Kukpowruk River 96-11 (Cretaceous of the United States)

Also known as Kukpowruk River/Cape Lisburne floras

Where: western North Slope County, Alaska (69.0° N, 162.9° W: paleocoordinates 79.8° N, 93.6° W)

• coordinate stated in text

• outcrop-level geographic resolution

When: Kukpowruk Formation, Albian (113.0 - 100.5 Ma)

• lower to middle Albian

• group of beds-level stratigraphic resolution

Environment/lithology: marginal marine; siltstone and fine-grained sandstone

• Description. See Figure 10.

•Unit 1. Indurated, fine-grained, grey/brown sandstone, ripple

•marked with rare plant fragments (Pityophyllum?). Thickness:

•5.5–6 m.

•Unit 2. Dark grey mudstone. 96 RAS 38 and 39. Sample 96 RAS

•39 is from the top of the unit. Thickness: 3.5 m.

•Unit 3. Fine-grained indurated sandstone, medium grey,

•weathering to light yellow/brown. The sandstones are ripplelaminated

•and incorporate claystone/shale interbeds no more than

•1 cm thick. Shales and sandstones contain comminuted plant

•debris. Thickness: 1 m.

•Unit 4. Dark grey/brown, silty claystone fining and becoming

•less-indurated upwards. No obvious plant material is present.

•Thickness: 2.3 m.

•Unit 5. Ripple-laminated light grey, weathering to orange, well

•indurated, fine-grained sandstones. Ripple surfaces are often coated

•in grey clay. Abundant comminuted plant debris occur on some

•bedding surfaces. Pityophyllum predominates but some Ginkgo

•fragments are also present. No obvious rooting. Thickness: 0.4 m.

•Unit 6. Dark grey mudstone, coarser at the bottom becoming

•finer in the middle and coarsening again towards the top. Plant

•material becomes abundant but highly fragmented towards the top

•of the bed. 96 RAS 40 from 2 m above the base of the unit.

•Thickness: 5.5 m.

•Unit 7.Well-indurated, poorly bedded, silty shale, with abundant,

•fragmentary plant remains dominated by Pityophyllum but and

•minor wood and Equisetites rhizomes. Thickness: 0.5 m.

•Unit 8. Dark grey shales. Thickness: 1.2 m.

•Unit 9. Light grey, weathering to brown, ripple-laminated, and

•cross-bedded sandstone. Ripples are often covered in clay drapes.

•Some sporadic thicker clay interbeds reach 0.2 m thick. Trace

•fossils are abundant. No shelly fauna is present but towards the top

•some bedding planes are covered in highly comminuted plant

•debris. There is no evidence of rooting. The contact with unit 8 is

•sharp and erosional. 96 RAS 41 was recovered as loose blocks of

•sediment derived from this unit. Thickness: 7.8 m.

•Unit 10. Poorly indurated, dark grey brown mudstone, with dark

•grey shale interbeds, showing no consistent grain size trend through

•the bed. Sparse horizons host comminuted plant debris, without

•signs of rooting. Thickness: 8 m.

•Unit 11. Light grey, weathering to brown, indurated, very fine

•sandstone. The sandstone has a blocky appearance owing to interbedding

•with mudstones a few cm thick. The sparsely rooted bed

•contains abundant large fragments of Equisetites rhizomes, and

•long and short leaves of Pityophyllum. Pityophyllum predominates.

•Thickness: 1 m.

•Unit 12. Mudstone, dark grey with highly comminuted plant

•debris. This passes up gradually to the next unit. Thickness: 1.5 m.

•Unit 13. Indurated, medium grey, weathering to yellow, very fine

•sandstone without obvious ripple marks. Roots occur throughout

•and the uppermost parts contain abundant, fragmented Pityophyllum,

•with long Equisetites rhizomes. This unit passes up

•gradually to the next unit. 96 RAS 42. Thickness: 0.8 m.

•Unit 14. Interbedded dark grey shale and lighter more indurated

•siltstones and fine sandstones with few if any ripple marks. The unit

•has a lumpy texture and contains numerous layers of ironstone

•nodules. There are at least eight layers of siltstones/sandstones each

•of approximately 0.5 m thick dispersed more or less evenly throughout

•the 16 m thickness of the unit. 96 RAS 43 from approximately

•0.5 m above 96 RAS 42.

