Late Cenozoic paleogeographic reconstruction of the San Francisco Bay area from analysis of stratigraphy, tectonics, and tephrochronology

ABSTRACT The Neogene stratigraphic and tectonic history of the Mount Diablo area is a consequence of the passage of the Mendocino triple junction by the San Francisco Bay area between 12 and 6 Ma, volcanism above a slab window trailing the Mendocino triple junction, and crustal transpression beginning ca. 8–6 Ma, when the Pacific plate and Sierra Nevada microplate began to converge obliquely. Between ca. 12 and 6 Ma, parts of the Sierra Nevada microplate were displaced by faults splaying from the main trace of the San Andreas fault and incorporated into the Pacific plate. The Mount Diablo anticlinorium was formed by crustal compression within a left-stepping, restraining bend of the eastern San Andreas fault system, with southwest-verging thrusting beneath, and with possible clockwise rotation between faults on its southeast and northwest sides. At ca. 10.5 Ma, a drainage divide formed between the northern Central Valley and the ocean. Regional uplift accelerated at ca. 6 Ma with onset of transpression between the Pacific and North America plates. Marine deposition ceased in the eastern Coast Range basins as a consequence of the regional uplift accompanying passage of the Mendocino triple junction, and trailing slab-window volcanism. From ca. 11 to ca. 5 Ma, andesitic volcanic intrusive rocks and lavas were erupted along the northwest crest of the central to northern Sierra Nevada and deposited on its western slope, providing abundant sediment to the northern Central Valley and the northeastern Coast Ranges. Sediment filled the Central Valley and overtopped the Stockton fault and arch, forming one large, south-draining system that flowed into a marine embayment at its southwestern end, the ancestral San Joaquin Sea. This marine embayment shrunk with time, and by ca. 2.3 Ma, it was eventually cut off from the ocean. Fluvial drainage continued southwest in the Central Valley until it was cut off in turn, probably by some combination of sea-level fluctuations and transpression along the San Andreas fault that uplifted, lengthened, and narrowed the outlet channel. As a consequence, a great lake, Lake Clyde, formed in the Central Valley at ca. 1.4 Ma, occupying all of the ancestral San Joaquin Valley and part of the ancestral Sacramento Valley. The lake rose and fell with global glacial and interglacial cycles. After a long, extreme glacial period, marine oxygen isotope stage (MIS) 16, it overtopped the Carquinez sill at 0.63 Ma and drained via San Francisco valley (now San Francisco Bay) and the Colma gap into the Merced marine embayment of the Pacific Ocean. Later, a new outlet for Central Valley drainage formed between ca. 130 and ca. 75 ka, when the Colma gap closed due to transpression and right-slip motion on the San Andreas fault, and Duxbury Point at the south end of the Point Reyes Peninsula moved sufficiently northwest along the San Andreas fault to unblock a bedrock notch, the feature we now call the Golden Gate.

Patterns of seagrass macrobenthic biodiversity in the warm-temperate Knysna estuarine bay, Western Cape: a review

Knysna estuarine bay in South Africa's Garden Route National Park is that country's most significant estuarine system for biodiversity and conservation value. One outstanding feature is support of 40% of South Africa's—and maybe 20% of the world's—remaining vulnerable and decreasing dwarf-eelgrass, Zostera capensis, whose associated benthic macrofauna has been studied since 2009. For these invertebrates, Knysna comprises several significantly different compartments: sandy mouth; well-flushed marine embayment; poorly flushed central sea-water 'lagoon'; and two disjunct but faunistically similar peripheral regions–marine backwater channels, and low-salinity upper estuary. Although macrofauna ranges from dilute brackish to fully marine, its abundance, local patchiness, and over considerable stretches, species density remains remarkably constant; further, one-third of species occur throughout. Intertidally, all but peripheral compartments are low density and infaunally dominated, while some peripheral areas, and much of the subtidal, are higher density and epifaunally dominated. Overall, seagrass macrobenthos appears maintained below carrying capacity (e.g., by abundant juvenile fish) and of random species composition within a site. Two further characteristics are notable: Unusually, seagrass supports fewer animals than adjacent unvegetated areas, probably because of lack of bioturbatory disturbance in them, and the vegetation cover may ameliorate ambient habitat conditions. Unfortunately, continual heavy and effectively unpreventable exploitation for bait occurs, and chlorophyte blooms have developed because of high nutrient input. Knysna presents a microcosm of problems facing biodiverse and high-value habitats set within areas of high unemployment where subsistence fishing provides the main source of protein and seagrass provides the only source of bait.

