SMITHSONIAN CONTRIBUTIONS TO THE MARINE SCIENCES* NUMBER 19

Parallel Laminated Deep-Sea Muds and Coupled Gravity Flow-Hemipelagic Settling in the Mediterranean

Daniel Jean Stanley

SMITHSONIAN INSTITUTION PRESS City of Washington 1983 ABSTRACT

Daniel Jean Stanley. Parallel Laminated Deep-Sea Muds and Coupled Gravity Flow-Hemipelagic Settling in the Mediterranean. Smithsonian Contri­ butions to the Marine Sciences, number 19, 19 pages, 7 figures, 1983.—The origin of fine-grained deep-sea facies is often blurred because of interplay of diverse transport mechanisms: sediment gravity flow, traction related to fluid-driven circulation, and pelagic and hemipelagic "rain" mechanisms. Physical and chemical attributes of the Mediterranean amplify petrologic differences, thus facilitating distinction between mud types in this sea. Important attributes include small distances between sediment input and depositional site, gener­ ally low bottom current velocities in the deep basins, and shallow depths that permit preservation of carbonate components, an important criterion for mud facies definition. Particularly important in the Mediterranean are periodic development of intense water mass stratification and pycnoclines which act as sediment barriers, i.e., deviation of low concentration sediment gravity flows, and temporary retention of particles from turbid layer flows and hemipelagic settling. Release and differential settling of terrigenous silt and clay floes and reworked benthic and planktonic (largely coccolith and foraminifera) com­ ponents from well-marked density interfaces occur in a manner such that particles are segregated according to size and density. The resulting varve-like deposits display fine parallel laminae of alternating coccolith- and terrigenous- rich layers that show diverse fining-upward trends. Finely laminated sections of this type accumulate more rapidly than hemipelagites and are distributed over larger surfaces than mud turbidites. Analysis of bedform, texture-fabric, composition, geometry, and rates of sedimentation help distinguish (1) fine parallel laminated muds derived from coupled sediment gravity flow and hemipelagic settling from (2) laminated mud turbidites, (3) laminated hemi­ pelagites, and (4) contourites as commonly defined. Study of mud lithofacies in small to moderate size seas, such as the Mediterranean, holds promise for better interpretation of deep-marine fine-grained deposits.

OFFICIAL PUBLICATION DATE is handstamped in a limited number of initial copies and is recorded in the Institution's annual report, Smithsonian Year. SERIES COVER DESIGN: Seascape along the Atlantic coast of eastern North America.

Library of Congress Cataloging in Publication Data Stanley, Daniel J. Parallel laminated deep-sea muds and coupled gravity flow-hemipelagic settling in the Medi­ terranean. (Smithsonian contributions to the marine sciences ; no. 19) Bibliography: p. Supt. of Docs. no. : SI 1.41:19 1. Marine sediments—Mediterranean Sea. 2. Sediment transport—Mediterranean Sea. I. Title. II. Series. GC389.S8 1983 551.46'083'38 82-600337 Contents

Page Introduction 1 Acknowledgments 2 Climate, Hydrography, and Sedimentation 2 Density Stratification Phases in the Mediterranean 3 Fine-grained Facies and Isothermal Hydrographic Regimes 5 Fine-grained Sedimentation and Density Stratification 7 Finely Laminated Mud Variants 9 Implications and Conclusions 14 Literature Cited 17 Dedicated to the memory of Professor Dr. Johan Ferdinand Maurits de Raaf 1902-1982 inspiring leader astute sedimentologist friend Parallel Laminated Deep-Sea Muds and Coupled Gravity Flow-Hemipelagic Settling in the Mediterranean

Daniel Jean Stanley

Introduction from mechanisms active just prior to, and at, the time of particle emplacement. It has also become Deposition of silt and clay lithofacies in the apparent that some silty deposits, earlier inter­ marine environment is attributed to settling of preted as turbidites, actually have a more com­ particles from suspension, to transport by fluid- plex origin. driven processes related to ocean circulation This paper considers the interplay of transport (Heezen and Hollister, 1971:335-421; Eittreim mechanisms that produces a continuum of mud and Ewing, 1972), and to sediment gravity flows types and thus blurs the origin of deep-sea fine­ (Piper, 1978; Stanley and Maldonado, 1981). grained facies. Specific attention-is paid herein to Theoretical and experimental studies indicate finely laminated muds whose petrology appears that suspension settling, traction, and gravity- to record the combined effects of sediment gravity driven high-concentration mass flow and low con­ flow, including turbidity current transport, and centration sediment flow mechanisms each result hemipelagic settling. The Mediterranean Sea is in characteristic bedforms and textural-fabric and an appropriate area in which to conduct a study compositional attributes of fine-grained deposits. of lamination in that (1) there are suitable num­ Distinct facies are thus believed to result from bers of closely spaced core sites, and (2) average pelagic "rain," tractive mechanisms related to basin depths approximate 3000 m, well above the bottom current transport (Stow and Lovell, carbonate compensation depth (CCD), such that 1979), and turbidity currents (Stow and Bowen, calcareous components, an important criterion of 1980). Muds from the latter process have received depositional regime, are fortuitously preserved. by far the most attention to date. Moreover, (3) Mediterranean basins are consid­ Conditions in marine settings tend to vary and erably smaller than those in major world oceans, be more complex than theoretical and experimen­ and present diverse temporal and spatial facies tal examples. For example, the transit of silt and variations, thus allowing more precise interpre­ clay floes to the deep marine floor usually involves tation of dispersal and transport patterns. It is two or more processes. Moreover, it is recognized also recalled that (4) there is strong evidence of that stratification features in mud deposits result large-scale Quaternary to Recent oceanographic changes in the Mediterranean (Stanley et al., Daniel Jean Stanley, Department of Paleobiology, National Museum 1975:287-289). These conditions provide an ideal of Natural History, Smithsonian Institution, Washington, D.C. 20560. setting in which to assess how climatically in- SMITHSONIAN CONTRIBUTIONS TO THE MARINE SCIENCES

