Transitional_carbonate-terrigenous_shelf.pdf

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Continental Shelf Research 25 (2005) 1836–1852

Transitional carbonate-terrigenous shelf sub-environments

inferred from textural characteristics of surficial sediments in

the Southern Gulf of Mexico

Hector A. Hernandez Aranaa,b,, Martin J. Attrillb,Richard Hartleyc, Gerardo Gold Bouchotd

aEl Colegio de la Frontera Sur, Avenida Centenario km 5.5 Apartado Postal 424 Chetumal, Quintana Roo C.P. 77000, Mé xicobMarine Biology & Ecology Research Centre, School of Biological Sciences, University of Plymouth, Drake Circus,

Plymouth PL4 8AA UK cSchool of Geography, University of Plymouth, Drake Circus, Plymouth PL4 8AA, UK

dCINVESTAV-IPN, Antigua Carretera a Progreso km 2.5 Mé rida, Yucatá n, C.P. 97310, Mé xico

Received 24 May 2004; received in revised form 20 June 2005; accepted 27 June 2005

Available online 26 August 2005

Abstract

The present study describes the spatial and temporal patterns of surficial sediments within the transition zone of theterrigenous and carbonate (CO) provinces in the Southern Gulf of Mexico after flood events during the rainy season of

1999. The sampling design consisted of two across-shelf (A, B) and two along-shelf (C, D) transects that followed depth

and sediment gradients. Twelve stations, approximately 7–8 km apart, were allocated to each transect. PVC cores of

10 cm in diameter were taken to a depth of 5 cm for organic matter (OM), CO content and grain-size analysis after

recording relevant information such as corer penetration, characteristics of the surficial layer of sediment and depth of

the soft ‘‘liquefied’’ layer if present. OM was determined by combustion and CO content was analysed by acid digestion

and titration. Size-frequency distributions (SFDs) were measured using a Malvern Mastersizer X laser particle sizer into

15 whole phi size intervals. A multivariate approach was chosen to look in detail at the derived sediment SFDs and pick

up depth-related sub-environments that would help to construct a conceptual model of sediment movement.

Additionally, OM and CO content were used to identify the relative influences of river input and CO sediment, together

with the bulk sediment surface area/OM relationship to strengthen the interpretation of sediment sources. Three sub-

environments were qualitatively identified within the Southern Gulf of Mexico and validated using a multivariate

approach, which reflect the across-shelf topography and depth gradient. The spatial pattern was temporally maintained

in relation to sediment size distribution and CO content. OM and CO content showed an inverse association in response

to the effect of fine sediment of terrigenous origin carrying adsorbed OM. In contrast, CO content seems to be related to

coarser material with less surface area and organic content. A number of differences were found between the present

ARTICLE IN PRESS

www.elsevier.com/locate/csr

0278-4343/$ - see front matterr 2005 Elsevier Ltd. All rights reserved.

doi:10.1016/j.csr.2005.06.007

Corresponding author at: El Colegio de la Frontera Sur, Avenida Centenario km 5.5 Apartado Postal 424 Chetumal, Quintana

Roo C.P. 77000, Mexico. Fax: +52 983 8350450.

E-mail address: [email protected] (H.A. Hernandez Arana).

http://www.elsevier.com/locate/csrhttp://www.elsevier.com/locate/csr


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and previous studies carried out on the transitional area of the southern Gulf in relation to sediment size and CO

content. It is considered that these differences are mainly the consequence of local hydrology, which makes transitional

environments highly variable. As in other CO–siliclastic transitions, climate and hydrological setting are the main

controls of the dispersion and deposition of fine materials on the Southern Gulf of Mexico shelf.

r 2005 Elsevier Ltd. All rights reserved.

Keywords: Shelf sediments; Grain size; Mixed sediments; Multivariate analysis; Gulf of Mexico

1. Introduction

Two provinces constitute the Southern Gulf of

Mexico: Campeche Bank and Campeche Bay. The

former is an extensive CO shelf characterised by a

gentle slope and irregular bottom with sandbanks,

coral reefs and autochthonous biogenic and

authogenic sediments along most of the coast of

the Yucatan Peninsula (Antoine, 1972; Martin and

Bouma, 1978). Because of its karstic topography,

there is an absence of surficial runoff and the

presence of clastic sediments across the south-

western region is due to transport by currents from

Campeche Bay (Logan et al., 1969; Rezak and

Edwards, 1972). The physical properties of the

water column are considered vertically uniform,

with high salinity and density due to high

evaporation and the lack of surficial river runoff (Monreal Gomez et al., 1992). Campeche Bay is

characterised by its narrow shelf with a steep

slope; sedimentary features change into a terrige-

nous shelf of very fine silt and clay bottom,

presumably with an area of persistently turbid

bottom water (Rezak et al., 1990) due to the

presence of the Grijalva-Usumacinta and San

Pedro-San Pablo rivers’ delta system. This coastal

plain is the largest deltaic fluvial system in Mexico,

accounting for 35% of the total drainage of the

country. However, the sediment load is low(o50ton km2) and at present is undergoing

erosive processes related to coastal currents

(Aguayo Camargo et al., 1999).

The south-western region of the bank and the

continental area of the Campeche Bay have been

studied intensively due to the presence of salt

domes with oil-trapping characteristics (Bishop,

1980; Klemme, 1980). These two characteristic

provinces contain surficial sediments of different

origins, being relict marine autochthonous sedi-

ments on Campeche Bank and terrigenous un-

consolidated sediments in Campeche Bay. The

dynamics of the area produce an extensive transi-

tion zone where the interaction of river discharges,

coastal currents and intruding oceanic water

occurs, generating an area of mixed surficial

sediments (Yan ˜ ez-Arancibia and Sanchez-Gil,

1983). The criterion used to identify the transition

zone is the percentage of CO content in recent

sediments. Different authors have proposed varied

levels of CO content for this transition region,

ranging from 25% to 75%. The isoline of 75% CO

content has been proposed as the limit between the

terrigenous and CO provinces (Bello and Cano,

1991; Carranza Edwards et al., 1993). Gutierrez

Estrada and Galaviz Solis (1991) proposed a

classification system based on the amount of CO

content and mean grain size (MGS) (phi units) forsurficial sediments, providing a tool that allows the

degree of mixing of CO and terrigenous sediments

to be evaluate.

Extensive research exists on the characterisation

of the obvious, different depositional environments

(i.e. river beds, coastal dunes and beaches).

