Geological note: Pyro‐intrusive veins in the northeastern Sydney Basin

Stratigraphic and sedimentological investigation of the interglacial succession within the Cryogenian-aged Umberatana Group of the Northern and Central Flinders Ranges reveals a complex array of sedimentary successions lying between the Sturtian and Marinoan glacial deposits. The Sturtian–Marinoan Series boundary was first defined from the Adelaide area at the uppermost contact of the Brighton Limestone. In the Northern Flinders Ranges the Sturtian–Marinoan Series boundary has been positioned at the uppermost contact of the Balcanoona Formation, which is thought to correlate with the Brighton Limestone. In the Northern Flinders Ranges a major unconformity separates the Sturtian and Marinoan-aged sedimentary successions (Nepouie–Upalinna Subgroups). In moderately deep marine depositional settings, this submarine unconformity is located at the base of the Yankaninna Formation where erosion has deeply incised (up to 300 m) into the underlying Tapley Hill Formation. In shallower marine settings the unconformity is found at the base of the Weetootla Dolomite. In very deep water depositional settings this unconformity is not recognised, and the Yankaninna Formation appears to conformably overlie the Tapley Hill Formation suggesting that this erosional feature is restricted to shallow and moderately deep depositional settings. This unconformity presents a regionally persistent chronostratigraphic marker horizon, which reliably marks the Sturtian–Marinoan Series boundary at the base of the Yankaninna Formation from shallow shelfal to deep-water basinal settings throughout the Northern Flinders Ranges. In the Central Flinders Ranges the post-Sturtian glacial stratigraphy records a very similar depositional record to that observed in the Northern Flinders Ranges. In the Central regions the Tapley Hill Formation is overlain by deep-marine carbonates and calcareous shales of the Wockerawirra Dolomite and Sunderland Formations, respectively. The base of the Wockerawirra Dolomite is found to be in erosional contact with the underlying Tapley Hill Formation. This stratigraphic relationship, together with lithological similarities, indicates the Wockerawirra Dolomite and Sunderland Formation of the Central Flinders Ranges are lateral correlatives of the Yankaninna Formation of the Northern Flinders Ranges. The regional nature of the Sturtian–Marinoan unconformity in the Adelaide Geosyncline suggest the possible existence of a glacio-eustatic event that may correlate with glacials/glaciation elsewhere on the Earth during the Cryogenian.     

Nature and significance of the Neoproterozoic Sturtian–Marinoan Boundary,Northern Adelaide Geosyncline,South Australia

The Cryogenian succession of the Northern Flinders Ranges reveals a complex sedimentary record between the Sturtian and Marinoan glacial deposits. A major unconformity separates the Sturtian and Marinoan-aged sedimentary successions in the area. This forms a subaerial erosion surface with terrestrial and marginal marine infill directly above the Angepena and Balcanoona Formations in their respective localities. This exposure surface is here correlated with the previously documented submarine unconformity between the Yankaninna Formation and the underlying deep marine Tapley Hill Formation. This erosional event provides a chronostratigraphic marker horizon that coincides approximately with thepreviously defined Sturtian–Marinoan Time Series boundary in the Northern Flinders Ranges. These stratigraphic relationships also constrain lateral facies relationships between the Oodnaminta ReefComplex (Balcanoona Formation) and the Angepena Formation. Similarly, the shallow-water Weetootla Dolomite is correlated with the deeper water carbonates of the Yankaninna Formation.     

由伊利石结晶度研究桂西右江地区区域极低级变质作用

运用伊利石结晶度Kübler指数将桂西右江地区下三叠统罗楼群和中三叠统百逢组下段划归为浅层变质带(K.I△2θ°为0.22～0.25);将中三叠统百逢组上段和河口组划归为近变质带,中三叠统百逢组上段为高级近变质带(K.I△2θ°为0.26～0.33);中三叠统上部河口组为低级近变质带(K.I△2θ°为0.38～0.40),不排除局部为成岩带的可能.地层柱自下向上,伊利石结晶度Kübler指数由小变大,变质程度由高变低,而且,变质作用级别与岩层在地层柱中位置协调以及变质带边界与地层界线趋于一致,证明为区域埋藏极低级变质作用.凌云明山金矿区剖面矿体和百逢组各层段伊利石结晶度Kübler指数为0.42～0.50,属成岩带,且没有明显时空变化规律.     

