Thursday, February 19, 2015 AGS Luncheon

"A tale of three deltas: Comparative analysis of ancient, river-dominated deltaic systems from outcrops of the Permian in Antarctica and the Cretaceous in Arctic Alaska and Colorado"

Noon Luncheon 11:30-1:00 pm


This talk provides a comparison between three river-dominated deltaic systems; one deposited under icehouse-to-greenhouse conditions during the Permian (Mackellar Formation) and two deposited under greenhouse conditions during the Cretaceous (Schrader Bluff-Prince Creek Formations and Loyd Sandstone).  The purpose of this talk is to 1) discuss the similarities and differences in facies, sedimentary structures, ichnology, sandbody and shale geometries, and stratal architectures between the three systems, 2) examine the reasoning behind the river-dominated interpretations, and 3) discuss the validity of these classifications.    

The Turnabout Ridge Delta in the Early Permian Mackellar Formation, Central Transantarctic Mountains, Antarctica is dominated by sedimentary structures and stratal geometries indicating recurring sediment-laden underflows.  Channel-form sandbodies encased in prodelta deposits are interpreted as shelfal turbidite channels and levees. Shelfal channels are overlain by sandy prodelta and delta-front hyperpycnites, mouthbars, and subaqueous terminal distributary channels of the delta front. The deltaic succession overlies interbedded prodeltaic turbidites and mudstone and is overlain by a sand-dominated braidplain.  Historically interpreted as either the deposits of a large glacial lake or inland sea, new ichnologic and sedimentologic observations are consistent with a river-dominated, marine deltaic system containing an ecosystem stressed by recurring freshwater and sediment input.  Results suggest that sediment-laden glacial meltwater freshets from braided rivers likely prepped a marine basin, producing recurring hyperpycnal flows along the delta front.  Strata at Turnabout Ridge were likely deposited in a proximal-axial position relative to a river-dominated delta along the shoreline of an Antarctic epeiric seaway during the Early Permian.

The Cretaceous Schrader Bluff-Prince Creek Delta of Arctic Alaska is interpreted as a muddy river-dominated delta that preserves evidence of both autogenic deltaic processes and allogenic erosional surfaces. During lobe reorganization and abandonment, the delta front and interdistributary bays of the delta transition into lakes and floodbasins containing immature soils on the lower delta plain, alongside distributary channels. Floodbasins were subsequently transgressed and overlain by proximal shelf and prodelta muds. Reactivation of the delta lobe was signaled by overlying delta front, interdistributary bay, terminal distributary channel, distributary mouth bar, and distributary channel deposits. These distal deltaic environments are ultimately incised into and overlain by braided channels during a marked basinward shift in the system. The preservation of hyperpycnites and numerous subaqueous terminal distributary channels, along with a lack of abundant sedimentary structures formed by waves-tides, indicate that this delta is best interpreted as river-dominated.

The Cretaceous Loyd Delta of Colorado contains abundant foresets composed of low-angle planar-lamination and ripple cross-stratification in Bouma-like sequences thought to be constructed by traction-dominated underflows (hyperpycnal flows), indicating that the delta should be classified as river-dominated.  In contrast, a high abundance and highly diverse trace fossil assemblage including Ophiomorpha, Thalassinoides, Planolites, Schaubcylindrichnus, Palaeophycus, Diplocraterion, Helminthopsis, and Bergaueria , deeply penetrating burrows, and flaser-wavy-lenticular bedded mud between foresets is evidence that the delta front experienced recurring, extended periods of slow sedimentation and oxygen-rich marine water influx during which marine fauna flourished and tidal and wave forces dominated.  The Loyd comprises a coarsening-upward succession overlying the Buck Tongue of the Mancos Shale that includes muddy-siltstone, low-angle planar laminated to ripple laminated sandstone interbedded with flaser-wavy-lenticular bedded mudstone, and gradational to erosively-based trough cross-stratified sandstone.  Interpreted depositional environments include prodelta, delta front, distributary mouth bars, and subaqueous to subaerial distributary channels.  Stratal architectures and sedimentary structures are broadly similar to those of other Cretaceous deltas interpreted as river-dominated, including the Ferron and Panther Tongue deltas.

