西藏青草山斑岩铜金矿床含矿斑岩锆石U-Pb年代学及岩石成因

西藏青草山Cu-Au矿床是班公湖-怒江缝合带北侧新发现的具有大型远景的斑岩型矿床,但该矿床含矿斑岩的年龄、成因及源区一直未得到有效的约束.对青草山花岗闪长岩以及含矿花岗岩闪长斑岩进行了锆石年代学、Hf同位素以及岩石地球化学研究.结果显示,花岗闪长岩与含矿花岗闪长斑岩的侵入时代分别为131.2±0.3 Ma与117.9±0.8 Ma,代表了班公湖-怒江缝合带早期的成岩作用以及斑岩Cu-Au成矿作用.二者具有相似的地球化学特征,表明二者可能具有相同的岩浆源区,是不同时期同源岩浆活动的产物.结合含矿花岗闪长斑岩锆石Hf同位素组成,认为青草山含矿斑岩形成于班公湖-怒江洋壳向北俯冲过程中,是下地壳部分熔融的产物,受到了少量地幔物质的混合.      

西藏多龙矿集区地堡Cu(Au)矿床含矿斑岩锆石U-Pb测年、Hf同位素组成及其地质意义

西藏多龙矿集区地堡铜(金)矿位于班公湖—怒江缝合带北侧,羌塘地块南缘,是多龙矿集区中具有较好找矿前景的斑岩—浅成低温热液矿床。本文首次对地堡含矿斑岩进行LA-ICP-MS锆石U-Pb测年、微量元素和Hf同位素分析。含矿斑岩23个锆石点测试,获得锆石~(206)Pb/~(238)U加权平均值年龄为122.0±2.5Ma(MSWD=0.34),与多龙矿集区成矿岩浆活动时限一致,是多龙矿集区的重要组成部分。锆石微量元素特征揭示地堡含矿斑岩中锆石为岩浆锆石,锆石Ti温度计计算出其结晶温度为663~850℃,平均为765℃,其岩浆源区可能经历了水饱和条件下的部分熔融作用。Hf同位素分析结果表明,地堡含矿斑岩锆石n(~(176)Hf)/n(~(177)Hf)值相对较高,为0.282726~0.283054,ε_(Hf)(t)为1.1~12.6,均为正值,其物质来源有幔源组分的加入,可能为壳幔混源的新生下地壳。     

西藏铁格隆南超大型铜(金、银)矿含矿斑岩岩石成因及其对多龙地区早白垩世成矿动力学机制的启示

铁格隆南是西藏多龙矿集区新发现的超大型斑岩-浅成低温热液型铜(金、银)矿床。作为班公湖-怒江成矿带西段早白垩世重大成矿事件的典型代表,铁格隆南矿床以及整个多龙矿集区的含矿斑岩岩石成因及成矿动力学机制仍存在明显争议。本文以铁格隆南矿床为核心,基于详细的矿床地质特征和岩石学特征,利用锆石的SHRIMP U-Pb年代学厘定花岗闪长斑岩侵位时代为121. 2±2. 4Ma,与区域早白垩世含矿斑岩岩浆侵位时间一致。同时,详细的岩石地球化学分析表明,铁格隆南矿床及多龙矿集区,含矿斑岩以花岗闪长斑岩为主,含少量闪长玢岩和花岗斑岩,属于高钾-钙碱性或钾玄岩系列,富集轻稀土和大离子亲石元素(Rb、Ba、U),亏损重稀土及高场强元素(Nb、Ta、Ti),具典型的弧岩浆特征。此外,其岩石地球化学特征及Sr-Nd-Pb-Hf同位素组成揭示,含矿斑岩的岩浆源区可能与俯冲板片流体交代的富集岩石圈地幔部分熔融有关。最后,详细的岩石学"探针"及区域岩浆活动特征表明,多龙矿集区白垩世重大成矿作用动力学机制与班公湖-怒江洋北向俯冲板片的折返(130～110Ma)有关。     

