Mike Pole - Atlas of Mongolian Geology 2013 v1.1

7/29/2019 Mike Pole - Atlas of Mongolian Geology 2013 v1.1

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An Atlas of Mongolian Geology

Mike Pole

www.mikepole.com

Version 1.1, 24 April 2013

2013 by Mike Pole. All rights reserved. Fair use for research or teaching is fine, providedacknowledgement is given.


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1 Introduction ......................................................................................................................................... 32 The Basic Framework of Mongolia .................................................................................................... 33 Lake Terrane ....................................................................................................................................... 74 Tsagaanolom Basin ........................................................................................................................... 195 Hangay-Henty Basin ......................................................................................................................... 216 Gobi Altai Terrane ............................................................................................................................ 327 Baytag Terrane .................................................................................................................................. 368 Dariv Terrane .................................................................................................................................... 389 Zoolen Terrane .................................................................................................................................. 4010 Middle Gobi Belt .............................................................................................................................. 4111 Atasbogd Terrane .............................................................................................................................. 4412 Post Accretion Sediments ................................................................................................................. 46

12.1 Permian ................................................................................................................................... 4612.2 Jurassic .................................................................................................................................... 5712.3 Late Jurassic-Early Cretaceous ............................................................................................... 59

12.3.1 Vakhar Basin ....................................................................................................................... 6012.3.2 Khukh Basin West .............................................................................................................. 6312.3.3 Zaraagiin Basin ................................................................................................................... 6712.3.4 Soochont Basin ................................................................................................................... 7012.3.5 Probable NE extension Shoochont Basin............................................................................ 8112.3.6 Zadgai Basin ....................................................................................................................... 8312.3.7 Uvuljuunii Basin.............................................................................................................. 84

12.4 Neogene Basin Fill ................................................................................................................. 8812.4.1 Neogene Mid-Basin Setting ................................................................................................ 8912.4.2 Neogene Alluviul Fan Setting ............................................................................................. 9012.4.3 Neogene Basin-Edge Setting .............................................................................................. 91

13 Acknowledgments ............................................................................................................................. 9414 References on Mongolian Geology ................................................................................................... 95

1


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INTRODUCTION

The purpose of this book is to place field photographs taken over about five years of working (mostly inSW Mongolia) into a broad outline of Mongolian geology that may be useful to someone. It doesntclaim any authority on the subject, but is merely a chance to get information that might otherwise belost, into the public domain. This Version (1.0) is little more than a rough dump of images that will gettidied up as I get the time.

Mongolia is a very large country with a correspondingly complicated geology. As a field geologistcoming to work in Mongolia it very soon became apparent how well the geology of the country had

been mapped by Mongolian and Soviet-era geologists. Sure, there is much to be gained by furtherspecialist mapping and by geologists looking from a different perspective, but the broader point is thatthe earlier geos didnt miss much. There was little chance of finding something new behind that hillover there because in most cases, it was clear someone had looked. Nevertheless, much of this earlierwork is very hard to obtain for a western geologist, and in any case, is mostly written in Mongolian orRussian. In my own work it has been useful to coin some words for geological units but on theunderstanding they may well be already known under different names in the Mongolian-Russianliterature.

2 THE BASIC FRAMEWORK OF MONGOLIA

Mongolia has a long and highly complex geological structure. To make some sort of order out of thisBadarch et al. (2002) used the terrane concept (Coney et al. 1980) to group large areas of Mongolia intoa series of named terranes. These terranes are used here as the basic framework of this book. In essence,Badarch et al. (2002), along with earlier authors, propose that Mongolia has its origins as a series of Pre-

Cambrian core cratons around which younger material, in the form of volcanic arcs, basins,subduction zones, and smaller continental fragments, was accreted, mostly in the Palaeozoic.

Figure 1. Map of Mongolia showing the core cratons as recognized by Badarch et al. (2002)


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Figure 2. Baydrag Terrane. Sedimentary manganese bed. North of Biger (photo 67012).

Figure 3. Baydrag Terrane. Ripple marks. North of Biger (photo 66994).


