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Brines and Evaporites

Brines and Evaporites

Peter Sonnenfeld, J.-P. Perthuisot

ISBN: 978-1-118-66754-5 March 2013 American Geophysical Union 126 Pages

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Published by the American Geophysical Union as part of the Short Courses in Geology Series, Volume 3.

This course is designed to present fundamental concepts and constraints of evaporitic mineral precipitation in different depositional environments, a discussion of the concentration of attendant accessory accumulations of clastics, base metals and hydrocarbons, an integrated overview of epigenetic alteration of evaporite deposits, and a systematic analysis of ancient evaporite basin configurations.

These notes present case histories of current evaporite deposition in the hope that they will provide the keys to a better understanding of ancient salt basins.

The data presented here essentially rely on basins studied by the author and his coworkers. Although this choice may appear somewhat limited to some readers familiar with classical models, the examples shown here cover the main present-day geological settings. Furthermore, observations on pre-evaporitic deposits were also introduced.

Part I. Genesis of Evaporites
P. Sonnenfeld

Preface 3

Introduction 5

Climatological factors 5

Freeze-drying 6

Evaporation 6

Aridity 6

Air masses 8

Hydrography 9

The Coriolis effect 10

The entrance restriction 11

Brines 11

Density stratification 13

Radiation and thermal effects 14

Anions in the concentrating brine 15

Cation surplus in the brine 16

Complexing in the brine 17

Biota in hypersaline brines 17

Brines moving through evaporites 18

Evaporitic rocks 19

Non-marine evaporites 20

Groundwater precipitation 20

The polar environment 22

Subtropical lakes 23

Sebkhas 25

Marine evaporites 25

Evaporite-related marine carbonates 26

Marine gypsum 27

Celestite and barite 27

Marine halite 27

Marine potash salts 28

Marine magnesium salts 34

Substitutions 34

Accessorieisn marinee vaporites 35

Siliciclastics 36

Base metals around evaporites 39

Organic matter in evaporites 40

Secondarayl teration of marinee vaporites  41

Dehydration of gypsum 41

Sulfatization of potash beds 43

Further alterations 46

Basin configuration 46

Basin modelling 51

The bull's eye model 51

The tear-drop model 53

The open shelf model 53

The barred basin model 54

The reflux model 55

The deep basin model 55

The deep dry basin or giant flood model  57

The synsedimentary subsidence model  61

Conclusion 64

Acknowledgments 64

Part II.  Recent Evaporites
J. P. Perthuisot 65

Preface 67

Abstract 69

Introduction 69

Main characteristics of modern evaporite basins 69

Conditions of evaporite formation 69

Tentative typology of present sites of evaporites 70

Salt precipitation 71

Salinity distribution and gradients 72

Rate of deposition of evaporites 72

The significance of water depth 73

Independence of evaporitic processes of depth of water 73

Consequences of a deep water body 73

Organic matter and evaporites 74

The origin of organic matter in paralice vaporite basins 74

Preservation of organic matter 75

Modern evaporite occurrences 80

Continental evaporitic areas 80

Groundwaterp recipitation: The pedological crusts 80

Intermittent lakes 80

Perennial lakes 85

Paralic evaporitic areas 92

Hydrophysical and hydrochemical arrangement of paralic areas

Experimental models: Salinas 94

The evaporitic tidal flats 98

The role of evaporitic tidal flats (sebkhas) and their feeder lagoons  101

Sporadically flooded basins 101

Evaporitic inlets 103

Paralic to deep basins with continuous seawater input 105

The necessity of a dynamic approach to evaporite deposits 116

Conclusion 116

Acknowledgments 118

Index of evaporitic minerals 119

References cited 121