SMITHSONIAN CONTRIBUTIONS TO THE MARINE SCIENCES • NUMBER 13 

Uniform Mud (Unifite) Deposition 

in the Hellenic Trench, 

Eastern Mediterranean 

Christian Blanpied 

and 

Daniel Jean Stanley 

SMITHSONIAN INSTITUTION PRESS 

City of Washington 

1981 
ABSTRAC T 

Christian Blanpied and Daniel Jean Stanley. Uniform Mud (Unifite) Deposition in the Hellenic Trench, Eastern Mediterranean. Smithsonian Contributions to the Marine Sciences, number 13, 40 pages, 15 figures, 2 tables, 1981.— 

Unifites are nearly structureless, often thick, layers of clayey silt and silty clay 

that appear compositionally homogeneous and generally show a subtle finingupward trend. Formed by uniform and faintly laminated muds, unifites are 

deposited from rapidly emplaced single gravity-flow events. Along the Hellenic 

Arc, unifites are restricted to small trench basins and interpreted as an endmember gravity-emplaced facies. Unifites are not truly homogeneous and the 

petrological distinctions observed are closely related with the trench basin 

depositional site relative to steep margins bounding the trench plain. The 

faintly laminated portions of unifites contain a higher silt content; the uniform 

mud portions are slightly better sorted and display an upward increase of 

planktonic tests. The sand fraction is dominated by clastic aggregates eroded 

from older margin sediments; unifites also comprise a large silt-size nannofossil 

content (including reworked forms). 

The increased uniformity basinward of unifites records deposition from 

turbidity current-related flows of diminished concentration that spread over 

large areas of a flat trench floor. Faint laminae may be related to phases of 

flocculation and depositional sorting of the sediment load during transport, 

and to the hydraulic jump affecting a flow upon its arrival on a near-flat 

basin floor. The slower-moving tail releases the uppermost nonlaminated, 

graded unifite mud term. The thickness of Hellenic unifites is a function of 

entrapment of moderate amounts of material in small trench plains. The 

homogenization process essential for unifite deposition involves relief bypass, 

i.e., the preferential entrapment of coarser or denser fractions in slope depressions, while finer or less dense particles are transported further downslope 

across irregular seafloor features. Unifite deposition records the interplay of: 

(1) complexity of dispersal paths and accessibility of sediment to the trench 

basin, (2) redepositional processes, grain-support mechanisms and gravityinduced flow characteristics, (3) type of material transported, (4) extent of 

textural segregation and compositional sorting during flow, (5) slope relief 

bypassing process, and (6) selective entrapment of essentially fine-grained 

particles in the more distal trench catchment basins. Mediterranean unifites 

can serve to interpret uniform mud facies on both active and passive margins 

and in the rock record. 

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 

Blanpied, Christian. 

Uniform mud (unifite) desposition in the Hellenic trench, eastern Mediterranean. 

(Smithsonian contributions to the marine sciences ; no. 13) 

Bibliography: p. 

Supt. of Docs, no.: SI 1.41:13 

1. Marine sediments—Helenic Trough. I.Stanley, Daniel J. II. Title. III. Series. 

GC389.B57 551.46'083'384 81-607825 AACR2 
Contents 

Page 

Introduction 1 

Acknowledgments 2 

Methodology and Abbreviations 2 

Geological Framework of the Study Area 4 

General Observations 7 

Regional and Environment-related Variations 10 

Contrasting Uniform and Faintly Laminated Mud Sequences 11 

Grain Size Analysis 13 

Composition 15 

Vertical Petrological Changes 17 

Contrasting Margin Flat and Basin Plain Sequences 17 

Environmental Control 20 

Discussion 21 

Evidence for Gravitative Origin of Fine-grained Mud Types 21 

Classification of Fine-grained Turbidite Mud Sequences 22 

Petrologic Variations Related to Flow Fluctuations 24 

Implications of Study and Conclusions 29 

Summary 35 

Literature Cited 38 
Uniform Mud (Unifite) Deposition 

in the Hellenic Trench, 

Eastern Mediterranean 

Christian Blanpied 

and Daniel Jean Stanley 

Introduction 

The increased interest in the depositional origin 

of fine-grained marine sediments has resulted in 

the recognition of diverse mud types. Several 

classifications have called attention to a structureless mud facies reported in some modern 

deep-sea environments and in the marine rock 

record (summaries in Piper, 1978, and Stow and 

Shanmugam, 1980). The premise of this study is 

that the Mediterranean region, with its well-exposed mudstone formations in the surrounding 

mountain chains and its thick, mud-rich postMiocene unconsolidated sequences in the various 

isolated basins (Stanley, 1977a), should be a particularly suitable sector in which to define the 

nature, distribution, and origin of such apparently homogeneous lutites. Insofar as the modern 

Mediterranean Sea is concerned, studies focusing 

on fine-grained sediment transport have been 

undertaken in several basin settings. Sedimentological research has advanced during the past 

fifteen years largely as a result of combined coring 

and subbottom profiling surveys in diverse topographic settings where unconsolidated deposits of 

Christian Blanpied, Compagnie Franqaise des Petroles, Department 

dExploration, Paris, France. Daniel Jean Stanley, Division of 

Sedimentology, National Museum of Natural History, Smithsonian 

Institution, Washington, D.C. 20560. 

suspension and gravity-emplaced origin have accumulated. 

Sedimentological studies of ponded (cf. Hersey, 

1965) Mediterranean mud facies have been undertaken in deep depressions, such as the western 

Alboran Sea (Stanley, Gehin, and Bartolini, 

1970), portions of the Algero-Balearic Basin Plain 

(Rupke and Stanley, 1974), Tyrrhenian Basin 

Plain (Ryan, Workum, and Hersey, 1965); Corsican Trough (Stanley, Rehault, and Stuckenrath, 1980); deep troughs in the Strait of Sicily 

(Maldonado and Stanley, 1976; Blanpied et al., 

1979), and some small basins in the Adriatic Sea 

(van Straaten, 1967), and on the Mediterranean 

Ridge (Kastens and Cita, in press). In the Hellenic Arc region of the eastern Mediterranean 

investigations of fine-grained sedimentation have 

been made by Hersey (1965), Ryan et al. (1973), 

Vittori (1978), and Maldonado, Kelling, and Anastasakis (1981). 

Detailed mapping of Quaternary unconsolidated sediment in different depositional environments of the Hellenic Trench reveals that clayey 

silt and silty clay, rather than sand, almost invariably dominate the depositional cover of this 

structurally and morphologically complex region. 

Seven fine-grained sediment types, or lutites, have 

been identified by Stanley and Maldonado (1981) 
SMITHSONIAN CONTRIBUTIONS TO THE MARINE SCIENCES 

in a suite of 24 cores collected in eight distinct 

depositional settings west and south of the Peloponnesus (Figure 1). Four of these mud types 

(slump, debris flow, turbiditic and hemipelagic) 

have received considerable attention in earlier 

studies of both modern and ancient deep marine 

sediments. A fifth type includes very well-laminated mud facies that accumulated throughout 

much of the Hellenic area (see Stanley and Maldonado, 1981, fig. 3b, c); this facies formed primarily during periods of marked water mass stratification, such as at time of sapropel formation, 

which affected most of the eastern Mediterranean. The present study focuses specifically on 

the other two, apparently related, fine-grained 

facies that are concentrated primarily in Hellenic 

Trench basins proper. These types are apparently 

structureless uniform mud and faintly laminated 

mud. 

Several possible mechanisms have been proposed for the emplacement of these two lutite 

types in the study area. Earlier studies indicated 

that homogeneous muds may have been deposited in part by fine pelagic suspension-related 

processes (Ryan, et al., 1973:268) or, alternately, 

by "giant" dense mud flows (Stanley and Knight, 

1979). More recent detailed analysis of the uniform and faintly laminated muds, however, suggest that these two lutite types most likely represent "single-event" gravitative deposits. The 

mechanisms involve the settling of material from 

slow moving and low concentration flows, which 

are related to turbidity currents that are preferentially ponded in small trench basins (Stanley 

and Maldonado, 1981, fig. 11). 

The term "unifite"1 (Stanley, 1980) is applied 

to the nearly structureless, often thick, layers of 

clayey silt and silty clay that are formed by 

uniform and faintly laminated mud facies described in this study. Such deposits generally 

appear, but are not truly, compositionally hoThe term "unifite" was formally introduced by D. J. 

Stanley in October 1980 at the Conference on "Sedimentary 

Basins of Mediterranean Margins" sponsored by the Consiglio Nazionale delle Ricerche at the University of Urbino, 

Italy. 

mogeneous, show various subtle fining-upward 

trends, and are deposited by gravity flow transport events. The formulation of a depositional 

model for uniform muds requires a refined description of the petrologic attributes of these finegrained, structureless deposits. Particular attention is paid here to selected uniform mud sections 

from seven piston cores collected in three Hellenic 

Trench basins during cruises of the R/V Trident 

(1975) and the R/V Marsili (1976). 

ACKNOWLEDGMENTS.—Our sincere appreciation is expressed to Mr. H. Sheng, Smithsonian 

Institution, who assisted with all aspects of the 

petrologic and laboratory analyses. Radiocarbon 

dates were generously provided by Dr. R. Stuckenrath, Smithsonian Institution Radiation Biology Laboratory, and selected bottom photographs from the 1978 Hellenic Trench Raie cruise 

in the Kithera-Antikithera Trench were furnished 

by Messrs. J. Jarry and R. Person, Centre National pour l'Exploitation des Oceans, France. 

Drs. S. Culver, U. S. National Museum of Natural History, G. Glacon, University of Paris VI, 

and C. C. Smith, U. S. Geological Survey, Washington, kindly identified selected collections of 

benthic foraminifera, planktonic foraminifera, 

and coccoliths, respectively. 

Discussions during the early phases of the Hellenic Trench study with R. J. Knight, PetroCanada Limited, and A. Maldonado, University 

of Barcelona, proved most useful. The paper was 

reviewed by Dr. R. W. Embley, National Ocean 

Survey, National Oceanic and Atmospheric Administration, Washington, D.C, Mr. P. H. Feldhausen, NUS Corporation, Rockville, Maryland, 

and Dr. H. D. Palmer, Interstate Electronics Corporation, Arlington, Virginia. The study, part of 

the continuing Mediterranean Basin (MEDIBA) 

Project, was supported by a fellowship to C. 

Blanpied from the French Ministry of Foreign 

Affairs, Paris, and by Smithsonian Scholarly 

Studies grant number 1233S101. 

Methodology and Abbreviations 

The seven western Hellenic Trench cores containing uniform mud (1975 cruise R/V Trident, 
NUMBER 13 

D Slope, steep smooth 

• Slope, broken high relief 

$L Canyon, depression 

^c Perched basin, proximal 

5fc Perched basin, distal 

©Trench basin, apron 

OTrench basin, flat margin 

# Trench basin, plain 

T T -34° 

FIGURE 1.—Western Hellenic Trench margin showing the location of R/ V Trident (TR 34-36) 

and R/ V Marsili (MA 10, 20, 22, 23) cores and the physiographic environments in which they 

were recovered (circled numbers = cores containing unifites; uncircled core numbers do not 

have obvious unifites; ZB = Zakinthos-Strofadhes Basin, MB = Matapan Deep; KB = KitheraAntikithera Basin). 
SMITHSONIAN CONTRIBUTIONS TO THE MARINE SCIENCES 

or TR, cores 34, 35, 36; 1976 cruise R/V Marsili, 

or MA, cores 10, 20, 22, 23) range in length from 

565 to about 1000 cm. For comparison purposes, 

other cores collected in this region were also 

examined. Complementary data concerning these 

and other cores cited in this paper, including core 

position, depth, and lithological information is 

provided elsewhere (Stanley, Knight, and Stuckenrath, 1978; Vittori, 1978; Stanley and Maldonado, 1981; Feldhausen et al., 1981). For the petrologic analyses, more than 250 samples were 

collected from uniform and faintly laminated 

mud layers at intervals ranging from about 5 to 

25 cm. These samples were selected primarily on 

the basis of x-radiography of split cores, which is 

the most certain method to recognize both uniform and faintly laminated mud types. 

All samples were treated in the same way. The 

sand fraction (>63 /xm) was recovered by sieving, 

while the silt-clay separation was made using the 

Andreasen pipette method. Determinations of the 

complete size distribution of the silt and clay 

(<2 tim) fractions were completed with a Coulter 

Counter Model TA-II with two apertures (140 

and 30 jum). The distribution (volumetric percent) of the entire silt and clay fraction was 

determined with the 140 micrometer aperture; 

selected samples from each core were processed 

using the 30 micrometer aperture to better define 

the fine silt and clay size distribution. 