duced changes in water mass stratification affect have been affected by a complex seafloor config­ pelagic settling and sediment gravity flows of low uration, including shallow ridges that separate concentration and, in turn, the formation of lam­ this sea into a series of quasi-isolated depressions inae in mud deposits. Identification of criteria for of highly variable size, shape, and depth. The laminated mud types emplaced by combined sed­ Strait of Sicily and contiguous Siculo-Tunisian iment gravity flow-suspension settling processes, (or Pelagian) Platform (Carter et al., 1972; Bur- and distinction of such facies from laminated ollet et al., 1979) is a long broad sill that effec­ mud turbidites and hemipelagic end-members, tively separates the eastern and western basins, are valuable outgrowths of the study. and thus is particularly important in control of ACKNOWLEDGMENTS.—The author acknowl­ Mediterranean circulation (Allan et al., 1972:11- edges valuable discussions during the initial phase 25). of the study with P.H. Feldhausen, NUS Corpo­ Present excess evaporation relative to precipi­ ration; and A. Maldonado, University of Barce­ tation and runoff results in the characteristic lona; and use of coarse fraction mineralogical Mediterranean hydrographic regime involving counts made by R. J. Knight, Petro-Canada Ltd. the eastward flow of a moderately thin layer of The paper was reviewed by R. D. Flood, Lamont- less saline Atlantic water above a relatively iso­ Doherty Geological Observatory; and J.W. thermal column of westwardly moving, dense Pierce, Smithsonian Institution; useful comments intermediate and deep water masses (Wiist, 1961; were also made by anonymous reviewers. Fund­ Lacombe and Tchernia, 1972). Circulation pat­ ing for this investigation, part of the Mediterra­ terns, however, were markedly altered in the past nean Basin (MEDIBA) Project, was provided by as a result of somewhat lower temperatures and Smithsonian Scholarly Studies grant 1233S101. higher rainfall and runoff than at present. Brad­ ley (1938) postulated that basins in the eastern Mediterranean (Ionian, Aegean, and Levantine) Climate, Hydrography, and Sedimentation were periodically characterized by oceanographic It is recalled that a major control of fine­ patterns involving Black Sea-type density strati­ grained sedimentation in the deep sea is ocean fication, in contrast to the present isothermal circulation whose driving force is the sun (Lisit- regime. zin, 1972:30-46). Climatic fluctuations, resulting What would be the sedimentary responses on in displacement of temperature and rainfall belts, the deep-sea floor to such Quarternary climatic- modified world ocean circulation in the geologic hydrographic oscillations? It can be predicted past (Hay, 1974:1-5). Well documented are the that gravity-driven, high-concentration mass dis­ Quarternary climatic oscillations (Climap Project placement and dense sediment gravity flows Members, 1976) that markedly altered circula­ transporting mixes of coarse silt, sand, and coarser tion patterns, even at great depths (Schnitker, particles downslope and onto basin plains would 1980). Such changes were of particularly large not be markedly influenced by development of magnitude in the case of small- to moderate-size water mass stratification. In contrast, it is envi­ basins with silled, restricted passages that limit sioned that dispersal and the resulting deposi­ exchange with adjacent water bodies. The Med­ tional patterns of low concentration flows, carry­ iterranean serves as an ideal example in view of ing mostly fine-grained material in suspension, its narrow, elongate form between Africa, South­ would have been greatly modified by the devel­ ern Europe, and the Middle East, and the re­ opment of a distinctly stratified water column of stricted exchange with Atlantic and Black Sea the type that may periodically have prevailed in waters at the shallow, narrow Gibraltar and Bos­ the Quaternary and Pliocene. This investigation porus-Dardanelles straits. considers the origin of laminated fine-grained Moreover, Mediterranean circulation patterns facies, other than sapropels (Ryan, 1972), and NUMBER 19 related organic-rich layers (Maldonado and Stan­ patterns in both eastern and western basins pe­ ley, 1976b), that preferentially accumulated at riodically were altered markedly from those op­ times when conditions of water mass stratification erating at present. Particularly important evi­ were clearly different than at present. dence in this respect is provided by dark, organic- rich fine-grained sapropel layers broadly distrib­ uted in the eastern Mediterranean (Figure 1A). Density Stratification Phases in the There is general agreement that reduced oxygen Mediterranean content favoring anaerobic conditions on the sea­ In a far-sighted essay referring to modifications floor resulted from density stratification (Kullen- of Mediterranean hydrography induced by Qua­ berg, 1952; Olausson, 1961). The distribution of ternary oscillations, Bradley predicted (1938:377) dated sapropels indicates that some stagnation that phases resulting from temporarily altered water mass stratification were basin-wide and occurred during the last glacial stage, the Mediterranean, because of primarily at depths in excess of 800 to 1000 m the different climate, would have had a surface layer of essentially fresh water overlying the oceanic water that filled (Stanley, 1978). The uppermost layer, dated at the deep basins. Furthermore, the oxygenated Atlantic water about 9000 to 7000 year B.P., formed during a would have had free access to the western basin of the warming phase (Ryan, 1972). The two underly­ Mediterranean through the Straits of Gibraltar beneath the ing sapropel layers are dated at about 25,000- outflowing surface stream of fresh water and in consequence 23,000 years B.P. (possibly during a cooling phase) the deep water of the western basin would have continued to be at least partially supplied with oxygen. But with a and at >40,000 years B.P. (Stanley and Maldon­ blanket of essentially fresh water covering the Mediterranean ado, 1979:40-42). and moving westward there appears to be no way in which Sapropels are absent in the three deep (to about significantly large volumes of the oxygen-bearing saline wa­ 1700 m) Strait of Sicily basins, and in the Ligur­ ter in the western basin could move across the sill at the Sicily Straits so as to cause circulation and afford an oxygen ian, Tyrrhenian, Algero-Balearic, and Alboran supply in the deep saline water of the eastern basin. For this seas. However, sections in many cores recovered reason the water in the eastern deep basin probably would in these central and western Mediterranean de­ have become stagnant and depleted of oxygen soon after the pressions, some dated at about 11,000 to 9,000 climatic change permitted fresh water to flood the surface of years B.P., display dark gray-olive streaked mud the Mediterranean. layers that contain pyritized tests and burrows Indirect, but strong, evidence for such physical (see, for example, core logs in Huang and Stanley, oceanographic changes during the late Pleisto­ 1972:536-538; Rupke and Stanley, 1974; 11,25; cene to Holocene has been provided during the Maldonado and Stanley, 1976a:53-56). The ra­ past two decades by studies of cores collected in diocarbon dates of these core sections may be different Mediterranean basins. Radiocarbon somewhat older than the age of actual sediment dating and facies analysis of cores establish a emplacement, due to the presence of reworked stratigraphic base for regional correlation of Late calcareous microfossil tests. It is likely that the Quaternary sediment sections (Stanley and Mal­ streaked, gray-olive, pyrite-rich mud sections of donado, 1979). Noteworthy is the remarkable western Mediterranean cores are chronologically systematic repetition, or cyclicity, of Quaternary equivalent to the sapropel zones of basins east of sedimentary sequences recorded by means of lith- the Strait of Sicily. The reduced, pyrite-rich sec­ ofacies (Maldonado and Stanley, 1976b), geo- tions of the western Mediterranean, like sapro­ chemical and isotopic (Vergnaud-Grazzini et al., pels, record phases of density stratification as 1977; Dominik and Mangini, 1979; Luz, 1979), depicted in oceanographic models presented for and faunal (Mars, 1963; Ryan, 1972; Thunell the early Holocene (Figure 1B). and Lohmann, 1979) analyses. In sum, lithofacies data support the hypothesis Lithological cyclicity indicates that circulation that an "estuarine-type" circulation regime and 48°-

