Bulletin of the Geological Society of America Vol. 71, Pp

BULLETIN OF THE GEOLOGICAL SOCIETY OF AMERICA VOL. 71, PP. 1346-1356. 2 FIGS. SEPTEMBER 1960

CRETACEOUS AMBER FROM THE ARCTIC COASTAL PLAIN OF ALASKA

BY R. L. LANGENHEIM, JR., C. J. SMILEY, AND JANE GRAY

ABSTRACT Amber is widespread in association with coal and carbonaceous shale in probable equivalents of the Chandler and Prince Creek formations that crop out in the Kaolak River, Ketik River, and Kuk River valleys of the Alaskan Arctic Coastal Plain. Re- worked amber is ubiquitous in recent stream deposits and in the Pleistocene Gubik formation. Fossil insect inclusions are rare, but as least four species representing the families Heleidae, Empididae, Eulophidae, and Ceraphronidae are present. The amber is generally associated with taxodiaceous fossils and is thus considered of taxodiaceous origin. Marine fossils appear to be absent from the amber-bearing sequence. Thus biostratigraphic and time-rock correlation rests entirely on abundant plant megafossils and microfossils. Two floras occur with the amber. The older Kuk River flora is composed predominantly of gymnosperm remains and is considered Early Cretaceous. The younger Kaolak River flora, however, consists predominantly of angiospermous megafossils and gymnospermous microfossils. Thus it may be either Early or Late Cretaceous.

CONTENTS

TEXT Page Fossil foliage 1351 Page Plant microfossils 1352 Introduction and acknowledgments 1345 Comparison of megafossil and microfossil Geology of the Kuk River amber deposits. 1347 floras 1353 General statement 1347 Conclusions 1355 Pleistocene geology 1348 References cited 1356 Cretaceous rocks 1349 Amber 1350 ILLUSTRATIONS Geologic occurrence of amber 1350 Figure Page Character of the amber 1350 1. Collecting localities in the Kuk River drain- Fossils in the amber 1351 age basin 1346 Marine invertebrate fossils 1351 2. Characteristic cutbank exposure of Creta- Paleobotany 1351 ceous rocks in the Kuk River drainage General statement 1351 basin 1348

INTRODUCTION AND ACKNOWLEDGMENTS this material was originally derived are unknown. No insects have been found in the abun- Amber from Cretaceous rocks of the Alaskan dant Late Cretaceous amber of the Atlantic Arctic Coastal Plain is of interest because of its Coastal Plain of North America. Other re- age and because it is a potential source of ports indicate that the amber is rare in Cre- fossil insects. Several large assemblages of taceous rocks and is either badly fractured or fossil insects are known from amber deposits altered. Thus the few fossil insects so far re- of Late Eocene and younger Tertiary age covered from the Cretaceous rocks of Alaska scattered around the world. Many fossil insects are unique records of Early Cretaceous insect have been described from the Jurassic Solen- life and proof of the preservation of such fossils hofen limestone and from Pennsylvanian and in ancient amber. Permian rocks. Although Carpenter and others Paleontologic data bearing on the age of the (1937) described a few insects of presumed fossil insects show striking differences in the Late Cretaceous age in amber from the beaches composition of the megafossil and microfossil of Ceda* Lake, Alberta, the rocks from which floras. The younger of the two floras accom- 1345

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LEGEND ••27 Collecting locality OC6 Camp N Plant fossils • Pollen sample A Amber sample A Placer amber Vt Insect fossils > Habitation

FIGURE 1.—COLLECTING LOCALITIES IN THE KUK RIVER DRAINAGE BASIN Base modified after sheets F19, G19, and G20, preliminary maps, Naval Petroleum Reserve No. 4 and after Utukok River and Wainvvright quadrangles, Alaska Reconnaissance Topographic Series, Ed. 1951

panying the amber consists predominantly between conceptual biostratigraphic units of angiosperm megafossils and gymnosperm which describe the distribution of fossils in microfossils. Inasmuch as Late Cretaceous rock strata and the time-rock concepts based on floras are generally distinguished from Early such units. Cretaceous floras by dominance of angiosperms Occurrence of amber in bedrock on the Arc- and gymnosperms respectively, the foliage tic Coastal Plain of Alaska was verified during might be considered Late Cretaceous and the the summer of 1955 by Usinger and Smith microfossils Early Cretaceous. Both mega- (1957; Kurd and others, 1958). These workers fossils and microfossils, however, are derived also found a piece of amber containing several from the same rocks and presumably are of the insects on a beach near the head of Kuk Inlet same age. We believe that this paradox is near Wainwright, Alaska. They discovered the best resolved by maintaining a strict distinction localities yielding well-preserved amber from

