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THE HISTORY OF THE MODERNMEDITERRANEAN BASIN
MESOZOIC TO HOLOCENE
LOCATION OF PLACES DISCUSSED IN MANY MED “RECONSTRUCTION” PAPERS
Many of the Mesozoic carbonates we see in theMediterranean (as seen during our Sicilian visit)developed on newly rifted continental margins that formed during the Mesozoic on the margins of both the northern and southern Tethyan seaway (see diagrams to follow for position of plates and their margins).
180 MaToarsian-Aalenian
MESOZOIC EVOLUTION OF THE TETHYS
SICILY
CLEAR CENTRAL ATLANTIC OPENING BEGINS
SICILY
NOTE SUSTAINED OPENING OF THE CENTRAL ATLANTIC
INCIPIENT N. ATLANTIC RIFTING
PYRENEAN SEA FLOOR
NEW ALBORAN-BALEARIC OCEAN FLOOR
SICILY
NORTH ATLANTIC SPREADING
PYRENEAN CLOSURE
SOUTH ATLANTIC OPENING
SICILY
There were numerous depositional facies groupings developed upon these rifted zones (as seen at Rocca Busambra- on our last day in the field), commonly formed within diverse environments (see rift figures to follow).They were deposited within different areas and ALSO during DIFFERENT time periods during this rifting phase. For example the Sicani or Imerase chains of Sicily, discussed in the literature (studies by Catalano, and Lentini, for example) are representative of different parts of these rifted zones. Each chain (later tectonized)is different because the sediments formed on different parts of the rifted margin or at different times.
Fig. 10a. A panoramic view of the southern slope of Piano Pilato (Rocca Busandra) show- ing stepped faults and paleoscarps; INI= lower Liassic peritidal limestones; J= Jurassic deposits; b= Geological map of the area (Basilone, 2008).
(Basilone, 2008).
The following figures demonstrate how a rifted margin develops and why segments of it receivesuch different sediments.
VERY SIMPLFIED DIAGRAM ILLUSTRATING THEFIRST STAGE IN DEVELOPMENT OF A RIFT ZONE-MAGMA IS STARTING TO RISE ALONG A LINEARRIFT ZONE WITHIN AN EXISTING CONTINENTALZONE (crust above initial rift is heated, uplifted, and stretched).
DIKES, VOLCANOES
INITIAL HEATING
DIAGRAM ILLUSTRATING MORE REALISTIC DEVELOPMENT OF FIRST STAGES OF RIFTING WITH
TILTING OF RIFTED BLOCKS
OPENING OF A RIFT ZONE WITH DEVELOPMENTOF NEW OCEAN FLOOR- MAY REMAIN CONTINENTAL (WITH OR WITHOUT INFILLING LAKES) OR MAY BECOME FLOODED WITH MARINE WATER.SUBSIDENCE OF CONTINENTAL MARGINS IS RAPID,DUE TO THINNED, STRETCHED CRUST+ COOLING. THINNING IS PARTLY DUE TO STRETCHING, BUT ALSO TO EROSION OF UPLIFTED (older) CRUSTAL SEGMENTS.
AMOUNT OF SUBSIDENCE AND TILTING OF BLOCKS IS UNEVEN, EVEN ALONG A SINGLEMARGINAL AREA.
ELONGATE LINEAR
SEAWAY
R
100 km
DIAGRAM OF A MESOZOIC TETHYAN PASSIVE MARGIN“R” IS A REEF STRUCTURE (weakly bedded to massive)
REEF MARGINAL AREAS (GREEN ARROW) USUALLY ARE WELL BEDDED. RED ARROW INDICATES AREAS OF
REEFAL TALUS AND SLUMPS
YELLOW ARROW INDICATES PELAGIC PLATFORMBERNOULLI, 1981
TRIASSIC REEF FACIES, GRUPPE SELLE, ITALIAN ‘DOLOMITES’
FORE-REEF DEBRIS]
REEF MARGIN DOWNSLOPE REWORKING
R
DEPOSITION AT THE BASE OF REEFSWITH ACCUMULATION IN GRABEN
OLISTOLITHS
GRUPPE SELLE, REEFAL OLISTOLITH,AT THE BASE OF THE MARGINAL SLOPE
REEFAL DEBRIS
ASSOCIATED PELAGIC PLATFORM
OFFSHORE PLATFORM WITH PELAGIC DEPOSITION
More confusingly they have been affected by later compressional tectonics that emplaced many separate deposits (even of different ages) together into a confused heap during the Cenozoic compression. These many segments are now shoved one upon the other in grouped chains that developed from related segments of the old Tethys rifted margins.
