FIG 8 - uploaded by Ashton Embry
Content may be subject to copyright.
—Middle Triassic Murray Harbour Formation overlying Lower Triassic Bjorne Formation (arrow points to contact). Thin transgressive sandstone (1) occurs at the base of the Murray Harbour Formation, which consists mainly of dark grey shale. Northern Ellesmere Island.
Source publication
Triassic sea-level changes are not well documented because of a scarcity of Triassic marine strata over many of the continental interiors and on passive continental margins. An excellent laboratory for studying Triassic sea-level changes is the Sverdrup Basin, which was a major depocenter in the Canadian Arctic Archipelago from the Carboniferous to...
Context in source publication
Context 1
... Triassic.- Middle Triassic strata contain two regional T-R cycles which are Anisian and Ladinian, respectively. Figure 7 il- lustrates a subsurface cross section for the Middle Triassic strata of the western Sverdrup, and the two T-R cycles are apparent. The transgression at the base of the first cycle is well dated by ammonites as early Anisian (Fig. 8). The overlying regressive shales of the Murray Harbour For- mation are commonly bituminous and phosphatic and grade upward into shallow-marine sandstone (Eldridge Bay Mem- ber, Roche Point Formation) on the basin ...
Similar publications
The Lunden Bay, an ancient lagoon, is located near the western coast of the Jutland Peninsula along the Southern North Sea. A non-disturbance core LN in the length of 719 cm was obtained with the gravity core sampler. The upper part buried less than 53 cm were observed and 7 sediment samples were taken in the field. Based on the core analyses on se...
It is clear from multiple modeling and field studies that deltas can attain a shelf-edge position under conditions of rising sea level, and this is accepted as an alternative way to form submarine fans without relative sea-level lowstand conditions. However, the relative importance and the range of controls that generate this type of shelf-edge del...
Citations
... Simms and Ruffell, 1989;Hallam, 2002;Tanner et al., 2004;Tanner, 2017;Rigo et al., 2020). The Pangea supercontinent began to rift apart during this interval, associated with episodes of volcanism which altered atmospheric composition and resulted in major (1988) suggesting sea level fall at the NRB and Embry (1988) suggesting sea level rise. Currently, no official Global Boundary Stratotype Section and Point (GSSP) has been selected for the base of the Rhaetian Stage, although candidates have been proposed in Austria (Krystyn et al., 2007a(Krystyn et al., , 2007b and Italy . ...
... Schlager, 1981). Haq et al. (1988) interpret eustatic sea level to be steady in the late Norian and falling across the NRB, whereas Embry (1988) interprets eustatic sea level to be falling in the late Norian and rising across the NRB. The apparent base level shift preserved in the Sinwa Formation is thus potentially consistent with the eustatic sea level rise at the NRB suggested by Embry (1988) but does not fully corroborate either past study. ...
... Haq et al. (1988) interpret eustatic sea level to be steady in the late Norian and falling across the NRB, whereas Embry (1988) interprets eustatic sea level to be falling in the late Norian and rising across the NRB. The apparent base level shift preserved in the Sinwa Formation is thus potentially consistent with the eustatic sea level rise at the NRB suggested by Embry (1988) but does not fully corroborate either past study. Regional effects such as basin subsidence, sediment loading, and faulting could also have been the cause of the rapid base level rise observed in the Sinwa Formation. ...
The Norian – Rhaetian boundary (NRB) is associated with significant faunal turnover in a wide variety of groups. Following the relative stability of the Norian Stage, this boundary potentially marks the beginning of a protracted and continuous episode of elevated extinction rates, which culminated with the end-Triassic mass extinction. Despite the importance of the NRB to paleontological trends in the Late Triassic, much about this event remains enigmatic, including potential causal mechanisms as well as the characteristics of the resulting paleoenvironmental changes. Fossiliferous limestone of the Sinwa Formation occurs in extensive outcrops throughout northwestern British Columbia and provides an exceptional record of Upper Triassic stratigraphy that represents a paleogeographic region largely uninvestigated prior. The present study integrates lithostratigraphic, paleontological, and geochemical data to reconstruct the shallow marine paleoenvironments recorded by the Sinwa Formation in two sections on Mount Sinwa, south of Atlin, within the Stikine Terrane. The progression of lithological facies observed in these sections suggests a gradual base level rise throughout the late Norian. Following this steady facies progression is a prominent shift from coral reef boundstone to shale near the top of both sections. This facies change approximately coincides with the NRB interval as evidenced by the first occurrence of the latest Norian – Rhaetian conodont species Mockina mosheri morphotype B, as well as by Re – Os isochron ages of organic-rich limestone. Although the base level rise observed at the NRB interval could be due to regional tectonics, it could also potentially be recording eustatic sea level rise given the lack of consensus around sea level change at the NRB. Measurements of late Norian ⁸⁷Sr/⁸⁶Sr ratios on Mount Sinwa are consistent with those recorded in Tethyan studies, but the Panthalassan record overall does not replicate the same drop across the NRB observed in the Tethys. The lithological facies shift is also immediately preceded by a negative excursion in the δ¹³C values of carbonate, indicating that the NRB interval on Mount Sinwa is associated with coral reef collapse as well as the globally observed disruption of carbon cycling.
