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Salty MattersJohn Warren - Saturday April 13, 2019 Evaporite interactions with magma Part 3 of 3: On-site evaporite and major events? Introduction 60 The previous two articles in this series dealt with heating evaporites, vola- tiles expelled into the atmosphere, 50 and major biotal extinction events. Emeishan Traps I argued that short-term heating of 40 a megaevaporite mass during em- Cental Atlantic (+ Yucatan ) placement of a Large Igneous Prov- 30 Magmatic Province

ince (LIP) or heating of evaporities at atmosphere into volatiles the site of a large bolide impact, will 20 of evaporitic volumes Large Carribean-Columbian move vast volumes of sulphurous Generic (%) Columbia Karoo Traps and halocarbon volatiles, as well as 10 Paraná Traps River Brito-Arctic Ontong-Java solids, CO2 and CH4 into the earth's No on-site upper atmosphere (Figure 1a). The Ethiopian Traps evaporites resulting catastrophic climatic effects 0 1 2 3 4 19 20 link in time and probable causes to A. Volume of ood (x 106 km3) earth-scale major extinction hori- Emeishan Traps Siberian Traps zons. (Figure 1b). In this article shall (269-265Ma) (253-250Ma) examine how three of the five major Deccan Traps CAMP, Brazil Phanerozoic extinction events have 50 3. End- (67-65Ma) an evaporite association, starting with (201.5Ma) the most intense of 40 1. Late Ordovican Capitanian 5. End-Cretaceous the Phanerozoic; the end-Permian 4.Late Triassic and its link to LIP emplacement into 30 two separate sequences of massive 2. Late Devonian bedded evaporite (Cambrian or De- 20 vonian mega-salts) in the Tunguska Basin, Siberia. 10 Extinction Intensity (%)

0 End-Permian - Saline 550 500 450 400 350 300 250 200 150 100 50 interactions during em- Camb. Ord. Sil. Devonian Carb. Perm. Trias. Jur. Cret. Pal. Neo. B. Years (Ma) placement of Siberian Figure 1. End Triassic Extinction. A) Comparison of generic extinction percentages (from Sepkoski, 1996) with estimated original volumes of coevaligneous provinces, which show no correspondence Traps between the two (from Wignall 2001), until the on-site evaporite association is added (previous The Siberian Traps LIP is of signif- article), whereby all significant extinction events (>20% extinction at generic level) have an associ- icant size (~7 × 106 km2) and total ation with thermally-disturbed saline giants. Note the scale splice on the volume axis. B) Intensity of volume (~4 × 106 km3) (Ivanov et al., extinction at the genera level across geologic time (replotted from data table in Rohde and Muller, 2005). Shows the 5 main extinction events (1-5) as first defined by Raup, 1982. Extinction intensity 2013 and references therein). It is, (%) is defined as the precent of genera, from a well-resolved diversity curve which are in their last however, smaller than the Late Creta- appearance. (diversity curves were published by Sepkoski, 2002). Igneous trap emplacement times ceous Deccan Traps and has a volume are from Jones et al., 2016). that is about a half of the Late Triassic Central Atlantic Magmatic Province it seems that the volume of igneous material in a LIP does not (CAMP). All three of these continental LIPs are dwarfed by the directly relate to the intensity of the extinction event (Figure 1b). Early Cretaceous marine Ontong-Java LIP (≈20 × 106 km3). So, Page 1 www.saltworkconsultants.com

85°E 90° 95° 100° 105° 110° 96 108 120 71°N Noril'sk A. 72 B. Kotuy Putorana Maymecha Plateau Norilsk

67° Severnaya R U S S I A

Nizhnyaya Tunguska

Enisey Traps 64 62° Abundant magnetite pipes

1400 m 1700 m

enisey Nepa Potash Y 1700 m 2000 m dyke (accessible) Angara region 57° Documented well Pipes with magnetite Ust-Ilimsk Krasnoyarsk Basalt pipes 1700 m Present-day Siberian Traps Bratsk Basalt lavas Bratsk Krasnoyarsk

56 a

1700 m r Volcaniclastic rocks Lava a

g

n 2000 m Doleritic intrusives 52° Volcaniclastic rocks A RUSSIA Devonian salt extent Intrusives Cambrian salt extent Thickness of Cambrian Tunguska Basin sediments Irkutsk al Irkutsk 500 km saline sediments (m) 500 km Lake Baik 2000 Lake Baikal Figure 2. Geological map of the Siberian Traps , Tunguska Basin, Russia. A) Shows present-day outcrop extent of lavas, volcaniclastics and intru- sives, along with thickness isopach of saline Cambrian carbonates and the position of the Cambrian Nepa otash region (after Black et al., 2012, 2015; Polozov et al., 2016, Zharkov, 1984). B) Shows present-day outcrop extent of lavas, volcaniclastics and intrusives, along with positions of explosive pipes with magnetite and basalt pipes as well as the approximate extent of halite dominated cambrian and devonian salt basin remnants (after Svensen et al., 2018). Maps have slightly different scales. Note the relative lack of pipes in the Nepa potash region.

The Siberian Traps include ultramafic alkaline, mafic and felsic Thickness of volcaniclastic material in the Siberian Traps ranges rocks that erupted in different proportions within a vast region from intercalated layers less than a meter thick on the Putora- extending over several thousands of square kilometres across na Plateau to hundreds of meters near the base of the volcanic Western and Eastern Siberia (Figure 2a). The Siberian Traps are sections in the Angara and the Maymecha-Kotuy areas (Figure considered have been emplaced atop a hotspot in a relatively 2a). The total volume of mafic volcaniclastic material has been short time frame (≈1 million years), when a large volume of estimated at >200,000 km3 or >5% of the total volume of the deep mantle-derived igneous material was intruded and erupted Siberian Traps (Black et al., 2015). Volcanic rocks of this age at the Permo-Triassic boundary (Burgess et al., 2017). are also present in drillcore in the West Siberian Basin (Ivanov et al., 2013). Trap Magma-sediment and magma-water interactions active during Near Noril'sk, lava outflows reach thicknesses of over 3 km, emplacement of the Siberian Traps in the upper lithosphere en- while further to the northeast in the Maymecha-Kotuy region, compass a variety of heated evaporite interactions: batholith half of the total lava pile is composed of ultramafic rocks in- metal-evaporite interactions, lava-water interactions and intense cluding magnesian rich meimechites (Figure 2a). The very high phreatomagmatic explosions via vents and pipes that MgO contents (8-40 wt %) of the meimechites in such low-de- formed saline-igneous volatile fountains reaching the upper at- gree melts indicates that the site of initial melting was very deep, mosphere. The positions of these fountains are perhaps indicated as much as 200 km, and either in the lowermost continental lith- by vent-related iron-rich diatremes (Figure 2a; Svensen et al., osphere or in the underlying asthenosphere (Arndt et al., 1995). 2009). All these interactions are critical inputs to the End-Perm- Melting probably was linked with the arrival of a ian extinction event that links vast volumes of altered evaporites that was in its turn the source of the Siberian basaltic flood vol- with the heating mechanisms inherent to Siberian Trap geology. canism.

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10 10 10 10 10 Voisey’s Bay: Mesoproterozoic rift (anorthosite-granite-troctolite magmatism) 5 6 7 8 t Ni t Ni t Ni t Ni Raglan Kambalda Agnew, Kambalda, Raglan, Thompson: Archean rifted continental margin with komatiite lava ows 66 @ 2.9 22.1 @ 3.12 Pechenga: Paleoproterozic rifted continental margin (ferropicrite sills) Thompson Noril’sk (E) Voisey Bay 89 @ 2.5 900 @ 2.7 Great Dyke: Archean intracratonic rift hosted in Archean greenstones 124.4 @ 1.66 Agnew Jinchuan Sudbury Jinchuan: Neoproterozoic sill rifted continental margin (Rodina break-up) 10 52 @ 1.9 1 4 t Ni 515 @ 1.06 1648 @ 1.2 Merensky Reef (Bushveld): Paleoproterozoic stratiform sills (norite to anorthosite with chromitite) Mt Keith Platreef (Bushveld): Paleoproterozoic concordant sills (norite to anorthosite with chromitite)

Grade (wt % Ni)Grade Flood-basalt related 478 @ 0.6 Komatiite-related Duluth: Mesoproterozoic rift (triple junction, ore within troctolitic and gabbroic igneous rocks) Basal Ni-Cu sulphides in mac-ultramac intrusions Duluth Magnesian-basalt related Sudbury: Palaeoproterozoic vein ore hosted in a norite melted by impact Astrobleme - impact-related 4000 @ 0.2 Noril’sk- Talnakh: End Permian rift (triple junction) with assimilated Devonian anhydrites 0.1 1 10 100 1000 10000 A. Production + reserves in Millions of tonnes

Voisey's Bay (Basal Ni-Cu sulphides in mafic-ultramafic intrusions) 2.2 Thompson (Ni-Cu sulphides in komatiites) 3.5 Pechenga (Basal Ni-Cu sulphides in mafic-ultramafic intrusions) 4 Great Dyke (Stratabound PGEs-Ni-Cu sulphides in mafic-ultramafic intrusions) 5.4 Jinchuan (Basal Ni-Cu sulphides in mafic-ultramafic intrusions) 5.5 Merensky Reef (Stratabound PGEs-Ni-Cu sulphides in mafic-ultramafic intrusions) 6.3 Platreef (Basal Ni-Cu sulphides in stratiform mafic-ultramafic intrusions) 6.5 Duluth (Ni-Cu sulphides in intrusions related to flood basalts) 8.0 Sudbury (?astrobleme-associated Ni-Cu sulphides) 19.8 Noril'sk (Ni-Cu sulphide intrusions with evaporite assimilation and flood basalts) 23.1 0 5 10 15 20 25 30 B. Ni reserves in Millions of tonnes Figure 3. Magmatic Sulphide deposits. A) Ore grade in wt.% Ni versus production and reserves in millions of tonnes for major magmatic Ni-sulphide deposits of the world. B) Ranking of these deposits by their published reserves (after Naldrett, 1999, 2004; Warren, 2016).

Evaporite basins (Devonian and Cambrian) Lake Siberian traps The Siberian Traps region is not only significant because of its A. Pyasina vast extent and its deep nickel-prone mantle source, but also (layered basalt) in that the immense volumes of igneous rocks that making up Talnakh the traps were emplaced into two chemically prone saline gi- Devonian ants with differing dominant and ages; 1) Cam- outcrop brian mega-halite sediments in the south, with interlayers of hydrated potash salts (mostly carnallitite) and 2) Devonian Noril’sk Lake Melkoe megasulphates in the north, containing two 50-100m beds of anhydrite (Figures 2b, 5). The interactions with the two types of Siberian traps 10 km (layered basalt) salt basins, one halite-dominant, the other anhydrite-dominant, gives rise to two distinct meta-evaporite indicator associations.

In the North, the interaction of picritic magmas with bedded 88°E Basalt thick anhydrites formed the supergiant Noril'sk nickel deposit, B. while in the south the LIP emplacement formed numerous mag- Kharaelakh North X netite-rich explosive breccia pipes, sourced at the stratigraphic intrusion level of the Cambrian salts (Figure 2b). projected Kharaelakh Fault to surface X’

Norils'k region & Devonian evaporites Talnakh Gabbroic dyke In the northern part of the Tunguska Basin the evaporite sedi- 69.5°N ments hosting the intrusives of the Siberian Traps are a combi- Quaternary soils 5km nation of Devonian anhydrites and carbonates, with overlying Carboniferous coals. Trap basalts, now cover this sedimentary Figure 4. Geology of the Talnakh-Noril’sk area. A) Scaled satellite sequence (Figure 4a), while sill-like tholeiitic intrusions, vary- image showing relative positions of the Talnakh and Noril’sk mines. B) ing in composition from subalkaline dolerite to gabbro-dolerite simplified geology map showing extent of the Kharaelakh and intrusion are emplaced in the sediment pile and were part of the feeder when projected to the surface (After Ripley et al., 2010). See Figure system to the flood basalts (Figures 4b, 5, 6). 6 for cross section X-X'.

