The Dasberg Event was a minor

extinction event An extinction event (also known as a mass extinction or biotic crisis) is a widespread and rapid decrease in the biodiversity on Earth. Such an event is identified by a sharp fall in the diversity and abundance of multicellular organisms. It occ ...

that occurred during the

Famennian The Famennian is the later of two faunal stages in the Late Devonian epoch. The most recent estimate for its duration is that it lasted from around 371.1 to 359.3 million years ago. An earlier 2012 estimate, still used by the International Commis ...

, the final

stage Stage, stages, or staging may refer to: Arts and media Acting * Stage (theatre), a space for the performance of theatrical productions * Theatre, a branch of the performing arts, often referred to as "the stage" * ''The Stage'', a weekly Brit ...

of the

Devonian The Devonian ( ) is a period (geology), geologic period and system (stratigraphy), system of the Paleozoic era (geology), era during the Phanerozoic eon (geology), eon, spanning 60.3 million years from the end of the preceding Silurian per ...

period. It is often considered to be one of the events contributing to the

Late Devonian extinction The Late Devonian mass extinction, also known as the Kellwasser event, was a mass extinction event which occurred around 372 million years ago, at the boundary between the Frasnian and Famennian ages of the Late Devonian period.Racki, 2005McGh ...

, which is believed by many

palaeontologists Paleontology, also spelled as palaeontology or palæontology, is the scientific study of the life of the past, mainly but not exclusively through the study of fossils. Paleontologists use fossils as a means to classify organisms, measure geolo ...

to have been a protracted event that took place over millions of years.

Timing

The Dasberg Event occurred during the late Famennian in the ''Palmatolepis gracilis expansa''

conodont Conodonts, are an extinct group of marine jawless vertebrates belonging to the class Conodonta (from Ancient Greek κῶνος (''kōnos''), meaning " cone", and ὀδούς (''odoús''), meaning "tooth"). They are primarily known from their hard ...

biozone In biostratigraphy, biostratigraphic units or biozones are intervals of geological strata that are defined on the basis of their characteristic fossil taxon, taxa, as opposed to a Lithostratigraphy, lithostratigraphic unit which is defined by the ...

, near the boundary between the lower and middle parts of the ''expansa'' biozone.

Causes

Anoxia has been implicated as the main cause of the Dasberg Event. In the deep-shelf Kowala site in the

Holy Cross Mountains Sacred describes something that is dedicated or set apart for the service or worship of a deity; is considered worthy of spiritual respect or devotion; or inspires awe or reverence among believers. The property is often ascribed to objects (a ...

of Poland, possible

evidence Evidence for a proposition is what supports the proposition. It is usually understood as an indication that the proposition is truth, true. The exact definition and role of evidence vary across different fields. In epistemology, evidence is what J ...

of either intermittent anoxia throughout the water column or of prevalent anoxia in surficial waters concurrent with oxygenated bottom water in the lower Dasberg shale comes from low ratios of

uranium Uranium is a chemical element; it has chemical symbol, symbol U and atomic number 92. It is a silvery-grey metal in the actinide series of the periodic table. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons. Ura ...

thorium Thorium is a chemical element; it has symbol Th and atomic number 90. Thorium is a weakly radioactive light silver metal which tarnishes olive grey when it is exposed to air, forming thorium dioxide; it is moderately soft, malleable, and ha ...

, the dominance of small

framboid A framboid is a micromorphological feature common to certain sedimentary minerals, particularly pyrite (FeS2). The first known use of the term is ascribed to Rust in 1935 and is derived from the French 'framboise', meaning 'raspberry', reflecting th ...

s combined with the presence of large framboids, and the presence of green sulphur bacterial

biosignature A biosignature (sometimes called chemical fossil or molecular fossil) is any substance – such as an element, isotope, molecule, or phenomenon – that provides scientific evidence of past or present life on a planet. Measurable ...

s. No evidence of anoxia exists in the sedimentary layers sandwiched in between the lower and upper Dasberg shale layers. During the deposition of the upper Dasberg shale, both bottom waters and the water column were anoxic. Both of the two intervals of anoxia are linked to

marine transgression A marine transgression is a geologic event where sea level rises relative to the land and the shoreline moves toward higher ground, resulting in flooding. Transgressions can be caused by the land sinking or by the ocean basins filling with water ...

s and microbial blooms of primary producers.