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bedrock exposures on the Ketik River only a collection on the upper Kuk River but could few days before the end of the field season, not examine the extensive coal exposures on and these localities therefore were not thor- the shores of Kuk Inlet because our outboard oughly explored. Previous bedrock collections motor failed. from the Killik Bend of the Colville River These studies were aided by a contract be- consisted of small pieces of shattered amber. tween the Office of Naval Research, Depart- Material collected from beaches and bars ment of the Navy and the Arctic Institute of along the Kuk and Colville rivers was of un- North America. The field party is especially known stratigraphic position. Thus two major grateful to Ira Wiggins, director of the Arctic problems remained at the end of the 1955 Research Laboratory during the summer of field season—obtaining detailed information on 1956, and to his staff for their many invaluable the stratigraphic range of the amber and col- suggestions and their efficient logistic support. lecting sufficiently large quantities of amber to Thanks are also due Wesley Ikak for trans- insure obtaining a representative insect fauna. porting the party to Wainwright. We also Langenheim and Smiley, therefore, undertook wish to thank R. L. Usinger and R. F. Smith field work to this end during the 1956 field for initiating the project and inviting our par- season. ticipation. George O. Gates, George Gryc, Examination of reports by Webber (1947, and their staff supplied information, maps, U. S. Geol. Survey open-file report) and and reports concerning U. S. Geological Survey Stefansson and Mangus (1949, U. S. Geol. work in the area. R. W. Chaney, J. W. Dur- Survey open-file report) and consultation with ham, W. L. Fry, J. H. Langenheim, R. L. Usinger and Smith as well as with George O. Usinger, and R. F. Smith have read and criti- Gates of the Alaskan Branch of the U. S. Geo- cized the manuscript, and their assistance is logical Survey led to a program of traversing gratefully acknowledged. The authors, how- as much of the Kaolak River as possible, ever, assume full responsibility for the form followed by trips up the Avalik and Ketik and content of the paper. Illustrations were rivers, and examination of exposures in Kuk prepared by Stephen Chen and Owen Poe. Inlet (Fig. 1). The Kaolak River was selected for the major effort because it was the only tributary of the Kuk River not examined by GEOLOGY OF THE KUK RIVER U. S. Geological Survey geologists during the AMBER DEPOSITS 1944-1953 examination of Naval Petroleum Reserve No. 4. The Kaolak River flows through General Statement generally higher country than the Ketik or Avalik rivers and thus would be expected to Cretaceous rocks form a broad asymmetric offer more bedrock exposures. Aerial reconnais- synclinorium between the Brooks Range and sance verified the latter assumption, and on the northern coast line of Alaska in the Arctic July 11, 1956, Langenheim, Smiley, and Clay Coastal Plain and Arctic Foothills physio- Kaigelak (an eskimo guide) were flown to an graphic provinces (Payne and others, 1951). oxbow lake at lat. 69° 48" N. (approximate) Rocks in the Coastal Plain province dip gently on the east side of the Kaolak River. From the southward, those of the Northern Foothills point of landing to the mouth of the Kaolak section generally form open Appalachian-type River we searched all 28 cutbank exposures folds, and those of the Southern Foothills for amber, measured and described strati- section are intensely folded and thrust-faulted graphic sections (Fig. 2), and examined 11 (Payne and others, 1951). Rocks seen by our gravel bars for amber. On August 1 and 2, party in the Northern Foothills section and supplies and an outboard motor were flown in, coastal plain, however, all dip less than 5°, and the accumulated collections were flown to and discontinuous outcrops prevented effec- Point Barrow. Thereafter, we explored the tive mapping of structural features, even Ketik River to lat. 70° 2' N. (approximate) though several reversals of dip were noted. and the lower 4 miles of the Avalik River; The best rock exposures are in cutbanks we measured and examined 4 cutbank ex- formed where streams reach the bounding posures and obtained 6 gravel-bar collections. bluffs of their flood plains, but resistant sand- The party then proceeded down the Kuk River stone ledges also form scattered outcrops in to Nasiksugvik, a prominent lookout point the river channels or bordering the flood plain near camp 23. We measured and examined for short distances. Outcrops are limited in three cutbanks and obtained one gravel-bar extent, however, except along Kuk Inlet, and

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more than 90 per cent of the area is covered by cap of gravel suggests that the relatively smooth tundra vegetation. Solifluction disrupts ex- high-level surface in the coastal plain is covered posed rock, and most outcrops are badly by Pleistocene sediments. slumped. Occurrence of Pleistocene debris at relatively

Locality 19. AMBER, Smpl.19-3 ' 'White, sondy Ostreo sp. — clay with some coal chips abundant AMBER,Smpl. 19-2 Cool

Scale Talus cover, clay or coal ? f ' Smpl.19-4-

10 20 Smpl.19-1 *^x; " .".*."." ."Unconsolidated to poorly consolidated

Badly slumped, blue and gray cloy

Sandstone outcrop littered with sandstone slobs and concretions

FIGURE 2.—CHARACTERISTIC CUTBANK EXPOSURE or CRETACEOUS ROCKS IN THE KUK RIVER DRAINAGE BASIN

Pleistocene Geology high topographic levels near the sea and at relatively low levels in the Northern Foothills Two prominent topographic surfaces are section seems anomalous. Flood-plain deposits present along the Kaolak River. The higher in the foothills are apparently deposits of surface is formed by the general crest level meltwater streams which flowed during the of the interfluves in the Northern Foothills wasting of glaciers in the Brooks Range. This section and is underlain by Cretaceous bed- explanation of course assumes that the Kuk rock mantled only by recent tundra soil. drainage system then extended to the Brooks This surface is presumably of erosional origin. Range and has since been beheaded by the Within the Kaolak valley the flood-plain sur- Utukok River. This hypothesis is supported face 10-25 feet above the summer stream chan- by the cobbles of chert and other rocks not nel is generally underlain by Pleistocene de- known from the Coastal Plain Cretaceous posits containing abundant wood and mammal which are abundant in gravel along the Kaolak bones. This terrace is the present flood plain and Kuk rivers. One such cobble noted on a of the river and is crossed by abandoned river sand bar in the Ketik River contained a channels and, within the distance traversed, Paleozoic coral; this rock must have originated contains two oxbow lakes. in the Brooks Range. The high-level gravel In the Arctic Coastal Plain province the in the Coastal Plain province is apparently a river system is drowned, forming Kuk Inlet sheet of near-shore and coastal-plain debris and the lower reaches of the Kuk and Avalik and well fits current concepts of the Gubik rivers. The latter, though fresh, are slow- formation (Payne and others, 1951). If the flowing, wide tidal rivers bordered by extensive high-level coastal gravel and the foothills peat deposits. Peat covers the flood plain and flood-plain deposits are of the same age an any fossil-bearing Pleistocene gravel that may explanation is required for what appears to be present. The slopes of the low hills bordering be a more rapid rate of downcutting in the the valley expose only Cretaceous rock, but at lower, partially tidal, part of the Kuk drainage Nasiksugvik just east of camp 23 a mesalike system than in the middle reaches of these

