Or do vi cian sea wa ter com po si tion: ev i dence from fluid in clu sions in ha lite
Fanwei MENG1, Yongsheng ZHANG2, Anatoliy R. GALAMAY3, Krzysztof BUKOWSKI4, *, Pei NI5, Enyuan XING2 and Limin JI6
1 Chi nese Acad emy of Sci ences, State Key Lab o ra tory of Paleobiology and Stra tig ra phy, Nanjing In sti tute of Ge ol ogy and Palae on tol ogy, Nanjing 210008, China
2 Chi nese Acad emy of Geo log i cal Sci ences, In sti tute of Min eral Re sources, Beijing 100037, China
3 Na tional Acad emy of Sci ences of Ukraine, In sti tute of Ge ol ogy and Geo chem is try of Com bus ti ble Min er als, Naukowa 3A, 79060 Lviv, Ukraine
4 Fac ulty of Ge ol ogy, Geo phys ics and En vi ron men tal Pro tec tion, AGH Uni ver sity of Sci ence and Tech nol ogy, Al. A. Mickiewicza 30, 30-059 Kraków, Po land
5 School of Earth Sci ences and En gi neer ing, Nanjing Uni ver sity, State Key Lab o ra tory for Min eral De pos its Re search, In sti tute of Geo-Fluid Re search, Nanjing, 210093, China
6 Chi nese Acad emy of Sci ences, Lanzhou Cen ter for Oil and Gas Re sources, In sti tute of Ge ol ogy and Geo phys ics, Lanzhou 730000, China
Meng, F., Zhang, Y., Galamay, A.R., Bukowski, K., Ni, P., Xing, E., Ji, L., 2018. Or do vi cian sea wa ter com po si tion: ev i dence from fluid in clu sions in ha lite. Geo log i cal Quar terly, 62 (2): 344–352, doi: 10.7306/gq.1409
Fluid in clu sions in ha lite can di rectly re cord the ma jor com po si tion of evap o rated sea wa ter; how ever, Or do vi cian ha lite is very rare. The Or do vi cian is a key time dur ing the evo lu tion his tory be cause pro found changes oc curred in the planet’s eco - sys tems. Ma rine life was char ac ter ized by a ma jor di ver si fi ca tion, the Great Or do vi cian Biodiversification Event and the Late Or do vi cian Mass Ex tinc tion, the first of the “big five” mass ex tinc tions. How ever, so far there is no data on the Or do vi cian sea wa ter. Data from the Or do vi cian-Si lu rian bound ary were avail able only. In this study, we re port the ma jor com po si tions from Mid dle Or do vi cian ha lite in China to give the ex act com po si tion of Or do vi cian sea wa ter. The ba sic ion com po si tion (K+, Mg2+, Ca2+, and SO42-) of in clu sion brines was es tab lished with the use of ultramicrochemical anal y sis. The data on the chem i - cal com po si tion of the brines in the pri mary in clu sions in di cated that the brines were of Na-K-Mg-Ca-Cl (Ca-rich) type, and cover a huge gap in the evo lu tion of sea wa ter chem is try. The chem i cal com po si tion of the pri mary in clu sion brine in ha lite con firmed the ear lier re sults for the Cam brian and Si lu rian ha lite orig i nat ing from other salt bas ins and the pre vi ous spec u la - tion of “cal cite sea” dur ing the Or do vi cian, in di cat ing a higher po tas sium con tent in the Lower Pa leo zoic sea wa ter than in the sea wa ter of other pe ri ods of the Phanerozoic.
Key words: Or do vi cian, fluid in clu sions, ha lite, sea wa ter com po si tion, cal cite sea.
