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Geodiversity assessment of the Xingudrainage basinJuliana P.
Silva a , Diamantino I. Pereira b , Alexandre M. Aguiar a
& Cleide Rodrigues aa Department of Geography, University of
São Paulo, São Paulo,Brazilb Geology Centre, University of
Porto/University of Minho, Braga,PortugalVersion of record first
published: 01 Mar 2013.
To cite this article: Juliana P. Silva , Diamantino I. Pereira ,
Alexandre M. Aguiar & CleideRodrigues (2013): Geodiversity
assessment of the Xingu drainage basin, Journal of
Maps,DOI:10.1080/17445647.2013.775085
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SCIENCE
Geodiversity assessment of the Xingu drainage basin
Juliana P. Silvaa∗, Diamantino I. Pereirab, Alexandre M. Aguiara
and Cleide Rodriguesa
aDepartment of Geography, University of São Paulo, São Paulo,
Brazil; bGeology Centre, University ofPorto/University of Minho,
Braga, Portugal
(Received 27 October 2012; Resubmitted 15 January 2013; Accepted
7 February 2013)
Geodiversity is a recent concept that refers to the abiotic
variety of nature. It is defined as therange of geological (rocks,
minerals, fossils), geomorphological (landforms, processes) andsoil
features, including their assemblages, relationships, properties,
interpretation andsystems. In this work, a method of quantitative
assessment of geodiversity was applied tothe Xingu drainage basin
(Amazônia – Brazil). The method is based on the quantificationand
integration of abiotic features represented on thematic maps at
scales ranging from1:250,000 to 1:2,500,000, overlaid by a 1:25,000
systematic grid. In order to calculate thefinal geodiversity index,
five partial numerical indices representing the main components
ofgeodiversity were drawn compiled: geology, geomorphology, soil,
palaeontology andmineral occurrences. The resulting Geodiversity
Index map is presented in the form of fiveisoline classes. The
objective of this method is to present such a mapping technique as
atool for environmental planning, particularly for the
identification and definition of priorityareas for
conservation.
Keywords: geodiversity; assessment; Amazonia; Xingu
1. Introduction
The evaluation and mapping of geodiversity are recent subjects,
which have received significantcontributions from amongst others,
Kozlowski (2004), Benito-Calvo, Pérez-González, Magri,and Meza
(2009), Serrano, Ruiz-Flaño, and Arroyo (2009), Hjort and Luoto
(2010), Zwoliñski(2010), Ruban (2010) and Pereira et al. (2012).
This work follows the definition of the conceptof geodiversity
established by Sharples (1993) and later, consolidated by Gray
(2004), whichdefines geodiversity as: ‘The natural range
(diversity) of geological (rocks, minerals, fossils),
geo-morphological (landforms, processes) and soil features. It
includes their assemblages, relation-ships, properties,
interpretation and systems’. Geodiversity maps are now
consideredpotentially useful for territorial management,
particularly for protected areas.
These maps are products that integrate the wide range of
elements that characterize the abioticenvironment, namely: relief,
rocks, soils, water and the occurrence of minerals and fossils.
The presented methodology was applied to the Xingu River basin,
located in the Brazilianstates of Pará and Mato Grosso (Figure 1).
The Xingu River is approximately 2600 km long
# 2013 Juliana P. Silva
∗Corresponding author. Email: [email protected]
Journal of Maps,
2013http://dx.doi.org/10.1080/17445647.2013.775085
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and is a southwest tributary of the Amazon River. The Xingu
Basin covers a total area of 511,000km2. Around 60% (305,000 km2)
of this area comprises 28 Indian territories and 18
conservationunits – an area legally protected from deforestation
(JUSBRASIL, 2009).
2. Methodology
The maps produced for the Xingu Basin were based on the
methodology presented by Pereiraet al. (2012). In this work, the
authors produced a map for the state of Paraná (SouthernBrazil) as
a result of the calculation of several geodiversity indices over an
overlay grid, whichdivided their area of study. Initially,
available maps of relief, rocks, soils, mineral resourcesand
fossils with scales ranging from 1:500,000 to 1:650,000 were used
and partial geodiversityindices calculated by counting the number
of occurrences of each element (e.g. the number ofgeological units,
the number of geomorphological units, the amount of mineral
resources ineach square). Following this procedure, five partial
numerical indices were obtained for: geologi-cal, geomorphological,
pedological, palaeontological and mineral occurrences.
Finally, these indices were aggregated in order to obtain a
geodiversity index score for eachgrid square. Thus, a Geodiversity
Index map was produced using isolines to join squares withsimilar
geodiversity values into five classes: very low, low, medium, high
and very high.