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The region of Devonian evaporites contains the Noril'sk-Tal- Individual faults may be over 500 km in length with throws of nakh ore deposit, the largest Phanerozoic nickel deposit in the up to a kilometre (Figure 4b; Naldrett, 1997). Mineralised in- world (Figures 3, 4; Naldrett 2004). In the mine area, ore-bear- trusions radiate outward and upward from intrusive centres and ing gabbroic-dolerites are differentiated, whereby picrite and penetrate all levels of the overlying sedimentary sequence. Most picritic dolerite are overlain by more felsic differentiates. The intrusive centres are associated with prominent block faulting Cu-Ni-platinoid mineralisation at Noril'sk forms relatively per- and fault intersections. The main Noril’sk-Kharaelakh fault oc- sistent stratabound horizons of massive sulphides in the lower curs within the Siberian Platform, but is parallel to the main fault portions of the three mineralised intrusions (Noril'sk, Talnakh, system that defines the boundary between the platform and the Kharaelakh), which are made up of segregations and accumula- nearby Yenisei Trough. The Kharaelakh-Noril’sk fault guided tions of pyrrhotite, pentlandite and chalcopyrite (Figures 5, 6). the main upwelling magma body (Figures 4b, 6). Individual sills splay off this fault control and are interlayered with sulphate At the world-scale, the supergiant Permian Noril'sk-Talnakh evaporite beds to can attain lateral lengths of 12 km, widths of 2 deposit is an unusual Cu-Ni deposit. It did not form in the Pre- km and thicknesses of 30 to 350 m. cambrian, and so is unlike almost all the world's other supergiant magmatic nickel-sulphide deposits (Figure 3). It Ivaninsky Suite (80-140m): Lava & tu formed at the end of the Palaeozoic and lavas & tu s straddles the Permo-Triassic bounda-

Upper Conglomerate ry (Black et al., 2014a). Magmatic Permian nickel ores at Noril'sk crystallised Noril’sk outside the influence of the reducing Tungusskaya Suite (280-330m): Sandstone planetary atmosphere that typifies Ar- siltstones, sandstones, coals, chaean Ni deposits and is conglomerates not tied to greenstone terranes and the Siltstone athenospheric transition to more sialic Middle Carbon. Talnakh plate-scale conditions. (Figure 3). The Upper Permian to high temperatures and near complete Argillite assimilation of Devonian sulphate Kalargonsky Suite (140-180m): dolomites, limestones, dolomitic marls evaporite blocks within the Noril’sk Coal magma mean that this is one of the more enigmatic (“salt is elsewhere”) Upper

Devonian Nakokhosky Suite (2-80m): styles of evaporite-related high-tem- dolomitic marls, anhydrites Marl perature ore deposits (Warren, 2016, Yuktinsky Suite (12-40m): dolomites Chapter 16). Notions of evaporite Limestone assimilation for ore deposits tied to Manturovsky Suite (110-210m): igneous-evaporite interactions are dolomitic marls, marls, dolomites, usually only one of multiple possible Middle anhydrites, salt (NaCl) lenses Devonian Dolomite explanations of a magmatic ore but, in my opinion, for Noril’sk this is the most likely scenario. So, I emphasise Razvedochninsky Suite (110-150m): Dolomitic marl the evaporite connection for the No- argillites, limestone layers and lenses, ril’sk-Talnakh deposit in this article. siltstones, sandstones Anhydrite Alternate non-evaporitic orthomag- Kharaelakh matic explanations can be found in Kureysky Suite (62-85m): marls papers such as Wooden et al., (1992); Salt (NaCl) Lightfoot et al. (1997), and Krivoluts- kaya (2016). Independent of the mode Zubovsky Suite (110-140m): dolomitic marls, anhydrites of nickel-ore fixation, most authors Lower Breccia Devonian working in the Tunguska Basin agree that the emplacement of the trap intru- Khrebtovsky Suite (30-90m): dolomitic marls, anhydrites, dolomites Unconformity sives drove the escape of a huge pulse of sediment-derived volatiles into the Yampakhtinsky Suite (50-100m): Intervals within Earth's atmosphere. dolomites with layers of anhydrite which the three main ore-bearing Regional structure of the Noril’sk Postichny Suite (96-105m): Noril’sk intrusions occur dolomitic marls, dolomites, anhydrites district is dominated by NNE-NE See Figure 6) Lower Permo-Triassic block faulting, which Silurian was coeval with magmatic activity. Figure 5. Stratigraphy of upper part of Paleozoic sedimentary rocks at Noril'sk and Ta1nakh ore junctions showing the positions of the ore-bearing intrusions. (after Czamanske et al., 1995; Naldrett, 2004) Page 4 www.saltworkconsultants.com

Mineralogical compositions of the Devonian sediments interlay- sists of a terrigenous-carbonate section with abundant salt-bear- ered with these sills are of great importance in understanding the ing strata, most of which consist of rock salt or brecciated geological responses to heating by intrusive igneous sills in the equivalents. This formation’s thickness is 100-210 m but ranges Noril'sk-Talnakh area (Figures 5, 6). Based on their lithological up to 500 m (Figure 6). The Middle Devonian Yuktinsky section features and paleontological character, the intruded Devonian is dominated by clastic–carbonate sediments ranging from 12 succession is subdivided into the Yampakhtinsky, Khrebtovsky, to 40 m thick, while in the troughs the thickness of interlay- Zubovsky, Kureysky, and Razvedochninsky Formations (Lower ered sulphate rocks reaches 55 m. The contacts with the under- Devonian), the Manturovsky and Yuktinsky Formations (Mid- lying and overlying Middle Devonian Manturovsky deposits are dle Devonian), and the Nakohozsky, Kalargonsky and Fokinsky considered comformable. The Upper Devonian Nakokhozsky Formations (Upper Devonian) (Figure 5; Krivolutskaya, 2016; Formation consists of folded calcium-sulphate-rich variegated Naldrett, 2004). The two main evaporite levels are the Middle shale–carbonate rocks with a thickness of 2–60 m that increases Devonian and Lower Devonian anhydrite-dominant succes- in the troughs to 80–130 m (Figure 5). The Upper Devonian Ka- sions, both deposited in a subsealevel transitioning rift (Figure largonsky Formation is characterised by a grey-colored terrige- 5, 6; Naldrett, 2005; Warren, 2016). nous-carbonate section that includes dolomites, dolomitic marl, dolomite–limestone, and anhydrite dominate in the basins. This The Yampaktinsky and Khrebtovsky Formations consist of Low- formation’s thickness is 170–270 m. The Kalargonsky Forma- er Devonian carbonates interbedded with abundant gypsum (in tion unconformably overlies the Middle Devonian Nakokhozsky outcrop) and anhydrite (subsurface), along with some of the old- sediments and the contact is typically a breccia (Figure 5). est lenses of celestite in the area (Figure 5). The total thicknesses of these two CaSO4 units are around 100 and 80 m, respective- The Middle Devonian Fokinsky Formation (as distinct from ly. The Lower Devonian Zubovsky Formation is composed of the mineralised Fokinsky intrusions) consists of evaporite sul- grey-colored dolomitic marls interbedded with argillaceous do- phate-rich clastic–carbonate sequences, primarily within the lomites, mudstones, and anhydrite with a total thickness of 110– troughs, and anhydrite, dolomitic marls interbedded with lime- 140 m. The Zubovsky Formation 1unconformably overlies the stone lenses of rock salt, and clay–carbonate (Krivo- Lower Devonian Khrebtovsky Formation in the Noril’sk region. lutskaya, 2016). The thickness of this formation is 220–420 m The Lower Devonian Kureysky Formation consists of mottled (approximately 500 m in the western part of the Vologochansky dolomite and calcareous mudstones and marls with rare siltstone Trough). and limestone. The thicknesses of all units in the outcrop section remain stratiform and vary within 50–60 m. The contacts with the overlying and underlying formations are conform- able. X X’ The Lower Devonian Razvedoch- ninsky Formation is dominated by siltstones, sandstones, and conglom- 500m Kharaelakh Intrusion Talnakh eratic sandstones with a thickness Intrusion that regionally does not exceed 1 km 110–150 m, but reaches 150–235 m in troughs, and decreases sharply to Quaternary cover the south until fully wedging out. Yampakhtinsky, Khrebtovsky and Zubovsky suites (Lower Devonian marls, anhydrites Morongovsky Basalt and dolomites) The Middle Devonian Manturovsky Nadezhdinsky Basalt Formation overlies the eroded Raz- Silurian dolomites Gudshichinsky Basalt vedochninsky Formation and con- Lower Talnakh intrusion

Syverminsky Basalt Extrusives Sills belonging to the Kharaelakh and 1 The various unconformities and Ivakinsky Basalt Talnakh intrusions breccias noted in the Devonian outcrop in the Kharayelakh and Talnakh intrusions Noril'sk-Talnakh region, as well the lateral Tungusskaya Series (terrigenous coal- Gabbrodolerites thickness variations (locally termed "troughs" bearing sediments) Picritic and taxitic gabbrodolerites with - are these possible dissolution sumps?), Kalargonsky, Nakokhzsky Yuktinsky Suite dissiminated sulfphides are not considered in the literature in terms (Middle Devonian dolomites, marls, Massive sulphides of being possible indicators and responses anhydrites to evaporite dissolution, nor are the various Manturovsky Suite (Middle Devonian marls, Trachydolerite sills documented sedimentary breccias (Figure 5). anhydrites, argillites Dolerite Nor is the idea considered that outcrop char- Kureysky and Razvedochninsky suites Noril’sk–Kharayelakh fault acter is not necessarily indicative of the thick- (Lower Devonian argillites, marls) ness and of subsurface evaporite Fault counterparts (see Warren 2016, Chapter 7 for Figure 6. East–west geological cross section showing the relationship between the Kharaelakh, Talnakh a relevant discussion of similar evaporite dis- and Lower Talnakh intrusions and the assimilation of layeres of organic-rich and anhydritic country solution features and bed thickness changes). rock (after Naldrett, 2005). Page 5 www.saltworkconsultants.com

The Fokinsky Formation is not recognised by all authors working in the region. This disparity in stratigraphic recognition across 300 µm the region underlines a problem inherent in the litho-stratigraph- A. ic descriptions of many bedded evaporite regions worldwide, where it is assumed that a layer-cake stratigraphy/correlation is present pre- and post-intrusion. Thereby the effects of evapo- rite collapse dissolution, bed wedge-out and possible salt flow are not quantified. In my opinion, sedimentary breccias in such regions are more likely to be diagenetic and laterally discontinu- ous (see Warren, 2016; Chapter 7). In summary, the Devonian stratigraphy in the vicinity of the No- ril'sk Mine retains significant thicknesses (50-100m) with varia- tions centred on transitions in and out of bedded anhydrite. There is a strong likelihood that the current outcrop geology interpre- tations under-illustrate former thicknesses of bedded evaporites during to ongoing dissolution, collapse and possible flowage. The anomalous Phanerozoic age of the Noril’sk-Talnakh ore de- posits, compared with the Precambrian ages of other magmatic 100 µm Ni-Cu deposits, and its relative enrichment in Ni, Cu, Pt and Pd B. compared with Sudbury and Jinchuan (Figure 3), is thought to reflect the anomalously high volumes of sulphur in the parent magma. Additional sulphur entered the evolving magma cham- ber via intrusion and assimilation of CaSO4 blocks and asso- ciated hydrothermal solutions altering and dissolving adjacent thick-bedded anhydrite successions (Figure 7; Naldrett 1981, 1993, 1997; Pang et al., 2013). Noril'sk-Talnakh's rich sulphur supply contrasts with that of the komatiitic Archaean Cu-Ni de- posits, where the sedimentary sulphur supply came from more ubiquitous, less-focused sulphur sources sometimes entrained in widespread sedimentary pyrite (Figure 3). Such pyrite charac- terises a significant portion of fine-grained sediments accumu- lated under an anoxic reducing Archaean to Palaeoproterozoic atmosphere. Figure 7. Anhydrite (Anh) in photomicrographs and backscattered elec- tron images of representative samples from the Norilsk contact aureoles, Abundant crystals of magmatic anhydrite today typify the oliv- Siberia (after Pang et al., 2013). A) Chlorite (Chl) and clinopyroxene ine-bearing (picritic) gabbros in the Kharaelakh intrusion, which (Cpx) crystals surrounded by an anhydrite porphyroblast in a calcareous hornfels (sample NOR-7c; crossed polars) B) Chlorite, either fibrous is located in the basin stratigraphy at the level of the Devonian (Chl(f)) or crystalline (Chl(c)), and fine clinopyroxene grain surrounded anhydrites (Figure 6; Li et al., 2009 Spiridonov, 2010). Along by coarse anhydrite and phlogopite (Phl) crystals in a calcareous hornfels with disseminated sulphides, the anhydrite crystals are charac- (sample MD48-4). terised by planar boundaries with co-associated olivine and au- Picritic magmas in mantle plumes can have melt temperatures gite. Dihedral angles of ~120°, characteristic of simultaneous as high as 1600°C (Hezberg et al., 2007). Assimilation of anhy- crystallisation, are common throughout the anhydrite-augite as- drite via partial melting of a cooler basaltic magma at shallower semblages. Inclusions of anhydrite in augite and vice-versa are depths can be more difficult, owing to the high melting point also typical. of pure anhydrite (melt temperatures typically rang between Rounded and subrounded sulphide inclusions composed of 1360 and 1450°C, although this is significantly lowered in the pyrrhotite, pentlandite, and chalcopyrite, that crystallised from presence of organics and water). Rather than only melting anhy- immiscible sulphide liquid droplets in the magma, are common- drite enclosed by picritic magma, additional fluxing mechanisms place within the magmatic anhydrite crystals and in the contact likely move additional anhydrite-derived sulphur into the melt, aureoles (Figure 7). Visual estimates by Li et al. (2009), based either by hydrothermal leaching of sulphate followed by partial on five polished thin sections, indicate that the ratio of anhydrite reduction, or via a process involving the dissolution of anhydrite to sulphide in mineralised samples varies from 0.05 to 0. The during thermochemical sulphate reduction (TSR; Warren, 2016; observation of abundant wollastonite in contact aureole rocks at Chapter 9). The latter process requires heat, anhydrite and or- this stratigraphic level suggests that reactions such as CaSO4 + ganics (generally in the form of hydrocarbons or kerogen). SiO + H O = CaSiO + H S + 2O occurred, and that sulphate 2 2 3 2 2 Some authors use the euhedral outline of anhydrite in miner- was likely reduced to sulphide before incorporation into the alised sills, as seen in Figure 7, to argue blocks anhydrite coun- magma (Ripley et al., 2007).

