Steven L. Forman

Groundwater sapping as the cause of irreversible desertification of Hunshandake Sandy Lands, Inner Mongolia, northern China

Significance In contrast to earlier assertions that deserts in northern China are 106 years old, our multidisciplinary investigation in the Hunshandake Sandy Lands, located in the eastern portion of China’s desert belt, shows that this desert is ca. 4,000 years old. This study documents dramatic environmental and landscape changes in this desert during the last 10,000 years. For the first time to our knowledge we present a case of desertification mainly triggered by changes in the hydrological and geomorphological system, associated with climate change at ca. 4.2 ka. Our research on the human–environment interactions in the Hunshandake suggests Chinese civilization may be rooted in the marginal areas in the north, rather than in the middle reaches of the Yellow River. In the middle-to-late Holocene, Earth’s monsoonal regions experienced catastrophic precipitation decreases that produced green to desert state shifts. Resulting hydrologic regime change negatively impacted water availability and Neolithic cultures. Whereas mid-Holocene drying is commonly attributed to slow insolation reduction and subsequent nonlinear vegetation–atmosphere feedbacks that produce threshold conditions, evidence of trigger events initiating state switching has remained elusive. Here we document a threshold event ca. 4,200 years ago in the Hunshandake Sandy Lands of Inner Mongolia, northern China, associated with groundwater capture by the Xilamulun River. This process initiated a sudden and irreversible region-wide hydrologic event that exacerbated the desertification of the Hunshandake, resulting in post-Humid Period mass migration of northern China’s Neolithic cultures. The Hunshandake remains arid and is unlikely, even with massive rehabilitation efforts, to revert back to green conditions.

EPISODIC EOLIAN SAND DEPOSITION IN THE PAST 4000 YEARS IN CAPE COD NATIONAL SEASHORE, MASSACHUSETTS, USA IN RESPONSE TO POSSIBLE HURRICANE/STORM AND ANTHROPOGENIC DISTURBANCES

The eolian sand depositional record for a dune field within Cape Cod National Seashore, Massachusetts is posit as a sensitive indicator of environmental disturbances in the late Holocene from a combination of factors such as hurricane/storm and forest fire occurrence, and anthropogenic activity. Stratigraphic and sedimentologic observations, particularly the burial of spodosol-like soils, and associated 14C and OSL ages that are concordant indicate at least six eolian depositional events at ca. 3750, 2500, 1800, 960, 430 and <250 years ago. The two oldest events are documented at just one locality and thus, the pervasiveness of this eolian activity is unknown. However, the four younger events are identified in three or more sites and show evidence for dune migration and sand sheet accretion. The timing of eolian deposition, particularly the initiation age, corresponds to documented periods of increased storminess/hurricane activity in the North Atlantic Ocean at ca. 2.0 to 1.6, and 1.0 ka and also a wetter coastal climate, which suppressed the occurrence of forest fire. Thus, local droughts are not associated with periods of dune movement in this mesic environment. Latest eolian activity on outer Cape Cod commenced in the past 300 to 500 years and may reflect multiple factors including broad-scale landscape disturbance with European colonization, an increased incidence of forest fires and heightened storminess. Eolian systems of Cape Cod appear to be sensitive to landscape disturbance and prior to European settlement may reflect predominantly hurricane/storm disturbance, despite generally mesic conditions in past 4 ka.

