Showing posts with label geological structures. Show all posts

14 May 2020

May 14, 2020 Comment

10 of the Best Learning Geology Photos of 2016

A picture is worth a thousand words, but not all pictures are created equal. The pictures we usually feature onLearning Geology are field pictures showing Geological structures and features and many of them are high quality gem and mineral pictures. The purpose is to encourage students and professionals' activities by promoting "learning and scope" of Geology through our blogs.

In the give up of 2016, we're sharing with you the 10 satisfactory snap shots of 2016 which we've got published on our page.

P.S: we usually try our best to credit every and each photographer or website, however now and again it?S not possible to track some of them. Please go away a remark in case you recognize approximately the lacking ones.

1. Folds from Basque France

Image Credits: Yaqub ShahYaqub Shah

2. Horst and Graben Structure in Zanjan, Iran

Image Credits:https://www.Instagram.Com/amazhda

three. A specific Normal Fault

four. The Rock Cycle

Therock cycle illustrates the formation, alteration, destruction, and reformation of earth materials, and typically over long periods of geologic time. The rock cycle portrays the collective system of processes, and the resulting products that form, at or below the earth surface.The illustration below illustrates the rock cycle with the common names of rocks, minerals, and sediments associated with each group of earth materials: sediments, sedimentary rocks, metamorphic rocks, and igneous rocks.

Image Credits: Phil Stoffer

5. An amazing Botryoidal specimen for Goethite fans!

Image Credits: Moha Mezane

6. Basalt outcrop of the Semail Ophiolite, Wadi Jizzi, Oman

Image Credits: Christopher Spencer

Christopher Spencer is founder of an high-quality technological know-how outreach program named as Traveling Geologist. Visit his website to research from him

7. Val Gardena Dolomites, Northern Italy

8. Beautiful fern fossil found in Potsville Formation from Pennsylvania.

The ferns maximum generally found are Alethopteris, Neuropteris, Pecopteris, and Sphenophyllum.

Image Credits: Kurt Jaccoud

9. Snowball garnet in schist

Syn-kinematic crystals in which ?Snowball garnet? With noticeably turned around spiral Si.

Porphyroblast is ~ five mm in diameter.

From Yardley et al. (1990) Atlas of Metamorphic Rocks and their Textures.

10. Trilobite Specimen from Wheeler Formation, Utah

The Wheeler Shale is of Cambrian age and is a international famous locality for prolific trilobite stays.

Image Credits: Paleo Fossils

12 May 2020

May 12, 2020 Comment

Siccar Point - the world's most important geological site and the birthplace of modern geology

Siccar Point is world-famous as the most important unconformity described by James Hutton (1726-1797) in support of his world-changing ideas on the origin and age of the Earth.

James Hutton unconformity with annotations - Siccar Point

In 1788, James Hutton first discovered Siccar Point, and understood its significance. It is by far the most spectacular of several unconformities that he discovered in Scotland, and very important in helping Hutton to explain his ideas about the processes of the Earth.At Siccar Point, gently sloping strata of 370-million-year-oldFamennian LateDevonianOld RedSandstone and a basal layer of conglomerate overlie near vertical layers of 435-million-year-old lowerSilurianLlandovery Epoch greywacke, with an interval of around 65 million years.

Standing on the angular unconformity at Siccar Point (click to enlarge). Photo: Chris Rowan, 2009

As above, with annotations. Photo: Chris Rowan, 2009

Hutton used Siccar Point to demonstrate the cycle of deposition, folding, erosion and further deposition that the unconformity represents. He understood the implication of unconformities in the evidence that they provided for the enormity of geological time and the antiquity of planet Earth, in contrast to the biblical teaching of the creation of the Earth.

How the unconformity at Siccar Point formed.

At this range, it is easy to spot that the contact between the two units is sharp, but it is not completely flat. Furthermore, the lowest part of the overlying Old Red Sandstone contains fragments of rock that are considerably larger than sand; some are at least as large as your fist, and many of the fragments in this basal conglomerate are bits of the underlying Silurian greywacke. These are all signs that the greywackes were exposed at the surface, being eroded, for a considerable period of time before the Old Red Sandstone was laid down on top of them.

