**Fractal Nature of the Band-Thickness in the Archean Banded Iron Formation in the Yellowknife Greenstone Belt, Northwest Territories, Canada**

Nagayoshi Katsuta, Ichiko Shimizu, Masao Takano, Shin-ichi Kawakami, Herwart Helmstaedt and Mineo Kumazawa

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/55700

**1. Introduction**

Bandedironformations (BIFs)are chemicallyprecipitateddepositsonthePrecambrianseafloor and are characterised by alternations of repeat Fe-rich and Si-rich layers [1]. Temporal varia‐ tions in the volumes of BIFs are considered to be related to early evolution of the atmosphere, oceans,lifeandtheEarth'sinterior[2,3].Ingeneral,BIFscontainvariousscalesofbanding.Bands with a thickness of several tens of meters to meters, a thickness of centimetres and a thickness of submillimetre to millimetres are named macrobands, mesobands and microbands, respective‐ ly [4]. Some depositions are related to periodic phenomena, such as annual cycles [4], tidal and solar cycles [5–7], and Milankovitch cycles [8, 9] in the Precambrian. On the other hand, quanti‐ tative analysis of the banding is limited to Paleoproterozoic Hamersley (Superior-type) BIFs, although BIFs occur within an age range from 3.8 Ga to about 0.7 Ga [10]. Therefore, it is necessa‐ ry to investigate different BIFs, in terms of both their age and type, clarified by size and litholog‐ icalfacies (i.e.,Superior-andAlgoma-types)tounderstandthenatureoftheirbandedstructures.

In this study, we analysed the banded structures in Archean BIFs using a nondestructive micro-X-ray fluorescence (XRF) imaging technique. This technique has been used recently to deter‐ mine the distribution of major and trace elements in Quaternary sediments and Phanerozoic sedimentary rocks for characterising the paleoclimatic and paleoenvironmental signals [e.g. 11-15]. It has also been used in the analysis of BIF bandings [16–19]. Sakai *et al*. [16] reported on an XRF imaging analysis conducted on an Antarctic BIF that showed a clear striped structure of alternating Fe-rich and Si-rich layers. Matsunaga *et al*. [17] investigated the influence of

© 2013 Katsuta et al.; licensee InTech. This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2013 Katsuta et al.; licensee InTech. This is a paper distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

alternationandweatheringonthebandingintermsoftheelementaldistributionandthechemical forms, showing that the titanium in the BIF preserved the primary depositional structures and that the chemical states of the iron and manganese present alternated with rhythmic changes in the banding. Fukuda *et al.* [18] revealed that titanium-rich layers in the Hamersley BIF are composed of Ti in silicate and titanium oxide layers and suggested that the oxide phase had precipitated in solution, as well as that the silicate phase had originated from a clastic input of terrigenous origin.Pufahl andFralik [19]found millimetre-scale chemical grading of Fe, Si,Mn, and Al in the mud lamina of a BIF deposited in Paleoproterozoic shallow water. They suggest‐ edthatthesechemicalstructuresresultedfromchangesintheFe2+/Mn2+ ratiointhewatercolumn, along with changes in the concentration of dissolved O2, together with the precipitation of inorganic SiO2 anda rainfallinputofterrigenous clay.Theseprevious studiesonBIFsusingXRF imaging techniques focused on internal structures having mesoband units. However, we are interested in a wider range of patterns in the fluctuations of BIF laminations [20].

The purpose of this study was to investigate the abundance and variations of the constituent materials in the BIFs, both in the mesobands and on longer spatial scales. In this study, we used an Algoma-type Archean BIF sample with a thickness of about 1.14m, which was collected from a >2.8 Ga Bell Lake Group exposed in the Dwyer Lake area of the Yellowknife greenstone belt, Northwest Territories, Canada (Fig. 1). Based on the results of our XRF imaging analysis and from petrographic observations, we have evaluated whether the banding is a primary or secondary structure, as the constituent materials of the BIF had been completely recrystallized into medium-grade metamorphic minerals under amphibole-facies conditions. After measur‐ ing the band-thicknesses of the Fe-rich and Si-rich mesobands using XRF imaging, we investigated the implications of the data for the morphology of the bandings recorded in our

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**Figure 2.** A simplified geological map of the Dwyer Lake area, modified after MacLachlan and Helmstaedt [21]. The U– Pb ages are after Isachsen and Bowring [22]. The sampling points are denoted by the sample names: *DLN*, *DL*, and *DLS*.

BIF samples.

**Figure 1.** A simplified geological map of the Yellowknife greenstone belt located in the southeastern part of Slave Province, Northwest Territories, Canada, modified from MacLachlan and Helmstaedt [21]. The U–Pb ages are after Isachsen and Bowring [22].

The purpose of this study was to investigate the abundance and variations of the constituent materials in the BIFs, both in the mesobands and on longer spatial scales. In this study, we used an Algoma-type Archean BIF sample with a thickness of about 1.14m, which was collected from a >2.8 Ga Bell Lake Group exposed in the Dwyer Lake area of the Yellowknife greenstone belt, Northwest Territories, Canada (Fig. 1). Based on the results of our XRF imaging analysis and from petrographic observations, we have evaluated whether the banding is a primary or secondary structure, as the constituent materials of the BIF had been completely recrystallized into medium-grade metamorphic minerals under amphibole-facies conditions. After measur‐ ing the band-thicknesses of the Fe-rich and Si-rich mesobands using XRF imaging, we investigated the implications of the data for the morphology of the bandings recorded in our BIF samples.

alternationandweatheringonthebandingintermsoftheelementaldistributionandthechemical forms, showing that the titanium in the BIF preserved the primary depositional structures and that the chemical states of the iron and manganese present alternated with rhythmic changes in the banding. Fukuda *et al.* [18] revealed that titanium-rich layers in the Hamersley BIF are composed of Ti in silicate and titanium oxide layers and suggested that the oxide phase had precipitated in solution, as well as that the silicate phase had originated from a clastic input of terrigenous origin.Pufahl andFralik [19]found millimetre-scale chemical grading of Fe, Si,Mn, and Al in the mud lamina of a BIF deposited in Paleoproterozoic shallow water. They suggest‐ edthatthesechemicalstructuresresultedfromchangesintheFe2+/Mn2+ ratiointhewatercolumn, along with changes in the concentration of dissolved O2, together with the precipitation of inorganic SiO2 anda rainfallinputofterrigenous clay.Theseprevious studiesonBIFsusingXRF imaging techniques focused on internal structures having mesoband units. However, we are

208 Climate Change and Regional/Local Responses

interested in a wider range of patterns in the fluctuations of BIF laminations [20].