Carbonate petrography, kerogen distribution, and carbon and oxygen isotope variations in an early Proterozoic transition from limestone to iron-formation deposition, Transvaal Supergroup, South Africa

The transition zone comprises Campbellrand microbialaminated (replacing "cryptalgalaminate") limestone and shale, with minor dolomite, conformably overlain by the Kuruman Iron Formation of which the basal part is characterized by siderite-rich microbanded iron-formation with minor magnetite and some hematite-containing units. The iron-formation contains subordinate intraclastic and microbialaminated siderite mesobands and was deposited in deeper water than the limestones. The sequence is virtually unaltered with diagenetic mineral assemblages reflecting a temperature interval of about 110 degrees to 170 degrees C and pressures of 2 kbars. Carbonate minerals in the different rock types are represented by primary micritic precipitates (now recrystallized to microsparite), early precompactional sparry cements and concretions, deep burial limpid euhedral sparites, and spar cements precipitated from metamorphic fluids in close contact with diabase sills. Paragenetic pathways of the carbonate minerals are broadly similar in all lithofacies with kerogen intimately associated with them. Kerogen occurs as pigmentation in carbonate crystals, as reworked organic detritus in clastic-textured carbonate units, and as segregations of kerogen pigment around late diagenetic carbonate crystals. Locally kerogen may also be replaced by carbonate spar. Carbon isotope compositions of the carbonate minerals and kerogen are dependent on their mode of occurrence and on the composition of the dominant carbonate species in a specific lithofacies. Integration of sedimentary, petrographic, geochemical, and isotopic results makes it possible to distinguish between depositional, early diagenetic, deep burial, and metamorphic effects on the isotopic compositions of the carbonate minerals and the kerogen in the sequence. Major conclusions are that deep burial thermal decarboxylation led to 13C depletion in euhedral ferroan sparites and 13C enrichment in kerogen (organic carbon). Metamorphic sparites are most depleted in 13C. Carbonates in oxide-rich iron-formations are more depleted in 13C than those in siderite-rich iron-formation whereas the kerogens in oxide banded iron-formations (BIF) are more enriched. This implies that the siderite-rich iron-formations were not derived from oxide-rich iron-formation through reduction of ferric iron by organic matter. Organic matter oxidation by ferric iron did, however, decrease the abundance of kerogen in oxide-rich iron-formation and led to the formation of isotopically very light sparry carbonates. Siderite and calcmicrosparite both represent recrystallized primary micritic precipitates but differ in their 13C composition, with the siderites depleted in 13C by 4.6 per mil on average relative to calcmicrosparite. This means that the siderites were precipitated from water with dissolved inorganic carbon depleted in 13C by about 9 per mil relative to that from which the limestones precipitated. This implies an ocean system stratified with regard to total carbonate, with the deeper water, from which siderite-rich iron-formation formed, depleted in 13C. Iron-formations were deposited in areas of very low organic matter supply. Depletion of 13C may, therefore, derive not from degradation of organic matter but from hydrothermal activity, a conclusion which is supported by 18O composition of the carbonate minerals and trace element and rare earth element (REE) compositions of the iron-formations.     

Interglacial carbonates of the Cryogenian Umberatana Group,northern Flinders Ranges,South Australia

A detailed sedimentological and chronostratigraphic analysis of the Umberatana Group in the northern Adelaide Geosyncline has uncovered a depositional history involving the rapid progradation (at least 20 km) of a giant reef complex (up to 1.1 km relief) during mid-Cryogenian interglacial times. The reef complex, which occurs in the Balcanoona Formation, displays facies similar to Phanerozoic reefs. These include a basal forereef (slope) facies, overlain by a reef-margin facies (consisting of both stromatolitic and non-stromatolitic frameworks), and an upper backreef (platform) facies consisting of shallow-water peloidal and oolitic carbonate. The thickening of the reef complex in a basinward direction, and the distribution of the key facies are consistent with the progradation of the platform into deep water. Progradation was contemporaneous with deposition of the upper Tapley Hill Formation and had largely ceased after a major margin failure event. Following this event, reef growth continued for a short time before becoming extinct, possibly as a result of global climatic cooling and/or eustatic sea-level fall.     

