ISSN:0954-4879    

DOI:10.1111/j.1365-3121.1993.tb00299.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

ISSN:0954-4879    

DOI:10.1111/j.1365-3121.1993.tb00300.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

ISSN:0954-4879    

DOI:10.1111/j.1365-3121.1993.tb00301.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

The identification of syn‐ and late‐orogenic flysch deposits, extending from the Betic Cordillera to the Southern Apennines, assists in the reconstruction of the tectonic‐sedimentary evolution of the perimediterranean chains. A microplate was located between the European and African Plates during the Late Jurassic–Early Cretaceous, bordered northwards by the Piemontese Ocean and southwards by another (North Africa ‘Flysch’ Basin or Maghrebian) Ocean. The Piemontese Ocean and the northern margin of the microplate were structured from the Late Cretaceous to the Eocene to create an Eo‐alpine Chain. The southern margin of the microplate was deformed in the Aquitanian, when the internal areas of the Maghrebian Ocean were characterized by syn‐orogenic flysch deposits. This episode culminated with metamorphism (25–22 Ma) and nappe emplacement, which destroyed the former palaeogeography and created an orogenic belt (AlKaPeCa). Afterwards, a lower Burdigalian late‐orogenic cycle started in the deformed area, which as a result of the opening of the Algero‐Provençal Basin, caused the fragmentation of the AlKaPeCa, its thrusting on the ‘Flysch’ Basin and the collision with the North Africa and South Iberia Margins. These latter were folded and thrusted, the ‘Flysch’ Units pushed over the External Domain and also back‐thrusted. Langhian late‐orogenic deposits suture the new tectonic features. Finally, the whole orogen was thrust onto the fored

ISSN:0954-4879    

DOI:10.1111/j.1365-3121.1993.tb00302.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

The South Asian Summer Monsoon induces vertical mixing in the surface Arabian Sea, leading to a reduction in the Sea Surface Temperature (SST) of the order of 3–4°C. This reduction in temperature is recorded by modern corals (Porites) that grow in the Lakshadweep Islands (coralline islands located at about 350 km off the south‐west coast of India) in their stable oxygen isotope ratios (denoted by δ18O). As large coral colonies of this genus are available, our results show that palaeomonsoon records for a few centuries back in time, a crucial input for climatic models aimed at predicting the Asian Monsoon, can be obtained from these corals. We also show that two corals separated by ˜ 60 km show similar (518O variations as does a giant clam (Tridacna maximus) that grew near one end of the coral colonies. As this clam is known to precipitate CaCO3 in isotopic equilibrium with the ambient sea‐water, it is possible to estimate the isotopic offset of coralline δ18O from that of the CaCO3 precipitated in isotopic equilibrium. This ‘disequilibrium effect’ appears to be constant around 4.5±0.2%0. Our calculations show that SST (t, °C) is related to the coral δ18O (δc) and the sea‐water δ18O (δw) by the equation t = 3.0–4.68 (δc‐ δw), which is in good agreement with such relationships for corals fr

ISSN:0954-4879    

DOI:10.1111/j.1365-3121.1993.tb00303.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

In continental areas it is often difficult to determine the cause of intraplate magmatism. Large volumes of magma, high eruption rates, and the presence of a hotspot trace on the adjacent ocean floor, are all evidence for the presence of an anomalously hot mantle. However, in many continental magmas there are chemical variations with time which are inferred to reflect changes from asthenospheric to predominantly lithospheric source regions, or vice versa. It is argued that these chemical characteristics constrain whether magmatism was triggered by the emplacement of a mantle plume, or by lithospheric extension.

ISSN:0954-4879    

DOI:10.1111/j.1365-3121.1993.tb00304.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

The orientation structures of lava flows and lava cracks in Hawaii (Big Island) have been analysed statistically. It is shown that the lava flows do not follow epigenetic random directions, but instead follow channels that have been endogenically predesigned. Similarly, the cracks in these flows have consistent directions at 45° to the edges of the lava flows. Thus, these cracks are not simply ‘cooling joints’ but features that correspond to the edge‐crevasses in glacier‐flow: they are shearing phenomena that occur in a similar fashion in any plastic

ISSN:0954-4879    

DOI:10.1111/j.1365-3121.1993.tb00305.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

The Dead Sea contains an anomalously high concentration of soluble radium, which is considerably in excess of its radiogenic parent uranium. Mass balance calculations demonstrated that the radium is brought to the Dead Sea by springs and shallow underground seepages. The primary source from which this radium‐excess is derived has not been identified previously. Using a combination of alpha‐spectrometry, delayed neutron activation (DNA), and gamma‐ray spectrometric analyses, it was found that the extensive oil shales within the Dead Sea watershed exhibit exceptional loss of radium. It is only the coastal hot springs and saline groundwater that have traversed the oil shales that exhibit radium‐excess. Thus, it is demonstrated that a significant portion of the radium‐excess of the Dead Sea brines is derived from the Upper Cretaceous o

ISSN:0954-4879    

DOI:10.1111/j.1365-3121.1993.tb00306.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Outlines of soft‐bodied sessile epibionts that grew attached to the surfaces of calcareous shells in ancient seas are sometimes preserved by a process termed ‘Epibiont Shadowing’. Processes that altered the surface of the shell were prevented from happening immediately beneath the attached epibiont, leaving a shadow of its attachment site following its death and decay. Microboring around the perimeter of the epibiont by presumed endolithic cyanobacteria gave rise to Endolithic Shadows, and dissolution of the calcareous substrate, maybe beneath larger smothering organisms, produced Solution Shadows of smaller organisms that protected their sites of attachment from such etching effects. Recognition of this type of preservation allows the stratigraphic range of certain soft‐bodied groups to be extended. Details of the shadows may yield information about the morphological construction of the groups in q

ISSN:0954-4879    

DOI:10.1111/j.1365-3121.1993.tb00307.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

ISSN:0954-4879    

DOI:10.1111/j.1365-3121.1993.tb00308.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY