The Nature of Early Tertiary Soils and Sediments Mineralogy and - - PowerPoint PPT Presentation

▶
the nature of early tertiary soils and sediments
SMART_READER_LITE
LIVE PREVIEW

The Nature of Early Tertiary Soils and Sediments Mineralogy and - - PowerPoint PPT Presentation

Jun 10, 2023 165 likes •587 views

The Nature of Early Tertiary Soils and Sediments Mineralogy and Petrology Jim Wood J. Reed Glasmann, PhD

slide-1
SLIDE 1

The Nature of Early Tertiary Soils and Sediments — Mineralogy and Petrology

Jim Wood

  • J. Reed Glasmann, PhD
slide-2
SLIDE 2

Abstract

The mineralogy and petrology of soils and sediments in the Early Tertiary section of the Sierra Nevada foothills of Northern and Central California were influenced by global tropical and subtropical climatic

  • regimens. Kaolinitic soils and sediments formed during the extremely warm/humid tropical climate of the

Paleocene to Early Eocene, while smectite clay dominates the later Eocene to Early Oligocene soils and

  • sediments. Micromorphological and micro+chemical investigations of both kaolinitic and smectitic sediments

show that large volumes of clay+rich materials were transported in these paleo fluvial systems as sand+sized aggregates derived from fluvial erosion of deeply weathered mature soils. The clay microfabric of the Early Tertiary paleosol clasts was stabilized by amorphous silica cement that precipitated in association with the intense chemical weathering in the warm/humid environment of the Early Tertiary. This pedogenic silica protected clay+rich aggregates from dispersion during fluvial transport in Early Tertiary rivers. Today, the pedogenic silica cement that stabilizes the granular smectitic sediments creates problems for soil engineers that design for construction on the exposed smectitic soils and sediments. The silica+stabilized smectitic clay in soils engineered from Late Eocene/Early Oligocene deposits can not be characterized by conventional ASTM soil test methods. The standard soil engineering tests classify the smectitic sediments as having low expansion potential. Following placement in engineered soils for construction, the paleo silica cement in these clay materials is prone to incremental dissolution allowing the expansive clays to freely interact with cyclic soil moisture conditions. Failure to properly classify these potentially highly expansive soils has contributed to widespread cases of structural damage throughout the urbanizing Sierra foothills and adjacent Sacramento Valley areas. .

2

slide-3
SLIDE 3

History of Current Research

  • Work began in 1980’s at UNOCAL Research Center as

part of a reservoir quality research project

  • Subsequent work over the last 10 years related to

consulting work on geotechnical problems in the Sierra foothills and Sacramento Valley areas 3

slide-4
SLIDE 4
  • J. D. Whitney (1873)

Baxter You Bet Chalk Bluff Quaker Hill Scott’s Flat Nevada City Key sample locations in the proximal Early Tertiary river system in Placer and Nevada Counties

4

slide-5
SLIDE 5

Matrix mineralogy of Early Tertiary river sediment mimics the contemporary regional soil mineralogy

  • Ione Fm proximal and distal sediments and the

underlying paleo Oxisols (ie., mature tropical soils)

– kaolinitic and quartzose

  • Chalk Bluff sedimentary section immediately above the

Ione Fm. unit has similar clay mineral assemblage as smectitic terrace bedrock paleosols and other regional soils* *see Wood and Glasmann, 2013—

!—on this website for greater detail on soil and sediment mineralogy

5

slide-6
SLIDE 6

The key to recognizing soil constituents in fluvial sediments is to know and understand the textures and morphologies

  • f the pedogenic constituents of the
  • riginal source soils from which the

sediments were derived

6

slide-7
SLIDE 7

From the soils literature describing mineralogy and micromorphology of Oxisols (Stoops, 1983):

  • All weatherable minerals are absent
  • Quartz is the dominant residual mineral of the parent

rock

  • Kaolinite is the dominant climax secondary clay

mineral

  • The soil fabric is comprised of granular arrangement of

clay aggregates (ie., micropeds). The soil fabric called “sapro+sands”. 7

slide-8
SLIDE 8

Pedogenic features revealed by soil petrography

  • Kaolinite occurs in numerous textures and

arrangements

– Largely determined by textures of precursor transitory clay minerals that form in the weathering front

  • Micropeds (ie., sand+sized clay aggregates) are

well developed

  • Pedogenic cements are prevalent.

