Quaternary Environments at Cape Deceit (Seward Peninsula, Alaska): Evolution of a Tundra Ecosystem

Abstract

Unconsolidated sediments at Cape Deceit near Deering, Alaska, range in age from latest early Pleistocene to Holocene. Plant and insect fossils from these sediments, as well as certain sedimentary features, provide evidence for documenting evolution of the terrestrial ecosystem at Deering. A tundra ecosystem functioned at Deering for most of the time represented by the Cape Deceit sedimentary sequence. The regional tundra environment of northern Seward Peninsula during early Pleistocene time was similar to that of the present; however, the local environment at Cape Deceit was quite different, being only scantily vegetated. Starting in the middle Pleistocene, the tundra of northern Seward Peninsula evidently became more grassy, a trend culminating with steppe-tundra by latest Wisconsin time. Former periods of warmer climate at Deering are indicated by evidence for westward movement of tree line. The last time forest or forest-tundra existed at Deering was no later than the penultimate interglacial. Spruce tree line probably stood closer to but not at Deering during the Sangamon interglacial. At least once, during latest early Pleistocene time, tree line at Deering was composed of larch instead of spruce. Except for the mammalian component, most ecosystem evolution at Cape Deceit during the last 400,000 yr or more has apparently involved little in situ evolution of taxa. The maximum degree of phyletic evolution to be documented here is reduction of the flight wings of the tundra beetle species, Tachinus apterus . Most of the phylogenetic splitting that has given rise to pairs or groups of closely related arctic species (especially among the beetles) probably occurred well before the early Pleistocene during initial formation of the lowland tundra realm.