Micromorphology of Paleosols of the Marília Formation and their Significance in the Paleoenvironmental Evolution of the Bauru Basin, Upper Cretaceous, Southeastern Brazil

Silva, Márcio Luiz da; Batezelli, Alessandro; Ladeira, Francisco Sérgio Bernardes

doi:10.1590/18069657rbcs20160287

Márcio Luiz da Silva ^** Corresponding author: E-mail: marcgeo10@yahoo.com.br

Instituto Federal de Educação, Ciência e Tecnologia do Sul de Minas, Campus Inconfidentes, Inconfidentes, Minas Gerias, Brasil.

Alessandro Batezelli

Universidade Estadual de Campinas, Departamento de Geologia e Recursos Naturais, Instituto de Geociências, Campinas, São Paulo, Brasil.

Francisco Sérgio Bernardes Ladeira

Universidade Estadual de Campinas, Departamento de Geografia, Instituto de Geociências, Campinas, São Paulo, Brasil.

* Corresponding author: E-mail: marcgeo10@yahoo.com.br

Figures (10)
Tables (4)

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Figure 1
Lithostratigraphic map and geologic section (A-B) of the Bauru Basin. The red square, circle, and triangle are the outcrop positions in the study area.

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Figure 2
Chronostratigraphic chart of the eastern portion of the Bauru Basin, based on Amaral et al. (1967) (CSN sample); Hasui and Cordani (1968) (samples AX, C-3, S-10, S-31, A-C2-4, OB-SN, SB, S-1, P, T-2, B-1); Sonoki and Garda (1988) (samples CT, CS, CCI); Machado Junior (1992) (sample CCII); Guimarães et al. (2012) and Fragoso et al. (2013) (Pterosaurs); Gobbo-Rodrigues (2001) and Dias-Brito et al. (2001) (Ostracods); Santucci and Bertini (2001) and Martinelli et al. (2011) (Allosaurus). Source: Batezelli (2015).

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Figure 3
Facies association and macromorphology of paleosol profiles. (a) Column with the lithofacies (Gc, Gt, Gm) pedofacies (P1, P2), and paleosol profiles of the Botucatu section (A1) with its horizons; (b) Column with the lithofacies (Gm), pedofacies (P3, P4, P5, P6, P7), and paleosol profiles of the Piratininga section (A2) with its horizons; and (c) Column with the lithofacies (Gm, Fm), pedofacies (P8, P9) and paleosol profiles of the Garça section (A3) with its horizons.

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Figure 4
Aspects of groundmass (gm) of paleosols with Bkm, Bt, and Btkm horizons. (a) Groundmass Bkm1 horizon (P1). Coarse material consisting predominantly of quartz (Q) in blocky format, medium sand (200-500 µm), and moderate to poor selection. Fine material mainly composed of micritic calcite (mC). Porphyric related distribution (p); (b) Idem with crossed nicols (represented by the abbreviation NC, LP, or XPL); (c) Groundmass (gm) Bt1 horizon (P5) showing close porphyric- (p) and chitonic- (q) related distributions, highlighted in crossed nicols. The coarse material consists predominantly of quartz (Q) in blocky format. The fine material consists of cement CaCO3 and clay minerals with iron oxides; (d) Idem with crossed nicols (NC, LP, or XPL). The red arrows identify granostriated and speckled b-fabric and yellow arrows identify clay coating; (e) Groundmass Btkm Horizon (P9) showing close porphyric-related distribution (p). In the groundmass, the coarse material consists predominantly of quartz (Q) in blocky format, while the fine material consists mainly of micritic calcite (mC) and clay minerals with iron oxides. Yellow arrows identify primary minerals in a physical-chemical weathering process. Iron nodule is indicated by the blue arrow; and clay coating is indicated through the green arrow; and (f) Idem with crossed nicols (XPL). Figures obtained by an optical microscope with a 2.5X objective and 100X eyepiece (250X magnification).

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Figure 5
Alteration patterns and minerals replacement. (a) Concomitant process of weathering and replacement of polycrystalline quartz by calcite (red arrow) in the Bt1 horizon (P5). Silicate replacement process by calcite (epigenesis) is very common in horizons with high CaCO3 content. The alkaline pH of these horizons causes a destabilization of quartz and its replacement by calcite, due to the opposite tendency in the solubility of silicon and carbonates as a function of the pH. In this replacement process called brecciation (indicated by the red arrow), the mineral grains are disintegrated into a series of separate fragments by the action of carbonates, but generally preserve the optical orientation of the original crystals. The quartz in the process of weathering presents a parallel linear and dotted alteration patterns with degree 3 (indicating that 75 to 97.5 % of the mineral was weathered); (b) Idem with XPL, a superimposition process of clayey material (iron oxides) on the carbonate features can be perceived with polarized light; (c) Partial alteration process with carbonate replacement in feldspar (Bk/Ck horizon – P8) (yellow arrow); feldspar shows irregular linear alteration pattern with degree 1 (indicating that 2.5 to 25 % of mineral was weathered); (d) Idem with XPL; (e) Parallel linear alteration pattern with degree 3 in biotite (B) of the Bkm1 horizon (P8) (yellow arrow); the red arrow indicates the dense discontinuous infilling feature (pedotubule), represented by the palygorskite mineral (P); Feldspar (F) is also present in the coarse material of the groundmass, as well as quartz (Q) in high proportions; and (f) Idem with XPL. Figures obtained by an optical microscope with a 10X objective and 100X eyepiece.

