Chapter 8 Summary and conclusions

10.1144/m53.8 ◽  
2020 ◽  
Vol 53 (1) ◽  
pp. 197-205 ◽  
Author(s):  
A. O. Wilson

AbstractThis chapter summarizes the main conclusions in this Memoir. Included is a comparison of the Arabian Intrashelf Basin events to the Haq (2017) revision of the Jurassic sea level curve. One conclusion is that the Mid- to Late Jurassic Arabian Intrashelf Basin, with its stable tectonic setting during deposition, extensive present-day outcrops and subsurface well and seismic control, may be an ideal place to evaluate global changes during its time span. The last part of this chapter lists and discusses topics and questions raised within this Memoir which warrant further evaluation.

1978 ◽  
Vol 9 (3) ◽  
pp. 265-287 ◽  
Author(s):  
James A. Clark ◽  
William E. Farrell ◽  
W.Richard Peltier

The sea-level rise due to ice-sheet melting since the last glacial maximum was not uniform everywhere because of the deformation of the Earth's surface and its geoid by changing ice and water loads. A numerical model is employed to calculate global changes in relative sea level on a spherical viscoelastic Earth as northern hemisphere ice sheets melt and fill the ocean basins with meltwater. Predictions for the past 16,000 years explain a large proportion of the global variance in the sea-level record, particularly during the Holocene. Results indicate that the oceans can be divided into six zones, each of which is characterized by a specific form of the relative sea-level curve. In four of these zones emerged beaches are predicted, and these may form even at considerable distance from the ice sheets themselves. In the remaining zones submergence is dominant, and no emerged beaches are expected. The close agreement of these predictions with the data suggests that, contrary to the beliefs of many, no net change in ocean volume has occurred during the past 5000 years. Predictions for localities close to the ice sheets are the most in error, suggesting that slight modifications of the assumed melting history and/or the rheological model of the Earth's interior are necessary.


2016 ◽  
Vol 155 (3) ◽  
pp. 729-746 ◽  
Author(s):  
SHERIF FAROUK ◽  
SREEPAT JAIN

AbstractThe Maastrichtian–Danian benthic foraminiferal diversity and assemblages through sequence stratigraphy were studied at Dakhla Oasis, Egypt. Benthic foraminifera numbers (BFN), high-flux species and characteristic benthic foraminiferal species and genera distribution are also incorporated to assess palaeobathymetry, palaeoenvironment and palaeoproductivity. All these proxies are then taken together to construct a sea-level curve and interpreted in terms of regional tectonics, climate and eustasy. Data suggest a remarkably highly equitable benthic environment deposited in a brackish littoral and/or marsh setting with moderate (?) to low oxygen conditions and reduced salinity (oligotrophic), possibly due to increased precipitation and terrestrial runoff. The interrupted dominance of calcareous forms and high-organic-flux species suggests occasional marine incursions and high palaeoproductivity, due to local upwelling. The inferred sea-level curve replicates the global eustatic curve and suggests that the curve is more influenced by the prevailing climate and global eustasy rather than by regional tectonics. The post-Cretaceous–Palaeogene boundary displays improvement in the environment in terms of diversity and number of species and specimens, with a marked reduction in the abundance of high-organic-flux species during early Paleocene (Danian) time, indicating a shift from a more mesotrophic open marine environment to much reduced oligotrophic conditions.


2018 ◽  
Author(s):  
David Patrick Gold ◽  
James P. G. Fenton ◽  
Manuel Casas-Gallego ◽  
Vibor Novak ◽  
Irene Pérez-Rodríguez ◽  
...  

