Middle Late Jurassic Transition Research Articles

A climate perturbation at the Middle –Late Jurassic Transition? Evaluating the isotopic evidence from south-central England

The Jurassic greenhouse is punctuated by short cooling intervals. Some published oxygen isotope records of belemnite rostra and fish teeth have been interpreted to reveal a prominent decrease in seawater temperature during the Late Callovian–Early Oxfordian. This is in part the basis for a proposed an ice age at the Middle-Late Jurassic Transition. In contrast relatively constant oxygen isotope records and therefore seawater temperatures as well as carbon isotope values characterized by significant scatter but showing more positive values during the middle and late Callovian have been reported from elsewhere. This research has constructed a stable isotope stratigraphy (from belemnites, Gryphaea and oysters) principally from the Callovian-Oxfordian interval (from southern England) and integrated these data with existing data to assess the pattern of carbon and oxygen isotopic change. Our marine macrofossil record reveals isotopic patterns that are generally comparable with other European basins. Carbon isotopic trends are consistent with bulk carbonate carbon isotope records displaying systematic fluctuations, the largest of which (Middle Callovian, Calloviense/Jason Zones to Early Oxfordian, Mariae Zone) corresponds to previously identified phases of environmental perturbation. Such a trend may have resulted from enhanced burial and preservation of organic matter, leaving the seawater enriched in the heavy carbon isotope. Inferred cooling, derived from our oxygen isotope data from southern England, occurs within the Late Callovian and the Early Oxfordian (Athleta to Mariae zones). Cooling post-dates this positive carbon isotope excursion. Enhanced carbon burial and atmospheric carbon dioxide draw down may have induced cooling. In this study the analysis of a single region (southern England) allows critical factors controlling the oxygen isotopic composition of the carbonates (e.g. temperature and the oxygen isotopic composition of the solution from which the carbonates precipitated) to be more comparable. If Jurassic polar climates were truly warm such a degree of cooling would undoubtedly lead to cooler polar temperatures – but only with seasonal ice.

The Shishugou Fauna of the Middle‐Late Jurassic Transition Period in the Junggar Basin of Western China

AbstractThe Middle–Late Jurassic transition period is a critical period for the evolution of terrestrial vertebrates, but the global fossil record from this time is relatively poor. The Shishugou Fauna of this period has recently produced significant fossil remains of dinosaurs and other vertebrate groups, some representing the earliest known members of several dinosaurian groups and other vertebrate groups and some representing the best‐known specimens of their group. These discoveries are significant for our understanding of the origin and evolution of several vertebrate lineages. Radiometric dating indicates that the fauna is aged approximately 159–164 Ma. Comparisons with other similarly‐aged terrestrial faunas such as Shaximiao and Yanliao show both taxonomic similarities and differences between these faunas and indicate that the Junggar deposits might have preserved the most complete vertebrate fossil record for a Middle–Late Jurassic Laurasian terrestrial fauna.

Middle Jurassic evolution of a northern Tethyan carbonate ramp (Alborz Mountains, Iran)

Here, we provide a detailed facies and depositional record from a NE-SW-directed, 250-km-long transect across a distally steepened, Middle Jurassic carbonate ramp in the northern Tethyan realm (Iran). Among the six main facies types described, two stand out because of their beyond-regional significance: (i) Middle Callovian microbial and microbial-skeletal mounds embedded in muddy intermound sediment and (ii) Upper Callovian conglomeratic debris-flow deposits truncating the mound unit. The mound features described here did not evolve into reefal structures and evidence for a framestone structure is lacking. They occur as low-relief, mud-dominated domical structures (a few metres wide). The development of the Middle Callovian mounds is perhaps best linked to a period of minimum sedimentation rates and sufficient accommodation space resulting from a long-term gradual sea-level rise commencing in the Late Bajocian. With respect to the Upper Callovian conglomeratic deposits overlying the mound interval, the absence of sedimentary structures such as grading, the nature of the sub-angular or rounded clasts and the very poor sorting are indicative of a catastrophic debris flow origin. Based on data compiled here, the conglomeratic deposits likely formed due to relative sea-level fall inducing the reworking of mound facies by the lowered wave base and currents, and basinward transport of reworked material to the distal outer ramp. Our findings are compared with coeval deposits from the western Tethyan domain and placed into a process-oriented context. The described northern Tethyan Late Bajocian to Middle Callovian deepening-upward trend, followed by relative sea-level fall in the Late Callovian near the Middle-Late Jurassic transition, is in agreement with observations from other coeval Tethyan basins/platforms. Data shown here have wider relevance for workers concerned with the Jurassic evolution of the Tethyan Ocean in general and shed light on the intricate relation of changes in accommodation space and ramp architecture.

