Abstract/Details

Biosignature preservation in Miocene evaporite and hot spring deposits of the southeast Cady Mountains, California, U.S.A.


2007 2007

Other formats: Order a copy

Abstract (summary)

The reliable detection of biosignatures in ancient geological materials is a developing field, with applications to studies of life on Earth and the exploration for life on other planets. In this study, we examined Miocene-aged evaporites and hot spring travertines of the Hector Fm. of the southern Cady Mts. of southeastern California. The paleoenvironments studied represent a broad range of temperature, pH and salinity, for comparing modes of biosignature capture and preservation.

Reconstruction of the depositional setting for the Hector Fm. evaporites suggests they represent a perennial, hypersaline lake system, with fluctuating water levels. Primary evaporites were gypsum and anhydrite, which experienced partial replacement by celestine during K-metasomatism by low temperature hydrothermal fluids. Intense, late stage hydrothermal alteration by Fe-rich fluids altered units adjacent to faults. Beds affected by this event have distinctive trace elemental suites and isotopic values (mean δ 34S 8.4‰ and mean δ18O = 13.3‰).

Petrographic and geochemical analyses of Hector Fm. travertines show evidence for early diagenetic recrystallization and cementation, followed by later hydrothermal alteration adjacent to brecciated fault zones. Fluids changed the geochemistry of these samples, while leaving primary microfabrics intact. Samples adjacent to faults have lower isotopic values (mean δ 18O = 20.1‰; mean δ13C = −1.28‰) than samples away from faults, regardless of microfabric.

Biosignatures preserved in evaporite and travertine deposits include a range of morphological, mineralogical and organic compounds. Organic geochemical analysis of samples yielded an organic suite (n-alkanes, β-carotane, CPI >1, OEP >1 and possibly gammacerane) consistent with a hypersaline lacustrine environment and biological sources that included cyanobacterial, algae and higher plants.

Results suggest while that important morphological, organic, and mineral indicators for biological activity may persist through extensive post-depositional alteration, while isotopic and elemental signatures indicative of primary environments are easily altered. The study demonstrates that the integration of evidence over a range of spatial scales, from outcrop to microfabric, to geochemistry, provides important constraints for paleoenvironmental and fossil biosignature analysis.

Indexing (details)


Subject
Geology;
Geochemistry
Classification
0372: Geology
0996: Geochemistry
Identifier / keyword
Earth sciences; Biosignature; Cady Mountains; California; Evaporite; Hot spring deposits; Miocene
Title
Biosignature preservation in Miocene evaporite and hot spring deposits of the southeast Cady Mountains, California, U.S.A.
Author
Schultz, Susan Eileen
Number of pages
216
Publication year
2007
Degree date
2007
School code
0010
Source
DAI-B 68/04, Dissertation Abstracts International
Place of publication
Ann Arbor
Country of publication
United States
University/institution
Arizona State University
University location
United States -- Arizona
Degree
Ph.D.
Source type
Dissertations & Theses
Language
English
Document type
Dissertation/Thesis
Dissertation/thesis number
3258164
ProQuest document ID
304895717
Copyright
Database copyright ProQuest LLC; ProQuest does not claim copyright in the individual underlying works.
Document URL
http://search.proquest.com/docview/304895717
Access the complete full text

You can get the full text of this document if it is part of your institution's ProQuest subscription.

Try one of the following:

  • Connect to ProQuest through your library network and search for the document from there.
  • Request the document from your library.
  • Go to the ProQuest login page and enter a ProQuest or My Research username / password.