Grebenka Section

Yelisseev Locality

This page describes the plant fossil inventory from each of the Yelisseev locality sites. Here only the plants that repeatedly occur throughout a range of sedimentological settings are listed because repeated occurrence is required for reliable community reconstruction. This is followed by an interpretation of the ecological associations and growth environment represented by each site.

Site 1
Sedimentary context: Conglomerate bed, tabular, massive bedded, clast supported, cobble-sized clasts.
Floral remains: No plant material visible.

Site 2 (25 and 25a) Fossil Images
Sedimentary context: These small exposures probably represent a lateral equivalent to the section represented by Sites 9 to 13 (see below). Fine to medium grained sandstone is underlying a conglomerate.

Floral remains: Birisia jelisejevii (Krysht.) Philipp., B. ochotica Samyl., Coniopteris (Birisia?) grebencaensis Philipp, Arctopteris penzhinensis E. Lebed., Asplenium dicksonianum Heer, Nilssonia serotina Heer, Cephalotaxopsis heterophylla Hollick, C. intermedia Hollick, Araucarites anadyrensis Krysht., Pseudolarix ? sp., Pityophyllum ex gr. nordenskioldii (Heer) Nath., Pityospermum aff. piniformis Samyl., Pityostrobus sp. 2, Menispermites minutus (Krysht.) Herman et Shczep., M. ex gr. septentrionalis Holl., Platanus louravetlanica Herman, Araliaephyllum dentatum Philipp., Scheffleraephyllum venustum (Phillipp.) Phillipp., Trochodendroides arctica (Heer) Berry, Grebenkia anadyrensis (Krysht.) E. Lebed..

Ecological interpretation: Lack of exposure prevented a reliable interpretation of the sedimentological context. The composition and preservation state of the floral assemblage, however, suggests an allochthonous sample of a semi-mature floodplain community consisting of a mixed conifer and angiosperm tree/shrub component with a fern and cycadophyte understorey.

Site 3 (28) Fossil Images
Sedimentary context: This is a small exposure which probably represents a lateral equivalent to Sites 9 to 13 (see below). Medium to coarse-grained sandstones occurr just above a sharp contact with a mudstone.

Floral remains: Thallites sp. cf. Marchantites jimboi (Krysht.) Krysht., Gleichenia zippei (Corda) Sew., Birisia jelisejevii (Krysht.) Philipp., Coniopteris? sp., Arctopteris penzhinensis E. Lebed., Hausmannia bipartita Samyl. et Shczep., Ginkgo ex gr. adiantoides (Ung.) Heer (very abundant),  Cephalotaxopsis heterophylla Holl., C. intermedia Holl., Araucarites anadyrensis Krysht., Pityophyllum ex gr. staratchinii (Heer) Nath., Pityostrobus sp. 2, Sequoia sp. (cone), Sequoia sp. (cone scale), Elatocladus smittiana (Heer) Sew., Grebenkia anadyrensis (Krysht.) E. Lebed.

Ecological interpretation: This assemblage is dominated by conifers, probably trees, with a minor angiosperm component (Grebenkia). The stature of Grebenkia is unknown but it may have been a shrub. The paucity of angiosperms may suggest a more mature seral developmental phase than that represented by Site 2. The understorey was dominated by a variety of ferns. Also represented here is a pond/stream margin component consisting of the water fern Hausmannia and cf. Marchantites, a colonizer of wet mud surfaces.

Site 4 (30a) Fossil Images
Sedimentary context: A small exposure, probably a lateral equivalent to part of the section represented by Sites 9 to 13 (see below). Medium- to coarse-grained sandstones occur, and the Site appears to be a laterally equivalent horizon to that of Site 3.

Floral remains: Birisia ochotica  Samyl., Coniopteris anadyrensis Phillipp., C. (Birisia?) grebencaensis Phillipp., Asplenium dicksonianum Heer, Nilssonia serotina Heer, Cephalotaxopsis intermedia Holl., Araucarites anadyrensis Krysht., Pagiophyllum triangulare Pryn., Pityophyllum ex gr. nordenskioldii (Heer) Nath., P. ex gr. staratchinii (Heer) Nath., Sequoia cf. minuta Sveshn., Tollia sp., Elatocladus smittiana (Heer) Sew., Menispermites ex gr.  septentrionalis Holl., Sorbites asiatica Phillipp., Myrtophyllum acuminata (Phillipp.) Herman, Araliaephyllum dantatum Phillipp., Scheffleraephyllum venustum (Phillipp.) Phillipp..