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Figure 6
Recrystallization process and bioturbation features in paleosol horizons. (a) CaCO3 recrystallization process in the C2 horizon (P1), resulting in a crystalline pedofeature (carbonate nodule with 1,768 µm) (yellow arrow); (b) Idem with XPL; (c) Bioturbation in the Bt1 horizon (P5), comprising a loose continuous infilling pedofeature with approximately 2,662 µm, filled with quartz grains (krotovine); (d) Idem with XPL; (e) Crystalline pedofeature, represented by the root mark (rhizolith CaCO3) in the Bk/Ck horizon (P8); and (f) Idem with XPL. Images A and B were obtained by an optical microscope with a 2.5X objective and 100X eyepiece. Images (c), (d), (e), and (f) were obtained by a binocular loupe 2X (20X magnification).

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Figure 7
(a) Typical carbonate nodule strongly impregnated and stable with approximately 781 µm (yellow arrow) in the micritic cement (mC) of the Bkm1 horizon (P8); (b) Idem with XPL; (c) Microcodium in the Bkm1 horizon (P8) (arrows); (d) Idem with XPL; (e) Replacement process and bioturbation feature in laminar Bkm1 horizon (P8); and (f) Idem with XPL. The red arrow indicates a calcified root mark, common in rhizogenic calcrete (consisting of calcite pendant, indicative moisture and high biological activity). Figures obtained by an optical microscope with a 2.5X objective and 100X eyepiece.

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Figure 8
(a) Chronology and hierarchical aspects of the Bkm horizon (P1). The hierarchy shows quartz grains (Q), microsparitic calcite (C), and palygorskite (P) at the first level, which is in the groundmass (second level). The yellow arrow indicates an altered biotite; (b) Idem with XPL; (c) Pedofeature coating in the Bt2 horizon (P5). The yellow arrow indicates a clay coating with iron oxides around the quartz grains (Q), typical autochthonous pedofeature. You can see the orientation of the illuvial process of the clay product; (d) Idem with XPL; (e) Aspect of the groundmass (hierarchy and chronology) and pedofeatures of the Btkm horizon (P9); and (f) Idem with XPL. Orange arrows show clay coatings with iron oxides (autochthonous pedofeatures), and yellow arrows show a weathered biotite. Around the biotite can be seen pedoplasmation processes with granostriated b-fabric. Figures obtained by an optical microscope with a 10X objective and 100X eyepiece.

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Figure 9
Scanning electron microscopy of the C1 horizon (P3). (a) Authigenesis of palygorskite (P), coating grains of quartz (Q) and calcite; (b) Detail of palygorskite (P) in the form of aggregates of entangled fibers coating the quartz grain (Q); (c) Formation of palygorskite (P) through the alteration of the smectite (E); palygorskite in the form of aggregate filling the voids of intertwined fibers can be observed, a typical feature of paleosols (Singer, 2002); and (d) Detail of fibrous aggregate with woven wire and with some guidance from palygorskite.

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Figure 10
(a) Pisolite showing concentric rings of iron-containing materials (Bt1 horizon - P5), with natural light (represented by the abbreviation LN or PPL). The yellow arrow also shows clay with iron oxides coating the pisolite. You can see the presence of chitonic/enaulic-related distribution (partially evidenced by the yellow arrow); (b) Idem with XPL; (c) Calcite pendant (pending calcite) in the Btkm horizon (P9), below the quartz grains (Q), indicated by the red arrow. The layers are pending calcite between the quartz grains (Q) and in the upper left portion, a porosity channel (v) can be seen; (d) Idem with XPL; (e) Cytomorphic Calcite (CYC) in the Btkm horizon (P9), indicated by the yellow arrow. The red arrow identifies a biotite, with little change; and (f) The decalcification zone, highlighted with crossed nicols, around the root channel filled by cytomorphic calcite (CYC) can be observed. Figures (a), (b), (e) and (f) obtained by an optical microscope with a 10X objective and 100X eyepiece (1000 times magnification). Figures (c) and (d) were obtained with an objective of 2.5X.

