Drilling for Scientific Purposes in the Tropical-Subtropical Andes: 10 Lake Titicaca, Bolivia/Peru Huatajata, Bolivia, May 18-22, 1998, Paul A

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WORKSHOP REPORTS: 10

Drilling for Scientific Purposes in the Tropical-Subtropical Andes: 10 Lake Titicaca, Bolivia/Peru Huatajata, Bolivia, May 18-22, 1998, Paul A. Baker

ON DEEP DRILLING PROJECT IN THE FOREARC OF THE HELLENIC ARC, 18 CRETE, GREECE Chania, Crete, Oct. 15-19, 1998, D.I. Papanikoulaou & B. Stoeckhert

CHICXULUB-WORKSHOP 74 Merida, March 22-24, 1999, J. Lauterjung

INTERNATIONAL WORKSHOP FOR A CLIMATIC, BIOTIC, AND TECTONIC, POLE-TO-POLE CORING TRANSECT OF TRIASSIC-JURASSIC PANGEA

Acadia University, Wolfville Nova Scotia, June 5-9, 1999

P. E. Olsen, D. V. Kent, R. Raeside, M. Withjack, G. McHone, F. Surlyk, K. Burke

AN NSF/ICDP WORKSHOP ONSCIENTIFIC DRILLING ON LAKES MALAWI 88 AND TANGANYIKA October 10-16, 1999, Club Makakola, Malawi, C. A. Scholz

APPENDIX I: ICDP Training Course 107 Drilling for Scientific Purposes in the Tropical-Subtropical Andes: Lake Titicaca , Bolivia/Peru

Report of a workshop sponsored by the International Continental Scientific Drilling Program

Huatajata, Bolivia, May 18-22, 1998

Report compiled by Paul A. Baker

Principal investigators:

Paul A. Baker, Duke University, Division of Earth and Ocean Sciences, Durham, NC, USA Sherilyn Fritz, Lehigh University, Department of Earth and Environmental Sciences, Bethlehem, PA, USA Geoffrey O.Seltzer, Syracuse University, Department of Earth Sciences, Syracuse, NY, USA

Other participating investigators:

Jaime Argollo, Universidad Mayor de San Andres, La Paz, Bolivia Robert B. Dunbar, Stanford University, Department of Geology, Palo Alto, USA Edmundo Moreno, Universidad Nacional del Altiplano, Puno, Peru Phillippe Mourguiart, ORSTOM, La Paz, Bolivia and Paris, France Mario Revollo, Autoridad Autonoma de Lago Titicaca, La Paz, Bolivia Catherine A. Rigsby, East Carolina University, Department of Geology, Greenville, USA

Contact address:

Professor Paul A. Baker Duke University Division of Earth Sciences Durham, NC 27708-0227 USA telephone: (919) 684-6450 fax: (919) 684-5833 email: [email protected] Introduction

A workshop was held in Huatajata, attended by scientists, engineers, and Bolivia, on May 18-20. The workshop was government officials from Bolivia, United followed by a two day field trip to States, France, and Germany (a complete Copacabana, Isla del Sol, and Isla de la list of participants and their affiliations is Luna, Bolivia. The workshop was given later in this report).

Purpose of the Workshop

The purposes of the workshop Lake Titicaca; and (3) to introduce were: (1) to discuss the scientific rationale government officials of Bolivia to the for drilling in Lake Titicaca; (2) to discuss possibility of scientific drilling in the the engineering feasibility of drilling in Bolivian-held portion of Lake Titicaca.

Scientific Rationale for Drilling Lake Titicaca

The most important goal of drilling in contains pelagic sedimentary sequences Lake Titicaca is to extract a record of that accumulated slowly and relatively tropical paleoclimate that extends back continuously. The only other long record temporally into at least the Middle from South America comes from the Pleistocene. Nowhere else that we know Sabana de Bogota, Columbia of in tropical South America will such a (Hooghiemstra and Sarmiento, 1991; record be possible. Other major goals of Hooghiemstra et al., 1993). That record this drilling are to increase our extends in time from the late Pliocene until understanding of the tectonic/neotectonic about 30,000 yr BP (but not thereafter) evolution of the northern Altiplano, to and is based primarily on pollen analysis. determine rates of erosion and the (2) Lake Titicaca is an old lake and we unroofing history of the eastern and now know as a result of recent seismic western Cordilleras, to determine the studies that it contains at least 300 meters extent and timing of tropical glaciers prior of sediment and it may contain sediments to the last Glacial stage, and to compile a as old as Pliocene, although little is known record of Quaternary volcanic activity in about the total thickness and structure of the Central Andes. its sedimentary fill. A seismic-reflection Lake Titicaca contains what we profiling cruise scheduled for January, believe to be one of the most significant 1999, should clarify these issues. climatic archives in all of South America. (3) It is located in the subtropical The importance of the Lake Titicaca site latitudes of the Western Hemisphere can be attributed to the following where no other long climatic records exist. characteristics. Climatological and climate modeling (1) It is the only large and deep fresh- studies have demonstrated that the water lake in South America, thus it northern Altiplano, including Lake Titicaca, has a climate that is broadly (6) Our studies of piston cores representative of large portions of the extending back to about 25,000 years BP southern tropics of South America. reveal that many of the sedimentary (4) It is today essentially a closed- components necessary for a successful basin lake, thus lake level, composition, paleoclimatic reconstruction are present and biota are most sensitive to changes in and well-preserved in young lake precipitation. sediments (Cross et al., in press, (5) Excellent calibration of the climatic Holocene, 1999). significance of the most recent lake sediments is possible because of the The Altiplano is the second largest availability of instrumental records of high plateau on Earth (after Tibet). It is precipitation, temperature, wind velocity, defined geomorphically as an endorheic relative humidity, atmospheric pressure, basin outlined by the Cordilleras insolation, and evaporation, that have Occidental and Oriental of the Andes. The been kept for at least the past three Cordillera Oriental is mostly comprised of decades (much longer for certain stations) Paleozoic clastic sediments derived from at many dozens of stations on the the Brazilian shield to the east and from Altiplano of Peru and Bolivia. River the Arequipa massif to the west. discharges for all of the major tributaries to Sedimentation was interrupted by the lake have been measured compressional orogenesis during the late continuously over the same period. Lake- Paleozoic. The Cordillera Oriental has level variations have been recorded been the locus of the inner magmatic arc continuously for the past 80 years. A since the Oligocene and it is intruded by a unique advantage to studies of variety of magmatic rocks of Tertiary age. paleohydrology and paleoclimatology in The Cordillera Occidental is the locus of the Altiplano is the presence at the the active volcanic arc. It was initiated in northern boundary of the watershed of the the Triassic birth of the Andean orogenic Quelccaya ice cap, a 1500-year record of cycle marking the beginning of the ice accumulation fully documented by subduction of Pacific oceanic lithosphere Thompson and co-workers (e.g. 1986, beneath western South America. As long 1988, 1989); the presence within 50 km of ago as 1929, Steinmann recognized that the watershed of the Volcan Sajama ice the Andean orogenic phase of the Central cap, a 30,000 year record of ice Andes was characterized by several accumulation (Thompson et al., in press, pulses of compressional tectonism. Many Science, 1998); and the presence within a other investigators have detailed these few 100 km to the north of the Huascaran events and related them to possible ice cap, a 20,000 year record of ice increases in the rate of plate convergence accumulation (Thompson et al., 1995). and arc magmatism. Between the two These ice caps may allow the cordilleras, the Altiplano has been a site of reconstruction of past temperatures pulsed subsidence for much of the (Broecker, 1997) and certainly do contain Cenozoic. The Altiplano had apparently the isotopic record of precipitation falling reached its present-day elevation by the on a portion of the Altiplano, an incredible Pliocene. In the late Pliocene and again in aid to isotopic modeling of paleohydrology the early Quaternary tectonic compression and paleoprecipitation (Baker et al., caused reverse faulting and folding on the manuscript in preparation, 1998). Altiplano. Neotectonic deformation in much of the High Andes today, and orthogonal to the compression observed in perhaps for the last 1 or 2 million years, is the sub-Andean and Pacific lowlands. characterized by normal faulting due to Neotectonic information is sparse for most north-south extension (Sebrier et al, of the northern Altiplano and non-existent 1985), possibly due to the effect of high for the sublacustrine portions of the basin. topography. A spectacular example is the Seismic reflection profiling in Lake Titicaca faulting of the Quaternary glacial deposits will be of great usefulness in mapping the along the southwestern margin of the extent and orientation of both old and Cordillera Real between Lake Titicaca and active structures under the lake. Drilling La Paz, faulting that may have been will provide the only opportunity to date associated with the creation of the modern reflectors and calculate rates of Lake Titicaca basin. The north-south deformation. extensional direction is approximately

Engineering Feasiblity of Drilling in Lake Titicaca The lake is relatively deep, up to 284 m. At the workshop Gene Pollard of Our forthcoming seismic profiling should the Ocean Drilling Program reviewed the reveal the optimum site for a drilling results of the ICDP-funded feasibility study platform. We want to ensure that we are for scientific coring on large lakes that was below wave-base of the lowest Holocene previously conducted by Fugro Engineers lake levels, probably more than 100 m B.V. He presented a Lake Titicaca below present lake level. Rough seas can scenario for hydraulic piston coring of develop on the lake during thunderstorms three holes to 200 m subbottom depth and in the rainy season. The rest of the year for rotary coring in Lake Titicaca to a we would not anticipate overly rough subbottom depth of as much as 1000 m. conditions: the strongest winds are The estimated cost for this "high-end" easterly and do not have a large fetch. We project was in the range of $2M to 3M. do not believe there is any hydrocarbon More recently, discussions between the hazard to drilling—seismic records show lake drilling community, Gene Pollard, and no gas and there is little gas in any of the engineers from DOSECC, have caused a cores we have recovered to date. There large downward revision of these cost is a very small oil deposit on the estimates (and a small downward revision Capachica peninsula to the west of the of targeted subbottom depths). The latter lake that produced a few hundred gallons alternative is discussed in the section on of very heavy weight oil around the turn of recommendations. Lake Titicaca is the century, but there is no evidence for oil readily accessible by road from La Paz. seeps in the lake or on the lakeshore. La Paz has major international airport.

International Collaboration for Drilling in Lake Titicaca

It is most important to involve binational (Peru and Bolivia) Autoridad Bolivian and Peruvian scientists and Autonoma de Lago Titicaca (AALT). The authorities in this research. The key P.I.’s relationship with this group was organization that makes drilling in Lake formalized in January, 1996, by the Titicaca a possibility is the ministry-level, signing of an official, five-year, climatology, tectonics, and volcanism, convenio between AALT and Duke and involving Bolivian, Peruvian, German, and Syracuse Universities. We assume that French teams, as well as studies being AALT would have the authority to issue undertaken by the P.I.’s. It is important to permits for scientific drilling in the lake. this drilling project to enlist the cooperation of these scientists and to provide samples There are several ongoing to them when drill core becomes available. scientific investigations of paleo-

Summary of the Proceedings of the Workshop

May 17 several aspects of the research on global Most participants arrived in the AM at change that is being done in Bolivia. Dr. the La Paz airport (El Alto) and were Gerhard Woerner presented a paper on transferred to the Crillon Hotel in the tectonic and volcanic history of the Huatajata on the shores of Lago Central Andes. Dr. Platt Bradbury gave a Huinaimarca. brief look at preliminary data from a 35 m long drill core taken (for the purpose of May 18 gold exploration) in the central Altiplano The workshop began with an greeting near Oruro. This drill core, like others and introduction by Ing. Julio Sanjines G., from the Salar de Uyuni, contains former Bolivian ambassador to the US. interbedded sediments representing an This was followed by a presentation on alternation between dry periods (fluvial or NSF funding structure for paleoclimatic salt beds) and wet periods (lacustrine research by Dr. Herman Zimmerman. Dr. sediments) on the Altiplano. Ulrich Harms presented an overview of the role of ICDP in supporting continental May 19 drilling, in general, and lake drilling, in Dr. Vera Markgraf presented results of specific. Dr. Steve Colman presented an her research in a number of lakes in overview of the history of PAGES southern Argentina, including other involvement in lake drilling and of scientific potential sites for drilling. Mr. Gene results in the Baikal drilling project. Drs. Pollard gave a report on the engineering Paul Baker, Geoff Seltzer, and Sheri Fritz feasibility and expenses for drilling in Lake summarized their work to date on the Titicaca. This was followed by a Quaternary paleoclimatic evolution of discussion on the importance of the tropical South America based on results involvement of Bolivian and Peruvian from piston coring and seismic reflection scientists and students in the drilling profiling in Lake Titicaca. program. Finally, there was a general Dr. Catherine Rigsby followed with a discussion on the scientific rationale for presentation of her work on the Holocene drilling followed by discussion on the and late Pleistocene fluvial history of the feasibility of drilling. Two fundamental Rio Desaguadero (the outlet river for Lake scientific problems to be addressed by Titicaca). Dr. Philippe Mourguiart gave an drilling were reiterated, especially, the overview of the history of ORSTOM need to recover a long-term (million year) studies of paleoclimatology on the record of tropical glaciation (at present Altiplano. Dr. Jaime Argollo spoke about there is only information available on the last glacial stage in the tropics; Lake such as the early Holocene lake-level fall Titicaca may be the only site anywhere in by 100 m that was likely driven by a long- the world where such a record can be term decrease in precipitation of over extracted), and the need to recover a long- 20%; when did this happen in earlier term record of hydrologic variations during portions of the Quaternary and might it the Quaternary (there is no accurate GCM happen again during warm periods in the model hindcast of hydrological variations future?). affecting the Altiplano and the Amazon

Summary

Lake drilling, in general, is of high or shallow marine drilling rig. The drilling priority to the paleoclimatic community and equipment would be stored and is of interest to many other scientists maintained at DOSECC. Individual studying tectonics of basins, science projects would obviously need to paleoseismicity, tephrochronology, and a bear the expenses of transportation, variety of other disciplines. Estimates of drilling personnel and expenses, as well the cost of deep drilling in large lakes are as scientific support. Core curation could high. It is therefore imperative that the perhaps take place within the Ocean community interested in lake drilling Drilling Program. Funding for the drilling becomes united in implementation of its equipment could perhaps be shared by goals, seeks the most cost-effective NSF and ICDP. methodology to provide the maximum scientific returns, and clearly sets forth the Minimum pre-drilling requirements scientific problems justifying the expense. for a particular lake should probably be similar to those for ocean drilling, namely Since this workshop was held, an acceptable site survey, including a discussions have taken place between seismic reflection profiling survey, several members of the lake drilling adequate near-surface sediment community and DOSECC. These characterization, and an objective site discussions have focused on a strategy for safety clearance (especially to avoid considerably decreasing the costs of lake environmental hazards). drilling (relative to the Fugro estimate). Estimated costs for purchase and Site survey information for Lake engineering an 800 m drill rig (including Titicaca will be acquired during January, hydraulic piston coring and rotary coring 1999, on a three-week long, USGS- capabilities), including drill string, and a funded, single-channel seismic reflection floating drilling platform, have been profiling and side-scan sonar survey. reduced to about $700K. The presently Previous seismic work on the lake proposed drilling platform would likely includes 3.5kHz profiling undertaken in have to be upgraded considerably to be 1997 (reported in Seltzer et al., Geology, safely utilized in large lakes or in shallow 1998) and a uniboom survey conducted in marine environments, nevertheless, a total May and June, 1998. About 20 piston of perhaps $1.2M would be sufficient for cores have been taken in the deeper the total initial capital expenses for a lake portions of the lake; the longest is about 13.5 m. These are well characterized governments. Representatives of both sedimentologically and geochemically nations support the concept of scientific (reported in Cross et al., Holocene, in drilling in Lake Titicaca. press, and Baker et al., manuscript in preparation). As mentioned previously, It is anticipated that a drilling there is no evidence for hydrocarbon proposal for Lake Titicaca will be prepared hazards anywhere within the lake. and submitted by the P.I.’s (and other Furthermore, the political situation in both interested investigators) to both NSF and Peru and Bolivia is stable and peaceful. ICDP in January, 2000. Both nations have democratically elected

Related Projects

P. Baker, G. Seltzer, S. Fritz and T. record high rates of precipitation on the Lowenstein have proposed to the Earth Altiplano; there is little ambiguity in this System History (ESH) initiative of the US interpretation. Geochronology using U/Th National Science Foundation the drilling of methods are more applicable in the Salar a related target on the Bolivian Altiplano, de Uyuni than in Lake Titicaca, hence the Salar de Uyuni, the largest salt pan in correlation of these records could enhance the world. Although presently dry most of the quality of an age model derived for the the year, this basin was formerly the site lake. In older sediments, these dates will of a deep, freshwater paleo-Lake Tauca be supplemented by Ar-Ar dating of (60,000 km2, 100 m deep, about 10 to 14 volcanic ashes. For a relatively small Ka) and late Pleistocene (ca. 25 to 30 Ka) investment, drilling in the Salar de Uyuni is paleo-Lake Minchin (Servant and Fontes, expected to greatly increase our ability to 1978; Bills et al., 1994). During periods of interpret the paleoclimatic record that we significantly increased precipitation on the will eventually extract from the drilling of Altiplano (Hastenrath and Kutzbach, 1985; Lake Titicaca. S. McGearey and B. Bills Kessler, 1988), Lake Titicaca overflowed have been funded by the Geophysics its outlet, the Rio Desaguadero, flooding program at NSF to collect seismic the downstream salars. Today the Salar reflection profiles in the region of the drill de Uyuni is capped by a 10 m thick halite holes. crust, but a 120 m drill core in the salar through this crust revealed (an undated) C. Rigsby and J. P. Bradbury are alternating sequences of halite and preparing a proposal to be submitted to lacustrine sediments (Risacher and Fritz, the ESH initiative in January, 1999, for the 1995). A new, longer (perhaps 300 m), drilling of the upstream portions of the and more-continuous drill core in the Salar paleolakes. The main purpose of their de Uyuni (and a companion hole in the proposed work is to closely constrain the Salar de Coipasa) would be invaluable for timing (within the range of C-14) and the confirming the chronology and the magnitude of the three or four most recent geochemical and biotic evidence of (perhaps the past 40 kyr or 40 m paleoclimatic change to be obtained from subbottom depth) large lakes on the Lake Titicaca drilling. For example, lake central Altiplano. Their strategy will be to deposits in Salar de Uyuni positively site drill holes at 10 to 20 m elevation steps from the Salar floor to 120 to 140 m above the Salar floor.

Workshop Participants

Paul A. Baker, Duke University, Jaime Argollo, Universidad Mayor de San [email protected] Andres Geoffrey O. Seltzer, Syracuse University, Hermann Zimmerman, US National [email protected] Science Foundation, Catherine A. Rigsby, East Carolina [email protected] University, [email protected] Gene Pollard, Sherilyn Fritz, Lehigh University, [email protected] [email protected] Ulrich Harms, ICDP, ulrich@gfz- James Broda, Woods Hole potsdam.de Oceanographic Institution, Matthew Grove, Duke University, [email protected] [email protected] Pattie Baucom, US Geological Survey, Philippe Mourguiart, ORSTOM, [email protected] [email protected] Steve Colman, US Geological Survey, Harold Rowe, Stanford University, [email protected] [email protected] Mario Revollo V., Autoridad Autonomo del Matthew Lachniet, Syracuse University, Lago Titicaca, [email protected] [email protected] Edward Revollo V., Autoridad Autonomo Platt Bradbury, US Geological Survey, del Lago Titicaca, [email protected] [email protected] Vera Markgraf, Julio Sanjines G., Autoridad Autonomo del [email protected] Lago Titicaca, [email protected] Kevin Thiesen, Stanford University Jaime Taborga T., Autoridad Autonomo Pedro Tapia, Lehigh University, del Lago Titicaca, [email protected] [email protected] Gerhard Woerner, Geochemisches Julio Campos, Autoridad Autonomo del Institut, Goettingen, Lago Titicaca, [email protected] [email protected] Maria Montenegro, ORSTOM WORKSHOP

ON DEEP DRILLING PROJECT IN THE FOREARC OF THE HELLENIC ARC, CRETE, GREECE

Chania, Crete, Oct. 15-19, 1998 CONTENT:

Programme 4

Summary of Scientific Results D.I.Papanikolaou & B. Stöckhert 8

Abstracts Terrane tectonics in the Aegean region 26 D.I.Papanikolaou

Crete - a world site for retreating subduction zones, past and present 26 B. Stöckhert

Accretion and Exhumation at a Steady-State Wedge: A New Analytical Model with 27 Comparisons to Geologic Examples Brandon M.T. & Fletcher R. C.

Crustal thickness and tectonic deformation of the Hellenides 28 J. Makris & F. Egloff

Crustal structure of the Hellenic subduction zone around Crete based on gravity 29 modeling U. Casten & J. Makris,

Seismicity in the accretionary complex of the Hellenic subduction zone around 30 Western Crete H.-P.Harjes & A.Vafidis

On the Hellenic Trench Subduction Zone: Earthquake Source Mechanisms in the 30 Hellenic Trench near Crete T. Taymaz

Mantle derived noble gases in the South Aegean volcanic arc: Indicators for 31 incipient magmatic activity and deep crustal movements V.J. Dietrich, R. Kipfer & F. Schwandner

The preneogene nappe pile of Crete 32 M. Bonneau

Remnants of pre-Alpidic crystalline basement in the lowermost tectonic units of 33 Crete E. Seidel

Analysis of Mesoscopic Elements and Microstructural Fabrics in Tectonites of the 34 Plattenkalk Group, Western Crete. Jacobshagen, V. & Manutsoglu, E.

Sequence Stratigraphic Analysis and Biostratigraphy of NW Crete Island 34 (Greece): The Neogene Kastelli Kissamou Basin as a Case Study. S. M. Bellas, H. Keupp & D. Frydas

The Island of Crete on and offshore seismic experiment: first results and tectonic 36 implications J. Makris, M. Bohnhoff, P. Harjes, D. Papanikolaou & G. Stavrakakis

Tectonics of the Central Mediterranean Region between Crete and Libya from 36 combined seismic reflection, swath bathymetry and bottom reflectivity data J. Mascle, C. Huguen and the Prismed Scientific Party

Active mud volcanism on the Mediterranean ridge: Physical properties, mud 39 breccia provenance, subsidence models, and extrusion dynamics from theoretical quantitative models (ODP Leg 160) A.Kopf

Seismic images of the Ionian basin and its margins 40 R. Nicolich

Deep structure of the Hellenides in relation to the assembly and evolution of the 40 orogen Z. Garfunkel

Geodynamics and Neotectonic Forearc Deformation: The view from Late Pliocene- 41 Recent Basins, Hellenic Arc Kleinspehn, K.L.

Deep Sea Drilling in the Eastern Mediterranean Sea: achievements and 42 opportunities A. Robertson

The Menderes Masif of Western Turkey and the Cycladic Massif in the Aegean - do 43 they really represent lateral continuations? U. Ring, K. Gessner & C.W. Passchier

Astronomically forced chemical cyclicity in Pliocene eastern Mediterranean 44 sediments H.-J. Brumsack & R. Wehausen

Biostratigraphical researches in Late Neogene deposits of the Chania area 45 D. Frydas

Kinematic analysis of the Heraklion Basin bounding faults. 46 C. Fassoulas

Crustal structure and seismic activity of the Nisyros volaano, East Aegean Sea 47 J. Makris, T. Chonia, D. Papanikolaou & G. Stavrakakis

Steady-State Fluxes in the Olympics Segment of the Cascadia accretionary wedge 48 M.T. Brandon, K.A. Farley, F.J. Pazzaglia, M.K. Roden-Tice, & G.E. Batt

Contribution of ductile flow to exhumation of low T - high P metamorphic rocks: 48 San Juan-Cascade nappes, NW Washington State M.T. Brandon & J.G. Feehan

The E.P.P.O. Permanent South Aegean Network and its contribution to the 49 monitoring of seismicity in the region. N. Melis & D. Papanikolaou Geological 3D-Modelling of the Plattenkalk Group, Western Crete 50 Manutsoglu, E., Jacobshagen, V., Spyridonos, E. & Skala, W.

Interpretation of Tectonic Lineaments using Satellite Imagery for Textural Analysis. 50 A Case Study in Western Crete Manutsoglu, E., Ott, N., Spyridonos, E. & Jacobshagen, V.

A linear source model for seismic hazard assessment in Crete and surrounding 51 region Papoulia J.

PROGRAMME THURSDAY, October 15th

09:00 - 09:30 Introduction to the Workshop 09:30 - 10:00 Terrane Tectonics in the Aegean Region D. Papanikolaou 10:00 - 10:30 Crete - a world site for retreating subduction zones, past and present B. Stöckhert 10:30 - 11:00 Accretion and Exhumation at a Steady-State Wedge: A New Analytical Model with Comparisons to Geologic Examples Brandon M.T. & Fletcher R. C.