Application of the Vineyard Geologic Identity Concept to Two Marquette-producing Vineyards in the Champlain Valley, Vermont, USA

<p>The concept of “Vineyard Geological Identity” (VGI) was introduced (Ferretti, 2019: <em>Catena</em>) in recognition of the role of geologic setting in contributing to fertility, hydrology, and other important aspects of vineyard soils.  This study applied the VGI concept to two vineyards in the Champlain Valley of Vermont, USA where a burgeoning wine-making industry has been catalyzed by the development of French-American hybrid grape variety capable of surviving cold winters and bringing fruit to ripeness in relatively cool summers.  The vineyards studied here, “LP” and “SV”, both produce the hybrid grape known as “Marquette”, are at a similar elevation (~100 m), have a similar macroclimate (MAT ~7 °C, MAP ~ 850 mm, ~1400 GDD), and were inundated by proglacial Lake Vermont during deglaciation (~15,000 years ago).  Notable differences between the sites are the lithology of the underlying bedrock (Ordovician carbonate at LP, and Cambrian quartzite at SV), and the fact that the SV site was located at the edge of a marine embayment at the Pleistocene/Holocene transition after Lake Vermont drained.  The hypothesis tested was the prediction that despite their broadly similar physical settings and geologic histories, the VGI of the two vineyards would vary as a result of differences in their underlying bedrock and the soil parent materials at these settings.  Samples were collected at depths of 25, 50, 75, and 100 cm from 10 locations within the Marquette block at in each vineyard.  All samples were evaluated for grain size distribution (with the hydrometer method and a laser scattering analyzer), thermogravimetric analysis (from 25 to 1000 °C), pH, nutrient status, base saturation, and cation exchange capacity.  The deepest samples were also analyzed for mineralogy (with XRD) and major element chemistry (with XRF).  Results confirm the tested hypothesis.  Most base cations are significantly more abundant in the samples from the LP site (reflecting the underlying carbonate bedrock), and the LP site is significantly finer grained (reflecting its former deepwater location in Lake Vermont).  Conversely, at the SV vineyard Na is significantly more abundant and samples are significantly coarser, consistent with the former location of this site in the nearshore zone of a marine embayment.  In future work these results could be used as a physical foundation for evaluating the possible role of terroir in controlling aspects of the flavors expressed in Marquette wines from these two vineyards.</p>

Crab Diets Differ Between Adjacent Estuaries and Habitats Within a Sheltered Marine Embayment

Portunid crabs contribute to significant commercial and recreational fisheries globally and are commonly fished in estuaries and/or marine embayments, which are amongst the most degraded of all aquatic ecosystems. Portunus armatus were collected seasonally between April and February from five locations across three systems in temperate south-western Australia. The dietary composition of crabs was quantified and compared between two estuaries (Peel-Harvey and Swan-Canning) and a sheltered marine embayment (Cockburn Sound) containing three distinct habitats: shallow seagrass, shallow sand and deep sand. Overall, crabs ingested large volumes of bivalves (both live organisms and dead shell), polychaetes, crustaceans (e.g., amphipods, small decapods), and smaller volumes of teleosts, echinoderms and plant material (seagrass, algae). Analysis of Similarities showed that dietary composition varied significantly among the five locations (two estuaries and three habitats within Cockburn Sound) and seasons, with greater location than seasonal differences in the two estuaries. Diets were most distinct in the Cockburn Sound seagrass due to greater volumes of decapods and teleosts and smaller volumes of bivalve shell consumed in this habitat. Crabs from both estuaries consumed greater quantities of bivalves than those from Cockburn Sound. Seasonal differences in both estuaries were greatest between summer and winter, with a more diverse range of prey and large quantities of bivalves ingested in summer, whereas small bivalves and bivalve shell in the Peel-Harvey and polychaetes and other crustaceans in the Swan-Canning, were consumed in greater quantities in winter. The summer diet in the Peel-Harvey Estuary in the current study was compared to that 20 years previous and with documented change in the benthic macroinvertebrate fauna. Currently, crabs consume smaller volumes of high-calorie prey, i.e., polychaetes, small bivalves and teleosts, and instead ingest greater proportions of calcareous material than previously. This marked shift in dietary composition parallels changes in benthic macroinvertebrates in the Peel-Harvey Estuary. Overall, prey availability appears to be the major factor influencing the spatial and temporal differences in P. armatus diets in these three coastal systems.

Temporal changes in the growth of a crustacean species, Portunus armatus, in a temperate marine embayment: evidence of density dependence

Growth is a key attribute influencing population dynamics and fishery production, and understanding factors that affect the growth of individuals in a population is essential in fisheries science and management. This study analyses 18 years of fishery-independent trawl data to determine the relationships among temperature, density, primary productivity and growth of the blue swimmer crab, Portunus armatus, in a temperate marine embayment. Growth was modelled using mixture distribution analyses and cohort-specific seasonal growth curves to estimate the size of crabs at the age of 0.5 and 1.5 years. Growth was highly seasonal, with size-at-age increasing during the austral summer periods and slowing/ceasing during the cooler winter months. The results from the mixture models were used to estimate the mean size of the 0.5- and 1.5-year-old crabs in each year. Linear models showed that the mean size of adult P. armatus at 1.5 years was negatively related to the density of juvenile (0.5 year) crabs in the previous year (i.e. the same cohort) and chlorophyll a concentrations in this year. Increased chlorophyll a levels may increase the survival of larval and megalopal P. armatus, leading to density-dependent effects such as increased competition among juveniles for food and spatial resources, and ultimately, reduced growth.