Structural geometry and controls on basement‐involved deformation in the northern Flinders Ranges,Adelaide Fold Belt,South Australia

In the northern Flinders Ranges, Neoproterozoic and Cambrian sedimentary rocks were deformed and variably metamorphosed during the ca 500 Ma Cambro‐Ordovician Delamerian Orogeny. Balanced and restored structural sections across the northern Flinders Ranges show shortening of about 10–20%. Despite the presence of suitable evaporitic detachment horizons at the basement‐cover interface, the structural style is best interpreted to be thick‐skinned involving basement with only a minor proportion of the overall shortening accommodated along stratigraphically controlled detachments. Much of the contractional deformation was localised by the inversion of former extensional faults such as the Norwest and Paralana Faults, which both controlled the deposition of Neoproterozoic cover successions. As such, both faults represent major, long‐lived structures which effectively define the present boundaries of the northern Flinders Ranges with the Gawler Craton to the west and the Curnamona Craton to the east. The most intense deformation, which resulted in exhumation of the basement along the Paralana Fault to form the Mt Painter and Babbage Inliers, coincides with extremely high heat flows related to extraordinarily high heat‐production rates in the basement rocks. High heat flow in the northern Flinders Ranges suggests that the structural style not only reflects the pre‐Delamerian basin architecture but is also a consequence of the reactivation of thermally perturbed, weakened basement.     

Diagenesis and Very Low‐grade Metamorphism of the Upper Permian Yangjiagou Formation in Eastern Changchun,China: Evidence from Clay Mineral Geothermobarometers

The metamorphic conditions of the Upper Permian Yangjiagou Formation in eastern Changchun, China, were evaluated based on the mineral assemblage, illite crystallinity, illite polytypism,the b dimension of illite, and the chemical composition of chlorite. The pelitic rocks in the Yangjiagou Formation are characterized by illite + kaolinite + chlorite ± mixed-layer chlorite/smectite and detrital quartz + plagioclase. Illite in the formation has a crystallinity of 0.38-0.55 and comprises mixed 2 M_1 and1 M_d polytypes, indicating a metamorphic temperature of 200℃. Based on the chemical composition of chlorite and the chlorite geothermometer, we estimated diagenetic to very low-grade metamorphic conditions with temperatures of 185℃～204℃. The b dimension of illite varies from 8.992 A to 9.005 A.We used a mathematical algorithm to extend Guidotti and Sassi's(1986) diagram relating illite b dimension with temperature and pressure, and used this diagram, together with illite crystallinity and chlorite chemical composition, to semi-quantitatively estimate the formation pressure at1.2 kbar. These reveal that the Yangjiagou Formation has experienced very low-grade metamorphism.     

Zones of Progressive Regional Burial Metamorphism in Part of the Tasman Geosyncline, Eastern Australia

A succession of metamorphic zones can be recognized along theMolong Geanticline, an ancient rise within the Tasman Geosynclineof Eastern Australia. In order of increasing grade, the zonesin the volcanogenic rocks are: (1) an albite-quartz zone, containingneither prehnite, pumpellyite, actinolite, nor biotite; (2)a prehnite zone; (3) a prehnite-pumpellyite zone; (4) an actinolitezone; and (5) a biotite zone. Zeolite associations are not developed.Zones 4 and 5 lie within the greenschist facies. The rocks alongthis geanticline are generally only slightly deformed, lackingcleavage. The grade of this metamorphism within the Molong Geanticlineincreases partly in accordance with increasing stratigraphicdepth and partly increases eastwards towards the adjacent HillEnd Trough. Within the Trough, rocks show metamorphic assemblagesakin to those of Zones 4 and 5 as defined within the MolongGeanticline, but deformation is more extreme and a regionalcleavage is characteristic. In the region about the Hill EndTrough and the adjacent geanticlines there is an apparent variationfrom essentially static burial metamorphism of the geanticlinesthrough transitional types to tectonic dynamothermal metamorphismof the trough. Both metamorphisms are envisaged as having arisenduring the same general period of metamorphism, but deformationof the geanticlines was much less than deformation in the interveningHill End Trough.     

广西百色盆地干酪根的研究--兼探干酪根的演化与粘土矿物的关系

本文用X射线、微区分析等方法对广西百色盆地那读三段泥岩中的干酪根进行了详细研究,该盆地干酪根的芳香度（Fa）为0.28至0.37,芳香核厚度（Le）为16.60A到20.76A,芳香片层数（n）为5到6层,证明属Ⅱ型干酪根,在同一剖面,fa随深度增加而变大,表明了干酪根向成熟方向转化。在干酪根中碳元素的分布是不均匀的,一般中间含量高,向边部则含量变低,铁及硅元素也向中间聚集,多数情况下形成FeS₂核,在核的周围分布有粘土矿物。干酪根成熟程度的变化趋势与粘土矿物的演化趋势在宏观上是一致的,即与蒙脱石转化为伊/蒙混层粘土矿物的趋势一致。并从化学健和能量方面对这种过程进行了一些探讨。     

Late cainozoic environments of part of Northeastern South Australia∗

In the Lake Frome area of South Australia there is a sedimentary sequence of non‐marine (or possibly distant marginal marine) pale‐green to grey, fine elastics and carbonates (Namba Formation). The base of these deposits is Medial Miocene in age and they are overlain unconformably by Pleistocene (and ? Pliocene) sediments. The Miocene sequence is equivalent to the Etadunna Formation of the Lake Eyre Basin, and the clay mineralogy is similar.