Figure 1. Location of the Xingu drainage basin and protected
areas. Source: IBGE, 2000.
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The present method provides similar weight to the diverse
components of geodiversity andavoids overrating any particular
element, a common issue with many other evaluation methods.All the
components – lithology, relief, hydrography, fossils, soils, and
minerals – were representedin a holistic way, considering the
quantification of the whole range of abiotic diversity.
This work uses a systematic cartographic grid with a 1:25,000
scale, generating 2462 gridsquares, each with an area of
approximately 13.8 × 13.8 km, in order to cover the wholeXingu
drainage basin, whose area corresponds to a medium-sized country.
Values were attributedto each square within the drainage basin,
according to each of the themes described below.
3. Geological diversity
For this index, a 1:250,000 scale digital base geological map
produced by Instituto Brasileiro deGeografia e Estatı́stica (IBGE,
2000) was used. An automatic count of the different geologicalunits
occurring in each grid square proceeded. To accomplish this, the
following operational pro-cedures were performed:
. Each geological unit was given a numeric code, e.g. Alter do
Chão Formation – code: 235.
. Multiple polygons of the same geological unit were ‘dissolved’
so that they would not betaken into consideration more than once;
this may occur where there are two or more iden-tical polygons
within each grid square.
. the geological units were linked to the 1:25,000 systematic
grid through a ‘union’procedure
. the number of different geological units inside each square of
the 1:25,000 grid werecounted (Figure 2A).
After these procedures, the partial geological diversity index
map was generated by transform-ing the systematic grid into a
points file and then generating a continuous surface by
interpolatingthe points using inverse distance weighting (IDW). The
resulting raster was reclassified into fivecategories, from very
low to very high (Figure 3A). IDW determines cell values using a
linearlyweighted combination of a set of sample points; the weight
is a function of inverse distance.
4. Geomorphological diversity
This index took into consideration three sub-indices:
(1) Geomorphological units. The method quantifies the
morphosculptural sub-units or tirthtaxon (Santos et al., 2009). To
quantify this sub-index, a 1:250,000 scale digital base
geo-morphological map (IBGE, 2000) was used. The counting procedure
was the same as thatdescribed for Geological Diversity (Figure
2F).
(2) Structural contacts between morphostructural units
corresponding to the first taxon(Santos et al., 2009). This method
attributes one point for each boundary between thefirst taxon
units. For squares where only one unit of this hierarchy occurs, it
was attributeda value of zero (Figure 2G). The counting procedure
was the same as for GeologicalDiversity.
(3) Hydrography. The official systematic maps of Amazon,
containing the hydrographicnetwork, were produced on various dates,
by different working groups and usingdiverse inputs, generating
different densities of information. For this reason, the1:2,500,000
scale shapefile of Brazilian hydrography (ANA, 2010) was adopted,
contain-ing information about the main rivers of the drainage
basin.
Journal of Maps 3
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This shapefile was cut around the Xingu Basin area and the
fluvial hierarchy was determinedbased on the method of Strahler
(1957). The value attributed to each river was hierarchy/2,rounded
up to the nearest unit (e.g. 5/2 ¼ 2.5, therefore, the resulting
score was 3). The values
Figure 2. Example of partial and total geodiversity indices in
an area of the Xingu River basin with high geo-diversity. (A)
Geology Index: the sum of the geological units represented by
different colors. (B) PedologyIndex: the sum of the occurrences of
super groups of soils represented by different colors. (C) Mineral
Occur-rences: the number of different occurrences in each square;
the symbols represent the occurrence of differentminerals and
geological sources of energy. (D) Palaeontology Index: the sum of
the number of units with fossilregistries (polygon color)
represented by different colors. (E) Geomorphology Index: the sum
of Geomorphol-ogy units, Structural contacts and Hydrography. (F)
Geomorphology units: the sum of the geomorphologicalunits
represented by different colors. (G) Structural contacts:
assignment of value 1 to those grid squares thathave
morphostructural contacts. (H) Hydrography: fluvial hierarchy/2.
(I) Geodiversity Index: the sum of theGeological, Geomorphological,
Soil, Palaeontological and Mineral Occurrences Indexes. Source:
IBGE,2000, 2003; ANA, 2010; CPRM, 2004, 2008.
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were inserted manually into the hydrography attribute table. The
value of the river with the great-est order assigned given to each
square (Figure 2H).
The sum of the three previous sub-indices resulted in the
geomorphological index attributed toeach square (Figure 2E). The
procedure to generate the partial geomorphological diversity
map(Figure 3B) is the same as that described for Geological
Diversity.