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Figure 8. Nature of sulphate assimilation at NORIL’SK 1 Putannaya Noril’sk-Talnakh. A) Isotopic composition of sulphur in unmineralised, mineralised economic and mineralised subeconomic intrusions of the TALNAKH (NE) Nuzhniy II Noril’sk - Talnakh region (after Grinenko, 1985; Naldrett, 1993, 1997). B) Sulphur isotopic composition of melt inclusions, using whole rock TALNAKH (NW) Nakakhoz data from Noril’sk (Ripley et al., 2003; Black 0 2 4 6 8 10 12 14 16 et al., 2014a and references therein). The upper Mineralised Economic horizontal axis in red applies only to the data δ34S ‰ Zelenya Griva points in red (from ore-bearing intrusions), which contain much higher sulphur concentrations. The F-81 Pyasina-Vologachan lower horizontal axis (in ppm) applies to all 34 other points. The bulk mantle δ SV-CDT value, with associated variation, is shown by the light grey PE-3 Nizhniy Talnakh bar. Solid curves show fractionation associated with degassing for Quartz–Fayalite–Magnetite Manturousk (QFM) and Nickel–NickelOxide(NNO) oxygen

F-88 Non-economic Mineralised fugacity conditions, assuming water saturation and 30 bars pressure (see Black et al. 2014 Daldykansky Imangada for details). The dashed black lines show the same curves with initial values shifted to ±2‰ 1st Falls of to encompass variation in initial mantle sulphur Unmineralised Mt Chernaya Kureyka River values. Dashed blue mixing lines describe an initial magma with δ34S = +0‰ and 1620 0 2 4 6 8 10 12 14 16 V-CDT 34 ppm S (as an approximation of the sulphur con- Khyukta δ S ‰ centration in unadulterated Siberian Traps melts 0 2 4 6 8 10 12 14 16 prior to degassing) contaminated with anhydrite 34 with 34S = +20‰, +25‰, 30‰, or +35‰. δ S ‰ A. δ V-CDT try rock was not assimilated. This is a specious argument as this type of anhy- drite was precipitated during cooling of an already sulphur-saturated magma, the euhedral spary outline does not relate to the source of the sulphur, which is more clearly indicated by its sulphur-isotope signature (Figure 8a - also Warren, 2016; Chapter 8). Isotopic analysis of δ34S in the magmatic anhydrites and associated metal sulphides in the Kharaelakh intrusives require the assimilation of externally-derived high- δ34S sulphur from the adjacent country rock (Figure 8: Ripley et al., 2007, 2010). Where complete sulphate reduction oc- curred, the δ34S values require mixtures of some 60% anhydrite-derived evaporitic marine sulphur (δ34S values near 20‰), with 40% mantle-derived sulphide (δ34S of 0‰) to produce the required measured magmatic sulphide values ≈12‰ (Figures 8a, b). The sulphur isotope data and the nature of the sampled contact aureoles suggest intense intracontinental rifting in the No- ril’sk region brought deeply-sourced maf- ic magmas into contact with supracrustal sulphur from evaporitic sulphates at the level of the Kharaelakh intrusion. Sulphur isotope data show the mineralised inter- B. vals at Noril’sk are anomalously heavy in Page 7 www.saltworkconsultants.com

34 Feeder dykes δ S (Figure 8a, b). These data are in- SW NE consistent with sulphur derived from mixing of the mantle magma sulphur (δ34S values near zero) with sulphur Siberian Trap lavas from an evaporitic sulphate source (Godlevski and Grinenko, 1963; Sediments Grinenko, 1985; Li et al., 2009; Pang Noril’sk Main Talnakh et al., 2012; Black et al., 2014a). High level magma chamber intrusion Fractionation of magma and Sulphur isotope values from Paleozo- Contaminated magma interaction with thick anhydrites ic evaporites vary between +10 and and coals +35‰ (Figure 8b; Claypool et al., 1980). Cambrian evaporites, includ- ing the major Irkutsk basin salts in Si- Mid-crustal level magma chamber 34 beria, are the most S-enriched evap- Fractionation and contamination orites in the Phanerozoic, with mean of magma δ34SVCDT = +30‰ (Claypool et al., 1980; Black et al., 2014a). Two-mem- ber mixing curves between mei- Deeper crustal level magma chamber. mechite and anhydrite sulphur (with Magma ushes through system δ34S = +20 to +35‰) convincingly re- produce the observed δ34S trends for Figure 9. Schematic of likely contamination and sulphur additions sites in the ascending magma pathway supplying the Ni-Cu Noril’sk and Talnalkh intrusions, Siberia (after Pirajno, 2007; Naldrett, 1997). the Noril'sk ores (Figure 8b; Black et al., 2014a). in Figure 8). To obtain this level of fractionation means more than 50% of the total sulphur in the intrusion was derived from As the magma rose through the sedimentary cover, it penetrat- marine evaporites in the footwall strata. The contaminated mag- ed and assimilated sulphur from extensive Devonian anhydrite ma was highly oxidised and able to dissolve up to one order of layers (Figure 9). Sulphur in calcium sulphate was reduced to magnitude more sulphur than pure mantle-derived basaltic mag- sulphide, CaO entered the magma, and iron from the magma ma. Such sulphur-contaminated magma, when erupted, would reacted with reduced sulphur so that the end result was droplets have released vast volumes of SO into the atmosphere (Black of immiscible iron sulphide dispersed through the melt (Naldrett 2 et al., 2012, 2014b). That is, the eruption of the anhydrite-con- and Macdonald, 1980). These droplets acted as collectors for Ni, taminated magma that is the Siberian Traps in the northern Tun- Cu and the platinum group elements, which are now so enriched guska Basin can help explain the intensity of the end-Permian in the Noril’sk ores. extinction. Naldrett (1991, 1997, 2005) concluded that prehnite + biotite In summary, such igneous - sulphate sediment interaction ex- + anhydrite + carbonate + zeolite + chlorite ± sulphide glob- plains, at least in part: (1) the vast amount of sulphide melt in ules, which typify chromite agglomerations in the picrite of the the Noril’sk-Talnakh ore field; (2) the heavy quasi-anhydrite Noril’sk intrusions, represent remnants of partially assimilated isotopic composition of sulphur in sideronitic and massive nick- sulphate-rich country rock. Assimilation of anhydrite-rich rocks, el ores; (3) the reduced contents of noble metals in these ores coupled with the reduction of sulphate to sulphide, would have (compared with the drop sulphides that occur toward base of introduced considerable oxygen into the silicate melt, which the intrusions and have a likely mantle sulphide source); and (4) then drove precipitation of chrome-spinel (chromite - the high contents of radiogenic (crustal) osmium in sideronit- FeCr O ; mangnesiochromite - MgCr O ). Inclusions of anhy- 2 4 2 4 ic and massive ores (Spiridonov, 2010; Walker et al., 1994). In drite-rich material, floating in the magma, would have served summary, the reserves of the world-class Ni-PGE deposit at No- as loci for chromite crystallisation, thus giving rise to the asso- ril’sk-Talnakh, with its anomalous Phanerozoic age, likely reflect ciation between the agglomerations and the globules. Tarasov a fortuitous occurrence of thick Devoninn anhydrites (ultimate (1970) pointed out that Middle Carboniferous coal measures sulphide source) atop an active later set of deep mantle-tapping were also assimilated and may have supplied organics that as- rift grabens that drove the LIP outlined by the Siberian Traps. sisted in the reduction of sulphur in the magmas (Figures 6, 7). Wherever these magmas vented into the Earth's atmosphere they Evidence of the assimilation of large volumes of anhydrite and carried significant volumes of sulphurous volatiles. coaly organics into the magma mass has implications beyond the formation of the Noril’sk-Talnakh ore deposits. Li et at. (2009) Cambrian evaporites, potash & breccia pipes identified magmatic anhydrite-sulphide assemblages in asub- 34 Salt deposits of late Vendian to Early Cambrian age in East volcanic intrusion associated with the Siberian Traps. The δ S Siberia cover an extensive area (ca. 2 million km2) located to values of anhydrite and coexisting sulphide crystals analysed the north-west of Lake Baikal with an extent showing it ex- by ion probing are 18‰–22‰ and 9‰–11‰, respectively, are tends across much of the Permian Siberian Traps (Figure 2b). much higher than the anhydrite-contaminated ore values shown The thickness of this upper Vendian-Lower Cambrian evaporite Page 8 www.saltworkconsultants.com

Russia Age Evaporite Series Stage Ma basin X X’

Middle Mirnyj Cambrian X’

X Litvintsevo North Toyonian Nepa 509-519 Angara

Tasyevo Lake Baikal Botomian Bratsk Lower Belsk Cambrian Zhigalovo 519-528 Atdabanian 500 km Irkutsk Usolye Carbonate-clay Vendian-Camb. Nearshore 528-530 Tommotian marine deposits evaporite basin deposits Upper Nemakit- Danilovo 530-543 Danilovo Bioherm Usolye Vendian evaporite basin evaporite basin Daldynian Shallow-water Belsk Angara carbonates evaporite basin Red-beds Sandstone Dolomite Anhydrite & evaporite basin dolomite Land Litvintsevo evaporite basin A. Limestone Rock Salt Boundary of saline series B. Figure 10. Cambrian evaporites, eastern Siberia. A) Extent of the various intracratonic saline basins. B) Stratigraphy of the Vendian to middle Cambrian saline sequences (after Peryt et al., 2005) succession is 2.0–2.5 km in the southern, western, and central Lower Cambrian Angara evaporites host the largest known bed- parts of the basin, and 1.3–1.5 km in the NE part (Nepa-Vilyui). ded potash deposit in Russia, which is not yet produced (Figure This saline giant (total volume of upper Ven- dian–Lower Cambrian evaporites is 785,000 Unit Unit Horizon Horizon Super horizon Super- km3; Zharkov, 1984) is characterised by the In- Index horizon dex No. occurrence of fourteen regional marker car- bonate units and 15 salt units (Figure 10; Zhar- Upper UA anhydrite kov, 1984, with references therein). Five major Upper rock URS 5th anhydrite-halite URS5 phases of salt deposition are distinguished, salt namely the late Vendian (Danilovo) and Early 4th anhydrite-halite URS4 Cambrian (Usolye, Belsk, Angara, and Litvint- sevo) salt basins (Figure 10a; Zharkov (1984), 3rd anhydrite-halite URS3 Kuznetsov and Suchy. (1992). 2nd anhydrite-halite URS2 1st anhydrite-halite URS1 Average thicknesses of the Cambrian evapo- Potassium K Halite “6” H6 Rock salt with sylvite and V rite deposits decreases with time (Figure 10b) Bearing carnallite as does the area (Figure 10a). The area of the Narigonda potassium K5 oldest Cambrian basin, the Usolye salt basin is horizon 2 almost 2 million km , and the average thick- Halite “5-6” H5-6 ness of deposited salt around 200 m (Zharkov, Uznmum potassium horizon K5 1984), while the area of the youngest, Litvint- sevo salt basin is 0.5 million km2 and the aver- Halite “4-5” H4-5 Spotty varicoloured sylvites IV and carnallites age thickness of its evaporite bed (rock salt and anhydrite) is 50 m (Figure 10; Zharkov, 1984). Dotkon potassium horizon K4 Halite “3-4” H3-4 Pink carnallites and sylvites III Most of the petroleum reservoirs in the region Chechei potassium horizon K3 are located in the Cambrian carbonates. The Halite “2-3” H2-3 Grey massive carnallites and II post-Cambrian stratigraphy contains major sylvites erosional breaks. As we saw in the Noril'sk Tunguaka potassium horizon K2 discussion, Devonian evaporites are rare in Halite “1-2” H1-2 Lower sylvites I the south but abundant in the north, whereas Ordovician rocks (limestones, marls) are lo- Bur potassium horizon K1 cally abundant in the central parts of the ba- Lower rock LRS Light-coloured equigranular LRS3 sin. Cambrian salt deposition is interpreted as salt rock salt mostly taking place in a deeper water basin: Green rock salt LRS2 Petrichenko (1988) concluded that at the ter- Smoky-grey rock salt LRS1 mination of halite deposition the final brine Lower LA depth was 50–260 m, and at the onset of potash anhydrite deposition it was ≈10–50 m. Table 1. Potash stratigraphy of the Nepa Basin (after Andreev et al., 1986; Garrett, 1995) Page 9 www.saltworkconsultants.com

11; Garrett, 1995; Warren 2016, Chapter 11). Potash salts occur is 2-18 m thick (4-6 m in the central area (Figure 11a; Table at the base of the Angara Formation in what is called the sixth 1). Two sylvinite zones in this horizon were mapped, with the halite series (Table 1). This intracratonic potash basin is one of central one being 16-26 km long and 6-8 km wide (Figure 11a). the larger potash-entraining salt sumps in the world, it is sever- In the lower horizon (K1) the sylvinite was 1.5-3 m thick, and al times larger than the Permian Upper Kama deposit and ap- averaged 15-50% KCl, 0.05-0.5% MgCl2,with 0.5% insolubles. proaches the Prairie Evaporite in aerial extent, but not in lateral The overlying K2 potash zone (Tunguaka) also entrains several continuity, thickness or purity (Figure 11) due in large part to the sylvinite beds and is some 679-880 m deep and 2.5-20 m thick. effects of igneous disburbance. It has a 15-45% KCl content and comparatively low MgCl2 and insoluble contents. This zone represents the major potash re- Plans were made in 1986 under the old Soviet regime to initiate serves of the deposit. In the upper potash beds (K2) the sylvinite a mining program in a section of this basin called the Nepskoye strata become more discontinuous, but some reasonably thick, deposit but were never fully implemented, although some ore high grade and extensive zones exist (Andreev et al. 1986). The was extracted in the mid 1980s (Andreev et al., 1986). The pro- sylvite ore sits in a more regional potash succession composed posed potash development region is located near the towns of of a combination of carnallitite and sylvinite (Figure 11b). The Nepa and Ust-Kut (300 km apart) in Irkutsk State. Regionally, broader Nepa potash region as generally mapped in Figure 2 has the dominant potash is carnallite, but high-grade sylvin- two interesting characteristics; 1) The igneous trap rocks as de- ite is intersected at depths of 600-1,000 m in beds some 1.5-5 m 2 fined in the drill-controlled cross sections ofMalykh and Geletii thick over an area ≈ 1,000 km (Garrett, 1995). The lower Bur (1988) sit below the potash level (Figure 11b), 2) There is a pau- or K1 bedded potash horizon lies at a depth of 750 - 960 m and city of magnetitic explosive breccia pipes in the Nepa potash region (Figure 2b).