The island of Jamaica forms the northern extent of the Nicaraguan Rise, an elongate linear tectonic feature stretching as far as Honduras and Nicaragua to the south. Uplift and subaerial exposure of Jamaica during the Neogene has made the island rare within the Caribbean region, as it is the only area where rocks of the Nicaraguan Rise are exposed on land. Biostratigraphic dating and palaeoenvironmental interpretations using larger benthic foraminifera, supplemented by planktonic foraminifera, nannopalaeontology and palynology of outcrop, well and corehole samples has enabled the creation of a regional relative sea-level curve through identification of several depositional sequences. This study recognises ten unconformity-bounded transgressive-regressive sequences which record a complete cycle of relative sea level rise and fall. Sequences are recognised in the Early to ‘Middle’ Cretaceous (EKTR1), Coniacian-Santonian (STR1), Campanian (CTR1), Maastrichtian (MTR1-2), Paleocene-Early Eocene (PETR1), Eocene (YTR1-3) and Late Eocene-Oligocene (WTR1). These transgressive-regressive cycles represent second to fourth order sequences, although most tie with globally recognised third order sequences. Comparisons of the Jamaican relative sea-level curve with other published global mean sea-level curves show that local tectonics exerts a strong control on the deposition of sedimentary sequences in Jamaica. Large unconformities (duration >1 Ma) are related to significant regional tectonic events, with minor overprint of a global eustatic signal, while smaller unconformities (duration <1 Ma) are produced by global eustatic trends. The relatively low rates of relative sea-level rise calculated from the regional relative sea-level curve indicate that carbonate production rates were able to keep pace with the rate of relative sea-level rise accounting for the thick successions of Maastrichtian carbonates and those of the Yellow and White Limestone Groups. Carbonate platform drowning within the White Limestone Group during the Oligocene to Miocene is attributed to environmental deterioration given the low rates of relative sea-level rise.


Fossil Record ◽  
1999 ◽  
Vol 2 (1) ◽  
pp. 25-61 ◽  
Author(s):  
W.-D. Heinrich

Tendaguru is one of the most important dinosaur localities in Africa. The Tendaguru Beds have produced a diverse Late Jurassic (Kimmeridgian to Tithonian) dinosaur assemblage, including sauropods (<i>Brachiosaurus, Barosaurus, Dicraeosaurus, Janenschia</i>), theropods (e.g., <i>Elaphrosaurus, Ceratosaurus, Allosaurus</i>), and ornithischians (<i>Kentrosaurus, Dryosaurus</i>). Contrary to the well studied skeletal anatomy of the Tendaguru dinosaurs, the available taphonomic information is rather limited, and a generally accepted taphonomic model has not yet been established. Assessment of unpublished excavation sketches by the German Tendaguru expedition (1909–1913) document bone assemblages of sauropod and ornithischian dinosaurs from the Middle Saurian Bed, Upper Saurian Bed, and the Transitional Sands above the <i>Trigonia smeei</i> Bed, and shed some light on the taphonomy of the Tendaguru dinosaurs. Stages of disarticulation range from incomplete skeletons to solitary bones, and strongly argue for carcass decay and post-mortem transport prior to burial. The sauropod bone accumulations are dominated by adult individuals, and juveniles are rare or missing. The occurrence of bones in different superimposed dinosaur-bearing horizons indicates that skeletal remains were accumulated over a long time span during the Late Jurassic, and the majority of the bone accumulations are probably attritional. These accumulations are likely to have resulted from long-term bone imput due to normal mortality events caused by starvation, seasonal drought, disease, old age and weakness. The depositional environment of the Middle and Upper Saurian Bed was mainly limnic to brackish in origin, while the palaeoenvironment of the Transitional Sands was marginal marine. <br><br> Tendaguru zählt zu den bedeutendsten Dinosaurier-Lagerstätten Afrikas. Aus den Tendaguru-Schichten sind zahlreiche Skelettreste von Sauropoden (<i>Brachiosaurus, Barosaurus, Dicraeosaurus, Janenschia</i>), Theropoden (z.B. <i>Elaphrosaurus, Ceratosaurus, Allosaurus</i>) und Ornithischiern (<i>Kentrosaurus, Dryosaurus</i>) geborgen worden. Sie stammen aus der späten Jura-Zeit (Kimmeridge — Tithon). Während der Skelettbau der Tendagurusaurier gut untersucht ist, wirft die Taphonomie des Sauriervorkommens von Tendaguru noch immer Fragen auf. Unklar ist bislang, wie die enormen Anreicherungen von Dinosaurierknochen in den Tendaguru-Schichten zustandekamen. Unveröffentlichte Grabungsskizzen der Deutschen Tendaguru Expedition (1909–1913) erweitern unsere Kenntnisse über die Taphonomie der Tendagurusaurier. In den ausgewerteten Grabungsskizzen sind Knochenansammlungen von Sauropoden und Ornithischiern aus dem Mittleren und Oberen Sauriermergel sowie aus den Übergangsschichten über der <i>Trigonia smeei</i>-Schicht dokumentiert. Die Lage und der Erhaltungszustand der Funde lassen auf erheblichen Zerfall der Kadaver und post-mortalen Transport von Skelettelementen vor der Einbettung schließen. Das Vorkommen von Saurierknochen in mehreren übereinanderliegenden Profilabschnitten der Tendaguru-Schichten zeigt, daß Skelettreste während der späten Jura-Zeit über einen längeren Zeitraum hinweg akkumuliert wurden. Die Ansammlungen von Skelettresten gehen wahrscheinlich auf „normale” Sterbe-Ereignisse zurück, wie z. B. Verhungern, Verdursten, Kankheit, Altersschwäche und jahreszeitliche Dürre. Als Ablagerungsraum der Mittleren und Oberen Saurierschicht kommt ein küstennaher limnischer, zeitweise wohl auch brackischer Küstenstreifen in Betracht. Die knochenführenden Übergangsschichten unter- und oberhalb der Saurierschichten sind randlich marine Ablagerungen. <br><br> doi:<a href="http://dx.doi.org/10.1002/mmng.1999.4860020102" target="_blank">10.1002/mmng.1999.4860020102</a>