INTRODUCTION
The in flu ence of con ti nen tal, me te or itic wa ters and ground - waters, as well as other pro cesses, on the change in the com po - si tion of ma rine brines in an cient salt bas ins is cur rently dis - cussed (e.g., Klein-BenDavid et al., 2004; Cendón et al., 2008;
Gar cia-Veigas et al., 2013). There are a num ber of ma rine bas - ins, in which the in flu ence of con ti nen tal fac tors had a sig nif i cant im pact on the change in the chem i cal com po si tion of brines (Gar cia-Veigas et al., 1995; Ayora et al., 2001; Cendón et al., 2003, 2008). There fore, the data on the chem i cal com po si tion of brines of pri mary in clu sions in ha lite are suit able for the re con - struc tion of the chem i cal com po si tion of the Phane rozoic ocean
only when the ma rine or i gin of the stud ied evaporite for ma tions is con firmed by the in de pend ent re sults of palaeogeographic, min - er al og i cal-petrographic and geo chem i cal stud ies.
To date, mod els of the chem i cal com po si tion of the Phanerozoic ocean have been de vel oped based on the chem i - cal com po si tion of the brines of pri mary in clu sions in ha lite (Kovalevich, 1990; Kovalevich et al., 1998; Lowenstein et al., 2001; Brennan and Lowenstein, 2002; Horita et al., 2002;
Kovalevych et al., 2002). These mod els rec og nized sea wa ter chem is try vari a tions chang ing be tween the Na-K-Mg-Ca-Cl (Ca-rich) type and the Na-K-Mg-Cl-SO4 (SO4-rich) type over geo logic time. The vari a tions of sea wa ter chem is try in time were cor re lated with other geo log i cal pro cesses on Earth (e.g., changes in seafloor spread ing rates, the in ten sity of mag matic pro cesses, global sea level changes; Horita et al., 2002).
Phanerozoic sea wa ter chem is try os cil lated be tween “cal cite sea” (Ca-rich and low-SO4) type and “ar agon ite seas” (SO4-rich and low-Ca) type with the change of pri mary min er al ogy of non-skel e tal lime stone (Sandberg, 1983). This is con firmed di - rectly by fluid in clu sions con tained in ma rine ha lite (Kovalevich
* Corresponding author, e-mail: buk@agh.edu.pl
Received: Received: September 19, 2017; accepted: January 26, 2018; first published online: May 8, 2018
et al., 1998; Lowenstein et al., 2001; Horita et al., 2002;
Kovalevych and Vovnyuk, 2010; Brennan et al., 2013), while late-stage pot ash salts in ma rine evaporites fluc tu ated be tween the KCl and MgSO4 types with the cal cite-ar agon ite os cil la tions (Hardie, 1996). Dur ing “cal cite seas” times (Ca-rich), evap o ra - tion and pre cip i ta tion of CaSO4 com pletely took all SO4
2 - away from the brines dur ing ha lite for ma tion, leav ing Ca2+ in ex cess in brine. Thus, the rem nant brines in fluid in clu sions of ha lite are of Na-K-Mg-Ca-Cl (Ca-rich) type, with out de tect able SO42 - (Kova - levich et al., 1998; Khmelevska et al., 2000; Petrychenko et al., 2005). The whole time, “ar agon ite seas” (SO4-rich and low-Ca), evap o ra tion and pre cip i ta tion of CaCO3 and CaSO4 took all Ca2+ away from the brines, leav ing SO42 - in ex cess dur ing the later brine evo lu tion. As a re sult, the rem nant brines in fluid in - clu sions of ha lite are of Na-K-Mg-Cl-SO4 (SO4-rich) type with out Ca2+ (Khmelevska et al., 2000; Lowen stein et al., 2001; Kovale - vych et al., 2009).
Al ter na tively to these mod els, the change in the Ca/SO4 ra - tio was ex plained as lo cal en vi ron men tal changes. Thus, sev - eral mech a nisms have been pro posed to ex plain the re moval of sul phate in evaporite bas ins: bac te rial sul phate re duc tion of dis - solved sul phate, sul phate con sump tion by cal cium-rich in flows re lated to dolomitization of base ment car bon ates, and in put of cal cium-rich hy dro ther mal infows (Ayora et al., 2001; Cendón et al., 2008; García-Veigas et al., 2011).
