Stable Isotope Geochemistry


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Rosalba Bonaccorsi <[log in to unmask]>
Reply To:
Stable Isotope Geochemistry <[log in to unmask]>
Fri, 13 Feb 2004 04:08:00 +0100
text/plain (246 lines)
Dear Prof. Beaudoin,

I would be interested in posted post-soc position. However, before applying for
I would like realizing whether a) my background would fit you interests and
needs; and b) as a non-Canadian Citizen I would be eligible for this specific

I did my PhD under the Italian Antarctic Research Program (PNRA) at the
University of Trieste by working on some Antarctic marine sediment cores to
constrain late Quaternary changes in the paleoceanography/ paleoenvironment of
the Ross Sea (last glacial/interglacial 10-30 kyr events).

Antarctic proximal sequences retain proxies (e.g., unusual concentrations of
microfossils and variations in coarse-grained ice rafted materials) for changes
in the size and extension of the Ross Ice Shelf-Ice Sheet system. In addition,
the study of subglacial diamicton from shallow cores provided evidences of
potential continental sources (i.e., Dry valley regions, subglacial pools) of
organics and mineral particles (e.g., carbonates, silicates) still
recognizable. However, the Ross Sea continental margin is also a quite complex
sedimentary setting owing to interactions among different components of the
Antarctic system (land, glaciers, ice shelves and the ocean).
So, I preferred to follow a multidisciplinary/interdisciplinary approach
integrating data set from sediment analysis, micropaleontological observations,
organic geochemistry and radiogenic isotopes (e.g., to see provenance of ice
rafted mineral materials).

Having found well-preserved polar carbonates (i.e., sea-ice associated forms of
the planktonic foraminifer N. pachyderma, left coiling) in some deep- sea cores
represents one of the major achievements from my PhD work and it is still
novel.  Layers of foram-rich Ice Rafted detritus are not only a reliable dating
tool for possible climate-induced ice rafting events of Antarctic ice shelves,
but also a wonderful mean to constrain glacials/interglacials sea-ice
More work should be done to understand the mechanism triggering the
preservation of calcareous foraminifers (bracketing 17-33 ka) in the Ross Sea.

Shortly after defending my PhD (February 2001) I served as a Sedimentologist
during a drilling cruise (ODP Leg 197 N. Pacific Transect - June 2001-August
2001). Most importantly, this participation allowed me to work on rare and
precious samples of subsurface volcanically-derived red fossil soils, plus
gaining experience on the recognition, the analysis and interpretation of a
variety of Tertiary age sedimentary sequences (e.g., nannofossil/foram to
diatom oozes and chalks) from the N. Pacific. I used smear slide analysis for
mud logging and made correlations betwees sediemntological and physical
proerties (MS, Bulk density, porosity, Pwave amplitude) from borehole data.

In 2002, I worked as technician/researcher for a private company where I gained
the basic experience on the analysis of Elemental and stable isotopes (13C and
15N) and data interpretation to track sources of bulk C-org and N in various
materials (sediment, fossil soil, food, compost).

From late 2001 until now I have been independently working on low-organics
early-Eocene sub- basement fossil soil and I proposed them as a new analogs for
a possible subsurface biosphere on Mars.  Currently, I am doing post-doc level
research at my department as a scientific collaborator (self-employed).  I am
looking now for a postdoc position or so on the geomicrobiology of deep
subsurface environments.

For brevity, I am providing you with a recently submitted abstract to let you
realize about my primary interest (see below, please) plus a list of
publications/presentations coming with next email.

Please, if you realize that I am not eligible for this post, let me know I
might fit some else position under your programme de géologie and or at
Université Laval.

Thank you very much in advance,

All the best,

Rosalba Bonaccorsi



 Why are Leg 197 red paleosoils test beds for deep subsurface soil and
biosphere on Mars? The sub-basement red paleosoils, or fossil soils, found in
the North Pacific seamounts [1] could be useful for this purpose because they
preserve organic concentrations (pristine and/or diagenetic) in a deeply buried
subsurface setting, which is isolated from the Earth surface and the ocean.

