Can conglomerate and a limestone be found in contact in the rock record?

Would it be likely that a conglomerate and a limestone be found in contact in the rock record?


Yes, it is likely for conglomerate and limestone to be found in contact but this does not occur more often.  Conglomerate are in most cases terrestrial such that, it is deposited in high flowing and swiftly streams, nearshore water bodies with strong water waves or places with alluvial fan. Limestone on the other hand are found in shallow water regions to deeper water regions of average to high energy environments. (Gautam, 299-310) This shows that the two can come in contact in the shallow water environments where the two rocks exist.  Conglomerate would be deposited a little closer off shore than limestone. However, in some cases limestone can also be found in nearshore marine environments where conglomerate is also deposited.

According to Lees, Alan, and Feely, one of the factors that makes the two not to be found in contact more often is, the fine detritus from the active river depositing conglomerate at the shoreline can kill off the reefal components that mainly comprises limestone.  However, limestone formation occurs in many ways, one of them is evaporation thus this does not rule out completely conglomerate and limestone coming in contact (1-25).

Environments where conglomerate and limestone are in contact have been identified by geologists. One of these environments is St. Lawrence valley Ordivician. The conglomerate in this environment are thought to have been caused by tsunami depositions in the region and contain carbonates. They are deposits caused by debris flow.

Although the two rocks are composed of distinct components, they can transform together. This can occur through metamorphism or weathering with the aid of high pressure and high temperatures.  Limestone does not undergo metamorphism while conglomerate does not undergo weathering.


Works cited

Lees, Alan, and Martin Feely. “The Connemara Eastern Boundary Fault: A review and assessment using new evidence.” Irish Journal of Earth Sciences 34 (2016): 1-25.

Sen, Gautam. “Sedimentary Rocks.” Petrology. Springer Berlin Heidelberg, 2014. 299-310.