TY - JOUR
T1 - The role of detrital composition and climate on the diagenetic evolution of continental molasses
T2 - evidence from the Cambro-Ordovician guaritas sequence, southern Brazil
AU - De Ros, Luiz F.
AU - Morad, S.
AU - Paim, Paulo S.G.
N1 - Funding Information:
L.F.D.R. and P.S.G.P. acknowledge the scholarships granted by Brazil National Council of Research, CNPq (grants 200465/92.9-GL and 204072/89.1-GL). S.M. thanks the Swedish Natural Science Research Council, NFR, for financial research support. L.F.D.R. thanks Rio Grande do Sul State Foundation for Research Support (FAPERGS), for funding field work and initial analyses, and the help from Dr. A.J.V. Garcia and the Vale dos Sinos University (Unisinos). P.S.G.P. thanks the field support of CNPq (grant 413321188-6), Companhia de Pesquisas de Recur-sos Minerais (CPRM) and Unisinos. Revisions by Drs. E.F. McBride, H. Fiichtbauer and K.A.W. Crook helped to substantially improve the manuscript. Suggestions of Dr. G.G. Zuffa were very useful. A.A.S. da Rosa and K. Goldberg were extremely helpful during initial data acquisition and organization. Thin sections were prepared at the Federal University of Rio Grande do Sul (UFRGS). We thank C. Wernstrrm for drafting the figures, I.S. AI-Aasm for the isotope analyses, C. Bick and B. Girs for photo work, and H. Harryson for aiding with the microprobe analyses.
PY - 1994/9
Y1 - 1994/9
N2 - The Cambro-Ordovician molassic Guaritas Sequence (Camaquã Basin, southern Brazil) comprises alluvial-fan and braided fluvial sandstones and conglomerates with intercalated aeolian and lacustrine-deltaic deposits and andesitic lava flows. The sediments display a complex detrital composition derived from plutonic/gneissic, acidic volcanic and low-grade metamorphic source rocks. This detrital assemblage was strongly modified by semi-arid continental near-surface diagenesis. Early cementation by hematite, smectite, quartz and calcite, and the relatively limited burial prevented strong compaction and preserved some primary macroporosity in most of the sandstones, whereas the absence of early cements and/or abundance of ductile grains promoted substantial porosity destruction by compaction and the inhibition of further diagenetic modifications. The diagenetic dissolution and replacement of volcanic rock fragments and detrital feldspars by clays and albite changed the original framework composition, as well as the tectonic provenance classification of the sandstones. Detailed quantitative petrographic study allowed the reconstruction of the original detrital compositions and the distinction of six different pathways of diagenetic evolution of the sandstones, attesting to the efficiency of this method for diagenetic modelling and provenance analyses of ancient sandstones.
AB - The Cambro-Ordovician molassic Guaritas Sequence (Camaquã Basin, southern Brazil) comprises alluvial-fan and braided fluvial sandstones and conglomerates with intercalated aeolian and lacustrine-deltaic deposits and andesitic lava flows. The sediments display a complex detrital composition derived from plutonic/gneissic, acidic volcanic and low-grade metamorphic source rocks. This detrital assemblage was strongly modified by semi-arid continental near-surface diagenesis. Early cementation by hematite, smectite, quartz and calcite, and the relatively limited burial prevented strong compaction and preserved some primary macroporosity in most of the sandstones, whereas the absence of early cements and/or abundance of ductile grains promoted substantial porosity destruction by compaction and the inhibition of further diagenetic modifications. The diagenetic dissolution and replacement of volcanic rock fragments and detrital feldspars by clays and albite changed the original framework composition, as well as the tectonic provenance classification of the sandstones. Detailed quantitative petrographic study allowed the reconstruction of the original detrital compositions and the distinction of six different pathways of diagenetic evolution of the sandstones, attesting to the efficiency of this method for diagenetic modelling and provenance analyses of ancient sandstones.
UR - http://www.scopus.com/inward/record.url?scp=0028585491&partnerID=8YFLogxK
U2 - 10.1016/0037-0738(94)90106-6
DO - 10.1016/0037-0738(94)90106-6
M3 - Article
AN - SCOPUS:0028585491
SN - 0037-0738
VL - 92
SP - 197
EP - 228
JO - Sedimentary Geology
JF - Sedimentary Geology
IS - 3-4
ER -