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Figure 4. Baydrag Terrane. Contact between diorite-granite, Biger region (Nik43699).

Figure 5. Baydrag Terrane. Graded intrusion. Biger region ( Nik43711).


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Figure 6. Baydrag Terrane. Calcite veins in granite. NW of Gobi Altai. (photo 68208).

Figure 7. Baydrag Terrane. Possible hydrothermal alteration of granitic material. NW of Gobi Altai. (photo 68231).


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3 LAKE TERRANE

The Lake Terrane was classified by Badarch et al. (2002) as an Island Arc terrane.Within this unit, thenorthern edge of the Gobi Altai consists of Vendian-Cambrian pelagic sediments with exceptionallywell preserved bedding, including bioturbation, flame structures, ash-falls and laminations and cross-

bedding. At least in one locality, these consistently indicate younging to the south. Broadly similarfacies are found in the Tsagoan Burgasnii Gol region of the Khantaishir Range to the NE.The only Paleozoic locality I know of with shelly fossils on the northern edge of the Gobi AltaiMountains lies mid-way between Tugrug and Khalium informally named here as the Bayanhoshuusediments. The regional map regards these as Silurian and record the brachopodsRostricellula,Tuvaella,Howellella and the trilobiteDalmaniturus.

Figure 8. Location of the Lake Terrane with respect to the core cratons.


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Figure 9. Lake Terrane. Looking like flute marks, but in fairly metamorphosed material (Photo 22914).

Figure 10. Lake Terrane. Marble-dominated breccia in a unit mapped as Vendian on the published geological maps

(Photo 23411).


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Figure 11. Lake Terrane. Graded beds. Grading (from light to dark) shows sequence youngs to north (top) (Photo

23381).

Figure 12. Lake Terrane. Malachite vein in syenite. Between Biger and Khalium (photo 67047).


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Figure 13. Lake Terrane. Multiple fractures with malachite/chalcopyrite. Between Biger and Khalium (photo 67051).

Figure 14. Lake Terrane. Surface view of fracture with malachite/chalcopyrite. Between Biger and Khalium (photo

67044).


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Figure 15. Lake Terrane. Bioturbation in pelagic green muds. North edge of Gobi Altai. Lens cap 88 mm diameter.

Figure 16. Lake Terrane. Flame structures in pelagic green mud. North edge of Gobi Altai. Lens cap 88 mm

diameter.


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Figure 17. Lake Terrane. Rhyolitic crystal tuff. Note fining upward. North edge of Gobi Altai. Lens cap 88 mm

diameter.

Figure 18. Lake Terrane. Microlaminated pelagic green mud. North edge of Gobi Altai. Lens cap 88 mm diameter.


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Figure 19. Lake Terrane. Tabular bedding in pelagic green mud and silt. North edge of Gobi Altai. Lens cap 88 mm

diameter.

Figure 20 (left). Lake Terrane. Tsagoan Chert beds. Tsagoan Burgasnii Gol region, Kantaishir Range.

Figure 21 (right). Lake Terrane. Detail of white chert. Silicified white beds are concentrated in an upper

part of the section. Tsagoan Burgasnii Gol region, Kantaishir Range.


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Figure 22. Lake Terrane. Tsagoan Burgasnii Gol Sediments-rhyolitic vitric tuff. Horizons of verycoarse, angular quartz, white ad pink feldspar are common in the green muds. They show a clear fining-upward trend. The younging direction is consistently toward the north. Tsagoan Burgasnii Gol region,

Kantaishir Range.

Figure 23. Lake Terrane. Mud cracks. Prob Vendian-Cambrian. North limit of Ulitzin Range (photo Nik7039).


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Figure 24. Lake Terrane. Mud cracks and ripples. Probably Vendian-Cambrian. North limit of Ulitzin Range (photo

Nik7040).

Figure 25. Lake Terrane. Ripples probably Vendian-Cambrian North limit of Ulitzin Range (photo Nik6942).


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Figure 26. Lake Terrane. Ripples East of Khurren Gol soum (Nik37681).