... Because confidentiality restrictions prevented much of this data from being published, the proofs of the early eustatic models from this team were not available, which was a cause of significant criticism (e.g., Miall, 1991Miall, , 1992Miall and Miall, 2001). This uncertainty led many other stratigraphers worldwide to seek supporting evidence of the EPR models, or to develop alternative models, often based on outcrop geology (e.g., Embry, 1988Embry, , 1997Hallam, 1992Hallam, , 2001Sahagian et al., 1996;House and Ziegler, 1997;Johnson et al., 1998;Izart et al., 2003;Miller et al., 2005a;Simmons et al., 2007;and see Section 13.4). Eustasy refers to global sea level that is independent of local factors, namely, the position of the sea surface with reference to a fixed datum (Myers and Milton, 1996) (Fig. 13.1). ...
... 13.4.1.7 Triassic Embry (1988Embry ( , 1997)-Provided seminal descriptions of the sequence stratigraphy of the Canadian Triassic succession with global comparisons to yield a eustatic signal that could also be linked to chronostratigraphic subdivision (i.e., stage and substage boundaries). See also Mørk (1994). ...
Isolation of the eustatic signal from the sedimentary record remains challenging, yet much progress is being made toward understanding the timing, magnitude, and rate of eustasy on both long-term and short-term scales throughout the Phanerozoic. Long-term eustasy is primarily driven by a number of factors relating to plate tectonics. The magnitude and rate of short-term eustatic change strongly suggests glacio-eustasy as the key driving mechanism, even in episodes of the Earth’s history often typified as having “greenhouse” climates. This notion is, in turn, supported by a growing body of both direct and proxy evidence for relatively substantial polar glaciation in many periods of the Earth’s history (with the possible exception of the Triassic). An understanding of eustasy is important for the development of the geologic time scale because it contributes to the sequence stratigraphic organization of sedimentary successions (including chronostratigraphic reference sections) and helps to understand the often incomplete nature of the geologic record. The integration of eustasy with our evolving knowledge of Earth systems science (e.g., paleoclimate evolution, orbital forcing of sedimentary systems, geochemical evolution of the oceans, and biological evolutions and extinctions) will help to provide the tools to develop a context for the subdivisions of the geologic
time scale.
... Triassic sea-level Trends and sequences of different relative magnitudes have been compiled for Boreal basins (e.g., Embry, 1988;Mørk et al., 1989;Skjold et al., 1998), the classic Germanic Trias (e.g., Aigner and Bachmann, 1992;Geluk and Röhling, 1997), the Dolomites and Italian Alps regions (e.g., De Zanche et al., 1993;Gaetani et al., 1998;, and other regions. Some of these sea-level trends appear to correlate on an interbasin to global scale (e.g., Haq et al., 1988;Haq, 2018;Hallam, 1992;Embry, 1997;Gianolla and Jacquin, 1998). ...
The Triassic is bound by two mass extinctions that coincide with vast outpourings of volcanic flood basalts. The Mesozoic begins with a gradual recovery of plant and animal life after the end-Permian mass extinction. Conodonts and ammonoids are the main correlation tools for marine deposits. The Pangea supercontinent has no known glacial episodes during the Triassic, but the modulation of its monsoonal climate by Milankovitch cycles left sedimentary signatures useful for high-resolution scaling. Dinosaurs begin to dominate the terrestrial ecosystems in latest Triassic. In contrast to the rapid evolution and pronounced environmental changes that characterize the Early Triassic through Carnian, the Norian–Rhaetian of the Late Triassic was an unusually long interval of stability in Earth history.
