The geology of
Denmark
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, song = ( en, "King Christian stood by the lofty mast")
, song_type = National and royal anthem
, image_map = EU-Denmark.svg
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, subdivision_type = Sovereign state
, subdivision_name = Danish Realm, Kingdom of Denmark
...
includes 12 kilometers of unmetamorphosed sediments lie atop the
Precambrian
The Precambrian (or Pre-Cambrian, sometimes abbreviated pꞒ, or Cryptozoic) is the earliest part of Earth's history, set before the current Phanerozoic Eon. The Precambrian is so named because it preceded the Cambrian, the first period of the ...
Fennoscandian Shield, the Norwegian-Scottish Caledonides and buried North German-Polish Caledonides. The stable Fennoscandian Shield formed from 1.45 billion years ago to 850 million years ago in the
Proterozoic
The Proterozoic () is a geological eon spanning the time interval from 2500 to 538.8million years ago. It is the most recent part of the Precambrian "supereon". It is also the longest eon of the Earth's geologic time scale, and it is subdivided ...
. The Fennoscandian Border Zone is a large fault, bounding the deep basement rock of the Danish Basin—a trough between the Border Zone and the Ringkobing-Fyn High. The Sorgenfrei-Tornquist Zone is a fault-bounded area displaying Cretaceous-Cenozoic inversion.
Geologic history, stratigraphy, and tectonics
Paleozoic (539-251 million years ago)
Cambrian
The Cambrian Period ( ; sometimes symbolized C with bar, Ꞓ) was the first geological period of the Paleozoic Era, and of the Phanerozoic Eon. The Cambrian lasted 53.4 million years from the end of the preceding Ediacaran Period 538.8 million ...
rocks record successive
marine transgression
A marine transgression is a geologic event during which sea level rises relative to the land and the shoreline moves toward higher ground, which results in flooding. Transgressions can be caused by the land sinking or by the ocean basins filling ...
and regression events. Feldspar-rich red bed sandstones deposited in windy floodplains followed by layers of glauconite-rich marine sandstones and offshore siltstone. Black alum shales deposited in the mid-Cambrian in a nearly anoxic epeireic basin with limestone layers, rich in
trilobite
Trilobites (; meaning "three lobes") are extinct marine arthropods that form the class Trilobita. Trilobites form one of the earliest-known groups of arthropods. The first appearance of trilobites in the fossil record defines the base of the At ...
fossils. Condensed, shallow limestone succeeded the black shales in the
Ordovician
The Ordovician ( ) is a geologic period and System (geology), system, the second of six periods of the Paleozoic Era (geology), Era. The Ordovician spans 41.6 million years from the end of the Cambrian Period million years ago (Mya) to the start ...
, with numerous
graptolite
Graptolites are a group of colonial animals, members of the subclass Graptolithina within the class Pterobranchia. These filter-feeding
Filter feeders are a sub-group of suspension feeding animals that feed by straining suspended matter and ...
fossils.
Devonian
The Devonian ( ) is a geologic period and system of the Paleozoic era, spanning 60.3 million years from the end of the Silurian, million years ago (Mya), to the beginning of the Carboniferous, Mya. It is named after Devon, England, whe ...
rocks have never been found in Denmark and marine
Carboniferous
The Carboniferous ( ) is a geologic period and system of the Paleozoic that spans 60 million years from the end of the Devonian Period million years ago ( Mya), to the beginning of the Permian Period, million years ago. The name ''Carbonifero ...
rocks are only known from drill holes at the southern edge of the Ringkobing-Fyn High, which formed at the time as a bulging area north of the Variscan collision zone.
Rotational block faulting in the Late Carboniferous resulted from Variscan wrench deformation, active along the Sorgenfrei-Tornquist Zone. Syn-rift clastic wedges began to accumulate in an emerging half-graben. Continental
red beds
Red beds (or redbeds) are sedimentary rocks, typically consisting of sandstone, siltstone, and shale, that are predominantly red in color due to the presence of ferric oxides. Frequently, these red-colored sedimentary strata locally contain ...
deposited and volcanism occurred.