Figure 27. Lake Terrane. Stromatolite frags East of Khurren Gol soum (Nik37667).


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Figure 28. Lake Terrane. Stromatolite East of Khurren Gol soum (Nik37663).

Figure 29. Lake Terrane. Stromatolite. East of Khurren Gol soum (Nik37671).


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Figure 30. Distribution of post terrane-accretion marine sediments (yellow). The Bayanhoshuu Sediments are barely

visible at this scale a small sliver on the edge of the projecting ridge of the Gobi Altai. North to top.

Figure 31. The Bayanhoshuu sediments form a thin sliver along the northern edge of the Gobi Altai. This view looks

east along strike of the Bayanhoshuu and shows it range of colours. The north edge of the Gobi Altai are visible at top

right.


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Figure 32. Crinoid ossicles in a block of Bayanhoshuu limestone.

Figure 33. Lake Terrane. Sudal Pb-Zn-Cu, veins in Devonian limestone related to Devonian granitoid (photo

Nik23710).

4 TSAGAANOLOM BASIN

The Tsagaanolom Basin consists mainly of Cambrian shelf carbonate rocks that were deposited on topof the Zavhan and Tarvagatay Terranes after these had amalgamated (Badarch et al. 2002).

The limestones are mostly recrystalised, but near the city of Gobi Altai specimens of archaeocyaths arelocally common, a group which is an entirely Cambrian group (Benton and Harper 1997; Wood 1998).


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Figure 34. The Tsagaanolom Basin (orange brickwork) and The Zavhan and Tarvagatay Cratons on which it was

deposited.

Figure 35. Tsagaanolom Basin. Limestone with abundant archaeocyaths from about 9 km SE of Altai. Archaeocyaths

are important in determining a Cambrian age for these limestones rather than Vendian. These sediments overlie the

latest PreCambrian Khantaishir Ophiolite. Lens cap 88 mm diameter.


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5 HANGAY-HENTY BASIN

The Hangay-Henty Basin was not mapped as a terrane per se by Badarch et al. (2002). The followingimages were taken near Delgerengui Soum, where a thick Devonian volcaniclastic pile includes zones

of jasper-magnetite (i.e. SEDEX) and other highly siliceous and Fe-rich beds. Individual beds ofjasperoid and magnetite can be traced for over a kilometer, and probably extend for at least two or threekilometers. Highly convoluted units of thin-bedded jasperoid appear to be the result of soft-sedimentdeformation (somewhat similar material is present in the BIFs of Soudan, Minnesota:

blogs.agu.org/mountainbeltway/2012/02/06/folded-bifs-of-soudan-minnesota/). There are also zones ofwhat appear to be ductile deformation, that include various hues of siliceous material. Andesite is veryrare, but it is not clear whether these are extrusive or shallowly intrusive. The unit was intruded bygranitoids in the Permian which caused some local alteration around the contact.

Figure 36. Hangay-Henty Basin. Thin-bedded yellowish weathering sandstone with fining-up beds.


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Figure 37. Hangay-Henty Basin. Example of the dark red and green banded facies. Rock hammer for scale.

Figure 38. Hangay-Henty Basin. Scribe projecting from a highly magnetic and specular inclusion within dark green

and red facies. Other bands of dark, specular and highly magnetic material can also be seen.


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Figure 39. Hangay-Henty Basin. Banding within red highly-siliceous jasperoid is on the same scale as thin=-beds

within unmineralizsed sandstone.

Figure 40. Hangay-Henty Basin. Banding within red highly-siliceous jasperoid is on the same scale as thin=-beds

within unmineralizsed sandstone.


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Figure 41. Hangay-Henty Basin. Highly convoluted bands within red highly-siliceous jasperoid. Rock hammer for

scale.

Figure 42. Hangay-Henty Basin. Plastic deformation.


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Figure 43. Hangay-Henty Basin. Cross-cutting beds in jasperoid. Although the bands may be relict bedding it isunlikely the cross-cutting was contemporary (it is not sedimentary). Point of rock hammer for scale.

