1. How Does Our Understanding of Modern Critical Zone Processes and Earth Systems Help Us Understand the Geologic Record?
Steven G. Driese, Department of Geology, Baylor University
Jennifer Roberts, Department
of Geology, University of Kansas

2. What would a paleo-Critical Zone look like in past geologic times?
Can we get our students to think about terrestrial rocks as records of ancient Critical Zones?
The present is the key to the past; and the record of the past may help predict the future!
Terrestrial ecosystem context is critical!

3. Paleosols Record Ancient Critical Zones
NSF (2012) Transitions document

4. Reconstructing biogeochemical properties of 65 m. y
Reconstructing biogeochemical properties of 65 m.y. old Paleosol P33, Big Bend
Nordt et al., 2012, GCA

5. Field Trip: Examining Triassic (215 m. y. ) Paleo-Vertisols, Chinle Fm
Field Trip: Examining Triassic (215 m.y.) Paleo-Vertisols, Chinle Fm., AZ
Red, well-drained Vertisol mudstone
Gleyed, poorly drained Vertisol mudstone

6. When, Where, What to Introduce this Concept?
After introduction of modern Critical Zone Concept (obviously)
Go with local rock sections? Literature?
Focus on specific Critical periods of climate or faunal changes (extinctions, PETM, Pleistocene-Holocene, e.g.?
In what course context?
Advanced Historical Geology?
Stratigraphy-Sedimentology course?
Earth System Science ?
Hydrology?
Soils?
Other?

7. Nordt and Driese (2010) AJS

8. Colloidal Properties of PaleoVertisols
Nordt and Driese (2010) AJS
Estimated using modern Vertisol – based “pedotransfer functions”
Paleosol Horizon
Depth (cm)
Clay (%)
Fine Clay (%)
Fine Clay/Total
Clay
Coefficient of Linear Extensibility (cm/cm)
Bulk Density
(g/cm3)
Cation Exchange Capacity (cmolc/kg)
Cation Exchange Capacity/Clay
CaCO3 (%)
pH (H2O)
Base Saturation (%)
Exchangeable Sodium Percent (%)
Electrical Conductivity (ds/m)
Fe Dithionite-extractable (Fed, %)
Oxalate-extractable Fe (Feo, %) A1 0- 17 69 41
0.59
0.17
1.12 52
0.75
7.2 94 15 5
1.2
~0.1 A2
17- 60 71 42
1.10
0.73
7.3 14 4
Bss1
60- 86 43
0.61
0.18
1.07 53
0.74
1.7
Bss2
86-
104 68 37
0.54
1.03 63
0.92
7.5 97 13
2.1 Bk
104-
135 67 33
0.49
0.10
n.d. 40
7.7
100 16 6
1.9

9. Reconstructing (and Direct Measure) of Colloidal Properties of Paleosols

10. Microbial contributions to early diagenesis
Organic carbon degradation
Transformed to CO2 and CH4
<1% of original OC buried in sediment remains in organic geochemical record.
Nitrogen
C:N ratio decreases as amino acids are stripped in first 10 cm
C:N ratio then increases as NH4+ is assimilated into the microbial population.
Phosphorous
C:P ratio balanced by stripping of P v. assimilation of P in microbial cells.
Balance between precipitation of fluorapatite, adsorption, biological uptake vs. surface mixing and diffusive losses to overlying water column
Cementation
Porosity enhancement
Overall increase in N and P ratios

11. Inorganic byproducts of chemoheterotrophy do not accumulate longterm
Inorganic byproducts of chemoheterotrophy do not accumulate longterm. They react with mineral phases and precipitate or diffuse upward to seafloor where they are used by chemolithoautotrophs.
Mineralogy also becomes zoned
Depth and spacing depends on carbon loading, available electron acceptors, flow.

12. Microbial interactions in CaCO3 cementation in marine intertidal stromatolites
Cyanos produce no net CaCO3
CaCO3 produced by heterotrophic activity
Offset by autotrophs
New paper by Meister et al., 2013 says that SRBs are ineffective at precipitating large quantities of carbonate mineral due to decrease in pH induced by metabolic pathway
Konhauser, 2007

13. As burial proceeds pore water geochemistry changes resulting in dissolution and precipiation. Formation of concretions
Konhauser, 2007

14. Konhauser, 2007 Carbon isotopic signatures
Talk about Isua—stable isotopes used to suggest biogenic origin of graphite apatite with a significant isotopic enrichment in the light stable isotope 12C was found in a banded iron formation in Greenland.
, later data suggests metasomatism as source of graphite.
We suggest that the isotopic composition of graphite in supracrustal rocks subjected to high-grade metamorphism does not in general, serve as a reli- able biomarker, since epigenetic processes may yield graphite with isotopic characteristics that overlap with isotopic signatures of metamorphosed organism remains.
Konhauser, 2007

15. Storrie-Lonmbardi et al. 2004
Some microorganisms create extensive biofilms or mats that may produce distinct sedimentary structures--such as the stromatolite above.

16. Konhauser, 2007

17. Limitation and Competition
Microbial metabolism can create environmental niches
They may also experience competition that effectively decreases their influence in a given environment.
Riding and Liang, 2005