Although sedimentary structures, stratal geometries, and ichnology vary in these three deltas, the predominance of traction dominated underflows (hyperpycnites) in each system indicates that fluvial-flood processes were the driving force behind the bulk of the preserved stratigraphy.


Peter P. Flaig
Bureau of Economic Geology, Jackson School of Geosciences, University of Texas, Austin

Peter Flaig earned his B.S. and M.S. from the University of Wisconsin - Milwaukee. For his Masters’ degree, Pete examined a Permian through Triassic alluvial succession in the Central Transantarctic Mountains of Antarctica to identify the driving force behind changes in facies, flora, fauna, fluvial style, accommodation, and stacking pattern across the Permian-Triassic boundary. During his PhD, Pete joined a team of scientists for three field seasons in Arctic Alaska (2005-2007) to investigate the dinosaur-bearing Prince Creek Formation, a Cretaceous fluvial-deltaic succession exposed along the Colville, Kogosukruk, and Kikiakrorak Rivers on the North Slope. Pete’s role was to collaborate with Dr. Anthony Fiorillo, curator of paleontology at the Perot Museum of Nature and Science and Dr. Paul McCarthy, sedimentologist and paleopedologist at the University of Alaska- Fairbanks (UAF) to reconstruct the Cretaceous coastal-plain of Arctic Alaska, placing the dinosaurs in a paleoenvironmental context.  Pete lived in Fairbanks for 4 years (2005-2009) while attending UAF. During this time Pete was involved in numerous additional investigations on North Slope Cretaceous-Tertiary stratigraphy. At UAF, Pete met his wife Dolores van der Kolk, who is currently a PhD student at the University of Texas at Austin (UT-Austin) investigating the marine-to-continental Schrader Bluff-Prince Creek Formation transitions along the Colville River.  

Pete received his PhD from UAF in 2010 and moved to Austin, Texas to accept a Postdoctoral Fellowship at the Jackson School of Geosciences, UT-Austin. Pete’s postdoctoral work at the Bureau of Economic Geology (BEG), UT-Austin included continuing research on North Slope fluvial-deltaic and shallow marine systems with Dolores, and investigations into continental-to shallow-marine deposits of the Cretaceous Western Interior Seaway in Utah, Colorado, New Mexico, and Alberta, Canada.  In 2010-2011 Pete joined a team of scientists for his second Antarctic field season in the Central Transantarctic Mountains. Pete collaborated with Dr. Stephen Hasiotis at the University of Kansas, with both expanding on their previous Antarctic work. They combined their expertise to examine the stratigraphy and trace fossil assemblages from the Devonian through the Jurassic, with a goal of reconstructing ancient Antarctic ecosystems.  Pete continues to collaborate with Stephen Hasiotis on a number of combined sedimentologic and ichnologic investigations in order to better clarify environments of deposition in continental to marine transitional stratigraphy along complex coastlines. Pete is also heavily involved in the comparative analysis of strata from high-latitude greenhouse depositional systems, and he enjoys working on fossil-bearing clastic successions.  

In 2011 Pete accepted a Research Associate position as a sedimentologist-stratigrapher at the BEG, UT-Austin where he is the lead scientist on fluvial-deltaic studies at the Quantitative Clastics Laboratory (QCL). Pete is currently the Primary Investigator at the QCL, a consortium of oil companies involved in studies to help quantify parameters in clastic systems including: reservoir dimensions, sandbody-shale lengths and geometries, channel sinuosities, porosity-permeability, net-to-gross, geochemistry, etc.  Pete is a professional photographer and uses high-resolution photographic imaging, GigaPan robotic photo-panorama technology, and Light Detection and Ranging (LiDAR) 3-D point clouds in facies and architectural analyses of outcrop belts. Pete continues to run field programs and core investigations on clastic systems, he provides expert advice to industry, and advises-mentors graduate students on QCL consortium projects.  Pete is also involved in the planning for the next deep-field camp at Shackleton Glacier in the Central Transantarctic Mountains of interior Antarctica.

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