Figure 44. Hangay-Henty Basin. Small lens of red jasperoid within dark green facies. Pen for scale.


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Figure 45. Hangay-Henty Basin. Lenses of various lithologies within dull red facies.

Figure 46. Hangay-Henty Basin. Breccia of very coarse grained intraformational mud clasts. This is the coarsest

sediment located within the sequence.


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Figure 47. Hangay-Henty Basin. Thin-bedded sand stone facies with some fining-up beds. Photograph is inferred to

be right-way up.

Figure 48. Hangay-Henty Basin. Flame-structures in thin-bedded sandstone facies.


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Figure 49. Hangay-Henty Basin. Outcrop of c. 10 m thick bed of hematite in foreground (hammer for scale) and

massive yellow-grey metasandstone in background.

Figure 50. Hangay-Henty Basin. "Clast" of red hematite (immediately to left of hammer) within greenschist.


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Figure 51. Hangay-Henty Basin. Red jasperoid with many cross-cutting quartz veins.

Figure 52. Hangay-Henty Basin. Purple-green metasediment.


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Figure 53. Hangay-Henty Basin. Red-green metasediment.

Figure 54. Hangay-Henty Basin. Dull black magnetite.


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Figure 55. Hangay-Henty Basin. Bedded purple-red hematite with pale laminae. Analysis indicates 9 % Fe.

Figure 56. Hangay-Henty Basin. Green (primarily epidote) metasediment with hematite. Analysis indicates 20.7 %

Fe.


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6 GOBI ALTAI TERRANE

The Gobi Altai Terrane is classified as a forearc-backarc terrane by Badarch et al. (2002)

Figure 57. Location of Gobi Altai Terrane and core cratons.

Figure 58. Devonian andesite, near Bayan Under Soum. Gobi Altai Terrane (photo Nik23581).


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Figure 59. Gobi Altai Terrane. Fossil log in interbedded shale and sandstone mapped as Devonian on the published

regional map. East of Shinejinst (Photo 21699).

Figure 60. Gobi Altai Terrane. Devonian corals. South of Shinejinst (photo 68329).


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Figure 61. Gobi Altai Terrane. Cobble of crinoid limestone. South of Shinejinst (photo 68296).

Figure 62. Gobi Altai Terrane. Migmatite boulder in limestone-dominated breccia. South of Shinejinst (photo 68320)


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Figure 63. Gobi Altai Terrane. Si-Epidote vein. South of Shinejinst (photo 68309).


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7 BAYTAG TERRANE

The Baytag Terrane in the SW of Mongolia was classified by Badarch et al. (2002) as an Island Arc

terrane. They reported Devonian-Carboniferous marine fossils and coal-bearing strata (see Rhuzentsevet al. 1992). Terrestrial plant fragments are also common, including lycopod stems, also consistent witha Paleozoic age.

Figure 64. Location of Baytag terrane and the core Mongolian cratons.


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Figure 65. Baytag Terrane. Lycopod stem (photo Nik44817).

Figure 66. Baytag Terrane. Lycopod stem (photo Nik44819).


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8 DARIV TERRANE

The Darive Terrane is classified as a Metamorphic Terrane by Badarch et al. (2002). The followingimages come from an area to the north of Biger, apparently within the bounds of this terrane, but

probably including some post-accretion rocks (the basalts).

Figure 67. Location of the Dariv Terrane with respect to the core cratons.

Figure 68. Dariv Terrane. Amygdaloidal basalt (photo 66763).


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Figure 69. Dariv Terrane. Chert beds (photo 66745).

Figure 70. Dariv Terrane. Epidote veins (photo 66765).


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9 ZOOLEN TERRANE

The Zoolen Terrane was classified as an Accretionary Wedge Terrane by Badarch et al. (2002). The unit

includes monotonous, drab sandstones, as well as extensive mlanges.

Figure 71. Location of Zoolen Terrane with respect to the core cratons.


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10 MIDDLE GOBI BELT

The Middle Gobi Belt was not mapped as a terrane per se by Badarch et al (2002), but was described asa volcanic-plutonic belt (p. 106). The following images come from a small skarn deposit to the SE ofErdenedalai.

