Jenis Geofisical loging

Untuk interpretasi maupun analisa baik kualitatif maupun kuantitatif,jenis-jenis Geofisical loging yang umum digunakan adalah :

a. Log Radioaktif

Log radioaktif adalah jenis log yang dihasilkan dari perekaman yang menggunakan elemen-elemen radioaktif yaitu log gamma Ray, Densitas dan Neutron

v Log Gamma Ray (GR Log)

Pada dasarnya gamma ray log merekam pancaran radioaktif dari formasi. Sinar radioaktif alami yang direkam berupa uranium, thorium, dan potassium. Log gamma ray sederhana memberikan rekaman kombinasi dari tiga unsur radioaktif, sedangkan spectral gamma ray menunjukkan masing-masing unsur radioaktif (Rider, 1996).

Log gamma ray merekam unsur radioaktif dalam skala API (American Petroleum Institute). Log gamma ray umumnya direkam dalam satu kolom bersama log caliper. Unsur-unsur radioaktif yang ada dalam suatu batuan cenderung untuk terkonsentrasi di dalam batuan yang memiliki kadar radio aktif tinggi, defleksi kurva sinar gamma pada batuan jenis ini akan relatif besar seperti pada batulempung. Batuan yang hanya mengandung sedikit unsur radioaktif dan akan memberikan defleksi kurva sinar gamma yang relatif kecil,seperti pada batubara.

Panci Almunium Ternyata dari Bauksit

Dulu waktu masih kecil sempat bingung, dari apa sih panci almunium yang biasanya buat memasak itu dibuat? jawaban itu baru saya dapat waktu semester 3 dulu pada saat mengikuti kuliah Bahan Galian Mineral Industri (BGI) pada kuliah tersebut dijelaskan Bauksit (Al2O3) adalah salah satu bijih aluminium, dengan komponen utama alumina, silika, besi dan titan.

Dari Mana Asal Air Tanah?

Gambar Siklus Hidrologi [www.pubs.usgs.gov]

Apa sih air tanah itu?

Airtanah merupakan air yang berada di bawah permukaan tanah dan terletak pada zona jenuh air.

BELAJAR LIPATAN Yukkkkk……

Lipatan merupakan Struktur berbentuk menyerupai gelombang yang umumnya berkembang pada batuan berlapis yang mengalami gaya kompresi horisontal atau gaya Vertikal.

Bagian Lipatan:

 Sayap Lipatan (Limbs) : Bidang miring yang membangun struktur antiklin atau sinklin

 

Inflection Point-

   limb point where sense of curvature changes

 

 

 

Axial Surface (Axial Plane)-

connects series of hinge lines within a fold

 

Fold Axis-

Imaginary straight line that when moved parallel to itself reproduces the form of a fold

Occurs only with Cylindrical folds

Hinge Line-

      connects points of maximum fold curvature

      

Cylindrical vs. Non-Cylindrical Folds

        Cylindrical Folds-

                Straight hinge lines

                Contains fold axes

    

Non-Cylindrical Folds-

                Curved hinge lines

                Does not contain fold axes

 

   Cylindrical        Non-Cylindrical

 

 

 

   Non-Plunging Folds

 

 

 

Plunging Folds

  

Landsat TM image of nortwest trending Mariscal Mountain Anticline, Big Bend National Park

 

                Limestone beds of Torcer Formation in syncline of Malone Mountains, south of Torcer station. Hudspeth County, Texas. Syncline plunging away from observer. USGS photo.

 

Fold Symmetry

Lipatan Simetri - Bidang Sumbu Tegak

Non-Simetri - Bidang Sumbu Miring 

 

Lipatan Simetrik    Lipatan Asimetrik 

 

 

Form vs Lithologic age relations:

  Antiform- Melipat Cembung keatas

  Synform- Melipat Cekung kebawah

These terms used when stratigraphic age     relations are unclear between folded layers.

 

   

Anticline-convex upward fold  wherein the oldest stratigraphic units occupy core of fold                                              

Syncline- concave upward fold  wherein the youngest stratigraphic units occupy fold core

Sideling Hill Syncline (photo by N. Heywood)

 

 

Green Pond Inlier folds, Newfoundland, NJ

 

 

Fold Classification:

     Dip of Axial Surface                      

          Upright:     70⁰-90⁰   

          Inclined:    10⁰-70⁰.                                  

          Recumbent 0⁰-10⁰.          

