptelea microphylla (Newberry) Hickey Description. Oblong microphyllous leaf with compound teeth, and pinnate craspedodromous secondary veins that curve upwards near the margin. Each secondary vein terminates at a major tooth. Teeth have angular sinuses and are convex on both flanks. Comments. Characters distinguishing Chaetoptelea from Ulmus are found in the wood, seeds, and tertiary venation (Hickey, 1977), none of which is preserved here. Although this specimen could be Ulmus, it closely matches published examples of Chaetoptelea (Wilf, 2000). Reference. Hickey [, 1977 #10416] Catalog numbers. KATM 44726, 44728 (counterpart) Family Dipterocarpaceae “Parashorea” pseudogoldiana (Hollick) Wolfe Description. Elliptic, nearly complete notophyllous untoothed leaf. Venation is pinnate with eucamptodromous, decurrent secondaries that form a small angle with the midvein. Tertiary veins are absent. Comments. This leaf compares most favorably with “Parashorea” pseudogoldiana (Hollick) Wolfe. Reference. Wolfe (1977) Catalog number. KATM 44726, 44728 (counterpart) Family Cercidiphyllaceae Cercidiphyllum genetrix (Newberry) Hickey Description. Elliptic microphyllous to notophyllous leaves with acrodromous secondary venation, and epimedial tertiaries are opposite percurrent forming chevrons. The margins have closely-spaced, regular crenations. Comment. This taxon, which is characterized by the features described above, is very common in the Paleogene of North America, Asia, and the Arctic. Reference. Hickey (1977) Catalog numbers. KATM 44731, (44732, 44733, 2 pieces) Family Juglandaceae “Carya” antiquorum Newberry Description. An elliptic, microphyllous, asymmetric leaf with a convex base and acuminate apex. Venation is pinnate with semicraspedodromous secondary veins that gradually increase in angle to the midvein towards the base of the lamina. Tertiary veins are opposite percurrent and strongly impressed. The margin has small, acute, regularly spaced teeth. Comments. The strongly impressed tertiary veins distinguishes this taxon from Aesculus hickeyi (Manchester, 2001). Reference. Manchester (1987) Catalog number. KATM 44742 Family Betulaceae Corylites sp. Gardner ex Seward Holttum Description. Elliptic, mesophyllous toothed leaves. Venation is pinnate with at least 12 pairs of prominent, craspedodromous secondary veins that gradually increase in angle with the midvein towards the base of the leaf. Tertiaries are closely-spaced and opposite percurrent. Teeth are compound with angular sinuses and variable in shape.

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Comments. The venation and margin indicate the specimens are in the Betulaceae and compare most favorably with the genus Corylites. Reference. Manchester and Chen (1996) Catalog numbers. KATM 44723, 44725 Family Menispermaceae Genus and species indeterminate Description. Ovate, microphyllous, palmately lobed, peltate leaf, with 2 teeth on each side of the lamina in the lower one third. The apex is acuminate. Nine primary veins diverge from the petiolar attachment. No other venation is visible. Comments. The leaf shape and primary venation are characters that are typical of the Menispermaceae. More precise determination is not possible because higher order venation is lacking. Catalog number. KATM 44738 Family Lauraceae Genus and species indeterminate Description. Obovate, notophyllous, untoothed leaf. Venation is pinnate; secondary veins are decurrent, eucamptodromous, and a prominent pair diverges ~0.5 cm above the base. Intersecondary veins are present, and tertiary veins are irregular in course. Comments. Prominent suprabasal and decurrent secondary veins are commonly found in Lauraceae. Catalog number. KATM 44730 Family indeterminate Indeterminate Genus and Species 1 Description. Oblong microphyllous leaf with a length: width ratio of 4:1, a decurrent base, and an acuminate apex. Venation is pinnate, with craspedodromous secondaries. Teriary veins are not preserved. Teeth are present, but poorly preserved. Comments. The leaf shape resembles many species of Salix, but there is no clear indication of glands as would be expected for this genus. Catalog number. KATM 44711 Indeterminate Genus and Species 2 Description. Untoothed, elliptic, microphyll with straight base and acuminate apex. Pinnate with closely-spaced, uniform eucamptodromous secondaries that curve upward within 2 mm of the margin. Catalog number. KATM 44734