In those samples (approximately 150) where 

sufficient sand size material was available, the 

composition of 150 to 500 sand grains was identified using a petrographic microscope. Eighteen 

mineralogic components are recognized, and 

these are grouped into four major categories: (1) 

terrigenous (light minerals, heavy minerals, 

mica); (2) biogenic (planktonic foraminifera, shell 

fragments, benthic foraminifera, spicules, pyritized planktonic foraminifera, pteropods, pyritized benthic tests, ostracodes, juvenile forms of 

pelecypods, radiolarians and diatoms); (3) oxidized or reduced aggregates (red, black and plateshaped); and (4) clastic aggregates consisting of 

cemented silt-sized particles. 

The silt size fraction (2 to 63 /xm) of all 250 

samples was examined. This fraction includes 13 

mineralogical components identified by highpower petrographic microscope and SEM, and 

these are grouped into five major categories: (1) 

terrigenous (quartz, feldspar); (2) biogenic (foraminifera, coccoliths, spicules, carbonate shell 

fragments); (3) volcanic products (palagonite, sideromelane, chlorite and heavy minerals, including microlite); (4) authigenic (recrystallized calcite and dolomite); and (5) clastic aggregates. 

The proportions of these silt-size groups are determined semiquantitatively by using a relative 

abundance scale, from 1 (trace amounts) to 5 

(abundant). 

The composition of the clay size fraction (<2 

jum) was determined by x-ray diffraction, SEM, 

and chemical probe analyses. Forty-four samples 

were selected from cores MA-10 and MA-20, and 

twenty additional samples were obtained from 

the other five uniform mud-bearing cores. In 

addition, about 105 samples were selected from 

the other 17 cores shown in Figure 1 to determine 

the clay mineral composition of silt size. 

Calcium carbonate content was determined for 

all mud samples using the standard ascarite absorption technique. These data were supplemented by thirty radiocarbon dates obtained 

from the seven uniform mud-bearing cores and 

two dates from slope core TR-37 (Table 1); nine 

of these were previously published in Stanley, 

Knight, and Stuckenrath (1978). Also utilized in 

this study were high-resolution 3.5 kHz records 

collected near the core sites during the 1975 

Trident and 1976 Marsili cruises, and a suite of 

about 300 bottom photographs collected in 1978 

in the Kithera Trench by the French Centre 

National pour l'Exploitation des Oceans. 

Abbreviations used in this study are as follows: 

FL = faintly laminated mud, KB = KitheraAntikithera Trench system, MA = Marsili cruise, 

MB = Matapan Deep Trench system, S = sapropel, TR = Trident cruise, U = uniform mud, ZB 

= Zakinthos-Strofadhes Trench system. 

Geological Framework of the Study Area 

The study area southwest of the Peloponnesus 

and west of Crete (Figure 1) occupies a seismically 
NUMBER 13 

TABLE 1.—List of 30 radiocarbon dates obtained for seven 

western Hellenic Trench basin cores containing unifites, and 

two dates for core TR-37 collected on the steep Zakinthos 

slope (B.P. = years before present) 

Core 

number 

MA-10 

MA-20 

MA-22 

MA-23 

TR-34 

TR-35 

TR-36 

TR-37 

Sample 

depth 

(cm) 

50- 63 

261-275 

495-507 

16- 30 

151-166 

272-287 

392-407 

589-604 

942-957 

89-106 

171-185 

239-254 

357-388 

686-698 

25- 40 

110-130 

250-264 

415-440 

495-507 

130-144 

187-200 

339-353 

667-679 

135-150 

220-235 

290-310 

470-490 

240-260 

450-465 

530-550 

50- 65 

240-255 

Radiocarbon 

date 

(B.P.) 

12,775±155 

15,170±130 

15,030±125 

12,090± 90 

11,880±110 

13,000±120 

12,450± 95 

14,045±110 

14,840±105 

11,260±160 

10,215±130 

19,290±325 

19,460±325 

25,300±370 

11,315± 95 

28,060±610 

29,100±550 

29,700±730 

26,860±460 

14,500±120 

17,810±175 

28,730±650 

25,240±350 

10,175± 75 

16,510±150 

18,600±140 

19,710±210 

16,510±130 

16,910±155 

20,100±220 

17,380±160 

>43,000 

active region in the western part of the Hellenic 

Arc. Overall, this sector occupies a technically 

complex, largely compressive setting, believed to 

have experienced subduction and considerable 

vertical and lateral offset. The roles of plate collision and transform fault motion are discussed 

by Comninakis and Papazachos (1972), McKenzie (1972), Makris (1976), Biju-Duval, Letouzey, and Montadert (1979), Mascle and Le 

Quellec (1979), Le Pichon and Angelier (1979), 

and many others. The structural and stratigraphic configurations of this investigated region 

have been detailed by means of several closely 

spaced, high-resolution seismic surveys, the results 

of which are summarized by Got, Stanley, and 

Sorel (1977), Vittori (1978), and Le Quellec 

(1979). These studies reveal a structurally deformed unconsolidated sediment series of highly 

variable thickness. This series, dated as probable 

Pliocene and Quaternary age, lies above indurated strata locally comprising deposits of Cretaceous (Ryan, et al., 1973), Miocene, including 

probable Messinian evaporites, and Pliocene age 

(Ariane, 1979; Le Pichon, 1980). 

Three distinct and well-individualized trenchbasin systems, clearly apparent on morphological 

charts (Carter et al., 1972), result from this geologically recent tectonic activity. The three separate trench slope and basin systems are delineated 

largely by NW-SE and WSW-ENE tectonic 

trends, involving some extension (Got, Stanley, 

and Sorel, 1977), as well as compression. From 

NW to SE the western Hellenic Trench basin 

plains lie at depths of about 4150 m, 5000 m and 

4615 m, and are named, respectively, the Zakinthos-Strofadhes system (ZB), the Matapan Deep 

system (MB), and the Kithera-Antikithera system 

(KB). Bathymetric and seismic profiles show that 

the trench basins proper are not simple U-shaped, 

elongated troughs. The trenches proper, as displayed in cross-sections of the Matapan Deep, 

include small depressions broken by ridges that 

subdivide, and thus limit, the size of the near-flat 

basin plains (Vittori, 1978:121; Le Quellec, 1979: 

60). The surface area of the flat trench basins 

proper ranges from little more than 100 (ZB) to 

about 250 km2 in the case of the Kithera-Antikithera Basin. 

The extremely complex morphology between, 

and within, each of the trench-slope and basin 

systems complicates the dispersal pattern of sediments transported from the Peloponnesus land 

mass and contiguous margin to the distal basin 

plains (Stanley, 1977b:435). Moreover, morphologic features of high relief which, include ridges 
Margin Flat 

TR-34 

SMITHSONIAN CONTRIBUTIONS TO THE MARINE SCIENCES 

Basin Plain 

'"FfiR7 3 5 

w.i jf$ffiffiP$ 

\~'$*&f%; 

MA-2 3 1 

5 (1 1 

MA-2 2 

MA-20 

, ..«_ ^ , - - - • -

MA- 10 

. " • 

FIGURE 2.—High-resolution 3.5 kHz subbottom profiles of the seafloor at core recovery sites 

(scale = 50 m). Core pairs, from top to bottom (from NW to SE), are: TR-34 and TR-35 in the 

Zakinthos-Strofadhes Basin (ZB), respectively 4060 and 4140 m; MA-22 and MA-23 in the 

Matapan Deep (MB), respectively 4090 and 4120 m; and MA-10 and MA-20 in the KitheraAntikithera Basin (KB), respectively 4300 and 4510 m. Profiles in the left column show trench 

margin flat sectors near the base of steep slopes; profiles in the right column illustrate trench 

basin plain subbottom configuration. 
NUMBER 13 

and submarine prolongations of the Peloponnesus, effectively separate trench basins and preclude gravitative transport from one basin to 

another (Stanley, 1974:248; Vittori, 1978:193). 

Sediments transported into the trench basin systems within the study area are derived primarily 

from the adjacent Peloponnesus landmass and its 

narrow shelf and slope margin (Emelyanov, 1972: 

364; Feldhausen and Stanley, 1980:M27-M29; 

Vittori et al., 1981) and also, to a certain extent, 

from the Aegean Sea (Stanley and Perissoratis, 

1977) and the Mediterranean Ridge, which 

bounds the trench basins to the west and south. 

Dispersal is also influenced by the water mass 

circulation patterns in the eastern Ionian Sea 

(Venkatarathnam and Ryan, 1971; Lacombe and 

Tchernia, 1972:33-34; Miller, 1972). From seismic evidence, there appears to be a general 

increase in the accumulation rate of Pliocene and 

Quaternary sediments from the NW toward the 

SE: the thicknness of the ponded unconsolidated 

strata is locally in excess of 500 m in the ZB basin, 

over 1000m in the MB basin, and ranges from 

about 700 to 1200 m in the KB basin. Considering 

the thickness of this Plio-Quaternary cover, minimal averaged long-term rates of sedimentation 

since the end of the Miocene (Messinian) range 

from about 10 to 20 cm per 1000 years. Higher 

rates are recorded toward the SE. Seismic profiles 

published by Vittori (1978) and others indicate 

that these trench basin deposits, including Quaternary strata are, in almost all cases, deformed, 

thus recording syndepositional tectonic activity. 

The two trench basin environments in which 

unifites are recovered are (1) the margin flat 

(trench plain near the base of steep basin slopes) 

and (2) the basin plain (near-flat plains away 

from steep margins). The configuration of the 

upper 30 to 70 m of sediment in these two environments is illustrated on 3.5 kHz profiles obtained on the Trident 1975 and Marsili 1976 traverses (Stanley, 1977b). Selected seismic lines 

from each of the three basins, showing near-horizontal acoustic reflectors near the sites of cores 

studied herein, are illustrated in Figure 2. Profiles 

obtained across the margin flat (close to cores 

TR-34, MA-23, MA-10) and the basin plain (near 

cores TR-35, MA-22, MA-20) reveal strong reflectors, probably sandy horizons. This assumption is confirmed by drilling at Joides Leg 13 sites 

127 and 128 (Ryan et al., 1973:243), which recovered sand layers. Thick (10-15 m) transparent 

acoustic layers are interpreted as largely mud 

strata. This is confirmed by the piston cores, 

particularly in the case of the 10-m long core 

MA-20 (Figure 2). Close-grid seismic traverses 

show the lateral continuity and extensive areal 

coverage of both hard and transparent acoustic 

layers across the basins and their discontinuity on 

slopes, thus demonstrating the ponding phenomenon as defined by Hersey (1965) and others. 

General Observations 

Three criteria enable us to identify unifites 

composed oi uniform muds (U), or faintly laminated 

muds (FL), or both. The most obvious criteria 

used to recognize these two lithofacies are primary bedform stratification and/or bioturbation 

structures (or their absence) as revealed in xradiographs (Figure 3), supplemented by color 

and texture observed in split cores. The stratigraphic position of a unifite can be defined with 

respect to previously identified diagnostic key 

horizons such as sapropels, oxidized layers, and/ 

or ash tephra (Stanley, Knight, and Stuckenrath, 

1978). Particularly valuable in this respect is the 

upper sapropel (Si) dated at about 8000 years 

before present throughout most of the eastern 

Mediterranean (Stanley, 1978). Determination of 

the relative stratigraphic position of the unifites 

examined in this study is facilitated by the availability of numerous radiocarbon dated core samples (Figure 4, Table 1). Most of these dates, 

however, prove too old as a result of high proportions of reworked carbonate material incorporated in unifites (page 17). 

Only x-radiographic analyses can satisfactorily 

reveal the absence of any bedform structures, 

which are characteristic of the uniform mud facies 

(Figure 3c), and the presence of vague or diffuse 

stratification that characterizes faintly laminated 
A 

260 

B 

28 77(L_ 

270 

280 

290 780 

300 790 

310 80£ _ 

FIGURE 3.—X-radiograph prints of the three fine-grained types discussed in text (core width 

~ 6 cm; numbers are depths in cm below core top): A, Well-developed fine-grained mud 

turbidite showing laminated and graded mud terms (core TR-34, 260-290 cm; see Figure 4). 

B, Faintly laminated mud overlain by uniform mud defining an FL+U sequence (core MA-23 

(unifites), 280-310 cm; see Figure 7). c, Uniform mud showing absence of bedform structures 

(core MA-20 (unifite), 770-800 cm; see Figure 6). 
NUMBER- 13 

Z A KINTHOS -

STROPHADE S 

BASIN S 

TRENCH: Margi n 

Flat 

TR-3 4 

lm 

X 

Z 

3m 

4m 

5m 

6m 

7m 

8m 

9m 

lOm1" 

Basin 

, Plain . 

TR -3 5 TR - 36 

145001 

MATAPA N 

DEE P 

Margi n 

Flat 

MA-23 

11315 

2 

28060|§p l 

29100 

29700 

26860 

,11260 

\ 

\ 

10215 

19290| 

19460| 

Basin 

Plain 

MA-2 2 

25300iyl|| l 

u 

FL 

Upper Units (Undifferentiated ) 

U C Date (year s B.P.) 

•Sapropel 

1

 Uni form Mud . 

