Dissolution pipes in northern Puerto Rico: An exhumed paleokarst

Abstract

Late Quaternary pipe-or wen-like paleokarst features are being exhumed and modified by modem coastal processes along the north-western and northern coasts of Puerto Rico. These features are cigar-shaped tubes dissolved into host rock, with depths up to 4 rn, and widths of -0.5 m. They can be so densely packed that much of the original deposit has been removed. Most contain evidence of a few millimeters thick calcrete lining, consisting of micrite laminae, and a zone of indurated rock up to several centimeters thick of micrite and microspar. Many pipes are filled with insoluble material similar in appearance to the insolubles of the host rock but more concentrated, and augmented by material which resembles terra-rossa, At one site the pipes have retained this primary fill material, now somewhat cemented.At the other site the primary fill material, probably sand rather than rerra-rossa, was completely removed, the pipes re-filled with marine debris and the whole complex cemented. Some pipes show more than one cycle of filling, emptying and re-filling, and some areas show more than one phase of pipe formation.The pipes formed in the vadose zone, in poorly lithified, coarse-grained, Late Quaternary sandy limestones, by dissolution and reprecipitation along focused flow paths in a climatic regime with rain and strong evaporation. They may have formed within a few thousand years of host rock emplacement.

PRESERVATION OF TRACE FOSSILS AND MOLDS OF TERRESTRIAL BIOTA BY INTENSE STORMS IN MID-LAST INTERGLACIAL (MIS 5c) DUNES ON BERMUDA, WITH A MODEL FOR DEVELOPMENT OF HYDROLOGICAL CONDUITS

“…Are conduits formed over hundreds of thousands of years by dissolution and diagenesis of limestone forming a solution pipe, or are they formed instantaneously (geologically) by molding and subsequent casting of vertical tree trunks? We emphasize that our conduit model above differs significantly in both fundamental process and time scale from the pedogenic evolution of solution pipes that develop in such aging limestone (see discussion in Herwitz, 1993;Lundberg and Taggart, 1995) as the Big Red Soil (BRS) in the early Pleistocene Walsingham Formation of Bermuda (Hearty, 2002) (Fig. 10B), which clearly is not a fossilized relict of a buried forest.…”

“…filled with soils, rhizoliths, and eventually terra rossa soils (Lundberg and Taggart, 1995;Grimes, 2009). This process might be described as top-down conduit formation because the development of the pipes enlarge from the surface downward, perhaps initially guided by hydrologic stemflow from plants.…”

Pinnacle Syngenetic Karst in Nambung National Park, Western Australia

“…Vertical tubes could have formed around a bigger plant-root (Lundberg & Taggart 1995), which, because of mechanical pushing and chemical dissolving of the sediment, triggered a focused water ow and therefore the solution of a vertical tube. e same process was suggested by Alonso -Zarza et al (2008), who interpreted certain vertical tube-like structures with cemented rims on Canary Island as "megarhizoliths", because they appear to be the remains of roots.…”

“…e same process was suggested by Alonso -Zarza et al (2008), who interpreted certain vertical tube-like structures with cemented rims on Canary Island as "megarhizoliths", because they appear to be the remains of roots. In addition to plantroots, focused water ow could also be concentrated by the upper parts of the plants (stem ow, see Lundberg & Taggart 1995), or it could just be focused beneath surface hollows in an exposed calcrete (Lundberg & Taggart 1995) or through porous patches in a developing calcrete (Grimes 2004, in prep.). Hearty and O'Leary (2008) suggested that the formation of the vertical tubes in e Pinnacles area resulted from burial of trunks of a former generation of trees, which grew on an older dune.…”

On the formation of dissolution pipes in Quaternary coastal calcareous arenites in Mediterranean settings

“…The wide set of vertical cone-shaped pipes found in these coastal areas can be defi ned as dissolution pipes (Lundberg and Taggart, 1995). These have been reported from many areas in the world and in different climatic and geomorphological settings: continental peri-glacial areas in Poland (Harasimiuk et al, 1975;Morawiecka and Walsh, 1997;Walsh and Morawiecka-Zacharz, 2001), temperate cold areas on the Belgian-Dutch border (Willems et al, 2007), arid continental areas such as Morocco (Castellani and Dragoni, 1983), coastal areas in temperate climate such as in England (Falcon, 1929;West, 1973;Ford, 1984;Morawiecka, 1993) but essentially from coastal areas in tropical or subtropical climate (Fairbridge, 1950;Jennings, 1968;Coetzee, 1975;Prasad, 1983;Herwitz, 1993;Pace et al, 1993;Herwitz and Muhs, 1995;Lundberg and Taggart, 1995;Mylroie et al, 1995;Grimes, 2002). In the Mediterranean area dissolution pipes have been reported from the coasts of Syria, Lebanon and Palestina (Day, 1928), while in Italy similar landforms have been investigated in Plio-Pleistocene calcareous arenites along the coasts of Apulia (Rudnicki, 1980;Delle Rose and Parise, 2003;Marsico et al, 2003) and in Sardinia (De Waele et al, 2009).…”