However, difficulties arise when the aim is to

differentiate samples from a more or less homo-

geneous environment (Hartmann and Christiansen,

1992; Sutherland and Lee, 1994). An additional

difficulty is present when human activities, such asoffshore oil production, contribute to a local

modification of the depositional environment. Oil

drilling activity is a prime issue of concern relating

to offshore oil production due to the use of oil-

based mud (Gray and Darley, 1981). These factors

vary in extent and are focused in localised areas of

the Southern Gulf of Mexico, providing an

opportunity to explore the interactions between a

number of natural and non-natural variables that

putatively influence surficial sediments. The present

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study aims to describe the spatial and temporal

patterns of surficial sediment within the transition

zone in the Southern Gulf of Mexico after flood

events of 1999 during the rainy season. A multi-variate approach was chosen to look in detail at the

derived sediment size-frequency distributions

(SFDs) and pick up depth-related sub-environ-

ments. Additionally, organic matter (OM) and CO

content were used to identify the relative influences

of river input and CO sediment, together with the

bulk sediment surface area/OM relationship to

strengthen the interpretation of sediment sources.

Distance of sampling stations to oilrigs was used to

determine any pattern of sediment characteristics

in relation to offshore oil-activities. Finally, we

aimed to construct a conceptual model of sediment

sources and transport from our own data and

previous studies.

2. Methods

2.1. Study area

The study area is located between latitude

191000 –191400N and longitude 911400 –921300W, in

the ‘transitional’ environment that occurs between

the CO and terrigenous provinces of the Cam-

peche Bank and Bay (Fig. 1). The study area

includes Mexico’s largest offshore oil productionregion, covering an area of 8000 km2 that includes

natural oil seeps and approximately 200 platforms

with a range of functions (Valdes and Ortega

Ramirez, 2000). The water circulation pattern is

driven by the Caribbean current during the spring

and summer, with a south to south-west direction,

but during autumn and winter the flow reverts to

an east to north-east direction (Boicourt et al.,

1998). The wind regime in the Southern Gulf of

Mexico is driven by the easterly trade all year

round, except when northern cold fronts or

‘‘northers’’ occur during autumn and winter.

‘‘Northers’’ can have high speeds (42 0 m s1)

and wind stress, and last for 1–3 days during the

winter season (Salas de Leon et al., 1992a); they

are also a mechanism for water mixing reaching

175 m deep (Vidal et al., 1994). Freshwater

discharge from the Grijalva-Usumacinta rivers

into the SW Gulf has been estimated to have an

annual average of 2.13 103 m3 s1 with peak

discharges from July to September/October

(CNA, 2001). River runoff in the SW Gulf

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Fig. 1. Study area indicating the location of stations along four transects A–D. Stations sampled for surficial sediments in November

1999, after the rainy season, and April 2000, after the northers season.

H.A. Hernandez Arana et al. / Continental Shelf Research 25 (2005) 1836–18521838


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produces a strong stratification of salinity and

density that reaches 42 km offshore from the river

mouth, affecting the top 15 m of the water column

in autumn (Monreal Gomez et al., 1992; Salas deLeon et al., 1992b). Water column stability

changes from stratified to homogeneous between

the ‘rainy’ and the ‘northers’ seasons, markedly

affecting the near-shore platform (o30 m depth)

(Czitrom et al., 1986).

2.2. Study design

The sampling design consisted of two across-

shelf (A, B) and two along-shelf (C, D) transects

(Fig. 1). Across-shelf transects started 40 km NW

off the Terminos Lagoon system and extended to

approximately 80 km offshore. Consequently,

these transects followed a depth gradient of

12–135 m and a sediment gradient of fine sand to

clay. Along-shelf transects followed a putative

sediment gradient from clay/silt to fine sand, and

CO content from 20% to 50%, whilst depth was

kept relatively constant, ranging from 30 to 50 m

(with the exception of stations D1 and D2 at 67 m

depth). These latter transects commenced

60–70 km N-NE offshore from the rivers’ mouths

and extended for approximately 80 km alongshore. Twelve stations, approximately 7–8 km

apart, were allocated to each transect. By sampling

along putative gradients in depth and sediment

size/CO content at different times, the sampling

design effectively allows for an examination of the

influence of river runoff, winter storms and the

presence of oil activities. The intersections were

sampled twice in November and only once in

April, making a total of 48 and 44 stations,

respectively.

2.3. Sampling methodology

Sampling was carried out from 11 to 13

November 1999 after the ‘rainy’ season and from

14 to 16 April 2000 after the ‘northers’ season.

Stations were located and positioned using the

satellite navigation system of the vessel, and

sampled (without replication) using a box corer.

The recovered core was sub-sampled for OM, CO

content and grain-size analysis after recording

relevant information such as corer penetration,

characteristics of the surficial layer of sediment

and depth of the soft ‘‘liquefied’’ layer if present.

Samples were taken using a PVC core of 10 cm indiameter to a depth of 5 cm, transferred to a

previously labelled plastic bag and frozen until

analysis.

2.4. Laboratory analyses

OM was determined by combustion (Dean,

1974) and CO content was analysed by acid

digestion and titration (Holme and McIntyre,

1984). SFDs were measured using a Malvern

Mastersizer X laser particle sizer (Wolfe and

Michibayashi, 1995) into 15 whole phi size

intervals. The analysis model was ‘‘very polydis-

persed’’, the scatter matrix for Mie theory correc-

tion was 2OHD and the particle refractive index

approximately 2.53. The analysis size spectrum

ranged from 0.1 to 2000 mm. Two sets of lenses

were employed, a 45 mm for the range size of

0.1–80 mm and a 1000mm for the size range of

4–2000 mm. Samples were dispersed in a 0.1%

sodium hexametaphosphate solution and soni-

cated for 30 s. The resultant grain-size distribu-

tions correspond to an average of five runsmeasured from the 1000 mm lens data and blended

with one reading on the 45 mm lens.

2.5. Data analysis

The Malvern Mastersizer X program was used

to calculate the moment descriptive statistics of

MGS, sorting, skewness and kurtosis. Additional

data included the specific surface area of the

sediments (SSAS, expressed as m2 g1 and calcu-

lated as spherical theoretical proxies assuming adensity of 2.65 g cm3 for the sediment), percen-

tage of sand, silt, clay and modal fractions. Based

on field observations of sediment characteristics

and depth intervals, the samples were divided into

three sub-environments. Initially, this included the

near-shore at depths lower than 30 m, inner shelf

at depth between 30 and 50 m and outer shelf at

depths greater than 50 m.

Multivariate analysis was undertaken using

the PRIMER (Clarke et al., 2001) and the

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Statgraphics plus 4.1v packages. Correlation-

based PCA ordination and discriminant analysis

(DA) were run with two data sets from both

sampling dates: (1) Arc-sin transformed data of the 92 SFDs plus bulk OM and CO content. (2)

Derived moment descriptive statistics (MGS,

sorting, skewness) from the 92 SFDs, SSAS, bulk

OM and CO content. The objective was to look at

particular sizes of sediment that could provide an

insight into any existing gradient or pattern of

depositional sub-environments and to compare

with the summarising statistics seeking to obtain a

better environmental ordination that allows vali-

dating a priori proposed classification. This type of

analysis has been used previously to identify

and differentiate sedimentary environments

(Ferna ´ ndez et al., 2003; Barcelo ´ et al., 1999;

Syvitsky, 1991). Histograms of SFD were em-

ployed to visualise our proposed conceptual model

of across-shelf sediment transport. In order to

further validate our proposed a priori classifica-

tion of sub-environments two textural classifica-

tion were employed. One was based on CO content

and sediment MGS (Gutierrez Estrada and

Galaviz Solis, 1991) and a further three compo-

nent classification scheme was based on sand/silt/

clay ratios using ternary plots in order to

distinguish between different hydrodynamic re-

gimes (Flemming, 2000). Spearman correlation

analyses were performed to investigate the correla-

tion between OM and CO content with sedimentgrain-size parameters as a tool to investigate

sediment sources.

