Formation and degradation of immature laterites in response to paleoclimatic changes in the eastern Amazon

Abstract

Lateritic formations are widespread in eastern Amazon, occurring as bauxite-bearing mature profiles on plateaus or as immature ones in lowlands. Climate and landscape evolution over the Neogene were analyzed via mineralogical (XRD), textural (optical microscopy), and geochemical (ICP-OES, ICP-MS) methods carried out in a selected lateritic profile outcropping in Abel Figueiredo. The profile features columnar and nodular iron crust, overlaid by a spherulitic horizon formed of hard fragments in clayey matrices, covered by yellow topsoil. Major minerals include hematite, goethite, kaolinite, and quartz, with minor anatase and heavy minerals. Hematite and goethite dominate lower horizons, while kaolinite, quartz, Al-goethite, and anatase appear in the matrix and topsoil. Trace elements were immobilized by iron oxyhydroxides and anatase or maintained in zircon and other resistate minerals. Mineralogy and geochemical distribution indicates a transition from iron crusts to fragmented iron crust, followed by physical reworking, leading to the formation of nodules and spherulites, with clay accumulation in between. In a final stage, a topsoil developed over the profile. This set of events requires an alternation between humid tropical climate with more arid conditions, with implications to rainforest and savanna development, resulting in mineral formation and chemical or physical decomposition.

KEYWORDS:
weathering; topsoil; hematite; goethite

1. INTRODUCTION

Lateritic Formations represent an important record of surface evolution, such as landscape dynamics, drainage, vertical variations of the water table, erosion cycles, and climate changes, and economic mineralizations (Bárdossy & Aleva, 1990; Price et al., 1997; Fu et al., 2014; Gu et al., 2013; Singh et al., 2020; Digafe et al., 2024). They are widely distributed in central and eastern Amazon, where they have been described as mature lateritic profiles (MLPs) and immature lateritic profiles (ILPs). MLPs are generally older and host mineralizations such as kaolin, bauxite, phosphate, and iron ore (Costa et al., 2009; Santos et al., 2016; Costa et al., 2016; Silva & Costa, 2020). ILPs are younger and have not reached the degree of differentiation necessary to form mineralizations (e.g., Myo Nwe et al., 2021). They typically consist of saprolite, mottled clay, and ferruginous duricrust, primarily composed of Fe₂O₃, Al₂O₃, and SiO₂, in the forms of goethite, hematite, kaolinite, and quartz (Costa, 1991).

K-Ar and ⁴⁰Ar/³⁹Ar dating in Mn oxyhydroxides found ages from 72 ± 6 Ma to as recent as 0.2 ± 0.2 Ma in Carajás, Southern Amazon. U-Th/He dating in the same region is consistent, demonstrating goethite formation during the entire Cenozoic (Vasconcelos et al., 1994; Ruffet et al., 1996; Monteiro et al., 2018). In central Amazon, U-Th/He ages in goethite range between 290 and 13 Ma, and analysis of radiation-induced defects in kaolinites from lateritic crusts yielded ages between 1.1 and 7 Ma (Allard et al., 2018; Albuquerque et al., 2020). All dating methods applied confirm continuous weathering from the Mesozoic to the present, with some periods of strong positive oscillations, which can be correlated to global lateritization events or local variations.

Mature laterites have been extensively studied in the eastern Amazon, especially those containing bauxite, aluminum phosphate, and iron ore (Truckenbrodt & Kotschoubey, 1981; Grubb, 1979; Kronberg et al., 1979a, 1982; Boulangé & Carvalho, 1997; Lucas, 1997; Costa et al., 2014; Oliveira et al., 2016), highlighting the importance of supergene enrichment in forming such mineralizations. ILPs are less documented. The first studies on Amazonian ILPs date back to the late 1970s, focusing on their mineralogy and chemical composition (Kronberg et al., 1979b; Sombroek & Camargo, 1983; Costa, 1997; Costa et al., 1997). It was later suggested that Amazonian latosols primarily result from the chemical degradation of immature lateritic crusts (Horbe & Costa, 1997, 2005).

The Paragominas-Rondon do Pará lateritic province comprises mature lateritic profiles hosting a clayey Bauxite horizon, nodular bauxite, spherulitic bauxite, and ferroaluminous crust, partially disintegrated at the top by root activity (Oliveira et al., 2016; Santos & Costa, 2021). This set of horizons is capped by nearly the 12 m thick Belterra Clay, extending to the surface (Negrão et al., 2018, 2021). The landscape is formed of plateaus protected from erosion by the forest. The scarps and valleys among the plateaus locally exhibit immature laterites, which raises some questions: Are they autochthonous or allochthonous? Are they derived from surficial reworking of bauxite-bearing MLPs, or do they have a different parent material? Were they formed under the same paleoclimatic conditions as the MLPs?

This work selected an immature lateritic profile outcropping at the border of the road BR-222 between Rondon do Pará and Abel Figueiredo (Figure 1). The aim was to understand its generation, subsequent evolution, and topsoil formation, and to infer and/or reinforce evidence of climate change during the Neogene.

Figure 1
Geological map of the area around Abel Figueiredo and Rondon do Pará (Serviço Geológico do Brasil, 2004), highlighting the location of the sampling site at the border of road BR-222.

2. GEOLOGICAL SETTING

The ILP samples selected for this study were obtained from an outcrop located 584 km southeast of Belém, at the border of road BR-222, between Abel Figueiredo and Rondon do Pará (Figure 1). The area around Abel Figueiredo (Figure 1B) exhibits plateaus with elevations ranging from 400 m in the south to 180 m in the north (Kotschoubey et al., 2005). These plateaus comprise mature lateritic formations hosting bauxite deposits, covered by the Belterra Clay, a 12-meter-thick layer of an unconsolidated yellow clay (Negrão et al., 2018, 2021). The plateaus are bordered by valleys and ravines, followed by gently undulating lower terrains with altitudes between 150 and 200 m (Kotschoubey et al., 2005).

The Abel Figueiredo region is geologically located in the southwestern portion of the Grajaú Basin (Figure 1). The stratigraphic succession consists of the Codó Formation, the Itapecuru Group and the Ipixuna Formation (Vasquez et al., 2008). The Codó Formation encompasses black shales, evaporites, limestones, and sandstones of mainly lacustrine origin (Paz & Rossetti, 2001; Rossetti & Góes, 2004). The Itapecuru Group includes a thick siliciclastic package composed of sandstones, siltstones, claystones, arkoses, and conglomerates (Góes, 1981; Kotschoubey et al., 2005). The Ipixuna Formation is composed of sandstones displaying cross-stratification, interspersed siltstones, and subordinate red claystones, covered by kaolin-bearing lateritic profiles (Góes, 1981).

During the Paleocene, the Grajaú Basin was exposed to a tropical climate, giving rise to lateritic formations (mature laterites) that produced extensive bauxite and kaolin deposits currently exploited in the region (Costa, 1991, 1997). These deposits are derived from the Itapecuru Group and Ipixuna Formation, respectively, and in the case of the bauxite-bearing ones, they are capped by a thick layer of Belterra Clay (Costa, 1997; Kotschoubey et al., 2005; Oliveira et al., 2016). Later, a new lateritization phase during the Late Miocene marked the formation of immature laterites at the tops of hills found on the lower surface (Costa et al., 2014).

3. MATERIALS AND METHODS

Fieldwork was conducted along BR-222, the road connecting Abel Figueiredo and Rondon do Pará, to evaluate the extent and characteristics of lateritic formations and their relationships with the neighboring rocks and the landscape. Various immature lateritic profiles were described near km 137 of BR-222, approximately 9 km northeast of Abel Figueiredo, at an altitude of 260 m. One representative iron crust profile, including its topsoil, was selected for detailed description, and ten samples were collected for analysis.

The samples were divided into three aliquots. The first was used to prepare a polished thin section; the second was crushed, homogenized, and quartered for the extraction of heavy minerals; and the third was powdered in an agate mortar for mineralogical identification via X-ray diffraction (XRD), whole-rock geochemistry, and the chemical extraction of anatase.

Heavy minerals larger than 0.063 mm were extracted using the following procedures: 1) crushing and disaggregating 100 g from each sample; 2) particle size separation by sieving to concentrate grains between 0.063 and 0.125 mm; 3) extraction of opaque minerals using a magnetic pen; 4) extraction of the transparent heavy minerals using bromoform; 5) mounting a small aliquot of the heavy mineral concentrate onto adhesive tape for SEM-EDS analysis; 6) setting on a thin section. Due to its nanometric size, the concentration of anatase followed a different path. Nanocrystals were concentrated by treatment with hexafluorotitanic acid (H₂TiF₆), which dissolved kaolinite and other phyllosilicates using the method of Sayin & Jackson (1975), followed by the removal of iron oxyhydroxides with 6N HCl treatment.

Ten thin sections from each horizon were examined under the optical microscope to evaluate their mineralogy and texture. A Zeiss AXIOLAB POL microscope coupled with a Canon A460 digital camera was used for this purpose. Heavy minerals were also identified and quantified under the optical microscope by counting 150 grains per section. Key references for laterite texture and heavy mineral identification included "Atlas of Micromorphology of Mineral Alteration and Weathering" (Delvigne, 1999) and "Heavy Minerals in Color" (Mange & Maurer, 1992), respectively.