Combining evidence from mineralogy, palynology, and vertebrate palaeontology, a warm high‐rainfall climate operating on a subdued topography is indicated for the lower part of the Miocene Lake Frome sequence. This caused the illite‐chlorite‐kaolinite suite of the largely Precambrian provenance to be transformed to smectite and randomly‐interstratified clay. A palygorskite‐dolomite assemblage accumulated in alkaline lakes of extreme marginal marine situation during periods of seasonal dry intervals superposed on the previous climate.

A change to illite‐dominated clay, stratigraphically about halfway up the sequence, occurred simultaneously with initial uplift of the Flinders Ranges. These ranges were previously represented by, at the most, a region of low hills. Uplift, without intervention of climatic change, is sufficient to alter the clay mineralogy by promoting increased leaching. Higher in the sequence, and correlated with the major phase of uplift in the Flinders Ranges, smectite re‐appears. In this case the clay suite is believed to have resulted from increased aridity. The smectite‐rich sediments accumulated above the water table in extensive fan and mud‐flow deposits.

The Neogene sequence records a major palaeogeographic change from low energy rivers, swamps, and lakes in a low relief terrain, probably connected to the sea, to a landscape approaching that of the present during Miocene‐Pliocene times. When the Pleistocene Millyera Formation accumulated, the landscape resembled the present, though the ancestral Lake Frome was larger, and rainfall higher.     

Illite Crystallinity Mapping of Very Low Grade Metamorphism of Triassic Metapelites in the Zoigê Area, Western China

X-ray diffraction methods for estimating the metamorphic grade of diagenetic, anchizone and epizone in metapelites are reviewed and applied to samples from a 7000?m+ borehole in western China and surface samples from the surrounding Zoigê area. Kübler’s illite crystallinity (IC) measurements provide more consistent results than calculated values of percentage of illite in the I/S mixed layers and percentage of I/S mixed layers. Down-borehole IC values display a typical burial metamorphic relationship between stratigraphic level and IC. A method for preparing very low grade metamorphic maps is described, and isograds plotted on a regional geological map at selected values of IC, delineating a high temperature diagenetic zone, an anchizone, and an epizone. The map shows that IC values are controlled by stratigraphic level in the north of the study area (i.e. burial metamorphism), and proximity to an igneous intrusive body in the south (i.e. contact metamorphism).     

江苏南部区域航磁异常特征及其地质意义

以江苏南部1∶50万航磁资料为基础,通过对区内岩矿石磁性特征的归纳与分析,对区内航磁异常形成的地质因素作了讨论,并对区内航磁异常进行了分类、分区及地质解释。通过进一步对区内航磁资料的数据处理,对区内深变质磁性基底面的埋深、形态特征及其地质意义作了讨论,对区内构造岩基带平面分布及垂向分布特征,特别是对长江断裂带也一并作了推断解释。     

Paleoproterozoic gold deposits in the Bald Hill and Coyote areas, Western Tanami, Western Australia

