The initial peopling of the Americas is a contested and evolving topic 1 , with the exact timing of the first arrivals still unknown. Historically, Mexico's understudied and controversial archaeological record has remained on the periphery of First Americans research 2 . However, in recent years, investigations have shown reliable evidence of a late-Pleistocene and early-Holocene human presence in the northwest region 3,4 , the Chiapas Highlands 5 , Central Mexico 6 , and the Caribbean coast [7][8][9] . Evidence of human presence at Chiquihuite Cave extends this antiquity and attests to the cultural variability of older-than-Clovis sites [10][11][12][13][14][15][16][17] and the earliest humans on the continent. Site settings and excavation context.

A new geological map at 1:50,000 scale of La Reforma Caldera Complex has been produced applying modern survey methodologies to volcanic areas. This map aims to represent a reliable and objective tool to understand the geological evolution of the region. La Reforma Caldera Complex is a Pleistocene nested caldera located in the central part of the Baja California peninsula, Mexico. The twelve formations defined within the Quaternary volcanic record were grouped into three phases (pre-caldera, caldera, and post-caldera). The pre-caldera phase (>1.35 Ma) is characterized by scattered eruptions, mostly occurred in submarine environment. The caldera phase (1.35-0.96 Ma) groups several distinct explosive and effusive eruptions that formed the present-day caldera depression. The post caldera phase includes scattered effusive eruptions (ended at 0.28 Ma) and resurgence, characterized by several hundred meters of uplift of the central block within the caldera depression.

No abstract

No abstract

The Joya Honda maar (JHm) is located in central Mexico, 35 km NNE of the city of San Luis Potosí. It lies in the Plio-Quaternary alkaline Ventura-Espíritu Santo Volcanic Field located in the eastern part of Mesa Central province. The JHm eruption occurred at 311±19 ka (40Ar/39Ar) along a fissure that formed an elliptical crater (c. 1.3×0.9 km wide and c. 270 m deep) with a major axis oriented to the ENE–WSW. The eruption generated pyroclastic surge deposits that preferentially extended up to a distance of 7 km to the NW–NE of the crater, with a very limited distribution to the south. At the crater rim, the sequence is 60–80 m thick on the NE–NW wall and 1–15 m thick on the south–SW rim. The JHm sequence is divided into five units with different structures, textures, granulometry and components. The juvenile basanite clasts of these units display differences in vesicularity, density and morphology under scanning electron microscopy. These units correspond to the same number of eruptive phases as follows: Phase 1 occurred as a series of alternating strombolian and phreatomagmatic explosions that dispersed fall deposits and base surges; Phase 2 began with strombolian activity that emplaced basanite scoria with low contents of mantle xenoliths; Phase 3 continued with phreatomagmatic explosions that emplaced wet and dry pyroclastic surges; Phase 4 generated strombolian explosions rich in mantle xenoliths; and Phase 5 produced a violent strombolian phase that dispersed fallouts rich in mantle xenoliths and intermixed with discrete phreatomagmatic explosions that emplaced pyroclastic surges. These eruptive fluctuations during the genesis of JHm are a response to the relative proportions of magma–water interaction through time and complex faulting of the calcareous rocks underneath the volcano. The distribution and textural characteristics of the deposits suggest that simultaneous or alternating vents were active during the eruption, possibly following a fissure. These variations may have been subordinated to factors such as the availability of groundwater, the velocity of magma ascent, the discharge rate and degassing.

No abstract

Parícutin in western Mexico is considered one of the most studied monogenetic volcanoes worldwide. The volcano began its formation in the middle of a cornfield in February 1943 and lasted until March 1952. Descriptions of the eruption documented the remobilization of unconsolidated primary ashfall by rainfall and wind in minor proportions. Despite these descriptions, the resulting reworked deposits have not yet been described in stratigraphic sequence. We present the first stratigraphic study of interfingered primary pyroclastic and reworked deposits of Parícutin's succession. We identify 13 units, of which seven correspond to reworked deposits dispersed around the volcano. These deposits display sedimentary structures produced by tephra remobilization due to lahars and stream flows. In addition, some layers display dunes and ripples generated by dust storms. By using GIS tools, we integrated the existing data with our new composite stratigraphic column, the distribution map of the syn-eruptive reworked deposits and a new isopach map. This new evaluation reveals that more than 70% of the total thicknesses around the volcano correspond to syn-eruptive reworked deposits (R1-R4 units). Therefore, previous studies had overestimated the distribution of primary tephra from the Parícutin explosive phases.The lowest and flattest areas with wide rill networks, which are located 4-6 km north of the volcano, are composed of up to 90% reworked deposits. In contrast, proximal locations with gentler slopes located at medium altitudes better preserve pyroclastic deposits. This study brings new light to understanding the sedimentary processes that occur during volcanic eruptions and highlights the importance of recognizing pyroclastic and reworked deposits during monogenetic eruptions.

No abstract