Ecological interpretation: This appears to be another sample, as with Site 2, of a semi-mature floodplain community consisting of a mixed conifer and angiosperm tree/shrub component with a fern and cycadophyte understorey. The assemblage is rich in well preserved conifer shoot remains, suggesting limited in-stream transport of these components.

Site 5 (30) Fossil Images

Sedimentary context: A small exposure, probably a lateral equivalent to part of the section represented by Sites 9 to 13 (see below). Isolated siltstone with no sedimentary structure detail.

Floral remains: Birisia jelisejevii (Krysht.) Phillipp., B. ochotica Samyl., B.? oerstedtii (Heer) E. Lebed., Coniopteris anadyrensis Phillipp., C. (Birisia?) grebencaensis Phillipp., Asplenium dicksonianum Heer, Cladophlebis sp. 1, Cephalotaxopsis heterophylla Holl., Pagiophyllum triangulare Pryn., Sequoia ex gr. reichenbachii  (Gein.) Heer, Sequoia sp.

Ecological interpretation: This assemblage lacks an angiosperm component but displays a diversity of ferns amongst the remains of three conifer genera. We interpret this as a mature conifer-dominated forest with a fern understorey.

Site 6 (31) Fossil Images

Sedimentary context: A small exposure, probably a lateral equivalent to part of the section represented by Sites 9 to 13 (see below). Medium-grained sandstones.

Floral remains: Birisia? oerstedtii (Heer) E. Lebed., Coniopteris (Birisia?) grebencaensis Phillipp., Asplenium dicksonianum Heer, Elatocladus smittiana (Heer) Seward, Scheffleraephyllum venustum (Phillipp.) Phillipp..

Ecological interpretation: This depauperate assemblage is too limited to interpret.

Site 7

Sedimentary context (Fig. 6): At a cliff section small scale leveé deposits are exposed. Here amalgamating proximal crevasse splay gravels and sands, with in situ tree trunks and roots, demonstrate that as the overbank floods passed, adult trees growing on the river bank were not killed and continued growing after the event. The trees slowed down the overbank flow profoundly, and caused rapid sediment deposition and limited erosion of the leveé. These crevasse splay deposits overlie a paleosol, with intensive rooting and destratification. The comparably mature soil at this section is rather untypical for the Yelisseev section at large, which in places has rootlet beds with only a very weak pedogenic overprint.

Ecological interpretation: This represents a mature riparian community dominated by trees. The lack of identifiable preserved plant material prevents a detailed taxon-based interpretation of the community.

Site 8 (33) Fossil Images

Sedimentary context: A small exposure, probably a lateral equivalent to part of the section represented by Sites 9 to 13 (see below). Isolated sandstones with poorly preserved plant remains and no sedimentary structure detail.

Floral remains: Phyllites sp. Equisetites sp., Gleichenites asiatica Phillipp., Birisia jelisejevii (Krysht.) Phillipp., B. ochotica Samyl., Coniopteris (Birisia?) grebencaensis Phillipp., Asplenium dicksonianum Heer, Hausmannia bipartita Samyl. et Shczep., Sphenopteris sp. 2, Florinia ? sp., Menispermites ex gr. septentrionalis Holl., Platanus sp., Scheffleraephyllum venustum (Phillipp.) Phillipp., Grebenkia anadyrensis (Krysht.) E. Lebed.

Ecological interpretation: This poorly preserved assemblage appears to have undergone a marked degree of transport and, although information on the sedimentary context is limited, the sandstone may represent a channel fill. The community represented is almost devoid of conifers and is made up of water plants (Hausmannia), early pioneer plants of disturbed river banks such as Equisetites, together with plants of slightly more stable settings such as the ferns Gleichenites and Birisia. The angiosperm component is typical of a shrub community in a frequently disturbed riparian setting.

Site 9

Sedimentary context: Small erosional gulley formed by stream action. Site 9 is located at the base with Sites 10 to13 at successively higher levels up the gulley.

