Middle Triassic Paleosols and paleoclimate of Antarctica

Retallack, Gregory J.; Alonso-Zarza, Ana María

doi:10.2110/jsr.68.169

Cited by 44 publications

(23 citation statements)

References 67 publications

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“…Small-scale cross-bedding and ripple laminae occur in fi negrained sandstone. White root casts similar to those described by Retallack and Alonso-Zarza (1998) (Vavra, 1982). Closed triangles are from the Fremouw Formation below the vertebrate-bearing beds.…”

Section: Lower Fremouw Boundary Sectionssupporting

confidence: 75%

Permian-Triassic boundary in the central Transantarctic Mountains, Antarctica

Collinson

Hammer

Askin

et al. 2006

Geological Society of America Bulletin

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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 fl ora 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 fl ora and occur near the top of the Buckley coal measures, just below a previously reported major negative δ 13 C excursion. In the Shackleton Glacier area, the Per mian Glossopteris fl ora, 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 CO 2 emissions from Siberian fl ood basalts and large methane gas releases. Changes in fl ora bracketing the fi rst of the major negative δ 13 C 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 fl oras.

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Section: Lower Fremouw Boundary Sectionssupporting

confidence: 75%

Permian-Triassic boundary in the central Transantarctic Mountains, Antarctica

Collinson

Hammer

Askin

et al. 2006

Geological Society of America Bulletin

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“…Sandstones throughout the Victoria Group are composed of moderately to well-sorted subangular to rounded quartz grains, with subordinate feldspar, mica, garnet and lithic clasts (mostly highly micaceous carbonaceous siltstone). The sedimentary features of the Victoria Group in the Coombs Hills area indicate fluvial deposition on broad floodplains (Smith et al 1998) interspersed with marshes (Krull 1999) and peat domes grown in distal overbank settings (Staub and Esterle 1994) or perhaps along the margins of lakes (Retallack and Alonso-Zarza 1998;Smith et al 1998). Diverse broadleaf plants and noncalcareous paleosols in the youngest Victoria Group rocks (Lashly Formation) suggest a humid, seasonally snowy climate with mean annual precipitation of about 1 metre/yr immediately prior to Ferrar-Karoo LIP volcanic time (Retallack and Alonso-Zarza 1998).…”

Section: Geology Of Coombs Hillsmentioning

confidence: 99%

“…The sedimentary features of the Victoria Group in the Coombs Hills area indicate fluvial deposition on broad floodplains (Smith et al 1998) interspersed with marshes (Krull 1999) and peat domes grown in distal overbank settings (Staub and Esterle 1994) or perhaps along the margins of lakes (Retallack and Alonso-Zarza 1998;Smith et al 1998). Diverse broadleaf plants and noncalcareous paleosols in the youngest Victoria Group rocks (Lashly Formation) suggest a humid, seasonally snowy climate with mean annual precipitation of about 1 metre/yr immediately prior to Ferrar-Karoo LIP volcanic time (Retallack and Alonso-Zarza 1998). The uppermost Victoria Group strata at Coombs Hills are inferred to have been wet and poorly indurated at the initiation of LIP volcanism on the basis of: (1) extensive peperite, swirly dikes and intrusive hyaloclastite along contacts with intrusions; (2) an abundance of quenched glassy basalt along intrusive contacts (quenched margins), and as a juvenile component of peperite and intrusive hyaloclastite; and (3) deformation and/or destruction of bedding in host Victoria Group sediments adjacent to intrusive contacts, suggesting local remobilisation of host sediment particles.…”

Section: Geology Of Coombs Hillsmentioning

confidence: 99%

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Large phreatomagmatic vent complex at Coombs Hills, Antarctica: Wet, explosive initiation of flood basalt volcanism in the Ferrar-Karoo LIP

