Quaternary Environments at Cape Deceit (Seward Peninsula, Alaska): Evolution of a Tunclra Ecosystem J. V. MATTHEWS, JR. Terrain Science; Division, Geological Survey of Canada, 601 Booth, Ottawa, Ontario, Canada K1A OE8 ABSTRACT latest early Pleistocene time, tree line at terrestrial environments in western Alaska Deering was composed of larch instead of — a result of the fact that sediments of that Unconsolidated sediments at Cape Deceit spruce. age in the area are predominantly nearshore near Deering, Alaska, range in age from Except for the mammalian component, marine in origin (Hopkins, 1967b). In con- latest early Pleistocene to Holocene. Plant most ecosystem evolution at Cape Deceit trast, the late Pleistocene environmental and insect fossils from these sediments, as during the last 400,000 yr or more has ap- history of western Alaska is better known well as certain sedimentary features, pro- parently involved little in situ evolution of (Colinvaux, 1967; Hopkins, 1972), al- vide evidence for documenting evolution of taxa. The maximum degree of phyletic though more work will be necessary to ob- the terrestrial ecosystem at Deering. evolution to be documented here is reduc- tain paleoenvironmental data comparable A tundra ecosystem functioned at Deer- tion of the flight wings of the tundra beetle to that now available in areas such as the ing for most of the time represented by the species, Tachinus apterus. Most of the north-central United States and western Cape Deceit sedimentary sequence. The re- phylogenetic splitting that has given rise to Europe. Much of this information will no gional tundra environment of northern pairs or groups of closely related arctic doubt come from continuing palynological Seward Peninsula during early Pleistocene species (especially among the beetles) prob- research in Alaska, but the most valuable time was similar to that of the present; ably occurred well before the early Pleis- studies are likely to employ a combination however, the local environment at Cape tocene during initial formation of the low- of several analytic techniques. Such a mul- Deceit was quite different, being only scant- land tundra realm. tifaceted study is the subject of this paper. ily vegetated. Starting in the middle Pleis- Fossils of pollen, plant macrofragments, tocene, the tundra of northern Seward INTRODUCTION and insects from Quaternary sediments at Peninsula evidently became more grassy, a Recent papers by Hopkins (1967a, 1972) Cape Deceit (Fig. 1; Guthrie and Matthews, trend culminating with steppe-tundra by have admirably summarized present 1971) are analyzed, and attention is also latest Wisconsin time. knowledge of Quaternary geology, paleon- given to the possible paleoclimatic implica- Former periods of warmer climate at tology, and biogeography of the Beringian tions of certain sedimentary structures oc- Deering are indicated by evidence for region, including eastern Siberia, western curring at the Cape Deceit exposure. westward movement of tree line. The last Alaska, and the intervening Bering and Oldest sediments at the Cape Deceit ex- time forest or forest-tundra existed at Deer- Chukchi epicontinental seas. Several gaps posure are of latest early Pleistocene age ing was no later than the penultimate in- in our knowledge of the history of this area (Cromerian). Fossils from them provide terglacial. Spruce tree line probably stood are also revealed by Hopkins' papers. The evidence of several climatic fluctuations closer to but not at Deering during the San- most obvious of these is the paucity of in- during which conifers expanded west to gamon interglacial. At least once, during formation on early and middle Pleistocene grow near Deering and Cape Deceit. Dur- Geological Society of America Bulletin, v. 85, p. 1353-1384, 17 figs., September 1974 1353 Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/85/9/1353/3428867/i0016-7606-85-9-1353.pdf by guest on 26 September 2021 1354 J. V. MATTHEWS, JR. ing one of these episodes, .a larch tree line existed in the Deering region. The oldest sedimentary unit at Cape Deceit also con- Sj tains the first North American record of the Eurasian rodent genus, Pliomys (Guthrie CAPE DECEIT and Matthews, 1971) and :he most primi- tive representatives of small mammal lineages whose members dominate contem- porary tundra faunas. The various lines of 73-67V , fossil locality evidence discussed below suggest that the 74-S7» ,A station 8 tundra environment in which these primi- * \ tive mammals lived was at least quantita- CHUKCHI tively and probably qualitatively different SEA from that of the present. But this fact is Caps most apparent in the upper (late Pleis- Thompson tocene) part of the Cape Deceit sequence because plant and insect fossils there sug- *t gest a former arctic grassland or steppe- W^ DEERING tundra. In other words, the character of the -> tundra environment at Cape Deceit has changed markedly during the Pleistocene but appears to have been most different from the present during latest Wisconsin time. The fossils discussed in this paper repre- sent