5. Pedological diversity
The same procedures adopted for Geological Diversity were used
with the 1:1,000,000 scale SoilsSurvey vector file (IBGE, 2003)
(Figure 2B). The pedological index values facilitate the tracing
ofthe pedological diversity map (Figure 4A).
6. Mineral diversity
To quantify the number of mineral occurrences, the Geological
Survey of Brazil basemap (CPRM,2004, 2008) was used. As the data
are composed of points, not polygons, the data were
‘intersected’
Figure 3. Geological index values (A) ranged from 1 to 7 and
geomorphological index values (B) rangedfrom 2 to 14. The values of
the 2462 points were interpolated and divided into five classes of
equal interval.Source: IBGE, 2000.
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with the systematic grid. The score of one point was given for
each type of mineral occurrence con-tained within a grid square
(Figure 2C). These values permitted the tracing of mineral
diversity(Figure 4B) using a procedure similar to that described
for Geological Diversity.
7. Palaeontological diversity
The quantification of fossiliferous units considers the score of
one point for each geological unitwith fossils information from the
geological map at a scale 1:250, 000 within each square of
thesystematic grid (Figure 2D). The digital procedure was the same
as in other themes based onvector polygon files, as described for
Geological Diversity (Figure 5A).
8. Geodiversity
The final geodiversity value in each square of the systematic
grid is the result of the sum of the partialindices (Figure 2I).
The Geodiversity Map was generated from the calculated points using
IDW
Figure 4. The pedological index values (A) ranged from 1 to 5
and the mineral diversity index values (B)ranged from 0 to 5. The
values of the 2462 points were interpolated and divided into five
classes of equalinterval. Source: IBGE, 2000; CPRM, 2004, 2008.
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(Figure 5B). IDW was chosen because is possible to control the
significance of known points on theinterpolated values. This method
assumes that the variable being mapped decreases in influence
withdistance from its sampled location, unlike other methods which
can produce a prolonged influence ofa sampling point as a function
of the distances of the samples. The location of protected areas
wasalso inserted in the map, in order to demonstrate the spatial
relationship between the indices of geo-diversity and the areas
currently protected by Brazilian Law (see Main Map).
9. Conclusion
The growing acceptance and importance of geodiversity in
territorial management, particularlyconcerning the preservation of
nature, will soon demand maps that express this concept.
Thedescribed procedure optimizes the geodiversity mapping
methodology proposed by Pereiraet al. (2012). This optimization is
obtained through the use of GIS, allowing its application
toextensive areas, such as the Xingu River drainage basin. It
represents a step forward in the evo-lution of the quantitative
assessment of abiotic environments.
Figure 5. The palaeontological index values (A) ranged from 0 to
5 and the geodiversity index values (B)ranged from 4 to 28. The
values of the 2462 points were interpolated and divided into five
classes of equalinterval. Source: IBGE, 2000; CPRM, 2004, 2008
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It is important to highlight, that in order to create the
Geodiversity Map, cartographic productsalready in existence are
used, such as geological, geomorphological, pedological and
mineralresources maps.
The index of geodiversity ranged from 4 to 28. The ‘hot spot’ of
geodiversity occurs at theboundary between the pre-Cambrian Complex
of Xingu and the Amazon Sedimentary Basin,near the area called
Volta Grande do Xingu, where there are many different types of
rocks,soils and landforms, and mineral occurrences. The second area
with high geodiversity occursnear the city of São Félix do Xingu,
where outcrops of older rocks, various types of relief andplentiful
mineral resources in a rugged region. There is also an area with
high geodiversity inthe south of the basin, due to the variety of
rock types and forms and the presence of siteswith high
fossiliferous potential (see Main Map).
In the specific case of the Xingu River Basin it is possible to
realize that in areas of highergeodiversity there is no kind of
legal protection (see Main Map). This fact demonstrates thatthe
criteria used in the definition of protected areas did not take
into account issues of abioticnature, and the hot spot of
geodiversity occurs exactly in the area where the Belo Monte
Hydro-electric Power Plant, which will be the third largest in the
world, is being constructed.
The same map also supports the increasing interest in decisions
that respect territorial manage-ment, particularly with regard to
the preservation of nature.
Software
Map design was performed using Esri ArcGIS 9.3 software.
AcknowledgementsThe Brazilian authors express their gratitude to
the research fostering institution ‘Cordenação de
Aperfeiçoa-mento de Pessoal de Nı́vel Superior’ (CAPES) for
awarding the doctorate scholarship that enabled this work.
The Portuguese authors express their gratitude for the financial
support given by the Fundação para aCiência e a Tecnologia to
the Geology Centre of the University of Porto, which partially
supported thisresearch.
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