11:00 - 11:30 Coffee break

11:30 - 12:00 Crustal thickness and tectonic deformation of the Hellenides J. Makris & F. Egloff 12:00 - 12:30 Crustal structure of the Hellenic subduction zone around Crete based on gravity modeling U. Casten & J. Makris, 12:30 - 13:00 Seismicity in the accretionary complex of the Hellenic subduction zone around Western Crete H.-P.Harjes & A.Vafidis

13:00 - 15:00 Lunch break

15:00 - 15:30 On the Hellenic Trench Subduction Zone: Earthquake Source Mechanisms in the Hellenic Trench near Crete T. Taymaz 15:30 - 16:00 Seismic tomography in the Eastern Mediterranean region G. Stavrakakis 16:00 - 16:30 Mantle derived noble gases in the South Aegean volcanic arc: Indicators for incipient magmatic activity and deep crustal movements V.J. Dietrich, R. Kipfer & F. Schwandner

16:30 - 17:00 Coffee break

17:00 - 17:30 The preneogene nappe pile of Crete M. Bonneau 17:30 - 18:00 Remnants of pre-Alpidic crystalline basement in the lowermost tectonic units of Crete E. Seidel 18:00 - 18:15 Analysis of Mesoscopic Elements and Microstructural Fabrics in Tectonites of the Plattenkalk Group, Western Crete. Jacobshagen, V. & Manutsoglu, E. 18:15 - 18:30 Sequence Stratigraphic Analysis and Biostratigraphy of NW Crete Island (Greece): The Neogene Kastelli Kissamou Basin as a Case Study. S. M. Bellas, H. Keupp & D. Frydas

FRIDAY, October, 16th

FIELDTRIP - 1st day: Western Crete (Start at 08:00) Route: Chania - Kastelli - Falassarna - Sfinari - Amigdalokefali - Elafonisi (beach) - Topolia - Chania

Stops: 1-1. Plakalona (Tectonic contact between the Phyllite - Quartzite and Tripolis units)

1-2. Falassarna (Neogene, active faults, sea level markers, A.D.365 event)

1-3. Platanos (Pindos and Tripolitza Unit, flysch)

1-4. Sfinari (HP-LT metamorphic Phyllite-Quartzite Unit)

1-5. Kambos (HP-LT metamorphic Phyllite-Quartzite Unit)

1-6. Amigdalokefali (Mass flow deposits in PQ, aragonite marbles)

1-7. Elafonisi (landscape, beach, swimming until late afternoon)

1-8. Topolia (Neogene fault scarp breccia) SATURDAY, October, 17th

FIELDTRIP - 2nd day: South of Rethymnon (Start at 07:00) Route: Chania - Vrises - Chora Sfakion - Rodakino - Sellia - Plakias (lunch) - Preveli - Kerames - Vatos - Rethymnon - Chania Stops:

2-1. Plattenkalk, Polje between Vrises and Chora Sfakion

2-2. Overview southern Coast from above Chora Sfakion

2-3. Rodakino (fault terminating Plattenkalk outcrop)

2-4. E´ Rodakino (Phyllite-Quartzite Unit)

2-5. W´ Sellia (Pindos, Uppermost Unit, Overview Plakias Graben)

2-6. E´Sellia (Ravdoucha beds, Overview tectonics)

2-7. Plakias (spectacular quaternary fault scarp, lunch)

2-8. Preveli (thrust plane, metamorphic rocks of uppermost unit on Pindos)

2-9. Preveli-Kerames (various slices of uppermost unit, tilted fluviatile Neogene)

this part depends on transportation (single large bus or several minibuses suitable for dirt roads)

2-10. Kerames-Vatos (Tripolitza Unit, Ophiolites and oceanic mass flows, Spili Graben, ascent by foot to a crest with beautiful overview over all tectonic structures - if weather is fine; late afternoon)

2-11. Fodele - Sisses (Upper Paleozoic - Lower Triassic of Plattenkalk)

Return via Rethymnon to Chania

SUNDAY, October, 18th

09:00 - 09:30 The Island of Crete on and offshore seismic experiment: first results and tectonic implications J. Makris, M. Bohnhoff, P. Harjes, D. Papanikolaou & G. Stavrakakis 09:30 - 10:00 Tectonics of the Central Mediterranean Ridge, between Crete and Libya, from combined seismic reflection, swath bathymetry and bottom reflectivity data J. Mascle, C. Huguen and the Prismed Scientific Party 10:00 - 10:30 Seismic images of the Ionian basin and its margins R. Nicolich 10:30 - 10:45 Active mud volcanism on the Mediterranean ridge: Physical properties, mud breccia provenance, subsidence models, and extrusion dynamics from theoretical quantitative models (ODP Leg 160) A. Kopf 10:45 - 11:00 Deep structure of the Hellenides in relation to the assembly and evolution of the orogen Z. Garfunkel

11:00 - 11:30 Coffee break

11:30 - 12:00 Geodetic measurements of the present day deformation of the Aegean area Billiris G. 12:00 - 12:30 Geodynamics and Neotectonic Forearc Deformation: The view from Late Pliocene-Recent Basins, Hellenic Arc Kleinspehn, K.L. 12:30 - 13:00 Deep Sea Drilling in the Eastern Mediterranean Sea: achievements and opportunities A. Robertson

13:00 - 15:00 Lunch break

15:00 - 15:15 The Menderes Masif of Western Turkey and the Cycladic Massif in the Aegean - do they really represent lateral continuations? U. Ring, K. Gessner & C.W. Passchier

15:15 - 15:30 Astronomically forced chemical cyclicity in Pliocene eastern Mediterranean sediments H.-J. Brumsack & R. Wehausen

15:30 - 15:45 Biostratigraphical researches in Late Neogene deposits of the Chania area D. Frydas 14:45 - 16:00 Kinematic analysis of the Heraklion Basin bounding faults. C. Fassoulas 16:00 - 16:15 Future ocean drilling based on the Ocean Drilling Program (ODP) and deliberations within the International Working Group on the Integrated Ocean Drilling Program H. Beiersdorf (ODP Executive Committee)

16:15 - 16:45 Coffee break

16:45 - 18:30 General Discussion MONDAY, October, 19th.

09:00 - 10:30 Working Groups

10:30 - 11:00 Coffee break

11:00 - 12:30 Working Groups - Conclusions

POSTER

• Crustal structure and seismic activity of the Nisyros volcano, East Aegean Sea J. Makris, T. Chonia, D. Papanikolaou & G. Stavrakakis • Steady-State Fluxes in the Olympics Segment of the Cascadia accretionary wedge M.T. Brandon, K.A. Farley, F.J. Pazzaglia, M.K. Roden-Tice, & G.E. Batt1 • Contribution of ductile flow to exhumation of low T - high P metamorphic rocks: San Juan-Cascade nappes, NW Washington State M.T. Brandon & J.G. Feehan; • The E.P.P.O. Permanent South Aegean Network and its contribution to the monitoring of seismicity in the region. N. Melis, D. Papanikolaou • Geological 3D-Modelling of the Plattenkalk Group, Western Crete Manutsoglu, E., Jacobshagen, V., Spyridonos, E. & Skala, W. • Interpretation of Tectonic Lineaments using Satellite Imagery for Textural Analysis. A Case Study in Western Crete 49 Manutsoglu, E., Ott, N., Spyridonos, E. & Jacobshagen, V. • A linear source model for seismic hazard assessment in Crete and surrounding region 50 Papoulia J. • Probable area for deep drilling site in Crete according to gravi-magnetic data 51 Ch. Metaxas This report to ICDP has also been attached to the related ODP proposal submitted by A. Kopf, A.H.F. Robertson, E.S. Screaton and J. Mascle

ICDP Workshop on a Deep Drilling Project in the Forearc of the Hellenic Subduction Zone, Crete, Greece Chania, Crete, October 15-19, 1998

Summary of scientific results

compiled by D. Papanikolaou (National Center for Marine Research, Ag. Kosmas 16604, Athens, Greece; [email protected]) B. Stöckhert (Institut für Geologie, Ruhr-Universität, D-44780 Bochum, Germany; [email protected])

in detail (although respective references The following report summarizes the are included). Ongoing research by scientific results of the October 1998 various groups has yielded a broad workshop, with emphasis on the role of a spectrum of new results, that are not yet combined onshore/offshore drilling fully evaluated and largely unpublished program discussed within a general (see program and abstract volume of the conceptual framework. An outline of workshop). It is expected, however, that a previous work on Crete and the Hellenic first overview based on recent results can subduction zone has been provided in the be prepared within a few months. proposal to ICDP and is not repeated here

Introduction acommodated by large scale plate Convergent plate boundaries are the sites convergence. In this case, extension at of formation and drastic modification of the front of the upper plate, constrained to continental crust. A simple classification within the forearc or localized in the distinguishes between island arcs (with backarc (marginal sea), is required to both plates being of oceanic type), active maintain crustal continuity. A prominent continental margins (with the upper plate example for such kind of situation over the being continental) and collision zones past ca. 35 million years is the Hellenic (with the lower plate being continental). subduction zone to the south and One fundamental driving force of plate southwest of Crete, including an convergence and subduction is the intermittent stage of collision with a negative buoyancy of aging oceanic microcontinent between about 30 and 20 lithosphere. It has been shown that this Ma. Today, the passive African margin negative buoyancy can cause subduction has commenced to collide with the to become more rapid as can be accretionary wedge since only a few been discussed at the International million years in the central section of the Conference on Continental Drilling at Hellenic subduction zone. Potsdam in August 1993 (see Zoback and Emmermann, 1994). A first meeting on Despite complications arising from the scientific drilling at Crete has been held at lateral heterogeneity of the downgoing the Technical University of Chania, Crete, plate, the westward drift of the Anatolian in April 1995, and a second one at the microplate, and the relative shortness of same place in November 1997, with the the convergent margin segment, the fundamental significance of a combined Hellenic subduction zone is regarded as a onshore/offshore approach being world site to study the yet poorly emphasized. In particular these aspects understood mechanics of a retreating were discussed at the ICDP-funded subduction zone, in particular due to the workshop, organized by D. Papanikolaou continuity of the structural record from the at Crete in October 1998. The workshop mid-Tertiary into the present. Thus, comprised two field trips providing insight geoscientific research has been intensified in the geological record of Crete, with in recent years, concentrating on various emphasis on structural relations relevant aspects of active tectonics and on the to the offshore areas of the forearc as crustal record, with emphasis on Crete. well. The correlated approach within the This island represents a prominent horst scope of ICDP and ODP favourably structure (developed within the last 5 corresponds to the concept proposing a million years) in the central forearc and merger of both into an Earth Drilling thus provides excellent onshore access to Program EDP from 2003. the internal structure of the forearc at various structural levels. The research In the following, we first give an overview program encompasses the option of of the present day geodynamic framework, scientific drilling, both onshore Crete and then of the crustal record for the past ca. offshore, in order to provide the required 35 million years (mainly based on complete information on the upper crustal information obtained on Crete) and how deformation history and the present this record is linked to the actual situation, physical state along a transect normal to then the fundamental questions and the the plate boundary. global significance of the region, and finally how deep drilling – on- and offshore For the Hellenic subduction zone, the role - could contribute to solve these questions of scientific drilling to get access to the and to gain a better understandig of the third dimension for studies of both the mechanical behavior of crust and mantle actual physical state as a function of depth in a retreating convergent margin setting. as well as the record of the tectonic evolution in the recent geological past has

Present Day Situation at the Hellenic Subduction Zone synoptic diagram in Fig. 2. It should be Here we concentrate on the southern noted that the tectonic situation changes segment of the Hellenic subduction zone, along strike and is different further to the along an approximately NNE-SSW west offshore mainland Greece. transect as displayed in Fig. 1. The principal features are shown on the in a notable net convergence rate of 4 to 5 Kinematics cm/year between Africa and Crete, with For the area of Crete (ca. 25° E / 35° N), Crete representing the southernmost the geology based NUVEL-1A model of piece of European (respectively Aegean) relative plate motion predicts a crust exposed above sea level. In convergence of Africa with respect to contrast, the GPS data do not indicate a stable Eurasia with a rate of 0.9 cm/year significant relative motion between Crete and a direction of 353°. The Euler pole for and the magmatic arc, represented by the the Africa – Europe relative motion is island of Santorini, despite convincing located at 21.0°N / 20.6°W, with an evidence of stretching and crustal thinning angular velocity of 0.12° per million years. beneath the Sea of Crete (see below). The actual kinematic framework is well This suggests that at present this part of constrained by space geodesy, with the forearc is internally rigid (despite the progressively increasing detail and high heat flow) and moves to the SSW, precision. According to these short term driven by either the westward escape of determinations, Crete and the southern the Anatolian microplate or roll back of the part of the Aegean is moving to the SSW Aegean subduction zone, or some with respect to stable Eurasia, with a combination (Fig. 1). velocity of ca. 3 to 4 cm/year (Jackson, 1994; Le Pichon et al., 1995). This results

Fig. 1: Present day geodynamic framework of Crete and approximate relative motion vectors (after Jackson, 1994; Le Pichon et al., 1995) for Crete and Africa with respect to stable Europe. The box shows the position of the proposed transect. For a schematic cross section see Fig. 2.

Topography mark sites of lateral displacement due to The forearc to the southwest of Crete is strain partitioning. To the south and marked by deep NW-SE trending furrows, southeast of Crete, the trench is replaced referred to as Hellenic Trench, with water by three NE-trending furrows that are depths that in places exceed 4 km (Fig. 1, interpreted as morphological expression of 2). To the south, respectively southwest of transform faults (McKenzie, 1978), the trench system an actively deforming although their trend deviates by several accretionary wedge, referred to as tens of degrees from the actual direction Mediterranean Ridge, has been identified of relative plate motion. Thus, they rather (e.g. Le Pichon et al., 1982, Kastens, represent transpressional features (Le 1991, Mascle and Chaumillon, 1997). Pichon et al., 1995). The island of Crete is Backthrusting of the outer part of the ridge a complex horst structure, bounded by E- onto an older inner ridge, and on the W as well as N-S trending normal fault backstop formed by rigid Aegean crust, systems with a cumulative displacement of with large scale slumping towards the 5 to 10 km. The highest elevations on trench has been revealed by seismic Crete are about 2,4 km, with the reflection surveys (Mascle and tectonically lowermost units exposed on Chaumillon, 1997). Mud volcanoes are top of the mountains. A relief of about 6 to associated with the backthrusts (e.g. Kopf, 7 km is maintained in the forearc within a 1999). Thus, the trench system does not small area. To the north of Crete, the mark the plate boundary, as commonly Cretan Sea reveals water depths of ca. 2 inferred, but represents a set of graben km, without accentuated physiographic structures (in a broad sense) in the features. forearc. Le Pichon et al. (1995) have proposed that in this situation the trenches ca.1cm/a uplift ca. 4 cm /a

"backstop" constriction extension

extension extension inactivated?

physical state of mantle wedge co up bending stres lin ses g s tre ss es

100 km

Fig. 2: Cartoon showing a schematic cross section of the Hellenic subduction zone; for position of the section see Fig. 1.

from surface kinematics. The distribution Arc Magmatism of hypocenters beneath the island of Crete Arc magmatism is active on a chain of does not unequivocally reveal the position islands, that trends along an arc from of the plate interface and some mainland Greece across the Aegean Sea hypocenters at a depth of 70 to 80 km to Turkey. From W to E, the Volcanoes have been recorded even to the south of active in the Quaternary are situated on Crete. At present, local arrays in western the islands of Aegina, Milos, Santorini and Crete and on the island of Gavdos are Nisyros. The Holocene eruption of used to gain a high resolution image of the Santorini at about 3.5 ka is among the distribution of seismicity related to material largest Plinian eruptions in historical times properties (Harjes et al., 1997 and worldwide, with about 30 km³ of unpublished results). pyroclastic material ejected and a caldera of 60 km² formed due to collapse of the magma chamber (e.g. Druitt et al., 1989) Seismic Tomography and Position of the Slab For the inferred position of the slab at Distribution of Seismicity greater depths, seismic tomography The distribution of seismicity marks a (Spakman, 1986; Meulenkamp et al. 1988, Benioff Zone reaching to a depth of ca. Wortel et al. 1990, Ligdas et al. 1992) has 190 km. Focal plane solutions (e.g. revealed a northward dipping zone with Taymaz et al., 1990) reveal a pattern, that velocities exceeding the PREM values by is largely consistent with what is expected between about 1 and 2 % to a depth of 600 km. In the upper 200 km, this feature is attributed to crustal extension, albeit is congruent to the Benioff zone and apparently not active today. From about consequently interpreted to represent the halfway between Santorini and Crete the slab. Hence, the length of subducted crustal thickness is increasing southwards oceanic lithosphere presumably amounts and the Moho is to 800 km at minimum. A mantle region located at a depth of 30 to 32 km beneath with anomalously slow velocities (1 to 2 % the island of Crete (Makris and Röwer, below PREM) is reported by the above 1986; Makris et al. 1998 and in authors beneath the backarc region, with a preparation). South of Crete, the thickness southern limit approximately beneath of the continental (Aegean) lid decreases Santorini. to less than 20 km within a distance of Beneath western Crete, the Moho of the about 30 km and remains between 15 and downgoing African plate has been located 20 km towards the „backstop“, about 100 using the receiver function approach at ca km from the southern coast of Crete. 50 to 60 km depth, increasing from S to N Assymmetric horst and graben structures, (Harjes et al., in preparation). The nature with sedimentary fills of up to 4 km of the material in the wedge between the thickness and a width of ca. 10 km have base of European crust and the subducted been identified by seismics (Makris et al., African Moho is still poorly constrained. 1998, and in preparation). These Beneath Crete (from bottom to top) this structures reflect the response of the wedge is expected to comprise African brittle upper crust to extension, with the oceanic crust, accreted and now high timing of this extension still poorly pressure - low temperature metamorphic constrained. Also, the marked trench sediments, and hydrated mantle system discussed above is interpreted as (serpentinite). A crustal low velocity a graben, respectively transtensional channel at 10 to 20 km depth has been structure within the continental lid of the identified beneath western Crete (Harjes forearc. In contrast, the Mediterranean et al., 1997). ridge to the south, respectively southwest of the backstop reveals contractional structures (Mascle and Chaumillon, 1997), Crustal structure of the forarc with backthrusting onto the backstop. Between the magmatic arc and the What is called the "backstop" thus marks backstop (Truffert et al., 1993; Lallemant (1) the southern edge of the continental et al., 1994; Mascle and Chaumillon, lid, thinned by southwards extension on 1997) the forearc is underlain by a lid of top of the retreating subduction zone, and Aegean continental crust. From Santorini, (2) the boundary between contractional where the Moho is located at a depth of deformation in the Mediterranean Ridge about 30 km, crustal thickness decreases accretionary wedge and (predominantly) towards the south and is reduced to less extensional deformation in the more than 16 km in places beneath the Sea of internal part of the forearc. Retardation of Crete (Makris, 1978; Makris and Röwer, convergence in the central part of the 1986; Makris et al. 1998 and unpublished Hellenic subduction zone has been data); this attributed to the onset of collision with the passive Libyan margin at between 6 and 3 Ma (Le Pichon et al., 1995). The incipient collision is also thought to be responsible for the switch from active N-S extension the shallow portions of the proposed drill on Crete to E-W extension in the Pliocene holes. (Armijo et al., 1992). However, the cause for the rapid uplift of Crete, that has presumably commenced not before 3 to 4 Heat Flow Ma, is not understood and requires a A heat flow of about 50 mWm-2 has been better understanding of the mechanical suggested by Makris and Röwer (1986) for state of the system at depth. The sudden central Crete. A significantly higher heat uplift can be taken as a first order signal of flow is recorded for the Sea of Crete, a tectonic reorganization, that is possibly where a temperature of ca. 500°C at 10 not clearly reflected by the present crustal km depth is indicated by the shallow structure due to predominance of not yet position of the Curie isotherm (Tselentis, fully overprinted earlier structures. The 1991), fully consistent with crustal thinning structural and sedimentary record of the well into the recent geological past, and past ca. 5 million years, covering the time possibly induced by convection in the span of this tectonic reorganization, is a mantle wedge. Reliable heat flow data for fundamental aspect to be deciphered in the forearc south of Crete are not available.

Tectonic evolution within the past 35 million years active continental margin, at that time The short overview of the tectonic history positioned several hundreds of kilometers is subdivided into time slabs, arranged to the north of present Crete (Le Pichon from past to present. The inferred history and Angelier, 1979; 1981). Remnants of of the subduction zone is displayed in Fig. the overriding European plate at this 3, a simplified and complemented version active margin are preserved in the of the model proposed by Thomson et al. „Uppermost Unit“ on Crete, with a (1999). This figure visualizes the relative prolongued history of convergence motion between the African and the (subduction and collision) recorded since Eurasian plate and the accelerated the Jurassic (e.g. Bonneau, 1982, subduction due to roll back and forearc Papanikolaou, 1992, 1996). Deposition of extension (Le Pichon and Angelier, 1979; clastic sediments, referred to as „flysch“, 1981), the effects of the collision of the prograded to the south on the crust of the microcontinent during Oligocene/Miocene subducted plate. times and the subsequent extensional

Situation at 30 to 20 Ma „buoyant escape“ model for this continental crust, as inferred from low- The microcontinent collided with the active temperature thermochronometric results continental margin. Sediments deposited (Thomson et al., 1998a, 1998b, 1999). on oceanic or transitional crust (Pindos Unit) were offscraped and underthrust by the sedimentary cover of the incoming Situation at > 35 Ma microcontinent (Tripolitza Unit). The bulk A microcontinent embedded in oceanic of the microcontinent including the lower crust of the African plate approaches the stratigraphic units of its sedimentary cover (now Phyllite Quartzite Unit) and a pressure - low temperature (HP-LT) carbonate platform originally covering the metamorphic overprint (Seidel et al., 1982; rear part (now Plattenkalk Unit) have been Jolivet et al., 1996; Thomson et al., 1998; subducted, as revealed by their high 1999; Stöckhert et al., 1999).

Fig. 3: Inferred tectonic history for the southern border of the Aegean since about 35 Ma, modified and complemented after Thomson et al. (1999).

subducted microcontinent is driven by Situation at 20 to 15 Ma buoyancy into the space created by The subducted and now HP-LT continued rollback of the subduction zone metamorphic microcontinent became (Fig. 3). A somewhat different model had rapidly exhumed by extension been proposed by Jolivet et al. (1996). concentrated in a low angle detachment Based on Thomson et al. (1998, 1999), fault, without significant erosion of the the microcontinent is suspected to „upper plate“ to the detachment and constitute the southern part of the present without significant internal deformation of forearc including the continental crust at the „lower plate“ before these rocks the backstop, with remnants of the pre- cooled to below 300°C and represented Miocene continental margin, including upper crust (Thomson et al., 1998; 1999; nappes formed by shallow accretion of Stöckhert et al., 1999). This rapid process sediments, forming a thin veneer on top of is attributed to roll back and a model the extensional detachment (Fig. 3, see termed „oblique buoyant escape“ has also Fig. 6). A short period of accelerated been proposed (Thomson et al., 1998; uplift and erosion occurred between ca. 17 1999). This model suggests that, after and 14 Ma (Thomson et al., detachment from the downgoing plate, the 1998a, b; 1999), but was insufficient to collision and high pressure metamorphism cause these remnants to become of the microcontinent. completely eroded. Most important, slices To verify, respectively falsify these that had remained at temperatures below predictions and, thus, to test the oblique about 110 °C since the Oligocene are still buoyant escape hypothesis relevant to the preserved (Thomson et al., 1998a and growth of continental crust at retreating unpubl. data). These rocks resided in the subduction zones, is one of the primary uppermost crust during the 25 to 20 Ma goals of drilling (see Fig. 6).

Fig. 4: Extremely simplified scheme for the structural style of the brittle upper crust resulting from crustal extension on Crete, with presumably analogous structures developed offshore. Miocene half graben structures developed at the hanging wall to the extensional detachment, with extensive wedges of scarp breccia, are overprinted by late Tertiary to Quaternary graben structures, bounded by steep normal faults.

4). From ca. 10 Ma, present Crete was Situation at 15 to 5 Ma largely covered by a shallow sea. As recorded by apatite fission track data Continued tectonic activity is reflected by on Crete, the HP-LT metamorphic cover of the stratigraphic record of small scale the microcontinent had reached the basins and swells (Meulenkamp et al. uppermost crust at temperatures < 100°C 1988, Frydas, Bellas, Keupp, in at ca. 15 Ma and was locally exposed to preparation). the surface at 12 Ma at the latest, when it started to become covered by Neogene sediments. Disintegration of the upper Situation at 5 to 0 Ma plate to the extensional detachment had The timing of the onset of intense uplift of resulted in half grabens and huge masses Crete is not well constrained. The uplift of fault scarp breccia exclusively derived accompanied by significant extension in from the unmetamorphic upper units (Fig. the upper crust resulted in the present structural relief of at least 6 to 8 km. The situation, with a thin lid of continental crust horst structure is bound by systems of of the overriding plate thrusted upon normal faults with predominantly E-W and incoming sediments in the N-S orientation (e.g. Armijo et al., 1992), Oligocene/Miocene, is recorded in the and predominantly NE-SW transtensional upper tectonic units on Crete. The structures. The deep-seated causes of the mechanics of these processes are poorly sudden uplift of the Cretan horst (a rather understood. atypical forearc high), and presumably simultaneous formation of the „trench“ system (in an atypical position) are not Fundamental questions related to the understood. The process may be related mechanical state of the retreating to the onset of collision with the Libyan subduction zone margin between 6 and 3 Ma, that caused The ideas on the kinematics of the a slight deceleration in the southward retreating Hellenic subduction over the motion of the central segment of the past 35 million years appear to be Aegean arc represented by Crete (Le straightforward, although many aspects Pichon et al., 1995). Insight into this major await a more detailed analysis and tectonic reorganization requires an verification. The dynamics of the improved resolution of the timing and processes, however, that means the spatial distribution of the tectonic mechanical coupling between the plates, processes for the past 5 million years. the transfer of forces and the resulting stress field that drives extension of the upper plate and recent localized uplift at Summary Crete, remain to be analyzed in much As shown in Fig. 3, the present day more detail. Hellenic forearc has recorded prolongued convergence at a retreating subduction zone, with the island of Crete providing an An improved understanding of these excellent window into the various processes promises an improved structural levels. A microcontinent that had understanding of lithospheric properties in entered the subduction zone in the general, in particular in convergent Oligocene/Miocene has been rapidly settings. exhumed. According to the buoyant Fundamental questions related to both, escape model, this microcontinent is the specific Hellenic setting (as a world expected to form the bulk of the crust in site for retreating subduction zones) and the present forearc, with a thin veneer of the general situation, can be formulated as remnants of the upper plate resting on top. follows: The backstop to the presently active (1) How is the mechanical coupling accretionary wedge of the Mediterranean between the plates? Ridge may be formed by the more or less disintegrated original southern passive (2) Which forces drive the extending margin of the microcontinent, thinned by forearc continental lid to slide onto the radial and tangential extension, and incoming plate? possibly now undergoing contraction due (3) At which level has the thin veneer of to incipient collision with the African upper plate material originally been passive margin. An analogous fossil decoupled? What are the subsequent (5) How is forearc extension partitioned in kinematic pathways and their structural space and time? Over which time span record? and by which process did the Sea of Crete form? When did the trenches form? What can be learnt from the lateral transfer of (4) What are the geometrical pathways of active deformation on the coupling the extensional exhumation of the between the plates? subducted microcontinent? Is the (6) What determines the position of the proposed asymmetric buoyant escape boundary between contractional and process feasible? Can this model serve as extensional deformation – the „backstop“? a general concept for continental growth at retreating subduction zones? (7) What makes Crete actually rise up? When and why did this uplift commence and what is the mechanical significance?

