Carbonate Petrography

Carbonate petrography is the study of limestones, dolomites and associated deposits under optical or electron microscopes greatly enhances field studies or core observations and can provide a frame of reference for geochemical studies.

25 strangest Geologic Formations on Earth

The strangest formations on Earth.

What causes Earthquake?

Of these various reasons, faulting related to plate movements is by far the most significant. In other words, most earthquakes are due to slip on faults.

The Geologic Column

As stated earlier, no one locality on Earth provides a complete record of our planet’s history, because stratigraphic columns can contain unconformities. But by correlating rocks from locality to locality at millions of places around the world, geologists have pieced together a composite stratigraphic column, called the geologic column, that represents the entirety of Earth history.

Folds and Foliations

Geometry of Folds Imagine a carpet lying flat on the floor. Push on one end of the carpet, and it will wrinkle or contort into a series of wavelike curves. Stresses developed during mountain building can similarly warp or bend bedding and foliation (or other planar features) in rock. The result a curve in the shape of a rock layer is called a fold.

10 of the Best Learning Geology Videos of 2017


Following are the best videos of 2017.
Some of the videos are part of our Live Virtual Field Tours project and Video Lecture Series while some videos were reposted by us.



1. Live from Kamokuna Ocean Entry, Big Island of Hawaii 

                                   
2. Live from Tucson Gem Show, Tucson, Arizona

                                            

3. The landslide of Maierato, Vibo Valentia, Calabria, Italy 






4. A double terminated Quartz being pulled from a pocket in the Alps. 





5. An incredible footage of a Flash flood





6. Live from Kaibab Limestone, South Rim, Grand Canyon



                                               

7. Earthquakes and the Richter scale with Fabiana from Geologia da Terra





8. Learn all about Actinolite with Chad keel



9. Soil Erosion 





10. Live from Mount Hood with Andrew Dunning of BetterGeology



Huge thanks to all who contribute videos to us and thanks to everyone for watching! :)

Want to contribute? Read guidelines here.

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 occur at the mid-ocean ridges.
2.      Convergent boundaries form where plates converge. One plate is usually subducted beneath the other 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 and are 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

2.      Orogenic Areas--------->

Sedimentation responds to TectonismPlate Tectonics and Sedimentary Basin

   Types

SB = Suture Belt
RMP = Rifted margin prism
S C = Subduction complex
FTB = Fold and thrust belt
RA = Remnant arc
Wilson Cycle
 
about opening and closing of ocean basins and creation of continental crust.



Structural Controls on Sedimentary Systems in Basins Forming:

Stage 1: Capacity < Sediment

Fluvial sedimentation

Stage 2: Capacity = Sediment

Fluvial lacustrine Transition


Stage 3: Capacity > Sediment

Water Volume > excess capacity
Shallow-water lacustrine sedimentation


Stage 4: Capacity >> Sediment

Water volume = excess capacity
Deep-water lacustrine sedimentation


Stage 5: Capacity > Sediment

Water volume < excess capacity
Shallow-water lacustrine sedimentation     
Contributed by:

Rehan.A Farooqui
M.Sc Geology,,
University of Karachi.