西藏班公湖—怒江成矿带斑岩-浅成低温热液型矿床岩浆作用与成矿:以改则县东窝东铜多金属矿床为例

西藏改则县东窝东铜多金属矿床位于西藏多龙矿集区东部,是近年来班公湖—怒江成矿带上新发现的铜多金属矿。对区内花岗闪长斑岩和花岗斑岩进行了LA-ICP-MS锆石U-Pb年代学测试显示,成岩年龄为(121.0±1.2)Ma和(121.5±1.0)Ma,与多龙矿集区内成岩成矿年龄相近。研究区含矿斑岩显示了富集轻稀土和大离子亲石元素,亏损重稀土和高场强元素,中等Eu负异常,高铝、低镁、低钛,高Sr、低Y及Yb的岛弧岩浆岩特征,暗示矿区含矿岩浆与多龙矿集区含矿岩浆具备相同的岩浆源区。矿区含矿斑岩的锆饱和温度介于779.6~844.5℃,地球化学数据显示高Sr低Nd及低εNd(t)值特征;含矿斑岩εHf(t)为+3.4~+11.1,两阶段模式年龄T2DMC为467~963 Ma;表明其与多龙矿区含矿斑岩具备相似的Sr-Nd-Hf同位素特征,暗示了矿区含矿斑岩是班公湖—怒江特提斯洋洋壳向北俯冲消减背景下,由玄武质新生下地壳在较高温度条件下部分熔融形成的产物,指示班公湖—怒江洋盆于早白垩世晚期尚未关闭。野外地质调查发现,矿区发育典型斑岩铜矿蚀变分带;具备与多龙矿集区的岩石组成、矿化及蚀变、成岩成矿时代、构造环境和物质来源相类似的特征,且空间位置相近,暗示两者受控于统一的构造-岩浆成矿系统。综合分析认为,东窝东地区为多龙矿集区东延部分,具有寻找斑岩-浅成低温热液型铜(金)矿床隐伏矿体的良好潜力。     

拉萨地块北部~90Ma斑岩型矿床年代学及成矿地质背景

近年来青藏高原多个大型—超大型斑岩Cu-Mo-Au矿床的发现已引起人们广泛的关注,现有研究显示这些含矿斑岩和斑岩型矿床的形成年龄主要集中在120～110Ma、～90Ma、54～45Ma和18～12Ma4个阶段,其中90Ma左右的斑岩型矿床的成矿地质背景仍存在很大争议。本文报道拉萨地块北部尼玛县拔拉扎斑岩型矿床含矿斑岩的LA-ICPMS锆石U-Pb定年以及辉钼矿Re-Os定年结果,并分析了该期的成矿地质背景。两件花岗闪长斑岩锆石206Pb/238U加权平均年龄分别为92.1±1.2Ma、93.8±1.2Ma,代表了岩浆的结晶时代;而辉钼矿Re-Os模式年龄为88.2～89.6Ma,代表了拔拉扎矿床的成矿年龄。依据区域地质资料,本文认为拉萨地块北部～90Ma岩浆活动和成矿作用既不可能是雅鲁藏布江结合带所代表的新特提斯洋平板俯冲或洋脊俯冲的产物,也不可能是班公湖-怒江洋盆南向俯冲消减直接的产物,而很可能是班公湖-怒江洋盆俯冲消减闭合之后碰撞过程的产物。因此本文认为拉萨地块中北部地区～90Ma的岩浆作用及其成矿作用是形成于碰撞的构造背景。     

黑龙江鹿鸣钼矿区花岗质杂岩锆石U-Pb年龄、Hf同位素、辉钼矿Re-Os年龄及其地质意义

鹿鸣超大型钼矿(钼金属量89万吨,平均品位0.084%)产于小兴安岭-张广才岭成矿带北段,矿体呈细脉浸染状赋存于二长花岗斑岩和二长花岗岩体内,围岩蚀变有钾化、绢云母化、硅化、绿泥石化、碳酸盐化等,矿化类型主要为斑岩型矿化。鹿鸣矿区含矿岩体二长花岗斑岩和二长花岗岩的锆石U-Pb定年、Hf同位素及辉钼矿Re-Os同位素定年研究表明:二长花岗岩和二长花岗斑岩锆石的U-Pb年龄分别为186.8±2.1Ma和183.2±1.9Ma,形成于燕山早期,二长花岗斑岩晚于二长花岗岩。6个样品辉钼矿Re-Os等时线年龄为176.7±4.4Ma(MSWD=0.92),Re含量变化于30×10-6~49×10-6。二长花岗岩的锆石εHf(t)值变化于1.1~3.8,Hf单阶段模式年龄为729Ma,两阶段模式年龄为1055Ma;二长花岗斑岩的锆石εHf(t)值变化于0.4~5.9,Hf单阶段模式年龄为741Ma,两阶段模式年龄为1075Ma。研究表明成矿与二长花岗斑岩有关,并且二长花岗岩和二长花岗斑岩岩浆为中新元古代新生的地壳物质熔融的产物,成岩成矿作用与古太平洋板块俯冲作用(或佳木斯与松嫩地块的拼合)有关。     