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streams. Postdepositional uplift of the coastal coal beds or carbonaceous shale layers and plain might be the most obvious hypothesis, has been mixed with shale in slumping. Some were it not for the drowned drainage pattern coaly material and amber, however, appear to of the Kuk River. Thus the flood-plain de- be scattered through the clay rock as originally posits and coastal-plain gravel probably repre- deposited. sent two episodes of Pleistocene deposition. Sandstone is the next most abundant rock Pleistocene flood-plain sediments in the in the Cretaceous of this area and, because of Northern Foothills section consist of gravel, its greater resistance to weathering, is the coarse to fine sand, and silty clay. Charac- best exposed of the Cretaceous sequence. teristic exposures have granule to cobble Fine- to medium-sized grains of subangular gravel composed largely of subrounded to quartz with lesser amounts of feldspar, coal, rounded flint with minor amounts of sub- limonite, and accessory minerals make up angular to subrounded sandstone fragments almost all the sandstone. Coarse sandstone is at the base. The sandstone fragments are iden- rare, and conglomerate has not been found tical to sandstone in the underlying Creta- within outcrops identified as Cretaceous. Most ceous rocks and are therefore presumably of of the sand is moderately well cemented to Cretaceous, and probably local, origin. Flint, well cemented with a calcareous, ferruginous however, is not known to occur within the matrix, but some is poorly cemented or loose. present Kuk drainage basin and is probably The sandstone is dark gray on fresh surfaces derived from the Brooks Range. The basal but weathers to buff gray or rusty buff. In gravel is as much as 15 feet thick and is gener- general the color of the mass clearly results ally gradationally succeeded by coarse sand from a blend of transparent quartz, black coal containing isolated pebbles. The sand is grada- and dark accessories, yellow limonite, whitish tionally succeeded by silty clay in some of feldspar, and gray to brown matrix. Many the thicker exposures. Cross-bedding is promi- specimens, however, have a "salt and pepper" nent in the sand and conglomerate, and scour aspect. Cross-bedding and scour and fill and fill structures are widespread. Bones of structure are widespread, but ripple marks are extinct mammals and well-preserved logs up rare. The lenticular sandstone bodies are to 8 inches in diameter occur at several local- almost all less than 10 feet thick, and many of ities and indicate the Pleistocene age of these them thin out within a single cutbank outcrop. sediments. All the fossil-bearing Pleistocene Coal and carbonaceous shale are next in exposures our party examined were uncon- abundance and are conspicuous because they solidated, and, therefore, lack of consolidation are black or gray. The coal is generally black is employed as a criterion for Pleistocene age with vitreous or dull luster and conchoidal in this study. Exceptions to this rule, however, fracture. Material on the outcrops is badly occur at localities 41, 48, and 50, where un- slacked. Much of it is finely laminated and consolidated sand crops out beneath fossil- formed of alternating layers of vitreous and iferous Cretaceous sandstone or well-consoli- dull coal up to 2 mm thick; the dull laminae dated sandstone of presumed Cretaceous age. are further laminated in layers approximately Also a well-cemented, strongly cross-bedded 0.1 mm thick. Coal of this type grades to dull conglomerate at locality 34 is assigned to the argillaceous coal and then to carbonaceous Pleistocene because it differs radically in its shale. coarseness and cross-bedding from the Cre- Bentonitic clay and bentonite are wide- taceous rocks along the Kaolak River. spread in the Kuk drainage basin. Relatively pure bentonite cropping out at localities 19 Cretaceous Rocks and 29 consists of white, puttylike material containing visible biotite flakes. Elsewhere Gray to black shale constitutes more than 75 per cent (estimated) of the Cretaceous rock bentonite outcrops are badly slumped or under in the Kuk drainage basin. Relatively thin water, and it is not apparent whether the layers of sandstone, coal, bentonite, and con- bentonite is relatively pure or mixed with cretionary beds make up the remainder of the shale. Bentonite is considered characteristic Cretaceous sequence (Fig. 2). The shale ranges of the Colville group and occurs in the upper from light gray to black, is noncalcareous, and part of the Nanushuk group (Gryc and others, contains scattered fragments of coaly material 1951; 1956). and amber. Much of the coal and amber is Calcareous concretions and nodular lime- undoubtedly derived from interbedded thin stone layers are conspicuous though quanti-

