Upper Colville River, Alaska
|Map of Northern Alaska||Upper Colville Fossil Images Unassigned||89JTP07 Fossil Images||89JTP07-8 Images|
This interactive map of part of the Colville River, Northern Alaska, shows the locations of plant fossil collections made by J.T. Parrish and R.A. Spicer in 1985 and 1989. Click on a number for more details on that site. The red outlined area links to another map showing positions of florules (plant fossil assemblages) collected by C.J. Smiley along both the Colville and Chandler Rivers.
This section was not sampled in 1985. Although mapped as KcK2, the upper Killik Tongue of the Chandler Formation by Chapman et al., (1964) its floral composition is more typical of the lower Killik (KcK1). Mull et al. (2003) reassigned the upper Killik to the upper part of the Nanushuk Formation. The flora is typical of that just prior to the arrival of the angiosperms as exemplified by the Kukpowruk Phase of floral evolution to which the composition of these assemblages should be compared. Although the Kukpowruk Flora is equivalent to that of the lower Killik this locality represents the very last occurrence of the Kukpowruk floral phase before the flowering plants arrive. The repeated associations of plant taxa with floodplain sediments described below allows the reconstruction of mid Cretaceous Arctic forest seral succession at this critical time in Arctic ecosystem evolution. The description is long, complex and makes tedious reading, but this format captures many subtleties in the associations. Of note is that the primary coal forming species are woody trees or bushes that produce Pityophyllum and Podozamites leaf forms.
It begins with a sandstone that is rooted at the top with Equisetites rhizomes, which is in trun overlain by a thin incipient coal with Pityophyllum, Podozamites and possible Sphenobaiera. This coal is overlain by a soft light gray clay that passes up into a mottled gray/brown nodular clay/silt/mudstone. Plant remains are highly fragmented with unidentified conifers, Equisetites (rooted and with nodules), Podozamites, and Pityophyllum present. Some scattered microphyllous conifers also present. Above this mudstone a crossbedded sandstone contains large logs aligned parallel to bedding. The basal part of the sandstone is a gray 'salt and pepper' color with fragmented wood, Pityophyllum, Podozamites, Sphenobaiera, taxodiaceous conifer shoots and needles. A silt layer approximately 30 cm thick separates the lower sand from an upper, thicker, gray, yellow-weathering sand containing the large logs (up to 30 cm in diameter). The siltstone contains abundant Pityophyllum, Podozamites and Sphenobaiera.
This yellow-weathering sand fines upwards to silt. This contains Podozamites in abundance, Pityophyllum, a microphyllous conifer, twigs, and bedding is poorly developed. Above this is a gray mottled fine/medium sand, which is rooted by Equisetites. This is overlain by a slightly coarser sand with small vertical woody stems (approximately 7.5 cm in diameter) in growth position. The top of this unit is covered by tree root impressions and overlain by a thin carbonaceous shale rich in Pityophyllum.
Locally orange ironstone float represents a poorly bedded claystone and contains abundant Pityophyllum, some Sphenobaiera and fern fronds. This part of the section was covered and inaccessible in 1989. The next exposed unit is a light gray fine sand 3-4 m thick and plant remains are rare. Small scale cross bedding and climbing ripples characterise this rapidly deposited unit. The sand fines upwards becomes heavily rooted and turns gray/brown in color. Nilssonia and Sphenobaiera were found as float. Pityophyllum and microphyllous conifers occur near the top of this unit. Overlying the sand is a light gray siltsone that is heavily rooted. Equisetites with nodules is present. Equisetites reappears after a short covered interval in the overlying unit, which is a heavily rooted gray/brown silty mudstone with rare Pityophyllum leaves. This passes up into a thin indurated gray clay with Pityophyllum. Overlying this is a heavily rooted gray/brown mottled 'lumpy' siltstone with Equisetites nodules. This underlies a coal supporting a rooted tree stump. Pityophyllum and ?Sphenobaiera fragments are in abundance. A gray clay overlies the coal and contains abundant Pityophyllum. This passes up into a more indurated gray siltstone with compressed logs and abundant well preserved Sphenobaiera, Podozamites (whole shoots as well as isolated leaves) and ferns. Above this is a yellow-weathering silt/fine sandstone with abundant Podozamites, branches, Pityophyllum staratchinii, all at various angles and not aligned parallel to bedding. Nilssonia was found as float and could well have been from this horizon. Sphenobaiera and Podozamites are also abundant in the unit above, which is a gray/brown mottled siltstone. Some branchwood also occurs along with some Pityophyllum before passing up into a thin carbonaceous shale rich in Pityophyllum.