Site 9 begins with a coarsening-upward bed. At the base of this sequence an organic-rich ripple-drift cross-laminated and horizontally laminated siltstone occurs, which includes rootlets, three dimensionally preserved plant remains, and invertebrate bioturbation. The siltstone grades into a ripple-drift and horizontally laminated very coarse-grained sandstone, with floating large plagioclase grains in a mud matrix (probably ash) at the top, sharply followed by massively bedded mudstone, and massively bedded coarse-grained sandstone. Petrographical evidence and sedimentary context suggest that the increasing grain-size was caused by increased sedimentation on the floodplain due to an influx of volcanic ash. Subsequent mud and sandstone beds represent further interfingering of floodplain fines and overbank sandstones.

Floral remains: Equisetites sp., Ginkgo sp., Nilssonia serotina Heer, N. yukonensis Hollick, Araucarites anadyrensis Krysht., Cephalotaxopsis intermedia Holl., Elatocladus smittiana (Heer) Sew., Pagiophyllum triangulare Prynada, Sequoia ex gr. reichenbachia (Gein.) Heer, Sequoia sp. (cone), Pityophyllum ex gr. staratchinii (Heer) Nath., P. ex gr. nordenskioldii (Heer) Nath., Menispermites ex gr. septentrionalis Holl., angiosperm leaf fragment.

Ecological interpretation: The floral remains are well preserved, minimally transported, and indicate that a mature forest was growing in the vicinity. Conifers dominate the assemblage and those with some xeromorphic features (Araucarites, Pagiophyllum, Sequoia reichenbachii and Elatocladus) are particularly abundant. Ferns are absent while cycadophytes and angiosperms are rare. The association with small in situ roots suggests that a herbaceous or pioneer community was also growing proximally and may be the source of some components of the assemblage (e.g. Equisetites). The increased sedimentation rate indicated by the sedimentary succession may explain why this forest community with a semi-dry aspect was preserved. Extraneous sediment influx, a sudden increase in discharge, or fall in the relative position of the valley floor, would have raised the water table and allowed erosion, transport and deposition of forest material from a previously well drained setting to be captured in the fossil record.

Site 10 Fossil Images

Sedimentary context: isolated coarse-grained siltstones and fine-grained sandstones with no records of sedimentary structures.

Floral remains: Equisetites sp., Coniopteris (Birisia?) grebencaensis Philipp., Birisia ochotica Samyl., ? tree fern rhizome (vertical stem) with scale leaf marks and rachis scars.

Ecological interpretation: Equisetites was particularly abundant at this Site and, together with the limited fern component, suggests an immature pioneer community, possibly similar to an Albian alaskan Birisia marsh (Spicer and Herman, in press).

Site 11 (53) Fossil Images

Sedimentary context: Fine-grained well sorted sandstone which appears to be wave rippled and cross-laminated. The leaves drape ripple surfaces. Some iron stained root traces occur.

Floral remains: Gleichenites asiatica Philipp., G. zippeii (Corda) Sew., Birisia jelisejevii (Krysht.) Philipp., B. ochotica Samyl., Coniopteris (Birisia?) grebencaensis Philipp., Asplenium dicksonianum Heer., Nilssonia alaskana Holl., Cladophlebis sp., Hausmannia bipartita Samyl. et Shczep., Platanus louravetlanica Herman, platanoid fruits, Menispermites markovoensis Philipp., Sapindophyllum sp., Menispermites sp., Araliaephyllum ? sp..

Ecological interpretation: This assemblage lacks conifers but contains early colonisers such as the ferns Gleichenites and Birisia, plants of open water such as Hausmannia and angiosperms typical of semi mature communities of frequently disturbed riparian environments. Some compound leafed angiosperms (Sapindophyllum sp.) were found with leaflets intact, suggesting minimal transport prior to deposition.

Site 12 (52) Fossil Images

Sedimentary context: Fine-grained well sorted sandstone. Plant material not only oriented parallel to bedding but also crossing bedding surfaces, although the surfaces are more or less obscured by plant material.

Floral remains: Asplenium dicksonianum Heer, Scheffleraephyllum venustum (Philipp.) Philipp..