The role of Scientific Drilling activity recorded in the Neogene Scientific drilling provides the access to stratigraphy and structures in space and the third dimension, which is required to time, or present day gradients in stress resolve specific structures and continuous field or heat flow, both related to the stratigraphic records not exposed at the mechanical coupling. Thus goals of surface. For the given physiographic onshore and offshore drilling are either situation, drilling provides the only access identical or complementary. to direct information on crustal properties, stratigraphy and structures offshore, in Thus, drilling serves three principal combination with marine geophysics. Both scientific goals, that are simultaneously are essential to resolve the forearc addressed at appropriate drill sites. evolution in space and time, in (1) Actual physical state of the crust, in combination with the excellent onshore particular stress field at a given depth (not access on Crete. Furthermore, drilling influenced by topography), heat flow (not provides the only means to obtain influenced by surface effects), hydraulic information on fundamental properties like properties and fluid flow. These properties heat flow and state of stress, undisturbed are intimately related to the mechanical by surface effects, that are particularly properties of the plate interface. critical for the given relief and present day tectonic activity. (2) Tectonic evolution in the past ca. 15 Ma, recorded by the Neogene sediments In view of the narrow island of Crete, covering the basement made up of pre- offshore drilling offers the opportunity to collisional (> 25 Ma) rocks, with thick study the crustal record, properties, and sequences in graben and half graben present day physical conditions along an structures developed in the brittle upper extended N-S baseline. Such prolongued crust due to tangential and radial baselines normal to strike are essential for stretching of the forarc. e.g. the test of the asymmetric buoyant escape model, the transfer of tectonic (3) Information on the collisional episode trailing edge less deeply buried, as could of ca. 30 to 20 Ma, in particular on the be expected? Are gradients in maximum nature and present whereabouts of the burial, recorded on Crete in E-W direction, crust of the microcontinent, and test of the also discernible in N-S direction, as could proposed exhumation concepts be expected? Is this due to the geometry (symmetric stretching or oblique buoyant of the Oligocene/Miocene subduction zone escape – pure shear vs. simple shear) or to the subsequent forearc extension, based on gradients in the record of the with Crete exposing a section oblique to high pressure metamorphic lower and original strike? Access to the structural, extremely thinned upper units along an burial and thermal history of the HP-LT extended baseline not accessible on metamorphic "lower plate" to the Crete. extensional detachment along a 100 to 150 km baseline (that can only be For illustration, point (3) comprises the accessed by onshore/offshore drilling in following questions: Is the southernmost suitable positions) would provide important part of the present day upper plates insight into processes of fundamental (Aegean) continental crust made up of significance for continental growth, material derived from the microcontinent? crustal/lithospheric stress field, rheology Is this southernmost edge also affected by and kinematics. HP-LT-metamorphism or was the

Concept for the Drilling Program sites proposed to ODP approximately The concept proposed for the scientific correspond to those labelled 1 and 2 in the drilling program is displayed on a scheme of Fig. 5. schematic cross section in Fig. 5. This figure reflects the preliminary concept The precise locations remain to be defined discussed at the workshop, based on the results of ongoing notwithstanding the fact that an ODP geophysical experiments and presite proposal has meanwhile been prepared by surveys. A. Kopf, A.H.F. Robertson, E.S. Screaton and J. Mascle, with much more detail. The Fig. 5: Cartoon showing the principal features of a combined onshore offshore drilling program dedicated to forearc tectonics at the retreating Hellenic Subduction Zone. The inferred present position of the microcontinent (that had collided in the Oligocene/Miocene) is marked in red.

collision at two sites roughly Offshore: 100 km apart (normal to the Phase 1 (ODP): Structure and tectonic margin) yields invaluable evolution of the forearc to the information on the mechanics south of Crete, with emphasis of a retreating subduction zone on the nature and structural and incipient collision. A later history of the backstop and phase 2 is envisaged to the inner Mediterranean extend the baseline Ridge. A respective ODP- northwards into the Sea of proposal is submitted in Crete, in order to obtain a March 1999. complete record of the The outcome of this ODP partitioning of forearc project is expected to correlate deformation in space and time. perfectly with the proposed Such information is the onshore drilling at Messara. essential input for future Correlation of both the late modeling of forearc dynamics. Neogene sedimentation and Phase 2 (ODP or EDP) as a proposed deformation history and the future complementation: record of the basement with Stretching history and nature of respect to Oligocene/Miocene the pre-Neogene basement in the Plattenkalk Unit, to obtain the Sea of Crete. information on the depth of burial and internal deformation of the basement during Onshore: collision, and finally on the Phase 1 (ICDP): Intermediate depth (3 to provenance of the 4 km) land-based drill hole in microcontinent. the Messara Graben (Fig. 6), to provide insight into The anticipated outcome of the drilling program is:

(a) late Tertiary to Quaternary a) substantial information on the Miocene sedimentary record of N-S to Quaternary extensional (and in extension and uplift of the episodes contractional?) history of the Crete forearc, in particular of the distribution in space and time along a transect. This (b) internal structure, tectonic provides the clue for thermomechanic evolution and thickness of the modelling of coupling between the plates Uppermost Unit, the remnants and accomodation of rollback in the upper of the front of the overriding plate. Furthermore, the tectonic continent at the early to mid- reorganization Tertiary subduction zone (c) the nature of the extensional detachment fault causing the sudden strong uplift of the between the upper and the island of Crete within the last 5 million lower units, and the thermal years requires an explanation. history of the high pressure - b) access to the exhumed microcontinent low temperature metamorphic along a baseline of > 100 km, that cannot rocks beneath the be established on land. The thermal detachment. history of the HP-LT metamorphic rocks beneath the extensional detachment Phase 2 (ICDP or EDP): Moderate depth provides a clue for the test of the oblique (1 to 2 km) land-based drill hole buoyant escape model, that may be (not shown on Fig. 5) at the fundamental to the growth of continental northern coast (?) of Crete to crust at retreating convergent margins. recover the basement of the c) information on the actual state of stress Plattenkalk Unit (continental as a function of depth, on heat flow and crust of the microcontinent). pore fluids, and thus on the mechanics of The most appropriate drilling a retreating subduction zone, which are site remains to be selected poorly understood. In particular the based on presite studies. A drill process of thin Aegean continental crust hole into the basement of the spreading upon the incoming subducting microcontinent, not plate and the nature of the backstop are of unequivocally identified at the central interest. A fossil analogue is surface, allows to test the represented by the Uppermost Tectonic hypothesis of „autochthony“ of Unit exposed on Crete, that formed the < 10 km thick continental lid on top of the at the time of collision with the retreating subduction zone at 30 to 20 Ma, microcontinent.

Fig. 6: Cross section (no vertical exaggeration) through the Messara basin, modified after Le Pichon & Angelier (1979), with approximate position of the extensional detachment between HP-LT metamorphic units and the unmetamorphic upper nappes included. Note that a more realistic structure of the upper units is represented by the scheme in Fig. 4, which implies highly variable thickness and casual omission of units.

Current research related to the drilling program the proposed transect (Hamburg); passive Current research activities directly related seismics using local arrays, designed to to the land-based drilling proposal include: obtain a high resolution image of Evaluation of existing data base, shallow seismicity and of seismic velocities as a drill holes and general coordination function of depth, in particular crustal low (Athens); combined onshore/offshore velocity channels and the slab position seismic program, designed to obtain a (Bochum, Chania), gravity (Hamburg, drastically improved image of crustal Bochum), stratigraphy and structural thickness and structure along and across record of Neogene deposits exposed on cover of the microcontinent and the Crete (Patras, Berlin, Iraklion), extensional detachment (Iraklion, Yale, geomorphology related to Quaternary and Frankfurt, Karlsruhe, Cologne, Bochum), active tectonics (Bayreuth), Plio- basement and autochthonous cover of the Quaternary clastic aprons (Minneapolis), microcontinent (Athens, Berlin, Stuttgart, low-temperature thermochronometry Cologne), pre-Neogene tectonic history of (Bochum), tectonic history of the high the upper nappes (Iraklion, Bochum). pressure – low temperature sedimentary

Concluding Remarks fundamental questions of forearc tectonics The Hellenic subduction zone represents can be addressed by shallow to a world site for retreating convergent intermediate drilling on Crete, but margins, with accretion of a continental essential information on the various fragment in the recent geological past, and forearc zones across strike and respective incipient collision with the passive African gradients can only be obtained by offshore margin in the central sector today. Within drilling. It is expected that a combination of the forearc, the island of Crete is a horst present ICDP and ODP approaches with a structural relief of a least 7 km significantly contributes to an improved developed within the last few million years data base for the understanding of the and provides a nearly continuous record of tectonics and mechanics of a retreating forearc evolution in the past 35 million subduction zones, with prospective mutual years, with additional information since the interaction. Mesozoic. Owing to the structural relief

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TERRANE TECTONICS IN THE AEGEAN REGION

D.I.Papanikolaou Department of Geology, University of Athens, Greece.

The tectonic units of the Hellenides can be including clastics and pelagic limestones grouped in nine domains, each one of Ammonitico Rosso facies, have been representing a distinct tectonostratigraphic deposited. The shallow-water carbonate terrane. Four terranes (Pindos-Cyclades, platform sedimentation covered the Vardar-Axios, Circum Rhodope and Volvi- previous syn-rift formations throughout East Rhodope) are of oceanic origin, Mesozoic-Early Tertiary. Flysch representing distinct basins of the Tethys sedimentation and subsequent orogenic ocean and five terranes (External events followed the arrival of each terrane Hellenides Platform, Internal Hellenides at the trenches and island arcs developed Platform, Paikon Block, Rhodope Massif successively at the front of the active and Vertiskos Massif) represent pre-alpine European margin during late Jurassic- continental crustal fragments with shallow- early Tertiary. water carbonate platform developed during their Mesozoic and Early Tertiary The overall alpine development of the paleogeographic evolution within the Aegean lithosphere is the result of a Tethys Ocean. continuous convergence process comprising (i) subduction of the Tethyan The rifting of the continental terranes oceanic basins and (ii) microcollision occurred along the northern passive events between the Eurasian plate and Gondwanian margin during Late the continental terranes. Paleozoic-Middle Triassic, when characteristic volcanosedimentary facies, CRETE - A WORLD SITE FOR RETREATING SUBDUCTION ZONES, PAST AND PRESENT

Bernhard Stöckhert Institut für Geologie, Ruhr-Universität, D-44780 Bochum

Crete represents a forearc high at the (Brix et al., in preparation) found for the retreating Hellenic subduction zone, about UM are between 65 and ca. 160 Ma, being 150 km to the south of the magmatic arc generally closely correlated with the age of and 100 km to the north of the inferred metamorphism of the different slices. In back stop of the active accretionary the flysch deposits the zircon FT age wedge. The tectonic record of Crete is signatures are imported from the source governed by collision of a microcontinent area. Current estimates on the closure with the active continental margin of a temperature for fission tracks in zircon are precursor of the present day subduction between about 250 and 300 °C. Thus, the zone in the Oligocene/Miocene. There are remnants of the overriding plate have two peculiar features: invariably resided in the upper crust at less than ca. 10 to 15 km depth since the (1) Rapid burial and subsequent earliest Tertiary. This finding indicates that extensional exhumation of the high the continental crust of the upper plate in pressure - low temperature the forearc of the Tertiary subduction zone metamorphic rocks representing the was very thin. The UM is considered as an sedimentary cover of the extensional melange that once formed a microcontinent. thin veneer sliding onto sedimentary cover (2) Preservation of remnants of the frontal (Pindos unit) of the incoming lower plate. part of the overriding plate. These It is proposed that both, the rapid remnants form a chaotic mixture of exhumation of the microcontinent as crustal slices with contrasting pre- described by Thomson et al. (1998a,b) Tertiary histories and are referred to as and the extreme thinning of the frontal part “uppermost tectonic unit” (UM) on of the upper plate are related to the long- Crete. term roll back of the subduction zone. The mechanics of the underlying processes The UM consists of a chaotic mixture of are poorly constrained, however, and slices of pre-Tertiary metamorphic rocks, remain to be explored in detail. ophiolites, and flysch deposits. Apatite Remarkably, the crustal structure in the fission track (FT) ages of ca. 30 Ma found forearc of the present day subduction for parts of the UM contrast with the 25 to zone appears to feature analogue 20 Ma age of HP-LT metamorphism and characteristics, with thinned continental show that the contribution of erosion to crust derived from the upper plate exhumation of the HP-LT metamorphic extending far to the south of Crete. Thus, rocks was insignificant. To explain the the forearc high of Crete provides insight rapid exhumation without significant into tectonic processes that may be similar erosion, Thomson et al. (1998a,b) have to those active today in the Hellenic proposed a model termed “buoyant subduction zone, and probably active in escape”. The zircon fission track ages many places worldwide throughout the geological history. This renders Crete a Thomson S.N., Stöckhert, B. and Brix, true “world site”. M.R. (1998) - In: Exhumation processes, edited by Brandon, Lister, Ring and References: Willett. Geol. Soc. London Spec. Publ. (in Thomson S.N., Stöckhert, B. and Brix, press) M.R. (1998) - Geology 26:

ACCRETION AND EXHUMATION AT A STEADY-STATE WEDGE: A NEW ANALYTICAL MODEL WITH COMPARISONS TO GEOLOGIC EXAMPLES

Brandon, M. T., Dept. of Geology & Geophysics, Yale University, New Haven, CT 06520; Fletcher, R. C., Dept. of Geological Sciences, University of Colorado, Boulder, CO 80309- 0399

A circulating cell model illustrates how orogenic events. Surficial erosion and accretion and erosion control deformation extensional flow act together to account and exhumation within a steady-state for the return flow in the upper wedge. contractional wedge. The model wedge is High erosion rates will reduce or remove composed of a homogeneous viscous fluid the extensional field. subjected to a horizontal velocity and vertical flux at its base representing basal slip and accretion, internal body forces We consider two examples of exhumed due to gravity, and an outward erosional accretionary wedges: the Cenozoic flux at its surface. The Abackstop@ is a Olympic subduction complex of the vertical boundary where horizontal velocity Cascadia margin and the Mesozoic is everywhere zero. The model is Torlesse accretionary wedge of southern described by 3 dimensionless numbers: New Zealand. In both settings, within- Rm, the ratio of tectonic to gravitational wedge strain was dominated by the stresses; Vr, the ratio of the underplating pressure-solution mechanism to depths of flux to convergence velocity; and Sigma, 20 km or more, which justifies our use of a the ratio of erosional flux to return flow by linear viscous rheology. Exhumed rocks in gravitational collapse. The model the Olympic Mountains show only illustrates the importance of return flow in horizontal contraction which is consistent the upper part of the wedge, a with other evidence indicating that phenomenon first noted by Cowan and exhumation occurred entirely by erosion at Silling (1978) and Platt (1986). Horizontal rates of ~1 km/m.y. Exhumed rocks of the strain rates within the model wedge are Otago culmination in the Torlesse wedge divided into a lower contractional field and record extensive horizontal extension and an upper extensional field. Material relatively slow exhumation rates (0.25 exhumed at the wedge surface will show a km/m.y.) which we interpret as evidence finite strain history that reflects flow of the that exhumation was dominated by ductile material through the two fields. Thus, a stretching. strain-rate history of early contraction and later extension need not imply separate CRUSTAL THICKNESS AND TECTONICS DEFORMATION OF THE HELLENIDES

J. Makris and F. Egloff University of Hamburg, Germany

During the last four years, on/offshore by much thinner sediments and of very seismic experiments using large numbers variable values depending on the of ocean bottom seismograhs and stand development of local basins due to alone seismic stations have been used to transtensional processes. So for example define crustal structure and thickness in the Cretan Sea south of Santorini has a different areas of the Hellenides. These sedimentary cover of 3 km whereas the projects were accomplished in cooperation Sporades Basin in the north Aegean Sea with several Greek research has sediments exceeding 6-8 km organizations, in particular the National thickness. The crust in general varies from Centre for Marine Research, Hellinikon, 18 to 24 km thickness and shows rapid and the Institute of Geodynamics, changes within very short distances Observatory of Athens. They contributed indicating that wrench faulting and significantly by logistic support and shearing have significantly affected the personnel in accomplishing the various evolution of the different parts of the projects. The results obtained summarised Aegean Basin by creating transtensional as follows revealed: structures.

The continent ocean transition offshore 2D and 3D gravity modeling constrained western Greece is located approximately by the seismic profiles defined the density at 60-80 km west of the Ionian Islands. To distribution of the crust and upper mantle the south, this transition was identified at below the Hellenides. This permitted us to about 100 km south of Crete. The crustal define the geometry of the main thickness indicates significant stretching of sedimentary basins, the crustal thickness a continental margin with values ranging (MOHO discontinuity) and lateral density between 24 to 18 km thickness of a crust changes in the upper mantle. The density covered by more than 6 km of sediments. models require significant lateral changes in density between the Hellenic arc and The Ionian oceanic crust bordering the the Aegean area due to the subduction of stretched continental margin of the oceanic lithosphere below the Aegean Hellenides to the west is only 6-7 km thick Sea, which subsequently mobilised high and in addition covered by 6-8 km of temperature magmas below the active sediments depending of the location. The volcanic arc in the Aegean Sea. The crust thickens below the Hellenides results will be discussed in conjunction significantly to values of more than 34 km with the tectonic elements mapped by at the Gulf of Patras and about 40 km geological and seismic studies. below the western Hellenides. The Aegean crust on the contrary is covered CRUSTAL STRUCTURE OF THE HELLENIC SUBDUCTION ZONE AROUND CRETE BASED ON GRAVITY MODELING

U. Casten, Ruhr-University of Bochum, Germany J. Makris, University of Hamburg, Germany

Within the frame of the "International structures. Density values have been Continental Drilling Project (ICDP)" one determined by using the velocity/density proposal is a deep drilling on the island of relation from Ludwig, Nafe and Drake. Crete with the task to study the Hellenic subduction zone. Several concepts of the One density model, including the local subduction model have been presented, anomalies of Crete, is representing the which are contradicting, mainly, because crustal structure along a 225 km long of sparse structural information. To section from the South to the North overcome this a new gravity map is under crossing Crete in its western part. The development. The interpretation will result model shows a crust of normal continental in a structural model of the Hellenic type below Crete (moho depth of 30 km) subduction zone around Crete and finally and thinned out continental type below the will help to reduce the number of Cretan Sea (moho depth of 23 km). To the subduction models. South, the structure is dominated by the subducting crust of oceanic type. The local About 2000 new gravity observations were anomalies of Crete are caused by isolated made in Crete during the past two years. source bodies of higher density (3 g/cm3 Data processing is still going on. and more) within the sedimentary cover Additionally, already existing data from the (2.35 g/cm3). Hellenic arc region were collected. The regional gravity field is dominated by long A second model of the crustal structure is wave anomalies reflecting the arched 500 km long and crosses Crete in its structure of the deeper crust of the western part, too, but runs perpendicular subduction zone. North of Crete, in the to the strike of the Hellenic Trough. This area of the Cretan Sea, the Bouguer model shows the regional structure of the anomalies are reaching 160 mGal and collisional zone between the European towards the African continent partly more and the African crust with subducting than 200 mGal. Crete with its local short oceanic layers in its centre. The European wave anomalies is situated within a gravity crust again is of continental type. The low of about 40 mGal. The local anomalies oceanic layers 1 and 2 are covered by are caused by shallow structures. sediments with a total thickness of more than 10 km. The depth to the inclined Interpretation of the Bouguer anomalies is Moho is more than 20 km. The model done by forward modeling with regard to contains a "backstop" at the outermost constraining structural data basically from front of the European crust. In both passive and active seismic experiments. models the mantle density beneath the These and other relevant data will be European crust has a lower value than presented. The geometrical parameters beneath the African one. In order to for gravity modeling are based on seismic demonstrate, that the second model is not the only possible one, a structural variation considers a low velocity layer It has to be pointed out, that the presented beneath Crete in a depth between 10 to results of gravity modeling are the first 15 km as found by passive seismic step of interpretation. The studies have to experiments. This layer can be explained be continued to get three dimensional by sedimentary material of oceanic origin, models. Further constraining data will help which has been pushed under Crete to limit model variations. during collisional processes.

SEISMICITY IN THE ACCRETIONARY COMPLEX OF THE HELLENIC SUBDUCTION ZONE AROUND WESTERN CRETE

H.-P. Harjes, Institute of Geophysics, Ruhr-University Bochum, Germany A. Vafidis, Dept. of Mineral Resources Eng., Technical Univ. of Crete, Chania

The Hellenic arc is the most tectonically and seismicity coincides well with the axis of the seismically active region in western Eurasia Hellenic trench marking the backstop in the due to the subduction of the African plate accretionary uedge. Under Crete the beneath the Aegean area. There, the island of distribution of hypocenters suggests a Crete is a structural high on the frontal part of rheological stratification with shallow seismicity the upper plate and simultaneously on top of which indicates a deformation of Crete the shallow portion of the presently active decoupled from the subducting slab. subduction zone. In this outstanding tectonic situation, the active processes and the physical The lower limit of hypocenters around 40 km state of the crust, particularly in terms of the suggests the downdip edge of the seismogenic stress field and kinematics change with depth. zone in accordance with data from other This makes Crete a favorable target for subduction zones. A joint inversion algorithm seismotectonic studies. yields a velocity-depth profile with a low- velocity region somewhere between 10 km and Our seismic data have been recorded during 20 km. two three-months field experiments carried out on western Crete in 1996 and 1997. In 1996 The deeper structure of the subducting slab the seismic network consisted of 6 four- was investigated using single station data element miniarrays (24 digital station) with an (receiver function) and array methods overall aperture of 30 km whereas in 1997 a (mislocation vector). These results indicate a conventional network of 47 three-components 20 degree slope of the African plate in NNE digital stations with an aperture of 60 km and direction below Crete where the top of the average station spacings of 5 km was installed. subducting slab dips from about 40 km below We located more than 1000 earthquakes within southern Crete to about 55 km below northern a radius of 150 km around western Crete. Most Crete. of these events were located offshore west and south of Crete. The southern border of the ON THE HELLENIC TRENCH SUBDUCTION ZONE: EARTHQUAKE SOURCE MECHANISMS IN THE HELLENIC TRENCH NEAR CRETE

T. Taymaz (1) Istanbul Technical University (ITU), Faculty of Mines, Department of Geophysics, Seismology Section, Maslak 80626-Istanbul, Turkey,e-mail: [email protected] (2) GeoForschungsZentrum(GFZ)-Potsdam, Telegrafenberg, 14473 Potsdam, Germany e-mail: [email protected]

In the Hellenic Trench south of Crete sediments of the Mediterranean Sea convergence between the southern underplate and uplift Crete. These events Aegean Sea and Africa occurs at a rate of have slip vectors in the direction 025 +/- at least 60 mm/yr. Previously published 12 degree which represents first motion fault plane solutions show a theconvergence direction between Crete variety of different fault orientations and and Africa along the SW-facing boundary types, but are not well constrained. of the Hellenic Trench.

Furthermore, the lack of reliable focal One of the events (August 17, 1982; depths for these earthquakes has Ms=6.6) in group (d) occurred beneath obscured any simple pattern of the Mediterranean Ridge and involved deformation that might exist. Nonetheless, high-angle reverse faulting with a WNW- the mechanisms of these earthquakes ESE P axis: almost perpendicular to the have strongly influenced views of the direction of shortening deduced from folds tectonics in the Hellenic Trench. at the surface. The Mediterranean Sea flor in this region appears to be in a state of E-W The improved estimates of the fault compression, for reasons that are not parametres and focal depths of clear. earthquakes fall into four groups: Furthermore, the existence of volcanoes, (a) normal faults with a N-S strike in the heat flow observations, an assumption of over-riding material above the subduction relatively low seismic-wave velocities and zone; variations in average S-P-wave travel-time (b) low-angle thrusts with an E-W strike at residuals provide evidence of lateral a depth of about 40 km; variations in structure beneath the Aegean (c) high-angle reverse faults with the same and Hellenic Trench near Crete. Residuals strike but shallower focal depths than (b): reflect systematic lateral variations that do (d) events within the subducting not correlate well with elevation or with lithosphere with approximately E-W P simple aspect of regional geology. axes.

The thrusting in groups (b) and (c) is probably the mechanism by which the MANTLE-DERIVED NOBLE GACES IN THE SOUTH AEGEAN VOLCANIC ARC: INDICATORS FOR INCIPIENT MAGMATIC ACTIVITY AND DEEP CRUSTAL MOVEMENTS

V.J. Dietrich, R. Kipfer and F. Schwandner Dept. of Earth Sciences, ETH Zurich, Switzerland

The islands of Nisyros, Yali, Kos, changes of major tectonic processes (e.g. Santorini, Milos, Poros, Methana and rapid extensional movements or crustal Aegina constitute the South Aegean displacements). volcanic island arc, which is a result of northward-directed subduction of the Results African plate beneath the Aegean microplate. Thirteen selected water samples from Milos and Methana and fumarolic The islands of Nisyros, Santorini, Milos condensates from Nisyros have been and Methana are considered today the analysed for their isotopic abundances most active areas in terms of a potential and ratios of helium, neon, argon, krypton volcanic reactivation. Therefore, these and xenon. The observed 3He/4He and islands were chosen for a detailed noble 4He/Ne ratios range from 1.419 x 10-6 to gas investigation. 7.5 x 10-6 and from 0.274 to 12.634, respectively. The Nisyros condensates fit Helium, as well as the other noble gases into the array of the Japanese island arc are dissolved mainly in CO2-rich waters samples which mark a mixing line 3 4 and CO2 gases and are accompanied by between atmospheric He/ He ratio of 1.4 -6 CH4 and H2 emanations. Helium shows x 10 and mantle derived helium with a distinct isotopic signatures in the main maximum ratio of approx. 10 x 10-6. This global reservoirs; the atmosphere also applies for some waters from Milos 3 4 -6 3 4 ( He/ He ≈[ ), the Earth’s crust with much lower He/ He ratios. These 3 4 -7 -8 ( He/ He ≈ - 10 ) and the Earth’s latter ratios as well as those from the 3 4 -5 mantle ( He/ He ≈ [ ). The Methana thermal springs represent a combination of noble gas ratios 3He/4He, mixing with radiogenic 4He due to crustal 20Ne/22Ne and 40Ar/36Ar compared to contamination during ascent of primordial stable isotope ratios of C and O will allow 3He through the crust. These results an appropriate discussion on the primary suggest that for the island of Nisyros, origin of the noble gases, the amount of mantle-derived helium may be related to atmospheric, meteoric and hydrothermal degassing of magmas, probably located at contamination, as well as the great crustal depth close to the determination of equilibrium temperatures mantle/crust boundary. in the hydrothermal systems. It is expected, that the noble gases are more The research is part of an interdisciplinary sensitive and precise as indicators of project on natural hazard - vulnerability - changes of the magmatic regime (e.g. risk assessment of Greek high-risk replenishment of new melts into magma volcanoes and earthquake activity reservoirs or emplacement of magmas between the National Centre for Marine from deep crustal levels to the surface) or Research (D. Papanikolaou, Director), the Institute of Geophysics, Hamburg, Department of Earth Sciences, Zurich, Germany (J. Makris, Director) and Switzerland.