Scanning electron microscopy coupled with an energy dispersive system (SEM-EDS) was used for complementary analyses of major minerals and the concentrated heavy minerals, including chemically extracted anatase, by imaging morphological aspects and performing semi-quantitative chemical determinations after gold sputtering. SEM analyses were performed using both Zeiss SIGMA UP LEO 1430 and Hitachi TM3000, with EDS conducted using an Oxford SwiftED3000 instrument.

A Bruker D2 Phaser diffractometer with a copper anode (λCu Kα = 1.54184 Å) was used for XRD analysis. The instrument operated at 30 kV voltage and 10 mA current, with a step size of 0.02° and a step time of 0.2 s and was equipped with a LynxEye detector. Data acquisition and evaluation were carried out using Bruker Diffrac.Suit software.

Whole rock chemical analyses for the ten samples were carried out at Acme Analytical Laboratories Ltd. Major elements were determined by inductively coupled plasma optical emission spectrometry after total fusion with lithium metaborate/tetraborate and nitric acid digestion, while trace and rare earth elements (REE) were determined by inductively coupled plasma mass spectrometry after similar fusion and digestion. The same instrument analyzed precious and base metals following aqua regia digestion. Loss on ignition (LOI) was determined after calcination at 1,000 °C.

The degree of chemical weathering and lateritization of the studied samples was evaluated using the Chemical Index of Alteration (CIA) and the Lateritization Index (IL). The CIA was calculated following Nesbitt and Young (1982, 1984), using the molar proportions of major oxides according to the formula: CIA = [Al₂O₃ / (Al₂O₃ + CaO* + Na₂O + K₂O)] × 100, where CaO* represents the calcium content associated exclusively with silicate minerals, excluding contributions from carbonates and phosphates. Given the absence of carbonates and phosphates in the samples studied, total CaO was considered as CaO*. The Lateritization Index (IL) was calculated according to the approach proposed by Bárdossy (1982), which expresses the enrichment of Fe₂O₃ and Al₂O₃ in relation to silica. The IL was calculated using the formula IL = (Fe₂O₃ + Al₂O₃) / SiO₂.

4. RESULTS

4.1 Regolith succession

From bottom to top, the immature lateritic profile at Abel Figueiredo features a columnar and nodular iron crust, a nodular-spherulitic horizon, and topsoil (Figure 2A).

Figure 2
A) The horizons of the immature lateritic profile and topsoil studied at road BR-222 between Abel Figueiredo and Rondon do Pará. B and C) Columnar iron crust in the field with surrounding clayey matrix. D) Nodular iron crust. E) Spherulitic horizon in the field with surrounding clayey matrix. F) Nodules collected at the bottom of the topsoil. G) Lumps of clayey matrix in the topsoil.

4.1.1 Iron crust

The iron crust has a minimum thickness of 2.5 m, is columnar in the lower section, and is nodular in the upper. The columnar zone consists of metric columns made of brownish-red iron oxyhydroxides embedded in a yellow, friable, silty-clayey matrix (Figures 2B and C). This zone often contains smaller fragments of columnar material with a nodular appearance. The nodular zone is composed of brownish-red iron oxyhydroxide nodules with concentric bands in various shades of brown, red, and yellow. These nodules typically exhibit dark brown films of iron hydroxides on the outermost band and are also embedded in a restricted, friable silty-clayey matrix (Figure 2D). Despite the contrasting textures, the mineralogical composition of the columnar and nodular-spherulitic iron crusts is similar, comprising hematite and goethite in the columns and nodules along with kaolinite, goethite and quartz in the matrix (Figures 3A and B).

Figure 3
Mineralogical composition of the Abel Figueiredo lateritic profile. Iron crust: Hard fragments (A) and matrix (B). Spherulitic horizon: Nodules/spherulites (C) and matrix (D). Topsoil: Spherulites (E) and matrix (F). Kln = kaolinite; Qtz = quartz; Hem = hematite; Gt = goethite; Ant = anatase.

4.1.2 Spherulitic Horizon

The spherulitic horizon is up to 1 m thick, transitioning gradually from the iron crust below to a sharpsharp contact with the topsoil above. The spherulites range from 0.2 cm to 1 cm in diameter, becoming finer towards the top. These spherulites are reddish-brown and embedded in a light red, clayey matrix (Figure 2E). Reddish-brown nodules, measuring between 0.2 and 5 cm in diameter and oriented sub-vertically, are also present (Figure 2F). The same minerals compose both the spherulites and nodules, as well as the matrix, but their relative abundances differ. Kaolinite dominates the matrix, while hematite and goethite are more abundant in the spherulites and nodules (Figures 33D).

4.1.3 Topsoil

The topsoil is approximately 1 m thick and consists of silty-clayey grains that transition from reddish at the bottom to yellow at the top (Figure 2G). These grains embed lumps and spherulites. The lumps are up to 3 cm in size, which crumble under finger pressure, and are composed of iron oxyhydroxides cementing clay minerals. The spherulites exhibit a reddish-brown interior and a light brown outermost film. They are formed of hematite with subordinate kaolinite, while the lumps consist of kaolinite, quartz, and goethite, with accessory anatase. This mineralogical composition is the same as the surrounding unconsolidated silty-clayey matrix (Figures 33F).

4.2 Micromorphology

In the iron crust, the columns and nodules microscopically exhibit a reddish-brown plasma containing micronodules and microspherulites. This plasma is composed of goethite and hematite, which are also predominant in the micronodules, where they sometimes appear intergrown with kaolinite (Figure 4A). The ferruginous plasma presents numerous cavities and locally evolves quartz grains showing fractures and dissolution forms, which are locally more evolved, forming the mentioned porosity (Figure 4B). The films frequently found in the plasma exhibit microcrystalline microbands formed of iron oxyhydroxides, mainly goethite (Figure 4C). Sub spherical features formed of aggregates of platy hematite are also common and occupy micropores in the ferruginous plasma (Figure 4D).

Figure 4
Iron crust: Nodule formed of iron oxyhydroxides plasma evolving micronodules (A); quartz grains and cavities within the plasma of iron oxyhydroxides (B); microbands formed of iron oxyhydroxides (C); aggregates of platy hematite infilling micropores (D). Spherulitic horizon: Nodules formed iron oxyhydroxide plasma with quartz grains and microcavities (E); botryoidal iron oxyhydroxides coating a cavity, reflecting microbands similar to those observed in Figure 4C for the iron crust, here visualized in the three dimensions (F), locally forming platy hematite crystals (G). Topsoil: Aggregates of kaolinite (H), associates with titanium oxides and iron oxyhydroxides as suggested by EDS spectrum (I).

In the spherulitic horizon, the spherulites are formed of an iron oxyhydroxide plasma, also presenting microcavities that evolve the quartz grains (Figure 4E). The iron oxyhydroxides appear as botryoidal (Figure 4F) or platy aggregates (Figure 4G) covering cavity walls within the spherulites. In the topsoil, kaolinite mass is formed of nanocrystalline aggregates (Figure 4H) covered with light gray plasma, probably formed of iron and titanium oxyhydroxides (Figure 4I).

4.3 Accessory minerals

4.3.1 Heavy minerals

Zircon, rutile, tourmaline, kyanite, and staurolite were identified in the horizons studied (Figure 5A). Zircon is the most abundant transparent heavy mineral, followed by rutile and tourmaline. Kyanite and staurolite are sporadic, with staurolite being confined to the lower portion of the iron crust. The relative abundance of zircon and rutile remains nearly constant throughout the profile, while tourmaline shows variation only in the spherulitic to nodular horizon (Figure 5B). Among the opaque minerals in the profile, primarily found in the columns, spherulites, and nodules (0.125 mm to 0.250 mm), hematite and magnetite are the most frequent.

Figure 5
A) The heavy minerals identified in the matrix of the iron crust, spherulitic horizon and topsoil at Abel Figueiredo under plan polarized optical microscopy. B) Relative frequency of heavy minerals in each horizon.

Rutile (13–23%) predominantly exhibits a partially truncated bipyramidal prismatic form, though rounded to sub-rounded grains are also observed. The color is typically red, with irregular grains usually appearing brownish. Microfractures and abrasion marks are present on these grains. Tourmaline (2–13%) occurs as brown or brownish-green grains that retain prismatic morphology, mostly with subrounded to rounded edges. Angular to sub-angular fragments are also observed. Evidence of surface erosion, such as grooves and conchoidal fractures, is common. Kyanite (<1%) is colorless and appears as subhedral prismatic crystals. Staurolite (<1%) is pale to intense yellow, with irregular to sub-rounded grains showing microfractures and opaque inclusions and is only observed in the lower portion of the profile.

Zircon (68–87%) is generally colorless, sometimes brown or yellowish with pinkish hues. The grains are primarily sub-rounded to rounded, with a lesser extent as euhedral to sub-euhedral crystals and rarely as bipyramidal prismatic forms, though with rounded edges. Opaque minerals and bubble- and needle-shaped inclusions are common in these zircons. Abrasion edges, conchoidal fractures, parallel fractures, polished surfaces, displaced plates, and circular cavities can be observed on the surfaces of the grains and crystals (Figure 6AF).