Contesting early archaeology in California

The peopling of the Americas is a topic of ongoing scientific interest and rigorous debate1,2. Holen et al.3 add to these discussions with their recent report of a 130,000-year-old archaeological site in southern California, USA: the Cerutti Mastodon (CM) site, which includes the fragmentary remains of a single mastodon (Mammut americanum), spatially associated stone cobbles, and associated lithic debris that they claim indicates prehistoric hominin activity. In sharp contrast, we contend that the CM record is more parsimoniously explained as the result of common geological and taphonomic processes, and does not indicate prehistoric hominin involvement. Whereas further investigations may yet identify unambiguous evidence of hominins in California around 130,000 years ago, we urge caution in interpreting the current record. There is a Reply to this Comment by Holen, S. R. et al. Nature 554, http://dx.doi.org/10.1038/nature25166 (2018). Holen et al.3 claim prehistoric hominin involvement at the CM site based primarily on four lines of evidence: a reliable radiometric age; the presence of stone artefacts; clear evidence of tool-imparted percussion damage to the remains of the mastodon; and an undisturbed geological context. We take no issue with the published age for the site, but we believe that the latter three claims warrant further examination. The CM site stone artefacts are an assortment of cobbles and fractured cobble fragments excavated from a sandy silt matrix. There is no evidence of formal stone tool forms or diagnostic lithic microor macro-debitage. Instead, the CM site artefacts are identified by their proximity to the remains of the mastodon and their large size relative to the enveloping sediment. Additionally, surface features such as the presence of pitting and scratching on cobble surfaces, the presence of several cobble fragments with fracture morphologies reminiscent of hammerstone and/or anvil usage, and the presence of several refitting cobble fragments are interpreted as evidence of hominin percussive activities on-site. The lack of discarded formal tools and diagnostic lithic debitage is noteworthy, and is unusual relative to most archaeological assemblages that purport hominin processing of proboscidean remains (although see Haynes4). We also note that upslope of the site there are numerous alluvial fans, with clastic material a common occurrence. The cobbles and pebbles at the CM site can be derived from modest alluvial fan input with fines subsequently winnowed with lower energy fluvial erosion. Crucially, none of the criteria that Holen et al.3 use to define stone artefacts either requires prehistoric hominin involvement or meets the accepted criteria for falsifying natural ‘geofacts’5. The range of possible geological interpretations for the lithic assemblage highlights the critical issue of equifinality, in which an end product such as a shattered cobble may be generated via many and potentially unrelated means. It is a principle that applies to the bone record as well. We contend that Holen et al.3 presented equivocal evidence in support of tool-imparted percussion damage to the remains of the mastodon. The critical observations are of spiral fractures, cone flakes, impact flakes, bulbs of percussion, impact notches, negative flake scars, anvil-polished specimens, percussion-fractured specimens, and refitting specimens. These bone damage features are inferred to implicate sole agency by prehistoric hominins. As with the stone artefact record, issues of equifinality must first be addressed, including the question of whether other processes could produce such bone damage. Haynes6 presents compelling evidence of non-cultural and/or non-prehistoric processes producing comparable damage at the 24,000-year-old Inglewood Mammoth Site (IMS), Maryland, USA. As at the CM site, the IMS contains the remains of a single juvenile proboscidean recovered in situ from a sealed deposit of sandy clays with pebbles and cobbles6. Haynes6 provides descriptions and images of curvilinear and spiral ‘green-bone’ fractures on cranial, axial and appendicular specimens. Some of these fractures are recent in origin, probably related to heavy earthmoving equipment working on-site6. Other damage may reflect perimortem injuries sustained by the mammoth. No evidence of prehistoric hominin activities are noted or suspected for the site. Post-burial bone notches, impact points and impact scratches occurred on a number of specimens. We report a similar record of fractured proboscidean bones at the Waco Mammoth National Monument (WMNM), Waco, Texas, USA. The site contains the remains of at least 26 mammoths buried in fluvial sands, silts and clays, and dates from 66,800 to 51,300 years ago7. The WMNM was initially investigated as a potential archaeological site, although no evidence of prehistoric human activities was discovered. Figure 1 shows post-burial damage to WMNM mammoth long bones morphologically consistent with observations from the IMS and CM sites. This includes damage that resembles spiral fractures with associated sedimentary abrasion, hammerstone pseudo-notches8, negative flake scars, partially detached flakes and incipient notches, and bulbs of percussion. Such damage, including spiral fractures, is well known in the fossil record from as early as the Triassic period9 and can occur post-burial6. They neither require nor solely indicate prehistoric human agency4,6,8. Other proboscidean assemblages share a similar taphonomic signature with the WMNM, IMS and CM sites. Holen and others report various combinations of spiral fractures, impact points, bulbs of percussion and bone flakes at numerous other late Pleistocene mammoth death sites in the Americas10,11. As with the CM site, these latter assemblages uniformly lack unambiguous stone tools, cut marks, or any other unquestionable evidence of hominin activities, and most predate well-vetted geochronological and palaeogenomic evidence of the initial peopling of the Americas around 15.5 thousand years ago1,2,12–14. Moreover, it is not just what is present at the CM site, but also what is missing. Specifically, hammerstone striae and/or pits (HSSP)15 are noticeably absent despite reasonable cortical bone preservation, several hundred bone fragments, purported hammerstones, and purported anvil abrasions on both the bones and the cobbles. Experimental studies show that hammerstone-percussed proboscidean limb bone fragments should bear HSSP on greater than 30% of specimens created when using a hafted hammerstone and anvil12. The absence of HSSP at the CM site—a proposed percussed bone assemblage—cannot be explained using current experimental models and contradicts the assumption of hammerstone-wielding hominin involvement in bone breakage. Lastly, we question the assertion of an “undisturbed geologic context” at the CM site. Although the distance between some refitted finds necessarily suggests pre-burial breakage and scattering of some items (for example the molar fragments), other features of the record plausibly reflect subsequent forces modifying the assemblage over the last 130,000 years. As fluvial deposits slowly covered the remains, the bones of the mastodon would have remained semi-pliable for years6. Proboscideans or other large mammals subsequently using the muddy watercourse could potentially trample, displace, fracture, abrade and reorient (for example the semi-vertical tusk) the interred materials4,6. Later sediment compaction by metres of overburden and then eventual