Or do vi cian ha lite is very rare (Valyashko, 1962; Ronov et al., 1980; Kovalevych et al., 2006b; Fig. 1). Pre vi ous data on the Or do vi cian sea wa ter chem is try come only from the up per - most Or do vi cian or Up per Or do vi cian–Lower Si lu rian de pos its of Mallowa Salt in the Can ning Ba sin, Aus tra lia (Brennan and Lowenstein, 2002; Horita et al., 2002; Kovalevych et al., 2006b). Their av er age com po si tion of brines was quite close to
the com po si tion of brines of the Early Cam brian and Late Si lu - rian bas ins, but a signifcant dif fer ence is lower po tas sium con - tent of fluid in clu sions from Mallowa Salt (Kovalevych et al., 2006b). In this pa per, we pro vide data on the sea wa ter chem is - try based on a study of fluid in clu sions from Mid dle Or do vi cian ha lite of the Ordos Ba sin in China, thereby cov er ing the gap in the pic ture of the sea wa ter chem is try evo lu tion (Kovalevich et al., 1998; Lowenstein et al., 2001; Horita et al., 2002).
GEOLOGICAL SETTING
There are sev eral Or do vi cian evaporite bas ins in the North China Plat form. One of them is the Ordos Ba sin – the sec ond larg est sed i men tary ba sin in China with an area of
~250,000 km2 (Fig. 2).Dur ing the Or do vi cian,the Ordos Ba sin
Fig. 2. Lo ca tion map of the Ordos Ba sin
Percent
Geological times
C O S D Carb P Tr J K Tert
0 1 2 3 4 5
Fig. 1. Vari a tion in abun dance of evaporite rocks through Phanerozoic time (af ter Ronov et al., 1980)
de vel oped a gently in clined car bon ate plat form in a very shal - low epi continental sea, con sist ing of car bon ates and evaporites. The Mid dle Or do vi cian evaporites of the Majiagou For ma tion de vel oped in a re stricted, shal low, and hypersaline en vi ron ment within the Mizhi De pres sion (Feng et al., 1998;
Wang and Al-Aasm, 2002; Yang et al., 2005; Li et al., 2011).
The Majiagou For ma tion con tains car bon ates and evaporites and can be di vided into six mem bers, from Majiagou Mem ber 1 to Majiagou Mem ber 6 (Ta ble 1; Bao et al., 2004). Majiagou 1, 3, 5 mem bers are mainly evaporites, and Majiagou 2, 4, 6 mem bers are mainly car bon ates (Ta ble 1).
The d34S val ues of anhydrite from Ma-5 Mem ber range from +27.1 to +28.0‰ (n = 5) (Yao et al., 2010), and co in cide with sul phur iso tope of ma rine Late Or do vi cian evaporites (mean value +25.5‰) (Fox and Videtich, 1997). These evaporites show a “bull’s eye pat tern” of fa cies as not “tear-drop pat tern”, so the ba sin was sep a rated from the outer ocean, within which a lim ited wa ter ex change ex isted, not strongly af fected by in flow of riverine wa ter (Bao et al., 2004). Our Or do vi cian ha lite sam - ples come from the Majiagou Mem ber 5 of the Majiagou For - ma tion from the Yu-9 and Zhenjia-1 bore holes, lo cated in the cen tre of the ba sin (Fig. 3).
SAMPLES AND FLUID INCLUSIONS
We have ana lysed 14 ha lite sam ples from two bore holes:
Yu-9 (n = 2) and Zhenjia-1 (n = 12). Of two sam ples from the Yu-9 bore hole – 33[34/61] and 14[2/57] – the lat ter is nearly de - void of fluid in clu sions. Pri mary and sec ond ary in clu sions were re vealed in Yu-33 [34/61] (Ma-5 Mem ber, Yu-9 bore hole), Zjy-47-21 (Ma-1 Mem ber), and Zjy-24-27 (Ma-6 Mem ber) sam - ples (Zhenjia-1 bore hole; Fig. 4).