Ecological interpretation: This assemblage is too limited for reliable interpretation.

Site 13 (51) Fossil Images

Sedimentary context: Well sorted siltstone to fine-grained sandstone with wave ripple cross-lamination, plant material sometimes oriented normal to the weakly developed bedding and some rooting.

Floral remains: Thallites sp. cf. Marchantites jimboi (Krysht.) Krysht., Equisetites sp., Gleichenia pseudocrenata E.Lebed., Gleichenites asiatica Philipp., G. zippeii (Corda) Sew., Birisia jelisejevii (Krysht.) Philipp., B. ochotica Samyl., Cladophlebis sp., Coniopteris (Birisia?) grebencaensis Philipp., Asplenium dicksonianum Heer, Hausmannia bipartita Samyl. et Shczep., Cephalotaxopsis ex gr. intermedia Holl., Menispermites ex gr. septentrionalis Holl., Scheffleraephyllum venustum (Philipp.) Philipp., Sapindophyllum sp., Cissites sp..

Ecological interpretation: Open water ferns (Hausmannia), very early colonizers (cf. Marchantites, Equisetites), and early successional ferns (Gleichenites and Birisia) all suggest a strong wetland pioneer plant component to this assemblage. However later successional phases such as that composed of angiosperms, and even the conifer Cephalotaxopsis, indicate a contribution from a nearby semi-mature floodplain community.

Site 14 (50) Fossil Images

Sedimentary context: isolated siltstone, no records of sedimentary structures.

Floral remains: Coniopteris (Birisia?) grebencaensis Phillipp., Scheffleraephyllum venustum (Philipp.) Philipp..

Ecological interpretation: This assemblage is too limited for reliable interpretation.

Site 15 (54 - Float) Fossil Images

Sedimentary context: isolated siltstone, no records of sedimentary structures.

Floral remains: Gleichenia pseudocrenata E. Lebed., Gleichenites asiatica Philipp., Birisia jelisejevii (Krysht.) Philipp., B. ochotica Samyl., B. ? oerstedtii (Heer) E. Lebed., Coniopteris (Birisia?) grebencaensis Philipp., Asplenium dicksonianum Heer, Hausmannia bipartita Samyl. et Shczep., Scheffleraephyllum venustum (Philipp.) Philipp., Cissites sp. 2.

Ecological interpretation: No interpretation is attempted on float.

Site 16

Sedimentary context: isolated siltstone, no records of sedimentary structures.

Floral remains: leaf mat of Grebenkia anadyrensis (Krysht.) E. Lebed., Cladophlebis sp., Birisia ochotica Samyl., Platanus louravetlanica Herman.

Ecological interpretation: This assemblage represents a mat of leaf material derived from Grebenkia. Evidently the leaves fell from the plant synchronously suggesting a deciduous habit. Although limited, the assemblage suggests a semi-mature riparian margin community.

Site 17 Fossil Images

Sedimentary context: isolated siltstones, no records of sedimentary structures.

Floral remains: Birisia jelisejevii (Krysht.) Philipp., B. ochotica Samyl., B. ? oerstedtii (Heer) E. Lebed., Coniopteris (Birisia?) grebencaensis Philipp., Arctopteris penzhinensis E. Lebed., Cycadites hyperborea (Krysht.) E. Lebed., Ginkgo ex gr. lepida Heer, Cephalotaxopsis intermedia Holl., Araucarites anadyrensis Kryst., Pityophyllum ex gr. staratchinii (Heer) Nath., Menispermites markovoensis Philipp., Myrtophyllum acuminata (Philipp.) Herman, Araliaephyllum medium (Philipp.) Herman, Scheffleraephyllum venustum (Philipp.) Philipp., Scheffleraephyllum sp., Cissites sp. 3, Grebenkia anadyrensis (Krysht.) E. Lebed..

Ecological interpretation: This assemblage represents a limited diversity (Araucarites, Pityophyllum, Cephalotaxopsis) conifer community with an angiosperm shrub layer and fern and cycadophyte groundcover. Some early pioneer plants are represented also (Birisia species) but these taxa persist into more stable communities and may not represent an admixture of seral stages.

Site 18

Sedimentary context: Site 18 is a marker bed 3 m above the base of the measured section (Fig. 5). Detailed sedimentological logging of the continuous section starts from this point.

