Field Geology - Science topic

After more than 48 years in geoscintific field work, my personal opinion and experience are: Mineral deposits are everywhere you can find them. New models you can only create when you leave the beaten tracks.

HGD

The geologists who have most impressed me during my career have been those who created their own niche in science. Some mapped whole regions and became the expert to consult for that area; some opened new fields to view for others to follow; some wrote textbooks in such clear and inspiring language that their words became internalized in me. And all of these geologists were also great teachers, able to impart their knowledge clearly to others. A few examples: Robert Compton, field geologist and author of textbooks on field geology; Adolf Seilacher, paleontologist and founder of the modern paradigm of ichnology; Robert Frey, ichnologist and editor of the first textbook on ichnology.

I agree with Federico Lucci Federico Lucci, a photo would be really helpful.

In general, what I observe in the field is that faults in carbonates can form as very thin structures. There´s not necessarily a breccia or a large damage zone involved.

So, it´s worth having a closer look for any markers, i.e. striation, gauge.

In other words: I can not imagine that the carbonate is not metamorphosed if the contact is original.

Hi

The UTM Geo Map software is so good for android.

Goodluck

Dear Šoster,

If the limestone is not hard and compacted (later case need thin sectioning), you can try to use boiling water and adding hydrogen pyroxide with a continuous stirrer for at least 72 hours (best for chalky and marly limestone). This method leads to getting better and clean tests usually. If they still coagulate, you can add, but be careful, very very little amount (one drop or two) of diluted sodium hydroxide (the later dissolved calcareous tests and etching siliceous tests).

Dear Toyin, use boiling water and hydrogen pyroxide for at least 72 hours with stirring give much better, clean residue chalky limestone, marly limestone, and shale.

Good Luck

It is a vuggy a oligo- to polygomictic breccia/conglomerate cemented with carbonates, lacking any pronounced bedding or typical vein structures. It looks like a carbonate sinter be in hydrothermal or not. It should be of young geological age, maybe Quaternary or Neogene. If sedimentary processes were involved they should be colluvial (alluvial) in origin. That is my rather vague image interpretation.

With kind regards

H.G.Dill

In this tissue other than olivine and pyroxene we see a kind of fossil structure with high cooling rate

- Aeolian silt and sand grains have frosted surfaces due to the the abrasion that they suffered when impacted to each other's.

- Aeolian silt might be better sorted than fluvial silts, while fluvial silts tend to be mixed with fine sand and clays and often have organic matter content.

-In a fluvial system, silts and finer sediments are related to flooding plains, so when the river level grows up and cover the plains around the river, after the energy decreases, the silts, clays and organic matter particles deposit on the flooding plain. Silts also occur in abandoned channels in meandering river systems.

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).

Nicolas has brought an interesting point. "Sexy" paper titles ARE IMPORTANT but need to be grammatically correct and fit the paper content and conclusions. A few hint regarding this and other issues on scientific publishing can be found in the link below. Regarding titles we have:

Titles and Abstracts

Title and abstract are the first things a reviewer will see.

First impressions count. The title and abstract are the first things that a reviewer will see. They are more likely to decide to review a paper that starts off with a clear scientific message. Here are some simple things to avoid.

Titles need to be about the science and findings, and not about how you did the science. For example, avoid titles with “Disentangling Impacts of …” or “Analysis of …” or “Revisiting …” or “Study of …” or “On the …” or “Insights into …” or “Toward the …” or “Assessing …”.

Abstracts should not have sentences such as, “The results of the analysis are discussed” or “the impacts are studied quantitatively.” Give the actual new science, and not a description of what you will discuss in the paper. You have to explain your methods, but then tell what you found.

In general random drill sampling is more typical of the recent porphyry discoveries.

Sampling for any ore body must be actual representative all of the ore body. Generally, aims of the sampling such as evaluation, geochemistry, mineralogy, isotopes, fluid inclusions or all of them indicate the sampling process. Correct sampling technique requires a random selection of each sample from the ore deposite. most of the ore deposites display trends and variations in the spatial distribution of their grade.