The detection of past life buried deep beneath the surface of a planet is a
fundamental step towards the understanding of the presence and evolution of
life on that planet.  Although not unequivocal, the near-surface Martian soil
is expected to be barren of life and organics owing to the interaction of UV
radiation with a potential oxidant (i.e., peroxide/superoxide) [e.g., 2] in the
soil itself. This interaction prevents the accumulation of near-surface
organics.  Furthermore, the present-day conditions on the surface of Mars are
drastically different from those on Earth.  Mars has a very low atmospheric
pressure (4-10 mbar) and surface temperatures (down to -125°C), which prevent
the stability of liquid water.  However, if there had been life in the past on
a wetter and warmer early Mars, some fossil record, biological signature or
microbial life (chemosynthetic communities [e.g., 3]) could have been preserved
beneath some tens- to hundreds meters of depth [e.g., 3, 4].   With sufficient
depth, the oxidant concentration would decrease owing to an effective shielding
from UV radiation.  Hence, we need to identify new suitable terrestrial analogs
(such as the fossil soil from Leg 197) to use as a test system for possible
surface-decoupled deep settings on Mars.

Early Eocene units of red-brown fossil soil were drilled deeply beneath the
volcanic basement (down to 46.8 to 309.9 meters below seafloor; mbsf) at
Nintoku Seamount (Site 1205, ~41° 20’N; ~170° 23’E) and Koko Seamount (Site
1206, ~34° 56’N; ~172° 9’E) during the Ocean Drilling Program (ODP) Leg 197.
These organics-poor (C-org = 0.01-0.12 wt%%, ± 0.02%, N = 36; N-tot = 0.01-
0.006, wt%; [8]) soil interbeds contain Fe-oxides/oxy-hydroxides, hematite,
magnetite, some feldspar, palagonite and clay minerals (e.g., smectite) and are
thought to represent the tropical weathering product of mafic igneous rocks and
basalts [1,5].

The complete isolation of these rare paleosoils is supported by two independent
lines of evidence such as: a) a well established model based upon literature
(i.e., surface formation, deep burial and isolation from the atmosphere and the
ocean), confirmed by results of Leg 197, and proposed for the atmosphere-ocean
decoupled subsurface [6]; and b) new geochemical information [7] suggesting
that some geochemical differentiation of the fossils soils from their exposed
counterparts (e.g., red-brown Hawaiian oxisols) [8] occurred after burial and
encapsulation in lava flows.   The single fossil soil unit (Core 197-1206A-
40R), in fact, has stable isotope values more negative (i.e., d13C-org = ~ -26
per mil. and d15N-tot = -9.5 per mil. to +2.5 per mil.) than those of Hawaiian
oxisols (i.e., d13C-org = ~-17 per mil. to ~ -23 per mil; and d15N-tot = 0 per
mil. to +8.5 per mil; unpubl. data). This could indicate a complex origin for
organic carbon and nitrogen such as terrestrial plants and past/present
microbial-induced activity (nitrogen fixation, nitrification, and
denitrification) [7].

The model proposed for the atmosphere-ocean decoupled subsurface consists of:
a) Sub-aerial formation of soil on the top of subsiding islands; b) burial by
lava flows in a high-land near shore environment prior to complete subsidence
below sea level (~1 to ~2 Ma), and isolation from the atmosphere; c) subsidence
and isolation from the ocean (from ~48 to ~54-55 Ma until present); Burial
rates of ~4 to ~25 metres/1000y), higher than average subsidence rates (e.g.,
present day ~2.5 mm/years), placed these fossil soils in a present-day sub-
basement setting and ensured soil decoupling from the atmosphere and the ocean.
These soils, indeed, are barren of marine microfossil [1, 5-6], which implied
isolation from lagoon and open seawaters.

