An AEM-TEM study of weathering and diagenesis, Albert Lake, Oregon: 2. Diagenetic modification of the sedimentary assemblage

Journal Article · Tue Oct 01 04:00:00 EDT 1991 · Geochimica et Cosmochimica Acta; (United States)

DOI:https://doi.org/10.1016/0016-7037(91)90445-B· OSTI ID:7114348

Banfield, J F; Veblen, D R ^[1]; Jones, B F ^[2]

---

1. Johns Hopkins Univ., Baltimore, MD (United States)
2. Geological Survey, Reston, VA (United States)

This paper compares the mineralogy and chemistry of clay minerals in sediments from various depths and positions in Abert Lake and surrounding playa with those of the weathered materials entering the lake in order to reveal the nature and extent of post-depositional mineralogical modification. Analytical electron microscope (AEM) data from individual clay particles reveal that each sample is comprised of a highly inhomogeneous smectite assemblage. The thin clay flakes (commonly less than 10 nm wide) display a complete range in octahedral sheet compositions from nearly dioctahedral to nearly trioctahedral. The very abundant Mg-rich lake smectites with an estimated composition K{sub 0.29} (Al{sub 0.23}Mg{sub 2.16}Fe{sub 0.30})Si{sub 3.80}Al{sub 0.20}O{sub 10}(OH){sub 2} are not formed by weathering. This confirms the importance of diagenetic Mg uptake. Smectite compositions within individual samples were highly variable, yet source-related characteristics such as the abundance of Fe-rich smectite were apparent. Little evidence for systematic K or Mg enrichment with depth was identified in samples from depths of down to 16 feet below the sediment-water interface. The most magnesian assemblages are associated both with weathering sources of Mg-rich smectite and playa environments subjected to repeated wetting and drying cycles. Other diagenetic reactions in the sediment include recrystallization of Na-rich silica gel and diatom fragments. Abundant, submicron-sized, untwinned, euhedral crystals of K-feldspar are interpreted to be authigenic in origin.

• OSTI ID: 7114348
• Journal Information: Geochimica et Cosmochimica Acta; (United States), Journal Name: Geochimica et Cosmochimica Acta; (United States) Vol. 55:10; ISSN GCACA; ISSN 0016-7037
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
580000* -- Geosciences
ALKALINE EARTH METALS
BRINES
CHEMICAL COMPOSITION
CHEMISTRY
CLAYS
CRYSTAL STRUCTURE
DEVELOPED COUNTRIES
DIAGENESIS
ELECTRON MICROSCOPY
ELEMENTS
FEDERAL REGION X
GEOCHEMISTRY
GEOLOGIC DEPOSITS
INTERFACES
LAKES
MAGNESIUM
METALS
MICROSCOPY
MINERALOGY
NORTH AMERICA
OREGON
SEDIMENT-WATER INTERFACES
SEDIMENTS
SORPTION
SORPTIVE PROPERTIES
SURFACE PROPERTIES
SURFACE WATERS
TRANSMISSION ELECTRON MICROSCOPY
USA
WEATHERING