OCEAN DRILLING PROGRAMLEG 161 SCIENTIFIC PROSPECTUSMEDITERRANEAN SEA II - THE WESTERN MEDITERRANEANDr. Maria Comas Dr. Rainer ZahnCo-Chief Scientist, Leg 161 Co-Chief Scientist, Leg 161Instituto Andaluz de Ciencias de la Tierra GEOMARCSIC, Universidad de Granada Wischhofstraße 1-3Campus Fuentenueva D-24148 Kiel18002 Granada Federal Republic of GermanySpainDr. Adam KlausStaff Scientist, Leg 161Ocean Drilling ProgramTexas A&M University Research Park1000 Discovery DriveCollege Station, Texas 77845-9547U.S.A.Philip D. RabinowitzDirectorODP/TAMUJack Baldauf /Manager (Science OperationsODP/TAMUTimothy J.G. FrancisDeputy DirectorODP/TAMUJanuary 1995Material in this publication may be copied without restraint for library, abstract service,educational, or personal research purposes; however, republication of any portion requiresthe written consent of the Director, Ocean Drilling Program, Texas A&M UniversityResearch Park, 1000 Discovery Drive, College Station, Texas 77845-9547, U.S.A., aswell as appropriate acknowledgment of this source.Scientific Prospectus No. 61First Printing 1995DistributionCopies of this publication may be obtained from the Director, Ocean Drilling Program,Texas A&M University Research Park, 1000 Discovery Drive, College Station, Texas77845-9547, U.S.A. Orders for copies may require payment for postage and handling.DISCLAIMERThis publication was prepared by the Ocean Drilling Program, Texas A&M University, asan account of work performed under the international Ocean Drilling Program, which ismanaged by Joint Oceanographic Institutions, Inc., under contract with the NationalScience Foundation. Funding for the program is provided by the following agencies:Canada/Australia Consortium for the Ocean Drilling ProgramDeutsche Forschungsgemeinschaft (Federal Republic of Germany)Institut Francais de Recherche pour 1'Exploitation de la Mer (France)Ocean Research Institute of the University of Tokyo (Japan)National Science Foundation (United States)Natural Environment Research Council (United Kingdom)European Science Foundation Consortium for the Ocean Drilling Program (Belgium,Denmark, Finland, Iceland, Italy, Greece, The Netherlands, Norway, Spain,Sweden, Switzerland, and Turkey)Any opinions, findings, and conclusions or recommendations expressed in this publicationare those of the author(s) and do not necessarily reflect the views of the National ScienceFoundation, the participating agencies, Joint Oceanographic Institutions, Inc., Texas A&MUniversity, or Texas A&M Research Foundation.This Scientific Prospectus is based on pre-cruise JOIDES panel discussions. Theoperational plans within reflect JOIDES Planning Committee and thematic panel priorities.During the course of the cruise, actual site operations may indicate to the Co-ChiefScientists and the Operations Superintendent that it would be scientifically or operationallyadvantageous to amend the plan detailed in this prospectus. It should be understood that anyproposed changes to the plan presented here are contingent upon approval of the Director ofthe Ocean Drilling Program in consultation with the Planning Committee and the PollutionPrevention and Safety Panel.Leg 161Scientific ProspectusPage 3ABSTRACTLeg 161 represents the second in a two-leg program to investigate (1) the tectonic history of theMediterranean Sea and (2) the origin of sapropels, laminated organic-rich layers deposited in theEastern Mediterranean Basin. Leg 161 will focus upon the tectonic evolution of the Alboran Sea, atypical "Mediterranean backarc basin," and the paleoceanography of the Western Mediterranean.The cause of the extension in basins such as the Alboran Sea Basin, and the rapid evolution of acollisional zone into superimposed regions of extension and adjacent contraction, has not yet beenadequately explained, and the Alboran basin presents an ideal situation to investigate competinghypotheses. The Neogene extensional basin beneath the Alboran Sea developed behind an arc-shaped mountain belt and is located on the site of a late Cretaceous/Paleogene orogen generatedfrom collisional stacking. The region straddles the boundary between the European and Africanplates which converged during the Neogene; the basin thus formed in an overall environment ofplate convergence. During the Miocene, the migration of the arcuate mountain front may have beennearly coeval with extension in the inner part of the arc that resulted in crustal attenuation andbasinal spreading on the Alboran Domain. The basin formed from early Miocene onward,whereas, outside the arc, the thrusting processes continued.Three proposed sites (Alb-2, Alb-3A, and Alb-4A) and corresponding alternate sites (Alb-2A,Alb-2B, Alb-3, and Alb-4) have been chosen to determine the origin and tectonic evolution of thebasin. Petro-structural and petrological studies, of the predicted-metamorphic basement rocks on astructural high in the Western Alboran Basin (proposed site Alb-2) will help to determine thehistory of convergent tectonism, and to which particular crustal domain, or units within thosedomains, the basement belongs. Combining drill results regarding the timing of later tilting anduplift of the basement high in the Western Alboran Basin (proposed site Alb-2), and the syn-riftand post-rift subsidence in the Eastern Alboran Basin (proposed site Alb-4 A), with seismic andcommercial well data will allow us to determine the magnitude of the extension and the relativeproportions of syn-rift to post-rift subsidence in the basin. The nature of the postulated lateMiocene to Holocene contractional reorganization that produced folding, strike-slip faulting, blockrotation, and pull-apart-type structures in the basin will be tested by drilling in the Eastern andSouthern Alboran Sea (proposed sites Alb-3A and Alb-4A).Leg 161Scientific ProspectusPage 4The transect of Leg 160 and Leg 161 sites across the entire Mediterranean will be drilled duringLeg 160 and Leg 161 to determine the history of water- mass circulation and the influence ofmonsoon-driven atmospheric forcing on Mediterranean climate. This Mediterranean-wide drillingprogram is needed to establish a database that will allow synoptical mapping of hydrographic andclimatic conditions throughout the Mediterranean. Leg 160 will core the easternmost sites ofsapropel formation in the Mediterranean Sea (proposed sites MedSap-2, -3, and -4), and Leg 161will concentrate on sampling the westernmost occurrence of sapropels and areas in the western