**Figure 1.** A simplified geological map of the Yellowknife greenstone belt located in the southeastern part of Slave Province, Northwest Territories, Canada, modified from MacLachlan and Helmstaedt [21]. The U–Pb ages are after

Isachsen and Bowring [22].

**Figure 2.** A simplified geological map of the Dwyer Lake area, modified after MacLachlan and Helmstaedt [21]. The U– Pb ages are after Isachsen and Bowring [22]. The sampling points are denoted by the sample names: *DLN*, *DL*, and *DLS*.

## **2. Samples and methods**

## **2.1. Sampling sites and sample collection**

The Yellowknife greenstone belt is the southernmost of approximately 26 granite-greenstone belts in the Slave craton (Fig. 1), and is approximately 35km long and 8–10km wide. The belt is 12km thick, steeply dipping southeast and younging, with homoclinical sequences of calcalkaline to tholeiitic metavolcanic rocks and metasedimentary rocks [21]. The main volcanic suite of the Yellowknife greenstone belt, composed mainly of tholeiitic pillow lavas, is the Kam Group (ca. 2.7 Ga). The metasedimentary rocks below the granodiorite basement and above the KamGroup(Fig.2)aredividedintotheBellLakegroup,whichwasinformallynamedbyIsachsen andBowring[22].Here,the termBellLake "Group" isusedtoindicate clearlythatithas the rank of a group [20]. The Bell Lake Group is the lowermost part of the Yellowknife Supergroup and comprises orthoquartzite, felsic volcanic rocks and BIF packages from the bottom to the top. In general,theBellLakeGroupis consideredto have been formedin adepositional setting, similar to that of a back-arc basin adjacent to a continental margin [21] during transgression [23].

The Bell Lake Group is well-exposed in the Bell Lake and Dwyer Lake areas (Fig. 1). The ages of these regions were determined using U–Pb zircon dates [24]. The felsic volcanic rock below the BIF in the Dwyer Lake region has been dated at 2853 +2/–1 Ma. In the Bell Lake region, the 3m-thick layer of felsic tuff within the 40m-thick BIF unit has an estimated age of 2826 ± 1.5 Ma. In these two regions, we collected continuous BIF tabular samples from the steeply dipped outcrops using a portable diamond cutter (Fig. 3) [14]. In the Bell Lake region, samples from five sequences were taken from the island inside the lake ([20], Fig. 1). On the other hand, in the Dwyer Lake region, the BIF samples were acquired from three sites (*DLN*, *DL*, and *DLS*) that were in close contact with the pillowed volcanic rocks (Fig. 2). The sample taken from *DLN* (62º41′174′′N, 114º18′885′′W) was approximately 112cm long, the sample taken from *DL* (62º40′609′′N, 114º18′740′′W) was approximately 113cm long and the sample taken from *DLS* (62º40′547′′N, 114º18′874′′W) was approximately 114cm long. In the laboratory, the acquired

Fractal Nature of the Band-Thickness in the Archean Banded Iron Formation in the Yellowknife Greenstone Belt…

of 3cm for XRF imaging analysis [14]. Hereafter, the sample from the Bell Lake and Dwyer Lake regions will be referred to as the Bell Lake and Dwyer Lake BIF, respectively. In this paper, we present a sequential profile of the *DLS* sample, because the Dwyer Lake BIF samples

The constituent minerals were identified using an optical microscope, a TOPCON DS-130C scanning electron microscope equipped with a HORIBA EMAX-770X energy dispersive X-ray spectrometer at Nagoya University (Japan) and a microfocused X-ray diffractometer (XRD) (Rigaku PSPC/MDG CN2175-A1) at Nagoya University, equipped with a CrK radiation source (wavelength = 2.2909 Å) and a Cr anode target. The diffraction patterns were matched with data from the Joint Committee on Power Diffraction Standards database [25]. The chemical composition of the amphiboles was analysed using a JEOL JCMA-733 electron-probe micro‐ analyser at Hokkaido University (Japan), operating at an accelerating voltage of 15kV and a beam current of 20nA. The X-ray intensities were converted to chemical abundances according to the oxide ZAF correction. The concentration of Fe2+ and Fe3+ was calculated from the total

We used a HORIBA XGT-2000V scanning X-ray analytical microscope (SXAM) [27] at Nagoya University to extract information from the lamination patterns on the BIF sample surfaces. The high-intensity incident X-rays were emitted from an Rh anode at 50kV and 1mA, focused into a microbeam using an X-ray guide tube with a diameter of 100µm, and irradiated perpendic‐ ular to the sample surface. The XRF from the sample surface was analysed using the hi-Si detector of the energy-dispersive spectrometer, and the transmitted X-rays were measured using a NaI scintillation detector. In the SXAM system, the sample was mounted on a motordriven *X*–*Y* stage and placed in an open space outside the vacuum chamber, so that there was little limitation on the sample size used. A surface area up to 200 × 200mm2 in size was scanned by the incident X-ray beam, and the XRF intensity data were stored at a resolution of either 256 × 256 pixels or 512 × 512 pixels. In the 512 × 512 pixel mode, seven elements between Na and U, as well as the transmitted X-rays, could be analysed simultaneously. Alternatively, 31

, and a thickness

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BIF samples were shaped into plates with an area of approximately 20 × 20 cm2

commonly have a similar pattern of its laminations.

**2.2. Analysis**

FeO content [26].

**Figure 3.** A field photograph of the Dwyer Lake BIF. The light and dark bands on the tabular samples correspond to the Si-rich and Fe-rich mesobands, respectively. The numbers on the sample's surface denote the distance described in intervals of 5cm.

