Trilobite - Olenus

                             TRILOBITE 

NAME OF THE GENUS : OLENUS 

 BIO STATUS 

  1) PHYLUM : ARTHROPODA

  2) CLASS     : TRILOBITA 

  3) ORDER    : OPISTHOPARIA 

SHAPE & SIZE OF

THE BODY CEPHALON :

                              Oval, about 3 cm. 

SHAPE : 

             Rectangular with a narrow border wider than the rest of the body. 

GLABELLA : 

             Sub - rectangular, often slightly tapering glabella not reaching the anterior border with 3 pairs of furrows. 

FACIAL SUTURE & CHEEKS : 

              Opisthoparian ; fixed cheek broad. 

EYES : 

          Connected by eye ridge to the front of the glabella. 

GENAL ANGLE : 

            With genal spines continuation of free cheek. 

THORAX : 

            13 to 15 free segments, spinose, with rather flat pleasure and narrow facets. 

PYGIDIUM : 

           Small triangular, segments fused. 

SPECIAL CHARACTERS : 

           Oval body ; rectangular Cephalon ; opisthoparian, eyes connected by a ridge with glabella, short genal spines, free glabellar field present ; 13 to 15 thoracic free spiny segments; pygidium small. 

Trilobite - Paradoxides

                               TRILOBITE 

NAME OF THE GENUS : PARADOXIDES

BIO STATUS 

 1) PHYLUM : ARTHROPODA

 2) CLASS    : TRILOBITA

 3) ORDER    : OPISTHOPARIA

SHAPE & SIZE OF

THE BODY CEPHALON : 

                                  Large, elongated, narrowed Posteriorly, almost 7 to 15cm. 

SHAPE :

           Semicircular with genal spines extended backward as long spines. 

GLABELLA : 

           Expands forwards to broadly rounded front, glabellar furrows usually well defined and may unite access mid part of glabella. 

FACIAL SUTURE & CHEEKS : 

           Extends from the anterior, traverse through the cheek & ends in the posterior margin of the Cephalon - Opisthoparian, free cheeks broad with genal spine. 

EYES : 

          Large ; arched. 

GENAL ANGLE : 

           In the from of the spines and with free cheeks. 

THORAX : 

           Long, tapers towards pygidium with 16 to 21 segments, pleasure grooved and ends in long sharp spines directed backward. 

PYGIDIUM : 

           Small, spade - plate with indication of several segments. 

SPECIAL CHARACTERS : 

           Head shield, semicircular, with long genal spines; Glabella expands forward to broadly rounded front ; Opisthoparian ; Crescentic eye ; Thorax tapers towards pygidium with 16 to 21 spiny pleural segments;

Pygidium small. 

Insta

Trilobite - Olenellus

                              TRILOBITE 

                             

SHAPE & SIZE  OF THE 

BODY CEPHALON  : 

                     Elongated. 

Shape : 

           Semicircular wide with a border. 

Glabella : 

            Extends to the anterior border and has four distinct lateral furrows. 

Facial Suture & Cheeks : 

             Marginal - protoparian, cheeks undivided. 

Eyes : 

         Large, cresentic joined to the front segment of the glabella.

Genal angle : 

Extended in the from of genal spines. 

Name Of The Genus : OLENELLUS 

Bio status 

  1) Phylum    : ARTHROPODA 

  2) Class       :  TRILOBITA 

  3) Order       :  PROTOPARIA 

THORAX : 

                The anterior part of the thorax contains 14segments with spinose pleurae, grooved, third segment larger than the order and with longer spines extended backward.

PYGIDIUM : 

                 Elongated, spine - like, caudal spine without lateral lobes on the axis. 

SPECIAL CHARACTERS : 

                 Head shield semicircular, with a border and genal spine. Facial suture protoparian, crescentic eye ridge connected to the first segment of the glabella, 14 thoracic segments with pleural spines, pygidium without lateral lobes and with a caudal spine. 

Factors affecting weathering

         FACTORS AFFECTING WEATHERING

              All the process of weathering are affected by rock structure, climate, topography, and vegetation. 

              Rock structure refers to mineralogical composition, joints bedding planes, faults, fractures, pores and its integral hardness. The degree of weathering of the source area, i.e., the area where weathering operates is controlled by the nature of pre-existing rocks to a greater extent. 