44°

less dense stagnant (h^S-rich) surface water deep water NUMBER 19 current reversal dominated the Mediterranean tigraphically correlated cyclothemic sequences for short periods of time (Bradley, 1938;377; from eastern and western Mediterranean basins Mars, 1963;67-7l). That the oceanography in the highlight the nonrandom vertical and lateral dis­ eastern basins at times of sapropel deposition, tributions of different fine-grained sediment types when oxygen-deficient conditions prevailed, may (Maldonado and Stanley, 1977; Stanley and Mal­ be likened to that of the present Black Sea is also donado, 1981). It is useful to compare silt and indicated by analysis of Sea of Marmara cores clay facies that accumulate in isothermal versus (Stanley and Blanpied, 1980). It is postulated stratified water regimens. that excess glacial melt waters moved westward as overflow from the Black Sea across the Bos­ Fine-grained Facies and Isothermal porus-Dardanelles portals, and then south across Hydrographic Regimes the Aegean Sea. After entry into the Levantine and Ionian seas, this less saline surface layer Mud types, including the fine silt, clayey silt, flowed westwardly to and across the strait of and silty clay, are most reliably identified as to Sicily and, eventually, Gibraltar (Figure 1). Den­ process of emplacement on the basis of structures ser Atlantic water, flowing eastward below the visible in radiographs, size analyses, and coarse- surface layer, entered the Alboran Sea and west­ fraction composition. Silt and sand-sized terrige­ ern Mediterranean producing some mixing and nous clasts and carbonate grains of biogenic precluding complete anaerobic conditions of the (largely coccoliths, foraminifera, and shell frag­ Algero-Balearic, Ligurian, and Tyrrhenian sea­ ments) and clastic (reworked limestone and do­ floor. lomite) origin are valuable criteria for distinguish­ Current reversal as outlined above remains ing mud types. within the realm of theory. There is little doubt, Muddy slump, dense mud flow, and muddy however, that the Quaternary sediment cover, debris flow deposits accumulated throughout the showing cyclothemic development of alternately late Quaternary independently of hydrographic reduced and oxygenated facies across much of the fluctuations (Stanley and Maldonada, 1981:278- Mediterranean, records the direct interaction be­ 283). These mass flow units are concentrated in tween climatically controlled water circulation areas of marked seafloor relief (slopes, ridge mar­ fluctuations and deep basin sedimentation. Stra- gins, base-of-slope environments) in association with sand and mud turbidites and hemipelagic FIGURE 1.—A, Chart showing distribution of youngest or­ muds. In upper Holocene to recent time, mud ganic-rich sapropel, Si (diagonal lines), deposited in the turbidite-hemipelagic mud assemblages gener­ eastern Mediterranean at about 9000 to 7000 years B.P., a ally prevail on basin margins in areas of low time when hydrographic conditions were markedly different from those at present. (Heavy arrows depict generalized flow relief, including perched slope basins and small patterns of less dense upper water mass; light arrows show depressions in cobblestone topography. In more fluvial input; Ae = Aegean Sea; B = Balearic Basin; Bo = distal, low relief environments, such as basin and Bosporus; BS = Black Sea; D = Danube; I = Ionian Sea; Le trench plains, a distinct mud turbidite-unifite- = Levantine Sea; Li = Ligurian Sea; N = Nile River input; hemipelagic mud assemblage is usually recovered P-A = Po-Adriatic Sea; R = Rhone River input; SS = Strait of Sicily; STP = Siculo-Tunisian Platform; T = Tyrrhenian (Figure 2). (Unifite is the descriptive term for Sea; Ly-II-3 = position of core Lynch cruise II core 3; after uniform, almost structureless mud, cf. Stanley, Stanley, 1978.) B, Scheme illustrating "estuarine-type" water 1981; Blanpied and Stanley, 1981:2.) mass regime in the Mediterranean at times of sapropel and Temporal and spatial distribution patterns of finely laminated mud deposition. Note marked stratification this latter distal basin and trench plain lithofacies of water masses and development of Black Sea-type anoxic conditions in the eastern basins unlike those presently exist­ assemblage provides insight on the relation be­ ing. (Arrows depict possible flow patterns of water masses; tween oceanographic conditions and silt and clay after Stanley et al., 1975.) transport processes in deep marine settings. Struc- SMITHSONIAN CONTRIBUTIONS TO THE MARINE SCIENCES