The irregular topography and basal conglomerate show that this is an erosional contact. Photo: Chris Rowan, 2009

The Siccar Point which is a rocky promontory in the county of Berwickshire on the east coast of Scotland.

11 May 2020

May 11, 2020 Comment

Banded-iron formations (BIFs) - Evidence of Oxygen in Early Atmosphere

Our knowledge about the rise of oxygen gas in Earth’s atmosphere comes from multiple lines of evidence in the rock record, including the age and distribution of banded iron formations, the presence of microfossils in oceanic rocks, and the isotopes of sulfur.

However, this article is just focus on Banded Iron Formation.

BIF (polished) from Hamersley Iron Formation, West Australia, Australia

Summary:Banded-iron formations (BIFs) are sedimentary mineral deposits consisting of alternating beds of iron-rich minerals (mostly hematite) and silica-rich layers (chert or quartz) formed about 3.0 to 1.8 billion years ago. Theory suggests BIFs are associated with the capture of oxygen released by photosynthetic processes by iron dissolved in ancient ocean water. Once nearly all the free iron was consumed in seawater, oxygen could gradually accumulate in the atmosphere, allowing an ozone layer to form. BIF deposits are extensive in many locations, occurring as deposits, hundreds to thousands of feet thick. During Precambrian time, BIF deposits probably extensively covered large parts of the global ocean basins. The BIFs we see today are only remnants of what were probably every extensive deposits. BIFs are the major source of the world's iron ore and are found preserved on all major continental shield regions.

Banded-iron formation (BIF) isconsists of layers of iron oxides (typically eithermagnetite orhematite) separated by layers ofchert (silica-rich sedimentary rock). Each layer is usually narrow (millimeters to few centimeters). The rock has a distinctively banded appearance because of differently colored lighter silica- and darker iron-rich layers. In some cases BIFs may containsiderite (carbonate iron-bearing mineral) or pyrite (sulfide) in place of iron oxides and instead of chert the rock may contain carbonaceous (rich in organic matter)shale.

It is a chemogenic sedimentary rock (material is believed to be chemically precipitated on the seafloor). Because of old age BIFs generally have been metamorphosed to a various degrees (especially older types), but the rock has largely retained its original appearance because its constituent minerals are fairly stable at higher temperatures and pressures. These rocks can be described as metasedimentary chemogenic rocks.

Jaspilite banded iron formation (Soudan Iron-Formation, Soudan, Minnesota, USA

Image Credits: James St. John

In the 1960s, Preston Cloud, a geology professor at the University of California, Santa Barbara, became interested in a particular kind of rock known as a Banded Iron Formation (or BIF). They provide an important source of iron for making automobiles, and provide evidence for the lack of oxygen gas on the early Earth.

Cloud realized that the widespread occurrence of BIFs meant that the conditions needed to form them must have been common on the ancient Earth, and not common after 1.8 billion years ago. Shale and chert often form in oceanenvironments today, wheresediments and silica-shelled microorganisms accumulate gradually on theseafloor and eventually turn into rock. But iron is less common in younger oceanicsedimentary rocks. This is partly because there are only a few sources of iron available to the ocean: isolated volcanic vents in the deep ocean and material weathered from continental rocks and carried to sea by rivers.

Banded iron-formation (10 cm), Northern Cape, South Africa.

Specimen and photograph: A. Fraser

Most importantly, it is difficult to transport iron very far from these sources today because when iron reacts with oxygengas, it becomesinsoluble (it cannot be dissolved in water) and forms asolid particle. Cloud understood that for large deposits of iron to exist all over the world’s oceans, the iron must have existed in a dissolved form. This way, it could be transported long distances in seawater from its sources to the locations where BIFs formed. This would be possible only if there were little or no oxygen gas in the atmosphere and ocean at the time the BIFs were being deposited. Cloud recognized that since BIFs could not form in the presence of oxygen, the end of BIF deposition probably marked the first occurrence of abundant oxygen gas on Earth (Cloud, 1968).

