Detailed facies analysis of Cenomanian–Turonian organic‐rich mudstones: Implications for depositional controls on source rocks

Emma L. Percy; Per K. Pedersen

doi:10.1002/dep2.106

PETROLEUM POTENTIAL OF THE NEOPROTEROZOIC WESTERN OFFICER BASIN, WESTERN AUSTRALIA, BASED ON A SOURCE ROCK MODEL FROM EMPRESS-IA

The APPEA Journal ◽

10.1071/aj98018 ◽

1999 ◽

Vol 39 (1) ◽

pp. 322 ◽

Cited By ~ 2

Author(s):

G.M. Carlsen ◽

S.N. Apak ◽

K.A.R. Ghori K. Grey ◽

M.K. Stevens

Keyword(s):

Organic Matter ◽

Western Australia ◽

Depositional Environments ◽

Source Rocks ◽

Petroleum Potential ◽

Organic Facies ◽

Organic Growth ◽

Rock Model ◽

Depositional Controls ◽

The Impact

The sedimentology, palaeontology and geochemistry of Neoproterozoic, organic-rich, clastic and related carbonate deposits in Western Australia provide new insights into the first-order depositional controls on hydrocarbon source rocks in the Neoproterozoic. Organic facies are correlated with depositional facies, revealing the impact of organic productivity and transport of organic rich sediments on the accumulation of organic matter in different depositional environments. Sedimentation is largely limited to ramp, platform, shoal, lagoon and sabkha environments.Growth of benthic organisms in the photic zone was the primary process controlling the production of organic matter in the ramp-shoreline system of the Kanpa Formation. Storms and floods were the primary mechanism for moving organic rich sediments into dysoxic and anoxic depositional environments. Variations in organic facies are indicated by: 1) changes in the palynomorph assemblages, particularly the increase in acritarchs within shallow-water ramp facies and cyanobacterial filaments in quiet-water sediments; 2) organic-rich laminae, containing abundant cyanobacterial filaments and mat material; and 3) the oxidation state of preserved organic remains.Periods of high organic growth rates or periods of mass mortality may have led to the development of an anoxic zone at the water-sediment interface. In the shoal and lagoonal settings, higher rates of clastic sediment dilution combined with oxygenated conditions resulted in lower TOC and hydrogen depleted organic facies.Condensed sections overlying stromatolitic dolomites represent the most effective organic facies of all of the potential source laminae sampled in Empress–IA. Most of the Officer Basin succession is currently within the oil-generating window and hydrocarbon shows encourage further exploration.

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Terciérní říční sedimenty v širším okolí Jihlavy

Geologické výzkumy na Moravě a ve Slezsku ◽

10.5817/gvms2019-1-2-24 ◽

2019 ◽

Vol 26 (1-2) ◽

Author(s):

Michal Francírek ◽

Slavomír Nehyba

Keyword(s):

Facies Analysis ◽

River System ◽

Flood Plain ◽

Depositional Environments ◽

Source Rocks ◽

Oxbow Lake ◽

Fine Grained ◽

High Concentrations ◽

Moldanubian Unit ◽

Organic Deposits

Tertiary deposits have been known around Jihlava city for many years. However, they have never been thoroughly studied. Most of the known occurrences are situated in the Jihlava Furrow. During the drilling research, these Tertiary deposits were newly detected in three wells: HGM-1, V1 and V4. Facies analysis, petrography and gamma spectrometry were performed on samples taken from all three wells. The model of basement of Cenozoic deposits has been constructed. Based on facies analysis, 8 lithofacies (7 studied deposits and 1 eluvium) have been described. The study of lithofacies has made the recognition of the depositional environments of the Tertiary deposits possible. The depositional environments of these deposits are interpreted as fluvial channelized gravels and non-channelized deposits (flood plain, crevasse splays, oxbow lake and lake). The channelized gravels have been found by the well HGM-1 in the overburden of the crystalline rocks of the Moldanubian. Their thickness is relatively low (1.7 m) and the channels were probably not deep. The non-channelized deposits are formed by clays, silts and fine-grained sands. In the upper part of the succession a layer of organic deposits (peat) has been detected. The results of petrography have shown that material originated from local sources, especially Moldanubian Unit and Jihlava Massif (gneisses, mica-schistes, granitoids, less importantly pegmatites and phyllites). High concentrations of Th and U have been found in the studied deposits. These high concentrations can be associated with the source rocks. The values of Th /U and Th /K ratios are signifi cantly higher in the studied deposits than in eluvium. This indicates conditions of weathering and sedimentation, and also points to input of the material from several sources. The model of crystalline basement shows that there were probably at least two spatially separated fluvial river systems. One river system was situated in the area of Velký Beranov and Měšín. The preserved remains of the second system are visible in the area of Jihlava city and its peripheral parts (Bedřichov and Pávov).

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