3. Results

Field observations provided insights for a

preliminary qualitative classification. Three sub-

environments were distinguished by sediment

compaction (measured qualitatively as depth of

main core penetration), bivalve and gastropod

shell abundance and the occurrence of a top layer

of liquid dense mud: near-shore, inner and outer

shelf (Table 1). The sampling after the rainy season

coincided with conditions derived from a very

heavy rainy season with serious flooding along the

south and south-western Gulf coast of Mexico.

Therefore, an increased sediment load was dis-

charged onto the continental shelf of the Cam-

peche Bay and Bank. Samples taken after the

‘northers’ season will have been affected by pulses

of strong northerly winds up to 17 m s1, which

occurred during autumn and winter and are

ARTICLE IN PRESS

Table 1

Preliminary classification of three sub-environments based on field observations of sediment characteristics during the sampling

programs of November 1999 and April 2000 in the Southern Gulf of Mexico

Sub-environment Core penetration (cm) Shell content Sediment firmness Other observations

Near-shore, 12–27m

deep. Stations 1–5 of

transects A and B

25–35 Abundant, particularly

oyster shells on transect

B

Top layer of dense

liquid mud 3–5 cm deep.

Absent in April. Below

it a well-compacted fine

matrix grey in color

Wood and seagrass

debris

Inner shelf, 30–50 mdeep. Stations 6–8 of

transects A and B.

Stations 1–12 of transect

C. Stations 3–12 of

transect D

35–60 A gradient of scarce toabundant from the SW

to NE of transects C

and D

Top layer of denseliquid mudo3cm,

below it a soft greenish

(plasticine consistency)

sediment of 10–20 cm

deep in November and

5–10 cm deep in April

Wood debris (south-west end of transect C)

and tar present at the

crossing of the transects

Outer shelf, 450–130m

depth. Stations 9–12 of

transects A and B.

Stations 1 and 2 of

transect D

40–55 Abundant pteropod and

Foraminifera shells

Top layer of soft greyish

(plasticine consistency)

sediment of 20 cm deep

in November and

5–15 cm deep in April

Tar in some samples



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associated with intense wave action. Mean and

extreme values of moment descriptive statistics for

each of the three sub-environments for both

sampling dates (Table 2) indicated a gradient of sediment grain size and skewness from the near-

shore to the outer shelf, i.e. a gradient of coarse silt

to fine silt across the shelf with an excess of fine

particles towards the deeper areas.

3.1. Multivariate statistical analysis

Fig. 2 displays the factor-scores of the PCA

ordination using SFD, OM and CO content

(Fig. 2a) and moment descriptive statistics, SSAS,

OM and CO content (Fig. 2b) for both sampling

dates. PC1 in Fig. 2a explains the largest amount

of variation (75.3%). Therefore, the most influen-

tial variable is CO content followed by the 32 mm

fraction; high CO content and high percentages of

coarse silt are accounting the most for the near-

shore separation (Table 3a). The inner and outershelf are characterised by a gradual increase of

finer material and dilution of CO content, inferred

form the negative loading of the third most

influential variable (4mm fraction) and the positive

loading of the CO content. The second PC

explains a small amount of variation (10%) and

the most influential variables with negative load-

ings were CO content and the 8–16 mm fraction.

PC1 in Fig. 2b explains 52% of variation and

shows a similar pattern of across-shelf changes in

ARTICLE IN PRESS

Table 2

Mean and extreme values of moment descriptive statistics for

three shelf sub-environments classified qualitatively based on

field observations of sediment characteristics during the

sampling programs of November 1999 and April 2000 in theSouthern Gulf of Mexico

Mean grain size Sorting Skewness Kurtosis

November 1999

Near-shore

Maximum 6.82 2.56 1.69 6.75

Minimum 4.79 1.45 0.14 3.12

Average 5.65 1.97 0.76 4.30

Inner shelf

Maximum 7.39 2.47 0.67 4.86

Minimum 6.24 1.56 0.63 2.62

Average 7.15 1.72 0.35 3.54

Outer shelf

Maximum 7.55 3.28 0.38 6.5

Minimum 6.38 1.55 1.1 3.21

Average 7.36 1.89 0.28 4.66

April 2000

Near-shore

Maximum 6.07 3.43 1.30 4.85

Minimum 4.67 1.82 0.26 2.04

Average 5.49 2.16 0.69 3.85

Inner shelf

Maximum 7.43 2.38 0.66 5.79

Minimum 6.86 1.59 1.13 3.14Average 7.17 1.77 0.25 3.78

Outer shelf

Maximum 7.60 2.24 0.42 6.61

Minimum 7.32 1.62 1.26 2.97

Average 7.44 1.78 0.07 4.21

PC1

P C 2

-15 -5 5 15 25 35 45-10

0

10

20

30

(a)

PC1

P C 2

-2.6 -0.6 1.4 3.4 5.4-1.8

0.2

2.2

4.2

6.2

(b)

Fig. 2. PCA ordinations plotting factor-scores for samples

taken during the rainy (open symbols) and northers (closed

symbols) seasons from the Southern Gulf of Mexico using dataof: (a) 92 SFDs, SSAS, bulk OM and CO content; (b) derived

sediment moment statistics, SSAS, bulk OM and CO content

(&, near-shore; n, inner shelf; B, outer shelf).



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sediment size, as noted from the most influential

variables such as SSAS, sediment MGS and the

dilution of CO material by terrigenous input

(indicated by the coefficient of OM and CO content).

PC2 explains 22% of variation and is influenced

mainly by sediment standard deviation (sorting) and

skewness, the difference in signs for sorting and

skewness coefficients indicating that their influence

occurs in opposite directions (Table 3b). In sum-

mary, the plots of PCA factor-scores showed a

depth-related gradient with the near-shore clearly

separated from the inner shelf, which in turn grades

smoothly into the outer shelf, with samples from the

outer shelf clustered together at the far right side of the plots.

The depth gradient observed in the PCA

ordinations along PC1 provides insight into the

hydrodynamics of the area. From the sediment

size spectrum histograms, a relative high contribu-

tion of coarse silt and sand fractions (432 mm) is

observed at the near-shore (Fig. 3). Those frac-

tions decrease at the inner shelf with a correspond-

ing increase of fine to medium silts (4 and 16 mm).

