A Tidally Influenced, High-Latitude Coastal-Plain: The Upper Cretaceous (Maastrichtian) Prince Creek Formation, North Slope, Alaska
Peter P. Flaig, Paul J. Mccarthy, Anthony R. Fiorillo, 2011. "A Tidally Influenced, High-Latitude Coastal-Plain: The Upper Cretaceous (Maastrichtian) Prince Creek Formation, North Slope, Alaska", From River to Rock Record: The preservation of fluvial sediments and their subsequent interpretation, Stephanie K. Davidson, Sophie Leleu, Colin P. North
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The Prince Creek Formation is an Upper Cretaceous, dinosaur-bearing, high-latitude alluvial succession deposited on an ancient coastal-plain that crops out in bluffs along the Colville, Kogosukruk, and Kikiakrorak Rivers of northern Alaska. Studies that document the complex stratigraphy and architecture of high-latitude alluvial systems deposited under greenhouse conditions are extremely rare. It is exceptionally uncommon to find extensive, accessible outcrops that also contain numerous Arctic dinosaur fossils; hence the Prince Creek Formation is of great significance not only to sedimentologists but also to paleontologists involved in reconstructing high-latitude dinosaur habitats.
Maastrichtian strata of the Prince Creek Formation record deposition on a tidally influenced high-latitude coastal-plain in (i) first-order meandering trunk channels, (ii) second-order meandering distributary channels, (iii) third-order fixed (anastomosed?) distributary channels, and (iv) on floodplains. Conglomerate and medium- to coarse-grained multistory sandbodies are found exclusively in regionally restricted 13–17-m-thick fining-upward successions (FUSs) that display inclined heterolithic stratification (IHS) capped by finer-grained, organic-rich facies. These relatively thick FUSs are interpreted as first-order meandering trunk channels. Thinner (2–6-m thick), single-story, heterolithic sheet sandbodies composed predominantly of IHS and including abundant mud-filled channel plugs are the most frequently encountered channel form. Trough cross-lamination at the base of the IHS records paleoflow at high angles relative to the dip of the inclined beds, indicating that lateral accretion of point-bars was the principal depositional mechanism. These single-story sandbodies are interpreted as second-order meandering distributary channels. Fine-grained 1.5–3.0-m-thick, ripple cross-laminated ribbon sandbodies deposited mainly by vertical accretion above an arcuate erosion surface and containing only minor IHS are interpreted as third-order fixed (anastomosed?) distributary channels. Thinner (0.2–1.0-m-thick) current-rippled sheet sands and silts are interpreted as small-scale crevasse splays and levees. Organic-rich siltstone and mudstone, carbonaceous shale, coal, bentonite, and tuff are interpreted as deposits of lakes, ponds, swamps, marshes, mires, paleosols, and ashfall on floodplains.
Heterolithic sheet sandstones deposited by small, sinuous meandering distributary channels typically appear lenticular along strike, commonly incise into pre-existing distributary channels, and interfinger with and incise into organic-rich floodplain facies. Fixed, ribbon-form (anastomosed?) distributaries incise either into meandering distributaries or into floodplain facies, with numerous ribbons typically preserved in tiers at the same stratigraphic level. Spatial relationships between channel types, and between channels and floodplain facies, indicate that the bulk of deposition took place on crevasse-splay complexes adjacent to trunk channels. Crevasse-splay complexes were constructed by the lateral migration of sinuous meandering distributaries and the vertical filling of fixed (anastomosed?) distributaries, with splay complexes separated from each other by organic floodplain facies. Flow in meandering distributaries and fixed (anastomosed?) distributaries may have been contemporaneous. Alternatively, fixed (anastomosed?) distributaries may record the initial or waning stages of flow during splay-complex formation or abandonment.
IHS composed of rhythmically repeating, coarse-to-fine couplets of current-rippled sandstone and siltstone or mudstone is found in all three types of channels. The rhythmic and repetitive nature of these couplets together with relatively thick, muddy fine-grained members in couplets suggest that flow in channels was likely influenced by tidal effects.
Drab colors in fine-grained sediments, abundant carbonaceous plant material, and common siderite nodules and jarosite suggest widespread reducing conditions on poorly drained floodplains influenced, in more distal areas, by marine waters. However, carbonaceous root traces found ubiquitously in all distributary channels and most floodplain facies along with common Fe-oxide mottles indicate that the alluvial system likely experienced flashy, seasonal, or ephemeral flow, and a fluctuating water table. The flashy nature of the alluvial system may have been driven by recurring episodes of vigorous seasonal snowmelt in the Brooks Range orogenic belt as a consequence of the high paleolatitude of northern Alaska in the Late Cretaceous.
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From River to Rock Record: The preservation of fluvial sediments and their subsequent interpretation
Over the last couple of decades, fluvial geomorphology and fluvial sedimentary geology have been developing in parallel, rather than in conjunction as might be desired. This volume is the result of the editors' attempt to bridge this gap in order to understand better how sediments in modern rivers become preserved in the rock record, and to improve interpretation from that record of the history of past environmental conditions. The catalyst for the volume was a conference with the same that was hosted at the University of Aberdeen School of Geosciences, in Aberdeen, Scotland, on 12-14 January 2009. The conferences brought together a broad spectrum of geomorphology and sedimentology researchers, from academia and industry. This interdisciplinary mix of experts considered and discussed ideas and examples ranging through timescales from the annual movement of individual river bars to sequence stratigraphic analysis of major sedimentary basins spanning millions of years. The articles in this volume are a mixture of novel concepts, new evaluations of the perceived wisdom about rivers and their sediments, and improved understanding derived from recent experience in interpreting the rock record. This volume usefully illustrates the current state of knowledge and will provide a stimulus for further research, particularly work that integrates geomorphological and sedimentological approaches and emphasizes crossdisciplinary communication.