[Unifor m Mud Sequence 

•Faintly Laminated Mud' ' = Unifit e 

KITHERA -

ANTI K ITH E R A 

B A S I N 

Margi n Basin 

Flat Plain 

MA-1 0 MA-2 0 

12090 

12775 

15170| 

150301.AAA 

11880 

13000 

•124501 

140451 

14840 1 

FIGURE 4.—Simplified lithofacies logs of the seven cores containing unifites detailed in this 

study, showing their stratigraphic position relative to the upper sapropel (Si) layer. (Numbers 

on left of logs are radiocarbon age determinations (Table 1), dotted lines correlate stratigraphic 

sections, age of the Si sapropel is ca 8000 years B.P., T and arrow in TR-34 core log denote a 

classic mud turbidite. Core positions are shown in Figures 1 and 2.) 
10 SMITHSONIAN CONTRIBUTIONS TO THE MARINE SCIENCES 

mud facies (Figure 3B). In some cases uniform 

mud overlies the faintly laminated mud facies 

(Figure 3B), while in others uniform mud overlies 

well-laminated turbidite sands and silts (Figure 

3A). The petrology of unifites in the various cores, 

regardless of stratigraphic position, is quite similar. In split cores, the uniform and faintly laminated sections are generally pale olive to grayish 

olive (10Y 4/2 to 10Y 6/2), and in few cases (TR35 at about 450 cm from the core top), are dusky 

yellow, or 5Y 6/4 to 8/4. These mud types, 

essentially poorly sorted silt and clay mixtures, 

have a sticky-plastic consistency, trace sand fractions (generally < 1 %), and an absence of macrofauna and bioturbation structures. These aspects 

of unifites result in the textureless and relatively 

homogeneous deposit observed in split cores. 

Typical unifite characteristics include: (1) high 

clay fraction content (<2 jim, ranging from 35 to 

60%) mixed with silt, (2) very low sand fraction, 

which usually consists of a mixture of both terrigenous and bioclastic (largely planktonic) components, (3) marked thickness (usually >1 m and 

to as much as 10 m in piston cores, and possibly 

even thicker in acoustically transparent layers 

from 3.5 kHz records), (4) continuity of such 

layers across large areas of the trench basin floors, 

as revealed by high-resolution subbottom profiles, 

(5) spatial restriction of the associated structureless and faintly laminated mud facies in trench 

basins, both on the plains proper and flat basinal 

sectors near sloping, usually steep margins, and 

(6) radiocarbon dates showing a consistently narrow range of time interval within any one mud 

stratum, regardless of the thickness of the unifite 

layer. Together, these observations and the close 

association of uniform muds with classic mud 

turbidites (Stanley and Maldonado, 1981) tend 

to indicate that unifites were deposited rapidly. 

Regional and Environment-related Variations 

There are distinct differences in the granulomer e and mineralogical characteristics of unifite 

(uniform and faintly laminated) mud core sections among the geographically separated trench 

basin systems. The marked regional trends characterizing the Zakinthos-Strofadhes system to the 

NW and the Kithera-Antikithera system to the 

SE are summarized in Figure 5. With few exceptions, the Matapan Deep, lying between these 

two basins, presents intermediate characteristics. 

These NW to SE regional trends occur regardless 

of stratigraphic position in a core, time of emplacement, or type of unifite bedform (FL or U) 

involved. Sediments in the KB system (SE sector 

of the study area) are characterized by (1) a 

somewhat coarser (siltier) grain size, (2) a slightly 

poorer sorting, (3) a sand-size fraction dominated 

by clastic aggregates and bioclastic fragments, 

and (4) a silt fraction dominated by coccoliths, 

recrystallized calcite and dolomite, volcanic products and attapulgite (= palygorskite). In contrast, 

the finer, somewhat more clay-rich, and better 

sorted sediments to the northwest (ZB system) are 

characterized by sand and silt fractions dominated by planktonic foraminifera and associated 

pyritized tests, and biogenic fragments, together 

with important proportions of terrigenous material. Sediments in the Matapan Deep, having 

accumulated in an intermediate geographic position, differ subtly from the ZB and KB trench 

basins: They have a bioclastic fraction with somewhat higher proportions of pteropods and benthic 

foraminifera than sediments in the other two 

trench basins. 

A synthesis of all mud (U and FL) sample data 

recorded for the three basins suggests that factors 

other than those related to geography account for 

most core-to-core petrologic differences. We can 

demonstrate, for example, that some petrologic 

distinctions are more closely related to specific 

morphologic attributes of environment than to 

geography per se. Thus, considerable effort has 

been made in this study to distinguish between 

petrologic differences among cores collected in 

the trench basin margin flat environment (i.e., 

cores MA-10, MA-23, TR-34) and cores recovered 

in the basin plain environment (i.e., cores MA-20, 

MA-22, TR-35, TR-36). The typical configuration of these two environments is illustrated in 

Figure 2. We recall that slopes bounding the 
NUMBER 13 11 

yC 

NW SE 

ZAKINTHOS-STROFADHES BASIN 

DOMINANT CHARACTERISTICS 

Cloy content 

Carbonate content 

Better sorted mud 

Sand components: 

Planktonic foraminifera 

& pyritized tests 

Spicules 

Light and heavy min 

Silt components: 

Foraminifera 

Spicules 

Quartz, feldspar 

Clastic aggregates 

Carbonate fragments 

rals 

MINIMAL 

CHARACTERISTICS 

Mean grain size (largest) 

Median grain size (largest) 

Sond ComponentsPteropods 

Benthic foraminifera 

& pyritized tests 

Radiolarians 

Diatoms 

KITHERA-ANTIKITHERA BASIN 

DOMINANT CHARACTERISTICS 

Silt content 

Sand Components: 

Clastic aggregates 

Ostracodes 

Pelecypods (juvenile forms) 

Shell fragments 

Mica 

Oxidized and reduced aggrega 

Silt components: 

Coccoliths 

Dolomite, recrystall ized 

Calcite, recrystall ized 

Volcanic products 

(palagonite, sideromelane, 

chlorite, microlrths) 

Attapulgite 

MINIMAL 

CHARACTERISTICS 

FIGURE 5.—Synthesis of the dominant petrographic characteristics of unifites collected in the 

three Hellenic Trench basins systems. This scheme emphasizes regional variations from NW to 

SE, i.e., Zakinthos-Strofadhes (ZB); Matapan Deep (MB); and Kithera-Antikithera (KB) 

sectors. Arrows show that characteristics that dominate in the KB system are often less 

important in the ZB system, and vice versa. In some respects, the Matapan Deep cores are 

intermediate, petrologically, to those of the two other trench systems; the listed sand and silt 

components of Matapan Deep cores are those that predominate in this basin and serve to 

distinguish it from the ZB and KB basins. 

trench basin floors are generally steep (>10°) as 

revealed by echograms and seismic records (cf. 

Vittori, 1978; Le Quellec, 1979). 

In general, the margin flat sediments tend to 

be somewhat less well sorted, display a slightly 

higher proportion of sand-sized terrigenous (especially light minerals) than biogenic components, and contain more benthic foraminiferal 

tests and silt-sized recrystallized calcite. In contrast, the basin plain sediments are somewhat 

better sorted, and contain (in both the sand and 

silt fractions) higher proportions of clastic aggregates and biogenic components, particularly 

planktonic tests. In addition, the silt fractions of 

basin plain core sections tend to contain more 

palagonite and recrystallized dolomite than the 

margin flat sediment. 

We can demonstrate that the above distinctions 

are only in part related to regional provenance 

differences but, more importantly, are related to 

transport processes effective in the different depositional environments. 

Contrasting Uniform and Faintly Laminated 

Mud Sequences 

As noted previously, unifite lithofacies are differentiated primarily by the presence or absence 

of stratification structures and by comprehensive 

grain size and compositional analyses. In the 
12 SMITHSONIAN CONTRIBUTIONS TO THE MARINE SCIENCES 

following sections we compare petrological attributes of unifite core sequences (Figure 4) formed 

essentially of structureless mud (U) with those 

containing faintly laminated mud and the directly overlying structureless mud (FL+U). 

MA-10 Margin Flat 

Cores MA-10 and MA-20 are designated as the 

type cores for unifites composed of uniform muds. 

These cores are, respectively, from the trench 

margin flat and basin plain environments of the 

Kithera Trench system (Figures 1, 6). Type 

MA-2 0 Basin Plain 

j§| Planktonic tests,pyritized 

I | Benthic Foraminifera 

g Benthic tests,pyritized 

Ostracods + juvenile Pelecypod 

MEAN(/Jrr 

FIGURE 6.—Detailed logs of selected unifites in the Kithera-Antikithera Basin cores MA-10 

(trench margin flat) and MA-20 (basin plain). Logs depict major bedform based on xradiography, grain size (silt content and mean), carbonate content, clastic aggregates, and other 

sand-size mineralogical components; the sand-size mineralogical components (excluding clastic 

aggregates) are recalculated to 100%. The abundance of silt-size attapulgite (=palygorskite) 

relative to dominant quartz (Q) or illite (I) is also shown. (E2 = graded mud term; E3 = 

ungraded mud term. Explanation in text.) 
NUMBER 13 13 

FL+U core sections are represented by cores MA23 and MA-22, respectively, from the trench margin flat and basin plain environments of the 

Matapan Deep (Figures 1,7). Detailed petrologic 

sections of cores TR-34, TR-35, and TR-36 (not 

shown here), recovered from the Zakinthos-Strofadhes Trench system, are most similar to core 

sequences MA-22 and MA-23. Simplified lithofacies logs of these seven cores may be compared 

in Figure 4. 

GRAIN SIZE ANALYSIS 

In both U and U+FL mud sequences the relative percent, by weight, of the sand fraction does 

MA-23 Margin Flat 

Depth 

(m) 

UJ M5BONA7 

(%) 

u 

\a 

LASTIC 

GGREGA 

(%) 

u < 

z 

g 

AND 

OM POSIT 

L-> U 

Depth 

(m) 

MA-22 Basin Plain 

E-3 

Pteropods 

Planktonic Foraminifera 

Planktonic tests, pyritized 

^ ^ ^ Benthic Foraminifera 

|^^ ^ Benthic tests, pyritized 

° ^ | Ostracods + juvenile Pelecypod Oxidized and reduced 

Aggregates 

FIGURE 7.—Detailed logs of selected unifites in the Matapan Deep cores MA-23 (trench margin 

flat) and MA-22 (basin plain). Logs depict major bedform based on x-radiography, grain-size 

(silt content and mean), carbonate content, clastic aggregates, and other sand-size mineralogical 

components; the sand-size mineralogical components (excluding clastic aggregates) are recalculated to 100%. (El = laminated mud term; E2 = graded mud term; E3 = ungraded mud 

term; explanation in text.) 
14 SMITHSONIAN CONTRIBUTIONS TO THE MARINE SCIENCES 
NUMBER 13 15 

not exceed 0.3 percent, and in general, there is 

more silt than clay (<2 jiim). However, the silt 

content in the U-type section displays a slightly 

higher average (58%) and a narrower range (50-

65%) than in the FL+U sections (average of 56%; 

range of 44-75%). The latter sequence records an 

enhanced silt content in the lower faintly laminated muds, and a vertical upward change from 

clayey silt to fine silty clay. The mean and median 

grain sizes of the uniform mud are somewhat 

smaller (range respectively, x = 6.4 to 7.5 /am and 

Md = 5.5 to 7.0 /mi) than in the FL+U sequence 

(x = 7.5 to 8.0 /xm and Md = 6.5 to 7.5 jim). It is 

noted that sediment of comparable size (fine silt) 

was earlier reported in the Matapan Deep by 

Pareyn (1968:66). Sorting values (cf. Folk and 

Ward, 1957) indicate that the uniform mud sequences are slightly better sorted (3.6 to 4.6) than 

FL+U sequences (3.5 to 5.3). These differences 

reflect the influence of the somewhat higher silt 

content in the lower, faintly laminated mud portions of the FL+U sequences. 

Vertical variations in silt content and mean 

grain size are apparent on core logs (Figures 6, 

7). Both U and FL+U sequences show an upward 

decrease in grain size. This fining-upward is most 

obvious in core MA-23 and coincides with a 

transition from the FL to U mud type; this trend 

FIGURE 8.—Scanning electron micrograph components in 

Hellenic Trench unifites (scales = 1 fim): A , Clastic aggregate 

composed of cemented silt-sized grains (from core MA-20, 

900 cm from core top, X 10K); B, Gephyrocapsa oceanica 

Kamptner (arrow 1) of Pleistocene to Recent age and Syracosphaera pulchra Lohman (arrow 2) of Late Pliocene to 

Recent age (from core TR-34, 500 cm from core top, X 

10K); c, poorly preserved test oi Discoaster (species not determined, arrow 1) with overgrowth, pre-Pleistocene in age, 

and Scapholithus sp. (arrow 2) (from core MA-20, 900 cm 

from core top, X 12K); D, Cyclococcolithus leptoporus (Murray 

and Blackman), possibly of Pleistocene to Recent age (from 

core TR-36, 610 cm from core top, X 10K); E, Rhabdosphaera 

clavigera (Murray and Blackman) (arrow 1), possibly of Pleistocene to Recent age, Scapholithus fossilis Deflandre (arrow 

2), possibly of Cretaceous to Recent age (from core TR-35, 

410 cm from core top, X 5K), and diatom (arrow 3); F, 

Helicopontosphaera kamptneri (Hay and Mohler) of Miocene to 

Recent age (from core TR-36, 610 cm from core top, X 7K). 

is less well developed in core MA-22 in the same 

basin. A less pronounced but nevertheless overall 

fining-upward trend is also apparent in cores 

MA-10 and MA-20 that contain only by U sections (Figure 4). 