There is little difference between the inner shelf

and outer shelf; however, the relative contribution

of sediment fractions between 16 and 63mm is

reduced and substituted by an increase in fractions

between 1 and 2 mm (clay and very fine silt). The

sediment grain-size distributions present a normal

gradient of deposition, changing from coarser to

finer with increasing depth and becoming more

negatively skewed (decreasing values) from the

near-shore towards the outer shelf, indicating an

across-shelf direction of transport. Temporal

differences were not observable at any of the three

shelf sub-environments.

A DA was performed to validate the proposedqualitative classification of three sub-environ-

ments. Fig. 4 displays the results of the first and

second discriminant functions (df) that best

separate the three sub-environments for the

combined sampling dates using SFD, OM and

CO content data, with 96.74%. The percent of

stations correctly classified within the three

proposed sub-environments. The relative percen-

tage of variation and the canonical correlation

value for the df1 and df2 were 83.59%, 0.95 and

16.41%, 0.82, respectively. Wilks lambda fordf1 and df2 was 0.026 and 0.32, with po0:0001.

A similar result was obtained for the data set

of moment descriptive statistics, SSAS, OM and

CO content, hence only one ordination plot is

presented.

3.2. Textural classification and sediment sources

The bivariate classification of surficial sediments

from the SW Gulf of Mexico using the data of the

ARTICLE IN PRESS

Table 3

Percentage of variation explained by the first two PCs and

coefficients in the linear combination of variables making up

the PCs

PC1 PC2

(a) For the ordination of arc-sin transformed data of 92 SFD,

bulk OM and CO content from the Southern Gulf of Mexico

% Variation 75.3 10.0

Variable loadings

OM 0.181 0.084

CO 0.360 0.276

0.1mm 0.008 0.004

0.125mm 0.025 0.006

0.25mm 0.06 0.002

0.5mm 0.114 0.015

1mm 0.179 0.044

2mm 0.262 0.0264mm 0.343 0.06

8mm 0.286 0.221

16mm 0.125 0.36

32mm 0.595 0.111

63mm 0.2 0.035

125mm 0.188 0.049

250mm 0.233 0.096

500mm 0.105 0.118

1000mm 0.04 0.157

(b) For the ordination of normalised data of derived sediment

moment statistics, SSAS, bulk OM and CO content from the

Southern Gulf of Mexico

% variation 52.1 22.5Variable loadings

SSAS (m2 gm1) 0.494 0.09

Moment MGS (phi) 0.504 0.1

Moment std. dev.(phi) 0.233 0.626

Moment skewness 0.228 0.691

Moment kurtosis 0.031 0.299

OM % 0.443 0.105

CO % 0.446 0.111

Note: Bold figures are the highest coefficients for the most

important variables along the first two PCs.



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ARTICLE IN PRESS

near shore November 1999

0

5

10

15

20

25

30

35

4045

50

0

. 0 6

0

. 2 5 1 4

1 6

6 3

2 5 0

1 0 0 0

near shore April 2000

0

5

10

15

20

25

30

35

4045

50

0

. 0 6

0

. 2 5 1 4

1 6

6 3

2 5 0

1

0 0 0

inner shelf November 1999

0

5

10

15

20

25

30

35

40

45

50

0 . 0

6

0 . 2

5 1 4 1 6

6 3

2 5 0

1 0 0 0

f r e q v o l %

f r e q v o l %

f r e q v o l %

f r e q v o l %

inner shelf April 2000

0

5

10

15

20

25

30

35

40

45

50

0 . 0

6

0 . 2

5 1 4 1 6

6 3

2 5 0

1 0 0 0

outer shelf November 1999

0

5

10

15

20

2530

35

40

45

50

0 . 0

6

0 . 2

5 1 4 1 6

6 3

2 5 0

1 0 0 0

microns

f r e q v o l %

outer shelf April 2000

0

5

10

15

20

25

30

0 . 0

6

0 . 2

5 1 4 1 6

6 3

2 5 0

1 0 0 0

microns

f r e q v o l %

Fig. 3. Histograms of sediment-SFD compiled by pooling stations for the near-shore, inner and outer shelf showing the across-shelf

change in sediment grain size.



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present study, as proposed by Gutierrez Estrada

and Galaviz Solis (1991), shows two sub-environ-

ments in relation to CO content and moment

MGS (Fig. 5).

(a) Fine silt of terrigenous and calcareous origin

(o50% CO content) on the outer shelf, the

central and SW areas of the inner shelf (sites

1–8 of transect D and 1–4 of transect C).

(b) Very coarse to medium silt of calcareous origin

mixed with terrigenous material (450% COcontent) on the near-shore, the central and NE

areas of the inner shelf (sites 5–12 of transect C

and 9–12 of transect D).

Flemming’s (2000) textural classification was

employed in order to demonstrate further the

consistency of the qualitatively proposed sub-

environments’ classification in relation to sediment

composition and hydrology regime. Figs. 6a and b

show that according to Flemming’s textural

classification the studied area corresponds to a

textural class between D-I and D-II (extremely

silty slightly sandy mud and very silty slightly

sandy mud) for the near-shore sub-environment.

The inner shelf part contains few stations within

the D-II and the rest of them within the E-II

textural class (very silty slightly sandy mud and

slightly clayey silt). Most of the stations from the

outer shelf were classified within the E-II category.

Thus, in terms of textural classification there is no

clear difference between the inner and outer shelf

sub-environments. From the two plots it can be

inferred that temporal differences are minimal; thearea can be considered depositional, presenting a

selective deposition across the shelf with a higher

energy regime on the near-shore, decreasing

towards the outer shelf.

Our data suggest a relationship between sedi-

ment MGS and CO with no difference between

seasons and with CO sediments being coarser than

terrigenous ones. Percentage of CO plotted against

SSAS confirms the association (Fig. 7a), where

carbonated sediments are coarser and with less

SSAS. Similarly, an inverse relationship betweenbulk CO and OM is observed (Fig. 7b) in

November and April. The correlation between

organic content and sediment grain size has been

explained in terms of adsorption to aluminosilicate

continental shelf sediments, and also would reflect

hydrodynamic equivalence between particulate

OM and fine size sediments (Mayer, 1994).

Considering Meyer’s hypothesis that the specific

surface area of sediment controls OM in con-

tinental shelves, we explored the relationship

ARTICLE IN PRESS

Df 1

D f 2

NS

IS

OS

Centroids

-4 0 2 4 6 8

-2.7

-0.7

1.3

3.3

5.3

-2

Fig. 4. DA ordination plot for samples taken during the rainy

and northers seasons from the Southern Gulf of Mexico using

data of 92 SFDs, SSAS, bulk OM and CO content (’, near-

shore; n, inner shelf; E, outer shelf).