Cloud further reasoned that, for dissolved iron to finallyprecipitate and be deposited, the iron would have had to react with small amounts of oxygen near the deposits. Small amounts of oxygen could have been produced by the first photosynthetic bacteria living in the open ocean. When the dissolved iron encountered the oxygen produced by the photosynthesizing bacteria, the iron would have precipitated out of seawater in the form ofminerals that make up the iron-rich layers of BIFs: hematite (Fe2O3) and magnetite (Fe3O4), according to the following reactions:

4Fe3 + 2O2 → 2Fe2O3

6Fe2 + 4O2 → 2Fe3O4

The picture that emerged from Cloud’s studies of BIFs was that small amounts of oxygengas, produced by photosynthesis, allowed BIFs to begin forming more than 3 billion years ago. The abrupt disappearance of BIFs around 1.8 billion years ago probably marked the time when oxygen gas became too abundant to allow dissolved iron to be transported in the oceans.

Banded Iron Formation

Source is unknown

It is interesting to note that BIFs reappeared briefly in a few places around 700 millionyears ago,during a period of extremeglaciation when evidence suggests that Earth’s oceans were entirely covered with sea ice. This would have essentially prevented the oceans from interacting with theatmosphere, limiting the supply of oxygengas in the water and again allowing dissolved iron to be transported throughout the oceans. When the sea ice melted, the presence of oxygen would have again allowed the iron toprecipitate.

References:

1. Misra, K. (1999). Understanding Mineral DepositsSpringer.

2. Cloud, P. E. (1968). Atmospheric and hydrospheric evolution on the primitive Earth both secular accretion and biological and geochemical processes have affected Earth’s volatile envelope.Science, 160(3829), 729–736.

3. James,H.L. (1983). Distribution of banded iron-formation in space and time.Developments in Precambrian Geology, 6, 471–490.

9 May 2020

May 09, 2020 Comment

The Messinian Salinity Crisis

You will have heard of The Messinian Salinity Crisis no doubt. From learned articles, geology textbooks, probably lectures at your college or University. Or possibly not. This was not always the hot topic it is now. In fact, the very idea of this happening, was for a while, challenged, even ridiculed. It seemed too incredible that this could happen as it did and Dessication/Flood theories took time to gain traction. But, if you had heard about it, you would remember that The Messinian Salinity Crisis, was a time when the Mediterranean Sea, very much as we know it today, evaporated – dried out, almost completely.

You will have heard of the rates of desiccation, influx and yet more desiccation, repeated in endless cycles over tens, even hundreds of thousands of years. On a human temporal scale, this would have been a long drawn out affair, covering a time hundreds of generations deep, more than the span of Homo sapiens existence. In Geologic terms however, it was a string of sudden events. Of incredibly hot and arid periods followed by rapid ingress of waters, either via spillways through what is now modern day Morocco and the southern Iberian peninsular, or headlong through a breach in the sill between the Pillars of Heracles, the modern day Straights of Gibraltar.

There were prolonged periods of dessication, of desolate landscapes beyond anything seen today in Death Valley or The Afar Triangle. These landscapes were repeatedly transgressed by brackish waters from storm seasons far into the African and Eurasian interiors, or the Atlantic, and these in turn dried out. Again and again this happened. It had to be so because the vast deposits of rock salt, gypsum and anhydrites could not have been emplaced in a single evaporite event. The salt deposits in and around the Mediteranean today represent fifty times the current capacity of this great inland sea. You may have heard too of the variety of salts production, as agglomerating crystals fell from the descending surface to the sea floor, or as vast interconnected hypersaline lakes left crystalline residues at their diminishing margins, as forsaken remnant sabkhas, cut off from the larger basins, left behind acrid dry muds of potassium carbonates – the final arid mineral residue of the vanished waters.

