Publication Abstracts

Rampino 1994

Rampino, M.L., 1994: Tillites, diamictites, and ballistic ejects of large impacts. J. Geol., 102, 439-456.

The primary evidence for the temporal and spatial distrbution of glaciation prior to the Cenozoic is the occurrence of tillites. These are diamictites (poorly sorted mixtures of very coarse-grained to fine-grained sediments), and associated deposits, which have features considered diagnostic of glacial action. The discovery that many diamictite-bearing sequences were the products of debris flows and related mass flows, with contemporaneous rainout of coarse sediment, has led to the reinterpretation of many tillites as glaciomarine debris-flow deposits. Fallout of ballistic ejecta from the impact of large asteroids or comets can also create large-scale debris flows with simultaneous rainout of debris. Recent calculations of the predicted volume and distribution of impact-generated diamictites suggests that they should be common in the geologic record. Moreover, ballistic debris-flow deposits can apparently exhibit a number of features considered characteristic of glacial deposits (e.g., striated clasts, eroded and striated pavements). The possible confusion between glacial and impact diamictites–a few diamictite deposits formerly interpreted as glacial or questionably glacial in origin are already known to be impact ejecta–suggests that a review of the properties of diamictites of various origins is required. Evidence of shock deformation in diamictites is the most important criterion for determining an impact origin. It is possible that some diamictites identified as glaciogenic may actually be ejecta of large impacts, which may help to explain climatic anomalies, such as Lower Proterozoic tillites at a time of predicted global warmth, and the low-latitude distribution of some Upper Proterozoic glacial deposits.

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BibTeX Citation

  author={Rampino, M. L.},
  title={Tillites, diamictites, and ballistic ejects of large impacts},
  journal={Journal of Geology},

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RIS Citation

ID  - ra01200l
AU  - Rampino, M. L.
PY  - 1994
TI  - Tillites, diamictites, and ballistic ejects of large impacts
JA  - J. Geol.
JO  - Journal of Geology
VL  - 102
SP  - 439
EP  - 456
ER  -

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