The actual estuary that occupies the Boina-Arade paleovalley
accommodated the Holocene sedimentary sequence
whose thickness does not exceed 35 m in the deepest zones,
as registered from geotechnical borehole data. We present here
the results of partial analyses of two continuous cores which
cross the Holocene sequence until the Pre-Quaternary
substratum. In the P5 core (Boina river), the sedimentary
column, which spans 20 m accumulated during ca 8500 years

Boski, T.

Moura, Delminda

Veiga-Pires, C.

Wilamowski, A.

Sapientia

6423rd IAS Meeting of SedimentologySedimentology and SocietyThe area of the Arade EstuaryThe actual estuary that occupies the Boina-Arade paleo-valley accommodated the Holocene sedimentary sequencewhose thickness does not exceed 35 m in the deepest zones,as registered from geotechnical borehole data. We present herethe results of partial analyses of two continuous cores whichcross the Holocene sequence until the Pre-Quaternarysubstratum. In the P5 core (Boina river), the sedimentarycolumn, which spans 20 m accumulated during ca 8500 years.In the light fraction of sandy layers, feldspars (both plagio-clases and orthoclases) and hydro-muscovite, originating inslates or feldspar alteration, are abundant. The heavy mineralswith a contribution of 10 to 19% of total weight are veryabundant. Pyrite, which is very abundant in the heavy fraction,comes from the reaction between iron and the sulfur releasedduring microbial sulfate reduction processes. The rest of theheavy mineral assemblage is made of pyroxenes and amphiboles(predominantly alkaline), titanite, biotite, rutile all originatingfrom the Monchique Massif and some minerals originatingfrom the slate-grauwacke substratum such as andalusite andepidotes. The sedimentary sequence from Odelouca-Arade riverestuary (P2) is similar to the above-described sequence. Whilethe clay mineralogy from both areas does not reveal significantdifferences, the sandy fraction mineralogy in P2 differs fromthe one of Boina area as follows: quantitatively smaller heavymineral fraction, more rounded quartz grains and quantita-tively fewer minerals originating from the nepheline massif.The area of the Guadiana EstuaryDuring the last 4 years, a series of boreholes has beencarried out with the aim to recognize the structure, mineralogyand geochemistry of the sedimentary sequence of theGuadiana river estuary (Boski et al., 2002). The deepest core,which will be discussed hereafter, reached the slate-grauwackesubstratum at a depth of 52 m, corresponding to 13000 years.The studied sequence starts with sandy fluvial deposits inwhich, besides quartz, lithic grains and hydromicas arepredominant. The rest of the sequence, up to the surface, ismainly silty-clay sediment composed of illite, interstratifiedand kaolinite, with mean contents of 58%, 29% and 12%,respectively. In this sequence, the benthic foraminiferaanalysis reveal three main steps for the estuary’s evolution:confined, open to marine circulation and confined duringterminal infilling. Regarding the geochemistry of the organicfraction, the lower section of the sequence (up to ca. 15 mdeep) is characterized by a mean organic carbon (OC) content5 1.1% and by the persistent occurrence of phytol, a marinephytoplankton biomarker coming from the incompletedegradation of chlorophyll (Gonzalez-Vila et al., 2003). Pyrite,which is an indicator of reducing conditions, has also beenobserved in several levels of this section together with sulphurcontents above 1% of dry weight.ReferencesBoski, T., Moura, D., Camacho, S., Duarte, D. N. R., Scott, D. B.,Veiga-Pires, C., Pedro P. and Santana, P. (2002) - Postglacial sealevel rise and sedimentary response in the Guadiana Estuary,Portugal/Spain border. Sedimentary Geology,150,103-121.Gonzalez-Vila, F. J., Polvillo, O., Boski, T. and Andrés, J. R. (2003)- A biomarker approach to the organic matter deposited in coastalestuarine sediments during Holocene: a case study in the GuadianaRiver estuary. Organic Geochemistry (in press).The material sources and processes during the infillingof estuaries in Algarve (South Portugal)T. BOSKI1, A. WILAMOWSKI2, D. MOURA1 and C. VEIGA-PIRES11CIMA – Centro de Inv. Marinha e Ambiental, Universidade do Algarve2Institute of Geological Sciences PAS, Poland