Figure 72. The Middle Gobi Belt Belt in relation to the core cratons.

Figure 73. Middle Gobi Belt, skarn deposit. Massive magnetite and quartz (photo Nik26143).


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Figure 74. Middle Gobi Belt, skarn deposit. Banded magnetite-quartz (photo Nik26144).

Figure 75. Middle Gobi Belt, skarn deposit. Breccia with malachite (photo Nik26110).


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Figure 76. Middle Gobi Belt, skarn deposit. Breccia with malachite (photo Nik26110).

Figure 77. Middle Gobi Belt, skarn deposit. Banded epidote-magnetite (photo Nik26157).


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11 ATASBOGD TERRANE

The Atasbogd Terrane, lying mostly alomng the Chinese border in the south of Mongolia, was classifiedas a backarc-forearc basin terrane by Badarch et al. (2002).

Figure 78. Location of Atasbogd Terrane and the core cratons.

Figure 79. Atasbogd Terrane. Laminated volcaniclastic sediments. About 70 km Nth Chinese border (Photo 23325).


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Figure 80. Atasbogd Terrane. Load casts in laminated sediments. About 70 km Nth Chinese border (Photo 23324).


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12 POST ACCRETION SEDIMENTS

12.1 Permian

Permian coal, identifiable in the field by Cordaites fossil leaves, occurs in a long, narrow, generallyNW-SE trending zone, along the northern edge of the Gobi Altai. Silicified and/or limonised tree logsare abundant in some facies, or as fragments in a surface lag. None of the wood has been noted ingrowth position. A typical example is the Zeegt coal pit near Chundman, where carbonaceous shale,with common Cordaites leaves, overlies coal. Sandstone is virtually absent at this pit.

Figure 81. Ust Chatsaren Gol. Black silicified log in brown fluvial sandstone.


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Figure 82. Sandstone bed with abundant woody fragments at Tsangilah Gol. This is a distinctive and common facies

in Tsangilah Gol, Khuren Gol, and in the area of Rio Tinto operations.

Figure 83. Micro-laminated black chert. Lens cap 88 mm in diameter.


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Figure 84. Close-up view of cyclic sedimentation. Some exhibit a grading upward into a muddier lithology.

Figure 85. Three apparent coarsening-upward sequences (This view looks at the sequence in the middle of the

previous figure, from the other side of the mountain). The sequences start with highly carbonaceous mud, grade up

into rusty sands, a may culminate in coarse, prominent channels before abruptly returning to carbonaceous mud.

Compare the left-most sequence with that from Harzat Gol in Figure ####.


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Figure 86. Fluvial sandstone wedging out within coal bed. This represents a channel avulsion event which spread

across a swamp.

Figure 87. Rhythmically bedded sandstones and muddy sandstones from approximately three-quarters of the way

across Figure ###.


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Figure 88. Detail of rhythmically bedded sandstones and muddy sandstones shown in Figure ###.

Figure 89. Abundant cordaitalean leaves on bedding surface.

Figure 90. Detail of leaves.


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Figure 91. Ulitzin Range. Poorly sorted gravel in a clay-rich muddy matrix.

Figure 92. Ulitzin Range. Two fining-up sequences (younging to the left), terminating in coal and abruptly overlain bychannel sandstone.


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Figure 93. Outsized subangular clast within fine sandstone.

Figure 94. Ulitzin Range. Typical occurrence of one of the thinner coal seams with many small sandstone beds

throughout,


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Figure 95. Ulitzin Range. Flame structures (above) ripples (below).


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Figure 96. Ulitzin Range. Cross-bedded channel sandstones.

Figure 97. Poorly sorted cobble conglomerate channel scouring into coal below.


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Figure 98. Matrix-support conglomerate.

Figure 99. Ulitzin Range. Cordaitalean leaf in shale. Important for confirming a Permian-Carboniferous age.


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Figure 100. North edge Dariv mountains. Pale silt-claystone lacustrine facies.