At the base of the measured section (Fig. 5) normal graded beds were observed, going from coarse-grained sandstone to silt- and mudstone. The beds are massively bedded in their lower part, trough cross-laminated near the top, and are interpreted as rapidly deposited hyperconcentrated flow deposits interfingering with floodplain fines. The sandstones are poorly- to fairly well-sorted, but grains are angular to subangular, indicating short transport from their source. To a large extent, the sandstones are composed of single crystal plagioclases, hornblendes, and biotites, and to a minor degree epiclastic rock fragments. We interpret these petrographically anomalous beds to be composed of only slightly reworked pyroclastic material (ash). Samples 96RAS68 and 96RAS69 where taken from here for 39Ar/40Ar analysis, and confirm that the biotites are of a very narrow age interval, i.e., not derived from reworked material from several sources.

At Site 18 level, the mud-, silt- and sandstones of the floodplain succession are followed abruptly by an approximately 40 m thick succession of amalgamating stream channel conglomerates with sandstone intercalations, which grade into pebbly stream channel sandstones. Typically, the sandy channels were gradually abandoned and filled by floodplain fines. This interval is barren with respect to well preserved fossils, only yielding a few beds with allochtonous drift wood and plant hash. Notably, the first major floodplain fines after the stream channel are barren. Upsection, however, they show a gradual increase in pedogenic activity and plant remains, i.e., repeated incipient plant colonization.

Site 19

Sedimentary context: Below and above Site 19 there are pebbly sandstone stream channel deposits. In these beds angular allochthonous wood pieces occur, 5 - 10 cm in length. Although fragmentary, these wood remains appear not to have been transported any great distance, i.e., they are not water worn or abraded. Site 19 is a bedding surface with transported platanoid leaves.

Floral remains: Coniopteris (Birisia?) grebencaensis Philipp., Ginkgo ex gr. adiantoides (Ung.) Heer, Cephalotaxopsis intermedia Holl., Araucarites anadyrensis Krysht., Pityophyllum ex gr. staratchinii (Heer) Nath., Pityostrobus sp., Platanus louravetlanica Herman (abundant and large leaved), Dicotylophyllum sp., cf. Palaeonuphar nordenskioldii (Heer) Bell.

Ecological interpretation: This assemblage is dominated by large platanoid leaves found together with ferns, ginkgos and several conifers. The context of a channel fill suggests that the platanoids, if not the other taxa, were river margin plants and it is likely that the other more delicate leaf remains (the ferns, other angiosperms, and even Cephalotaxopsis) were similarly situated. The more robust components (Araucarites and Ginkgo) may have been transported further within the stream channel, but equally could have come from a more mature community incised by a cut bank.

Site 20

Sedimentary context: One metre above Site 19 stream channel sandstones are followed by fragmentary plant horizons (Site 20). These are composed of plant hash and small wood fragments forming thin, 1 cm thick, laminae within medium- to coarse-grained massively bedded sandstones, fining up to siltstone over 1 m. Rooting is common above these hash horizons. These beds are interpreted to represent channel abandonment fill with incipient paleosol formation.     

Floral remains: Sagenopteris variabilis (Velen.) Velen., Nilssonia alaskana Holl., N. serotina Heer, Cephalotaxopsis intermedia Holl., Araucarites anadyrensis Krysht., Menispermites ex gr. septentrionalis Holl., Dalembia vachrameevii E. Lebed. et Herman, Grebenkia anadyrensis (Krysht.) E. Lebed., Dicotylophyllum cf. Paleonuphar nordenskioldii (Heer) Bell., Dicotylophyllum sp. B.           

Ecological interpretation: This conifer/angiosperm dominated assemblage represents the communities growing around an abandoned channel during its infill stage. This assemblage appears to have been formed during rapid influx of silt- and sand-laden water during flooding of a nearby active channel. This washed in plant material from the intervening vegetation. Ferns and early successional plants are notably absent suggesting a predominantly cycadophyte understorey beneath a conifer forest with a diverse angiosperm shrub layer. Plants subsequently colonised the shallow water, or subaerial sediments, that captured this assemblage.

