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Reconstruct sedimentation rate and time from downhole logging data at Lake Chalco, Central México

Understanding the evolution of lower latitude climate from the most recent glacial periods to post-glacial warmth in the continental tropical regions has been obstructed by a lack of continuous geological records. Here we present results from a lacustrine record from tropical North America. Specifically, we examine sediments from Lake Chalco, located in the Valley of Mexico, central Mexico (19°30’N, 99°W). The basin represents a hydrological closed system surrounded by the Trans-Mexican Volcanic Belt aging from the Oligocene to the present. We used borehole logging data to conduct a cyclostratigraphic analysis of the Lake Chalco sediments. More than 400 m were logged for several geophysical properties including magnetic susceptibility and spectral gamma radiation (SGR). SGR is a particularly useful tool as it is non-destructive, fast, affordable, and applicable even in cased boreholes. Among the lake deposit of the Chalco sub-basin, 388 total tephra layers (≥1 mm in thickness) were reported from the core description. Tephra layers with specific gamma-ray signatures present a challenge for extracting the primary signals caused by climatic agents. We propose a protocol to identify tephra layers embedded in other sediments using high-resolution SGR. After extracting the non-volcanic primary signal, we applied a suite of evolutive cyclostratigraphic methods to the Lake Chalco downhole logging data, with a focus on gamma-ray. The high-resolution gamma-ray results suggest that the Lake Chalco sediments contain several rhythmic cycles with a quasi-cyclic pattern comparable with Pleistocene climate evolution, allowing to calculate of a ~500-kyr time span for the Lake Chalco sediment deposition.

Details

Author
Mehrdad Sardar Abadi, Christian Zeeden, Thomas Wonik
Institutionen
Leibniz Institute for applied Geophysics, Germany
Veranstaltung
GeoKarlsruhe 2021
Datum
2021
DOI
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