The Bell Lake Group is well-exposed in the Bell Lake and Dwyer Lake areas (Fig. 1). The ages of these regions were determined using U–Pb zircon dates [24]. The felsic volcanic rock below the BIF in the Dwyer Lake region has been dated at 2853 +2/–1 Ma. In the Bell Lake region, the 3m-thick layer of felsic tuff within the 40m-thick BIF unit has an estimated age of 2826 ± 1.5 Ma. In these two regions, we collected continuous BIF tabular samples from the steeply dipped outcrops using a portable diamond cutter (Fig. 3) [14]. In the Bell Lake region, samples from five sequences were taken from the island inside the lake ([20], Fig. 1). On the other hand, in the Dwyer Lake region, the BIF samples were acquired from three sites (*DLN*, *DL*, and *DLS*) that were in close contact with the pillowed volcanic rocks (Fig. 2). The sample taken from *DLN* (62º41′174′′N, 114º18′885′′W) was approximately 112cm long, the sample taken from *DL* (62º40′609′′N, 114º18′740′′W) was approximately 113cm long and the sample taken from *DLS* (62º40′547′′N, 114º18′874′′W) was approximately 114cm long. In the laboratory, the acquired BIF samples were shaped into plates with an area of approximately 20 × 20 cm2 , and a thickness of 3cm for XRF imaging analysis [14]. Hereafter, the sample from the Bell Lake and Dwyer Lake regions will be referred to as the Bell Lake and Dwyer Lake BIF, respectively. In this paper, we present a sequential profile of the *DLS* sample, because the Dwyer Lake BIF samples commonly have a similar pattern of its laminations.

## **2.2. Analysis**

**2. Samples and methods**

210 Climate Change and Regional/Local Responses

intervals of 5cm.

**2.1. Sampling sites and sample collection**

The Yellowknife greenstone belt is the southernmost of approximately 26 granite-greenstone belts in the Slave craton (Fig. 1), and is approximately 35km long and 8–10km wide. The belt is 12km thick, steeply dipping southeast and younging, with homoclinical sequences of calcalkaline to tholeiitic metavolcanic rocks and metasedimentary rocks [21]. The main volcanic suite of the Yellowknife greenstone belt, composed mainly of tholeiitic pillow lavas, is the Kam Group (ca. 2.7 Ga). The metasedimentary rocks below the granodiorite basement and above the KamGroup(Fig.2)aredividedintotheBellLakegroup,whichwasinformallynamedbyIsachsen andBowring[22].Here,the termBellLake "Group" isusedtoindicate clearlythatithas the rank of a group [20]. The Bell Lake Group is the lowermost part of the Yellowknife Supergroup and comprises orthoquartzite, felsic volcanic rocks and BIF packages from the bottom to the top. In general,theBellLakeGroupis consideredto have been formedin adepositional setting, similar to that of a back-arc basin adjacent to a continental margin [21] during transgression [23].

**Figure 3.** A field photograph of the Dwyer Lake BIF. The light and dark bands on the tabular samples correspond to the Si-rich and Fe-rich mesobands, respectively. The numbers on the sample's surface denote the distance described in The constituent minerals were identified using an optical microscope, a TOPCON DS-130C scanning electron microscope equipped with a HORIBA EMAX-770X energy dispersive X-ray spectrometer at Nagoya University (Japan) and a microfocused X-ray diffractometer (XRD) (Rigaku PSPC/MDG CN2175-A1) at Nagoya University, equipped with a CrK radiation source (wavelength = 2.2909 Å) and a Cr anode target. The diffraction patterns were matched with data from the Joint Committee on Power Diffraction Standards database [25]. The chemical composition of the amphiboles was analysed using a JEOL JCMA-733 electron-probe micro‐ analyser at Hokkaido University (Japan), operating at an accelerating voltage of 15kV and a beam current of 20nA. The X-ray intensities were converted to chemical abundances according to the oxide ZAF correction. The concentration of Fe2+ and Fe3+ was calculated from the total FeO content [26].

We used a HORIBA XGT-2000V scanning X-ray analytical microscope (SXAM) [27] at Nagoya University to extract information from the lamination patterns on the BIF sample surfaces. The high-intensity incident X-rays were emitted from an Rh anode at 50kV and 1mA, focused into a microbeam using an X-ray guide tube with a diameter of 100µm, and irradiated perpendic‐ ular to the sample surface. The XRF from the sample surface was analysed using the hi-Si detector of the energy-dispersive spectrometer, and the transmitted X-rays were measured using a NaI scintillation detector. In the SXAM system, the sample was mounted on a motordriven *X*–*Y* stage and placed in an open space outside the vacuum chamber, so that there was little limitation on the sample size used. A surface area up to 200 × 200mm2 in size was scanned by the incident X-ray beam, and the XRF intensity data were stored at a resolution of either 256 × 256 pixels or 512 × 512 pixels. In the 512 × 512 pixel mode, seven elements between Na and U, as well as the transmitted X-rays, could be analysed simultaneously. Alternatively, 31 elements, as well as the transmitted X-rays, could be analysed in the 256 × 256 pixel mode. The standard measurement time required to acquire a 512 × 512 pixel image was about 40 hours.

## **3. Results**

## **3.1. Distribution of the major elements**

The major elements in the Dwyer Lake BIF samples detected by our SXAM analysis were Fe, Si, Ca, Mn, K, P, S, and Ti (Fig. 4a). Because the concentration of Ti was relatively low, the first seven elements were selected for SXAM imaging analysis in the 512 × 512 pixel mode. The weight percentage of these seven elements was estimated to be > 95%. The scanning area for the imaging analysis was fixed at 51.2 × 51.2mm2 , and the scan step size was 100µm. The XRF images were acquired allowing overlapping with the adjacent sections above and below to obtain continuous sequence data. The XRF images were reduced to one-dimensional profiles using lamination trace techniques [28] that enabled us to obtain the average value along the deformed bedding planes. After the weighted averages of the overlap sections had been calculated, the sequential profiles shown in Fig. 5a were obtained.

In the XRF images shown in Fig. 4b, the Fe-rich and Si-rich mesobands correspond to the green and white layers shown in the outcrop in Fig. 3, respectively. Fe, Ca, and Mn were enriched in the Fe-rich mesobands, while the Si-rich mesobands contained thin Fe-rich layers (millimetre bands) 0.3–2.0mm thick. Potassium was concentrated locally in the strikingly deformed and altered layers, while phosphorus occurred in thin layers in the Fe-rich mesobands together with Ca. Sulphur was irregularly distributed in both the Fe-rich and Si-rich mesobands. Because K, P, and S occurred in low concentrations and showed no distinct patterns, they are not shown in the XRF images in Fig. 4b.

