Source Rock Deposition Research Articles

RELATIONSHIP BETWEEN PETROLEUM COMPOSITION AND DEPOSITIONAL ENVIRONMENT OF PETROLEUM SOURCE ROCKS FROM THE GULF OF SUEZ AND THE WESTERN DESERT OF EGYPT

ABSTRACT Crude oils from the Gulf of Suez and the North Western Desert of Egypt have been analyzed for geochemical biomarkers using GC and GC-MS techniques. The biomarker compositions of the crude oils have been used to differentiate crude oils of non-marine, normal marine and marine carbonate sources. The geochemical features of Zaafarana crude oil from the Gulf of Suez Basin indicate a marine carbonate depositional setting. One crude oil from Budran however, possesses geochemical characteristics consistent with an origin from source rock deposited in normal marine conditions. Bahar and Morgan show normal marine source rock deposition environment with terrigenous organic matter input. On the other hand, the crude oils from the North Western Desert have bulk and biomarker characteristics cosistent with non-marine depositional setting, with the exception of one oil sample which appears to have a mixed marine/terrestrial sources. The presence of oleanane in some of these oils suggests source rocks deposited in deltaic or near shore environment in Post Cretaceous Basin.

OCCURRENCE AND DISTRIBUTION OF BICYCUC AND TRICYCLIC AROMATIC HYDROCARBONS IN CRUDE OILS FROM THE GULF OF SUEZ, EGYPT

ABSTRACT The distribution patterns of methylhomologs of naphthalene and phenanthrene in five crude oils from the southern part of the Gulf of Suez, Egypt, have been examined by quantitative capillary gas chromatography (GC) and computerized gas chromatography/mass spectrometry (GC/MS). In general, the relative abundance of individual naphthalenes and phenanthrenes were not significantly different in the five oil samples. Correlation between the source rock deposition and the abundance of specific methylnaphthalene and melhylphenanthrene isomers are consistent with a marine type source materials for the analyzed Gulf of Suez oils. Maturity parameters based on methylnaphthalene and methylphenanthrene isomers were almost identical and are consistent with an advanced stage of maturity. Further, calculated vitrinite reflectance (Re) confirmed that the sediments have a range of maturity within the “oil window”.

Abstract: Sedimentology, Mineralogy and Organic Geochemistry of Pre-Salt Formations, Congo Basin, West Africa: Implications for the Deposition of Lacustrine Source Rocks

Abstract: Sedimentology, Mineralogy and Organic Geochemistry of Pre-Salt Formations, Congo Basin, West Africa: Implications for the Deposition of Lacustrine Source Rocks

Abstract: Sedimentological and Geochemical Evidence of High Frequency Climatic Cycles Controlling the Deposition of Source and Reservoir Rocks in a Lower Cretaceous Rift Lake, Sergipe-Alagoas Basin, Brazil

Abstract: Sedimentological and Geochemical Evidence of High Frequency Climatic Cycles Controlling the Deposition of Source and Reservoir Rocks in a Lower Cretaceous Rift Lake, Sergipe-Alagoas Basin, Brazil

Factors Controlling the Burial of Organic Carbon in Laminated and Bioturbated Sediments off NW Mexico