Significant gold deposits in the western Tanami region of Western Australia include deposits in the Bald Hill and Coyote areas. The ca. 1,864 Ma Bald Hill sequence of turbiditic and mafic volcanic rocks hosts the Kookaburra and Sandpiper deposits and a number of smaller prospects. The ca. 1,835 Ma turbiditic Killi Killi Formation hosts the Coyote deposit and several nearby prospects. The Kookaburra deposit forms as a saddle reef within a syncline, and the Sandpiper deposit is localized within graphitic metasedimentary rocks along a limb of an anticline. Gold in these deposits is hosted by anastomosing quartz–(–pyrite–arsenopyrite) veins within quartz–sericite schist with disseminated arsenopyrite, pyrite, and marcasite (after pyrrhotite). Based on relative timing relationships with structural elements, the auriferous veins are interpreted to have been emplaced before or during the ca. 1,835–1,825 Ma Tanami Orogeny (regional D₁). Gold deposition is thought to have been caused by pressure drops associated with saddle reef formation (Kookaburra) and chemical reactions with graphitic rocks (Sandpiper). The Coyote deposit, the largest in the western Tanami region, consists of a number of ore lenses localized along the limbs of the Coyote Anticline, which formed during the Tanami Orogeny. The largest lenses are associated with the Gonzalez Fault, which is located along the steeply dipping southern limb of this fold. Gold was introduced at ca. 1,790 Ma into dilatant zones that formed in local perturbations along this fault during later reactivation (regional D₅) towards the end of a period of granite emplacement. Gold is associated with quartz–chlorite–pyrite–(arsenopyrite–galena–sphalerite) veins with narrow (<?5 mm) chloritic selvages. A quartz–muscovite–biotite–K–feldspar–(tourmaline–actinolite–arsenopyrite) assemblage, which is interpreted to relate to granite emplacement, overprints the regional greenschist facies metamorphic assemblage. The mineralogical similarity between this overprinting assemblage and the vein assemblage suggests that the auriferous veins at the Coyote deposit are associated with the granite-related metamorphic–metasomatic assemblage. Gold deposition is thought to have been caused by pressure drops within dilatant zones.     

A comparison of the lead phosphates from the Oxidised Zone,broken hill ore body,with those of some other Australian localities

A method of using the X‐ray fluorescence spectrometer has been adopted for the analyses of lead phosphates, and eight samples of phosphates from Broken Hill and three from the Flinders Ranges, South Australia, were analysed by this means. Of these, five were found to be mimetite and six pyromorphite, several being rich in calcium. Dividing the sources into geochemical areas we find that the specimens from Broken Hill have no vanadium and a low alkaline metal earth content while those from the Flinders Ranges have a small, but noticeable vanadium content and high alkaline metal earth content. A poorer X‐ray diffraction fit of a calcium‐rich mimetite to the hexagonal structure indicates that the monoclinic structure could be of more importance in the members of this composition.     

利用干酪根热解动力学模拟实验研究塔里木盆地下古生界古地温

通过热解动力学模拟实验，对塔里木盆地塔参1井奥陶系干酪根的热演化过程进行了模拟，以此基础上利用KINETICS软件求取干酪根镜质体反射率（R0）的生成动力学参数，并结合塔参1井的沉积埋藏史，计算塔参1井寒武－奥陶系的古地温，这对于研究塔里木盆地下古生界高过成熟烃源岩的古地温是一种新方法。     

South Australian earthquakes, 1980–92

The seismicity of South Australia over the period 1980–92 is presented as a follow‐up to earlier studies. The South Australian seismic network has undergone a significant expansion in the last decade, and with it an increase in the number and precision of located earthquakes. The distribution of recent seismic activity is similar to the historical pattern of earthquakes and the previous instrumental seismicity maps, all of which show the three main areas as being the Flinders‐Mt Lofty Ranges, Eyre Peninsula, and the southeast. The one notable exception in the recent study is the presence of earthquake activity in the Musgrave Block, a previously aseismic region. Intensity characteristics are reported for earthquakes that were sufficiently widely felt. Fault plane solutions for three Flinders Ranges earthquakes (previously unpublished) are also presented; the focal mechanisms are consistent with predominant northeast‐southwest compression. The seismic moment method was used to estimate the seismic risk for the major population centres in terms of probability of exceedance of seismic intensity within a given period. These estimates are based on the recurrence parameters and intensity attenuation function for the region. The results place Adelaide close to the AS2121 ‐ 1979 Earthquake Code Zone I/Zone 2 boundary.     

Variation of illite/muscovite <Superscript>40</Superscript>Ar/<Superscript>39</Superscript>Ar age spectra during progressive low-grade metamorphism: an example from the US Cordillera