              Climate is the sum-total of the meteorological elements like temperature, moisture, including both humility and precipitation, wind, air - pressure and evaporation. Climate determines whether physical or chemical weathering will predominate and the speed with which these process will operate.

             Topography directly affects weathering by exposing rocks and indirectly though the amount of precipitation, temperature and vegetation. 

              Surface covered with vegetation are protected and bare surface are weathered to a greater extent. 

Biological Weathering

                   BIOLOGICAL WEATHERING

          This process of weathering is mainly related to the activities of various organisms. Organisms mainly plants and bacteria, take part in the transformation of rocks at the surface, in the following ways : 

           1) Bio-physical processes

           2) Bio-chemical processes 

1) Bio-physical Processes : 

                     a) Plant - roots, growing between joint blocks and alone minute fractures between mineral grains, exert an expansive force tending to widen those opening and sometimes create new fractures.

                     b) Insects like earth - worm, snail etc. Loosen the soli cover and create suitable conditions for the various external agencies to have their own action on the underlying rocks, which ultimately lead to rock weathering. 

2) Bio-chemical Processes : 

                     a) Sometimes, certain groups of bacteria, algae and mosses break rock - forming Silicates down directly, removing from them elements like silicon, potassium, phosphorus, calcium, magnesium, that they need as nutrients. 

                    b) After the death of animals or plants, with their subsequent decay and degeneration, chemically active substances are produced, which are cable of bringing about rock weathering. For example, humic acid which is formed during decay and degeneration of plant life is capable of bringing about rock weathering effectively, to some extend. 

           Thus in nature the processes of weathering is being carried out by various external agencies. 

Chemical Weathering

                     CHEMICAL WEATHERING 

     It is also known as mineral alteration, consists of a number of chemical reactions, all these reactions change the original silicate minerals of igneous rock, the primary minerals, into new compounds, the secondary minerals, that are stable in the surface environment. Besides, sedimentary and metamorphic rocks are also substantially affected by the chemical process of weathering. Chemical is more important than mechanical weathering in almost all the climatic regions. 

Three processes are notably responsible for chemical weathering : 

         a) Oxidation 

         b) Hydration

         c) Carbonation 

Oxidation : 

                  The presence of dissolved oxygen in water in contact with mineral surface leads to oxidation. Which is the chemical union of oxigen atoms with atoms of other metallic elements. Oxygen has a particular affinity for iron compounds and these are among the most commonly oxidized materials.

Hydration : 

                   The chemical union of water with a mineral is called hydration. It is sometimes confused with hydrolysis. The reaction between water and a compound. The process of hydration is particularly effective of some aluminum bearing minerals, such as feldspar. 

Carbonation : 

                     Carbon dioxide is a gas and is a common constituents of the earth's atmosphere. Rain water in course of its passage through the atmosphere, dissolves some of the carbon dioxide present in the air. It thus turns into a week acid called Carbonic acid, and is the most common solvent acting on the crust. The effect of this process is well noticed in the limestone or chalk areas in the humid regions of the world. 

                    Besides the above, another process known as Solution is quite significant in bringing about the chemical weathering of rocks. In this case, some of the minerals got dissolved by water and thus removed in solution, for example gypsum halite etc..

Physical Weathering

                      PHYSICAL WEATHERING 

                       This process refes to the mechanical disintegration of rocks in which their mineralogical composition is not changed. This is brought about chiefly by temperature changes, e.g, thermal expansion and contraction. The following are some of the important process of physical weathering.

           a) Exfoliation 

           b) Crystal growth 

           c) Freezing of water 

           d) Differential expansion 

Exfoliation : 

                    In this case thin sheets of rock split off owing to differential expansion and contraction during heating and cooling over the diurnal temperature range.

                   Sometimes, it is the result of unloading in which case, because of the removal of the overlying rocks, the pressure on the igneous rocks beneath them is also diminished and this results in the expansion of igneous rocks and in the formation of large scale fractures parallel to the surface topography. Sheets b/w the fractures are detached the main mass which thus suffers fragmentation. 