METHODS
The anal y sis of in di vid ual brine in clu sions was car ried out by the ultramicrochemical (UMCA) method (or the method of glass cap il lar ies) of Petrichenko (1973). The method can de ter - mine the con tent of ma jor ions (K, Mg, Ca and SO4) in brine in - clu sions (ex cept for Na and Cl) with an er ror of ~20%. The method has been used to ana lyse the an cient sea wa ter chem - is try from fluid in clu sions of ha lite (e.g., Kovalevich et al., 1998;
Kovalevich et al., 2002; Galamay et al., 2003; Kovalevych et al., 2005, 2006a, b, 2009; Meng et al., 2014).
Chem i cal com po si tion of in clu sion brine was stud ied in pri - mary fluid in clu sions of Zjy-47-21 sam ple only (Ta ble 2) be - cause the rest of in clu sions were too small for UMCA anal y sis;
only ~50–100 mm in clu sions were used for anal y ses.
The fol low ing meth od ol ogy was ap plied for es tab lish ing Br– and Cl– con cen tra tions: firstly, the pure ha lite sam ples were dis - solved in pure dis tilled wa ter, fol lowed by ox i da tion by chlor - amines T and chromogenesis achieved us ing fluorescein. In weak acid so lu tions, a chem i cal re ac tion be tween Br– and fluorescein pro duces a strong ab sorp tion peak at 510 nm wave - length, which was mea sured us ing a VIS7200 spectro photo - meter (Tan et al., 2006).
For chlo rine iso to pic anal y sis, we care fully se lected pure frag ments of ha lite crys tals (with Cl– con tent ~10 mg/mL) un der a ste reo scopic mi cro scope. These were dis solved in high-pu rity wa ter pro duced by sub-boil ing dis til la tion. Sec ondly, we passed
the sam ple so lu tion through a Ba-resin col umn to re move in ter - Fig. 3. The lithostratigraphy of drill cores from the Yu-9 and Zhenjia-1 bore holes
T a b l e 1 The stra tig ra phy of Or do vi cian car bon ate and evaporitic rocks of the east ern Ordos Ba sin (af ter Bao et al., 2004)
Stra tig ra phy
Thick ness [m]
Li thol ogy Geo log i cal ages For ma tion Mem ber
Car bon if er ous Benxi up per part is dark grey mudstone interbedded with
coarse-grained lithic quartzose sand stone; basal part is grey ish bauxitic mudstone
Or do vi cian
Majiagou
Ma 6 0–10 micrite, ab sent in most area of the east ern Ordos Ba sin Ma 5 220–350 up per part is silty do lo mite* and micrite, and lower part is ha lite,
anhydrite interbedded with silty do lo mite
Ma 4 120–180 mostly micrite with do lo mite
Ma 3 80–150 silty do lo mite, ha lite and anhydrite
Ma 2 50–110 silty do lo mite, ar gil la ceous do lo mite and do lo mite con tain ing anhydrite
Ma 1 20–80 silty do lo mite, ha lite and anhydrite
Liangjiashan–Yeli 0–150 silty do lo mite con tain ing chert beds or nod ules
Cam brian Fengshan silty do lo mite and spatulate** dolostone
*fol low ing Ren et al. (2017: fig. 2f)
**in Chi nese lit er a ture on the Ordos Ba sin, ”spatulate” is used for a char ac ter is tic tex ture (see Lu et al., 2017: fig. 4)
Fig. 4. The rem nant pri mary fluid in clu sions in Or do vi cian ha lite from the Majiagou For ma tion of North China A – ha lite from the Yu-9 bore hole; B – ha lite from the Zhenjia-1 bore hole