## **3.2. Petrology and mineralogy**

The Fe-rich mesobands were composed of actinolite, magnetite, quartz, and trace amounts of apatite and pyrite (Fig. 6a). The Si-rich mesobands were composed of quartz, magnetite and trace actinolite. The nomenclature used for the amphiboles follows Leake *et al.* [29]. The Ferich mesobands corresponded to the layers shown in the XRF maps of Fe, Ca, and Mn.

axis. The actinolite lacked any exsolution textures. Actinolite also occurred locally in the quartz matrix of the Si-rich mesobands. The magnetite grains in Fe-rich mesobands and in microbands within the Si-rich mesobands were relatively large (length = approximately 100µm), and were mostly oblate. Outside the Fe-rich mesobands and microbands, magnetite occurred in small grains included within polygonal quartz grains or at the boundaries of quartz grains. The

**Figure 4.** Micro-XRF analysis of a BIF sample (*DLS* 35–45). (a) Cumulative energy spectrum captured using SXAM for an Fe-rich mesoband. The terms ESC and SUM denote the escape and the sum peak, respectively. The Rh peaks denote signals from the Rh target. (b) XRF images of a BIF sample. Key: F = Fe-rich mesoband, and S = Si-rich mesoband. The size of the digitised images represents 512 × 512 pixels. The step size in the *x*–*y* scan is 100μm. The XRF intensity is

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The schistosity was determined from the preferred orientation of the actinolite grains in the Fe-rich mesobands and in the quartz matrix, and by the preferred orientation of the oblate magnetite. The schistosity was subparallel to the banded structures in the Dwyer Lake BIF

quartz showed an undulatory extinction.

represented by the X-ray photon count (cnt).

samples.

Magnetite grains in the Fe-rich mesobands formed several hundred µm-thick layers (Fig. 6a). The Si-rich mesobands were composed of quartz and magnetite, with minor actinolite (Fig. 6b), which correspond to the layers shown in the Si map. The constituent minerals in the

Dwyer Lake BIF samples correspond to the medium- to high-grade metamorphic zones described by Klein [10]. Magnetite grains in the Si-rich mesobands were either included in the quartz matrix or arranged as microbands (Fig. 6b).

The actinolite in the Fe-rich mesobands was green in colour and was either euhedral or subhedral (Fig. 6a). The dimensions of the actinolite were typically approximately 100µm in the direction of the crystallographic *c*-axis and <50µm in the direction perpendicular to the *c*- elements, as well as the transmitted X-rays, could be analysed in the 256 × 256 pixel mode. The standard measurement time required to acquire a 512 × 512 pixel image was about 40 hours.

The major elements in the Dwyer Lake BIF samples detected by our SXAM analysis were Fe, Si, Ca, Mn, K, P, S, and Ti (Fig. 4a). Because the concentration of Ti was relatively low, the first seven elements were selected for SXAM imaging analysis in the 512 × 512 pixel mode. The weight percentage of these seven elements was estimated to be > 95%. The scanning area for

images were acquired allowing overlapping with the adjacent sections above and below to obtain continuous sequence data. The XRF images were reduced to one-dimensional profiles using lamination trace techniques [28] that enabled us to obtain the average value along the deformed bedding planes. After the weighted averages of the overlap sections had been

In the XRF images shown in Fig. 4b, the Fe-rich and Si-rich mesobands correspond to the green and white layers shown in the outcrop in Fig. 3, respectively. Fe, Ca, and Mn were enriched in the Fe-rich mesobands, while the Si-rich mesobands contained thin Fe-rich layers (millimetre bands) 0.3–2.0mm thick. Potassium was concentrated locally in the strikingly deformed and altered layers, while phosphorus occurred in thin layers in the Fe-rich mesobands together with Ca. Sulphur was irregularly distributed in both the Fe-rich and Si-rich mesobands. Because K, P, and S occurred in low concentrations and showed no distinct patterns, they are

The Fe-rich mesobands were composed of actinolite, magnetite, quartz, and trace amounts of apatite and pyrite (Fig. 6a). The Si-rich mesobands were composed of quartz, magnetite and trace actinolite. The nomenclature used for the amphiboles follows Leake *et al.* [29]. The Ferich mesobands corresponded to the layers shown in the XRF maps of Fe, Ca, and Mn.

Magnetite grains in the Fe-rich mesobands formed several hundred µm-thick layers (Fig. 6a). The Si-rich mesobands were composed of quartz and magnetite, with minor actinolite (Fig. 6b), which correspond to the layers shown in the Si map. The constituent minerals in the

Dwyer Lake BIF samples correspond to the medium- to high-grade metamorphic zones described by Klein [10]. Magnetite grains in the Si-rich mesobands were either included in the

The actinolite in the Fe-rich mesobands was green in colour and was either euhedral or subhedral (Fig. 6a). The dimensions of the actinolite were typically approximately 100µm in the direction of the crystallographic *c*-axis and <50µm in the direction perpendicular to the *c*-

, and the scan step size was 100µm. The XRF

**3. Results**

**3.1. Distribution of the major elements**

212 Climate Change and Regional/Local Responses

not shown in the XRF images in Fig. 4b.

quartz matrix or arranged as microbands (Fig. 6b).

**3.2. Petrology and mineralogy**

the imaging analysis was fixed at 51.2 × 51.2mm2

calculated, the sequential profiles shown in Fig. 5a were obtained.

**Figure 4.** Micro-XRF analysis of a BIF sample (*DLS* 35–45). (a) Cumulative energy spectrum captured using SXAM for an Fe-rich mesoband. The terms ESC and SUM denote the escape and the sum peak, respectively. The Rh peaks denote signals from the Rh target. (b) XRF images of a BIF sample. Key: F = Fe-rich mesoband, and S = Si-rich mesoband. The size of the digitised images represents 512 × 512 pixels. The step size in the *x*–*y* scan is 100μm. The XRF intensity is represented by the X-ray photon count (cnt).

axis. The actinolite lacked any exsolution textures. Actinolite also occurred locally in the quartz matrix of the Si-rich mesobands. The magnetite grains in Fe-rich mesobands and in microbands within the Si-rich mesobands were relatively large (length = approximately 100µm), and were mostly oblate. Outside the Fe-rich mesobands and microbands, magnetite occurred in small grains included within polygonal quartz grains or at the boundaries of quartz grains. The quartz showed an undulatory extinction.

The schistosity was determined from the preferred orientation of the actinolite grains in the Fe-rich mesobands and in the quartz matrix, and by the preferred orientation of the oblate magnetite. The schistosity was subparallel to the banded structures in the Dwyer Lake BIF samples.