Volcanic activity Volcanism, vulcanism, volcanicity, or volcanic activity is the phenomenon where solids, liquids, gases, and their mixtures erupt to the surface of a solid-surface astronomical body such as a planet or a moon. It is caused by the presence of a he ...

from the Yakutsk-Vilyuy Large Igneous Province or the Kola-Dnieper Large Igneous Province has been put forward as an

explanation An explanation is a set of statements usually constructed to describe a set of facts that clarifies the causes, context, and consequences of those facts. It may establish rules or laws, and clarifies the existing rules or laws in relation ...

for the occurrence of anoxia. Pulses of activity from these

large igneous province A large igneous province (LIP) is an extremely large accumulation of igneous rocks, including intrusive ( sills, dikes) and extrusive (lava flows, tephra deposits), arising when magma travels through the crust towards the surface. The format ...

s have been suggested as causes for other Late Devonian biotic crises. However, this association is highly tentative, as there exist no estimates precise enough for the timing of these pulses to conclusively prove their responsibility for causing the Dasberg Event.

Effects

The Dasberg Event caused the

extinction Extinction is the termination of an organism by the death of its Endling, last member. A taxon may become Functional extinction, functionally extinct before the death of its last member if it loses the capacity to Reproduction, reproduce and ...

of many

pelagic The pelagic zone consists of the water column of the open ocean and can be further divided into regions by depth. The word ''pelagic'' is derived . The pelagic zone can be thought of as an imaginary cylinder or water column between the sur ...

species A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...

, particularly

ammonoids Ammonoids are extinct, (typically) coiled-shelled cephalopods comprising the subclass Ammonoidea. They are more closely related to living octopuses, squid, and cuttlefish (which comprise the clade Coleoidea) than they are to nautiluses (family N ...

. One of its other consequences was the appearance of the Etroeungt fauna, an unusual faunal assemblage consisting of very large

brachiopods Brachiopods (), phylum Brachiopoda, are a phylum of animals that have hard "valves" (shells) on the upper and lower surfaces, unlike the left and right arrangement in bivalve molluscs. Brachiopod valves are hinged at the rear end, while the fron ...

and solitary

rugose coral The Rugosa or rugose corals are an extinct class of solitary and colonial corals that were abundant in Middle Ordovician to Late Permian seas. Solitary rugosans (e.g., '' Caninia'', '' Lophophyllidium'', '' Neozaphrentis'', '' Streptelasma ...

s; this short-lived fauna died out a few million years later in the much more severe

Hangenberg Event The Hangenberg event, also known as the Hangenberg crisis or end-Devonian extinction, is a mass extinction that occurred at the end of the Famennian stage, the last Stage (stratigraphy), stage in the Devonian Period (roughly 358.9 ± 0.4 million y ...

. This event, like many

anoxic event An anoxic event describes a period wherein large expanses of Earth's oceans were depleted of dissolved oxygen (O2), creating toxic, euxinic ( anoxic and sulfidic) waters. Although anoxic events have not happened for millions of years, the geol ...

s, resulted in the widespread deposition of

black shale Shale is a fine-grained, clastic sedimentary rock formed from mud that is a mix of flakes of clay minerals (hydrous aluminium phyllosilicates, e.g., kaolin, Al2 Si2 O5( OH)4) and tiny fragments (silt-sized particles) of other minerals, especiall ...

s. In addition to black shales, widespread organic-rich

limestone Limestone is a type of carbonate rock, carbonate sedimentary rock which is the main source of the material Lime (material), lime. It is composed mostly of the minerals calcite and aragonite, which are different Polymorphism (materials science) ...

s were also deposited during the event.

References

{{Reflist Late Devonian extinctions Famennian extinctions

Timing

Causes

Effects

See also

References