Sylvinite 25 To the south and west, between Ir- Carnallitite 46 2 4 24 4 A. kutsk and Taseyevo some 400 km Halite 12 6 8 to the west, other large potash oc- Well (No.) 6 8 8 6 Nepa region 10 43 4 23 currences have been reported in the 56 105 100 109 47 same general but poorly delineated 138 4 137 54 110 evaporite basins. For instance, in 8 111 86 46 116 120 53 48 15 Ust’Kul’sk the Kanak-Taseyevo basin, potash 136 121 4 4 4 6 37 122 51 beds (sylvite-carnallite containing 8 8 125 6 123 32 6 72 63 52 Lake 3-24% K2O) have been intersected 127 4 126 16 Baikal 87 128 at depths of 1,240-1,415 m (Garrett, 1 8 11 Irkutsk 1995). Potash beds at these depths 62 84 8 31 would require a solution mining 4 km 16 12 250 km 65 methodology, but the at-surface cli- mate would mean either cryogenic Elevation B. (msl) km NW SE pan processing or evaporators, mak- 0.5 ing recovery more difficult and ex- pensive (Warren, 2016; Chapter 11). 0.0

-0.5 Basaltic breccia pipes, Tungus- ka Basin Siberia -1.0 Basalt pipes form a rim to the main -1.5 basalt body of the Siberian Traps -2.0 and are genetically linked to trap

after Malykh and Geletii, 1988 emplacement (Figure 2b; Polozov et 20 km al., 2016). The pipes pierce through 1. Ordovician sediments 5. Potash horizons all sedimentary strata, even dolerite 2. Upper Cambrian (Verkho-Lena, Ilgin Formations. 6. Motsk Fm. clastic-carbonates sills higher in the Permo-Carbonif- 3.Vendian-Lower Cambrian carbonate and sulphate 7. Siberian traps erous portion of the basin stratigra- 4. Rock salt dominant, less sulphate and carbonate 8. Crystalline basement phy, and are considered to be a type of 2diatreme. Importantly, the basalt Figure 11. Potash distrubution in the Nepa region. A) Potash occurrence at the base of the Cambrian pipes with magnetite cores tend to Angara Formation in the Nepa Region of Siberia. Note that the region posted as sylvinite-carnallitite occur across the southern Tunguska and halite is the K1potash (Bur) level and is isopached at the level of the K2 potash (Tunguaka) zone, this region is only some 30 km across and occurs roughly within the red rectangle indicating the pot- Basin, while unmineralised basalt ash-rich Nepa Region (After Andreev et al. 1986; Garrett 1995 B) Geologic cross section through pipes are more widespread (Figure the Nepa potash area of the eastern Siberian Basin (after Malykh and Geletii, 1988). Lithologies 3 to 6: Vendian-Lower Cambrian sediments (Litvintsev, Angara, Bulay, Belsk, Usolsk, Motsk formations 2 A diatreme, sometimes known as see figure 10). a maar-diatreme , is a volcanic pipe Page 10 www.saltworkconsultants.com

Figure 12. The Korshunovskoe magnetite breccia pipe, Siberia (56.558330N, 104.151707E). A) Map View. B) Section A-B (after Soloviev, 2010).

2b). Some of the basalt pipes bearing magnetite mineralisation We shall focus one of the largest magnesite deposits in the re- are of commercial grade and are mined for their iron ore. gion, the Korshunovshoe (Korshunovsky) magnetite breccia pipe, with an estimated reserve of 1.5 Gt of ore to a depth of Regionally, it is difficult to estimate the total number of pipes 1700 m (Soloviev, 2010; Polozov et al., 2016). It is mined (open (both “barren” basalt and magnetite-enriched) because repeat- pit) and so the interior structures and relationships are well doc- ed glaciations have flattened relief, while thick taiga forest cov- umented (Figure 12). The currently mined pipe is adjacent to ers significant parts of Siberia. Thus, many pipes are hidden by another explosion pipe to the immediate south-east, with the swampy coniferous forests and so are difficult to map. However, mineralised breccias sourced mainly at the level of the Cambrian conservative estimates based on prospecting surveys for iron evaporites (halite, potash and anhydrite; Mazurov et al., 2007). mineralization in the southeern portion of Tunguska Basin, and At outcrop and in the pit little evidence, other than secondary geological mapping elsewhere, suggest there are more than three textures (dissolution-collapse and brecciation), remains of the hundred magnetite-bearing basalt pipes. This includes 6 large primary minerals of the mother saline layer, although remnant, (>100 Mt of iron ores), 14 medium (20–100 Mt) and 19 small recrystallised evaporite clasts (including halite and anhydrite) <20 Mt) sized iron deposits. All other mineralised basalt pipes typify the mineralised breccia in the lower parts of the pipe (Ma- are currently of sub-economic grade or underexplored (Polozov zurov et al., 2007, 2018). Textures at the evaporite level in the et al., 2016). diatremes are not unlike those seen in regions of Eocene sill in- The magnetite deposits are consistently located in the Tungus- teraction with hydrated salts in the Zechstein potash mines of ka Basin region underlain by Cambrian evaporites and mainly East Germany (Schofield et al., 2014; Warren 2016 and part 1 in defined by subvertical and cylindrical breccia bodies with mag- this series of Salty Matters articles). nesio-ferrite and magnetite as the primary ore minerals (Figure The Korshunovshoe pipe is filled with tuff breccias and frag- 2b). In many ways these deposits are similar to iron oxide, gold mentals composed of the surrounding saline country rocks which and copper (IOGC) deposits worldwide, but are classified in the have undergone considerable metasomatic alteration. They in- Russian literature as Angara–Ilim type deposits, named after corporate fragments and larger blocks of sedimentary (60 to 80 the two rivers where a large number of iron- mineralised basalt vol.%; sandstones, siltstones, limestones, evaporite residues and pipes crop out (Soloviev, 2010; Warren 2016, Chapter 16). argillites) and igneous (10 to 40 vol.%; gabbro-dolerites, doler- ites and basalts) rocks, cemented by essentially chloritic materi- Korshunovsky (Korshunovskoye) region, Siberia al as well as by fine-grained carbonate (Figure 13). The central This region, in the Irkutsk district, is the eighth largest iron ore part of the magnetitic diatreme characterised by intense multi- producer in Russia, with an annual output of 5 Mt of iron ore ple brecciation, with rock fragments in the breccias represented concentrate. Across the region, the pipes are sourced in the Cam- mostly by variably-altered dolerites. They are cemented by a brian evaporite part of the basin stratigraphy and pierce younger finely-dispersed matrix, entirely replaced by skarn, post-skarn Paleozoic sediments composed of argillites, limestones, marls, alteration assemblages and iron oxides. siltstones, sandstones and clays of the late Cambrian Lena, Outside of this zone, intense fracturing has occurred, locally Ust'kut, Mamyr and Ordovician Bratsk groups and overlying with brecciation in altered sedimentary rocks. The fractures are Early Carboniferous limestone. filled with magnetite, accompanied by chlorite and calcite. Final- ly, the outermost zone is characterised by weak, predominantly formed by a gaseous explosion. When rising magma makes contact with phre- sub-horizontal fractures within sedimentary host rocks, locally atic ground water (or structural water in hydrated salt beds), a rapid expansion replaced by skarns. Steeply-dipping dykes of gabbro-dolerite, of heated water vapor occurs and the resulting highly-pressured volcanic gases drive a series of at-surface explosions and gassy phreato-magmatic fountains. dolerite, dolerite-porphyry, and basalt-porphyry are present, Page 11 www.saltworkconsultants.com

matrix, but only to a minor degree in sediments without a saline carbonate component) at a depth of some 700 to 1500 m from the surface; ii) Stock-like, lensoid, layered and columnar bodies of magnetite within the altered pyroclastics of the breccia pipe; and iii) Steeply dipping vein-like masses in zones of intense 1 brecciation and replacement by skarns. Together these mineralisation styles form two large continuous bodies in the Korshunovshoe pipe (Figure 12). The main deposit has the form of a sub-vertical breccia pipe with plan dimensions of approximately 2400 x 700 m. Mineralisation has been traced by drilling to a depth of 1200 m, and by geophysical data to at least 3 km below the surface (Soloviev, 2010). The bulk of the ore is associated with brecciation and occurs within sediments, tuffs and igneous rocks and are demonstrably 2 due to the partial replacement and alteration of the host. Massive and banded ores are less well developed. The mineralisation is mostly magnetite (≈82% of iron resources), with minor mag- 7 no-magnetite, hematite and martite. The main orebody compris- es vertically overlapping zones, with variable amounts of he- matite and 3martite in the upper layers, calcite and magnetite in middle layers, and halite and magnetite in lower layers. The magnetite of the upper to middle zone is accompanied by py- roxene, chlorite and minor epidote with lesser amphibole, ser- 2 pentine, calcite and garnet, and rare quartz, apatite and sphene and occurs as oolites, druses, masses and disseminations. Calcite increases downwards to 20 to 30%. In the lower part of the de- 6 posit, halite, amphibole and Mn-magnetite are more abundant. Pyrite, chalcopyrite and pyrrhotite are found throughout. Much 3 of the magnetite is magno-magnetite which contains up to 6% MgO. Across the region of magnetite breccia pipes, ore is extracted from magmatic diatremes that completely penetrated the highly evaporitic lower Phanerozoic succession (Figure 14; Mazurov et al., 2007, Polozov et al., 2016). Early work on this intrusive magnetite style, which surrounds brecciated diatreme-like pipes, classified it as a skarn association, forming a halo around a set 5 4 of explosive pipes that accompanied regional trap magmatism (Ivashchenko and Korabel’nikova, 1960). Characteristic spinel-forsterite magnesian skarns are confined to the overdome parts of large doleritic bodies and are the result of interactions of massive evaporitic and petroliferous dolomites Figure 13. Contact of dolerite with rock salt. The sample is 6 cm wide. (1) Halitite (gray salt), (2) dolerite, (3) zonal anhydrous magnesian with fluids released from liquid magma (Mazurov et al., 2007). skarn, (4) hydrated pargasite–phlogopite–chlorite magnesian skarn, Magnesian skarns of the postmagmatic stage are localised in the (5) magnetite impregnation, (6) serpentine selvage, (7) hydrothermal marginal parts and on the front (outwedged portions) of doler- halite (After Mazurov et al., 2007). itic sills, apophyses, and the branches of intrusive bodies host- both within and outside the breccia pipes, while sub-horizon- ed at the level of the Cambrian carbonate-evaporite successions tal dolerite sills occur at depth (Soloviev, 2010; Mazurov et al., (Figure 14). The skarns penetrating the evaporite levels have a 2007, 2018). banded or layered structure and resemble gravel conglomerates, with carbonate cements. The round fragments (metasomatic Magnetite pipe orebodies at Korshunovshoe are texturally and pseudo-conglomerates) are composed of globules of disintegrat- mineralogically complex (Figures 12, 14) and are composed of: ed doleritic porphyrite, completely or partially substituted by i) Banded masses of metasomatic magnetite that are within, and zonal magnesian skarns. Their mesostasis is cryptocrystalline, conformable to saline to calcareous members of the host sedi- and early phenocrysts of olivine, plagioclase, and pyroxene have mentary wall rocks (dominantly in dolomitic limestones, marls, calcareous argillites and sandstones with a calcareous or limy 3 Describes hematite pseudomorphs after magnetite, formed under conditions of increasing oxygen fugacity Page 12 www.saltworkconsultants.com

Volcanomicrite in traced down to deep levels close to Explosion breccias and lava ows crater lake (collapse) the root zones in some basalt pipes (Permo-Triassic) (Triassic) Local mineralised In the Korshunovsk iron-ore deposit, veins and ssures such a brecciated body extends from Coal-bearing sequence (late stage) Zone (Permo-Carb.) Crater the main diatreme pipe some 5 km to Near vertical Red siltstone, marlstone brecciated clasts the west and 9 km to the south-west (Silurian) Sandstone with limestone in ore pipe (Von der Flaass and Nikulin, 2000). interlayers (Silurian) Telescoping Red mudstone/marlstone orebodies in Although not discussed in terms of a (Ordovician) diatremes Quartz sandstone volatilisation mechanism in the pub- Limestone Magnesian skarn ores (Ordovician) lished literature, I would argue that the lateral apophsyes are indicative Marlstone with thin

sandstone interlayers Diatreme Zone of the former presence of hydrated Ore (Cambrian) stockwork salt layers, probably carnallitite beds showing similar responses to those Litvintsevo Formation seen in the potash mines of East Ger- many (Shofield et al., 2014; or part 1 Magnesian skarn ores in this current series of Salty Matters Halite and dolomite Angara Fm (halite) (Cambrian) Skarns, mixing of Intrusive igneous bodies articles). Root Zone Root intrusives of trap complex. Sills and evaporites laccoliths, dikes, and Bulai Formation The diatreme chimney atop the root oset dolerite bodies Belsk Fm (halite) zone indicates the rapid rise of a over- pressured and upward flowing gas- Riphean and Precambrian metamorphics charged rock mass. Basalt magma served as the ultimate source of iron 1 km for the magnetite in the breccia pipes. Figure 14. Schematic cross section of an ore-magmatic pipe system of the Angara–Ilim iron ore type Extraction of iron from the melt and (after Mazurov et al., 2007) its transition and accumulation took undergone dispersion and substitution. Unaltered cores of the metasomatic ‘conglomerate’ are in contact with a 4fassaite zone, Stratigraphy Organics Sills Pipes which passes outward into a spinel-fassaite zone and then into a Coal forsterite-magnetite and 5calciphyre zone.