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12.2 Jurassic

A second zone of coal in the Gobi Altai has a more E-W trend and is dated as Jurassic, based onboth palynology and occasional fossils ofGinkgo leaves (Cordaites are absent). A typical example is theShinejinst coal pit and surrounding area, where coal alternates with meter-scale tabular and trough

cross-bedding.

Figure 101. Shine Jinst coal field. Tabular cross-bed set (Photo ).

Figure 102. Shine Jinst coal field. Soft sediment deformation structures in sandstone (Photo ).


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Figure 103. Shine Jinst coal fiels. Planar section of large trough set. These are obviously difficult to photograph, but

the dotted line and the rock hammer give an indication of their size (Photo ).

Figure 104. Another location with probable Jurassic coal lies c. 90 km SW of Ulaangom in NW Mongolia (UTM Z 46

413108 5449770, photo 56070).


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12.3 Late Jurassic-Early Cretaceous

Sometime around the end of the Jurassic or Early Cretaceous, a series of basins were created in the GobiAltai region. These have a broadly SW-NE orientation and cut obliquely across the dominant NW-SEtrend of the mountains and larger valleys. The outlines can be traced off very clearly from LANDSAT

images. The basin-fill ranges from breccia, to fluvial with associated floodbasins and soils, andlacustrine, sometimes with evaporitic units. There are often with basaltic flows. Fossils are locallycommon, but in contrast to the Bayanhongor region further west, dinosaurs and other vertebrates areeither absent or at least very rare. For my own use Ive applied names to some of these basins, but theymay well already have names in literature not available to me.

Figure 105. Cretaceous basins (green) in the Gobi Altai region between Shinejinst coal mine (near Shinejinst Soum)

and Zeegt coal mine (near Chundman Soum). The names are my informal terms. Brown = basement mountains, blue

= Jurassic coal basins (elongate more E-W).


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12.3.1Vakhar Basin

Figure 106. Vakhar Basin. Basalt flow over reddish fluvial sands. The basalt is overlain by more fluvial sands off-

picture to the left. (Photo 21393).

Figure 107. Vakhar Basin. Basalt amygdales. (Photo 21392).


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Figure 108. Vakhar Basin. Well-developed pedogenic structures in red soil. (Photo 21384).

Figure 109. Vakhar Basin. Oblique detail of pedogenic structures. (Photo 21386).


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Figure 110. Vakhar Basin . Possible coprolite in shales south of Alag Tsahir. Note outsized clast immediately above

(Photo 21436).


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12.3.2Khukh Basin West

The base of the succession is composed of red-matrix breccia which passes upwards into interbbededgrey conglomerate and red pebbly mudstone. Soil-forming processes at the time have often blurred thecolour distinction between these two facies. This is interpreted as distal fan deposits passing upwardsinto braided river and associated flood basins.

The red-beds pass abruptly upwards into a prominent zone of grey mud has abundant layers of fibrousgypsum (the crystals are oriented perpendicular to the bedding. This is possibly the satin-spar variety) aswell zones of more complex networking of gypsum. This is interpreted as a sequence of sedimentaryevaporates.

The sediments then become generally browner and yellower. Fluvial sands and conglomeratespredominate along with grey mud. Thin red beds are sometimes present. They are clearly the uppersurface of soil profiles and often have large calcareous concretions within their profiles. This isinterpreted as a progression to a more distal sedimentary environment.

Fresh water mollusc fossils are present in at least two localities. A large and a small species of bivalveand a large and small species of gastropod are present. The creatures appear to have been abundant for ashort lacustrine period in a predominantly fluvial setting.

The whole succession is capped by a layer of basalt.

Figure 111. Khukh Basin West. Interbedded grey conglomerate and pebbly red muds (Photo 23437).


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Figure 112. Khukh Basin West. Evaporite layers of fibrous gypsum in grey mud (Photo 23428).

Figure 113. Khukh Basin West. Fluvial channels with sand and conglomerate (light tones) in grey mud (Photo 23452).