Crystal growth : 

                       The soluble constituents of the rocks or minerals, enter the rocks through fractures and joints, along with water. With the evaporation of water the solution is precipitated to from crystals or crystalline aggregates and as they grow, they exert large expansive stresses, which help in breaking up some rocks. 

Freezing of water : 

                       Water, as we know, expands by about 9.05 present in volume when it freezes. The water seeps down into the fractures and under suitable climatic condition, begins to freeze at the top of the fracture first. As freezing continues, the pressure exerted on the walls became more and more intense. Which results in widening the existing fracture and new fracture from. This is the dominant mode of weathering, in climates where there is repeated freezing and thawing. This is also known as Frost action. 

Differential expansion : 

                        Rock - forming minerals expand when heated, but contract when cooled. Where rock surfaces are exposed daily to intense heating by direct solar rays, alternating with intense cooling by longwave radiation at night, the resulting expansion and contraction of mineral grains tends to break them apart. 

PROCESS OF WEATHERING

               PROCESS OF WEATHERING

Introduction : 

                      Weathering is the general term applied to the combined action of all processes causing rocks to be disintegrated physically and decomposed chemically because of exposure at or near ty earth's surface.

                     In particular, weathering occurs, where rocks and minerals come in contact wiy the atmosphere, surficial water, and organic life under conditions that are normal to the surface the earth.

                     Weathering helps erosion, but is not a part of it. There can be weathering without erosion and erosion without weathering.

Types of weathering : 

                     There are three main types of weathering,

                   1) Physical Weathering,

                   2) Chemical Weathering,

                   3) Biological Weathering.

1) Physical Weathering : 

                    This process refer to the mechanical disintegration of rocks in which their mineralogical composition is not changed. This is brought about chiefly by temperature changes, e.g., thermal expansion and contraction. The following are some of the importance process of physical weathering.

2) Chemical weathering : 

                     It is also known as mineral alteration, consists of a number of chemical reaction, all these reactions change the original silicate minerals of igneous rock, the primary minerals, into new compounds, the secondary minerals, that are stable in the surface environment.

3) Biological Weathering : 

                     This process of weathering is mainly related to the activities of various organisms. Organisms, mainly plants and bacteria, take part in the transformation of rocks at the surface. 

THE CORE

                                THE CORE 

It is separate from the mantle by the Gutenberg Weichert Discontinuity and extends up to the centre of the earth. 

It consists of three parts : 

             1) Outer Core 

             2) Middle Core 

             3) Inner Core 

1) Outer Core : 

                It extends from 2900 to 4982 kms. It is considered to be in a state of homogenous fluid and it does not transmit S - Waves.

2) Middle Core :

               It is a transition layer, extends from 4982 kms to 5121 kms. The material is in a fluid to semi - fluid state.

3) Inner Core : 

               It is believed to contain metallic nickel and Iron and is called “ nife ”. It is probably solid with a density of about 18. Its thickness is 1250 kms. 

THE MANTLE

                           THE MANTLE

It is separated from the over - lying crust by the Mohorovicic - Discontinuity which is a first order discontinuity. Its thickness is about 2865 kms. It forms 83% of the earth by volume and 68% by mass. 

It is the source - region of most of earth's internal energy and of forces responsible for ocean - floor spreading, continental drift, orogeny and major earthquakes. 

The material is olivine - pyroxene complex, which exists in solid state. It is believed that the upper mantle has a mix of 3 parts of ultramafic rocks and 1-part of basalt and the mix is known as Pyrolite. The lower mantle extends from 1000km to the core boundary.

Within the mantle, a number of second - order discontinuities have been located, which are as follows : 

1) Density break at 80 km depth : Density changes from 3.36 to 3.87 above and below the level respectively. 

2) Gravity break at 150 km depth : gravity changes from 984cm/ sec² till it reaches at a depth of 1200 kms. 

3) At 700 km - depth, there changes the capability of the materials in storing amount of elastic - stain energy. Up to 700 kms the capability is more.

4) Repetiti discontinuity : At 950 km depth. It marks the lower limit of the very rapid rise in the velocity of seismic vibrations.

5) Gravity - break : At 1200 km depth, gravity attains its minimum value i.e., 974cm/sec² , therefore it rises upto 1068 cm/ sec² at the core boundary.