   

 

                      

      Interlimb Angle

A. Gentle:          120⁰-180⁰

B. Open:             60⁰-120⁰

C. Tight:              10⁰-60⁰

D. Isoclinal:          0-10⁰.

 

 

Dip Isogon Analysis-

Dip isogons connect points of equal dip on the upper and lower boundary of a folded layer

Measure bed thickness change throughout fold

 

 

Class 1- convergent dip isogons

     

 Class 1A- limb thickening

       

 

Class 1B (Parallel)-

          equal bed thickness throughout the fold

 

 

 

Class 1C- slight hinge thickening

 

    

 

Class 2 (Similar)-

        parallel dip isogon patterns-

        limb thinning; hinge thickening

 

 

 

Class 3:

        divergent dip isogon pattern-

        limb thinning, hinge thickening

 

 

Distinctive Fold types:

Monoclines

 

Basins

 

 

Domes

Chevron Folds

 

Mechanics of Folding:

      Passive Folding  (Shear Folding) 

            slip on surfaces not parallel to rock layering

            rock layering (black layer) does not influence fold development

           black bedding layer merely acts as a “passive” recorder of strain

                card deck analogy in which slip occurs on individual cards;

           the surface of individual card records no strain

           produces similar (Class 2) folds 

 

 

 

 

 

 

 

 

 

Passive folding in layered leucogabbro, Siroua, Morocco

 

 

 

 

 

Flexural Slip Folding

    Folding is controlled by rock layering

    Slip (bending) occurs between rock layers

   No strain on the bedding plan surface

   Circles become ellipses in the profile plane

    Amount of slip increases from the hinge line to the inflection point

    produces parallel (Class 1B) folds

 

                Flexural Slip Folding

 

                

 

Neutral Surface Folding – produces concentric folds

    X-axis is normal to hinge line along top of folded layer

   Neutral surface (no strain) occurs in middle of folded layer

    X-axis is parallel to hinge line along bottom of folded layer

   produces parallel (Class 1B) folds

   

 

Superposed Folds- refolded folds

Specimen of refolded isoclinal folds in schist. Riverside Mountains, Riverside County, California. January 1967. Photo by Warren B. Hamilton, USGS. 

 

Transposed Folds – hinges distended from limbs

 

 

Extensional Folds: folds may also be generated by tension

        Reverse Drag

 

Soft Sediment Deformation- Lastly, folds may occur due to soft sediment deformation, commonly in turbidity current environments

 

Pelagic Zone

The pelagic zone is the part of the open sea or ocean that is not near the coast. In contrast, the neritic zone comprises the water that is near to (and is significantly affected by) the coast or the continental shelf. The name is derived from the Greek πέλαγος (pélagos), which might be roughly translated as “sea” but is more accurately translated as “open sea.” When used on its own, “pelagic” describes something that exists in the open sea as opposed to inland or coastal waters.

Sub-sections of the pelagic zone

The pelagic zone (also known as the open-ocean zone) is further divided into sections, creating a number of sub-zones, based on their different ecological characteristics (which is roughly a function of depth):

• Epipelagic (from the surface down to around 200 m) (656 feet) – the illuminated surface zone where there is enough light for photosynthesis. Due to this, plants and animals are largely concentrated in this zone. Here one will typically encounter fish such as tuna and many sharks,as well as colorful dolphinfish & jellies.
• Mesopelagic (from 200 m down to around 1,000 m) (3,280 feet) – the twilight zone. Although some light penetrates this deep, it is insufficient for photosynthesis. The name stems from Greek μέσον, middle. Animals such as swordfish, squids, wolffish, a few species of cuttlefish, and other semi-deepsea creatures live here.
• Bathypelagic (from 1,000 m down to around 4,000 m) (13,123 feet) – by this depth the ocean is almost entirely dark (with only the occasional bioluminescent organism,such as lanternfish). There are no living plants, and most animals survive by consuming the snow of detritus falling from the zones above, or (like the marine hatchetfish by preying upon others. Giant squid (as well as smaller squids & dumbo octopi ) live at this depth, and here they are hunted by deep-diving sperm whales. From Greek βαθύς (bathys), deep.
• Abyssopelagic (from 4,000 m down to above the ocean floor) – no light whatsoever penetrates to this depth, and most creatures are blind and colourless. The name is derived from the Greek άβυσσος (ábyssos), abyss, meaning bottomless (a holdover from the times when the deep ocean was believed to be bottomless).
• Hadopelagic (the deep water in ocean trenches) – the name is derived from Hades, the classical Greek underworld. This zone is mostly unknown and very few species are known to live here (in the open areas). However, many organisms live in hydrothermal vents in this and other zones.

The bathypelagic, abyssopelagic, and hadopelagic zones are very similar in character, and some marine biologists elide them into a single zone or consider the latter two to be the same. Some define the hadopelagic as waters below 6,000 meters (19,685 feet), whether in a trench or not.

Scale diagram of the layers of the pelagic zone.

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