Appendix B Systematic descriptions of the fossil wood of the Ketavik Formation, with terminology following recommendations of the IAWA (IAWA Committee, 1989, 2004). Accession number is KATM 00298; catalog numbers for each specimen are listed with each taxon (Table 1). Cupressaceae s.l. Cupressinoxylon sp. Description. Growth rings present, distinct. Longitudinal and horizontal resin canals absent. Intertracheary pitting uniseriate. Tangential diameter of earlywood tracheids averages 23 μm (SD=7), range 12–35 μm. Helical thickenings absent. Rays exclusively uniseriate, homocellular, composed exclusively of ray parenchyma with smooth walls. Cross-field pits small, probably cupressoid, usually with 2–3 per cross-field. Average ray height in cell number 8, range 3–16 cells. Axial parenchyma not obvious. Comments. The absence of resin canals and ray tracheids combined with narrow longitudinal tracheids with cupressoid crossfield pits indicates this wood belongs to the cupressoid group of the Cupressaceae (e.g., Phillips, 1948). Wood of this group is homogeneous and recognition of individual genera difficult. Many species of

fossil wood have been assigned to Cupressinoxylon, most reflecting differences in locality and age, rather than in anatomy. Catalog number. KATM 44743 Metasequoia sp. Growth rings present, distinct. Earlywood tracheids polygonal in cross-sectional outline. Latewood narrow, 1–3 rows of radially narrower tracheids. Tangential diameter of earlywood tracheids averages 40 (SD = 6) μm, range 28–58 μm. Helical thickenings absent. Radial wall intertracheary pitting predominantly biseriate and opposite. Rays uniseriate, homocellular, composed only of ray parenchyma. Average uniseriate ray height in cell number 15 (SD = 12), range 2–44 cells. Ray tracheids absent, ray parenchyma with smooth walls. 1–3 taxodioid pits per cross-field in regular horizontal rows. Axial parenchyma rare, with smooth end walls. Comments: The combination of relatively wide tracheids that commonly have biseriate intertracheary pitting, taxodioid crossfield pits, and rays that are more than 30 cells high is one found in Glyptostrobus, Metasequoia, and Sequoia. According to Phillips (1948), Sequoia has abundant axial parenchyma and frequently biseriate rays, features not seen in the Ketavik wood. Visscher and Jagels (2003) summarized criteria useful for distinguishing Metasequoia from Glyptostrobus. Rarity of axial parenchyma, cross-field pits arranged in regular horizontal rows, maximum width of the longitudinal tracheids >48 μm, and smooth parenchyma end walls are characteristics of Metasequoia, not Glyptostrobus. Metasequoia milleri from the middle Eocene Allenby Formation of British Columbia has taller rays (frequently more than 50 cells high and up to 80 cells, Basinger, 1981) than this Ketavik wood, whose ray features are similar to the extant Metasequoia glyptostroboides. Metasequoia is reported to be the dominant element in the highlatitude, middle Eocene Axel Heiberg forests (Williams et al., 2003), but anatomical details on those woods that would enable comparing them to this Ketavik wood could not be found (Young, 1991; Basinger, 1991). Pinaceae Cedrus penhallowi Barghoorn and Bailey Growth rings present, distinct. Transition from earlywood to broad latewood gradual. Traumatic resin canals in tangential lines. Tangential diameter of earlywood tracheids averages 35 (SD = 9) μm, range 22–51 μm. Helical thickenings absent. Radial wall intertracheary pitting predominantly uniseriate, occasionally biseriate and opposite, crassulae prominent. Rays uniseriate, occasional fusiform rays with traumatic horizontal resin canals. Average uniseriate ray height in cell number 10 (SD = 6), range 3– 30 cells. Ray tracheids rare, absent from most rays; ray parenchyma with smooth walls. 1–3 cupressoid–taxodioid pits per crossfield. Axial parenchyma not obvious. Comments. The occurrence of both trauamatic axial and horizontal resin canals indicates this wood is Cedrus (Barghoorn and Bailey, 1938; Phillips, 1948).This wood resembles Cedrus penhallowii from the Eocene Auriferous Gravels of California (Barghoorn and Bailey, 1938) and C. alaskensis from the Cretaceous of Alaska (Arnold, 1953). Unfortunately, the descriptions of these two species did not include details on cell dimensions or ray sizes. The only apparent difference between Cedrus penhallowii and C. alaskensis is that C. penhallowi has crystals in the marginal ray cells and C. alaskensis does not Given that crystal occurrence can be variable in extant species, it is questionable whether this constitutes a significant difference between the two wood types. The Ketavik wood is referred to Cedrus penhallowii, described before C. alaskensis. A