COMPOSITION 

The total calcium carbonate content of U sequences averages 35% and ranges from 30 to 50%; 

that of FL+U sequences averages 39% and ranges 

from 26 to 60%. Higher carbonate contents are 

recorded particularly in some faintly laminated 

muds, such as those in core MA-23 (Figure 7). In 

general, carbonate content tends to fluctuate 

markedly but, unlike grain size, no distinct vertical trend in either U or FL+U sequences is 

noted. 

Grain counts of the sand size fraction in all 

seven cores reveal a predominance of clastic aggregates formed by poorly cemented silt-size fragments (Figure 8A). Aggregates constitute as much 

as 90% of the sand fraction, but tend to diminish 

upward in U-type sequences, as illustrated in logs 

of MA-10 and MA-20 (Figure 6). In FL+U sequences their upward increase, from about 5 to 

80%, is related to the transition from faintly 

laminated to uniform mud type (see core MA-23, 

Figure 7). To better evaluate fluctuations of the 

sand size components, clastic aggregates were 

excluded in the point-counts of the terrigenous 

biogenic components (sand composition column 

in Figures 6 and 7). Although there are compositional differences from core to core, the dominant components almost always comprise planktonic foraminifera, quartz, shell fragments and 

altered volcanic products. The U sequences generally contain higher proportions of sand-sized 

biogenic components and planktonic tests than 

the FL+U sequences. Proportions of planktonic 

foraminifera tend to be higher in faintly laminated (FL) muds (MA-23, Figure 7). In both U 

and FL+U sequences, there is an upward increase 

of planktonic tests in the upper, somewhat finergrained, sections. Moreover, pyritized foraminiferal tests abound in the FL+U sequences, often 

in the laminated mud portions. They tend to 
16 SMITHSONIAN CONTRIBUTIONS TO THE MARINE SCIENCES 
NUMBER 13 17 

increase upward, particularly in cores TR-34, 

TR-35, and TR-36. This upward increase in the 

three Zakinthos-Strofadhes Trench basin cores 

appears related to the presence of the overlying, 

well-developed sapropels (Figure 4). Pyritized 

tests associated with sapropels in other regions of 

the eastern Mediterranean generally signal the 

development of reducing conditions, the most 

recent event of this type occurring from about 

9000 to 7000 years ago (Ryan et al., 1973:713; 

Stanley, 1978; Thunell and Lohmann, 1979). 

In the silt-size fraction, nannofossils are the 

dominant component within both U and FL+U 

sequences in all seven cores; their relative abundance in a core sample is often proportional to 

the carbonate content. Coccoliths include upper 

Pleistocene to Holocene species, as well as much 

older (Miocene and Pliocene) reworked forms 

(Figures 8, 9). Volcanic products (palagonite, sideromelane, chlorite, microlite) and recrystallized 

dolomite are somewhat more abundant in the U 

than in the FL+U sequences. Conversely, quartz 

and feldspar are somewhat less abundant in U 

sequences. In the silt fraction of both types of 

sequences, recrystallized calcite is abundant, 

while spicules, foraminifera and fragments of carbonate tests occur in lower proportions. No distinct vertical trends of silt size components are 

recorded. 

Illite dominates the clay mineral suite in this 

region as noted by Venkatarathnam and Ryan 

(1971) and Vittori (1978:131). Minerals of the 

FIGURE 9.—Scanning electron micrographs of components 

in Hellenic Trench unifites (scales = 1 jum): A, Rod-shaped 

attapulgite (arrow) (from core MA-20, 600 cm from core 

top, X 10K). B, Discoaster variabilis (Martin and Bramlette) 

from late mid-Miocene to Pliocene in age (from core MA20, 600 cm from core top, X 9K). c, Discoaster cf. brouweri 

Tan Sin Hok (4-ray form), from late Miocene to Pliocene in 

age (from core TR-36, 550 cm from core top, X 8K). D, 

Discoaster asymetricus Gartner from the middle Pliocene (from 

core MA-20, 50 cm; X 4.5K). E, Discoaster cf. brouweri Tan 

Sin Hok (6-ray form), badly overgrown and poorly preserved, possible late Miocene to Pliocene in age (from core 

TR-34, 240 cm, X 10K). F, Discoaster perplexus Bramlette and 

Riedel, possibly of late Oligocene to Pliocene age (from core 

MA-20, 600 cm, X 10K). 

attapulgite (palygorskite) group, recorded in 

many areas of the eastern Mediterranean (Chamley and Millot, 1975), occur only in the silt fraction of uniform muds in cores MA-10 and MA20 (Figure 9A). Attapulgite (palygorskite) is abundant in these cores (the attapulgite to illite plus 

quartz ratio generally exceeds unity), but no obvious vertical trend is recorded (Figure 6). The 

sedimentological significance of the attapulgite 

distribution as a tracer of disperal is dicussed 

elsewhere (Stanley, Blanpied, and Sheng, 1981). 

Vertical Petrological Changes 

CONTRASTING MARGIN FLAT AND BASIN PLAIN 

SEQUENCES 

The marked vertical changes in grain size and 

compositon recorded in the U and FL+U cores 

collected in the margin flat and basin plain environments bear on unifite deposition. 

Although almost structureless, analysis of core 

MA-23 recovered in the Matapan Deep margin 

flat reveals distinct vertical bedform, grain size, 

and compositional changes. These nonrandom 

trends are cyclic in nature. The FL+U sequences 

are about 450 cm thick (100 to 550 cm from the 

core top). Size histograms (Figure 10) reveal an 

overall upward size decrease involving two superposed fining-up cycles. The latter are revealed by 

the vertical variations in silt content and mean 

grain size (Figure 7). The two granulometric 

"breaks" correlate well with the presence of 

faintly laminated mud seen in x-radiographs at 

about 550 and 300 cm from the core top. The 

lower cycle is coarser (about 60% silt content), 

and its upward-fining trend is more pronounced 

(decrease in mean size from about 15 to 7 jum); 

the upper cycle is finer (about 55% silt content), 

and shows a more gradual upward diminution in 

grain size (mean size decreases from 8 to 5 jum). 

The vertical distribution of the modal class shows 

a less marked distinction between the two cycles 

(Figure 10). In this repetitively graded mud section, we find that the lower coarser, faintly laminated terms (i.e., any petrologically distinct divi-
18 SMITHSONIAN CONTRIBUTIONS TO THE MARINE SCIENCES 

sion of a unifite cycle) contain a somewhat higher 

carbonate content with higher proportions of siltsized carbonate components, lower proportions of 

sand-size clastic aggregates but larger amounts of 

biogenic components (mainly planktonic tests), 

MATAPAN DEEP 

MA-2 3 

Margin Flat 

MA-22 

Basin Plain 

10 20 40 60 

icrometers 

and minor amounts of mica than the overlying 

material. In contrast, the upper finer-grained uniform mud terms in the sequence contain higher 

amounts of terrigenous components and volcanic 

products in both the sand- and silt-size fractions. 

KITHERA-ANTIKITHERA BASIN 

MA-10 MA-2 0 

Margin Flat Basin Plain 

I0% 

10 20 40 

licrometers 5 10 20 40 60 

micrometers 

FIGURE 10.—Size distribution histograms of Matapan Deep and Kithera-Antikithera Basin 

unifite core samples (sample position shown on logs in Figures 6 and 7). Data (in volumetric 

percent) obtained using a Coulter Counter Model TII-A (size in jtim). (Shaded area depicts 

primary modal class. Note expanded complete size histogram of one core MA-22 sample; dotted 

portion of histogram depicts finest particle distribution as determined from a separate Coulter 

Counter run. FL = faintly laminated mud; U = uniform mud.) 
NUMBER 13 19 

The FL+U sequence in core MA-22 in the 

Matapan Deep basin plain is about 500 cm thick 

(from 200 to 700 cm from the core top) and, like 

core MA-23, shows two superposed sequences, 

revealed by the vertical changes in silt content 

and mean grain-size distribution. The upward 

changes shown by these trends, however, are less 

pronounced than in core MA-23. The major granulometric "break" within this sequence is associated with faintly laminated muds at about 450 

cm from the core top (Figure 7). As in core MA23, the lower cycle is coarser (about 57% silt) than 

the overlying portion of the cycle (about 53%). 

An upward decrease in mean grain size ranges 

from 10 to 6 jum. An examination of the vertical 

sequence of size histograms (Figure 10) shows less 

cyclicity of the primary modal class than in core 

MA-23; a systematic upward size decrease, nevertheless, appears in the upper 200 cm above the 

faintly laminated term (Figure 7). Moreover, histograms of this core (unlike those of MA-23 core 

samples) display a slight bimodal size distribution: a primary mode ranging from 8 to 25 jum, 

and a less pronounced modal class of about 3 /xm. 

An example of an expanded size distribution 

histogram of the clay and fine silt size range (from 

0.3 to 10 /am) is shown in Figure 10. In contrast 

with the uniform mud term (U), the faintly laminated mud segment at about 450 cm contains a 

somewhat lower carbonate content, fewer sandsized clastic aggregates, and a higher proportion 

of biogenic (more planktonic) components. The 

major fluctuation in proportions of sand-sized 

components (Figure 7), particularly the planktonic versus the terrigenous elements, appear 

closely related to grain size changes. For example, 

in the lower cycle, the rapid upward decrease in 

terrigenous components and volcanic products 

coincides with a decrease in grain size. These 

concomitant compositonal and grain size fluctuations appear to correlate with tonal (densitometric) variations, recording differences in sediment density observed on x-radiographs; lighter 

tones generally denote somewhat coarser, or denser, sections. 

Observed vertical and core-to-core changes in 

the largely uniform (U) mud sequences in Kithera-Antikithera Basin cores MA-10 and MA-20 

are different than those in the Matapan Deep 

and Zakinthos-Strofadhes cores. The two MA 

trench basin cores consist essentially of uniform 

mud (faintly laminated sections are absent) but 

nevertheless show an overall upward decrease in 

silt content and mean grain size. 

The margin flat MA-10 core sequence exceeds 

5 m in thickness, and displays an overall upward 

decrease in silt content (from about 60 to 55%), 

mean grain size (from 8 to 6 jum), and modal class 

size (12 to 6 /am, Figures 6 and 10). This is 

accompanied by a slight upward decrease in carbonate content, clastic aggregates, sand-sized terrigenous fraction, and concomitantly, an upward 

increase in biogenic components (mainly planktonic). The proportions of terrigenous and volcanic components of silt size, and of attapulgite 

(palygorskite), also increase upward. A major textural break at 200 cm is accompanied by a 

marked increase in carbonate content and sandsized planktonic foraminifera, and conversely, a 

decrease in the terrigenous fraction and clastic 

aggregates (Figure 6). Many of the compositional 

variations in this U sequence correlate directly 

with grain size fluctuations. 

Basin plain core MA-20 recovered the thickest 

section (about 1000 cm) of uniform mud in the 

study area, and as in MA-10 core, displays an 

overall upward decrease in both silt content (63 

to 54%) and mean grain size (from about 9 to 6 

jum). Unlike core MA-10, however, there is no 

sharp textural break within this vertical sequence 

and, unlike cores MA-22 and MA-23, no obvious 

repetitive grading or cycles are noted (Figure 6). 

While the lower 6 m display some minor textural 

variations, the upper 4 m fine-upward gradually 

and are almost uniform in texture. Grain size 

histograms show an overall range of modal class 

variation between 8 and 20 tim, and a bimodal 

distribution in the lower 6 m comparable to that 

in basin plan core MA-22. Although the vertical 

textural distribution is fairly constant, there are 

some marked compositional fluctuations as noted 

by carbonate content, clastic aggregates, sand-
20 SMITHSONIAN CONTRIBUTIONS TO THE MARINE SCIENCES 

size components (particularly planktonic foraminifera), and attapulgite. Noteworthy are the upward increase in biogenic components and decrease in clastic aggregates. Fluctuations of various compositional components are most closely 

related to the observed subtle grain size changes. 

These grain size variations, in turn, correlate with 

observed tonal-density differences observed on xradiographs. 