Optically Stimulated Luminescence Dating and the Peopling of the Americas

The measurement of time is a critical parameter in archaeology and particularly in evaluating the timing of the peopling of the Americas. New geochronometers, like optically stimulated luminescence (OSL), are needed where organic matter is absent for radiocarbon dating to distinguish amongst Folsom, Clovis, and pre-Clovis lithic cultures, like at the Debra L. Friedkin site, Texas, which has a sedimentary record spanning from ca. 1000 to >25,000 calendar years ago (cal yr BP) (Waters et al. 2011). In this and other contexts OSL dating has provided meaningful age control and has encouraged a healthy debate in the community on what is credible evidence for a preClovis occupation (Haynes 2015; Madsen 2015; Morrow et al. 2012). However, we note that within the pages of PaleoAmerica, an unsupported bias has emerged regarding the use of OSL dating. Both Haynes (2015) and Madsen (2015) have presented negative opinions about the reliability of OSL ages, with Madsen (2015, 235) going so far as to state that “...there is a bit of magic involved in making these determinations.” We assure the readership that there is no “magic” in OSL dating; instead it reflects scientific advances in radiation dosimetry, solid-state physics, and Quaternary geochronology during the past 50 years. In this Perspective, we explain the basis of luminescence dating so the PaleoAmerica readership can evaluate objectively the limitations and promise of OSL dating. In turn, we discuss specific OSL dating parameters for the Debra L. Friedkin site and explain why we believe these are robust age estimates. OSL dating provides a measure of time since sediment grains were deposited and shielded from further light or heat exposure, which often effectively resets the luminescence signal. Common silicate minerals like quartz and potassium feldspar contain lattice-charge defects formed during crystallization and from subsequent exposure to ionizing radiation. These charge defects are potential sites of electron storage with a variety of trap-depth energies. A subpopulation of stored electrons with trap depths of ∼1.3–3 eV is a subsequent source for time-diagnostic luminescence emissions. Free electrons are generated within the mineral matrix by exposure to ionizing radiation from the radioactive decay of parent and daughter isotopes in the U, U, and Th decay series, and a radioactive isotope of potassium, K, with lesser contributions from the decay of Rb and cosmic sources. This technique, known as thermoluminescence, was originally developed in the 1950s and 1960s to date fired archaeological materials like ceramics (Aitken 1985). Ensuing research in the 1970s documented that marine and other sediments with a prior sunlight exposure of hours to days were suitable for thermoluminescence dating (Wintle and Huntley 1980). Discoveries in the 1980s and 1990s that exposure of quartz and feldspar grains to a tunable light source, initially with a green laser and later by blue light emitting diodes, yield luminescence components that are solar reset within seconds to minutes, expanding greatly the utility of the method (Aitken 1998; Huntley et al. 1985; Hütt et al. 1988). In the past 15 years there have been significant developments in OSL dating with the advent of singlealiquot and single-grain analyses, which together provide new approaches for dating deposition for eolian, littoral, fluvial, lacustrine, and colluvial environments spanning the past 100,000 years (Duller 2012; Murray and Wintle 2003; Wintle and Murray 2006). In the Quaternary geologic community there have been many tests of the reliability of OSL Correspondence to: Steven L. Forman. Email: steven_forman@baylor.edu

