Lower Cretaceous peritidal limestones at 2,700-m depth, Blake nose, Atlantic Ocean

Geology ◽  
1979 ◽  
Vol 7 (2) ◽  
pp. 83 ◽  
Author(s):  
Paul Enos ◽  
Tom Freeman
Keyword(s):  
Atlantic Ocean ◽  
Lower Cretaceous

Geodynamic evolution of the Tunisian margin during the Albian–Cenomanian: structural evidence of the Austrian orogenic phase and the early tectonic inversion of the Tunisian Atlas

2021 ◽  
pp. jgs2019-195
Author(s):  
Mohamed Ben Chelbi
Keyword(s):  
Atlantic Ocean ◽  
Compressive Stress ◽  
Lower Cretaceous ◽  
Geodynamic Evolution ◽  
Stress Regime ◽  
Alpine Orogeny ◽  
Excellent Opportunity ◽  
Test Models ◽  
Tunisian Atlas ◽  
Compressional Deformation

The Zebbag and Fahdene formations outcrop onshore Tunisia and provide an excellent opportunity to test models of the tectonosedimentary evolution of this region during the Albian–Cenomanian. A NW–SE compressive stress regime resulted in shortening of the Tunisian margin and this compressional tectonism defines the Austrian phase described in the surrounding margins. This event is not widely documented, but regionally extensive tectonism is suggested by NE–SW thrusting and folding, which produced an angular unconformity, active halokinetic diapirs and transpressional NW–SE pull-apart basins. The observed compressional deformation can be considered as a precursor to the Alpine Orogeny and led to the inversion of palaeoblocks inherited from Tethyan Jurassic and Lower Cretaceous rifting. A late Albian–Cenomanian onset of compressional deformation along the Tunisian margin may be intimately related to the drift of Africa with respect to Europe and to opening of the Atlantic Ocean.

scholarly journals Deep drilling results of Leg 47b (Galicia Bank area) in the framework of the early evolution of the North Atlantic Ocean

1980 ◽  
Vol 294 (1409) ◽  
pp. 51-61 ◽  
Keyword(s):  
Atlantic Ocean ◽  
Continental Margin ◽  
North Atlantic ◽  
Lower Cretaceous ◽  
North Atlantic Ocean ◽  
Regional Scale ◽  
Upper Jurassic ◽  
Borehole Data ◽  
The North ◽  
The North Atlantic

Lithologic and stratigraphic evidence from D.S.D.P. Site 398 (3910 m water depth, 1740m total penetration) and regional seismic reflexion data are placed in the context of the early tectonic evolution of the North Atlantic ocean. The morphology of the western Iberian continental margin is the result of two main tensional episodes dated Permo— Lias and Upper Jurassic - Lower Cretaceous, during which the initial basins between Grand Banks and Iberia were created by subsidence and tilting of continental blocks. A limited oceanic opening had probably occurred in Jurassic time between these two tensional episodes. There was no relative motion during Lower Cretaceous between North America and Iberia. One of the main results is that the 398 drillhole penetrated into the basement structure of a tilted block of the continental margin. Borehole data indicate an Uppermost Aptian age for the end of the Upper Jurassic - Lower Cretaceous tensional episode at the level of the site. The subsequent beginning of sea floor spreading in the Uppermost Aptian is associated with a change of sedimentary facies from graded sequences interbedded with slump beds or debris flows to dark, detritic shales. The continental margin had subsided on a regional scale since this time.

Optimum microfossil sequences and cyclic sediment patterns in Early Cretaceous pelagic strata

1993 ◽  
Vol 30 (2) ◽  
pp. 391-411 ◽  
Author(s):  
Felix M. Gradstein ◽  
Zehui Huang ◽  
Inger L. Kristiansen ◽  
James G. Ogg
Keyword(s):  
Spectral Analysis ◽  
Atlantic Ocean ◽  
Sea Level ◽  
Early Cretaceous ◽  
Lower Cretaceous ◽  
Planktonic Foraminifera ◽  
Power Spectra ◽  
Calcareous Nannofossils ◽  
Data Set ◽  
Sea Level Fluctuations

Three sequencing methods were used to calculate the most likely biozonation and the periodicity of sedimentary cycles in Lower Cretaceous pelagic strata of the Atlantic and Indian oceans.A database was built of 378 first and last stratigraphic occurrences of calcareous nannofossils, dinocysts, foraminifers, and geomagnetic reversals in highest Jurassic through Lower Cretaceous deep marine strata at 10 Atlantic Ocean and 3 Indian Ocean drilling sites. There are 135 different events in total, about one third of which are unique to either ocean. Using the complete data set, the quantitative stratigraphy methods STRATCOR and RASC calculated closely comparable optimum sequences of average first- and last-occurrence positions. The preferred zonal solution, based on the STRATCOR method, includes 56 events, each of which occurs at three or more sites. The events comprise 6 geomagnetic reversals, 25 nannofossils, 5 planktonic foraminifera, 8 benthic foraminifera, and 12 dinocysts occurrences. Nine assemblage zones have been recognized of Tithonian through Albian age. All but 2 of 18 nannofossil events in the Atlantic Ocean optimum sequence were reported in the same stratigraphic order in a standard Mesozoic nannofossil zonation.Our quantitative examination, using Walsh spectral analysis, of the Lower Cretaceous cyclic sequences at three Deep Sea Drilling Project (DSDP) sites in the Atlantic Ocean generally supports the hypothesis that they are the product of cyclic climatic changes controlled by the Milankovitch orbital cycles. The peaks in the power spectra usually can be related to obliquity and precession cycles; some peaks seem to correspond to the eccentricity cycle. Obliquity seems to be the most important and persistent orbital element responsible for cyclic sedimentation in the Early Cretaceous Atlantic Ocean.The actual pelagic sedimentation rates were calculated for some cores using the results of spectral analysis. The correlation of the actual pelagic sedimentation rate with cyclic patterns and the occurrence of calcareous turbidites indicate that the changes in cycle pattern are the reflection of changes in the oceanographic setting. The changes in oceanographic setting are related to relative-sea-level fluctuations. The intervals dominated by laminated limestone were deposited during higher sea-level periods.

Organic geochemistry of margin sediments and its significance for hydrocarbon generation

1980 ◽  
Vol 294 (1409) ◽  
pp. 187-187
Keyword(s):  
Organic Matter ◽  
Atlantic Ocean ◽  
Lower Cretaceous ◽  
Western Europe ◽  
North Atlantic Ocean ◽  
Thermal Evolution ◽  
Organic Geochemistry ◽  
Black Shales ◽  
Hydrocarbon Generation ◽  
Marine Origin

Organic-rich shales and mudstones have been drilled during the D.S.D.P. legs 47a off northwestern Africa and legs 47b and 48 off western Europe. Early Miocene black shales of the Tarfaya Basin contain an organic matter of marine origin and deposited in a reducing environment. Cretaceous dark shales and mudstones are widespread in the north Atlantic Ocean, but they contain mainly detrital organic matter of terrestrial origin. Thus, their potential for petroleum generation is rather low. An immature stage of thermal evolution can be assigned to all Miocene and Cretaceous cores. In other parts of the Atlantic Ocean black shales containing abundant organic matter of marine origin have been found in the same series of Lower Cretaceous age. The widespread occurrence of Lower Cretaceous organic rich sediments from very different sources suggests that the conditions of preservation may be the controlling factor for black shale sediments.

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