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AbstractThis page describes the Cretaceous Period, including stratigraphy, paleogeography, and famous lagerstätten, followed by a sketched outline of some of the major evolutionary events.
Keywords: Cretaceous, Cretaceous biota, fossil record, evolution
The earliest concept of the Cretaceous was formailsed in 1822 when d’Halloy defined what he called the “Terraine Crétacé”. However, the base of the period has been modified over the years, most recently by the inclusion of the Berriasian as the lowermost stage in the Cretaceous System.
Lower (Jurassic–Cretaceous) Boundary
As yet there is no ratified GSSP for the base of the Berriasian Stage (= the base of the whole Cretaceous System) although, by common usage, it lies near the first appearance datum (FAD) of the ammonite, Berriasella jacobi. Unfortunately, this ammonite is largely confined to the Mediterranean realm, so the datum is not much use internationally.
Upper (Cretaceous–Paleogene) Boundary
The GSSP for the base of the Danian Stage (= Cretaceous-Paleogene boundary) was established in 1996 in the clay layer containing the famous “K/T” iridium anomaly and nickel-rich spinels at a section of Oued Djerfane, 8 km west of El Kef, in Tunisia (see Molina et al. 2006).
The base of the Cretaceous, though not yet formally defined, is approximately 145 Ma. The top, however, has been very accurately dated: it is 66.04 Ma.
Major Tectonic Events
At the beginning of the Cretaceous, Pangaea was breaking up into Laurasia in the north and Gondwana in the south. By the end of the period, at least the Gondwana continents had largely separated and were starting to migrate into their present day positions.
[Add something about Antarctica/Australia/New Zealand breakup & set scene for Drake Passage etc. in the Paleogene]
Land and Sea
Major Evolutionary Events
“Angiosperms first appeared in the fossil record as pollen during the Valanginian-Hauterivian [~139.8 to 129.4 Ma]; they spread out of the tropics in the Aptian and Albian [~125.0 to 100.5 Ma], and radiated in the Late Cretaceous” (Harris & Arens 2016, p. 640).
Hell Creek Formation: Montana and the Dakotas; non-marine fluvial channel-fill and floodplain deposits, primarily sandstone, siltstone and mudstone; diachronously overlain by lignites; almost entirely Late Cretaceous but in some places earliest Paleogene at the very top; iridium found in some of the overlying lignites may be related to the “K/T” iridium anomaly; dinosaurs have been known from the Hell Creek Formation since at least Barnum Brown’s AMNH expedition of 1902; diverse assemblage of theropods, ornithopods, pachycephalosaurs, ankylosaurs and ceratopsids, including the type and a few other specimens of Tyrannosaurus rex. See Lofgren 1997.
Pierre Shale: Late Cretaceous (Campanian) North Dakota, USA; arthropods, vertebrates, including mosasaurs
Hajoula Limestone: Cretaceous Lebanon; sublithographic limestone; fossil arthropods and fish
Sierra de Montsech: Cretaceous Spain; fossil spiders, insects, crustaceans and vertebrates; Selden 1989
Santana Formation: This spectacular locality is one of the most prolific sources of Early Cretaceous fish fossils. It is located in north east Brazil at the foot of Araripe Plateau, on the border of Ceará State. The fossils occur in shales, thin limestone bands, and commonly in rounded calcareous concretions. The site is most famous for fossil fish, but arthropods, molluscs, dinosaurs and pterosaurs, as well as some plants are also known.
Jehol Group: Early Cretaceous Northeastern China; finds include the famous “feathered” dinosaurs, early birds, putative basal angiosperms, and primitive mammals. Detailed soft-tissue preservation of organisms is known.
Yixian Formation: Cretaceous (possibly some latest Jurassic? check this) Sihetun, Liaoning Province, China; true birds, dinosaurs, and several of the so-called ‘feathered dinosaurs’ [check if this is not the same as the previous entry]
Surely the most widely reported – and in the lay media, at least, the most widely misreported – of all extinction events is that which brought the age of the dinosaurs to an end at the close of the Maastrichtian: the “K/T” extinction.
The exact timing and nature of the end-Cretaceous mass-extinction event is famously contentious, so let us be clear about two things right from the outset: First, a bolide did strike the Earth at the end of the period. In fact the Cretaceous-Paleogene boundary is defined by this event, so any suggestion that the impact occurred before or after the end of the Cretaceous is simply nonsensical. But, second, the almost unimaginably vast Deccan Traps volcanism was in full swing at the same time. Both of these events inevitably influenced the climate, the atmosphere, and life, to a great degree. One may resonably argue about which event had the most influence over a particular group of organisms at a particular place and time, but to adopt one or other phenomenon as a complete explanation for the mass extinction, to the outright exclusion of the other, strikes me as ideological. That is not science.
“The idea of mass extinctions of life, traditionally by great floods, still has a strong hold on western imagination. Everyone has a favourite theory for major extinctions, all united by the common theme of attributing dominant importance to physical factors, and playing down the importance of normal biological mechanisms. Our own work strongly favours the diversification of both mammals and birds at least 30 million years before the extinction of dinosaurs – there must be ecological consequences for small dinosaurs from this early diversification” (Penny 2001). Fossil evidence also supports a progressive change in the composition of mammal communities across the K-T boundary, although dating uncertainties have complicated any simple interpretation of this data (e.g. Lofgren 1995).
