Geological
setting and structural elements
Western
Latvia and the adjacent Baltic Sea shelf are situated within the
northern part of a single sedimentary basin called the Baltic Syneclise.
The
Baltic Syneclise is a large marginal depression within the East-European Platform,
whose most important features in the Baltic Region (including Latvia) is
subsidence of the top crystalline basement towards south and south-west;
it is characterised by the maximum thickness of the sedimentary cover
(it reaches 2 km in Latvia) and stratigraphically most complete section;
its structure is faulted, in some places, block structure is observed.
The
main structural components of the Baltic Syneclise in Latvia are: the Liepaja-Saldus
Ridge, Gdansk-Kura and Liepaja depressions, as well as
the Latvian-Estonian and Lithuanian Border Zones.
The
Liepaja-Saldus Ridge
is a regional faulted zone with a complex structure, oriented SW-NE. It
transverses from the central part of the Baltic Sea onshore to central
Latvia over a distance of more than 300 km. The Liepaja-Saldus Ridge is
bounded by major faults, with displacement of Caledonian sediments up to
600 m.
The high incorporates several structures of lesser rank, with
which most Latvian oil prospects are associated.
The
Gdansk-Kura Depression
is a large regional structure, continuing as far as Poland. Only its
northern part reaches Latvia, incorporating the southern part of Western
Latvia and the adjacent part of the Baltic Sea. Several oil discoveries
were made there in Lithuania and Kaliningrad District; several oil
prospective local highs were discovered in Latvia as well.
The Liepaja
Depression
is located, predominantly, in the Baltic offshore area, also occupying a
small area in onshore. It is an important relatively simple structure
that is considered as a possible oil generation zone.
The
Latvian-Estonian and the Lithuanian
Border Zones are situated
in the border zones of the Baltic Syneclise and are characterised my
monoclinal layering and relatively shallow basement where small
anticline and reefoid structures were discovered.
The
Latvian area is a part of an old platform, the geological section of
which displays two components characteristic of palaeoplatforms: the
crystalline basement and sedimentary cover. The sedimentary cover,
unconformably overlying the heavily eroded surface of the crystalline
basement, consists of the terrigenous, carbonate and sulphate rocks of U.
Proterozoic (Vendian Complex) and Phanerozoic – Cambrian through
Jurassic. The Cambrian, Ordovician, Silurian and Devonian rocks are the
most abundant, while Carboniferous, Permian, Triassic and Jurassic
deposits were observed in SW Latvia alone. The major depositional stages
are separated by periods of non-deposition and erosion; these
unconformities within the sedimentary succession reflect the major
tectonic events.