T a b l e 2 Con cen tra tions of ma jor com po nents in pri mary fluid in clu sions of Or do vi cian ha lite
Sam ple
Con cen tra tion, g/l (mean value in the pa ren the ses)
K+ Mg2+ Ca2+ SO42-
Zjy-47-21 21.4; 23.1; 21.6; 17.3 (20.9) 35.9; 39.2; 48.6; 41.5 (41.3) 49.8; 76.0; 55.4; 74.6; 69.1; 71.6 (66.1) <0.5 Mod ern sea wa ter sat u rated with re spect to:
Ha lite* 3.9 12.6 0.22 17.6
Sylvite** 33.8 75.7 – 79.1
* af ter McCaffrey et al. (1987); ** af ter Valyashko (1962)
fer ing SO42 - ions, and sub se quently passed it through an H-resin col umn to re move cat ions and con vert the Cl– into HCl. Fi nally, a pure CsCl so lu tion was pro duced by pass ing the pure HCl so - lu tion through Cs-resin. This could then be ana lysed by mass spec trom e try, us ing ef fec tively the same meth ods as de scribed by Vengosh et al. (1989), Xiao and Zhang (1992) and Xiao et al.
(1995). Mea sure ments were per formed us ing a VG 354 ther - mal ion iza tion mass spec trom e ter (Tan et al., 2006). The de ter - mi na tions of sta ble chlo ride iso tope con tent were per formed on two ha lite sam ples from the Yu-9 bore hole (sam ples 14[2/57]
and 33[34/61]).
RESULTS
The tested ha lite crys tals are large and clear. Large fluid in clu sions (>100 µm) oc cur within trans par ent ha lite crys tals of sam ple 33[34/61]. In the cen tral parts, they pre serve some par al lel growth bands in ter preted as pri mary fluid in clu sions in chev rons (Fig. 4). On the pe riph ery of chev ron ha lite crys - tals there are large liq uid in clu sions. They are ar ranged with - out any reg u lar ity. Their shapes are close to cu bic or ir reg u lar and the size var ies from 0.2 to 1 mm (Fig. 5). Al though these trans par ent parts of ha lite can form af ter sed i men tary stage (dur ing diagenesis), the co-ex ist ing pri mary fluid in clu sions in the cen tral por tions of crys tal im ply that the ha lite was recrystallized at a very shal low depth. Ho mog e ni za tion tem - per a ture of fluid in clu sions of sparry cal cite fill ing pores of dolomites from Majia gou For ma tion range from 49–74°C, and in di cates recry stalliza tion be low 170 m (Zhang et al., 1997; Feng et al.,1998).
The ma jor ion com po si tion of in clu sion brines has been de - ter mined in the pri mary fluid in clu sions of sam ple Zjy-47-21 (Zhenjia-1 bore hole) and in the sec ond ary fluid in clu sions of sam ples Yu-33[34/61] (Yu-9 bore hole) and Zjy-24-57 (Zhenjia-1 bore hole). In the re main ing sam ples, there were not enough in clu sions of suit able sizes to carry out UMCA stud ies.
The Ca2+ and Mg2+ con cen tra tions were de ter mined in brines from banded pri mary fluid in clu sions of sam ple Zjy- 47-21. In the brine from six in clu sions, the mean Ca2+ con cen - tra tion was 66.1 g/l (from 49.8 to 76.0 g/l). The mean Mg2+ con -
cen tra tion was 41.3 g/l (from 35.9 to 48.6 g/l), and the mean K+ con cen tra tion was 20.9 g/l (from 17.3 to 23.1 g/l) (Ta ble 2).