Figure 6
SEM images of nanometric anatase crystals in the residue derived from the clayey matrix of the columnar iron crust (A), nodular iron crust (B), spherulitic horizon (C), and topsoil (D). EDS spot analyses from selected points shown in the images (E). XRD pattern of a representative concentrate from the iron crust highlighting the dominance of anatase, along with quartz and rutile (F).

4.3.2 Anatase

The efficiency of anatase concentration is demonstrated through visual, chemical, and structural evidence. Anatase crystallites in the concentrate are nanometric to sub-micrometric in size, mostly ranging from 100 nm to 300 nm and not exceeding 400 nm (Figure 6AD), forming subhedral plates similar to those observed in Juruti bauxites and Belterra Clay (Costa et al., 2014). EDS spot analyses confirm titanium dominance in these phases, with Ti concentrations ranging from 50.1% to 58.4% (Figure 6E), indicating effective anatase enrichment. X-ray diffraction further supports this, showing that anatase was successfully concentrated, yielding a mineral assemblage rich in anatase, quartz, and rutile (Figure 6F).

4.4 Chemical composition

4.4.1 Major elements

The horizons of the studied lateritic profile and the topsoil are predominantly composed of SiO₂, Fe₂O₃, Al₂O₃, and TiO₂ (Table 1), which together constitute an average of 86.8% of the total chemical composition, or 99.6% when accounting for the loss on ignition (LOI). Within each horizon, there is a marked contrast between the hard fragments (columns, nodules, and spherulites) and the surrounding clayey matrix. Consequently, the horizon will be described with particular emphasis on distinguishing the hard fragments (columns, spherulites, and nodules) from the matrices that encase them.

Table 1
Chemical composition of the iron crust (columns and matrix), spherulitic horizon (spherulites and matrix) and topsoil (base and top) and chemical composition of the upper continental crust, UCC (Rudnick & Gao, 2003).

	Columnar iron crust		Nodular iron crust (bottom)		Nodular iron crust (top)		Spherulitic horizon		Topsoil		UCC
	Columns	Matrix	Columns	Matrix	Nodules	Matrix	Spherulites	Matrix	Base	Top
SiO2 (%)	9.40	39.09	7.9	35.83	9.93	33.74	20.12	37.96	40.69	42.98	66.62
Al2O3	9.30	33.73	8.33	30.48	9.54	28.97	17.26	32.28	33.61	30.87	15.4
Fe2O3	68.26	9.97	73.49	18.36	70.23	21.94	52.13	13.4	8.35	7.89	5.04
TiO2	0.38	1.71	0.46	1.67	0.5	1.55	0.86	1.69	1.91	2.28	0.64
MgO	<0.01	0.02	<0.01	0.01	<0.01	0.01	<0.01	0.02	0.03	0.04	2.48
CaO	<0.01	0.02	<0.01	<0.01	<0.01	<0.01	<0.01	0.01	0.02	0.02	3.59
K2O	<0.01	0.03	0.01	0.02	<0.01	0.02	<0.01	0.02	0.03	0.03	2.8
MnO	<0.01	0.01	<0.01	0.01	<0.01	0.01	<0.01	0.01	0.01	0.02	0.1
P2O5	<0.01	<0.01	<0.01	<0.01	<0.01	<0.01	<0.01	<0.01	<0.01	0.02	0.15
LOI	12.1	15.3	9.3	13.4	9.2	13.5	9.3	14.4	15.1	15.6	-
Total	99.52	99.85	99.57	99.78	99.46	99.76	99.71	99.83	99.82	99.75	-
Sc (ppm)	20	14	18	15	20	16	13	14	14	14	14
V	2419	237	2066	476	2608	684	1201	303	185	176	97
Cr	253.1	143.5	424.2	185	547.4	219	554.2	177.9	136.8	123.2	92
Co	0.9	1.1	0.9	1	1.1	1.1	0.4	0.9	1.2	1.6	17.3
Cu	26.4	1.2	14.6	3.4	23.2	8	1.4	1.4	0.9	1	28
Zn	6	4	2	3	4	4	<1.0	3	4	4	67
Ga	36.6	45.5	66.5	49.8	73.1	53.7	68.5	48.6	45.7	39.5	17.5
As	40.2	2.8	29.8	6.3	31.9	9.3	46.6	5.1	1.8	1.4	4.8
Se	2.7	0.5	1.9	0.5	3	1.5	3.1	0.5	0.5	0.5	0.09
Rb	0.1	0.7	<0.1	0.4	<0.1	0.4	<0.1	0.5	0.8	1	84
Sr	1.6	11.4	1.9	11.2	2.6	10.2	3.9	10.7	13.3	13.4	320
Y	6	15.9	6.8	17.6	9	15.9	7.8	17.2	18.4	25.5	21
Zr	238.9	698	302.8	847.3	317.9	738	437.4	737.6	970.6	1454	193
Nb	6.3	31.2	8.8	30.9	9.5	28	14.8	30.5	36.3	43.4	12
Mo	3.8	0.7	4.9	1	6.9	1.8	10.2	1.1	0.6	0.5	1.1
Ag	0.4	<0.1	0.7	0.1	1.2	0.3	1.6	0.2	<0.1	<0.1	0.07
Sn	1	5	2	5	2	5	3	5	6	5	2.3
Sb	2.7	0.1	2.8	0.3	3.2	0.6	1.9	0.2	0.1	<0.1	0.3
Cd	0.1	0.1	0.1	0.1	0.1	0.1	0.1	0.1	0.1	0.1	0.09
Cs	1	1	1	1	1	1	1	1	0.2	0.2	5.8
Ba	2	15	1	14	4	15	4	16	15	16	624
Hf	5.8	18.8	7.8	20.9	8.6	18.8	11.1	19.5	24.7	36.8	5.3
Ta	0.5	2.4	0.7	2.3	0.7	2.2	1.1	2.4	2.7	3.4	0.9
W	0.9	2.9	1.1	2.8	1.3	2.5	2.4	2.4	2.7	3.2	1.9
Hg	0.65	0.2	0.86	0.18	1.01	0.31	1.21	0.28	0.21	0.16	0.05
Pb	44.2	3.8	53.3	12.3	65.6	19.7	26.4	6.3	2.8	2.8	17
Bi	0.5	0.3	0.9	0.4	1.1	0.6	1	0.4	0.3	0.3	0.16
Th	3.8	32.3	48.6	38.2	51	38.8	34.8	35.1	33.3	34.7	10.5
U	4.5	2.4	3.9	3.1	4.6	3.1	1.7	2.7	2.8	4.1	2.7
La	5.9	19.5	4.9	24	8.3	21.6	8	21.2	20.2	18.5	31
Ce	7.5	24	6	29.2	14.1	28.2	9.4	25.2	26.4	24.7	63
Pr	1.22	2.44	0.85	2.88	1.89	2.92	1.05	2.6	2.77	2.52	7.1
Nd	4.7	7.4	2.7	8.7	7.3	9.5	3.3	8.3	8.1	8	27
Sm	0.95	1.47	0.47	1.49	1.8	1.8	0.59	1.44	1.59	1.61	4.7
Eu	0.22	0.36	0.17	0.36	0.45	0.48	0.14	0.29	0.41	0.44	1
Gd	1.12	1.7	0.65	1.87	1.85	1.99	0.79	1.53	1.82	2.2	4
Tb	0.21	0.33	0.14	0.37	0.34	0.39	0.17	0.36	0.41	0.51	0.7
Dy	1.49	2.61	1.07	2.73	2.33	2.91	1.24	2.48	3	3.95	3.9
Ho	0.28	0.6	0.25	0.71	0.49	0.66	0.31	0.55	0.72	0.96	0.83
Er	0.87	2.04	0.84	2.19	1.48	2.21	1.1	2.19	2.52	3.38	2.3
Tm	0.13	0.35	0.15	0.4	0.23	0.39	0.2	0.39	0.46	0.58	0.3
Yb	1.05	2.69	1.17	2.91	1.67	2.83	1.35	2.83	3.34	4.35	2
Lu	0.16	0.43	0.19	0.49	0.24	0.45	0.23	0.46	0.54	0.75	0.31
ƩREE	25.8	65.92	19.55	78.3	42.47	76.33	28.07	69.82	72.28	72.45	148.1
Zr/Hf	41.19	37.13	38.82	40.54	36.96	39.25	39.4	37.82	39.29	39.5	36.41

The hard fragments within the lateritic profile (CIC, NIC, and SFH) exhibit high Fe₂O₃ content (ranging from 52.13% to 73.49%), with the highest concentrations observed in the columns (73.49% to 68.26%) and decreasing in the spherulites (52.13%), always exceeding the Fe₂O₃ content of the matrices. This variation reflects the differential distribution of hematite and goethite. Conversely, SiO₂ and Al₂O₃ values are significantly lower in the hard fragments (7.9% to 9.93% and 8.33% to 9.54%, respectively) compared to the matrices.