3cm NUMBER 19 tureless and vaguely laminated unifites (Figure of planktonic tests (usually >75% of sand frac­ 2E,F) are distinctly restricted to flat basin and tion). Moreover, layer thickness and rates of ac­ trench plains where they are associated with fine­ cumulation (<10 cm/1000 years; Rupke and grained mud turbidites (Figure 2B-D): both mud Stanley, 1974:33) of hemipelagites tend to be types are laterally continuous across basins (Fig­ much lower. Structures and mineralogical com­ ure 2A). Petrologically, unifites appear similar to position suggest that hemipelagic muds accumu­ nearly structureless muds that are referred to as late largely from suspension "rain" mechanisms "homogenites" by some workers (cf. Kastens and rather than from sediment gravity flows. Cita, 1981). Radiocarbon dating of unifite sec­ Under conditions of poorly developed water tions records very high rates (>200 cm/1000 column stratification, such as that displayed by years) of accumulation. Both structureless and the present Mediterranean, gravity-driven flows, vaguely laminated unifites are somewhat finer such as turbitity currents of moderately low den­ grained than turbiditic muds with which they are sity that carry clay- and silt-size floes primarily associated. Unifites and turbidites fine upward in suspension, would likely move downslope. gradually and contain comparable proportions of These flows would move relatively unhampered terrigenous and reworked fauna carbonate com­ along the bottom, from proximal sites (outer shelf ponents (usually >30% of the sand-size fraction). to upper slope, ridge, basin margin) to the base- Spatial distribution patterns, rapid sedimentation of-slope and well onto basin plains. The turbulent and textural and mineralogical attitudes indicate head of such flows would entrain in a downslope that both fine-grained, almost structureless tur­ direction pelagic material, settling, or recently bidites and unifites are released from thick, low deposited, from suspension "rain"; in some cases density or lower velocity sediment gravity flows flows would also resuspend and transport basin- (Stanley and Maldonado, 1981:284, 290). Uni­ ward surfical biogenic and clastic material eroded fites appear to be the dilute end-products from from basin slopes. This process would result in turbidity currents, turbid layer flows, and suspen- heterogeneous mixtures of displaced planktonic sate-rich clouds (Stanley, 1981; Blanpied and tests, terrigenous grains, and older reworked Stanley, 1981:29-35). faunas, typically recovered from associated uni­ Typical Mediterranean hemipelagic mud lay­ fites and fine-grained turbidites restricted to basin ers, in contrast to fine-grained turbidites and plains. unifites, are more commonly bioturbated and There is a decreased proportion of unifites in show speckling as a result of high concentrations the eastern Mediterranean at times of sapropel deposition. This suggests that the flow patterns of low density "clouds" were in some manner mod­ FIGURE 2.—A, Subbottom 3.5 kHz record showing part of the Zakinthos Trench plain in the western Hellenic Arc ified during downslope movement by a barrier (arrow points to thick, laterally continuous, acoustically effect resulting from distinct density differences transparent layer, probably a fine-grained turbidite and/or that periodically developed within the water col­ associated unifite). B-D, Radiograph prints of selected core umn. sections showing typical sharp-based, fining-upward lami­ nated mud turbidites (t) and hemipelagic mud (He) with speckling. (Note cross-stratification in B and D, and distinct Fine-grained Sedimentation and Density fining-up trend of entire laminated section in c.) E, Faintly Stratification laminated unifite. F, Structureless unifite. (B and D, respec­ tively, Marsili cores 12 and 18 in the Kithera Trench sector; Water masses of different temperature, salinity, F, Trident core 172-34 in the Zakinthos Trench, Hellenic Arc or both, are separated by a sharp vertical gradient (locations shown in Stanley and Maldonado, 1981); c, Lynch cruise II core 8A in the Algero-Balearic Basin; E, Western in density, or pycnocline. Theoretical calcula­ Alboran Basin core 91 (locations for c and E, respectively, in tions, supported by field observation, show that Rupke and Stanley, 1974, and Huang and Stanley, 1972).) sharp density gradients may temporarily retain 8 SMITHSONIAN CONTRIBUTIONS TO THE MARINE SCIENCES particles settling through the water column and is thus possible that midwater and bottom masses modify the flow path of very low concentration transported silt and clay size particles over larger plumes (Pierce, 1976). Pycnoclines would induce geographical areas than they do today, perhaps detachment of a suspensate-rich flow from the in the manner nepheloid layers in other world seafloor into the water column, rather than allow­ oceans presently distribute substantial volumes of ing a bottom-hugging turbid layer flow of the material (Eittreim and Ewing, 1972). type necessary to deposit a fine-grained mud Some aspects of a generalized model for sus­ turbidite with typical structures and/or associ­ pended sediment transport in a stratified system, ated structureless unifite. Flow detachment is ex­ including detachment (Figure 3), may be applied pected wherever suspended sediment-enriched to the Mediterranean. For example, detailed water encounters a denser water layer. Off Cali­ lithofacies analyses of Nile cone cores indicate fornia, for example, Drake et al. (1972:328) have that there exists a rather direct relation between shown that minimal concentrations of 100 mg per rates of sedimentation and the frequency of lam­ liter, and generally much higher (~2500 mg/1; inated layers in upper Quaternary sections (Mal­ cf. Pierce, 1976:441), are needed to overcome donado and Stanley, 1978, 1979). It has been density interfaces resulting from temperature postulated that at times of sapropel formation, changes in the water column. low density turbid flows emanating from the In the Mediterranean, much of the fine-grained mouth of the Nile and moving downslope were sediment presently introduced by rivers (notably retained above the cone as detached layers. Con­ the Nile, Rhone, Po, Ebro, and Seyhan) and by centration of fine-grained material along pycno­ wind tends to spread out away from the coast clines on the Nile cone is schematically depicted along the upper major intermediate and deep in Figure 4. water (Emelyanov and Shimkus, 1972). At times More specific lithologic evidence recording when stratification was better developed, deposi­ probable influence of density stratification on tional patterns almost certainly were more com­ fine-grained sedimentation is provided by suites plicated. Particle aggregates settling from the of cores recovered from the western Hellenic upper pycnocline would reconcentrate along one Trench. These show that the most recent major of several lower density interfaces before finally phase of finely laminated mud deposition oc­ settling to the bottom. In a multiply stratified curred from about 17,000 to 6000 years B.P. This column, one envisions a sequence involving (1) period coincides with rapid eustatic sealevel rise detachment of a turbid layer from the bottom, and progressive climatic warming at the end of (2) aggregation, (3) particle settling, (4) renewed the Pleistocene and early Holocene. It is recalled accumulation along a lower density interface, and that the most recent sapropel, Si, was deposited (5) subsequent settling across still deeper pycno­ between about 9000 to 7000 years B.P. (Ryan, clines prior to (6) deposition on the seafloor (cf. 1972:150). The finely laminated mud facies, as Pierce, 1976 Fig. 2). the Si sapropel layer, was broadly distributed Open ocean suspended sediment studies show areally over highly diverse and irregular Hellenic that, eventually, particles either become incor­ Trench slope and basin topography; however, porated in a near-bottom turbid (nepheloid) unlike Si which accumulated in less than 2000 layer, or settle directly onto the bottom. Still years, finely laminated muds were deposited dur­ limited investigations of suspended sediment con­ ing a period lasting 10,000 or more years. Finely centrations in the Mediterranean show no well- laminated muds during this same period also developed nepheloid layers in the western basins accumulated over large and topographically var­ at present (Pierce and Stanley, 1976; Pierce et al., ied areas in other eastern and western Mediter­ 1981). Nepheloid layers in this sea, however, con­ ranean sectors and Strait of Sicily basins. Their ceivably may have been important in the past. It rate of accumulation is generally lower (<25 cm/ NUMBER 19

FIGURE 3.—Schematic of suspended sediment transport possibly applicable to the Mediterra­ nean at times when water masses were stratified. Concentrations of suspensates (stippled areas) are shown as detached turbid layers along pycnoclines, and as bottom nepheloid layer, driven by bottom current circulation, on slope to basin plain. (Large arrows depict flow of water masses, a pattern similar to off U.S. East Coast, after Pierce, 1976.)

1000 years) than that of other mud types em- broadly on density interfaces in the water column placed by sediment gravity flows, but distinctly as continuous or detached turbid layers. The higher than that of hemipelagites (<10 cm/1000 progressive release of silt and clay size material years). It is recalled that the proportion of thick over large areas of the seafloor is contrasted to unifites, emplaced by low concentration bottom- material carried along the bottom by turbidity hugging flows, is reduced during the period of currents which, morphologically constrained, are finely laminated mud deposition. more limited in seafloor surface distribution. These considerations provide the basis for a Closer examination of finely laminated mud types generalized depositional model relating finely elucidates this model. laminated facies with low concentration flows in a stratified water column (Figure 5). The scheme Finely Laminated Mud Variants emphasizes introduction of particles from (1) gravity-driven flows entering along basin mar­ Finely laminated facies are most reliably rec­ gins, and from (2) hemipelagic settling from sur­ ognized by combined radiography and petrogra­ face waters. Concentrations of particles spread phy. The most diagnostic criterion is closely 10 SMITHSONIAN CONTRIBUTIONS TO THE MARINE SCIENCES

NORTH

FIGURE 4.—Plexus of sediment processes on the Nile cone during phases of Mediterranean stratification (after Maldonado and Stanley, 1978). Dense turbidity currents (TC) cross pycnoclines as they flow downslope along the bottom, while lower concentration suspensate- rich zones form detached turbid layers (DTL) on pycnoclines. (Other symbols: AC = Alexandria Canyon; HBP = Herodotus Basin plain; RB = Rosetta Branch; RCD = Relict coastal and neritic deposits; SB = stratification barrier; SL = slump; SO = shelf-edge spill-over; SP = sand pods on Nile cone; TD = sediment turbid discharge off the Rosetta Branch of the Nile.) spaced, parallel (<0.5-5.0 mm) laminae. These Trench basins are dark olive gray. Most laminae are sometimes visible in split cores (Ryan et al., are varve-like in that they consist of paired alter­ 1973; Hsu et al., 1978), but always much better nating layers of different mineralogy; a lamellar defined by density differences observed in radio­ pair is termed a couplet. Some individual lami­ graphs (Figure 6). Parallel laminae in some Med­ nae, or couplets, do not clearly display a fining- iterranean basins are often indistinct, particularly upward texture (Figure 6D). Commonly, however, in shallower (<1500 m) settings (Figure 6B). In laminae couplets show diverse fining-upward contrast, they are well developed in deeper basins trends (Figure 6c, E-G) involving changes from and particularly those in the Hellenic Trench clayey silt to silty clay (textural data from Smith­ area (Got et al. 1977, fig. 4; Stanley and Maldon­ sonian Sedimentology Laboratory data base). ado, 1981, fig. 3). SEM analysis of the silt fraction shows that the Core sections that comprise largely fine lami­ layering apparent in radiographs consists of alter­ nated facies in some of the deeper Hellenic nating coccolith- and silty clay-enriched oozes. NUMBER 19 11

