Electron images are either secondary electron images (SEIs) or Backscattered electron images (BEIs). SEIs are created from low energy electrons which escape from the surface of the specimen. They give detailed morphological information; our JEOL JSM 820 can produce excellent images at 50,000X, and has a maximum resolution of 20 nm. BEIs are produced as impinging electrons are scattered back by the specimen. Light elements (carbon, etc) are less capable of backscattering. Iron and heavier elements are more capable of backscattering. Therefore, heavy elements appear bright, and lighter elements appear dark. Backscattering occurs from deeper in the specimen, and from a larger volume. Therefore, BEIs have at least an order of magnitude poorer resolution than SEIs. However, for most of our applications, backscatter resolution is more than adequate. In these specimens, pyrite is usually bright framboids and easy to recognize. Feldspars are often lath to squarish and frequently show disequilibrium as in photo 1638. Silica occurs as detrital quartz grains, microfossils, and mostly as amorphous cement. Calcite is not common except in carbonate hard streak or as fossils. Gypsum and sphene are fine grained minor accessory phases.
|
Photo # |
Well and Depth | Magnification/Type/Description |
| 1430 | 418-1430.5 | 250X BEI concentrations of heavy elements appear bright and lighter elements appear dark. Shows pyritized (bright) microfossil tests in a matrix of silica (dark gray), patches of hydrocarbon (black), and tiny curved calcareous test (bright gray). Pyrite framboids appear as 5m white circles in the matrix. |
| 1636 | 418-1631.5 V | 500X BEI shows hydrocarbon (black), silica, feldspars, pyrite |
| 1637 | 418-1631.5V | 500X SEI shows hydrocarbon, silica, feldspars, pyrite. Same field as 1636. There appears to be a textural difference between the silica immediately surrounding the hydrocarbon, and the open porosity (recognized by the charging edges of the open pores). |
| 1638 | 418-1631.5V | 750X BEI showing alteration (?) of feldspar; sodic patches (dark) and potassic (brighter). |
| 1639 | 418-1631.5V | 250X BEI This seems to show a silica fossil whose pores are filled with hydrocarbon. |
| 1640 | 418-1631.5V | 750X BEI which is a higher magnification than the previous, showing a diatom fossil filled with hydrocarbon. |
| 1641 | 418-1631.5 | l000X BEI pyritized shell-gypsum in chamber. The lathlike pieces at the bottom are calcium carbonate. Large detrital (?) grains are plagioclase and ksp |
| 1723 | 418 1723.7A | 250X BEI/ fractures, etc. "clay rich". Note that calcite rhombs in alteration region are more abundant than in majority portion of section. Fractures are filled with blue epoxy. |
| 1724 | 418 1723.7A | 1000X BEI of alteration region along fracture. The 10 semi-quantitative point analyses indicated that there are small quantities of Al(2)0(3) with the silica phase. Sphene, pyrite, and feldspar (anorthoclase) were found. |
| 1754 | 418 1754.5A | 250X BEI/ fine grained "cherty" sample. Pyrite, calcite, and other detrital phases constitute approximately 1-2% of the rock. |
| 1755 | 418 1754.5A | 1000X BEI. The groundmass analyzes as mostly silica, with contamination by fine grained authigenic phases (framboidal pyrite, calcite). Detrital albite is the large grain. Note: vey fine porosity; unpenetrated by epoxy. |
(Filename:Thinsections)
Last Update: 1/16/95
The first set of samples selected for petrographic analysis were the following (H = horizontal and V = vertical):
| Sample | Description/reason |
Optical Petrographic Description? |
SEM Slide Done? | Optical Slide Done? |
| 1145.7 | Opal A-Vertical Fx | Yes | No | No |
| 1186.5 | Opal A-No tendency to vertical fx | Yes | No | Yes |
| 1753.5 | Opal CT- non-fracturing | Yes | No | No |
| 1757.5 | Opal CT-Fractured | Yes | No | No |
| 1228.8 | Opal A-Low clay, High So | Yes | No | No-V and H |
| 1230.4 | Opal A-High clay, Low So | Yes | No | No-B |
| 1401.5 | Carbonate Hard Streak | Yes | No | No-V |
| 1526.7 | Sample w/ carbonate cement above and below | Yes | Yes | No-V and H |
| 1465.5 | Opal A/CT transition: Low clay, A rich | Yes | No | No |
| 1522.6 | Opal A/CT transition: 50:50 | Yes | No | Yes-V |
| 1631.5 | Opal A/CT transition: High Clay, CT rich | Yes | Yes | Yes-V and H |
| 1754.5 | Siltstones | Yes | Yes | Yes-V |
| 1681.5 | Opal CT-low clay | Yes | No | No-H |
| 1723.7 | Opal CT-high clay | Yes | Yes | Yes-V and H |
| 1753.5 | Cherty, downsection | Yes | No | No-V and H |
| 1622 | Opal A/CT Transition w/ So=0 | No | No | No |
The samples were sent for polished thin sections and two sections were requested for each sample--one cut parallel to the bedding (H) and one cut perpendicular to the bedding (V).
| SELECTED LATER | ||||
| Sample | Description/reason |
Optical Petrographic Description? |
SEM Slide Done? | Optical Slide Done? |
| 1660 | Yes | No | No | |
| 1572.4 | Yes | Yes | Yes-V and H | |
| 1424.5 | Yes | No | No | |
| 1399.5 | Yes | No | No | |
| 1573.5 | Yes | No | Yes-V | |
| 1756.5 | Yes | No | Yes-V | |
| 1757.5 | Yes | No | No-V and H | |
| 1634.8 | Yes | -V and H | ||
| 1431.5 | Yes | -V and H | ||