THE NAPPE PILE OF CRETE

M. Bonneau Dept. Geotectonique, Université P. et M. Curie, Paris, FRANCE

Crete is comprised of two main groups : resticted bands where it is related to later (Oligo-miocene) extension. 1-1. Neogene to present sediments with very implicated stratigraphic and 2-4. The lower most unit (Plattenkalk or sedimentologic features, due to the fact Ida unit), mainly composed of that they are syntectonic. They rest metacarbonates, is an equivalent to the uncorformably on. ionian zone of mainland Greece. Its metamorphism (not very well known) is 1-2. Alpine nappes piled upper one similar to that of the phyllite-quartzite another before Lower miocene times. To nappe. This unit constitutes 70% of the be short, they comprise, from top to outcrops of pre neogene Crete and all the bottom. highest mountains in Crete (2500 m) are made of it. 2-1. Ophiolitic bearing nappes displaying the charachteristics of the eo hellenic (upper Jurassic) obduction. They are The tectonic emplacement of 2-1, 2-2 and associated with huge slices of HP-HT 2-3 are most probably related to an old crystalline rocks yeilding 75 Ma subduction zone that also produced the radiometric ages. HP-LT metamorphism of the Cycladic belt (45 Ma). 2-2. Not or very weackly metamorphic rocks related to the classical Pindos and Metamorphism in the lower most unit Tripolitza sequences of mainland Greece, could be related to the newly formed and an additional one the Arvi nappe, subduction zone associated with the made of mainly of tholeïtic basalts of retreating Hellenic subduction zone. uppermost Cretaceous age. The uplift of the hole nappe pile on top of 2-3. The Phyllite-quartzite nappe, made of the lower most unit could be due to the siliciclastic rocks and slices of engulfing of a pice of continental «Hercynian» basement. The ages of the lithosphere belonging to the Paxos (Pre sediments range in age (biostratigraphy) apulian) zone into the Hellenic subduction from middle (?) Permian to middle (?) zone. Triasic. The whole nappe has suffured HP-LT (8-10 Kbar - 400° C). The This could be tested by drilling near the deformation is not strong, appart from base of the lower most unit (in the Talea Ori Mountains). But the disadvantage is the location in the northernmost part of depth) could decide if it is feasible. Crete. Only geophysical data (moho

REMNANTS OF PRE-ALPIDIC CRYSTALLINE BASEMENT IN THE LOWER- MOST TECTONIC UNITS OF CRETE

E. Seidel Mineralogisch-Petrologisches Institut, 50674 Koln, Germany

The structure of Crete is characterized by northeast of Crete. There, K-Ar dating on a pile of nappes consisting of rock units hornblendes and muscovites yielded from different paleogeographic zones. The model ages mainly between 320 and 230 sedimentary record within the different Ma. The crystalline basement is covered units goes back to the Permo-Triassic. For by siliciclastic sediments of Permo- most of the units it is assumed that there Triassic age. was an underlaying continental crystalline basement during the deposition of the Mudrocks, sandstones and conglomerates Permo-Triassic sedimentary sequences, of Early Permian age occur at the base of but direct observations of the the Plattenkalk Unit which has the basement/cover relationships are scarce. lowermost tectonic position in the Cretan nappe edifice. They contain detrital grains Remnants of pre-Alpidic crystalline of muscovite, paragonite, biotite, and basement were first recognized in eastern plagioclase as well as pebbles of mica Crete. There, slices of crystalline rocks schists and very low-grade metamorphic (amphibolites, gneisses, micaschists) are rocks. Locally the siliciclastic rocks are intermingled with the Permo-Triassic associated with phyllites. K-Ar and Ar-Ar volcano-sedimentary sequence of the dating on muscovites from those phyllites allochthonous Phyllite-Quartzite Unit. gave greatly differing model ages between Fragments of the crystalline rocks in 300 and 80 Ma. If the phyllites represent Scythian sediments testify to a pre- pre-Alpidic basement rocks of the Triassic age of metamorphism. K-Ar Plattenkalk Unit the dates have to be dating on hornblendes and muscovites explained by a partial reset of the K-Ar yielded model ages between 315and 205 systems by the Alpidic metamorphism. Ma. The cluster of dates around 300 Ma This interpretation is supported by the K- and the few younger dates fit well with the Ar dating on different sieve fractions of concept of a Hercynian basement only muscovite clasts from a sandstone. The weakly affected by the Alpidic very low- coarse sieve fraction (500-315 µm) grade high P/T metamorphism. yielded a model age of 305 Ma, the finer fractions gave 296 and 288 Ma, Crystalline rocks closely resembling the respectively. The dates indicate the Hercynian metamorphites within the exposure of Hercynian basement in the Phyllite-Quartzite Unit of eastern Crete are source region of the siliciclastic rocks at known from the islands of Kalymnos, the base of the Plattenkalk Unit. Leros and Lipsi in the Dodecanese far So far, there is no clue about the basement in the external zones of the existence of pre-Hercynian crystalline Hellenides.

ANALYSIS OF MESOSCOPIC ELEMENTS AND MICROSTRUCTURAL FABRICS IN TECTONITES OF THE PLATTENKALK GROUP, WESTERN CRETE

Jacobshagen, V. & Manutsoglu, E. FR Allgemeine Geologie, Freie Universität Berlin, Malteserstr. 74-100, D-12249 Berlin, Germany, email: [email protected]

The metamorphic Plattenkalk Group grains of < 3 µm. Measurements of the represents the lowermost tectonic unit crystallinity index reveal enormous beneath the nappe pile of Crete. In differences in the recrystallisation western Crete the Plattenkalk Group forms processes of quartz grains. They an E-NE/W-SW striking, northeasterly developed during a prograde dynamic, dipping anticline. Its formation is reflected very low grade metamorphism. Quartz-c- by a great number of mesoscopic axis data from the coarse grained structures. Field observations (e.g. the crystallisate indicate either random distribution of deformational markers) distribution or small circles around X, indicate that the lithological sequence was indicating axial symmetric elongation or differentiated into low- and high-strain plane strain. The gross opening angle of domains. Low-strain domains do not show the circles indicate that deformation and evidence of shortening, whereas high- dynamic recrystallisation of chert took strain domains show two types of places at shallow structural levels, close to southerly dipping ductile shear zones: (a) the ductile-brittle transition. Further hints shear zones with a simple-shear geometry for this are a) undeformed, radial growth of along thrust sheets boundaries and (b), calcite and/or dolomite crystals in the shear zones showing pure shear within former canals of the porifera, b) the thrust sheets. The high-strain zones pseudomorphs of micro- and mega-quartz do not show evidence of multiphase after lepispheres in poriferal remains and ductile deformation. Some of the flat-lying c) brittle deformed quartzitic layers within shear zones with a top-to-the-north sense ductile calcitic mylonit zones. of shear show a continuation into nearly vertical limbs of chevron-folds. Calcitic tectonites developed as deformed calcitic marbles and calcitic mylonites. The dominant rocks are calcitic marbles Calcitic marbles are coarse grained and and meta-cherts. Therefore the main do not show dynamic recrystallisation. The lithologies were in both deformed domains calcitic mylonites form discrete layers analysed in order to compare the which can be recognized from the abrupt microscopic tectonic fabric. Two groups of decreas in grainsize of calcite. In both meta-cherts exist with respect to the cases deformational twinning can be grainsize 1) dynamically recrystallized observed. Curved thick twins and twins in quartz-grains >50 µm , and 2) twins occur, however, only in intensively cryptocrystalline to fine grained quartz- deformed marbles. In calcitic tectonites with a considerable stretching factor with the shearing plane parallel to the structural elements of dynamic thrust plane. Accumulation of deformation recrystallisation did not develop. markers (e.g. globular porifera) show considerable gradients in strain increasing It is concluded that during the deformation from the lower to the upper parts of the not only simple shear processes were sequence. Furthermore we conclude that active but also coaxial non-rotational the processes of deformation of the deformation. Strain is accumulated by a Plattenkalk Group in western Crete have combination of pure shear with stretching occurred authochthonously. parallel to the thrust plane and axial symmetric elongation, and simple shear

SEQUENCE STRATIGRAPHIC ANALYSIS AND BIOSTRATIGRAPHY OF NW CRETE ISLAND (GREECE): THE NEOGENE KASTELLI KISSAMOU BASIN AS A CASE STUDY

S. M. Bellas1, H. Keupp1 & D. Frydas2

1. Institute of Palaeontology, Free University of Berlin, Malteserstr. 74-100, D-12249 Berlin, Germany, email : [email protected] 2. Department of Geology, Patras University, GR-26110, Rion/Patras, Greece

The Kastelli Basin is located at the Chania and sequence architecture of the Province, NW Crete island. The basin’s lithofacies point to different intensities of infill is mainly represented by two marine the relative subsidence rates (tectonic vs. lithofacies (Facies-Type A and B after Sea Level fluctuations) during the basin’s FRYDAS & KEUPP, 1996) and a Transitional development. one. Several subordinate but significant sublithofacies, including deposits of both Detailed study of more than twenty marine and terrestrial palaeoenvironments outcrops has shown that variably thick were documented as well (BELLAS et al., Breccia (e.g. Topolia-Facies) and 1998a). The older studied strata were Conglomerates (e.g. Lower Delta-Facies) deposited during the Tortonian, while the were widely deposited at the start of rift younger marine sediments have been deformation and during the pre-existing dated as Early Pleistocene by use of LST, on the SB1 unconformity surface of combined nannofossils and foraminifera the pre-neogene substrata (upper Middle biostratigraphy (FRYDAS & KEUPP 1996; to lower Late Miocene). Thick marine BELLAS et al., 1998b). The basin type is an facies (primarily of the marginal type A asymmetric one, bordered by the and type B) represent palaeoenvironments unconformably underlying pre-neogene of the TST in the Tortonian. At the strata to the west, while normal faults Tortonian/ Messinian an intense dominate the east and south margins. karstification at the south and eastern Orientation of the faults generally follows margins of the basin is evidenced by that of the South Aegean Arc System. cavities with reddish laminated infilling Variation of the depositional thicknesses cutting pre-existing red-algae and/or coral- reefal facies (SB2). At the deeper central BELLAS, S., KEUPP, H. & FRYDAS, D. basin, the SB2 is simultaneously marked (1998a): The first Neogene (Upper through the Megabalanus bioevent and its Miocene) marine Transgressional- related facies. The deeper part was never Regressional cycle of NW. Crete. subaerially exposed. The second SB Evidence based on sedimentologic and surface is followed by a SMST biostratigraphic data.- 15th Intern. depositional system in Early Messinian. At Sedimentol. Assoc. Conf. (IAS98), first, subsidence rates relatively increase Alicante/Spain (13.-17.04.1998), pp. (marine Type B and Transitional Facies) 182-183. but afterwards decrease at the BELLAS, S., KEUPP, H. & FRYDAS, D. Early/Middle Messinian when Reefal- (1998b): Nannofossil biostratigraphy of Bioclastic subfacies occurred adjacent to Late Miocene marine sedimentary the margins, while at the deep-water basin sequences from NW Crete island, (to the NE) evaporitic sequences were Greece.- Reg. Comm. Mediter. developed (“Messinian Salinity Crisis”). In Neogene Stratigr. (RCMNS), Interim- the Pliocene, the basin was emerged and Colloquium, “Mediterranean Neogene therefore a third SB is postulated, above Cyclostratigraphy in marine-continental which a new TS was locally developed palaeoenvironments”, Patras/Greece during the Early Pleistocene. Last (27.-29.05.1998), p. 8. renewing uplift produced widely FRYDAS, D. & KEUPP, H. (1996): distribution of alluvial fans (Upper Red Biostratigraphical results in Neogene Conglomerates). deposits of NW Crete, Greece, based on calcareous nannofossils.- Berliner Selected literature geowiss. Abh. (Misc. Palaeontol. 5), E 18: 169-189; Berlin.

THE ISLAND OF CRETE ON AND OFFSHORE SEISMIC EXPERIMENT: FIRST RESULTS AND TECTONIC IMPLICATIONS

J. Makris1, M. Bohnhoff1, P. Harjes2, D. Papanikolaou3, G. Stavrakakis4 1 University of Hamburg, Germany 2 Ruhr University of Bochum, Germany 3 National Centre for Marine Research, Athens, Greece 4 National Observatory of Athens, Institute of Geodynamics

In Autumn 1997, an on and offshore Onshore seismic energy was generated seismic experiment was performed along by 20 kg shots fired in 30 m deep and across the island of Crete, the Cretan boreholes. Sea and the northern part of the Libyan Sea south of Crete. Ocean bottom The evaluation of the data was performed seismographs and stand alone seismic by inversion and 2-point ray tracing stations recorded seismic energy forwards modelling of the observed generated by a 48 litre airgun array, shots traveltime sections. The main results in being distributed at 120 m spacing. summary are as follows: controlled by shear zones that affect the Between Santorini and the Libyan Sea, island of Crete as well as the offshore the crustal variation is laterally areas to the south and to the east of the inhomogenous. Below the Cretan Sea, the island. The crustal transition below the stretched continental crust is Mediterranean Ridge is marked by a approximately 18 km thick, thickening dramatic increase of the sedimentary rapidly below Crete to about 30-32 km. In thickness with the sediments exceeding the Cretan Sea, the sediments do not 10 km. exceed 3.000 m in thickness and are mainly composed by Messinian From the velocity values (Pn) at the sequences. The high velocity Plattenkalk crustal mantle boundary, there are strong was not identified here. Onshore Crete the indications that to the south and the west Plattenkalk was clearly seen to compose of the Aegean Sea, Pn values are normal part of the Hellenic Nappes and was and range at about 8.0 km/s, while below traced south of Crete and within the the Cretan and the southern Aegean Sea Messaras Basin and its continuation along in general, Pn is approximately 7.7 km/s. the Cretan coast to the west. South of This lateral velocity differences are also Crete, the stretched continental crust of confirmed by density modeling and also by the Aegean domain extends to more than high heat-density values indicating that the 100 km before contacting the oceanic upper mantle below the southern Aegean crust of the Libyan Sea, located below the Sea is overheated and reduced in Pn Hellenic arc. The crust is laterally velocity and density. inhomogenous and the basins are

TECTONICS OF THE CENTRAL MEDITERRANEAN RIDGE, BETWEEN CRETE AND LIBYA, FROM COMBINED SEISMIC REFLECTION, SWATH BATHYMETRY AND BOTTOM REFLECTIVITY DATA

Jaen Mascle, Caroline Huguen and the Prismed Scientific Party Geosciences Azur, B.P.48,06235 VILLEFRANCHE-SUR-MER CEDEX (FRANCE)

Since the last 80 My, the Eastern West, i.e. towards the only important Mediterranean is a domain where several remain of Mesozoic (Tethyan?) oceanic episodes of subduction and continental crust, the deep Ionian sea (probably since collision have occurred as consequences the from relative plate convergence between Africa and Eurasia. Within this area, last 10-5My). Today this plates interaction microplates such as the Aegean-Anatolian induces a relative converging motion microplate or the former Apulian domain, between Africa and Aegea-Anatolia, at a are partly independently moving. The rate estimated on the order of 35 to 38 Aegean-Anatolian block for example, mm/year. One of the most spectacular almost totally land-locked between geological results of this plate Eurasia, Africa and Arabia, is configuration consists in the edification of progressively expelled towards South- a large-scale tectono-sedimentary wedge: the Mediterranean Ridge (M.R). This 3.5 Khz echo-sounding, gravity and accretionary complex extends from the magnetic measurements were deep Ionian sea to the Levantine basin, on concurrently used for this survey. About more than 1500 km long and varies, 50.000 km2 of the Central M. R. bottom between the african margin and the surface has thus been mapped at aegean border, from 150 to 300 km in 100% coverage during the recent width. Prismed II cruise.

The M.R. intense bottom deformations, Within the investigated area the M.R. strengthened by thick incoming messinian shows the three main morpho-structural evaporites, have, until recently, strongly provinces previously recognized along its prevented the record of reliable acoustic- Western (or Ionian) and Eastern (or seismic images of its internal geological Levantine) branches. Along N-S transects arrangement. However, recent across the feature, each of these multichannel seismic profiling, wide-angle provinces can similarly be divided into refraction data and expanded seismic several morphostructural domains: profiles, together with gravity modeling • A topographically flat and relatively have revealed some characteristics of its deep, Northern domain, lying between crustal and internal sedimentary the Hellenic trench system and the structures; detailed near-bottom side scan M.R. back-thust front. By comparison sonar surveys, together with swath with results from the Ionian domain, bathymetry and back-scattering recording, this area may be rooted by a thin have also allowed to better image its crustal section, eventually parts of the present day superficial tectonics. stretched Cretan continental margin. This area acts presently as a rigid In this presentation, we intent to show, back-stop for the M.R. compression and discuss, a set of data, respectively wedge. recorded in 1993 and 1998 during two • A wide, topographically subdued, cruises, PRISMED I and II, conducted by Central or Crestal zone, bounded Geosciences-Azur group, across the northward by backthrusts, extends by Central Mediterranean Ridge, area relatively shallow water (less than 2000 extending between the Cretan, active, and meters on average), and is Libyan, passive, continental margins. characterized by important mud flows These data consist of: and mud volcanisms as previously (a) Several multichannel seismic reflection shown by side scan sonar images. profiles recorded using a 96 channels • An external domain, quite narrow south streamer and a 10 GI guns array of Crete, is bounded southward by the (Prismed I cruise), and present day compressive front of (b) 14 North-South oriented profiles (120 deformation where evidences of NM long, and 7 NM-spaced) recorded, thrusting and folding are abundant. at 10knots, between the lower Libyan continental slope and the middle MCS data have clearly illustrated that Cretan margin; swath bathymetric imbricated backthrusts bound the M.R. all mapping, acoustic imagery along its northern borders against the (backscattering) recording system, 6 backstop area; they also demonstrated channels seismic reflection profiling, that the M.R. outer front, facing the Ionian and Herodotus abyssal plains, proceeds drastic differences between the from progressive sedimentary thickening morphostructural provinces previously itself due to thrust stacking and, locally, identified on the M.R. intense folding. In this area shortening, and resulting deformational features, are The outer zone, almost directly into directly controlled by the presence or contact with the Libyan continental slope, absence of incoming Messinian evaporites shows a relatively high backscattering, acting as decollement levels and by the mostly due to its intense surface thickness of Plio-Quaternary sediments. deformation. The axial domain is itself Within the axial domain, where typical characterized by a less intense bottom evaporites are absent, or very thin, the reflectivity, but locally displays high M.R. exhibits only small wave-length backscattering patches partly already surface deformations and only scarce and known and includes an East-West strongly disrupted internal reflectors; trending belt of low reflectivity, which brecciated shales have been sampled divides the area into three sub-zones. within this Finally, the northern inner domain shows a very low backscatterring answer. area particularly in several mud volcanoes Incorporation of these data, together with and/or mud diapirs fields. It has been seismic reflection profiles and swath suggested that mud breccia are extruded bathymetry, indicates the following: from deep-seated decollement levels, (a) The Libyan continental margin, possibly from over-pressured Aptian which trends on average N110, consists of shales. thick sedimentary sequences, some way A second, and more recent decollement faulted at depth, and either slightly tilted level, located near the top of Messinian southwards (near the Libyan promontory), formations, has induced significant or almost tabular everywhere else. increase of the M.R. accretionary wedge, (b) The contact between the Libyan since the last 5 MY. continental slope and the accretionary wedge shows strong lateral structural We will mostly focus here on the M.R. variations all over the study area. To the shallow deformationnal pattern, as West, the deformation front is made of revealed by new data recorded over more imbricated thrusts, while eastwards, in an than 50.000 km2 (within the so-called area where the presence of underlying Herodotus ridge), extending between evaporites is well substantiated by seismic southern Crete and the Libyan continental data, the outer zone includes folds, margin. Actually, this wide domain reverse faults and is cut by a set of constitutes the narrowest and shallowest conjugate N140 and N40 trending normal M.R. segment, probably as a faults. consequence of ongoing continental (c) The structural style of the southern collision processes between the stretched axial M.R. remains difficult to asses: a Aegean continental crust and the probable intense tectonic deformation is Cyrenaica promontory. attested by strong disruption of the underlying reflectors; however, its Within this domain, backscattering records relatively subdued topography may are one of the most useful tool to illustrate indicate an important erosional episod (in Messinian times ?); its very low and contains at depth typical seismic homogenous backscattering pattern may messinian sequences shows as an almost as well indicate a fluid-rich and seismically reflectivity free zone and seems to be homogenized domain. The northern sector progressively gliding northwards. includes several mud flow fields, which are related to thrust and to transtensive fault We believe that most of the structural zones. Mud features (flows, diapirs and characteristics of the Herodotus area can volcanoes) are not randomly distributed be best explained by an ongoing but are concentrated into areas (at least continental collision between the African- three distinct fields) where major back Cyrenaica Margin promontory, acting as thrusts can be inferred facing southern an indenter, and the Southern stretched extensions of the back stop domain. Aegean continental crust. (d) Finally, the inner M.R. domain shows as a series of, almost flat, plateau Our hypothesis has to be tested by deep basin-like features wedged between major penetrating seismic investigations, backthrust-related reliefs and northern combining MCS and wide angle data bordering deep, often quite narrow, and acquisition, and by Deep Drilling in order discontinuous, depressions which to address geological, mechanical and constitutes a transition between the Ionian geochemical parameters of incipient Matapan trench to the West and the Pliny continental collision. trench to the East. This area, which

ACTIVE MUD VOLCANISM ON THE MEDITERRANEAN RIDGE: PHYSICAL PROPERTIES, MUD BRECCIA PROVENANCE, SUBSIDENCE MODELS, AND EXTRUSION DYNAMICS FROM THEORETICAL QUANTITATIVE MODELS (ODP LEG 160)

Achim Kopf GEOMAR, Wischhofstrasse 1-3, 24148 Kiel, Germany

Drilling two submarine mud volcanoes Messinian evaporites) and pelagic situated in the Olimpi field on the northern carbonate, reflecting Pleistocene to mid- flank of the Mediterranean Ridge Miocene ages. Provenance studies on accretionary complex documented sandstones provide evidence for both a episodic eruptive activity over the last 1 to southern origin (e.g African metamorphic >1.5 million years. An evolution beginning basement, carbonate from North African with extrusive building of a cone, followed shelf) as well as a northern origin (i.e. from by successive eruptions of clast-bearing thrusted rock on Crete). Vitrinite mud debris flows and subsequent reflectance data support this distinction subsidence can be deduced for both between the clasts. domes. The mud breccias recovered are gas-rich and contain up to 65% of The collision of Africa with Eurasia is polymictic clasts. Clast lithologies consist believed to be the driving force of mud of sandstones, claystones, halite (i.e. extrusion. The mud follows the decollement, and then ascends along mud breccias, and compiled data from backthrusts in the evaporite-dominated mud domes on land, the diameter of the accretionary wedge adjacent to the rigid feeder channel and the depth of origin for backstop (c. 100 km hinterlandwards of the overpressured muds could be reliably the deformation front). The majority of the estimated for the first time. Feeder clasts may have originated from the channels are likely 2-3 m wide. Gas efflux overlying accretionary wedge. Using the estimates constrain a source depth about Lopatin method, the depth of mobilisation 5.7-6 km below sea floor in the Olimpi of the mud can be calculated using field. This is in accordance with both thermal maturity of organic matter within estimates made from the thermal maturity the mud breccia. An estimate of 4.5 km to of solid organic carbon in the mud 6 km below the sea floor (depending on breccias, and with the assumed level of the thermal gradient chosen) is in the decollement from seismic profiles. A agreement with geometric considerations comparison of mud efflux rates and the concerning the plate boundary from total volumes of mud extruded shows that seismic data. A Messinian age of the mud, only a fraction of the time span as inferred from the subsidence models, is constrained from biostratigraphic data (c. reflected by the fossil and lithologic 1 Ma) is needed to build up mud cones of composition of the mud breccia matrix. the size of the Milano and Napoli domes (i.e 12-58 ka duration of activity). Results from permeability tests, grain size Therefore, mud volcanism here is a highly analyses, and shear strength tests provide episodic phenomenon. clues concerning the mechanism of mud volcanism. The lowest permeabilities Acknowledgments (~10-9 mm/s) were found at the crest of Parts of the results presented were Napoli dome, although fluid venting and obtained in close cooperation with Jan free gas has been documented. This Behrmann (Freiburg, Germany), Ben allows temporary plugging of the conduit Clennell (Leeds, U.K.), Angelo of the dome, build-up of overpressure at Camerlenghi (Trieste, Italy), Rachel depth, and results in episodic activity of Flecker the mud volcanoes. (Cambridge, U.K.), Jean Mascle Based of modifications of Stokes’ law, (Villefranche-sur-Mer, France), Alastair mud extrusion rates were calculated for Robertson (Edinburgh, U.K.), and Hans mud volcanoes of the Mediterranean Schulz (Clausthal, Germany). Pierre Ridge accretionary complex. Mud ascent Henry, Yossi Mart, Liz Screaton, and John velocities are estimated to range between Woodside are thanked for discussion. 60-300 km/a, and are comparable to those Funding was provided by Deutsche of silicate magmas. Using physical Forschungsgemeinschaft and BASF AG. property, structural and flux data of the SEISMIC IMAGES OF THE IONIAN BASIN AND ITS MARGINS

Rinaldo Nicolich Inst. di Minere e Geofisica Applicata, Univ. Trieste, Italy

The crustal structure of the Ionian basin has Escarpment. There the structure of the crust been investigated by OBS and ESP seismic and its thickness show features inherited refraction experiments which have not been from the Mesozoic evolution as a passive able to firmly resolve one of the principal margin, which incorporated the Ionian basin scientific problems for this region, that is crust to the southern plate of Africa and then whether the Ionian basin is floored by to Europe convergence along the Calabrian oceanic crust or by highly attenuated Arc and along the Hellenic Arc. The seismic continental crust. A second elusive problem images mark the lithospheric deformation at is the nature of the transition of the the collision zones with uplifted and mobilised boundaries between the Ionian basin and its continental crustal blocks which overrode the margins. subsiding basin. The load of the sediments in the collisions produce significant flexures of The penetration through the deeper crust is the extremely thin, cold and brittle crust of the achieved on normal-incidence reflection basin. The back-stops of the Hellenic and profiles by using industrial-grade reflection Calabrian basement nappes are also seismic with improved marine sources. Deep responsible of the development of large out- seismic reflection data reveal the presence of of-sequence transportation of huge masses. a layered high-amplitude reflections near the The deep sediments entering in the collision base of the crust, an image that contrast with beneath the basement back-stop structures the well known reflection patterns of are imaged. Furthermore the existence of Mesozoic oceanic crust investigated in the lithospheric transcurrent faults is revealed. Atlantic ocean. These faults cut the whole crust, displacing the Moho. They have a considerable length, The reflective band, characterised by low and seismotectonic implications. frequencies in the range of 8 to 10 Hz, dips down towards the edge of the Malta

DEEP STRUCTURE OF THE HELLENIDES IN RELATION TO THE ASSEMBLY AND EVOLUTION OF THE OROGEN

Z. Garfunkel Institute of Earth Sciences, Hebrew University, Jerusalem, Israel 91904

It is generally agreed that the Hellenides the external western zones. Much are built of large thrust sheets that were knowledge exists regarding the structure assembled during the Alpine orogeny. and history of the upper orogenic levels. Subduction and nappe stacking More recent studies of metamorphic zones progressed from the internal zones in the of the orogen, geophysical data, and east towards advances in understanding of orogenic structures in general, now allow to discuss terranes, which record subduction, the deep structure of the Hellenic orogenic recrystallization at high-P conditions, edifice and how it relates to the shallow penetrative deformation and thrusting at structure. This question is examined here depth, and subsequent exhumation. Flat with reference to two crustal-scale cross shallow detachments and structures sections: from Korfu to Olympus and from indicating stretching and shearing most the Peloponese to the Cyclades. likely contributed to unroofing of the metamorphics, but it is very doubtful that The Hellenides are interpreted as a these structures are quantitatively tectonic wedge which was thrust over the adequate to account for exhumation from Apulian foreland. At depth the foreland 30-50 km depth (indicated by basement extends perhaps half the way metamorphic mineral parageneses). Thus, from the Ionian Sea to the Aegean Sea, the kinematics of exhumation remains but farther east it was juxtaposed with incompletely understood. However, since other crustal units. The high-level thrust the known shallow structures do not sheets are, in great part, thin skinned, account quantitatively for any exhumation while their basement was detached and model, and their ages do not fit well the subducted. This probably resulted from metamorphic history, it appears that the changes in the configuration of crustal- deep orogenic deformation differed from scale deep thrusts. Interpretation of the that at shallow levels. Better external flysch basins as flexural lows in understanding of the deep structure, which front of advancing nappes allows to can be gained from geophysical studies constrain the amount of basement still (mainly seismic reflection) and from deep remaining at the early stages of nappe drilling is required to constrin the formation. The development of the deep processes that shaped the Hellenide orogenic levels is further constrained by orogenic edifice. information from the metamorphic