**3.3. Modal compositions**

described in Katsuta *et al.* [20].

The measured XRF intensity in the element images for a given pixel is related to the bulk concentration of the elements of the constituent mineral for that pixel. Therefore, we assumed that the XRF intensity was linearly proportional to the volume proportion in the mineral, and therefore determined the modal proportions of the constituent minerals in the Dwyer Lake BIF samples (Figs 5b and 7) using the algorithm of Togami *et al*. [30]. The minor minerals were ignored in our calculations and we approximated the samples as being a mixture of three minerals: quartz, magnetite and actinolite. The modal proportions of these three minerals were determined from the XRF intensity profiles of Si, Fe, Ca, and Mn (Fig. 5a). The minor phases of apatite and pyrite were estimated to be <1%. Details of the computation methods are

**Figure 6.** Photomicrographs of BIF sections (*DLN*) cut normally to the banded structures. Left: plane-polarised light.

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Right: crossed-polarised light. (a) Fe-rich mesoband and (b) Si-rich mesoband.

The modal proportion of actinolite was typically 0.6–1.0 in the Fe-rich mesobands, and <0.2 in the Si-rich mesobands. The modal proportion of magnetite was 0.3–0.8 in the Fe-rich meso‐

**Figure 5.** Chemical profiles of the Dwyer Lake BIF samples (*DLS*) in the direction orientated perpendicular to the band‐ ed structures. (a) Elemental profiles. The relative abundance of Si, Fe, Ca, Mn, K, P and S are represented by the X-ray photon counts acquired during the micro-XRF analysis. (b) Mineral profiles are calculated from the XRF intensity for Si, Fe, Ca, and Mn. The shaded area corresponds to the XRF images in Fig. 4 and the mineral mode profiles shown in Fig. 7. The abbreviations of the mineral phases follow Kretz [35].

Fractal Nature of the Band-Thickness in the Archean Banded Iron Formation in the Yellowknife Greenstone Belt… http://dx.doi.org/10.5772/55700 215

**Figure 6.** Photomicrographs of BIF sections (*DLN*) cut normally to the banded structures. Left: plane-polarised light. Right: crossed-polarised light. (a) Fe-rich mesoband and (b) Si-rich mesoband.

## **3.3. Modal compositions**

(a)

214 Climate Change and Regional/Local Responses

(b)

7. The abbreviations of the mineral phases follow Kretz [35].

**Figure 5.** Chemical profiles of the Dwyer Lake BIF samples (*DLS*) in the direction orientated perpendicular to the band‐ ed structures. (a) Elemental profiles. The relative abundance of Si, Fe, Ca, Mn, K, P and S are represented by the X-ray photon counts acquired during the micro-XRF analysis. (b) Mineral profiles are calculated from the XRF intensity for Si, Fe, Ca, and Mn. The shaded area corresponds to the XRF images in Fig. 4 and the mineral mode profiles shown in Fig.

The measured XRF intensity in the element images for a given pixel is related to the bulk concentration of the elements of the constituent mineral for that pixel. Therefore, we assumed that the XRF intensity was linearly proportional to the volume proportion in the mineral, and therefore determined the modal proportions of the constituent minerals in the Dwyer Lake BIF samples (Figs 5b and 7) using the algorithm of Togami *et al*. [30]. The minor minerals were ignored in our calculations and we approximated the samples as being a mixture of three minerals: quartz, magnetite and actinolite. The modal proportions of these three minerals were determined from the XRF intensity profiles of Si, Fe, Ca, and Mn (Fig. 5a). The minor phases of apatite and pyrite were estimated to be <1%. Details of the computation methods are described in Katsuta *et al.* [20].

The modal proportion of actinolite was typically 0.6–1.0 in the Fe-rich mesobands, and <0.2 in the Si-rich mesobands. The modal proportion of magnetite was 0.3–0.8 in the Fe-rich meso‐ bands and approximately 0.7 in the Si-rich mesobands. The magnetite peaks shown in Fig. 7 correspond to a high Fe content in the XRF map (Fig. 4b). The distributions of Ca and Mn in the XRF maps show high concentrations of actinolite. The relationship between actinolite and magnetite in the Fe-rich mesobands and that between magnetite and quartz in the Si-rich mesobands show an inverse correlation.

**Figure 7.** Mineral mode profiles corresponding to the XRF images shown in Fig. 5. The shaded and white bands indi‐ cate Fe-rich and Si-rich mesobands, respectively.

schistosity defined by the preferred orientation of elongated actinolite and magnetite was approximately parallel to the boundary between the Fe-rich and Si-rich mesobands. Because of this, it was difficult to evaluate whether the bandings were primary sedimentary structures

**Figure 8.** Frequency distributions of the band-thicknesses of the Dwyer Lake BIF samples (*DLS*). Left: a linear scale. Right: a logarithmic scale. (a) Fe-rich mesobands. (b) Si-rich mesobands. *R*: correlation coefficient. *D*: fractal dimension.

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217

In a previous study, we investigated the banded structures in Bell Lake BIF samples [20], which have the same stratigraphic position (Bell Lake Group) as the Dwyer Lake BIF samples (Fig. 1). The Bell Lake BIF had metamorphosed to amphibolites facies and had the schistosity subparallel to the banded structures, as the Dwyer Lake BIF had. Meanwhile, in the Bell Lake BIF samples, we found that the schistosity clearly intersected the boundary between the Ferich and Si-rich mesobands in a locally developed intrafolial fold. This implies that the alternating structures of the Fe-rich and Si-rich mesobands already existed at the time of peak

In the Bell Lake BIF samples, the Fe-rich mesobands were mainly composed of hornblende, grunerite, and magnetite. The hornblende was concentrated in the middle part of the Fe-rich mesobands, and was sandwiched between grunerite layers at the margins of the Fe-rich mesoband, which suggests that metamorphic differentiation occurred in the Fe-rich meso‐

or secondary metamorphic layers.

metamorphism.

#### **3.4. Band-thicknesses**

The thickness of the Fe-rich and Si-rich mesobands was analysed using the element and mineral profiles (Figs 5 and 7). The results of our analysis are shown in Fig. 8. The Fe-rich mesobands had a thickness range of 0.1 to 1.4cm (average = 0.35cm) and the Si-rich mesobands had a thickness range of 0.1 to 1.1cm (average = 0.25cm). A thickness of approximately 0.1cm was the cutoff scale for these two mesobands. The number of these mesobands that could be identified was 190 over the entire *DLS* sequence (114cm in length). The frequency distribution showed an exponential decrease in the number of thicker bands.