Site 21

Sedimentary context: A descrete well-sorted planar-laminated siltstone bed approximately 30 cm thick within the channel-fill sequence containing Site 20. Site 21 is interpreted to be a floodplain pond sediment, set within an abandoned channel sequence, with incipient paleosol development.

Floral remains: Well preserved accumulation of Cycadites hyperborea (Krysht.) E. Lebed. leaves.

Ecological interpretation: Well preserved Cycadites leaves form a mat within the pond sediments suggesting a very local source for the leaves and a deciduous habit (seasonal leaf shedding) for the plant. The absence of other taxa suggests an isolated pond, with little water flow, within a monospecific community bounding the pond and acting as both a source of the preserved leaves and a filter against the influx of more distally growing species.

Site 22 (22, 22a) Fossil Images

Sedimentary context: A small exposure outside the measured section with abundant floral remains. Well-sorted planar-laminated siltstone approximately 30 cm thick. Within the silt bed mature poorly preserved silicified tree trunks (approximately 20 cm diameter, but frequently branched and with nearby fallen branch remains) were observed in growth position. Also within the siltstone was a single, oblique-to-bedding, burrow approximately 1.5 cm in width. In the uppermost part of the silt bed current ripples were observed indicating a main paleocurrent direction to the south. This sequence is interpreted to represent floodplain pond sedimentation. Above and below this siltstone coarse-grained sandstones with chaotically oriented 5 - 6 cm long wood fragments occur.

Floral remains: Gleichenites asiatica Philipp., Birisia ochotica Samyl., Asplenium dicksonianum Heer, Coniopteris (Birisia?) grebencaensis Philipp., Arctopteris  penzhinensis E. Lebed., Hausmannia bipartita Samyl. et Shczep., Cladophlebis sp. 2, Cladophlebis sp. 3, Sagenopteris variabilis (Velen.) Velen., Nilssonia serotina Heer, Ginkgo ex gr. adiantoides (Ung.) Heer, Pseudotorellia ? sp., Sphenobaiera vera Samyl. et Shczep., Desmiophyllum sp., Cephalotaxopsis ex gr. intermedia Holl., Araucarites anadyrensis Krysht., female cone of ?Araucarites sp., Sequoia sp. (cone), Elatocladus smittiana (Heer) Sew., Magnoliaephyllum alternans (Heer) Sew., Menispermites markovoensis Philipp., M. minutus (Krysht.) Herman, M. ex gr. septentrionalis Holl., Diospyros aff. streenstrupii Heer, Myrtophyllum acuminata (Philipp.) Herman, Scheffleraephyllum venustum (Philipp.) Philipp., Zizyphus sp., Trochodendroides arctica (Heer) Berry, Cissites sp. 1, Dalembia vachrameevii E. Lebed. et Herman, Grebenkia anadyrensis (Krysht.) E. Lebed. (abundant), Dicotylophyllum sp. cf. Paleonuphar nordenskioldii (Heer) Bell. Alaliaephyllum sp., Sapindophyllum sp., root fragments, branch wood.

Ecological interpretation: This assemblage is the most diverse in the Yelisseev locality for a single depositional setting. Being a pond environment the sediments received wind-blown leaves from the surrounding communities with most leaves being derived from the pond margin plants (Spicer, 1981). The current ripples were formed by water flow, either from wind generated circulation or by inflowing stream action. Some plant debris could have been transported to the pond by stream flow. Angiosperms are particularly diverse and are likely to have fringed the pond margin (as in many modern settings) and made up the semi-mature community colonizing the pond margins. Conifers probably dominated the mature community behind them. Ferns and cycadophytes formed the ground cover along the pond edges and within the forest. This locality yielded the largest fern frond fragments which is strong evidence for minimal transport. Aquatic plants are represented by the fern Hausmannia.

Site 23

Sedimentary context: Cross-bedded coarse-grained ephemeral stream channel sandstones with intermittant rooted horizons and mature trees in growth position. Tree roots penetrated through an erosion surface at the interface between two sandstone beds. The tree tissues were poorly preserved as powdery organic material, and not silicified. Sediments surrounding the tree trunk consisted of massively-bedded poorly-sorted coarse-grained sandstone overlain by a gravelly sandstone at the level of the root flair. This in turn was overlain by a horizontally laminated well-sorted siltstone with plant remains dominated by Araucarites anadyrensis Krysht. shoots and branches.