GEODYNAMICS AND NEOTECTONIC FOREARC DEFORMATION: THE VIEW FROM LATE PLIOCENE-RECENT BASINS, HELLENIC ARC

Kleinspehn, K. L. Department of Geology & Geophysics, University of Minnesota, 310 Pillsbury Drive S.E., Minneapolis, MN 55455 USA ([email protected])

Fore-arc regions display a wide range of is to complement plate reconstructions kinematic behaviors, including deformation and geodetic data that provide a 2- internal to the fore-arc. Our study is a new dimensional plan view of fore-arc multidisciplinary initiative directed at the deformation with data from sedimentary relationship between subduction-zone basins that record the vertical component dynamics and observed neotectonic strain of deformation. By combining of the southern and southeastern Hellenic tectonostratigraphy, structural mapping/- fore-arc as a function of the obliquity of kinematic analyses, and age relations with lithospheric convergence. Our approach three-dimensional modeling of the fore-arc deformation, we will address the changing and geohistory analyses to establish kinematics as a function of increasing vertical displacements, and documenting obliquity of convergence along the strike the syn- and post-depositional deformation of the arc. Arc-parallel extension, which is as well as adjacent basement kinematics, the most commonly observed strain the neotectonic deformation internal to the internal to fore-arcs globally, can produce fore-arc will emerge. The ability to substantial rapid uplift of the fore-arc and quantify the lithospheric response to has been suggested as a mechanism oblique convergence relies on dating driving young uplift of Crete where the deformation using combined 40Ar/39Ar plate where convergence is nearly geochronology, magnetostratigraphy and orthogonal. In contrast, our preliminary biostratigraphy of the basins. Three- observations indicate that the young dimensional numerical basins have experienced shortening suggesting that the strain is more complex model results will be compared to the than simple extension and may be a observed tectonostratigraphic and partitioned response to oblique deformational patterns to link lithospheric convergence. By examining the geodynamics to the strain. An ultimate kinematics recorded by young basins goal is to compare the Hellenic system to along strike in the fore-arc going eastward other global examples of internally from Crete to Rhodos, where the deforming fore-arcs. Deep drilling in other convergence vector is highly oblique, fore-arc regions is focussing on a basic several alternative hypotheses concerning description of the behavior of the lower the mechanisms driving neotectonic fore- crust , which also may be a goal of deep arc uplift will be addressed: (1) arc-parallel drilling on Crete. However, before extension, (2) radial extension, (3) comparisons can be made between the shortening, or (4) transpressive or lower and upper crust, the behavior of the transtensive partitioned strain. By using upper crust needs to be known in detail, the fill of Late Pliocene-Recent basins for which is a goal of our study. temporal control, using facies relationships

DEEP SEA DRILLING IN THE EASTERN MEDITERRANEAN SEA: ACHIEVEMENTS AND OPPORTUNITIES

Alastair Robertson Dept of Geology and Geophsysics, University of Edinburgh. West Mains Road, Edinburgh EH93JW, United Kingdom

Achievements related crustal processes in the Eastern The Deep Sea Drilling Project and the Mediterranean, specifically the incipient Ocean Drilling Program have already collision of a continental fragment, the successfully carried out three cruises Eratosthenes Seamount, with the Cyprus within the Eastern Mediterranean (DSDP active margin to the north and its relation Legs 13 and 42A and ODP Leg 160, the uplift of the Troodos ophiolite. New 1995). The latter investigated collision- information was also provided on processes of mud volcanism 1) Subduction-accretion processes related related to the Mediterranean Ridge to incipient continental collision.The accretionary complex, south of Crete. Mediterranean Ridge is a classic example of an accretionary prism in the initial Future plans stages of collision, associated with both ODP in its present form is expected to frontal thrusting and backthrusting. The continue until 2003. The drillship (JOIDES wedge is rheologically influenced by the RESOLUTION) is currently in the Pacific presence of Messinian evaporites. Ocean and will return to the Atlantic and Improved seismic profiling now allows key adjacent seas only if very highly ranked sites to be targeted for future drilling. A proposals are available. Given the lead deep hole (with riser) through e.g. the time, any new proposal would have to be near frontal part of the accretionary submitted processes could help constrain the deeper in the near future to stand a chance of structure, fluid flow and the role of salt in drilling up to 2003. accretion. In addition, a suite of shallower For the post-2003 era a multi-platform holes through the various tectonic scenario is possible. The Japanese may domains of the Mediterranean Ridge (e.g. build a new ship capable of riser drilling, frontal accretion and backstop areas) allowing deep penetration, high recovery, would also help constrain the role of and obviating hydrocarbon hazard. If built, subduction versus collision and the effects this ship may focus in the seas around E of salt e.g. on fluid flow and mud Asia for a number of years. In addition, if volcanism. sufficient demand and funding(!) exist a riserless ship, similar to the present 2) Extensional processes JOIDES RESULTION, may continue to The Agean region is characterised by high operate worldwide. rates of active extension and is thus a target for studies of fundamental Future drilling in the Eastern processes of detachment faulting, related Mediterranean? vertical motions and rift-related The Eastern Mediterranean Sea has the sedimentation. Both riser and non riser potential interest to attract future deep sea targets exist. A good opportunity for drilling. Indeed, its location between the parallel land-based studies (i.e. S Aegean two converging continents of Africa and islands) exits. Eurasia makes this an ideal location for the study of fundamental lithosphere 3) Evolution of Neotethys deformation processes in extensional, Drilling of continental blocks can help plate-convergent and collisional settings. constrain the timing of rifting, spreading The following generic problems could be and collision in the Eastern Mediterranean tacked in the future with or without riser region. For example, deeper pentration of capability. Riser holes (>2 km) will require the Eratosthenes Seamount (i.e. with much time on site and will be very riser) than that achieved during Leg 160 carefully selected based on global would shed light on rift-drift timing and considerations. Non-riser drilling (typically related processes. Also, drilling of e.g. the <1 km) remains ideal for multihole Anaximander Seamounts would help programmes. constrain the timing and processes of collision. sea integration, shedding light e.g. on the 4) Seismo-tectonics operation of the Tyrrhenian-Aegean- The highly active nature of the entire Cyprus active margin as a linked plate Mediterranean region offers opportunities convergence system. It is the stated to study earthquake processes (and objective of ODP to involve as many hazards) by direct long-term observations outside earth science programmes as (i.e. monitoring) of processes in possible. Drilling would clearly benefit from seismogenic zones (e.g. Aegean arc). collaboration with future programmes Little consideration has been given to this involving continental drilling of selected potential as yet (using riser drilling?). areas. It also essential to involve fully the substantial land-based earth science Land-sea integration communities in the countries around the Further drilling of various parts of the Mediterranean. Mediterranean would allow improved land-

THE MENDERES MASSIF OF WESTERN TURKEY AND THE CYCLADIC MASSIF IN THE AEGEAN — DO THEY REALLY REPRESENT LATERAL CONTINUATIONS?

U. Ring, K. Gessner & C. W. Passchier Institut f. Geowissenschaften, Johannes Gutenberg-Universitaet, 55099 Mainz, Germany

The rocks of the eastern Mediterranean as a huge, laterally continuous belt in are traditionally subdivided into a series of paleogeographic reconstructions. tectonic units or 'isopic zones' that are differentiated largely according to rock type, stratigraphy and metamorphism and Overall the Menders Massif has an largely are related to pre-collisional similar lithology as the Cycladic Massif. paleogeography. Accordingly, the However, the architecture, the age of Menderes Massif of western Turkey is basement, the pre-Alpine tectonometamorphic history and Alpine contraction commonly viewed as the eastern and subsequent crustal thinning in the continuation of the Cycladic Massif in the Menderes Massif differs fundamentally Aegean, i.e. basement and cover of both from that of the Cycladic Massif. This massifs have been correlated and it has challenges the commonly held opinion that been assumed that both massifs both massifs correlate laterally and underwent a experienced a similar tectonic development. Our work similar tectonic development. Such a view indicates that the Cycladic Massif overlies has considerable paleotectonic the Menderes nappes in western Turkey. consequences because it allows to treat In the Aegean, the Cycladic Massif the Pelagonian-Cyclades-Menderes zone overlies the external Hellenides. This implies that the Menderes Massif had (1) a more external position in pre-Alpine an Eocene high-pressure metamorphism. paleogeography than the Cycladic Massif In the Aegean, thrusting and high- and (2) that it has a similar tectonic pressure metamorphism propagated position as the external Hellenides. towards the external Hellenides. In However, the latter and the Menderes contrast, post-high-pressure out-of- Massif cannot be regarded as lateral sequence thrusting of the Dilek/Selcuk continuations because lithology, protolith and the Lycian nappes on top of the ages and the pre-Alpine and Alpine history Menderes nappes did not cause Tertiary differ entirely from each other. high-pressure metamorphism in the latter. The succeeding extensional history of The basement of the Cycladic Massif was both massifs was remarkably differential first consolidated during the Variscan with pronounced extension and crustal orogeny. In contrast, the basement of the attenuation in the Aegean and much less Menderes Massif was largely formed crustal thinning in western Turkey. Severe during the Pan-African orogeny and was crustal stretching in the Aegean was not affected by a Variscan event. The controlled by multi-stage roll back of the occurrence of Middle Triassic granitoids in Hellenic subduction zone. We speculate both massifs indicates that the basements that in western Turkey the Eocene of both massifs were close to the Eurasian subduction zone did not roll back due to margin by Middle Triassic time and rifted collision of the relatively large continental away from Eurasia during subsequent block of the Menderes Massif. This opening of Neotethys. During closure of collision subsequentely governed the Neotethys, the Cycladic Massif, both in the different Alpine orogenic evolution of Aegean and in western Turkey western Turkey. (Dilek/Selcuk nappes), was overprinted by

ASTRONOMICALLY FORCED CHEMICAL CYCLICITY IN PLIOCENE EASTERN MEDITERRANEAN SEDIMENTS

H.-J. Brumsack & R. Wehausen Inst. of Chemistry & Biology of the Marine Environment (ICBM); Carl-von Ossietzky-Univ.; P.O. Box 2503; D-26111 Oldenburg; F.R. Germany;e-mail: [email protected] oldenburg.de

High resolution geochemical investigations composition. Besides carbonate cycles or were carried out on Pliocene sediment frequently occuring enrichments in trace cores which were recovered during Ocean elements, that are typical for sapropels or Drilling Program (ODP) Leg 160 in the burned-down sapropels, a distinct cyclicity eastern Mediterranean. Sapropel is seen in the composition of terrigenous- containing intervals from Sites 964 (Ionian detrital matter, as displayed by Si/Al, Ti/Al, Sea), 969 (Mediterranean Ridge) and 967 Mg/Al, K/Al, or Zr/Al ratios. Sapropels or (Eratosthenes Seamount), stratigraphically ghost-sapropels and sapropelic layers are classified as nannofossil zones 17-16b, characterized by distinct peaks in the display cyclic variations in their chemical Ba/Al profile. Such peaks, which represent periods of enhanced bioproductivity, illite, there exist two important K sources appear at distinct locations of the cycles in for Sites 964 and 969. This might be the terrigenous-detrital matter composition, reason why K/Al cyclicity is less well e.g., in the minima of the Ti/Al curve. displayed in the sediment chemistry at Since sedimentary cycles and sapropel these locations. occurrences correspond with the precession index or the 65°N insolation References target curve cyclic element/Al records Calvert SE (1983) Oceanol. Acta 6:255- reflect climatically induced variations in 267 provenance. De Visser JP, Ebbing JHJ., Gudjonsson L, Hilgen FJ, Jorissen FJ, Verhallen We propose that during times of sapropel PJJM, Zevenboom D (1989 formation a higher fluvial contribution and Palaeogeogr., Palaeoclimatol., during deposition of light colored layers a Palaeoecol. 69:45-66 higher sediment flux existed. This Emeis K-C, Robertson AHF, Richter C, et assumption is supported by clay al. (1996) Proc. ODP, Sci. Res. 160 mineralogical investigations carried out by Foulcault A, Mélières F (1995) C.R. De Visser et al. (1989) and Foucault and Académie des Sciences Paris 321:869- Mélières (1995). At Eratosthenes 876 Seamount (Site 967) a higher Nile runoff Higgs NC, Thomson J, Wilson TRS, during sapropel formation causes lower Croudace IW (1994) Geology 22:423- Mg/Al and K/Al ratios because Nile 426 suspended matter is characterized by high Hilgen FJ (1987) Newslett. Stratigr. smectite, moderate 17:109-127 kaolinite and low illite and chlorite Hilgen FJ (1991) Earth Planet.Sci. Lett. abundances. Ionian Sea (Site 964) and 104:226-244 Mediterranean Ridge (Site 969) sites are Lourens LJ, Antonarakou A, Hilgen FJ, influenced by rivers of the northern Van Hoof AAM, Vergnaud-Grazzini C, borderlands of the eastern Mediterranean Zachariasse WJ (1996) Paleoceanogr. (NBEM). 11:391-413 Higher runoff from the NBEM leads to Thomson J, Higgs NC, Wilson TRS, higher illite and chlorite abundances in the Croudace IW, De Lange GJ, Van sapropels and thus to higher K/Al and Santvoort PJM (1995) Geochim. Mg/Al ratios. During oligotrophic intervals Cosmochim. Acta 59:3487-3501 and a more arid climate in the Tomadin L, Lenaz R, Landuzzi V, Mediterranean realm desert dust from the Mazzucotelli A, Vannucci R (1984) Sahara or from the Arabian peninsula may Oceanol. Acta 7:13-23 be an important source for terrigenous Van Santvoort PJM, de Lange GJ, detrital matter. Eolian material likely is Thomson J, Cussen H, Wilson TRS, Krom responsible for high Si/Al (quartz), Ti/Al MD and Ströhle K (1996 Geochim. (e.g., ilmenite), and Zr/Al ratios (zircon). Cosmochimica Acta 21:4007-4024 As dust from the south also contains K- rich minerals like potassium feldspars and BIOSTRATIGRAPHICAL RESEARCHES IN LATE NEOGENE DEPOSITS OF THE CHANIA AREA, CRETE

D. Frydas University of Patras, Department of Geology, Greece

The Neogene facies of NW-Crete varies significantly in a small scale due to synsedimentary tectonics. On the fault blocks mainly littoral bioclastic limestones were deposited during Late Miocene, while the four basins which are from West to East: Platanos, Kastelli, Maleme and Platanias are characterized by their hemipelagic to littoral sediments. The lithological spectrum contains partly alternating beds of yellow sands and sandy marls, grey to blue marls, silty clays, finely laminated diatomite beds, and bioclastic limestons. Gypsum deposits accompanied the sedimentation of the studied area only in the Kastelli and Maleme Basins. The sedimentation of the Platanos Basin is dominated by yellow sands and sandy marls and contains two sedimentary cycles corresponding to the stratigraphical intervals Tortonian/Messinian (subzones CN8b-CN9b) and Uppermost Zanclean to Lower Piacenzian (subzones CN11b-CN12a).

The studied sections Platanias and Stalos in the Platanias Basin represent the stratigraphic equivalent of the first sedimentation cycle containing calcareous nannofossils of the biozene CN9 (=Discoaster quinqueramus: Upper Miocene). Sediments of Pliocene age were not found here. Consequently, we presume that there was no sedimentation after the gypsum deposits during the Messinian time. However, a second sedimentation cycle which corresponds to the Upper Zanclean (subzone CN10c= Discoaster asymmetricus) was recognized for the first time in Western Crete in the Maleme Basin near the village of Loutraki. Key words: Biostratigraphy-Neogene-Calcareous Nannoplankton-Chania, Crete- Correlation.

KINEMATIC ANALYSIS OF THE HERAKLION BASIN BOUNDING FAULTS

C. Fassoulas Natural History Museum of Crete, University of Crete, Heraklion 71409, Greece.

The Heraklion Basin comprises the Giouchtas to the east. The Alpine western part of the tectonic subsidence occurrences of Agia Varvara and Profitis located in central Crete between the Elias trace the border of the Heraklion and Psiloritis and Dicti mountains. Neogene Messara basin to the south. and Tertiary sediments, with thickness not exceeding 1 Km (Nomikou 1997), cover Geological mapping and kinematic the alpine basement, which however is analysis of fault planes (Angelier 1979) outcropped in a few places. The basin is indicated that three fault groups affected bounded by two major fault zones, i.e. the the area. The first, comprising scattered Kroussonas – Tylissos to the west and east-west trending normal faults, is attributed to the latest stages of the indicate a northwest – southeast lateral Miocene north – south trending displacement which is consistent with this extensional event, which affected whole latest deformation. Crete causing exhumation of the lower nappes and thinning of continental crust The resulted stress field from Pliocene to (Fassoulas 1994). The second group present is consistent with the model clearly post-dates the previous fault group. proposed from Meijer and Wortel (1997) North – south trending normal faults such consuming subduction roll-back plus as the Kroussonas – Tylissos and Anatolia push. Giouchtas, constitute this second group. Kinematic analysis of the fault planes References indicate that the maximum extensional ANGELIER J. (1979). Determination of the stress axis generally trends east – west mean principal directions of stresses for a with a clockwise rotation going to the given fault population, Tectonophysics, 56 center of the basin. Considering that the T17-T26. second fault group affects the Pliocene FASSOULAS C. (1994) Post-nappe stacking sediments its age is suggested to be Late extension and exhumation of HP/LT rocks Pliocene – Pleistocene. The third group in central Crete. Tectonics, 13, 127-138. comprises northeast – southwest to east – MEIJER P. & WORTEL M. (1997). Present- west trending normal faults that overprint day dynamics of the Aegean region: a the earlier structures. These faults are model analysis of the horizontal pattern of attributed to the latest (present day?) stress and deformation, Tectonics, 16, 879- north/norhtwest to south/southeast 895. extension, that sunk the northern NOMIKOU P. (1996). Geodynamic evolution of Heraklion coast forming the Heraklion Heraklion Basin. Diploma work. Uni. marine basin. What is impressive is that Athens. the latest activation of the Giouchtas fault

CRUSTAL STRUCTURE AND SEISMIC ACTIVITY OF THE NISYROS VOLCANO, EAST AEGEAN SEA

J. Makris, T. Chonia, Institute of Geophysics, Hamburg, Germany, D. Papanikolaou, National Centre for Marine Research, Athens, Greece G. Stavrakakis, Geodynamic Institute, Athens, Greece

The deformation of the Aegean Sea is has been poorly investigated and it is now dominated by transtensional processes the focus of several geophysical studies. and mechanisms of subsidence. It is affected by intense volcanic activity along In October 1997 an active and passive a volcanic arc extending from Nisyros, seismic experiment was conducted along east Aegean Sea, to the north-western a profile extending for 140 km from the part of the island of Evia, Lichades. In island of Chalki to the island of Leros particular, the eastern Aegean volcanism crossing the volcanoes of Nysiros, Yali and Cos. For the active seismic experiment, 20 Ocean Bottom Seismographs and 20 landstations were A velocity tomographic study of Nisyros deployed and recorded 1023 shots fired was performed by firing shots at two by a tuned 48 litre airgun array at 120 m circles at 1,7 and 5 km distance around intervals. The final velocity-depth model the island of Nisyros. The final 3D model presents a rather thinned continental crust for the velocity structure below Nisyros ranging from 20 to 25 km thickness. The shows that the energy penetrated up to 7 sediments are laterally very variable and km depth and mapped a volcanic strongly tectonized. They exceed 5 km at intrusion. The shallowest penetration some parts and indicate the location of a depth of this magma is only 1.8 km below large volcanic caldera extending from surface. With increasing depth the Nisyros to the southern coast of Cos. intrusion widens and covers a large part of the volcano. In summary, the shallow A seismicity study was accomplished by depth of the intruded magma has elevated deploying 22, 3-components, digital the isotherms below the volcano stations onshore. It showed that the significantly, so that the aquifers above the activity within the caldera is high, ranging intrusion have reached a mean from 17 to 30 events per day. The temperature of 2900C. If the high seismic locations of 1200 hypocenters indicate activity prevailing at present would fracture that a fault system between Mandraki and open the overlying lithological units, (Nisyros) and Yali is extremely active and thus decreasing the lithostatic pressure, that this system is truncated by an east the overheated aquifers could react north-east oriented fault. The hypocenters explosively as was the case in 1873. are located at the upper crustal section and mostly at depths less than 10 kms.

STEADY-STATE FLUXES IN THE OLYMPICS SEGMENT OF THE CASCADIA ACCRETIONARY WEDGE

M. T. Brandon1, K. A. Farley2, F. J. Pazzaglia3, M. K. Roden-Tice3, and G. E. Batt1 1Dept. of Geology and Geophysics, Yale Univ., P.O. Box 208109, New Haven CT 06520- 8109; 2Div. of Geol. and Plan. Sciences, Cal Tech, MS 170-25, Pasadena CA 91125; 3Dept. of Earth and Planetary Sciences, Univ. of New Mexico, Albuquerque NM 87131; 4Ctr. for Earth and Env. Science, SUNY Plattsburgh, Plattsburgh NY 12901

The Olympic Mountains contrasts with erosion was caused by early emergence other parts of the Cascadia forearc high of this part of the forearc high, at ~12 to 17 because of its high topography (up to Ma, which provided a longer time to 2427 m) and deep exhumation (>13 km). develop and erode the emergent forearc A pervasive late Cenozoic margin-parallel high. Early emergence is attributed to the cleavage indicates that the uplift formed relatively shallow slab beneath the by SW-NE shortening, parallel to the Olympics. The margin has less convergence direction. Relatively deep "accommodation space" there so the wedge was able to rise above sea level ages) is similar to the accretionary flux at earlier than other parts of the margin. the toe of the wedge (~63 km2/m.y.). Cooling ages indicate steady erosion in the core of the uplift, starting with zircon All of this evidence indicates that the flux FT = 13.7 Ma @ ~240 C and 10 km depth, balance at the Olympics segment of the then apatite FT = 6.7 Ma @ ~115 C and Cascadia margin has been close to steady 4.4 km depth, and finally U-Th/He apatite state since ~14 Ma. Furthermore, these = 2.5 Ma @ ~80 C at 2.8 km depth. results imply that: 1) the Olympics were Average erosion rates during exhumation able to achieve this steady-state condition of the core have been ~0.8 to 1 km/m.y. very quickly after emergence, and 2) Late Pleistocene strath terrace uplift rates erosion rates have not been strongly determined along the western flank of the influenced by climate change during the Olympics late Cenozoic. Thus, we infer that erosion rates must have closely tracked changes uplift agree with long-term erosion rates in uplift rates in the Olympics, which determined from apatite FT cooling ages. suggests that bedrock landsliding has Furthermore, the long-term erosional flux been the rate-limiting geomorphic process. out of the Olympics cross-section (~54 km2/m.y. based on apatite FT cooling

CONTRIBUTION OF DUCTILE FLOW TO EXHUMATION OF LOW T - HIGH P METAMORPHIC ROCKS: SAN JUAN-CASCADE NAPPES, NW WASHINGTON STATE

M. T. Brandon & J. G. Feehan Department of Geology and Geophysics, Yale University, New Haven, CT 06520-8109

The San Juan-Cascade (SJC) nappes indicates plane-strain uniaxial shortening were subducted to a depth of ~18 km, at the regional scale, with Sx, Sy, and Sz metamorphosed under high pressure-low = 1.01, 0.91, and 0.58. The average temperature conditions, and then flattening plane (XY) dips 30° to the NE, exhumed, all within ~16 m.y. During and the average X direction plunges 20° exhumation, penetrative deformation by to the N. The large shortening in Z was solution mass transfer (SMT) resulted in a compensated by a mass-loss volume widespread spaced cleavage. Strain strain of ~47%. The difference between directions were determined for 27 strains at the local and regional scales is sandstone samples, and absolute strain due to the variability of the X and Y measurements for a subset of 19 samples. directions at the local scale. The result is Z directions generally plunge moderately that local Sx and Sy values are averaged to the LE, and X and Y directions are out at the regional scale. scattered in the plane perpendicular to Z. SMT deformation is constrictional at the Our measurements indicate a vertical local scale, but the tensor average shortening of 36%, which indicates that some exhumation occurred by ductile dependent ductile flow and no reversal of thinning. We show that the contribution of principal strain rates with depth, this model ductile thinning to exhumation is not indicates that ductile thinning of the SJC directly equivalent to the finite vertical nappes accomplished only 13% of the strain measured in exhumed rocks, but total exhumation, despite the vertical instead depends on the velocity-gradient shortening of 36%. There is no evidence field in the wedge and the path through that normal faulting contributed that field. We outline a simple one- significantly to exhumation. We conclude dimensional model that illustrates the that erosion operating at an average rate relationship between finite strain and of ~1.1 km/m.y. was the dominant ductile exhumation for a steady-state exhumation process. convergent wedge. Assuming depth-

THE E.P.P.O. PERMANENT SOUTH AEGEAN NETWORK AND ITS CONTRIBUTION TO THE MONITORING OF SEISMICITY IN THE REGION

N. Melis & D. Papanikolaou Earthquake Planning and Protection Organization (E.P.P.O.) 32 Xanthou Str., GR-154 51 Athens, GREECE. Tel: +30-1-6728000, Fax: +30-1-6779561, E-mail: [email protected]

An attempt to contribute to the monitoring Geraneia for serving the radio-linked of seismicity in the South Aegean Region telemetry assuring sufficient transmission was taken during 1997 by E.P.P.O.. A of the seismic signal to the Athens plan to deploy a permanent seismic E.P.P.O. Headquarters base station for network in the region was finalized in 1997 processing and analysis. and the deployment of seismic stations started the same year. At base a GPS timing device is used to synchronize the digitizing PC-system at The network consists of six outstations UT time. Automatic detection is used at with one component short period first stage signal processing and in a seismometers and their analogue signal is following stage manual phase picking and transmitted via radio telemetry to the event location is performed. Athens E.P.P.O. Headquarters where it is digitized and processed with a personal A mobile network of five portable 24bit computer system consisting of three PCs digital seismographs is also available to linked via a Novell Network. strengthen the permanent network at areas of locally increasing seismicity. An The selected sites are: Gavdos and Chrisi interface is also available in combining Islands South of Crete and Kithira, Milos, permanent and portable network data for Amorgos and Nisiros Islands at the South improved event location. Aegean region. There are six repeater sites selected at South Crete (Spili, Last but not least, an interface is under Achedrias), Milos, Kithira, Naxos and development to allow the link of the above mentioned available data into the National strengthening the permanent network with Hellenic Seismic Network and its deployment of the portable network, in six operational components. months intervals, with result the coverage of the areas, western, central and eastern, Finally a proposal to contribute to regional of the Peloponnesos - Crete - Dodekanisa projects in Crete (i.e. Deep Drilling region in terms of seismicity monitoring. Project) can be made by means of

GEOLOGICAL 3D-MODELLING OF THE PLATTENKALK GROUP, WESTERN CRETE

Manutsoglu, E., Jacobshagen, V., Spyridonos, E. & Skala, W. F.U. Berlin, Institut für Geologie, Geophysik und Geoinformatik, Malteserstr. 74 – 100, 12249 Berlin

Today’s geotectonical setting of the island of Crete is interesting for the scope of the In our work we used the integrated International Continental Drilling Project software package. It enables geologists to (I.C.D.P.). Although the lowermost tectonic describe the topography, geological unit of Crete, the Plattenkalk Group, forms surfaces, or bodies by a number of lines the biggest part of the island, good and/or points. Like in any other CAD outcrops of its formations are rare. The package, the co-ordinates are stored as Samaria and real-world co-ordinates. Thus, data from the Imbros Gorges offer large and deep maps of different scales may easily be sections throughout the group. Thus they integrated. This system allowed us to are appropriate for a detailed geological implement the geometrical model in a study of the Plattenkalk Group based on a number of successive steps. At first, a reliable geological map. Digital Terrain Model describing the topography of the investigated areas is set Three-dimensional digital representations up. All geological boundaries are digitised can convey much more information about and then overlain to the topography digital the author’s conceptual model than the model to obtain the proper elevations. traditional map. That way, they drastically Based on this data, contacts of geological reduce the risk of mismapping and units are interactively constructed to misinterpretation. By applying define the tectonic setting. In our study we computerised modelling systems integrated data from field work and from geologists may set up static or even geological maps. dynamic digital representations of the subsurface domain. Static models are As a result we propose an anticline generated to describe the geometry of structure with an N.NE-S.SW striking axis geological bodies as well as to predict dipping to the east in contrast to the selected properties and their spatial existing model which proposes a syncline distribution structure with the same strike and dip. INTERPRETATION OF TECTONIC LINEAMENTS USING SATELLITE IMAGERY FOR TEXTURAL ANALYSIS. A CASE STUDY IN WESTERN CRETE

Manutsoglu E., Ott N., Spyridonos E. & Jacobshagen V. F.U. Berlin, Institut für Geologie, Geophysik und Geoinformatik, Malteserstr. 74 – 100, 12249 Berlin

In addition to 3-D geological modelling of recognition and interpretation of prominent two areas in western Crete, digital image structures such as block boundaries. processing of satellite imagery (Landsat Thematic Mapper) in an integrated GIS We used texture filtering second order and image processing environment was (variance) with a 5X5 matrix. This filter applied. The scope of this work was to was calculated on a single band recognise large scale structures and monochrome TM band 4 (near IR) and corresponding also on a three band colour composite TM band 7,4,1. lineaments and figure out the regional fault pattern and also to correlate structure field The results were digitised in a GIS. Within work data with those of the satellite the data-base additional items have been imagery. defined to calculate the directional statistics and the lengths of the Using texture analysis, visual lineaments. Finally the digitised interpretation of lineaments was improved. lineaments were classified by length. In contrast to other filter techniques which smooth the data or prefer selected Thus, we have recognised the northern directions (e.g. Laplace, Edge fold limb of the Gigilos anticlinal dipping to Enhancement and Directional Filtering) all the NW. There was also a preferred E-W directions of linear structures are clearly direction of extended faults, which might visible. Additionaly, the length of the be correlated to the formation of the interpreted lineaments increases Gigilos anticlinal. dramatically. This is of importance for the

A LINEAR SOURCE MODEL FOR SEISMIC HAZARD ASSESSMENT IN CRETE AND SURROUNDING REGION

Papoulia J. National Center for Marine Research, Institute of Oceanography, Agios Kosmas, Hellinikon, 16604-Athens, e-mail:[email protected]

A simplified tectonic scheme for seismic of the regional seismic hazard is done hazard purposes is proposed for the area applying the fault rupture model, its most of Crete, southern Greece. The scheme important advantage being the recognition considers major fault lines with that, the length of fault rupture during an documented seismicity. The assessment earthquake is an important consideration in probabilistic calculations of seismic hazard. The results identify a seismic belt in the southwesternmost part of the island, running almost parallel to the front of the subduction of the African plate. The sensitivity of seismic hazard calculations to statistical uncertainties in models and parameters is investigated, considering a site in the high seismicity area. Amongst other, the dependance of hazard on the physical law, describing the attenuation of seismic waves from the fault to the site, seems to play a most significant role.