McClintock

White

2005

Bull Volcanol

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The Mawson Formation and correlatives in the Transantarctic Mountains and South Africa record an early eruption episode related to the onset of Ferrar-Karoo flood basalt volcanism. Mawson Formation rocks at Coombs Hills comprise mainly (≥80% vol) structureless tuff breccia and coarse lapilli tuff cut by irregular dikes and sills, within a large vent complex (>30 km 2 ). Quenched juvenile fragments of generally low but variable vesicularity, accretionary lapilli and country rock clasts within vent-fill, and pyroclastic density current deposits point to explosive interaction of basalt with groundwater in porous country rock and wet vent filling debris. Metre-scale dikes and pods of coherent basalt in places merge imperceptibly into peperite and then into surrounding breccia. Steeply dipping to sub-vertical depositional contacts juxtapose volcaniclastic rocks of contrasting componentry and grainsize. These sub-vertical tuff breccia zones are inferred to have formed when jets of debris + steam + water passed through unconsolidated vent-filling deposits. These jets of debris may have sometimes breached the surface to form subaerial tephra jets which fed subaerial pyroclastic density currents and fall deposits. Others, however, probably died out within vent fill before reaching the surface, allowing mixing and recycling of clasts which never reached the atmosphere. Most of the ejecta that did escape the debris-filled vents was rapidly recycled as vents broadened via lateral quarrying of country rock and bedded pyroclastic vent-rim deposits, which collapsed along the margins into individual vents. The unstratified, poorly sorted deposits comprising most of the complex are capped by tuff, lapilli tuff and tuff breccia beds inferred to have been deposited on the floor of the vent complex by pyroclastic density currents.involved interaction of large volumes of magma and water. We infer that recycling of water, as well as recycling of pyroclasts, was important in maintaining water supply for phreatomagmatic interactions even when aquifer rock in the vent walls lay far from eruption sites as a consequence of vent-complex widening. The proportion of recycled water increased with vent-complex size in the same way that the proportion of recycled tephra did. Though water recycling leaves no direct rock record, the volcaniclastic deposits within the vent complex show through their lithofacies/structural architecture, lithofacies characteristics, and particle properties clear evidence for extensive and varied recycling of material as the complex evolved.

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“…A source of silica may have been devitrified volcanic shards, which are common in Yanwa paleosols. The mechanism of silicification may have involved silica precipitating anaerobic micro-organisms such as Desulfovibrio (Birnbaum et al, 1989), as in Triassic volcaniclastic sequences in Antarctica (Retallack and Alonso-Zarza, 1998).…”

Section: Traces Of Land Lifementioning

confidence: 99%

Eocene and Oligocene Paleosols of Central Oregon

Retallack¹,

Bestland²,

Fremd³

1999

Eocene and Oligocene Paleosols of Central Oregon

141

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Scenic red color-banded claystones of the Clarno and Painted Hills areas of central Oregon are successions of fossil soils that preserve a record of Eocene-Oligocene paleoclimatic change. Conglomerates of the middle Eocene Clarno Formation near Clarno contain largely weakly developed paleosols compatible with an environment of volcanic lahars around a large stratovolcano. Deeply weathered paleosols (Ultisols) around a volcanic dome and overlying these conglomerates indicate a climate that was subtropical (mean annual temperature or MAT 23-25°C) and humid (mean annual precipitation or MAP of 900-2,000 mm). Comparable paleoclimates are indicated by fossil floras from the conglomerates, which show diversity and adaptive features similar to modern vegetation of Volcan San Martin, Mexico. An erosional disconformity in the Clarno area separates these older beds from less deeply weathered red paleosols (Alfisols) in the middle Eocene upper Clarno Formation. The change in paleosols may represent a decline in both temperature (MAT 19-23°C) and rainfall (MAP 900-1,350 mm), with dry seasons. Strongly developed lateritic paleosols (Oxisols and Ultisols) in the uppermost Clarno and lowermost John Day Formations in the Painted Hills record return to more humid conditions during the late Eocene. These paleosols are similar to soils of southern Mexico and Central America in climates that are subtropical (MAT 23-25° C) and humid (MAP 900-2,000 mm). Kaolinitic and iron-rich, red paleosols (Ultisols) of the lower Big Basin Member of the John Day Formation near Clarno and the Painted Hills are erosionally truncated and abruptly overlain by smectitic and tuffaceous paleosols (Inceptisols and Alfisols) of the middle Big Basin Member. This truncation surface can be correlated with the local Eocene-Oligocene boundary. Paleosols of the middle Big Basin Member are most like those of the Central Transmexican Volcanic Belt and indicate an early Oligocene paleoclimate appreciably cooler (MAT 16-18° C) and drier (MAP 600-1,200 mm) than during the late Eocene. Root traces and clay accumulations in the paleosols indicate forest vegetation, also evident from fossil leaves of the lake-margin Bridge Creek flora.The mid-Oligocene upper Big Basin Member of the John Day Formation includes distinctive brown as well as red paleosols (Alfisols). Its paleosols indicate a paleoclimate drier (MAP 500-700 mm) than before, and more grasses in the forest understory.Another erosional truncation marks the base of the late Oligocene (early Arikareean), olive-brown lower Turtle Cove Member of the John Day Formation. Calcareous paleosols with near-granular soil structure (Inceptisols and Aridisols) indicate an even

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Middle Triassic Paleosols and paleoclimate of Antarctica

Cited by 44 publications

References 67 publications

Permian-Triassic boundary in the central Transantarctic Mountains, Antarctica

Permian-Triassic boundary in the central Transantarctic Mountains, Antarctica

Large phreatomagmatic vent complex at Coombs Hills, Antarctica: Wet, explosive initiation of flood basalt volcanism in the Ferrar-Karoo LIP

Eocene and Oligocene Paleosols of Central Oregon

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