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Figure 114. Khukh Basin West. Calcareous concretions (at level of rock hammer) within a red soil profile, terminated

by a conglomerate-filled channel (Photo 23450).

Figure 115. Khukh Basin West. Freshwater bivalves covering a bedding surface (Photo 23716).


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Figure 116. Khukh Basin West. Large freshwater gastropods (Photo 23717).

Figure 117. Khukh Basin West. Small freshwater gastropods (Photo 23719).

Figure 118. Khukh Basin West. Small freshwater bivalves, possibly ostracods. Scale in millimeters (Photo 23719).


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12.3.3Zaraagiin Basin

Figure 119. Zaraagiin Basin - Aman Gol coal, Lower seam of coal sharply overlain by breccia. Doted line shows

continuation of seam top below surface slump. Sample location is marked by shovel. View to west (Photo 22906).

Figure 120. Zaraagiin Basin - Aman Gol coal, overlain by schist breccia. Same seam as previous figure. Rock

hammer for scale. View to east (Photo 21252).


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Figure 121. Zaraagiin Basin - Aman Gol coal. One of the middle seams. Rock hammer for scale (Photo 22905).

Figure 122. Zaraagiin Basin - Aman Gol coal. Many thin seams of coal separated by mud and sharply and

unconformably overlain by recent alluvium. View to north (Photo 21253). Rock hammer for scale.


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Figure 123. Cretaceous, pillow basalt, mid-way between Zaraagin and Vakhar Basin (photo Nik23347).


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12.3.4Soochont Basin

Figure 124. Soochont Basin - Slabs of sandstone with rippled surfaces are locally common.

Figure 125. Soochont Basin - Stacked ripple beds. The current direction remains consistent.


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Figure 126. Soochont Basin - Two units of lacustrine mud with contrasting competencies. The lower is jointed, the

upper not (Photo 19209).

Figure 127. Soochont Basin -Fluvial sediments (horizontal strata in center picture) on-lapping onto a granitebatholith. View to south (Photo ).


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Figure 128. Soochont Basin -Fluvial sediments on-lapping granite (Photo 19256).

Figure 129. Soochont Basin -Superimposed channels with conglomerate fill (Photo 19176).


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Figure 130. Soochont Basin -Trough cross-bedding (Photo 19180).

Figure 131. Soochont Basin -Soft sediment deformation in fine fluvial sandstone (Photo 19182).


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Figure 132. Soochont Basin -Distal splay deposits in flood-basin sediments (Photo 19016 ).

Figure 133. Soochont Basin -Red soil horizons within grey-yellowish sands (Photo 21354).


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Figure 134. Soochont Basin - Channel in floodbasin/red soil deposits (Photo 19205).

Figure 135. Soochont Basin - Red soil development in floodbasin deposits. Note the increase in red weathering

towards the top of each flood event (Photo 19204).


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Figure 136. Soochont Basin -Two small sandstone-filled splay channels within muddy floodbasin deposits (Photo

19154).

Figure 137. Soochont Basin- Isolated conglomerate unit within a dominantly sand and shale sequence (Photo 19141).


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Figure 138. Soochont Basin Shale and mudstone (Photo ).

Figure 139. Soochont Basin -Symmetrical ripple marks (Photo 19266).


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Figure 140. Soochont Basin -Mud cracks (Photo 19268).

Figure 141. Soochont Basin - Arthropod (?) fossil (Photo 21527).


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Figure 142. Soochont Basin -Imbricated gravel (current flow was to the left) (Photo 19286).

Figure 143. Soochont Basin -Mass-flow, debris flow deposit (Photo 19292).


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Figure 144. Soochont Basin -Red soil development within breccia (Photo 19283).

Figure 145. Soochont Basin -Breccia with red matrix (Photo ).


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12.3.5Probable NE extension Shoochont Basin

Figure 146. Flint nodules amongst sandstone. Fragments of silicified wood also common here. Probably NE extension

of Soochont Basin (Photo 21462).

Figure 147. Stromatolite. Probably NE extension of Soochont Basin (Photo 21531).