Architecture and sedimentary evolution of the southwestern Gissar carbonate platform (Uzbekistan) during the Middle‒Late Jurassic

Abstract Sedimentological investigations have been carried out in the southwestern part of the Gissar Range (Uzbekistan) in order to document the stratigraphic evolution of a vast Middle–Upper Jurassic carbonate platform developed on the northern margin of the Amu Darya Basin. Two major sequences are distinguished, based on their contrasting facies pattern, platform configuration and carbon isotope signature: (1) a Callovian Sequence and (2) an Upper Jurassic Sequence, potentially Oxfordian to Kimmeridgian in age. A carbonate ramp with a double proximal-distal polarity developed during the Callovian Sequence. Oo-bioclastic grainstones were produced in two permanently agitated shallow water areas developing to the north and to the south. Patch and pinnacle reefs mainly built up close to the storm-wave base, passing distally to pellet- and foraminiferal-oncoid-rich mid-to outer-ramp deposits. The top of the Callovian Sequence is a regional discontinuity that could have formed by subaerial exposure of the platform. This probable hiatus could record a major climatic change associated to the Middle‒Late Jurassic transition. The Upper Jurassic Sequence consists of metre-thick alternations of pellet/algal-pack- to grainstones, microbial oncoid floatstones, ooid grainstones, and mudstones, which have likely accumulated in a vast lagoon protected by a large-scale barrier reef observed south of the study area. Gypsum and anhydrite content gradually increased towards the top of the Upper Jurassic Sequence, ending up with a thick chicken-wire gypsum accumulation recording the progradation of a large-scale sabkha over the lagoon. This phenomenon is related to a progressive aridification and restriction of the Amu Darya Basin that could have begun during the Middle/Late Oxfordian and reached its climax during the Tithonian with massive halite deposition. Comparable events occurred in Jurassic platforms located along the Tethyan margins, pointing to regional and global controls on sedimentation.

Clumped isotope record of salinity variations in the Subboreal Province at the Middle–Late Jurassic transition

Abstract Results of clumped isotope, oxygen isotope and elemental (Mg/Ca, Sr/Ca) analyses of exceptionally well-preserved belemnite rostra and ammonite shells from the uppermost Callovian–Upper Kimmeridgian (Lamberti–Mutabilis zones) of the Russian Platform are presented. Despite a significant decrease in belemnite δ18O values across the Upper Oxfordian–Lower Kimmeridgian, the clumped isotope data show a constant seawater temperature (ca. 16 °C) in the studied interval. The decrease in belemnite δ18O values and lower δ18O values measured from ammonite shells are interpreted as a result of the salinity decline of the Middle Russian Sea of ca. 12‰, and salinity stratification of the water column, respectively. The postulated secular palaeoenvironmental changes are linked to the inflow of subtropical, saline waters from the Tethys Ocean during a sea-level highstand at the Middle–Late Jurassic transition, and progressive isolation and freshening of the Middle Russian Sea during the Late Oxfordian–Kimmeridgian. The obtained clumped isotope data demonstrate relative stability of the Late Jurassic climate and a paramount effect of local palaeoceanographic conditions on carbonate δ18O record of shallow epeiric seas belonging to the Subboreal Province. Variations in Mg/Ca and Sr/Ca ratios of cylindroteuthid belemnite rostra, which are regarded by some authors as temperature proxies, are, in turn, interpreted to be primarily dependent on global changes in seawater chemistry. The paleoenvironmental variations deduced from clumped and oxygen isotope records of the Russian Platform correspond well with changes in local cephalopod and microfossil faunas, which show increasing provincialism during the Late Oxfordian and the Early Kimmeridgian. Based on the review of literature data it is suggested that the observed salinity decrease and restriction of Subboreal basins during the Late Jurassic played a major role in the formation of periodic bottom water anoxia and sedimentation of organic rich facies.