•Unit 15. A fine-grained, light grey, weathering to yellow, wellbedded,

•lenticular sandstone containing horizontal, ‘U’-shaped

•burrows. Thickness: 3 m.

•Unit 16. Poorly indurated, brown siltstone interbedded with

•three fine-grained sandstone layers, the lowermost layer is about

•0.1 m thick, the middle is 0.2 m thick, and upper is 0.5 m thick.

•Thickness: 2.5–3 m.

•Unit 17. Flaggy, lenticular sandstone (as all the sandstones in the

•outcrop). Thickness: 3 m.

•Unit 18. Interbedded siltstones and claystones with an

•incipient nodular texture containing abundant plant remains

•that are often minimally fragmented. Birisia alata dominates.

•There are abundant Y-shaped roots. 96 RAS 44 to 63. Thickness:

•c. 5m.

•Unit 19. Shale. Thickness: 1 m.

•Unit 20. Sandstone. Thickness: 3 m.

•Interpretation. The basal portion of this section represents marginal

•marine facies deposited under varying water depth and varying

•terrigenous clastic input. While this section is in most part marine,

•a blocky brown bedded siltstone with an incipient nodular texture

•dipping to the south occurs at the southern end of the outcrop. This

•contains abundant plant remains, predominantly Birisia alata, as

•large frond fragments. Equisetites occurs as rhizomes (but some

•branched aerial parts do occur), together with Parataxodium

•wigginsii, Arctopteris rarinervis, Heilungia sp. cf. H. oloensis, Pityophyllum

•ex gr. staratschinii, and, in the coarser units Ginkgo ex gr.

•adiantoides. Burial was evidently rapid and frequent as plant remains

•occur on numerous bedding surfaces over at least three metres of

•section. The plants are commonly preserved cross-cutting bedding

•planes indicating rapid and repeated influxes of sediment. Birisia

•fronds are by far the most abundant element and their occurrence

•adjacent to a marginal marine setting must indicate that Birisia

•formed coastal ‘marshes’. The sequence contains roots throughout

•suggesting that after each successive influx of sediment destroyed

•the marsh vegetation Equisetites and Birisia rapidly recolonised the

•fresh sediment. Evidently this sequence is a good example of marsh

•vegetation very close to the shoreline and it is likely that the plants

•were, to some degree, tolerant of mildly saline, or periodically

•saline, conditions.

•The marine units are characterised by predominantly organicrich

•shales, probably formed in deeper water, interspersed with

•coarser siltstones and fine sandstones exhibiting a variety of ripple

•forms, mud drapes, worm tracks and Rhizocorallium. No megafaunal

•remains were seen which possibly indicates a near distributary

•environment with variable salinity. These siltstones are mostly

•devoid of plant remains except water-worn wood fragments.

Size class: macrofossils

Collection methods: quarrying,

• Material stored at the Earth Sciences Department, The Open University, collection # 96 RAS.

Primary reference: R. A. Spicer and A. B. Herman. 2001. The Albian-Cenomanian flora of the Kukpowruk River, western North Slope, Alaska: stratigraphy, palaeofloristics, and plant communities. Cretaceous Research 22:1-40 [D. Royer/D. Royer/D. Royer]more details

Purpose of describing collection: general faunal/floral analysis

PaleoDB collection 34195: authorized by Dana Royer, entered by Dana Royer on 21.08.2003

Creative Commons license: CC BY (attribution)

Taxonomic list

Birisia alata
occurs in siltstones; many large frond fragments
Arctopteris aff. kolymensis
occurs in siltstones
Arctopteris rarinervis
occurs in siltstones
Heilungia cf. oloensis
occurs in siltstones
Parataxodium cf. wigginsii
occurs in siltstones
Pityophyllum ex gr. staratschinii
occurs in siltstones
 Equisetales - Equisetaceae
Equisetites ex gr. burejensis
occurs in silty shales and fine sandstones