Abstract Shelf deposition following lowstand delta building at the shelf edge has been documented for the northeast Gulf of Mexico between the Mississippi River and Apalachicola River deltas. Fifty-two vibracores, foraminiferal data, and bathymetry data have been used to detail the quartz-rich terrigenous clastic sediments that dominate the entire coastal to shelf depositional system. Because of low subsidence rates that characterize most of the study area, reworking and hydrodynamic winnowing occurred during repeated cycles of sea-level rise and fall in response to Pleistocene glaciation and deglaciation, producing sandy coastal-plain and continental-shelf deposits. Moreover, during the postglacial rise and present highstand in sea level, the eastern two-thirds of the shelf has been sediment starved, enabling additional reworking of the shelf sands during the passage of strong cold fronts and hurricanes, thus concentrating there a nearly uniform thickness of clean, multicyclic quartz sand known as the Mississippi–Alabama–Florida (MAFLA) shelf sand sheet. In the northeast Gulf of Mexico, variations in shelf width and morphology (e.g., shoals and shelf-edge deltas) are a function of glacio-eustatic changes in sea level, relative river discharge, size of drainage-basin area, and river location and frequency. Four surficial sediment types characterize the shelf: the MAFLA sand sheet, the St. Bernard prodelta deposit, the Chandeleur sand deposit, and outer-shelf carbonates. The MAFLA sand sheet dominates, covering about 75% of the shelf surface, and consists of a fine- to medium-grained quartz sand. Although relatively thin (3.5 to 5.5 m thick), the areal extent of the sand sheet is continuous and extensive (at least 400 km along strike; 60 km along dip), producing a sand volume of ∼ 7.2 × 10 10 m 3 . Furthermore, five major shoal complexes are located in the study area: Cape St. George shoals, Cape San Blas shoals, South Perdido shoal trend, North Perdido shoal trend, and St. Bernard shoals. The St. Bernard shoals consist of the Chandeleur sand deposit, whereas the other four formed within and consist of the MAFLA sand sheet. A composite stratigraphic column was compiled for the late Quaternary geology of the northeastern Gulf of Mexico shelf, which is up to 35 m thick and has seven depositional environments (Units 1–7) and five erosional surfaces. This composite stratigraphic column synthesizes the modern transgressive and highstand systems tracts preserved on the shelf. Unit 1 is a Pleistocene strandline deposit capped by a well-developed soil horizon, and represents the top of the last highstand and/or falling-stage systems tract. This unit is truncated by an erosional unconformity (Type 1 sequence boundary) produced when the entire shelf was subaerially exposed during the last sea-level lowstand, at about 18 ka. This unconformity was further eroded and reworked during the ensuing transgression to form a flooding surface (bay ravinement), thus creating a combined erosional surface (SB–FS). Overlying the sequence boundary is Unit 2, a fine-grained estuarine unit with occasional rip-up clasts and shell layers. The estuarine unit was planed off to form a regional transgressive surface of erosion (shoreface ravinement). Unit 3, a shelf sand sheet (MAFLA), sits on top of the transgressive surface of erosion and is dominated by fine-to-medium quartz sand up to 5.5 m thick with a distinctive shell bed and quartz pebbles at its base. The maximum flooding surface (MFS) overlies the MAFLA sand sheet and represents the boundary between the transgressive systems tract below (Units 2 and 3) and the highstand systems tract above (Units 4–7). Unit 4 is a prodelta deposit dominated by laminated silty clay that ranges in thickness from 12 to 16 m. The prodelta deposit grades upward into delta-front sediments (Unit 5) that are characterized by interlaminated silty sand and silty clay averaging 8 to 10 m thick. The delta-front unit is cut by channel-base diastems caused by the erosional scour of distributaries. Distributary sands (Unit 6) are 4 to 7 m thick and tend to be oriented shore-normal. Together, Units 4, 5, and 6 are coarsening-upward, shallow-water deltas, and represent parasequences within the modern highstand systems tract. In the western part of the study area, the shallow-water deltas overlie the MAFLA sand sheet, the result of the eastward progradation of the St. Bernard delta complex of the Mississippi River. The deltaic avulsion process (autocyclic) caused the St. Bernard delta complex to become abandoned, thus creating a local transgressive surface of erosion (parasequence boundary). The composite section is capped by a shelf sand shoal (Unit 7), which is a retrogradational parasequence up to 3.5 m thick within the modern highstand systems tract. The MAFLA sand sheet serves as an actualistic modern-day analog for shallow marine sandstones deposited under regional transgression in the ancient sedimentary record. These sandstones—commonly known as “transgressive lags” or “sheet sands”—are poorly documented with respect to sedimentary characteristics of recognition, stratigraphic framework, and reservoir architecture. This study provides additional insight to the geologic characterization of shelf sand sheets. Transgressive shelf sandstones can be significant hydrocarbon reservoirs in certain sedimentary basins of North America and elsewhere. This study offers examples that suggest that the preservation and resource potential of transgressive shelf sandstones commonly are misinterpreted in reconstructions of ancient sedimentary successions.

