Gloria Gill GEO 543Evaporites Lab

Evaporites:

McLeod 19

1) The mineralogy of the sample consists of mostly gypsum and some Anhydrite. The arrangement is a columnar prisms that grow off the fine grained sediment.

2) The evaporite crystals developed on the water-sediment interface.3) N/A4) The environment of these particular evaporite crystals was most likely a deep water environment (but its is hard to tell how deep) since it would have required a calm, undisturbed environment for the crystal formation in a columnar prism arrangement.

McLeod 20

1) The mineralogy of the sample consists of gypsum prisms in a columnar arrangement.2) The gypsum evaporite crystals precipitated within sediment.3) The inclusions present in the grains give evidence for displacement.4) The environment of these particular evaporite crystals was most likely a deep water

environment since it would have required a calm, undisturbed environment for the crystal formation in a columnar prism arrangement.

McLeod 21

1) The mineralogy of the sample consists of halite in a cubic arrangement.2) They probably precipitated at the water surface and piled on to the sediment after water

evaporated3) N/A4) A shallow water environment or sabkah are the probable environments for the halite

formation.5) The inclusions are large and cubic. Fluid inclusion are evident by the bubbles present in the

sample grains.

PR-5

1) The mineralogy of the sample constitutes of gypsum with small inclusions of aragonite and anhydrite arranged in form of veins.

2) It formed within sediment.3) It formed via incorporation and displacement.4) It was mist likely formed in a sabkah environment evident by the nodular and chicken wire

texture. 5) The probable sequence of sedimentation is an alternation between hydrous gypsum and

anhydrite. Although not evident, this sample most likely started as Gypsum, precipitated from solution. The first top layer is of anhydrite that indicates an environment where water had dried, and gypsum was dehydrated to form Anhydrite. This anhydrite was later exposed to water and through hydration once again became Gypsum evident by the relic anhydrite inclusions. This cycle is characteristic of the sabkah environment.

PR4-10

1) The thin section is characterized by high birefringence silt sized particles and singular gypsum crystal randomly distributed iron oxides. Also present are molds where larger crystals dissolve away. Due to the shape these molds may have been gypsum. These molds are partly filled with blocky calcite cements and Fe-oxides.

2) Evaporite crystals have precipitated within the sediment3) Formed by replacement.4) The environment where the evaporites developed in a high energy shallow water

environment or sabkah environment.

Castile

1) Mineralogy: Massive Gypsum with calcite laminations that formed due to varves and seasonal variations of input

2) Evaporite crystals have precipitated within the sediments3) Formed by replacement.4) The environment where the evaporites formed were probably in a deepwater environment due

to the fact that the deposits are extensive according to Professor Rasbury. 5) The minerals that formed the dark laminae are most likely calcite varves. These layers of

calcite have a dull birenfringes because the layers are rich in organic matter.

Chert:

550014:

1) The relative proportions are major amounts of microquartz and minor amounts of mega-quartz.

2) The textural relationship is depositional.3) The chert is in a bedded plane form since the mega-quartz exists in the form of veins.

550001:

1) The relative proportions are major amounts of micro-quartz.2) Textural relationship is pore-filling.3) This is nodular chert because the lack of organic matter or organism remnants.

GL1-4:

1) The relative proportions of the minerals are major amounts of microquartz, minor amount of chalcedony and trace amount of megaquartz.

2) The textural relationship is depositional.3) This is bedded chert because the chert is preserved within the fossils is in the form of

chalcedony.

550015:

1) The relative proportions include major amounts of microquartz and some trace amount of chalcedony and megaquartz.

2) The textural relationship is replacement where chert is replacing the carbonate.3) The contact between carbonate and chert in low magnification is primarily sharp since there is a

clear divide between the chert and the carbonate. However under greater magnification the contact appears to be gradual evident by an increased number of carbonate inclusions in the chert near the contact.

550019:

1) The relative proportions include major amounts of micro-quartz and minor amounts of chalcedony, and trace amounts of mega-quartz.

2) The textural relationship is pore filling, 3) Chert replaces the original carbonate oolites, some are replaced by microqurartz and others by

macroquartz mosaic. 4) Chalcedony is a primary cement since it is between the grains and coats in layers across more

than one grain rather than replace grains. 5) Compaction features include grain fractures and dissolution of grains. See photograph

Iron-Rich Sediments

W-67:

AH014:

1) There is an ooltic grainstone texture which can be found more commonly in carbonates.2) The nuclei of the oolites are hard to distinguish since they have been replaced by micro

crystalline quartz.

99:

1) The important textural feature is laminations which is comparable to laminations found in carbonates and evaporites, however they are preserved here better.

Phosphorites

AJM 18: (I couldn’t find 575000…but this was in the phophorites tray

1) The non-isotropic materials found in the pelloids are micrite and are diagenetic.2) The non-isotropic material between pelloids is massive and is detrital, unless it replaced an

oringal matrix which in that case it would be diagenetic too.

Monterey Phosphorite:

1) The black material might be organic material called collophane. 2) Collophane is non-crystalline phosphate which if metamorphosed turns to apatite. The

collophane in shell fragments represents organic material that has been replaced. 3) The host sediment might be made up of quartz (sandy and coarse grained), which is indicative

the environment the shell came from (maybe beaches).

Various Phosphorite Hand Samples: