The Chignik Area
|Map and Localities||Geology||Correlations||Chignik Formation||Tolstoi Formation||Tolstoi Fossil Images|
The oldest Paleogene deposits overlying Mesozoic strata were named the Tolstoi Formation by Burk (1965) who designated a type locality along the east shore of Pavlof Bay, between Tolstoi Peak and Cone Peak (Port Moller B-5 and CS 1:63,360 quadrangles). Although regarded as the type section of the Tolstoi by Detterman et al., (1996; their section 17) these rocks are not typical of the rest of the formation as mapped by either Burk (1965) or Detterman et al., (1996) to the northeast of the type locality. The Tolstoi Formation at Pavlof Bay is in part a shallow-water marine deposit, whereas northeastward along the peninsula the formation is a non-marine fluvial floodplain and delta deposit containing abundant conglomerate, crossbedded sandstone, coal, and carbonaceous shale. Consequently Detterman et al., 1996) designated a reference section (section 18) along the east shore of Ivanof Bay, in the Stepovak Bay 0-5 I :63,360 quadrangle, beginning at the northeast corner of sec. 3 and continuing south along the shore to the southeast corner of sec. 10, T. 50 S., R. 66 W. (fig. 13).
The Tolstoi Formation contains conspicuous volcaniclastics but these do not form a major part of the Tolstoi sediments. A few thin tuff beds are present in all sections, and some of the sandstones are tuffaceous but most of the volcanic clasts are not fresh-appearing and may have been reworked from a Mesozoic source. This is in sharp contrast to the overlying Stepovak Formation and the Meshik Volcanics, whose sandstones are composed almost entirely of fresh volcanic debris (Detterman, et al., 1996).
Detterman et al. (1996) consider that the Tolstoi was deposited by onlap onto the underlying Mesozoic rocks. At Pavlof Bay and Korovin Island marine molluscs indicate a late middle Eocene age for the Tolstoi Formation (Marincovich, 1988). Marine mollusks are restricted almost entirely to the Pavlof Bay and Korovin Island localities where the marine and nonmarine beds inter-finger. Turritella uvasana stewarti Merriam and Microcallista (Costacallista) conradiana (Gabb) comprise the main elements of the fauna, which also includes Nuculana sp., Tellina sp., Ostrea sp., Solena sp.. Corbicula sp., Volsella sp., and Glycymeris sp. According to Marincovich (1988) this fauna represents an extremely shallow-water, warm temperate to subtropical marine environment (Marincovich, 1988).
On Korovin Island the same bed that yielded the Turritella uvasana stewati also contained the dinoflagellates Impagidinium californiense, Adnatosphaeridium multispinosom, Turbiosphaera filosa, Glaphyrocysta retiintexta, and Rhombodinium sp. and indicate an early to middle Eocene age (Nairn Alberl, written commun., 1985 cited in Detterman et al., 1996).
The reference section at Ivanof Bay yielded an abundant fossil megaflora including Acer arcticum Heer, Alnus sp., Cocculus flabella (Newberry) Wolfe, Grewiopsis auriculaecrodatus (Hollick) Wolfe, Liquidambar sp.. Metasequoia occidentalis (Newberry) Chaney, Protophyllum semotum Hickey, and Thuites interruptus (Newberry) Bell as identified by J .A. Wolfe (1981). This suggests a late Paleocene to middle Eocene age, and was interpreted by Wolfe (1981) as representing a paratropical rain-forest environment with a mean annual temperature of about 22°C. Both the megaflora and megafauna therefore suggest a warm temperature for the area at the time of deposition of the Pavlof Bay rocks.
Throughout most of the Alaska Peninsula the lower contact of the Tolstoi Formation is a major unconformity and the base of the formation rests locally on the Hoodoo, Chignik, Staniukovich, or Naknek Formation. A yellowish-orange weathered zone commonly occurs at the contact belween the Tolstoi and the underlying formations and marks a definite erosional break. The uppercontact of the Tolstoi is disconformable where it is overlain by the sedimentary rocks of the Stepovak Formation. Where the Tolstoi is overlain by the Meshik Volcanics, the contact is an unconformity.
Above: Type section of the Tolstoi Formation at Pavlov Bay (Section 17 of Detterman et al. 1996), and the Tolstoi reference section at Ivanof Bay (Section 18 of Detterman et al., 1996).
Plant fossils indentified by Jack A. Wolfe as given in Detterman et al. (1996).
Locality 11416: Acer arcticum Heer, Alnus (new species), Cocculus (new species), Hamamelidaceae (new species), Liquidambar (new species), Platycarya (new species), Protophyllum semotum Hickey, Metasequoia occidentalis (Newberry) Chaney, Thuites interruptus (Newberry) Bell.
Locality 11415: Acer arcticum Heer, Alnus (new species).
Locality 11413: Cocculus flabella (Newberry) Chaney.
Locality 11412: Metasequoia occidentalis (Newberry) Chaney, Thuites interruptus (Newberry) Bell.
Locality 11411: Chaetoptelia microphylla (Newberry) Hickey, Dicotylophyllum richardsoni (Heer) Wolfe, Grewiopsis auriculaecordatus (Hollick) Wolfe, Protophyllum semotum Hickey, Metasequoia occidentalis (Newberry) Chaney, Thuites interruptus (Newberry) Bell.
M8385 and M8385: Bivalves Microcallista (Costacallista) conradiana (Gabb) Turner, Nuculana sp., Corbicula? sp..
M8380 and M8386: Bivalves Solena cf. S. clarki (Weaver and Palmer), Corbicula sp..
M8382 Gastropod Turritella uvasana sterwarti Merriam, interterminate plant debris.
M8906 Bivalves Microcallista(Costocallista) canadiana (gabb (Turner), Corbicula? sp., Ostrea sp. indet., Gastropod Turritella uvasana stewarti Merriam.