Seawater temperatures and carbon isotope variations in central European basins at the Middle–Late Jurassic transition (Late Callovian–Early Kimmeridgian)

Oxygen and carbon isotope values and elemental ratios of well-preserved belemnite rostra, brachiopod shells and bulk-carbonates from the Upper Callovian–Lower Kimmeridgian of the Polish Jura Chain, Kujawy (Poland) and Swabian Alb (Germany) are investigated to reconstruct environmental conditions and perturbations in the marine carbon cycle. Belemnite δ18O values show relatively constant temperatures (ca. 12°C) of bottom waters in the Polish Jura Chain basin during a major part of the Late Callovian–Middle Oxfordian, except for a short-term cooling (to ca. 9°C) at the Callovian–Oxfordian transition. Belemnite and brachiopod δ18O values show a gradual increase in temperature during the Submediterranean Late Oxfordian; the highest temperatures (ca. 16°C) are calculated for the Submediterranean Oxfordian–Kimmeridgian transition. Belemnite and brachiopod Mg/Ca and Sr/Ca ratios are disregarded as a paleotemperature proxy because of their weak correlation with δ18O values.The belemnite and brachiopod isotope data confirm that the carbon isotope composition of belemnite rostra is affected by a metabolic effect, which results in a depletion of belemnite calcite in the 13C isotope. Belemnite rostra are considered, nevertheless, as a valuable tracer of temporal variations in the carbon isotope composition of marine carbonates. Belemnite δ13C data show the presence of two positive excursions (in the Upper Callovian and the Middle Oxfordian) in the carbon isotope record of peri-Tethyan carbonates. The excursions are divided by a Lower Oxfordian interval characterized by decreased δ13C values. This is most likely a regional feature caused by upwelling. Lowest belemnite and brachiopod δ13C values are observed in the lower part of the Submediterranean Upper Oxfordian and are linked to a well-mixed state of the seawater in the basins studied. The carbon isotope record of bulk carbonates differs from those of belemnites and brachiopods probably because of strong variations in carbonate production in the Polish Jura Chain basin.

Carbon cycle and sea-water palaeotemperature evolution at the Middle–Late Jurassic transition, eastern Paris Basin (France)

A very high-resolution carbon and oxygen stable isotope analysis (bulk-carbonate) of a biostratigraphically well-constrained Callovian–Oxfordian series is provided here for the first time. The homogeneity of the clayey series and the weak diagenetic alteration allow the isotopic signal variations to be considered as primary in origin. A prominent and brief negative excursion in the δ13C curve (−2‰), occurring at the start of the Middle Callovian (Jason Zone – Obductum Subzone) and correlated regionally, suggests a possible methane release. The increasing δ13C values thereafter up to the Early Oxfordian, concomitant with a warming episode, highlight the burial of carbon in organic-rich layers which, in return, may have triggered a decrease in atmospheric pCO2. At higher frequencies, observed fluctuations of the δ13C and δ18O values are orbitally driven (405-kyr and 100-kyr eccentricity cycles) and may correspond to the salinity and temperature variability recorded in sea water. The δ18O isotopic measurements from well-preserved diagenetically screened belemnites and bivalves along the series, compared to available data from Tethyan domains, agree with the scenario of a global cooling at the Middle-Late Jurassic transition. The well-dated δ18O isotopic curve suggests that the onset of this cooling event occurred at the end of the Coronatum Zone (Middle Callovian).

Middle–Upper Jurassic (Upper Callovian–Lower Kimmeridgian) stable isotope and elemental records of the Russian Platform: Indices of oceanographic and climatic changes

