Deposition and deformation of fluvial–lacustrine sediments of the Upper Triassic–Lower Jurassic Whitmore Point Member, Moenave Formation, northern Arizona

ABSTRACT Two types of unusual concretions with similar biotic contents but markedly different shapes and distributions were found in close stratigraphic proximity within the Lower Jurassic Whitmore Point Member of the Moenave Formation in St. George, Utah. Both types of concretions formed in lacustrine sediments and contain abundant ganoid fish scales, numerous ostracode carapaces, and apparent rip-up clasts. Elongate, cylindrical concretions developed in parallel and regularly spaced rows in one horizon, and comparatively flat and irregularly shaped and distributed concretions formed in an overlying layer only a few centimeters above. Microprobe and Raman analyses of concretion samples reveal abundant hematite in both concretions as well as groundmass minerals dominated by silica in the cylindrical concretions and dolomite in the flat concretions. The abundance of fish skeletal debris in concretions from two consecutive horizons may suggest recurring fish mass mortality in ancient Lake Dixie, the large lake that occupied the St. George area during the Early Jurassic. We propose a model for the formation of the concretions based on their shapes, distributions, and chemistry. In this model, accumulations of disarticulated fish debris were colonized and consolidated by microbial mats and shaped by oscillatory flow (in the case of the cylindrical concretions) or lack thereof (in the case of the flat concretions). Then, after burial, groundwater chemistry and possibly the metabolic activities of microorganisms led to the precipitation of minerals around and within the masses of fish material. Finally, diagenetic alteration changed the mineral makeups of the cylindrical and flat concretions into what they are today.

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The ‘Last Hurrah of the Reigning Darwinulocopines’? Ostracoda (Arthropoda, Crustacea) from the Lower Jurassic Moenave Formation, Arizona and Utah, USA

Journal of Paleontology ◽

10.1017/jpa.2017.150 ◽

2018 ◽

Vol 92 (4) ◽

pp. 648-660 ◽

Cited By ~ 3

Author(s):

Lucas S. Antonietto ◽

Lisa E. Park Boush ◽

Celina A. Suarez ◽

Andrew R.C. Milner ◽

James I. Kirkland

Keyword(s):

Asexual Reproduction ◽

Fossil Record ◽

Late Jurassic ◽

Lacustrine Sediments ◽

Lower Jurassic ◽

Late Triassic ◽

Geographical Isolation ◽

Central Atlantic Magmatic Province ◽

Central Atlantic ◽

Moenave Formation

AbstractAn ostracode fauna is described from lacustrine sediments of the Hettangian, Lower Jurassic, Whitmore Point Member of the Moenave Formation. The Moenave is well known for its rich, Late Triassic?–Early Jurassic fossil record, which includes fossil fishes, stromatolites, ostracodes, spinicaudatans, and a diverse ichnofauna of invertebrates and vertebrates. Four ostracode species, all belonging to the suborder Darwinulocopina, were recovered from these sediments:Suchonellina globosa,S. stricta,Whipplella? sp. 1, andW.? sp. 2. The diversity and composition of the Whitmore Point Member ostracode fauna agree with previous interpretations about Lake Dixie and nearby paleoenvironments as shallow lakes inhabited by darwinulocopine species that survived the effects of the Central Atlantic Magmatic Province and the subsequent end-Triassic extinction and quickly recolonized these areas, thanks to asexual reproduction by parthenogenesis. The Lake Dixie region, in its geographical isolation, could represent the last episode of darwinulocopine dominance in nonmarine environments before the Late Jurassic diversification of the cypridocopine/cytherocopine modern ostracodes.

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MESOZOIC RADIOLARIANS FROM RHYTHMICALLY LAYERED SEDIMENTS OF THE RIMSKY-KORSAKOV ISLANDS (PETER THE GREAT BAY, JAPAN SEA) AND THEIR SIGNIFICANCE FOR DETERMINING THE TRIASSIC-JURASSIC BOUNDARY

Tikhookeanskaya Geologiya ◽

10.30911/0207-4028-2021-40-2-39-54 ◽

2021 ◽

pp. 39-54

Author(s):

O.L. Smirnova ◽

◽

E.A. Bessonova ◽

T.A. Emelyanova ◽

◽

...

Keyword(s):

Peter The Great Bay ◽

Japan Sea ◽

Research Area ◽

Lower Jurassic ◽

Upper Triassic ◽

Peter The Great ◽

Great Bay ◽

The Pacific ◽

Stratigraphic Division ◽

First Time

The results of the biostratigraphic study based on the radiolarian analysis of the rhythmically layered terrigenous deposits from the Islands of the Rimsky-Korsakov Archipelago (Peter the Great Bay, Japan Sea) have been presented. These deposits are most similar to the medium-grained turbidites. For the first time the distribution and stratigraphic division of the boundary sediments of the upper Triassic and lower Jurassic separated by a marking layer were substantiated in the research area. On the basis of comparisons with isochronous zonal units of the Pacific and Tethyan areas in the upper Triassic sediments of the studied sections, layers with Globolaxtorum tozeri (upper Rhaetian) were established, and in the lower Jurassic zone Pantanellium tanuense Zone (Hettangian) was traced and layers with Parahsuum simplum (Sinemurian – Pliensbachian) were established.

