P. Fralick - Academia.edu (original) (raw)

Papers by P. Fralick

Proceedings and Abstracts - Institute on Lake Superior Geology, Annual Meeting 4, Sep 9, 1995

AGU Fall Meeting Abstracts, Dec 1, 2015

Precambrian Research, 2009

ABSTRACT Sediments deposited in volcanically active areas preserve a record of the geochemistry o... more ABSTRACT Sediments deposited in volcanically active areas preserve a record of the geochemistry of eroded igneous units. In some instances this record can be more complete than the remaining volcanic rocks. Whole rock geochemistry and detrital zircon geochronology were performed on sedimentary rocks of the Balmer assemblage in the Birch-Uchi Greenstone Belt, western Superior Province, to investigate the types and ages of igneous rocks that were present in the source area at approximately 2.9Ga. Spatially juxtaposed Mesoarchean volcanic rocks were also analyzed for comparative purposes. The detrital zircon geochronology revealed that the sandstones studied are significantly younger than the adjacent volcanic rocks, inferring that their stratigraphic position is the result of tectonic interleaving and they do not belong in the Balmer assemblage. As well, the majority of the detrital zircons were older than the adjacent volcanic rocks severely limiting the potential role of these volcanic units as a source terrain. Extreme geochemical heterogeneity within the sandstone sample set implies the depositional environment was supplied by multiple sediment fed systems, which probably delivered detritus to a submarine ramp environment. A subset of the sandstone samples are HFSE enriched and had, in part, an alkalic igneous source. This infers that the ocean plateau tholeiitic basalts, which are abundant in northwest Superior Province, may have been associated with alkalic eruptive units, similar to modern intra-plate igneous activity. Either erosive or tectonic processes have removed these alkalic igneous units from the preserved rock record, but their detritus is present and identifiable in the sedimentary succession.

Journal of the Royal Astronomical Society of Canada, Oct 1, 1997

Introduction: The best way to study the surficial processes of other planets, apart from direct o... more Introduction: The best way to study the surficial processes of other planets, apart from direct observation through rovers and orbiters, is through the use of analogues. Studying the surface of Mars has become a popular topic as more sophisticated, direct measurements are undertaken using analytical techniques such as Laser Induced Breakdown Spectroscopy (LIBS) and Alpha Particle X-Ray Spectrometry (APSX) on board the Mars Science Laboratory (MSL) Curiosity Rover. Studies of Martian meteorites, observations from orbit and observations from rovers suggest the late crust of Mars is primarily basaltic with some felsic igneous rocks [1,2,3]. Through weathering, the basaltic crust was broken down and now comprises material analyzed by Curiosity. Therefore, investigating the possible effects of weathering on basalts in a low oxygen atmosphere is important in order to better understand data retrieved from rovers such as Curiosity.

Geology

Sedimentary molybdenum (Mo) isotope compositions are a promising paleoredox indicator because the... more Sedimentary molybdenum (Mo) isotope compositions are a promising paleoredox indicator because the Mo isotope composition of seawater reflects the balance between anoxic and oxic sinks. Most available data are from shales; however, the Mo isotope composition of carbonates also reflects the composition of ancient seawater. Here, we provide an expanded data set of carbonate Mo isotope compositions, including the first data for carbonates older than 2.64 Ga, which we evaluate against a compilation of published data for carbonates, shales, and iron formations spanning geological time. Archean carbonate samples reveal maximum δ98Mo values that are generally above 1‰. These heavy values indicate that Mn(IV)-oxide or Fe(III)-oxide sinks were sufficiently important to influence the Mo isotope composition of seawater as far back as 2.93 Ga. Comparison of Mo isotope and rare earth element data, as well as residence time considerations, indicates that this metal-oxide influence was likely globa...

Geochimica et Cosmochimica Acta

Precambrian Research, 2016

The ~1880 Ma Gunflint Formation has played a critical role in shaping our view of the evolution o... more The ~1880 Ma Gunflint Formation has played a critical role in shaping our view of the evolution of the Precambrian biosphere and the redox state of Earth's early oceans. Herein we present a study of the petrology and geochemistry of calcic grainstones and stromatolitic limestones present at the very top of the Gunflint Formation and compare them with underlying ankeritic grainstones that dominate the shore-proximal portion of the basin. Meteoric calcite cements in the upper limestones formed prior to the unit being brecciated and/or buried by debris carried by the blast cloud from the 1850 Ma Sudbury impact event. The intraclastic grains and cements in the limestone are highly enriched in V, Cr, U and REEs, with REE patterns similar to those of modern groundwater. Cr isotopes have a distinctly positive signature in most samples indicating formation of oxidized, hexavalent Cr during subaerial weathering. These redox-sensitive metals were transported in oxygenated groundwater and precipitated where the fluid encountered reducing conditions. In contrast, the underlying ankeritic marine grainstones have REE patterns similar to those of some modern-day venting hydrothermal fluids and earliest Paleoproterozoic seawater. This work suggests that significant levels of oxygen existed in the atmosphere at the time, whereas, even shallow areas of the world ocean remained very oxygen-deficient. The contrast in redox state of anoxic shallow-marine water verses oxic groundwater was probably linked to strong sub-seafloor hydrothermal circulation and extensive upwelling onto shallow shelves, which could have sustained widespread marine anoxia. More broadly, our study highlights the importance of investigating and understanding lateral geochemical gradients, and the flux rates that control them, in shallow paleomarine settings.

Archean to Anthropocene: Field Guides to the Geology of the Mid-Continent of North America, 2011

Sedimentary Geology, 1999

Chute-and-pool structures consist of an inclined surface leading into a pool where a hydraulic ju... more Chute-and-pool structures consist of an inclined surface leading into a pool where a hydraulic jump causes deposition of backset laminae. Structures fitting this description are present at the base of a very fine-grained sandstone bed in the fluvial Matinenda Formation of northern Ontario. Reconstruction of the paleohydraulic system indicates that a depth of approximately 1 cm and a velocity of approximately 65 cm=s formed these bedforms during the initial stage of a flow with increasing depth and decreasing velocity. This type of deposit should be most common at the base of sandy beds deposited as emergent bars are overtopped during increasing discharge events.

Ejecta-bearing debrisites from the 1850 Ma Sudbury impact are described from eight base surge dep... more Ejecta-bearing debrisites from the 1850 Ma Sudbury impact are described from eight base surge deposits north of Lake Superior. Despite being deposited on stromatolites, evidence suggests that the study area was sub-aerial before, during and after the base surges.

Over recent years, there has been considerable interest in the suggestion that after about 1.84 G... more Over recent years, there has been considerable interest in the suggestion that after about 1.84 Ga the Proterozoic ocean was characterised by widespread sulfidic conditions for a period of up to one billion years. Much of this interest stems from the ensuing implications for oxygen production, climate and biological evolution. However, both the spatial and temporal extent of sulfidic conditions over this period have been questioned. In particular, suboxic conditions have been proposed for the deeper ocean, while other studies have suggested a global sulfidic state. All of these previous studies are limited either by considering relatively few samples with little stratigraphic context, or by utilising poorly-constrained models. To provide a robust assessment of the redox structure of the ocean during the transition from ferruginous conditions at 1.84 Ga, we have investigated over 400 samples from the 1.9-1.8 Ga Animikie Basin, Ontario, Canada. Samples come from 6 cores spread over a ...