Continuing up section the carbonaceous shale is succeded by a thin gray clay that passes up into mottled gray/brown lumpy siltstones containing abundant Pityophyllum, some Podozamites and occasional Sphenobaiera. This unit is also rooted and passes up into a Podozamites-rich carbonaceous shale, which in then becomes a gray/brown mottled lumpy siltstone with Podozamites and Pityophyllum in abundance. A laterally equivalent exposue of this siltstone has abundant well preserved Sphenobaiera, and is rooted with Equisetites. The siltstone is followed by a gray clay underlying a 40 cm thick coal. The top part of this coal is Pityophyllum-rich with some lesser quantities of Podozamites.
The clay overlying the coal coarsens upwards and becomes more indurated passing into a bedded light olive gray siltstones and then rippled sands weathering to light yellow gray. The sands are largely devoid of identifiable plant matter but hash is common along with water-worn branch wood. this unit passes up into a thin (30 cm) lumpy gray/brown Equisetites rooted siltstone. This underlies 20 cm of silty gray clay, which coarsens upward abruptly to a yellow/gray fine sand with climbing ripples. Plant debris is fragmented and unidentifiable. Above this is a gradational transition to a lumpy gray/brown rooted siltstone, which in turn passes up into a medium gray rooted siltstone and thence into a gray rooted clay that immediately underlies a 20 cm thick coal. The basal part of the coal is papery but with no identifiable plant fossils.
The coal is overlain by 3 m of cover. This is followed by gray siltstones and fine sandstones in alternating succession. The sands display climbing ripples and are infrequently rooted. Plant remains a fragmented and some water worn wood fragments occur along with finely comminuted plant debris. Rooting with Equisetites rhizomes becomes more frequent towards the top of this succession. Above this is a thin (5 cm) clay layer, followed by a yellow-weathering gray siltstone with flow oriented elongate woody fragments and Pityophyllum.
After 1 m of cover 'salt and pepper' medium sandstone, with clay and silt interneds pass up into a cross bedded medium sand. Plant hash and water-worn woody fragments occur on some sandy bedding planes. Podozamites occurs in orange-weathering silty clay horizons together with fern pinnules, Pityophyllum and conifer needles. This unit passes up into lumpy, brown-weatheringrooted horizon underlying gray clays and silts. A thin nodular horizon is overlain by 30 cm of fine gray sand, above which are gray clays and Pityophyllum in carbonaceous shales, followed by more gray clays that are overlain by thick cross-beddeds medium light gray sands with occasional surfaces covered in abraded woody fragments. Abraded Pityophyllum and Podozamites are sometimes recognizable. 1- 2 cm diameter quartz pebbles occur on bedding planes covered in woody fragments 5-6 cm long. This sand fines upwards into rooted fine sands and silts with Equisetites, Pityophyllum nordenskioldii, conifer leafy shoots, ferns, and Podozamites.
The silts pass upwards into a carbonaceous shale, followed by a sand and then another carbonaceous shale. This is overlain by a rooted fine gray sand underlying a coal about 30 cm thick, which in turn passes up into a crabonaceous shale containing Pityophyllum and Podozamites and a gray clay. This clay then passes up into a nodular, lumpy rooted brown siltstone that appears to be a palaeosol, overlain by 3m of gray fine sand that weathers orange/yellow and is rooted throughout. The upper third of this sandstone contains more silty horizons that yield conifer shoots, abundant ferns and Ginkgo leaves (some very large and with long petioles) in abundance. Towards the top of the unit Equisetites rhizomes, often with nodules, become abundant, before passing up into an obvious seat earth, 5 cm thick, underlying a 2.5 m thick coal. The coal has occasional sandstone stringers (< 1 cm thick). The coal is rich in fusainite (charcoal) and large compressed logs. At the very top of the coal the only recognizable plant remains are Pityophyllum leaves.