Just under six million years ago, Geologic processes isolated what was left of the ancient Tethys ocean, the sea we know as the Mediterranean, home to historic human conflicts and marine crusades of Carthage, Rome, Athens and Alexandria, a Sea fringed by modern day Benidorm, Cyprus, Malta and Monaco. At a time 5.96 million years ago – evaporation outpaced replenishment. Indeed, just as it does today, but without the connecting seaway to replenish losses. Inexorable tectonic activity first diverted channels, then – sealed them. Cut off from the Atlantic in the West, water levels fell, rose briefly and fell again, and again. The mighty Nile - a very different geophysical feature of a greater capacity than today, and the rivers of Europe cut down great canyons hundreds and thousands of metres below present Eustatic sea and land surface levels, as seismic cross sections show in staggering detail. The cores taken at depth in the Mediterranean, show Aeolian sands above layers of salt, fossiliferous strata beneath those same salts, all indicating changing environments. The periods of blackened unshifting desert varnished floors and bleached playas, decades and centuries long, were punctuated often by catastrophic episodes, with eroded non conformable surfaces of winnowed desert pavement, toppled ventifracts, scours and rip up clasts. Species of fossilised terrestrial plant life, scraping an arid existence have been found, thousands of meters down, in the strata of the Mediterranean sea floor.

There is much evidence too, in the uplifted margins of Spain, France, and Sicily, of those hostile millennia when the sea disappeared. Incontrovertible evidence, painstakingly gathered, analysed and peer reviewed, demonstrates via the resources of statistical analysis, calculus and geophysical data that the Messinian Salinity Crisis was a period during the Miocene wherein the geology records a uniquely arid period of repeated partial and very nearly complete desiccation of the Mediterranean Sea over a period of approximately 630,000 years. But for the Geologist, the story doesn’t end there. The Geologists panoptic, all seeing third eye, sees incredible vistas and vast panoramas. Of a descent from the Alpine Foreland to the modern day enclave of Monaco, gazing out southwards from a barren, uninhabited and abandoned raised coast to deep dry abyssal plains, punctuated by exposed chasms, seamounts and ridges, swirling and shifting so slowly in a distant heat haze. A heat haze produced by temperatures far above any recorded by modern man and his preoccupation with Global Warming. An unimaginable heat sink would produce temperatures of 70 to 80 degrees Celsius at 4000M depth within the basins.

Looking down upon this Venusian landscape, the sun might glint on remaining lakes and salt flats so very far away and so very much farther below. Hills and valleys, once submerged, would be observed high and dry – from above, as would the interconnecting rivers of bitter waters hot enough to slowly broil any organism larger than extremophile foraminifer. All this, constantly shimmering in the relentless heat. Only the imagination of the geologist could see the vast, hellish, yet breathtaking landscape conjured up by the data and the rock record. And finally, the Geologist would visualise a phenomenon far greater in scope and magnitude than any Biblical flood – The Zanclean Event.

Also known as The Zanclean Deluge, when the drought lasting over half a million years was finally ended as the Atlantic Ocean breached the sill/land bridge between Gibraltar and North West Africa. Slowly perhaps at first until a flow a thousand times greater than the volumetric output of the Amazon cascaded down the slopes to the parched basins. Proximal to the breach, there would be a deafening thunderous roar and the ground would tremor constantly, initially triggering great avalanches above and below the Eustatic sea level as the far reaching and continuous concussion roared and rumbled on, and on, and on. For centuries great cataracts and torrents of marine waters fell thousands of metres below and flowed thousands of kilometers across to the East. Across to the abyssal plains off the Balearics, to the deeps of the Tyrrhenian and Ionian seas, into the trenches south of the Greek Islands and finally up to the rising shores of The Lebanon. The newly proximal waters to the final coastal reaches and mountains that became islands, must have had a climatological effect around the margins of the rejuvenated Mediterranean. Flora and Fauna both marine and terrestrial will have recolonised quickly. Species may have developed differently, post Zanclean, on the Islands. And in such a short period, there must surely have been earthquakes and complex regional depression and emergence. Isostacy compensated for the trillions of cubic meters of transgression waters that now occupied the great basins between the African and Eurasian plates, moving the land, reactivating ancient faults and within and marginal to the great inland sea, a region long active with convergent movements of a very different mechanism.