directly or indirectly the state of sev- eral trophic levels at different instants of geologic time, and the sedimentary struc- GULF OF ALASKA tures refer to former conditions of the abi- otic environment. Thus, the documented Figure 1. Location of Cape Deceit, Deering, and the fossil locality. Numbers refer to collection sites of surface sequence of environmental change actually pollen samples (Fig. 10, Table 1). Surface sample 97-69 located at "Pingo" (Fig. 2). represents the stages in the evolution of an ecosystem—in this case, the terrestrial with 0.635-mm screens at the fossil locality. as keys and illustrations in Beijerinck tundra ecosystem at Cape Deceit, Alaska. The residue was then sieved again with (1947), Berggren (1969), Bertsch (1941), 0.317-mm screens in the laboratory to re- Brouwer and Stahlin (1955), Martin and METHODS move remaining silt and clay. Next, seeds Barkley (1961), and Katz and others were skimmed from the floating fraction of (1965), aided identification of plant mac- Pollen Samples the residue, and if extremely abundant, a rofossils. I identified most of the insect fos- Pollen samples discussed here have been randomly selected sub sample was used for sils using comparative material in my own prepared using a modified version of a analysis. Finally, the insect fraction of the and museum collections. K.G.A. Hamilton schedule developed by Mehringer (1967) original sieve residue was concentrated identified Homoptera fossils, W.R.M. for alluvial pollen samples. My using a flotation technique developed by Mason examined some of the Hymenoptera modifications (greater numoer of swirls, Coope (1961). A dissecting microscope was fossils, J. M. Campbell checked Tachinus prolonged HF treatment, and elimination then used to isolate identifiable insect frag- arid Micralymma determinations, C. H. of HN03 treatment) help to concentrate ments, which were either stored in alcohol Lindroth examined specimens of Harpalus sufficient pollen for analysis, a common or immediately glued to macrofossil slides. cf, alaskensis Lth., and R. E. Leech problem with samples representing tundra, Samples of felted (oedded) peat, which identified spider fossils. to preserve the partly degraded pollen usu- occur at some levels in the exposure, were The entire fossil collection is presently ally occurring in colluvial sediments. processed differently because they often housed at the Geological Survey of Canada contain exceptionally well-preserved, partly (Ottawa). Macrofossils articulated insect fossi s. Such peat samples The initial step in Mehringer's procedure were collected in blocks and carefully pried GEOGRAPHIC AND of processing pollen is to wash approxi- apart in the laboratory. Articulated fossils BI OTIC SETTING mately 50 ml of sediment through were removed individually and glued to Quaternary exposures discussed here 0.254-mm screen to remove large organic macrofossil slides. Partly articulated insect occur adjacent to Cape Deceit, a prominent and mineral fragments. Residue left on the fossils also occurred occasionally in car- landmark in the low-lying northern coastal screen often contains plant and insect mac- bonate-cemented siltpeds. region of Seward Peninsula (Figs. 1, 2). rofossils, which provide, in some cases, al- De:ering, a small Eskimo village at the ternate evidence for interpretation of pollen Identification Aids mouth of the Inmachuk River, is within 4 data. Pollen and spores were identified using km of the Cape and Quaternary exposures Large sediment samples (200+ kg) from keys, illustrations in current palynological (Fig. 1). Deering is in a region of continuous selected levels in the Cape Deceit exposure literature (Faegri and Iversen, 1964; permafrost. Mean annual temperatures were processed in order to obtain assem- Erdtman, 1965, 1966, 1969; Erdtman and range from —4° to — 8°C, and mean annual blages (samples) of plant and insect mac- others, 1961, 1963; Beug, 1961), and refer- precipitation is between 130 and 150 mm rofossils. Silt and peaty silt were first sieved ence slides. Herbarium specimens, as well (Hulten, 1968). Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/85/9/1353/3428867/i0016-7606-85-9-1353.pdf by guest on 26 September 2021 QUATERNARY ENVIRONMENTS, CAPE DECEIT, ALASKA 1355 i i i gion, grasses are relatively rare, except at 166° W 162° W I5Q= w very dry sites. Artemisia was observed growing only on the unstable, deeply thawed coastal bluffs. Detailed descriptions of the vegetation on other areas of western Alaska are outlined in Hopkins and Sigafoos (1950), Hanson (1953), and Johnson and others (1966). The last report, dealing with the Cape Thompson area, describes several "vegeta- tion types" that also occur in the Deering region. Papers concerned with more north- ern parts of Alaska (Hultén, 1968; Wiggins and Thomas, 1962; Britton, 1966) show that some important plants of the Deering region — Betula, Alnus — do not occur farther north (Young, 1971). A more severe regional climate is probably the cause. Spruce tree line is located approximately 75 km east of Deering (Fig.