James W. Collinson

Depositional setting and paleobotany of Permian and Triassic permineralized peat from the central Transantarctic Mountains, Antarctica

Abstract Silicified peat is known from two sites in the central Transantarctic Mountains. Both are within a 2-km-thick Permo-Triassic sandstone-shale sequence that was deposited by braided streams in a rapidly subsiding foreland basin along the paleo-Pacific margin of Antarctica. Upper Permian permineralized peat occurs as scattered boulders just above a channel-form sandstone in the upper part of the Buckley Formation on Skaar Ridge overlooking the Beardmore Glacier. These boulders are erosional remnants of fine-grained deposits that accumulated in shallow lakes or swamps on a flood plain. At Fremouw Peak, the peat occurs near the top of the Fremouw Formation in strata that are probably Middle to Late Triassic in age. The peat consists of large blocks that were rafted into a sandy braided stream channel during a flood and then stranded and buried as flood waters receded. Both sites are characterized by exceptionally well-preserved plant material, although the composition and diversity of the two floras are very different. Permineralization apparently took place rapidly and was enhanced by the dissolution of siliceous volcanic detritus that is abundant in both formations.

Tetrapod and Large Burrows of Uncertain Origin in Triassic High Paleolatitude Floodplain Deposits, Antarctica

Abstract Two types of large diameter burrows, recognized by non-overlapping size distributions, occur in high paleolatitude floodplain deposits of the Lower Triassic Fremouw Formation, Shackleton Glacier area, Antarctica. Type G (giant) burrows are gently dipping tunnels 8 to 19 cm in diameter. Type L (large) burrows are 2 to 6.5 cm in diameter, curved or subhorizontal tunnels that rarely branch; scratch markings on both burrow types generally are parallel or tangential to the long axis of the burrows. Type G burrows are interpreted as produced by tetrapods based on similarity in size, architecture, and surface markings to Permian burrows from South Africa that contain complete skeletons of therapsids. These are the first tetrapod burrows described from Antarctica. Type L burrows have characteristics of both fossil tetrapod and crayfish burrows, precluding identification of an unique producer. Triassic tetrapods, including therapsids, that lived in high southern latitudes probably burrowed to dampen the effects of seasonal environmental fluctuations, just as do many of their mammalian counterparts living today in high latitudes. The paleolatitudinal and paleooclimatic distributions of burrowing therapsids and their mammalian descendents can be assessed by focusing search efforts on very large burrows, and by identifying producers using criteria delineated herein; this will clarify the extent to which the burrowing habit originated and persisted in high latitudes.

Permian-Triassic boundary in the central Transantarctic Mountains, Antarctica

The Permian-Triassic boundary occurs within a relatively complete terrestrial sequence in the Shackleton Glacier area of the central Transantarctic Mountains. The boundary is within a 7- to 10-m-thick interval between the Permian Glossopteris flora and the Lower Triassic Lystrosaurus fauna. This interval, representing on the order of 200 k.y., records some of the events that occurred in the transition from the Permian to Triassic. In the best-documented section at Graphite Peak in the Beardmore Glacier region, Protohaploxypinus microcorpus zone palynomorphs, which we assign to the latest Permian, record the declining Glossopteris flora and occur near the top of the Buckley coal measures, just below a previously reported major negative δ13C excursion. In the Shackleton Glacier area, the Permian Glossopteris flora, including fossil wood, roots, and leaves, occurs within the lower part of the Fremouw Formation. The Antarctic Lystrosaurus assemblage of Early Triassic age has several species in common with the South African fauna that lived 20° to 35° closer to the equator. The migration of vertebrates from southern Africa into Antarctica in the Early Triassic supports hypotheses of runaway greenhouse warming possibly related to CO2 emissions from Siberian flood basalts and large methane gas releases. Changes in flora bracketing the first of the major negative δ13C anomalies near the boundary in Antarctica and in East Greenland support the hypothesis that a global event, perhaps through mutations caused by enhanced ultraviolet radiation, may have played a role in the destruction of floras.

Depositional history of Paleocene-lower Eocene Flagstaff Limestone and coeval rocks, central Utah

The Flagstaff Limestone of Paleocene and early Eocene age, and coeval rocks of the North Horn and Colton Formations of central Utah, were deposited in the Lake Flagstaff lacustrine-alluvial complex. The Flagstaff lake basin formed in response to postorogenic deformation along the Sevier thrust belt and Laramide basement uplifts that blocked drainage. The Flagstaff Limestone of the Wasatch Plateau consists of three members; the lower member, designated Ferron Mountain, and the upper, the Musinia Peak, represent major high stands of the lake. They consist of mudstone, brecciated and massive carbonate rock with rootlets and pedogenic features, laminated and structureless limestone, fossiliferous limestone, and oncolitic and sandy limestone. During deposition of the Ferron Mo ntain Member, the eastern margin of the lake was vegetated, very shallow, and episodically exposed. In contrast, a relatively steep, high-energy shoreline along active structural elements bounded the west side of the lake. The middle member, designated Cove Mountain, consists of mud-cracked dolomicrite, mudstone, and bedded and nodular gypsum. These beds reflect repeated contractions and expansions of the lake across a broad carbonate mud flat. Freshwater limestones that were deposited during expansions of the lake probably were altered to dolomicrite during contractions by evaporative pumping of brine on mud flats.