The coal passes up into gray clays and then into mottled, lumpy, gray-brown rooted siltstone with Equisetites and Pityophyllum, before being overlain by gray-brown sandy units with occasional silts. These are rooted and bear woody fragments with Podozamites, conifer leafy shoots and cones and Equiseties. Occasional finer-grains horizons occur with Pityophyllum. Continuing upward other horizons have abundant Pityophyllum, Podozamites and Sphenobaeira together with a possible Ginkgo. A gray clay contains Pityophyllum, Sphenobaeira. Podozamites and conifers are more common towards the top of this unit. Above this rooted gray/brown lumpy rippled silts continue up to yellow-weathering medium sand that wedges in. Overlying this is a 40 cm thick rooted and cross bedded sand under a seat earth beneath a 2m thick bituminous woody coal with some fusainite. At the top of this coal there is abundant Pityophyllum in leaf mats.
The coal is overlain by a brown/gray lumpy siltstone devoid of roots and with some plant hash apparently consisting of conifer and Equisetites fragments. Equisetites rhizomes become common towards the top of the unit, before passing up into a medium gray siltstone and then into a coal that is mostly covered for 2 m. Sphenobaiera and Podozamites occur in a carbonaceous shale along with logs and branches. This is overlain by a 15 cm thick yellow-weathering indurated ironstone layer, followed by further indurated layers containing small leaved conifers, Pityophyllum, Podozamites. This is overlain by a light gray rippled fine sand with abundant Pityophyllum, prone logs and branch wood. Rare Sphenobaiera occurs in a carbonaceous shale layer, which is overlain by a 40 cm thick gray/brown mottled rooted siltstone (features indicative of pedogenic processes) with log impressions.
Above this is a carbonaceous shale with numerous Podozamites leaves. This is succeeded by a series of carbonaceous shales separated by more indurated silts and fine sands. The uppermost carbonaceous shale is underlain by a gray poorly bedded silt with a narrow-leaved conifer and Podozamites. This passes up into a carbonaceous shale apparently dominated by Pityophyllum with long and short shoots. This is overlain by a gray, weathering to yellow, poorly bedded fine sand and is rooted. Above this is a 40 cm thick coal, the basal part of which is a carbonaceous shale with Podozamites and Pityophyllum in abundance. The upper part of the coal is also a carbonaceous shale overlain by rippled rooted fine gray, weathering to yellow, sands with abundant narrow-leaves conifer (not Pityophyllum staratschinii), plus abundant ferns. This unit is rooted at the top and passes up into a carbonaceous shale followed by a 1 m thick coal. The basal part of this coal contains Pityophyllum.
The coal is overlain by a 30 cm thick gray, weathering to yellow, rooted silt, which in turn passes into a thin carbonaceous shale with abundant conifer remains, before passing up into a more heavily rooted gray/brown lumpy siltstone, incipient carbonaceous shales and sandstones. Equisetites, Pityophyllum and occasional horizons with Podozamites occur throughout. In thicker, lumpy gray/brown siltstones Pityophyllum, some Podozamites and some ferns occur. All horizons are rooted in this part of the succession.
This silty succession passes up into ~ 3 m of carbonaceous shales, poorly exposed, the upper part of which has numerous thin coals before passing up into lumpy gray/brown rooted siltstones with abundant Podozamites, Sphenobaiera,and Pityophyllum and a small tree base in life position. This unit is overlain by a thin carbonaceous shale followed by 1 m of fine sand largely devoid of plant debris. This is followed by a series of rooted gray/brown lumpy silts. Each silty episode (0.5 - 1 cm thick) is separated by a thin carbonaceous shale. Some cross bedding is sometimes visible. Equisetites is abundant together with rare Nilssonia, Podozamites, and rare Pityophyllum. This succession is eroded into by thick cross bedded yellow/gray medium grained channel sandstone in which trees are found in growth position and rooted in the top of the carbonaceous shale. Above the tapered edge of the channel sand body Podozamites occurs in some abundance overlain by fining upward siltstones rooted with Equisetites. Equisetites occurs in abundance below a coal where the basal carbonaceous shale is dominated by Pityophyllum. The coal contains a silty split that is heavily rooted with Equisetites. Above the coal is 115 cm of carbonaceous shale dominated by Pityophyllum.
Overlying the carbonaceous shale is a 3.5 m thick sandstone containing ferns. A tree base over 1 m high projects into this sand and is a accompanied by horizontal logs. The upper part of the sand is rooted and fines upwards to gray fine sand rooted with Equisetites and passes up into a 2.1 m thick woody coal containing Pityophyllum and fusainite throughout. The upper surface of the coal is eroded into by a thick cross-bedded fine gray, weathering to yellow, containing fern remains.