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Table 1
Morphological properties of the paleosols in the Botucatu Section (A1)

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Table 2
Morphological properties of the paleosols in the Piratininga Section (A2)

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Table 3
Morphological properties of the paleosols in the Garça Section (A3)

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Table 4
Synthesis of the fabric of the Bkm, Btkm, and Bt horizons of paleosols of the Marília Formation

Profile and horizon	Depth	EST	Texture	Colors	B	Nodules	RHCl	TRS
	m
P1Bkm1	0.00-0.42	EB	Sandy (poorly selected)	10YR 8/1, 2.5YR 5/6, 2.5YR 6/6	A	Clasts clay	Reactive	Smooth and clear
P1Bkm2	0.42-0.81	EB	Sandy (poorly selected)	10YR 8/1, 2.5YR 3/6, 2.5YR 5/8	A	Clasts clay	Strongly reactive	Smooth and gradual
P1C1	0.81-1.56	M	Sandy	10YR 8/1, 2.5YR 5/6	R	Carbonate, clay and quartz clasts	Strongly reactive	Smooth and abrupt
P1C2	1.56-2.78	M	Sandy (poorly selected)	10YR 8/1, 5YR 4/6, 5Y 8/6	R	Carbonate, clay and quartz clasts	Reactive	-
P2C1	0.00-2.65	M	Sandy (poorly selected)	5YR 7/4, 10YR 7/8, 10YR 8/1	A	-	Reactive	Smooth and abrupt
P2C2	2.65-3.04	M	Sandy (poorly selected)	10YR 8/1, 10R 3/6, 7.5YR 7/8, 5Y 2.5/1	R	-	Reactive	-

Profile and horizon	Depth	EST	Texture	Colors	B	Nodules	RHCl	TRS
	m
P3C	0.00-4.50	M	Very fine sand to fine (BS)	5YR 7/4, 5YR 6/8, 2.5YR 4/8, 10YR 8/1	A	Sandy clasts with oxide films, nodule CaCO₃	RSR	-
P4-1C	2.30-2.90	M	Fine sandy bar to the average (MS)	5YR 7/4, 10YR 8/1	C	Clasts of quartz and clay	LRN	SC
P4-2C	2.90-3.50	M	Fine sandy bar to the average (MS)	5YR 8/3, 10YR 8/1, 2.5YR 5/8	C	Few clay clasts	NR	AS
P4-3C	3.50-4.50	M	Fine sandy bar to the average (MS)	5YR 8/3, 10YR 8/1, 5YR 7/6	C	Few clay clasts	NR	AS
P4-4C	4.50-4.90	M	Fine sandy bar to the average (MS)	5YR 8/3, 10YR 8/1, 5YR 7/6	C	Clay clasts	NR	AS
P4-5C	4.90-5.67	M	Fine sandy bar to the average (MS)	5YR 7/4, 2.5YR 4/8, 10YR 8/1	C	Clay clasts	NR	AS
P4-6C	5.67-6.64	M	Fine to coarse sand (SM)	5YR 8/3, 10YR 8/1, 5YR 7/6, 5YR 4/6	A	Carbonate, few clay clasts	R	SC
P4Bt1	6.64-7.42	P	Fine to medium sand (SMB)	5YR 7/4, 5YR 5/8, 10YR 8/1	CP	Clay clasts and carbonate nodules	R	SG
P5C1	0.00-3.20	M	Fine to medium sand (SMB)	5YR 7/4, 2.5YR 4/8, 10YR 8/1	A	Few clay clasts	R	SG
P5Bt1	3.20-3.56	PB	Fine to coarse sand (SM)	5YR 7/4, 2.5YR 5/8, 10YR 8/1	A	Few clay clasts	LR	SG
P5Bt2	3.56-4.18	PB	Fine to coarse sand (SM)	5YR 7/4, 2.5YR 6/8, 10YR 8/1	A	Clay nodules	RSR	SG
P5Btc	4.18-4.59	PM	Fine to coarse sand (SM)	5YR 7/4, 10YR 8/1	A	Few clay clasts	R	-
P6C1	0.00-1.19	M	Medium sand (SM)	5YR 7/4, 5YR 6/8, 10YR 8/1	A	Few clay clasts	LR	-
P7C1	0.00-0.28	M	Fine to medium sand (SMB)	5YR 6/6, 5YR 5/6, 2.5YR 4/8, 10R 6/4, 10YR 8/1	C	Few clay clasts	LR	AS
P7Btkm1	0.28-0.72	P	Fine to coarse sand (SM)	5YR 7/4, 2.5YR 5/6, 10YR 8/1	A	Abundant carbonate, clay clasts	R	SC
P7Btkmc	0.72-1.35	PM	Fine to coarse sand (SM)	5YR 7/4, 5YR 8/4, 2.5YR 6/8, 10YR 8/1	F	Abundant carbonate, clay clasts	RSR	-