Terminal Pleistocene to early Holocene volcanic eruptions at Zuni Salt Lake, west-central New Mexico, USA

Zuni Salt Lake (ZSL) is a large maar in the Red Hill–Quemado volcanic field located in west-central New Mexico in the southwestern USA. Stratigraphic analysis of sections in and around the maar, coupled with optically stimulated luminescence (OSL) and accelerator mass spectrometry (AMS) 14C dating, indicate that ZSL volcanic activity occurred between ∼13.4 and 9.9xa0ka and was most likely confined to a ≤500-year interval sometime between ∼12.3 and 11.0xa0ka. The basal volcanic unit consists of locally widespread basaltic ash fallout interpreted to represent a violent or wind-aided strombolian eruption tentatively attributed to Cerro Pomo, a scoria cone ∼10xa0km south of ZSL. Subsequent eruptions emanated from vents near or within the present-day ZSL maar crater. Strombolian eruptions of multiple spatter and scoria cones produced basaltic lava and scoria lapilli fallout. Next, a phreatomagmatic eruption created the maar crater and surrounding tephra rim and apron. ZSL eruptions ended with strombolian eruptions that formed three scoria cones on the crater floor. The revised age range of ZSL is younger and more precise than the 190–24xa0ka 2-sigma age range derived from previous argon dating. This implies that other morphologically youthful, argon-dated volcanoes on the southern margin of the Colorado Plateau might be substantially younger than previously reported.

Pre-Clovis projectile points at the Debra L. Friedkin site, Texas—Implications for the Late Pleistocene peopling of the Americas

Stemmed projectile points are ~13,500 to ~15,500 years old and lie stratigraphically below ~13,000-year-old Clovis artifacts. Lanceolate projectile points of the Clovis complex and stemmed projectile points of the Western Stemmed Tradition first appeared in North America by ~13 thousand years (ka) ago. The origin, age, and chronological superposition of these stemmed and lanceolate traditions are unclear. At the Debra L. Friedkin site, Texas, below Folsom and Clovis horizons, we find stemmed projectile points dating from ~13.5 to ~15.5 ka ago, with a triangular lanceolate point form appearing ~14 ka ago. The sequential relationship of stemmed projectile points followed by lanceolate forms suggests that lanceolate points are derived from stemmed forms or that they originated from two separate migrations into the Americas.

Relating the long-term and short-term vertical deformation across a transect of the forearc in the central Mexican subduction zone

Author(s): Ramirez-Herrera, MT; Gaidzik, K; Forman, S; Kostoglodov, V; Burgmann, R; Johnson, CW | Abstract:

Views on grand research challenges for Quaternary geology, geomorphology and environments

Citation: Forman SL and Stinchcomb GE (2015) Views on grand research challenges for Quaternary geology, geomorphology and environments.