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DEBRIS FLOW|-»"rTURBIDIT1 Y CURRENT -\7 j TURBID LAYER FLOW *— DEPOSIT LARGELY T FROM GRAVITATIVE (CHAOTIC -(DEBRIFS FLOW (COMPLETE PROCESSES: MASS) DEPOSIT) TURBIDITE) ROLE OF STRATIFICATION I DETACHED TURBID LAYER FLOW"! • ••••••••••I INTERFACE AS BARRIER DEPOSIT FROM GRAVITATIVE & SUSPENSION-RELATED PROCESS rnTrrr"WELL-LAMINATED MUD- !•»»-) DISTAL BASIN OCCURRENCE: PRIMARILY AREA OF RELIEF WIDESPREAD DISTRIBUTION IN STUDY AREA PLAIN

FIGURE 5.—Depositional model showing a basinward transformation continuum of gravity- driven processes, i.e., mechanisms of decreasing concentrations, from slumping to low density turbid layer flows. An important stratification interface in the water column serves as a barrier to particles released from low concentration turbidity currents and turbid layer flows and also from hemipelagic (H.P.) suspension settling. As a result of the interface, particles are distributed over large areas of a basin and eventually settle out as finely laminated layers, often graded. The nature of the stratification interface controls the degree of grain retention and ultimate release of terrigenous grains and pelagic components particles, which settle according to size and density. Periodic variations in organic productivity and fluctuations in particle density and settling rate give rise to varve-like alternations of coccolith- and terrigenous-rich layers, many of which display fining-upward trends (see Figure 6E-F).

Radiographs reveal no two identical sequences of mud from different parts of the Mediterranean, parallel laminated structures. Variations occur reveals that in almost all instances, the bulk with respect to proportions and thicknesses of (>70%) of the coarse fraction comprises plank­ coccoliths and silty clay-rich layers (compare, for tonic tests. Foraminifera dominate, but pteropods example, Figure 6c and D). Varved and graded may be locally important. Benthic shell material finely laminated sections also vary with respect usually accounts for less than 10%, while terrige­ to coarseness of material. Occasionally, large nous grains generally exceed 10%. Within-core planktonic tests such as pteropod shells are ob­ and core-to-core variations in the above-cited served, and these usually are flat-lying and buried proportions of these mineralogical components by fine laminae (Figure 6A). Alternations of coc­ are observed. coliths and clastic silt and clay aggregates may in On the basis of structure, texture, and compo­ some instances enclose important proportions of sition the Mediterranean deep-water finely lami­ larger particles, such as disseminated organic nated facies generally can be distinguished from matter (Figure 7A, B) and concentrations of plank­ muds of purely pelagic (with little or no terrige­ tonic tests (usually foraminifera, Figure 7c). nous components) suspension and even from Petrographic examination of the coarse frac­ those of essentially hemipelagic (mixed plank­ tion (>62 jtim), separated from finely laminated tonic and terrigenous components) settling origin. 12 SMITHSONIAN CONTRIBUTIONS TO THE MARINE SCIENCES

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FIGURE 7.—Selected radiograph prints: A,B, disseminated organic matter (some pyritized); c, concentrations of planktonic foraminiferal tests in finely laminated core sections. (Cores are from the western Hellenic Trench: A, Trident core 172-34, Zakinthos Trench; B, Marsili core 8, Matapan Deep; c, Marsili core 14, Gulf of Laconia, south of Peloponnesus; locations shown in Stanley and Maldonado, 1981.)

The amount of sand fraction in laminated mud weight); sand in the latter commonly produces (about 2% by weight) is lower than that in typical speckling observed in radiographs (He in Figure Mediterranean hemipelagic muds (to >5% by 2D). Moreover, hemipelagite sections, such as those in the Hellenic Trench, generally contain FIGURE 6.—Selected radiograph prints showing variations of higher (>80%) contents of foraminifera and pter- finely laminated muds: A,B, examples of distinct and vague opods in the sand fraction and contain coccoliths fine parallel laminations; C,D, two different types of varve- in the silt fraction. like stratification, both showing importance of coccolith Parallel laminated muds also can be distin­ (light) layers; individual pairs, or couplet, of laminae show fining-upward trends, but overall the entire laminated se­ guished from some laminated mud turbidites on quence is not graded (unlike turbidite section in Figure 2c); the basis of associated structures and composition. E-G, thicker fining-upward (arrows) type of finely laminated Unlike laminated mud turbidites (Figure 2c; also sections, comprising largely coccoliths and pelagic compo­ examples in Stow and Bowen, 1980), fine parallel nents rather than terrigenous silty clay in typical laminated laminated deposits (Figure 2B-D) are not sharp- mud turbidites (Figure 2B-D). (Arrow in A points to pteropod buried by finely laminated coccolith ooze; A,D, Trident core based nor are they texturally graded, i.e., showing 172-34 in Zakinthos Trench basin; c, E-G, Trident core 172- a progressive decrease in mean grain size and 36 in Strofadhes Trench basin, in western Hellenic Arc (core lamina thickness from the base to the top of the locations shown in Got et al., 1977).) laminated bed. Moreover, bedforms commonly 14 SMITHSONIAN CONTRIBUTIONS TO THE MARINE SCIENCES