西藏班公湖-怒江成矿带西段拿厅斑岩Cu(Au)矿床的火成岩岩石成因与成矿物质来源

位于西藏班公湖-怒江成矿带西段多龙矿集区内的拿厅斑岩Cu(Au)矿床是近年来开展勘查取得重大找矿突破的矿床之一,控制Cu资源量已达到大型规模。但目前对该矿床的地质特征、成矿岩石成因及成矿物质来源还缺乏深入的了解和研究。本文基于系统的野外地质观察、岩相学研究,结合精细的锆石SIMS U-Pb定年、锆石Hf-O同位素、岩石地球化学和蚀变-矿石矿物的H-O-S同位素分析,认为该矿床是形成于121～118Ma的斑岩型Cu(Au)矿床,与多龙Cu(Au)矿集区内多不杂、波龙、拿顿、色那、拿若和铁格隆南(荣那)矿床为同一期岩浆-热液成矿事件,其成岩-成矿峰期为120～118Ma。拿厅斑岩铜(金)矿床成矿岩体显示轻稀土富集的分配型式和缺少Eu异常,且富集大离子亲石元素(如Rb、Ba等),而亏损高场强元素(如Nb、Ta等),显示弧岩浆的特征,形成于班公湖-怒江洋向北俯冲的大陆边缘弧背景。锆石Hf-O同位素模拟结果显示,矿区早期的安山-英安质次火山岩(ε_(Hf)(t)=-2. 0～10. 3;δ~(18)O=5. 07‰～6. 77‰)具有早期幔源岩浆和经历MASH过程混入壳源的岩浆(10%～20%壳源物质)的特征;而二长花岗斑岩和成矿花岗闪长斑岩(ε_(Hf)(t)=1. 7～3. 3;δ~(18)O=6. 40‰～6. 95‰)则是MASH过程逐渐演化(壳源-幔源混合,约20%～40%壳源物质)的产物。在形成拿厅斑岩铜金矿成矿岩浆的过程中,没有发生陆壳加厚的过程;岩浆演化过程中有较少斜长石分离结晶,主要为角闪石和钛铁氧化物结晶分异。另外,热液蚀变(石英、磁铁矿)和硫酸盐-硫化物(硬石膏、黄铜矿、黄铁矿)的H-O-S同位素结果显示,拿厅成矿流体和成矿物质主要来源于岩浆,与岩浆流体出溶过程密切有关。     

西藏多龙矿集区与蒙古国Ulaan Khajuu铜矿区花岗岩类主量元素特征

多龙矿集区位于特提斯—喜马拉雅成矿域班公湖—怒江(陆缘岩浆杂岩)成矿带西段,已普查多不杂(SBZ)、波龙(BL)两个大型矿床。可继续开展普查工作的还有尕尔勤(DL)斑岩铜金矿、拿若斑岩铜金矿、拿顿金矿、铁格隆斑岩铜矿、地堡那木岗斑岩铜金矿、赛角等多个矿床(点)。最近对蒙古国西部Ulaan Khajuu铜矿区(以下简称UK铜矿区)进行了考察,本文仅就这2个地区花     

哀牢山构造带南段扭只二长花岗斑岩地球化学特征及其锆石U-Pb年代学研究

本文对云南墨江县扭只二长花岗斑岩进行了锆石U-Pb年代学、岩石地球化学分析。LA-ICP-MS锆石U-Pb测年显示扭只二长花岗斑岩年龄为(263.5±1.7)Ma,形成于晚二叠世。岩石地球化学分析显示:扭只二长花岗斑岩Si O2含量为55.30%~74.37%,全碱(Na2O+K2O)含量2.56%~7.57%,且Na2OK2O;岩石富集轻稀土,负铕异常明显(δEu:0.74~1.06),相对富集Sc、Co、Cs、As等元素,亏损Cr、Ni、Zn、Rb、Sr、Ba、Zr、Ta、Th、U、W等元素。根据图解显示扭只二长花岗斑岩形成于岛弧向陆陆碰撞或者陆弧碰撞的构造环境,表明哀牢山构造带的古特提斯支洋或弧后盆地在晚二叠世((263.5±1.7)Ma)可能已经闭合。     