Although the chemical composition of the matrices within CIC, NIC, and SFH differs from that of the hard fragments, it is consistent with the composition of the topsoil. Both the matrix of the lateritic profile and the topsoil exhibit high SiO₂ contents, particularly in the topsoil (42.98%), and Al₂O₃ values (28.97% to 33.73%), reflecting the dominance of kaolinite, with limited quartz. The TiO₂ content ranges from 0.38% to 2.28%, likely representing anatase and rutile, both observed after concentration treatments as previously reported. Anatase is more concentrated in the matrix and topsoil, while rutile constitutes, on average, 18% of the heavy mineral content, equivalent to approximately 0.18% of the samples. Na₂O, K₂O, CaO, and MgO are found in concentrations ≤ 0.02%, likely leached from the profile, as expected at the top of the profile in the iron crust. K₂O may reach up to 0.03% in the topsoil, likely due to the presence of accessory mica.

The transition from the nodular crust to the spherulitic horizon is marked by significant chemical changes, including increased SiO₂, Al₂O₃, LOI, and TiO₂ contents, and decreased Fe₂O₃, which becomes more pronounced in the topsoil (Figure 7). These changes are accompanied by the loss of hematite and goethite, along with a relative enrichment in kaolinite, quartz, and anatase, indicating the decomposition of iron minerals and the corresponding enrichment in kaolinite, quartz, and anatase.

Figure 7
Vertical distribution of SiO₂, Al₂O₃, Fe₂O₃, TiO₂, and loss on ignition (LOI) contents (Wt. %) in the Abel Figueiredo lateritic profile, distinguishing the hard fragments and the evolving matrices within each horizon.

4.4.2 Trace elements

The concentrations of trace elements (Table 1) show significant variations when compared to those in the upper continental crust (UCC). Some elements are present in much higher concentrations than in the UCC, while others are lower, and a few exhibit similar values. This wide range of variations is reflected in the enrichment factor (EF), which corresponds to the ratio between the content in the investigated samples and the UCC. Based on the EF, the trace elements can be classified into four groups as follows. Group I (EF > 4): Se, V, Ag, Hg, Mo, Sb, As, Zr, Bi, Cr. Group II (2 < EF < 4): Ga, Nb, Sn, Hf, Ta, Th, Pb. Group III (1 < EF < 2): Sc, Cd, W, U. Group IV (EF < 1): Co, Ni, Cu, Zn, Y, Cs, Rb, Sr, Ba. Chemical elements highlighted in bold represent those with concentrations that vary, being either above or below the UCC levels, depending on the specific horizon.

The hard fragments (nodules and spherulites) concentrate the elements in Group I (EF > 4), which iron oxyhydroxides may have sequestered. Group II elements (2 < EF < 4) are primarily concentrated in the matrix and topsoil (including Nb, Ta, Sn, and Hf, as well as Zr), with some also concentrated in the iron crust (Ga, Pb, and Th), within the iron oxyhydroxides. Group IV elements (EF < 1), on the other hand, are more concentrated in the matrix and topsoil (mainly Rb, Sr, and Ba) than in the iron crust, except for Cu.

Most REE concentrations are below those of the UCC, except for Er and Lu, with the light rare earth elements (LREE) being much more abundant than the heavy rare earth elements (HREE). The ƩREE is higher in the matrix and topsoil, totaling 72.5 ppm, compared to 27.78 ppm in the crusts, spherulites, and nodules. This indicates REE fractionation between the matrix and topsoils: the matrix concentrates LREE, while the topsoils concentrate HREE.

5. DISCUSSION

The integrated mineralogical and textural data, along with geochemical correlations (Figures 8 –10, further discussed), confirm that the Abel Figueiredo lateritic profile belongs to the upper section of an immature lateritic profile, that is, the supergene fractionation did not evolve enough to form a bauxite horizon. This is evidenced by the absence of aluminum hydroxide minerals in the iron crust, contrasting with the aluminum-rich duricrusts covering the mature bauxite-bearing lateritic formations found across the Eastern Amazon and worldwide (Santos & Costa, 2021; Boeva et al., 2022). Thus, a bauxite horizon is not expected to occur just below the investigated profile, and it does not comprise a regional extension of the bauxite-bearing lateritic formations of Paragominas and Rondon do Pará, both located to the north of Abel Figueiredo (Kotschoubey et al., 2005; Oliveira et al., 2016; Santos & Costa, 2021).

Figure 8
Main geochemical correlations identified in the Abel Figueiredo lateritic profile and topsoil. A) SiO₂ x Fe₂O₃.B) Al₂O₃ x Fe₂O₃. C) Fe₂O₃ x V. D) Fe₂O₃ x Ga. E) Fe₂O₃ x Cr. F) Zr x TiO₂. G) Zr x TiO₂.

Figure 9
A) Distribution curve pattern of SiO₂, TiO₂, Al₂O₃, Fe₂O₃ and trace elements for matrix samples and topsoils normalized to the average of {iron crust (rocky) + spherulites + nodules}. B) Distribution patterns of REEs normalized to the chondrites of Evensen et al. (1978), showing two distinct fields: low ratio values for crust + spherulites + nodules (blue) and high for matrix + topsoil (red).

Figure 10
Chemical Index of Alteration (A) and Lateritization Index (B) of the Albel Figueiredo lateritic horizons. The hard portions of each horizon are represented in blue and the surrounding clayey matrix and the topsoil are in yellow.

The Abel Figueiredo profile likely developed from a distinct parent material than those of Paragominas and Rondon do Pará, with lower aluminum content, or experienced milder weathering conditions over a shorter duration of time, thereby inhibiting bauxite formation. In the second case, the most probable parent material is the Itapecuru Group or lateritic profiles truncated at the saprolite. Both are widespread in the regional geological maps (Figure 1). The geomorphological aspects of the region also point to distinct lateritization events. The oldest formed the mature bauxite-bearing laterites, followed by intense erosion and formation of plateaus surrounded by gently undulating lowlands (Dantas & Teixeira, 2013). Then, a younger lateritization event affected the lowlands, producing immature laterites. Depending on the truncation level (Figure 11A), these profiles can overlay saprolitic horizons or the sedimentary sequences of the Itapecuru Group (Figure 1).

Figure 11
Positioning of the Abel Figueiredo lateritic profile in the regional geomorphological context (Digital Elevation Model from - Shuttle Radar Topography Mission), highlighting the occurrence of mature laterites in plateaus and immature ones in the surrounding lowlands. Textural, mineralogical and geochemical evolution of the Abel Figueiredo lateritic profile. B) Consolidation of the nodular iron crust under humid to arid transition. C) Partial transformation of the nodular iron crust into columnar iron crust due to roots activity and development of the spherulitic horizon due to surficial reworking. D) Development of rainforest and clayey topsoil under more humic climate.

The nodular texture of the iron crust, dominated by subspherical concretions with smooth surfaces and subrounded morphology (Figure 4A), indicates cyclic dissolution and reprecipitation of ferruginous phases (e.g., Horbe & Anand, 2011). Their nucleation and cementation indicate the contribution of microbial activity. Colloidal iron oxyhydroxides, embedding the nodules along the iron crust framework (Figure 4C), also suggest partial hematite dissolution, followed by goethite precipitation, a process that requires acidic conditions, possibly provided by organic compounds produced by vegetation (e.g., Tardy, 1993; Kotschoubey et al., 2005; Costa et al., 2014).

Quartz dissolution in the iron crust (both columnar and nodular) results in cavities ranging from 0.1 mm to 0.4 mm in diameter (Figure 4B). The predominant coating of these cavities with dark brown goethite and hematite, like that from the Paragominas bauxite-bearing laterites, also supports iron cycling (e.g., Truckenbrodt et al., 1995; Boulangé & Carvalho, 1997). This process requires a humid climate with a fluctuating water table, promoting segregation and spatial reordering of ferruginous phases (Breuning-Madsen et al., 2007). The final consolidation of the iron crust indicates a transition from humid to at least semi-arid climate, conditions typically required for duricrust final consolidation (Figure 11B).

Once formed, the iron crust became the substratum of tree vegetation, whose roots have drilled it, leading to partial destruction of the top. This is evidenced by the columnar structure, in which iron crust exhibits vertical tubes, partially infilled by clayey matrix, leading to the formation of the columnar iron crust (Figure 11C). This transformation requires a gradual climate transition back from semi-arid to at least slightly humid, allowing vegetation development. Thus, the columnar structure indicates a post-lateritic weaker weathering, in which root bioturbation penetrated the crust to significant depths, facilitating water infiltration and localized mineral alteration.

In addition to the mechanical changes, vegetation activity biochemically decomposes the crust, contributing to the formation of spherulites (e.g., Delvigne, 1999; Horbe & Costa, 2005; Costa et al., 2014). This process leads to an upwards comminution of the iron crust, nodular at the bottom, then perforated by roots and finally forming loose nodules and spherulites at the top (e.g., Tardy, 1993; Horbe & Costa, 1999). In addition to the biological participation, the conversion of the columnar iron crust into loose ferruginous spherulites with silty-clay matrix in between certainly occurred in response to climatic conditions becoming more arid, favoring physical reworking (Figure 11C). The smooth wavy contact between the spherulitic horizon and topsoil represents a stone line, suggestive of paleosurface, indicating that undulating hills with open valleys (e.g., Thomas, 1974; 1994) were place to surficial running water transporting crust fragment and converting them into spherulites (in addition to the biological contribution), depositing them along with the silty-clay matrix.