It is possible that for each of those phases different organic traces were
produced preserved, and/or overprinted and microbial ecologies were selected by
changing environmental conditions. For instance, the heating effect, which
derives from contact with lava flows, and post-burial diagenetic conditions
might have caused the observed geochemical divergence from their still exposed
counterparts (typical tropical oxisoils).   Further geomicrobiological
investigations (e.g., using molecular techniques for the study of Microbial
community) on subsurface materials from a nutrient- limited deep earth system
(no sun light, and reducing conditions), which remained isolated both from the
ocean and the atmosphere for millions of years, will help to develop a new
analog model for deep drilling of a possible subsurface biosphere (that are
well-known for subsurface environments on Earth [e.g., 9]) preserved on Mars.
This knowledge could be then applied to the understanding of samples eventually
returned from future Mars drilling/sample return missions [4, 6].

REFERENCES: [1] Tarduno, J.A., and the Leg 197 Science shipboard Party, 2002)
Proc. ODP, Init. Repts., 197; [2] Zent, A.P., and McKay, C.P., 1994 Icarus
108,146-157;  [3] Boston, et al., 1992 Icarus 95, 300-308;  [4] Mancinelli,
R.L., 2000 Planet. Space Sci., 48,1035-1043;  [5] Holmes, M.A., 1995 Proc. of
the Ocean Drilling Program, Scientific Results, 144,381-398; [6] Bonaccorsi,
R., in press. S-213 Bioastronomy 2002: Life Among the Stars (ASP) IAU
Publications;  [7] Bonaccorsi, R., 2002 Eos Trans. AGU, 83(47), Fall Meet.
Suppl., Abstract;  [8] Bonaccorsi, R., (in prep.) Proc. ODP, Sci. Results
197;   [9] Childers, S.E., et al., 2002 Nature 416,767-769.

Quoting Georges Beaudoin <[log in to unmask]>:

> Red-bed copper deposits of the Québec Appalachians
> Post-doctoral fellowship
> 2004-2006
> A Post-doctoral fellowship is available for a
> metallogenic study of red-bed copper deposits in
> the Quebec Appalachians. The successful applicant
> will have expertise in metallogeny with advanced
> knowledge in sedimentology, diagenesis,
> petrography, geochemistry (major, trace, stable
> and radiogenic isotopes), fluid inclusion
> petrology, and a field mapping and core logging
> experience.
> The succesful candidate will be part of the
> sedimentary basin mineral deposits group of the
> DIVEX research team. The researcher will be based
> at the Département de géologie et de génie
> géologique, Université Laval, Québec, Canada.
> The one year position is renewable for a second
> year. The researcher is expected to undertake the
> project in May 2004. A Ph.D. in mineral deposit
> geology is the minimal requirement. The
> fellowship has a value of 35 000 $ CDN/year.
> Applicants must send their curriculum vitae to
> Georges Beaudoin
> Département de géologie et de génie géologique
> Université Laval
> Québec, QC
> Canada G1K 7P4
> Tel. : 418.656.3141
> Fax. : 418.656.7339
> eamil: [log in to unmask]
> --
> Georges Beaudoin, Géo., Ph.D.
> Professeur titulaire
> Directeur du programme de géologie
> Département de géologie et de génie géologique
> Université Laval
> Québec, Qc
> Canada G1K 7P4
> tel. 418-656-3141
> fax. 418-656-7339
> Visitez ma page WEB


Rosalba Bonaccorsi  (Ph.D.)
        University of  Trieste.
        Dipartimento di scienze Geologiche,
        Ambientali e Marine - Via E. Weiss, 2
        (c/o Comprensorio di S. Giovanni)
        34127 Trieste (Italy).

        Phone: 39(040)5582069 (office)
               39(040)5582047 (secretary)
        Fax:   39(040)5582048
        E-mail: [log in to unmask]
                [log in to unmask]