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Figure 148. Rod-shaped fossils (no idea what they are). Probably NE extension of Soochont Basin (Photo 21533).


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12.3.6Zadgai Basin

Figure 149. Zadgai Basin. Red beds with light-coloured root casts (Photo 21936).


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12.3.7 Uvuljuunii Basin

This is a small basin lying well to the NW of the previous set of basins.

Figure 150. Distribution of Uvuljuunii Basin.

Figure 151. Uvuljuunii Basin. Bioturbation extending from a muddy unit down into a fine sand unit.


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Figure 152. Uvuljuunii Basin. Typical example of very-well rounded cobbles in a distinctly brown matrix.

Figure 153. Uvuljuunii Basin. Resistant bed of fluvial channel sandstone, overlying paleosol and underlying finer

overbank sands and silt.


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Figure 154. Uvuljuunii Basin. Detail of channel sandstone showing cross-beds and contact with underlying paleosol.

Figure 155. Uvuljuunii Basin. Detail of contact between channel sands and paleosol.


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Figure 156. Uvuljuunii Basin. Plan section of soil-associated bioturbation.


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12.4 Neogene Basin Fill

Figure 157. Highly dissected Neogene strata on the southern flank of the Khantaishir Range. Note the consistent

pattern of colour.

Figure 158. Distribution (yellow) of some of the Neogene sediments observed during mapping. North to top.


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12.4.1Neogene Mid-Basin Setting

Figure 159. Thick red silt and sand. On the sky-line note a vehicle sitting on top of more recent grey gravel.

Figure 160. Lithological variation within predominantly red silts-sands. Resistant white units are carbonate.

Notebook for scale.


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12.4.2Neogene Alluviul Fan Setting

Figure 161. Reddish sands and silts with more resistant layers of gravel, in a scarp above the Houm Gol. Much

coarser material erodes down from where it mantles the deposit.

Figure 162. Very poorly sorted unit with randomly oriented clasts over and underlain by a more sorted unit of

smaller and imbricated clasts. The upper contact is sharp, while the lower one is more subtle, and occurs near the

junction of the hammer handle and head.


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Figure 163. A thin drape of mud (possibly rippled) moulds the surface of the gravel below which has since eroded

away.

12.4.3Neogene Basin-Edge Setting

Figure 164. Detail of Neogene geology showing transition from quartz-dominated gravel to greenschist. North to top.


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Figure 165. Steeply tilted basin fill on the south side of than Khantaishir Range. Note the oldest sediments (at rear)

are red. These contain quartz-rich gravel units. In the foreground, yellow, grey sediments contain greenschist-

dominated gravels. The youngest unit is a white-silt.

Figure 166. Closer view of predominantly green-schist gravels in yellowish silts.


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Figure 167. Gravels with sub-rounded and often imbricate greenschist-dominated clasts within yellowish silts-sands.

Figure 168. Steeply-dipping quartz-dominated gravel exemplifying the sharp distinction with the surrounding red

silt/sand.


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Figure 169. Very poorly sorted gravels with tabular cross-beds.

13 ACKNOWLEDGMENTS

These images were taken while working as an exploration geologist for Gobi Coal and Energy. Id liketo express special thanks towards the staff of GCE, especially Nyambayar Ordogol and the variousdrivers who accompanied us on our trips.


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Owen, L.A., Windley, B.F. Cunningham, W.D. Badamgarov, G. & Dorjnamjaa, D. 1997. Quaternaryalluvial fans in the Gobi Desert, southern Mongolia: evidence for neotectonics and climate change.

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Xiao, W., Windley, B.F., Badarch, G., Sun, S., Li, J., Qin, K. and Wang, Z.2004. Palaeozoic accretionary and convergent tectonics of the southern Altaids: implications for thegrowth of Central Asia.Journal of the Geological Society, 161: 339-342.

Yanshin, A.L. 1989 (ed.) Geologic map of the Mongolian Peoples Republic. Scale 1: 1 500 000.Akademia Nauk, Moscow.

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Mike Pole - Atlas of Mongolian Geology 2013 v1.1

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