ENVIRONMENTAL CONTROL 

The major overall difference between the margin flat and basin plain unifites in the three 

trench systems examined is that the former comprise primarily FL+U sequences, while U sequences dominate basin plains proper. Moreover, 

the basin plain (MA-20, MA-22, TR-35, TR-36) 

core samples contain, for the most part, somewhat 

higher carbonate, sand-sized planktonic foraminifera and clastic aggregate contents, but less 

terrigenous material of sand and silt size than in 

the basin margin flat (MA-10, MA-23, TR-34). 

A synthesis of the petrologic characteristics 

(Table 2) indicates that vertical variations are 

environmentally related. There are some compositional components whose proportions are similar in both margin flat and basin plain cores. 

These are identified as "constants" in Table 2: 

sand-sized pteropods, shell fragments, mica and 

silt-sized recrystallized dolomite, and volcanic 

products prevail in the finer terms of either U or 

FL+U cycles; sand-sized benthic foraminifera, 

heavy minerals, oxidized and reduced aggregates 

and silt-sized foraminifera, coccoliths, spicules, 

carbonate fragments and volcanic products dominate the coarser terms of either U or FL+U 

cycles. Overall, however, there are major comTABLE 2.—Comparison of dominant compositional characteristics of unifites collected on trench 

margin flat and basin plain environments 

Fraction 

Trench margin 

flat dominant 

characteristics 

Constant 

components 

Trench basin 

plain dominant 

characteristics 

Sand 

Silt 

Sand 

Silt 

Radiolarians & 

diatoms 

Benthic tests, 

pyritized 

Light & heavy 

minerals 

Clastic aggregates 

Chlorite & quartz 

Foraminifera & 

coccoliths 

Sideromelane 

Planktonic species & 

tests 

Shell fragments, 

pyritized 

Mica 

Feldspars, aggregates 

Recrystallized calcite 

Dolomite 

Carbonate content 

FINE TERMS OF CYCLES 

Pterpods & shell 

fragments 

Mica 

Palagonite & 

sideromelane 

Dolomite 

COARSE TERMS OF 

Benthic tests 

Heavy minerals 

Aggregates, oxidis 

reduced 

CYCLES 

led & 

Palagonite, sideromelane 

Foraminifera & 

coccoliths 

Spicules & carbonate 

fragments 

Planktonic species & 

pyritized planktonic 

tests 

Shell fragments 

Mica 

Feldspars & aggregates 

Recrystallized 

calcite 

Dolomite 

Carbonate content 

Radiolarians & diatoms 

Benthic tests, pyritized 

Light & heavy minerals 

Clastic aggregates 

Chlorite & quartz 

Foraminifera & 

coccoliths 

Sideromelane 
NUMBER 13 21 

positional differences between margin flat and 

basin plain cores as summarized in Table 2; the 

coarse terms clearly differ from the fine terms of 

FL+U and U cycles. 

In margin flat cycles, the sand-sized components in the coarser-grained, often faintly laminated terms are generally dominated by planktonic tests (foraminifera, including pyritized tests 

and pteropods), bioclastic shell fragments and 

mica; in contrast, the sand fraction in the finer 

(often U) part of cycles is enriched by terrigenous 

material, mainly light minerals, and benthic tests 

(including pyritized benthic foraminifera and spicules) . The highest total carbonate content occurs 

in the coarsest cycles. The silt fraction of the 

faintly laminated terms of the FL+U cycles shows 

enhanced amounts of clastic aggregates, feldspars 

and recrystallized calcite. In the silt fraction of 

the fine terms of the FL+U cycles, quartz and 

volcanic products (chlorite, sideromelane) dominate, along with important proportions of planktonic foraminifera and coccolith tests. 

In basin plain cycles the above listed components of sand and silt size also occur, but in a 

reversed order of importance. Table 2 depicts this 

"reversal" phenomenon: Mineralogical components that are dominant in the coarsest terms of 

margin flat cycles abound in the finer terms 

(largely U sequences) of basin plain cycles; components important in the finer terms of the margin flat cycles dominate the coarser, faintly laminated terms of basin plain cycles in those cases 

where they occur. It is recalled that fine-grained, 

U-dominated cycles prevail in the basin plain 

environments. 

Discussion 

EVIDENCE FOR GRAVITATIVE ORIGIN OF 

FINE-GRAINED MUD TYPES 

An examination of all cores collected in the 

western Hellenic Trench area (Figure 1) has revealed a high proportion of classic fine-grained 

turbidites in most environments, including proximal settings, areas of relief, slopes, and perched 

slope basins and trench plains (Vittori, 1978; 

Stanley and Maldonado, 1981). In contrast, unifites are restricted to trench basin plains (Stanley 

and Knight, 1979; Stanley, 1980). In this study 

we show that trench basin FL+U and U sequences are laterally extensive in each of the 

basin plains (Figure 2). The emplacement of such 

unifites is apparently rapid, a contention supported by their stratigraphic position (Figure 4), 

radiocarbon-14 dates, and the common association of unifites with classic, well-graded mud 

turbidites (Stanley and Maldonado, 1981, figs. 5, 

10). Moreover, statistical analyses of over 450 

samples collected from all of the cores shown in 

Figure 1 show that, regardless of sediment type, 

there is a general decrease seaward in the percentage of the sand size material in muds. The 

Hellenic sediments, for the most part mixtures of 

silt and clay, thus reveal a lateral fining toward 

the three distal trench basins (Vittori, 1978:177; 

Feldhausen et al., 1981). 

The present study also indicates that the finegrained lithofacies distribution is not random 

within basins, but rather is specifically related to 

trench margin flat and basin plain environments. 

This distinct relation between environment and 

mud type is exemplified by the markedly increased proportion of uniform mud relative to 

faintly laminated mud in basin plains proper, 

away from basin slopes. We believe that such 

environment-related lithofacies variations are 

most readily attributable to the influence of transport processes, and evaluation of all data collected 

(seismic profiles and petrology) sheds light on the 

mud emplacement mechanisms involved. 

Although the unifites are very fine-grained, 

usually clayey silt with a fine silt mean size class, 

deposition from primarily suspension-related 

processes (hemipelagic "rain") is minimized. The 

specific restriction of unifites to basin plains 

would not occur if accumulation was largely by 

suspension-related mechanisms (related to water 

mass circulation). The core analysis data base 

does not support a settling "rain" origin for unifite emplacement. We recall that calculated minimum sedimentation rates for entire thick sequences are extremely high (in some cases 

>300cm/1000 years). The sand fraction in unifite 
22 SMITHSONIAN CONTRIBUTIONS TO THE MARINE SCIENCES 

mud is very low (<0.5%) and comprises mostly 

clastic aggregates of reworked, indurated silts and 

only low amounts of planktonic tests. Bioturbation structures are not observed in x-radiographs. 

Moreover, the proportion of the terrigenous sandsize fraction, excluding clastic aggregates, frequently exceeds 50%, and an important part of 

the biogenic fraction of silt consists of older, 

reworked coccolith tests (Figures 8, 9). 

Although unifites almost always contain an 

assemblage of modern and much older reworked 

fauna and, in some cases, display faint laminae 

(the only bedform observed in x-radiography), we 

eliminate strong bottom currents as a dominant 

transport process. This conclusion is supported by 

the extensive regional distribution and lateral 

continuity of the very thick, evenly bedded units 

within each of the three morphologically isolated 

deep basins (as noted in 3.5 kHz profiles), the 

cyclic nature of the almost structureless mud 

sequences, and poor textural sorting of sediment 

recorded by size analyses. A bottom current origin 

would not satisfactorily explain the overall finingupward trend in all sequences, even the thickest, 

including the 10-m-thick unifite in core MA-20. 

Our study does not lend strong support to 

pelagic settling, or to erosion of the sea floor by 

currents, or to combinations thereof for the origin 

of uniform muds as suggested by Ryan et al. 

(1973:268) and Kastens and Cita (in press). In 

contrast, the data base strongly supports a turbidity current-related origin for the thick unifite 

sequences of both uniform and faintly laminated 

muds. Numerous size analyses demonstrate that 

all ponded unifites display an overall upward 

graded bedding (Figures 6, 7); graded muds are 

characterized by very poor sorting (Figure 10). 

Lateral distality-related changes beween the baseof-slope and the basin plain proper include a 

decrease in laminated mud terms, an increase in 

the proportion of graded and ungraded mud 

terms, and a somewhat higher content of sandsized biogenic (largely planktonic) tests of relatively low density. The basinward increased uniformity of mud bedforms and compositional characteristics suggest deposition from flows moving 

across, and spreading over, large areas of the flat 

trench floor. All vertical and lateral petrologic 

changes observed within the three trench basins 

examined tend to support deposition from sediment gravity flows of diminished concentration 

as depicted by the transformation continuum 

model presented by Stanley and Maldonado 

(1981, fig. 11). 

CLASSIFICATION OF FINE-GRAINED TURBIDITE 

M UD SEQUENCES 

The vertical succession of bedforms and general 

fining-upward of unifites in the seven cores is 

generally comparable to that of idealized finegrained turbidite units, Te*, defined by Rupke 

and Stanley (1974:9) and others. The several mud 

types recognized as a result of detailed petrologic 

analyses can be related to specific mud turbidite 

subdivisions defined by Piper (1978:165) and 

Stow and Shanmugam (1980:38). 

The most complete FL+U sequence recovered, 

that in the core MA-23 (Figure 7), serves as a 

reference section. The unit, from 530 and 490 cm, 

corresponds to the vertically graded laminated 

medium and fine silt, and also to the laminated 

mud (El), terms illustrated by Piper (1978:165) 

and, more specifically, to the indistinct laminated 

subdivision, T4, of Stow and Shanmugam (1980: 

38). This is overlain, from 490 to about 470 cm, 

by a graded mud division, coded respectively E2, 

or T6, by these authors. This is topped, from 470 

to 310 cm, by a mud sequence that shows only 

vague grading, i.e., the ungraded mud division, 

E3 or T7. A marked change is observed at about 

310 cm: Faint laminae reappear from 320 to 310 

cm (El or T4); this is followed by graded mud 

from 230 to 140 cm (E2 or T6), and finally by 

faint, but graded, laminae at 140 to 110 cm (El 

or T4). The position of the above E terms, corresponding to those defined by Piper (1978), are 

depicted on the logs in Figure 7. 

On closer inspection, the thick, apparently ungraded division (E3, or T7) shows subtle fluctuations of grain size, i.e., a slight upward increase 

in silt content from 470 to 390 cm (= ungraded 

mud), and then a slight decrease from 390 to 310 

cm (= graded mud). The variations in content of 
NUMBER 13 23 

clastic aggregates and sand-sized mineralogic 

components parallel, and actually magnify, 

otherwise subtle grain-size fluctuations in both 

graded and ungraded muds. Thus, grain size and 

mineralogy, supplementing bedform, reveal from 

base to top a complex succession of terms: 

E1-*E2^E3^E2 ; E1^E2 ; and El. The three 

El terms are characterized by a high carbonate 

(mostly silt-size coccoliths) and low clastic aggregate content, and a sand-size fraction dominated 

by biogenic components. In the E2 terms, the 

content of carbonate decreases, but that of clastic 

aggregates is high but fluctuates, and terrigenous 

components dominate the sand fraction. Proceeding upward in the sequence, each successive 

faintly laminated El term contains progressively 

larger proportions of clastic aggregates and sandsized biogenic components. Thus, all three El 

terms in the MA-23 sequence are interpreted as 

an integral succession emplaced by a single flow 

event and do not represent the base of three 

separate deposits. The overall decrease of silt 

content, and vertical trends of mean (Figure 7) 

and modal (Figure 10) grain sizes favor this "single event" interpretation. Further support for this 

is provided by (1) the rapid upward increase in 

sand-sized planktonic, and concomitant decrease 

in terrigenous fractions within the lower, ungraded (E3) mud section, and (2) the lack of 

correlation between planktonic-terrigenous content and grain-size changes associated with the 

middle laminated El division. The overall cyclicity of this Matapan Deep margin flat FL+U 

sequence, and the variations within both E2 and 

E3 terms, probably record velocity and turbulence fluctuations in a single flow event. 

The FL+U sequence in core MA-22 in the 

Matapan Deep basin plain reveals trends generally similar to core MA-23 (Figures 7, 10). There 

is overall fining-upward (decrease in silt content 

and mean grain size), and cyclicity is apparent, 

but somewhat less marked than in core MA-23. 

The vertical succession includes ungraded mud, 

E3 or T7, from 710 to 550 cm; graded mud, E2 

or T6, from 550 to 470 cm; faintly laminated 

mud El or T4, from 470 to 440 cm; graded mud, 

E2 or T6, from 440 to 220 cm; and faintly laminated mud, El or T4, from 220 to about 210 cm. 

The three cycles in this core are: E3—»E2; 

El—»E2; El. As in core Ma-23, there are compositional and granulometric fluctuations, sometimes important, within both vaguely graded and 

ungraded terms. Differences, however, include 

somewhat less pronounced overall vertical grading, an upward trend in carbonate content that 

does not parallel grain-size variations, and a 

higher proportion of clastic aggregates throughout the sequence. 