The weathering transformation of the lateritic crusts and overlying spherulites into soil is the final step of supergene evolution at Abel Figueiredo, with a well-defined progression from massive to nodular crusts toward more friable, soil-like materials. In the upper portion, fragments of the crust are embedded in a clayey matrix. These fragments become progressively smaller and more rounded as they approach the surface, while the matrix increases in volume until it forms a fully developed loose soil. Both the matrix and the fragments are products of the progressive weathering of the iron crust under a tropical climate, following a pathway comparable to the transformation of parent rock into saprolite (e.g., Horbe & Costa, 1999).

For topsoil formation, iron oxyhydroxides are decomposed by plant activity (e.g., Wilson, 2004) and resistant minerals (mainly zircon) and anatase are concentrates, indicating a return to humid conditions (Figure 11D). The heavy minerals signature is additional evidence of the close affinity of the iron crust and spherulites with the clayey matrix and topsoil. This fact, together with geochemical correlations (further presented), suggests that the clay has a lateritic origin, partly derived from small amounts of kaolinite in the iron crust and from older lateritic profiles truncated at the saprolite in a higher altitude neighboring area. Additionally, quantitative studies of litterfall nutrient cycling in Amazonian ecosystems show significant recycling of elements, especially of Si within the forest system, acting as a Si source for kaolinite formation (Lucas et al., 1993). Similar evolution, with transformation of iron crusts and bauxites into topsoil was demonstrated in the Amazon (Horbe & Costa, 1997, 1999, 2005; Balan et al., 2005; Mathian et al., 2020) and in Central Africa (Beauvais & Colin, 1993; Beauvais & Tardy, 1993). The substitution of iron by aluminum in goethite during this process indicates precipitation within aluminum-rich environments, a typical characteristic of tropical weathering (Mendelovici et al., 1979; Beauvais, 1999).

The negative correlations between SiO₂ and Fe₂O₃, as well as Al₂O₃ and Fe₂O₃ (Figures 88B), are typical of wet tropical weathering. This process leads to a decrease in Fe₂O₃ and an increase in Al₂O₃ and SiO₂ content (e.g., Ojong Ashu et al., 2022), as well as the formation of kaolinite towards the top of the profile, with partial formation of new goethite, which imparts the yellow color to the topsoil (Nahon et al., 1989; Beauvais and Tardy, 1993; Lucas et al., 1993; Tardy, 1993; Horbe & Costa, 1997; Costa et al., 2014; Allard et al., 2018; Mathian et al., 2020).

The positive correlation between TiO₂ and Al₂O₃ (Figure 8C) suggests low mobility of Al and Ti, likely due to the accumulation of anatase and kaolinite, respectively (e.g., Costa et al., 2014; Santos et al., 2016). In the topsoil, kaolinite, goethite, quartz, and anatase are much more abundant, while hematite is absent. These characteristics are typical of oxisols, which are commonly formed in tropical zones and strongly influenced by the upper parts of lateritic profiles. These soils are generally depleted in most chemical elements, including macro- and micronutrients (Nahon et al., 1989; Horbe & Costa, 2005).

Iron oxyhydroxides play a significant role in retaining trace elements, as indicated by the strong positive correlation between Fe and elements such as V, Ga, and Cr (Figures 8DF). The ability of iron oxyhydroxides to incorporate these elements is well established in tropical soils and lateritic profiles (McLennan et al., 1980; Hieronymus et al., 2001; Cornell & Schwertmann, 2003). Additionally, the strong positive correlation between TiO₂ and Zr, and their strong positive correlation with REE, demonstrates that zircon is the primary REE carrier, accumulating upwards along with anatase and rutile (e.g., Santos et al., 2016).

The fixation of the silt-clayey (oxisol) latosol or topsoil cover (Figure 11D), with slight loss of kaolinite and iron oxyhydroxides (and related chemical elements), increasing quartz contents at the near surface top (SiO₂ increasing and Al₂O₃ decreasing) as well as anatase (TiO₂) and zircon (Zr) and related trace elements indicate the dominance of a deep humid tropical climate and consequent establishment of a deep rain forest. Under such conditions, kaolinite and goethite + hematite are gradually destroyed near surface but newly formed in the subsurface. This must have been established at the limit Pleistocene/Holocene (Figure 10C), intensifying more and more for modern times, with short, very dry oscillations from time to time.

This leads to the partial leaching of Fe and associated trace elements (V, Cr, Se, As, Mo, Ag, Sb, Hg, Pb, Th), the mobile, and enrichment of those linked to Ti, and Zr (Y, Nb, Ta, Hf, HREE, U, etc.), the residual, immobile (Figure 11C). The SiO₂ input to kaolinite formation comes from plant activity and its decomposition, observed in the formation of tropical soils (Lucas et al., 1993).

The processes described above are consistent with the paleoclimatic evolution of the Amazon during the Cenozoic (Costa, 1991; Horbe & Costa, 1997 and 1999; Kotschoubey et al., 2005). The Miocene was humid and covered by rain forest (Colinvaux & Oliveira, 2001), allowing lateritic weathering of Itapecuru sedimentary sequences. Pliocene was semi-arid to arid, leading to the final consolidation of the nodular iron crust. The Late Pliocene was subtropical (Latrubesse et al., 2010), and The Pleistocene was humid, compatible with the formation of the root-derived columnar structures, but with some long-term dry period involving forest retreating and savannah development, compatible with surficial reworking, that is, erosion and deposition of iron crust fragments as colluvium (Häggi et al., 2017; Zular et al., 2019). It is not possible to correlate the origin of the investigated horizons with these regional scale paleoclimatic events without consistent geochronological data. On the other hand, the studied profile notably records strong climatic oscillations, ranging from humid to arid conditions, which are consistent with the pattern observed in the Amazon

To evaluate the influence of the iron crust (hard fragments) on the chemical composition of the nodular horizon, clayey matrices, and topsoil, these components were normalized to the hard fragments (Figure 9A). The geochemical pattern od show an enrichment in SiO₂ and Al₂O₃ (attributed to kaolinite and minor amounts of quartz), TiO₂ (anatase and rutile), Zr, Y, Nb, Ta, Hf, and REE (zircon), in addition to Co, Sr, Sn, and W. The other elements (Fe₂O₃, V, Cu, Ga, As, Se, Mo, Ag, Sb, Cs, Hg, Pb, Bi, Th, and U) are more enriched in the hard fragments of the iron crust and spherulitic horizon (e.g., Ojong Ashu et al., 2022), due mainly to the abundance of iron oxyhydroxides, in accordance with the geochemical associations presented.

The chondrite-normalized REE curves differentiate two geochemical domains: the first represented by the hard fragments, which display the lowest values, and the second comprising the clayey matrices and topsoil, which exhibit higher values and are enriched in zircon and anatase, with zircon being the primary potential REE carrier (Figure 9B). The curves also indicate LREE enrichment, subtler in the hard fragments and more pronounced in the topsoil and matrices. This suggests fractionation during the transition from the hard fragments to the latter (e.g., Horbe & Costa, 1997, 1999; Kotschoubey et al., 2005; Costa et al., 2014), similar to the patterns observed by Kotschoubey et al. (2005) in lateritic bauxites of the Paragominas region.

The similar mineralogical and chemical composition, particularly in the loose nodules and spherulites, suggests that they are relics of an earlier lateritic profile, isolated by differential biochemical and mechanical grinding. The Abel Figueiredo profile maintains the elemental composition of the original crust throughout its weathered materials. Despite the evident mineralogical changes associated with the weathering process, the overall distribution of trace elements and REE remains largely unchanged from crust to soil. This chemical uniformity indicates, for ferruginous components, a greater contribution of in situ reworking of the exposed lateritic crust (because of tropical weathering) than surficial transportation.

The clay enclosure indicates exposure of the laterites to some surface reworking, introducing transported Al- and Si-bearing materials into the system, opposite to the ferruginous components, which are mostly residual. This is confirmed by the contrast in the Chemical Index of Alteration and Lateritization Index between hard fragments and clayey matrix (Figure 1010B), suggesting both materials comprise the same horizon due to a surficial reworking. Conversely, the chemical and mineralogical equivalence between the hard fragments, matrix, and topsoil, which display similar patterns of trace elements and REE, further supports the presence of products of the decomposition of the iron crust within the clayey matrix and topsoil.

6. CONCLUSIONS

The Abel Figueiredo lateritic profile provides valuable interpretations into the mineralogical, geochemical, and paleoclimatic evolution of immature lateritic systems in the western Amazon. Its transformation from columnar iron crust to nodular and spherulitic horizons, and eventually into topsoil, reflects a complex interplay of tropical weathering, bioturbation, and surface reworking. The dissolution and reprecipitation of iron oxyhydroxides, influenced by root activity, organic acids, and water table fluctuations, played a central role in this evolution, resulting in the gradual comminution of the iron crust and the formation of ferruginous nodules and spherulites.

The topsoil is the product of chemical weathering acting on lateritic crusts along with surficial reworking, bringing additional Al and Si to the system. The result is the formation of a clayey matrix and topsoil derived from transportation of lateritic profiles truncated at the clayey saprolite level, with some contribution of vegetation recycling and residual kaolinite in the iron crust. Conversely, the preservation of the heavy mineral composition, similar trace-element pattern, and REE slight fractionation between the ferruginous fragments and the clayey matrix and topsoil indicates they host components of the iron crust.

