A proposed Laramide proto-Grand Canyon

A Karst Connection model for Grand Canyon, Arizona, USA

“…Most probably these gravels were brought down from the north during the Miocene after a regional drainage reversal (from north to south) had occurred by at least 25 Ma (Young and McKee, 1978). In the time frame of 16-6 Ma these gravels were transported southward and southeastward across the Paria Plateau and along the west side of the Kaibab arch (Hill and Ranney, 2007;Fig. 4).…”

“…Canaan Peak-type quartzite gravels were being transported from the north down the Kanab (K), Paria (P), and Escalante (E) watersheds. The gray-shaded areas represent locations where Canaan Peak-type gravels have been found Hill and Ranney, 2007). Since an ancestral Colorado River flowing west (dotted line) would have blocked the movement of Canaan Peak-type gravels southward, this implies that an ancestral Colorado River never flowed west from the Glen Canyon area in the time period of 16-6 Ma.…”

Response to Comments on the "Age and Evolution of the Grand Canyon Revealed by U-Pb Dating of Water Table–Type Speleothems"

“…Although it is true that this concept does contradict pre-early 1990s knowledge, it does not contradict more recent findings (7)(8)(9)(10)(11)(12), including a paper on the pre-Colorado River drainage in the Western Grand Canyon (5). The 16-to 6-Ma "western" canyon that we proposed is similar in both age and extent to that proposed by Young (5 (1).…”

“…One possible reason for the lack of siliciclastics that was recently offered (5) invoked a "precursor" western canyon having only 1 to 2% of the runoff of a modern Colorado River discharge, which consequently resulted in a relatively small amount of eroded sediment. Another reason could be that if a Laramide "proto" Grand Canyon did exist in the central Grand Canyon, as recently proposed (6,7), then the lack of siliciclastics in the Muddy Creek Formation could have been because the upper Paleozoic clastic units (Toroweap, Coconino, and Supai) had already been largely incised in the Laramide. Given that the incision of these units happened earlier in time, very little clastic material would have been supplied by a 16-to 6-Ma precursor canyon that followed this earlier incised paleocanyon route (7).…”

“…Another reason could be that if a Laramide "proto" Grand Canyon did exist in the central Grand Canyon, as recently proposed (6,7), then the lack of siliciclastics in the Muddy Creek Formation could have been because the upper Paleozoic clastic units (Toroweap, Coconino, and Supai) had already been largely incised in the Laramide. Given that the incision of these units happened earlier in time, very little clastic material would have been supplied by a 16-to 6-Ma precursor canyon that followed this earlier incised paleocanyon route (7). Incision in Upper Granite Gorge down to about Mississippian level by 16 Ma (6) could also explain the presence of the 11-to 6-Ma Hualapai Limestone Member of the Muddy Creek Formation: The Mississippian Redwall karst aquifer was dewatered by this incision, releasing carbonate-rich water that flowed to the mouth of the "precursor" western canyon to be deposited as the Hualapai Limestone.…”