CO %

M G

S φ

NS IS OS

20 30 40 50 60 70 80

4.6

5.1

5.6

6.1

6.6

7.1

7.6

Fig. 5. Scatter plot of bivariate classification of surficial

sediments from the Southern Gulf of Mexico (see text for

explanation) based on CO content and sediment MGS: o50%

CO content ¼ terrigenous sediments with carbonate influence;

450% CO content¼

carbonate sediments mixed with terrige-nous material (&, near-shore; n, inner shelf; B, outer shelf).



10/17

ARTICLE IN PRESS

Fig. 6. Textural classification of surficial sediments from the Southern Gulf of Mexico using ternary plots based upon Flemming’s

scheme of textural classes: (a) samples taken after the rainy season in November 1999 and (b) samples taken after the norther season in

April 2000 (J, near-shore; K, inner shelf; &, outer shelf).



11/17

between SSAS for bulk sediment samples and bulk

OM. Our results indicate an overall positive

relationship (Fig. 7c) for both rainy and norther

seasons.

3.3. Along-shelf sediment characteristics

Our sampling design allowed us to remove the

previously demonstrated depth effect by consider-ing transects C and D independently. As high-

lighted earlier, there is an increasing CO content

from SW to NE along the isobaths. Table 4

contains Spearman correlation coefficients be-

tween SSAS, sediment MGS, OM and CO for

both sampling dates. The assumption previously

made, in relation to CO content with MGS and

SSAS, seems invalid after the rainy season where

no association was present, but in April there was

a weak association between CO and sediment

MGS, and CO with SSAS. The inverse relation-ship between OM and CO is maintained for both

sampling dates, although with low but significant r

coefficients. Furthermore, there is no association

between OM and sediment MGS or SSAS for the

sampling during November 1999, but a weak

relationship in April.

It is therefore a possibility that additional

sources of OM, not associated with sediment

particles, exist after the rainy season. This may

relate to the presence of oil rigs; to explore this

ARTICLE IN PRESS

CO %

S S A S m 2 / g

20 30 40 50 60 70 80

0

0.2

0.4

0.6

0.8

1

(a)

CO %

O M %

20 30 40 50 60 70 80

0

3

6

9

12

15

18

(b)

SSAS m2 /g

O M %

0 0.2 0.4 0.6 0.8 1

0

3

6

9

12

15

18

(c)

Fig. 7. Scatter plots of the association between: (a) CO content

and SSAS, r ¼ 0:

75, po0:

05; (b) OM % and CO content,r ¼ 0:60 and 0.73 for the rainy and norther season,

respectively, po0:05 and (c) OM % and SSAS, r ¼ 0:57 and

0.64 for the rainy and norther season, respectively, po0.05

(K, rainy season; +, northern season).

Table 4

Spearman correlation coefficients for the association between

specific surface area of sediment (SSAS), mean grain size

(MGS), organic matter (OM), carbonate content (CO) and

distance to oil fields on the along shelf transects sampled inNovember 1999 and April 2000

SSAS MGS OM CO

(a) Along-shelf transects C and D after the rainy season

November 1999

SSAS

MGS 0.87

OM 0.18 0.21

CO 0.28 0.35 0.41

Dist to oil fields 0.08 0.02 0.19 0.15

(b) Along-shelf transects C and D after the northers season April

2000

SSASMGS 0.83

OM 0.30 0.47

CO 0.46 0.69 0.41

Dist to oil fields 0.11 0.23 0.22 0.39

Note: Bold figures represent the highest significant r coefficients.



12/17

further sediment variables were plotted against

estimated distances to oil rigs (distances were

roughly estimated from Nautical chart S.M. 840.

Secretaria de Marina, 1994). No relationship wasobserved between OM, sediment MGS or any of

the individual sediment size fractions and distance

to oilfields. However, it is worth pointing out that

of those sites sampled in November 1999, and with

an organic content higher than 10%, half of them

included tar balls (observed from the field and

during sample processing). In April 2000, the three

highest values of OM were found at sites where tar

balls were recorded.

4. Discussion

Both multivariate techniques allowed the pro-

posed three sub-environments to be separated,

although DA resolved the group separation better.

This outcome supports the ability of multivariate

techniques to separate spatial and temporal

patterns when present (Syvitsky, 1991; Ferna ´ ndez

et al., 2003). The clear separation of near-shore

stations from those on the inner and outer shelf

suggests that the 30m isobath is a natural

boundary for differential depositional environ-ments. The depth gradients observed in the multi-

variate ordinations can be interpreted in terms of

hydrodynamics affecting the deposited sediment

coming from river discharges, the CO shelf and in

situ production. A relatively high contribution of

coarse silt and sand fractions is observed at the

near-shore. Winnowing of the fine spectra of the

sediment grain-size distribution occurs, sizes

o32 mm being preferentially removed by the

hydrology regime occurring at the near-shore.

These finer sediments are then subsequentlydeposited across the inner shelf, where the wind

generated currents and waves are less likely to

reach the bottom (Mooers, 1976). Temporal

differences were not observable, indicating that

the mechanisms involved in the sediment transport

and deposition are continuously present within the

sampling time span.

Sediment particle size distribution is thought to

reflect the hydrodynamics of the depositional area,

and can be used to infer direction of transport

(Flemming, 2000). McLaren and Bowles (1985)

proposed a model for sequential deposits where

‘‘grain-size distributions change with the direction

of transport and can become finer, better sortedand more negatively skewed with a decreasing

energy regime’’. The Southern Gulf of Mexico

transitional continental shelf can be described as a

depositional environment, with decreasing energy

regime as depth increases. In consequence, we

would expect a change in the grain-size distribu-

tion becoming finer and more negatively skewed

(decreasing values) towards the inner and outer

shelf. Indeed sediment became finer, as noted from

the histograms of SFD and ternary plots, and

skewness values decreased along the depth gradi-

ent. Sediment type in our study area is mainly silt,

with variable amounts of sand and clay ranging

from 10% to 25%. When waves and currents act

over a cohesive sediment structure they contribute

to fluidisation and liquefaction, and the complex

mixture behaves as a dense suspension which can

be transported by weak bottom currents (Teisson

et al., 1993). Field observations were made of a

dense liquid surficial layer of sediment at the near-

shore and inner shelf during November 1999.

Drake (1999) characterised the sediment grain-size

distribution of a flood layer on the Eel shelf (Northern California) and points out that this

layer has high porosity, grain-size variability and

presents a marked change in compaction at the

pre-flood layer. We did not measure vertical

variation of grain-size distribution down the core,

but we believe that the qualitative differences on

the near-shore and inner shelf are result of the

discharges after the heavy rainy season and the

action of waves and bottom currents over a fine

sediment matrix.

Explaining the interactions between the terrige-nous and CO provinces has been difficult due to

the sampling scale applied by the few studies

undertaken in the Southern Gulf. One of the

proposed approaches is the bivariate classification

of Gutierrez Estrada and Galaviz Solis (1991).