The Ca2+ and Mg2+ con cen tra tions were also de ter mined in brines from large sec ond ary in clu sions lo cated in the outer edge of chev ron ha lite crys tals. The pres ence of K-Mg salt min - er als in the in clu sions pro vides the ev i dence of high con cen tra - tion of par ent brines (Ta ble 3). The Ca2+ con cen tra tion was from 77.8 to 140.4 g/l, Mg2+ from 36.2 to 63.2 g/l, and the mean K+ con cen tra tion var ied from 20.0 to 35.7 g/l (Ta ble 3).
The Br con tent in Or do vi cian ha lite is from 163 ppm (sam ple 14[2/57]) to 249 ppm (sam ple 33[34/61]). The Br con tent of nor - mal sea-orig i nated ha lite ranges from 50 to 100 ppm, and in - creases to a max i mum value of 277 ppm at the on set of bit tern pre cip i ta tion (Valyashko, 1956). Thus, the Br con tents in the Or - do vi cian im ply that the evap o ra tion pro cess can be near to bit - tern pre cip i ta tion. It is also con firmed by pot ash min er als trapped within in clu sions.
The d37Cl val ues ob tained for the Or do vi cian ha lite were –0.36 and +0.24‰ (Ta ble 4).
DISCUSSION
In ha lite sam ples, both pri mary and sec ond ary in clu sions were found. Pri mary fluid in clu sions are microdroplets of brine, trapped dur ing crys tal growth. These in clu sions were usu ally ar - ranged in bands lo cated par al lel to crys tal growth faces (Fig. 4).
Sec ond ary fluid in clu sions are usu ally large and can have a cu - bic shape and oc cur in di vid u ally out side the pri mary struc tures (Fig. 5A). This kind of large fluid in clu sions formed in early stages of diagenesis and their ma jor ion com po si tions can be sim i lar to those of pri mary fluid in clu sions. There are also sec - ond ary large-size and ir reg u lar in clu sions (Fig. 5B) and they are typ i cal for recrystallized ha lite (Roedder et al., 1987; Kovalevich et al., 1998).
Pre vi ous stud ies (Roedder et al., 1987; La zar and Hol land, 1988; Bein et al., 1991; Kovalevich et al., 1998) showed that recrystallized ha lite, which orig i nally pre cip i tated from SO4-rich brines, could con tain in clu sions of two chem i cal as sem blages:
SO4-rich and Ca-rich. There fore, the oc cur rence of sec ond ary SO4-rich in clu sions also in di cates that the ba sin brines and sea -
Fig. 5. Sec ond ary fluid in clu sions from the Yu-9 bore hole
A – in clu sion on the pe riph ery of a sed i men tary struc ture of ha lite; B – large multi-phase in clu sion with nu mer ous anisotropic crys tals (anhydrite?) within clear, recrystallized ha lite
wa ter were SO4-rich. In turn, en tirely Ca-rich sec ond ary in clu - sions sug gest that the ba sin brines and sea wa ter were Ca-rich.
We have to stress that the study of sec ond ary in clu sions does not al low for es ti ma tion the ion ra tios of con tem po ra ne ous brines and sea wa ter (Kovalevych et al., 2006a).
The pri mary min er al ogy of non-skel e tal car bon ate rocks and other ev i dences im ply the Or do vi cian sea wa ter should be of Na-K-Mg-Ca-Cl (Ca-rich) type and have a high Ca con tent (Sandberg, 1983; Kovalevich et al., 1998; Lowenstein et al., 2001). The spec u la tion has no other ev i dence; how ever, the fluid in clu sions in ha lite can pro vide the di rect ev i dence.