The FL+U sequences recovered in the three 

Zakinthos-Strofadhes Trench basin cores (Figure 

4) display cyclicity involving vertical successions 

of bedform, grain-size, and composition. This 

cyclicity is similar to that noted in Matapan Deep 

cores MA-22 and MA-23. Specific differences in 

mineralogical components between MB and ZB 

unifites are related primarily to a different provenance (lateral source input from the northwest 

Peloponnesus) rather than to transport mechanisms. We interpret the unifite mud sequences in 

cores MA-22, TR-34, TR-35, and TR-36 as gravitative deposits emplaced by mechanisms similar 

to that of MA-23, i.e., transport and deposition 

by turbidity current-related flows of diminishing, 

but fluctuating, velocities and turbulence. An 

example of a classic, well-graded mud turbidite 

occurs above one of the unifites (see section from 

310 to 180 cm in core TR-34, marked by T and 

arrow in Figure 4, and also the x-radiography 

print in Figure 3A). 

Cores MA-10 and MA-20 in the Kithera-Antikithera Basin (Figure 6) differ most obviously 

from the five above-cited cores in that they comprise only uniform (U) mud sequences and display less obvious vertical cyclicity. The higher 

proportion of sand-sized clastic aggregates, and 

silt-size attapulgite and volcanic products (glass 

shards, etc.) reflect local provenance and dispersal 

factors rather than a different emplacement process per se. While both cores display an overall 

fining-upward trend, comparable to the Te* turbidite sequence of Rupke and Stanley (1974), 

close inspection shows petrologic "breaks" within 
24 SMITHSONIAN CONTRIBUTIONS TO THE MARINE SCIENCES 

the U sequences. In MA-10, this occurs at about 

200 cm, separating a lower ungraded mud (E3 or 

T7) from an upper graded mud (E2 or T6); the 

break in MA-20, although less well marked, is 

noted at about 400 cm, separating a lower E3 (or 

T7) from an upper E2 (or T6) term. Unlike the 

FL+U sequence in reference core MA-23, the 

principal mineralogical changes in both MA-10 

and MA-20 closely parallel major textural 

"breaks." A sudden decrease in clastic aggregates 

and increase in sand-size biogenic components 

correlates with a decrease in grain size. The 

"break" between E2 and E3 terms in MA-10 and 

MA-20 unifites indicates superposition of two 

important successive depositional episodes. In 

each case, the superposition is related to a major 

turbidity current flow event. Vertical variations 

of both grain size and mineralogical components 

are observed within the ungraded mud, E3 or T7, 

terms in these (Figure 6) as well as in cores of 

other basins (Figure 7). 

From this classification we propose a vertical 

succession of terms that characterizes, from base 

to top, an idealized complete unifite cycle: (1) a 

faintly laminated, generally siltier term, which 

may be graded and contain a sand-size fraction 

that is largely biogenic; (2) a graded fining-upward mud term with terrigenous components 

dominating the sand-fraction; (3) an ungraded 

mud term that, on close inspection, actually 

shows slight coarsening-upward and/or may display cyclic fluctuations and that contains a sandsize fraction dominated by terrigenous components; and finally (4) a graded mud (fining-upward) term with an enhanced biogenic fraction. 

This cycle may be repeated and, in thick sequences, some terms may be absent. Cores MA10 and MA-20 comprise the thickest E2 and E3 

terms examined. 

PETROLOGIC VARIATIONS RELATED TO FLOW 

FLUCTUATIONS 

The general upward-temporal and lateral-spatial fluctuations (larger scale cycles as well as 

more subtle changes in bedform, grain size, and 

composition) are comparable in the three Hellenic basins. Insight on transport mechanisms 

involved in unifite deposition is provided by the 

vertical petrologic changes within each core and 

lateral variations between trench margin flat and 

basin plain cores. We have shown that a complete 

unifite sequence includes laminated (El), graded 

(E2), and ungraded (E3) mud terms, and that 

their succession varies within a core, and laterally 

from core to core. Variations in mud type cyclicity, associated with an overall decrease in grain 

size, record internal fluctuations within a flow of 

diminishing velocity and sediment concentration. 

The development of faint laminae, for example, 

may be related to phases of flocculation and to 

the depositional sorting during flow; i.e., a reorganization of mud and silt floes and their concentration result in their settling through the boundary layer at the base of a flowing turbidity current. Formation of fine-grained laminae by increased shear at the bottom boundary layer, as 

invoked by Stow and Bowen (1978), seems an 

appropriate explanation. We note that the faintly 

laminated El terms comprise a unimodal grainsize distribution consisting of a mode generally 

larger than 20 jum (Figure 10). 

We are unable to ascertain why several such 

flocculation-induced laminated terms appear 

within a single sequence deposited from one major event (cf. core MA-23, Figure 7). Several 

possibilities may explain the presence of successive laminated zones within a single unifite. In all 

cases, the following are considered as constants: 

(1) steep gradients of the walls that bound trench 

basins (Le Quellec, 1979:64), (2) irregularities on 

these steep slope surfaces (Figure 11) and in canyon thalwegs (Vittori, 1978:37-117), (3) flocculation initiated within the flow on the slope as a 

result of particle collision (Kranck, 1975), and (4) 

hydraulic jump phenomenon that produces a 

sudden reduction in velocity and density and 

thickening of the flow as it reaches the flat basin 

floor just beyond that base of slope (Komar, 

1971). As noted in most experimentally produced 

sediment gravity flows, larger or denser grains are 

concentrated at the head and near the base of the 
NUMBER 13 25 

body of a rapidly downslope-moving gravity-entrained flow; the upper interface of the flow 

incorporates ambiant seawater and is thus more 

dilute (Kuenen, 1965:69). Both large and small 

topographic irregularities on the slope induce 

turbulence and, in consequence, a continuous 

rearrangement of the sediment load and its concentration. Inasmuch as the transported load consists largely of silt and clay particles, continuous 

flocculation and disaggregation occur within the 

flow as it moves downslope. 

In the simplest case of unifite deposition on the 

margin flat province, we envision a flow column 

of roughly even thickness moving along a fairly 

FIGURE 11.—Selected bottom photographs obtained from the deep-tow Raie system in the 

northern part of the Kithera-Antikithera Trench, near location of core MA-20 (1978 cruise 

Raicette, depth about 4400 m, near 35°50'N latitude and 22°13'E longitude): A, Slope swept 

partially free of thin surficial sediment veneer; note current lineations and minor scour-and-fill 

structures around burrows (circular structures are about 3 cm in diameter); the arrows are 

oriented along the predominant downslope transport direction, B, Eroded slope surface (arrow); 

note stirring of thin surficial sediment veneer by bottom compass. Compass and vane are about 

30 cm long, c, Recently eroded block of mud ~1 m in length, lying near base of slope, D, 

Turbid flow, triggered by deeptow compass touching the slope, displaying multilobe configuration. Much larger flows of this type are believed to displace the thin sediment veneer 

downslope and probably produce the current-lineated erosional bedforms illustrated in 'V ' 

(Photographs generously provided by the Centre National pour l'Exploitation des Oceans, 

Brest, France.) 
26 SMITHSONIAN CONTRIBUTIONS TO THE MARINE SCIENCES 

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28 SMITHSONIAN CONTRIBUTIONS TO THE MARINE SCIENCES 

smooth slope and which, upon arrival on the 

near-horizontal basin floor, is subjected to hydraulic jump effects (Figure 12A). AS a result of 

the jump, deposition of larger and denser grains 

and floes concentrated at the head and near the 

base of the flow will settle out through the bottom 

boundary layer as flow velocity is rapidly reduced; this accounts for the deposition of the 

lower, faintly laminated El term. The rapid settling of finer materials above the basal El term 

produces both graded and ungraded muds (E2 

and E3). During and following the passage of the 

flow head and deposition of this first cycle, the 

hydraulic jump effect above the same base-ofslope sector continues to induce rearrangement of 

grains that are entrained by the body of the 

downslope-moving flow; flocculation occurs 

again as a result of particle collision (cf. Kranck, 

1975) due to temporary intensified turbulence. 

Thus, larger floes settle once again, resulting in 

accumulation of a second cycle of laminated mud, 

followed by settling of finer, or less dense, material. This repetitive deposition of laminated, 

graded and ungraded muds continues as long as 

there is sufficient concentration of material carried by the downslope-moving flow over this sector and as long as flocculation is induced by 

hydraulic jump turbulence. The final passage of 

the slower-moving dilute tail is recorded by the 

uppermost nonlaminated mud. 

A somewhat more complex but more probable 

unifite origin involves a flow column of uneven 

thickness, characterized by partially superposed 

and successive, imbricated lobes (Figure 12B). 

These lobes may record the development of major 

turbulence within the flow induced by large seafloor irregularities upslope; the lobes are thus 

viewed as perturbations produced by a succession 

of hydraulic jump effects along the flow path. As 

each major lobe passes above the same base-ofslope sector, it releases material; the resulting 

deposit resembles that accumulated from a rapid 

succession of turbid flows. Analysis of the sediment load in each individual imbricated lobe 

would probably reveal that each has its own 

distinct, internal grain-to-grain distribution pattern. As each lobe reaches the base-of-slope and, 

in turn, is affected by the hydraulic jump, a cyclic 

deposit consisting of superposed El, E2, and E3 

terms will accumulate. Each lobe will release 

progressively finer material over the same baseof-slope sector. 

The minor variations in grain-size and composition within any one cycle is accounted for by 

smaller-scale fluctuations of turbulence, velocity, 

and load concentration. Planktonic tests and clastic aggregates, on the one hand, and terrigenous 

components, on the other, have different densities; inasmuch as they become segregated during 

transport they are sensitive indicators of turbulence-related changes in a flow. We thus interpret 

cyclicity, repetition of laminated and uniform 

muds, and variations in mineralogical components on margin flats as largely the result of 

hydraulic jump effects both upslope and at the 

base of the slope. We conclude that the vertical 

variations observed in unifite sequences illustrated in Figures 6 and 7 do not represent timeseparated turbid-layer flows of the type described 

by Moore (1969:83). Moreover, Hellenic unifites 

are petrologically unlike lithologic sections emplaced by current flows that cross and repeatedly 

rebound from basin pond walls, as illustrated by 

Van Andel and Komar (1969). While not completely ruled out, we tend to discount this latter 

process primarily on the basis of (1) the observed 

cyclicity, (2) unusual thickness (as much as 1 m) 

between each El term, (3) narrow range of petrologic variations, (4) very poor sorting of the 

mud throughout an entire sequence, and (5) the 

vertical distribution pattern of planktonic tests 

between the base and top of sequences. 

Unifites on the trench basin proper differ markedly from those on margin flat sectors near the 

steep basin walls, particularly with respect to 

vertical variations in grain-size and composition, 

and a higher proportion of planktonic tests. This 

difference records changes that occur within the 

gravity-entrained flow as it moves away from the 

base-of-slope toward the more distal, near-horizontal trench basin plain proper (Figure 12A). 

The mineralogical "reversal phenomenon" that 
NUMBER 13 29 

occurs between these two trench basin environments (Table 2) probably is most closely related 

to hydraulic jump effects; i.e., a transfer of energy 

markedly enhances turbulence and grain support 

characteristics within the turbidity current flow 

just beyond the base-of-slope break. 

The hydraulic jump effect thus induces a sharp 

modification of the grain-to-grain configuration, 

which accounts for a temporary disorganization 

of the sediment load distribution within the flow 

column. Disaggregation within flow recurs as the 

turbidity current moves basinward across the 

plain; an increased regularity in settling of suspended grains accompanies diminished turbulence-related flocculation and floe rearrangement. Thus, the E2 and E3 terms that dominate 

more distal sectors contain progressively finer 

uniform mud terms, with lower proportions of 

denser terrigenous components. The observed 

subtle normal fining-up and reversed grading 

highlight a cyclic pattern even in the more distally deposited fine-grained ungraded (E3) unifites (core MA-20, Figure 7). This textural configuration attests to the still turbulent and moderately concentrated character of the slower, basinward moving flow. The uppermost graded mud 

term of idealized complete unifites on both basin 

margins and in trench plains proper records final 

phase settling of the sediment load, over large 

areas of the basin plain, from the tail of a flow. 

Implications of Study and Conclusions 

Hellenic Trench unifites have been interpreted 

as the end-members of a depositional series that 

are initiated in proximal, generally steep slope 

settings (Stanley, 1980). A theoretical complete 

transport continuum from slumps, to dense mass 

flows (debris flow), to turbidity currents, and 

eventually to very low concentration but still 

turbid layer flows, referred to as a transformation 

series, has been depicted by Stanley and Maldonado (1981, fig. 11). This continuum series depositional model is based on the recovery of a diverse 

suite of gravitative deposits whose distribution in 

the western Hellenic Arc study area appears nonrandom. Slumps, debris and other dense mass 

flows, and coarse-grained turbidites abound on 

slopes, while associations of finer deposits, including well-developed, classic silt turbidites and unifites, occur at the base-of-slope and in basin 

plains. 