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tatively unimportant in the Cretaceous rocks. high water sweeping over the flood plain re- Characteristically this material is very fine- enters the main channel. These latter accumu- grained and has conchoidal fracture. Con- lations, when excavated by pick mattock, cretionary rock is black on fresh surfaces but yielded the largest individual collections weathers rusty brown. Some samples of the obtained. A relatively few large fragments of rock effervesced weakly, others freely, in cold amber are scattered over flat bars in essentially dilute hydrochloric acid. Thus the concretion- straight stretches of the river where they ary rock is siderite or calcite-cemented clay. apparently were stranded by falling water. Their scarcity suggests that the circumstances AMBER of their deposition may have been unusual. All the amber, approximately 2 cubic feet Geological Occurrence of Amber packed loose, was collected piece-by-piece from the kinds of places described. We at- Amber is widespread, occurring in most of tempted to separate amber and vegetation by the Cretaceous outcrops on the Kaolak and means of a sluice box, as laboratory experi- Ketik rivers. No amber was noted on bedrock ments with bulk collections of organic debris exposures along the Kuk River, but only three indicated that vegetation could be floated outcrops were examined; only locality 54 was away from the amber. This technique failed, studied in detail, but a thorough search of however, because the vegetable debris in the this large outcrop failed to uncover any amber. field was invariably wet and of approximately Characteristically amber is concentrated on the same specific gravity as the amber. It was the surface of the ground at and immediately not practical to dry large masses of water- downslope from coal outcrops. Thickness of soaked debris in the field. the coal is not a factor in controlling abundance of amber, and in many instances thick coal Character of the Amber layers (4-5 feet) yield little or no amber (localities 23, 26, 35, 54), while very thin layers Clear amber from this area ranges from light (6 inches to 1 foot) are relatively rich (localities golden yellow to deep red and almost to black. 16, 25, and 14). We could not determine Much is opaque and resembles dried pine gum. whether amber occurs in noncoaly shale Most clear amber is crack-free and has sub- because of slumping in the soft poorly con- conchoidal to conchoidal fracture, but the solidated rocks, but we found some amber on opaque amber is generally granular. Most shale outcrops that apparently were unrelated clear pieces contain no bubbles or debris, but to coal beds. We found a few pieces of amber small bubbles and/or small plant fragments imbedded in coal, and in a few instances the are abundant in some specimens. These im- coal appeared to show woody texture. No purities are characteristically distributed in amber was seen in sandstone. Thus we conclude flow layers or bands. Most unbroken speci- that the amber occurs only in association with mens are small (an eighth of an inch in diam- coal or carbonaceous sediments and was eter) teardrop masses, subcylindrical pieces originally deposited in company with woody up to a quarter of a inch in diameter, or debris. irregularly mammillary blobs. The teardrops Amber is ubiquitous in recent river gravel appear to have fallen from a tree branch into and sand along the entire traversed portion of standing water, and the cylinders are the Kuk drainage basin. Almost every sand apparently broken from frozen runnels of sap bar examined yielded at least one piece. The attached to the surface of a branch. These amber is rather well segregated because its cylinders are longitudinally striated in a flow specific gravity is very close to 1.0, and small pattern. The mammillary blobs include speci- fragments as much as half an inch in diameter mens with a sagging pattern of striations and are concentrated in windrows of waterlogged bulges on one side and an apparent attachment twigs, grass, and caribou droppings along the scar suggesting bark patterns on the other. water line. Large particles as much as 2 inches All these shapes indicate that the amber in diameter are relatively abundant in accumu- originated as a sticky viscous liquid exposed lations of twigs, wood, and caribou droppings to the atmosphere. Several occurrences of deposited at the site of eddies formed on bars amber in coal with woody texture, however, by willow stumps, large rocks, or dunelike indicate that at least part of the amber was masses of gravel. Similar accumulations also derived from gum caught in pockets within occur in the lee of the flood-plain banks where the trunks of trees and was, therefore, not in a

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position to trap insects or wind-blown plant occur in the soft shale. Fossil wood is also debris. locally abundant but is not well preserved. Plant microfossils, including at least SO different species of microspores, megaspores, pollen, Fossils in the Amber and algal-like forms similar to Tetraedron and Although shreds of plant debris are wide- Cosmarium, have been recovered from 20 spread, identifiable insect inclusions occur in macerated coal and shale samples. Many of the species, however, are rare or localized in less than 0.1 per cent of the amber particles distribution. larger than 2 mm in diameter. We assume that some of the amber accumulated as gum pocks, within tree trunks, but the abundance of flow- Fossil Foliage marked amber requires an additional explanation for the scarcity of insects. Possibly Two floral types are recognized on the basis insects were not abundant in the amber-proof the 19 megafossil florules studied. One, ducing forest, or the sap may have flowed at a characterized by Podozamites, includes plant season of relatively low insect population, or remains from localities 1, 2, 5, and 9 at the most of the insects of the amber forest may not south end of our traverse, and from our northern- have been highly mobile. most locality, 54. This genus is also present at The following insects, tentatively identified localities 14, 15, and 16 in florules that are by R. L. Usinger and R. F. Smith, have been considered of transitional character. Plants recovered from amber at the indicated lo- most commonly associated with Podozamites calities: are the large-needled conifer Cephalotaxopsis Cretaceous bedrock at locality 21: magnifolia and ferns of the genus Asplenium. Fly of the family Heleidae Baiera and Ginkgo also occur in the northern- Placer accumulation approximately 5 miles most florule as does Nageiopsis. Angiosperm north of locality 54 on the west side of Kuk impressions are rare at localities 2, 5, and 54, Inlet at Pugnik Beach. All specimens of the and taxodiaceous conifers, though present, are first two species here listed from this locality subordinate. This Podozamites flora is desig- are preserved in a single piece of amber: nated the Kuk River flora on the basis of its One fly of the family Empididae representation at locality 54 and contains the Four specimens representing a new genus following genera: and species of the family Eulophidae Asplenium fFicus (Chalcidoidea) Baiera Ginkgo One specimen of a new genus of parasitic Cephalotaxopsis Nageiopsis wasps in the family Ceraphronidae. Cladophlebis Podozamites Credneria Protophyllocladus MARINE INVERTEBRATE FOSSILS Dalbergites Taxodium or Paralax- odium The only marine invertebrate fossil found The second floral type is distinguished by an was a single, fragmental Ostrea collected from abundance of Platanus-\\ke foliage and the soil at the top of the cutbank at locality 19. taxodiaceous conifers Glyptostrobus, Sequoia, This specimen was not necessarily derived and Taxodium or Parataxodium. Regional from bedrock at that locality, and it is specif- relationships indicate that this latter flora ically indeterminate. occurs stratigraphically above the Kuk River flora. Angiosperm-conifer florules occur in the PALEOBOTANY middle part of the traverse at localities 18, 19, 21, 26, 28, 34, and 35. Plants indicative of this General Statement floral type occur also in the southern transitional florules and in the northern transitional Plant megafossils are widespread, and leaf florules at localities 44 and 50 (Fig. 1). Common impressions and cones occur in quantity at associates are the conifer Elatocladus (perhaps many outcrops. Most of the imprints are found Torreya) and the angiosperm Cercidiphyllum. in calcareous nodules or concretions, in some Podozamites, Cephalotaxopsis, ferns, and gink- cases disposed in concentric layers, as in mud goids are rare or absent at the intermediate balls. Impressions in the sandstone members localities. This flora is designated the Kaolak are rare and generally indistinct, and none River flora based on the several localities along

