Regional Geology - Science topic

It appears to me that the previous answers relate to each responder’s pet technique.

The question was, “Now, it is required to determine the exact position (orientation and width) of the fault zones to design appropriate foundation treatment measures before starting construction.”

A three-dimensional seismic survey designed to focus on very shallow horizons with geophone locations closely spaced, and utilizing a high-frequency energy source will answer the question.

Well, I'd say that, generally, quartzites do not represent unconformities. However, on a global evolutionary scale, it could be that before terrestrial plants evolved, one could imagine land surface as exposed igneous/metamorphic rocks with no vegetation to trap the finer particles on-land. Therefore, much of the surface (at this time) could have been composed of SiO2 aeolian dunes. If this were the case, your argument might hold up for quartzites older than terrestiral plants (700 Ma) and directly overly basement.

Anderson's Theory assumes one of the principal stress axes to be vertical as the earth's surface (i.e. air) has no shear stress (like every fluid). Only normal stress is acting. Thus, the theory is only applicable at the earth's surface, not in deeper parts of the crust (where shear stress increases).

First, you should develop a conceptual model to understand what kind of materials and what kind of controls are acting on your slope instability.

1) you should define the type of landslide you expect: shallow landslide within the soil cover? large bedrock slide? Relatively shallow earthslide? For each typology, the shape and the location of slip surface can be different (for instance, for shallow landslides within soil cover we usually assume the failure parallel to the slope, located at the soil-bedrock contact).

2) you should make a hypothesis (that you'll demonstrate or not) on the geological control. Is the slide occurring on fractured bedrock? In this case, the slip surface is controlled by the joints. Is the slide occurring on soil or extremely fractured rocks (according to the scale of the landslide)? In this case, the slip surface can be circular, sub-circular or logarithmic spiral. Is the slide occurring on layered materials? In this case, different layers can control the slip surface.

3) you should finally evaluate other possible controls, such as groundwater level, slope morphology, the presence of tension cracks on the top, water seepage, geological structures (faults, major discontinuities), etc.

Once you have developed your conceptual model, you can run numerical simulations with either a stress-strain approach or a limit equilibrium approach, as Kreuzer commented above. However, if you don't have a clear conceptual model of teh landslide and a good geological model, you would spare time with millions of useless attempts.

Regarding the literature, it's huge, but you should direct your search to the appropriate type of landslide and type of materials.

In my paper in Palaeontology in 1986, on pseudoplanktonic fossil crinoids, I found growth lines on brachial plates that suggested that benthic isocrinids reached full size in just 4 or 5 years while the pseudoplanktonic pentacrinitids grew significantly faster and attained a similar size (arm length of about 10-15cm) in just 2 or 3 years. Download the paper at http://www.habitas.org.uk/staff/staff_pdf_files/Simms%202.pdf

Another key reference should be that of Blenkinsop 2011 in the GSA special volume. Search for it online with this reference.

Blenkinsop, T.G., 2011, Archean magmatic granulites, diapirism, and Proterozoic reworking in the Northern Marginal Zone of the Limpopo Belt,  Geological Society of America Memoir 207, p. 1–24, doi:10.1130/2011.1207(13).

David

Hi, have a look at dinoflagellate cyst literature. Although you will not find many cysts in the salt deposits you will find distinct assemblages for both low and high salinity environments just prior to, during and just after the crisis. Here are some references I have in my database to start with:

Santarelli, A. Brinkhuis, H. Hilgen, F. J. Lourens, L. J. Versteegh, G. J. M. and Visscher, H., 1998. Orbital signatures in a Late Miocene dinoflagellate record from Crete (Greece). Marine Micropaleontology 33, 273-297.

Popescu, S. M. Dalesme, F. Jouannic, G. Escarguel, G. Head, M. J. Melinte-Dobrinescu, M. C. Sütő-Szentai, M. Bakrac, K. Clauzon, G. and Suc, J. P., 2009. Galeacysta etrusca complex: dinoflagellate cyst marker of Paratethyan influxes to the Mediterranean sea before and after the peak of the Messinian Salinity Crisis. Palynology 33, 105-134.

Londeix, L. Benzakour, M. Suc, J. P. and Turon, J. L., 2007. Messinian palaeoenvironments and hydrology in Sicily (Italy): The dinoflagellate cyst record. Geobios 40, 233-250.

Louwye, S. de Schepper, S. Laga, P. and Vandenberghe, N., 2007. The Upper Miocene of the southern North Sea Basin (northern Belgium): a palaeoenvironmental and stratigraphical reconstruction using dinoflagellate cysts. Geological Magazine 144, 33-52.

Interesting photos and discussion.

Need to look at TS and CS in thin sections for texture and structure. as pointed out, the photos are insufficient to justify any concrete conclusion.

Possible options:

Hydrothermal vent deposits (observed in marine sediments deposited in proximity of volcanic vents where the gaseous fluids create tubular deposits of chert / carbonates with a concentric laminate pattern;

Ichnofossils - organic chert / calcite binding along tubular habitats of burrowing organisms - that leave behind such features

Simple fluid escape structures produced during lithification of silicic sediments under special conditions, where the fluids remain trapped in the lower strata and then are triggered into escape through tubular vents....(akin to mud-volcanoes)

....

I am assuming that since these are found in sedimentary rocks, other processes should not be brought into consideration, although even biogenic superficial weathering by soil-dwelling burrowers could also yield such features.

The answer given by Volker Kaminske is quite good, the oceanic lithosphere takes some 12-15 Ma to become brittle. But some precision should be made in the question issued by Carlos Ganade de Araujo itself. There's NO "MORB" lithosphere, MORB is a term specific for mid ocean ridge basalts, which make up oceanic crust, not lithosphere. The lithosphere under the oceanic crust  call the LID or oceanic mantle lithosphere, which comprises usually more than 90% of the thickness of an oceanic lithospheric plate, is not made of basalt, but of ultramafic rocks,such as peridotite, dunite and  pyroxenite, often serpentinized and tectonized.  

Dear Ibukunoluwa

there some work which deals with exploration history and its relationship to structral evolution such as:

link http://nora.nerc.ac.uk/6692/1/MIDLAND_VALLEY_PAPERv72accpetedchangesforbgsreview.pdf

link

Regards

Massih

Amalgamated accumulations resulting from climatic and eustatic changes, Akchar Erg, Mauritania. GARY KOCUREK1, KAREN G. HAVHOLM1, MAX DEYNOUX2 and

RONALD C. BLAKEY3. Sedimentology Volume 38, Issue 4, pages 751–772, August 1991

Journal of African Earth Sciencs

You can also check out our GSA field forum guide citing a lot of the literature on the SNB that is out there.