Study on Yanshanian metallogenic granitoids magmatism in Baoshan deposit,southern Hunan ProvinceSCIEI北大核心CSCD

本文对湘南宝山花岗闪长斑岩进行了系统的锆石和磷灰石U-Pb定年、岩石地球化学以及锆石Hf同位素研究,并探讨了宝山花岗闪长斑岩的岩石成因和构造意义。锆石和磷灰石的LA-ICP-MS U-Pb定年显示,宝山花岗闪长斑岩的成岩年龄为160Ma。综合元素和同位素地球化学证据,宝山花岗闪长斑岩的成因可能为新生地壳与古老地壳的混合熔融,同时宝山花岗闪长斑岩中发现的890±20Ma的继承锆石,验证了新元古代新生地壳的参与。磷灰石的主微量元素研究显示花岗闪长斑岩具有较高的氧逸度和Cl含量,Sr/Th比值具有较大变化,而La/Sm比值变化不大等特征,表明形成花岗闪长斑岩岩浆的母岩受到俯冲板片脱水形成的流体交代作用影响。在上述过程中,富含Cl和H2O的流体从板片中释放出来,引发地幔楔熔融,并对矿床中成矿金属元素进行提取。由于古太平洋板块俯冲引发的伸展-减薄运动,在地幔上涌过程中,新元古代新生地壳发生部分熔融,这些高温岩浆底侵老地壳源区,诱发老地壳部分熔融,进而发生了强烈的壳-壳混合作用,产生花岗闪长质岩浆。     

Police, politics, and the right to the city

Space and spatiality have recently been at the core of debates concerning the political possibilities of the city. The arguments advanced in this paper might be seen as an attempt to contribute to these debates through a reflection on the spatiality of (in) justice, politics, and the right to the city. The case of French urban policy, with its focus on distressed urban areas, and the `suburban problem' in France are used as examples to make arguments more concrete.     

Isotopic systematics of He,Ar, S,Cu, Ni,Re, Os,Pb, U,Sm, Nd,Rb, Sr,Lu, and Hf in the rocks and ores of the Norilsk deposits

This paper reports the first results of a study of 11 isotope systems (³He/⁴He, ⁴⁰Ar/³⁶Ar, ³⁴S/³²S, ⁶⁵Cu/⁶³Cu, ⁶²Ni/⁶⁰Ni, ⁸⁷Sr/⁸⁶Sr, ¹⁴³Nd/¹⁴⁴Nd, ^206–208Pb/²⁰⁴Pb, Hf–Nd, U–Pb, and Re–Os) in the rocks and ores of the Cu–Ni–PGE deposits of the Norilsk ore district. Almost all the results were obtained at the Center of Isotopic Research of the Karpinskii All-Russia Research Institute of Geology. The use of a number of independent genetic isotopic signatures and comprehensive isotopic knowledge provided a methodic basis for the interpretation of approximately 5000 isotopic analyses of various elements. The presence of materials from two sources, crust and mantle, was detected in the composition of the rocks and ores. The contribution of the crustal source is especially significant in the paleofluids (gas–liquid microinclusions) of the ore-forming medium. Crustal solutions were probably a transport medium during ore formation. Air argon is dominant in the ores, which indicates a connection between the paleofluids and the atmosphere. This suggests intense groundwater circulation during the crystallization of ore minerals. The age of the rocks and ores of the Norilsk deposits was determined. The stage of orebody formation is restricted to a narrow age interval of 250 ± 10 Ma. An isotopic criterion was proposed for the ore-bearing potential of mafic intrusions in the Norilsk–Taimyr region. It includes several interrelated isotopic ratios of various elements: He, Ar, S, and others.     