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that river and contains the following genera: with younger florules in the middle, suggests a Cercidiphyllum Populites local syncline superimposed upon the major Elatodadus (perhaps Sequoia synclinal structure in the Arctic Coastal Torreya) Plain province and in the Northern Foothills Glyplostrobus Taxodium or Par- section of the Arctic Foothills province (Payne ataxodium and others, 1951). Laurophyllum Viburnum Platanophyllum Plant Microfossils The floral change recognized in the Kaolak- Kuk area appears to have a rough parallel in Many of the plant microfossils are not yet Cretaceous rocks of the Colville River valley. identified, but distinctive morphologic features Here Arnold (1952) reports a gymnospermous make it possible to separate them readily into flora with abundant Podozamites in the Lower characteristic pteridophyte spores and pollen Cretaceous Nanushuk group and a taxodiaceous of gymnosperm or angiosperm origin. The conifer-angiosperm flora lacking Podozamites relative abundance of microfossils in each in the Upper Cretaceous Colville group. This group can be determined because they are floral development from gymnospermous to numerous in samples from many localities. angiosperm-taxodiaceous conifer aspect seems Gymnosperm pollen is generally most to have occurred regionally and is of sufficient abundant in all samples for which population magnitude to serve as a biostratigraphic counts were made; this includes localities of datum. The Nanushuk flora appears somewhat both the Kuk River and Kaolak River floras. older than the Kuk River flora because of the Pollen of conifers, ginkgoes, and the extinct association in the former of the cycad Nilssonia Caytoniales is included. With the exception of a with Podozamites, but the Kuk River flora is single sample, angiosperm pollen of a type still considered of Early Cretaceous age (per- characteristic of dicotyledons is least abundant haps Aptian or Albian). The flora of the Col- and is absent or forms a minor element in the ville group is approximately equivalent in microfossil floras. No genera or species have composition and age to the Kaolak River flora yet been identified. With a single exception, which is perhaps Albian or Cenomanian. spores are more plentiful than dicotyledonous On the west, the nonmarine Corwin for- pollen and in a few instances are more abun- mation, as restricted by Sable (1956), re- dant than gymnosperm pollen. Most of the portedly contains Ginkgo digitata (Brongniart) spores are unidentified, but some have been Heer, G. laramiensis Ward, Cladophlebis tentatively related to the Polypodiaceae browniana (Dunker) Seward, Nilssonia serotina (Laevigatosporites type), the Osmundaceae Heer, and Asplenium foersteri Debey and (Osmundaf), and the Schizaeacae (Mohriaf Ettingshausen. Thus the Corwin flora appears and Lygodium?). equivalent to both the Kuk River flora and the Microspore populations in more than half Nanushuk flora. of the transitional samples and those associ- Accordingly, the plant-bearing rocks of the ated with the Kuk River flora are characterized Kuk drainage basin are considered to range in by predominance of gymnosperm pollen over age from late Early Cretaceous (perhaps pteridophytic spores. In the remaining spectra Aptian or Albian) to early Late Cretaceous from localities 8, 13, and 54, however, spores (Albian or Cenomanian). In the Kuk drainage are slightly more abundant than pollen. Winged basin transitional florules at localities 14, 15, conifer grains of the Picea and Pinus type are and 16 at the south and localities 44 and 50 the most conspicuous gymnosperm elements at the north contain a mixture of genera and occur throughout the area. With the characteristic of both the Podozamites and exception of the occurrence of 54 per cent angiosperm-taxodiaceous conifer floras. This bladdered grains in sample 26, they are very record of gradual floral change suggests that abundant, however, only in association with sediments were deposited here without any the Kuk River flora or in transitional rocks. appreciable discontinuity sometime between Locality 26 is associated with the Kaolak the Aptian and Cenomanian. An Aptian age, River flora. however, seems unlikely in view of the fact Small pinelike grains are also present in that no verified occurrences of Aptian rocks most spectra and are somewhat abundant in are known in this area (Imlay and Reeside, Kuk River and transitional samples, especially 1954). Concentration of the older florules at 3, 4, and 16. Grains of the same sort were first the northern and southern ends of the area, related to the Caytoniales by Thomas (1925)

