Geology Reference
In-Depth Information
The present-day temperatures in the Mesozoic deposits, i.e., after they
have been overlain by the Paleogene-Miocene and Pliocene-Quaternary
deposits, were calculated as follows. The present-day temperatures at the
PS/RBS base were built-up by the Paleocene-Miocene temperature gradi-
ents within the section. These values at the base were then built-up by tem-
perature gradients in Mesozoic rocks through their entire thickness to the
crystalline basement.
The described innovative temperature reconstruction technique is based
on the following theoretical concept: temperature values at any depth are
determined by the heat-conductivity of overlying rocks and the tempera-
ture of underlying rocks. This approach is based on the actual well data. It,
therefore, enables reconstructions of the deep temperature regime by cir-
cumventing unavoidable significant errors occurring while using complex
heat-conductivity equations.
Tables 6.1 through 6.3 present the paleo- and present-day temperatures
calculated by the authors. They are determined for each complex at each
stage of geological evolution and for each region in the South-Caspian Basin.
Over the entire life of the basin (185 to 190 MMY), the Mesozoic complex
was heated up in its top portion to 167-216
°
C (present depth at 6 to 11 km)
and at its base portion to 287-424
C (present depth of 12.5 - 21.5 km). Over
55-60 MMY, the Paleogene-Miocene complex was heated to 76-118
°
°
C
(present depth of 3 to 6 km) and to 154-237
C (present depth of 6-11 km).
Over 6-8 MMY, the Pliocene-Quaternary complex was heated to 66-112
°
°
C
at the contact zone with the underlying section (depth of 3-6 km).
These temperatures have been converted to a scale of vertical zona-
tion of oil and gas generation (Kartsev
et al
., 1971) and then calculated
as the corresponding depths by way of determining
H
as a function of
temperatures (Rachinsky, 1983). The following was established for differ-
ent complexes:
1.
The Mesozoic Complex.
In most regions of the South-Caspian
Basin, from the time of deposition to the present, sediments (at
a depth of 5.5 to 11 km) went through all lithogenetic trans-
formation stages of their organic matter. The stages began with
diagenesis D and went through the proto- (PC), meso- (MC)
and apo- (AC) catagenesis to metagenesis (MG). Each strati-
graphic unit went through the following stages:
a. Upon subsiding to a depth of 0.16 km, the biogenic gas
generation terminated (stage
D
).
b. Upon subsiding to a depth of 1.8 km, the early-catage-
netic methane had been generated (substage
PC, PC
1
-PC
3
grade).