 The porphyry deposits are low grade but usually very large in size, as a result of the low grade and size few porphyries support expensive underground mining techniques and most are mined by open pit methods.

Thanks

Find here useful another manual for your purpose.

Sorry for too much late!

Dear Sanaullah,

You asked:

"[...] there could be a debate on the importance/non-importance of spatial context in a particular study, whether constructed/attributed or real? Please correct if I am wrong, that, if geographers succeed to explore or attribute a spatial context to the problem under study, only then it can be claimed as their domain. "

I hope I understand your problem as you raise it. However, I suggest a different approach. First, I try to provide an analogy.

Analogy: In physical geography vs. geology similar "authority"/"our domain" approach was typical for the second half of the 20th century. I would formulate what happened this way (please note this is strong simplification): (physical) geographers are responsible to study the landscape and what is on the top of the surface (say down to 1 m depth), what is below, belongs to geology. (Again, it is a simplification.)

What happened in the 1990s? A convergence took place, because many (real, interested) researchers realized the constraints of this division. Pedology, landslide research, erosion studies and a number of other fields needed urgently integrated data, because they could not solve their problems without this integrative approach. Many researchers coming from various fields (remote sensing specialists, engineering geologists, pedologist) invaded the field of geomorphology, coming up with valuable studies, quantifications, new models for surface processes. And now, if you look at the scientific programme of Geomorphology Division of the European Geosciences Union, you will find that a colourful variety characterizes this field, and many researchers of various disciplines present their relevant studies in this framework.

Returning back to your problem: Taking the aforementioned example into account, I suggest a different approach.

Consider that some researchers (not preferring spatial approach) simply leave out that context and carry out their study like this. Is their study complete?

If yes, there was no (known) spatial relevance to their study.

If no, that means someone can suggest a proper concept using geospatial approach.

This way the outcome verifies the applied tools and IMHO it does not matter who could provide a tool for that.

The statements like "You are not a geographer, therefore you cannot/are not allowed to study that problem" are simply outdated. ("Geographer" here can be replaced by "social scientist" or other.) This is because the fields of competences became wider; inter- and transdisciplinary approaches are proven to be successful in many cases.

I think the evolution of regional science is a good example for that. 50-60 years ago these studies would have been categorized either to economics or (human) geography or perhaps sociology. But the interactions of these research objects (cities, urban areas, rural zones, etc.) could not be studied properly anymore, if you insist to keep these categories. The discipline first gained attention then recognition. It was certainly not easy and not short, but Paul Krugman in 2008 in his Nobel Prize lecture referred to aspects of regional science, too . (Just around that time [surprise, surprise] a department of our university was renamed to Dept. of Regional Science.)

Summary: the battlefield of authority/competence over a certain research area or using certain tools will fade out as the belligerents get older/die out, or if a new approach dismantles the battlefield into unimportant, therefore negligible chunks.

I would be happy to read your comments on that and/or experience, case histories showing contrasting patterns.

Kind regards, Balázs

Dear Mr. Dalwai,

if you refer to spectroscopy, the answer wil be no. Transmittance is the way of measuring (opposed to reflectance) and the intensity the height of a peak or its strength. This is the only way to give you a rather general and simple answer to a general question which is difficult to come to grips with.

Kinf regards

H.G.Dill

Dear Mr. Pdah,

your question finds an answer in the unmetamoprhosed lithological setting as well.

A granite intrusion into country rocks,  effusive rocks overlying basement rocks or dykes and sills are younger than the enclosing country rocks.

With kind regards

H.G.Dill

Simply save the GoogleTM Earth images as KMZ. Then import them to Global mapper.

 Then export them to shape file to Arc Gis. 

 Run Geometric calculate. you will find satisfy answer. 

I also see a marine origin and in upper case probably a turbidite.