attributed to traction, such as wave ripples and analysis of laminated turbidite core sections call cross-laminations that commonly occur in mud attention to systematic upward and lateral-down- turbidites (Figure 2B, D), are absent from finely slope decreases in modal grain size and laminae laminated facies. Finely laminated muds do not thickness. In contrast, lamination in typical fine­ show load structures and only rarely do they show grained contourites (the term is used here as bioturbation. applied by Heezen and Hollister, 1971:420) re­ Both laminated mud turbidites and finely lam­ sults from fluctuations in sediment flux and ac­ inated muds may contain comparable propor­ cumulation by both traction and suspension tions of sand (to about 2% by weight), but sand release mechanisms. Some criteria of mud con­ in turbidites usually contain a higher (to >30%) tourites are sharp base and top of bedding con­ terrigenous grain content (from mineral count tacts, both normal and reverse grading, common data base, RJ. Knight, in litt.). SEM analyses cross-lamination, and preferred grain orientation reveal reworked biogenic components, including parallel to the bedding plane throughout a bed pre-Pleistocene coccoliths, in both mud turbidites (Hollister and Heezen, 1972; Stow and Lovell, and finely laminated facies. However, there is a 1979). However, review of published radiographs higher proportion of coccoliths in the silt fraction and descriptions of laminated mud core sections and foraminifera in the sand fraction of some in large basins, such as the Atlantic, show that finely laminated mud couplets than in turbidites. petrologic distinction between fine-grained tur­ It is noted that some fining-upward laminated bidites and contourites is by no means clear-cut. core sections cannot strictly be attributed to fine The petrology of certain laminated mud sections parallel laminated mud, laminated mud turbi­ interpreted as turbidites suggests a more complex dite, or hemipelagic mud facies. Apparently there origin involving release from suspension and/or exists a petrologic continuum among these types. fluid-driven circulation; other sections inter­ preted as contourites appear difficult to distin­ guish from low concentration turbidity current or Implications and Conclusions turbid layer deposits. An association of different laminated end- Physical and chemical attributes of the much member mud types most likely occurs in settings smaller and shallower Mediterranean serve to where two or more transport processes are in­ amplify petrologic differences that are not so volved. A continuum of fine-grained facies and a apparent among fine-grained, deep-water depos­ blurring of their origin should be expected where its in large ocean basins. Important Mediterra­ long distance transport increases the possibility of nean characteristics include periodic develop­ interplay among turbiditic, traction, and hemi­ ment of well-stratified water masses, relatively pelagic settling mechanisms. The Northwest At­ small distance between point of sediment input lantic margin off the U.S. East Coast and Cana­ and final depositional site, generally low bottom dian Maritime Provinces, where most sedimen- current velocities in deep basins, and preservation tologic studies of fine-grained deposits have been of carbonate components. During specific periods made, serves as a good example. In this region in the recent past, oceanographic conditions, and the possible origins for lamination are reviewed thus sedimentation in the Mediterranean were by Stow and Bowen (1980). In the case of the somewhat more comparable to other world mud turbidite end-member, these authors pro­ oceans. Sediment transport involved (1) periodic pose a model involving thick flows of low concen­ injection of sediments and their displacement tration in which laminae formation results from downslope by gravity flows of low concentration, depositional sorting by increased shear near the (2) deviation of such flows diagonally or parallel base of the bottom boundary layer. to the margin by current-driven circulation, (3), Theoretical considerations and textural-fabric incorporation, concentration, and displacement NUMBER 19 15 of particles from turbidity current-derived sus- and settling rates through the column by density pensates and hemipelagic settling on pycnoclines and size, thus resulting in (1) more effective sep­ and in near-bottom nepheloid layers, and (4) aration of coccolith from terrigenous silty clay eventual release of these particles through density layers and (2) better development of fining-up­ interfaces and from nepheloid layers to the sea­ ward trends of laminae sets (Figure 6E-G). The floor. A laminated sequence resulting from this varve-like configurations in Figure 6A-D record plexus of mechanisms is neither a mud turbidite, repetition of depositional events and modifying hemipelagite, or contourite in the strict sense. effects of pycnoclines, i.e., injection of material by On the basis of the petrology of Mediterranean turbidity currents and turbid layers, retention of laminated muds, described in the previous sec­ periodic planktonic blooms, largely coccoliths, tion, it is possible to distinguish (1) laminated and their subsequent settling to the seafloor. mud turbidite and (2) hemipelagic mud end- Compositional segregation of coccoliths from ter­ members from (3) a deposit originating by cou­ rigenous clayey silts, as distinct laminae, appears pled sediment gravity flow-hemipelagic settling. less well developed in laminated mud turbidites The multiple-origin deposits, "(3)," are varve-like than in the fine parallel mud facies. On the basis and record episodic fluxes preserved as thin, al­ of an averaged depositional rate of 20 cm/1000 ternating sequences of clastic components that years, each laminae couplet is deposited during a include reworked benthic and planktonic faunas 2 to 20 year period. mixed with clayey silt and layers comprising al­ On the other hand, the downslope decrease of most entirely tests of recent pelagic organisms. grain size and laminae thickness measured in Two other diagnostic criteria of these finely lam­ mud turbidites (cf. Stow and Bowen, 1980) is less inated sequences are rates of deposition and areal obvious in finely laminated facies. In this respect, distribution. Core sections show that fine parallel the geometry of Mediterranean upper Pleistocene laminated facies, like those of hemipelagites, tend to lower Holocene finely laminated facies (Huang to accumulate over broad areas of a basin and its and Stanley, 1972; Maldonado and Stanley, contiguous margins (cf. Stanley and Maldonado, 1976a; Stanley and Maldonado, 1981), recalls the 1981, fig. 7). These muds, recording periodic configuration and distribution of fine parallel, injection by sediment gravity flows, accumulate silt-rich layers mapped over large sectors of the at higher rates (>15 cm/1000 years) than hemi­ Delaware River Basin of Texas-New Mexico in pelagic deposits. In contrast to turbidites and middle Permian time. These latter laminated, not unifites that are somewhat richer in terrigenous conspicuously graded, facies, deposited as a func­ components and accumulate at higher rates, re­ tion of density-stratified water mass conditions, gional core surveys show that finely laminated show no obvious proximal to distal changes muds display a regionally more consistent thick­ (Harms, 1974). Hydrography and sediment grav­ ness and broader distribution, and are less re­ ity flows are major factors in both these modern stricted to specific depositional environments. and ancient deposits. Sediment gravity flows that The model emphasized here (Figure 5) indi­ displace at least 1 km' of sediment are not uncom­ cates that stratification interfaces in the water mon in Mediterranean basins (Blanpied and column that affect particle retention are impor­ Stanley, 1981:29). Flows of this magnitude intro­ tant for interpreting some types of fine-grained duced into the isothermal regime, which has pre­ lamination. This scheme suggests that distinct vailed during the past 6000 years, are responsible pycnoclines modify particle concentration and for turbidites and unifites ranging in thickness particle release rates through the water column from 30 cm to over 1000 cm in small basins, such so as to segregate terrigenous silt and clay floes as those of the Hellenic Trench. However, dis­ from planktonic tests. A well-marked density in­ placement of equivalent sediment volumes as low terface amplifies differences in particle release concentration flows, at times of a stratified water 16 SMITHSONIAN CONTRIBUTIONS TO THE MARINE SCIENCES