Chicxulub-Workshop, Merida, March 22-24, 1999

Minutes

Participants: 18 Scientists from Mexico , 20 Scientists and Engineers from Canada, USA, Germany, Netherlands, Russia and GB.

Program: March 22: Presentation and Discussion of results of recent and ongoing investigations March 23: Presentaion and Discussion of results of recent and ongoing investigations Discussion of future planning, setting-up of Principal Investigators and CoPI's, Definition of scientific goals

During the first part of the workshop available results have been presented and discussed broadly. The presentations included data from available boreholes, field work, laboratory investigations and especially the results of geophysical surveys i.e. magnetic data, gravity data, seismic data especially off-shore (PEMEX and BIRPS).

Based on this part of the workshop the participants discussed following points:

(1) Principal Investigators.

As a result the following group has been established

Principle Investigators: L. Marin, Mexico J. Urrutia Fuccugauchi, Mexico V. Sharpton, USA

Co-Principal Investigators: D. Moran, Mexico A. Camargo, Mexico D. Stoeffler, Germany R. Buffler, USA J. Smit, Netherlands B. Ivanov, Russia

(2) Chicxulub-Drilling-Project, Strategy The project shall be organized as a multi-phase program over several years, including drilling opperations, geophysical survey and field work as well as laboratory investigations. In a first step it was decided to drill a hole of 1600-2000 m depth to a key location. One major issue for the site selection is to obtain a complete profile of the impact melt sheet because this meets most of the scientific issues.

(3) Scientific goals of the first phase

In the first phase a 1600 – 2000 m deep hole shall be drilled. Goals of this phase are: (a) Recover a complete sequence of impact rock within the Chicxulub Crater (b) Recover a complete record of tertiary sediments

(4) Site selection

Available are good and dense magnetic and gravity data. Also available are offshore seismic data of high quality, especially the BIRPS profiles shot in 1996. Together with older PEMEX data and the results from several boreholes a sufficient clear picture of the Chicxulub-structure is available and was used for a preliminary site selection at the southwest edge of the crater ring between two existing boreholes Y6 and U2. After inspection of all available data the scientific objectives of the first phase can be best achieved at this site. In all cases older PEMEX seismic profiles available for this portion of the crater shall be revisited in the next future.

(5) Financing issues

Potential funding agencies for the project have been identified: ICDP, NSF and CONASYTE. As the project is a modified version of the Chicxlub-proposal submitted by Marin et al. to ICDP in 1996. At this time ICDP decided to provide funds for the Chicxulub project (1.000.000 US$ over a period of 5 years). This money is still reserved and could be used to start to project rather soon to get the project off.

J. Lauterjung April 1, 1999

The Chicxulub Scientific Drilling Project Proposal to the International Continental Drilling Program - As developed at the International Meeting on Chicxulub Drilling

Luis E. Marín Stillman & Jaime Urrutia Fucugauchi Instituto de Geofísica Universidad Nacional Autónoma de México Ciudad Universitaria, Mexico City, CP 04510, Mexico

Virgil L. Sharpton Department of Geology and Geophysics University of Alaska Fairbanks, AK 99775, USA

PROJECT SUMMARY

also of global wildfires, global cooling, acid The birth of the Chicxulub multiring rain, and widespread death in the seas and impact basin approximately 65 million years on the continental landmasses. The ago represents one of the most dramatic extinction event initiated by this cosmic events in Earth's history since the onset of collision marks the end of the Mesozoic Era the Phanerozoic. When the 10-15 km comet and is one of the most profound excursions or asteroid struck the shallow sea over what in biological evolution since the inception of is not the northern Yucatan platform, it life on Earth. The terrestrial production rate explosively released the energy equivalent of craters such as Chicxulub, whose of well over a hundred million megatons of diameter exceeds 200 km, is less than one TNT. While the vast majority of this energy per 100 million years and, to date, only two was transferred to the near surface materials others have been recognized. These are the at the impact site, this collision clearly had Sudbury structure (Ontario, Canada) and the global effects. A discrete layer of ejected Vredefort structure (South Africa). Both are dust, ash, and spherules is distributed nearly 2 billion years old, heavily eroded worldwide at the Cretaceous-Tertiary and otherwise modified. Chicxulub, on the boundary. Associated with this layer is other hand, is relatively young and because evidence not only of its impact origin but it formed in an area of active deposition (a the nature of the target rocks (relevant to shallow sea over a stable carbonate constraining the KT kill mechanism and platform), its interior morphology has been understanding the evolution of the Yucatan shielded from the effects of erosion. Only Platform) and (2) understanding how those near its high-standing rim has erosion target materials were shocked, comminuted, modified the crater materials substantially. mixed, and emplaced onto the crater floor Chicxulub, therefore, offers a unique during the impact process (relevant to opportunity to gather new and important understanding the nature of large-body constraints on the nature of such large impact). The core samples would also multiring impact basins and how their enhance interpretations of seismic reflection formation affects geological and biological data used to constrain the large-scale evolution. Given the importance of studying configuration of the impact basin. Another this crater and the fact that it is completely important goal is to recover a continuous buried by up to one kilometer of Cenozoic section through the Tertiary cover rocks sediments, it is surprising that not a single above the impactites, from which scientific bore hole has been drilled into the information about post-impact faunal crater floor materials. recovery and long-term modification of the crater can be gleaned. Finally, we hope to Funds are requested to conduct the penetrate into the upper part of the disturbed Chicxulub Scientific Drilling Project Cretaceous-Jurassic platform rocks below, in (CSDP). The International Continental order to provide additional constraints on Drilling Program (ICDP) convened a target-rock compositions and deformation workshop held in Merida, Mexico on 22-23 styles characteristic of the regions flanking March 1999, to develop a strategy for the collapsed central excavation cavity of exploring the Chicxulub impact crater the impact basin. through drilling and geophysical exploration techniques. The consensus of the workshop Existing geophysical and well-log data, was that the next step in this plan should be along with a consideration of the scale and an intermediate-depth (2-3 km) drill-coring symmetry of this extremely large impact project to provide new and important feature, indicate that these coring goals can samples within a reasonable funding level be achieved at a distance of 60-80 km from (~$1 M US). It was determined that the the basin center. The well will be located in primary coring goal of CSDP should be to the southern part of the crater to promote recover a complete sequence of impact- correlations with existing oil-exploration generated rocks overlying the downfaulted wells and to facilitate a prospective onshore Mesozoic target rocks from within the seismic line that would tie this well to others crater. This would provide the first complete in the vicinity. The Investigator Team (3 PIs section through the sequence of melt-rocks and 6 Co-Pis) is augmented by 20-25 and breccias at any large (>50 km) impact additional Science Team members from crater. These samples, therefore, would be around the world. of immeasurable importance in (1) assessing INTERNATIONAL WORKSHOP FOR A CLIMATIC, BIOTIC, AND TECTONIC, POLE- TO-POLE CORING TRANSECT OF TRIASSIC-JURASSIC PANGEA

Steering Committee: P. E. Olsen, D. V. Kent, R. Raeside, M. Withjack, G. McHone, F. Surlyk, K. Burke

The ICDP and US NSF funded International Triassic-Jurassic boundary Workshop for a Climatic, Biotic, and marked a mass extinction, Tectonic, Pole-to-Pole Coring Transect of perhaps of greater Triassic-Jurassic Pangea was held on June 5-9, 1999 at Acadia University, Wolfville Nova Scotia, the purpose of which was to define the science goals of this global scientific coring program. Fifty six scientists from thirteen countries participated in this workshop, the results of which are planned to be published by ICDP.

RATIONALE The Late Triassic and Early Jurassic was a critical time in Earth history, representing one of the end members of Earth system states. The continents were united in the supercontinent of Pangea, with recent proxy data indicating the highest CO2 levels since the early magnitude than that at the Paleozoic. Although, all major Figure 1: Time scale for the Late Triassic based groups of living terrestrial on the NBCP cores. Adapted from Olsen and vertebrates evolved during Kent (1999). the early Mesozoic, the the Cretaceous-Tertiary continuous record of astronomical transition. Either coincident climate forcing in the World, which in turn with the Triassic-Jurassic led to the development of an mass-extinction or shortly astronomically tuned geomagnetic thereafter, began what may polarity time scale for the Late Triassic have been the largest and earliest Jurassic spanning roughly 31 igneous event in Earth history million years (Olsen et al., 1996; Kent et - the 6000 km diameter al., 1995; Olsen and Kent, 1996, 1999a; Central Atlantic Magmatic Kent and Olsen, 1999). Subsequent Province (CAMP) event, studies have shown that this time scale which may also mark the can be used for high-resolution initiation of the earliest correlation to other areas, hundreds to Atlantic Ocean sea-floor. thousands of kilometers distant (e.g. Kent Fortunately, the extension and Olsen, 1997; Olsen and Kent, 1999b; leading up to the break up of Kent and Clemennson). The NBCP and Pangea resulted in the related work demonstrates that it is formation of the largest possible to obtain records equivalent in known rift province and quality to those from the Neogene, but at associated basins, the result a spatial and temporal scale hitherto of which is a spectacular unavailable. This fine-scale temporal sedimentary and igneous framework should allow exploration of record of Triassic-Jurassic major events and processes at tectonic, climatic, and biotic unprecedented precision and scale. events with the interval being It is within this exciting new context that represented virtually in many the ICDP and US NSF funded workshop basins on all continents. was held to develop a prioritized plan to A high-resolution record of one of these core specific targets along a largely pole basins, the Newark rift basin of New York, to pole transect of Triassic-Early Jurassic New Jersey, and Pennsylvania, USA, has Pangea. It is only with continuous core already been recovered in nearly its entirety that the the extremely large magnitude in 6700 m of core by the US National global events and processes cane be Science Foundation- funded Newark Basin examined at appropriate (large and Coring Project (NBCP) (Figure 1). Analysis small) levels of temporal and spatial of this record produced the longest resolution.

SCIENTIFIC THEMES The meeting was structured around three basic science themes: 1) climate, astronomical forcing, and chaos; 2) Pangean break-up; and 3) biotic change in a Hot-House world. 1) The climate, astronomical forcing, calibration of part of the chaotic behavior and chaos theme involves the of the planets outlined by Laskar (1990) development of a global high (Figure 2). However, a fuller resolution (~20 ky) spatio- understanding and tests of these temporal matrix to examine observations require equally detailed how astronomical forcing records from other latitudes, especially plays out over latitude in where obliquity is prominent (e. g. high continental and marine latitudes). Records in which obliquity is environments. Although prominent are also needed to refine the efforts are underway to finally Triassic-Jurassic general precessional obtain comparable climatic “constant”, needed to constrain the records from the Quaternary evolution of the Earth-Moon system as and well as certain as yet poorly constrained Figure 2: Range of possible g3 and g4 values based on the Newark cores andlimited by the size of the rest of geophysical parameters of the Earth. The chaotic zone as defined by Laskar (1990) for the the development of this high-resolution last 200 million years and possible range of those Neogen spatio-temporal matrix will result in values that satify the data from the NBCP cores (from Olsen and Kent, 1999a) e by general methodologies for producing others, insolation curves for time periods far it is distant from the 20 my limit imposed by essential to obtain the chaotic behavior of the planets. comparably detailed records 2) The Pangean break-up theme focuses from more ancient times to on the evolution of the rift system itself understand the long term and the initiation of oceanic crust behavior of the climate production and drift. The high-resolution system, its forcings, and its time scale now available for the Late age-independent aspects. In Triassic and Early Jurassic allows a addition, the climatic transect quantitative understanding of continental for Triassic-Jurassic Pangea extension and ultimate rupture, both at can be obtained for longer the basin and trans-continental scales. time periods and at more Recent efforts by Contreras et al. (1997) modest expense than for indicate that it is possible to derive the virtually any other geologic large scale behavior of rift-basins (e.g. period, including the The Newark basin) from first-order fault Neogene. growth models. However, understanding Integral to this goal of understanding of the linkages between basins and the astronomical forcing over latitude, is the time- and geography- dependent aspects exciting realization that it provides a matrix of continental rifting will require additional for exploring the long-term behavior of the high resolution records from different rifts planets. The million year-scale cycles of within the same and different rift systems. eccentricity expressed as modulations of Especially notable is the realization that climatic precession already documented the CAMP igneous event (Figure 3) was from Triassic-Jurassic tropical regions of gigantic proportions but of very short (Olsen and Kent, 1999a), has allowed duration (Marzoli et al., 1999; Olsen, 1999b). It is plausible that the CAMP Large their contemporaries, is of obvious Igneous Province (LIP) was related to the intrinsic interest, and sheds light on the development of the extensive suite of origin of major groups. Critically needed seaward-dipping reflectors (SDRs) are high-resolution records to provide bordering the south-central Atlantic (Oh et chronologies for the diverse biotic al, 1995; Talwani et al. 1995). Because this assemblages that have been discovered may very well be the largest continental LIP to date, as well new material from known and it appears temporally associated particular critical episodes of biotic with the Triassic-Jurassic mass-extinction, it change such as the Triassic-Jurassic is critical to understand the links between boundary. these entities, and this requires deep There is now growing evidence that the sampling of the seaward-dipping reflectors Triassic-Jurassic mass extinction was of themselves and the related rifts. Obviously, very large magnitude and very abrupt. the relation between the CAMP, the The cause is as yet unknown as is the seaward-dipping reflectors, and rifting is temporal scale outside the Newark basin. integral to the understanding of the However, very recent work by McElwaine fundamental processes of plate-motion, and et al. (1999) on sections from Greenland the deep Earth. and Sweden shows that the extinction 3) The biotic change in a Hot-House world appears to have been associated with an theme deals with biological patterns at abrupt CO2 increase. Such an increase three scales: global biogeographic patterns of CO2 could have resulted from massive characteristic of the Hot-House world; outgassing associated with the CAMP Triassic-Jurassic evolution; and the flood basalts or even an asteroid impact. Triassic-Jurassic mass extinction. In any According to Zeigler et al. (1993) Hot- case, the House Pangea may have been temporal characterized by a unique phytogeography and with extraordinarily limited equatorial humid geograph zones. High resolution climate and ic phytographic data is needed over a wide framewor swath of geography to allow tests of the k for the efficacy of global climate models under boundary appropriately constrained boundary and its conditions, at appropriate temporal and relationsh spatial scales. ip to the Mammals, lizards, turtles, frogs, CAMP salamanders, dinosaurs and pterosaurs event evolved during the Triassic. All but require the high-resolution sampling that pterosaurs survived both the Triassic- a pole-to-pole coring transect would Jurassic and Cretaceous-Tertiary mass uniquely provide. extinctions (dinosaurs in the form of birds). Understanding the chronology, tempo, and mode of their evolution, as well as that of Science Focus Areas which is the largest of the A main result of the workshop was the logistically accessible basin delineation of six geographic areas in which to provide a climatic record coring could best address the principle dominated by precession, scientific themes. At the present time, the but with some obliquity areas known in enough knowledge to forcing, address biotic proceed fall into three conjugate margin transects and three additional areas of Figure 3: Dimensions of the CAMP igneous interest. These are: 1) Low latitude event at 202 Ma. From Olsen (1999). conjugate margin transect; 2) Mid-latitude change at the Triassic conjugate margin transect; 3) High latitude Jurassic boundary, and conjugate margin transect; 4) Colorado provide a chronology of Plateau; 5) Sicily; and 6) Siberia. tectonic events related to The low latitude conjugate margin transect the volcanic and non would focus on coring targets related to the volcanic margin boundary. Pangean break-up theme, specifically the Complimentary record, but relationship between the CAMP event, the less thick is available in seaward dipping reflectors, and the Morocco and Iberia. Triassic-Jurassic boundary. Off- and The high latitude conjugate transect is onshore southeastern United States is the principally Greenland and northern main area of interest for coring from the Europe. Existing data shows that shallowest areas the seaward-dipping Greenland has a climatic record that has reflectors could be sampled on the obliquity forcing recorded (Clemmensen, continental shelf, to onshore where lavas et al., 1998), and hence cores from connected to the SDRs overlie or are Greenland and the complimentary interbedded with rift basin sedimentary Germanic basin are critical to strata (e.g. South Georgia Rift). The understanding the climatic effects of conjugate margin of Mauritania, Senegal, astronomical forcing in the Hot-House and Mali can provide critical data on the higher latitudes and planetary behavior, CAMP rocks on the surface and in the as well as constraining the Triassic- subsurface. Jurassic boundary in the same regions. A The mid-latitude transect Triassic Germanic basin coring project is comprises the Nova-Scotian already underway (Bachmann, pers. and Newfoundland margin comm.). The workshop stressed and and its conjugate Moroccan- validated the critical role of Iberian counterpart. This magnetostratigraphy in that project. transect straddles the In addition to these three conjugate boundary between volcanic margin transects, the workshop focused and non-volcanic margins. on three other areas. First, while not a Coring was identified as rifting area, the Colorado Plateau needed specifically in the comprises a classic Triassic-Jurassic Fundy basin of Nova Scotia, sequence in which many of the richest faunal assemblages from that period have Argentina) and polar (Australia, been recovered. However, the relationship Antarctica) targets are desirable but that between the stratigraphy of the Colorado further work was needed to identify Plateau and the rifting area remains very specific target areas. controversial, as does the existence of the so called “J1-Cusp” and the amount of ACTION ITEMS rotation of the Plateau itself, which The workshop concluded with the historically have strongly influenced recommendation for five specific short- paleolatitudinal estimates of virtually all of term action items: 1) Propose to Pangea. The workshop concluded that a NSF/ICDP to core East-Greenland; 2) core or cores through the Triassic Jurassic Produce a letter of intent to ODP for sequence on the Plateau as well as off the coring the seaward dipping reflectors and Plateau would resolve these issues. landward targets; 3) Produce a letter of Second, marine sections in Sicily, intent to ODP/ICDP/NSF for coring the particularly Monte Triona and Pizzo Fundy basin of Nova Scotia; 4) Produce Mondelo should provide ideal places for a proposal to NSF to core the Colorado coring to resolve marine/continental Plateau; and 5) Forge linkages to other correlations as well as provide a marine programs, (e.g. German Consortium, record of orbitally forced climate MARGINS, RIDGE). overlapping in time with that of the A www site for viewing a description of continents. Third, polar areas in the Triassic the meeting and its field trips as well as Jurassic specifically Siberia, have the draft report of this meeting is at: continental basins (with abundant coal) in which cores should allow examination of http://www.ldeo.columbia.edu/~polsen polar climate during Hot-House times. /nbcp/pangeaworkshop.html The workshop concluded that high-latitude Southern Hemisphere (e.g. Karoo, Paul E. Olsen*, Dennis V. Kent, and Robert Raeside LDEO, Columbia University, New York An NSF/ICDP Workshop on Scientific Drilling on Lakes Malawi and Tanganyika

October 10-16, 1999 Club Makakola, on the southwestern lakeshore of Lake Malawi

Workshop Report

EXECUTIVE SUMMARY

Introduction During the week of October 10, Africa and Europe. Support for the 1999, a group of 47 scientists, engineers, workshop was provided by the U.S. local institutional representatives, and National Science Foundation funding agency administrators met at Club (Paleoclimate, Continental Dynamics, and Makakola, Malawi, on the shore of Lake Geology and Paleontology programs), and Malawi, to review the prospects for from the International Continental scientific drilling on Lakes Malawi and Scientific Drilling Program. Tanganyika. The meeting was opened by Major topics considered during the the Hon. Harry Thomson, Minister for meeting included reviews of the major Natural Resources and Environmental scientific themes to be addressed through Affairs of Malawi, and was followed by an drilling, roles of local institutions, open discussion of the natural resources engineering and logistical concerns, and of Lake Malawi. Participants included the funding environments within likely representatives from Malawi, Tanzania, target funding agencies. the United States, and 8 other nations in

Workshop Agenda Many of the workshop discussions speakers presented science reviews in the were centered around the current proposal areas of crustal structure and rift basin submitted to the ICDP and NSF for the evolution, paleoclimatology, environmental GLAD800 drilling rig, a lightweight coring background to human origins, system designed for sampling lake basins paleoecology and evolutionary biology, to a total drilling depth of 800-1200 and geochronology and paleomagnetic meters. Administrative, financial and studies in lacustrine basins. Several engineering infrastructure of the GLAD800 breakout sessions provided the concept were considered during this opportunity for international groups to opening session. consider key questions to be addressed Following brief summaries of the during scientific drilling. Summary white existing science programs, several papers on the four main scientific themes are presented following this summary. A Limnological Field Station at Senga Bay 1-day field trip to the Lake Malawi port provided participants with a sense of local facility and shipyard at Monkey Bay, the infrastructure around the lakeshore. container port at Chipoka, and to the

Plenary Sessions Following the science reviews, there Site Survey Data, Engineering and were several plenary discussions covering Logistical Issues, and Funding Conditions the following topics: Roles for Local within Target Funding Agencies. Institutions, Reviews of Seismic Reflection

Roles for Local Institutions Developing opportunities for capacity equipment and instrumentation building within the geosciences community infrastructure at Universities and within in East Africa is a high priority objective of government-supported laboratories. the local institutions that were represented In addition to capacity building, a top at the workshop. The drilling program priority for local governments is to expand should develop a plan for expanding the understanding of the regional geology educational opportunities at various levels, of Lakes Malawi and Tanganyika. In order including training of graduate students at for countries such as Malawi and local universities and abroad, and Tanzania to best manage their natural enhancing professional growth of the resources, it is critical to improve the state present staff of professionals in University of knowledge of the subsurface structure, and government positions. In addition to stratigraphy and lithofacies variability of training, it is important for the project to the lakes of the western branch of the rift explore opportunities for improving the valley.

Reviews of Seismic Site Survey Data Considerable amounts of seismic part of the lake. Since 1992, several reflection data of different type and vintage medium-resolution single-channel seismic have been acquired on Lakes Malawi and surveys have been undertaken over Tanganyika. In the mid-1980's Project selected areas on both lakes. These PROBE acquired about 4500 km of 24- seismic images provide information on the fold seismic reflection data on the two seismic stratigraphy of the lakes to 1-2 km lakes, in reconnaissance grids with line sub-bottom, at a vertical resolution of 1-2 spacing s of 8-16 km. These data show m. These data reveal the complex facies that the lakes are each underlain with geometries evidently inherent on such upward of 5-6 km of syn-rift lacustrine tropical lakes, and reveal that several sediment. In the case of Lake Malawi, unconformities exist in the stratigraphic which has the greatest concentration of section. In the case of Lake Malawi, data, it appears that the sedimentary shallow unconformities produced by section thins from a maximum of 5-6 km in dramatic drops in lake level are observed the northern part of the rift valley to a few in water depths of more than 500 m, hundred m thickness at the southernmost suggesting that it will be necessary to drill in water depths >500 m in order to obtain a continuous stratigraphic record in that lake.