The Mg+2 con cen tra tion in an cient sea wa ter was in a di rect re la tion with SO42 - con cen tra tion and in an in verse re la tion with Ca+2 con cen tra tion. This kind of re la tion caused sig nif i cant changes of the Mg+2/Ca+2 ra tio in sea wa ter. The max i mum Mg+2/Ca+2 ra tios for the sea wa ter of “cal cite sea” times (rich in Ca and poor in SO4), such as Cam brian, Si lu rian, and Cre ta - ceous, were found di rectly by the mea sure ment of ma jor com - po si tions of fluid in clu sions (Kovalevich et al., 1998; Lowenstein et al., 2001). The new data from pri mary fluid in clu sions of Or - do vi cian ha lite in di cate that Mid dle Or do vi cian sea wa ter was un doubt edly Ca-rich with the mo lar ra tio Mg+2/Ca+2 = 1.03 (for me dium val ues). These re sults are con sis tent with pre vi ous cal - cu la tions con sid er ing the Mg+2/Ca+2 mo lar ra tio in Or do vi cian sea wa ter at ~1.0 (Lowenstein et al., 2001).
The d37Cl val ues of Or do vi cian ha lite in this study were -0.36 and +0.24‰. Be cause all pub lished d37Cl data for ma rine evaporites fall within a nar row range of 0.0 ±0.5‰ (Eastoe et al., 2007 with ref er ences), we con clude that d37Cl val ues con firm a ma rine, or i gin of Or do vi cian salts of the Majiagou For ma tion.
CONCLUSIONS
Fluid in clu sions in Or do vi cian ma rine ha lite pro vide di rect ev i dence of Ca-rich Or do vi cian sea wa ter (cal cite sea) with Na-K-Mg-Ca-Cl com po si tion. This study cov ers a huge gap on the evo lu tion of sea wa ter chem is try. A se ries of the bit tern pre - cip i tates of late-stage pot ash salts in Or do vi cian ma rine evaporites is of KCl type (dom i nated by sylvite lack ing pri mary MgSO4 salts). The brines from the sec ond ary in clu sions, lo - cated in the trans par ent parts of chev ron ha lite and/or in the pe - riph er ies of crys tals, showed a higher con tent of po tas sium and cal cium than the brines from the pri mary in clu sions. Based on our anal y sis of the chem i cal com po si tion of the brines of the Cam brian, Or do vi cian and Si lu rian salt bas ins (Ta ble 5), we could as sume a higher po tas sium con tent in the Lower Pa leo - zoic sea wa ter.
T a b l e 3 Con cen tra tions of ma jor com po nents in sec ond ary fluid in clu sions of ha lite from Or do vi cian ha lite
Fluid in clu sion, No.
Con cen tra tion, g/l (mean val ues
in brack ets)
Re marks
K+ Mg2+ Ca2+ SO42-
Yu-9 bore hole, sam ple 33[34/61]
1 –* 63.2 136.9; 132.5; 151.7 (140.4) <0.5 in clu sion with sylvite daugh ter crys tal
2 – – 87.9; 75.8 (81.9) <0.5 gas + liq uid in clu sions
3
18.6; 21.4 (20.0)
33.0** – – <0.5 sylvite oc cu pies ~1.3 vol% of the in clu sion
4
26.6; 22.8 (24.7)
35.7** – – <0.5 sylvite oc cu pies ~1.1 vol% of the in clu sion
5 – 42.4; 32.3
(37.4)
124.5; 81.2; 111.5; 118.7;
98.9 (106.9) <0.5 in clu sion with sylvite daugh ter crys tal 6
21.2 31.2**
43.0; 29.3
(36.2) 131.2; 121.0 (126.1) <0.5 sylvite oc cu pies ~1 vol% of the in clu sion Zhenjia-1 bore hole, sam ple Zjy-24-57
1
21.2; 22.8 (22.0)
34.0** 37.1 65.5; 73.2; 94.8 (77.8) <0.5 sylvite oc cu pies ~1.2 vol% of the in clu sion
* not de ter mined; ** cal cu lated value, based on vol ume of sylvite daugh ter crys tal
T a b l e 4 Con tent of bro mine, chlo ride and d37Cl of the Or do vi cian ha lite sam ples from the Ordos Ba sin
Sam ple d37Cl Er ror SD (n = 3) Cl [mass frac tion, %] Br [ppm]
Yu-9 bore hole 14[2/57] 0.24 0.15 60.34 163
Yu-9 bore hole 33[34/61] –0.36 0.09 60.31 249
The d37Cl val ues of chlo ride iso topes of Or do vi cian ha lite are close to 0.0‰ and can be ex plained by the pre cip i ta tion from ma rine brines. These val ues are com pat i ble with those mea sured in ear lier stud ies of other Phanerozoic ma rine ha lite.