The geometry of pipe emplacement is broken down into three 0 related styles; i) Root zone, ii) Diatreme zone, iii) Crater zone (Figure 14). The upper crater zone is sometimes complicated by Zone Crater the presence of reworked crater-lacustrine deposits (Polozov et al., 2016). The root zone is typically brecciated with pseudocon- Ordovician-Permian glomerated and other saline volatilisation textures described in the previous paragraphs. The root zone can be traced out from the pipe stem as disturbed zones with considerable lateral ex- 1000 Oil/gas

tents at the level of the Cambrian evaporite beds. Subhorizontal zone Breccia brecciated dolerite “sills” of the Kapaevsk iron deposit were ce- P mented with calcite, magnetite and halite in various ratios and P

4 Fassaite is an augite with a very low iron content thought to be a con- P tact mineral formed at high temperature on the interface between volcanic rocks Depth (m) and limestone. Cambrian

5 Is a near-obsolete term for a meta-carbonate rock containing a con- Root zone spicuous amount of calcium silicate and/or magnesium silicate minerals. 2000 P Figure 15. Nepa district stratigraphy in the Tunguska Basin showing levels Halite/sulphate with petroleum occurrences (after Svensen et al., 2009). The stratigraphy P Ediacaran Evaporitic carbonate is representative for the basin segment with outcropping or subcropping P pipes. Thicknesses of the Precambrian strata vary considerably (1–10 km) Carbonate/marl but has not been drilled in the central parts of the basin. Sill intrusions P Petroleum are present throughout the basin stratigraphy. The pipes are rooted in the Cambrian evaporite or possibly deeper, but have only been drilled P Sandstone to Upper Cambrian levels, as at Nepa. The inferred source region of the Shale pipes, where intense magma-sediment interactions took place, is likely 3000 Cryogenian-Torian Precambrian within the hydrated salt levels of the lower Cambrian strata. Craters can source rocks be filled with up to 750 m of crater-lake sediments. Page 13 www.saltworkconsultants.com

place in the presence of chlorine-rich fluids, which were formed Hydrocarbons are abundant in the Cambrian and Ordovician in the course of thermal decomposition of halite-hosted hydrat- sections of the Tunguska Basin, while coals are widespread in ed salt beds (carnallite). In the later stages of ore formation, the Permo-Carboniferous Tunguska Series sediments (Figure some chlorine was fixed in scapolites, while sodium was fixed 15). The juxtaposition of a vast volcanic province with its dykes, in albitites and scapolitites (6dipyres). In the tuffs of a number sills and diatremes interacting with extensive intracratonic sa- of diatremes and paleovolcanoes of the Siberian Platform, na- line Cambrian beds containing evaporites sealing substantial oil tive iron can form metal balls in association with 7moissanites accumulations and interacting with coal-bearing deposits, likely and (Goryainov et al. 1976). The occurrence of such produced massive quantities of halocarbons along with meth- phases, as well as bitumen in calderas and carbonaceous matter ane and CO2. Notably, contact metamorphism with hydrother- in pisolite tuffs, points to the migration of hydrocarbon fluids mal systems rich in chlorine, created during pressure dissolution through the volcano-tectonic structures (Ryabov et al., 2014). and dehydration of the surrounding evaporites, potentially syn- thesized large amounts of the organohalogens methyl chloride (CH Cl) and methyl bromide (CH Br) (Beerling et al., 2007; 6 A variety of scapolite with the components marialite and meionite in 3 3 a ratio of about 3:2 Visscher et al., 2004; Svensen et al., 2018). 7 Moissanite is naturally occurring (SiC) and its various In terms of rapid transfer of volatiles to the atmosphere, the phre- crystalline polymorphs. It has a Moh's hardness of 9.5 and is rare, having been atomagmatic-sediment pipes (diatremes) generated tall, explo- found in only in a few high pressure terrestial rocks, ranging from rock to . It occurs naturally as inclusions in diamonds, , and sive volatile-rich eruption columns, which at times reached the such ultramafic rocks as and lamproite. It has also been identified as stratosphere (Svensen et al., 2009). Such features simultaneous- pre-solar grains in carbonaceous meteorites.

Weighted mean > 252.2 Ma Carbon record 206Pb/238U date (Ma) A. B.

251.3 Tunguska sediments a 251.4 Stage 3 252.2 251.9 Ma Stage 1 251.5 34 Volcanic loading Dominantly vertical transport via dike-sill system b 251.6 33

251.7 251.9 Ma Stage 2 hiatus Extrusive 251.8 Gas liberation during contact metamorphism Lateral transport and widespread (Halocarbons, SO , CH , CO ) heating during initial sill-complex 28 2 4 2 growth c Max extinction 251.9 level Reduced gas emissions 251.9 251.5 Ma 25 Stage 2 252.0

252.1 Continued sill intrusion d 22 Stage 1 Waning gas emissions 252.2 251.5 251 Ma Renewed eusion -4 -2 0 2 4 13 δ Ccarb 252.3 Ma

Stage 3 Continued sill intrusion e

Figure 16. Stages of Siberian Traps LIP magmatism relative to timing of mass extinction (after Burgess et 2017). Stages are color coded to the 206 238 13 dominant style of magmatism at the time, purple for extrusive, and green for intrusive. A) Weighted mean Pb/ U zircon dates and δ Ccarb values. Stars show the stratigraphic locations of U/Pb dates. B) Time series of Siberian Traps LIP emplacement. a] Pre-emplacement basin. b] Em- placement of a volcanic load during stage 1. The feeder system is unresolved, and most likely situated below lavas . c] Beginning of stage 2, with lateral sill complex growth, widespread heating, and prolific gas generation. d] Continued sill emplacement during stage 2. e] Renewed extrusive magmatism during stage 3. Page 14 www.saltworkconsultants.com

ly promote removal of highly soluble EMPLACEMENT OF SIBERIAN TRAPS volcanic gases, such as HCl and SO2, and potentially deliver large volumes Occurs in evaporite settings Enhancement in evaporite-prone settings of sulphur, halocarbons water, meth- Hydrated salts ane and CO2 to the upper atmosphere Thermogenic methane (Black et al., 2015). Halocarbons SO 2 emissions CO 2 emissions

Increased Increased Timing of trap emplacement Ozone Acid continental seawater destruction rain faster weathering 87Sr/ 86Sr Siberian Traps magmatic activi- Long term reaction Global warming rates ty at the end-Permain is segment- Short term eutrophication Global cooling ed into three distinct emplacement (nuclear winter) stages (Figure 16; Burgess et al.,

2017). Stage 1, beginning just before Increased Positive Increased UV Soil TERRESTRIAL marine C-isotope 252.24±0.1 Ma, was characterised penetration erosion MASS EXTINCTION productivity excursion by initial pyroclastic eruptions fol- lowed by lava effusion. During this Disturbed landscapes Oceanic anoxia stage, an estimated two-thirds of the Genetic Negative C-isotope mutation siltation total volume of Siberian Traps lavas excursion Abundant 6 3 MARINE were emplaced (>1×10 km ). Stage microbial MASS EXTINCTION 2 began at 251.907±0.067 Ma, and growth was characterised by cessation of ex- trusion and the onset of widespread sill-complex formation. These sills Figure 17. Model of likely environmental consequences of the emplacement of the Siberian Traps. 6 2 are exposed over a >1.5 × 10 km Charts the flow of consequences due to atmospheric buildups of halocarbons, sulphurous emissions, area and form arguably the most ae- CO2 and methane. Causal links are indicated by solid black lines, and possible second-order controls rially extensive continental sill com- on the negative carbonate C-isotope excursion at the end-Permian Extrinction event are indicated by a dashed line The red shading indicates processes driven by the presence of anhydrite, halite and plex on Earth. Intrusive magmatism hydrated salts with some saltbeds acting as hydrocarbon seals, others as source rocks, versus the continued throughout stage 2 with processes enhanced by emplacement of igneous material into organic-prone saline carbonate beds no apparent hiatus. Stage 2 ended at typically entrained in a saline giant (in part after Benton and Newell, 2014; Warren 2016). 251.483±0.088 Ma, when extrusion of lavas resumed after an ~420 ka hiatus, marking the beginning ma-water interactions in areas with abundant groundwater or of stage 3. Both extrusive and intrusive magmatism continued hydrated salts, and 3) lava flows and lava fountaining during the during stage 3, which lasted until at least 251.354 ± 0.088 Ma, main stage of effusive volcanism (Jerram et al., 2016a,b). Each an age defined by the youngest sill dated in the province. A max- stage has a differing set of expressions in terms of the interacting imum date for the end of stage 3 is estimated at 250.2 ± 0.3 Ma. evaporites and the landscape expression of these interactions. Integration of LIP stages with the record of mass extinction and Outcomes of the end-Permian igneous evaporite inter- carbon cycle at the Permian-Triassic Global Stratotype Section play and Point (GSSP) shows three important relationships (Burgess et al., 2017). (1) Extrusive eruption during stage 1 of Siberi- A unusual aspect of the Siberian trap eruption compared to many an LIP magmatism occurs over the ~300 kyr before the onset but not all LIPs is the saline and kerogen-rich nature of region- of mass extinction at 251.941 ± 0.037 Ma. During this interval, al geology in the Siberian platform that interacted with the LIP the biosphere and the carbon cycle show little evidence of in- magmas. The main lithologies of the region are large volumes of stability. (2) The onset of stage 2, marked by the oldest Siberian Devonian anhydrites in the north, Cambrian halite and hydrat- Traps sill, and cessation of lava extrusion, coincides with the ed-potash salts in the south, hydrocarbon source rocks and evap- beginning of mass extinction and the abrupt (2–18 kyr) negative orite-sealed hydrocarbons, and coals in the Permo-Carbonifer- 13 ous portions of the stratigraphy sitting directly below the basaltic δ CPDB excursion immediately preceding the extinction event (Figure 16a). The remainder of LIP stage 2, which is charac- otflows. Notably, contact metamorphism and the development of terised by continued sill emplacement, coincides with broadly hydrothermal systems rich in chlorine (produced from the pres- 13 sure dissolution and volatilisation of the surrounding evaporites, declining δ CPDB values following the mass extinction. (3) Stage 13 kerogens, coals and hydrocarbons with evaporite seals) poten- 3 in the LIP begins at the inflexion point in δ CPDB composition, after which the carbon reservoir trends positive, toward pre-ex- tially synthesized large amounts of the organohalogens methyl tinction values. chloride (CH3Cl) and methyl bromide (CH3Br) along with vast volumes of sulphurous gases, CH4 and CO2 (Figure 17). Explosive volcanism in the Siberian Traps can be classified in three distinct groups: 1) deep-rooted sediment–magma interac- In terms of rapid transfer of these volatiles to the atmosphere, the tions and pipe eruption where feeder sills are emplaced in evapo- phreatomagmatic-sediment pipes generated tall, explosive water rites (Cambrian and Devonian country rock), 2) shallower mag- and volatile-rich eruption columns, which at times reached the Page 15 www.saltworkconsultants.com

stratosphere. Such features simultaneously promoted removal of supercontinent (Figure 18; Marzoli et al., 2018). CAMP extends highly soluble volcanic gases such as HCl and SO2 and potential- across the former Pangaea from modern central Brazil northeast- ly delivered large volumes of sulphur, water methane and CO2 ward some 5000 km across western Africa, Iberia, and north- to the upper atmosphere (see Part 2 of this series for detail of western France, and from Africa westward for 2500 km through atmospheric transfer mechanisms for these volatiles). The jux- eastern and southern North America and as far west as Texas and taposition of a volcanic province with dykes and sills interact- the Gulf of Mexico (Figure 18 - dashed red line). The Province ing and intruding thermally-reactive chemical sediments compsed of two types of saline giant deposits (meg- CAMP lava ows asulphate versus megahalite) signifi- Messejana Dyke, Spain cantly degraded atmospheric quality CAMP sills 201.585±0.034, єH =1.7 at the end of the Permian (Figure 17). f Dykes The eruption of the Siberian Traps Tiqurjdal overlaps, within geochronologic un- CAMP boundary Group certainty, the catastrophic end-Perm- ian mass extinction (Cao et al., 2018; Shelburne Dyke, Canada

Burgess et al., 2014, 2017). Conse- 201.364±0.084, єHf=2.07 quently, Siberian Traps magmatism is likely a direct or indirect trigger for the end-Permian extinction. Ex- Holyoke Group MERICA plosive volcanism provides a much A Foum Zguid dyke, Morroco more efficient vehicle for injection NORTH 201.111±0.071, єH =1.3 of climate-modifying ash and aero- f sols, such as sulphur and chlorine, Recurrent Group into the atmosphere compared to AFRICA purely effusive volcanism (Thordar- Carolina Group ? son et al. 2003). While the enormous Hodh sill, Mauritania volume and volatile-rich budget of 201.440±0.031, єHf=0.1 the Siberian Traps produced large High-Ti Fouta Djalon sill, Guinea fluxes of sulphur and halogen gases Group (Black et al., 2015), explosive deliv- 201.493±0.051, єHf=2.13 ery of those gases to the stratosphere was likely a prerequisite for lasting global environmental effects. Figure Kakoulima intrusion, Guinea 17 documents the effects of bedded evaporites when heated during rapid 201.635±0.029, єHf=2.82 emplacement of sills during the for- mation of a LIP. Processes such as ? the release of CO2 and methane to the atmosphere are enhanced, while Amazonas sill, Brazil others such as high levels of SO2 201.364±0.023, єHf=7.49 and halocarbons in the stratosphere are direct responses to the heating of anhydrite and halite-hydrated salts, ? Amazonas sill, Brazil respectively. 201.525±0.065, єHf=2.32 ? End-Triassic extinction Amazonas and SOUTH event - Saline interac- Solimões basin AMERICA tions with CAMP mag- mas Tarabaco sill, Bolivia 500 km The Central Atlantic Magmatic Prov- 201.612±0.046, єHf=2.91 ince (CAMP) was emplaced at the end of the Triassic (≈201 Ma) in a Figure 18. Position of CAMP dykes, sills and lava flows and relevant dates are shown as well, as region created by the tectonic unzip- approximate locations of the present day continents and country borders. Also shown in grey are the ping (rifting-breakup) of the Pangean areas of dyke occurrences of the Tiourjdal (NW-Africa), Holyoke, Recurrent, and High-Ti groups (in pink), all other CAMP rocks belong to the Prevalent-CAMP group (after Davies et al., 2017; Marzoli et al., 2018). Page 16 www.saltworkconsultants.com

