Pangean shelf carbonates: Controls and paleoclimatic significance of Permian and Triassic reefs

Abstract

Late Paleozoic to Liassic reefs and shelf carbonates, forming at the time of accretion and dispersal of Pangea, are specific because of the frequency of reef types other than framework reefs, the importance of microbial contribution, an increase of bioerosional control, the probable invention of algal/coral symbiosis, and the occurrence of major evolutionary crises of reef biota partly connected with extinction events.The data base is biased with regard to time intervals and geographic regions. The use of reef distribution in paleoclimatic reconstructions is strongly dependent on paleomaps available. The current three-step processes model describing the evolution of Mesozoic reefs must be modified. Important constituents of Pangean shelf and reef biota include algae, sponges, and corals exhibiting distinct changes in taxonomic composition, diversity, skeletal mineralogy, and the contribution to reef-building. Reef evolution is characterized by the development of various reef types with different time ranges during accretion and dispersal times of Pangea. Changes in the composition of reef biota with regard to taxa and guild membership are evident during the Permian and Triassic. Reef gaps might have existed during the Early Triassic and perhaps also during the lowermost Early Jurassic. Crucial questions concerning reef evolution in the time of Pangea concern the mode of biotic changes; the lack of Paleozoic holdovers in Triassic reef biotopes and the Scythian reef gap; the coincidence of the late Triassic reef crises with other major modifications of paleogeography, paleoceanography, and climate during the Carnian; and the meaning of the apparently synchronous end-Triassic reef extinction. Both biological and nonbiological processes depending on paleoclimate and paleolatitudes and connected with sea-level changes of different orders should have been active in the control of the evolution of reefs. The latitudinal distributional patterns of Late Paleozoic reefs, however, might not necessarily reflect low-latitudinal warm-water regions as would be derived from recent distributional patterns. Control of reef development, especially by water temperature and light, may have been different for the various types of reef mounds and reefs originating during Pangean times as compared with Holocene coral reefs. Comparisons of distribution patterns of ancient reefs and global circulation models could help in understanding climatic shifts (as indicated by apparently different paleolatitudinal maxima ofCarboniferous to Triassic reefs), in testing long-lasting factors that might have limited reef distribution (e.g., storm tracks, high precipitation areas) as well as in interpreting biogeographical patterns on the shelves around Pangea. Flügel, E., 1994, Pangean shelf carbonates: Controls and paleoclimatic significance of Permian and Triassic reefs, in Klein, G. D" ed., Pangea: Paleoclimate, Tectonics, and Sedimentation During Accretion, Zenith, and Breakup of a Supercontinent: Boulder, Colorado, Geological Society of America Sp...

An early Middle Anisian (Middle Triassic) Tubiphytes and cement crusts-dominated reef from North Dobrogea (Romania): facies, depositional environment and diagenesis

“…This is recorded after the end-Palaeozoic or Early-Middle Triassic extinctions (Della Porta et al 2004), which deeply affected the carbonate production in the following time intervals. The Early Triassic 'reef gap' lasted more than 5 Ma (Payne et al 2006), before the reef communities re-diversified during the Middle Triassic (Flügel and Stanley 1984;Stanley 1988;Senowbari-Daryan et al 1993;Flügel 1994Flügel , 2002. During this time, the intense hothouse climate that caused the extinction persisted and the equator to pole temperature gradient was very low (Preto et al 2010).…”

“…It was formed by a micro-framework consisting of Tubiphytes, very small encrusting and low-growing organisms, as well as abundant fine-grained internal sediment, microbial crusts, and autochthonous micrite (automicrite), all reinforced by large volumes of marine cement, showing similarities with both Permian (Wood 1999(Wood , 2000Weidlich 2002) and Ladinian reefs (Flügel 2002). From a compositional point of view, the Tubiphytes-reef is a microbial reef, one of the eight major compositional reef types distinguished by Flügel (1994Flügel ( , 2002.…”

Subdivision of the dinoflagellate cyst Family Suessiaceae and discussion of its evolution

“…During the Carboniferous to Jurassic, the main global reef production shifted from the Southern Hemisphere to the Northern Hemisphere (Flugel, 1994;Flugel & Kiessling, 1996). Reef distribution was restricted to a latitudinal zone from 30"N to 30% during the Middle Triassic and, during the Jurassic, bioherms seem to have been concentrated near 30"N, especially in Europe and at the eastern margin of North America (Flugel, 1994;Fiiigel & Kiessling, 1996).…”

“…Reef distribution was restricted to a latitudinal zone from 30"N to 30% during the Middle Triassic and, during the Jurassic, bioherms seem to have been concentrated near 30"N, especially in Europe and at the eastern margin of North America (Flugel, 1994;Fiiigel & Kiessling, 1996). A similar trend is discernible in the distribution of suessiacean dinoflagellate cysts.…”

Triassic mid‐oceanic sedimentation in Panthalassa Ocean: Sambosan accretionary complex, Japan

“…An approximately 20 my interval of Middle to Late Triassic is an important period, when the modern evolutionary fauna rapidly evolved and was diversified after the delayed biotic recovery from the end‐Permian crisis (Erwin 1993; Flügel 1994). For example, it was in the Anisian period when the metazoan reef ecosystem first reappeared after the Late Permian demise of calcisponge reefs (Flügel 1994).…”