Delivery of Trace Metals (Al,Fe, Mn,V, Co,Ni, Cu,Cd, Ag,Pb) from the Trinity River Watershed Towards the Ocean

The Trinity River (Texas, USA) contains in its watershed 23 different reservoir lakes, the largest one being Lake Livingston situated in the lower Trinity River watershed and two potentially polluting metroplexes, Dallas and Houston. In order to determine fluxes of nutrients and trace metals to Galveston Bay, a survey that included 24 discreet samples collected over a year and at various stages of discharge was carried out during 2000–2001. Geochemical (i.e., sorption by Fe oxyhydroxides), biological (i.e., seasonal uptake by sinking algae in Lake Livingston), and hydrological (i.e., dilution effects by increasing flow rates) controls were found to be mainly responsible for variations in dissolved trace metal concentrations rather than pollution sources. The Trinity River loads of suspended sediments and pollutant trace metals entering Galveston Bay at Anahuac were <20% of those reaching Lake Livingston, and only a few percent of the total upstream trace metal load is entering the Gulf of Mexico. Thus, during the transit through the 23 man-made lakes and an estuary, >96% of the pollutant trace metal load is lost to sediments.     

Composition,formation conditions,and genesis of the Talatui gold deposit,the Eastern Transbaikal Region,Russia

The mineral composition of the Talatui gold deposit has been studied with modern methods. Previously unknown minerals (ilmenite, siegenite, glaucodot, wittichenite, matildite, hessite, pilsenite, zircon, tremolite, cummingtonite, hercynite, and goethite) have been identified in the ore. A high Re content has been detected in molybdenite. The spatiotemporal separation of Au and Ag is caused by different mineral species of these elements and their diachronous precipitation during the ore-forming process. Gold crystallized along with early mineral assemblages, beginning from virtually pure gold (the fineness is 996). Silver precipitated largely at the end of the process as hessite (Ag₂Te) and matildite (AgBiS₂). The temperature of ore deposition varied from 610 to 145°C, the pressure was 3370–110 bar, and the salt concentration ranged from 56.3 to 0.4 wt % NaCl equiv. The heterogeneous state (boiling) of fluid at the early stages has been documented. The chemical and isotopic compositions of the fluid testify to its magmatic nature and the participation of meteoric water at late stages in the ore-forming process. Thermodynamic modeling reproduces the main specific features of ore formation, including separation of Au and Ag. A physicochemical model of the gold mineralization in the Darasun ore district has been proposed. On the basis of several attributes, the Talatui deposit has been referred to the prophyry gold-copper economic type.     

Influences of the unsaturated,saturated, and riparian zones on the transport of nitrate near the Merced River,California, USA

Transport and transformation of nitrate was evaluated along a 1-km groundwater transect from an almond orchard to the Merced River, California, USA, within an irrigated agricultural setting. As indicated by measurements of pore-water nitrate and modeling using the root zone water quality model, about 63% of the applied nitrogen was transported through a 6.5-m unsaturated zone. Transport times from recharge locations to the edge of a riparian zone ranged from approximately 6 months to greater than 100 years. This allowed for partial denitrification in horizons having mildly reducing conditions, and essentially no denitrification in horizons with oxidizing conditions. Transport times across a 50–100-m-wide riparian zone of less than a year to over 6 years and more strongly reducing conditions resulted in greater rates of denitrification. Isotopic measurements and concentrations of excess N₂ in water were indicative of denitrification with the highest rates below the Merced River. Discharge of water and nitrate into the river was dependent on gradients driven by irrigation or river stage. The results suggest that the assimilative capacity for nitrate of the groundwater system, and particularly the riverbed, is limiting the nitrate load to the Merced River in the study area.     