Carbonaceous facies in geological records deposited at shallow palaeodepths exhibiting the combination of high carbon contents, laminations and high hydrogen index (HI) values have been typically interpreted as reflecting conditions of enhanced preservation of organic carbon under an intense oxygen minimum. However, recent investigations on the distribution of organic carbon on continental margins have failed to reveal significant differences in HI values between contemporary sediments that have accumulated within, above and below the oxygen minimum in a given geographic region. This discrepancy between the depositional conditions typically inferred for carbonaceous facies in rocks and the modern environments that are supposes to provide an analogue is critically examined. Factors controlling the burial of organic carbon on the NW Mexican margin in late Quaternary and Recent sediments are assessed using a suite of box and piston cores, strategically located on the shelfslope-rise with respect to the intense oxygen minimum in this region. An array of sedimentary parameters was determined to evaluate organic carbon quantity (wt.% organic carbon (TOC) and nitrogen), quality (Rock-Eval parameters, Corga~io/ Ntota I ratio, 13 5 Corganio, lignin biomarkers, I/Corganic ratio), variations in biogenic components (wt.% opal and Ba/A1 ratio) and texture (sand content, Sinonbio/A1 ratio and Zr/A1 ratio). In late Quaternary sediments, the lowest HI values occur concurrently with large increases in grain size on the upper-slope . This hydrocarbon impoverishment is attributed to increased degradation of organic material due to sediment reworking during glacial periods. This conclusion is supported by the presence of winnowed coarse-grained organic-poor shelf deposits which are depleted in hydrocarbons ( 300 mg HC/g TOC) are observed in the fine-grained deposits that correspond with the broad organic carbon maximum that characterizes much of the Mexican continental slope. Thus, the degree of winnowing is the primary factor affecting the preservational quality of organic matter deposited on this margin. Over the last 140,000 years, the rates of accumulation of organic carbon and opal, and in certain cores biogenic baryte concentrations, are all higher in the interglacial intervals when compared with the glacial deposits. Despite the cyclic change in predominantly marine organic matter accumulation, matrix-corrected hydrogen index (HI) values in the midand lower-slope cores are invariant and are similar to values in the laminated intervals from the oxygen-minimum site. This suggests that the cyclic changes in organic carbon accumulation on this margin during the late Quaternary are controlled by productivity variations and are not due to differential preservation induced by variations in bottom water oxygen concentrations. A comparison of matrix-corrected HI values from sediments of late Quaternary to Recent age from several continental margins and euxinic basins reveals that in general the organic matter preserved in these environments corresponds to Type II, irrespective of bottom water oxygen concentrations. Therfore, the preservation of Type II 'oil-prone' kerogen in productive continental margin settings does not appear to be restricted to sediments deposited under conditions of low bottom water oxygen concentrations as envisioned in models of petroleum source-rock deposition.

Tectonic significance of syn-rift sediment packages across the Gabon-Cabinda continental margin

Tectonic significance of syn-rift sediment packages across the Gabon-Cabinda continental margin

Geochemical evaluation of hydrocarbons and their potential sources in the western South Caspian depression, Republic of Azerbaijan

The western South Caspian depression, located in offshore Azerbaijan, contains significant accumulations of oil and gas in Upper Tertiary fluvial-deltaic sediments. The active Tertiary hydrocarbon system is a product of unique paleogeographic and tectonic events that led to Paleogene deposition of organic-rich source rocks, rapid Pliocene subsidence concurrent with voluminous supply of clastic sediments, and development of anticlinal traps with abundant shale diapirs. Molecular characterization of selected oil samples indicates most of the oils are sourced from similar organic facies. The molecular characteristics are consistent with oils sourced from a Tertiary, slightly calcareous, marine clastic facies. Examination of oil molecular characteristics, oil-oil correlations, molecular characteristics of selected source rock samples, maturation models, and potential migration pathways suggests the oil is not syngenetic, but most likely sourced from deeper Miocene and older marine shales. Most of the oils have low to moderate organic maturities (VRE 0.75–0.85) relative to conventional peak generation windows. Significant variations in oil gravity and whole oil gas chromatogram character suggest post-emplacement bacterial and fractionation alteration. Several oils display characteristics consistent with multiple phases of trap charging. The bulk of reservoired gases examined in this study have been sourced from mixed terrestrial-marine kerogen generated at organic maturities of VRE 0.80–1.00 with some biogenic-low maturity mixing. None of the gases examined were sourced from the thermal destruction of liquid hydrocarbons. We postulate multi-stage hydrocarbon emplacement into evolving structural traps. The first phase of emplacement occurred in the Middle Pliocene when tectonic movement and increased subsidence initiated early trap/reservoir formation, hydrocarbon generation, and migration. Late rapid subsidence from Quaternary tectonic activity produced additional hydrocarbons to replenish older, depleted traps and charge newly formed traps. This late tectonic activity also extensively redistributed hydrocarbon accumulations, degassed some that were breached by faults, and destroyed other oil pools. Thermal disequilibrium from the rapid subsidence delayed hydrocarbon generation and increased the minimum depth required for the onset of liquid hydrocarbon generation.