PLATE MOTION(why Sicily is such a mess)
Figure 3
Best for Spain Best for Sicily/Calabria
Best fit for E. Mediterranean
Position of Africa shown here presented with respect to Europe (for the past 175 Ma). Poles of rotation were worked out from magnetic position of Europe with respect to North America and then of Africa relative to North America. Rotation parameters were determined by comparing the finite difference solution of central and North Atlantic rotation parameters between the 2 areas. Then the motion changes of Africa with respect to Europe were directly related.
AFRICAN MOTION(early portion)
LATER AFRICAN MOTION(eastern Mediterranean pivoting
northward)
SUCCESSIVE PHASES OF MOTION OF THE NORTH AFRICAN COAST
SEPARATE SEGMENTS OF PLATES CONSIDEREDIN PLATE MOTION STUDY OF Dewey, Helman et al., 1989
Dewey, Helman et al. Were able to adjust the sense of rotation obtained from spreadingmotion based on detailed information obtained from each of the segments indicated above.
S
C
Dewey, Helman et al., 1989
OCEAN CRUST
MESOZOICCARBONATEPLATFORM
SENSEOF
MOTION
SENSEOF
MOTION
SICILY
ESTIMATED ANGLE OF ROTATION
OCEAN CRUST
Dewey, Helman et al., 1989
OCEAN CRUST
SICILY
S
C
OCEAN CRUST
ESTIMATED ANGLE OF ROTATIONESTIMATED ANGLE OF ROTATION
Dewey, Helman et al., 1989
OCEAN CRUST
SICILY
S
C
OCEAN CRUST
TORTONIAN
Dewey, Helman et al., 1989
OCEAN CRUST
SICILY
CALABRIA
S
C
OCEAN CRUST
OCEAN CRUST
MESSINIAN
Dewey, Helman et al., 1989
OCEAN CRUST
OCEAN CRUSTS
C
PLIOCENE
S
C
Dewey, Helman et al., 1989
EVOLUTIONARY DIAGRAM SHOWING HOW THE STRUCTURES OBSERVED IN CALABRIA CAN BE RELATED TO THE SEQUENTIAL DEVELOPMENT OF THE APENNINE THRUST SYSTEM AND THE EXTENSIONIN THE TYRRHENIAN SEA FLOOR.
Because Sicily is made up of differentsegments with diverse history, each segment responded to compression with different behavior.Also compression in the central and eastern Mediterranean changed direction about 9 Ma ago(see Dewey, Helman et al. Fig 3, as marked) so that much of the last phases of tectonism are about 90° rotated from the earlier stages.
ROVERI et al., 2008
DURING THE MESSINIAN THE MEDITERRANEAN BECAME A RESTRICTEDWATER BODY BECAUSE INFLOW AND CIRCULATION OF MARINE WATER WAS LIMITED. SPORADIC PARTIAL DRAWDOWN PROBABLY TOOK PLACE.
DEVELOPMENT OF THE MESSINIAN BASINSIN SICLY AND WHAT HAPPENED TO THE MESSINIANMARGINAL SEDIMENTS DURING THEINCREASING SYNSEDIMENTARY TECTONISMAND BASINAL COMPRESSION
ROVERI et al., 2008
Cross-section A-A’ from previous figure
- note development of sub-basins (west to east) and the different styles and degrees of reworking of the gypsum formed at the margins.
REFERENCES
Bernoulli, D. 1981. Ancient continental margins of the Tethyan Ocean. In:Geology of Passive Continental Margins. In: AAPG Education Course Note Series #19. Geology of Passive ContinentalMargins. Chapter 5, 36 pp.
Basilone, L., 2008. Mesozoic tectono-sedimentary evolution of Rocca Busombra in western Sicily.Facies. V. 54:
Cavazza, W. Roure, F., & Ziegler, P.A. 2004. The Mediterranean Area and the Surrounding Regions:Active Processes, Remnants of Former Tethyan Oceans and Related Thrust Belts. In: Cavazza, W. et al. “The TRANSMED Atlas”:
Dewey, J. F., M. L. Helman, E. Turco, D. W. H. Hutton, and S. D. Knott .1989. Kinematics of thewestern Mediterranean. In: M. P. Coward, D. Dietrich and R. G. Park, eds.,Alpine Tectonics. Geological Society Special Publication 45. pp. 265-283
Roveri, M. , Lugli, S., Manzi, V., Schreiber, B.C. (2008) The Messinian Sicilian stratigraphy revisited: toward a new scenario for the Messinian salinity crisis. Terra Nova, 20, 1-6.
Stamfli, G.M. and Borel, G., 2004. The TRANSMED Transects in Space and Time: Constraintson the Paleotectonic Evolution of the Mediterranean Domain. In: Cavazza, W. et al. “The TRANSMED Atlas”: 53-80.