The rock is a limestone with some type of coral (Syringopora?) that is cut so you are looking down on it.  I do not see any kind of glacial striations on the rock, but could have easily been transported by a glacier.  What part of the country is the sample from?

Good luck,

Paul Grover

Dear Gianna,

many thanks for your kind message. It should be very nice exchange our ideas and make some comparisons between these two localities. Please keep me up to date on the developments in your work.

My best regards

Michele

The rolled, concentric shape and internal spiraling suggest to me an algal (microbialite, thrombolite) origin for this, perhaps rolling into this position by falling  off a nearby algal buildup, down the steep open-water face into the euxinic basin. Three dimensional form and thin section work might confirm, but I have seen similar pictures and wondered....unable to get back to the outcrop. 

 Thank you again!

Volcanic rocks and red beds generally involve punctuated volcanic activity and either the development of soil profiles or in some cases the input of easily oxidized ash, palaeo-climate is also very important. There is no requirement for subduction, these features are extrememly common on rifted margins both in the form of continental flood basalts and more localized volccanism on magma poor margins. The chemistry of the volcanic rocks can give good insights into the tectonic setting.... and the literature depending on where in the world you are looking at!

Rock fragment. Veins are standing out on the weathered surface. The fragment is too weak to be of real use as a tool.

Certainly not mud cracks.  Mudcracking normally develops roughly polygonal patterns due to contraction towards central foci.  The feature shown is jointing, in which the long partings going across the picture are bedding joints and the shorter partings at right angles to the bedding are dilation joints.  Indeed these carbonate rocks are not dissimilar to Carboniferous limestones found in northern England - see photo.

Dear Mr. Sobolev:

Chakhmouradian (2006) recorded it from carbonatites, where its crystallization is controlled by other Ti, Nb, and Zr minerals, such as perovskite, pyrochlore, ilmenite, baddeleyite, and zircon. It is present in the Chilwa Alkaline Province (Malawi) and it is common in pegmatites as demonstrated by Szełęg and Škoda  (2008) from the Y, REE-rich Skalna Brama pegmatite near Szklarska Poręba. Maybe this paper comes closer to your issue: Zaccarini , F., S tumpf l, E .F. & Garuti, G . (2004): Zirconolite and Zr–Th–U minerals in chromitites of the Finero complex, Western Alps, Italy: evidence for carbonatite-type metasomatism in a subcontinental mantle plume. Can. Mineral. 42, 1825-1845.

Best regards

H.G.Dill

Dear Ming Chen: one things are ophiolites, another are peridotite-serpentinite bodies. Real ophiolites are tectonized parts of oceanic plates, small or big, complete or dismembered, frequently metamorphosed and deformed. Other peridotite-serpentinite bodies are not real ophiolites,a s they represent mantle lithosphere located originally under volcanic arcs or even continental blocks. A large body here in Venezuela, the Tinaquillo Peridotite, results to be a part of subcontinental mantle lithosphere of South America, tectonicalley emplaced in a complex traspressional setting, during the collision of the Caribbean Plate with the South American continental margen. As such, it is in direct contact with granulites of the lower continental crust, in one or two creeks the continental Moho itself is actually exposed. Other ophiolites, as described by Mark Keiter, are slices of back-arc basins, which actually are a sort of oceanic crust in most respects. And others, quite rare indeed, are intraoceanic blocks, like that described by Bo Liu... So there are classical ophiolites and other ophiolites, and alpine-type peridotite bodies which represent subcontinental or subarc lithosphere! Regards, Sebastian.   

Dear Aitalokhai,

It is not easy to see on these photographs, but I think, theses deposits could be related to volcanism. The last picture looks like a lapilli tuff, the first picture seems to show convolut bedding. The stratigraphic situaton (underlaying, water-saturated sandstones and overlaying, impermeable claystones) would fit the scenario of convolut bedding as the result of spontantenous dewatering of the sandstones during an (volcanic driven?) earthquake. But the deposits are obviously intensely weathered and coated by Fe oxides, making it hard to visually analyze the deposits. Hope this helps!

All the best,

Elmar

Dear Mrs. Patridge,

If you are a novice in pyroclastic deposits but have some knowledge in sedimentology apply what you have learnt for arenaceous and fluvial deposits to what you suspect of being  a surge deposit. Pyroclastic flow deposits are more difficult to interpret due to the complex mode of transport and the welding process which may be occur in these deposits also known as ignimbrites and nuees ardentes. For a more detailed interpretation I refer to the textbook: Fisher,R.V., Schmincke,H.-U. 1984. Pyroclastic Rocks. Springer-Verlag, 196 pp which is still worth to be consulted in a case like that.

You may also download the paper "DILL, H.G., TECHMER, A., BOTZ, R., DOHRMANN, R. and   KAUFHOLD, S. (2012) Hypogene and supergene alteration of  the zeolite-bearing pyroclastic deposits at  Tell Rimah, Jordan, and rift-related processes along the Dead-Sea-Transform Fault System during the Quaternary.- Journal of Volcanology and Geothermal Research,  239-240: 49-68.

It may provide you with some kind of a guideline how to deal with such pyroclastic deposits (of economic interest) in the field, from the bird’s eye view and the laboratory.

As far as the interpretation of your images are concerned I concur with Mr. Lages, even if I am a bit reluctant to hand down remote-controlled diagnosis of this kind.

I wish you much success

H.G.Dill

Dear Fernando,

I think it could be both ice-keel scour marks in low depth near shoreline (because some structures seem to be curvilinear) and also ice-crystal imprints if it is possible that the surface was emerged. Indeed, ice-crystal growth in fine sediment could leave such structures.

I saw similar both structures (but on different surfaces) in the Late Ordovician sedimentary record. See Fig. 11e and Fig. 12 in Girard et al. 2015 (Earth Sciences Reviews - ask me if you want the pdf).

I also observed present-day ice-crystals in a puddle in Alps Mountains that could leave similar structures that you found, if their growth occurred in fine argillaceous sediment and their imprints were then preserved. See photography :

Best regards,

Flavia

In internal parts of folded belts extensional collapse can occur following thrusting because the crust is overthickened, becomes unestable and collapses, in these areas Negative Inversion is common ( i. e. Thrust faults that reactivate as normal faults) and additional normal faulting above thrust sheets. Himalayas, Western Alps, Canadian Rockies, Pyrenees and Betic Cordillera are examples of those.

In foreland areas in front of compressional structures, flexural extension characterized by normal fualts occurs due to the flexure generated by thrust sheet loading. If compression further propagates also inversion of previous flexural normal faults can occur. In other caes thrusting can use normal fault steps for ramping generated complex wedges. The best example I know is the Western Venezuela fold and thrust belt just north of the worlds oil larges accumulation the so-called Faja de Orinoco ( Heavy oil belt).

Hello Gaël,

Layer-parallel compaction (LPC) or tectonic compaction is a significant component of shortening. In couple of papers we quantified LPC in sand models it to "lithology", basal friction, stratigraphic location, and amount of bulk shortening. This is easy to quantify in models where the initial dimensions and boundary conditions are better known. We have also compared LPC in models to that in Pyrenees where we measured 16-23% depending in different sections. If you are interested, send me your email address and I will send the PDF of those articles.

Cheers,

Hemin

Again thank's to Professor Kamenov the pertrographic expertise has shown that this spicement is actually - slight metamorphosed Biotite Granite. Prime minerals are Quartz,  Potasium Feldspar and Orthoclase.  Accessory minerals are Magnetite, Titanite, Zirconium, Anatase.

Please check if the boundary between quartenary deposits and the limestone has the same orientation like the other geological boundaries. It could be that the quartenary deposits hide geological units below them.