## **4. Discussion**

#### **4.1. Influence of metamorphism on banded structures**

The Dwyer Lake BIF suffered amphibole-facies metamorphism and the constituent minerals were completely recrystallized into medium-grade metamorphic minerals (Fig. 6). The

Fractal Nature of the Band-Thickness in the Archean Banded Iron Formation in the Yellowknife Greenstone Belt… http://dx.doi.org/10.5772/55700 217

bands and approximately 0.7 in the Si-rich mesobands. The magnetite peaks shown in Fig. 7 correspond to a high Fe content in the XRF map (Fig. 4b). The distributions of Ca and Mn in the XRF maps show high concentrations of actinolite. The relationship between actinolite and magnetite in the Fe-rich mesobands and that between magnetite and quartz in the Si-rich

**Figure 7.** Mineral mode profiles corresponding to the XRF images shown in Fig. 5. The shaded and white bands indi‐

The thickness of the Fe-rich and Si-rich mesobands was analysed using the element and mineral profiles (Figs 5 and 7). The results of our analysis are shown in Fig. 8. The Fe-rich mesobands had a thickness range of 0.1 to 1.4cm (average = 0.35cm) and the Si-rich mesobands had a thickness range of 0.1 to 1.1cm (average = 0.25cm). A thickness of approximately 0.1cm was the cutoff scale for these two mesobands. The number of these mesobands that could be identified was 190 over the entire *DLS* sequence (114cm in length). The frequency distribution

The Dwyer Lake BIF suffered amphibole-facies metamorphism and the constituent minerals were completely recrystallized into medium-grade metamorphic minerals (Fig. 6). The

showed an exponential decrease in the number of thicker bands.

**4.1. Influence of metamorphism on banded structures**

mesobands show an inverse correlation.

216 Climate Change and Regional/Local Responses

cate Fe-rich and Si-rich mesobands, respectively.

**3.4. Band-thicknesses**

**4. Discussion**

**Figure 8.** Frequency distributions of the band-thicknesses of the Dwyer Lake BIF samples (*DLS*). Left: a linear scale. Right: a logarithmic scale. (a) Fe-rich mesobands. (b) Si-rich mesobands. *R*: correlation coefficient. *D*: fractal dimension.

schistosity defined by the preferred orientation of elongated actinolite and magnetite was approximately parallel to the boundary between the Fe-rich and Si-rich mesobands. Because of this, it was difficult to evaluate whether the bandings were primary sedimentary structures or secondary metamorphic layers.

In a previous study, we investigated the banded structures in Bell Lake BIF samples [20], which have the same stratigraphic position (Bell Lake Group) as the Dwyer Lake BIF samples (Fig. 1). The Bell Lake BIF had metamorphosed to amphibolites facies and had the schistosity subparallel to the banded structures, as the Dwyer Lake BIF had. Meanwhile, in the Bell Lake BIF samples, we found that the schistosity clearly intersected the boundary between the Ferich and Si-rich mesobands in a locally developed intrafolial fold. This implies that the alternating structures of the Fe-rich and Si-rich mesobands already existed at the time of peak metamorphism.

In the Bell Lake BIF samples, the Fe-rich mesobands were mainly composed of hornblende, grunerite, and magnetite. The hornblende was concentrated in the middle part of the Fe-rich mesobands, and was sandwiched between grunerite layers at the margins of the Fe-rich mesoband, which suggests that metamorphic differentiation occurred in the Fe-rich meso‐ bands. The mineral phases and petrographic textures are markedly different from those in the Dwyer Lake BIF samples.

The differences between the Bell Lake and Dwyer Lake BIF samples could have arisen from different initial bulk compositions and perhaps from different metamorphic temperatures. It has been suggested that the Bell Lake BIF had possibly been subjected to a stronger influence of metamorphism compared with the Dwyer Lake BIF. Therefore, we regard the banding and band-thickness of the Dwyer Lake BIF to be a primary sedimentary structure. As has been discussed for the Bell Lake BIF [20], the source of the constituent materials in the Fe-rich mesobands was interpreted as being from mafic pyroclastic materials arising from submarine volcanic eruptions, given that the Bell Lake Group was formed at a time of continental breakup and rifting.

## **4.2. Causes of the banding in the Dwyer Lake BIF**

As shown in Fig. 8, the frequency distribution of the band-thickness in the Fe-rich and Si-rich mesobands in the Dwyer Lake BIF shows an exponential decrease in the number of thicker bands. This suggests that the band-thickness follows a power law distribution. Hence, we determined the scaling exponent, *D*, of the band-thickness, *r*, (above the 0.1cm cutoff scale) using the equation

$$N\left(r\right) = a \cdot r^{-D} \,, \tag{1}$$

However, such depositional processes are different from those of the Fe-rich mesobands in the Dwyer Lake BIF. This is because the constituent materials of the successions are clastic sediments that were supplied from a continental shelf by turbidity currents and deposited in a shelf embayment dominated by tidal currents. Accordingly, we must assign another cause

Fractal Nature of the Band-Thickness in the Archean Banded Iron Formation in the Yellowknife Greenstone Belt…

http://dx.doi.org/10.5772/55700

219

Presently, we consider the hypothesis of Morris [32] to be the most suitable depositional model for explaining the fractal nature of the Dwyer Lake BIF. It is well known that the banding of mesoband types is well developed in the Hamersley BIF of Western Australia. According to Morris [32], the Fe-rich mesobands resulted from the periodic convection-driven upwelling of pyroclastic materials from a mid-ocean ridge (MOR) or hot spot. Moreover, Morris concluded that the different mesoband types that are intermediate in scale between mesobanding and microbanding were produced by a modified deep-water supply because of varied MOR activity or partial blocking of upwelling water. In the Dwyer Lake BIF, we consider that such an irregular supply of deep seawater may have resulted in the formation of the fractal-like bandings. In addition, the difference in the bandings between the Dwyer Lake and Bell Lake BIFs that have a fractal-like and hierarchical structure [20], respectively, could be explained

We have investigated the bandings in Archean metamorphic BIF samples collected from the Dwyer Lake area in the Yellowknife greenstone belt, Canada. Chemical and petrographic