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who found them within the caytonialean If present, dicotyledonous pollen generally microsporophyll, Antholithus arberi, from the amounts to less than 3 per cent of the micro- Jurassic of England. Harris (1941) instituted flora, although more than 13 per cent is present the name Caytonanthus for the pollen-bearing in one sample from the area of the Kuk River structures and delimited three species for flora at locality 8. This occurrence, however, is microsporophylls and microspores of the discredited because angiosperm pollen is Caytonanthus type from the Jurassic of England nowhere else so abundant and because most and Greenland. The Alaskan specimens so of the grains are of the same morphologic type. closely resemble these microspores in mor- Thus, some of the dicotyledonous pollen at phology and size as to leave no doubt of their locality 8 is probably derived largely from a relationship, but they appear distinct from the plant living in the area today and represents species described by Harris. Caytoniales contamination of the sample. Angiosperm pollen has also been recorded from the Keuper pollen from all the rock samples is three- of Poland (Pautsch, 1958), Rhaetic-Liassic of furrowed and simple with a smooth or reticu- Sweden (Thomas, 1925; Seward, 1931), and lated surface pattern. Lower and Upper Cretaceous of Russia (Zauer In samples associated with the Kaolak River and Mschedvischvili, 1954). J. L. Browning, flora gymnosperm, pollen and spores are almost (1958, personal communication) also reports equally abundant, although pollen is slightly pollen of the same type as abundant in Alaskan more plentiful at localities 21, 23, and 26. Jurassic rocks. "Taxodiaceous-like" pollen is far more Pollen similar to that of some living members numerous in spectra from localities 19, 21, and of the Podocarpaceae occurs in subordinate 23 than winged grains of the Pinaceae and amounts among all Kuk River and transitional Podocarpaceae, but the reverse condition microfossil floras, but reference of this mate- obtains in population 26. Where present the rial to the podocarps is only tentative. Grains Caytoniales and Ginkgoales are a minor of the "taxodiaceous type," probably repre- element in the Upper Cretaceous microfossil senting several genera or even families, are pres- floras. Angiosperm pollen is scarce as in the ent but abundant in only a few places in underlying rocks except at locality 23 where it most Kuk River and transitional populations. still constitutes less than 5 per cent of the More than 45 per cent of taxodiaceous pollen population. Simple, smooth, monolete and in sample 4 is, however, an exception to the trilete spores are most abundant among the general rarity of this material in the Kuk pteridophytes, as in the underlying transition River and transition populations. Pollen of and Lower Cretaceous rocks. the Ginkgoales also occurs as a minor con- stituent in most spectra from the older rocks. Comparison of Megafossil and Microfossil Spore content differs considerably between Floras populations in the Kuk River and transition rocks. Most abundant and widespread are Differences and similarities between the smooth, reniform monolete Laevigato-sporites megafossil and microfossil floras may be pointed type and simple, psilate, trilete types sug- up through a brief comparison. Only two genera gesting Polypodiaceae and/or Gleicheniaceae. of fern megafossils occurring at five Kuk River Osmunda-\ike spores are associated in micro- and transitional localities are noted. These fossil floras from localities 4, 8, 16, 35, and 54, genera have affinities with the Osmundaceae and grains characteristic of the Schizaeaceae, and Polypodiaceae, and possibly both are a family now chiefly tropical American in represented by the microfossils that appear to distribution, occur in samples 4, 8, and 16. be related to these families. The wide dis- Microspores similar to the Alaskan fossils are tribution and general abundance of spores found among several schizaeaceous genera, at indicate that ferns and fern allies were wide- least two of which appear to be represented spread and diverse in this area during dep- among the Cretaceous material. Rare speci- osition of both the Kuk River and Kaolak mens of the Mohria type have also been noted River floras. Their foliage, however, apparently in Kaolak River samples 19 and 25, although is largely unpreserved. they are abundant only at locality 8 which is Nageiopsis, Podozamites, and Elatodadus in the area of the Kuk River flora. Spores of among the megaflora gymnosperms are of the Lygodium type are confined to transitional unknown affinities, but the remaining gymno- samples 16 and 44, and questionable specimens sperms are members of the Ginkgoales, Cepha- occur at locality 8. lotaxaceae, and Taxodiaceae. Pollen repre-