New isotope (δ18O, δ13C) and elemental (Mg/Ca, Sr/Ca) data of well-preserved belemnite rostra, ammonite and gastropod shells from the Middle Oxfordian–Lower Kimmerdgian (Densiplicatum–Kitchini zones) of the Russian Platform are presented. This record is supplemented with published data from the Upper Callovian–Lower Kimmeridgian interval (Athleta–Kitchini zones). Significant differences in average temperatures calculated from δ18O values of particular fossil groups (5–15°C) show the thermal gradient and the presence of cold bottom waters in the Middle Russian Sea during the Late Callovian–Middle Oxfordian. An Upper Oxfordian–lowermost Kimmeridgian decrease in δ18O values and an increase in Sr/Ca ratios of cylindroteuthid belemnite rostra likely reflect a warming of the bottom waters of ca. 3.5°C. The gradual Late Oxfordian–earliest Kimmeridgian warming is followed by an abrupt temperature rise of 3–6°C that occurred at the transition of the Early Kimmeridgian Bauhini and Kitchini chrons.The occurrences of cold bottom waters and of (Sub)Mediterranean ammonites and belemnites in the Middle Russian Sea at the Middle–Late Jurassic transition are regarded as a result of the opening of seaways during a sea level highstand. The bottom waters are considered to have been formed in the cool Boreal Sea. The subsequent retreats of the cold bottom waters and of the (Sub)Mediterranean cephalopods from the Middle Russian Sea in the Late Oxfordian are explained by the restriction of water circulation during a sea-level fall. The Early Kimmeridgian rise of bottom temperatures of the sea is linked to a global climate warming. The data presented do not support a major cooling of the Arctic and a consequent glaciation in this region at the Middle–Late Jurassic transition. Since occurrences of cold water masses are diachronous in different European basins, the observed variations in sea water temperatures are interpreted as a result of changes in marine currents and water circulation.δ13C values of belemnite rostra from the Russian Platform are scattered but show the long-term Upper Callovian–Middle Oxfordian positive excursion consistent with the previously published isotope records of the Boreal Realm and terrestrial organic matter.

Episodic sedimentation on a peri-Tethyan ridge through the Middle–Late Jurassic transition (Villány Mountains, southern Hungary)

The Villany area, as a central part of the Tisza microcontinent/terrane along the European margin of Tethys, was characterized by intense subsidence in the Early and Middle Triassic, followed by a long interruption of subsidence in the Late Triassic to Middle Jurassic. During the Middle–Late Jurassic transition, marine sedimentation started with three distinct sedimentary episodes dated as Late Bathonian, Early Callovian, and Middle–Late Callovian, respectively. The succession is terminated by a thick limestone of Middle Oxfordian age. The sedimentary features, microfacies, and macroinvertebrate associations of these four stratigraphic units are documented and illustrated. The Middle to Late Jurassic sedimentary episodes of the Villany succession record an interplay of local and global factors and paleogeographical changes. At the beginning, local tectonic movements governed the main features of sedimentation, though the role of eustasy was also essential. From the mid-Callovian onwards, global climatic, biotic, and paleoceanographical changes controlled the nature and formation of the local carbonate sediments. The Callovian stromatolites are attributed to the activity of sulphate-reducing bacteria in a deep sublittoral, current-swept environment. Upwelling of eutrophic Tethyan waters is recorded by the prevalence of the Bositra filament microfacies in the Callovian. The long submarine hiatus at around the Callovian–Oxfordian transition mirrors a serious restriction of the carbonate budget, due to sudden cooling and a change in the oceanic current system (opening of a circumglobal Tethyan Passage), and to a higher amount of dissolved CO2. In the Middle Oxfordian, the carbonate production considerably increased in accordance with the sudden global warming.

Reconstructing the palaeoenvironment of the Middle Russian Sea during the Middle–Late Jurassic transition using stable isotope ratios of cephalopod shells and variations in faunal assemblages

Oxygen and carbon isotope data of well-preserved belemnite rostra and ammonite shells are presented from the Callovian–Oxfordian boundary (uppermost Lamberti to lowermost Cordatum zones) of the Dubki section near Saratov in the Russian Platform. Palaeotemperatures calculated for nektobenthic belemnites (averages of 5°C and 8°C for cylindroteuthids and belemnopseids, respectively) show the presence of cold bottom waters in the central part of the Middle Russian Sea during the studied interval. Palaeotemperatures calculated for ammonites, which are assumed to have lived in near-surface waters, are considerably higher (average 13°C). The presented data show a vertical thermal gradient in the Middle Russian Sea. The belemnite oxygen isotope record and the relative abundances of ammonite families in the Dubki section do not correlate with each other probably as a result of different depth habitats of ammonites and belemnites. A review of literature isotope data shows the climatic zonation in European seas at the Middle–Late Jurassic transition. Despite the flux of cold polar waters to the Middle Russian Sea and the area of Scotland there is no evidence for glaciation at the Middle–Late Jurassic transition. Changes in water circulation during a sea-level highstand were likely a source of spreads of cold bottom waters and cardioceratid ammonite fauna in this time period.The belemnite isotope record of the Callovian–Oxfordian boundary in the Russian Platform is characterized by significant scatter of δ13C values. No temporal carbon isotope trend is observed. The δ13C values of Russian belemnite rostra average 2.6‰ VPDB being 1 to 2‰ higher than the values of coeval Lower Oxfordian belemnites from the area of the Submediterranean ammonite province. Higher (than Submediterranean) δ13C values of Russian belemnite rostra are likely related to high biologic productivity and/or high organic matter burial in semi-isolated Boreal–Subboreal marine basins.