**1.** The Fe-rich and Si-rich mesobands in the Dwyer Lake BIF are regarded as being primary structures formed before metamorphic alternation, based on a comparison with Bell Lake

**2.** The band-thickness of both the Fe-rich and Si-rich mesobands showed a power law

**3.** The thickness and spacing of the Fe-rich mesobands could have been created by an

We express our cordial thanks to John A. Brophy and Bill Padgham, Northwest Territories Geoscience Office, for their support in our research activities in Canada. We thank S. Hori, T. Okaniwa, H. Yoshioka, A. Yoshihara, S. Ito, and Y. Isozaki for collecting the BIF samples; S. Yogo for preparing the thin sections; and T. Goto for technical advice on the SEM-EDS analysis. This study was supported by the Decoding Earth Evolution Program (DEEP) Grant-in-Aid for Scientific Research on Priority Areas (No. 07238104); a Grant-in-Aid for Scientific Research for

for the morphology of the bandings preserved in the Dwyer Lake BIF.

by the hypothesis of Morris [32].

analysis revealed the following.

distribution, suggesting a fractal-like nature.

irregular upwelling of submarine pyroclastic materials.

**5. Conclusions**

BIF samples.

**Acknowledgements**

where *N* is the number of bands and *a* is a constant. Consequently, the value of *D* for the Ferich mesobands was 1.75 with a correlation coefficient of *R* = –0.95 and the value of *D* for the Si-rich mesobands was 2.28 where *R* = –0.98. This statistically significant result implies that the Fe-rich and Si-rich mesobands have a fractal nature.

It is well known that the BIFs have hierarchical structures comprising macrobands (meters thick), mesobands (centimetres thick), and microbands (millimetres thick) [4]. On the other hand, evidence that BIFs have fractal dimensions of the band-thickness, i.e., *D*, has also been observed in the Archean BIF, Kola Peninsula, Russia [31]. Goryainov *et al.* [31] reported that the magnetite bands had a thickness distribution of *D* = 1.74 ± 0.1. This is comparable to that of Fe-rich mesobands in the Dwyer Lake BIF (*D* = 1.75).

In the Dwyer Lake BIF, the most striking feature is that not only the Fe-rich mesobands but also the paired Si-rich mesobands exhibit a fractal nature. In general, it is believed that the absence of silica-secreting organisms in the Precambrian seawater may have led to it be saturated with respect to dissolved silica and the silica was maintained at a saturated level throughout periods of both high and low iron supply [32]. If this model is applied to the bandings in the Dwyer Lake BIF, then the thickness and spacing of the Fe-rich mesobands could be interpreted as indicating deposition by a nonstochastic process.

To our knowledge, the geological evidence that bed thickness follows a power law is limited to observations on turbidite sequences [33] and biocalcarenitic tidal dune successions [34]. However, such depositional processes are different from those of the Fe-rich mesobands in the Dwyer Lake BIF. This is because the constituent materials of the successions are clastic sediments that were supplied from a continental shelf by turbidity currents and deposited in a shelf embayment dominated by tidal currents. Accordingly, we must assign another cause for the morphology of the bandings preserved in the Dwyer Lake BIF.

Presently, we consider the hypothesis of Morris [32] to be the most suitable depositional model for explaining the fractal nature of the Dwyer Lake BIF. It is well known that the banding of mesoband types is well developed in the Hamersley BIF of Western Australia. According to Morris [32], the Fe-rich mesobands resulted from the periodic convection-driven upwelling of pyroclastic materials from a mid-ocean ridge (MOR) or hot spot. Moreover, Morris concluded that the different mesoband types that are intermediate in scale between mesobanding and microbanding were produced by a modified deep-water supply because of varied MOR activity or partial blocking of upwelling water. In the Dwyer Lake BIF, we consider that such an irregular supply of deep seawater may have resulted in the formation of the fractal-like bandings. In addition, the difference in the bandings between the Dwyer Lake and Bell Lake BIFs that have a fractal-like and hierarchical structure [20], respectively, could be explained by the hypothesis of Morris [32].

## **5. Conclusions**

bands. The mineral phases and petrographic textures are markedly different from those in the

The differences between the Bell Lake and Dwyer Lake BIF samples could have arisen from different initial bulk compositions and perhaps from different metamorphic temperatures. It has been suggested that the Bell Lake BIF had possibly been subjected to a stronger influence of metamorphism compared with the Dwyer Lake BIF. Therefore, we regard the banding and band-thickness of the Dwyer Lake BIF to be a primary sedimentary structure. As has been discussed for the Bell Lake BIF [20], the source of the constituent materials in the Fe-rich mesobands was interpreted as being from mafic pyroclastic materials arising from submarine volcanic eruptions, given that the Bell Lake Group was formed at a time of continental breakup

As shown in Fig. 8, the frequency distribution of the band-thickness in the Fe-rich and Si-rich mesobands in the Dwyer Lake BIF shows an exponential decrease in the number of thicker bands. This suggests that the band-thickness follows a power law distribution. Hence, we determined the scaling exponent, *D*, of the band-thickness, *r*, (above the 0.1cm cutoff scale)

where *N* is the number of bands and *a* is a constant. Consequently, the value of *D* for the Ferich mesobands was 1.75 with a correlation coefficient of *R* = –0.95 and the value of *D* for the Si-rich mesobands was 2.28 where *R* = –0.98. This statistically significant result implies that the

It is well known that the BIFs have hierarchical structures comprising macrobands (meters thick), mesobands (centimetres thick), and microbands (millimetres thick) [4]. On the other hand, evidence that BIFs have fractal dimensions of the band-thickness, i.e., *D*, has also been observed in the Archean BIF, Kola Peninsula, Russia [31]. Goryainov *et al.* [31] reported that the magnetite bands had a thickness distribution of *D* = 1.74 ± 0.1. This is comparable to that

In the Dwyer Lake BIF, the most striking feature is that not only the Fe-rich mesobands but also the paired Si-rich mesobands exhibit a fractal nature. In general, it is believed that the absence of silica-secreting organisms in the Precambrian seawater may have led to it be saturated with respect to dissolved silica and the silica was maintained at a saturated level throughout periods of both high and low iron supply [32]. If this model is applied to the bandings in the Dwyer Lake BIF, then the thickness and spacing of the Fe-rich mesobands

To our knowledge, the geological evidence that bed thickness follows a power law is limited to observations on turbidite sequences [33] and biocalcarenitic tidal dune successions [34].