Geochemical analyses reveal two distinct domains: iron-rich crust fragments, which retain Fe₂O₃ and trace elements such as V, Cr, and Ga, and clayey matrices and topsoil, enriched in SiO₂, Al₂O₃, TiO₂, Zr, and REE. These patterns suggest a transition in element mobility and mineral stability during lateritic and post-lateritic processes, with zircon identified as the primary REE carrier. Conversely, in the clayey matrix and saprolite, an important part of the trace element pattern is attributed to the presence of goethite, which appears to retain elements released during the dissolution of hematite.

The exposition of the lateritic products to the described transformations reveals alternating humid and arid phases. Humid conditions drove intense lateritic weathering of the Itapecuru sedimentary sequences or clayey lateritic material, while semi-arid phases consolidated the nodular iron crust. Humidity enabled biological-driven weathering, forming columnar structures and spherulites, which represent the initial decomposition of the iron crust. Physical reworking and more intense development of the spherulitic horizon as stone lines is more compatible with more arid conditions, while the development of the clayey topsoil represents a return to tropical weathering conditions.

ACKNOWLEDGEMENTS

The authors thank Votorantim Metals/Nexa Resources for their support in fieldwork; the National Council for Scientific and Technological Development (CNPq) for financial support to the first author (grant numbers 305015/2016-8, 304519/2009-0, 442871/2018-0; 304967/2022-0); the Coordination for the Improvement of Higher Education Personnel (CAPES) for providing a scholarship to the second author; the National Institute of Amazonian Geosciences (GEOCIAM) for financial support (grant number 573733/2008-2); the Postgraduate Program in Geology and Geochemistry (PPGG) of the Institute of Geosciences of the Federal University of Pará (UFPA) for the analytical facilities; and the Dean of Research and Graduate Studies (PROPESP/UFPA) for financial assistance.

• ID BJGEO-2025-0022.R1.
• How to cite:
  Costa, M. L., Abreu, D. S., Santos, P. H. C., & Leite, A. S. Formation and degradation of immature laterites in response to paleoclimatic changes in the eastern Amazon. Braz. J. Geol. (2025), 56:e20250022. https://doi.org/10.1590/2317-4889e20250022
• Financial support:
  Council for Scientific and Technological Development, CNPq (grant numbers 305015/2016-8, 304519/2009-0, 442871/2018-0 and 304967/2022-0); Coordination for the Improvement of Higher Education Personnel, CAPES (grant number 573733/2008-2); Dean of Research and Graduate Studies (PROPESP/UFPA).
• Data availability statement:
  The data supporting the findings may be obtained from the authors upon request.