δ 13C compositions of saturate and aromatic fractions of lacustrine oils and bitumens: evidence for water column stratification

Saturate fractions of oils and source rocks are generally depleted in 13C relative to the aromatic fraction. The isotopic difference between these two fractions ( Δδ aro-sat) is largest typically in lacustrine oils and bitumens, and smallest in marine samples. Depletions of 13C in saturate fractions in samples from three lacustrine basins (China, Argentina and U.S.A.) correlate strongly with hopane abundance. Extremely 13C depleted hopanes have been documented in ancient and modern lacustrine settings and are explained by input from methanotrophic bacteria. As these bacteria thrive at the chemocline of stratified lakes, extremely 13C depleted hopanes in geologic samples is evidence for paleostratification. Comparatively low Δδ aro-sat values in marine samples are related to abundant sulfate in marine environments, since sulfate reducers out-compete methanogens for metabolic intermediates and attenuate the methane cycle. The strong positive correlation of quantitative hopane abundance with the 13C-depletion in saturate fractions of lacustrine samples provides circumstantial evidence for biogenic input from methanotrophic bacteria and for stratified water columns during source rock deposition. Further, this observation explains why the “Sofer-plot” effectively differentiates stratified lacustrine samples from open marine and non-stratified lacustrine samples. The wide distribution of our sample set suggests that this is a global phenomenon.

The hydrocarbon systems of North Africa

North Africa's hydrocarbon reserves are spread over a wide range of reservoirs and play types but derive from only a few key source rock intervals, particularly those in the Silurian, Late Cretacous and Eocene. Source rock maturity, together with the timing of the generation relative to trap forming and destructive events, seem to be the key controlling factors on success or failure at a basin level. In most cases, generation clearly post-dates trap formation, although a more complex relationship is evident in various parts of Algeria, where some traps did not form until gas was being generated. Source rock deposition and maturation can be tied to two main extensional tectonic cycles which ended in the compressional and destructive events of the Hercynian and Alpine orogenies. Remaining exploration potential in mature provinces may be tied largely to subtle and stratigraphic traps. In addition, significant frontier potential can be identified in two main fairways, corresponding to regions where Silurian/Devonian and Cretaceous/Eocene sources respectively are likely to have generated petroleum. Critical factors in these areas are timing of generation and preservation. The gas discoveries in the Ahnet Basin provide analogues for Palaeozoic generation/preservation models in the interior Silurian/Devonian source fairway. Similarly, the key to success for the Mesozoic basins of the Atlas region lies in demonstrating a favourable relationship between trap formation/destruction and generation from Late Cretaceous and Eocene source rocks.

Sequence Stratigraphy, Basin Dynamics, and Petroleum Geology of the Miocene from Eastern Tunisia

On the eastern margin of Tunisia, Miocene limestones, marl, and siliciclastic deposits crop out poorly and are lacking in age-diagnostic faunal content. The biostratigraphic and lithostratigraphic subdivisions of these series are not clearly defined. A regional study of subsurface sequences of this margin (Cap Bon, Gulf of Hammamet, and Sahel) by means of sequence stratigraphy and subsurface structural analyses permits the identification of seven third-order sedimentary sequences of inferred Langhian to Messinian age, the boundaries of which are characterized by downlap and onlap/toplap relationships. These sequences include turbidites, sands, and sandstones deposited in connection with eustatic sea level changes and tectonic movements of east-west and south-north deep-se ted faults due to the Alpine and Atlassic paroxysm. Stratal sequences are organized around Miocene syndepositional grabens, half-grabens, platforms, and folds occurring inside and outside of regional tectonic corridors. The geodynamic evolution of Miocene basins has led to the deposition of turbiditic black argillaceous source rocks, and sandstone and carbonate reservoirs that present new Miocene petroleum targets. The basin subsidence in response to the Alpine/Atlassic orogeny has permitted the maturation of Miocene source rocks, oil generation, and the formation of oil traps, stratigraphic pinch-outs, and structural enclosures on the flanks of folds and on the borders of grabens.