2021 ◽  
Author(s):  
Mohammadsadegh Dehghanian

Abstract Asmari Formation is the thick sequence of carbonate sediment in the range of Oligocene-Miocene which is deposited in the foreland basins of the Zagros and is considered as the original and most famous reservoir rock of Zagros basin. To study of lithostratigraphic units and sequence stratigraphy of this Formation, the section in the southeast of Norabad was selected. Field study indicated that Asmari Formation possessed the thickness of 401.5m and included 9 lithostratigraphic units. According to the study of microfacies, Stacking pattern and identification of main sequence level, three depositional sequences including two-second order and one-third order sequence were recognized. The sea-level curve in the studied section indicated that it was correspondence to the global sea level curve. These facies deposited in five environmental sedimentations as follow Open Sea Shelf (Fore Barrier), Bar, Lagoon, Back bar shelf, and Shoal. The environment is part of a carbonate platform that has been formed on an open shelf. In addition, according to the Study of foraminifer dispersion pattern the range of Asmari Formation in Norabad was suggested to be Oligocene (Rupelian- Chattian) to lower Miocene (Aquitanian- Burdigalian).


2021 ◽  
Author(s):  
Kathrine Maxwell ◽  
Hildegard Westphal ◽  
Alessio Rovere

&lt;p&gt;The Last Interglacial (LIG), as well as other warmer periods in the Earth&amp;#8217;s geologic history, provides an analogue for predicted warming conditions in the near future. Analysis of sea-level indicators during this period is important in constraining regional drivers of relative sea-level change (RSL) and in modeling future trajectories of sea-level rise. In southeast Asia, several studies have been done to examine LIG sea-level indicators such as coral reef terraces and tidal notches. A synthesis of the state-of-the-art of the LIG RSL indicators in the region, meanwhile, has yet to be done. We reviewed over 50 published works on the LIG RSL indicators in southeast Asia and used the framework of the World Atlas of Last Interglacial Shorelines (WALIS) in building a standardized database of previously published LIG RSL indicators in the region. In total, we identified 38 unique RSL indicators and inserted almost 140 ages in the database. Available data from Indonesia, the Philippines, and East Timor points to variable elevation of sea-level indicators during the LIG highlighting the complex tectonic setting of this region. Variable uplift rates (from as low as 0.02 to as high as 1.1 m/ka) were reported in the study areas echoing various collision and subduction processes influencing these sites. Although several age constraints and elevation measurements have been provided by these studies, more data is still needed to shed more light on the RSL changes in the region. With this effort under the WALIS framework, we hope to identify gaps in the LIG RSL indicators literature in SE Asia and recognize potential areas that can be visited for future work. We also hope that this initiative will help us further understand the different drivers of past sea-level changes in SE Asia and will provide inputs for projections of sea-level change in the future.&lt;/p&gt;


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