Regional sagging began in the mid-Permian, leaving the Ringkobing-Fyn High as a high point. Marine transgression began, connecting the region with a narrow seaway to the Shetland Islands. The Danish Basin and the neighboring North German Basin were both highly saline and brackish, leaving behind carbonate and anhydrite layers on southern edge of the High. Up to 1.2 kilometers of
halite
Halite (), commonly known as rock salt, is a type of salt, the mineral (natural) form of sodium chloride ( Na Cl). Halite forms isometric crystals. The mineral is typically colorless or white, but may also be light blue, dark blue, purple, p ...
accumulated in the North Permian Basin, thinning toward the Fennoscandian Border Zone. Subsequent salt tectonism has produced salt diapirs 10 kilometers in diameter, rising five kilometers through overhead rock and some are less than 200 meters deep in Quaternary rocks.
Mesozoic (251-66 million years ago)
North-south rifting with the breakup of
Pangea
Pangaea or Pangea () was a supercontinent that existed during the late Paleozoic and early Mesozoic eras. It assembled from the earlier continental units of Gondwana, Euramerica and Siberia during the Carboniferous approximately 335 million y ...
in the
Triassic
The Triassic ( ) is a geologic period and system which spans 50.6 million years from the end of the Permian Period 251.902 million years ago ( Mya), to the beginning of the Jurassic Period 201.36 Mya. The Triassic is the first and shortest period ...
segmented the Ringkobing-Fyn High into a narrow graben. Sedimentation occurred in fault-bound alluvial fan deposits with occasional small marine transgressions, such as the Muschekalk Sea in the mid-Triassic in the Ringkobing-Fyn High. Triassic outcrops are only found on southern shore of Bornholm. Extensional faulting occurred throughout the
Mesozoic
The Mesozoic Era ( ), also called the Age of Reptiles, the Age of Conifers, and colloquially as the Age of the Dinosaurs is the second-to-last era of Earth's geological history, lasting from about , comprising the Triassic, Jurassic and Cretaceo ...
, but overall, conditions remained the same into the
Cretaceous
The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of th ...
. Oscillating marine transgressions in the
Rhaetian
The Rhaetian is the latest age of the Triassic Period (in geochronology) or the uppermost stage of the Triassic System (in chronostratigraphy). It was preceded by the Norian and succeeded by the Hettangian (the lowermost stage or earliest age ...
to
Middle Jurassic
The Middle Jurassic is the second epoch of the Jurassic Period. It lasted from about 174.1 to 163.5 million years ago. Fossils of land-dwelling animals, such as dinosaurs, from the Middle Jurassic are relatively rare, but geological formations co ...
shifted deposition from delta sands to offshore mudstones and regional updoming took place at the junction of the Central Graben, Moray Firth and Viking Graben. Deltas were drowned and replaced with deepwater basins and major rifting in the Late Jurassic produced block tilting.
Sedimentation shifted in
Albian
The Albian is both an age of the geologic timescale and a stage in the stratigraphic column. It is the youngest or uppermost subdivision of the Early/Lower Cretaceous Epoch/Series. Its approximate time range is 113.0 ± 1.0 Ma to 100.5 ± 0.9 M ...
through
Danian
The Danian is the oldest age or lowest stage of the Paleocene Epoch or Series, of the Paleogene Period or System, and of the Cenozoic Era or Erathem. The beginning of the Danian (and the end of the preceding Maastrichtian) is at the Cretaceous ...
times from siliclastic to carbonaceous, marked by
marl
Marl is an earthy material rich in carbonate minerals, clays, and silt. When hardened into rock, this becomes marlstone. It is formed in marine or freshwater environments, often through the activities of algae.
Marl makes up the lower part o ...
and glauconite sandstones. Sea level fell in the
Maastrichtian
The Maastrichtian () is, in the ICS geologic timescale, the latest age (uppermost stage) of the Late Cretaceous Epoch or Upper Cretaceous Series, the Cretaceous Period or System, and of the Mesozoic Era or Erathem. It spanned the interval from ...
