Page 71 - The Petroleum System From Source to Trap

64 Klemme

Table 3.5. Petroleum Geotectonic Realm of Upper Table 3.6. Location by Basin Type of Upper Jurassic
Jurassic Source Rocks Source Rocksa
Mature Source Rock Total World Mature Average
BOE Area Volume BOE Area Source Rock Source Rock
Petroleum Realm {%) {%) {%) {%) (%) BOE Area Volume Thickness
Boreal 27 49 30 23 28 Basin Type (%) (%) (%) (m)
Tethyan 72 49 69 68 1 7
Southern Fold belt and
(
Gondwana 0 0 0 4 38 foreland 60 1 5 ) 34 (40) 43 (32) 1 4 8 (148)
Pacific 1 1 1 5 1 7 Rifted 27 (47) 49 (20) 31 (25) 250 (320)
Divergent margin 1 2 (38) 1 6 (40) 26 (43) 405 (405)
aNumbers in parenthese exclude the Han�a-Arab(l) and Bazhenoveocoian(!)
supergiant petroleum systems.
LOWER-MIDDLE JURASSIC SOURCE
ROCKS
for deposition of a laminated lime mudstone in an anoxic
Lower-Middle Jurassic sedimentary rocks occupy environment to form bituminous source rocks.
essentially the same position as and underlie much of the
Upper Jurassic (Figures 3.1-3.5). At approximately 30
locations, Lower and Middle Jurassic source rocks occur LOWER CRETACEOUS SOURCE ROCKS
that result in some hydrocarbon production (for
locations see Figure 3.1). This represents only 5% of the In certain areas, Jurassic source rocks extend up into
total production from all Jurassic source rocks. the Lower Cretaceous. Lower Cretaceous (Berriasian­
Two organic facies of Lower-Middle Jurassic source Barremian) deltaic to open marine sedimentary rocks
rocks are related to their depositional paleolatitudes were deposited in 30 areas where production was
generated from Lower-Middle Jurassic source rocks and
(Table 3.2). Tethyan facies of shales and carbonates (Xrc)
and evaporites (XTE were deposited in rift-sag structural in 20 areas where production originated from Upper
)
forms in low paleolatitudes (0°-301 along the margin of Jurassic source rocks. Where sediments were derived
the Neo-Tethys (Triassic-Jurassic opening of the Tethys) from the craton or continental interior, they were
(Figures 3.1-3.5). These Tethyan facies were developed deposited as regressive deltaic sequences that grade to
on the southern margin of Laurasia and the northern open marine. These sequences usually occur in the fold
margin of Gondwana and occupied the north and south belt and foreland basins as well as in rifted basins.
sides of a seaway that was separated by a central zone of However, there is a tendency for more open marine
deep water with red, nodular, pelagic limestone and sediments to occur in the divergent margin basins.
radiolerites located along the axis of the seaway (Wilson, In the West Siberian basin and the northwest Europe
1975). The Tethyan-like facies deposited between 30° and shelf province, the deposition of Upper Jurassic source
40° paleolatitude appears to be a mixture ("mixed rocks continued into the Early Cretaceous (pre-Wealden
facies") of the low latitude Tethyan hypersaline or Purbeckian-Ryazann). There are a few source rocks
carbonate facies mixed with the "humic facies" of coals, within the Wealden (Valangian-Barrernian) stages of the
Lower Cretaceous in this area (Cornford, Chapter 33, this
humic shales (XHc), and lacustrine source rocks (XHL).
Although it is present in minor amounts at all paleolati­ volume).
tudes, the Humic facies is found predominantly north of Minor production attributed to Lower Cretaceous
40 ° paleolatitude. source rocks occurs in the (1) lacustrian shales of Lower
Two-thirds of the area covered by Lower-Middle Saxony basin (Kockel et al., Chapter 34, this volume), (2)
Jurassic source rocks is overlain by Upper Jurassic source low rank source shales in West Siberia (Peterson and
rocks, while one-third lacks these overlying rocks. Where Clarke, 1991), (3) marine shales of the Neuquen basin
Upper Jurassic source rocks are absent and production (Urien and Zambrano, Chapter 32, this volume), (4)
came from Lower-Middle Jurassic source rocks, two­ marginal marine shales of the Cooper subbasin (Kantsler
thirds of the hydrocarbon occurrences are related to et al., 1984), and (5) possibly some of the marine shales of
regional or local uplift. This uplift is a departure from the the Scotia shelf (Grant et al., 1986). The upper Lower
Vail sea level curve that rises during the Upper Jurassic Cretaceous (Barremian-Aptian) contains some source
(Vail et al., 1977) because this is the initiation of the rocks (South Atlantic divergent margin basins of South
worldwide Neocomian regressive clastic depositional America and Africa), which initiate the Cretaceous
event. These regressive sequences most often occur (Aptian-Turonian) "bloom" of worldwide source rocks.
stratigraphically above the Mixed and Humic organic Generally, the Neocornian regressive phase contains
facies. The other one-third of the hydrocarbon occur­ more reservoir rocks than source rocks, while the trans­
rences occur above the Tethyan facies where either the gressive (rising sea level) Cretaceous (Aptian-Turonian)
open marine carbonate facies or the deep marine starved includes worldwide source rocks that have generated
basin facies were developed, but an intershelf depres­ even more BOE than the Upper Jurassic (30% or more of
sion, either in or on the open marine shelf, was lacking the world's discovered BOE).