Abstract The Quaternary record of the Uinta Mountains of northeastern Utah has been studied extensively over the past decade, improving our understanding of the Pleistocene glacial record and fluvial system evolution in a previously understudied part of the Rocky Mountains. Glacial geomorphology throughout the Uintas has been mapped in detail and interpreted with reference to other well-studied localities in the region. In addition, studies in Browns Park and Little Hole in the northeastern part of the range have provided information about paleoflooding, canyon cutting, and integration of the Green River over the Uinta Mountain uplift. Notable contributions of these studies include (1) constraints on the timing of the local last glacial maximum in the southwestern Uintas based on cosmogenic surface exposure dating, (2) insight into the relationship between ice dynamics and bedrock structure on the northern side of the range, and (3) quantification of Quaternary incision rates along the Green River. This guide describes a circumnavigation of the Uintas, visiting particularly well-documented sites on the north and south flanks of the range and along the Green River at the eastern end.

Abstract According to C. J. Gregory (1977) , Gregory had made two unsuccessful attempts to visit parts of South America, and each time Gregory said ‘an international disaster had stopped him, so he had better not arrange a visit a third time lest some cataclysm took place’, which it did, but of a personal nature. One of his reasons for retiring early was that it freed him to depart during the austral summer, but it was not until 1932 that he was able to organize a party to explore part of Peru. The intention was to make a reconnaissance of the main Andean range and determine the age of the rocks, especially the time when they were exhumed from the Pacific, to examine the structure of parts of the Peruvian coast, the geology of the desert belt between the coast and the western front of the Andes, to visit Inca ruins and to return by one of the headwaters of the Amazon and the Amazon through Brazil to a seaport on the Amazon. However, from surviving correspondence (in the author's possession) with one of Gregory's old students, William Quarrier Kennedy (1903–1979), it is clear Gregory was also hoping to bring some samples of the Andean volcanic rocks, probably typical andesites, for Kennedy who was working on establishing the primary igneous magmas. This was an arduous undertaking for a man of 68 years, whose last previous expedition had been nine years earlier.

ABSTRACT A two-day, ~300-mile field trip follows the path of ancient Ice Age megafloods through the eastern Channeled Scabland plexus and explores abundant evidence for the last outburst floods from the late Pleistocene within the Cheney-Palouse Scabland Tract, Washington, USA. Features unique to the scablands include spectacular, headward-retreating cataract canyons; giant ripples, bars, and scour holes along with dry waterfalls; battleship-sized, streamlined loess islands; and anastomosing channel networks. Some noteworthy flood features within the Cheney-Palouse tract include a massive 530-ton, ice-rafted, granitic boulder; the hidden Cove Coulees; and a close-up inside a giant flood bar covered with giant current ripples. Also, along the route are two regions with bedrock fracture zones preferentially and spectacularly eroded by megafloods. Less common, but no less significant, is evidence for much older (>130,000 yr) exhumed, middle-to-early Pleistocene flood deposits. These are recognized by >1-m-thick, pedogenic, calcrete caps and paleosols overlying flood deposits. Some of these ancient flood deposits also have a reversed magnetic polarity of early Pleistocene age >780 ka (i.e., Matuyama Reversed Epoch). Older flood deposits like these sometimes lie deeply buried within eolian Palouse loess. Thus, it appears the growth and erosion of windblown loess hills in the Channeled Scabland also extend back to the early Pleistocene.

Abstract The submerged sill in the Strait of Messina, which is located today at a minimum depth of 81 m below sea level (bsl), represents the only land connection between Sicily and mainland Italy (and thus Europe) during the last lowstand when the sea level locally stood at about 126 m bsl. Today, the sea crossing to Sicily, although it is less than 4 km at the narrowest point, faces hazardous sea conditions, made famous by the myth of Scylla and Charybdis. Through a multidisciplinary research project, we document the timing and mode of emergence of this land connection during the last 40 kyr. The integrated analysis takes into consideration morphobathymetric and lithological data, and relative sea-level change (both isostatic and tectonic), resulting in the hypothesis that a continental land bridge lasted for at least 500 years between 21.5 and 20 cal ka BP. The emergence may have occurred over an even longer time span if one allows for seafloor erosion by marine currents that have lowered the seabed since the Last Glacial Maximum (LGM). Modelling of palaeotidal velocities shows that sea crossings when sea level was lower than present would have faced even stronger and more hazardous sea currents than today, supporting the hypothesis that earliest human entry into Sicily most probably took place on foot during the period when the sill emerged as dry land. This hypothesis is compared with an analysis of Pleistocene vertebrate faunas in Sicily and mainland Italy, including a new radiocarbon date on bone collagen of an Equus hydruntinus specimen from Grotta di San Teodoro (23–21 cal ka BP), the dispersal abilities of the various animal species involved, particularly their swimming abilities, and the Palaeolithic archaeological record, all of which support the hypothesis of a relatively late land-based colonization of Sicily by Homo sapiens .