Origin of Beach-Stranded Tars from Source Rocks Indigenous to Seychelles

Tarballs have been found stranded as traction deposits on a beach on northwest Mahe Island, Seychelles, with every ebbing tide. Weekly collections from mid-1993 to mid-1994 gathered nearly 4750 samples of two types of tar: a dominant black malleable tar and a less common brownish-black hard tar. Both tars represent moderately degraded extracts of crude oils seemingly derived from mature source rocks dominated by a combination of oil-prone phytoplanktonic and algal organic matter over gas-prone land-plant organic matter. Source rock deposition occurred principally in paralic to open-marine environments. The presence of minor oleanane and bicadinane, and a general preponderance of diasteranes and tricyclic terpanes in the hard tar suggest derivation from a Late Cretaceous c astic source rock with possible carbonate interbeds. By contrast, no samples of the malleable tar contain oleanane or bicadinane, but all contain significant norhopane and tetracyclic terpanes, which, along with significant sulfur and low diasterane contents, indicate derivation from a carbonate source rock of perhaps pre-Late Cretaceous age. Both these tars differ markedly from a tar that is stranded only on Coetivy Island that contains minor amounts of steranes, oleanane, bicadinane, and botryococcane, but has high pristane and tricyclic terpane contents, suggesting derivation from a Late Cretaceous clastic deltaic source rock. All three tar types can be related to depositional environments that developed during the multiphase rift-drift origin of the Seychelles microcontinent from eas Africa, Madagascar, and India. Additionally, maturity and limited geochemical data from proven and potential source rocks present in the offshore wells enable the malleable and hard tars to be equated with specific units in the Seychelles stratigraphy; the malleable tar is seemingly derived from a Middle Jurassic carbonate of Tethyan affinity and the hard tar possibly originated from either Campanian or Maastrichtian-Paleocene shales. These tars are thus concluded to be natural seepage products derived from source rocks indigenous to Seychelles, and their persistent beach stranding significantly reduces the risk of hydrocarbon exploration in this frontier province.

Tectonic controls on Upper Jurassic to Lower Cretaceous reservoir architecture in the Jeanne d’Arc Basin, with some comparisons from the Porcupine and Moray Firth Basins

Abstract Seismic, wireline log and core data from three geographically separate basins in the North Atlantic provide an understanding of the regional dynamics of the basin system, and quantify the sedimentary geometry response to a composite rift episode. The response to the Late Cimmerian rift episode in the Jeanne d’Arc, Porcupine and Moray Firth Basins is broadly comparable, with an initial episode of clastic reservoir facies deposition associated with active growth faulting. This was followed by a mid-rift period where subsidence outstripped sedimentation, resulting in organic-rich source rocks and culminating in a mappable maximum flooding surface. During the final phase of the rift episode, the decrease in subsidence rate resulted in the return of reservoir-quality clastics. The reservoir-scale response to the initial rifting is illustrated in cored sequences from the Jeanne d’Arc Basin. These indicate the development of axial and lateral sandy and conglomeratic braided fluvial and alluvial fan systems, with periods of muddy lacustrine deposition. Pedogenic surfaces offer much potential for detailed correlation and the analysis of sandbody geometry. The onset of anoxic conditions conducive to source rock deposition during the mid-rift phase of Late Cimmerian tectonism, and the preferential development of reservoir facies at the base and top of syn-rift sediment fill, are characteristics of considerable importance to exploration of the North Atlantic borderland rift basins.

Structural Styles in Rift Basins: Interpretation Methodology and Examples from Southeast Asia: ABSTRACT

The authors present graphical solutions to the extensional fault-related folding equations of Xiao and Suppe (1992), simplifying the prediction of normal fault location or rollover geometry from subsurface data. These equations also predict the extent of bed thinning and elongation in hanging wall strata. They have derived new equations that relate change in fault slip across a fault bend to fault geometry. Applying these equations in seismic interpretation makes it easier to (1) construct balanced cross-sections, (2) account for the slip observed, and (3) determine the growth history of extensional fault-related folds. They have applied these concepts to several southeast Asian rift basins in Malaysia, Myanmar, Indonesia, and Thailand. These basins were formed by early Tertiary crustal extension, producing rollover structures in which sediment supply generally did not keep up with subsidence. These under-filled, internally drained depressions periodically contained lakes, providing the environment for deposition of organic-rich strata that ultimately became hydrocarbon source rock. Typically, the main basin bounding faults dip 35-55[degrees] near their upper terminations and flatten to become subhorizontal. Synthetic and antithetic secondary faults are usually present. Late compaction faulting often propagates upward from major extensional faults and may reactivate the upper portions of these faults. In manymore » basins, late compression produced inversion structures. By applying the concepts of extensional fault-related folding to these basins, they can (1) explain observed geometries, (2) predict poorly imaged geometries, (3) predict the location of source and reservoir facies, and (4) determine the timing of faulting relative to deposition of source and reservoir rocks.« less

シーケンス層序学 その可能性を求めて 石油探鉱における堆積リズム解析の可能性 第四紀日本海海洋循環ダイナミックスの復元を例として

Sedimentary rhythm analysis is a method to study sedimentary cycles through the systematic sampling and analysis of the sequences, derivation of multiple paleoenviron-mental parameters from the analytical data, and examination of the frequencies in variation of these parameters and their phase relationships. Through sedimentary rhythm analyses, it is possible to study the dynamics of paleo-ocean circulation. In this short paper, I would like to show the application of this method to reconstruct dynamic behaviour of the surface and deep water circulation within the Japan Sea corresponding to the glacial-interglacial sea-level oscillations during late. Quaternary. Reconstruction of this sort is useful to understand the paleoenvironment as well as mechanism(s) of the petroleum source rock deposition within marginal seas.