8

slide-9
SLIDE 9

Oxisol Clay Mineralogy

Kaolinite pseudomorphously replaces precursor clay minerals Saprolite Weathering front Illite (sericite) K K I smectite

9

slide-10
SLIDE 10

Paleo Oxisol — Saprolite

Packing voids

Thin section: plane light (pl)

Wood 1994

10

slide-11
SLIDE 11

Wood 1994

11

slide-12
SLIDE 12

Paleo Oxisol — Saprolite

Packing voids

Thin section: plane light (pl)

Wood 1994

12

slide-13
SLIDE 13

Soil Cement Fluorescence

Irradiated with blue light

13

slide-14
SLIDE 14

Soil Cement Fluorescence

Wood 1994

14

slide-15
SLIDE 15

paleo Oxisol — oxic horizon

sand+sized clay aggregates with cement coatings

Packing voids

Thin section: plane light (pl)

Red dye fills porous clay fabric from Wood 1994

15

slide-16
SLIDE 16

Cement Coatings

Fluorescent view

From Wood 1994

16

slide-17
SLIDE 17

Chemical Weathering of Silicates Produces Excess Silica in Solution

4 KAlSi3O8 + 4 H+ + 2 H2O 4 K+ + Al4Si4O10(OH)8 + 8 SiO2

K feldspar Kaolinite

17

slide-18
SLIDE 18

Cement coatings are siliceous

kaolinite + excess silica + other cations

18 Microprobe EDS analysis:

excess silica

slide-19
SLIDE 19

Pedogenic silica in another paleo Oxisol near Friant

  • pal A peak = >20% amorphous silica

XRD Wood et. al. 1995

19

excess silica Microprobe EDS

slide-20
SLIDE 20

Spongy microfabric of opaque cement coatings causes refraction of light

Microprobe views Wood 1994

20

kaolinite platelets

slide-21
SLIDE 21

Ione kaolinitic sandstone (Quaker Hill)

K

Kaolinite micropeds plag

21

K

slide-22
SLIDE 22

Initially, the sandy sediments with transported Initially, the sandy sediments with transported micropeds micropeds posseses posseses substantial intergranular substantial intergranular porosity at the time of deposition porosity at the time of deposition

Transported Clay Clasts to Pseudomatrix

22

slide-23
SLIDE 23

Consolidation and compaction from overburden pressure caused plastic clay clasts to deform and form pseudo+matrix 23

slide-24
SLIDE 24

Squashed clay clasts comprise ≈ 50% of sand constituents

Ione Sandstone – Apricum Hill

pl xpl From Wood, 1994

24

slide-25
SLIDE 25

Ione sandstone

Weatherable minerals present in trace amounts — amphibole (A), K+feldspar (K), adjacent squashed clay clasts have variable clay textures (a verses b); prominent silica cements lining clay clasts (c) (from Wood, 1994).

25

slide-26
SLIDE 26

Squashed clay clasts form pseudomatrix

Microprobe back+scattered electron image Wood, 1994 26

slide-27
SLIDE 27

Hydrodynamically equivalent quartz and clay clasts have different average grain size due to different bulk density

27

slide-28
SLIDE 28

Ione Sandstone – Apricum Hill

Abundant mica and kaolinized mica

pl view 28

slide-29
SLIDE 29

xpl 29

kaolinized mica muscovite mica

slide-30
SLIDE 30

Oxisol — Saprolite

Packing voids

Thin section: plane light (pl)

30

slide-31
SLIDE 31

Ione claystones

xpl

Clay and silt sized kaolinite clay particles 31

slide-32
SLIDE 32

Top of Ione claystone section

xpl

Top of section — silt and sand sized smectitized mica particles

32

slide-33
SLIDE 33

Chalk Bluff unit smectitic sandstones

Squashed clay clast

33

slide-34
SLIDE 34

Chalk Bluff unit smectitic sandstones at Baxter

smectite clast kaolinite clast

Wood 1994 34

slide-35
SLIDE 35

Smectitic Sandstone – Rancho Murieta

1 mm 0904+13 xpl 6.3x Sandstone composition about 80% smectite

35

slide-36
SLIDE 36

1 mm 0904+13 pl rl 6.3x Matrix largely smectitic silt and clay with silica cement Smectitic sand clasts with silica cement Hematite cemented clay clasts Reflected Light view Smectitic sand clasts with silica cement

36

slide-37
SLIDE 37

Rancho Murieta ASTM test results

10 20 30 40 50 60 70 80 90 100 Plasticity Index (PI) 10 20 30 40 50 60 Liquid Limit (LL) MH CH CL ML

(ASTM D4318) (ASTM D4318) 37

slide-38
SLIDE 38

Smectitic sediments

Sacramento

38

slide-39
SLIDE 39

XRD Results

Smectite Smectite <200 mesh fraction (silt and clay) Sand fraction (>200 mesh)

39

slide-40
SLIDE 40

Summary

  • Clay in Early Tertiary sandstones occurs largely as silica cemented sand sized clasts

that were transported as bedload constituents

  • The clay in claystones/mudstones was derived from clay and silt in suspension
  • Weatherable minerals occur in trace amounts in the kaolinitic Ione sandstones but

show little, if any signs of post+depositional leaching or alteration

  • The fabric of sandstones and claystones do not possess pedogenic morphologies

such as packing voids indicative of significant post+depositional weathering activity

  • The cemented sandy form of smectite in sediments of Chalk Bluff lithology defies the

ASTM test methods and leads to latent expansion problems for soil engineering in the region

40