, restricting the sea to deeper areas of the Central Graben. The Stevns Klint type locality contains the Fish Clay with an iridium anomaly indicative at the
K-Pg mass extinction.
Cenozoic (66 million years ago-present)
During the Damian Stage, carbonate deposit stopped, bringing an erosional unconformity. As the
Selandian
The Selandian is a stage in the Paleocene. It spans the time between . It is preceded by the Danian and followed by the Thanetian. Sometimes the Paleocene is subdivided in subepochs, in which the Selandian forms the "middle Paleocene".
Stratigr ...
transgressive phase got underway
glauconite
Glauconite is an iron potassium phyllosilicate ( mica group) mineral of characteristic green color which is very friable and has very low weathering resistance.
It crystallizes with a monoclinic geometry. Its name is derived from the Greek () m ...
sand and older, reworked Cretaceous and Devonian sediments deposited, overlain by pelagic
smectite
A smectite (from ancient Greek ''σμηκτός'' smektos 'lubricated'; ''σμηκτρίς'' smektris 'walker's earth', 'fuller's earth'; rubbing earth; earth that has the property of cleaning) is a mineral mixtures of various swelling sheet sil ...
clay. Erosion in the
Neogene
The Neogene ( ), informally Upper Tertiary or Late Tertiary, is a geologic period and system that spans 20.45 million years from the end of the Paleogene Period million years ago ( Mya) to the beginning of the present Quaternary Period Mya. ...
and
Pleistocene
The Pleistocene ( , often referred to as the ''Ice age'') is the geological Epoch (geology), epoch that lasted from about 2,580,000 to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations. Before a change was fina ...
has eroded most rock units that would likely have indicated open marine conditions. A break in sedimentation in the
Oligocene
The Oligocene ( ) is a geologic epoch of the Paleogene Period and extends from about 33.9 million to 23 million years before the present ( to ). As with other older geologic periods, the rock beds that define the epoch are well identified but the ...
was followed by a marine transgression and sediment accumulated in the Danish Basin, with significant coarse quartz sand compared to older Paleogene clays.
The deepest point of deposition—the depocenter—moved toward the North Sea and Central Graben during the Oligocene and the coastline shifted to the Fennoscandian Border Zone in Jylland. This was a result of regional uplift of the Norwegian Caledonides and the Fennoscandian Shield. The Caledonides were actually eroded to a nearly flat
peneplain
390px, Sketch of a hypothetical peneplain formation after an orogeny.
In geomorphology and geology, a peneplain is a low-relief plain formed by protracted erosion. This is the definition in the broadest of terms, albeit with frequency the usage ...
by the Permian and so the uplift was a non-orogenic and comparatively recent one. Shallow marine deposition continued until the
Pleistocene
The Pleistocene ( , often referred to as the ''Ice age'') is the geological Epoch (geology), epoch that lasted from about 2,580,000 to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations. Before a change was fina ...
with increasing sand and coal from the
Miocene
The Miocene ( ) is the first geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and means "less recen ...
. Up to three kilometers of sand accumulated in the Central Graben.
During the Pleistocene the region was glaciated multiple times, leaving glaciofluvial plains in the west and clay soils in the east. Isostatic rebound and post-glacial thin-skinned folding and thrusting have been common geologic forces in the
Holocene
The Holocene ( ) is the current geological epoch. It began approximately 11,650 cal years Before Present (), after the Last Glacial Period, which concluded with the Holocene glacial retreat. The Holocene and the preceding Pleistocene togethe ...
.
Natural resource geology
Denmark has few natural resources although some small oil and gas fields have been found offshore since the 1970s. Gravel, sand, and chalk are all mined for building material and in North Jylland plastic clay and
diatomite
Diatomaceous earth (), diatomite (), or kieselgur/kieselguhr is a naturally occurring, soft, siliceous sedimentary rock that can be crumbled into a fine white to off-white powder. It has a particle size ranging from more than 3 μm to le ...
are extracted as insolation material.
References
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