Our re sults re corded mod er ately high bro mine con tents (163 pp and 249 ppm) for pri mary ha lite and sup port the con clu sion on the ma rine gen e sis of these salts, close to the be gin ning of bit - tern crys tal li za tion.
Ac knowl edge ments. This re search was sup ported by Na - tional Nat u ral Sci ence Foun da tion of China (Nos: 41473039 and 4151101015), AGH grant No. 11.11.140.320 (to KB) and Bu reau of In ter na tional Co-op er a tion, Chi nese Acad emy of Sci - ences. We thank D.I. Cendón and S. Shekhunova for their crit i - cal com ments.
T a b l e 5 Av er age con cen tra tions of ma jor com po nents in pri mary fluid in clu sions of ha lite from the Cam brian, Îrdovician
and Si lu rian de pos its (ha lite pre cip i ta tion stage)
Lo ca tion Pe riod, time
Age [Ma]
Ion content [g/l] Jänecke unit [mol %]
N/n* Ref er ences
K+ Mg2+ Ca2+ SO42- K Mg Ca SO4
Mich i gan Ba sin, Sa lina Fm., USA
S2,
Ludlowian ~420 413**
(14.4)
1264**
(27.3) 831**
(29.7) <0.5 9.0 54.9 36.1 – 41/46 Brennan and Lowenstein
(2002) Ordos Ba sin,
Majiagou Fm., China O2 ~470 20.9 41.3 66.1 <0.5 7.4 47 45.6 – 1/3 Our data
East Si be rian Ba sin, Angara Fm., Rus sia
Î1,
Toyonian ~516 20.2 35.5 50.1 <0.5 8.7 49.2 42.1 – 5/13 Petrichenko
et al. (2005) East Si be rian Ba sin,
Belsk Fm., Rus sia Î1,
Botomanian ~515–519 20.7 46,8 59.1 <0.5 7.2 52.6 40.2 – 1/5 Petrichenko
et al. (2005) East Si be rian Ba sin,
Usolsk Fm., Rus sia
Î1, Atdabanian Tommotian
~519–530 23.3 33.9 52.6 <0.5 9.9 46.4 43.7 – 5/5 Petrichenko
et al. (2005) Modern sea wa ter concentrated to the be gin ning of pre cip i ta tion of:
Ha lite 3.9 12,6 0.22 17.6 6.7 68.9 – 24.4 McCaffrey et al. (1987)
Epsomite 26.1 85,9 – 115.0 – McCaffrey et al. (1987)
Sylvite 33.8 75,7 – 79.1 -– Valyashko (1962)
*N/n – ra tio of the num ber of re sults in cluded into ta ble (N) to the over all num ber of stud ied sam ples (n)
**Val ues in millimoles/kg H2O; in brack ets – cal cu lated ap prox i mate value in g/l
Fig. 6. Com po si tions of fluid in clu sions in ha lite from Cam - brian, Mid dle Or do vi cian and Si lu rian salts in the Mg-2K-SO4
and Mg-Ca-2K Jänecke di a grams at 25° (di a grams af ter Eugster et al., 1980: fig. 9)
SW – mod ern sea wa ter sat u rated with re spect to ha lite (af ter McCaffrey et al., 1987), SW’ – an cient sea wa ter (ΖC, J–K)
sat u rated with re spect to ha lite (af ter Kovalevich, 1990)
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