Hollywood and Pinewood have yet to match the imagination of the Earth Scientist, of the many chapters of Earths dynamic history held as fully tangible concepts to the men and women who study the rocks and the stories they tell. The movies played out in the mind of the geologist are epic indeed and – as we rightly consider the spectre of Global Warming, consider too the fate of future populations (of whatever evolved species) at the margins of the Mediterranean and the domino regions beyond, when inexorable geologic processes again isolate that benign, sunny holiday sea. Fortunately, not in our lifetime, but that of our far off descendants who will look and hopefully behave very differently from Homo Sapiens.

Note: This blog is written and contributed by Paul Goodrich. You can also contribute your blog or article on our website. See guidelineshere.

5 May 2020

May 05, 2020 Comment

"Why I left Electrical Engineering and choose Geology?" with Rana Faizan

When I was studying in the 8^th grade, my father had a wish to make me an Electrical Engineer. Honestly speaking at that time I have no idea about my future goals and even I didn’t knew anything about Electrical Engineering.

One day I was in my class, my teacher gave us a lecture on future planning which really inspired me to think about future aims. This was the first time I started thinking about my future goals. I reached home and asked my father about this concern. He advised me to choose Electrical Engineering in future and told me that this is his dream about me. At that time, I was not familiar with the Geology. Days were passed and I completed my 10^th grade exams with good percentage and took admission in 11^th grade (pre-engineering), and I started study hard to fulfill my parent’s dream.

Then a day come, my father was sharing his university life experiences with me and this was the first time I heard about Geology because his hostel mates were Geology students. My father told me about the geology field work experience that his friends shared with him. And his friend is currently settled in Canada and working as a Geologist. He told me about some more people and some of them are now my professors.

These all things sums up and gave me inspiration about geology, I searched about geology on internet and I found it an interesting field as geologists ruin tourism in their daily life. They can work in natural resource companies, environmental consulting companies, government agencies, non-profit organizations, and universities. Many geologists do field work at least part of the time. Others spend their time in laboratories, classrooms or offices. All geologists prepare reports, do calculations and use computers. I found that geology is a practical and professional field, all sciences and engineering required geology work in some disciplines. Another thing is the study of mountains, different rocks, minerals, structures and more over their observations in field with naked eye is so interesting. Moreover thin section study and geological mapping was another cause that inspired me to pursue my career in this field.

Due to all these things, I mentally prepared myself to choose geology in future but my father wanted me to become an engineer.

After few months, I completed my 12^th grade with good percentage and I applied for electrical engineering as per my father’s wish. And I also applied for geology as per my wish. Unfortunately, I didn’t get admission in any geology institute and get admission in electrical engineering. My parents were very happy because their wish was near to fulfill at that time but I was not so happy because I wanted admission in geology. Then unwillingly, I have to study the electrical engineering. This was little bit interesting subject for me especially circuits. I liked working on C++ programming. I completed my first semester with good CGPA and got 2^nd position but still I wasn’t satisfied in this field.

Next year, when I was studying 2^nd semester in engineering, the admissions in geology get opened and again I tried to get admission in this field but my parents, relatives and friends even my engineering professors advised me that I should not leave this field (engineering) now because that decision would effected my future and one year of my study would be wasted. I listened to my heart voice and applied for admission and I was surprised to know that I got admission in geology. I left engineering and join geology field. My friends and professors of engineering institute asked me again not to leave this field. I still remembered, I simply told them that I don’t want high marks, I want to fulfil my interests so that I can give my 100% in that work. I thought what if I done electrical engineering with good percentages and get job. But what if I am not satisfied with my decision then what is the benefit of that job? Geology may not give me highly paid jobs easily as I could find in electrical engineering but I would definitely find peace and satisfaction in geology.

Me (left) discussing geological map of Pakistan with my class mate (right).

Photo © Rana Faizan

Describing about Salt Range (Sub-Himalayas) model

Photo © Rana Faizan

Now, I’m studying geology and I am fully satisfied with my decision. I have completed my two and half years of bachelor’s degree with three field works and I have learnt many things about geology. I found all things as same as I imagined, when I was in 12^th grade. This was my dream that one day I will become a geologist and will study from the same institute from my father’s friends have studied. Everyone has its own interest. Some like engineering, some like medical and some go for other. My purpose here is not to degrade anyone especially electrical engineering students, no doubt it is also a good field as technology is becoming a need of everyone. So, I have an advice for everyone, always listen to your own decisions and do not bother what other say.