Floral remains: Cladophlebis sp.?, Nilssonia serotina Heer, Ginkgo ex gr. adiantoides (Ung.) Heer, Araucarites anadyrensis Krysht., male cone of ? Araucarites sp., female cone of Araucarites sp., branch wood of ? Araucarites sp., Pityophyllum staratchinii (Heer) Nath., Cephalotaxopsis intermedia Holl., Grebenkia anadyrensis (Krysht.) E. Lebed., Scheffleraephyllum venustum (Philipp.) Philipp., Menispermites sp., platanoid and non-platanoid angiosperm leaf fragments, fern fragments.

Ecological interpretation: This sequence is interpreted as the inundation of a tree-vegetated paleosurface by stream sediments, followed by the development of a small floodplain pond. Based on the abundance of fossil remains the vegetation was dominated by Araucarites with Cephalotaxopsis and Pityophyllum also being common. The shrub layer consisted of Grebenkia and Sheffleraephyllum with ferns as the ground cover. The paleosol was only weakly developed so the forest, although mature, had not been established long enough to develop a mature soil profile. Following sediment inundation and pond development Araucarites shoots and branches continued to enter the sedimentary system showing little or no transport abrasion or sorting. This suggests they were derived from a nearby source, possibly the same trees as are preserved here.

Site 24

Sedimentary context: This Site is 12 m along section to the south of Site 23 and about 1 m above (Fig. 4). Here a massively bedded siltstone occured at the top of a channel fill, with abundant organic material grading up into a thinly laminated carbonaceous paper shale. The development of the organic-rich horizon was terminated abruptly by a pebbly channel sandstone.

Floral remains: Birisia ochotica Samyl., Ginkgo ex gr. adiantoides (Ung.) Heer, Nilssonia serotina Heer, large shoots of Cephalotaxopsis intermedia Holl. associated with cones, Araucarites anadyrensis Krysht., male and female cones possibly belonging to Araucarites anadyrensis, Pityophyllum ex gr. staratchinii (Heer) Nath., Sapindophyllum sp., Dicotylophyllum sp. cf. Paleonuphar nordenskioldii (Heer) Bell., entire-margined angiosperm leaf fragments, branch wood fragments.

Ecological interpretation: A mature conifer-dominated forest forming an organic-rich immature paleosol at the top of a channel fill. As at Site 23, the forest was dominated by Araucarites with Cephalotaxopsis, Pityophyllum and Ginkgo as subordinate elements. Angiosperms and ferns formed the understorey.

Site 25 (35) Fossil Images

Sedimentary context: A fine-grained horizontally laminated sandstone grading upwards to medium-grained trough cross-bedded sandstone with abundant rootlets. This is interpreted as a microdelta infill of a floodplain pond.

Floral remains: Gleichenites asiatica Phillip., Sagenopteris variabilis (Velen.) Velen., Nilssonia serotina Heer, Nilssoniocladus chukotensis Spicer et Herman, Ginkgo ex gr. adiantoides (Ung.) Heer, Sphenobaiera vera Samyl. et Shczep., Phoenicopsis ex gr. angustifolia Heer, Pseudotorellia sp., Cephalotaxopsis ex gr. intermedia Holl., Pityospermum semiovale Samyl., Sequoia sp. (cone), Magnoliaephyllum alternans (Heer) Sew., Menispermites ex gr. septentrionalis Holl., Platanus louravetlanica Herman, Scheffleraephyllum venustum (Philipp.) Philipp., Cissites sp. 1, Trochodendroides ex gr. arctica (Heer) Berry, Dalembia vachrameevii E. Lebed. et Herman, Grebenkia anadyrensis (Krysht.) E. Lebed., Dicotylophyllum sp. cf. Palaeonuphar nordenskioldii (Heer) Bell.