Engineering, logistics, and drilling strategies drill string to 1200 m from 800 m, through Several engineering presentations use of a narrower-diameter drill string. covered the proposed GLAD 800 lake Thus the GLAD rig appears to be drilling rig, Ocean Drilling Project- type adequate for subsurface sampling to drilling tools, and deployment of this depths of several hundred meters in both equipment on a modular barge system Malawi and Tanganyika. ODP with dynamic positioning. The GLAD 800 drilling/sampling tools, including the concept was originally proposed for small- Advanced Piston Corers, are effectively medium lakes, but is also adaptable for off-the-shelf technology and are easily fit large lake drilling, including extending the to the GLAD rig. Adapting local vessels for drilling capability. Given the rapidly changing sea operations is probably the most states on the lakes, this may be the most economical means of providing a drilling advisable choice of positioning platform for a single drilling operation. technology, according to the engineering However it was demonstrated that over team present at the workshop. the lifespan of several large lake projects it Several strategies were discussed for may be cost effective to acquire a modular initial drilling, which will likely be proposed (@C-Float@) barge system to serve as a first for Lake Malawi, on account of its drilling platform on successive lake drilling favorable infrastructure and thorough site projects. Options for positioning the survey geophysical data sets already in- drilling platform included an anchor hand. Since distances across Lake mooring system, dynamic positioning Malawi are significant, it is likely that 2 system, or hybrid system involving a support vessels will be required for combination of dynamic positioning and servicing the drilling platform. Additionally, anchoring technologies. Whereas drilling operations will likely be carried out anchoring/mooring systems are simple on a 24 hour per day, 7 day per week and robust, they are slow to deploy and basis during the favorable weather window require a large anchor-handling tug for (December-March). It is unlikely that the mooring deployment. Dynamic GLAD drilling rig will be able to operate in Positioning Systems involve large up-front sea states greater than 1-2 m, therefore it costs and require careful maintenance and will be necessary to factor in weather oversight during operations, but offer the delays when developing drilling operation greatest flexibility and rapid deployment time lines.

Reviews of funding environments at NSF and ICDP Several presentations considered the fiscal framework. The ICDP will fund up state of funding of the Earth System to 1/3 of total operational costs for any History Program at the U.S. National given drilling program, with the balance of Science Foundation, and at the the funds to be derived from national International Continental Scientific Drilling science agencies. In addition, ICDP is Program. These presentations placed the able to provide additional funding for proposed scientific effort into a realistic ancillary tasks such as downhole geophysical logging. It is expected that the total drilling budget for a 4-site project will be in the vicinity of $2M, USD.

Excursions to scientific staging sites On October 14, we ran an vessels included the S/V Timba (Dept. of excursion to the potential engineering Surveys), the R/V Usipa (Lake Malawi staging sites at Monkey Bay, Chipoka, and Biodiversity Project) and the R/V to the Lake Malawi Biodiversity Project Ndunduma (Dept. of Fisheries). In lakeside facility at Senga Bay, a possible addition, two other vessels were inspected site for core handling and conducting as possible drilling platforms: the barge preliminary whole-core analyses. All three Viphya (52 m), and the container ship sites were observed to be highly suitable. Katundu (~70 m), operated by Malawi In Monkey Bay, local engineers provided a Lake Services. The initial impression of tour of the local shipyard with its machine the engineer from Seacore Ltd., was that ships, slipway, two main piers, and dry- the barge Viphya, with modifications, dock facility. Three possible support would be an adequate drilling platform for vessels were in port in Monkey Bay, and Lake Malawi. seen by the participating scientists. These

Recommendations Several general recommendations to the for Lake Malawi, given its favorable scientific community arose out of the local infrastructure and extensive workshop. seismic and sediment core datasets. • An initial drilling program be proposed • Engineering scoping of possible or 8 site drilling program. A four-site platforms should continue. drilling program would include 1) a Cost/benefit analyses should be southern basin site that would sample carried out on platform options the southern lake/ southern latitude including 1) modification of the existing response to paleoclimate change, barge Vipyha on Lake Malawi and 2) provide nearshore sequences for acquiring a modular C-Float type evolutionary biology studies and also barge. This should be completed serve as an initial test site for coring within the context of a single Lake operations; 2) a central basin site that Malawi program, and alternatively, will penetrate through the Bruhnes- using a scenario that includes drilling Matayama paleomagnetic reversal and both Lake Malawi and Lake provide an undisputed chronology for Tanganyika. the existing stratigraphic framework, • A local planning committee be and 3) two northern basin sites that established for prioritizing local needs. sample the rich upwelling regions of • A European scientific participant the Livingstone Basin, along an offset committee be establish to explore drilling transect to extend the record avenues of additional support from back beyond the Pleistocene. In an 8 European science agencies. site scenario, the offset transect would • Likely scenarios for a Lake Malawi be extended to include an additional 3- drilling program include proposals for 4 4 sites to provide a record of continuous stratigraphic section back site survey activity on Lake through the Pliocene. Tanganyika. Because of the greater • Following final agency decisions on depth and volume of Tanganyika, it the GLAD 800 proposal to ICDP/NSF, was likely to have been a much more consult with agency program substantial lake than Malawi during the managers and DOSECC on the best severe arid intervals of the proposal framework for the project. Pleistocene. • Explore funding options for additional

Thematic Science Summaries

The following pages contain four separate Studies, Evolutionary Biology, and thematic summaries covering areas of Environmental Background to Human Paleoclimate Studies, Basin Evolution Origins

Paleoclimate Studies

The large lakes of the East African Rift glacial-interglacial timescale variations Valley are unique among the large lakes in wet and dry conditions, and how of the world in terms of their sensitivity to have these varied over time? climate change and their long, continuous, - How has interannual African climate high-resolution records of past climate variability changed in association with change in the tropics. The paleoclimate longer-term climate variations? group identified three main questions to be - What are the dominant interannual addressed by deep drilling in Lake Malawi: modes of variability (ENSO, NAO)? - How have these modes changes in - What is the climatic linkage between association with changes in African tropical Africa and the high latitudes at climate? orbital and longer-period timescales? - What is the long-term evolution of - Did tropical African climate tropical East African climate? predominantly respond to changes in - What is the dominant Milankovitch low-latitude precessional insolation frequency back through time? i.e. do (23-19 kyr) or high-latitude ice volume we see a shift from the present day (100 kyr and 41 kyr) forcing? 100 ka dominance to 41 ka dominance - Has Lake Malawi always responded to to 21 ka dominance, as observed in southern hemisphere insolation the marine record? forcing, as data for the period since - In this region of tropical Africa, do we the last 40 ka suggest? see a significant change in vegetation - Are high-frequency climate variations as the Earth shifted from a 41-ka world (analogous to Dansgaard-Oeschger or to a 100 -ka world? Heinrich events) superimposed on - Elaboration: What is the climatic linkage between tropical Africa and the high-latitudes?

Terrestrial and marine records of and the large lakes to the north (Finney subtropical African paleoclimate variability and Johnson, 1991; Finney et al., 1996; during the late Pleistocene document the Johnson, 1996). Such regional variability dual but separate influences of high- and can only be detected by drilling the low-latitude processes (deMenocal et al., individual lakes across a latitudinal 1993; deMenocal, 1995; Clemens et al., gradient of the African continent. 1996). The evolution of African climate African paleoclimate variability during over the last five million years reflects the late Pleistocene also exhibited strong changes in the relative influence of these millennial-scale variability, also associated end-member climate forcing factors. Prior with changes in high-latitude temperature to the onset of Northern Hemisphere changes. In the North Atlantic this glacial cycles near 2.8 Ma, African climate variability consists of ~1.5 ka Dansgaard- evidently responded primarily to variations Oeschger cycles, which are bundled into in monsoonal circulation due to orbital longer, larger amplitude Heinrich events, changes in low-latitude insolation. which recur every 5-10 ka (Bond et al., Following the growth of Northern 1993). These same millennial-scale Hemisphere glacial cycles after 2.8 Ma, variations are also observed in subtropical African climate was evidently subjected to Africa (e.g. Younger Dryas in Lake Albert periodic and large amplitude cool, dry – Beuning et al., 1998 and in Lake Magadi cycles which were in-phase with high- – Roberts et al., 1994), and in marine latitude glacial maxima. The coupling sediments from the Atlantic Ocean and between high- and low-latitude climate Arabian Sea, again documenting the close increased toward the present, with linkage between high- and low-latitude significant increases in the amplitude of climates, although the causal mechanisms glacial arid cycles in subtropical African of this linkage remain obscure. occurring at ~1.7 Ma and ~1.0 Ma Finally, well-dated, detailed (deMenocal, 1995). These observations reconstructions of African paleoclimate are based on ODP cores from the deep variability indicate that the climate sea off Africa, and reflect a broad-scale transitions themselves are extremely integration of signals from across much of rapid, with large transitions occurring the African continent. However there are within decades to centuries (Gasse and regional differences in climate evolution VanCampo, 1992; Johnson et al., 1996; within east Africa on orbital time scales. deMenocal et al., 1999; Street-Perrott and One example of this is the out-of-phase Perrott, 1990). relationships in lake level between Malawi

Are high-frequency climate variations (analogous to Dansgaard-Oeschger or Heinrich events) superimposed on glacial-interglacial timescale variations in wet and dry conditions?

Grounds for anticipating centennial- to Holocene conditions in Lake Malawi and millennial-scale variations are provided by other lakes of tropical Africa. records of the transition from LGM and Geomorphological evidence (strandlines, deltas, incised fluvial channels, etc.) and ended abruptly. The transition to drier indicate generally low-lake or dry basin conditions that led to early Holocene low conditions at the LGM and rising levels levels in L. Malawi seems to have from 15 to 12 ka in equatorial Africa. This occurred within a few hundred years rising trend was interrupted by a number around 9.8 14C ka (Ricketts and Johnson, of short-lived reversals, which are also 1996), while the period of particularly high reflected in palynological records and early to mid-Holocene levels in most north several geochemical and biological African lakes ended equally abruptly palaeolimnological proxies preserved in around 4.0 14C ka. Some events seem to lacustrine sediments. These indicate be local equivalents of high-latitude regional excursions in temperature, P/E climatic excursions, such as the Younger balance or wind-driven vertical mixing of Dryas and "8.2 ka event" (Alley et al., the water bodies. Interglacial conditions, 1997), but others have as yet no as reflected in Holocene proxy records, recognized equivalents outside Africa. also contain evidence of short-term climatic reversals. Some of these began

How does interannual African climate variability change in association with longer- term climate variations? varved from the present back to about Laminated sediments recovered in box 2000 ybp, and between 6500 and 10000 cores and multi-cores from northern Lake C-14 ybp. Within these time windows, Malawi consist of alternating bands of varve thickness analyses will provide diatom ooze (light laminations) and silty insight into the existence of climate cycles clays (dark laminations), representing the on an interannual scale. Will the ENSO- dry, windy season (June-September) and scale cycles also dominate the early the warm, rainy season (December- Holocene record or will the early Holocene March), respectively. Pb-210 dating of climate record be devoid of such several cores has demonstrated that the variability, as appears to the case in the laminations are varves. Similar annually- Peruvian Andes (Rodbell et al., 1999). laminated sediments occur in deep water And with deep drilling in this part of Lake cores from Lake Tanganyika. The Malawi, will we find similar inter-annual thickness of the light layers and dark variability in the varved record further back layers can be measured quite precisely in time? using computerized image enhancement While short, discrete intervals of piston and analysis tools. Presumably, the cores from sites further south in Lake thickness of the light layers is linked to Malawi are laminated, the sediments are upwelling intensity and diatom mostly homogeneous, even though they productivity, whereas the thickness of the accumulated in anoxic deep waters. This dark layers is a proxy for annual rainfall is probably due to long sediment transport intensity. Spectral analysis of lamination pathways from the major rivers in the thickness variability over the past 300 north, resulting in a blurring of seasonal years reveals significant cyclicity at ENSO variability as the sediments settle, get re- frequencies (Barry, in prep). suspended and ultimately arrive at their The sediments in the north basin of final burial site. Lake Malawi are almost continuously What is the long-term evolution of tropical East African climate?

Evolution of the Milankovitch climate seismic reflection records over the last half spectrum has been observed in both the of the Pleistocene (Scholz, 1995; Lezzar marine record (deMenocal and et al., 1996). These acoustic facies Bloementhal, 1996) and the record of couplets consist of hemipelagic high-stand continental lakes (Williams et al., 1998) deposits and coarse-grained lowstand during the last three million years. The deposits, and are accumulating in both first major change in both records occurs lake basins with a frequency of about 100 between 3.0 and 2.5 Ma, when power in kyr (Figure 1). Drilling in Lakes Malawi the obliquity band (41 ka) increases at the and Tanganyika will test this depositional expense of power in the precessional model and constrain both the timing and band (21 ka). A second major change phasing of these coupled occurs at about one million years ago highstand/lowstand packages. We will when power in the eccentricity band (100 determine if changes in the cyclicity of the ka) increases at the expense of the sedimentary record of these lakes are obliquity band. Pronounced depositional similar to those changes observed in the cyclicity, produced by high-amplitude marine record. changes in lake level, is observed in both the Lake Malawi and Lake Tanganyika

Figure 1. Acoustic Facies Couplets observed on central L. Malawi seismic profile, suggesting 100 kyr lake level and depositional cyclicity.

Geochronology: In addition, there are a series of We are confident that the suite of carbonate-rich horizons deposited during geochronometers available in Lake Malawi periods of evaporative concentration of sediments will provide sufficient control to lake waters. These have the potential to develop a rigorous age-depth model. be dated by uranium series techniques Magnetostratigraphic and low-field- (isochron method, e.g. Bischoff and susceptibility measurements will provide Fitzpatrick, 1991), developing the backbone of our geochronological chronologies for the last 400 ka. Finally, work. These the numerous volcanic ash layers present, techniques have been applied particularly in the northern basin, provide successfully in other ancient lakes (i.e. opportunities for Ar-Ar dating. This should Lake Baikal). This record will be be possible for sediments older than 25 calibrated using a series of horizons dated ka, given the abundance of crystalline by a range of independent techniques. material in some of the young ash layers Reliable radiocarbon chronologies using in the northern basin. In addition, trace woody material and charcoal exist for the element fingerprinting of these ash layers last 20 ka. We anticipate that this will provide a means of developing approach will provide age control to 40 ka. stratigraphic linkages among cores.

References

Alley, R.B., P.A. Mayewski, T. Sowers, M. deMenocal, P.B., and J. Bloemendal, Plio- Stuiver, K.C. Taylor, and P.U. Clark, Pleistocene subtropical African climate Holocene climatic instability: A prominent, variability and the paleoenvironment of widespread event 8200 yr ago, Geology, hominid evolution: A combined data-model 25 (6), 483-486, 1997. approach, in Paleoclimate and Evolution Barry, S., in prep. The high resolution With Emphasis on Human Origins, edited stratigraphy of sediment cores from the by E. Vrba, G. Denton, L. Burckle, and T. northern basin of Lake Malawi: varves, Partridge, pp. 262-288, Yale University turbidites and tephras. M.S. thesis, Water Press, New Haven, 1995. Resource Sciences, University of Minnesota. Finney, B. P. and Johnson, T. C., 1991. Bond, G., W.S. Broecker, S. Johnsen, J. Sedimentation in Lake Malawi (East McManus, L. Labeyrie, J. Jouzel, and G. Africa) during the past 10,000 years: a Bonani, Correlations between climate continuous paleoclimate recod from the records from North Atlantic sediments and southern tropics. Palaeo-3, v. 85, 351-366. Greenland ice, Nature, 365, 143-147, Finney, B. P., Scholz, C. A., Johnson, T. C., 1993. Trumbore, S. and Southon, J., 1996. Late deMenocal, P.B., Plio-Pleistocene African Quaternary lake level changes of Lake Climate, Science, 270, 53-59, 1995. Malawi. In Johnson, T. C. and Odada, E. deMenocal, P.B., W.F. Ruddiman, and E.M. O. (eds.), The Limnology, Climatology and Pokras, Influences of high- and low- Paleoclimatology of the East African latitude processes on African climate: Lakes: Gordon and Breach, Amsterdam, Pleistocene eolian records from equatorial 495-508. Atlantic Ocean Drilling Program Site 663, Gasse, F., V. Lédée, M. Massault, and J.C. Paleoceano., 8 (2), 209-242, 1993. Fontes, Water level fluctuations of Lake Tanganyika in phase with oceanic high-resolution reflection seismic data and changes during the last glaciation and piston core evidence, Basin Research 8: deglaciation, Nature, 342, 57-59, 1989. 1-28. Gasse, F., R. Téhet, A. Durand, E. Gibert, and Ricketts, R. D. and Johnson, T. C., 1996. Early J.C. Fontes, The arid-humid transition in Holocene changes in lake level and the Sahara and Sahel during the last productivity in Lake Malawi as interpreted deglaciation, Nature, 346, 141-146, 1990. from oxygen and carbon isotopic Gasse, F., and E. Van Campo, Abrupt post- measurements of authigenic carbonates. glacial climate events in West Asia and In Johnson, T. C. and Odada, E. O. (eds.), North Africa monsoon domains, Earth and The Limnology, Climatology and Planet. Sci. Lett., 126, 435-456, 1994. Paleoclimatology of the East African Johnson, T. C., 1996. Sedimentary processes Lakes: Gordon and Breach, Amsterdam, and signals of past climatic change in the 475-493. large lakes of the East African Rift Valley. Rodbell, D.T., G.O. Seltzer, D.M. Anderson, In Johnson, T. C. and Odada, E. O. (eds.), M.B. Abbot, D.B. Enfield, and J.H. The Limnology, Climatology and Newman, An ~15,000-year record of El Paleoclimatology of the East African Niño-driven alluviation in southwestern Lakes: Gordon and Breach, Amsterdam, Equador, Science, 283, 516-520, 1999. 367-412. Scholz, C.A., 1995, Deltas of the Lake Malawi Lezzar, K.E., Tiercelin, J.-J., De Baptist, M., Rift, East Africa: Seismic Expression and Cohen, A.S., Bandora, T., Van Exploration Implications, AAPG Rensbergen, P., Le Turdu, C., Mifundi, BULLETIN, v. 79, p. 1679-1697. W., and Klerx, J., 1996, New seismic Street-Perrott, F.A., and R.A. Perrott, Abrupt stratigraphy and late-tertiary history of the climate fluctuations in the tropics: the north Tanganyika basin, East African Rift influence of Atlantic Ocean circulation, Nature, system, deduced from multichannel and 343, 607-612, 1990.

Basin Evolution Studies

Lakes Malawi and Tanganyika are 1999) to deep-crustal control of among the largest Aclosed@ sedimentary extensional deformation and associated systems on earth, and hence are ideal vertical movements that impact regional sites for evaluating processes of basin climate. There are three main sets of evolution. Their stratigraphic record questions to be considered under the contains a rich history of interplay between framework of Basin Evolution: Chronology surface, near-surface, and crustal and Active Tectonics, Lithofacies processes ranging from climatic forcing of Calibration, and Thermal Structure. sediment loadings (e.g. Soreghan et al.,

I. Chronology and Active Tectonics footwall uplift and denudation and Using dated drill cores, extensive catchment evolution (e.g. van der Beek et seismic reflection grids (e.g. Rosendahl, al.,1998), we can generate well- 1987; Scholz, 1995), and information on constrained models of sediment mass and flux rates unavailable from other expand the chronology determined sedimentary systems. In order to from the cores into the seismic accurately study tropical paleoclimate reflection grid.) history and evolutionary biological records • Quantify rates of footwall uplift and on a time scale of 10-1000 kyr it is associated subsidence in the vicinity of necessary to determine the the drill core, and assess the morphotectonic boundary conditions for episodicity of these rates and their the rift basins. Additionally, a well- sedimentary response. constrained basin chronostratigraphy will • Active tectonics controls the allow us to assess with high temporal development of the watershed of the precision the evolution of linked fault basin, at the regional and local scale. systems (e.g. Anders and Schlische, We intend to quantify denudation rates 1994) within the basin at different scales in and the response time of the space and time. uplift/denudation/sedimentation system (e.g. Foster and Gleadow, The main question: What are the 1993). rates of fundamental basin-forming and • Changes in the basin drainage basin-filling processes (e.g. subsidence, networks will be characterized through heat flow, extension, margin uplift, sediment provenance studies, and sediment supply, lake level change, reflect forcing by tectonic and climatic sediment compaction) in continental rifts processes on the scale of 10 kyr to 5 and how episodic or continuous are these myr. processes? In order answer this question, • Improve models of sediment flux and we set the following goals: mass balance in continental extensional basins. GOALS • Assess the development of • Establish the chronostratigraphy of the topographic highs and determine their sedimentary section. Place the current impact on local climatic and sequence stratigraphic framework, depositional conditions. determined from seismic reflection data, into a rigorous TOOLS chronostratigraphic context. (i.e. • Radiocarbon, paleomagnetics, 3. Cosmogenic exposure age-dating tephrachronology (Ar-Ar), and U-Th as for estimation of denudation rates our first-order dating techniques. and sediment transport times • Physical properties measurements of 4. GPS campaigns for estimating continuous core and down-hole instantaneous extension rates geophysical data to correlate drill 5. Volumetric modeling of basin infill cores and seismic reflection data sets. using DEM=s and seismic • Expand basin evolution studies reflection data beyond the borehole using the 6. Construction of temporally following techniques: calibrated balanced-cross sections, 1. Fission track thermochronology to determine rates of extension (e.g. Foster and Gleadow, 1993) and subsidence 2. U-Th-He thermochronology A stratigraphic test of the major part of provide the principal basis for renewed sedimentary section (through the capacity-building in the East African Pliocene) in these lakes is the highest regional geoscience community. priority for local institutions, and will

II. Lithofacies calibration, Sedimentology and Sedimentary Geochemistry

The first-order indicator of Deriving the three-dimensional environmental change in the Lake Malawi variability of depositional facies in rift and Lake Tanganyika rift basins is basins is fundamental for extracting sediment lithology (texture and paleoclimate and deformational histories. composition) (Soreghan and Cohen, 1996; This 3-D geometry is well-established from Soreghan et al., 1999; Wells et al, 1999). existing seismic reflections data. However High-amplitude and high-frequency shifts the seismic facies framework must be in lake water levels exert extreme forcing calibrated using continuous sediment on sediment character (Scholz and cores, and down-hole geophysical data. Rosendahl, 1988; Scholz et al., 1990); this is accomplished through changes in base Principal goals are to : level, sediment supply, catchment area - Calibrate and refine existing lithofacies conditions, and limnological and biotic and sequence stratigraphic models for boundary conditions. Rapid facies lacustrine rift basins based on variations, both laterally and vertically are continuous sediment cores, and down- the paradigm in these basins. hole geophysical data. - Characterize and calibrate the The main question: What are the distinctive acoustic facies couplets principal controls on the deposition of the observed in reflection records and main sedimentary facies in tropical rift determine the timing of the observed basins, what are the first-order cyclicity. characteristics of these lithofacies, and - Quantify organic matter content both how do they accumulate in space and down-core and spatially, around the time? basin, and determine the origin of the organic matter in space and time. - Geochemical characterization of the - Assess the diagenetic history of the sediments, with respect to provenance sediments as a function of lake water and diagenetic processes chemistry and geothermal conditions.

III. Thermal Structure of the Rift Basin

The main question: In this project, we propose to use new What is the nature of heat flow across heat flow observations obtained from the the Lake Malawi rift basin, and how has drill holes in Lake Malawi to critically the thermal history impacted the evolution evaluate models for the structural of extensional faults in the rift basin. development of rift faults. Although there is a large volume of scientific literature on continental rifting, substantial gaps still remain in our understanding of how Degens et al., 1973), but the uncertainties continental rifts form and evolve associated with these measurements are structurally. In particular, little is known so large (>50%) that the data provide only about fault growth during the earliest weak constraints the thermal structure of stages of rifting, in part because fault the rifted lithosphere. Nonetheless, they growth is directly linked to the thermal and suggest that crustal temperatures beneath mechanical structure of the lithosphere the rift are elevated, while most fault (Cowie, 1998; Jackson and Blenkinsop, models assume that the crust is cold and 1997; Hayward and Ebinger, 1996; brittle (Cowie, 1998; Jackson and Ebinger et al., 1999; Scholz and Blenkinsop, 1997; Hayward and Ebinger, Contreras, 1998), for which we have few 1996; Ebinger et al., 1999; Scholz and constraints. Heat flow observations Contreras, 1998). The proposed drill provide a first-order constraint on the holes in Lake Malawi would afford us an thermal structure of the lithosphere, and opportunity to make high quality without such constraints it is not easy to conventional heat flow determinations that assess the mechanical state of the would indicate to what extent the rifted lithosphere at the time of rifting. crust is thermally modified. While heat flow measurements have Heat flow observations can be made in been made in other areas of East Africa, the drill holes by logging temperatures they either come from unrifted parts of the several times after drilling is complete. East African Plateau (Nyblade et al., 1990, From the multiple measurements, the Nyblade, 1997), or else from regions of the disturbance to the thermal field around the Kenya rift where the crustal thermal drill hole can be determined and an regime has been hydrologically disturbed estimate of the equilibrium temperatures (Whieldon et al., 1997). Marine type heat can thus be obtained. In addition to flow measurements were made several temperature measurements in the drill decades ago in Lakes Malawi, holes, core samples will be needed to Tanganyika, and Kivu (Von Herzen and measure thermal conductivities. Vacquier, 1967; Degens et al., 1971;

References Anders, M. H. and Schlische, R.W., an East African rift lake, Geol. Runsch., Overlapping faults, intrabasinal highs, and 62, 245-277, 1973. the growth of normal faults, Journal of Ebinger, C.J., J.A. Jackson, A. N. Foster, and Geology, v.102, 165-179, 1994. N.J. Hayward, Extensional basin geometry Cowie, P.A., A healing-reloading feedback and the elastic lithosphere, Phil. Trans. R. control on the growth rate of seismogenic Soc. Lond. A, 357, 741-765, 1999. faults, J. Struct. Geol., 20, 1075-1087, Foster, D.A.and Gleadow, A.W., Episodic 1998. denudation in East Africa; a legacy of Degens, E.T., R.P. Von Herzen, and H.K. intracontinental Wong, Lake Tanganyika: water chemistry, tectonism, Geophysical Research sediments and geologic structures, Letters, v. 20, n. 21, p. 2395-2398, 1993. Naturwissenschaften, 58, 229-240, 1971. Hayward, H., and C. Ebinger, Variations in the Degens, E.T., R.P. Von Herzen, H.K. Wong, along-axis segmentation of the Afar rift W.G. Denser, and H. W. Jannasch, Lake system, Tectonics, 15, 244-257, 1996. Kivu: structure, chemistry and biology of Jackson, J. and T. Blenkinsop, The Bilila- Soreghan M.J., and Cohen, A.S., Textural and Mtakataka fault in Malawi: an active, 100 compositional variability across littoral km long normal fault segment in thick segments of Lake Tanganyika: The effect seismogenic crust, Tectonics, 16, 137-150, of asymmetric basin structure on 1997. sedimentation in large rift lakes, AAPG Nyblade, A.A., H.N. Pollack, D.L. Jones, F. Bulletin, 80, 382-409, 1996. Podmore, and M. Mushayandebvu, Soreghan, M.J., Scholz, C.A., and Wells, J.T., Terrestrial heat flow in east and southern Coarse-grained deep-water sedimentation Africa, J. Geophys. Res., 95, 17371- along a border fault margin of Lake 17384, 1990. Malawi, Africa: Part 1- Seismic Nyblade. A.A., Heat flow across the East Stratigraphic Analysis, Journal of African Plateau, Geophys. Res. Lett., 24, Sedimentary Research, V 69, p 832-846. 2083-2086, 1997. Wells, J.T.,, Scholz, C.A, and Soreghan, M.J. Rosendahl, B.R., Architecture of continental Processes of sedimentation on a rifts with special reference to East Africa, Lacustrine border fault margin: Reviews of Earth and Planetary Sciences, Interpretation of cores from lake Malawi, 15, 445-503, 1987. East Africa. Journal of Sedimentary Scholz, C.A., Deltas of the Lake Malawi Rift, Research, 69, p. 816-831. East Africa: Seismic Expression and ExplorationWheildon, Implications, J., P. Morgan, AAPG K.H.BULLETIN Williamson,, v. 79, T.R. p. 1679-1697, 1995 Scholz, C.A., Rosendahl, B.R. and Scott, D.L. Evans, and C.A.Swanberg, Heat flow in Development of Coarse-grained Facies in the Kenya rift zone, Tectonophysics, 236, Lacustrine Rift Systems: Examples from 131-150, 1997. East Africa. GEOLOGY, v. 18, pp. 140- Van der Beek, P. Mbede, E., Andriessen, P., 144, 1990. and Delvaux, D., Denudation history of the Scholz, C.A. and Rosendahl, B.R., Low Lake Malawi and Rukwa Rift Flanks, (East Stands in Lakes Malawi and Tanganyika, African Rift System) from apatite fission East Africa, Delineated with Multifold track thermochronology, Jrnl. Afr. Earth Seismic Data. SCIENCE, V. 240, pp. Sciences, 26, 363-385, 1998. 1645-1648, 1988. Von Herzen, R.P., and V. Vacquier, Terrestrial Scholz, C.H., and J.C. Contreras, Mechanics heat flow in Lake Malawi, Africa, J. of continental rift architecture, Geology, 26, Geophys. Res., 72, 4221-4226, 1967. 967-970, 1998.

