- Email: [email protected]
Messinian Evaporites from the Mediterranean and Red Seas
Marine Geology, 26 (1978) 71-72 @Elsevier Scientific Publishing Company, Amsterdam - Printed in The Netherlands
MESSINIAN EVAPORITES FROM THE MEDITERRANEAN AND RED SEAS KENNETH J. HSU’, PETER STOFFERS’ and DAVID A. ROSS3 ‘Geological Institute, ETH, Zurich (Switzerland) ?Laboratorium fur Sedimentforschung, Heidelberg ( F . R . G . ) 3Woods Hole Oceanographic Institution, Woods Hole, Mass. (U.S.A.) (Received March 28, 1977)
ABSTRACT Hsu, K.J., Stoffers, P. and Ross, D.A., 1978. Messinian evaporites from the Mediterranean and Red Seas. Mar. Geol.. 26: 71-72. A prominent subbottom reflector (M- in the Mediterranean and S- in the Red Sea) has been identified by deep sea drilling as the top of an Upper Miocene evaporite formation. The Mediterranean evaporite minerals are dolomite, gypsum, anhydrite, halite, polyhalite, kainite, sulphoborite, possibly bishofite and lunebergite, a borate and phosphate mineral. The Red Sea evaporite minerals include dolomite, magnesite, gypsum, anhydrite, halite, polyhalite, and possibly tachyhydrite. Analcite and length-slow chalcedony are present locally in both regions, probably as diagenetic minerals. The sedimentary structures of the evaporites from both regions indicate a genesis in sabkha environments. The bromine profiles of the halites are also typical of deposition in shallow brine-pools. On the other hand, the sediments immediately below and above the evaporite in the Mediterranean, and those immediately above the evaporite in the Red Sea are typically hemipelagic marls, containing deep-water benthonic fossils. We believe, therefare, that the evaporites were deposited in pre-existing deep hasins, and that the evaporites, at least those from the intervals penetrated by deep sea drilling, were deposited after the basins were partially or wholly desiccated. Isotopic analyses of the carbonates and of the interstitial waters from the evaporites suggest considerable freshwater influx into the desiccating basins. That the Messinian basins were host to fresh or brackish water lakes is further proven by the occurrence of a Paratethys ostracod-fauna and an epiphytic diatom-flora in the upper levels of the Mediterranean evaporites. While the Red Sea might have received its freshwater supply from African rivers, the eastern Mediterranean lac mer with its Cyprideis pannonica, might have been a part of the Paratethys, which was a great brackish water body extending from Vienna Basin to Aral Sea. The stratigraphy of the evaporites under the Red Sea is remarkably similar t o that under central Ionian abyssal plain (Site 374). A dark gray, dolomitic marl (or mud) unit is present between a n anhydrite-halite unit of Late Messinian and a normal marine hemipelagic marl of Pliocene age. The dolomitic sediment is largely unfossiliferous except for some nannofossils (latest Miocene o r earliest Pliocene) and it may represent a more euxinic, or more basinal equivalent of Upper Messinian Cyprideis-bearing beds elsewhere (e.g. Florence Ridge, Sites 375-376). The simultaneous wcurrence of an evaporite by desiccation during the latest Miocene and the simultaneous submergence under normal marine waters during the earliest Pliocene suggest that the Mediterranean and the Red Sea Basins were parts of one and
72 the same hydrographic system. As the Mediterranean is demonstrably an Atlantic province during the Mio-Pliocene, we suspect that the Red Sea was not connected with the Indian Ocean when its evaporites were being formed. The Strait of Bab el Mandeb was opened during a more recent episode of seafloor spreading. This event, together with an isolation from the Mediterranean by the Isthmus of Suez, rendered the Red Sea an appendix of the Indian Ocean.
MESSINIAN EVAPORITES FROM THE MEDITERRANEAN AND RED SEAS KENNETH J. HSU’, PETER STOFFERS’ and DAVID A. ROSS3 ‘Geological Institute, ETH, Zurich (Switzerland) ?Laboratorium fur Sedimentforschung, Heidelberg ( F . R . G . ) 3Woods Hole Oceanographic Institution, Woods Hole, Mass. (U.S.A.) (Received March 28, 1977)
ABSTRACT Hsu, K.J., Stoffers, P. and Ross, D.A., 1978. Messinian evaporites from the Mediterranean and Red Seas. Mar. Geol.. 26: 71-72. A prominent subbottom reflector (M- in the Mediterranean and S- in the Red Sea) has been identified by deep sea drilling as the top of an Upper Miocene evaporite formation. The Mediterranean evaporite minerals are dolomite, gypsum, anhydrite, halite, polyhalite, kainite, sulphoborite, possibly bishofite and lunebergite, a borate and phosphate mineral. The Red Sea evaporite minerals include dolomite, magnesite, gypsum, anhydrite, halite, polyhalite, and possibly tachyhydrite. Analcite and length-slow chalcedony are present locally in both regions, probably as diagenetic minerals. The sedimentary structures of the evaporites from both regions indicate a genesis in sabkha environments. The bromine profiles of the halites are also typical of deposition in shallow brine-pools. On the other hand, the sediments immediately below and above the evaporite in the Mediterranean, and those immediately above the evaporite in the Red Sea are typically hemipelagic marls, containing deep-water benthonic fossils. We believe, therefare, that the evaporites were deposited in pre-existing deep hasins, and that the evaporites, at least those from the intervals penetrated by deep sea drilling, were deposited after the basins were partially or wholly desiccated. Isotopic analyses of the carbonates and of the interstitial waters from the evaporites suggest considerable freshwater influx into the desiccating basins. That the Messinian basins were host to fresh or brackish water lakes is further proven by the occurrence of a Paratethys ostracod-fauna and an epiphytic diatom-flora in the upper levels of the Mediterranean evaporites. While the Red Sea might have received its freshwater supply from African rivers, the eastern Mediterranean lac mer with its Cyprideis pannonica, might have been a part of the Paratethys, which was a great brackish water body extending from Vienna Basin to Aral Sea. The stratigraphy of the evaporites under the Red Sea is remarkably similar t o that under central Ionian abyssal plain (Site 374). A dark gray, dolomitic marl (or mud) unit is present between a n anhydrite-halite unit of Late Messinian and a normal marine hemipelagic marl of Pliocene age. The dolomitic sediment is largely unfossiliferous except for some nannofossils (latest Miocene o r earliest Pliocene) and it may represent a more euxinic, or more basinal equivalent of Upper Messinian Cyprideis-bearing beds elsewhere (e.g. Florence Ridge, Sites 375-376). The simultaneous wcurrence of an evaporite by desiccation during the latest Miocene and the simultaneous submergence under normal marine waters during the earliest Pliocene suggest that the Mediterranean and the Red Sea Basins were parts of one and
72 the same hydrographic system. As the Mediterranean is demonstrably an Atlantic province during the Mio-Pliocene, we suspect that the Red Sea was not connected with the Indian Ocean when its evaporites were being formed. The Strait of Bab el Mandeb was opened during a more recent episode of seafloor spreading. This event, together with an isolation from the Mediterranean by the Isthmus of Suez, rendered the Red Sea an appendix of the Indian Ocean.