REFERENCES

• Albuquerque, M. F. S., Horbe, A. M. C., & Danišík, M. (2020). Episodic weathering in Southwestern Amazonia based on (U–Th)/He dating of Fe and Mn lateritic duricrust. Chemical Geology, 553, 119792. https://doi.org/10.1016/j.chemgeo.2020.119792
  » https://doi.org/10.1016/j.chemgeo.2020.119792
• Allard, T., Gautheron, C., Riffel, S. B., Balan, E., Soares, B. F., Pinna-Jamme, R., Derycke, A., Morin, G., Bueno, G. T., & Nascimento, N. (2018). Combined dating of goethites and kaolinites from ferruginous duricrusts: deciphering the Late Neogene erosion history of Central Amazonia. Chemical Geology, 479, 136-150. https://doi.org/10.1016/j.chemgeo.2018.01.004
  » https://doi.org/10.1016/j.chemgeo.2018.01.004
• Balan, E., Fritsch, E., Allard, T., Sélo, M., Falguères, C., Chabaux, F., Pierret, M.-C., & Calas, G. (2005). Formation and evolution of lateritic profiles in the middle Amazon basin: insights from radiation-induced defects in kaolinite. Geochimica et Cosmochimica Acta, 69(9), 2193-2204. https://doi.org/10.1016/j.gca.2004.10.028
  » https://doi.org/10.1016/j.gca.2004.10.028
• Bárdossy, G. (1982). Karst bauxites: bauxite deposits on carbonate rocks (Developments in Economic Geology, Vol. 14). Elsevier. 441 p.
• Bárdossy, G., & Aleva, G. J. J. (1990). Lateritic bauxites (Vol. 27). Elsevier.
• Beauvais, A. (1999). Geochemical balance of lateritization processes and climatic signatures in weathering profiles overlain by ferricretes in Central Africa. Geochimica et Cosmochimica Acta, 63(23-24), 3939-3957. https://doi.org/10.1016/S0016-7037(99)00173-8
  » https://doi.org/10.1016/S0016-7037(99)00173-8
• Beauvais, A., & Colin, F. (1993). Formation and transformation processes of iron duricrust systems in tropical humid environment. Chemical Geology, 106(1-2), 77-101. https://doi.org/10.1016/0009-2541(93)90167-H
  » https://doi.org/10.1016/0009-2541(93)90167-H
• Beauvais, A., & Tardy, Y. (1993). Degradation and dismantling of iron crust under climatic changes in Africa Central. Chemical Geology, 107(3-4), 277-288. https://doi.org/10.1016/0009-2541(93)90190-T
  » https://doi.org/10.1016/0009-2541(93)90190-T
• Boeva, N. M., Makarova, M. A., Shipilova, E. S., Slukin, A. D., Sobolev, S. V., Zhegallo, E. A., Zaitseva, L. V., & Bortnikov, N. S. (2022). Gibbsite and boehmite in weathering crusts of different ages affected by lateritization: location and formation. Doklady Earth Sciences, 504(2), 353-361. https://doi.org/10.1134/S1028334X22060046
  » https://doi.org/10.1134/S1028334X22060046
• Boulangé, B., & Carvalho, A. (1997). The bauxite of Porto de Trombetas. In A. Carvalho, B. Boulangé, A. J. Melfi & Y. Lucas (Eds.), Brazilian bauxites (pp. 55-73). USP/FAPESP/ORSTOM.
• Breuning-Madsen, H., Awadzi, T. W., Bender Koch, C., & Borggaard, O. K. (2007). Characteristics and genesis of pisolitic soil layers in a tropical moist semi-deciduous forest of Ghana. Geoderma, 141(1–2), 130-138. https://doi.org/10.1016/j.geoderma.2007.05.009
  » https://doi.org/10.1016/j.geoderma.2007.05.009
• Colinvaux, P. A., & Oliveira, P. E. (2001). Amazon plant diversity and climate through the Cenozoic. Palaeogeography, Palaeoclimatology, Palaeoecology, 166(1-2), 51-63. https://doi.org/10.1016/S0031-0182(00)00201-7
  » https://doi.org/10.1016/S0031-0182(00)00201-7
• Cornell, R. M., & Schwertmann, U. (2003). The iron oxides: structure, properties, reactions, occurrences and uses (2nd ed.). Wiley-VCH. https://doi.org/10.1002/3527602097
  » https://doi.org/10.1002/3527602097
• Costa, M. L. (1991). Aspectos geológicos dos lateritos da Amazônia. Revista Brasileira de Geociências, 21(2), 146-160. https://doi.org/10.25249/0375-7536.1991146160
  » https://doi.org/10.25249/0375-7536.1991146160
• Costa, M. L. (1997). Lateritization as a major process of ore deposit formation in the Amazon region. Exploration and Mining Geology, 6(1), 79-104.
• Costa, M. L., Moraes, E. L., & Horbe, A. M. C. (1997). Lateritização imatura sobreposta a lateritos maturos em Mãe do Rio – Pará. In M. L., Costa & R. S. Angélica (Eds.), Contribuições à geologia da Amazônia (pp. 339–357). Falangula.
• Costa, M. L., Sousa, D. J. L., & Angélica, R. S. (2009). The contribution of lateritization processes to the formation of the kaolin deposits from eastern Amazon. Journal of South American Earth Sciences, 27(2–3), 219-234. https://doi.org/10.1016/j.jsames.2008.11.008
  » https://doi.org/10.1016/j.jsames.2008.11.008
• Costa, M. L., Cruz, G. S., Almeida, H. D. F., & Poellmann, H. (2014). On the geology, mineralogy and geochemistry of the bauxite-bearing regolith in the lower Amazon basin: evidence of genetic relationships. Journal of Geochemical Exploration, 146, 58-74. https://doi.org/10.1016/j.gexplo.2014.07.021
  » https://doi.org/10.1016/j.gexplo.2014.07.021
• Costa, M. L., Leite, A. S., & Pöllmann, H. (2016). A laterite-hosted APS deposit in the Amazon region, Brazil: the physical-chemical regime and environment of formation. Journal of Geochemical Exploration, 170, 107-124. https://doi.org/10.1016/j.gexplo.2016.08.015
  » https://doi.org/10.1016/j.gexplo.2016.08.015
• Digafe, B., Getaneh, W., & Atnafu, B. (2024). Lateritization and enrichment of ferruginous protore during the peneplanation between uplifts – the case of Mekaneselam iron deposit, NW Ethiopian plateau. Geology, Ecology, and Landscapes, 9(4), 1365-1381. https://doi.org/10.1080/24749508.2024.2429207
  » https://doi.org/10.1080/24749508.2024.2429207
• Dantas, M. E., & Teixeira, S. G. (2013). Origem das paisagens. In: X. S. J. João S. G. Teixeira & D. D. F. Fonseca (eds.). Geodiversidade do Estado do Pará Companhia de Pesquisa de Recursos Minerais.
• Delvigne, J. E. (1999). Atlas of micromorphology of mineral alteration and weathering (The Canadian Mineralogist Special Publication, No. 3). Orstom Editions.
• Evensen, N. M., Hamilton, P. J., & O’nions, R. K. (1978). Rare earth abundances in chondritic meteoritic. Geochimica et Cosmochimica Acta, 42(8), 1199-1212. https://doi.org/10.1016/0016-7037(78)90114-X
  » https://doi.org/10.1016/0016-7037(78)90114-X
• Fu, W., Yang, J., Yang, M., Pang, B., Liu, X., Niu, H., & Huang, X. (2014). Mineralogical and geochemical characteristics of a serpentinite-derived laterite profile from East Sulawesi, Indonesia: implications for the lateritization process and Ni supergene enrichment in the tropical rainforest. Journal of Asian Earth Sciences, 93, 74-88. https://doi.org/10.1016/j.jseaes.2014.06.030
  » https://doi.org/10.1016/j.jseaes.2014.06.030
• Góes, A. M. (1981). Estudo sedimentológico dos sedimentos Barreiras, Ipixuna e Itapecurú, no nordeste do Pará e noroeste do Maranhão [Master’s dissertation]. Universidade Federal do Pará.
• Grubb, P. L. C. (1979). Genesis of bauxite deposits in the lower Amazon basin and Guianas coastal plain. Economic Geology and the Bulletin of the Society of Economic Geologists, 74(4), 735-750. https://doi.org/10.2113/gsecongeo.74.4.735
  » https://doi.org/10.2113/gsecongeo.74.4.735
• Gu, J., Huang, Z., Fan, H., Jin, Z., Yan, Z., & Zhang, J. (2013). Mineralogy, geochemistry, and genesis of lateritic bauxite deposits in the Wuchuan–Zheng’an–Daozhen area, Northern Guizhou Province, China. Journal of Geochemical Exploration, 130, 44-59. https://doi.org/10.1016/j.gexplo.2013.03.003
  » https://doi.org/10.1016/j.gexplo.2013.03.003
• Häggi, C., Chiessi, C. M., Merkel, M., Mulitza, S., Prange, M., Schulz, M., & Schefuß, E. (2017). Response of the Amazon rainforest to late Pleistocene climate variability. Earth and Planetary Science Letters, 479, 50-59. https://doi.org/10.1016/j.epsl.2017.09.013
  » https://doi.org/10.1016/j.epsl.2017.09.013
• Hieronymus, B., Kotschoubey, B., & Boulègue, J. (2001). Galium behaviour in some constrating lateritic profiles from Cameroon and Brazil. Journal of Geochemical Exploration, 72(2), 147-163. https://doi.org/10.1016/S0375-6742(01)00160-1
  » https://doi.org/10.1016/S0375-6742(01)00160-1
• Horbe, A. M. C., & Costa, M. L. (1997). Solos gerados a partir do intemperismo de crostas lateríticas sílico-ferruginosas. Acta Amazonica, 27(4), 241-256. https://doi.org/10.1590/1809-43921997274256
  » https://doi.org/10.1590/1809-43921997274256
• Horbe, A. M. C., & Costa, M. L. (1999). Relações genéticas entre latossolos e crostas lateríticas luminosas e alumino-ferruginosas na região de Paragominas, Pará. Revista Brasileira de Geociências, 29(4), 497-504. https://doi.org/10.25249/0375-7536.1999294497504
  » https://doi.org/10.25249/0375-7536.1999294497504
• Horbe, A. M. C., & Costa, M. L. (2005). Lateritic crust and related soils in eastern Brazilian Amazonia. Geoderma, 126(3-4), 225-239. https://doi.org/10.1016/j.geoderma.2004.09.011
  » https://doi.org/10.1016/j.geoderma.2004.09.011
• Horbe, A. M. C., & Anand, R. R. (2011). Bauxite on igneous rocks from Amazonia and Southwestern of Australia: implication for weathering process. Journal of Geochemical Exploration, 111(1-2), 1-12. https://doi.org/10.1016/j.gexplo.2011.06.003
  » https://doi.org/10.1016/j.gexplo.2011.06.003
• Kotschoubey, B., Truckenbrodt, W., & Calaf, J. M. C. (2005). Evolução geológica da porção meridional da Província Bauxitífera de Paragominas durante o Neógeno/Pleistoceno (noroeste da Bacia do Grajaú, nordeste do Pará e extremo oeste do Maranhão). Revista Brasileira de Geociências, 35(2), 263-272. https://doi.org/10.25249/0375-7536.2005352263272
  » https://doi.org/10.25249/0375-7536.2005352263272
• Kronberg, B. I., Couston, J. F., Stilianidi Filho, B., Fyfe, W. S., Nash, R. A., & Sudgen, D. (1979a). Minor elements geochemistry of the Paragominas bauxite. Economic Geology and the Bulletin of the Society of Economic Geologists, 75(8), 1869-1875. https://doi.org/10.2113/gsecongeo.74.8.1869
  » https://doi.org/10.2113/gsecongeo.74.8.1869
• Kronberg, B. I., Fyfe, W. S., Leonardos, D. H. Jr, & Santos, A. M. (1979b). The geochemistry of some Brazilian soils: element mobility during intense weathering. Chemical Geology, 24(3-4), 211-229. https://doi.org/10.1016/0009-2541(79)90124-4
  » https://doi.org/10.1016/0009-2541(79)90124-4