( ) , *<sup>D</sup> Nr ar*- = × (1)

Dwyer Lake BIF samples.

218 Climate Change and Regional/Local Responses

**4.2. Causes of the banding in the Dwyer Lake BIF**

Fe-rich and Si-rich mesobands have a fractal nature.

of Fe-rich mesobands in the Dwyer Lake BIF (*D* = 1.75).

could be interpreted as indicating deposition by a nonstochastic process.

and rifting.

using the equation

We have investigated the bandings in Archean metamorphic BIF samples collected from the Dwyer Lake area in the Yellowknife greenstone belt, Canada. Chemical and petrographic analysis revealed the following.


## **Acknowledgements**

We express our cordial thanks to John A. Brophy and Bill Padgham, Northwest Territories Geoscience Office, for their support in our research activities in Canada. We thank S. Hori, T. Okaniwa, H. Yoshioka, A. Yoshihara, S. Ito, and Y. Isozaki for collecting the BIF samples; S. Yogo for preparing the thin sections; and T. Goto for technical advice on the SEM-EDS analysis. This study was supported by the Decoding Earth Evolution Program (DEEP) Grant-in-Aid for Scientific Research on Priority Areas (No. 07238104); a Grant-in-Aid for Scientific Research for Young Scientists (B) (No. 19740319, 24700947); Dynamics of the Sun-Earth-Life Interactive System, Number G-4, the 21st Century COE Program for the Ministry of Education, Culture, Sports, Science and Technology, Japan; the Saijiro Endo Memorial Foundation; and the Fujiwara Natural History Foundation.

[8] Simonson BM, Hassler SW. Was the deposition of large Precambrian iron formations linked to major marine transgressions? Journal of Geology 1996;104(6) 665–675.

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221

[9] Pickard AL, Barley ME, Krapež B. Deep-marine depositional setting of banded iron formation: sedimentological evidence from interbedded clastic sedimentary rocks in the early Palaeoproterozoic Dales Gorge Member of Western Australia. Sedimentary

[10] Klein C. Some Precambrian banded iron-formations (BIFs) from around the world: Their age, geologic setting, mineralogy, metamorphism, geochemistry, and origin.

[11] Böning P, Bard E, Rose J. Toward direct, micron-scale XRF elemental maps and quan‐ titative profiles of wet marine sediments. Geochemistry Geophysics Geosystem

[12] Katsuta N, Takano M, Kawakami SI, Togami S, Fukusawa H, Kumazawa M, et al. Climate system transition from glacial to interglacial state around the beginning of the last termination: Evidence from a centennial- to millennial-scale climate rhythm.

[13] Katsuta N, Takano M, Kawakami SI, Togami S, Fukusawa H, Kumazawa M, et al. Advanced micro-XRF method to separate sedimentary rhythms and event layers in sediments: its application to lacustrine sediment from Lake Suigetsu, Japan. Journal

[14] Katsuta N, Tojo B, Takano M, Yoshioka H, Kawakami S, Ohno T, et al. Non-destruc‐ tive method to detect the cycle of lamination in sedimentary rocks: rhythmite se‐ quence in Neoproterozoic cap carbonate. In: Vickers-Rich P, Komarower P. (ed.) The Rise and Fall of the Ediacaran Biota. Geological Society, London, Special Publication.

[15] Kuroda J, Ohkouchi N, Ishii T, Tokuyama H, Taira A. Lamina-scale analysis of sedi‐ mentary components in Cretaceous black shales by chemical compositional map‐ ping: Implications for paleoenvironmental changes during the Oceanic Anoxic

[16] Sakai H, Shirai K, Takano M, Horii M, Funaki, M. Analysis of fine structure of chert and BIF by measurement of high resolution magnetic field and scanning X-ray ana‐ lyzed microscope. Proceedings of the NIPR symposium on Antarctic Geosciences

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## **Author details**

Nagayoshi Katsuta1 , Ichiko Shimizu2 , Masao Takano3 , Shin-ichi Kawakami1 , Herwart Helmstaedt4 and Mineo Kumazawa3

1 Faculty of Education, Gifu University, Japan

2 Department of Earth and Planetary Science, Graduate School of Science, University of To‐ kyo, Japan

3 Graduate School of Environmental Studies, Nagoya University, Japan

4 Department of Geological Science, Queen's University, Canada

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**Chapter 9**

. In recent

**Trace Elements and Palynomorphs**

Sueli Yoshinaga Pereira, Melina Mara de Souza, Fresia Ricardi-Branco, Paulo Ricardo Brum Pereira,

Additional information is available at the end of the chapter

Park Hermogenes de Freitas Leitao Filho is located in Campinas (SP), limited by the Cidade Universitaria I and Cidade Universitaria II neighbourhoods and the State University of Campinas (UNICAMP), in the Barão Geraldo district, whose population was estimated in 2011 to be around 60,000 inhabitants [1]. The park has an estimated area of 123,901.06 m2 and of this

decades, effluent from the University has been released into the pond. In 2004, this release was captured by the sewage system of the municipal sanitation company. Currently, the pond receives urban drainage water from the Cidade Universitária II neighbourhood and a Centro Médico Hospital, on the right bank, and the university campus and the Cidade Universitaria

Thus, in this study we sought the presence of trace elements (As, Co, Cr, Cu, Ga, Ni, Pb, Th, V and Zn) and Al2O3, Fe2O3, MnO and Loss on Ignition (LOI, 105 ºC and 1,000 ºC) in recent sediments of the pond and correlate it with the occurrence of pollen and spores derived from the surrounding vegetation. Accordingly, a 65 cm-deep core, named T-UNICAMP, forming

one passes through the campus of UNICAMP, draining an area of 325.813 m2

corresponds to the surface of a pond formed by the damming of two streams:

© 2013 Pereira et al.; licensee InTech. This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use,

© 2013 Pereira et al.; licensee InTech. This is a paper distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

distribution, and reproduction in any medium, provided the original work is properly cited.

**in the Core Sediments**

Fabio Cardinale Branco and Renato Zázera Francioso

http://dx.doi.org/10.5772/55703

**1. Introduction**

total, 80,111.17 m2

II neighbourhood on the left bank.

the subject matter of this article.

**of a Tropical Urban Pond**