There is a drilling dtabase of the BGR where you can check this topic:

the first photo appears to be of a brecciated rock.  Brecciation could either be caused by faulting or by forced intrusion of magma.  Personally I feel it is the former.  Check the matrix for calcite/quartz/ore content; any of these are likely to be present if it is a fault breccia.  If the matrix is fine-grained igneous, then David's suggestion is most likely.  I am afraid that I cannot suggest anything for the second photo.

George

When the field work is planned? Is it organzed by UNAM?

Dear Miroslav,

I am afraid it's just sandstone concrections - no fossils, sorry.

thomas

There are a couple of good field photos and drawings on blocky and fluidal peperites in the attached JVGR paper. These are examples from the Miocene to Pliocene Bakony-Balaton Highland volcanic field in Hungary.

Hi, thank you for the very useful suggested papers!!

The p.out file of RAYINVR is a postscript with the results seen in the RAYINVR window: the velocity model, the traced rays, and the predicted and picked arrivals. If RAYINVR is compiled with the graphical libraries it should produce both the image on screen and the postscript file.

However, the postscript identifier on the first line (%! xpltlib) may be unknown for some programs. You can try to replace it with %!PS-Adobe-3.0 EPSF-3.0 or some other identifier that your editing program uses.

Your problem is most likely related to the file identifier. You should also consider checking the BoundingBox parameters in case the image seems to be croped.

I suggest that the hole is the top of an abandoned well originally drilled for oil and gas exploration, but finding a natural accumulation of N2 (nitrogen) that is left venting to the atmosphere.

Well, strictly hornfels perhaps not flint - flint has a more specific meaning Miroslav. But you know more than when you began :-) Paul, I agree that colour is the least important, but if it were say dark green (and lots of men have trouble with distinguishing green and brown, and poor image reproduction can make it look very dark grey because it is their mist common colour blindness) one might expect some other possibilities involving green minerals. And the enquirer can see the colour so it is no extra work. My message being that such enquiries need the enquirer to do all their home work before posting an enquiry, and I am not sure that these basic approaches are always still taught, because we pampered geos with access to equipment in First World laboratories simply x-ray, probe and thin sections. I work in some obscure places and also often want to have some idea what I am looking at while still there. Hence my attempt at mentoring :-). Amazing what you can do with a flame platinum wire, borax and a blow-torch as well, but you would have to be permanently in such a place to bother, and I think those skills are pretty much dead and superfluous (but they are easy with things like K-rich rocks etc - emission spectroscopy by bunsen burner). And yes, I missed mentioning fracture, although flint, rhyolite and horfels can all give that.

Dear Damepaia,

I will add to your list:

Furthermore, I will advice you to follow road and rivers to find outcrops. I will also not make to deep pre-fieldwork processing of Arcgis,etc...let it for post-field work. I will just focus on topographic maps and use steoreoscopic image

I supported the views of Dr. James A Green, USA. It is very difficult to say something on the bases of photographs only. It is true that the rocks samples in Sujit's photographs are not identical bifacial tools or it does not looks like an artifact. It does not show clear man-made flakes scars. These may be broken pieces of rocks of nearby source as these were found along hilly stream in Rajgir, Bihar, India.

There are indeed inherited zircons in island arc setting. They can result from remelting of some parts of the arc and are only slightly older; they can also be much older, coming from continental areas. In that case, the interesting point is to understand how they came there. More the island arc is located far from continents and more the origin is difficult to constrain. For discussion on that topic, you could have a look at 2 publcations concerning the Neoproterozoic juvenile Arabo-Nubian shield in which much older zircons have been found while the Nd isotopes of the enclosing rocks are strongly positive:

Liégeois, J.P., Stern, R.J., 2010. Sr–Nd isotopes and geochemistry of granite-gneiss complexes from the Meatiq and Hafafit domes, Eastern Desert, Egypt: No evidence for pre-Neoproterozoic crust. Journal of African Earth Sciences, 57, 31–40

Stern, R.J., Ali, K.A., Liégeois, J.P., Johnson, P., Wiescek, F., Kattan, F., 2010. Distribution and Significance of pre-Neoproterozoic zircons in juvenile Neoproterozoic igneous rocks of the Arabian-Nubian shield. American Journal of Science, 310, 791–811

Hi if you check out the Ferron Sandstones in Utah you will find a copy of your last picture. From it I may say that this is a transegressive surface, highly burrowed with Thalassinoides. You can also notice that the burrows are compacted and the shape is no longer circular, but oval.

