Kukpowruk River

The map on the right shows the localities along the Kukpowruk River sampled both by Smiley (reported in Smiley 1969a), Spicer and Herman (1996) and by Bob and Andrew Spicer in 1998. Click on the locality numbers to see further details of the sites and the fossil floras.

Sedimentary log of the section at Kukpowruk River 96-11 locality. For unit descriptions refer to the panel to the left.

Locality 96-11: 69° 00' 02" N  162° 57' 44" W

Kukpowruk Formation

Specimens: 96 RAS 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63

Description.

Unit 1. Indurated fine gray/brown sandstone, ripple marked with rare plant fragments (Pityophyllum?). Thickness: 5.5 - 6 m.

Unit 2. Dark gray mudstone. 96 RAS 38 and 39. 39 is from the top of the unit. Thickness: 3.5 m.

Unit 3. Fine indurated sandstone, medium gray, weathering to light yellow/brown. Ripple laminated with clay/shale interbeds no more than 1 cm thick, interbeds and sands contain comminuted plant debris. Thickness: 1 m.

Unit 4. Dark gray/brown silty claystone fining upwards, also becoming less indurated upwards. No obvious plant material. Thickness 2.3 m.

Unit 5. Ripple-laminated light gray, weathering to orange, fine-grained sandstones. Well indurated. Ripple surfaces often coated in gray clay. Abundant comminuted plant debris on some bedding surfaces. Pityophyllum predominates but with some Ginkgo fragments. No obvious rooting. Thickness: 0.4 m.

Unit 6. Dark gray mudstone, coarser at the bottom becoming finer in the middle and coarsening towards the top again. Towards the top plant material becomes abundant but highly fragmented. 96 RAS 40 from 2 m above the base of the unit. Thickness: 5.5 m.

Unit 7. Well indurated silty shale, poorly bedded, with abundant plant remains, all fragmented, dominated by Pityophyllum but with some woody fragments and fragments of Equisetites rhizomes. Thickness 0.5 m.

Unit 8. Dark gray shales. Thickness 1.2 m.

Unit 9. Light gray. weathering to brown, ripple laminated and cross bedded sandstone. Ripples often covered in clay drapes. Some thicker clay interbeds up to 0.2 m thick occur sporadically throughout. Trace fossils are abundant. No shelly fauna but towards the top some bedding planes are covered in highly comminuted plant debris. No evidence of rooting. Contact with Unit 8 is sharp and erosional. 96 RAS 41 was recovered as float derived from this unit. Thickness: 7.8 m.

Unit 10. Dark gray brown mudstone, with dark gray shale interbeds, poorly indurated, no obvious grain size trend through the thickness, occasional horizon with comminuted plant debris, no signs of rooting. Thickness: 8 m.

Unit 11. Light gray, weathering to brown, indurated very fine sandstone. Lumpy appearence with mudstone interbeds a few cm thick. Sparsely rooted. Abundant plant remains, some quite large fragments of Equisetites rhizomes, and long and short leaves of Pityophyllum. Pityophyllum predominates. Thickness: 1 m.

Unit 12. Shaley mudstone, dark gray with highly comminuted plant debris. This passes up gradually to the next unit. Thickness: 1.5 m.

Unit 13. Indurated medium gray, weathering to yellow, very fine sandstone. Rooted. No obvious ripple marks. 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 gray shale and lighter more indurated silts and fine sands. Few, if any, ripple marks. Lumpy texture with 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 thickness of the unit. 96 RAS 43 from approximately 0.5 m above 96 RAS 42. Thickness 16 m.

Unit 15. Lenticular sandstone (lens shaped), fine, light gray, weathering to yellow, well bedded. Horizontal "U" shaped burrows. Thickness: 3 m.

Unit 16. Poorly indurated brown siltstone interbedded with three fine sandstone layers, the bottom most layer is about 0.1 m thick, the middle is 0.2 m thick, and upper is 0.5 m thick. Thickness: 2.5 to 3 m.

Unit 17. Flaggy, lenticular, sandstone (as all the sandstones in the outcrop). Thickness: 3 m.

Unit 18. Lumpy interbedded siltstones and claystones containing abundant plant remains that are often minimally fragmented. Birisia alata dominates. There are abundant "Y" shaped roots. 96 RAS 44 to 63. Thickness: about 5 m.

Unit 19. Shale. Thickness: 1 m.

Unit 20. Sandstone. Thickness: 3 m.

Interpretation. The basal portion of this section represents marginal marine facies of varying depth and varying terrigous clastic input. While this section is in most part marine, a blocky/lumpy brown bedded siltstone 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 cf. 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. Often the plants are 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 is rooted 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 its is likely that the plants were, to some degree, tolerant of mildly saline, or periodically saline, conditions.

The marine units are characterised by predominantly organic rich shales, probably formed in deeper water, interspersed by coarser silts and fine sands 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 silts are mostly devoid of plant remains except water-worn wood fragments.