EVOLUTION of BIODIVERSITY and ECOLOGY in ANCIENT LAKES: BIOLOGICAL OBJECTIVES of DEEP DRILLING in LAKES MALAWI and TANGANYIKA

The Biological Significance of Lakes Malawi And Tanganyika

Lakes Malawi and Tanganyika are evolutionary and ecological changes in aquatic island systems of elevated their biota at time scales of decades, over endemic biodiversity, unparalleled for their hundreds of thousands to millions of potential to test hypotheses of years. comparative evolution on large scales. Despite their long histories and The sedimentary record of these lakes geological similarities, the patterns of offers us the opportunity to resolve both diversity and genetic differentiation of the biota differ dramatically between Lakes divergent lineages (Michel, 1994; Park and Malawi and Tanganyika. Both lakes were Downing, in press). The living colonized by cichlid fishes, thiarid prosobranch gastropod fauna of Lake gastropods and ostracode crustaceans, Malawi has undergone only limited but these exemplar taxa currently have differentiation and few if any endemic contrasting aspects in the two lakes. ostracodes are reported from this lake Approximately 1000 fish species are (Martens, 1994; Michel, 1994). estimated to have evolved within the Understanding the history of the cradle of Lake Malawi, which is Malawi and Tanganyika radiations, their approximately 10% of all freshwater fish similarities and differences, represents an species in the world. Despite their extraordinary opportunity for evolutionary astonishing multitude, these species biology. encompass a rather modest degree of In these lakes we have a unique molecular genetic and morphological opportunity to investigate the dynamics of change (Kornfield, 1978; Moran et al., evolutionary and ecological change. 1994; Parker and Kornfield, 1997). The Patterns of speciation, the origin of major fishes in Tanganyika are genetically and morphological evolution, and the origin of morphologically much more diverse than major reorganizations in community those in Malawi (Sturmbauer and Meyer, structure can all be investigated in a 1992, 1993)., yet total only 300 species comparative setting in these two lakes, in (which is still more than all the species in the context of high resolution, long the 10s of thousands of North American stratigraphic records. Paleoenvironmental, lakes combined). In Lake Tanganyika, tectonic and climatic reconstructions about 240 out of 250 species of obtained from other components of this prosobranch gastropods and ostracode drilling program will provide the context for crustaceans are unique to that lake, and interpreting those dynamics. like the cichlid fish, form numerous distinct,

MAJOR QUESTIONS TO BE ADDRESSED IN EVOLUTIONARY BIOLOGY AND PALEOECOLOGY

For our purposes of evolutionary small (easily obtained in cores), can be studies the most promising groups of fossil identified to species level as fossils, and organisms are the gastropod molluscs and provide interesting targets for evolutionary ostracode crustaceans. In addition to their studies. preservation potential these animals are

Timing of diversification of the endemic radiations in Lakes Malawi & Tanganyika.

We propose to determine the duration more frequent resetting of its evolutionary and extent of evolutionary radiations in clock than the biota of Lake Tanganyika, target groups of readily preserved fossil as a result of more frequent and profound lineages. We will test the hypothesis that disruption of the Lake Malawi ecosystem the Lake Malawi biota has undergone by climatically-driven lake level fluctuations and perhaps salinity crises. As a result of its second phase in Lake Tanganyika we its lesser depth and simpler tectonic will compare these records with the more configuration (fewer basins), habitat diverse Lavigeria lineage, a related thiarid stability is predicted to have been much gastropod, and the Gomphocythere less in Lake Malawi and the lake may lineage for ostracodes (Michel in press; have frequently dried, eliminating nascent Park and Downing, in press). In both lakes evolutionary novelty, similar to Lake we will compare the records of Victoria in the Late Pleistocene (Johnson evolutionary change with our developing et al., 1996). The more complex basin understanding of lake level, climate and configuration and deeper waters of Lake tectonic history, to determine if more Tanganyika provided more time and less frequent and/or extensive desiccation and severe perturbations to the evolving biota, disappearance of habitat is characteristic stimulating greater levels of morphological of Lake Malawi, and if those changes are diversification and genetic differentiation. linked to extinction events. Furthermore in From cores in Lake Malawi we will Tanganyika we predict that the evolution document changes in the Melanoides of multiple basins of the lake (whose age gastropod lineage through time, as this will also be determined by drilling) is linked group currently includes 12 extant, to episodes of diversification (e.g. Michel endemic species (Brown, 1994). Similarly, et al., 1992; Meyer et al., 1994; Cohen et the Gomphocythere ostracode lineage will al., 1997). be a focal taxon. When drilling moves to

Rates of diversification in ancient lakes

Recent phylogenetic studies of living molluscs and crustaceans. We further fish and molluscs suggest a “burst-like” predict that these bursts will be linked to pattern of initial radiation in the faunas of significant episodes of tectonic or climatic Lakes Malawi and Tanganyika (Meyer et change (i.e. Verheyen et al., 1996), al., 1994; Michel, in press; West and analogous to the rapid speciation inferred Michel, in press). We will test whether to have occurred in Lake Victoria benthic fossil lineages support an subsequent to its Pleistocene desiccation, interpretation of rapid morphological during its > innovation and species divergence among

Evolutionary escalation and predator/prey arms races

Present-day Lakes Malawi and marine snail morphologies (West et al., Tanganyika display strikingly different 1991; West and Cohen, 1996). The patterns of predator-prey interactions in gastropods deposit multiple cross-lamellar their benthic and demersal habitats. In layers (up to 4) of skeletal carbonate, Lake Tanganyika, endemic crabs and fish strengthening the shell in a fashion are specialized for effective predation, and analogous to plywood. Furthermore, the natural selection has resulted in heavily Lake Tanganyika gastropods can repair armored gastropods, remarkably their shells after attack (a trait rarely seen convergent on thick-shelled, spinose in freshwater snails, but again common in marine ones). None of these We hypothesize that the modern characteristics or interactions are well extreme biotic differences between the two developed in Lake Malawi (Brown, 1994). lakes reflects different ages of their The question of why these two similar respective aquatic ecosystems, Malawi lakes have undergone such radically being the younger, less co-evolved system different histories of predator-prey and Tanganyika the older. We can test this interactions can only be answered through hypothesis through the acquisition of shell a detailed analysis of the history of thickness, repair and cross lamellar count character acquisition for the heavily- data. Knowing the age of changes in each shelled molluscs in modern Tanganyika, of these factors will allow us to determine and a comparison of this history with that their rates of change. Furthermore, age of the fossil molluscs of Lake Malawi. It is data can be superimposed on existing entirely possible that similar bouts of phylogenies that map out the acquisition of coevolutionary “arms-races” have occurred multiple cross lamellae, telling us what the in the past in either lake, only to be pattern of evolution of these characters eliminated through periodic extinction has been (e.g. West and Cohen, 1996). events. Repeated episodes of escalatory We can then use the shell repair data to coevolution among fish species have been determine long-term predation intensity, inferred from the fossils of Pliocene Lake testing whether the unusual mollusc shell Idaho, but the timing on rates of evolution characters in Tanganyika are part of a of these complexes is poorly constrained coevolved complex. Lake Tanganyika (Smith, 1987). Viviparid gastropods exhibit promises a clearer documentation of anti-predatory morphologies, coincident actual rates of predator-prey coevolution with increased species diversity, through than any other biotic system from any several sedimentary cycles of the Lake environment. In Malawi our interest will be Edward-Albert fossil deposits, but lose to see if earlier episodes of escalation both diversity and armor in the relict living have occurred during periods of lake-level fauna (van Damme & Pickford, 1999). stability, subsequently eliminated in the modern lake fauna.

q Community response to environmental change at varying time scales

Ecologists have grappled with the contrast, paleoecological studies typically question of how communities change over cover much longer intervals but are poorly time, whether as coordinated groups of resolved in time. In Lake Tanganyika organisms responding en masse through “long-term” ecological research on cichlid invasion and local extinction, or through fish communities, spanning about a individualistic shifts of species’ relative decade, supports a model of community abundances. This problem has been a coordination and stability, at odds with particularly thorny issue because of our lower resolution but longer duration inability to sample community dynamics at ostracode community data within the same a wide and continuous range of time lake (Hori et al., 1993; Cohen, in press). scales. On the one hand, neo-ecological Are these contradictions real (resulting studies are generally performed with an from differences between organismal abundance of data but over time intervals groups or habitat) or are they a result of encompassing few generations. In sampling at very different time scales? The sedimentary records of Lakes understanding of how adjacent habitat Malawi and Tanganyika allow sampling of patches and populations interact with one ecological change at annual to decadal another over time. In Lakes Malawi and resolution, over time intervals spanning Tanganyika we have the possibility of hundred of thousands to millions of years, inferring these patch interactions over very thereby addressing this important long time periods. question. Analysis of change at varying We can attack the problems outlined time scales through a series of cores will above using ostracode, diatom and allow us to see how our perceptions of palynological records. The former two data change are affected by our scale of sets will give us records of the tempo of observation, an important question for community change and patch dynamics in almost all of community ecology. We can the lakes, and through comparison extend our analysis from the temporal to between the lakes, an understanding of the spatial scale through the analysis of how community change relates to larger- adjacent cores (in our proposed drilling scale differences in lake history. The program three cores will be routinely pollen record will allow us to see collected at each coring site, to provide vegetational response to shifting climatic assurance of complete core recovery). variables, and whether these responses This is also important because much differ between the subequatorial climate of current speculation about community the Lake Malawi basin and the equatorial stability or instability rests on an climates of the Tanganyika basin.

Regional Research Questions

In addition to the questions outlined Downing, in press, West and Michel, in above, all of which have broad press). This hypothesis may be testable significance for evolutionary ecology in with data to be acquired in the combined general, issues of more regional concern Tanganyika/Malawi drilling program, in can be tested with fossils in the Malawi combination with earlier-collected outcrop and Tanganyika cores. The biogeography data from the Kaiso Rift and Lake Rukwa. of dispersal among freshwater ecosystems of the African Great Lakes can be Another important regional question for addressed for the taxa amenable to core paleobiology is the role that external analysis (primarily ostracodes and forcing mechanisms have played in molluscs, since fish are rarely preserved constraining the phylogeny of ostracodes well enough to identify to species level). and molluscs. Through close collaboration Some data suggests that Lake Tanganyika with our colleagues in paleoclimatology has acted as a long-term crucible or and tectonic interpretation of the cores we refugium during periods of severe hope to be able to provide realistic and dessication in other lake systems, and that detailed scenarios of evolution within the faunas of the other African Great different sub-basins of the lakes, relating, Lakes are derived from within for example, the establishment of “Tanganyikan” clades (Meyer et al. 1994; particular barriers to dispersal with Van Damme and Pickford, 1999; Park and particular diversification events. The endemic fauna as a tool for paleoclimatic and tectonic data acquisition

Fossil organisms can be powerful tools molluscs have been a mainstay of for paleoenvironmental and chronostratigraphy in the ancient chronostratigraphic interpretation. Ostra- Cretaceous rift lake basins of Brazil and codes, molluscs and diatoms have all West Africa, a testimony to their rapid been widely used to infer composition and evolution in those systems, so similar in concentration of water masses, water many respects to the large rift lakes of depths and habitat zonation. Carbonate in Africa. Although these are not, in our view, ostracode and mollusc shells can also be fundamental questions of ecology and analyzed for stable isotopes and minor evolution, they are nevertheless of critical elements, again for the purpose of importance to the drilling program as a paleoenvironmental and paleoclimatic whole. interpretation. And finally, ostracodes and

CONSTRAINTS ON DRILLING TARGETS

As we have alluded to above, not all the additional effort of obtaining such lacustrine organisms are going to be records well worthwhile. This justification is equally amenable to study in this project. further strengthened when one considers Our best hopes for evolutionary records the potential of these same, shallow-lake clearly lie with small, benthic, shelled organisms for providing paleoclimatic invertebrates. These organisms are proxies such as carbonate, growth completely restricted to the oxic zones of banding (for bivalves), trace elements and the two lakes today, and will not be found stable isotope records, all of which are therefore in deep water sediments, except unobtainable in deep water. during periods of significant lake level Our experience suggests that large decline. This assertion is based on structural platforms or perhaps distal considerable coring experience of the deltaic environments are the best sites for authors in Holocene and Late Pleistocene collecting the types of records we require, sediments and the observation that deep with paleowater depths of 0-100m. Clearly water transport of dead shell material, depth will change over time, but the lakes while a real phenomenon on steep slopes, seem to return to similar spillway is unlikely to be important in the types of elevations repeatedly, so modern depth locations where we will drill (flat, away ranges are probably realistic guides for from rocky highs). For this reason we locations of abundant fossils in cores. strongly advocate that at least some cores Our prior experience in the large lake in each lakes be taken from relatively coring in these types of environments shallow, sublittoral sites, or sites that have suggests that decadal-scale resolution is likely been at such depths over geologic quite feasible. Bioturbation exists in these time. We recognize that these areas may water depths, but is relatively unimportant not be ideal for other purposes, such as (2-3cm mixing depths) for the likely the highest resolution paleoclimate sampling spacing we would employ. studies. Nevertheless, the added Depositional hiatuses during lake low information such shallow sites will provide stands are a greater concern for our us for evolutionary ecology studies makes records, but these hiatal intervals in the shallow site records would be dovetailed record at the millenial scale considering with records from deeper basinal sites, so the lakes in their entirety. we can expect a reasonably complete

References Brown, D.S., 1994, Freshwater Snails of Martens, K., 1994, Ostracod speciation in Tropical Africa and their Medical ancient lakes: a review. In Martens, K., Importance 2nd ed., Taylor and Francis, Goddeeris, B. and Coulter, G. (eds.) London. Speciation In Ancient Lakes. Arch. Cocquyt, C. and Vyverman, W., 1994, Hydrobiol. Beih. Ergebn. Limnol. 44:203- Composition and diversity of the algal flora 222. in the East African Great Lakes: a Meyer, A., Montero, C. and Spreinat, A., 1994, comparative survey of Lakes Tanganyika, Evolutionary history of the cichlid fish Malawi (Nyasa) and Victoria. In Martens, species flocks of the East African great K., Goddeeris, B. and Coulter, G. (eds.) lakes inferred from molecular phylogenetic Speciation In Ancient Lakes. Arch. data. In Martens, K., Goddeeris, B. and Hydrobiol. Beih. Ergebn. Limnol. 44:161- Coulter, G. (eds.) Speciation In Ancient 172. Lakes. Arch. Hydrobiol. Beih. Ergebn. Cohen, A.S., Lezzar, K.E., Tiercelin, J.J. and Limnol. 44:407-423. Soreghan, M., 1997, New Michel, A.E., Cohen A.S., West, K., Johnston, palaeogeographic and lake-level M.R. and Kat, P.W., 1992, Large African reconstructions of Lake Tanganyika: lakes as natural laboratories for evolution: implications for tectonic, climatic and Examples from the endemic gastropod biological evolution in a rift lake. Basin fauna of Lake Tanganyika. Mitt. Internat. Research 9:107-132. Verein. Limnol. 23:85-99. Cohen, A.S., in press, Linking spatial and Michel, A.E., 1994, Why snails radiate: A temporal change in the diversity structure review of gastropod evolution in long-lived of ancient lakes: Examples from the lakes, both recent and fossil. In Martens, ostracod ecology and paleoecology of K., Goddeeris, B. and Coulter, G. (eds.) Lake Tanganyika. In Rossiter, A. (ed.) Speciation In Ancient Lakes. Arch. Biology of Ancient Lakes Academic Press. Hydrobiol. Beih. Ergebn. Limnol. 44:285- Hori, M.,Gashagaza, M.M., Nshombo, M., and 317. Kawanabe, H., 1993, Littoral fish Michel, E., in press, Phylogeny of a gastropod communities in Lake Tanganyika: species flock: Exploring speciation in Lake Irreplaceable diversity supported by Tanganyika in a molecular framework. in intricate interactions among species. Rossiter, A. (ed.) Biology of Ancient Lakes. Conservation Biol. 7:657-666. Academic Press. Johnson, T.C., Scholz, C.A., Talbot, M.R., Moran, P., Kornfield, I., and Reinthal, P., 1994, Kelts, K., Ricketts, R.D., Ngobi, G., Molecular systematics and radiation of the Beuning, K., Ssemmanda, I. And McGill, haplochromine cichlids of Lake Malawi. J.W., 1996, Late Pleistocene dessication Copeia p.274-288. of Lake Victoria and rapid evolution of Parker, A. and Kornfield, I., 1997, Evolution of cichlid fishes. Science 273:1091-1093. the mitochondrial DNA control region of Kornfield, I., 1978, Evidence for rapid the mbuna (Cichlidae) species flock of L. speciation in African cichlid fishes. Malawi, E. Africa. Jour. Mol. Evol. 45:70- Experientia 34:335-336. 83. Park, L.E. and Downing, K. in press, Verheyen, E., Ruber, L., Snoeks, J. and Implications of phylogeny reconstruction Meyer, A., 1996, Mitochondrial for ostracod speciation models in Lake phylogeography of rock-dwelling cichlid Tanganyika. in Rossiter, A. (eds.) Biology fishes records evolutionary influence of of Ancient Lakes Academic Press. historical lake level fluctuations of Lake Sherbakov, D.Y. 1999, Molecular phylogenetic Tanganyika. Phil. Trans. Roy. Soc. Lond. studies on the origin of biodiversity in Lake B 351:797-805. Baikal. Tren. Ecol. Evol. 14:92-95. West, K., Cohen, A.S., and Baron, M., 1991, Smith, G.R., 1987, Fish speciation in a western Morphology and behavior of crabs and North American Pliocene rift lake. Palaios gastropods from Lake Tanganyika, Africa: 2:436-445. Implications for lacustrine predator-prey Sturmbauer, C. and Meyer, A., 1992, Genetic coevolution. Evolution 45:589-607. divergence, speciation and morphological West, K. and Cohen A.S., 1996, Shell stasis in a lineage of African cichlid fishes. microstructure of gastropods from Lake Nature 358:578-581. Tanganyika, Africa: Adaptation, Sturmbauer, C. and Meyer, A., 1993, convergent evolution and escalation. Mitochondrial phylogeny of the endemic Evolution 50:672-681. mouthbrooding lineages of cichlid fishes West, K. & Michel, E. in press The dynamics of from Lake Tanganyika, Africa. Mol. Biol. endemic diversification: Co1 phylogeny Evol. 101:751-768. suggests explosive origin of the Van Damme, D. and Pickford, M., 1999, The gastropods of Lake Tanganyika late Cenozoic Viviparidae (Mollusca, (Cerithioidea: Thiaridae).in Rossiter, A. Gastropoda) of the Albertine Rift Valley. (ed.) Biology of Ancient Lakes. Academic Hydrobiologia 390:171-217. Press.

Impact of Lake Malawi/Tanganyika Drilling on Issues of Human Origins

A Prospectus

½ Lakes Malawi and Tanganyika are centrally located in the geographic belt (Ethiopia to S. Africa) that records the earliest human ancestors (2 to 5 million years old) and the oldest known fossils of our own species, Homo sapiens (>100,000 years old). ½ Ancient lake basins of eastern Africa preserve the longest and most precisely dated sequences of hominid fossils and archeological evidence bearing on human origins. ½ High-resolution study of African lake history is thus directly pertinent to understanding the link between past environmental change and human evolution.

Abstract Paleoclimate research focusing on Africa has made a rich contribution to the development of hypotheses regarding human evolutionary history.

Two examples: The turnover pulse 1998) were developed as a direct result of hypothesis (advanced by E. Vrba, 1980- the past two decades of research on 1995) and the variability selection global paleoclimates and environmental hypothesis (advanced by R. Potts, 1996- change in ancient African lake basins. Turnover pulse means that species removed from the places where hominids origins and extinctions, including episodes lived. involving hominids, were initiated by Recovery of high-resolution cores from dramatic climatic change (aridity and Lakes Malawi and Tanganyika would cooling) in Africa during the late Pliocene provide an unparalleled record of and again in the Pleistocene. Variability environmental change relevant to the time selection draws attention to the oscillation and place of early human origin and the evidenced in global and regional evolutionary history of our own species. sedimentary records. According to this An international contingent of geologists, body of evidence, environmental paleontologists, and archeologists are fluctuation caused inconsistencies in the ready to dedicate themselves to adaptive settings of early humans and comparing the records from these African thus had a formative impact on the origin lakes to those of past lakes and of toolmaking, brain enlargement, and associated settings inhabited by hominids. other advances in human adaptability. Cores drilled from Lakes Malawi and So far, these ideas have mainly been Tanganyika will offer a body of evidence tested by looking at evidence of directly pertinent to the fact that human environmental change in terrestrial adaptations have evolved in association sediments (e.g., the Turkana and with African lakes for over 4.4 million Olorgesailie basins) and deep-sea cores. years. This body of evidence signifies an Terrestrial records, however, have many opportunity that is otherwise unavailable gaps due to erosional unconformities, for testing the link between human while the marine record is rather far evolution and change in climate and the biota.

Potential Case Studies

½ Olorgesailie, a Pleistocene lake basin corresponded with a widening range of in southern Kenya, provides the best habitat perturbation. Comparison with calibrated record of hominid stone Quaternary cores from modern African tools, change in the African biota, and lakes would allow us to find out if these climatic fluctuation between 1.2 million perturbations were widespread or and 49,000 years ago. Recent local, whether fluctuations in eastern research suggests that environmental African lakes were tightly correlated, variability has escalated through the and thus whether early human Quaternary in the Olorgesailie region. populations faced inescapable shifts in One implication is that important their survival conditions over a wide changes in hominid technology, geographic area. Testing these ideas formation of the modern suite of large would have an immediate impact on mammals, and perhaps the origin of our understanding of human evolution. the modern human lineage, all

½ Since the early 1990s, considerable reasoning is that if key events in effort has been put into examining the human evolution occurred in response record of human evolution against to changes in aridity or monsoons, deep-sea dust records (terrestrial there should be a strong correlation material blown from Africa). The between these events and environmental markers in the dust most hypotheses of human record. Drilling of Lakes Malawi and evolutionary history are based on Tanganyika is likely to offer the correlation between geological, biotic missing link in this analysis – i.e., the and anthropological data sets, high- link between the terrestrial records resolution records from modern African (where evidence of hominids is found), lakes will provide a much more sound the aquatic lake record on land, and basis than we presently have for records from the deep sea. Since determining any such correlations.

Submitted by Dr. Richard Potts, Director, Human Origins Program, National Museum of Natural History, Smithsonian Institution, Washington, DC 20560, U.S.A. (October 1999) Environmental background to human origins WORKSHOP PARTICIPANTS

Hon. Harry I. Thomson Andrew Cohen Box 349, Blantyre Minister of Natural Dept. of Geosciences Resources University of Arizona Ulrich Harms and Environmental Affairs, Scientific Drilling Program, GFZ-Potsdam, Kristina Beuning Steven M. Colman Dept. of Earth and Environ. Paleoclimatology Program Sciences U.S. National Science Robert Hecky Wesleyan University Foundation Canada Center for Inland Waters Kingston Peter Blisniuk M..B. Dolozi Institute fuer Dept. of Geography and Geowissenschaften Earth Sciences Thomas C. Johnson University of Potsdam University of Malawi Large Lake Observatory Harvey Bootsma University of Wisconsin - Peter deMenocal Leonard Kalindekafe Milwaukee Lamont-Doherty Earth Director of Mines Observatory Lilongwe , c.org Christina Gallup, Dept. of Charles Kaphwiyo Erik Brown Geology Malawi Geological Survey, Large Lake Observatory University of Minnesota- Box 27, University of Minnesota- Duluth Zomba, Duluth org> Francoise Gasse Alex Bulirani Europole Mediterraneen de E. Kaseko Fisheries Research Unit l'Arbois Dept. of Mines Monkey Bay CEREGE, Aix-en-Provence Box 251, Lilongwe John King A. Chapuma Robert M. Goodden Graduate School of Ministry of Natural [email protected], Oceanography Resources and [email protected] University of Rhode Island Environmental Affairs, [email protected] P/Bag 350 D.O.C. Gondwe Lilongwe Surveyor General´s Elias Kilembe Department Tanzania Petroleum Department Eric Odada P/Bag 394 Lilongwe Pan African START Daniel A. Livingstone Secretariat (PASS) Department of Zoology and M. Mzunzu Department of Geology EOS Director of Hydrographic University of Nairobi Duke University Surveys Box 127, Monkey Bay Fraser Phiri E.E. Lodzeni Dennis Nielson Commissioner of Mines Deputy Secretary for DOSECC Ministry of Natural Ministry of Natural University of Utah Resources and Resources and Environmental Affairs, Environmental Affairs P/Bag 350, Lilongwe S.A. Nirenda Kiram Lezzar Ministry of Natural Christopher Scholz Dept. of Earth Sciences Resources and Dept. of Earth Sciences Syracuse University Environmental Affairs Syracuse University P/Bag 350, Lilongwe [email protected]

G.W.P. Malunga Hudson Nkhotagu Michael Talbot M.D.C. , P.O. Box 566 University of Dar es Salaam Geological Institute Blantyre, [email protected] University of Bergen [email protected] [email protected] Lisa Park S.A. Mapira Department of Geology J.C. Tambala Director of Fisheries University of Akron Ministry of Natural P.O. Box 545, Lilongwe Resources and Environment, P/Bag 350 Odala Matupa K. Nyasulu Lilongwe Director of Energy, P/Bag Director of Forestry 309 Lilongwe J.L. Thabwa Lilongwe Ministry of Natural Andrew Nyblade Resources and M.B. Mbewe Dept. of Geosciences Environmental Affairs Principal Secretary for Pennsylvania State Ministry of Natural University Jean-Jacques Tiercelin Resources and Insitut Universitaire Environmental Affairs Europeen del la Mer, France Richard Potts Ellinor Michel Human Origins Program Inst. for Systematics and Smithsonian Institution Population Biology University of Amsterdam Eugene Pollard