Selfie at Harno River, Abbottabad, Pakistan.

Photo © Rana Faizan

Had a rainy fieldwork at Indus River, Pakistan

Photo © Rana Faizan

I still remember a quote:

"Think100timesbefore youtake a decision,

But once thatdecision is taken, stand by it as one man."

We have a lot of hidden potential that we don’t know. And if we know then we don’t utilize it because we fear what people would say. More than that there is our own voice shouting inside that you can do this. What if we stop listening to those voices and listen only to our heart.

I have observed many geological things during field work and some pictures below are describing about the beauty of geology. I have many pictures related to rocks, minerals, structures and other features. Some beautiful pictures are given below:

Hammering slates

Photo © Rana Faizan

Plunging anticline fold observed during fieldwork.

Photo © Rana Faizan

Enjoying fieldwork after mapping sedimentary area

Photo © Rana Faizan

Note: This article is originally written and contributed by Rana Faizan. You can also contribute your article by sending us at geologylearn@gmail.com. We would love to share your field experiences with our readers. See guidelines here.

4 May 2020

May 04, 2020 Comment

Basics of Basin Analysis

· A sedimentary basin is an area in which sediments have accumulated during a particular time period at a significantly greater rate and to a significantly greater thickness than surrounding areas.

· A low area on the Earth’s surface relative to surroundings e.g. deep ocean basin (5-10 km deep), intramontane basin (2-3 km a.s.l.)

· Basins may be small (kms2) or large (106+ km2)

· Basins may be simple or composite (sub-basins)

· Basins may change in size & shape due to:

1. erosion

2. sedimentation

3. tectonic activity

4. eustatic sea-level changes

· Basins may overlap each other in time

· Controls on Basin Formation

1. Accommodation Space,

a. Space available for the accumulation of sediment

b. T + E = S + W T=tectonic subsidence E= Eustatic sea level rise S=Rate of sedimentation W=increase in water depth

2. Source of Sediment

a. Topographic Controls

b. Climate/Vegetation Controls

c. Oceanographic Controls (Chemical/Biochemical Conditions)

· The evolution of sedimentary basins may include:

1. tectonic activity (initiation, termination)

2. magmatic activity

3. metamorphism

4. as well as sedimentation

· Axial elements of sedimentary basins:

1. Basin axis is the lowest point on the basement surface

2. Topographic axis is the lowest point on the depositional surface

3. Depocentre is the point of thickest sediment accumulation

· The driving mechanisms of subsidence are ultimately related to processes within the relatively rigid, cooled thermal boundary layer of the Earth known as the lithosphere. The lithosphere is composed of a number of tectonic plates that are in relative motion with one another. The relative motion produces deformation concentrated along plate boundaries which are of three basic types:

1. Divergent boundaries form where new oceanic lithosphere is formed and plates diverge. These occurat the mid-ocean ridges.

2. Convergent boundaries form where plates converge. One plate is usually subducted beneath theother at a convergent plate boundary. Convergent boundaries may be of different types, depending on the types of lithosphere involved. This result in a wide diversity of basin types formed at convergent boundaries.

3. Transform boundaries form where plates move laterally past one another. These can be complex andare associated with a variety of basin types.

· Many basins form at continental margins.

Using the plate tectonics paradigm, sedimentary basins have been classified principally in terms of the type of lithospheric substratum (continental, oceanic, transitional), the position with respect to a plate boundary (interplate, intraplate) and the type of plate margin (divergent, convergent, transform) closest to the basin.

· Plate Tectonic Setting for Basin Formation

1. Size and Shape of basin deposits, including the nature of the floor and flanks of the basin

2. Type of Sedimentary infill

· Rate of Subsidence/Infill

· Depositional Systems

· Provenance

· Texture/Mineralogy maturity of strata

3. Contemporaneous Structure and Syndepositional deformation

4. Heat Flow, Subsidence History and Diagenesis

· Interrelationship Between Tectonics - Paleoclimates - and Eustacy

1. Anorogenic Areas------>

· Climate and Eustacy Dominate