is composed of basic igneous rocks emplaced in a combination Basin (Ibanez et al., 2016) of shallow intrusions and erupted large lava flow fields extend- ing over a land surface area in excess of 10 million km2. During Th Amazonas-Solimoes intracratonic sag basin is developed on its emplacement, sill intrusions into evaporites are particularly the same scale as the Alberta basin of Canada and entrains the widespread in the vast Amazonas and Solimões intracratonic ba- Carboniferous (Pennsylvanian, ≈305 Ma) saline Nova Olinda sins (≈1 ×106km2), representing up to 70% of the total CAMP sill Formation. It is made up of a large laterally extensive set of cy- volume (Svensen et al., 2018). clic evaporite beds, dominated by interbedded combinations of anhydrite, shale and halite (Figures 20c, 21). These evaporites Sedimentary rocks intruded by sills in the Amazonas and So- occur within the Carboniferous-Permian megasequence, known limões basins include a lower (Ordovician–Mississippian) and as the Tapajós Group, which can be up to 1600m thick (Milani upper (Pennsylvanian–Permian) Paleozoic series (Milani and and Zalan, 1999). The lowest part of the megasequence is a Zalán, 1999). The lower Paleozoic series consists of sandstones blanket of eolian sandstones (Monte Alegre Formation), which and shales, some of which are particularly organic-rich (total or- is covered by marine-influenced carbonates and evaporites (Itai- ganic content up to 8wt.%; Milani and Zalán, 1999; Gonzaga et tuba and Nova Olinda Formations, respectively), along with al., 2000). The upper Paleozoic series is dominated by evaporite subordinate sandstones and shales (Figure 19c). The Tapajós and carbonate deposits of varying abundances, interlayered with megacycle is closed by a suite of Permian continental redbeds clastics. Sills are widespread within the upper Paleozoic evapo- (Andirá Formation) of Permian age. Subsequent east-west re- ritic sequence, extending almost continuously from the western gional extension facilitated a pervasive intrusion of magmatic margin of the Solimões Basin to the eastern margin of the Ama- bodies during the end-Triassic to Early Jurassic (Penatecaua dol- zonas Basin (Fig.19c). Sills within the lower Paleozoic unit are erites and equivalents). restricted to the eastern part of the Amazonas basin. As illustrat- ed in Fig.19c, high-Ti sills are found only in the lower Paleozoic Individual halite beds in the Nova Olinda evaporite cycles are series. Let's look now at the saline geology of the region and 20-80 m thick, while the Nova Olinda Fm. has an average thick- then at the effect its assimilation had on sill geochemistry. ness of 900m. Because of the high levels of entrained anhydrite beds in the Nova Olinda Fm., evaporite layers are not halokinet- Saline geology ic, but are subject to collapse and flow about the basin margin, especially in areas of intense meteoric dissolution (Figure 20). A significant, as yet poorly delineated, set of variable hydrated potash salts and sylvinites occur in bedded halite in the Amazon Early Petrobras drilling programs conducted in the Amazon Ba- Basin, Brazil (Figures 19a, 20; Szatmari et al. 1979). The Ama- sin from 1953 to 1963, defined the presence of halite but did zon Basin is about 2,100 km long and 300 km wide, it is an in- not appreciate that persistent sylvinite/carnallite beds cap a num- tracratonic sag basin atop an aulacogen between the Guyana and ber of the beds of NaCl in The Nova Olinda Formation. During Guaporé cratons (Figure 19b). The basin fill contains a number the late 1960s and 1970s, higher-resolution gamma-ray logging of stacked mega-sequence cycles (as defined by wireline inter- tools were used, along with better mud technology and associat- pretation) ranging in age from Lower Ordovician (Autaz Mirim Member 68°W 64°W Guyana 60°W 56°W of Trombetas Formation) to Lower Shield Permian (Figure 19b; Andirá Forma- 2°S tion; Gonzaga et al., 2000). The basin Manaus has a widespread Upper Cretaceous cover (Alter do Chão Formation) and was affected by widespread tholeiitic 4°S magmatic activity at the end-Trias- Guapor Potash Shield Halite sic (e.g.Penatecaua dolerites of the Anhydrite CAMP), making seismic-based hy- 200 km Limestone drocarbon exploration difficult, espe- A. cially as much of the basin still lies 60° W 56° W 52° W beneath thick tropical jungle. Since Guyana shield Monte Alegre Jatapu Cuminá the recognition of a widespread ig- 2°S platform half-graben subs. Thermal platform Permian Andirá neous overprint of the Palaeozoic Oriximina Manaus half-graben Tucamá sedimentary succession in the 1970s, half-graben half-graben Nova Olinda Tapajós Group Tapajós

Penn. Itaiuba hydrocarbon exploration efforts have subsid. Mamuru

Monte Alegre Mechanical been subdued (Thomaz-Filho et 4°S platform Abacaxis Hercynian orogeny half-graben Platform Carboniferous al., 2008). However, in the past few Miss. Accommodation zone years, SRTM studies are proving use- 100 km Guaporé shield Hinge fault volcanic sills ful, in front of seismic surveys and B. C. drilling, in the general identification Figure 19. Amazon Basin, Brazil. Amazon Basin, Brazil (after Warren, 2016). A) Distribution of potash of geological features in the Amazon and other evaporite salts in the Nova Olinda Fm (after Szatmari et al., 1979). B) Basin architecture in the main evaporite area (after Gonzaga et al., 2000). C) Relevant stratigraphy. Page 17 www.saltworkconsultants.com

ed narrower calliper measures. This work identified a number of called informally, lower (milky or white sylvinite), middle (sul- (0.5 - 2m thick) layers of sylvinite, within the halites (Szatmari phates) and upper zones (red sylvinite) (Figure 20). The lower et al. 1979). For example, the fifth and seventh depositional cy- zone (milky-white sylvinite zone) contains sylvinite, with halite cles define isolated salt sub-basins that accumulated significant and subordinate intercalated kieserite and anhydrite beds. The potash salts in Fazendinha and Arari regions (Figure 20). KCl lower potash zone is persistent within the basin and so covers an contents of these beds are between 28-33% in beds some 2.47- extensive area, whereas the upper potash zone is patchier. The 2.65 m thick (Garrett, 1995). The average ore depth at Fazend- greater extent of the lower potash zone is perhaps because it is inha, the larger of the known potash areas, is 1,050m (Figure the best isolated from any dissolution driven by circulation of 20). Much of the halite and potash distribution is controlled by undersaturated pore fluids through the overburden. the underlying rift-basin architecture (Figure 19b). Potential pot- ash reserves poorly defined, but are interpreted to be large (Sza- The middle zone is composed of a combination of sulphate and tmari et al., 1979; Garrett, 1995). chloride salts and is informally termed the sulphate zone. It hosts a variety of K, Mg and sulphate minerals that include a number Based on its texture, structure and chemistry, the potash inter- of hydrated salts. Typical mineral assemblages encompass syl- section in the Amazon Basin is divided into three distinct zones, vinite, sylvite, and langbeinite (K2SO4.2MgSO4) as well as the

Massive anhydrite Nodular anhydrite Dark grey salty shale Markers M-10 Dark-grey coarse-sized, recrystallised halite with a network Cycle VIIa Cycle M-10 of discontinuous shale chips M-10a 22m Fine to locally coarse recrystallised rose-coloured halite, laminated at base M-11 1050m M-10b Medium to coarsely-crystalline red sylvinite with M-11 6m Upper interval discontinous intercalations of anhydrite Sulphate zone with a complex mixture of sulphates (kainite, Middle kieserite, anhydrite and polyhalite) and chlorides (sylvinite 50m interval and halite)

Lower 1100m Fine/medium crystalline white milky, laminated sylvinite M-11a (ore) ZONE POTASH interval with ne laminations of light grey halite and anhydrite 17m M-12 Light grey, nely crystalline, laminated halite with increasing

Cycle VII Cycle upwards dissemination of white sylvinite

NOVA OLINDA NOVA 19m M-11a Massive medium grey, locally white, anhydrite M-13 8m 1150m M-14 11m 59° 00’W 57° 00’W 55° 00’W M-15 11m 100 km Faro potash M-16 9m 2° 00’S deposit 2° 00’S M-17 Arari potash M-17a 4m 11m deposit M-18 3m M-18a Amazon State 2° 00’S 1200m 10m Para State M-19 12m M-20

VI Amazon Basin 4° 00’S 4° 00’S Amazon Basin potash intersects Petrobras well with potash Sylvinite (ore) Halite Anhydrite Fazendinha Petrobras well with no potash potash deposit 4° 00’S Limestone Marl Siltstone Shale 59° 00’W 57° 00’W 55° 00’W Figure 20. Potash occurrences, distributions and stratigraphy (complied by Saltworks® from published information in Wolf et al., 1986 and Sad et al., 1982, as well as data extracts from the Saltworks version 1.9 database). ell stratigraphy and relative thicknesses are based on core and wireline information collected in the Fazendinha and Arari regions. Marker beds were chosen by Petrobras from wireline data (gamma and density logs are the most useful)

Page 18 www.saltworkconsultants.com

hydrated salts; polyhalite (K2SO4.2MgSO4.2CaSO4.2H2O), ka- in turn, overlain by impermeable shale beds some 20 m thick. inite (MgSO4.KCl.3H2O) and kieserite (MgSO4.H2O). The sul- It is underlain by an impervious, at times sparry, halite inter- phate distribution in this unit changes from anhydrite and poly- val some 70m thick (Figure 20). At the time it was described halite in the west (Fazendinha) to langbeinite and kainite in the (1970s-mid 1980s) little was known of the significance of halite east (Faro area). Towards the basin centre, chloride beds replace crystal textures in terms of their primary versus diagenetic sig- marginal sulphate beds in the sulphate unit. A gradual increase natures. Such a study of the nature of the halites enclosing the in potash concentration from west to east is interpreted by Sad et potash zone in the Amazon basin would aid in the definition of al., 1982, as indicating the inflow direction was from the basin's an ore genesis model. We do know that a single potash zone does western boundary. not extend across the basin. This is seen in a compilation of ex- isting Petrobras wells in the Amazon Basin, which intersect the The upper potash zone consists of coarsely-crystalline red syl- Nova Olinda Fm. Instead, potash salts accumulated in a series of vinite, with thin halite and anhydrite laminations. This level in- sumps atop a persistent thick halite unit (Figure 20). cludes the best K2O grades drilled so far, averaging 23% K2O (between 33% to 16%). Red sylvinite is interpreted as a sec- Elevated sulphate content in the potash zone of the Amazon ond generation product formed diagenetically by incongruent Basin reflects the MgSO4-enriched nature of the world ocean leaching of primary carnallite, but, as yet no carnallite (KCl. during the Carboniferous. Potentially high levels of sulphate in

MgCl2.6H2O) has been identified in the upper unit. proximity to adjacent sylvinite ore targets will complicate the processing of potential ore (see Warren 2016, Chapter 11). But The potash zone is overlain by impermeable coarsely-crystalline in terms of supplying high levels of volatiles during sill intru- halite, with minor shale intercalations in a zone up to 25 m thick, sions, it is highly likely the various hydrated sulphate salts in the

(1) (2) (3) (4) (5) (5) Guyana French A. ATZ OAST MA MAST IBST IB Venezuela Suriname Guiana B. Atlantic Ocean Columbia Post Palaeozoic Post Post Palaeozoic Post 500 4 5 2 3

1

1000 Peru 700

Upper Palaeozoic Amazonas Basin

Upper Palaeozoic 500 Lower Palaeozoic Lower 300 Boreholes 1 = ATZ Upper Palaeozoic Clastics 100 2 = OAST Carbonate/evaporite Acre 1500 BasinAmazonas Basin 3= MA

Upper Palaeozoic Solimões Basin Depth (m) Low-Ti dolerite 4 = MAST High-Ti dolerite Bolivia 5 = IBST/IB Dolerite (Ti unknown) Lower Palaeozoic Lower

W Solimões Basin Amazonas Basin E 2000 C. 0 0

2 2

2500 Lower Pal.

Lower Palaeozoic Lower 4 4 Depth (km)

Cretaceous-Cenozoic Upper Palaeozoic (Pennsyl.-Permian) Lower Palaeozoic (Ordovician.-Miss.)

3000 L. Pal. Basement Proterozoic Low-Ti dolerite sill Hi-Ti dolerite sill Dolerite sill (Ti ?)

Figure 21. Sill geology in the Amazonas and Solimões Basins, Brazil (after Heimdal et al., 2019). A) Borehole geology in the Amazonas Basin (wells numbered 1=5). The majority of dolerites sills in the Upper Paleozoic section (dominated by evaporites and carbonates, interlayered with lesser clastic sediments) have low TiO2 concentrations (<2 wt.%; red colour). Boreholes with known stratigraphy show that sills with high TiO2 con- centrations (>2.0 wt.%; purple color) are restricted to the lower Paleozoic section. Sills with unknown TiO2 concentrations are marked in pink. Sills with available sample material, which have been analyzed by Heimdal et al., 2019,are marked by a star symbol. B) Map showing the location of the wells in the Amazonas and Solimões sedimentary basins. Coloured contour lines represent the cumulative sill thickness, which peaks in the central parts of the basins and decreases toward the margins, and show that the sills are distributed throughout a large area across both basins. Note that the location of borehole SOL (drilled in the Solimões Basin) is not known. C) Schematic cross-section of the Solimões and Amazonas basins based on sill and formation depths from boreholes shows that sills are widespread in upper Paleozoic rocks (dominated by evaporite and carbonate, interlayered with clastic rocks), extending almost continuously from the eastern margin of the Amazonas Basin to the western margin of the Solimões Basin. Sills within lower Paleozoic sedimentary rocks are restricted to the eastern part of the Amazonas Basin. Page 19 www.saltworkconsultants.com

Temp. decrease 100 5 Clastic host Evaporite host Evaporite host OAST ATZ Clastic host 80 Cl input from 1B-990 SOL 4 SOL-6 MA-2883/2884 SOL-6 evaporite MA-1490/1508 60 3

