Late Holocene (<2500 yr B.P.) tephras bury a sequence of pre-Hispanic archaeological sites in the Tetimpa area, on the northeast flank of Popocatepetl volcano. From measured stratigraphic sections, 14 C dates, and isopach maps, this paper reconstructs the eruptive chronology and the regional extent of deposits associated with the Tetimpa archaeological sites. A regionally extensive paleosol defines the base of the late Holocene sequence in the Tetimpa area. Deposits from two periods of explosive volcanism unconformably overlie this paleosol. Eruptive sequence I was deposited at ca. 2100 yr B.P. and blanketed Late Tetimpa archaeological sites with 1-1.5 m of yellow andesitic (~62% SiO 2 ) pumice and locally with 20-40 m of olivine-bearing andesitic lavas. Isopach and isopleth maps of the pumice deposit suggest a Plinian-style eruption event that covered >240 km 2 on the east side of the volcano with >25 cm of tephra. Lavas from eruptive sequence I dammed drainage in the lowland area near the town of San Nicolas and caused local upstream deposition of as much as 30 m of lacustrine silts, clays, and sands. These lacustrine deposits record an eruptive hiatus for the Tetimpa area of about 750 14 C yr: between ca. 2100 and ca. 1350 yr B.P., no major tephras were deposited in the Tetimpa area. In upland areas, this time period is represented by an unconformity and by Entisols formed in the top of pumice deposits and lavas from eruptive sequence I. Artifacts, agricultural furrows, and dwellings record human reoccupation of this surface. At the end of this hiatus, several lahars were deposited above the lacustrine sequence and locally above the Entisol in upland positions adjacent to streams. Between ca. 1350 and ca. 1200 yr B.P., tephras from eruptive sequence II buried these paleosols, occupation sites, lacustrine sediments, and lahars. Andesitic (~62% SiO 2 ) pumice lapilli deposits in the Tetimpa area record three pumice-fall eruptions directed northeast and east of the crater. The first and smallest of these (maximum Tetimpa area thickness = 12 cm; >52 km 2 covered by >25 cm) took place at ca. 1350 yr B.P. and was accompanied by pyroclastic surge events preserved in the Tetimpa area by charcoal, sand waves, and cross-stratified sand-sized tephra. At ca. 1200 yr B.P., the products of two Plinian-style events and additional pyroclastic surges reached the Tetimpa area. The largest of these tephra-fall events covered the Tetimpa area with 0.5-1 m of tephra and blanketed an area of >230 km 2 with a thickness of >25 cm. The Tetimpa record confirms two of the four periods of explosive volcanism recognized by studies conducted around Popocatepetl in the past 30 yr. Eruptive sequence I corresponds to the explosive period between 2100 and 2500 yr B.P., and eruptive sequence II corresponds to the period between 900 and 1400 yr B.P. The archaeology and lacustrine stratigraphy of the Tetimpa area help constrain the timing of the Plinian phase of eruptive sequence I to ca. 2100 yr B.P. and suggest that the pumice-fall eruptions of eruptive sequence II took place in at least two intervals between ca. 1350 and ca. 1200 yr B.P.
|Original language||English (US)|
|Number of pages||15|
|Journal||Bulletin of the Geological Society of America|
|State||Published - Jan 1 1999|
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