[3] The Hangenberg Event can be recognized by its unique multi-phase sequence of sedimentary layers, representing a relatively short interval of time with extreme fluctuations in the climate, sea level, and diversity of life.

The entire event had an estimated duration of 100,000 to several hundred thousand years, occupying the upper third of the 'Strunian' (latest Famennian), and a small portion of the early Tournaisian.

It is named after the Hangenberg Black Shale, a distinctive layer of anoxic sediment originally found along the northern edge of the Rhenish Massif in Germany.

Sequences equivalent to the Rhenish succession have been found at over 30 other sites on every continent except Antarctica, confirming the global nature of the Hangenberg Event.

In some places the Wocklum Limestone grades into the Drewer Sandstone, a thin turbidite deposit which initiates the lower crisis interval.

Increased erosion and siliciclastic input indicates that the Drewer Sandstone was deposited during a minor marine regression (sea level fall).

The black shale was deposited during a large marine transgression (sea level rise), as indicated by flooding reducing the input of terrestrial spores and increasing eutrophication.

[1][2][4][5] The Hangenberg Black Shale corresponds to the Postclymenia zone (UD VI-E), an ammonoid genozone based on massive extinctions within the group, rather than new occurrences.

A major marine regression occurred during the middle crisis interval, as indicated by the increased amount of erosion and river-supplied siliciclastic material.

[7] This regression was caused by a cooling episode, and time-constrained glacial deposits have been found in Bolivia and Brazil (which would have been high-latitude areas), as well as the Appalachian Basin (which would have been a tropical alpine environment).

[8] The upper crisis interval begins with the return of prominent carbonate rocks: a marly unit, the Stockum Limestone, spans the Devonian–Carboniferous (D–C) boundary.

The base of the Stockum Limestone also sees the beginning of the Protognathodus kockeli conodont zone and further ammonoid diversification within the upper Acutimitoceras (Stockumites) genozone (LC I-A1).

'Survivor' faunas of marine invertebrates, such as the last cymaclymeniid ammonoids and phacopid trilobites, also die out at this time, making it the second largest extinction pulse of the Hangenberg Crisis.

The base of the Hangenberg Limestone is characterized by the first occurrence of gattendorfiine ammonoids (making up the Gattendorfia genozone, LC I-A2) and the MFZ1 foraminifera zone.

Depending on the method used, the Hangenberg Event typically falls between the fifth and tenth deadliest post-Cambrian mass extinctions, in terms of marine genera lost.

[19] McGhee et al. 2013 attempted to tackle extinction rates via a new resampling protocol designed to counter biases in biodiversity estimates, such as the Signor–Lipps effect and Pull of the Recent.

[16] Even in areas with oxygenated seabeds, such as parts of Morocco, the ecospace of Hangenberg event communities was restricted to only a few ecological groups, particularly slow-moving pelagic predators (i.e. ammonoids and acanthodians) and epifaunal sessile filter feeders (i.e. bivalves and bryozoans).

[1] Nevertheless, in the absence of pressures from metazoan communities, there was a brief resurgence of microbial carbonate in the early Tournaisian, a similar pattern to other mass extinctions.

[1] Bivalves in the family Naiaditidae apparently took advantage of the Famennian glaciation to expand from polar regions towards the equator, sparking diversification in the Carboniferous tropics.

[29][27][30] Placoderm diversity had already decreased in the Kellwasser Event, and all remaining subgroups (arthrodires, antiarchs, phyllolepids, and ptychodontids) died out abruptly at the end of the Devonian.

[1][27][29] Some large fish, namely rhizodonts, megalichthyids, and a few acanthodians, survived but failed to significantly increase their ecological disparity, eventually dying out later in the Paleozoic.

[29] Among the most major ecological changes associated with the extinction are the rise of chondrichthyans (sharks and kin) and actinopterygians (ray-finned fish), which took over in diversity and relative abundance during the Early Carboniferous.

"tetrapods" in the broad sense of the term) evidently survived, eventually leading to the earliest true amphibians, who gave rise to the fully terrestrial (amniote) sauropsids and synapsids in the Carboniferous.

[34] However, recent and continued discovery of many Visean and Tournaisian "tetrapods" has helped to close in this gap, suggesting that the Hangenberg Event affected some vertebrates less severely than previously thought.

[35][36][37] Coprolitic evidence from early Tournaisian deposits in eastern Greenland has also supported the notion that tetrapods were not as affected by the Hangenberg Event as previously thought.

[38] During the Famennian, the world was covered by a fairly homogenous and low-diversity land plant flora, dominated by giant Archaeopteris trees.

As oceans flooded terrestrial basins, water would have entered areas with high nutrient levels, leading to an algal bloom, removing oxygen and then creating hydrogen sulfide as the algae decayed.

[51] Ozone depletion could just as easily be explained by an increase in greenhouse gas concentrations resulting from an intense period of arc volcanism.

[52] The spore malformations may not even be related to UV radiation in the first place, and could simply be a result of volcanism-related environmental pressures such as acid rain.

[50] Evidence of coronene and mercury spikes occurring in the Tien Shan Mountains of southern Uzbekistan near the Devonian–Carboniferous boundary has led some researchers to hypothesise a volcanic cause for the Hangenberg event.