40 2 % of Analyses 20 %) (wt. Cl in biotite 1

0 0 >1 1-2 2-3 3-4 4-5 A. B. 0 2 4 6 Cl in biotite (wt. %) Biotite TiO2 (wt.%) Figure 22. Dolerite sills chemistry in the Amazonas and Solimoes Basin (see figure 20 B for well locations; after Heimdal et al., 2019). A) Cl ver- sus TiO2 levels in biotite from showing a clear correlation between host-rock lithology and Cl concentrations in the analyzed biotites. Biotite from sills emplaced in clastic host-rocks have Cl concentrations <1.0 wt.%, whereas biotites from sills emplaced in an evaporitic host-rock show a wide range in Cl. Analysed samples come from wells OAST, IB-990, SOL-6 and MA-1490/1508 and represent biotite analyses from individual dolerite samples, whereas columns SOL and ATZ include biotite measurements from several sills from the respective boreholes MA-2883/2884 includes biotite analyses from two individual samples from the same sill. B) The positive correlation between Cl and TiO2 biotite concentrations observed for sills emplaced in clastic host-rocks (OAST, IB-990 and MA-2883/2884; white circles) is interpreted to represent a Cl degassing trend during cooling and crystallization of a non-Cl contaminated magma, here represented by sample SOL-6 (red stars). In contrast, the increase in Cl with decreasing TiO2 observed for sills emplaced in evaporitic host-rock (ATZ, SOL and MA-1490/1508; green circles) represent an input of evaporite derived Cl into the magmatic system during the crystallization of the dolerites. potash zone focused sill emplacement and contributed to elevat- low-and high-Ti CAMP magmatism were active simultaneously, ed levels of halocarbons and sulphurous gases escaping into the although low-Ti magmatism likely started earlier. earth's atmosphere at the end Triassic. As yet, no phreato-mag- matic pipes have been documented in the Nova Olinda, but as Detailed studies of CAMP sill geochemistry showing likely the sourcing evaporite unit lie a kilometer beneath the surface assimilation of chloride salts from the Nova Olinda evaporites and the dense tropical Amazon Jungle, this is not surprising. In- are published in Heimdal et al., 2019, and summarised in this creasing future use of STRM data may help solve this (Ibanez section. They show the bulk of the dolerites as sampled in the et alo., 2016) wells, illustrated in Figure 22, are characterised by phenocrysts of clinopyroxene and plagioclase in subophitic to intergranular Saline sediment-sill interaction textures, Fe–Ti oxides, and rare olivine and orthopyroxene. A different mineralogical assemblage (microphenocrysts of al- Sills from the Amazonas Basin have previously been described kali-feldspar, quartz, biotite and apatite) is found in small in- as low-Ti tholeiitic basalts and andesitic basalts (De Min et al., dependent domains, localised within the framework of coarser 2003), and sills from both basins are generally characterised by plagioclase and clinopyroxene laths. These fine-grained evolved a mineral assemblage of clinopyroxene, plagioclase, Fe–Ti ox- domains crystallised in late-stage, evolved melt pockets in the ides, rare olivine and orthopyroxene and accessory quartz-feld- interstitial spaces between earlier crystallised coarser grained spar intergrowths. crystals. 8 Recent studies report the presence of high-Ti sills in the eastern The majority of the studied dolerites are generally evolved part of the Amazonas Basin (Figures 18, 21; Davies et al., 2017; tholeiitic basalts and basaltic andesites with low TiO concentra- Heimdal et al., 2018, 2019; Marzoli et al., 2018), but no high-Ti 2 tions (<2.0 wt.%). Four samples have high TiO2 concentrations occurrences have been observed in the Solimões Basin. (>2.0 wt.%), and are found in the eastern part of the Amazonas High-precision U–Pb dates from four dolerites from the Amazo- Basin (Figure 20a, c). nas and Solimões basins overlap in age, with U–Pb ages for low- Whole-rock major and trace element and Sr-Nd isotope geo- Ti dolerites of 201.525 ±0.065 (Amazonas Basin) and 201.470 chemistry of both low- and high-Ti sills is similar to that of ±0.089 (Solimões Basin), and for high-Ti dolerites in the Ama- previously published CAMP rocks from the two magma types. zonas Basin of 201.477 ±0.062 and 201.364 ±0.023 Ma (Figure 18; Davies et al., 2017; Heimdal et al., 2018). This suggests that ferent mantle sources. While the low-Ti CAMP magmas are likely derived from a lithospheric mantle enriched by recycled crust, high-Ti magmas originated from the asthenosphere and were enriched by melts derived from metasomatic veins 8 Previous studies summarized in Heimdal et al, 2018 have shown that (see Marzoli et al., 2018 and references therein). the high- and low-Ti magma types cannot be derived from one another by either closed-or open-system magmatic evolution, suggesting that they derive from dif- Page 20 www.saltworkconsultants.com

Low-Ti sills show enriched isoto- 143 144 pic signatures ( Nd/ Nd201Ma from 87 86 0.51215 to 0.51244; Sr/ Sr201Ma from 0.70568 to 0.70756), coupled with crustal-like characteristics in the incompatible element patterns (e.g. depletion in Nb and Ta). Unaltered high-Ti samples show more depleted 143 144 isotopic signatures ( Nd/ Nd201Ma from 0.51260 to 0.51262; 87Sr/86Sr-

201Maf from 0.70363 to 0.70398). Low-Ti dolerites from both the Am- azonas and Solimões basins contain biotite with extremely high Cl con- centrations (up to 4.7 wt.%). They show that there is a strong correla- tion between host-rock lithology and Figure 23. Reconstuction of the early Paleogene of the Chicxulub impact site, Yucatan Peninsula, Cl concentrations in biotite from the Mexico. (image credit D. Van Ravenswaay/SPL) dolerites, and interpret this to reflect large-scale crustal contamination of focus on the saline geology of the Yucatan impact site, but rec- the low-Ti magmas by halite-rich evaporites (Figure 21). The ognise the arguments of some authors that the Shiva site is close- findings of Heimdal et al. (2019) support the hypothesis that ly linked in time with the extrusion of the Deccan Traps. More sill-evaporite interactions increased volumes of volatile released importantly, voluminous Deccan Traps eruptions and intrusions during the emplacement of CAMP, and underlines the case for had likely already degraded the end-Cretaceous atmosphere. A the active involvement of this LIP in the end-Triassic extinction large bolide crashing into an anhydrite saltern in the palaeo-Gulf event. of Mexico was perhaps the coup de grâce for many already -stressed late Mesozoic communities (Wang et al., 2018) End-Cretaceous extinction event - Saline Saline Geology of the Yucatan site interactions driven by a bolide impact) About 66 million years ago, at the end of the Cretaceous, one or As it is covered by a Tertiary-age sediment carapace, there are no possibly multiple large collided with the Earth. Paul current evaporite outcrops on the Yucatan Peninsula. However, Renne dated this impact at 66.043±0.011 million years ago on the region is underlain by thick Cretaceous anhydrite beds and the Yucatan Peninsula, based on argon-argon dating (Renne, has a nearby giant oil field, Cantarell, reservoired in a carbonate 2013). He went on to conclude that the main end-Cretaceous breccia trap possibly related to the impact (Grajales-Nishimura mass extinction event occurred within 32,000 years of this date. et al., 2000). Ongoing petroleum exploration means a number of The bolide produced a crater some 150x180 km in diameter exploration wells sample the Cretaceous geology of the Yucatan named the Chicxulub (Figure 23). Worldwide, a Peninsula (inset in Figure 24). Regionally, Cretaceous (Albian) record of this event is evidenced by an iridium-enriched interval, saltern anhydrite beds extend from Guatemala, across the Yu- in what is now called the Cretaceous-Tertiary Boundary Clay catan Peninsula and north possibly to Veracruz. Depositionally (KTBC) (Alvarez et al., 1980). similar, back-reef saltern beds typify the early Cretaceous (Al- bian) Ferry Lake Anhydrite, which extends across the onshore Other authors favouring additional bolide impacts at the end of northern, and offshore eastern, Gulf of Mexico (Pittman, 1985; the Cretaceous, such as Lerbekmo (2014) and Chaterjee (1997), Petty, 1995; Loucks and Longman, 1982). have argued that some 40,000 years later, a much larger meteor- ite struck the shelf of the -Seychelles continent, which was Pemex wells drilled on the Yucatan Peninsula, penetrate some drifting northward in the southern Indian Ocean, producing a 1300 –3500 m of bedded Tertiary, Cretaceous, and Jurassic stra- crater, some 450x600 km across, named the 9Shiva impact (Le- ta (Figure 24; Ward et al., 1995). Palaeozoic metamorphic rocks rbekmo, 2014; Chaterjee, 1997). If a bolide-related feature, the are intersected at 2418 m in well Y4 and at 3202 m in well Y1. Shiva crater was split by subsequent plate tectonism and today ‘‘Volcanic rock/andesite,’’ now broadly interpreted as an ‘‘im- is not widely recognised by the scientific community as a K-T pact-melt rock’’ or is intersected in the lower parts of impact site. wells Y6 and C1. Based on the well geology there are seven major biostratigraphic-lithostratigraphic units in the Mesozoic As for any sound scientific hypothesis, there are ongoing argu- section overlying basement rocks in the vicinity of the Chixulub ments for the Chicxulub site being the "smoking gun" for the impact site (Units A-F; Ward et al., 1995 and references there- end-Cretaceous extinction event, many of these arguments and in). The regional depositional setting is typical of a Cretaceous the supporting literature is discussed in (Kring, 2007). I shall carbonate platform, which at times became sufficiently isolated 9 Shiva is the Hindu goddess of destruction and rejuvenation to deposit stacked anhydrite saltern beds in a rudistid back-reef Page 21 www.saltworkconsultants.com

T1 Y2 Y1 Y6 C1 Y5 Y4 NW 0 E 0

500 G G 500 D U F 1000 Tertiary F 1000 ? Cret. E ? 1500 E D 1500 D 1581 m 1645 m C Depth m 2000 C 2000 B salt D 90° 88° A 2500 U B Centre of Gulf of 2425 m 2500 Chicxulub Mexico 22° crater 3000 C1 Y4 3000 A Y6 3003 m 3175 m Y5A 3226 m Y2 Dolomite Shale 3500 T1 3488 m 20° 3500 Y1 Limestone Breccia

Sea Anhydrite Melt rock Caribbean 100 km Sandstone Basement

Figure 24. Correlation sections through Pemex wells of northern Yucatan Peninsula. Datum is ground level, which is within several metres above sea level at all locations. Y wells = Yucata´n Nos. 1, 2, 4, 5A, and 6; C well = Chicxulub No. 1; T well = Ticul No. 1. Large-scale units of Meso- zoic (units A–G) are based on lithology, correlative fossil zones, and electric-log characteristics. Unit boundaries are defined by log correlation. Approximate ages of units: A = Jurassic–Early Cretaceous, B = Albian, C = Albian-Cenomanian, D = Cenomanian-Turonian, E = Turonian, F = Coniacian?-Maastrichtian, G = late Maastrichtian (redrafted after Ward et al., 1995). setting (Warren, 2016; Chapter 5). Unit E consists of shallow-platform limestones with intervals containing abundant small planktic foraminifers. The unit con- Unit A consists of red and grey sandstone, shale, and silty dolo- tains rudist-bearing limestones considerd by López Ramos mite near the base of wells Y1, Y2, and Y4. This unit is Jurassic (1975) as Turonian, and a similar age is indicated by the pres- to Early Cretaceous in age (López Ramos, 1975). ence of Marginotruncana pseudolinneiana and Dicarinella Unit B is predominantly dolomite in its lower part, becomes rich imbricata in samples from Y1, Y2, Y4, and Y5A. in intercalated anhydrite and dolomite upward. Rock salt was Unit F consists of dolomitized shallow-platform limestone with cored in this unit in T1 at 2378–2381 m. Nummoloculina sp. benthic foraminifers. Abundant textularid and miliolid foramin- was identified in Y2, suggesting an Albian age. ifers are at the top of unit F (Fig. 2). The presence of Margi- Unit C is predominantly shallow-water limestone in the lower notruncana schneegansi and Globotruncana fornicata in well part, becoming more dolomitic upward. At the base of unit C in Y5A suggests a Santonian age for that part of this unit. wells Y1 and Y2 is a horizon with the large benthic orbitulinid Unit G is a thick interval of breccia with abundant sand- to grav- foraminifer Dicyclina schlumbergeri? (Figure 23\4). Nummo- el-sized angular to subrounded fragments of dolostone, anhy- loculina (N. heimi?) also occurs in the lower part of this unit in drite, and minor limestones suspended in a dolomicrite matrix. cores Y1 and Y4. Nearer the platform margin (Y4), the upper The poorly-sorted fabric is similar to that of debris-flow depos- part of this unit contains a rudist limestone, but in other wells the its. López Ramos (1973) reported marl and limestone intercala- rocks reflect more restricted depositional environments across tions within the thick breccia from 1090 to 1270 m in well C1 the platform interior. Shallow-subtidal to intertidal dolomite (Figs. 1 and 2). In addition, Y4 and Y4 contain dolomite that makes up most of this section in Y5A, where anhydrite is inter- may separate an upper breccia with rare or no planktic foramin- layered with dolomite in the upper parts of the unit in Y1, Y2, ifers from a lower breccia with abundant planktic foraminifers. and T1. The fossil assemblage indicates an Albian-Cenomanian Core in Y2 is composed of finely crystalline anhydrite, possibly age for unit C. also representing a less disturbed sedimentary layer or anhydrite Unit D is predominantly somewhat deeper-subtidal limestone block within the breccia interval. and marl, with horizons containing abundant tiny, mainly tro- Clasts of carbonate rocks in these breccias are fragments of chospiral planktic foraminifers as seen in samples from Y1, Y2- many different kinds of dolostone and limestone, with differ- Y4, and Y5A. ent diagenetic histories. Anhydrite fragments typically make up Page 22 www.saltworkconsultants.com

15%–20% of the breccia; much of the anhydrite is composed pacts, and at higher temperatures the equilibrium pressure would of tiny angular splinters. Some breccia layers contain be considerably higher. Because the system is open, SO2 and grey-green fragments of altered volcanic ‘‘glass’’ and spherules. oxygen would escape to the atmosphere as they did in the labo- Other minor but significant constituents of the breccia are frag- ratory crucible of Rowe et al. (1967) and would continue to do ments of melt rock and basement as seen in Y6 (1295.5–1299 so as long as post-impact temperatures were elevated. m), Y6 (1377–1379.5 m), and C1 (1393–1394 m). In addition, Hildebrand et al. (1991) found from Y6 (1208 Published discussions of the impact site geology all consid- –1211 m), and Sharpton et al. (1994) reported shock-deformed er anhydrite as the evaporite mineralogy, with minor volumes quartz and feldspar grains and melt inclusions in the dolo- of halite (well T1 in Figure 24). This lower salinity end of the mite-anhydrite breccia. evaporite series is typical of mega-sulphate settings, worldwide (Warren, 2016; Chapter 5) In addition, there is no evidence for Planktic and benthic foraminifers are present in the breccia ma- hydrated potash salts in the region and this too is typical of starn trix and include Abathomphalus mayaroensis, Globotrun-cani- salterns in a meg-sulphate basin. There is, however, the addition- ta conica, Rosita patelliformis, Pseudoguembelina palpebra, al possibility that not all of the saltern gypsum had converted to Racemiguembelina fructicosa, and Hedbergella monmouthen- anhydrite at the time of the impact. If so, this would have further sis, which indicate a late Maastrichtian (end-Cretaceous) age for detabilised and volatised the various lithologies at the site of the formation of the breccia (Ward et al., 1995). impact.

