Remnants Blocks of Pyroclastic Surge Deposits in Bambili, Cameroon Volcanic Line: New Insights into the Lithostratigraphy of Mount Bamenda
Merlin Gountié Dedzo *
Department of Life and Earth Sciences, Higher Teachers’ Training College, University of Maroua, P.O.Box 55, Maroua, Cameroon
Pierre Kamgang
Department of Earth Sciences, University of Yaoundé, P.O.Box 812, Yaoundé, Cameroon.
Emmanuel Njonfang
Laboratory of Geology, Higher Teachers’ Training College, University of Yaoundé, P.O.Box 47, Yaoundé Cameroon.
Ghislain Zangmo Tefogoum
Department of Earth Sciences, University of Maroua, P.O.Box 46, Maroua, Cameroon
David Guimolaire Nkouathio
Department of Earth Sciences, University of Dschang, P.O.Box 67, Dschang, Cameroon
Armand Kagou Dongmo
Department of Earth Sciences, University of Dschang, P.O.Box 67, Dschang, Cameroon
*Author to whom correspondence should be addressed.
Abstract
Field studies in Bambili locality (NE of Bamenda city, West-Cameroon), situated in the central part of Cameroon Volcanic Line, have recently permitted us to identifier above the welded massive lapilli tuff (mlT), remnant blocks (up to 6.5 x 11 m) of pyroclastic surge deposits. The latter are characterized by well-sorted and distinctly stratified layers with thicknesses ranging from 8 to 35 cm and showing graded bedding. The layers are matrix-supported and heterolithic, with the lithic fragments consisting of devitrified fiammes, vitrophyres, trachytic and rhyolitic cognates, granites and ignimbrites. The mineralogy of these surge deposits is quasi identical to that of the welded mlT which consists of alkali feldspar (sanidine), quartz, plagioclase, clinopyroxene, biotite and Fe-Ti oxides. The presence of these remnants blocks of pyroclastic surge deposits in the Bambili locality, emitted probably from Mt Oku vent, permit to reconsider the chronostratigraphy of the Bamenda Highlands. In fact, after a trachytic lava flow, a pyroclastic flow deposits allowed the formation of the welded ignimbrites represented by dark grey and whitish units; pulsating hydrostatic and magma pressures have subsequently produced alternating phreatomagmatic pyroclastic surges, which have afterward covered the massif, followed by basaltic flows.
Keywords: Surge deposits, welded ignimbrites, Bamenda volcano, West-Cameroon.