regime, would result in much broader distribu­ There, it has been shown that small-scale and tion of material. Varve-like sets released from short-term changes in oxygen content can induce about 1 km3 of sediment spread over large parts rather significant alterations in organic produc­ of basins, such as the Ionian or Algero-Balearic, tivity, including coccolith and foraminiferal would likely be less than 1 cm thick (Stanley, blooms, and modifications of benthic popula­ 1981:83). tions. Physico-chemical changes needed to trans­ Laminae preservation also sheds light on dep­ form hospitable to inhospitable conditions at ositional origin. Some cores from the Aegean, depth may be small; moreover, such changes may Siculo-Tunisian (Pelagian) Platform (Maldonado occur suddenly or gradually and, as in the case of and Stanley, 1976a; Blanpied, 1978), Corsican lakes, seasonally (cf, Hiilseman and Emery, Trough (Stanley et al., 1980), Alboran Sea 1961:289). Inhospitable conditions on the sea­ (Huang and Stanley, 1972), and other areas show floor, such as at times of sapropel formation, indistinct (Figure 6B) or disturbed laminae re­ result in diminution or absence of benthic popu­ cording the influence of bottom currents, or or­ lations and enhanced probability of lamina pres­ ganisms, or both. In contrast, 10 to 40 cm-thick ervation (Moore and Scruton, 1957). Bottom sections of undisturbed laminated units in the camera and sediment sampling surveys in various Hellenic Trench region indicate that deposition Mediterranean basins demonstrate that, at pres­ was rapid, that the influence of bottom currents ent, conditions above the seafloor are highly suit­ was negligible and, more importantly, unfavora­ able for sustaining important benthic popula­ ble oxygen-deficient conditions on the seafloor tions. High concentrations of feeding and burrow­ reduced benthic populations, thus minimizing ing structures indicate that fine lamination de­ disturbance of surficial sediments. Moreover, it is veloped in recent time, at least since about 6000 recalled that the well-preserved finely laminated years B.P., would not likely be preserved. mud sections have a basin-wide and temporally In summary, the study emphasizes the signifi­ extensive distribution. It thus appears that upper cance of climatic-oceanographic factors, the in­ Pleistocene to Holocene lamination in the Medi­ volvement of two or more processes in the devel­ terranean was not produced by an oxygen mini­ opment of lamination of fine facies in deep-ma­ mum layer restricted to a specific horizon in the rine environments, and that laminated muds are water column as recorded in the present Gulf of not necessarily turbidites or contourites in the California (Calvert, 1964). Preservation of lami­ strict sense. Observations made here commonly nae is most likely related to the formation of prevail and are not unique to the Mediterranean. thicker, more extensive columns of oxygen-defi­ In consequence, mud deposits of the type de­ cient water and to anoxic seafloor conditions of scribed herein—redeposition of margin sediments the Black Sea (Arkhangel'skiy, 1927) and deep by gravity flows coupled with hemipelagic set­ fjord (Strom, 1939) types; the absence of benthic tling through a stratified water column—could organisms is an important factor in the preser­ probably be recognized in diverse marine settings. vation of well-defined parallel laminae, as illus­ The mechanism deserves to be quantified. Con­ trated by Miiller and Stoffers (1974, fig. 4). tinuing investigation of mud lithofacies in small The varved aspect calls to mind the relation to moderate seas holds promise for better inter­ between sedimentary structures and organisms in pretation of fine-grained deposits in the larger some stratified basins off Southern California. world oceans and the sedimentary rock record. Literature Cited

Allan, T.D., T. Akal, and R. Molcard tors, Shelf Sediment Transport, pages 307-331. 1972. Oceanography of the Strait of Sicily. Saclanl ASW Stroudsburg, Pennsylvania: Dowden, Hutchinson Research Centre Conference Proceedings, 7:1 -229. La & Ross. Spezia, Italy. Eittreim, S., and M. Ewing Arkhangel'skiy, A.D. 1972. Suspended Particulate Matter in the Deep Waters 1927. On the Black Sea Sediments and Their Signifi­ of the North American Basin. In A.L. Gordon, cance in Sedimentology. Moskovskoe Obshchestvo is- editor, Studies in Physical Oceanography, Georg Wiist pytatelei prirody Biullelen\ Otdel Geologicsku, 5:199- Tribute, 2:123-167. New York: Gordon & Breach. 289. Emelyanov, E.M.. and K.M. Shimkus Blanpied, C. 1972. Suspended Matter in the Mediterranean Sea. In 1978. Structure et sedimentation superficielles en mer D.J. Stanley, The Mediterranean Sea—A Natural Sed­ pelagienne. 119 pages. Thesis, Universite Pierre et imentation Laboratory, pages 417-439. Stroudsburg, Marie Curie, Paris. Pennsylvania: Dowden, Hutchinson & Ross. Blanpied, C, and D. J. Stanley Got, H., D.J. Stanley, and D. Sorel 1981. Uniform Mud (Unifite) Deposition in the Hellenic 1977. Northwestern Hellenic Arc: Concurrent Sedimen­ Trench, Eastern Mediterranean. Smithsonian Con­ tation and Deformation in a Compressive Setting. tributions to the Marine Sciences, 13: 40 pages. Marine Geology, 24:21-36, 7 figures. Bradley, W.H. Harms, J.C. 1938. Mediterranean Sediments and Pleistocene Sea 1974. Brushy Canyon Formation, Texas: A Deep-Water Levels. Nature, 88:376-379. Density Current Deposit. Bulletin of the Geological Burollet, P.F., P. Clairefond, and E. Winnock Society of America, 85:1763-1784. 1979. La mer pelagienne. Geologic Mediterraneene; 4:1-345. Hay, W.W. Calvert, S.E. 1974. Studies in Paleo-Oceanography. Society of Economic 1964. Factors Affecting Distribution of Laminated Dia- Paleontologists and Mineralogists Special Publication, tomaceous Sediments in the Gulf of California. In 20: 218 pages. T.H. van Andel and G.G. Shor, Jr., editors, Ma­ Heezen, B.C., and CD. Hollister rine Geology of the Gulf of California. American 1971. The Face of the Deep. 659 pages. New York: Oxford Association of Petroleum Geologists Memoir, 3:311-330. University Press. Carter, T.G., J.P. Flanagan, CR. Jones, F.L. Marchant, Hollister, CD., and B.C. Heezen R.R. Murchison, J.H. Rebman, J.C. Sylvester, and J.C. 1972. Geologic Effects of Ocean Bottom Currents: West­ Whitney ern North Atlantic. In A.L. Gordon, editor, Studies 1972. A New Bathymetric Chart and Physiography of in Physical Oceanography, Georg Wiist Tribute, 2:37- the Mediterranean Sea. In D.J. Stanley, editor, 66. New York: Gordon & Breach. The Mediterranean Sea—A Natural Sedimentation Lab­ Hsu, J.K., L. Montadert, Shipboard Scientific Party oratory, pages 1-23. Stroudsburg, Pennsylvania: 1978. Initial Reports of the Deep Sea Drilling Project. Volume Dowden, Hutchinson & Ross. 42, part 1, 1249 pages. Washington, D.G: Na­ Climap Project Members tional Science Foundation. 1976. The Surface of the Ice-Age Earth. Science, 191: Huang, T.-C, and D.J. Stanley 1131-1144. 1972. Western Alboran Sea: Sediment Dispersal, Pond­ Dominik, J., and A. Mangini ing and Reversal of Currents. In D.J. Stanley, 1979. Late Quaternary Sedimentation Rate Variations editor, The Mediterranean Sea—A Natural Sedimenta­ on the Mediterranean Ridge, as Results from the tion Laboratory, pages 521-559. Stroudsburg, Penn­ 230th Method. Sedimentary Geology, 23:95-112. sylvania: Dowden, Hutchinson & Ross. Drake, D.E., R.L. Kolpak, and P.J. Fischer Hiilsemann, J., and K. O. Emery 1972. Sediment Transport on the Santa Barbara-Ox- 1961. Stratification in Recent Sediments of Santa Bar­ nard Shelf, Santa Barbara Channel, California. In bara Basin as Controlled by Organisms and Water D.J.P. Swift, D.B. Duane, and OH. Pilkey, edi­ Characteristics. Journal of Geology, 69:279-290.