... east-west and 300 km north-south with its depocenter located in northern Ellesmere Island and Axel Heiberg Island (Fig. 1). The basin margins lay to the west, south, and east and opened to the northwest into the Boreal Ocean, although connection was limited due to the presence of Crockerland-an island or structural high that formed the northern basin rim (Embry, 1988(Embry, , 1989(Embry, , 2009Fig. 1). ...
... 1). Lower Triassic strata belong to the Blind Fiord Formation, a thick succession of offshore mudstone, siltstone, and shelf-slope sandstone that passes into paralic and terrestrial strata of the Bjorne Formation (Embry, 1988(Embry, , 2009Devaney, 1991;Embry and Beauchamp, 2008;Midwinter et al., 2017). The Blind Fiord Formation is divided into three members: the Confederation Point Member of Griesbachian to Dienerian age consists of heterolithic strata ranging from shale to sandstone; the Smith Creek Member of Smithian age consists of fine sandstone and siltstone; and the Svartfjeld Member of Spathian age consists of shale (Fig. 1). ...
... The Blind Fiord strata are arranged into a series of coarsening up/progradational packages punctuated by flooding events that saw expanded shale deposition. These can be correlated with transgressive-regressive cycles elsewhere in the world and are probably of eustatic origin (Embry, 1988(Embry, , 1989. A latest Permian unconformity underlies the Blind Fiord Formation and cuts deeper into older Permian sediments toward the basin margins. ...
Microbially induced sedimentary structures (MISS) are reportedly widespread in the Early Triassic and their occurrence is attributed to either the extinction of marine grazers (allowing mat preservation) during the Permo-Triassic mass extinction or the suppression of grazing due to harsh, oxygen-poor conditions in its aftermath. Here we report on the abundant occurrence of MISS in the Lower Triassic Blind Fiord Formation of the Sverdrup Basin, Arctic Canada. Sedimentological analysis shows that mid-shelf settings were dominated by deposition from cohesive sand-mud flows that produced heterolithic, rippled sandstone facies that pass down dip into laminated siltstones and ultimately basinal mudrocks. The absence of storm beds and any other “event beds” points to an unusual climatic regime of humid, quiet conditions characterized by near continuous run off. Geochemical proxies for oxygenation (Mo/Al, Th/U, and pyrite framboid analysis) indicate that lower dysoxic conditions prevailed in the basin for much of the Early Triassic. The resultant lack of bioturbation allowed the development and preservation of MISS, including wrinkle structures and bubble textures. The microbial mats responsible for these structures are envisaged to have thrived, on sandy substrates, within the photic zone, in oxygen-poor conditions. The dysoxic history was punctuated by better-oxygenated phases, which coincide with the loss of MISS. Thus, Permo-Triassic boundary and Griesbachian mudrocks from the deepest-water settings have common benthos and a well-developed, tiered burrow profile dominated by Phycosiphon. The presence of the intense burrowing in the earliest Triassic contradicts the notion that bioturbation was severely suppressed at this time due to extinction losses at the end of the Permian. The notion that Early Triassic MISS preservation was caused by the extinction of mat grazers is not tenable.
... We address this with a new record from the Sverdrup Basin (Arctic Canada). Our study presents brachiopod range data from the Degerböls and Lindström Formations of Ellesmere Island, Permian-aged mixed spiculitic chert/carbonate units that formed on a cool, siliciclastic ramp in the Boreal Ocean (Embry, 1988;Embry andBeauchamp, 2008, 2019;Beauchamp et al., 2009). We assessed the role of redox changes during this interval using a combination of petrographic and geochemical approaches, and we further examined the link between these factors and the Emeishan large igneous province using the mercury proxy for volcanism. ...
... It extends ∼1200 km eastwest and 400 km north-south from present-day Ellesmere and Axel Heiberg Islands (Nunavut, Canadian High Arctic) in the northeast to Melville Island in the west ( Fig. 1; Balkwill, 1978;Embry and Beauchamp, 2008). The basin margins lay to the west, south, and east of our study area on Ellesmere Island and opened to the north into the Boreal (Arctic) Ocean, although connection was likely limited by the presence of Crockerland, a structural high that formed the northern basin rim (Embry, 1988(Embry, , 1989 Beauchamp et al., 2009;Embry and Beauchamp, 2019). The succession is composed of white to pale-gray spiculitic cherts and numerous limestone interbeds . ...