Sterane and triterpane patterns as diagnostic tools in the mapping of oils, condensates and source rocks of the Gulf of Mexico region

Four hundred and eighty-one Gulf of Mexico oils and condensates can be subdivided into nine major families based on their sterane ( m/ z 217, 218) and triterpane ( m/ z 191, 177) biomarker mass chromatogram patterns. These families are (1) carbonate-sourced oils reservoired in Jurassic-Cretaceous reservoirs onshore and Plio-Pleistocene reservoirs offshore, (2) Austin Chalk reservoired oils, (3) Tuscaloosa oils, (4) Wilcox reservoired oils (La), (5) South Texas Palaeogene reservoired oils, (6) Mississippi delta oils, (7) post-mature oils of uncertain affinities, (8) migration contaminated oils (showing attributes of a mixing of immature and post-mature sources), and (9) oils and condensates lacking biomarkers. Each oil family is concentrated in specific age-defined producing trends, ranging in age from Jurassic to Pleistocene. For Tertiary reservoirs, these producing trends shift geographically with time, in a manner analogous to the clockwise migrating Cenozoic depocenter model for the northern Gulf of Mexico. At least six ages of marine source rock deposition may be implicated in the genesis of these oils (1) The Kimmeridgian-Oxfordian (including Smackover and Norphlet formations), (2) The Aptian (including Pine Island, Bexar and Sunniland formations), (3) The Albian (Paluxy formation), (4) The Cenomanian-Turonian (including Eagle Ford and Tuscaloosa formations), (5) The Coniacian-Santonian (Eagle Ford and Austin Chalk), and (6) The Palaeocene (Wilcox, Midway, Sparta formations). The Jurassic and Cretaceous source rocks correspond to described oceanic anoxic events of probable global significance. This paper will concentrate on describing the biomarker patterns of the oils and postulated source rocks, but due to reasons of space, isotopic, elemental and other data will only be briefly discussed.

Thermal Maturation and Organic Richness of Potential Petroleum Source Rocks in Proterozoic Rice Formation, North American Mid-Continent Rift System, Northeastern Kansas

A recent well in northeastern Kansas penetrated 296 ft (90.2 m) of dark gray siltstone in the Precambrian Mid-Continent rift (Proterozoic Rice Formation). Correlations indicate this unit may be as thick as 600 ft (183 m) and is possibly time-equivalent to the Nonesuch Shale (Middle Proterozoic) in the Lake Superior region. The upper half of this unit qualifies as a lean source rock (averaging 0.66 wt. % TOC), and organic matter in it is in the transition stage between oil and wet gas generation. The presence of the gray siltstone in this well and similar lithologies in other wells is encouraging because it indicates that source rock deposition may be common along the Mid-Continent rift, and that parts of the rift may remain thermally within the oil and gas window. Microscopic examination of calcite veins penetrating the dark gray siltstone reveals numerous oil-filled and subordinate aqueous fluid inclusions. Homogenization temperatures indicate these rocks have been subjected to temperature of at least 110-115°C (230-239°F). Burial during the Phanerozoic is inadequate to account for the homogenization temperatures and thermal maturity of the Precambrian rocks. With the present geothermal gradient, at least 8250 ft (2.5 km) of burial is necessary, but lesser burial may be likely with probably higher geothermal gradients during rifting. Fluorescence colors and gas chromatograms indicate compositions of oils in the fluid inclusions vary. However, oils in the fluid inclusions are markedly dissimilar to the nearest oils produced from Paleozoic rocks.

