An Early Permian Paleopolar, Postglacial, River-dominated Delta From Antarctica

An Early Permian, paleopolar, postglacial, river-dominated deltaic succession in the Mackellar–Fairchild formations at Turnabout Ridge, Central Transantarctic Mountains, Antarctica

Authors:

Flaig et al

Abstract:

Turnabout Ridge, a remote outcrop belt in the Beardmore Glacier Region of the Central Transantarctic Mountains, comprises subglacial–glaciomarine deposits of the Pagoda Formation (Fm) overlain by a postglacial deltaic succession of the Mackellar–Fairchild formations (fms). Four depositional environments were identified in the Mackellar–Fairchild fms: 1) prodelta to distal-delta-front deposits that record the initial filling of a newly formed intracratonic basin; 2) an interval dominated by subaqueous terminal distributary channels and levees that signal the advancement of a delta into the region; 3) mouth bars and associated subaqueous terminal distributaries representing the proximal delta front; and 4) an overlying sand-dominated braidplain.

A companion ichnologic study identified 30 ichnogenera in the Mackellar Fm that combine to form six ichnocoenoses. Twelve traces are known only from marine settings, 18 are found across marine, brackish, and freshwater systems, and none are known solely from freshwater systems. The ichnology refines paleoenvironmental and paleosalinity interpretations for the Mackellar Fm, and indicates a predominantly brackish water paleoenvironment.

Subaqueous terminal distributary channels record the highest energies, suspended sediment concentrations, and sediment loads, and are the conduits that delivered sediment to the delta front and prodelta. Abundant traction deposits (hyperpycnites) displaying only minor wave or tide modification suggest that the delta is best classified as river-flood dominated. The succession exhibits similarities to the Panther Tongue and Ferron Notom deltas of the Cretaceous Western Interior Seaway, USA, and a Late Ordovician proglacial delta from the Murzuq Basin in Libya.

The combined ichnologic and sedimentologic evidence suggests that sediment-laden glacial outburst floods produced freshets that recurrently prepped a shallow-marine basin, reducing salinities and allowing for abundant channelization and hyperpycnite deposition along the delta front. Turnabout Ridge likely occupied a proximal and axial position relative to an Antarctic freshwater- and sedimentation-stressed, river-dominated marine deltaic system along the shoreline of an epeiric seaway during the Early Permian.

Habitat Preferences of Polar Dinosaurs in Maastrichtian Cretaceous Alaska

A Multi-disciplinary Perspective on Habitat Preferences among Dinosaurs in a Cretaceous Arctic Greenhouse World, North Slope, Alaska (Prince Creek Formation: Upper Maastrichtian)

Authors:

Fiorillo et al

Abstract:

The Prince Creek Formation of northern Alaska is the most abundant source of polar dinosaur remains in the world and now corroborating data from this well-studied rock unit allow for making inferences about the paleoecological preferences for these extinct polar animals. The rock unit records high-latitude, alluvial sedimentation and soil formation on a low gradient, muddy coastal plain. Compound and cumulative andic Entisols and Inceptisols formed on levees, point bars, crevasse splays, and along the margins of floodplain lakes, ponds and swamps. Abundant organic matter, carbonaceous root traces, Fe-oxide depletion coatings and zoned peds indicate periodic waterlogging, anoxia and gleying, consistent with a high water table. In contrast, Fe-oxide mottles, ferruginous and manganiferous segregations, bioturbation, and less common illuvial clay coatings indicate recurring oxidation and periodic drying-out of some soils. An integrated reconstruction of pedogenic processes and biota suggests that this ancient Arctic coastal plain was influenced by seasonally fluctuating water table levels and floods, and in distal areas, marine waters. Four of the five bonebeds in this study are from more distal areas, represented by lower delta plain facies, while the fifth bonebed is from a more proximal part of the basin, represented by a somewhat better drained coastal plain facies.

Bonebeds in the distal areas are dominated by Edmontosaurus sp. while the more proximal bonebed is dominated by the remains of the ceratopsian Pachyrhinosaurus perotorum. The distribution of these bonebeds, sedimentological facies, paleosols and biota, suggest that Pachyrhinosaurus may have preferred more upland environments while Edmontosaurus preferred lowland, deltaic environments. This distribution may be the result of physiological adaptation to the pronounced seasonality provided by polar terrestrial ecosystems. In contrast to a preferred habitat distribution of these large herbivores, the large predatory dinosaur, Nanuqsaurus hoglundi seems to have had a more ubiquitous distribution across the landscape.

Highly Productive Polar Forests in Permian Antarctica Before Siberian Traps Eruptions

Highly Productive Polar Forests from the Permian of Antarctica

Authors:

Miller et al

Abstract:

Two stratigraphically closely spaced bedding planes exposed at Lamping Peak in the Upper Buckley Formation, Beardmore Glacier area, Antarctica contain abundant in situ stumps (n=53, n=21) and other plant fossils that allow reconstruction of forest structure and biomass of Glossopteris forests that thrived at ~ 75o S paleolatitude in the Permian. Mean trunk diameter is 14 and 25 cm, corresponding to estimated mean maximum heights of 12 and 19 m. Basal areas are 65 and 80 m2ha- 1. The above ground biomass was calculated using allometric equations for Ginkgo biloba, yielding biomasses of 147 and 178 Mg ha- 1. Biomass estimates based on comparison with biomass of modern forests with equivalent basal areas are higher (225 – 400 Mg ha- 1). The amount of above ground biomass added each year (Annual Net Primary Productivity), based on biomass estimates and growth rings in silicified plant material from the Buckley Formation nearby, is poorly constrained, ranging from ~ 100 – 2000 g m- 2 yr- 1.

Compared to modern forests at all latitudes, the Permian forests have high basal areas and high biomass, exceeded in both only by forests of the U.S. Pacific northwest and Sequoia forests. The estimated range of productivity (ANPP) is within that of many very productive modern forests. The Lamping Peak forests’ basal areas and calculated biomass are also larger than younger high paleolatitude fossil forests except for Arctic Cenozoic forests.

Presence of these highly productive fossil forests at high paleolatitude is consistent with hothouse conditions during the Late Permian, prior to the eruption of the Siberian flood basalts.