Profile and horizon	Depth	EST	Texture	Color	B	Nodule	RHCl	TRS
	m
P8C1	0.72-2.72	Massive	Medium to coarse sand (poor selection)	5YR 7/4, 10YR 8/1, 2YR 7/6	Common	Sparse	Little reactive	AS
P8Bkm1	3.10-3.75	Laminar	Fine sand (moderate selection)	2.5YR 8/1, 2.5YR 7/4	Abundant	Abundant carbonate, few clay clasts	Reactive to strongly reactive	WC
P8Bkm2	3.75-4.36	Laminar	Fine sand (moderate selection)	10YR 5/4, 2.5YR 7/4, 10YR 8/1, 10YR 7/8	Abundant	Common carbonate, few clay clasts	Reactive	SC
P8Bk/Ck	4.36-4.63	Laminar tending to massive	Fine sand (moderate selection)	2.5YR 4/8, 5YR 7/4, 10YR 8/1	Rare	Few carbonate	Reactive	AS
P8Ckm1	4.63-5.31	Massive	-	-	Rare	-	-	AS
P9C1	0.00-1.18	Massive	Fine to coarse sand (poor selection)	5YR 7/3, 10YR 8/1, 2YR 7/6	Common	Rare carbonate, few clay clasts	Reactive	AS
P9Btkm	1.29-1.82	Prismatic	Fine sand (moderate selection)	5 YR 4/6, 5YR 7/4, 5YR 7/1, 7.5YR 8/6	Abundant	Few carbonate, scarce clay clasts	Reactive to strongly reactive	SC
P9Btkm/C	1.82-2.27	Prismatic tending to massive	Fine to medium sand (moderate selection)	5 YR 4/6, 5YR 7/4, 5YR 7/1, 7.5YR 8/6	Rare	-	Reactive	AS

Profile and horizon	Coarse material		Fine material		c/f-Related Distribution	GR	Pedofeature	Pedality

	Composition	Selection	Composition	FB
P1Bkm	Qt (md), NF, Cal, Fel	MP	CC (d), MAOF	Ct	PA-Q-F	AA	HtgCe, PDCR, NTS	PBMDPA
P1Bkm2	Qt (md), PNF, Cal, Fel	MP	CC (d), MAOF	Ct	PA-Q	AA	HtgCe, PDCR, NTS	PBMFDAP
P4Bt1	Qt (md), PNF, FM	MB	CC, FMAOF	Gt, Pt, Me	PF-Q-E	ArA	RA, PDCR, NTS, PD	PPPFPA
P5Bt	Qt (md), PNF, Fel	MB	CC, FMAOF	Gt, Pt	PF-Q	AA	RA, PDCR, NTS, PD	PCMP
P5Bt2	Qt (md), PNF, Fel	M	CC, FMAOF	Gt, Pt	PF-Q	AA	RA, PDCR, NTS, PD	PCFP
P5Btc	Qt (md), PNF, Fel	M	CC, MAOF	Gt, Pt	PF-Q	ArA	RA, PDCR, NTS, PD	PCFP
P7Btkm1	Qt (md), PNF, Fel	M	CC (d), FMAOF	Gt	PF-Q	AA	RA, PDCR, NTS, HtgCe	PPPFPA
P7Btkmc	Qt (md), PNF, Fel, PB	M	CC (d), MAOF	Gt, Ct, Me, Sg	PF-Q	ArA	RA, PDCR, NTS, HtgCe	PCFP
P8Bkm1	Qt (md), PNF, Cal, Fel	M	CC (d), MAOF	Ct	PA	AA	HtgCe, PDCR, NTS	PLMFP
P8Bkm2	Qt (md), PNF, Cal, Fel	M	CC (d), MAOF	Ct	PA	AA	HtgCe, PDCR, NTS	PLMFP
P8Bkm/Ckm	Qt (md), PNF, Cal, Fel	M	CC (d), MAOF	Ct	PF-Q	AA	HtgCe, PDCR, NTS	PLFP
P9Btkm	Qt (md), NF, Cal, Fel, PB	M	CC (d), FMAOF	Pt, Gt, Sg	PF-Q-E	AA	RA, PDCR, NTS, HtgCe	PPMP
P9Btkm/C	Qt (md), PNF, Cal, Fel, PB	M	CC (d), MAOF	Ct, Pt, Gt, Sg	PF-E-Q	ArA	RA, PDCR, NTS, HtgCe	PPMP

[1] * Corresponding author: E-mail: marcgeo10@yahoo.com.br

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Micromorphology of Paleosols of the Marília Formation and their Significance in the Paleoenvironmental Evolution of the Bauru Basin, Upper Cretaceous, Southeastern Brazil

ABSTRACT