This classification involves sediment MGS and CO

content measurements providing 14 sedimentary

units ranging from terrigenous gravel to CO

clay, with several units of mixed sediment of

different sizes. These authors draw the limit of the

ARTICLE IN PRESS



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transition zone as 50% CO content and the

present study area was previously classified into

three sub-environments: (a) mixed calcareous clay

at the near-shore; (b) mixed clay at the inner shelf and (c) calcareous silt at the outer shelf. However,

when plotting our own data we found only two

sub-environments. There is an agreement in the

range of values for CO content but not in sediment

MGS. The data in this study indicate sediment

MGS within the range of very coarse to fine silt

distributed from the near-shore towards the outer

shelf, different from other studies where finer

sediment MGS (clay) was reported for the outer

shelf (see cited references in the methods section),

although sediment grain sizes were determined by

different methods. Similarly, Flemming’s textural

classification scheme using ternary plots classified

the present study area in mainly two textural

classes: (a) extremely silty slightly sandy mud and

(b) slightly clayey silt. The CO content in this

classification scheme is not considered, but it is an

important feature for the Southern Gulf of Mexico

sediment classification.

The assumption made in relation to CO sedi-

ments being coarser than terrigenous ones should

consider their physical properties. Tucker and

Wright (1990) advice caution when interpretinggrain-size data of CO material because of differ-

ences in biological destruction, disintegration and

unique hydrodynamic properties. They noted that

lime mud on the Bahamas shelf comes from

biological disintegration of calcareous algae (e.g.

Halimeda and Penicillus) and transported across

shelf. According to Logan et al. (1969), coralline

algae represent up to 30% of total grained

constituents on the inner shelf/near-shore environ-

ment of the northern part of Campeche Bank. We

considered that the association between CO andsediment size (MGS or SSAS) is useful for

inferring that CO material is continuously being

supplied towards the transitional environment,

both by direct deposition and biological disinte-

gration of shell debris (as observed from the

amount of shell fragments) and by continuous

transport from the northern shelf. There is a

frontier of influence probably resulting from an

interaction of counter-currents feeding terrigenous

material.

The association between CO and sediment MGS

contrasts with the relationship between OM and

sediment MGS. In the Western Gulf of Mexico,

rivers are the main source of terrestrial OM, whichtends to accumulate on the continental shelf

depending upon local input and shelf width

(Hedges and Parker, 1976). The correlation found

between bulk OM, CO content and SSAS provides

evidence to suggest that the interaction of terrige-

nous and CO material at the transition zone is a

consequence of the hydrodynamic behaviour of

fine sediments and the associated OM adsorbed on

its surface (Mayer, 1994). The major interaction

occurs within the near-shore sub-environment

decreasing gradually until replaced by a terrige-

nous depositional environment on the outer shelf

and the SW extreme of the inner shelf.

4.1. Across-shelf transport conceptual model in the

context of the hydrology of the Southern Gulf of

Mexico

Forcing mechanisms of sediment entrainment

and transport in the continental shelf of the Gulf

of Mexico are generally the passage of cold fronts,

plus occasional tropical storms and hurricanes

(Fuentes Yaco et al., 2001). For example, in 1999extreme wind speed during autumn and winter

reached 17 m s1 (CNA, pers. commun.) and these

winds are able to generate wave heights on the

range of 3 m. Fig. 8 depicts our conceptual model

of sediment movement and extent of the transi-

tional zone in the Southern Gulf of Mexico that

includes information from the present and pre-

vious studies. The depth profile along transects

A–B running from SE to NW shows two changes

in slope, the first occurring at 30 m deep, which we

consider as a natural boundary of wave shearstress of re-entraining sediments. Rosales Hoz et

al. (1999) have inferred a south-west bottom

current near-shore; this type of current is likely

to move the entrained material from the near-

shore to the inner shelf. A second bottom current,

with N-NE direction, was inferred to be coming

from the river mouths, which they interpreted as

being responsible of transporting the terrigenous

load. This situation is likely to occur during

autumn and winter when the general superficial

ARTICLE IN PRESS



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shelf circulation of the western and south-western

Gulf is shifted to flow towards the Campeche Bank(Boicourt et al., 1998). This physical setting can

explain the along-shelf spatial distribution where

terrigenous sediments are present at the SW

extreme of transects C–D and CO content

increases towards the NE.

The second change in slope that occurs at

50–60 m deep is proposed to delimit the transition

area between the inner and outer shelves. Accord-

ing to McGrail and Carnes (1983), atmospheric

forcing from autumn and winter winds in the

northern Gulf produce inertial oscillations,which propagate through the water column and

cause 20–40 cms1 bottom currents at 100 m

depth. These are able to carry sediments offshore

beyond the shelf break, as proved during

current meter mooring observations on the

Texas shelf, where a nepheloid bottom layer is

present throughout the year. This benthic nephe-

loid layer develops more easily on a muddy

substrate with an along-isobath component

(Shideler, 1981).

There has not been any published information

in relation to bottom suspended sediments in thesouthern Gulf, but the suggestion of the existence

of sediment-laden water near the bottom in

the southern Gulf area (Rezak et al., 1990) is

attractive to explain the large area of influence of

terrigenous sediments. In this situation, very dense

liquid mud generated by flocculation and sedi-

mentation from the rivers load, or from re-

entraining by hydrological conditions, can be

transported long distances by along-shelf currents,

particularly in extreme conditions of river dis-

charges as those presented during the rainyseason of 1999.

A number of models of spatial distribution of

surficial sediments have depicted the depth-related

gradient of silt and clay on the terrigenous

province, as well as the continuous transitional

change towards the CO province, as the main

characteristics in the southern Gulf. All current

models contain a highly variable description of

the transition zone as a consequence of the

extensive areas covered during those studies. There

ARTICLE IN PRESS

Fig. 8. Conceptual model of sediment transport in relation to shelf topography, wind and wave stress and regional hydrology, and

location of the transitional area based on the criteria of 25–50% carbonate content (shadowed areas) from data obtained in this and

previous studies. Current patterns were drawn from the various studies referenced in the text, with bottom currents as interpreted from

Rosales Hoz et al. (1999). Drawn isolines of 25% and 75% from Carranza Edwards et al. (1993) and isoline of 50% from Gutierrez

Estrada and Galaviz Solis (1991).



15/17

are a number of differences between the present

model and those derived from previous studies

(Fig. 8). Carranza Edwards et al. (1993) proposed

the transitional area as the one between 25% and75% of CO content and the outer shelf area

was considered within the terrigenous province.

However, here we found that CO content is

425% for the outer shelf and the 75% limit was

not reached within our area. The most commonly

used criterion for the limit for the transitional area

is the 50% CO content and this study comple-

ments previous ones (see earlier references).