... As in other regions, notably the lithostratigraphically similar Svalbard and Barents Sea, the Permian-Triassic boundary lies a few meters above the major lithological change at the formational contact (Beauchamp et al., 2009). The Blind Fiord Formation is a thick succession of offshore mudstones, siltstones, and shelf-slope sandstones that record major flooding, as well as the famous Permian-Triassic mass extinction, at its base (Embry, 1988;Embry and Beauchamp, 2008;Grasby and Beauchamp, 2008;Beauchamp et al., 2009). ...
Until recently, the biotic crisis that occurred within the Capitanian Stage (Middle Permian, ca. 262 Ma) was known only from equatorial (Tethyan) latitudes, and its global extent was poorly resolved. The discovery of a Boreal Capitanian crisis in Spitsbergen, with losses of similar magnitude to those in low latitudes, indicated that the event was geographically widespread, but further non-Tethyan records are needed to confirm this as a true mass extinction. The cause of this crisis is similarly controversial: While the temporal coincidence of the extinction and the onset of volcanism in the Emeishan large igneous province in China provides a clear link between those phenomena, the proximal kill mechanism is unclear. Here, we present an integrated fossil, pyrite framboid, and geochemical study of the Middle to Late Permian section of the Sverdrup Basin at Borup Fiord, Ellesmere Island, Arctic Canada. As in Spitsbergen, the Capitanian extinction is recorded by brachiopods in a chert/limestone succession 30−40 m below the Permian-Triassic boundary. The extinction level shows elevated concentrations of redox-sensitive trace metals (Mo, V, U, Mn), and contemporary pyrite framboid populations are dominated by small individuals, suggestive of a causal role for anoxia in the wider Boreal crisis. Mercury concentrations—a proxy for volcanism—are generally low throughout the succession but are elevated at the extinction level, and this spike withstands normalization to total organic carbon, total sulfur, and aluminum. We suggest this is the smoking gun of eruptions in the distant Emeishan large igneous province, which drove high-latitude anoxia via global warming. Although the global Capitanian extinction might have had different regional mechanisms, like the more famous extinction at the end of the Permian, each had its roots in large igneous province volcanism.
... The Permian (251 Mya), which was the largest extinction, is noted to coincide with the supervolcano that essentially created modern Siberia [10], as well as the development of the chemical pathways necessary to decompose organic matter that had accumulated on the sea floor for the eons prior, both of which could have drastically altered the climate [11]. The Triassic extinction (200 Mya) is possibly associated with sea level change from the breakup of Pangaea [12], but the cause of this extinction is particularly uncertain. As mentioned earlier, the Cretaceous extinction (66 Mya) was caused by the Chicxulub impact. ...
Do mass extinctions affect the development of intelligence? If so, we may expect to be in a universe that is exceptionally placid. We consider the effects of impacts, supervolcanoes, global glaciations, and nearby gamma ray bursts, and how their rates depend on fundamental constants. It is interesting that despite the very disparate nature of these processes, each occurs on timescales of 100 Myr-Gyr. We argue that this is due to a selection effect that favors both tranquil locales within our universe, as well as tranquil universes. Taking gamma ray bursts to be the sole driver of mass extinctions is disfavored in multiverse scenarios, as the rate is much lower for different values of the fundamental constants. In contrast, geological causes of extinction are very compatible with the multiverse. Various frameworks for the effects of extinctions are investigated, and the intermediate disturbance hypothesis is found to be most compatible with the multiverse.
... The Permian (251 Mya), which was the largest extinction, is noted to coincide with the supervolcano that essentially created modern Siberia [Kamo et al., 2003], as well as the development of the chemical pathways necessary to decompose organic matter that had accumulated on the sea floor for the eons prior, both of which could have drastically altered the climate [Rothman et al., 2014]. The Triassic extinction (200 Mya) is possibly associated with sea level change from the breakup of Pangaea [Embry, 1988], but the cause of this extinction is particularly uncertain. As mentioned earlier, the Cretaceous extinction (66 Mya) was caused by the Chicxulub impact. ...