The material sources and processes during the infilling of estuaries in Algarve (South Portugal)

Universidade do Algarve

64
23rd IAS Meeting of Sedimentology
Se
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 S
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The area of the Arade Estuary
The actual estuary that occupies the Boina-Arade paleo-
valley accommodated the Holocene sedimentary sequence
whose thickness does not exceed 35 m in the deepest zones,
as registered from geotechnical borehole data. We present here
the results of partial analyses of two continuous cores which
cross the Holocene sequence until the Pre-Quaternary
substratum. In the P5 core (Boina river), the sedimentary
column, which spans 20 m accumulated during ca 8500 years.
In the light fraction of sandy layers, feldspars (both plagio-
clases and orthoclases) and hydro-muscovite, originating in
slates or feldspar alteration, are abundant. The heavy minerals
with a contribution of 10 to 19% of total weight are very
abundant. Pyrite, which is very abundant in the heavy fraction,
comes from the reaction between iron and the sulfur released
during microbial sulfate reduction processes. The rest of the
heavy mineral assemblage is made of pyroxenes and amphiboles
(predominantly alkaline), titanite, biotite, rutile all originating
from the Monchique Massif and some minerals originating
from the slate-grauwacke substratum such as andalusite and
epidotes. The sedimentary sequence from Odelouca-Arade river
estuary (P2) is similar to the above-described sequence. While
the clay mineralogy from both areas does not reveal significant
differences, the sandy fraction mineralogy in P2 differs from
the one of Boina area as follows: quantitatively smaller heavy
mineral fraction, more rounded quartz grains and quantita-
tively fewer minerals originating from the nepheline massif.
The area of the Guadiana Estuary
During the last 4 years, a series of boreholes has been
carried out with the aim to recognize the structure, mineralogy
and geochemistry of the sedimentary sequence of the
Guadiana river estuary (Boski et al., 2002). The deepest core,
which will be discussed hereafter, reached the slate-grauwacke
substratum at a depth of 52 m, corresponding to 13000 years.
The studied sequence starts with sandy fluvial deposits in
which, besides quartz, lithic grains and hydromicas are
predominant. The rest of the sequence, up to the surface, is
mainly silty-clay sediment composed of illite, interstratified
and kaolinite, with mean contents of 58%, 29% and 12%,
respectively. In this sequence, the benthic foraminifera
analysis reveal three main steps for the estuary’s evolution:
confined, open to marine circulation and confined during
terminal infilling. Regarding the geochemistry of the organic
fraction, the lower section of the sequence (up to ca. 15 m
deep) is characterized by a mean organic carbon (OC) content
5 1.1% and by the persistent occurrence of phytol, a marine
phytoplankton biomarker coming from the incomplete
degradation of chlorophyll (Gonzalez-Vila et al., 2003). Pyrite,
which is an indicator of reducing conditions, has also been
observed in several levels of this section together with sulphur
contents above 1% of dry weight.
References
Boski, T., Moura, D., Camacho, S., Duarte, D. N. R., Scott, D. B.,
Veiga-Pires, C., Pedro P. and Santana, P. (2002) - Postglacial sea
level rise and sedimentary response in the Guadiana Estuary,
Portugal/Spain border. Sedimentary Geology,150,103-121.
Gonzalez-Vila, F. J., Polvillo, O., Boski, T. and Andrés, J. R. (2003)
- A biomarker approach to the organic matter deposited in coastal
estuarine sediments during Holocene: a case study in the Guadiana
River estuary. Organic Geochemistry (in press).
The material sources and processes during the infilling
of estuaries in Algarve (South Portugal)
T. BOSKI1, A. WILAMOWSKI2, D. MOURA1 and C. VEIGA-PIRES1
1CIMA – Centro de Inv. Marinha e Ambiental, Universidade do Algarve
2Institute of Geological Sciences PAS, Poland


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The material sources and processes during the infilling of estuaries in Algarve (South Portugal)

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