Lystrosaurus Zone (Triassic) Fauna from Antarctica

Tetrapod skeletons recently found in the Fremouw Formation in the Shackleton Glacier area, Transantarctic Mountains, include several forms that closely compare to South African species. Faunal similarities that confirm a close connection between Antarctica and Africa during the Triassic Period lend further support to the concept of Gondwanaland and continental drift.

Paleozoic-Mesozoic crayfish from Antarctica: Earliest evidence of freshwater decapod crustaceans

Discovery of an Early Permian claw from Antarctica extends the fossil record of crayfish by ∼65 m.y. and demonstrates that decapod crustaceans had radiated into freshwater habitats by the late Paleozoic. Burrows in Lower Triassic rocks of Antarctica are among the oldest apparently constructed by crayfish. Their morphology is similar to modern crayfish burrows, and this demonstrates that burrowing behavior was established early in the evolution of this group. The new discoveries show that the earliest Permian crayfish were distributed in high paleolatitudes of southernmost Pangea, where they lived in freshwater lakes fed by glacial meltwater. Modern crayfish habitat, used as a guide to crayfish temperature tolerance, indicates that summer temperatures of streams and lakes near the South Pole that supported the crayfish probably reached 10–20 °C during Permian-Triassic interglacial intervals.

A new Triassic vertebrate fauna from Antarctica and its depositional setting

AbstrackA new fauna of late Early to early Middle Triassic vertebrates has been found in the upper member of the Fremouw Formation in the Beardmore Glacier area of Antarctica. It includes Cynognathus, a kannmeyeriid, and other therapsid (mammal-like) reptiles representing new, more derived genera of carnivorous and gomphodont cynodonts. New genera of temnospondyl amphibians belonging to the capitosauroid evolutionary complex also occur. The unusual abundance of well-preserved amphibians may offer new insights concerning the evolution and distribution patterns of early Mesozoic temnospondyls. These fossils represent only the second terrestrial vertebrate fauna from the mainland of Antarctica. The fossils occur on a prominent sandstone platform, which represents part of the exhumed channel of a braided stream deposit. The platform is over 200 metres above the well-known Lystrosaurus fauna of the lower Fremouw Formation. The locality is near the axis of a major foreland basin that paralleled the present trend of the Transantarctic Mountains. Conditions of rapid subsidence and aggradation of fluvial units were ideal for the preservation of vertebrate faunas.

A petrified Glossopteris flora from Collinson Ridge, central Transantarctic Mountains: Late Permian or Early Triassic?

The Permian^Triassic boundary in Gondwana has traditionally been based on lithology and a change from the glossopterid-dominated flora in the Permian to the Dicroidium-dominated flora in the Triassic.There have, however, been a few reports of Glossopteris occurring in the Lower Triassic of Tasmania, Antarctica, South Africa and India, usually as a minor element in floras dominated by Dicroidium.The material described here was collected from a lens of silicified peat from Collinson Ridge in the central Transantarctic Mountains, Shackleton Glacier area of Antarctica.Based on lithology, this site appears to be in the lower part of the Fremouw Formation, which has previously been dated as Early Triassic.However, the discovery of a dominant Glossopteris flora, including petrified leaf fragments, Vertebraria and Araucarioxylon-type wood, along with the absence of Dicroidium, suggests a latest Permian age.5 2002 Elsevier Science B. All rights reserved.

Permian-Triassic boundary in eastern Nevada and west-central Utah

The Permian-Triassic boundary in eastern Nevada and west-central Utah is placed at a disconformity above the Gerster Formation (Wordian) and below the Thaynes Formation (Smithian and Spathian). Evidence of subaerial erosion at the disconformity includes local truncation of Gerster beds by channels filled with chert and quartzite-pebble conglomerate. Westward onlap of Lower Triassic sedimentary deposits, as demonstrated by conodont zones, suggests an east-facing paleoslope over which the Early Triassic sea slowly advanced. The Sonoma orogeny, which coincided with the Late Permian—Early Triassic hiatus, may have been the cause of regional upwarping in eastern Nevada that produced the eastward paleoslope.

Trace fossils from Permian and Triassic sandy braided stream deposits, central Transantarctic Mountains

Sandy braided streams delivering sediment to the foreland basin along the paleo-Pacific margin of Gondwana during the Permian and Triassic were inhabited by an active infaunal animal, probably an arthropod. This animal moved horizontally and vertically within the sediment, producing four types of traces, including vertical shafts, horizontal endostratal trails, bilobed endostratal trails and chevron traces. A common producer is indicated by congruence of size distributions of the traces, and by the fact that single traces change from one type to another. Unable to survive high flow conditions, the animal colonized channel bar sands during slack water and moved in unlined burrows throughout the upper 20 cm of sediment. Its opportunism and behavioral plasticity may have been keys to its survival and success in sandy fluvial habitats throughout the Late Permian and Triassic.