Climatic outcomes of the Yucatan impact Intercalated carbonates, kerogens and other organic sediments at the collision site contributed additional CO2, CH4, H2O, and Widespread Jurassic anhydrites, hydrocarbon reservoirs and halocarbons to the atmosphere, as well as vast quantities of heat source rocks surround the Yucatan impact region; their vaporisa- and particulates. The following discussion of the various con- tion on bolide impact and rapid entry into the upper atmosphere tributors to climatic changes, driven by the Chicxulub impact, is added a good deal to the ensuing climatic mayhem (Figure 24) taken mostly from Kring, 2007 (and contained references). As we discussed for LIP emplacement, anhydrite decomposes at Acid rain; Because the Chicxulub impact occurred in a region high temperatures, to form SO2 gas, CaO, and oxygen. Thermo- dynamic calculation and extrapolation using the free energy of with anhydrite, sulphurous vapour was injected into the strato- formation of anhydrite and its reaction products as a function of sphere, producing sulphate aerosols and eventually sulphuric temperature up to 1120°C (Robie et al., 1979), give an equilibri- acid rain. Estimates of the amount of S liberated vary, consen- sus ranges from 7.5 × 1016 to 6.0 × 1017 g S, which would have um pressure of 1 bar SO2 over the reaction: produced 7.7 × 1014 to 6.1 × 1015 mol of sulphuric acid rain. In

2CaSO4 = 2CaO + 2S02 + O2 addition, the earth’s atmosphere was shock-heated by the im- pact event, producing nitric acid rain as well. Independent of at a temperature around 1500°C (Brett, 1992; Yang and Ahrens, the geology of the impact siter, the earth's atmosphere is heat- 1998). Experimental studies by Rowe et al. (1967) indicate that ed when pierced by a bolide as the vapour-rich plume expands anhydrite decomposes in an open crucible above 1200°C. Tem- out from an impact site, and ejected debris rains through the at- peratures higher than 1500°C are well in the range of tempera- mosphere. In a Chicxulub-sized , the ejecta debris tures of material subjected to strong shock in large bolide im- 14 is, estimated to produce ≈1×10 mol of NOx in the atmosphere

reball radiation airblast Reentering earthquakes Local & regional tsunamis e ects ejecta burial beneath ejecta burning soot cooling pyrotoxins Fires: acid rain H O and CO no photosynthesis Dust Dust loading 2 2 loss of vision cooling Production: Soot greenhouse NOx warming acid rain NO ozone x ? cooling Production: SO2

cooling SO2 acid rain Production:

Heavy metal poisoning? increasing Temperature “nuclear winter” H2O and CO2 Time greenhouse Immediate Months Year Decades Hours Weeks Years A. B. Days Months Decades Figure 25. A) Relative time scales of the environmental perturbations caused by Chicxulub impact event. B) Thermal excursions produced by Chicx- ulub impact event as a function of time. Pre-impact ambient temperature is marked with a green dashed line (redrafted from Kring, 2000, 2007).

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and, thus, ≈1×1015 moles of nitric acid rain. Impact-generated Ozone destruction; Ozone-destroying Cl and Br is produced wildfires may have produced an additional ≈3×1015 mol of nitric from the vaporised projectile, vaporised target lithologies, and acid. Sulphuric and nitric acid rain fell over a few months to a biomass burning. Over five orders of magnitude more Cl than few years (Figure 25a). is needed to destroy today's ozone layer was injected into the stratosphere, compounded by the addition of Br and other re- Wildfires; Evidence of impact-generated fires is recovered from actants. The affect on the ozone layer may have lasted for sev- K/T boundary sequences worldwide in the form of fusinite pyro- eral years, although it is uncertain how much of an effect it had litic polycyclic aromatic hydrocarbons, carbonised debris, on surface conditions. Initially, dust, soot, and NO2 may have and charcoal. The distribution of the fires is still poorly under- absorbed radiation, and sulphate aerosols may have stood and may have had a restricted geographic distribution lim- scattered the radiation. The settling time of dust was probably ited to the vicinity of the impact event, produced not by impact rapid relative to the time span of ozone loss, but it may have ejecta but by the direct radiation of the impact fireball which taken a few years for the aerosols to precipitate. had a plasma core with temperatures over 10,000 °C. Several additional parameters influence the outcome (e.g., the trajectory Greenhouse gases; Water and CO2 were produced from Chicx- of the impacting object, its speed, and mass of the ejecta). The ulub's target lithologies and the projectile, which could have amount of soot recovered from K/T boundary sediments (imply potentially caused greenhouse warming after the dust, aerosols, 4 2 3 that the fires released ≈10 GT of CO2, ≈10 GT CH4 and 10 GT and soot settled to the ground. Significant CO2, CH, and H2O

CO, which is equal to or larger than the amount of CO2 produced were added to the atmosphere. Some of these components came from vapourised target sediments. This likely had a severe effect directly from target materials. These include carbonates, which on the global carbon cycle (Figure 25a). liberate CO2 when vaporised, and also includes hydrocarbons, the remainder of which has subsequently migrated into cata- Dust and aerosols in the atmosphere; Calculations suggest that clastic dykes beneath the crater and impact breccias deposited dust and sulphate aerosols from the impact event, and soot from along the Campeche Bank (e.g. Cantarell field). Water was liber- post-impact wildfires, caused surface temperatures to fall by pre- ated from the saturated sedimentary sequence and the overlying venting sunlight from reaching the surface where it was needed ocean (the lesser of the two sources). for photosynthesis. The base of the marine food chain, com- posed of photosynthetic plankton, collapsed. Slight increases or The residence times of gases like CO2 are greater than those of decreases in average water temperatures cannot extinguish pho- dust and sulphate aerosols, so greenhouse warming may have tosynthetic plankton, nor the presence or absence of organisms occurred after a period of cooling. Estimates of the magnitude of higher up the food chain. Photosynthesisers are primarily affect- the heating vary considerably, from an increase of global mean ed by the availability of their energy source, light. Consequent- average temperature of 1 to 1.5 °C (based on estimates of CO2 ly, the loss of photosynthetic plankton following the Chicxulub added to the atmosphere by the impact) to ≈7.5 °C (based on impact event is evidence that sunlight was significantly blocked, measures of fossil leaf stomata). whether it was by dust, soot, aerosols, or some other agent. Local and regional effects; The local and regional effects of The timescale for particles settling through the atmosphere the impact were enormous. Tsunamis radiated across the Gulf range from a few hours to approximately a year (Figure 25a, b). of Mexico, crashing onto nearby coastlines, and also radiated The time needed for the bulk of the dust to settle out of the atmo- farther across the proto-Caribbean and Atlantic basins. Tsunamis sphere is ambiguous, however, because the size distribution of were 100 to 300 m high when they crashed onto the gulf coast the dust is unclear. Some sites seem to be dominated by spherules and ripped up sea floor sediments down to water depths of 500 ≈250 μm in diameter, which would have settled out of the atmo- m. The Gulf of Mexico region was also affected by the high-en- sphere within hours to days. However, if there is a substantial ergy deposition of impact ejecta, density currents, and seismical- amount of submicron material, then it may remain suspended in ly-induced slumping of coastal sediments following magnitude the atmosphere for many months. Soot, if it were able to rise into 10 earthquakes. Tsunamis may have penetrated more than 300 the stratosphere, would have taken similarly long times to settle. km inland. The local landscape (both continental and marine) Soot that only rose into the troposphere, however, would have was buried beneath a layer of impact ejecta that was several hun- been flushed out of the atmosphere promptly by rain. dred meters thick near the impact site and decreased with radial distance. Peak thicknesses along the crater rim may have been The dust, aerosols, and soot caused surface cooling after the 600 to 800 m. Along the Campeche bank, 350 to 600 km from brief period of atmospheric heating that immediately followed Chicxulub, impact deposits of ≈50 to ≈300 m are logged in the the impact. The magnitude of that cooling is unclear, however, Cantarell boreholes. because the opacity generated by the three components is un- certain and their lifetime in the atmosphere is also uncertain. Impact events also produce shock waves and air blasts that radi- Nonetheless, significant decreases in temperature of several de- ate across the landscape. Wind speeds over 1000 km/h are pos- grees to a few tens of degrees have been proposed for at least sible near the impact site, although they decrease with distance short periods. Short-term cooling likely had a severe effect on from the impact site. The pressure pulse and winds can scour the global carbon cycle, in what is popularly termed a “nuclear soils and shred vegetation and any animals living in nearby winter’ scenario (Figure 25). ecosystems. Estimated radii of the area damaged by an air blast range from ≈900 to ≈1800 km.

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Significant heat would have been another critical regional- ef better tie down impact age, actual geographic extent of LIP em- fect. Core temperatures in the plume rising from the crater were placement, extent of evaporite breccias and evaporite volumes. over 10,000° C, possibly high enough to generate fires out to distances of 1500 to 4000 km. The intense thermal pulse would References have been relatively short-lived (5 to 10 min). Additional heat- ing and spontaneous wildfires were ignited when impact ejecta Alvarez, L. W., W. Alvarez, F. Asaro, and H. V. Michel, 1980, fell through the atmosphere (3 to 4 days; Figure 25a). Extraterrestrial Cause for the Cretaceous-Tertiary Extinction: Science, v. 208, p. 1095. The end-Cretaceous bolide impact had both short and long term effects on the Earth's climate and its atmospheric temperatures Andreev, R. Y., V. N. Apollonov, G. A. Galkin, G. M. Drugov, (Figure 25b). Over hours to days following impact, there was M. A. Zharkov, Y. G. Mashovich, A. L. Protopopov, V. F. Sa- severe atmospheric heating as ejecta rained down through the dovyi, and K. S. Khechoyan, 1986, The Potassium-Containing atmosphere. This was following by a period of weeks to years Horizons of the Nepa Basin: Soviet Geology and Geophysics, v. 27, p. 38-45. of cooler temperatures as the atmosphere was polluted by SO2, NO and soot from the impact preventing sunlight reaching the x Arndt, N., K. Lehnert, and Y. Vasil'ev, 1995, Meimechites: high- surface (nuclear winter scenario). Then, across time frame of de- ly magnesian lithosphere-contaminated alkaline magmas from cades to millennia, after the atmosphere cleared, increased CO 2 deep subcontinental mantle: Lithos, v. 34, p. 41-59. levels drove a period of global warming. The legacy of the im- pact and the biotal recovery over the next few hundred thousand Beerling, D. J., M. Harfoot, B. Lomax, and J. A. Pyle, 2007, The years is documented in a recent paper by Lowery et al., 2018. stability of the stratospheric ozone layer during the end-Perm- They showed that life reappeared in the basin just years after ian eruption of the Siberian Traps: Philosophical Transactions of the impact and a high-productivity ecosystem was established the Royal Society of London, ser. A, Mathematical and Physical within 30 kyr. Sciences, v. 365, p. 1843 –1866. Benton, M. J., and A. J. Newell, 2014, Impacts of global warm- Extinction events intensified by heating ing on Permo-Triassic terrestrial ecosystems: Gondwana Re- evaporites search, v. 25, p. 1308-1337. Evaporite salts are more chemically reactive at earth surface con- ditions than other sediments. Subsurface evaporites are prone to Black, B. A., L. T. Elkins-Tanton, M. C. Rowe, and I. U. Peate, dissolution, alteration and reprecipition from the time they first 2012, Magnitude and consequences of volatile release from precipitated and throughout their subsurface journeys in the di- the Siberian Traps: Earth and Planetary Science Letters, v. agenetic and metamorphic realms (Warren 2016). The same is 317‚Äì318, p. 363-373. true, but perhaps more so, if bedded salts are exposed to a heat Black, B. A., E. H. Hauri, L. T. Elkins-Tanton, and S. M. Brown, source outside the normal geothermal gradient experienced in 2014a, Sulphur isotopic evidence for sources of volatiles in Si- burial. Additional heat can come for the emplacement of igneous berian Traps magmas: Earth and Planetary Science Letters, v. sills, magma bodies or the hot hydrothermal circulation it drives. 394, p. 58-69. Or it can come from near instantaneous heating to thousands of degrees associated with a bolide impact. Volatile products that Black, B. A., C. A. Shields, J.-F. Lamarque, J. T. Kiehl, and L. result from this heating, as they enter the earth's atmosphere, can T. Elkins-Tanton, 2014b, Acid rain and ozone depletion from be inimical to life and include vast volumes of halocarbons, SO2, pulsed Siberian Traps magmatism: Geology, v. 42, p. 67-70. methane and CO2. Methane and CO2 come from kerogens and hydrocarbons stored in intercalated mudstones and limestones Black, B. A., B. P. Weiss, L. T. Elkins-Tanton, R. V. Veselovs- while volatilisation of carbonates can supply CO . kiy, and A. Latyshev, 2015, Siberian Traps volcaniclastic rocks 2 and the role of magma-water interactions: Geological Society of The reactivity of evaporites and the vast volumes of volatiles America Bulletin, v. 127, p. 1437-1452. released explains the intimate association of saline giants, heat- ing and the three most devastating of the five major Phanerozoic Brett, R., 1992, The Cretaceous-Tertiary extinction: A lethal extinction events. mechanism involving anhydrite target rocks: Geochimica et Cosmochimica Acta, v. 56, p. 3603-3606. Interestingly, two other events on the list of the "big five;" the Emeishan and late Devonian events (Figure 1) also have possi- Burgess, S. D., S. Bowring, and S.-z. Shen, 2014, High-preci- ble associations with heated evaporites. The Emeishan LIP in- sion timeline for Earth’s most severe extinction: Proceedings of tersects the edge of the anhydrite-rich Sichuan basin, while the the National Academy of Sciences, v. 111, p. 3316. 120km-diam., Late Devonian, Woodleigh bolide impacted the Burgess, S. D., J. D. Muirhead, and S. A. Bowring, 2017, Initial intracratonic Silurian Yaringa Fm. salts (including potash beds) pulse of Siberian Traps sills as the trigger of the end-Permian on the coast of West Australia (SaltWork GIS database version mass extinction: Nature Communications, v. 8, p. 164. 1.8 overlays, Chen et al., 2018; Glikson et al, 2005). But, before definitive conclusions can be made, more work is required to

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