Page 118 - Introduction to Petroleum Engineering

104 PETROLEUM GEOLOGY

Laurasia
225 MYA Equator Pangaea Equator 200 MYA

Gondwana

135 MYA Equator Equator 65 MYA

Present Equator

FIGURE 6.4 Tectonic plate movement. (Source: U.S. Geological Survey Historical
(2013).)

The theory describing the movement of lithospheric plates is known as plate
tectonics. According to plate tectonics, the land masses of the Earth have been
moving for millions of years. Using radiometric dating and similarities in geologic
structures, a reconstruction of lithologic history is sketched in Figure 6.4 for the past
225 million years.
The movement of tectonic plates is responsible for much of the geologic hetero-
geneity that is found in hydrocarbon‐bearing reservoirs. The figure begins at the
time that all surface land masses were gathered into a single land mass known as
Pangaea. Pangaea was formed by the movement of tectonic plates, and the ongoing
movement of plates led to the breakup of the single land mass into the crustal
features we see today.
Table 6.1 is an abridged version of the geologic time scale beginning with the
formation of the Earth. The most encompassing period of time is the eon, which is
subdivided into eras and further subdivided into periods. The acronym MYBP stands
for millions of years before the present. The geologic time scale is from the Geological
Society of America (Gradstein et al., 2012; Cohen et al., 2015). Our understanding of
the chronology of the Earth is approximate.