“Recent field and laboratory investigations have established that the latest Cretaceous (i.e. Campanian-Maastrichtian) sedimentary succession exposed within the James Ross Basin, Antarctica is in excess of 2 km in total thickness. Comprising essentially fine-grained, shallow-water, volcaniclastic rocks that are in places intensely fossiliferous, it represents one of the best opportunities to investigate palaeobiological and palaeoenvironmental changes leading up to the K-T boundary anywhere in the southern hemisphere. The exceptionally early extinction patterns of the inoceramid bivalves and belemnites can be confirmed, but it is apparent that other key groups such as the ammonites and trigoniid bivalves go right up to the boundary itself. Studies throughout the 1000 m thick Maastrichtian sequence indicate that, although molluscan assemblages are abundant, they are never particularly diverse. The benthic element has a distinctly temperate aspect and there is both sedimentological and palaeontological evidence to suggest that it was subjected to periodic intervals of reduced oxygen levels. The comparatively small, but nevertheless still abrupt, extinction event at the end of the Cretaceous in Antarctica may well have been buffered to some extent by both the high-latitude position and unusual sedimentological setting of the basin” (Crame 1999).
A number of authorities have reported multiple iridium spikes in the vicinity of the Cretaceous-Tertiary boundary (Ganapathy et al. 1981; Donovan et al. 1988; Graup & Spettel 1989; Bhandari et al. 1995, 1996; Zhao et al. 2002). These observations do not fit comfortably with the theory of a single, massive bolide impact being largely responsible for numerous end-Cretaceous phenomena. In the Nanxiong Basin, China, the evidence suggests that “the K/T event was not marked by an instantaneous geochemical environmental change, but stretched out over a considerable time” (Zhao et al. 2002, p. 10).
New Zealand Occurrences
Bhandari, A.; Shukla, P.N.; Ghevariya, Z.G.; Sundaram, S.M. 1995: Impact did not trigger Deccan volcanism: Evidence from Anjar K/T boundary layer in Deccan intertrappean sediments. Geophysics Research Letters 22: 433-436. Geo Res Lett.
— 1996: K/T boundary layer in Deccan intertrappean at Anjar, Kutch. In Ryder, G. et al. (eds.) 1996: The Cretaceous-Tertiary event and other catastrophes in Earth history . Geological Society of America Special Paper 307. : 417-424.
Crame, A. 1999: Changes in molluscan faunas across the K-T boundary in Antarctica. Palaeontological Association 43rd Annual Meeting, University of Manchester, 19-22 December 1999 (Oral Presentation).
d’Halloy, J.G.J.d’O. 1822: Observations sur un essai de cartes géologiques de la France, des Pays-Bas, et des contrées voisines. Annales de Mines 7: 353-376.
Donovan, A.D.; Baum, G.R. et al. 1988: Sequence stratigraphic setting of the Cretaceous-Tertiary boundary in Central Alabama. In Wilgus, C.K. et al. (eds.) 1988: Sea-level changes - An integrated approach. Soc. Econ. Paleontol. Mineralog. Special Publication 42. : 299-307.
Ganapathy, R.; Gartner, S.; Jiang, M. 1981: Iridium anomaly at the Creataceous-Tertiary boundary in Texas. Earth and Planetary Science Letters 54: 393-396. E Pl Sci Lett.
Graup, G.; Spettel, B. 1989: Mineralogy and phase-chemistry of an Ir enriched pre-K/T layer from the Lattengebirge, Bavarian Alps, and significance for the KTB problem. Earth and Planetary Science Letters 95: 271-290. E Pl Sci Lett.
Harris, E.B.; Arens, N.C. 2016: A mid-Cretaceous angiosperm-dominated macroflora from the Cedar Mountain Formation of Utah, USA. Journal of Paleontology 90 (4): 640-662.
Lofgren, D.F. 1997: Hell Creek Formation. In Currie, P.J.; Padian, K. (eds.) 1997: Encyclopedia of dinosaurs. Academic Press: 1-869. : 302-303.
Lofgren, D.L. 1995: The Bug Creek Problem and the Cretaceous-Tertiary Transition at McGuire Creek, Montana. University of California Press.
Molina, E.; Alegret, L.; Arenillas, I.; Arz, J.A.; Gallala, N.; Hardenbol, J.; von Salis, K.; Steurbaut, E.; Vandenberghe, N.; Zaghbib-Turki, D. 2006: The Global Boundary Stratotype Section and Point for the base of the Danian Stage (Paleocene, Paleogene, “Tertiary”, Cenozoic) at El Kef, Tunesia - Original definition and revision. Episodes 29: 263-273.
Ogg, J.G.; Ogg, G.; Gradstein, F.M. 2008: The Concise Geologic Time Scale. Cambridge: 1-177.
Penny, D. 2001: Molecular Evolution: Introduction. Nature Encyclopedia of Life Sciences [doi:10.1038/npg.els.0001701].
Zhao, Z.; Mao, X.; Chai, Z.; Yang, G.; Kong, P.; Ebihara, M.; Zhao, Z. 2002: A possible causal relationship between the extinction of dinosaurs and K/T iridium enrichment in the Nanxiong Basin, South China: evidence from dinosaur eggshells. Palaeogeography, Palaeoclimatology, Palaeoecology 178: 1-17.
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