⁴⁰Ar/³⁹Ar step-heating data were collected from micron to submicron grain-sizes of correlative illite- and muscovite-rich Cambrian pelitic rocks from the western United States that range in metamorphic grade from the shallow diagenetic zone (zeolite facies) to the epizone (greenschist facies). With increasing metamorphic grade, maximum ages from ⁴⁰Ar/³⁹Ar release spectra decrease, as do total gas ages and retention ages. Previous studies have explained similar results as arising dominantly or entirely from the dissolution of detrital muscovite and precipitation/recrystallization of neo-formed illite. While recognizing the importance of these processes in evaluating our results, we suggest that the inverse correlation between apparent age and metamorphic grade is controlled, primarily, by thermally activated volume diffusion, analogous to the decrease in apparent ages with depth observed for many thermochronometers in borehole experiments. Our results suggest that complete resetting of the illite/muscovite Ar thermochronometer occurs between the high anchizone and epizone, or at roughly 300 °C. This empirical result is in agreement with previous calculations based on muscovite diffusion parameters, which indicate that muscovite grains with radii of 0.05–2 μm should have closure temperatures between 250 and 350 °C. At high anchizone conditions, we observe a reversal in the age/grain-size relationship (the finest grain-size produces the oldest apparent age), which may mark the stage in prograde subgreenschist facies metamorphism of pelitic rocks at which neo-formed illite/muscovite crystallites typically surpass the size of detrital muscovite grains. It is also approximately the stage at which neo-formed illite/muscovite crystallites develop sufficient Ar retentivity to produce geologically meaningful ⁴⁰Ar/³⁹Ar ages. Results from our sampling transect of Cambrian strata establish a framework for interpreting illite/muscovite ⁴⁰Ar/³⁹Ar age spectra at different stages of low-grade metamorphism and also illuminate the transformation of illite to muscovite. At Frenchman Mtn., NV, where the Cambrian Bright Angel Formation is at zeolite facies conditions, illite/muscovite ⁴⁰Ar/³⁹Ar data suggest a detrital muscovite component with an apparent age ≥967 Ma. The correlative Carrara Fm. is at anchizone conditions in the Panamint and Resting Spring Ranges of eastern California, and in these locations, illite/muscovite ⁴⁰Ar/³⁹Ar data suggest an early Permian episode of subgreenschist facies metamorphism. The same type of data from equivalent strata at epizone conditions (greenschist facies) in the footwall of the Bullfrog/Fluorspar Canyon detachment in southern Nevada reveals a period of slow-to-moderate Late Cretaceous cooling.     

Structural changes of young kerogen during laboratory heating as revealed by alkaline potassium permanganate oxidation

Kerogen was isolated from a marine sediment from Tanner Basin, offshore California. Samples of the kerogen were heated under an inert atmosphere at various temperatures and times. The heated and unheated kerogens were subjected to alkaline potassium permanganate oxidation followed by GC/ MS analysis of the products. The kerogens yielded primarily aliphatic C₂–C₁₄ α,ω-dicarboxylic acids and benzene mono-to-pentacarboxylic acids. Yields of aliphatic dicarboxylic acids from kerogen decreased with increasing thermal alteration. Yields of benzenecarboxylic acids increased steadily with increasing thermal alteration. The data support the concept that thermal maturation during natural burial of this type of kerogen results in the generation of aliphatic hydrocarbons from an increasingly aromatic residue.     

Note on the palaeoenvironmental significance of the nuccaleena formation (upper Precambrian), central Flinders Ranges,South Australia

Four distinct sedimentary facies have been recognized within the upper Precambrian Nuccaleena Formation in the central Flinders Ranges of South Australia. Three dolomite facies, containing tepee structures within either well‐laminated or stromatolitic dolomite, were deposited within supratidal and intertidal environments, whilst an interbedded shale and dolomite facies originated under very shallow submerged conditions.     

Kerogen-mineral reactions at raised temperatures in the presence of water

Kerogen has been artificially matured under “hydrous pyrolysis” conditions in the presence of various minerals in order to investigate the influence of the latter on the organic products. In addition to three clay minerals (montmorillonite, illite, kaolinite), calcium carbonate and limonite were also employed as inorganic substrates. Kerogen (Type II) isolated from the Kimmeridge Blackstone band was heated in the presence of water and a 20-fold excess of mineral phase at two different temperatures (280 and 330°C) for 72 hr. Control experiments were also carried out using kerogen and water only and kerogen under anhydrous conditions. This preliminary study describes the bulk composition of the pyrolysates with detailed analyses of the aliphatic hydrocarbon distributions being provided by gas chromatography and combined gas chromatography-mass spectrometry.In the 280°C experiments, considerably more organic-soluble pyrolysate (15% by weight of original kerogen) was produced when calcium carbonate was the inorganic phase. At 330°C, all samples generated much greater amounts of organic-soluble products with calcium carbonate again producing a large yield (40% wt/wt). Biomarker epimerisation reactions have also proceeded further in the 330°C pyrolysate formed in the presence of calcium carbonate than with other inorganic phases. Implications of these and other observations are discussed.