• Kronberg, B. I., Fyfe, W. S., Mckinnon, B. J., Couston, J. F., Stilianidi Filho, B., & Nash, R. A. (1982). Model for bauxite formation: Paragominas (Brazil). Chemical Geology, 35(3-4), 311-320. https://doi.org/10.1016/0009-2541(82)90008-0
  » https://doi.org/10.1016/0009-2541(82)90008-0
• Latrubesse, E. M., Cozzuol, M., Silva-Caminha, S. A. F., Rigsby, C. A., Absy, M. L., & Jaramillo, C. (2010). The Late Miocene paleogeography of the Amazon Basin and the evolution of the Amazon River system. Earth-Science Reviews, 99(3-4), 99-124. https://doi.org/10.1016/j.earscirev.2010.02.005
  » https://doi.org/10.1016/j.earscirev.2010.02.005
• Lucas, Y., Luizão, F. J., Chauvel, A., Rouiller, J., & Nahon, D. (1993). The relation between biological activity of the rain forest and mineral composition of soils. Science, 260(5107), 521-523. https://doi.org/10.1126/science.260.5107.521 PMid:17830432.
  » https://doi.org/10.1126/science.260.5107.521
• Lucas, Y. (1997). The bauxite of Juruti. In A. Carvalho, B. Boulangé, A. J. Melfi & Y. Lucas (Eds.), Brazilian bauxites (pp. 107–133). USP/FAPESP/ORSTOM.
• Mange, M. A., & Maurer, H. F. W. (1992). Heavy minerals in color. London: Chapman & Hall.. https://doi.org/10.1007/978-94-011-2308-2
  » https://doi.org/10.1007/978-94-011-2308-2
• Mathian, M., Bueno, G. T., Balan, E., Fritsch, E., Nascimento, N. R., Selo, M., & Allard, T. (2020). Kaolinite dating from Acrisol and Ferralsol: A new key to understanding the landscape evolution in NW Amazonia (Brazil). Geoderma, 370, 114354. https://doi.org/10.1016/j.geoderma.2020.114354
  » https://doi.org/10.1016/j.geoderma.2020.114354
• McLennan, S. M., Nance, W. B., & Taylor, R. (1980). Rare earth element-thorium correlation in sedimentary rock and the composition of the continental crust. Geochimica et Cosmochimica Acta, 44(11), 1833-1839. https://doi.org/10.1016/0016-7037(80)90232-X
  » https://doi.org/10.1016/0016-7037(80)90232-X
• Mendelovici, E., Yariv, S., & Villalba, R. (1979). Aluminum‑bearing goethite in Venezuelan laterites. Clays and Clay Minerals, 27(5), 368-372. https://doi.org/10.1346/CCMN.1979.0270507
  » https://doi.org/10.1346/CCMN.1979.0270507
• Monteiro, H. S., Vasconcelos, P. M. P., Farley, K. A., & Lopes, C. A. M. (2018). Age and evolution of diachronous erosion surfaces in the Amazon: combining (U–Th)/He and cosmogenic 3He records. Geochimica et Cosmochimica Acta, 229, 162-183. https://doi.org/10.1016/j.gca.2018.02.045
  » https://doi.org/10.1016/j.gca.2018.02.045
• Myo Nwe, H., Myat, A. K., Hla, K. M., & Khaing, M. M. (2021). Geochemical properties of laterite and lateritization processes in HPA-AN township, Kayin State. Journal of Myanmar Academy of Arts and Science, XIX(5A), 423-432.
• Nahon, D., Melfi, A., & Conte, C. N. (1989). Présence d’un viex système de cuirasses ferrugineuses latéritiques en Amazonie du Sud: as transformation in situ en Latossols sous la forêt équatoriale actuelle. C. R. Académie des Sciences, Paris, 308, 755-760.
• Negrão, L. B. A., Costa, M. L., & Poellman, H. (2018). The Belterra Clay on the bauxite deposits of Rondon do Pará, Eastern Amazon. Brazilian Journal of Geology, 48(3), 473-484. https://doi.org/10.1590/2317-4889201820180128
  » https://doi.org/10.1590/2317-4889201820180128
• Negrão, L. B. A., Poellman, H., & Alves, T. K. C. (2021). Mineralogical appraisal of bauxite overburdens from Brazil. Minerals, 11(7), 677. https://doi.org/10.3390/min11070677
  » https://doi.org/10.3390/min11070677
• Nesbitt, H. W., & Young, G. M. (1982). Early Proterozoic climates and plate motions inferred from major element chemistry of lutites. Nature, 299(5885), 715-717. https://doi.org/10.1038/299715a0
  » https://doi.org/10.1038/299715a0
• Nesbitt, H. W., & Young, G. M. (1984). Prediction of some weathering trends of plutonic and volcanic rocks based on thermodynamic and kinetic considerations. Geochimica et Cosmochimica Acta, 48(7), 1523-1534. https://doi.org/10.1016/0016-7037(84)90408-3
  » https://doi.org/10.1016/0016-7037(84)90408-3
• Ojong Ashu, E. L., Tiomo, I. F., Annoh, O. N., Tsabze, N. G., Yende, R., & Tematio, P. (2022). Paleo-lateritization and metalliferous ore formation over the metadioritic rock in the Poli group – Northern Cameroon. Journal of African Earth Sciences, 195, 104661. https://doi.org/10.1016/j.jafrearsci.2022.104661
  » https://doi.org/10.1016/j.jafrearsci.2022.104661
• Oliveira, S. B., Costa, M. L., & Prazeres Filho, H. (2016). The lateritic bauxite deposit of Rondon do Pará: A new giant deposit in the Amazon Region, northern Brazil. Economic Geology and the Bulletin of the Society of Economic Geologists, 111(5), 1277-1294. https://doi.org/10.2113/econgeo.111.5.1277
  » https://doi.org/10.2113/econgeo.111.5.1277
• Paz, J. D. S., & Rossetti, D. F. (2001). Reconstrução paleoambiental da Formação Codó (Aptiano), borda leste da Bacia do Grajaú, MA. In D. F., Rossetti A. M. Góes & W. Truckenbrodt (Eds.), O Cretáceo na Bacia de São Luís-Grajaú (pp. 77–100). Museu Paraense Emílio Goeldi.
• Price, G. D., Valdes, P. J., & Sellwood, B. W. (1997). Prediction of modern bauxite occurrence: implications for climate reconstruction. Palaeogeography, Palaeoclimatology, Palaeoecology, 131(1-2), 1-13. https://doi.org/10.1016/S0031-0182(96)00145-9
  » https://doi.org/10.1016/S0031-0182(96)00145-9
• Rossetti, D. F., & Góes, A. M. (2004). In Rossetti, D. F., Góes, A. M., & Truckenbrodt, W. (Eds.), O Neógeno na Amazônia Oriental (pp. 13–52). Belém: Museu Paraense Emílio Goeldi.
• Rudnick, R. L., & Gao, S. (2003). Composition of the continental crust. Treatise on Geochemistry, 3, 1-64. https://doi.org/10.1016/B0-08-043751-6/03016-4
  » https://doi.org/10.1016/B0-08-043751-6/03016-4
• Ruffet, G., Innocent, C., Michard, A., Féraud, G., Beauvais, A., Nahon, D., & Hamelin, B. (1996). A geochronological ⁴⁰Ar/³⁹Ar and ⁸⁷Rb/⁸⁷Sr study of K-Mn oxides from the weathering sequence of Azul, Brazil. Geochimica et Cosmochimica Acta, 60, 2219-2232. https://doi.org/10.1016/0016-7037(96)00080-4
  » https://doi.org/10.1016/0016-7037(96)00080-4
• Santos, P. H. C., Costa, M. L., & Leite, A. S. (2016). The Piriá aluminous lateritic profile: Mineralogy, geochemistry and parent rock. Brazilian Journal of Geology, 46(4), 617-636. https://doi.org/10.1590/2317-4889201620160101
  » https://doi.org/10.1590/2317-4889201620160101
• Santos, P. H. C., & Costa, M. L. (2021). Mineralogy, geochemistry and parent rock of Décio bauxite-bearing lateritic profile (Rondon do Pará, Eastern Amazon). Brazilian Journal of Geology, 51(4), 21. https://doi.org/10.1590/2317-4889202120210037
  » https://doi.org/10.1590/2317-4889202120210037
• Sayin, M., & Jackson, M. L. (1975). Anatase and Rutile determination in kaolinite deposits. Clays and Clay Minerals, 23(6), 437-443. https://doi.org/10.1346/CCMN.1975.0230605
  » https://doi.org/10.1346/CCMN.1975.0230605
• Serviço Geológico do Brasil. (2004). Geological Map of Brazil. SGB. https://rigeo.sgb.gov.br/handle/doc/2385
  » https://rigeo.sgb.gov.br/handle/doc/2385
• Silva, A. C. S., & Costa, M. L. (2020). Genesis of the “soft” iron ore at S11D Deposit, in Carajás, Amazon Region, Brazil. Brazilian Journal of Geology, 50(1), e20180128. https://doi.org/10.1590/2317-4889202020180128
  » https://doi.org/10.1590/2317-4889202020180128
• Singh, J., Sangode, S. J., Bagwan, M. F., Meshram, D. C., & Dhobale, A. (2020). Episodic ferricretization of the Deccan laterites (India): inferences from ore microscopy, mineral magnetic and XRD spectroscopic studies. Journal of Earth System Science, 129(1), 76. https://doi.org/10.1007/s12040-019-1334-z
  » https://doi.org/10.1007/s12040-019-1334-z
• Sombroek, W. G., & Camargo, M. N. (1983). Groundwater laterite and ironstone soils in Brazil, with examples from the Amazon Region. In Proceedings of the 2nd International Seminar on Lateritization Processes, 541-552.
• Tardy, Y. (1993). Pétrologie des latérites et des sols tropicaux. Masson. 459 p.
• Thomas, M. F. (1974). Tropical Geomorphology: a study of weathering and landform development in warm climates. Macmillan. 332 p.
• Thomas, M. F. (1994). Geomorphology in the tropics: a study of weathering and denudation in low latitudes. Wiley. 468 p.
• Truckenbrodt, W., & Kotschoubey, B. (1981). Argila de Belterra – cobertura terciária das bauxitas amazônicas. Revista Brasileira de Geociências, 11(3), 203-208. https://doi.org/10.25249/0375-7536.1981203208
  » https://doi.org/10.25249/0375-7536.1981203208
• Truckenbrodt, W., Kotschoubey, B., & Hieronymus, B. (1995). Aluminization: an important process in the evolution of Amazonian bauxites. Travaux ICSOBA, 22(1), 27-42.
• Vasconcelos, P. M., Renne, P. R., Brimhall, G. H., & Becker, T. A. (1994). Direct dating of weathering phenomena by 40Ar/39Ar and K-Ar analysis of supergene K-Mn oxides. Geochimica et Cosmochimica Acta, 58(6), 1635-1665. https://doi.org/10.1016/0016-7037(94)90565-7
  » https://doi.org/10.1016/0016-7037(94)90565-7
• Vasquez, M. L., Rosa-Costa, L. T., Silva, C. M. G., & Klein, E. L. (2008). Compartimentação Tectônica. In M. L. Vasquez & L. T. Rosa-Costa (Eds.), Geologia e recursos minerais do estado do Pará. Ministério de Minas e Energia/CPRM.
• Wilson, M. J. (2004). Weathering of the primary rock-forming minerals: Processes, products and rates. Clay Minerals, 39(3), 233-266. https://doi.org/10.1180/0009855043930133
  » https://doi.org/10.1180/0009855043930133
• Zular, A., Sawakuchi, A. O., Chiessi, C. M., Horta, F. M., Cruz, F. W., Demattê, J. A. M., Ribas, C. C., Hartmann, G. A., Giannini, P. C. F., & Soares, E. A. A. (2019). The role of abrupt climate change in the formation of an open vegetation enclave in northern Amazonia during the late Quaternary. Global and Planetary Change, 172, 140-149. https://doi.org/10.1016/j.gloplacha.2018.09.006
  » https://doi.org/10.1016/j.gloplacha.2018.09.006

Edited by

• SCIENTIFIC EDITOR:
  Carlos Henrique Grohmann https://orcid.org/0000-0001-5073-5572

• ASSOCIATE EDITOR:
  Claudio Riccomini https://orcid.org/0000-0002-7249-5706

Publication Dates

• Publication in this collection
  26 Jan 2026
• Date of issue
  2026

History

• Received
  19 May 2025
• Accepted
  22 Sept 2025