Dear Lofti,

Like Brian said, if you just have one sensor image you can use DN whitout any problem, and for other images processing before you convert to reflectance you must do the atmospheric correction for all the sensors.

If you have your image in reflectance, like you said, you can do it too.

Bencaabane:

The answer provided by Dr. Martin Rittner would have some meaning if you would kindly take the trouble of making thin sections of the Limestone and provide pictures in higher magnification.

Best

Syed

I guess I could add to the confusion a bit. So what do you mean by the density being different? What is the suspected environment of deposition of the "host" rock? I suspect that if you showed an enlarged photo of the cavities it might help, but it really needs a fully description if you wish people to do meaningful remote- sensing identification. :-) I am very doubtful that it has anything to do with glacial activity given the rock types involved, and I even wonder if it is really a boulder (and of course vesicle is not an appropriate term). I also wonder if the cavities are really cubic, and I would be very surprised if they were after sulphide minerals given the lack of iron-staining or other ochres in their vicinity formed from weathering of the original minerals. The cavities look to me as if they are confined to a zone that forms an internal shell, that may be of different composition to the rest of the "boulder". The cavity shapes and matrix might help to give an answer - my first guess would be a sulphate or a carbonate, perhaps some late diagenetic redistribution. Some cavities look almost rounded, and I wonder if these cavities could be after bladed, disc-like crystals of gypsum?

Sorry, I just saw this question.

GMD bhai I have no idea about shale gas.

for your possible interest

Check out the clinker beds of the Eocene Wasatch Formation in the Powder River Basin of Wyoming.

Dear Mr. Koehl:

The mineral aggregates have a birefringence of between 0.030 and 0.100 (it is difficult to give a better assessment based upon the images), its color and pleochroism attest to an Fe-bearing phyllosilicate. Phyllosilicates which fulfill these optical properties belong to the

-biotite-group

-nontronite-group (dioctahedral Fe-bearing smectite)

-stilpnomelane-group

 Intermediate optical properties may be attained in case of an intimate intergrowth of biotite (< 0.100) and vermiculite (approx. 0.02).

As it is a postmagmatic process and a typical fault gauge I suspect of a mineral of the nontronite- or biotite-vermiculite alteration.

Any further classification on my part would be speculative.

I suggest a separation of the material either for XRD and/or CEC analysis.

Best regards

H.G.Dill

Within the last three samples the crystallinity seems to increase. Therefore the radiating arrangement of the crystals  in the "aggregates"is barely , but is recognizable. In the last two sample in particular in the last, the spherulitic nature is obviuos.

Is this a previously polished surface?? or a natural surface?

In either case Jane is right no acid at all..... Mild near neutral soap can be used with a soft (very) brush do not apply too much pressure.

Hi David, it seems that classic thermobarometry is going out of fashion. For a study on metasedimentary rocks in Pyrenean gneiss domes I have applied several thermometers and barometers, GB-GASP of Holdaway (2000, 2001, in the 2005 DOS program), TWQ 2.03 (Berman 2007) and several from Wu et al. (GBMAQ, GM-GMPQ, GBPQ). Some of my schist and gneiss didn't have plagioclase but cordierite, so GASP wasn't applicable to all. Then I tried Average P and T from the ThermoCalc package. Its approach is similar to TWQ, e.g. it calculates and independent set of reactions of all phases in chemical equilibrium. I found the greatest agreement between GB-GASP and AveragePT.