17 18 SMITHSONIAN CONTRIBUTIONS TO THE MARINE SCIENCES

Kastens, K.A., and M.B. Cita Pierce, J.W. 1981. Tsunami-induced Sediment Transport in the 1976. Suspended Sediment Transport at the Shelf Break Abyssal Mediterranean Sea. Bulletin of the Geological and over the Outer Margin. In D.J. Stanley and Society of America, 92:845-857. D.J.P. Swift, editors, Marine Sediment Transport and Kullenberg, B. Environmental Management, pages 437-458, 8 figures. 1952. On the Salinity of the Water Contained in Marine New York: Wiley-Interscience. Sediments. Meddelanden frau Oceanografska Institution Pierce, J.W., and D.J. Stanley Goteborgs, 21:1 -38. 1976. Suspended Sediment Concentration and Mineral­ Lacombe, H., and P. Tchernia ogy in the Central and Western Mediterranean 1972. Caracteres hydrologiques et circulation des eaux and Mineralogic Comparison with Bottom Sedi­ en Mediterranee. In D.J. Stanley, editor, The Med­ ment. Marine Geology, 19:M15-M25. iterranean Sea—A Natural Sedimentation Laboratory, Pierce, J.W., S. Tucci, and G. Fierro pages 25-36. Stroudsburg, Pennsylvania: Dow­ 1981. Assessing Variations in Suspensates, Ligurian Sea den, Hutchinson & Ross. (Northwestern Mediterranean). Geo-Manne Letters, Lisitzin, A.P. 1:149-154. 1972. Sedimentation in the World Ocean. Society of Eco­ Piper, D.J.W. nomic Paleontologists and Mineralogists Special Publi­ 1978. Turbidite Muds and Silts on Deepsea Fans and cation, 17: 218 pages. Abyssal Plains. In D.J. Stanley and G. Kelling, Luz, B. editors, Sedimentation in Submarine Canyons, Fans, and 1979. Paleo-Oceanography of the Post-Glacial Eastern Trenches, pages 163-176. Stroudsburg, Pennsylva­ Mediterranean. Nature, 278:847-848. nia: Dowden, Hutchinson & Ross. Maldonado, A., and D.J. Stanley Rupke, N.A., and D.J. Stanley 1976a. Late Quaternary Sedimentation and Stratigraphy 1974. Distinctive Properties of Turbiditic and Hemipe­ in the Strait of Sicily. Smithsonian Contributions to the lagic Mud Layers in the Algero-Balearic Basin, Earth Sciences, 16: 73 pages. Western Mediterranean Sea. Smithsonian Contribu­ 1976b. The Nile Cone: Submarine Fan Development by tions lo the Earth Sciences, 13: 40 pages. Cyclic Sedimentation. Marine Geology, 20:27-40. Ryan, W.B.F. 1977. Lithofacies as a Function of Depth in the Strait of 1972. Stratigraphy of Late Quaternary Sediments in the Sicily. Geology, 5:111-117. Eastern Mediterranean. In D.J. Stanley, editor, 1978. Nile Cone Depositional Processes and Patterns in The Mediterranean Sea—A Natural Sedimentation the Late Quaternary. In D.J. Stanley and G. Laborlory, pages 149-169. Stroudsburg, Pennsyl­ Kelling, editors, Sedimentation in Submarine Canyons, vania: Dowden, Hutchinson & Ross. Fans, and Trenches, pages 239-257. Stroudsburg, Ryan, W.B.F., J.K. Hsu, and Shipboard Scientific Party Pennsylvania: Dowden, Hutchinson & Ross. 1973. Initial Reports of the Deep Sea Drilling Project. Volume 1979. Depositional Patterns and Late Quaternary Evo­ 13, parts 1 and 2, 1447 pages. Washington, D.C: lution of Two Mediterranean Submarine Fans: A National Science Foundation. Comparison. Marine Geology, 31:215-250. Schnitker, D. Mars, P. 1980. Quaternary Deep-Sea Benthic Foraminifers and 1963. Les faunes et la stratigraphie du Quaternaire Med­ Bottom Water Masses. Annual Review, Earth and iterranean. Recueil des Travaux, Station Maritime Planetary Sciences, 8:343-370. d'Endoume, 28:61-97. Stanley, D.J. Moore, D.G., and P.C. Scruton 1978. Ionian Sea Sapropel Distribution and Late Qua­ 1957 Minor Internal Structures of Some Recent Uncon­ ternary Paleoceanographic Considerations in the solidated Sediments. Bulletin of the American Associ­ Eastern Mediterranean. Nature, 274:149-152. ation of Petroleum Geologists, 41:2723-2751. 1981. Unifites: Structureless Muds of Gravity-Flow Or­ Miiller, G., and P. Stoffers igin in Mediterranean Basins. Geo-Manne Letters, 1974. Mineralogy and Petrology of Black Sea Basin 1:77-83. Sediments. In E.T. Degens and D. Ross, editors, Stanley, D.J., and C. Blanpied The Black Sea—Geology, Chemistry, and Biology. 1980. Late Quaternary Water Exchange between the American Association of Petroleum Geologists Memoir, Eastern Mediterranean and the Black Sea. Nature, 20:200-248, 22 figures. 285:537-541. Olausson, E. Stanley, D.J., and A. Maldonado 1961. Studies of Deep-Sea Cores. Reports of the Swedish 1979. Levantine Sea—Nile Cone Lithostratigraphic Ev­ Deep-Sea Expedition, 1947 1948, 8:353-391. olution: Quantitative Analysis and Correlation NUMBER 19 19

with Paleoclimatic and Eustatic Oscillations in Ancient Sediments. Earth-Science Review, 14:251- the Late Quaternary. Sedimentary Geology, 23:37- 291. 65. Strom, K.M. 1981. Depositional Models for Fine-grained Sediment in 1939. Land-locked Waters and the Deposition of Black the Western Hellenic Trench, Eastern Mediterra­ Muds. In P.D. Trask, editor, Recent Marine Sedi­ nean. Sedimenlology, 28:273-290, 12 figures. ments, pages 356-372. Tulsa, Oklahoma. American Stanley, D.J., A. Maldonado, and R. Stuckenrath 1975. Strait of Sicily Depositional Rates and Patterns, Association of Petroleum Geologists. and Possible Reversal of Currents in the Late Thunell, R.C, and GP. Lohmann Quaternary. Paleogeography, Paleoclimalology, and Pa­ 1979. Planktonic Foraminiferal Fauna Associated with leoecology, 18:279-291. Eastern Mediterranean Quaternary Stagnations. Stanley, D.J., J.P. Rehault, and R. Stuckenrath Nature, 281:211-213. 1980. Turbid-Layer Bypassing Model: The Corsican Vergnaud-Grazzini, C, W.B.F. Ryan, and M.B. Cita Trough, Northwestern Mediterranean. Marine Ge­ 1977. Stable Isotopic Fractionation, Climate Change ology, 37:19-40. and Episodic Stagnation in the Eastern Mediter­ Stow, D A.V., and AJ. Bowen ranean during the Late Quaternary. Marine Micro­ 1980. A Physical Model for the Transport and Sorting paleontology, 2:353-370. of Fine-grained Sediment by Turbidity Currents. Sedimenlology, 27:31 -46. Wiist, G. Stow, D .A.V., and J.P.B. Lovell 1961. On the Vertical Circulation of the Mediterranean 1979. Contourites: Their Recognition in Modern and Sea. Journal of Geophysical Research, 66:3261-3271.