Do mass extinctions affect the development of intelligence? If so, we may expect to be in a universe that is exceptionally placid. We consider the effects of impacts, supervolcanoes, global glaciations, and nearby gamma ray bursts, and how their rates depend on fundamental constants. It is interesting that despite the very disparate nature of these processes, each occurs on timescales of 100 Myr-Gyr. We argue that this is due to a selection effect that favors both tranquil locales within our universe, as well as tranquil universes. Taking gamma ray bursts to be the sole driver of mass extinctions is disfavored in multiverse scenarios, as the rate is much lower for different values of the fundamental constants. In contrast, geological causes of extinction are very compatible with the multiverse. Various frameworks for the effects of extinctions are investigated, and the intermediate disturbance hypothesis is found to be most compatible with the multiverse.
... Coeval nonmarine and marginal-marine deposits include fluvial and deltaic siliciclastics, which accumulated from northwestward-to westward-flowing fluvial systems, and peritidal carbonates (Blakey, 1974;Ochs and Chan, 1990;Nielson, 1991;Paull and Paull, 1993;Baker and Huntoon, 1996). The intertonguing marine and nonmarine facies relationships indicate that three major Early Triassic transgressions and regressions affected the tectonically stable interior seaway ( Fig. 1C; Carr and Paull, 1983;Dubiel, 1994;Paull and Paull, 1993;Lucas et al., 2007a) and their timing matches those recognized in the Canadian Arctic and Svalbard supporting their eustatic origin (Embry, 1988;Haq, 2018). ...
Widespread Lower Triassic microbial carbonates occur after the end-Permian mass extinction (EPME) and are commonly attributed to reduced metazoan competition after the EPME, or to paleoceanographic conditions that suppressed metazoan abundance and increased ocean carbonate saturation. Testing these hypotheses requires direct spatial (versus temporal) linkages between Lower Triassic microbial deposits and lithologic or geochemical proxy evidence for environmental perturbations. This study uses facies within and associated with an extensive Lower Triassic (Smithian) microbial carbonate mound complex, which developed across a > 400-km-wide middle-to-inner shelf in southern Utah, U.S.A., to assess potential controls on microbial carbonate development. Middle-shelf microbial mounds (1–2 m tall) are composed of stromatactis-rich peloidal boundstones that are laterally linked by microbial intermound beds. Inner-shelf microbial mounds (<1 m) are composed of microbial laminites that are linked by flat-lying microbial laminite intermound beds. Both mound types nucleated atop non-mound microbial carbonates in deep- to shallow-subtidal environments and aggraded during sea-level rise. During sea-level fall, mounds broadened, shortened, and terminated growth when higher current energies inhibited substrate stability and mat nucleation. Middle- and inner-shelf mound morphologies and facies differences reflect across-shelf accommodation space variations and proximity to nearshore terrigenous sediment influx. Sparse, but persistent benthic fauna and bioturbation in all microbial facies and the lack of lithologic indicators of bottom-water anoxia indicate sufficient O 2 levels to support animal life. The broad Utah shelf study area implies that shelf-edge, upwelling-derived, carbonate-saturated waters did not control microbial carbonate precipitation. Regional controls on microbial mound complex development include deposition during sea-level rise along a wide shallow shelf that maximized the areal extent of clear-water, low-energy subtidal environments and promoted growth of prolific photosynthesizing microbial communities. Probable global controls include the post-EPME reduction in skeletal metazoan competition, which permitted microbial mats to flourish, and elevated global-ocean carbonate saturation states and promoted extensive carbonate precipitation.
... Carbonate strata dominate the Carboniferous to mid-Permian portion of the fi ll with younger strata being almost exclusively siliciclastics. The comprehensive references for the detailed stratigraphy of the Carboniferous-Cretaceous succession are Balkwill (1978Balkwill ( , 1983, Davies and Nassichuk (1991), Beauchamp and Henderson (1994), Beauchamp and Thériault (1994), Beauchamp (1995), Beauchamp et al. (2001Beauchamp et al. ( , 2009), Beauchamp and Olchowy (2003), Embry (1988bEmbry ( , 1991bEmbry ( , 1993Embry ( , 1997 and Embry and Beauchamp (2008). ...
... The stratigraphy of the Triassic succession of Sverdrup Basin has been described in detail in numerous publications with the most relevant ones for this study being Embry (1988bEmbry ( , 1991bEmbry ( , 1997, Embry and Johannessen (1993), and Embry and Beauchamp (2008). The sequence stratigraphy of the succession has been presented and illustrated in these publications. ...