Calcareous nannofossil productivity and carbonate production across the Middle-Late Jurassic transition in the French Subalpine Basin

The distribution pattern of calcareous nannofossils was analysed across the Middle-Late Jurassic transition in the French Subalpine Basin (south-eastern France). This basin is characterized in the hemipelagic-pelagic domain by a continuous sedimentary succession, allowing a good biostratigraphic resolution for this time interval. The nannofossil assemblages are consistently dominated by Watznaueria britannica. However, major changes in trophic and paleoenvironmental conditions are recorded across the Middle-Late Jurassic transition. An increase in marine primary productivity and cooling of surface waters is recorded across the Callovian-Oxfordian boundary, as already shown in the higher latitude setting of the eastern Paris Basin. Increased precipitation and runoff under contrasting seasonal climatic conditions (monsoon-type) has led to eutrophication of marine surface waters in the French Subalpine Basin at this period. Then, decreased runoff and associated nutrients certainly linked to drier climatic conditions lead to a decrease in calcareous nannofossil productivity during the middle part of the Early Oxfordian ( mariae- cordatum ammonite Zone transition). At the Early-Middle Oxfordian transition, more favourable conditions for the nannofossil community (warmer and mesotrophic surface waters) prevailed. The pelagic (nannofossil) carbonate contribution is limited, and the carbonate fraction is predominantly of nektonic/benthic origin at the Callovian-Oxfordian transition and of allochthonous origin from carbonate platforms at the Early Oxfordian-Middle Oxfordian transition.

Oxygen and carbon isotope composition of Callovian–Lower Oxfordian (Middle–Upper Jurassic) belemnite rostra from central Poland: A record of a Late Callovian global sea-level rise?

Oxygen and carbon isotope data of well-preserved and stratigraphically well-dated belemnite rostra are presented from a Callovian–Lower Oxfordian succession of the Polish Jura Chain (south-central Poland) that was deposited in a deep shelf environment. Palaeotemperatures calculated from belemnite δ 18O values (9 to 14 °C) indicate relatively constant climatic conditions during studied Callovian and Early Oxfordian intervals. Belemnite δ 13C temporal trends, which are interpreted to record primary variation in the isotope composition of dissolved inorganic carbon reservoir, display a prominent positive carbon isotope shift (up to around 1.7‰ VPDB) in the Upper Callovian. This excursion is preceded and followed by a drop in average δ 13C values of belemnite rostra of around 1‰. The Late Callovian carbonate carbon isotope excursion is likely linked to the enhanced storage of organic carbon in shelf sediments during a global sea-level rise. The presented data are not compatible with the theory of prolonged global glaciation at the Middle–Late Jurassic transition.

Palaeoceanographic and palaeoclimatic reorganization around the Middle–Late Jurassic transition

A Middle to Upper Jurassic succession of submarine hardgrounds overlain by nodular limestones is exposed in the Jura mountains and in the Helvetic of the Swiss Alps. These sediments were accumulated along the northern shelf of the east–west trending Tethys seaway. Submarine hardgrounds and nodular limestones were also formed on the Briançonnais High, today outcropping in the middle Penninic nappe pile of the Alps. Hardgrounds record strong and persistent current activity along the northern Tethys shelf and on the Briançonnais High during the Callovian and Early Oxfordian. The transition from hardgrounds to nodular limestones corresponds to a major reorganization of Tethys oceanography. The change occurred in Plicatilis ammonite Zone (Middle Oxfordian). Carbon isotope stratigraphy, calibrated against an ammonite-dated reference section in the French Subalpine Basin, serves as a correlation tool between ammonite-dated sections and successions with poor biostratigraphic resolution. Correlation demonstrates that the end of hardground formation was synchronous over wide parts of the northern Tethys. The change in shelf sedimentation coincides with a positive carbon isotope excursion with an amplitude of 1.5‰. The change in C-isotope stratigraphy indicates that observed reorganization of current patterns along the northern Tethys shelf was coupled with global change in oceanography and climate. We propose that the change in northern Tethys sedimentation was caused by opening of new seaways at a time of progressive collapse of Pangaea.

