In the geological timescale, the Tithonian is the latest age of the Late Jurassic Epoch and the uppermost stage of the Upper Jurassic Series. It spans the time between 149.2 ±0.7 Ma and 143.1 ±0.6 (million years ago). It is preceded by the Kimmeridgian and followed by the Berriasian (part of the Cretaceous).
Stratigraphic definitions The Tithonian was introduced in scientific literature by German stratigrapher Albert Oppel in 1865. The name Tithonian is unusual in geological stage names because it is derived from Greek mythology. Tithonus was the son of Laomedon of Troy and fell in love with Eos, the Greek goddess of dawn. His name was chosen by Albert Oppel for this stratigraphical stage because the Tithonian finds itself hand in hand with the dawn of the Cretaceous. The base of the Tithonian stage is at the base of the ammonite biozone of Hybonoticeras hybonotum. A global reference profile (a GSSP or golden spike) for the base of the Tithonian had in 2009 not yet been established. The top of the Tithonian stage (the base of the Berriasian Stage and the Cretaceous System) is marked by the first appearance of small globular calpionellids of the species Calpionella alpina, at the base of the Alpina Subzone .
Subdivision The Tithonian is often subdivided into Lower/Early, Middle and Upper/Late substages or subages. The Late Tithonian is coeval with the Portlandian Age of British stratigraphy. The Tithonian stage contains seven ammonite biozones in the Tethys domain, from top to base:
zone of Durangites zone of Micracanthoceras micranthum zone of Micracanthoceras ponti or Burckardticeras peroni zone of Semiformiceras fallauxi zone of Semiformiceras semiforme zone of Semiformiceras darwini zone of Hybonoticeras hybonotum
Sedimentary environments Sedimentary rocks that formed in the Tethys Ocean during the Tithonian include limestones, which preserve fossilized remains of, for example, cephalopods. The Solnhofen limestone of southern Germany, which is known for its fossils (especially Archaeopteryx), is of Tithonian age.
Tithonian extinction The later part of the Tithonian stage experienced an extinction event. It has been referred to as the Tithonian extinction, Jurassic-Cretaceous (J–K) extinction, or end-Jurassic extinction. This event was fairly minor and selective, by most metrics outside the top 10 largest extinctions since the Cambrian. Nevertheless, it was still one of the largest extinctions of the Jurassic Period, alongside the Toarcian Oceanic Anoxic Event (TOAE) in the Early Jurassic.
Potential causes
Cooling and sea level fall The Tithonian extinction has not been studied in great detail, but it is usually attributed to habitat loss via a major marine regression (sea level fall). There is good evidence for a marine regression in Europe across the Jurassic-Cretaceous boundary, which may explain the localized nature of the extinction. On the other hand, there is no clear consensus on a correlation between sea level and terrestrial diversity during the Jurassic and Cretaceous. Some authors support a fundamental correlation (the so-called "common cause hypothesis"), while others strongly voice doubts. Sea level fall was likely related to the Tithonian climate, which was substantially colder and drier than the preceding Kimmeridgian stage. Northern coral reef ecosystems, such as those of the European Tethys, would have been particularly vulnerable to global cooling during this time.
Volcanism or asteroid impacts Few Jurassic-Cretaceous boundary sections are precisely associated with carbon isotope anomalies. Several Arctic outcrops show a moderate (up to 5‰) negative organic δ13C excursion in the middle part of the Tithonian. This excursion, sometimes called the Volgian Isotopic Carbon Excursion (VOICE), may be a consequence of volcanic activity. The Tithonian stage saw the emplacement of the Shatsky Rise, a massive volcanic plateau in the North Pacific. During the Late Jurassic and Early Cretaceous, numerous volcanic deposits can be found along the margin of Gondwana, which was beginning to fragment into smaller continents.
Three large impact craters have been tentatively dated to the Tithonian: the Morokweng Impact Structure (South Africa, 75 to 240 km diameter), Mjølnir crater (Barents Sea, 40 km diameter), and Gosses Bluff crater (Australia, 22 km diameter). These impacts would have caused local devastation, but likely had minimal impact on global ecosystems. Most volcanic events or extraterrestrial impacts in the Late Jurassic were concentrated around Gondwana, in contrast to the extinction event, which was centered on Laurasian ecosystems. An iridium anomaly was found in Tithonian strata of north-eastern Brazil along with mercury and tellurium. The iridium is plausibly linked to the Morokweng structure whereas mercury and tellurium indicate volcanic input.
Sampling bias It has been suggested that the putative extinction is a consequence of sampling biases. The Late Jurassic is packed with marine lagerstätten, exceptionally diverse and well-preserved fossil beds. A lack of earliest Cretaceous marine lagerstätten may appear as a loss of diversity, simply looking at the raw data alone. Sampling bias may also explain apparent extinctions in terrestrial environments, which have a similar disconnect in fossil abundance. This is most obvious in sauropod-bearing deposits, which are abundant in the Late Jurassic and rare in the earliest Cretaceous. Most studies relevant to the Tithonian extinction attempt to counteract sampling biases when estimating diversity loss or extinction rates. Depending on the sampling method or the taxonomic group, the Tithonian extinction may still be apparent even once sampling biases are accounted for.
Impact on life In 1986, Jack Sepkoski argued that the Late Tithonian extinction was the largest extinction event between the end of the Triassic and the end of the Cretaceous. He estimated that a staggering 37% of genera died out during the Tithonian stage. Benton (1995) found a lower estimate, with the extinction of 5.6 to 13.3% of genera in the Tithonian. Proportional extinction was higher for continental genera (5.8–17.6%) than marine genera (5.1–6.1%). Sepkoski (1996) estimated that about 18% of multiple-interval marine genera (those originating prior to the Tithonian) died out in the Tithonian. Based on an updated version of Sepkoski's genera compendium, Bambach (2006) found a similar estimate of 20% of genera going extinct in the Late Tithonian.
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