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A hyper-robust sauropodomorph dinosaur ilium from the Upper Triassic–Lower Jurassic Elliot Formation of South Africa: Implications for the functional diversity of basal Sauropodomorpha

Journal of African Earth Sciences ◽

10.1016/j.jafrearsci.2016.08.004 ◽

2016 ◽

Vol 123 ◽

pp. 177-184 ◽

Cited By ~ 7

Author(s):

Blair W. McPhee ◽

Jonah N. Choiniere

Keyword(s):

South Africa ◽

Functional Diversity ◽

Lower Jurassic ◽

Upper Triassic

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An ichthyosaur forefin from the Triassic of British Columbia exemplifying Jurassic features

Canadian Journal of Earth Sciences ◽

10.1139/e91-139 ◽

1991 ◽

Vol 28 (10) ◽

pp. 1553-1560 ◽

Cited By ~ 16

Author(s):

C. McGowan

Keyword(s):

British Columbia ◽

North America ◽

Lower Jurassic ◽

Upper Triassic ◽

New Material ◽

Important Site

New ichthyosaur material is reported from an Upper Triassic locality on Williston Lake, northeastern British Columbia. The paucity of ichthyosaurs from the Triassic of North America make this a potentially important site. An isolated forefin is described, which is unlike that of any Triassic species from North America but which compares closely with certain Lower Jurassic species from England and Germany. The new material suggests that the transition in the ichthyosaurian fauna at the close of the Triassic may have been less abrupt than was previously supposed.

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Geothermal Reservoir Quality of Upper Triassic – Lower Jurassic Paralic Sandstones in Copenhagen

Fourth Sustainable Earth Sciences Conference ◽

10.3997/2214-4609.201702125 ◽

2017 ◽

Author(s):

M. Olivarius ◽

H. Vosgerau ◽

U. Gregersen ◽

L. Kristensen ◽

R. Weibel ◽

...

Keyword(s):

Lower Jurassic ◽

Upper Triassic ◽

Geothermal Reservoir ◽

Reservoir Quality

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Fault-controlled dolomitization in the Montagna dei Fiori Anticline (Central Apennines, Italy): record of a dominantly pre-orogenic fluid migration

Solid Earth ◽

10.5194/se-10-1355-2019 ◽

2019 ◽

Vol 10 (4) ◽

pp. 1355-1383 ◽

Cited By ~ 2

Author(s):

Mahtab Mozafari ◽

Rudy Swennen ◽

Fabrizio Balsamo ◽

Hamdy El Desouky ◽

Fabrizio Storti ◽

...

Keyword(s):

Field Work ◽

High Amplitude ◽

Lower Jurassic ◽

Upper Triassic ◽

Fluid Migration ◽

Central Apennines ◽

Elevated Salinity ◽

Siliciclastic Rocks

Abstract. The Lower Jurassic platform and basinal deposits exposed in the Montagna dei Fiori Anticline (Central Apennines, Italy) are pervasively affected by dolomitization. Based on the integration of field work, petrography, and geochemistry, two fault-related dolomitization events were recognized and interpreted as having occurred before and during the Apenninic orogeny. Fluid inclusion analysis indicates moderate to elevated salinity values of 3.5 to 20.5 and 12.8 to 18.6 eq. wt % NaCl in the first and the second event, respectively. The estimated salinities, in combination with δ18O values and 87Sr∕86Sr ratios, suggest significant involvement of evaporitic fluids in both events, most likely derived from the underlying Upper Triassic Burano Formation. In addition, the 87Sr∕86Sr ratios up to 0.70963 suggest the circulation of deep-sourced fluids that interacted with siliciclastic rocks and/or the crystalline basement during the dolomitization events. Two major dolomite types (D1 and D2) were recognized as pertaining to the first event, both postdated by high-amplitude bed-parallel stylolites, supporting a syn-burial pre-layer-parallel shortening dolomitization. A possible geodynamic framework for this dolomitization event is Early Jurassic to Late Jurassic rift-related extensional tectonism. The second dolomitization event (D3, D4, and D5) is characterized by a temperature upturn (up to 105 ∘C) and interpreted as associated with the inflow of hydrothermal fluids, possibly related to major changes in the permeability architecture of faults during early- to syn-thrusting and folding activity. Based on the timing of deformation in the Montagna dei Fiori Anticline, the second dolomitization event likely occurred in Late Miocene to Pliocene times. The findings regarding characteristics and timing of dolomitization here illustrates the long-term controlling role of the evaporitic detachments in the dolomitization process. This study shows that the Mg-rich fluids that were most likely derived from evaporites may prime the tectonically involved successions for repeated dolomitization, and hence the formation of potential reservoirs during sequential tectonic modifications (extensional vs. compressional).

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