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senting the latter groups is probably present designated transitional or Late Cretaceous in in the microfloras, and a great abundance of age (perhaps Albian or Cenomanian). If the taxodiaceous-like grains parallels the abundance microfossil floral evidence from the same of taxodiaceous foliage in the Kaolak River localities and from other localities in the same flora. None of the megafossil floras, however, stratigraphic sequence is considered alone and contains species referable to the single most according to the same standard, the conclusion abundant and conspicuous microfossil element, is that these rocks may be as young as late the Pinaceae, nor is there evidence of the Early Cretaceous but cannot be Late Cre- presence of the Caytoniales. Both pine and taceous. These correlations are further sup- spruce, or closely related plants, must have ported by consideration of the known oc- been abundant in the Alaskan Cretaceous currences of some of the specific elements of vegetation according to their microfossil both the microfossil and megafossil floras. occurrence, and thus their absence in the The differences in composition between the megafloras is conspicuous. The Caytoniales, Kaolak River megafossil flora and associated represented by Sagenopteris, are widespread microfossil flora require explanation. Many of in Early Cretaceous megafossil floras else- the fossil pollen grains and spores could not where and would be expected in rocks of this have been derived from any of the plants in age in northern Alaska. We cannot be certain the megafossil flora. Many leaves are not how persistent this group may have been after represented by plant microfossils. Many causes the Early Cretaceous, but caytonialean pollen may contribute to these differences; the fol- is such a minor element in association with the lowing are of possible importance: inadequate Kaolak River flora that the group was probably collections, misidentification of fossils, failure becoming extinct in this area at the time of of preservation or selective preservation during deposition. fossilization, differential destruction of pollen Nothing comparable to the angiosperm- during extraction, differences in dissemination conifer florules in the Kaolak River flora is of megascopic and microscopic plant parts, present in the accompanying microfossil floras and variation in the number of leaves and where dicotyledonous pollen is scarce or absent microspores produced by different plants. in all samples. No resemblance was noted Our collections should be adequate. We between any of the fossil grains and Recent searched every available outcrop for leaf pollen either of angiosperm genera represented fossils, obtained rock specimens from several by fossil leaves or of Recent related genera. beds at most outcrops, and sampled most of The floristic similarity between the megafossil the coal beds. We obtained microfossils in large floras and microfossil floras is thus not pro- quantity from most of these collections. Thus nounced, nor are the microfossil floras closely all abundant species should be represented in related floristically to other microfossil floras our collections. Misidentifications of fossils of similar age to which they have been com- also seem a minor factor, because most of the pared. This is of limited significance, however, leaves or the spores would have to have been because few Mesozoic pollen floras are known incorrectly identified to produce the observed from high northern latitudes. The presence of conflict. abundant conifer pollen with affinities with Leaves and other megascopic plant parts the Pinaceae and Taxodiaceae? and of some may not be preserved for many reasons. The dicotyledonous pollen as a minor element in plants may grow in an unfavorable location in these microfossil floras does, however, pose an regard to basins of deposition, or growth interesting problem. Arnold (1952) pointed habits may largely prevent dissemination. out that in this general area, "In distinguishing The leaves may remain attached to the plant between Upper and Lower Cretaceous on the until they rot, or leaves and other organs may basis of plant remains, the criterion is mainly decay readily. These causes could account for the relative abundance of dicotyledons and the rarity of fern and fernlike foliage in com- other plant types." This criterion has also had parison to the abundance of spores produced wide application elsewhere. Thus, correlation by these plants. The tremendous number of has been based on assigning floras with an spores produced by modern ferns having insignificant angiosperm content to the Lower relatively little foliage suggests that spores of Cretaceous and those dominated or wholly ancient Pteridophyta should be much more composed of dicotyledonous plants to the abundant than leaves in sediments. Pollen of Upper Cretaceous. On this basis, megafossil Cercidiphyllum, Populus, and members of the florules from localities 14 through 50 have been Lauraceae is thin-walled and delicate. Thus,

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if the pollen of the ancient and living plants is qualifications, but correlation has been similar, possibly, microspores of Cercidiphyllum, generally satisfactory. These correlations are Populites, and Laurophyllum were not pre- statements of the similarity or dissimilarity of served or were destroyed in the extraction leaf-fossil collections and are not per se cor- process. Pollen from plants pollinated by relations of like or unlike prehistoric plant agents other than wind may not reach the assemblages or correlations of synchronous or sites of sedimentary accumulation. Further- heterochronous rocks. Correlation or compari- more, entomophilous plants produce smaller son of fossil occurrences is based directly on amounts of pollen in proportion to the per- observable phenomena and is valid to the fection of their adaptation to entomophily. extent of the observer's competence. Interpre- This is significant because the nearest living tations of the age of the rocks or the purported relatives of Dalbergites and Viburnum and some composition of the plant assemblages involve members of the mulberry family, to which the at least one additional level of abstraction. genus Ficus belongs, are insect pollinated. The Thus statements that rocks containing leaf absence of platanaceous pollen belonging to fossils are Early or Late Cretaceous may be Credneria and Platanophyllum is more difficult confidently accepted as indicating only that the to explain, because living sycamores produce fossils are dominantly angiosperms or gymno- large amounts of light, wind-borne pollen. sperms. Assertion that gymnosperm forests Finally, the pollen of some Cretaceous angio- were replaced by angiosperm forests during sperms may be so different from pollen of their a very short period of time, which marked the modern counterparts that generic identification end of an Early Cretaceous time period, is no of these fossil pollen grains is unlikely. more than a convenient interpretation of The great abundance of coniferous pollen presently available evidence. In the case of the grains, particularly pinaceous types, in our Kaolak River megafossil flora and its associ- collections may result in part from the enormous ated microfossil flora, we have strong evidence pollen production of these trees and the adap- that fossil leaf assemblages do not necessarily tability of their microspores to wind dissemi- furnish an unbiased record of the plant com- nation over wide areas. Therefore pine and/or munities living at the time. This also applies spruce forests growing on uplands and unlikely to the fossil pollen and spores. The conflicting to supply foliage to deposits of nearby lowland evidence regarding the composition of the basins could contribute large quantities of flora of this area at the time the rocks under pollen to sediments characterized by plant consideration were deposited further dis- megafossils representative of the lowland credits the notion that the Early Cretaceous- environment. The presence of Platanophyllum Late Cretaceous boundary, as currently de- and Taxodium or Parataxodium in our foliage fined by megafossil floras, is of essentially the collections reinforces this hypothesis. same age wherever noted. An important general conclusion to be drawn from the above CONCLUSIONS argument seems to be that many of the time- rock units described in the literature are If current assumptions concerning the time better treated as biostratigraphic units. A at which angiosperms became dominant over clear distinction should be made between gymnosperms are accepted, the megafossil interpretive, formal time-rock units and de- flora is most readily interpreted as Late Cre- scriptive, empirical biostratigraphic units. taceous, but the associated microfossil flora Lack of marine fossils, abundance of plant should be considered Early Cretaceous. Inas- debris and coal, and widespread evidence of much as the leaves probably could not be channel-type deposition indicate that the significantly younger than the pollen and Cretaceous rocks of the Kuk drainage basin spores, the basic assumption that an angio- are almost, if not entirely, of nonmarine origin. sperm flora is Late Cretaceous and a gymno- Bentonitic sediments are abundant, particularly sperm assemblage is Early Cretaceous must be in the middle portions of our traverse. Gryc critically evaluated. Heretofore distinction (Gryc and others, 1951) and Detterman (in between rocks of these two ages has been Gryc and others, 1956) state that bentonite is exclusively based on evidence from leaf fossils. typical of the nonmarine Prince Creek for- As a result, correlations have been precise and mation of the Colville group and that all but consistent insofar as available collections are the uppermost Niakogon tongue of the non- dominated either by angiosperms or gymno- marine Chandler formation of the Nanushuk sperms. Some mixed assemblages introduce group contain little or no bentonite or tuff. The