The transitional area extends to 60 km N-NE off

the rivers’ mouth at the near-shore and up to

140 km along the inner shelf. In relation to

sediment size, the SE portion of transects A–B

and NE extremes of transects C–D have been

classified as sandy, sandy mud and calcareous

mud. In this study, those areas range from sandy

mud to mud, based on Folk’s classification of

sand:mud ratio (Folk, 1954). The rest of the area

is muddy with some sandy-mud sites located near

to the oil fields. It is considered that these

differences with previous studies are mainly the

consequence of local hydrology, which makes

transitional environments highly variable. As in

other CO–siliclastic transitions (Murray et al.,1982; Roberts, 1987; Roberts and Murray, 1988;

Murray et al., 1988), climate and hydrological

setting are the main controls of the dispersion and

deposition of fine materials on the Southern Gulf

of Mexico shelf.

5. Conclusions

Three sub-environments were identified within

the Southern Gulf of Mexico using a multivariateapproach, which reflect the across-shelf topogra-

phy and depth gradient. The spatial pattern was

temporally maintained in relation to sediment

grain-size distribution and CO content. OM and

CO content showed an inverse association in

response to the effect of fine sediment of terrige-

nous origin carrying adsorbed OM. On the

contrary, CO content seems to be related to

coarser material with less SSAS and organic

content.

Re-entrainment of sediments o32 mm from the

near-shore and subsequent transport towards the

inner and outer shelf are probably caused by the

combination of wave and currents generated bywind forcing coupled to bottom currents. The

near-shore sub-environment is limited by the

730 m isobath and considered a natural boundary

for wind-wave effect on the seabed. Differences

between the inner and outer shelf are small,

grading smoothly from one to another, but

identifiable at 50–60 m depth.

River influence, measured in terms of CO

content and OM, is estimated to extent 70 km

from the river’s mouth to the shelf break and

200 km along the isobaths, covering an area of

approximately 14,000 km2 as a result of hydro-

logical dynamics. However, no increase in fine

material was observed as expected because the

very heavy rainy season of 1999. No temporal

differences were found in the amount of fine

material after 5 months, showing a conservative

transitional area in which its interaction with the

neighbouring provinces can only be measured

relative to the prevailing physical setting.

The presence of oil rigs did not show any

association with the analysed variables at the

studied scale; however, individual observations of the presence of tar balls in the sediments suggested

a local contribution from oil activities.

Acknowledgements

The British Council and CONACyT (Mexico)

are thanked for providing financial support

through a scholarship to H.A.H.A. Special thanks

are due to D. Salas de Leon and E. Escobar

Briones for providing logistic support within theoceanographic research programs PROMEBIO 2

and 3 (ICMyL-UNAM Mexico). The authors

express their gratitude to the commander and

crew of the oceanographic vessel ‘‘B./O. Justo

Sierra’’ and the M.Sc. students that provided help

during the sampling program and onboard proces-

sing of samples. H. Weissenberger is thanked for

map editing. Two anonymous referees are thanked

for their comments which contributed to the

improvement of the final manuscript.

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References

Aguayo Camargo, J.E., Gutierrez Estrada, M.A., Araujo

Mendieta, J., Sandoval Ochoa, J.H., Vazquez Gutierrez,

F., 1999. Holocene and recent geodynamics of the fluvial-

deltaic Grijalva-Usumacinta system, Southwest Gulf of

Mexico. Revista de la Sociedad Mexicana de Historia

Natural 49, 29–44.

Antoine, J.W., 1972. Structure of the Gulf of Mexico. In:

Rezak, R., Henry, V.J. (Eds.), Contributions on the

Geological and Geophysical Oceanography of the Gulf of

Mexico. Gulf Publishing Company, Houston, pp. 1–34.

Barcelo ´ , C., Pawlowsky, V., Bohling, G., 1999. Classification of

compositional data using mixture models: a case study using

granulometric data. In: Harff, J., Lemke, W., Statteger, K.

(Eds.), Computerized Modelling of Sedimentary Systems.

Springer, Berlin, pp. 389–400.

Bello, A.A., Cano, R., 1991. Subsuelo marino en el areade la Sonda de Campeche. In: Conference Proceedings of

the Soil Mechanics and Foundation Engineering, vol. 1.

Sociedad Chilena de Geotecnia, Vin ˜ a del Mar, Chile,

pp. 183–195.

Bishop, W.F., 1980. Petroleum geology of Northern Central

America. Journal of Petroleum Geology 3 (1), 3–59.

Boicourt, W.C., Wiseman, Jr., W.J., Valle-Levinson, A.,

Atkinson, L.P., 1998. Continental shelf of the southeastern

United States and the Gulf of Mexico: in the shadow of the

western boundary current. In: Robinson, A.R., Brink, K.H.

(Eds.), The Sea. The Global Coastal Ocean. Regional

Studies and Syntheses. Wiley, New York, pp. 135–181.

Carranza Edwards, A., Rosales Hoz, L., Monreal Gomez, A.,

1993. Suspended sediments in the southeastern Gulf of Mexico. Marine Geology 112, 257–269.

Clarke, K.R., Gorley, R.N., 2001. PRIMER v5: User Manual/

Tutorial. PRIMER-E Ltd., Plymouth.

CNA, 2001. Compendio basico del agua en Mexico, 2001.

Comision Nacional del Agua. Online, Annual Report.

www.cna.gob.mx.

Czitrom, S.P.R., Ruiz, F., Alatorre, M.A., Padilla, A.R., 1986.

Preliminary study of a front in the Campeche Bay, Mexico.

In: Nihoul, J.C.J. (Ed.), Marine Interfaces Ecohydrody-

namics. Elsevier, Amsterdam, pp. 301–311.

Dean, Jr., W.E., 1974. Determination of carbonate and organic

matter in calcareous sediments and sedimentary rocks by

loss on ignition: comparison with other methods. Journal of Sedimentary Petrology 44 (1), 242–248.

Drake, D.E., 1999. Temporal and spatial variability of the

sediment grain size distribution on the eel shelf: the flood

layer of 1995. Marine Geology 154, 169–182.

Ferna ´ ndez, M., Roux, A., Ferna ´ ndez, E., Calo ´ , J., Marcos, A.,

Aldacur, H., 2003. Grain-size analysis of surficial sediments

from Golfo San Jorge, Argentina. Journal of the Marine

Biological Association of the United Kingdom 83,

1193–1197.

Flemming, B.W., 2000. A revised textural classification of

gravel-free muddy sediments on the basis of ternary

diagrams. Continental Shelf Research 20, 1125–1137.

Folk, R., 1954. The distinction between grain-size and mineral

composition in sedimentary rock nomenclature. Journal of

Geology 62, 344–359.

Fuentes Yaco, C., Salas de Leon, D.A., Monreal-Gomez, M.A.,

Vera-Herrera, F., 2001. Environmental forcing in a tropicalestuarine ecosystem: the Palizada river in the Southern Gulf

of Mexico. Marine and Freshwater Research 52, 735–744.

Gray, G.R., Darley, H.C.H., 1981. Composition and Properties

of Oil Well Drilling Fluids. Gulf Publishing Company,

Houston.