The thickness of a depositional unit is, in large 

part, a function of the volume of material transported relative to the surface area on which it 

accumulates. The remarkable thickness of individual fine-grained Hellenic Trench unifites (>10 

m) detailed in this study is closely related to the 

very small surface area (100 to 250 km ) of the 

flat trench basins that trapped the sediment gravity flows. The estimated volume of sediment carried by individual flows that actually reached the 

trench basin floor ranges from about 0.5 to 1.0 

km3, based on both core and seismic data. Such 

volumes are moderate when compared to those 

calculated for turbidites in modern ocean abyssal 

plains (Normark, 1970; Heezen and Hollister, 

1971:183; Pilkey, Locker, and Cleary, 1980) and 

in the rock record (Scholle, 1971; Hesse, 1975; 

Rupke, 1976; Mutti, 1977). 

In the larger Mediterranean basins, such as the 

Algero-Balearic Basin in the western Mediterranean (Rupke and Stanley, 1974:11) and the Ionian and Herodotus Basin plains in the eastern 

Mediterranean, thin unifites comprising mixes of 

modern and reworked microfossils in fact are 

difficult to distinguish from thin mud turbidites 

and planktonic-rich hemipelagites. The gravitative deposits are more likely to display an absence 

of bioturbation and contain more reworked microfossils. Mediterranean basins are extremely diverse in terms of shape, size, and depth (Stanley, 

1977a: 128) and in consequence probably contain 

unifites of variable thicknesses. Unifite thickness, 

frequency in cores, and rates of accumulation 

depend not only on basin size and sediment flux, 

but also on dispersal and degree of accessibility 

of sediment to a basin plain. 

The western Alboran Basin between Spain and 

Morocco and the Golo Basin in the Corsican 

Trough exemplify small ponds that are bounded 

by smooth slopes and have relatively direct access 
30 SMITHSONIAN CONTRIBUTIONS TO THE MARINE SCIENCES 

to substantial volumes of fluvial-derived and biogenic sediment transported basinward by gravity 

flows. As a result, relatively important proportions of thick structureless mud layers, or unifites, 

are recovered (cf. Huang and Stanley, 1972:539; 

Stanley, Rehault, and Stuckenrath, 1980:30). In 

contrast, other isolated basins are bounded by 

topographically more complex margins, and have 

limited or no direct access from land or proximal 

source terrains. It is noted that some of these 

basins nevertheless contain thick unifites. Examples include many of the topographically isolated 

Hellenic Trench basins of the type discussed in 

this study, as well as depressions on the Mediterranean Ridge, some Tyrrhenian and Aegean Sea 

basins, and narrow troughs in the Strait of Sicily. 

Many of the unifites in such settings are most 

probably related to earthquake tremors that trigger failure, initiate progressive downslope displacement, and in some manner insure sediment 

entry into basins. 

Fine-grained laminated and unlaminated mud 

alternations usually form sequences 1 to 10 cm 

thick in most ocean cores and in rock slabs studied 

to date (Piper, 1978, fig. 12-6; Stow and Shanmugam, 1980, fig. 2). The typical ponded Hellenic unifite serves as an ideal example for study 

in that its thickness expands almost one hundred 

times that of commonly studied, much thinner, 

compacted gravitative deposits and magnifies the 

fluctuations of fine-grained bedform sequences. 

The vertical petrologic trends detailed in the 

expanded sections of such thick, fine-grained 

units are most valuable in that they record shortterm fluctuations of flow characteristics. Important among the latter are changes in turbulence, 

velocity, grain-support mechanisms, and settling 

phenomena that may occur over a short time and 

limited space in small ponded basins. 

Petrologic difference between unifites in the 

three Hellenic Trench basins examined demonstrate that major changes in flow properties affecting largely silt and clay-size loads occur rapidly and over a small area, i.e., within a few 

kilometers. Both 3.5 kHz profile and core data 

suggest that, upon entering basins, mud-carrying 

turbidity current flows deposit laminated sequences that thin distally. Moreover, proportions 

of larger, more buoyant planktonic tests, tend to 

increase relative to smaller, denser terrigenous 

components in a direction away from the site of 

the flow entry on the basin floor: this in large 

part accounts for the "reversal" petrologic phenomenon illustrated in Table 2. In the case of 

larger basins, we postulate that a flow of diminishing turbulence, velocity, and concentration of 

the type envisioned eventually becomes a dilute, 

almost stationary cloud. The end-member deposit 

of such a flow would be difficult to distinguish 

from hemipelagic, largely suspension-emplaced 

layers: both are likely to be thin to moderately 

thick, foraminifera- and coccolith-rich mud layers. The former flow deposits, however, would 

likely contain somewhat more reworked microfossils than hemipelagites. 

Combined factors of accessibility and transport 

process are largely responsible for the petrologic 

variations in ponded western Hellenic Trench 

unifites. We recall that these basins are separated 

from each other and from the Peloponnesus and 

Crete by physiographic features of marked relief, 

and are bounded by steep slopes, many of which 

include perched basins (Got, Stanley, and Sorel, 

1977; Vittori, 1978:44; Le Quellec, 1979:144) 

likely to trap sediment moving downslope. The 

physiographic complexity, a result of geologically 

recent displacement resulting from plate motion, 

minimizes the paths along which sediment can be 

moved directly from adjacent land and proximal 

margin sectors, and from the Mediterranean 

Ridge, to the trench basin plains. It is our contention that the direct land and shelf-H>slope—»basin 

plain sediment dispersal pattern, important in 

some of the larger oceanic trenches (cf. Piper, von 

Huene, and Duncan, 1973; Schweller and Kulm, 

1978; Underwood, Bachman, and Schweller, 

1980), does not prevail in the study area. 

Our scheme, involving a succession of downslope dispersal events between shallow proximal 

and deep distal settings, has been depicted by 

Vittori (1978). This model involves transport 

through submarine valleys that extend from shal-
NUMBER 13 31 

low gulfs to slope depressions and perched basins, 

and iri some cases, further still to the trench basins 

proper. Sediment is moved from proximal to 

distal settings by a succession of redepositional 

events; the time span between gravitative flows is 

variable, but generally short. The diminished 

basinward proportions of sarid and compositional 

homogenization of fine-grained sediments in the 

distally located cores (Figure 1) are accounted for 

by a barrier or dam effect, resulting from the 

complex topographic setting. This complexity induces preferential entrapment of coarser fractions 

in slope-perched catchment basins (Vittori, 1978: 

44; Feldhausen and Stanley, 1980; Feldhausen et 

al., 1981). The major evidence that sediment has 

been carried into Hellenic Trench basins via submarine valleys is the presence of low-gradient 

basin aprons localized along some base-of-slope 

sectors (Figure 13). These aprons are actually 

small fan deposits. Cores recovered from such 

canyon-related aprons comprise large proportions 

of well-developed mud turbidites, a few sandy 

turbidites, but no thick unifites (Stanley and 

Maldonado, 1981, figs. 6, 8). Moreover, some core 

FIGURE 13.—Hellenic sediment dispersal scheme emphasizing near-continuous downslope transport from proximal margin to distal sectors. A sediment gravity flow may be channeled into a 

submarine valley (SV) and carry material into perched slope basins (PB) and, eventually, onto 

the trench basin apron (A) and near-flat basin plain (BP). In this manner, coarse material is 

selectively entrapped in submarine valleys, perched slope basins, and depressions in the 

cobblestone terrain. Line drawings of selected 3.5 kHz profiles (on the right) from the ZakinthosStrofadhes Trench system illustrate examples of sediment deposited in a valley (SV), perched 

basin (PB), and basin plain (BP). Hellenic core surveys indicate that the acoustically transparent 

layers in the basin (BP) include mud hemipelagites and enhanced proportions of mud turbidites 

and unifites. 
32 SMITHSONIAN CONTRIBUTIONS TO THE MARINE SCIENCES 

samples from these aprons include reworked shallow water microfossils and volcanic materials, 

and relatively important contents of terrigenous 

fractions of both silt and sand size (Feldhausen 

and Stanley, 1980). 

Some unifites, particularly those in the Zakinthos-Strofadhes Trench basin, were probably emplaced by canyon-derived turbidity currents 

spreading across trench basins. Here the deposits 

contain sand-size shallow water benthic species 

derived from the adjacent shallow margin. However, the petrologic characters of most FL+U and 

U unifite sequences we examined indicate that 

other types of dispersal were probably even more 

important in the introduction of fine-grained deposits onto basin floors. For example, the absence 

of shallow marine faunas and the dominance of 

clastic aggregates in the sand fraction are noted 

in many unifites, particularly those in the Kithera-Antikithera Basin. Clastic aggregates (Figure 

9A) are almost certainly reworked from older, 

semi-consolidated sediments that cover slopes and 

high-relief features, including those adjacent to 

trench basins. The clastic aggregates (clasts of 

cemented silt particles) are always associated with 

reworked microfossils of Pliocene and, in some 

cases, Miocene age; they sometimes occur with 

pyritized planktonic tests from resedimented sapropels and with disseminated silt and sand-size 

volcanic particles (glass shards, palagonite, etc.) 

reworked from several Quaternary ash layers, 

including the Ischia Tephra (cf. Ninkovich and 

Heezen, 1967). 

This reworked assemblage records a mixing of 

slope sediments of different age and origins as a 

result of successive resedimentation events. The 

failure of older sediment formations that form 

slopes constitutes a primary source of material 

reaching trench basins; this is recorded by direct 

observation made during submarine dives (Drake 

and Delauze, 1968; Pareyn, 1968) and from bottom camera photographs. These reveal a thin (or 

absent) unconsolidated sediment veneer on steep 

gradients (Figure 11A) that is metastable and 

easily set in motion (Figure 11D). Downslopeoriented bedforms (Figure 11A, B, arrow) record 

recent seafloor erosion of the slope. Large individually displaced (allochthonous) blocks observed 

on high-resolution sparker profiles (Vittori, 1978: 

81) and on 3.5 kHz records (Figure 14) and 

smaller detached blocks of mud directly observed 

on dives and in photographs (Figure 1 lc) provide 

further evidence for the failure of silt and clay on 

slopes. Graphic depiction of localized slope failure 

as an important source of trench fill sediments is 

also presented on the trench deposition models 

illustrated by Piper, von Huene, and Duncan 

(1973, fig. 7), Schweller and Kulm (1978, fig. 21) 

and Underwood, Bachman, and Schweller, 

(1980). 

The episodic, but almost constant, downslope 

displacement of sediments, involving failure of 

slope deposits and subsequent movement via canyons is thus envisioned (Figure 13). Sediment 

gravity flows, sometimes widespread, sometimes 

localized, are able to displace admixtures of both 

originally land-derived terrigenous and biogenic 

fragments and also incorporate during their 

downslope descent eroded clastic aggregates and 

planktonic foraminifera. Similar examples of such 

reworking in ancient marine examples have been 

described by Scholle (1971). Successive gravitative events apparently result in size-sorting effects 

and, consequently, in changes downslope in the 

proportions of mineralogical components. Repeated redeposition may explain, for example, 

the downslope increase in clastic aggregates and 

planktonic tests relative to the sand-size terrigenous fraction (Feldhausen and Stanley, 1980). The 

increased proportion of attapulgite (palygorskite) 

downslope in the Kithera-Antikithera Trench is 

still further evidence of gravity-induced processes 

involving slope erosion (Stanley, Blanpied, and 

Sheng, 1981). We do not believe, however, that 

canyon transport and slope erosion models in 

themselves satisfactorily account for the remarkably limited range of textural and compositional 

variations that characterize many Hellenic unifite 

sequences. 

The exceptional homogenization of sediment 

that must occur prior to its arrival at the base-ofslope requires that another phenomenon be considered. We suggest that homogenization results, 
NUMBER 13 33 

FIGURE 14.—Line drawings of selected 3.5 kHz seismic profiles from the Zakinthos-Strofadhes 

Trench system that show sediment failure on steep slopes: A, Slumps with poorly defined 

internal structure, B, Overlapping series of mass failure deposits, c, Failed sediment accumulating in immediately adjacent depression in cobblestone terrain (arrow), D, Slump deposits 

showing undefined internal structure at base-of-slope (arrow 1); note improved definition of 

bedding basin ward (arrow 2), and well-stratified ponded facies in the basin plain (arrow 3). 

to a considerable extent, from a slope relief bypassing-related mechanism (Figure 15); i.e., the 

upper, less concentrated portions of thick gravitative flows, initiated in canyons or on slopes, 

probably spill over and carry some of the fine 

sediment load onto and across topographic highs. 

In this manner, coarser-grained elements would 

accumulate preferentially in depressions, including submarine valleys, lows between cobblestone 

topography (Stanley, 1977b) and perched slope 

basins (Vittori, 1978:193). This model emphasizes 

the progressive seggregation of sand from mud 

and its preferential entrapment on the slope, 

whereas finer grained sediments are carried further downslope across irregular slope relief features toward the basin plain. 