We have identifi ed 57 large-magnitude, sequence boundaries in the Phanerozoic succession of the Canadian High Arctic. The characteristics of the boundaries, which include angular unconformities and signifi cant changes in depositional and tectonic regimes across the boundaries, indicate that they were primarily generated by tecton-ics rather than by eustasy. Boundary frequency averages 10 million years throughout the Phanerozoic and there is no notable variation in this frequency. It is interpreted that each boundary was generated during a tectonic episode that lasted two million years or less. Each episode began with uplift of the basin margins and pronounced regression. This was followed by a rapid subsidence and the fl ooding of the basin margins. Each tectonic episode was terminated by a return to slow, long-term subsidence related to basin forming mechanisms such as thermal decay. The tectonic episodes were separated by longer intervals of tectonic quiescence characterized by slow subsidence and basin fi lling. The tectonic episodes are interpreted to be the product of changes in lithospheric stress fi elds with uplift being related to increased, compressional horizontal stress and the following time of rapid subsidence refl ecting a decrease in such stresses or an increase in tensional stresses. Conversely, the longer intervals of tectonic quies-cence would refl ect relatively stable, horizontal stress fi elds. The episodic changes in stress fi elds affecting the Canadian High Arctic throughout the Phanerozoic may be a product of intermittent, plate tectonic reorganizations that involved changes in the
... Siliciclastics were common in the Siberia and Arctic regions (Figs. 2.8 and 2.9; Embry 1988Embry , 1997Nikishin et al. 1996;Golonka and Ford 2000;Golonka et al. 2003a;Golonka 2007aGolonka , b, 2011Toro et al. 2016); the Sverdrup Basin of Arctic Canada was a main depocenter with the Late Triassic succession of fluvial to marine slope deposits being over 2500 m thick (Embry 1997). Triassic, restricted-marine shelf basins contain black shales that have source rock potential (Leith et al. 1993;Golonka et al. 2003a;Golonka 2007b). ...
... Late Triassic, large-magnitude, sequence boundaries, which have been recorded in different basins throughout Pangaea, have been biostratigraphically dated as near the base Carnian, mid-Carnian, near the base Norian, mid-Norian, near the base Rhaetian and latest Rhaetian. Initially, these boundaries were interpreted to be the product of eustasy, including a significant sea level fall followed by sea level rise (Haq et al. 1987(Haq et al. , 1988Embry 1988;De Zanche et al. 1993;Gianolla and Jacquin 1998). Given a climate change/continental glaciation explanation was not possible, the authors appealed to changes in the volume of the world ocean (tectono-eustasy) as the main driver of such large scale eustatic changes. ...
The Late Triassic was the time of the Early Cimmerian and Indosinian orogenies that closed the Paleotethys Ocean, which occurred earlier in the Alpine-Carpathian-Mediterranean area, later in the Eastern Europe-Central Asia and latest in the South-East Asia. The Indochina Southeastern Asian and Qiangtang plates were sutured to South China. The new, large Chinese-SE Asian plate, including North and South China, Mongolia and eastern Cimmerian plates, was consolidated by the end Triassic, leaving open a large embayment of Panthalassa, known as Mongol-Okhotsk Ocean, between Mongolia and Laurasia,. The Uralian Orogeny, which sutured Siberia and Europe continued during Late Triassic times and was recorded in Novaya Zemlya. The onset of Pangaea break-up constitutes the main Late Triassic extensional event. Continental rifts originating then were filled with clastic deposits comprising mainly red beds. The pulling force of the north-dipping subduction along the northern margin of Neotethys caused drifting of a new set of plates from the passive Gondwana margin, dividing the Neotethys Ocean. Carbonate sedimentation dominated platforms on the Neotethys and Paleotethys margins as well as the Cimmerian microplates. Synorogenic turbidites and postorogenic molasses were associated with the Indosinian orogeny. The late stages of the Uralian orogeny in Timan-Pechora, Novaya Zemlya and eastern Barents regions filled the foreland basin with fine-grained, molasse sediments. Siliciclastics were common in the Siberia and Arctic regions. The widespread, large magnitude, base-level changes of the Late Triassic are interpreted as an expression of relatively rapid and substantial changes in the horizontal and vertical stress fields that affected the Pangaea supercontinent. Such stress changes may be due to abrupt changes in the speed and/or direction of plate movements, which episodically affected Pangaea.