Gutierrez Estrada, M., Galaviz Solis, A., 1991. Clasificacion

binaria de los sedimentos superficiales del suroeste del Golfo

de Mexico. Jaina 2 (2), 6.

Hartmann, D., Christiansen, C., 1992. The hyperbolic shape

triangle as a tool for discriminating populations of sediment

samples of closely connected origin. Sedimentology 39,

697–708.

Hedges, J.I., Parker, P.L., 1976. Land-derived organic matter insurface sediments from the Gulf of Mexico. Geochimica et

Cosmochimica Acta 40, 1019–1029.

Holme, N.A., McIntyre, A.D., 1984. Methods for the Study of

Marine Benthos. Blackwell Scientific Publications, Oxford.

Klemme, H.D., 1980. Petroleum basins-classifications and

characteristics. Journal of Petroleum Geology 3 (2),

187–207.

Logan, B.W., Harding, J.L., Ahr, W.M., Williams, J.D., Snead,

R.G., 1969. Carbonate sediments and reefs, Yucatan shelf,

Mexico. American Association of Petroleum Geologists,

Memoir 11, 1–198.

Martin, R.G., Bouma, A.H., 1978. Physiography of Gulf of

Mexico. In: Bouma, A.H., Moore, G.T., Coleman, J.M.

(Eds.), Framework, Facies, and Oil-Trapping Characteris-tics of the Upper Continental Margin. The American

Association of Petroleum Geologists, Tulsa, OK, pp. 3–19.

Mayer, L.M., 1994. Surface area control of organic carbon

accumulation in continental shelf sediments. Geochimica et

Cosmochimica Acta 58 (4), 1271–1284.

McGrail, D.W., Carnes, M., 1983. Shelf dynamics and the

nepheloid layer in the Northwestern Gulf of Mexico. In:

Stanley, D.J., Moore, G.T. (Eds.), The Shelfbreak: Critical

Interface on Continental Margins. Society of Economic

Paleontologists and Mineralogists, Tulsa, pp. 251–264.

McLaren, P., Bowles, D., 1985. The effects of sediment

transport on grain size distributions. Journal of Sedimen-

tary Petrology 55 (4), 457–470.Monreal Gomez, M.A., Salas de Leon, D.A., Padilla Pilotze,

A.R., Alatorre Mendieta, M.A., 1992. Hydrography and

estimation of density currents in the southern part of the

Bay of Campeche, Mexico. Ciencias Marinas 18 (4),

115–133.

Mooers, C.N.K., 1976. Introduction to the physical oceano-

graphy and fluid dynamics of continental margins. In:

Stanley, D.J., Swift, D.J.P. (Eds.), Marine Sediment

Transport and Environmental Management. Wiley, New

York, pp. 7–21.

Murray, S.P., Hsu, S.A., Roberts, H.H., Owens, E.H., Crout,

R.L., 1982. Physical processes and sedimentation on a

ARTICLE IN PRESS


http://www.cna.gob.mx/http://www.cna.gob.mx/


17/17

broad, shallow bank. Estuarine, Coastal and Shelf Science

14, 135–157.

Murray, S.P., Roberts, H.H., Young, M.H., 1988. Control of

terrigenous-carbonate facies transitions by baroclinic coastal

currents. In: Doyle, L.J., Roberts, H.H. (Eds.), Carbonate– Clastic Transitions. Elsevier, Amsterdam, pp. 289–304.

Rezak, R., Edwards, G.S., 1972. Carbonate sediments of the

Gulf of Mexico. In: Rezak, R., Henry, V.J. (Eds.),

Contributions on the Geological and Geophysical Oceano-

graphy of the Gulf of Mexico. Gulf Publishing Company,

Houston, pp. 263–280.

Rezak, R., Gittings, S.R., Brigth, T.J., 1990. Biotic assemblages

and ecological controls on reefs and banks of the northwest

Gulf of Mexico. American Zoologist 30 (1), 23–35.

Roberts, H.H., 1987. Modern carbonate–siliclastic transitions:

humid and arid tropical examples. Sedimentary Geology 50,

25–65.

Roberts, H.H., Murray, S.P., 1988. Gulfs of northern Red Sea:

depositional settings of distinct siliclastic–carbonate inter-

faces. In: Doyle, L.J., Roberts, H.H. (Eds.), Carbonate–

Clastic Transitions. Elsevier, Amsterdam, pp. 99–142.

Rosales Hoz, L., Carranza Edwards, A., Mendez Jaime, C.,

Monreal Gomez, M.A., 1999. Metals in shelf sediments and

their association with continental discharges in a tropical

zone. Marine and Freshwater Research 50, 189–196.

Salas de Leon, D.A., Monreal-Gomez, M.A., Ramirez, J.A.,

1992a. Periodos caracteristicos en las oscilaciones de

parametros meteorologicos en Cayo Arcos, Mexico. At-

mosfera 5, 193–205.

Salas de Leon, D.A., Monreal-Gomez, M.A., Colunga-En-

riquez, G., 1992b. Hidrografia y circulacion geostrofica en el

sur de la Bahia de Campeche. Geofisica International 31 (3),315–323.

Shideler, G.L., 1981. Development of the benthic nepheloid

layer on the south Texas continental shelf. Marine Geology

41, 37–61.

Sutherland, R.A., Lee, C.-T., 1994. Discrimination between

coastal subenvironments using textural characteristics.Sedimentology 41, 1133–1145.

Syvitsky, J.P.M., 1991. Factor analysis of size frequency

distributions: significance of factor solutions based on

simulation experiments. In: Syvitsky, J.P.M. (Ed.), Princi-

ples, Methods, and Application of Particle Size Analysis.

Cambridge University Press, New York, pp. 249–263.

Teisson, C., Ockenden, M., Hir, P.L., Kranenburg, C., Hamm,

L., 1993. Cohesive sediment transport processes. Coastal

Engineering 21, 129–162.

Tucker, M.E., Wright, V.P., 1990. Carbonate Sedimentology.

Blackwell Scientific Publication, Oxford.

Valdes, V.M., Ortega Ramirez, R., 2000. Issues and challenges

in the requalification of offshore platforms in Mexico.

Journal of Offshore Mechanics and Artic Engineering 122,

65–71.

Vidal, V.M.V., Vidal, V.F., Hernandez, F.A., Meza, E.,

Zambrano, L., 1994. Winter water mass distributions in

the western Gulf of Mexico affected by a colliding

anticyclonic ring. Journal of Oceanography 50, 559–588.

Wolfe, K.J., Michibayashi, K., 1995. Basic entropy grouping

of laser derived grain-size data: an example from the

great barrier reef. Computers and Geosciences 21 (4),

447–462.

Yan ˜ ez-Arancibia, A., Sanchez-Gil, P., 1983. Environmental

Behavior of Campeche Sound Ecological System, Off

Terminos Lagoon Mexico: preliminary results. Anales del

Instituto de Ciencias del Mar y Limnologia. UNAM 10 (1),117–136.

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