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Niakogon tongue, however, does contain Carpenter, F. M., and others, 1937, Insects and arachnids from Canadian amber: Toronto appreciable bentonite (Gryc and others, 1956). Univ. Studies, Geol. ser., v. 40, p. 7-62, 12 In addition, the rocks of the nonmarine Corwin Figs. formation, described by Sable (1956) at Cape Gryc, G., Patton, W. W., Jr., and Payne, T. G., Corwin, appear to resemble the Cretaceous 1951, Present Cretaceous stratigraphic nomen- clature of northern Alaska: Washington Acad. rocks of the Kuk drainage basin. Thus evidence Sci. Jour., v. 41, p. 159-167 from both plant megafossils and lithologic Gryc, G., and others, 1956, Mesozoic sequence in character indicates that the rocks of the Kuk Colville River region, Northern Alaska: Am. drainage basin are equivalent in part to the Assoc. Petroleum Geologists Bull., v. 40, p. 209-254 Chandler and Prince Creek formations of the Harris, T. M., 1941, Caytonianthus, the micro- Colville River region and the Corwin formation sporophyll of Caytonia: Annals of Botany, n. of Cape Corwin. However, the Kuk drainage s., v. V, no. 17, p. 47-58 basin is well separated from the type areas of Kurd, P. D., Jr., Smith, R. F., and Usinger, R. L., 1958, Cretaceous and Tertiary insects in the Chandler, Prince Creek, and Corwin Arctic and Mexican amber: 10th Internat. formations, and no physical continuity has Cong. Entomology, Montreal Proc., 1956, v. been established. Thus definite formational 1, p. 851 assignments are premature. Imlay, R. W., and Reeside, J. B., Jr., 1954, Correla- Leaves of taxodiaceous conifers are abun- tion of the Cretaceous formations of Greenland dantly represented at the eight localities where and Alaska: Geol. Soc. America Bull., v. 65, p. 223-246 both amber and plant megafossils occur. Kirschner, G., 1950, Amber inclusions: Endeavour, Taxodiaceous conifers occur at three localities v. 9, no. 34, p. 70-75 which did not yield amber, and amber was Pautsch, M. E., 1958, Keuper sporomophs from collected at seven bedrock localities which did Swierczyna, Poland: Micropaleontology, v. 4, not provide plant fossils. Amber, however, was no. 3, p. 321-325 never found with florules lacking remains of Payne, T. G., and others, 1951, Geology of the Arc- tic slope of Alaska: U. S. Geol. Survey Oil and taxodiaceous conifers. Although the Pinacae Gas Inv., Map OM 126 are also strongly represented in our collections Sable, E. G., 1956, New and redefined Cretaceous by pollen, pines are not considered likely formations in western part of Northern Alaska: sources of amber in this region. There is no Am. Assoc. Petroleum Geologists Bull., v. 40, direct relationship between the occurrence of p. 2635-2643 Seward, A. C., 1931, Plant life through the ages, a pine pollen and amber, and pine pollen is most geological and botanical retrospect: Cambridge abundant in the rocks containing the Kuk University Press, xxi plus 601 p. River flora where amber is absent or rare. Thomas, H. H., 1925, The Caytoniales, a new group Smiley has since collected amber in associ- of angiospermous plants from the Jurassic rocks ation with taxodiaceous conifer remains in a of Yorkshire: Royal Soc. London Philos. Trans., lignite quarry in southwestern North Dakota. ser. B, v. 213, p. 299-363 Kirschner (1950) reports that twigs of Tertiary Usinger, R. L., and Smith, R. F., 1957, Arctic amber: Pacific Discovery, v. 10, p. 15-19 swamp cypresses ("cupressoids" sic) are more Zauer, V. V., and Mchedvischvill N. D., 1954, abundant among amber inclusions than are Spore-pollen complexes from Mesozoic and needles of pines and firs. Thus the fossil resin Cenozoic deposits of the region about Tiumen: of the Kuk drainage basin was probably Materialy po palinologii i stratigrafii, Sbornik, originally derived from taxodiaceous trees Vsesoivznyi Geol. Inst., Leningrad, p. 124-158 growing close to lakes, coastal swamps, or other DEPARTMENT or GEOLOGY, UNIVERSITY OF ILLI- water bodies. NOIS, URBANA, ILL.; DEPARTMENT OF GEOLOGY, MACALESTER COLLEGE, ST. PAUL, MINN.; GEO- REFERENCES CITED CHRONOLOGY LABORATORIES, UNIVERSITY OF Arnold, C. A., 1952, Paleobotanical investigations ARIZONA, TUCSON, ARIZ. in Naval Petroleum Reserve No. 4, Alaska: MANUSCRIPT RECEIVED BY THE SECRETARY OF THE Science, v. 116, no. 3003, p. 61-62 SOCIETY, MARCH 30, 1959

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