Perturbation of the carbon cycle at the Middle/Late Jurassic transition: Geological and geochemical evidence

A compilation of new and published stratigraphic, paleontological and geochemical data is used to detect the reciprocal influences of carbon cycling and global environmental changes in the Jurassic. A major perturbation of the surface carbon cycling accompanied by pronounced climate and sea level fluctuations (waxing and waning of continental ice?) affected Earth history around the Middle/Late Jurassic transition (MLJT). We establish the respective timing of changes of carbonate and organic matter sedimentation, and global fluctuations of sea surface temperatures (paleobiogeography and O-isotope paleothermometry) and sea level (sequence stratigraphy), so that causative mechanisms and feedback effects can be considered. It is apparent that the global sea level rise and warming initiated in the Late Bathonian led to a constriction of carbonate platforms to low latitudes and enhanced marine organic deposition. Sea level and temperature optima were achieved several million-years later during the Middle Callovian. A detailed record of sea surface temperatures in the Northern Hemisphere based on migration of marine fauna and isotopic thermometry indicates that a drastic climatic decline set in during the early Late Callovian, just post-dating the increased capture of organic matter by marine sediments. This decline in temperature is interpreted in terms of an inverse greenhouse effect, triggered by drawdown of CO 2 consequent upon excess carbon burial. The magnitude of refrigeration and its coincidence in time with an abrupt global-scale fall of sea level are both suggestive of continental ice formation at this time. Carbonate sedimentation was jeopardized at the MLJT as a result of both global cooling and presumed P C O 2 lowering, and resumed abruptly during the Middle Oxfordian by spreading again over mid-latitude zones. Salient conclusions are that (1) the pattern of excess carbon burial, coincident with elevated temperature but followed by climatic deterioration supports the general hypothesis that a major control on Mesozoic climate was the abundance of atmospheric CO 2 ; (2) significant masses of continental ice may have formed during this part of the Jurassic and correlatively, high CO 2 levels were certainly not sustained throughout this period; (3) the global carbonate sedimentation budget correlated with the surface temperature and sea level, but the latitudinal spreading of type-tropical carbonates was not simply related to the thermal status of seawaters; (4) on a global scale, the C o r g and C i n o r g burial rates were coupled, apparently through the correlation existing between the CO 2 level and surface temperature.

Ice age at the Middle–Late Jurassic transition?

A detailed record of sea surface temperatures in the Northern Hemisphere based on migration of marine invertebrate fauna (ammonites) and isotopic thermometry (δ18O values of shark tooth enamel) indicates a severe cooling at the Middle–Late Jurassic transition (MLJT), about 160 Ma ago. The magnitude of refrigeration (1–3°C for lower middle latitudes) and its coincidence in time with an abrupt global-scale fall of sea level documented through sequence stratigraphy are both suggestive of continental ice formation at this time. Ice sheets may have developed over the high-latitude mountainous regions of Far-East Russia. The drastic cooling just post-dated the Middle–Late Callovian widespread deposition of organic-rich marine sediments (e.g. northwestern Europe, Central Atlantic, and Arabian Peninsula). This thermal deterioration can thus be ascribed to a downdraw in atmospheric CO2 via enhanced organic carbon burial which acted as a negative feedback effect (i.e. the inverse greenhouse effect). The glacial episode of the MLJT climaxed in the Late Callovian, lasted about 2.6 Myr, and had a pronounced asymmetrical pattern composed of an abrupt (∼0.8 Myr) temperature fall opposed to a long-term (∼1.8 Myr), stepwise recovery. The glacial conditions at the MLJT reveal that atmospheric CO2 levels could have dropped temporarily to values lower than 500 ppmv during Mesozoic times.