扬子北缘马元铅锌矿床闪锌矿微量元素及S-Pb-He-Ar-C同位素地球化学研究

马元铅锌矿床是近年扬子陆块北缘铅锌找矿的新突破。矿体呈层状、似层状产于碑坝隆起翼部震旦系灯影组角砾状白云岩层间构造带中,围岩蚀变很弱。矿石中硫化物以闪锌矿、方铅矿为主,中粗粒晶质结构,充填于白云岩角砾间。闪锌矿富集Cd、Ge、Ag,贫In、Tl、Se,Ga/In为6~132,Ge/In多1000,成矿温度以中-低温为主。金属硫化物ε~(34)S值相对集中,为12.9‰~19.4‰,平均为17.4‰,来自于海相硫酸盐的还原。铅同位素组成稳定,~(206)Pb/~(204)Pb为17.858~17.918:~(207)Pb/~(204)Pb为15.603~15.694;~(208)Pb/~(204)Pb为37.756~38.046,具有造山带和上地壳铅的特征,震旦系可能提供了金属成矿物质。闪锌矿中流体包裹体的~3He/~4He为0.03Ra~1.05Ra,~(40)Ar/~(36)Ar为326.1~765.1,~(38)Ar/~(36)Ar为0.183~0.204,表明成矿流体主要为地壳流体和饱和大气水(大气降水或海水)的混合。闪锌矿内流体包裹体挥发分δ~(13)C_(CH_4)值为-36.01‰~-28.80‰,δ~(13)C_(C_2H_6)值为-27.72‰~-22.44‰,δ~(13)C_(CO_2)值为-23.24‰~-9.68‰,表明有机流体参与了成矿作用。石英、方解石的H-O同位素结果表明具有海水和有机水混合的特征。可见,成矿流体具有两种流体混合的特征,一为蒸发海水与围岩反应所形成的盆地卤水,二为有机流体。推测矿区可能存在一个古油气藏,由于TSR生成一高硫气藏,为区内还原性有机流体的主要来源。当富含Pb、Zn等成矿物质的成矿流体运移至富含CH_4和H_2S的还原性流体的矿区角砾岩带时,两种流体混合,Pb、Zn等遇到H_2S发生反应而沉淀成矿,并伴生热液白云石等,形成了马元铅锌矿床。综上所述,我们认为马元矿床属MVT型铅锌矿床。     

Rb-Sr, K-Ar, H-and O-Isotope systematics of the Middle Riphean shales from the Debengda Formation, the Olenek Uplift, North Sibera

Clay subfractions (SFs) of <0.1, 0.1–0.2, 0.2–0.3, 0.3–0.6, 0.6–2 and 2–5 μm separated from Middle Riphean shales of the Debengda Formation are studied using the TEM, XRD, K-Ar and Rb-Sr isotopic methods. The oxygen and hydrogen isotope compositions in the SFs are studied as well. The low-temperature illite-smectite is dominant mineral in all the SFs except for the coarsest ones. The XRD, chemical and isotopic data imply that two generations of authigenic illite-smectite different in age are mixed in the SFs. The illite crystallinity index decreases in parallel with size diminishing of clay particles. As compared to coarser SFs, illite of fine-grained subfractions is enriched in Al relative to Fe and Mg, contains more K, and reveals higher K/Rb and Rb/Sr ratios. The Rb-Sr age calculated by means of the leachochron (“inner isochron”) method declines gradually from 1254-1272 Ma in the coarsest SFs to 1038-1044 Ma in finest ones, while the K-Ar age decreases simultaneously from 1225–1240 to 1080 Ma. The established positive correlation of δ¹⁸O and δD values with dimensions of clay particles in the SFs seems to be also consistent with the mixing systematics. The isotopic systematics along with data on mineral composition and morphology lead to the conclusion that mixedlayer illite-smectite was formed in the Debengda shales during two periods 1211–1272 and 1038–1080 Ma ago. The first period is likely close to the deposition time of sediments and corresponds to events of burial catagenesis, whereas the second one is correlative with the regional uplift and changes in hydrological regime during the pre-Khaipakh break in sedimentation.     

Breakthroughs in the biodiversity, biogeography, biostratigraphy, and basin analysis of the Beaufort group

Over the past decade researchers working on the rocks of the Beaufort Group in the main Karoo Basin of South Africa have vastly increased our understanding of this important Permo-Triassic sequence. Many new fossil forms have been discovered, allowing for breakthroughs into the biodiversity, biogeography and biostratigraphy of the group. Taxonomic and phylogenetic advances are many and varied, and cover most of the vertebrate taxa, but with emphasis placed on the temnospondyl amphibians, archosauriforms and non-mammalian synapsids, in particular the anomodontia. Biostratigraphic breakthroughs have centered on the Middle Permian Eodicynodon and Tapinocephalus assemblage zones, the Late Permian Dicynodon Assemblage Zone, and the Triassic Lystrosaurus and Cynognathus assemblage zones. Correlation of these biozones with better dated sequences in Europe, Russia and China has allowed for many chronostratigraphic refinements, which are in turn vital for sequence stratigraphical analysis of the basin fill. Based on fossil data, both the lower (Ecca–Beaufort) and upper (Beaufort–Molteno) contacts of the group have been proved to be highly diachronous. The refined chronostratigraphic framework has also allowed for a better analysis of the basin evolution through time, particularly in terms of the correlation of external stimuli that affect basin sedimentation patterns.