Ecological interpretation: The stream feeding the microdelta undoubtedly transported plant material to the pond. This stream-transported component of the assemblage would have primarily represented stream side communities. The delta assemblage therefore represents both stream margin and pond margin communities. Differentiating between these is not straightforward, but the association of Platanus leaves with other channel fill sediments suggests that this may have been a stream side community component. At this locality Platanus was closely associated with Sphenobaiera vera and they may have grown together. Araucarites was absent at this Site but the earlier phases of conifer forest development were represented in the form of Cephalotaxopsis and Pityophyllum. Angiosperms are particularly diverse and this may be explained by them occuring in pond margin plant communities as with Site 22.

Site 26 (37) Fossil Images

Sedimentary context: Horizontally laminated lightly-rooted siltstone interpreted as an immature paleosol developed on a microdelta pond-fill deposit. This bed is immediately overlain by a coarse-grained channel sandstone.

Floral remains: Thallites sp. cf. Marchantites jimboi (Krysht.) Krysht., Birisia jelisejevii (Krysht.) Philipp., Coniopteris (Birisia?) grebencaensis Philipp., Asplenium dicksonianum Heer, Sphenopteris sp. 1, Nilssonia sp., Florinia ? sp., Magnoliaephyllum alternans (Heer) Sew., Platanus louravatlanica Herman, Scheffleraephyllum venustum (Philipp.) Philipp., Dalembia vachrameevii E. Lebed. et Herman, Dalbergites sp..

Ecological interpretation: This represents a delta surface pioneer community dominated by the ferns Coniopteris and Birisia, admixed with rare angiosperms derived from streamside and semi-mature pond margin communities.

Site 27 (42) Fossil Images

Sedimentary context: Fine-grained sandstones, interpreted as a channel fill.

Floral remains: Birisia jelisejevii (Krysht.) Philipp., Asplenium dicksonianum Heer, Cladophlebis aff. septentrionalis Holl., Sagenopteris variabilis (Velen.) Velen., Nilssonia serotina Heer, Ginkgo ex gr. adiantoides (Ung.) Heer, Sphenobaiera vera Samyl. et Shczep., Cephalotaxopsis heterophylla Holl., C.  intermedia Holl., Pityophyllum ex gr. nordenskioldii (Heer) Nath., P. ex gr. staratchinii (Heer) Nath., Sequoia sp., Menispermites ex gr. septentrionalis Holl., Myrtophyllum acuminata (Philipp.) Herman, Araliaephyllum dentatum Philipp., A. medium (Philipp.) Herman, Scheffleraephyllum venustum (Philipp.) Philipp., Trochodendroides arctica (Heer) Berry, Dalembia vachrameevii E. Lebed. et Herman., Dicotylophyllum sp. A.

Ecological interpretation: This channel fill assemblage appears to contain representatives of most communities on the floodplain, but is biased towards early successional plants. Pioneer and understorey elements are abundant in the form of Birisia and Asplenium, but stream side components such as Ginkgo and Sphenobaiera occur admixed with representatives of semi-mature angiosperm communities typical of frequently disturbed sites, and early successional conifer forest plants such as Cephalotaxopsis, Sequoia, and Pityophyllum. Forest understorey elements are present as Nilssonia and Sheffleraephyllum.

Site 28 (45 - Float 10m above 42) Fossil Images

Sedimentary context: isolated fine-grained sandstones with no record of sedimentary structures.

Floral remains: Cephalotaxopsis ex gr. intermedia Holl., Pityophyllum ex gr. staratchinii (Heer) Nath., Menispermites ex gr. septentrionalis Holl..

Ecological interpretation: No ecological interpretations are attempted on float.

Site 29 (46 - Float 20 to 30 m above Site 24) Fossil Images

Sedimentary context: isolated fine-grained sandstones with no record of sedimentary structures.

Floral remains: Thallites sp. cf. Marchantites jimboi (Krysht.) Krysht., Birisia jelisejevii (Krysht.) Philipp., Coniopteris (Birisia?) grebencaensis Philipp., Cladophlebis sp. 1, Cephalotaxopsis intermedia Holl., Araucarites anadyrensis Krysht., Pityophyllum ex gr. nordenskioldii (Heer) Nath., Sequoia cf. minuta Sveshn., Sequoia sp., Menispermites ex gr. septentrionalis Holl., Platanus louravatlanica Herman, Grebenkia anadyrensis (Krysht.) E. Lebed..

Ecological interpretation: No ecological interpretations are attempted on float.