However, when I put an extensive chapter in the manuscript my co-author suggested it's way to long; the editor voiced a similar opinion. In the end all that was left was a small paragraph and a table. Most of the metamorphic data was derived from pseudosections. The main criticism on traditional thermobarometry is that the assumption that the phases involved in the calculations are actually in chemical equilibrium as it is required is really hard to prove. So, forward modelling à la ThermoCalc or Theriak. I am sure you are aware of that. I think it would be difficult today to publish a paper on metamorphism of say pelitic rocks based only on classical thermobarometry.

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

Martin:

Youmay like to consult: The Cambrian System in Northwestern Argentina: etc. (2003) by Acenolaza, Geologica Acta, Vol. 1, 23-29.

Best

Syed

I understand that you are investigating dead or past oil seeps, as detectable at the surface in outcrop, not necessarily exumed oil fields.

On this basis, I suggest to distinguish oil seeps in incoherent terrain and oil seeps in rocks.

Incoherent terrain or soil: the main physical characteristic is presence of some kind of hydrocarbon-related substance, like tar, asphalt, or even wax, concentrated in the soil at the spot of the dead seep. This may also indicate an active seep, possibly with low seepage rate. The main difference would be the absence of gaseous or liquid active seepage in a really dried-up paleo-seep.

Rocks: like-wise, the presence of some  kind of hydrocarbon-related substance, like tar, asphalt, or even wax, at the spot of the dead seep is the main indicator. It would be useful to distinguish seeps in porous rocks (porous and permeable sandstone, porous and permeable calcarenite or grainstone in case of carbonate rock) and naturally fractured rocks (tight clastic rocks, massive limestone or dolomite, without matrix porosity). In porous rocks, the rock in the immediate vicinity of the paleo-seep would be impregnated of heavy hydrocarbons or asphalt/tar, indicating irreducible saturation in the matrix porosity. In naturally fractured rocks, the main sign would be asphalt/tar stain on the walls of the natural fractures where hydrocarbons were seeping out. Again, a live seep can be differentiated from a dried-up seep by the presence of gaseous components and light ends, that are absent in a dead seep.

An oil spill on incoherent soil, even decades old, could be detected by the absence of bio-indicators typical of active oil seeps, because an occasional oil spill is generally not enough to induce the start of a local colony of hydrocarbon-feeding micro-organisms. An oil spill on rock would be easy to detect becouse of lack of deep impregnation in the rock matrix.

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.

Hi.

I can send you the maps in question via Dropbox to your e-mail, probably this afternoon...

Best regards from the Canaries,

Rubén

Dear Aser

you can check the link below which deals with Tassy et al. (2015) entitled Egyptian Tethyan margin in the Mesozoic: Evolution of a mixed carbonate-siliciclastic shelf edge (from Western Desert to Sinai).

link: http://www.sciencedirect.com/science/article/pii/S0264817215301124

Abdou et al. (2009) have been documented subsurface Jurassic sediments of Western Desert (see link below0

 http://ajbasweb.com/old/ajbas/2009/1206-1222.pdf

Regards

Massih 

We used in our EM modeling:

brine flushed sandstone 0.6 Ohm m

and for reduced (+-70%) oil saturated 16 Ohm m  

So you see that it can range a lot depending on porosity and saturation. 300 Ohm m is certainly not the minimum.

Dear Mr. Xaba:

4 terms need to be distinguished: Paleosome, neosome, melanosome, and leucosome. As the prefix indicates paleo is old, neo new, leuco light, and melano dark. Whereas paleo and neo is timely, leuco and melano is the color. In practice this means that the neosome is the product of anatexis that can be formed by reactions that produce for example graitic melt + garnet during fluid absent melting. In this case the quartzofeldspatic part is the leucosome, together with garnet forming the neosome. If you don't have an additional melanocratic phase like garnet or cordierite during anatexis, leucosome and neosome is the same. On the other hand the melanosome is the restite that did not melt and is formed by dark minerals, whereas the paleosome is the original rock of which the melt was extracted. The latter two terms are very difficult to distinguish is field and often chemical analyses is necessary.

Another detail of the same taxon.