Cretaceous Source Rocks in Pakistan

Pakistan is located at the converging boundaries of the Indian, Arabian, and Eurasian plates. Evolution of this tectonic setting has provided an array of environmental habitats for deposition of petroleum source rocks and development of structural forms. The potential Cretaceous source rocks in Central and South Indus Basin are spread over an area of about 300,000 km[sup 2]. With 2% cutoff on Total Organic Carbon, the average source rock thickness is 30-50 m, which is estimated to have generated more than 200 billion bbl of oil equivalent. To date, production of more than 30,000 bbl of oil and about 1200 million ft[sup 3] of gas per day can be directly attributed to Cretaceous source. This basin was an area of extensional tectonics during the Lower to Middle Cretaceous associated with slightly restricted circulation of the sea waters at the north-western margin of Indian Plate. Lower Cretaceous source rocks (Sembar Formation) were deposited while the basin was opening up and anoxia was prevailing. Similarly Middle to Upper Cretaceous clastics were deposited in setting favorable for preservation of organic matter. The time and depth of burial of the Cretaceous source material and optimum thermal regime have provided the requisite maturation level formore » generation of hydrocarbons in the basin. Central Indus basin is characterized by Cretaceous source rocks mature for gas generation. However, in South Indus Basin Cretaceous source rocks lie within the oil window in some parts and have gone past it in others.« less

Tectonosedimentary History of the Sedimentary Basins in Northern West Siberia

Sedimentary basins of northern west Siberia belong to the Arctic tectonosedimentary province. This basin evolved dissimilarly compared to those in the Urengoy and more southern areas, which resulted in substantial differences in the geologic characteristics. Seismic surveys indicate that the basement surface in northern west Siberia occurs at great depths, in places exceeding 15 km. The depressions of the basement surfaces are filled with the thick Paleozoic and Mesozoic sequences. The paper discussed the results of seismostratigraphic analysis of more than 13,000 km of regional common-depth-point profiles. These profiles identified systems of east-west-trending and isometric structures in the region. Some of the structures are buried; others are mapped in the upper horizons of the sedimentary cover and decrease in magnitude with depth. Cretaceous marine sediments that were deposited under deep-water conditions and did not compensate for the tectonic subsidence are widely present in the region. Noncompensated sedimentation was the longest from the Late Jurassic to the Hauterivian-Barremian on the Gydan peninsula and in adjacent areas. The Jurassic section is dominate by ingressive marine sediments. Sediments that did not compensate for tectonic subsidence widely occurred in the Early Jurassic and resulted in deposition of petroleum source rocks. Triassic and Jurassic stratamore » occur conformable in most of northern west Siberia. Significant deformation of the Triassic sediments are identified in the periphery of the Triassic marine basin. This indicates that surrounding structures were thrust against northern west Siberia at the Triassic and Jurassic time boundary. Isometric structures of high magnitude were formed during the Paleozoic structure stage and these structures continued to grow through the Triassic and Jurassic. These and other results of seismostratigraphic analysis suggest the high oil potential of the region.« less

Tectonic Controls on Deposition of Mesozoic Source Rocks, Northern Margin of African Plate

Tectonic Controls on Deposition of Mesozoic Source Rocks, Northern Margin of African Plate

Depositional Environment and Organic Geochemistry of the Upper Permian Ravnefjeld Formation Source Rock in East Greenland

The Upper Permian Ravnefjeld Formation in East Greenland is composed of shales that laterally pass into carbonate buildups and platforms of the Wegener Halvo Formation. The Ravnefjeld Formation is subdivided into five units that can be traced throughout the Upper Permian depositional basin. Two of the units are laminated and organic rich, and were deposited under anoxic conditions. They are considered good to excellent source rocks for liquid hydrocarbons with initial average TOC (total organic carbon) values between 4 and 5% and HI (hydrogen index) between 300 and 400. The cumulative source rock thickness is between 15 and 20 m. The source rocks are separated and enclosed by three units of bioturbated siltstone with a TOC of less than 0.5% and an HI of less than 100. The e siltstones were deposited under relatively oxic conditions. The organic geochemistry of the source rocks is typical for marine source rocks with some features normally associated with carbonate/evaporite environments [low Pr/Ph (pristane/phytane), low CPI (carbon preference index), distribution of tricyclic and pentacyclic terpanes]. The establishment of anoxic conditions and subsequent source rock deposition was controlled by eustatic sea level changes. The subenvironment (paleogeographic setting, influx of carbonate material, water depth, salinity) has some influence on a number of bulk parameters [TOC-HI relations, TOC-TS (total sulfur) relations] and, in particular, biomarker parameters such as Pr/Ph and terpane ratios. All the basal shales or shales in the vicinity of carbonate buildups or platforms are characterized by low Pr/Ph, high C23 tricyclic terpanes, and high C35 and C33 hopanes.