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Paleocene–lower Eocene Cedrus wood from Kamchatka differs as it commonly has ray tracheids (Blokhina, 1998). Catalog number. KATM 44748 Pinus sp. Section Parrya Description. Growth rings present, distinct. Transition from earlywood to latewood gradual. Longitudinal resin canals with thinwalled epithelial cells, concentrated in the outermost latewood and often in tangential lines. Earlywood longitudinal tracheids with biseriate opposite intertracheary pits on radial walls, small uniseriate tangential wall pitting likely present. Tangential diameter of earlywood tracheids averages 40 (SD = 10), range 26–61 μm. Helical thickenings absent. Rays uniseriate, biseriate and fusiform with resin canals with thin-walled epithelial cells. More than 70% of the rays without resin canals are biseriate. Biseriate ray height averages 11 cells, range 4–15; uniseriate ray height averages 4 cells, range 2–7. Rays predominantly homocellular, composed only of ray parenchyma, rarely heterocellular with smooth-walled ray tracheids. Cross-field pits small, usually 3–4 per cross-field. Comment. Pine wood is distinctive as it has normal longitudinal and horizontal resin canals with thin-walled epithelial cells. Within the genus, small cross-field pits and smooth ray tracheids of rare occurrence are features of some species of Section Parrya (Phillips, 1948; van der Burgh, 1973; Ickert-Bond, 2001). According to Phillips, woods of Subsection Balfourianae have such characteristics. Section Parrya has been suggested to be the most ancient of pine groups (e.g., Wang et al., 1999). Millar's (1998) list of Eocene pines includes two species of macrofossils (not wood) referred to Subsection Balfourianae, P. balfouroides from Thunder Mt., Idaho (age 46–47 my; Axelrod, 1986) and P. crossii from Copper Basin, Nevada (age 40–44 my; Axelrod, 1966). Pinus similkameensis wood from the Eocene Allenby Formation, British Columbia, has features of section Parrya according to Miller (1973). However, this wood does not have a high proportion of biseriate rays or biseriate intertracheary pits. The common occurrence of biseriate intertracheary pitting and biseriate rays is unusual for Pinaceae and not a general characteristic of presentday pine wood. None of the aforementioned authors or Greguss (1955) indicate these features occur in Subsection Balfourianae or any other Pinaceae. One sample (KATM 44750) may represent yet another species of Pinus Section Parrya. It has resin canals in both earlywood and latewood, a lower incidence of biseriate rays, and ray tracheids are easier to observe. Catalog numbers. KATM 44750, 44744, 44746 Platanaceae Platanoxylon sp. Description. Growth rings present, but not distinct, marked by radially narrower fibers and slightly noded rays. Diffuse porous, vessels solitary and in tangential and oblique pairs. Vessels narrow, with a mean tangential diameter of 54 μm (SD = 10), and range of 41–77 μm and numerous, 40–60 per sq. mm. Only scalariform perforation plates observed with 12 to more than 20 bars. Intervessel pits opposite, vessel-ray parenchyma pits not observed. Axial parenchyma difficult to see, likely diffuse to diffusein-aggregates. Fibers thick-walled, pits not observed. Rays predominantly multiseriate and commonly >15-seriate, more than 1 mm high, appearing to be homocellular composed exclusively of procumbent cells. Comments. Platanoid woods are common in the Late Cretaceous and Paleogene of the Northern Hemisphere. Such

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woods are characterized by numerous, narrow vessels that are solitary and in small groups, tall and wide homocellular rays. Present-day and Neogene woods have a mixture of simple and scalariform perforations and usually are assigned to Platanus, whereas the Cretaceous and Paleogene woods have exclusively scalariform perforation plates, and can be assigned to Platanoxylon. This wood is like other Eocene platanoid woods as it has exclusively scalariform perforation plates. Its rays are somewhat narrower than other Eocene platanoid woods, which often have rays more than 20 cells wide. Catalog numbers. KATM 44754 References Arnold, C.A., 1953. Silicified plant remains from the Mesozoic and Tertiary of western North America. II. Some fossil woods from northern Alaska. Papers of the Michigan Academy of Science, Arts and Letters 38, 9–20. Axelrod, D.I., 1966. The Eocene Copper Basin flora of northeastern Nevada. University of California Publications in Geological Sciences 59. 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