The fine-grained, largely silty clay or clayey 

silt veneer resides on slopes, particularly the steep 

ones, only temporarily; this sediment fails easily 

(Figure 11D) and apparently can be displaced 

basinward by means of successive gravitative 

events. Steep slopes are thus locally devoid of 

unconsolidated sediment cover as observed by 

Drake and Delauze (1968) and others. Downslope 

flows that displace the thin sediment veneer can 

also form erosional bedforms on slopes (figure 

11A, B). AS they progress downslope, flows pick 

up and incorporate recent planktonic foraminifera, coccoliths, and clay that settle through the 

water column over most of the seafloor; these 

hemipelagic components are eventually transported to trench basins along with the gravitydisplaced, size-sorted, fine-grained material. This 

process helps explain the high proportions of older 

(pre-Pleistocene) coccoliths. 

Earthquake tremors affect most of the Hellenic 

Arc and are particularly frequent and intense in 

the study area (Comninakis and Papazachos, 

1972). These are the dominant triggers that set in 

motion material of mixed terrigenous and biogenic origin. The almost continuous failure of 

slope sections, gravity-induced transport through 

canyons and channels, and sediment gravity flows 

spilling over and bypassing areas of relief result 
34 SMITHSONIAN CONTRIBUTIONS TO THE MARINE SCIENCES 

<b HP(b „ P ( b H p ^ 

FIGURE 15.—Sedimentation model, depicting relief bypassing along the Hellenic Arc margin, emphasizes textural 

segregation and progressive fining and homogenization of 

muds toward base-of-slope and basin plain environments: A, 

Line drawing of a 3.5 kHz seismic profile in the ZakinthosStrofadhes Trench sector illustrating preferential sediment 

entrapment in depressions in cobblestone terrain, B, Schematic profile depicting a thick, turbulent sediment gravity 

flow (SGF) traversing irregular topography. Arrows show 

selective deposition in the depressions of coarse or denser 

particles, released largely from the base of the flow; the less 

dense and finer material carried in the upper, less concentrated portion of the flow are thus able to bypass relief. (HP 

= hemipelagic "rain.") 

in stratigraphically disrupted (repeated or incomplete) core sections throughout the study area 

(Stanley, Knight, and Stuckenrath, 1978). Anomalous sequences of radiocarbon-dated core sections (Figure 4), irregular distribution or absence 

of key horizons (sapropels, oxidized layers, tephra), dilution of sapropels by incorporation of 

terrigenous material, and the extremely high rates 

of deposition in trench basins relative to slope 

environments (Stanley and Maldonado, 1981) 

support this active and complex provenance-dispersal model. 

Depositional events of the type described above 

have occurred during much of the Quaternary, 

including the late Pleistocene to the recent. 

Noted, in this respect, are the unusually thick 

unifites in the Kithera-Antikithera Trench basin, 

which consist of material radiocarbon-dated from 

about 15,000 to 11,000 years B.P. (Figure 4), or 

from late Pleistocene to early Holocene. It is 

important, however, to signal the absence in both 

cores MA-10 and MA-20 of the upper sapropel 

(Si), a key stratigraphic layer that is widely distributed throughout the eastern Mediterranean 

and which is dated about 8000 years B.P. (Stanley, 

1978; Thunell and Lohmann, 1979). This absence 

of the upper sapropel suggests that the two thick 

unifites were deposited at their present trench 

basin sites since Si time, i.e., in the mid-Holocene 

or more recently. We recognize that radiocarbon 

dates are influenced by the presence of older 

reworked material, and thus likely indicate the 

time of earlier deposition on the slope, and not 

the time of final sedimentation of the unifites in 

the trench plain. It is possible that the final 

gravity flow emplacement of unifites in the two 

Kithera-Antikithera Trench cores is related to a 

regionally widespread tsunami triggered by the 

major Thera explosive event at about 3500 years 

B.P., a suggestion proposed by Kastens and Cita 

(in press). The presence, however, of similar unifites of older but variable ages below the upper Si 

sapropel in other cores of this same trench basin 

indicates that transport events of this type occurred during much of the Quarternary (cf. Lamont-Doherty Geological Observatory core RC184, illustrated in Stanley, 1974, fig. 8; Joides 

drilling at sites 127 and 128, in Ryan et al., 1973: 

243-322). There is no reason to restrict unifite 

deposition to tsunami events. Earthquake tremors 

in this zone of high seismicity are the most likely 

cause of almost constant remobilization and basinward displacement of the underconsolidated 

and unstable slope sediments. 

Some thick (>1 m) single-event silt and clayrich shales and marls described in the geological 

record (e.g., Scholle, 1971; Ricci Lucchi, 1975; 

Rupke, 1976) may have a similar origin to the 
NUMBER 13 35 

Hellenic unifites. Paleogeographic analyses suggest that most of these ancient examples accumulated in small, or at least topographically restricted, catchment basins. As shown in the 

present Hellenic study, the thickness of a single 

redepositional sequence does not necessarily correlate directly with distance from source. Rather 

than proximity, the fine-grained "distal" characteristics of the Hellenic unifites we examined are 

primarily the result of progressive sorting by repetitive downslope displacement events across 

highly irregular slope surfaces, i.e., textural segregation involving the relief bypass phenomenon 

(Figure 15). We would also expect that in the 

case of some ancient unifites, this type of textural 

and compositional sorting prior to final trench 

basin emplacement also resulted from flow spillover and selective bypassing of progressively finer 

grains across topographically highly complex 

slope terrains. 

Unifites accumulating on an active margin, 

such as those along the Hellenic Arc, often do not 

represent distal facies in the geographic sense. In 

contrast, however, some thick unifites have accumulated in small to moderate size basins in 

locales truly distant from shelves and slopes; these 

geographically distal unifite facies represent a 

bypassing of morphologically less complex margins. In larger basins, a unifite may represent the 

low concentration or slow moving end-member of 

a gravity flow transformation continuum (i.e., 

settling from the tail of a turbidity current or 

from a turbid layer flow), or may be deposited 

from a near-stationary cloud. 

In summary, thick unifites are closely related 

to the interplay of a number of factors: (1) the 

degree of accessibility to sediment flux, (2) redepositional processes and particularly gravity-induced flow characteristics, (3) type of material 

transported, (4) degree of textural segregation 

and compositional sorting during flow, (5) efficiency of slope relief bypassing, and (6) entrapment in relatively restricted catchment basins. 

We suspect that continued research on unifites 

will demonstrate that this facies occurs in a diversity of modern ocean and ancient marine settings that include both active and passive margins. 

Summary 

1. Unifites are nearly structureless muds, usually thick layers of clayey silt and silty clay that 

appear homogeneous in composition and often 

show an overall fining-upward trend; along the 

Hellenic Arc, unifites are restricted to small, isolated trench basins and interpreted as an endmember facies of gravity-emplaced transport 

processes. 

2. Unifites are formed by uniform muds, or 

faintly laminated muds, or both; uniform mud 

may overlie either faintly laminated mud or classic mud turbidites, but in either case it appears 

to be deposited from a single gravity-induced 

flow event. 

3. Rapid deposition of unifites from sediment 

gravity flows is implicated by the association of 

unifites with turbidites, their spatial restriction to 

trench basins, their lateral continuity and consistent thickness across large areas of trench basins, their marked thickness (to >10 m), their 

high clay fraction (to 60%) and very low sand 

fraction content (<0.3%), and a consistently small 

accumulation time range as indicated by 

radiocarbon dates. 

4. This study shows that unifites are not truly 

homogeneous petrologically, and that the textural and compositional distinctions observed 

within a unifite appear closely related with the 

geographic position of a trench basin depositional 

site relative to the steep margins bounding the 

trench plain, i.e., the base-of-slope margin flat 

setting versus the flat, more distal basin floor 

proper. 

5. Unifites recovered well within basin plains 

tend to comprise higher proportions of uniform 

mud, are somewhat better sorted texturally, and 

generally contain higher proportions of planktonic tests, but somewhat fewer benthic forami-
36 SMITHSONIAN CONTRIBUTIONS TO THE MARINE SCIENCES 

niferal tests and terrigenous components than 

unifites along trench margins. 

6. In detail, unifites display an overall, albeit 

subtle, fining-upward trend; the faintly laminated portions of unifites contain a somewhat 

higher silt content, while the uniform mud portions are slightly better sorted. 

7. A complete unifite sequence may display a 

vertical cyclic trend formed by four terms, from 

the base up: a faintly laminated, generally siltier, 

fining-up term characterized by a largely biogenic 

sand-size content; a graded mud term with terrigenous components dominating the sand fraction; an ungraded mud displaying textural fluctuations and an important sand-size terrigenous 

fraction; and an upper fining-upward term with 

increased proportions of sand-size biogenic components. 

8. The sand fraction of Hellenic Trench unifites is commonly dominated by clastic aggregates 

eroded and reworked downslope from older margin sediments; unifites also comprise a large siltsize nannofossil content (including an important 

proportion of reworked pre-Quaternary forms), 

and an upward increase of planktonic tests. 

9. A petrological "reversal" phenomenon, attributable largely to the influence of transport 

processes, involves a change in the proportion of 

mineralogical components between the edge and 

the center of a near-flat trench basin; for example, 

components that are dominant in the coarsest 

terms of margin flat cycles may, in contrast, 

abound in the finer (largely uniform mud) terms 

of basin plain cycles. 

10. The increased uniformity of unifites in a 

basinward direction indicates deposition from 

turbidity current-related flows of diminished concentration that move across, and spread over, 

large areas of a flat trench floor; the observed 

subtle petrologic variations probably record 

changes in flow character (turbulence, velocity, 

grain-support) that likely occur during a singletransport event over a brief time and limited area 

in a small ponded basin. 

11. Faint laminae may be related to phases of 

flocculation and depositional sorting of the sediment load during flow; a reorganization of mud 

and silt floes and changes in their concentration 

may induce accelerated settling of particles 

through the boundary layer at the base of a flow. 

12. The faintly laminated terms in unifites are 

herein related to the hydraulic jump effect that 

produces a sudden rearrangement of the sediment 

load at the head and in the body of a flow and 

flocculation upon its arrival on the near-flat 

trench basin floor; the eventual passage of the 

slower moving dilute tail of the flow beyond the 

base-of-slope is recorded by the uppermost nonlaminated, graded unifite mud term. 

13. The mineralogical "reversal" phenomenon 

that occurs between the margin flat and somewhat more distal basin plain environments is also 

attributed to hydraulic jump effects, which induce a transfer of energy and changes in turbulence and grain support characteristics within the 

flow over a short distance beyond the base-ofslope. 

14. Unifite thickness is in large part the result 

of the available volume of material transported 

relative to the surface area on which it accumulates, i.e., the thick Hellenic unifites do not necessarily record transport of particularly large sediment loads or a direct dispersal of concentrated 

flows between proximal and distal environments. Rather the unifites indicate entrapment 

of moderate amounts of material carried by sediment gravity flows into small trench basins. 

15. The homogenization process essential for 

the deposition of fine-grained unifites along the 

Hellenic Arc results in large part from a barrierdam effect, i.e., a modification of flows as they 

move basinward across the highly irregular slope 

topography characteristic of this region. 

16. Homogenization involves both textural 

and mineralogical segregation. Coarser or denser 

fractions are preferentially trapped in slope depressions, while finer or less dense silt and clay 

particles in thick gravity flows are transported 

further downslope across irregular seafloor features (relief bypass phenomenon). 

17. The failure of the thin, metastable sedimentary veneer on steep slopes is most frequently 
NUMBER 13 37 

triggered by earthquake tremors that affect large 

sectors of the Hellenic Arc; this episodic but 

frequent downslope transport of sediment, much 

of it reworked from older sedimentary strata, 

deposits by successive basinward displacement of 

progressively finer material that includes both 

land-derived terrigenous and biogenic fragments. 

18. Much of the thin silty clay veneer on present Hellenic slopes has been emplaced by the 

relief bypass process and this sediment resides 

only temporarily on high gradient, seismically 

unstable features; core analysis shows that during 

much of the late Quaternary to the present sediments on the margin have been transported basinward through a series of repetitive displacement events that produced textural and compositional sorting on the slope prior to final trench 

basin accumulation. 

19. The petrologic attributes of unifites record 

the interplay of several factors more important 

than proximality or distance from source: (1) 

complexity of dispersal paths and the degree of 

accessibility of sediment flux to the trench basin, 

(2) redepositional processes, grain-support mechanisms and gravity-induced flow characteristics, 

(3) type of material transported, (4) extent of 

textural seggregation and compositional sorting 

during flow, (5) role of the slope relief bypassing 

process, and (6) selective entrapment of essentially fine-grained particles in relatively restricted 

trench catchment basins. 

20. Continuing studies in the Mediterranean 

Sea indicate that unifites occur in diverse settings 

on both active and passive margins and that these 

modern ocean deposits can serve as examples to 

interpret some uniform mud facies in the rock 

record. 
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